Low-density optical glass
阅读说明：本技术 低密度的光学玻璃 (Low-density optical glass ) 是由 B·施罗德 U·沃尔夫 S·汉森 于 2021-05-06 设计创作，主要内容包括：本发明涉及具有高折射率的同时具有低密度的玻璃,其适用于在增强现实AR领域中使用,特别是适用于AR眼镜。(The present invention relates to glasses having a high refractive index and at the same time a low density, suitable for use in the field of augmented reality AR, in particular for AR glasses.)
1. Glass having a density p and a refractive index ndThe ratio of (a) to (b) is low,
-wherein the refractive index ndIn the range of 1.80 to 2.00,
-the internal transmittance of the glass is at least 80% (450nm, 10mm) and the dispersion vdIs in the range of 19.0 to 27.0,
characterized by a ratio of rho/nd<1.97。
2. Glass according to claim 1, having a refractive index ndIs 1.85 to 1.95 and/or the ratio rho/nd<1.95。
3. The glass of claim 1 or 2, wherein Ta2O5、WO3And/or GeO2Is less than 5.0% by weight, in particular less than 1.0% by weight.
4. The glass of any of the preceding claims, wherein Nb2O5、TiO2And BaO in a combined amount of at least 30% by weight, in particular at least 45% by weight.
5. The glass of any one of the preceding claims, having:
-a Knoop hardness of 500 to 650,
a glass transition temperature Tg of from 500 ℃ to 650 ℃, in particular from 520 ℃ to 630 ℃, and/or
Chemical resistance corresponds to that according to DIN 12116: 2001, stage 0, stage 1 or stage 2.
6. The glass of any one of the preceding claims, wherein boron cation B is present in the glass in mole percent3+With silicon cation Si4+Content ratio B of3+/Si4+At most 2.5.
7. The glass according to any of the preceding claims, comprising the following components in wt.%:
。
8. The glass according to any of the preceding claims, comprising the following components in wt.%:
。
9. The glass according to any of the preceding claims, comprising the following components in wt.%:
。
10. The glass of any of the preceding claims, wherein the glass is substantially free of La selected from the group consisting of2O3，Gd2O3，Y2O3，GeO2，Ta2O5，MgO，Li2O，ZrO2，P2O5，WO3And combinations thereof.
11. The glass of any of the preceding claims, wherein the glass is substantially free of one or more components selected from the group consisting of lead, bismuth, cadmium, nickel, arsenic, antimony, and combinations thereof.
12. A glass article comprising the glass of any of the preceding claims, the glass article being in the form of
Glasses for spectacles, in particular in the form of wafer stacks,
wafers, in particular wafers having a maximum diameter of 5.0cm to 40.0cm,
a lens, in particular a spherical lens, a prism or an aspherical lens, and/or
-an optical waveguide, in particular a fiber or a plate.
13. Use of a glass or glass article according to any of the preceding claims in AR eyewear, wafer level optics, optical wafer applications, or classical optics; and/or as a wafer, lens, spherical lens or optical waveguide.
Technical Field
The invention relates to optical glass, a glass product and application thereof.
Background
The present invention relates to glasses that can be used in the field of Augmented Reality (AR). For AR glasses, high refractive glasses (and thus high index glasses) are advantageous because they increase the field of view (FoV). On the other hand, the density of such glasses generally increases disproportionately with the increase in refractive index. This means that even if it were possible to make the wafer thinner for AR applications, the glass for eyeglasses would become quite heavy, which makes it uncomfortable to wear AR eyeglasses for extended periods of time. Since it is a trend to change from a head-mounted type to a standard eyeglass shape and then the eyeglass shape should be worn longer or always as common eyeglasses can be worn, it is necessary to make the eyeglasses lighter. Such weight reduction is also advantageous for many other application areas, since the camera optics in the DSLR field are also often either bulky or very heavy, which also significantly increases the battery power requirements for auto-focusing.
