Method for ceramizing glass by using nucleation and growth density and viscosity change

文档序号：862758 发布日期：2021-03-16 浏览：13次中文

阅读说明：本技术 利用成核和生长密度以及粘度变化对玻璃进行陶瓷化的方法 (Method for ceramizing glass by using nucleation and growth density and viscosity change ) 是由 C·A·克里克 I·杜塔 O·古比腾 J·M·霍尔 M·G·J·休伯特 A·P·奇托森于 2019-07-15 设计创作，主要内容包括：将玻璃制品陶瓷化为玻璃陶瓷的方法包括将玻璃制品放入加热设备中,并且以第一预定加热速率将玻璃制品加热至第一保持温度。玻璃制品在第一保持温度下保持第一预定持续时间。在第一预定持续时间内,玻璃制品的粘度保持在对数粘度±1.0泊之内。然后,将玻璃制品以第二预定加热速率从第一保持温度加热至第二保持温度。玻璃制品在第二保持温度下保持第二持续时间。从自第一保持温度加热玻璃制品开始到整个第二持续时间,监测玻璃制品的密度,并且当玻璃制品的密度变化速率的绝对值小于或等于0.10(g/cm~3)/min时,结束第二持续时间。(A method of ceramming a glass article into a glass ceramic includes placing the glass article into a heating apparatus and heating the glass article to a first holding temperature at a first predetermined heating rate. The glass article is held at the first holding temperature for a first predetermined duration. The viscosity of the glass article remains within 1.0 poise of the logarithmic viscosity for a first predetermined duration. The glass article is then heated from the first holding temperature to a second holding temperature at a second predetermined heating rate. The glass article is held at the second holding temperature for a second duration. From a first holding temperatureMonitoring the density of the glass article throughout the second duration from the start of heating the glass article, and when the absolute value of the rate of change of the density of the glass article is less than or equal to 0.10 (g/cm) 3 ) At/min, the second duration ends.)

1. A method for ceramming a glass article into a glass-ceramic, comprising:

placing the glass article into a heating apparatus;

heating the glass article to a first holding temperature at a first predetermined heating rate;

holding the glass article at the first holding temperature for a first predetermined duration, wherein the viscosity of the glass article is maintained within a range of the logarithmic viscosity of the target viscosity ± 1.0 poise for the first predetermined duration;

heating the glass article from the first holding temperature to a second holding temperature at a second predetermined heating rate;

holding the glass article at the second holding temperature for a second duration, wherein the density of the glass article is monitored from the heating of the glass article from the first holding temperature to the entire second duration; and

when the absolute value of the rate of change in density of the glass article is less than or equal to 0.10 (g/cm)³) At/min, the second duration ends.

2. The method of claim 1, wherein the absolute value of the rate of change of density of the glass article is equal to 0.00 (g/cm)³) At/min, the second duration ends.

3. The method of claim 1, wherein the viscosity of the glass article is maintained within a range of ± 0.1 poise of the logarithmic viscosity of the target viscosity for the first predetermined duration.

4. The method of claim 1, wherein the viscosity of the glass article is maintained within a range of ± 1.0 poise of the logarithmic viscosity of the target viscosity for at least a portion of the time the glass article is heated from the first holding temperature to the second holding temperature.

5. The method of claim 1, wherein the viscosity of the glass article is maintained within a range of ± 1.0 poise of the logarithmic viscosity of the target viscosity for a first predetermined duration using data from an automatic viscosity control system.

6. The method of claim 1, wherein the density of the glass article is monitored in situ during heating of the glass article from the first holding temperature to the second holding temperature and holding the glass article at the second holding temperature for the second duration.

7. The method of claim 6, wherein the density of the glass article is monitored in-situ with a dilatometer during heating of the glass article from the first holding temperature to the second holding temperature at a second predetermined heating rate and holding of the glass article at the second holding temperature for a second duration.

8. The method of claim 1, wherein the second duration is ended when the density of the glass article is constant for at least 50 minutes.

9. The method of claim 1, wherein the second duration is ended when the density of the glass article is constant for at least 100 minutes.

10. The method of claim 1, wherein the first predetermined heating rate is determined based at least in part on performance of an automatic viscosity control system.

11. The method of claim 1, wherein the second predetermined heating rate is determined based at least in part on performance of an automatic viscosity control system.

12. The method of claim 1, further comprising applying a weight restraining force to the glass article.

13. The method of claim 1, wherein the glass article has a temperature differential from the programmed temperature within ± 8 ℃ for the first predetermined duration.

14. The method of claim 1, wherein the glass article has a temperature differential from the programmed temperature within ± 5 ℃ for the first predetermined duration.

15. The method of claim 1, wherein the temperature difference of the glass article from the programmed temperature is within ± 8 ℃ for the second duration.

16. The method of claim 1, wherein the temperature difference of the glass article from the programmed temperature is within ± 5 ℃ for the second duration.

17. The method of claim 1, wherein heating the glass article to the first holding temperature at the first predetermined heating rate comprises multi-stage heating.

18. The method of claim 1, wherein the viscosity of the glass article is maintained at greater than or equal to 11.0 poise logarithmic viscosity during heating of the glass article to the first holding temperature at the first predetermined heating rate.

19. The method of claim 1, wherein the viscosity of the glass article is maintained at greater than or equal to a logarithmic viscosity of 11.0 poise for a first predetermined duration.

20. The method of claim 1, wherein the viscosity of the glass article is maintained at or above 11.0 poise log viscosity during heating of the glass article from the first holding temperature to the second holding temperature.

21. The method of claim 1, wherein the viscosity of the glass article is maintained at greater than or equal to a logarithmic viscosity of 11.0 poise for the entire duration of the method.

22. The method of claim 1, wherein the viscosity of the glass article is maintained at less than 11.0 poise logarithmic viscosity for a first predetermined duration.

23. The method of claim 1, wherein the second duration is ended when the density of the glass article is constant for at least 15 minutes.

FIELD

The present specification relates generally to methods of ceramming glass articles to form glass-ceramic articles, and more particularly to methods of ceramming glass articles to form glass-ceramic articles by adjusting the ceramming cycle based on changes in nucleation and growth density and article viscosity during the ceramming cycle.

Technical Field

There is a continuing need for high strength glass that can be used in portable electronic devices. Several materials are currently used as housings for portable electronic devices, such as glass, zirconia, plastic, metal, and glass-ceramic. The benefits of using glass-ceramics include high strength and high transmission, which makes glass-ceramics a desirable choice for optical displays and electromagnetic charging.

However, forming glass-ceramics can be difficult, particularly when attempting to achieve high yields in the ceramming process. For example, forming glass-ceramics requires precise control of the thermal profile of the glass articles during the ceramming process, which becomes difficult when stacking the glass articles in a heating apparatus such as an annealing lehr.

SUMMARY

According to a first aspect, a method for ceramming a glass article into a glass-ceramic comprises: placing the glass article into a heating apparatus; heating the glass article to a first holding temperature at a first predetermined heating rate; holding the glass article at the first holding temperature for a first predetermined duration, wherein the viscosity of the glass article is maintained within a range of the logarithmic viscosity of the target viscosity ± 1.0 poise for the first predetermined duration; heating the glass article from the first holding temperature to a second holding temperature at a second predetermined heating rate; holding the glass article at the second holding temperature for a second duration, wherein the density of the glass article is monitored from the heating of the glass article from the first holding temperature to the entire second duration; when the absolute value of the rate of change in density of the glass article is less than or equal to 0.10 (g/cm)³) At/min, the second duration ends.

A second aspect includes the method of the first aspect, wherein when the absolute value of the rate of change of density of the glass article is equal to 0.00 (g/cm)³) At/min, the second duration ends.

A third aspect includes the method of any one of the first and second aspects, wherein the viscosity of the glass article is maintained within a range of ± 0.1 poise of the logarithmic viscosity of the target viscosity for a first predetermined duration.

A fourth aspect includes the method of any one of the first to third aspects, wherein the viscosity of the glass article is maintained within a range of ± 1.0 poise of the logarithmic viscosity of the target viscosity for at least a portion of the time the glass article is heated from the first holding temperature to the second holding temperature.

A fifth aspect includes the method of any one of the first to fourth aspects, wherein the viscosity of the glass article is maintained within a range of the logarithmic viscosity of the target viscosity ± 1.0 poise for a first predetermined duration using data from the automatic viscosity control system.

A sixth aspect includes the method of any one of the first to fifth aspects, wherein the density of the glass article is monitored in situ during heating of the glass article from the first holding temperature to the second holding temperature and holding the glass article at the second holding temperature for the second duration.

A seventh aspect includes the method of the sixth aspect, wherein the density of the glass article is monitored in situ with a dilatometer during heating of the glass article from the first holding temperature to the second holding temperature at a second predetermined heating rate and holding of the glass article at the second holding temperature for a second duration.

An eighth aspect includes the method of any one of the first to seventh aspects, wherein the second duration is ended when the density of the glass article is constant for at least 15 minutes or preferably at least 50 minutes.

A ninth aspect includes the method of any one of the first to eighth aspects, wherein the second duration is ended when the density of the glass article is constant for at least 100 minutes.

A tenth aspect includes the method of any one of the first to ninth aspects, wherein the first predetermined heating rate is determined based at least in part on a performance of an automatic viscosity control system.

An eleventh aspect includes the method of any one of the first to tenth aspects, wherein the second predetermined heating rate is determined based at least in part on a performance of an automatic viscosity control system.

A twelfth aspect includes the method of any one of the first to eleventh aspects, further comprising applying a weight restraining force to the glass article.

A thirteenth aspect includes the method of any one of the first to twelfth aspects, wherein the glass article is part of a glass stack.

A fourteenth aspect includes the method of the thirteenth aspect, wherein the glass stack comprises: a first positioner; a plurality of glass sheets disposed on the first positioner; and a second locator located on the stack of glass sheets.

A fifteenth aspect includes the method of the fourteenth aspect, wherein the plurality of glass sheets includes at least 10 glass sheets.

