MANUFACTURING PROCESS FOR STRIAE-FREE MULTICOMPONENT CHALCOGENIDE GLASSES VIA MULTIPLE FINING STEPS

Abstract

The present invention provides for synthesizing high optical quality multicomponent chalcogenide glasses without refractive index perturbations due to striae, phase separation or crystal formation using a two-zone furnace and multiple fining steps. The top and bottom zones are initially heated to the same temperature, and then a temperature gradient is created between the top zone and the bottom zone. The fining and cooling phase is divided into multiple steps with multiple temperature holds.

Claims

1. A striae-free chalcogenide glass made by the method, comprising: loading germanium, arsenic, selenium, and tellurium precursors into an ampoule, wherein the germanium, arsenic, selenium, and tellurium precursors are sufficient to constitute a glass with the composition of x % at. germanium, y % at. arsenic, z % at. selenium, and (100-x-y-z) % at. tellurium, wherein 0.5≤x≤25, 30≤x+y≤55, and 0.5≤z≤20, sealing the ampoule, and placing the ampoule in a rocking furnace, wherein the rocking furnace comprises a top zone and a bottom zone, wherein the top and bottom zones are two independently controllable temperature zones; heating both the top and bottom zones at a rate of 3° C. per minute to a Step 1 temperature, wherein the Step 1 temperature is the same for both the top and bottom zones; maintaining the Step 1 temperature in the top and bottom zones while rocking the furnace at an inclination angle of +45° for 15 hours; increasing the temperature of the top zone at a rate of 0.6° C. per minute to a Step 3 top zone temperature and maintaining the Step 1 bottom zone temperature as the Step 3 bottom zone temperature while rocking the furnace at an inclination angle of +45°, wherein there is a temperature gradient of 100° C. between the Step 3 top zone temperature and the Step 3 bottom zone temperature; setting the furnace to a vertical position and maintaining the Step 3 top zone temperature and the Step 3 bottom zone temperature for 3 hours; decreasing the temperature of the top zone at a rate of 10° C. per minute to a Step 5 top zone temperature, decreasing the temperature of the bottom zone at a rate of 10° C. per minute to a Step 5 bottom zone temperature, and maintaining the Step 5 top zone temperature and Step 5 bottom zone temperature for 3 hours, wherein the Step 5 top zone temperature is 100° C. lower than the Step 3 top zone temperature, and wherein the Step 5 bottom zone temperature is 100° C. lower than the Step 3 bottom zone temperature; decreasing the temperature of the top zone at a rate of 10° C. per minute to a Step 6 top zone temperature, decreasing the temperature of the bottom zone at a rate of 10° C. per minute to a Step 6 bottom zone temperature, and maintaining the Step 6 top zone temperature and Step 6 bottom zone temperature for 3 hours, wherein the Step 6 top zone temperature is 100° C. lower than the Step 5 top zone temperature, and wherein the Step 6 bottom zone temperature is 100° C. lower than the Step 5 bottom zone temperature; decreasing the temperature of the top zone at a rate of 10° C. per minute to a Step 7 top zone temperature, decreasing the temperature of the bottom zone at a rate of 10° C. per minute to a Step 7 bottom zone temperature, and maintaining the Step 7 top zone temperature and Step 7 bottom zone temperature for 30 minutes; and removing the ampoule from the furnace and water quenching the glass.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a schematic overview of a prior art process to synthesize chalcogenide glasses by melt processing.

[0023] FIG. 2 is a schematic overview of a rocking furnace in vertical (90°) fixed position of a prior art process.

[0024] FIG. 3A is a schematic diagram of thermal convection current in the Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z glass melt and glass condensation drops on top of the cooler ampoule inside the furnace of a prior art process. FIG. 3B is a photo of said ampoule after quenching with glass condensation above the solid glass.

