Glass material with a high index of refraction

Abstract

A composition for a glass material comprising, on an oxide basis: one or more network formers chosen from the group of silicon dioxide (SiO.sub.2) and phosphorous pentoxide (P.sub.2O.sub.5); one or more alkali metal oxides chose from the group consisting of lithium oxide (Li2O) and sodium oxide (Na.sub.2O); 8 to 15 percent by weight zirconium oxide (ZrO.sub.2); and one transition metal oxide consisting of 9 to 45 percent by weight niobium pentoxide (Nb.sub.2O.sub.5). In an embodiment, the composition consists of: 35 to 60 percent by weight silicon dioxide (SiO.sub.2); 9.25 to 15.0 percent by weight lithium oxide (Li.sub.2O); 0.5 to 2 percent by weight sodium oxide (Na.sub.2O); 8 to 15 percent by weight zirconium oxide (ZrO.sub.2); 0 to 3.5 percent by weight phosphorous pentoxide (P.sub.2O.sub.5); and 9 to 45 percent by weight niobium pentoxide (Nb.sub.2O.sub.5). In an embodiment, the glass material is a light guide for an augmented reality device.

Claims

1. A composition for a glass material comprising, on an oxide basis: 35 to 60 percent by weight silicon dioxide (SiO.sub.2); 9.25 to 15.0 percent by weight lithium oxide (Li.sub.2O); 0.5 to 2 percent by weight sodium oxide (Na.sub.2O); 8 to 15 percent by weight zirconium oxide (ZrO.sub.2); 0 to 3.5 percent by weight phosphorous pentoxide (P.sub.2O.sub.5); and 9 to 45 percent by weight niobium pentoxide (Nb.sub.2O.sub.5).

2. The composition of claim 1, wherein, the composition comprises 35 to 60 percent by weight silicon dioxide (SiO.sub.2), and 0.1 to 3.5 percent by weight phosphorous pentoxide (P.sub.2O.sub.5).

3. The composition of claim 1, wherein, the composition comprises 39 to 59 percent by weight silicon dioxide (SiO.sub.2), and 1.9 to 3.0 percent by weight phosphorous pentoxide (P.sub.2O.sub.5).

4. The composition of claim 1 comprising: 9 to 15 percent by weight lithium oxide (Li2O); and 0.5 to 2 percent by weight sodium oxide (Na.sub.2O).

5. The composition of claim 1, wherein, the composition consists of: 37 to 43 percent by weight silicon dioxide (SiO.sub.2); 9.25 to 10.25 percent by weight lithium oxide (Li.sub.2O); 0.75 to 1 percent by weight sodium oxide (Na.sub.2O); 8.5 to 10 percent by weight zirconium oxide (ZrO.sub.2); and 36 to 45 percent by weight niobium pentoxide (Nb.sub.2O.sub.5).

6. A glass material comprising, on an oxide basis: 37 to 43 percent by weight silicon dioxide (SiO.sub.2); 0 to 3.5 percent by weight phosphorous pentoxide (P.sub.2O.sub.5); 9.25 to 10.25 percent by weight lithium oxide (Li.sub.2O); 0.75 to 1 percent by weight sodium oxide (Na.sub.2O); 8.5 to 10 percent by weight zirconium oxide (ZrO.sub.2); and 36 to 45 percent by weight niobium pentoxide (Nb.sub.2O.sub.5); wherein, an index of refraction of the glass material at 633 nm is between 1.6070 and 1.7660; wherein, a density of the glass material is between 2.70 g/cm.sup.3 and 3.29 g/cm.sup.3; and wherein, a liquidus temperature of the glass material is less than 1200° C.

7. The glass material of claim 6, wherein, the glass material comprises 37 to 41 percent by weight silicon dioxide (SiO.sub.2); and 0 percent by weight phosphorous pentoxide (P.sub.2O.sub.5).

8. The glass material of claim 6, wherein, a dynamic viscosity of the glass material as a liquidus is between 14.9 and 25.1 poise.