A sixteenth aspect includes the method of the fourteenth aspect, wherein the plurality of glass sheets includes at least 20 glass sheets.

A seventeenth aspect includes the method of any one of the first to eighteenth aspects, wherein the glass article has a temperature difference from the programmed temperature within ± 8 ℃ for the first predetermined duration.

An eighteenth aspect includes the method of any one of the first to seventeenth aspects, wherein the glass article has a temperature difference from the programmed temperature within ± 5 ℃ for the first predetermined duration.

A nineteenth aspect includes the method of any one of the first to eighteenth aspects, wherein the glass article has a temperature differential from the programmed temperature within ± 8 ℃ for the second duration.

A twentieth aspect includes the method of any one of the first to nineteenth aspects, wherein the glass article has a temperature differential from the programmed temperature within ± 5 ℃ for the second duration.

A twenty-first aspect includes the method of any one of the first to twentieth aspects, wherein heating the glass article to the first holding temperature at the first predetermined heating rate includes multi-stage heating.

A twenty-second aspect includes the method of any one of the first to twenty-first aspects, wherein the viscosity of the glass article is maintained at greater than or equal to a logarithmic viscosity of 11.0 poise during heating of the glass article to the first holding temperature at the first predetermined heating rate.

A twenty-third aspect includes the method of any one of the first to twenty-second aspects, wherein the viscosity of the glass article is maintained at or above 11.0 poise logarithmic viscosity for a first predetermined duration.

A twenty-fourth aspect includes the method of any one of the first to twenty-third aspects, wherein the viscosity of the glass article is maintained at greater than or equal to a logarithmic viscosity of 11.0 poise during heating of the glass article to the first holding temperature at the first predetermined heating rate.

A twenty-fifth aspect includes the method of any one of the first to twenty-fourth aspects, wherein the viscosity of the glass article is maintained at greater than or equal to a logarithmic viscosity of 11.0 poise for the entire duration of the method.

A twenty-sixth aspect includes the method of any one of the first to twenty-fifth aspects, wherein the viscosity of the glass article is maintained at greater than or equal to a logarithmic viscosity of 11.0 poise for the entire duration of the method.

Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the various embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description describe various embodiments, and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments described herein and together with the description serve to explain the principles and operations of the claimed subject matter.

Brief Description of Drawings

FIG. 1 schematically depicts a glass stack according to embodiments disclosed and described herein;

FIG. 2A graphically depicts temperature versus time measurements and nucleation and crystallization (growth) relationships for a ceramming cycle in accordance with embodiments disclosed and described herein;

FIG. 2B graphically depicts nucleation and crystal growth rates versus temperature during a ceramming cycle in accordance with embodiments disclosed and described herein;

FIG. 3 is a flow diagram of proportional-integral-derivative (PID) logic used during an Automatic Viscosity Control (AVC) nucleation phase in a ceramming cycle according to embodiments disclosed and described herein;

FIG. 4 is a block diagram illustrating a system for handling an AVC nucleation phase in a ceramming cycle according to embodiments disclosed and described herein;

FIG. 5 graphically depicts log viscosity (in poise) versus time (in minutes) during a ceramming cycle, in accordance with embodiments disclosed and described herein;

FIG. 6 graphically depicts temperature (in degrees Celsius) versus time (in minutes) during a ceramming cycle, in accordance with embodiments disclosed and described herein;

FIG. 7 schematically illustrates a dilatometer that may be used in situ to measure the density of a glass article according to embodiments disclosed and described herein;

FIG. 8 graphically depicts density (in grams/cubic centimeter) versus time (in minutes) in a ceramming cycle, in accordance with embodiments disclosed and described herein;

FIG. 9 graphically depicts density (in grams/cubic centimeter) versus time (in minutes) in a ceramming cycle, in accordance with embodiments disclosed and described herein;

FIG. 10 graphically depicts viscosity (in log10 poise) versus time (in minutes) in a ceramming cycle, in accordance with embodiments disclosed and described herein;

FIG. 11 graphically depicts temperature (on the left y-axis, in degrees Celsius) versus time (on the y-axis, in hours) and viscosity (on the right y-axis, in log10 poise) versus time (on the x-axis, in hours) during a ceramming cycle according to embodiments disclosed and described herein;

fig. 12A illustrates warpage of a glass-ceramic article cerammed by a ceramming cycle in accordance with embodiments disclosed and described herein;

fig. 12B illustrates warpage of a glass-ceramic article cerammed by a ceramming cycle in accordance with embodiments disclosed and described herein;

fig. 12C illustrates warpage of a glass-ceramic article cerammed by a ceramming cycle in accordance with embodiments disclosed and described herein;

fig. 13A illustrates warpage of a glass-ceramic article cerammed by a ceramming cycle in accordance with embodiments disclosed and described herein;

fig. 13B illustrates warpage of a glass-ceramic article cerammed by a ceramming cycle in accordance with embodiments disclosed and described herein;

fig. 13C illustrates warpage of a glass-ceramic article cerammed by a ceramming cycle in accordance with embodiments disclosed and described herein;

FIG. 14 graphically depicts a relationship of viscous sag (in mm) versus disk radius (in mm) for a glass-ceramic article cerammed by a ceramming cycle in accordance with embodiments disclosed and described herein;

FIG. 15A graphically depicts a horizontal position of a measurement device within a chamber of a heating apparatus according to embodiments disclosed and described herein;

FIG. 15B graphically depicts a vertical position of a measurement device within a chamber of a heating apparatus according to embodiments disclosed and described herein;

FIG. 16 graphically depicts temperature (in degrees Celsius) versus time (in seconds) recorded by a measuring device in an empty chamber of a heating apparatus, in accordance with embodiments disclosed and described herein;

FIG. 17 graphically depicts temperature (on the left y-axis in degrees Celsius) versus time (on the x-axis in seconds) for glass sheets and temperature difference (on the right y-axis in degrees Celsius) between glass sheets versus time (on the x-axis in seconds) for ceramming in accordance with a ceramming cycle of embodiments disclosed and described herein;

FIG. 18 graphically depicts temperature (in degrees Celsius) versus time (in seconds) for a glass sheet cerammed by a ceramming cycle in accordance with embodiments disclosed and described herein, including an expanded view of various portions of a graph of glass articles;

FIG. 19 graphically depicts the effect of multi-stage heating on temperature difference of a glass sheet (in degrees Celsius) versus time (in minutes) in accordance with embodiments disclosed and described herein;

FIG. 20 graphically depicts the effect of multi-stage heating on temperature difference of a glass sheet (in degrees Celsius) versus time (in minutes) in accordance with embodiments disclosed and described herein;

FIG. 21 graphically depicts the effect of multi-stage heating on temperature difference of a glass sheet (in degrees Celsius) versus time (in minutes) in accordance with embodiments disclosed and described herein;

FIG. 22 graphically depicts temperature (in degrees Celsius) versus time (in minutes) in a ceramming cycle and a conventional ceramming cycle, in accordance with embodiments disclosed and described herein;

FIG. 23 graphically depicts density (in grams/cubic centimeter) versus time (in minutes) for a ceramming cycle and a conventional ceramming cycle in accordance with embodiments disclosed and described herein.

Detailed Description

The method for ceramming the glass article will be described in detail below, embodiments of which are shown in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. In one embodiment, a method for ceramming a glass article into a glass-ceramic comprises: placing the glass article into a heating apparatus; heating the glass article to a first holding temperature at a first predetermined heating rate; holding the glass article at the first holding temperature for a first predetermined duration, wherein the viscosity of the glass article is maintained within a range of the logarithmic viscosity of the target viscosity ± 1.0 poise for the first predetermined duration; heating the glass article from the first holding temperature to a second holding temperature at a second predetermined heating rate; holding the glass article at the second holding temperature for a second duration, wherein the density of the glass article is monitored from the heating of the glass article from the first holding temperature to the entire second duration; the second duration ends when the density of the glass article is constant. Various embodiments for ceramming glass articles are described herein with particular reference to the accompanying drawings.

Generally, a method for forming a glass-ceramic includes forming a glass article and ceramming the glass article to convert the glass article into a glass-ceramic form. Referring to fig. 1, an exemplary stacked structure 100 for ceramming is shown. The stacking structure 100 includes a carrier plate 102 supporting two positioning plates 104 and a glass stack 106 positioned between the positioning plates 104.

In some embodiments, an insulating layer (not shown) may be located on the top surface of the upper locating plate 104 and on the bottom surface of the lower locating plate 104. The insulating layer may be formed of any material having a low thermal conductivity and may reduce or even eliminate the axial temperature gradient of the glass sheets 108 on the top and bottom of the glass stack 106.

As shown in fig. 1, glass stack 106 includes a plurality of glass sheets 108, each glass sheet 108 being separated from an adjacent glass sheet 108 by a release layer 110. The release layer 110 reduces or even eliminates adhesion of the glass sheet 108 in the glass stack 106 during the ceramming process. Although not shown in fig. 1, in some embodiments, the glass stack 106 can further include a release agent layer 110 between the glass sheet 108 and the locating plate 104. In other embodiments, such as the various embodiments described below, the locating plate 104 is made of a material that does not react with the glass sheet 108 and the release layer 110 is not required to prevent interaction between the glass sheet 108 and the locating plate 104.

Generally, to form the glass-ceramic, the glass stack 106 is heated above its annealing point for a time sufficient to form nuclei (also referred to as "nucleation"). The heat treatment may be performed in, for example, an annealing furnace or a heating furnace. After heating above its annealing point, the glass is typically then further heated at a higher temperature between the glass annealing point and the glass softening point to form a crystalline phase (also referred to as "growth" or "crystallization"). In various embodiments, the heat treatment or ceramming process includes heating the glass stack to a nucleation temperature, maintaining the nucleation temperature for a predetermined period of time, heating the glass stack to a crystallization temperature, and maintaining the crystallization temperature for a predetermined period of time.