[0025] FIG. 4A is an IR-image of a hot steel grating viewed through a 1 inch diameter, 4.0 inches thick cylinder (both faces polished) of Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z glass showing striae in the bulk glass. FIG. 4B is an IR-image of a human hand and fingers viewed through a 1 inch diameter, 4.0 inches thick cylinder (both faces polished) of Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z glass showing striae in the bulk glass.

[0026] FIG. 5A shows an ampoule containing a Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se glass made by a prior art process, where 0≤x≤10, 0≤z≤10 and 30≤x+y≤45, showing crystals above the glass. FIG. 5B shows an enlargement of area 73 from FIG. 5A.

[0027] FIG. 6 is a schematic overview of a furnace used in the current invention to synthesize chalcogenide glasses by melt processing.

[0028] FIG. 7 is a schematic overview of a rocking furnace in vertical (90°) fixed position such that the axis of the ampoule is vertical.

[0029] FIG. 8A is a photo of an ampoule with no glass condensation above the glass. FIG. 8B is an IR-image of a hot steel grating viewed through a 1 inch diameter, 4.0 inches thick Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z glass cylinder with both faces polished showing no striae in the uniform bulk glass. FIG. 8C is an IR-image of a human hand and fingers viewed through a 1 inch diameter, 4.0 inches thick Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z glass cylinder with both faces polished showing no striae in the uniform bulk glass.

[0030] FIG. 9A is an IR image of human hand and fingers viewed through a Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z glass cylinder produced from the process of the present invention. FIG. 9B is an IR image of human hand and fingers viewed through a Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z glass cylinder produced from a prior art method revealing refractive index perturbations in the art glass of the prior art.

[0031] FIG. 10A is a photo of a 3.0 inches thick glass Ge.sub.xAs.sub.ySe.sub.zTe.sub.(100-x-y-z) ingot (83). FIG. 10B shows an IR-image of a hot steel grating viewed through a 55 mm diameter, 3.0 inches thick Ge.sub.xAs.sub.ySe.sub.zTe.sub.(100-x-y-z) glass cylinder with both faces polished showing no striae in the uniform bulk glass. FIG. 10C shows an IR-image of a human hand and fingers viewed through a 55 mm diameter, 3.0 inches thick Ge.sub.xAs.sub.ySe.sub.zTe.sub.(100-x-y-z) glass cylinder with both faces polished showing no striae in the uniform bulk glass.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention provides a new method to synthesize striae-free chalcogenide glass using melt processing. High optical quality multicomponent chalcogenide glasses without refractive index perturbations due to striae, phase separation or crystal formation are synthesized using a two-zone furnace and multiple fining steps. The top and bottom zones are initially heated to the same temperature, and then a temperature gradient of about 100° C. is created between the top zone (750° C.) and the bottom zone (650° C.). The fining and cooling phase is divided into multiple steps with multiple temperature holds. The glass melt is fined for 3 hours at high temperature—above the temperature at which crystal precipitation is known to begin—and then rapidly cooled to a lower temperature below the temperature at which crystal precipitation occurs where it is held for 3 hours. The glass melt is then cooled and held at another lower temperature for 3 more hours.

[0033] The method of the present invention to synthesize striae-free chalcogenide glass using melt processing is described herein by example using Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z glass.

EXAMPLE 3

Process of the Present Invention to Make Striae-Free Ge.SUB.x.As.SUB.y.S.SUB.(100-x-y-z).Se.SUB.z .and Other Multicomponent Chalcogenide Glasses

