阅读说明：本技术 一种低烧成收缩率氧化铝陶瓷及其制备方法 (Low-firing-shrinkage alumina ceramic and preparation method thereof ) 是由 梁绍臻 马征 王志义 于 2021-08-03 设计创作，主要内容包括：本发明涉及一种低烧成收缩率的氧化铝陶瓷及其制备方法,属于特种陶瓷领域。本发明氧化铝陶瓷烧成收缩率不大于10％,主要采用工业α-Al-(2)O-(3)粉和RO-Al-(2)O-(3)-SiO-(2)烧结助剂,经高温烧结而成,其中,所述RO-Al-(2)O-(3)-SiO-(2)烧结助剂中的SiO-(2)由金属硅粉按等摩尔引入。本发明克服了现有技术生产安全风险过大的弊端,全面适用于氧化铝陶瓷的生产过程,在不改变陶瓷显微结构和力学性能的前提下,大幅度降低产品烧成变形度,提高制品的加工性能,降低加工成本。(The invention relates to an alumina ceramic with low firing shrinkage and a preparation method thereof, belonging to the field of special ceramics. The sintering shrinkage of the alumina ceramic is not more than 10 percent, and the industrial alpha-Al is mainly adopted 2 O 3 Powder and RO-Al 2 O 3 ‑SiO 2 The sintering aid is prepared by high-temperature sintering, wherein the RO-Al 2 O 3 ‑SiO 2 SiO in sintering aid 2 The metal silicon powder is introduced according to the equimolar amount. The invention overcomes the defect of overlarge production safety risk in the prior art, is comprehensively suitable for the production process of the alumina ceramic, greatly reduces the sintering deformation degree of the product on the premise of not changing the microstructure and the mechanical property of the ceramic, improves the processing performance of the product and reduces the processing cost.)

1. The low-sintering shrinkage alumina ceramic has sintering shrinkage not greater than 10%, and is produced with industrial alpha-Al₂O₃Powder and RO-Al₂O₃-SiO₂The sintering aid is prepared by high-temperature sintering, and is characterized in that the RO-Al is prepared by₂O₃-SiO₂SiO in sintering aid₂The metal silicon powder is introduced according to the equimolar amount.

2. The low firing shrinkage alumina ceramic of claim 1, wherein the RO-Al is₂O₃-SiO₂The introduction amount of the metal silicon powder in the sintering aid is not more than 5% of the blank amount according to the mass ratio.

3. The low firing shrinkage alumina ceramic of claim 1, wherein the median particle diameter D of the silicon metal powder₅₀Not more than 5um, and the mass content of silicon is not less than 98 percent.

4. The method for preparing the alumina ceramic with low firing shrinkage as claimed in claim 1, wherein when the ceramic body is formed by a dry method, the metal silicon powder can be directly added into the ceramic blank for forming.

5. The method for preparing the alumina ceramic with low firing shrinkage as claimed in claim 1, wherein when the ceramic body is formed by a wet method, the metal silicon powder needs to be pre-modified, and the process comprises the following steps:

(1) slowly adding the metal silicon powder into the absolute ethyl alcohol under the condition of strong stirring, and stirring for 1-5 hours;

(2) slowly adding organosilane, and uniformly stirring;

(3) slowly adding the silica sol with the adjusted pH value at a certain temperature, and continuously stirring for 4-6 hours;

(4) and cooling the mixture to room temperature, centrifugally separating out the modified metal silicon powder, and drying at 50-200 ℃ for use.

6. The method for preparing an alumina ceramic with low firing shrinkage according to claim 5, wherein the amount of the silica sol and the organosilane is determined according to the mass ratio of silica to organosilane being 1: 3-6; the absolute ethyl alcohol accounts for 20-40% of the total mass of the silica sol and the organosilane; the molar ratio of the metal silicon powder to the silicon dioxide in the silica sol is 5-10.

7. The method for preparing an alumina ceramic with low firing shrinkage according to claim 6, wherein the amount of the silica sol and the organosilane is determined according to the mass ratio of the silica to the organosilane being 1: 4-5; the absolute ethyl alcohol accounts for 30-40% of the total mass of the silica sol and the organosilane; the molar ratio of the metal silicon powder to the silicon dioxide in the silica sol is 6-8.