The glass sheet 108 can be made of any glass composition suitable for forming a glass-ceramic article, but it is understood that the glass composition of the glass sheet 108 can affect the mechanical and optical properties of the glass-ceramic article. In various embodiments, the glass composition is selected such that the resulting glass ceramic article has a petalite crystalline phase and a lithium silicate crystalline phase, wherein the petalite crystalline phase and the lithium silicate crystalline phase have a higher weight percentage than other crystalline phases present in the glass ceramic article.

By way of example and not limitation, in various embodiments, glass sheet 108 may be formed from a glass composition comprising about 55 wt.% to about 80 wt.% SiO₂About 2 to about 20 weight percent Al₂O₃From about 5% to about 20% by weight of Li₂O, about 0 to about 10 wt.% of B₂O₃About 0% to about 5% by weight of Na₂O, about 0 to about 10 weight percent ZnO, about 0.5 to about 6 weight percentP₂O₅From about 0.2 to about 15 weight percent ZrO₂。

Oxide SiO involved in glass formation₂Can stabilize the network structure of glass and glass ceramic. In various glass compositions, SiO₂Should be sufficiently high so as to form a petalite crystalline phase when the glass sheet is heat treated for conversion into a glass ceramic. Due to pure SiO₂Or high SiO₂The melting temperature of the glass is too high, which can limit SiO₂In order to control the melting temperature of the glass. In some embodiments, the glass or glass-ceramic composition comprises about 55 wt.% to about 80 wt.% of SiO₂. In some embodiments, the glass or glass-ceramic composition comprises about 69 wt.% to about 80 wt.% SiO₂. In some embodiments, the glass or glass-ceramic composition may comprise from about 55% to about 80%, from about 55% to about 77%, from about 55% to about 75%, from about 55% to about 73%, from about 60% to about 80%, from about 60% to about 77%, from about 60% to about 75%, from about 60% to about 73%, from about 69% to about 80%, from about 69% to about 77%, from about 69% to about 75%, from about 69% to about 73%, from about 70% to about 80%, from about 70% to about 77%, from about 70% to about 75%, from about 70% to about 73%, from about 73% to about 80%, from about 73% to about 73%, from about 73% to about 75%, from about 70% to about 73%, from about 73% to about 80%, from about 73% to about 77%, from about 73% to about 75%, from about 75% to about 75%, about 75% to about 77% by weight, or about 77% to about 80% by weight, of SiO₂And any and all subranges formed by any of the foregoing endpoints.

Al₂O₃It is also possible to stabilize the network and also to improve the mechanical properties and chemical resistance. However, if Al₂O₃Too high, the proportion of lithium silicate crystals may decrease, possibly to the extent that an interlocking structure cannot be formed. Can adjust Al₂O₃In order to control the viscosity. In addition, if Al₂O₃Of (1) containsToo high an amount generally increases the viscosity of the melt. In some embodiments, the glass or glass-ceramic composition comprises from about 2 wt.% to about 20 wt.% Al₂O₃. In some embodiments, the glass or glass-ceramic composition comprises about 6 wt.% to about 9 wt.% Al₂O₃. In some embodiments, the glass or glass-ceramic composition may comprise from about 2% to about 20%, from about 2% to about 18%, from about 2% to about 15%, from about 2% to about 12%, from about 2% to about 10%, from about 2% to about 9%, from about 2% to about 8%, from about 2% to about 5%, from about 5% to about 20%, from about 5% to about 18%, from about 5% to about 15%, from about 5% to about 12%, from about 5% to about 10%, from about 5% to about 9%, from about 5% to about 8%, from 6% to about 20%, from about 6% to about 18%, from about 6% to about 15%, from about 6% to about 12%, from about 6% to about 10%, about 6 wt% to about 9 wt%, 8 wt% to about 20 wt%, about 8 wt% to about 18 wt%, about 8 wt% to about 15 wt%, about 8 wt% to about 12 wt%, about 8 wt% to about 10 wt%, 10 wt% to about 20 wt%, about 10 wt% to about 18 wt%, about 10 wt% to about 15 wt%, about 10 wt% to about 12 wt%, about 12 wt% to about 20 wt%, about 12 wt% to about 18 wt%, or about 12 wt% to about 15 wt% of Al₂O₃And any and all subranges formed by any of the foregoing endpoints.

In the glasses and glass-ceramics described herein, Li₂O contributes to the formation of petalite and lithium silicate crystalline phases. Indeed, in order to obtain petalite and lithium silicate as the predominant crystalline phases, it is desirable to have at least about 7% by weight Li in the composition₂And O. It has additionally been found that once Li is present₂The O content becomes too high (greater than about 15 wt%), the composition becomes very flowable. Thus, in some embodiments, the glass or glass-ceramic composition comprises from about 5 wt.% to about 20Weight% of Li₂And O. In other embodiments, the glass or glass-ceramic composition comprises from about 10 wt.% to about 14 wt.% Li₂And O. In some embodiments, the glass or glass-ceramic composition may comprise from about 5% to about 20%, from about 5% to about 18%, from about 5% to about 16%, from about 5% to about 14%, from about 5% to about 12%, from about 5% to about 10%, from about 5% to about 8%, from about 7% to about 20%, from about 7% to about 18%, from about 7% to about 16%, from about 7% to about 14%, from about 7% to about 12%, from about 7% to about 10%, from about 10% to about 20%, from about 10% to about 18%, from about 10% to about 16%, from about 10% to about 14%, from about 10% to about 12%, from about 12% to about 12%, from about 18% to about 18%, about 12 wt% to about 16 wt%, about 12 wt% to about 14 wt%, about 14 wt% to about 20 wt%, about 14 wt% to about 18 wt%, about 14 wt% to about 16 wt%, about 16 wt% to about 20 wt%, about 16 wt% to about 18 wt%, or about 18 wt% to about 20 wt% of Li₂O, and any and all subranges formed by any of the foregoing endpoints.

As mentioned above, Li₂O is commonly used to form various glass-ceramics, but other alkali metal oxides tend to reduce the formation of glass-ceramics and form aluminosilicate residual glass in the glass-ceramic. It has been found that greater than about 5 wt% Na₂O or K₂O or a combination thereof leads to an unfavourable residual glass amount, which may lead to deformations during crystallization and undesired microstructures from the point of view of mechanical properties. The composition of the residual glass can be adjusted to control viscosity during crystallization, minimize distortion or undesirable thermal expansion, or control microstructural properties. Thus, the glass sheets can generally be made from glass compositions having small amounts of non-lithium alkali metal oxides. In some embodiments, the glass or glass-ceramic composition may comprise from about 0 wt.% to about 5 wt.% of R₂O, wherein R is a baseOne or more of the metal cations Na and K. In some embodiments, the glass or glass-ceramic composition may comprise from about 1% to about 3% by weight of R₂O, wherein R is one or more of alkali metal cations Na and K. In some embodiments, the glass or glass-ceramic composition may comprise from 0 wt% to about 5 wt%, from 0 wt% to about 4 wt%, from 0 wt% to about 3 wt%, from 0 wt% to about 2 wt%, from 0 wt% to about 1 wt%,>from 0% by weight to about 5% by weight,>from 0% by weight to about 4% by weight,>from 0% by weight to about 3% by weight,>from 0% by weight to about 2% by weight,>0% to about 1%, about 1% to about 5%, about 1% to about 4%, about 1% to about 3%, about 1% to about 2%, about 2% to about 5%, about 2% to about 4%, about 2% to about 3%, about 3% to about 5%, about 3% to about 4%, or about 4% to about 5% by weight of Na₂O、K₂O or a combination thereof, and any and all subranges formed by any of the foregoing endpoints.

The glass and glass ceramic compositions may comprise P₂O₅。P₂O₅Can act as a nucleating agent to promote bulk nucleation. If P₂O₅If too low, the precursor glass will crystallize only at higher temperatures (due to the lower viscosity) and crystallize inward from the surface, thus producing a weak and often deformed object, although it does. However, if P₂O₅Too high, devitrification may be difficult to control upon cooling during glass sheet formation. Embodiments may include >0 wt.% to about 6 wt.% of P₂O₅. Other embodiments may include > 2% to about 4% by weight of P₂O₅. Still other embodiments may include > 1.5 wt.% to about 2.5 wt.% of P₂O₅. In some embodiments, the glass or glass-ceramic composition may comprise from 0 wt% to about 6 wt%, from 0 wt% to about 5.5 wt%, from 0 wt% to 5 wt%, from 0 wt% to about 4.5 wt%, from 0 wt% to about 4 wt%, from 0 wt% to about 3.5 wt%%, 0% to about 3% by weight, 0% to about 2.5% by weight, 0% to about 2% by weight, 0% to about 1.5% by weight, 0% to about 1% by weight,>from 0% to about 6% by weight,>0% to about 5.5% by weight,>from 0% by weight to 5% by weight,>0 wt% to about 4.5 wt%,>from 0% by weight to about 4% by weight,>0% to about 3.5% by weight,>from 0% by weight to about 3% by weight,>0 wt.% to about>2.5 wt%, 0 wt% to about 2 wt%,>0% to about 1.5% by weight,>0% to about 1%, about 0.5% to about 6%, about 0.5% to about 5.5%, about 0.5% to about 5%, about 0.5% to about 4.5%, about 0.5% to about 4%, about 0.5% to about 3.5%, about 0.5% to about 3%, about 0.5% to about 2.5%, about 0.5% to about 2%, about 0.5% to about 1.5%, about 0.5% to about 1%, about 1% to about 6%, about 1% to about 5.5%, about 1% to about 5%, about 1% to about 4.5%, about 1% to about 4%, about 1% to about 1%, about 1% to about 5%, about 1% to about 1%, about 1% to about 2%, about 1% to about 1%, about 1% to about 5%, about 1% to about 1%, about 2%, about 1% to about 5%, about 1.5% to about 6%, about 1.5% to about 5.5%, about 1.5% to about 5%, about 1.5% to about 4.5%, about 1.5% to about 4%, about 1.5% to about 3.5%, about 1.5% to about 3%, about 1.5% to about 2.5%, about 1.5% to about 2%, about 2% to about 6%, about 2% to about 5.5%, about 2% to about 5%, about 2% to about 4.5%, about 2% to about 4%, about 2% to about 3.5%, about 2% to about 3%, about 2% to about 2.5%, about 6.5%, about 2% to about 5%, about 2.5%, about 5%, about 2% to about 5%, about 2.5%, about 5% to about 5%, about 2.5%, about 2.5 wt.% to about 3.5 wt.%, about 2.5 wt.% to about 3 wt%%, about 3% to about 6% by weight, about 3% to about 5.5% by weight, about 3% to about 5% by weight, about 3% to about 4.5% by weight, about 3% to about 4% by weight, about 3% to about 3.5% by weight, about 3.5% to about 6% by weight, about 3.5% to about 5.5% by weight, about 3.5% to about 5% by weight, about 3.5% to about 4.5% by weight, about 3.5% to about 4% by weight, about 4% to about 6% by weight, about 4% to about 5.5% by weight, about 4% to about 5% by weight, about 4% to about 4.5% by weight, about 4.5% to about 6% by weight, about 4.5% to about 5.5% by weight, about 4.5% to about 5% by weight, about 5% to about 6.5% by weight, about 5% to about 5% by weight, or about 5% by weight of P₂O₅And any and all subranges formed by any of the foregoing endpoints.