[0034] Germanium, arsenic, sulfur, and selenium precursors sufficient to constitute a glass with the composition of x % at. Ge, y % at. As, z % at. Se and (100-x-y-z) % at. S, where (0≤x≤10, 0≤z≤10 and 30≤x+y≤45) or (0.5≤x≤10, 0.5≤z≤10 and 30≤x+y≤45) are loaded in a silica ampoule under an inert nitrogen gas atmosphere. FIG. 6 shows a schematic overview of the furnace used in the present invention to synthesize chalcogenide glasses by melt processing comprising a sealed quartz ampoule 200 containing melted Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z precursors 203 inside a rocking furnace 30 having two independently controllable heaters 31, 32 with a ±45° inclination angle 101. The ampoule 200 is cylindrical in shape and has an axis 201 and a diameter 202, and is then connected to a vacuum pump and evacuated for 4 hours at about 1×10.sup.−5 Torr. The ampoule has a length, parallel to its axis, and a diameter, perpendicular to the axis, such that the length is greater than the diameter, but the ampoule is not limited to this geometry and may have a diameter greater than its length, as is useful for casting large diameter glass for large optics. Furthermore the ampoule may have another shape similar to the shape of a glass product such as a lens or lens preform used in precision lens molding processes. The ampoule is then sealed using a methane (or hydrogen)/oxygen torch and placed inside a rocking furnace with a ±45° angle of inclination and two independently controllable temperature zones where it is heated and rocked according to a glass melting schedule, an example of which is shown in Table 3. The bottom of the ampoule is placed at the center of the bottom zone where the glass melt is entirely within the bottom zone.

[0035] In Step 1, the top and bottom zones of the furnace are heated at a rate of 3° C./min from 20° C. (room temperature) to 680° C. (top) and 680° C. (bottom). In Step 2, the temperatures of the top zone (680° C.) and bottom zone (680° C.) are held constant for 15 hours while the furnace is rocked at an inclination angle of ±45° to facilitate mixing and homogenization of the elemental components. In Step 3, the top zone temperature is increased at a rate of 0.6° C./min to 750° C. and the bottom zone temperature is decreased at a rate of 0.6° C./min to 650° C. while the furnace is rocked at an inclination angle of ±45° to establish the temperature gradient of 100° C. between the top and bottom zones. In Step 4, the furnace motion is stopped and the furnace was set to a vertical position (90° fixed angle). This furnace position and temperature profile were held for 3 hours to facilitate fining and settling of the glass melt. In Step 5, the temperatures of the top zone and the bottom zone are reduced at a rate of 10.0° C./min to 650° C. (top) and 550° C. (bottom) and held for 3 hours. In Step 6, the temperatures of the top zone and the bottom zone are reduced at a rate of 10.0° C./min to 550° C. (top) and 450° C. (bottom) and held for 3 hours. In Step 7, the temperatures of the top zone and the bottom zone are reduced at a rate of 10.0° C./min to 450° C. (top) and 350° C. (bottom) and held for 0.5 hours. In Step 8, the hot ampoule is removed from the furnace, submerged in a room temperature water bath for 9 seconds to quench the glass, and is placed in another furnace at 195° C. for 10 hours to anneal the solid glass.

TABLE-US-00003 TABLE 3 Glass melting schedule for a Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z glass composition in a two-zone furnace using the present invention. Heating Rate Temperature (° C.) Temperature (° C.) Dwell Step (° C./min) Top Zone Bottom Zone (hours) Furnace Position 1 3 680 680 1 Horizontal 0° fixed 2 — 680 680 15 Rocking at ±45° inclination 3 +0.6(T), 750 650 1 Rocking at ±45° inclination −0.6(B) 4 — 750 650 3 Vertical 90° fixed. Fining. 5 −10.0 650 550 3 Vertical 90° fixed. Fining. 6 −10.0 550 450 3 Vertical 90° fixed. Fining. 7 −10.0 450 350 0.5 Vertical 90° fixed. 8 Water quench

[0036] In general, the steps in the present invention are similar to steps in the prior art Example 2 to make striae-free 2-component chalcogenide glass (As.sub.39S.sub.61), but the differences described herein enable the fabrication of multicomponent IR-transmitting chalcogenide glasses with improved uniformity and without striae.

[0037] Step 1 in the present invention allows for an initial melting of precursor materials prior to rocking for homogenization and reduces the potential of abrasion of the ampoule by solid precursors during the next step. This differs from Step 1 in the prior art of Example 2 in that both furnace zones are set to the same temperature in order to prevent distillation of chemicals from 1 zone to the other via sublimation and condensation.