8. The method for preparing the alumina ceramic with low sintering shrinkage as claimed in claim 5, wherein the reaction temperature is 30-70 ℃, and the modified metal silicon powder is dried at 50-60 ℃ and then at 200 ℃ for 30-60 minutes at 180-.

9. The method for preparing the alumina ceramic with low firing shrinkage rate as claimed in claim 8, wherein the reaction temperature is 30-40 ℃, and the modified metal silicon powder is dried at 50 ℃ and then at 200 ℃ for 30 minutes.

10. The method for preparing the low firing shrinkage alumina ceramic according to claim 5, wherein the silica sol has a pH of 2 to 4 and a solid content (mass) of 25 to 35%; the organosilane is any one of methyltrimethoxysilane, gamma-glycidoxypropyltrimethoxysilane and gamma- (methacryloyloxy) propyltrimethoxysilane.

Technical Field

The invention relates to an alumina ceramic with low firing shrinkage and a preparation method thereof, belonging to the field of special ceramics.

Background

The shrinkage of the ceramic material is a problem which is generated in the sintering process of the product, the shrinkage is an important reason of the deformation and the cracking of the product, and the qualification rate of the product is directly reduced. The precision of the product is seriously affected by excessive shrinkage, and the method of reserving a large machining allowance is usually adopted in the technology to machine the burned product.

The alumina ceramic is the most widely used structural and functional material in the industry at present, has high strength, high hardness and strong brittleness, adopts a high-allowance production mode, and is extremely difficult to process and extremely high in cost. In particular, in recent years, as the particle size of the raw material is made ultrafine, the firing shrinkage of the alumina ceramic product is gradually increased from about 17% to about 23%, which causes a series of problems such as deformation, cracking, and increase in the machining allowance and difficulty during production.

Currently, there are few studies on reduction of firing shrinkage of alumina ceramics. Patent ZL201110282186.0 discloses a method for reducing the sintering shrinkage of alumina ceramics, which is realized by replacing alumina with superfine (less than or equal to 10um) high-purity (more than or equal to 98 percent) metal aluminum powder. However, the patent technology has serious potential safety hazard: the metal aluminum powder is a severely limited flammable and explosive product, is flammable, and the fine powder and air can form a flammable and explosive mixture; in the embodiments 1 and 2, it is clearly indicated that the metal aluminum powder is mixed with other raw materials after wet ball milling for 2 hours, and then the mixture is subjected to slip casting or spray drying, so that the high-purity metal aluminum powder is very easy to react with water, and particularly, during the mixing and slip casting processes, a large amount of hydrogen is generated, and aluminum hydroxide is generated, which not only seriously increases the explosion risk, but also does not achieve the purpose of 'low shrinkage of alumina ceramic caused by volume expansion of alumina due to oxidation of high-temperature aluminum powder', so that the feasibility is questionable. Only example 3 is theoretically possible, that is, under the premise of strictly ensuring safety, the ceramic product with low shrinkage rate can be prepared by dry mixing and hot-press molding (anhydrous molding mode), and obviously, the practicability of the ceramic product is seriously limited.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide an alumina ceramic with low firing shrinkage and a preparation method thereof, and particularly relates to an alumina ceramic with low firing shrinkage and a preparation method thereof, which utilize safe metal silicon powder to replace silicon dioxide in an alumina ceramic sintering aid, utilize high-temperature oxidation expansion of the metal silicon to effectively offset shrinkage of the alumina ceramic in the firing process, and simultaneously carry out pre-coating modification treatment on the metal silicon powder to avoid hydration reaction of the metal silicon powder in the wet forming process, thereby realizing the applicability of dry forming (hot-press casting forming and press forming) and wet forming (slip casting forming and slip casting forming) of the alumina ceramic.

The aim of the invention can be achieved by the following technical measures:

the low-firing shrinkage alumina ceramic has a firing shrinkage of not more than 10 percent and is mainly prepared from industrial alpha-Al₂O₃Powder and RO-Al₂O₃-SiO₂The sintering aid is prepared by high-temperature sintering, wherein the RO-Al₂O₃-SiO₂SiO in sintering aid₂Introducing metal silicon powder according to equimolar; the introduction amount of the metal silicon powder is not more than 5% of the blank amount according to the mass ratio; the median particle diameter D50 of the metal silicon powder is not more than 5um, wherein the mass content of silicon is not less than 98%.