ZrO is commonly found in various glass and glass ceramic compositions₂Li can be increased by significantly reducing glass devitrification during forming and lowering liquidus temperature₂O—Al₂O₃—SiO₂—P₂O₅Stability of the glass. At a concentration of more than 8 wt.%, ZrSiO₄The primary liquidus phase may be formed at high temperatures, which significantly reduces the liquidus viscosity. When the glass contains more than 2% by weight of ZrO₂In this case, transparent glass can be formed. With addition of ZrO₂It may also help to reduce petalite grain size, which helps to form a transparent glass-ceramic. In some embodiments, the glass or glass-ceramic composition comprises from about 0.2 wt.% to about 15 wt.% ZrO₂. In some embodiments, the glass or glass-ceramic composition comprises about 2 wt.% to about 4 wt.% ZrO₂. In some embodiments, the glass or glass-ceramic composition may comprise from about 0.2% to about 15%, from about 0.2% to about 12%, from about 0.2% to about 10%, from about 0.2% to about 8%, from about 0.2% to about 6%, from about 0.2% to about 4%, from about 0.5% to about 15%, from about 0.5% to about 12%, from about 0.5% to about 10%, from about 0.2% to about 4%, from about 0.5% to about 12%, from about 0.5% to about 10%, from about 0.2% to about 12%, from about 0.2% to about 15%, from about 0% to about 2%, from about 0% to aboutFrom 5% to about 8%, from about 0.5% to about 6%, from about 0.5% to about 4%, from about 1% to about 15%, from about 1% to about 12%, from about 1% to about 10%, from about 1% to about 8%, from about 1% to about 6%, from about 1% to about 4%, from about 2% to about 15%, from about 2% to about 12%, from about 2% to about 10%, from about 2% to about 8%, from about 2% to about 6%, from about 2% to about 4%, from about 3% to about 15%, from about 3% to about 12%, from about 3% to about 10%, from about 3% to about 8%, from about 3% to about 6%, from about 3% to about 4%, from about 4% to about 4%, from about 4%, about 4 wt% to about 12 wt%, about 4 wt% to about 10 wt%, about 4 wt% to about 8 wt%, about 4 wt% to about 6 wt%, about 8 wt% to about 15 wt%, about 8 wt% to about 12 wt%, about 8 wt% to about 10 wt%, about 10 wt% to about 15 wt%, about 10 wt% to about 12 wt%, or about 12 wt% to about 15 wt% ZrO, based on the total weight of the composition₂And any and all subranges formed by any of the foregoing endpoints.

B₂O₃It is advantageous to provide a glass sheet having a low melting temperature. Furthermore, the addition of B to the glass sheet and thus to the glass-ceramic article₂O₃Helps achieve an interlocking crystal microstructure and may also improve the damage resistance of the glass-ceramic article. When the boron in the residual glass is not charge balanced by the alkali metal oxide or divalent cation oxide, it will be in a delta coordination state (or tridentate boron), which opens up the structure of the glass. The network around these three coordinated boron does not have the rigidity of tetrahedrally coordinated (or tetradentate) boron. Without being bound by theory, it is believed that glass sheets and glass-ceramics comprising tridentate boron may tolerate some degree of deformation prior to crack formation. By allowing some deformation, the Vickers indentation crack initiation value (Vickers indentation crack initiation value) is increased. Fracture toughness of glass sheets and glass-ceramics containing tridentate boron may also be improved. Without being bound by theory, it is believed thatGlass flakes) reduces the viscosity of the residual glass (or glass flakes) and thereby promotes the growth of lithium silicate crystals, particularly large crystals having a high aspect ratio. It is believed that the large amount of tridentate boron (relative to tetradentate boron) results in a glass ceramic with a greater vickers indentation crack initiation load. In some embodiments, the amount of tridentate boron (as total B)₂O₃Percent) of the total weight of the composition may be about 40% or more, 50% or more, 75% or more, 85% or more, or even 95% or more. The boron content should generally be controlled to maintain the chemical resistance and mechanical strength of the cerammed bulk glass-ceramic.

In one or more embodiments, the glass or glass-ceramic composition comprises 0 wt.% to about 10 wt.% or 0 wt.% to about 2 wt.% of B₂O₃. In some embodiments, the glass or glass-ceramic composition may comprise from 0 wt% to about 10 wt%, from 0 wt% to about 9 wt%, from 0 wt% to about 8 wt%, from 0 wt% to about 7 wt%, from 0 wt% to about 6 wt%, from 0 wt% to about 5 wt%, from 0 wt% to about 4 wt%, from 0 wt% to about 3 wt%, from 0 wt% to about 2 wt%, from 0 wt% to about 1 wt%,>from 0% to about 10% by weight,>from 0% to about 9% by weight,>from 0% to about 8% by weight,>from 0% to about 7% by weight,>from 0% to about 6% by weight,>from 0% by weight to about 5% by weight,>from 0% by weight to about 4% by weight,>from 0% by weight to about 3% by weight,>from 0% by weight to about 2% by weight,>0% to about 1%, about 1% to about 10%, about 1% to about 8%, about 1% to about 6%, about 1% to about 5%, about 1% to about 4%, about 1% to about 2%, about 2% to about 10%, about 2% to about 8%, about 2% to about 6%, about 2% to about 4%, about 3% to about 10%, about 3% to about 8%, about 3% to about 6%, about 3% to about 4%, about 4% to about 5%, about 5% to about 8%, about 5% to about 7.5%, about 5% to about 6%,or about 5 to about 5.5 wt.% of B₂O₃And any and all subranges formed by any of the foregoing endpoints.

MgO can enter petalite crystals in the form of partial solid solution. In some embodiments, the glass or glass-ceramic composition comprises from about 0 wt.% to about 8 wt.% MgO. In some embodiments, the glass or glass-ceramic composition may comprise from 0 wt% to about 8 wt%, from 0 wt% to about 7 wt%, from 0 wt% to about 6 wt%, from 0 wt% to about 5 wt%, from 0 wt% to about 4 wt%, from 0 wt% to about 3 wt%, from 0 wt% to about 2 wt%, from 0 wt% to about 1 wt%, from about 1 wt% to about 8 wt%, from about 1 wt% to about 7 wt%, from about 1 wt% to about 6 wt%, from about 1 wt% to about 5 wt%, from about 1 wt% to about 4 wt%, from about 1 wt% to about 3 wt%, from about 1 wt% to about 2 wt%, from about 2 wt% to about 8 wt%, from about 2 wt% to about 7 wt%, from about 2 wt% to about 6 wt%, from about 2 wt% to about 5 wt%, from about 2 wt% to about 4 wt%, about 2 wt% to about 3 wt%, about 3 wt% to about 8 wt%, about 3 wt% to about 7 wt%, about 3 wt% to about 6 wt%, about 3 wt% to about 5 wt%, about 3 wt% to about 4 wt%, about 4 wt% to about 8 wt%, about 4 wt% to about 7 wt%, about 4 wt% to about 6 wt%, about 4 wt% to about 5 wt%, about 5 wt% to about 8 wt%, about 5 wt% to about 7 wt%, about 5 wt% to about 6 wt%, about 6 wt% to about 8 wt%, about 6 wt% to about 7 wt%, or about 7 wt% to about 8 wt% MgO, and any and all subranges formed by any of the foregoing endpoints.

ZnO can enter petalite crystals in the form of partial solid solution. In one or more embodiments, the glass or glass ceramic composition comprises from about 0 wt.% to about 10 wt.% ZnO. In some embodiments, the glass or glass-ceramic composition may comprise from 0 wt% to about 10 wt%, from 0 wt% to about 9 wt%, from 0 wt% to about 8 wt%, from 0 wt% to about 7 wt%, from 0 wt% to about 6 wt%, from 0 wt% to about 5 wt%, from 0 wt% to about 4 wt%, from 0 wt% to about 3 wt%, from 0 wt% to about 2 wt%, from 0 wt% to about 1 wt%, from about 1 wt% to about 10 wt%, from about 1 wt% to about 9 wt%, from about 1 wt% to about 8 wt%, from about 1 wt% to about 7 wt%, from about 1 wt% to about 6 wt%, from about 1 wt% to about 5 wt%, from about 1 wt% to about 4 wt%, from about 1 wt% to about 3 wt%, from about 1 wt% to about 2 wt%, from about 2 wt% to about 10 wt%, from about 2 wt% to about 9 wt%, about 2 wt% to about 8 wt%, about 2 wt% to about 7 wt%, about 2 wt% to about 6 wt%, about 2 wt% to about 5 wt%, about 2 wt% to about 4 wt%, about 2 wt% to about 3 wt%, about 3 wt% to about 10 wt%, about 3 wt% to about 9 wt%, about 3 wt% to about 8 wt%, about 3 wt% to about 7 wt%, about 3 wt% to about 6 wt%, about 3 wt% to about 5 wt%, about 3 wt% to about 4 wt%, about 4 wt% to about 10 wt%, about 4 wt% to about 9 wt%, about 4 wt% to about 8 wt%, about 4 wt% to about 7 wt%, about 4 wt% to about 6 wt%, about 4 wt% to about 5 wt%, about 5 wt% to about 10 wt%, about 5 wt% to about 9 wt%, about 5 wt% to about 8 wt%, about 5% to about 7%, about 5% to about 6%, about 6% to about 10%, about 6% to about 9%, about 6% to about 8%, about 6% to about 7%, about 7% to about 10%, about 7% to about 9%, about 7% to about 8%, about 8% to about 10%, about 8% to about 9%, or about 9% to about 10% by weight ZnO, as well as any and all subranges formed by any of the foregoing endpoints.