9. A head mounted wearable device comprising: an image forming device that generates visible light to a light guiding device, which includes a glass material through which the visible light propagates, wherein the glass material comprises on an oxide basis: 37 to 43 percent by weight silicon dioxide (SiO.sub.2); 0 to 3.5 percent by weight phosphorous pentoxide (P.sub.2O.sub.5); 9.25 to 10.25 percent by weight lithium oxide (Li.sub.2O); 0.75 to 1 percent by weight sodium oxide (Na.sub.2O); 8.5 to 10 percent by weight zirconium oxide (ZrO.sub.2); and 36 to 45 percent by weight niobium pentoxide (Nb.sub.2O.sub.5); wherein, an index of refraction of the glass material at 633 nm is between 1.6070 and 1.7660; wherein, a density of the glass material is between 2.70 g/cm.sup.3 and 3.29 g/cm.sup.3; and wherein, a liquidus temperature of the glass material is less than 1200° C.

10. The head mounted wearable device of claim 9, wherein, the glass material comprises 37 to 41 percent by weight silicon dioxide (SiO.sub.2); and 0 percent by weight phosphorous pentoxide (P.sub.2O.sub.5).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is graph illustrating both the index of refraction of the novel glass material disclosed herein as a function of mole percentage niobium pentoxide (Nb.sub.2O.sub.5) in the composition (top line) and (b) the density of the resulting glass material as a function of mole percentage niobium pentoxide (Nb.sub.2O.sub.5) in the composition (bottom line);

(2) FIG. 2 is a graph of the index of refraction of the glass material as a function of the density of the glass material, for the compositions of Examples 4-11 below;

(3) FIG. 3 is a graph illustrating the axial transmittance of electromagnetic waves of various wavelengths (from 200 nm to 2000 nm) through 1.0 mm thick samples of the glass material made from each of the compositions set forth in Examples 8-10 below;

(4) FIG. 4 is a differential scanning calorimetry (DSC) analysis of the glass materials made from the compositions of Examples 8-10 and a Comparative Example below, revealing the glass transition temperature (T.sub.g), the crystallization peak temperature (T.sub.x), and the melting temperature (T.sub.m) of various glass materials; and

(5) FIG. 5 is an overhead view of a head mounted wearable device including an image forming device and a light guiding device, illustrating the light guiding device incorporating the novel glass material of the present disclosure.

DETAILED DESCRIPTION

(6) In the tables below, the formulas of the components of the composition are the oxide mole percent and oxide weight percent, as is recognized in the art of glass science. The weight percentages of the oxides are calculated from the mole percentages and provided for convenience. Any difference from a total of 100 mole or weight percent is due to rounding. In all the example compositions, silicon dioxide (SiO.sub.2) is the primary network former of the glass material, and in all the examples, there is of sufficient mole percentage to form a stable glass network.

(7) In Table 1, there are three glass material compositions presented. All three glass material compositions incorporate zirconium dioxide (ZrO.sub.2) in varying amounts, the amount of zirconium dioxide increasing by example number. Alkali metal oxides, here lithium oxide (Li.sub.2O) and sodium oxide (Na.sub.2O) are added to increase melt ability of the glass material and decrease the viscosity. Like silicon dioxide (SiO.sub.2), phosphorous pentoxide (P.sub.2O.sub.5) is a network former but with a higher index of refraction.

(8) TABLE-US-00001 TABLE 1 Example Component (mol %/wt %) 1 2 3 SiO.sub.2 60.3 64.2 59.3 61.8 58.3 59.6 Li.sub.2O 30.2 16.0 29.7 15.4 29.2 14.9 Na.sub.2O 1.3 1.4 1.3 1.4 1.3 1.4 ZrO.sub.2 6.9 15 8.5 18 10.0 21.0 P.sub.2O.sub.5 1.3 3.3 1.3 3.2 1.3 3.1 n (at 633 nm) 1.5776 1.588 1.5974 ρ (g/cm.sup.3) 2.58