[0038] Steps 2 & 3 encourage mixing and homogenization of the melted material during rocking. In Step 3 of the present invention, a temperature gradient of 100° C. between the top zone (750° C.) and bottom zone (650° C.) is established while the furnace is rocking. This is done in the last hour of the rocking phase so that the gradient is established prior to vertical fining in the next steps. The 100° C. temperature gradient is held throughout the remaining process steps 3-7 in order to 1) reduce convection currents within the glass melt and 2) prevent condensation and mass fluxing within the glass melt. Both phenomena contribute to inhomogeneity and striae in the final glass and are reduced in this invention. This differs from the prior art in Example 2, which establishes and maintains a temperature gradient throughout the entire rocking phase of the process and may contribute to inhomogeneity in multicomponent glass melts.

[0039] Steps 4-7 differ from the prior art method in Example 2, in that the fining and cooling phase is divided into multiple steps with multiple temperature holds. In Steps 4-7, the ampoule containing the glass melt is positioned such that the glass melt is largely confined within the bottom zone of the furnace and it is being fined for 3 hours first at high temperature (Step 4) above the temperature at which crystal precipitation (or another phase separation process) is known to begin and then rapidly cooled to a lower temperature safely below (generally 20-200° C. below) the temperature at which crystal precipitation/phase separation occurs where it is held for 3 hours (Step 5) to allow for the volume of glass to reach the same temperature or thereabouts. The glass melt is then cooled and held at another lower temperature for 3 hours (Step 6) to allow for the volume of glass to reach the same temperature or thereabouts and then cooled to the quenching temperature (Step 7). These multiple fining steps (3-7) and a consistent 100° C. higher temperature in the top zone prevent thermal convection within the glass during cooling which allows the uniform conditions in the molten glass established in the previous steps to remain and prevents the reincorporation of surface glass into the bulk glass as in the case of the prior art Examples 1 and 2. The fast cooling rate (10° C./min) and shorter overall processing time prevent formation of intermediate phases including precipitated crystals and crystal nuclei during cooling of the glass melt.

[0040] FIG. 7 shows the measuring points 401, 402, 403, 404, 405 in the furnace during the dwell portion of Step 7 in this example. The short dwell steps allow the entire volume of the glass melt to reach the same temperature, or thereabouts, prior to the next cooling step. The temperature was measured various points 401, 402, 403, 404, 405 along the length of the quartz ampoule 200 containing Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z glass melt 203. The heater 30 of the top zone 33 was set to 450° C. and the heater 32 of the bottom zone 34 was set to 350° C. in this example. The measured temperatures were as follows: T.sub.401=451° C., T.sub.402=450° C., T.sub.403=352° C., T.sub.404=351° C., and T.sub.405 =350° C.

[0041] During water quenching of Step 8, the viscosity of the glass increases rapidly as the glass melt cools but thermal stresses are less than those in the method of the prior art due to shorter quench time in the present invention. FIG. 8A shows a photo of a Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z glass of the present invention inside an ampoule 201 with no glass condensation or crystal nuclei above the glass melt 81. FIG. 8B shows an IR-image of a hot steel grating 52 viewed through a 1 inch diameter, 4.0 inches thick Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z glass cylinder 82 with both faces polished showing no striae in the uniform bulk glass. FIG. 8C shows an IR-image of a human hand and fingers 62 viewed through a 1 inch diameter, 4.0 inches thick cylinder 82 (both faces polished) of a Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z glass with no detectable striae, crystallites or refractive index perturbations in the bulk glass.