In various embodiments, the glass or glass-ceramic composition may further comprise one or more components, such as, but not limited to, TiO₂、CeO₂And SnO₂. Additionally or alternatively, an antimicrobial component may be added to the glass or glass-ceramic composition. Antimicrobial components that may be added to the glass or glass-ceramic may include, but are not limited to, Ag, AgO, Cu, CuO, Cu₂O and the like. In some embodiments, the glass or glass-ceramic composition may further comprise a chemical fining agent. Such fining agents include, but are not limited to, SnO₂、As₂O₃、Sb₂O₃F, Cl and Br. Additional details of Glass and/or Glass-ceramic compositions suitable for use in various embodiments can be found, for example, in U.S. patent application publication No. 2016/0102010, filed on 8/10/2015, entitled "High Strength Glass-ceramic with Petalite and Lithium Silicate Structures" (High Strength Glass-Ceramics with Glass Ceramics and Lithium Silicate Structures), the entire contents of which are incorporated herein by reference.

In various embodiments, the glass composition may be formed into a sheet by methods including, but not limited to, slot draw, float, roll, and other sheet forming methods known to those skilled in the art.

Controlled bulk nucleation and growth is essential to produce the desired glass-ceramic product. As shown in fig. 2A, bulk nucleation (both homogeneous and heterogeneous) is performed at elevated temperatures for a period of time. Historically, the nucleation temperature and time were empirically selected to be above the glass transition temperature (Tg) or the annealing temperature, as shown in fig. 2B. Similarly, growth temperatures and times above the nucleation temperature are also empirically selected. The optimum time and temperature can be achieved by varying the time and temperature of the nucleation and growth phases during processing. Nucleation and crystal growth events tend to overlap. Thus, physical properties such as viscosity change with time during both the nucleation and growth steps. However, the rate of increase in density and/or viscosity changes when transitioning from the nucleation phase to the growth phase. When the rate of increase in density and/or viscosity changes significantly, the ceramming process may not produce the desired final glass-ceramic product.

To avoid sagging, sticking or adhesive deformation, the time and temperature of the processing cycle should be controlled. Most conventional methods include trial and error based testing in a thermal cycle of intuitive design, which is improved by material characterization methods. Some examples of such characterization methods are measurement of the heat flow of the crystallization peak as a function of annealing time using differential scanning calorimetry or in situ analysis of the X-ray diffraction peak over time. Most of these methods do not help the developer to find the optimal conditions for dimensional stability and they are very laborious and time consuming. To overcome all of these disadvantages, embodiments disclosed and described herein for ceramming glass articles automatically determine a ceramming cycle that will result in a desired glass-ceramic article. Embodiments of the ceramming method include two analytical tools: (1) an Automatic Viscosity Controller (AVC) for determining a period of a nucleation step and a transition heating step from nucleation to crystal growth; (2) a non-contact in-situ density measurement method that determines the duration of crystal growth. The whole ceramming cycle can be directly obtained using both methods.

The goal of Automatic Viscosity Control (AVC) is to maintain the glass at a constant viscosity to determine the time-temperature period with minimal sag during the ceramming cycle of the glass. In this embodiment, a constant viscosity is maintained by: a) calculating instantaneous viscosity using the rate of deflection of the glass beam under constant stress in a three-point beam bending apparatus, and b) dynamically varying the heating/cooling rate using a proportional-integral-derivative (PID) control loop that determines the power output provided to the furnace. The PID logic automatically increases the temperature as the viscosity of the glass article increases, and decreases the temperature as the viscosity of the glass article decreases. The PID control loop ensures a power output that varies with deviation from the target viscosity, thereby avoiding overshoot. Fig. 3 shows an embodiment implementing AVC software logic. FIG. 3 is a PID flow chart showing the initial calculation of the instantaneous temperature ramp rate using a PID control loop for the target viscosity-the current measured viscosity. The PID logic then calculates the ramp rate to calculate the controller setpoint. Next, it is determined whether the previously calculated set point has changed relative to the last set point. If the calculated set point has changed, the controller set point is changed and the PID logic will end and reset. If the calculated set value is not changed, the PID logic is ended and reset.

Fig. 4 illustrates communication between software logic, a furnace, and a measurement device, according to some embodiments. This method is applied to a three-point bending viscometer based on the idea of constant stress, known geometry and varying furnace temperature. As shown in fig. 4, a computer (e.g., PC) is connected to the furnace controller and analog input device. The furnace controller modifies a parameter within the furnace, such as temperature, based on input information received from the PC. The furnace is also connected to a linear variable differential controller (LVDT) which collects furnace output information (e.g., related to temperature, viscosity, etc.) and transmits this data to an analog input device. As previously described, the PC receives data from the analog input device and calculates a set point, such as a temperature set point, for transmission to the furnace controller. With this control, the viscosity of the glass article can be kept relatively constant (e.g., within ± 1.0 poise of log viscosity) during the nucleation stage.

The time-temperature cycle is obtained by defining a target constant viscosity that the glass article is to maintain. In this step (according to some embodiments), the maximum temperature, maximum heating rate, target viscosity, sample geometry, sample size, sample density, total applied load, span size of the three-point bending apparatus are all input information in the software. The AVC then automatically defines a time-temperature schedule, following software logic, as explained with reference to FIG. 3, until the beam deflection (glass viscosity) is outside the measurement range. The viscosity measurement range is generally good enough to capture the nucleation step and the transition from the nucleation step to the crystal growth step (heating range change). However, viscosity measurements do not accurately capture the crystal growth phase itself.

Fig. 5 shows an embodiment of a method for three different viscosity determinations by AVC. After the target viscosity is reached (e.g., about 11.00 in fig. 5), the viscosity is maintained by AVC until the crystal growth rate accelerates (e.g., about 305 minutes). During the crystal growth phase, the AVC heating rate cannot maintain a constant viscosity and the viscosity begins to increase. When the deflection falls below the measurable range, viscosity fluctuations are observed due to the limited reliability of the viscosity data. Therefore, the AVC determined time-temperature period should be limited to a time when viscosity cannot be maintained.

Fig. 6 shows an example of time-temperature cycles determined by AVC for 5 different target logarithmic viscosities 10.7, 10.8, 10.9, 11.0 and 11.1. In fig. 6, the same maximum temperature was reached for all cycles, since 800 ℃ was entered in the software as the maximum temperature. Above this temperature, AVC is not expected to control viscosity and therefore is not monitored or controlled in some embodiments. Similarly, after the transition is complete, the heating rate is linear and the heating rate values are the same for each composition. This corresponds to the maximum heating rate value provided to the software to avoid overheating when the deflection rate (viscosity) is outside the measurement range. Thus, the data obtained from AVC is limited to the initial nucleation range and the non-linear transition range. Also, this data does not accurately describe the course of the crystal growth phase. To measure the progress of the crystal growth phase, the in situ density was monitored.

According to one or more embodiments, the in-situ density is calculated by measuring the one-dimensional strain as a function of time and temperature, and assuming that the glass ceramming process is isotropic. Thus, it is believed that there is a linear relationship between volume and one-dimensional strain. The noncontact dilatometer measurements were made using a model DIL806 optical dilatometer from TA instruments. Fig. 7 schematically shows a measuring device comprising a light source emitting light into a pan furnace and into a glass sample. After the emitted light contacts the glass sample, it is transmitted to a detector, which can determine the change in light received therein, which can then be used to measure the density of the sample. Basically, this method involves measuring the shadow of both ends of the sample when it is heat treated in a heating furnace. The light source is located on the opposite side of the furnace from the detector and the movement of the shadow is related to the density change during crystal growth. Unlike conventional expansion methods, the sample can stand freely on the sample holder without applying external forces. According to some embodiments, the ceramming process typically occurs in the logarithmic viscosity range of 9-12 poise viscosity, with negligible viscous flow induced by gravity on the process time scale.

According to some embodiments, the AVC-determined nucleation and transition time-temperature periods are provided to the optical dilatometer software. The final crystal growth temperature is then varied and an isothermal step input is provided that is longer than any expected duration of crystal growth to ensure that the crystal growth process is complete. When the density increases to reach the saturation point, it is believed that there is no significant change in crystal size and, therefore, the viscosity and density are constant over time. This step helps identify any unwanted crystal formation or unexpected drop in viscosity above the desired growth temperature. The final ensemble (ensemble) and phase of the glass-ceramic can be determined and compared to the data collected from the density measurements to determine how the process affects the ensemble and phase of the glass-ceramic.

As used herein, when the absolute value of the rate of change of density of the glass article is less than or equal to 0.10 (g/cm)³) Min, e.g. less than or equal to 0.09 (g/cm)³) Min is less than or equal to 0.08 (g/cm)³) Min is less than or equal to 0.07 (g/cm)³) Min is less than or equal to 0.06 (g/cm)³) Min, less than or equal to 0.05 (g/cm)³) Min is less than or equal to 0.04 (g/cm)³) Min is less than or equal to 0.03 (g/cm)³) Min is less than or equal to 0.02 (g/cm)³) Min is less than or equal to 0.01 (g/cm)³) A/min, or 0.00 (g/cm)³) At/min, the density was considered constant. These ranges include all ranges and subranges included within the broad ranges disclosed above.