According to the preparation method of the low-sintering shrinkage alumina ceramic, disclosed by the invention, when the ceramic blank is formed by a dry method, the metal silicon powder can be directly added into the ceramic blank for forming. When the ceramic blank is formed by a wet method, the metal silicon powder needs to be subjected to pre-coating modification treatment, and the process comprises the following steps:

(1) slowly adding the metal silicon powder into the absolute ethyl alcohol under the condition of strong stirring, and stirring for 1-5 hours;

(2) slowly adding organosilane, and uniformly stirring;

(3) slowly adding the silica sol with the adjusted pH value at a certain temperature, and continuously stirring for 4-6 hours;

(4) and cooling the mixture to room temperature, centrifugally separating out the modified metal silicon powder, and drying at 50-200 ℃ for use.

Wherein the dosage of the silica sol and the organosilane is determined according to the mass ratio of the silica to the organosilane of 1: 3-6; the absolute ethyl alcohol accounts for 20-40% of the total mass of the silica sol and the organosilane; the molar ratio of the metal silicon powder to the silicon dioxide in the silica sol is 5-10. More optimally, the dosage of the silica sol and the organosilane is determined according to the mass ratio of the silica to the organosilane of 1: 4-5; the absolute ethyl alcohol accounts for 30-40% of the total mass of the silica sol and the organosilane; the molar ratio of the metal silicon powder to the silicon dioxide in the silica sol is 6-8.

The reaction temperature is 30-70 ℃, and the modified metal silicon powder is dried at 50-60 ℃ and then dried at 180-200 ℃ for 30-60 minutes. More preferably, the reaction temperature is 30-40 ℃, and the modified metal silicon powder is dried at 50 ℃ and then at 200 ℃ for 30 minutes.

The pH value of the silica sol is 2-4, and the solid content (mass) is 25-35%. The organosilane is any one of methyltrimethoxysilane, gamma-glycidoxypropyltrimethoxysilane and gamma- (methacryloyloxy) propyltrimethoxysilane.

The purpose of metal silicon powder modification is to coat a layer of compact hydrophobic silicon dioxide film layer on the particle surface, thereby effectively avoiding the hydration reaction of the metal silicon powder in a wet environment, ensuring that the metal silicon powder completely keeps the shape of a simple substance in the ceramic forming process, and obtaining the performance of oxidation expansion at high temperature.

Compared with the prior art, the invention has the following remarkable technical progress:

1. the invention overcomes the defect of overlarge production safety risk in the prior art and can realize large-scale industrial production;

2. the technical measures of the invention are comprehensively applicable to the production process of the alumina ceramic, especially the wet forming process, and have great value for the production of complex devices.

3. The technological measures of the invention reduce the sintering shrinkage of the alumina ceramic from 23% to below 10%, do not change the microstructure (crystalline phase and microstructure) and mechanical properties, improve partial properties such as bending strength, greatly reduce the sintering deformation of the product, improve the processing performance of the product and reduce the processing cost.

Drawings

FIG. 1: scanning electron microscope photograph of the section of 90 alumina porcelain;

FIG. 2 is a drawing: introducing a section scanning electron microscope photo of the metal silicon powder on the basis of 90 ceramics;

FIG. 3: the XRD spectrogram of metal silicon powder with different contents is introduced on the basis of 90 ceramics: curves a-e correspond to the introduction of the metal silicon powder of 4%, 3%, 2%, 1% and 0%, respectively.

Detailed Description

Example 1

(1) Pre-coating treatment of metal silicon powder:

under the condition of strong stirring, slowly adding 88g of metal silicon powder into 88g of absolute ethyl alcohol, and stirring for 1 hour; slowly adding 120g of methyltrimethoxysilane, stirring for 2 hours, slowly adding 100 gPH-3.5 silica sol at 40 ℃, and continuously stirring for 4 hours; and cooling the mixture to room temperature, centrifugally separating out the modified metal silicon powder, drying at 50 ℃ for 6 hours, drying at 200 ℃ for 0.5 hour, and cooling for later use.