Some prior art glasses are derived from niobium phosphate or titanium phosphate systems and therefore contain a substantial proportion of P2O5And niobium or titanium. These glasses are somewhat problematic due to oxygen loss during the manufacturing process. Oxygen loss is due to, for example, excessive melting and fining temperatures in phosphate systems, which are characterized by reduction, resulting in low oxidation states. In the case of niobium this is for example an oxidation state below V, and in the case of titanium this is an oxidation state below IV. In the case of niobium systems, this can lead to intense brown to black coloration or, in the case of titanium systems, to yellowish green to brown coloration. In addition, titanium significantly increases the tendency to crystallize, which is a known problem in the field of flint, of existing high-refractive glasses which can no longer be reshaped afterwards, for example by compression. In contrast to niobium, titanium, even in the highest oxidation state, absorbs at the edges of the visible range, which is the cause of the known yellowing of barium titanosilicate at higher contents.
Furthermore, the family of niobium phosphate glasses (e.g. the family of high refractive pyrophyllite or lanthanum pyrophyllite) not only has a tendency to crystallize at the interface, but also shows a very rapid crystal growth, which is crucial when the glass optionally containing seeds should be subsequently cooled (stress cooling or refractive index adjustment). It is also known that glass is relatively brittle and therefore difficult to polish to very thin wafers.
On the other hand, despite P2O5But the weatherability is relatively good, at least in the case of niobium phosphate glass, and its density is very low at the same time as the refractive index is high, which increases the wearing comfort. These families are known in the literature.
Commercially available eyeglasses N-LASF46B, N-SF66 and P-SF67 are in the range of refractive indices of interest for AR applications. N-SF66 and evenHas a good combination of refractive index and density, but as mentioned above, is difficult to process into wafers and there is a yield loss. The lanthanum heavy flint system is characterized by a refractive index ndMuch worse in combination with density (essentially, the high density of the glass is the higher v of the lanthanum heavy flint glassdFor that reason) and the hardness is high, which requires long grinding time, increasing the wafer production cost. In general, the cost of the starting glass is already quite high, since tungsten oxide, tantalum oxide and other expensive raw materials are used for these glass raw materials from the rare earth field. In the field of heavy flint, Nb2O5Usually this mixture is a cost driver, compared to other raw materials, which are relatively cheap even in terms of optical quality.
On the one hand, P-SF glasses in the Abbe number range are problematic due to the high cost of the mixtures and, in addition, are problematic due to Bi2O3At higher levels, the glass was very soft (easily scratched) and the uv-transmitting edge was relatively poor. In addition, both glasses are not continuously prepared in a platinum crucible, which may cause problems in a platinum alloy bath and in the reduction of Bi (iii) to Bi (0).
As already mentioned above, some glasses are more or less suitable, but are usually still in a too low refractive index range (typical heavy flint glasses) or are difficult to handle (typical lanthanum heavy flint glasses).
Disclosure of Invention
The object of the invention is to provide a glass having a high refractive index ndWhile having as low a density as possible. The glass should have as high an internal transmission as possible, be easily thermoformed, and be easily handled. For this reason, the hardness cannot be too low (otherwise there are more scratches and microcracks) nor too high (otherwise long grinding and the resulting microcracks result). In addition, the thermal expansion of the glass should not be too high and the chemical resistance should be as good as possible.
In one aspect, the invention relates to a glass having a densityAnd refractive index ndIn which the refractive index n of the glass is lowdIn the range from 1.80 to 2.00 and an internal transmission of at least 80%, in particular at least 85% or at least 90%, at a wavelength of 450mn and a sample thickness of 10 mm. The dispersion v of the glassdIs 19.0 to 27.0, in particular>20.0 to 26.0 or>20.0 to 25.5. The glass is characterized by a ratioIn particular<1.95 or less than 1.93 or even less than 1.90 or less than 1.89 or less than 1.87, less than 1.85, less than 1.83, less than 1.81 or even less than 1.80. In one embodiment, the refractive index ndFrom 1.83 to 1.99, in particular at least 1.84, at least 1.85 or at least 1.87.