(9) The index of refraction (n) of visible light at a wavelength of 633 nm of the glass material made from all three of the compositions was determined. Zirconium dioxide (ZrO.sub.2) is added to reduce devitrification, to decrease the liquidus temperature of the glass material, and also to increase the index of refraction. Surprisingly, moderately high indices of refraction can be achieved by increasing the amount of zirconium dioxide (ZrO.sub.2) in the composition while maintaining the density of the glass composition at a low level (i.e., below 3.3 g/cm.sup.3). The examples illustrate that the index of refraction of the glass material is a function of the mole percentage (or weight percentage) of the zirconium dioxide (ZrO.sub.2)—the more zirconium dioxide (ZrO.sub.2) included in the composition, the higher the index of refraction of the resulting glass material. Although the density of only the first composition (Example 1) was specifically measured, it can safely be assumed from the indices of refraction that the densities of the glass material made from compositions of Examples 2 and 3 were in the same range and below 3.3 g/cm.sup.3. Therefore, to obtain a glass material (and lens made therefrom) with a moderately high index of refraction (between 1.5776 and 1.5974) but a low density (under 3.3 g/cm.sup.3), the following mole percentages can be utilized: (a) silicon dioxide (SiO.sub.2) between 58.3 and 60.3 mole percent; (b) lithium oxide (Li.sub.2O) between 29.2 and mole 30.2 percent; and (c) zirconium dioxide (ZrO.sub.2) between 6.9 and 10 mole percent. The composition can further include sodium oxide (NaO.sub.2) and phosphorus pentoxide (P.sub.2O.sub.5), such as between 1 and 3 percent each.

(10) In Table 2 below, there are eight additional example compositions for the glass material presented. All eight compositions continue to incorporate zirconium dioxide (ZrO.sub.2) in varying amounts, but the amount of zirconium dioxide decreases by example number. Again, the alkali metal oxides lithium oxide (Li.sub.2O) and sodium oxide (Na.sub.2O) are added, as well as network former phosphorous pentoxide (P.sub.2O.sub.5). In these example compositions of Table 2, ever increasing amounts of niobium pentoxide (Nb.sub.2O.sub.5) were added. However, the inventors have discovered that niobium pentoxide (Nb.sub.2O.sub.5) can surprisingly be utilized to greatly increase the index of refraction of the glass material (>1.7600) while allowing the glass material to have a low density (<3.30), without the inclusion of alkaline earth metal oxides such as calcium oxide (CaO) and without the inclusion of titanium dioxide (TiO.sub.2). In other words, the mole percentage of niobium pentoxide (Nb.sub.2O.sub.5) can be manipulated to produce glass materials with an index of refraction between 1.6073 and 1.7655 while still having a density below 3.3 g/cm.sup.3. The last composition listed in Table 2 is a comparative example. The comparative example is a commercially available glass material, which, while incorporating niobium pentoxide (Nb.sub.2O.sub.5) in the composition, has a suboptimal density of 3.65 g/cm.sup.3. The index of refraction of the comparative example (1.800) is only slightly higher than the index of refraction of Example 11 (1.7655) while having a much higher density (3.65 versus 3.25). In all eight of the example compositions, there is a complete lack of boron trioxide (B.sub.2O.sub.3), potassium oxide (K.sub.2O), alkaline earth metal oxides such as calcium oxide (CaO) or barium oxide (BaO), and fluorine (F).

(11) Referring now to FIG. 1, both (a) the index of refraction of the resulting glass material as a function of mole percentage niobium pentoxide (Nb.sub.2O.sub.5) in the composition (top line) and (b) the density of the resulting glass material as a function of mole percentage niobium pentoxide (Nb.sub.2O.sub.5) in the composition (bottom line) are plotted. The relationships are linear in both cases. The data points on the extreme left are from the composition of Example 1 from Table 1 above. The remainder of the data points are from the compositions of Examples 4-11 below.

(12) Referring now to FIG. 2, the index of refraction of the glass material is plotted as a function of the density of the glass material, for the compositions of Examples 4-11 below. As the figure reveals, the relationship is linear.