(2) Weighing alpha-type aluminum oxide powder and dolomite powder according to the following mass percentage, adding pretreated metal silicon powder according to the formula after wet ball milling, mixing, performing injection coagulation molding, drying, biscuiting, fine fettling and sintering to obtain the product.

α-Al2O3Powder	Dolomite powder	Pretreated silicon powder
			93	4.5	2.5

Wherein, part of the technological parameters are as follows: ball milling time of a 550rpm rapid mill is 4 hours, and the median particle diameter D50 of the powder is 1 μm; the median particle diameter D50 of the metal silicon powder is 1 mu m; adopting AM system for injection-coagulation molding, wherein the biscuit firing temperature is as follows: 1100 ℃; a firing system: and (3) keeping the temperature for 2 hours at the temperature of 900-1450 ℃, wherein the heating speed is 5 ℃/min, the maximum sintering temperature is 1550 ℃.

The shrinkage rate of the prepared alumina product after firing is 5%, the microstructure and the crystal phase composition are shown in figures 1, 2 and 3, and the bending strength is 243.61MPa and is higher than that of the basic composition, namely 231.1 MPa.

Example 2

(1) Pre-coating treatment of metal silicon powder:

slowly adding 90g of metal silicon powder into 100g of absolute ethyl alcohol under the condition of strong stirring, and stirring for 1 hour; slowly adding 100g of methyltrimethoxysilane, stirring for 2 hours, slowly adding silica sol of which the temperature is 90 gPH-3.0 at the temperature of 30 ℃, and continuously stirring for 6 hours; and cooling the mixture to room temperature, centrifugally separating out the modified metal silicon powder, drying at 50 ℃ for 6 hours, drying at 200 ℃ for 0.5 hour, and cooling for later use.

(2) Weighing alpha-type aluminum oxide powder and dolomite powder according to the following mass percent, adding 0.5 wt% of polyvinyl alcohol PVA (1750 +/-50), carrying out wet ball milling, adding pretreated metal silicon powder according to the formula, mixing, carrying out spray granulation, carrying out dry pressing molding, drying, carrying out biscuit firing, finely trimming, and firing to obtain the product.

α-Al2O3Powder	Dolomite powder	Pretreated silicon powder
			93	3.5	3.5

Wherein, part of the technological parameters are as follows: ball milling time of a 550rpm rapid mill is 4 hours, and the median particle diameter D50 of the powder is 1 μm; the median particle diameter D50 of the metal silicon powder is 1 mu m; biscuit firing temperature: 1100 ℃; a firing system: and (3) keeping the temperature for 2 hours at the temperature of 900-1450 ℃, wherein the heating speed is 5 ℃/min, the maximum sintering temperature is 1550 ℃.

The shrinkage rate of the prepared alumina product after being fired is 3 percent, and other properties are the same as the basic composition.

Example 3

Weighing industrial alumina powder and dolomite powder according to the following mass percent, carrying out dry ball milling, adding 0.5 wt% of oleic acid, carrying out secondary ball milling, adding metal silicon powder according to the formula, carrying out mixed milling, drying, adding paraffin and oleic acid for mixing, carrying out hot-press casting molding, removing wax, finely trimming, and firing to obtain the product.

α-Al2O3Powder	Dolomite powder	Metal silicon powder
			93	5	2

Wherein, part of the technological parameters are as follows: dry milling time of a 550rpm rapid mill is 1 hour; the secondary ball milling time is 4 hours; the mixing and grinding time is 0.5 hour; drying temperature: drying for 2 hours at 120 ℃ until the water content of the dry material is less than 1 percent; addition amount of paraffin and oleic acid: adding 12 wt% of No. 58 paraffin and 0.5 wt% of oleic acid; hot-press molding: the molding temperature is 90 ℃; a dewaxing system according to a conventional dewaxing system; a firing system: and (3) keeping the temperature for 2 hours at the temperature of 900-1450 ℃, with the heating rate of 5 ℃/min and the maximum sintering temperature of 1500 ℃. The shrinkage of the prepared alumina product after firing is 7 percent, and other properties are the same as the basic composition.