The internal transmission or the internal transmittance can be measured by methods known to the person skilled in the art, for example according to DIN5036-1: 1978. In this specification, the information given about internal transmission relates to a wavelength of 450nm and a sample thickness of 10 mm. The information given about "sample thickness" does not mean that the glass has that thickness, as this only means that the information given about internal transmission is related to that thickness.
Unless otherwise specified or apparent to one skilled in the art, the measurements described herein were performed at 20 ℃ and a gas pressure of 101.3 kPa.
The density of the glass may be from 3.0g/cm3To 3.9g/cm3. Preferably, the density is at most 3.85g/cm3At most 3.8g/cm3Or at most 3.7g/cm3. Preferably, the density is from 3.2 to 3.6g/cm3Or from 3.1 to 3.5g/cm3。
Thus, the refractive index range of the glass is adjacent to and above the known heavy flint range, but the density is reduced. Normally, an increase in refractive index is the opposite specification of a decrease in density, since in conventional glass development, an increase in refractive index is achieved either by heavier elements (and thus generally an increase in density and a decrease in dispersion), or by creating a narrower network of glass, so that the volume of the glass is reduced and thus the density is also increased, and the refractive index and dispersion are also increased. The inventors have succeeded in increasing the refractive index so that neither the volume nor the molar mass is changed, or in decreasing the molar mass and increasing the volume, respectively, while maintaining the refractive index. When considering that "molecular refraction" of individual components is often discussed in the theory of development of optical glasses, and many developments are achieved by factors reflecting the refractive index portions of the components in the glass, the difficulty of solving the object becomes apparent.
Nb2O5、TiO2And BaO in a combined amount of at least 30.0% by weight, in particular at least 45.0% by weight. Optionally, the content of these oxides is at most 75.0 wt.% or at most 70.0 wt.%.
Optionally, the glass has Ta2O5、WO3And/or GeO2Is less than 5.0% by weight, in particular less than 1.0% by weight.
In one embodiment, the glass has a knoop hardness of 500 to 650, in particular 520 to 600 or up to 580. The hardness should not be too low (otherwise more scratches and microcracks occur) but not too high (otherwise long grinding times and hence microcracks occur).
During production, glass should be produced that is free of striations having a net width of at least 200mm or better at least 300mm and has an ingot thickness of at least 20mm, better at least 40mm or at least 50 mm. In one embodiment, the invention relates to an ingot made of the glass described herein, in particular an ingot having a width of at least 200mm and/or a thickness of at least 20 mm. Optionally, the ingot has a width of at least 300mm and/or a thickness of at least 40mm or at least 50 mm. Therefore, a lower tendency to crystallize is important, since melts with low viscosity are very sensitive to the formation of intermediate streaks and also to the formation of streaks which can penetrate into the volume and at the boundaries. This is particularly critical for glasses in the field of heavy flint systems, since titanium and zirconium are known as nucleating agents. Thus, if possible, ZrO2Should not be used in glass orIt should be used in low amount. Titanium should be particularly stable to avoid crystal formation at the interface. In the glasses described here, this stabilization has been achieved. Therefore, glass can be manufactured into wafers with high yield.
In one embodiment, the glass has a glass transition temperature Tg of from 500 ℃ to 650 ℃, in particular from 520 ℃ to 630 ℃. Alternatively, the Tg may be at most 650 ℃, at most 625 ℃, at most 620 ℃ or at most 615 ℃. The glass is well suited for thermoforming and processing.