FIG. 8 illustrates the evolution of density at six different growth temperatures according to one embodiment. When the density reaches a plateau, the process is considered complete or nearly complete, which can be confirmed by other characterization methods, such as X-ray diffraction (XRD), and used as the duration of the last step of the ceramming process. At high temperatures (i.e., 780 ℃ and 800 ℃), the density changes non-monotonically, possibly due to the formation of undesirable phases or phase separation.

According to some embodiments, it is desirable to adjust the ceramming cycle of the glass-ceramic to achieve minimal warpage. FIG. 9 shows in-situ density measurements of glass-ceramics during ceramming for various ceramming plans. In fig. 9, a plot of density in grams/cubic centimeter (plotted on the y-axis) versus time in minutes (plotted on the x-axis) is shown. The figure shows that during the nucleation, temperature rise and growth phases, the glass article undergoes not only temperature dependent thermal expansion and contraction, but also dynamic time dependent non-thermal contraction. As shown in fig. 9, during the nucleation hold at constant temperature (i.e., from about 100 minutes to about 350 minutes), the part shrinks due to material changes, which is indicated by an increase in density. During the temperature increase from nucleation to growth, a first decrease in density is observed, followed by a rapid increase in density, the latter due to material shrinkage caused by rapid crystallization.

FIG. 10 illustrates in-situ viscosity measurements of a glass-ceramic during ceramming according to various ceramming cycles of the embodiment shown in FIG. 9. In fig. 10, the y-axis represents log viscosity (log 10) poise and the x-axis represents test time in minutes. During the nucleation phase, the viscosity has similar temperature-dependent and time-dependent non-thermal behavior. During the maintenance of nucleation at constant temperature, the viscosity increases, the rate of increase depending on the nucleation temperature. During the temperature rise, the viscosity first decreases and then increases, resulting in a dip and a local minimum. A unified ceramization viscosity model was established using the Beam Bending Viscosity (BBV) measurements and in situ viscosity measurements of the precursor glass and ceramic as shown in fig. 11. The composition of the glass shown in fig. 10 is shown in table 1 below.

TABLE 1

Components	By weight%
		SiO₂	73.89
Al₂O₃	7.60
		P₂O₅	2.11
Li₂O	11.50
		Na₂O	0.05
K₂O	0.15
		ZrO₂	4.24
SnO₂	0.40
		Fe₂O₃	0.06

Viscoelastic numerical simulations were then performed in some embodiments to understand the effect of these viscosity changes on warpage. Numerical modeling has found that local minimum viscosity, combined with in-plane temperature gradients generated during warming, can trigger viscous buckling and cause warping. Fig. 12A-12C show warpage for three hypothetical cycles (A, B, C). Period a is the base case; period B has a faster viscosity increase rate during nucleation and a higher minimum viscosity during temperature ramp; cycle C has a slower viscosity increase rate during nucleation and a lower minimum viscosity during temperature ramp. The warpage values for these cases are: c > A > B (shown in FIG. 12C, FIG. 12A, and FIG. 12B, respectively). A lower minimum viscosity will produce a greater viscous buckling type of warpage. In other words, increasing the minimum viscosity facilitates reducing buckling-type warpage.

In some embodiments, the minimum viscosity may be maintained at or above 11.0 poise logarithmic viscosity for any and/or all of the ramp and hold portions of the heating cycle. For example, for a ramp up to a first heating ramp up phase, a second heating ramp up phase, or an entire heat treatment cycle, the minimum viscosity may be maintained at or above 11.0 poise logarithmic viscosity. In some embodiments, the minimum viscosity may be maintained at or above 11.0 poise logarithmic viscosity for any and/or all of the ramp and hold portions of the heating cycle. In some embodiments, the viscosity of the glass article may be maintained less than 11.0 poise logarithmic viscosity at least during the nucleation stage, which may be advantageous when 3D forming the glass article during heat treatment.

Fig. 13A-13C show the warpage of three ceramming cycles corresponding to nucleation and growth temperatures of ± 10 ℃. Cycle A was carried out at a nucleation temperature of 560 ℃ for 4 hours, a growth temperature of 730 ℃ for 1 hour (as shown in FIG. 13A), cycle D at a nucleation temperature of 570 ℃ for 4 hours, a growth temperature of 740 ℃ for 1 hour (as shown in FIG. 13B), cycle E at a nucleation temperature of 580 ℃ for 4 hours, and a growth temperature of 750 ℃ for 1 hour (as shown in FIG. 13C). The warpage values in these cases are: e < D < a. Again, the same trend is shown, i.e. increasing the minimum viscosity will reduce buckling-type warpage. In cycle E, the minimum viscosity remains above 11.0 poise log viscosity during temperature rise, resulting in very little warpage, e.g., <1 μm.

When the goal is to ceramming the flat glass with minimal warpage, in some embodiments, period E is preferred over other periods due to the lower minimum viscosity value during growth ramp. Note that, in the nucleation phase, the lower viscosity of the period E is less likely to cause warpage because Δ T is lower during temperature holding (compared to during temperature rising).

More generally, in some embodiments, to minimize buckling-related warpage, a period that produces a higher "minimum viscosity" during the "ramp-to-growth" phase (where the highest Δ T is observed) may be preferred. This may be referred to as the "minimum viscosity" during the ramp-up phase, and the model may be used as a screening tool to predict the effect of this minimum on the final warpage.

In addition to increasing the local minimum viscosity to reduce buckling-type buckling, some weight restraining force may be applied to increase the buckling threshold. In a stacked configuration, having the weight on top of the stack be sufficient to prevent buckling of the uppermost piece of glass will ensure that the underlying layers will not buckle. Applying a weight restraining force to the top of the stack may also reduce the minimum acceptable viscosity to prevent buckling of the glass articles.

When the part is placed horizontally on the locator material, gravity will cause warping in addition to viscous buckling if the locator is not flat. The tack drop analysis is shown in figure 14. In the region of 30mm diameter, the viscous sag would reach about 100 μm at a logarithmic viscosity of 11.0 poise and 0.5 hour. Figure 14 shows that larger areas (diameter >30 mm)/lower viscosity (log viscosity <11 poise)/longer duration (>0.5 hours) will produce a viscous sag of >100 μm. If the flatness of the positioner is better than 100 μm, the glass will sag and conform to the positioner under these conditions. If the flatness of the fixture is greater than 100 μm, the tack droop will also be greater than 100 μm. Thus, to minimize gravity-induced warpage, the positioner needs to be flat (e.g., less than or equal to 100 microns).

When the objective is to form the glass into a 3D shape, in some embodiments, a cycle with a lower viscosity will be preferred, and the application of the forming pressure will coincide with the period of time during the cycle with the lower viscosity. The 3D shaping can be performed before nucleation, during nucleation-to-growth temperature elevation, and in some cases even during the growth maintenance phase. The proper selection may depend on various factors such as the 3D geometry to be formed, the viscosity of each stage (depending on temperature, time and rate of temperature rise), and warpage. For example, since ceramming 3D-shaped glass can result in significant warpage, forming pre-nucleated glass may be one means to reduce the final post-ceramming warpage of the 3D article.

When 3D forming is to be performed during the nucleation hold, in some embodiments, period E (described above with reference to fig. 13) may be preferred over periods a and D because its viscosity is lower than the other periods about 100 minutes from the start of the nucleation hold. The results of fig. 14 show that for curve E, the viscosity is low enough to cause sagging of several millimeters under gravity within 60 minutes. Thus, in the nucleation hold stage, many 3D shapes can be formed under these conditions with the additional forming pressure. In the case of single-mold forming, this pressure may be in the form of a partial or complete vacuum on the side of the mold, or positive air pressure (typically N) on the other side of the forming mold₂Or air). In the case of two (or more) presses, pressure is applied from both sides.

Alternatively, in some embodiments, 3D shaping may be completed completely in the nucleation to growth warming phase. In this case, in some embodiments, period a will be more desirable than periods D and E. In this case, the buckling risk can still be controlled due to the constraining forces of the die contact/forming pressure.

It is also contemplated to use a new cycle for the formation during nucleation. For example, the nucleation temperature may be further increased during a first portion of the cycle, such as up to 590 ℃, 600 ℃, or even 610 ℃, for a sufficient time to just complete the 3D formation, and then decreased for the remainder of the cycle (and if desired, the duration of the nucleation hold may be shortened) so that the final crystal content at the end of the cycle is the same as the base cycle a. Higher temperatures initially produce lower viscosities and allow more challenging shapes to be formed in a shorter time. Having the same crystal content as the basic case would mean that, in addition to having a favorable phase distribution, the low viscosity of curve a during the temperature ramp to growth can be replicated, providing another opportunity for completing the 3D shaping.

The 3D forming and ceramming may be performed in the same cycle or in multiple cycles. For example, in one embodiment, the precursor glass may be shaped into a 3D shape and then a separate cycle may be utilized to ceram the 3D article. In another embodiment, the glass preform may be partially or fully "pre-nucleated" in a first cycle, then 3D formed in a second cycle, and then ceramming may be completed in the second cycle or in a third separate cycle. Because 3D forming of only one glass article can be accomplished at a time, pre-nucleating the glass preform can improve throughput by allowing the stack to nucleate as compared to nucleating and 3D forming in the same cycle.

When the glass preform is fully pre-nucleated, the temperature increase to the growth temperature is a natural choice for 3D forming. As previously mentioned, in some embodiments, in such a case, cycle a may be more desirable than cycle D or E because of the lower viscosity during the warming to the growth temperature. When the glass is only partially pre-nucleated, the 3D forming may be performed during the nucleation, during the ramp to the growth temperature, or partially during the nucleation and partially during the ramp to the growth temperature.

To prevent warping of the 3D article during the ceramming cycle, ceramming may be performed on a mold (one, two, or three pieces), the temperature gradient should be kept low (e.g., using a mold of a high thermal conductivity material, such as graphite or SiC), and a load should be applied to force the 3D article to remain in conformance with the mold during ceramming.