(13) TABLE-US-00002 TABLE 2 Example Component (mol %/wt %) 4 5 6 7 8 SiO.sub.2 59.1 58.2 57.9 53.7 56.7 49.2 55.6 45.8 53.4 39.9 Li.sub.2O 29.5 14.4 28.9 13.1 28.3 12.2 27.8 11.4 26.7 9.92 Na.sub.2O 1.3 1.3 1.2 1.1 1.2 1.1 1.2 1.1 1.1 0.85 ZrO.sub.2 6.9 13 6.6 13 6.5 12 6.3 11 6.1 9.3 p.sub.2o.sub.5 1.3 3.0 1.2 2.6 1.2 2.5 1.2 2.3 1.1 1.9 Nb.sub.2O.sub.5 2.1 9.1 4.1 17 6.1 23 7.9 29 11.5 38.0 n (at 633 nm) 1.6073 1.6364 1.6629 1.6874 1.7327 ρ (g/cm.sup.3) 2.71 2.82 2.91 3.00 3.15 T.sub.liquidus (° C.) 1170 Example Component (mol %/wt %) 9 10 11 Comparative SiO.sub.2 54.1 40.7 53.4 39.2 52.8 37.8 40.1 28.5 Li.sub.2O 27.0 10.1 26.7 9.76 26.4 9.41 11.3 4.00 Na.sub.2O 1.2 0.93 1.1 0.83 1.1 0.81 0 0 ZrO.sub.2 6.2 9.6 6.1 9.2 6.0 8.8 3.8 5.5 P.sub.2O.sub.5 Nb.sub.2O.sub.5 11.6 38.6 12.6 40.1 13.6 43.1 4.8 15 B.sub.2O.sub.3 2.4 2.0 CaO 22.9 15.2 La.sub.2O.sub.3 5.4 21 TiO.sub.2 9.3 8.8 n (at 633 nm) 1.7411 1.7537 1.7655 1.800 ρ (g/cm.sup.3) 3.17 3.21 3.25 3.65 T.sub.liquidus (° C.) 1155 1180 1175 1095 η.sub.liquidus (poise) 25 20 15 15

(14) The compositions of Table 2 also surprisingly exhibit liquidus temperatures sufficiently low to allow for production of the glass material in a common commercial crucible without an undue risk of corrosion. As Table 2 reveals, the liquidus temperature of Examples 8-11 are between 1155° C. and 1180° C., well below the 1300° C. to 1400° C. range where the common commercial crucible becomes less tenable. The liquidus temperature is the temperature at which crystals first appear while decreasing the temperature of the glass material from a liquid state, or the temperature at which the last crystals melt as the temperature of the glass material is increased from a lower temperature. Similarly, as Table 2 again reveals, the liquidus viscosity of the glass materials made from the compositions of Examples 9-11 are acceptable (15-25 poise) and similar to the comparative example (15 poise).

(15) The above compositions also surprisingly exhibit adequate transmissivity. Referring now to FIG. 3, glass material from each of the compositions described above as Examples 8-10 were tested for transparency. More specifically, the axial transmittance of electromagnetic waves of various wavelengths (from 200 nm to 2000 nm) through 1.0 mm thick glass material made from each of the aforementioned compositions were tested. As the graph illustrated in the figure reveals, each of the glass materials made from the compositions of Examples 8-10 were adequately transparent (85% or greater) to visible light (400-700 nm) as well as longer wavelengths in the infrared region (greater than 700 nm).

(16) The above compositions also surprisingly exhibit good thermal stability, without incorporating boron trioxide (B.sub.2O.sub.3) as a network former. Referring now to FIG. 4, a differential scanning calorimetry (DSC) analysis of the glass materials made from the compositions of Examples 8-10 is illustrated. In addition, the figure illustrates a DSC analysis of the glass material made from the composition of the Comparative Example. In a DSC analysis, pulverized glass material is subjected to progressively increasing temperature. The pulverized glass material either absorbs heat or generates heat at any specific temperature. The heat generated or absorbed is measured. The data is plotted, revealing a DSC curve, with the heat absorbed or generated plotted as a function of temperature. Changes in the slope of the DSC curve reveal the glass transition temperature (T.sub.g), the crystallization temperature (T.sub.x), and the melting temperature (T.sub.m) of the glass material being analyzed. Each of those temperatures can be further subdivided into an onset, a peak/midpoint, and an offset temperature. For example, the change in slope identifying the glass transition temperature (T.sub.g) can be a range including a temperature where the change in slope begins (onset), a temperature where the change in slope ends (offset), and a temperature in between (midpoint). The areas of the curve identifying the crystallization temperature (T.sub.x) and the melting temperature (T.sub.m) tend to have peaks instead of midpoints, due to the slope of the curve changing from positive to negative, or vice-versa, thus forming an apex.