The chemical resistance should be suitable for use in AR glasses. The lenses are often cleaned and must be resistant to chemical attack to some extent. The chemical resistance may correspond to that according to DIN 12116: 2001, grade 0, 1 or 2. Sufficient chemical resistance is also important for the treatment of glass. In some post-treatment processes, a portion of the sodium can leach out and form salts with surrounding chlorides. Preferably, in the case of such glass, this does not occur.
In addition, the average Coefficient of Thermal Expansion (CTE) in the temperature range of 20 to 300 ℃ should not be too high, preferably in the range of 8.0 to 12.0ppm/K, in particular in the range of 9.0 to 11.0 ppm/K. CTE is according to DIN ISO 7991: 1987.
Preferably, the glass of the present invention comprises niobium and/or titanium. It is known that glasses containing niobium are characterized by a poor internal transmission in the near ultraviolet visible spectral range and a strong tendency to crystallize at the interface due to the titanium content. In the case of the glasses described here, these disadvantages do not occur or occur only to a controlled extent.
Optionally, the glass contains a significant amount of niobium, followed by titanium and barium. Here, niobium may be replaced with titanium. Nb2O5/TiO2Should be between 0.3 and 3.5. In the case of medium density, these components result in a high refractive index. In one embodiment, Nb in the glass2O5Is present in an amount of at least 10.0 wt.%, in particular at least 11.0 wt.%, at least 12.0 wt.% or at least 20.0 wt.%. In some embodiments, the content is even at least 20.0 wt% or at least 25.0 wt%. OptionallyMay be formed of Nb2O5Is limited to at most 55.0 wt.%, at most 50.0 wt.%, at most 45.0 wt.% or at most 40.0 wt.% or at most 35.0 wt.%.
TiO2May be present in an amount of at least 10.0 wt.%, particularly at least 11.0 wt.%, or at least 12.0 wt.%. In some embodiments, the content is even at least 14.0 wt.%, or at least 15.0 wt.%, or at least 17.0 wt.%. Alternatively, TiO may be added2Is limited to at most 50.0 wt.%, at most 45.0 wt.%, at most 42.0 wt.% or at most 40.0 wt.% or at most 39.0 wt.%.
The glass may contain BaO. The content of BaO may be at least 0.1% by weight, at least 0.2% by weight, at least 0.5% by weight or at least 1.0% by weight, in particular at least 2.0% by weight. Alternatively, the content of this component is limited to at most 35.0 wt.%, at most 30.0 wt.%, at most 25.0 wt.% or at most 22.0 wt.% or at most 20.0 wt.%, at most 15.0 wt.%, at most 10.0 wt.% or at most 5.0 wt.%. Alternatively, BaO and TiO2May be from 0.05 to 0.90, in particular from 0.05 to 0.80 or from 0.01 to 0.50.
SiO2Is a glass former. The oxides greatly improve the chemical resistance but also increase the treatment temperature. When used in very high amounts, the refractive index according to the invention cannot be achieved. Optionally, the glass comprises SiO2At least 6.0 wt%, at least 8.0 wt%, or at least 10.0 wt% or at least 11.0 wt% or at least 14.0 wt% or at least 16.5 wt%; the content thereof may be limited to at most 35.0 wt.%, at most 32.0 wt.%, or at most 30.0 wt.%, or at most 29.0 wt.%, or at most 28.5 wt.%.
Boron cation B in mol%3+With silicon cation Si4+Content ratio B of3+/Si4+It may preferably be at most 2.5, in particular at most 1.5 or at most 0.9. Due to its corrosiveness with respect to the ceramic bath, B2O3The content of (B) may be limited to especially at most 12.0% by weight, at most 9.5% by weight, or at most 8.0% by weight or at most 7.0% by weight. In certain embodiments, the glass may also be boron-free, or boron may be limited to up to 1.0 weight percent.