As noted above, precise control of the glass article temperature is required to achieve the desired glass-ceramic article. Thus, according to some embodiments, thermal uniformity within the heating apparatus (e.g., lehr or furnace) and within the glass stack is an important attribute of the process. For example, in some embodiments, the temperature provided to the stack varies by less than or equal to ± 8 ℃, such as less than or equal to ± 7 ℃, less than or equal to ± 6 ℃, less than or equal to ± 5 ℃, or less than or equal to ± 4 ℃, where the temperature is measured on the glass sheet itself.

To achieve the above-described thermal uniformity, thermal mapping is performed on the interior chamber of the hollow heating device prior to inserting the fixtures (e.g., the brackets, locators, and glass stack) into the heating device. Thermal mapping of the empty heating device cavity is performed, and the space within which thermal uniformity can be maintained within a desired tolerance is determined, thereby determining the available heating space within the heating device cavity. For example, portions of the heating apparatus chamber that fail to maintain thermal uniformity that differs from the programmed cycle temperature by less than or equal to ± 8 ℃ will be excluded from the heating space in which the glass stack can be placed. After mapping the empty heating apparatus chamber to determine the available heating space, the fixture is placed in the currently determined heating space and the thermal uniformity of the glass stack is measured to determine whether the glass sheets in a given glass stack can be maintained within the desired temperature tolerance of the programmed cycle temperature. Once the thermal uniformity is determined, the glass stack can be configured and placed in the heating space using the obtained thermal uniformity measurements.

A method for determining thermal uniformity within the interior chamber of a heating apparatus will now be described with reference to fig. 15A and 15B. In some embodiments, the placement of the measuring device (e.g., thermocouple) within the chamber of the heating apparatus should take into account the design of the heating apparatus, e.g., walls, doors, heating elements, vents, etc., of the chamber of the heating apparatus. The measurement device should be placed at a location remote from the design elements in order to reduce any thermal non-uniformities caused by such design elements during the thermal mapping process. Furthermore, the measuring device should be placed in the chamber of the heating device in such a way that the thermal homogeneity of the entire heating space can be determined. For example, the measurement device should be placed within the heating apparatus chamber such that measurements are taken at multiple locations within the heating apparatus chamber to minimize "dead spots" or locations without measurements.

Fig. 15A and 15B show the horizontal and vertical arrangement of the measuring device within the chamber of the heating apparatus, respectively. First, the expected heating space 310 (indicated by the space within the dotted line in fig. 15A and 15B) is estimated in consideration of the design elements of the heating apparatus chamber. As shown in fig. 15A and 15B, the desired heating space 310 is selected such that there is a space between the top, bottom and side walls of the heating device chamber. Fig. 15A shows a horizontal arrangement of the measuring device (i.e., as viewed from the top or bottom of the heating apparatus chamber) according to some embodiments. As shown in fig. 15A, fifteen measuring devices (elements 1 to 15) are placed in a spaced configuration in each horizontal cross section of the heating apparatus chamber. According to the embodiment shown in fig. 15A, placing the measurement devices 1-15 horizontally in the heating apparatus chamber would be expected to provide sufficient thermal mapping for the horizontal space of the heating apparatus chamber. However, it should be understood that other horizontal arrangements of the measuring devices may be used in alternative embodiments.

Similarly, fig. 15B shows a vertical arrangement (i.e., a side view) of the measurement device in the heating apparatus chamber. Three rows of measuring devices, top, middle and bottom, are indicated by "T", "M" and "B", respectively, in FIG. 15B, and are placed in a spaced configuration into the chamber of the heating apparatus. According to the embodiment shown in fig. 15B, placing the measurement devices vertically in the upper, middle, and lower rows of the heating device chamber would be desirable to provide adequate thermal mapping for the vertical space of the heating device chamber. However, it should be understood that other horizontal arrangements of the measuring devices may be used in alternative embodiments. When viewed together, fig. 15A and 15B show 45 measurement devices in a spaced configuration (three rows top, middle and bottom, 15 measurement devices in each row) that would be expected to adequately map the desired thermal performance of the heated space 310. However, it should be understood that other arrangements of the measuring device may be used in alternative embodiments.

In some embodiments, the measuring devices are arranged as little as possible at each corner, all centerlines, and all spatial center points within the intended heating space. If thermal non-uniformity design elements are present, additional measurement devices may be placed near such elements to map the effects of these elements on thermal uniformity and determine how close the heating space may be to these thermal non-uniformity design elements. The vertical arrangement of the measuring device should be considered and in some embodiments will determine the height at which the glass stack and/or the fixing device can be placed within the heating apparatus chamber. If the top or bottom surface of the heating apparatus chamber has been heated or not, the adjacent measurement devices should take into account the location of the heater elements, as well as any other non-flat surfaces that may disturb or interrupt the thermal response of the measurement devices. In one or more embodiments, the vertical spacing of the heating device cavity is every 25mm from the bottom 320 of the heating device cavity to a distance between 50mm and 100mm from the top 330 of the heating device cavity.

Once the measuring device is placed in the heating apparatus cavity, a heating cycle is performed. According to some embodiments, the heating cycle may include the same heating conditions as the cycle used for ceramming the glass articles. During this heating cycle, the measuring devices periodically or continuously measure their temperature at their respective locations within the heating apparatus chamber. These temperatures measured by the measuring means can then be analyzed and compared to determine if one or more locations within the heating apparatus chamber are not within a tolerance, e.g., ± 8 ℃, expected from the programmed cycle temperature. If one or more locations of the heating apparatus chamber do not fall within the desired tolerances, those locations of the heating apparatus chamber are excluded from the heating space that may be used in the ceramming cycle. In some embodiments, if one or more locations of the heating apparatus chamber do not fall within the desired tolerance, the measurement device may be moved to exclude locations within the heating apparatus chamber that do not fall within the desired tolerance, and one or more additional heating cycles may be run to perform additional thermal mapping. This process may be repeated any number of times to determine a heated space within the heating apparatus chamber that may be maintained within desired tolerances.

Once the measuring device is in a position such that all measuring positions of the heating apparatus chamber fall within the desired tolerance, the space within the heating apparatus chamber determined by the measuring device will be considered a heated space. In some embodiments, once the heating space is determined, the glass stack and the fixture (e.g., bracket) can be designed and/or configured so that they fit within the heating space. The designed glass stack and fixture are then loaded into a heating space within the chamber of the heating apparatus, and the measuring device centrally located in the heating space is removed to accommodate the fixture. A heating cycle is performed to determine the effect of the fixture on thermal uniformity within the heating space, which in some embodiments is the same heating cycle used to determine the heating space. The programmed thermal profile can then be adjusted to accommodate the effects of the fixture and the glass stack.

According to some embodiments, after determining the effect of the heating space and the glass stack and fixture on the thermal response within the chamber of the heating apparatus, the thermal uniformity within the glass stack can be found by placing the measuring device into the glass stack and removing any measuring devices used in the previous steps to determine the effect of the heating space and the glass stack and fixture on the thermal response.

According to some embodiments, placement of the measuring device within the glass stack is important to provide reliable and repeatable data. The thermal conductivity of the glass should be considered for each layer, so that only one piece of glass between the positioner and the measurement device will provide a sufficient thermal characterization of the glass sheet and will capture the thermal influence of the positioner on the stack. Thus, in some embodiments, the number of measurement devices included in the glass stack will vary depending on the physical dimensions of the glass stack and the desired thermal mapping details. For example, in one or more embodiments, nine measuring devices can be placed in the stack, with three measuring devices placed along the centerline of the glass sheet below the top positioner; three measuring devices are placed along the center line of the glass sheet at the geometric center of the glass stack; three measuring devices are placed along the centerline of the glass sheet above the bottom locator. As used in this example, a centerline is a line drawn along the length of the glass sheet that is substantially parallel to two edges of the glass sheet, substantially perpendicular to the other two edges of the glass sheet, and intersects the geometric center of the glass sheet. It should be understood that as used herein, "substantially parallel" and "substantially perpendicular" refer to a centerline that is parallel or perpendicular, respectively, to such edges in view of manufacturing-induced edge irregularities. In the above embodiment where three measuring devices are placed along the centerline of the glass sheet, one measuring device (e.g., thermocouple) is placed on the centerline near the left side of the glass sheet, one measuring device is placed at the geometric center of the glass sheet, and one measuring device is placed along the centerline of the glass sheet near the right side of the glass sheet. This configuration was followed for all three glass sheets considered. The middle layer of the stack typically provides a middle reference for the entire stack. It should be understood that the arrangement of the measurement devices disclosed above is merely exemplary, and other arrangements may be employed in some embodiments depending on the desired specificity of the desired thermal mapping. For example, in embodiments where thermal uniformity is to be tightly controlled, more measurement devices will be placed on each glass sheet to obtain a more detailed thermal map. Any number of measuring devices can be used in the glass stack as long as the number of measuring devices does not substantially interfere with the thermal profile of the glass sheets. All layers to be measured can then be measured to understand the response of the thermal profile of the glass to the programmed thermal profile, as discussed in more detail below.

Figure 16 shows the stacked glass temperature differential (Δ T) between the top (i.e., the glass sheet below the top positioner), the middle (i.e., the glass sheet at the geometric center of the glass stack), and the bottom (i.e., the glass sheet above the bottom positioner) of the glass stack, as measured by a measuring device located at or near the geometric center of each glass sheet. Such a map can be used to understand the magnitude and location of the temperature deviation. Figure 16 shows the temperature of a glass stack having 18 glass sheets and three positioners interspersed within the stack such that there are six glass sheets between each two positioners. As shown in fig. 16, the temperature of the glass sheets located near the bottom of the glass stack is lower than the temperature of the glass sheets located near the middle of the glass stack and the glass sheets located near the top of the glass stack. Such a determination is indispensable because the time and temperature at which the ceramic article is cerammed may affect the change in the measurement after ceramming of the desired attribute (e.g., color, haze, stress, phase ensemble, etc.). Thus, understanding and controlling the temperature differential between the glass sheets in the glass stack has an effect on the final properties of the glass-ceramic article.