(17) The first change in slope on the DSC curve can be the glass transition temperature (Tg), which is the temperature range where the glass material transitions between hard and rubbery. The next change in slope in the direction of increasing temperature is the crystallization temperature (T.sub.x), which is the temperature range at which crystals precipitate from the glass material. The next change in slope in the direction of increasing temperature is the melting temperature (T.sub.m), which is the temperature range at which the glass liquefies.

(18) The magnitude of the difference Δ between the T.sub.g and the T.sub.x (that is, Δ=T.sub.x−T.sub.g) of the glass material is an indication of the thermal stability, i.e., the resistance to devitrification during reheating of the glass material. The larger the difference Δ, the greater the thermal stability of the glass material. This is because to mold the glass material, the glass material must be reheated to at least the glass transition temperature Tg. However, if the temperature of the glass material reaches the crystallization peak temperature (Tx), then devitrification will occur. Therefore, a larger Δ provides a wider temperature range within which to mold the glass material into the lens without causing devitrification. A Δ of 100° C. can be considered a minimum for the glass material to have thermal stability, with the Δ being more preferably at least 150° C. or more. As the graph of FIG. 4 reveals, all of the glass materials (made from the compositions of Examples 8-10) have sufficiently high Δ (approaching 200° C.) to be considered to have thermal stability, and have only a slightly less Δ than the Comparative Example. In addition, another indication of thermal stability is that the glass material has a T.sub.x of above 500° C., and more preferably above 550° C. All of the glass materials (made from the compositions of Examples 8-10) have a T.sub.x above 500° C. and either above or close to 550° C.

(19) Further, another indication of thermal stability is the area between the baseline of the DSC curve and the apex of the curve denoting the crystallization temperature (T.sub.x). The area between the apex and the baseline is the enthalpy of crystallization. Therefore, the greater the enthalpy of crystallization, the faster the crystallization occurs at that temperature range of crystallization. In other words, the greater the enthalpy of crystallization, the vigorous and energetic devitrification will be as the temperature of the glass material is within that temperature range. As the DSC curve at FIG. 4 reveals, the glass materials made from the compositions of Examples 8-10 have an almost non-existent area between the apex and the baseline and therefore a small enthalpy of crystallization, and much smaller than the enthalpy of crystallization for the Comparative Example. Therefore, the glass materials made from the compositions of Examples 8-10 are very thermally stable and more thermally stable than the Comparative Example. This is a surprising result, considering the lack of boron trioxide (B.sub.2O.sub.3) as a network former and the large weight/mass percentages of niobium pentoxide (Nb.sub.2O.sub.5) included in those compositions.

(20) Similarly, a glass transition temperature T.sub.x below 650° C. makes the glass material suitable to make a lens from the glass material via direct molding (precision press molding). The glass materials (made from the compositions of Examples 8-10) all have a glass transition temperature T.sub.x below 650° C.

(21) Referring now to FIG. 5, a head mounted wearable device 10 includes an image forming device 12 and a light guiding device 14. The image forming device 12 includes a light source 16 and can include a lens 18 that manipulates visible light 20 that the light source 16 projects before the visible light 20 propagates into the light guiding device 14. The light guiding device 14 includes an embodiment of a novel glass material 22 disclosed above. (The lens 18 can also be made of the novel glass material 22.) Reflecting repeatedly within the glass material 22 (e.g., for a distance of 20 mm to 300 mm), the visible light 20 propagates through the glass material 22 and exits the glass material 22 such that it is incident to an eye 24 of a user 26 that is wearing the head mounted wearable device 10. Thus, the glass material 22 acts as a light guide transmitting visible light 20 from the light source 16 to the eye 24 of the user 26. Consequently, the user 26 can sense the visible light 20 (such as a virtual image) and the external world image in a superimposed manner. The user 26 wears the head mounted wearable device 10 on a head 28 of the user 26.

(22) It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the claims.