ZrO2Which helps to achieve a high refractive index, but also increases the tendency of the glass to crystallize, and therefore its content is optionally limited. In one embodiment, it is present in an amount of up to 5.0 wt%, up to 3.0 wt%, or up to 2.0 wt%, or up to 1.0 wt%. Some examples do not contain ZrO2Or only 0.1% by weight or less of ZrO2。
Al2O3Are optional components of glass and can help to improve chemical resistance. The content thereof may be from 0.0 to 5.0 wt% or up to 3.0 wt%, or up to 2.0 wt% or up to 1.0 wt%. Some examples do not contain Al2O3Or only 0.5% by weight or less of Al2O3。
Alternatively, ZnO, CaO and SrO may be used in glasses which lower the melting temperature and stabilize the glass against crystallization without reducing chemical resistance to some extent, such as alkali metal oxides. The ZnO content can be 0.0 to 12.0 wt.%, up to 9.5 wt.% or up to 8.0 wt.% or up to 6.0 wt.%. Some embodiments do not contain ZnO. The SrO content may be 0.0 to 8.0 wt%, or up to 5 wt% or up to 3.0 wt%. Some embodiments do not contain SrO. The CaO content may be 0.0 to 12.0 wt%, up to 10.0 wt% or up to 8.0 wt% or up to 6.0 wt%. Some embodiments include at least 0.1 wt%, or at least 1.0 wt%, or at least 1.5 wt%, or at least 2.0 wt%, or at least 2.5 wt%, or at least 3.0 wt% CaO.
Li2O，Na2O and/or K2O can be used in glass, but too high a level reduces chemical resistance. K2The content of O may be limited to at most 25.0 wt.%, preferably at most 20.0 wt.% or at most 18.0 wt.% or at most 15.0 wt.%. In one embodiment, K in the glass2The content of O is at least 0.5 wt% or at least 1.0 wt% or at least 2.0 wt% or at least 3.0 wt%. Alternatively, Na2Containing of OThe amount is at least 2.0 wt%, at least 3.0 wt% or at least 3.5 wt%. Na (Na)2The content of O may be limited to at most 20.0 wt.%, at most 15.0 wt.%, or at most 11.0 wt.%, or at most 10.5 wt.%. Due to Li2O can attack the material of the crucible and the bath and is therefore used at most in small amounts, in particular in amounts of less than 1.0% by weight, in particular in amounts of less than 0.5% by weight. The combined content of the three alkali metal oxides mentioned can be from 5.0 to 20.0% by weight, in particular from 8.0 to 17.0% by weight. Alkali metal oxides contribute to good handleability, but reduce chemical resistance.
Sb2O3，As2O3And SnO2Can be used as a clarifying agent, but is used only in small amounts. The health hazards, particularly arsenic and antimony, cause controversy. The glass may be refined without the use of chemical fining agents. Alternatively, vacuum clarification may be used.
To increase the refractive index, HfO2The amount may be 0.0 to 1.0 wt%, up to 0.5 wt% or up to 0.2 wt%. Some embodiments are free of HfO2。