In some embodiments, the temperature difference from the expected thermal profile is measured and analyzed in both the vertical and horizontal planes. The vertical deltat is generally affected by the choice of fixture materials, the height of the glass stack, and the heating and cooling rates of the process equipment. The level Δ T is generally affected by the non-uniformity of the process equipment, the placement of the glass stack within the heating space, and the heating design (how the heat is directed to the glass stack). According to some embodiments, controlling Δ T within the stack is important to achieve uniformity of high throughput glass sheets. It should be understood that the tolerance for Δ T will vary depending on the glass composition and the desired properties of the final glass-ceramic article.

In embodiments where the glass article has a glass composition as disclosed and described herein, the Δ T within the glass stack may be maintained within ± 5 ℃ of the programmed temperature profile during the isothermal hold (also referred to as "soak") phase of the ceramming process (i.e., the phases corresponding to the nucleation phase and the growth phase). When Δ T is outside this tolerance range in isothermal holding during the nucleation and growth phases, the various glass-ceramic sheets from the resulting ceramming process may have undesirable attributes such as warpage, bow, haze, etc. Fig. 17 shows the results for a glass stack comprising eighteen measuring devices. In fig. 17, the x-axis is time measured in seconds, the right y-axis is Δ T in degrees celsius, and the left y-axis is temperature of the glass sheet in degrees celsius. The tight groupings of the plotted lines represent the temperature of the glass sheet (corresponding to the left y-axis), while the wider groupings of the plotted lines show the Δ T of the glass sheet (corresponding to the right y-axis). As shown in fig. 17, during the first ramp-up cycle to heat the glass stack from ambient temperature to about 570 ℃, Δ T (measured relative to the programmed ceramming temperature) exceeded 40 ℃ for some of the glass sheets in the glass stack. However, after the completion of the temperature-raising cycle and the start of isothermal holding, the Δ T of the glass sheet decreases and is maintained at ± 5 ℃ or less during isothermal holding. In some embodiments, the ceramming cycle is adjusted based on the obtained Δ T measurements.

For example, in one or more embodiments, it is desirable that the duration of the programming isothermal hold occur within ± 5 ℃ of Δ T. As shown in fig. 17, constant temperature maintenance at about 570 ℃ was initiated before the Δ T of the glass stack was within ± 5 ℃ of the program ceramming cycle. Thus, the programming isothermal hold can be extended such that the initial duration of the isothermal hold is within ±. deg.c at Δ T. By way of non-limiting example, if an isothermal hold of about 570 ℃ is initially programmed to have a duration of 4 hours, it may be desirable to hold the glass stack within a range of Δ T of + -5 ℃ for a duration of 4 hours (i.e., to match the initially programmed isothermal hold time). For this reason, isothermal incubation may need to be extended beyond 4 hours to compensate for the time it takes for the Δ T of the glass stack to reach the ± 5 ℃ range. The data collected in the manner shown in fig. 17 can be used to determine how much time the isothermal hold is adjusted and to determine the time it takes for the Δ T of the entire glass stack to be within ± 5 ℃. In one or more embodiments, the duration of the isothermal hold of the nucleation phase may be adjusted to + 10%, e.g., + 9%, + 8%, + 7%, + 6%, + 5%, + 4%, + 3%, + 2%, or + 1%.

Similar to the above description, fig. 17 shows that the Δ T during the ramp up period from about 570 ℃ to about 750 ℃ exceeds ± 5 ℃, and can exceed 20 ℃ in certain glass sheets within the glass stack. However, as with the constant temperature hold at about 570 ℃ during the nucleation phase, the Δ T returns to within + -5 ℃ after a period of constant temperature hold at about 750 ℃ during the growth phase. As with isothermal holding at about 570 ℃, in some embodiments, it may be desirable to maintain the glass stack to within ± 5 ℃ at for the initial program duration of isothermal holding during the growth phase. Thus, the duration of the growth phase isothermal hold can be adjusted as described above such that the glass stack is maintained at a Δ T within ± 5 ℃ for the duration of the growth phase isothermal hold initially programmed. In one or more embodiments, the duration of the isothermal hold of the growth phase may be adjusted by + 10%, e.g., + 9%, + 8%, + 7%, + 6%, + 5%, + 4%, + 3%, + 2%, or + 1%.

Figure 18 shows a detailed view of the thermal response of a glass stack according to some embodiments. The temperature difference of each glass sheet in the glass stack during the various ramp-up and cool-down cycles is shown in the expanded view in the graph of fig. 18. This information helps to understand how the glass stack thermally responds to the heating profile as programmed. Deviations in the measured temperature of the glass sheet from the programmed heating profile during the transition may or may not affect the glass properties, but it may limit the process if the thermal processing apparatus is operated at 100% or near 100% power output to achieve the desired thermal profile. This data can be used to fine tune the thermal profile to improve or maintain the properties of the final glass-ceramic article.

The temperature profile within the heating apparatus chamber and within the glass stack provides important information that can be used to adjust the programmed heating profile used in the ceramming cycle in various embodiments. In some embodiments, these adjustments to the programmed heating profile will improve the properties of the final glass-ceramic article, e.g., warpage, bending, haze, transparency, and the like. However, in other embodiments, these adjustments to the programmed heating cycle may not affect the properties of the final glass-ceramic article, but may improve the throughput of the ceramming process. However, in other embodiments, it may not be necessary to adjust the programmed heating period based on the measured temperature uniformity. For example, certain end products have high tolerance requirements and therefore require very transparent flat glass articles. For such products, it may be necessary to adjust the programmed heating cycle. However, other end products may have greater tolerance for the transparency, color, flatness, and stress of the glass. For such products, it may not be desirable to adjust the programmed heating period based on thermal uniformity within the glass stack.

As discussed in detail above, in some embodiments, it may be desirable to adjust the programmed heating period in view of the collected thermal uniformity data. However, thermal uniformity within the glass stack can also be controlled. As described above, the vertical Δ T may be controlled by modifying the stack structure, the locator material, the locator structure (e.g., inserting an intermediate layer of locator material between the top locator and the bottom locator), and so forth. Another way in which thermal uniformity within the glass stack can be controlled is to employ multiple stages of heating during the ceramming cycle. Reducing the rate of temperature increase during the nucleation and/or growth stages by employing multi-stage heating will result in slower heating of the glass stack and, therefore, will increase the thermal uniformity of the glass sheet. Exemplary embodiments of multi-stage heating are disclosed below.

By setting the heating source (e.g., radiant heater, convection heater, etc.) at multiple intermediate levels during heating, thermal uniformity of the glass sheet can be improved due to the adjustment of the heating rate. The effectiveness of this multi-stage heating operation can be evaluated using a complete lehr thermal model having a capacity of 9 stacks of 23 glass sheets in each stack on a single carriage. A nine stage heating protocol was investigated for heating from room temperature to nucleation conditions, and table 2 summarizes the controlled heater temperature levels in each stage. Figure 19 shows that the glass sheet temperature change is significantly reduced compared to a single stage heating with the heater set to a nucleation temperature of 570 ℃. For multi-stage heating, the heating rate is reduced and a longer heating time is required to reach the target nucleation temperature. For the nine-stage heating described above, 180 minutes were required to reach the nucleation temperature, while the single-stage heating was performed for 100 minutes. The multi-stage heating can be optimized to reduce thermal variation below a favorable level without increasing a substantial amount of heating time.

TABLE 2

The multi-stage heater arrangement can also be applied to growth stage heating and to reduce thermal variations on the glass sheet. The same effect is shown in fig. 20, which shows that the maximum glass sheet temperature change is reduced from 40 ℃ to about 25 ℃ with a three-stage heater arrangement. The actual heater temperatures for the three-stage heating were set at 620 ℃, 680 ℃ and 740 ℃, while the heater for the single-stage heating was set at a constant value of 740 ℃.

In some embodiments, it is important to keep thermal variations at a low level during cooling after growth in order to meet the stress and warpage requirements of the glass ceramic product. By controlling the thermal environment to which the hot glass stack dissipates heat, the cooling rate can be moderated, which can potentially reduce thermal variation of the glass sheets. In Lehr operation, this may be accomplished by setting the heaters at a plurality of intermediate levels during the cooling stage. The effectiveness of the multi-stage cooling was evaluated using a complete annealing furnace thermal model with mass production capability. As shown in fig. 21, the glass sheet temperature change is significantly reduced compared to single stage cooling. The multistage cooling is carried out in four stages, and the heaters are controlled at 665 deg.C, 590 deg.C, 515 deg.C and 440 deg.C, respectively. For single stage cooling, the heater was set at 300 ℃. One compromise point in multi-stage cooling is that the cooling rate is lower or takes longer to reach the target outlet temperature. For the four stage cooling described above, the average cooling rate was 3.3 ℃ lower than 5.3 ℃ for the single stage cooling case.

In view of the above disclosure, the thermal uniformity of the glass stack can be controlled, in part, by the configuration of the glass stack, the positioner, and the intermediate layer. In addition, the thermal uniformity of the glass stack can be partially controlled by the heating cycle used to heat the glass stack to the nucleation and growth temperatures. One or more of these controls can be used for ceramming cycles where the thermal uniformity tolerances are small, such as when it is desired to control Δ T to within ± 5 ℃.

Fig. 22 shows a conventionally obtained ceramming cycle (labeled COR) with two isothermal steps and linear heating rates compared to the AVC cycles for various target viscosities. As shown by the overlapping nucleation and growth steps, there is no isothermal step in the AVC process and the temperature increases at a relatively slower rate than the transition step. This also helps to shorten the total ceramming duration.

Fig. 23 shows the evolution of the density of the same conventional COR period and AVC period as shown in fig. 22. As expected, the density remained constant during the nucleation step, so minimal deformation/flow gradients were observed until the crystal began to grow. The transition then follows a smoother trend, unlike the conventional approach, where unavoidable non-monotonic behavior is observed with sudden drop in density.

It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit or scope of the claimed subject matter. Thus, it is intended that the specification cover modifications and variations of the various embodiments described herein provided such modifications and variations fall within the scope of the appended claims and their equivalents.

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