Y2O3Amounts of 0.0 to 5.0 wt%, up to 3.5 wt%, up to 2.0 wt%, up to 1.0 wt%, up to 0.5 wt% or up to 0.2 wt% may be used. Some examples do not contain Y2O3。
In one embodiment, the glass comprises the following components in weight percent:
SiO2
6.0 to 35.0
B2O3
0.0 to 12.0
Nb2O5
10.0 to 55.0
TiO2
10.0 to 50.0
ZrO2
0.0 to 5.0
Al2O3
0.0 to 5.0
ZnO
0.0 to 12.0
CaO
0.0 to 12.0
BaO
1.0 to 35.0
SrO
0.0 to 8.0
Na2O
0.0 to 20.0
K2O
0.0 to 25.0
Sb2O3
0.0 to 2.0
As2O3
0.0 to 2.0
In one embodiment, the glass comprises the following components in weight percent:
SiO2
6.0 to 35.0
B2O3
0.0 to 12.0
Nb2O5
10.0 to 55.0
TiO2
10.0 to 50.0
ZrO2
0.0 to 5.0
Al2O3
0.0 to 5.0
ZnO
0.0 to 12.0
CaO
0.0 to 12.0
BaO
0.1 to 35.0
SrO
0.0 to 8.0
Na2O
0.0 to 20.0
K2O
0.0 to 25.0
Sb2O3
0.0 to 2.0
As2O3
0.0 to 2.0
The glass may comprise the following components in weight%:
SiO2
10.0 to 29.0
B2O3
0.0 to 8.0
Nb2O5
12.0 to 45.0
TiO2
15.0 to 40.0
ZrO2
0.0 to 2.0
Al2O3
0.0 to 2.0
ZnO
0.0 to 8.0
CaO
0.0 to 6.0
BaO
2.0 to 22.0
SrO
0.0 to 5.0
Na2O
2.0 to 15.0
K2O
0.0 to 18.0
Sb2O3
0.0 to 0.3
As2O3
0.0 to 0.3
The glass may comprise the following components in weight%:
SiO2
10.0 to 29.0
B2O3
0.0 to 8.0
Nb2O5
12.0 to 45.0
TiO2
15.0 to 40.0
ZrO2
0.0 to 2.0
Al2O3
0.0 to 2.0
ZnO
0.0 to 8.0
CaO
0.0 to 10.0
BaO
0.2 to 22.0
SrO
0.0 to 5.0
Na2O
2.0 to 15.0
K2O
0.0To 18.0
Sb2O3
0.0 to 0.3
As2O3
0.0 to 0.3
The glass may comprise the following components in weight%:
SiO2
11.0 to 20.0
B2O3
0.0 to 7.0
Nb2O5
17.0 to 40.0
TiO2
15.0 to 34.0
ZrO2
0.0 to 2.0
Al2O3
0.0 to 1.0
ZnO
0.0 to 6.0
CaO
1.0 to 4.0
BaO
6.0 to 21.0
SrO
0.0 to 1.0
Na2O
3.0 to 11.0
K2O
1.0 to 10.0
Sb2O3
0.0 to 0.5
As2O3
0.0 to 0.5
The glass may comprise the following components in weight%:
SiO2
14.0 to 27.25
B2O3
0.0 to 7.0
Nb2O5
13.5 to 40.0
TiO2
16.0 to 37.0
ZrO2
0.0 to 2.0
Al2O3
0.0 to 1.0
ZnO
0.0 to 6.0
CaO
0.4 to 5.0
BaO
2.95 to 20.5
SrO
0.0 to 1.0
Na2O
3.4 to 10.5
K2O
0.8 to 10.0
Sb2O3
0.0 to 0.5
As2O3
0.0 to 0.5
The glass may comprise the following components in weight%:
SiO2
16.5 to 28.5
B2O3
0.0 to 7.0
Nb2O5
12.5 to 40.0
Y2O3
0.0 to 5.0
TiO2
17.0 to 39.0
ZrO2
0.0 to 2.0
Al2O3
0.0 to 1.0
ZnO
0.0 to 6.0
CaO
1.5 to 8.0
BaO
0.2 to 10.0
SrO
0.0 to 1.0
Na2O
3.0 to 10.5
K2O
3.0 to 15.0
Sb2O3
0.0 to 0.5
As2O3
0.0 to 0.5
In one embodiment, at least 95.0% by weight, in particular at least 98.0% by weight or at least 99.0% by weight of the glass consists of the above-mentioned components, in particular the components listed in the table above. In one embodiment, the glass consists essentially entirely of these components.
In one embodiment, the glass is substantially free of La selected from the group consisting of2O3，Gd2O3，Y2O3，GeO2，Ta2O5，MgO，Li2O，ZrO2，WO3And combinations thereof.
Due to the niobium content, the glass is particularly free of other expensive components, such as tantalum, tungsten and/or germanium. Although these components improve various optical properties in some types of glass, they are not used here, which is also due to the fact that: it has been found that an increase in these components worsens the density/refractive index ratio. The latter is true for e.g. lanthanum, gadolinium, but also for lithiumWhere applicable, it is therefore preferred not to use these components. In addition, lanthanum and gadolinium and yttrium increase the melting temperature of the mixture, thereby increasing the oxygen loss of the melt. In addition, when these components are used, the tendency to crystallize at the seed crystal and the interface increases. Known as Li2O is corrosive to ceramic bath and crucible materials and therefore, if possible, is not used or is only applicable in low amounts.
The melt of the glass may be fined with conventional fining agents, but because of the glass' melting temperature of most interest, typically below 1300 ℃, and because of its low viscosity, fining at relatively moderate temperatures is possible. For example, Sb2O3，As2O3And/or SnO2Can be reduced (e.g., to<0.1 wt%) to facilitate uv transmission, or may be omitted (purely physically clear). Optionally, the glass may include one or more of the following components in the given weight percent amounts that provide fining:
Sb2O3
0.0 to 0.5
As2O3
0.0 to 0.5
SnO2
0.0 to 0.5
Optionally, the glass is phosphate-free (P)2O5) Since phosphates lead to a melt with significant reducing properties and thus increase the oxygen demand of the melt, which in turn increases the consumption of platinum.
Optionally, the glass is substantially free of one or more components selected from the group consisting of lead, bismuth, cadmium, nickel, arsenic, antimony, and combinations thereof.
When in this specification it is mentioned that the glass contains no component or no component, it is meant that it is at most permissible for the component to be present as an impurity in the glass. This means that this component is not added in large amounts. According to the invention, not adding substantial amounts means an amount of less than 100ppm (m/m), preferably less than 50ppm, most preferably less than 10ppm (m/m).
In one aspect, the invention relates to a glass article comprising or consisting of the above glass. The glass article may have different forms. Optionally, the article is in the form of:
glasses for spectacles, in particular in the form of wafer stacks,
wafers, in particular wafers having a maximum diameter of 5.0cm to 40.0cm,
a lens, in particular a spherical lens, a prism or an aspherical lens, and/or
-an optical waveguide, in particular a fiber or a plate.
In another aspect, the invention relates to the use of the above glass or glass article in AR eyewear, wafer level optics, optical wafer applications, or classical optics. Alternatively or additionally, the glass or glass article described herein may be used as a wafer, lens, spherical lens, or optical waveguide.
Drawings
Fig. 1-4 show internal transmittance spectra for example glasses 17 (fig. 1), 29 (fig. 2), 30 (fig. 3), and 34 (fig. 4).
Detailed Description
Examples of the invention
The exemplary compositions shown in tables 1 to 6 below were melted and their properties were investigated. For some glasses, the internal transmission is determined.
Composition and Properties
TABLE 1
TABLE 2
TABLE 3
TABLE 4
TABLE 5
TABLE 6
By weight%
41
42
43
SiO2
22.50
23.50
23.00
B2O3
1.50
Nb2O5
21.90
21.90
22.00
Y2O3
3.00
3.00
4.00
TiO2
31.00
31.50
31.00
CaO
5.00
4.50
4.50
BaO
2.20
1.00
0.50
Na2O
6.50
6.50
6.50
K2O
6.50
9.00
9.00
As2O3
0.05
0.05
0.05
nd
1.8816
1.8459
1.8692
vd
22.1
22.0
22.4
Tg
610
611
615
Density of
3.3645
3.3159
3.3278
Density/nd
1.7881
1.7964
1.7803
The exemplary glasses exhibit excellent density to refractive index ratios. These glasses have low density, while having high refractive index, low dispersion and relatively low Tg.
Internal transmission
Fig. 1-4 show internal transmittance spectra for example glasses 17 (fig. 1), 29 (fig. 2), 30 (fig. 3), and 34 (fig. 4).