[0042] The process of the present invention produces high optical quality multicomponent chalcogenide glasses without refractive index perturbations due to striae, phase separation or crystal formation. Comparing the photographs of the glasses inside the ampoules for the glass made using the prior art method (FIG. 5A) and the glass made using the present invention (FIG. 8A), it is evident that the formation of crystals has been reduced by the present invention. Furthermore, comparing the IR images of the glass prepared using the present invention (FIGS. 8B and 8C) with those of the glass prepared using the prior art methods (FIGS. 4A and 4B) reveals a dramatic improvement in optical quality and homogeneity for these glasses. This is demonstrated in FIGS. 9A and 9B, where the Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z glass 82 produced from the process of the present invention (FIG. 9A) is clear when viewed with an infrared camera, while the glass 50 of the prior art (FIG. 9B) contains many refractive index perturbations 61.

EXAMPLE 4

Process of the Present Invention to Make Striae-Free Ge.SUB.x.As.SUB.y.Te.SUB.(100-x-y-z).Se.SUB.z .and Other Multicomponent Chalcogenide Glasses

[0043] In this example, glass containing germanium, arsenic, selenium, and tellurium is fabricated without striae and without crystallite inclusions using the process described in Example 3 above with the main difference being the precursor elements and their quantities and the details of the heating schedule. Germanium, arsenic, selenium and tellurium precursors sufficient to constitute a glass with the composition of x % at. Ge, y % at. As, z % at. Se, and (100-x-y-z) % at. Te, where (0≤x≤25, 30≤x+y≤55, and 0≤z≤20) or (0.5≤x≤25, 30≤x+y≤55, and 0.5≤z≤20) are loaded in a silica ampoule under an inert nitrogen gas atmosphere. The ampoule is then sealed using a methane/oxygen or hydrogen/oxygen torch and placed inside a rocking furnace with a ±45° angle of inclination and two independently controllable temperature zones where it is heated and rocked according to a glass melting schedule, an example of which is shown in Table 4 and described in more detail below. The bottom of the ampoule is placed at the center of the bottom zone such that the glass melt is entirely within the bottom zone.

[0044] In general, the steps in this example correspond to steps in the Example 3 but with different starting precursors and the times and temperatures used in the heating schedule.

TABLE-US-00004 TABLE 4 Glass melting schedule for a Ge.sub.xAs.sub.ySe.sub.zTe.sub.(100-x-y-z) glass composition in a two-zone furnace using the present invention Heating Rate Temperature (° C.) Temperature (° C.) Dwell Step (° C./min) Top Zone Bottom Zone (hours) Furnace Position 1 3 650 650 1 Horizontal 0° fixed 2 — 650 650 15 Rocking at ±45° inclination 3 +0.6(T), 750 650 1 Rocking at ±45° inclination −0.6(B) 4 — 750 650 3 Vertical 90° fixed. Fining. 5 −10.0 650 550 3 Vertical 90° fixed. Fining. 6 −10.0 550 450 3 Vertical 90° fixed. Fining. 7 −10.0 300 200 0.5 Vertical 90° fixed. 8 Water quench

[0045] In Step 1, the top and bottom zones of the furnace are heated at a rate of 3° C./min from 20° C. (room temperature) to 650° C. (top) and 650° C. (bottom). In Step 2, the temperatures of the top zone (650° C.) and bottom zone (650° C.) are held constant for 15 hours while the furnace is rocked at an inclination angle of ±45° to facilitate mixing and homogenization of the elemental components. In Step 3, the top zone temperature is increased at a rate of 0.6° C./min to 750° C. and the bottom zone temperature is remained at 650° C. while the furnace is rocked at an inclination angle of ±45° to establish the temperature gradient of 100° C. between the top and bottom zones. In Step 4, the furnace motion is stopped and the furnace was set to a vertical position (90° fixed angle). This furnace position and temperature profile were held for 3 hours to facilitate fining and settling of the glass melt. In Step 5, the temperatures of the top zone and the bottom zone are reduced at a rate of 10.0° C./min to 650° C. (top) and 550° C. (bottom) and held for 3 hours. In Step 6, the temperatures of the top zone and the bottom zone are reduced at a rate of 10.0° C./min to 550° C. (top) and 450° C. (bottom) and held for 3 hours. In Step 7, the temperatures of the top zone and the bottom zone are reduced at a rate of 10.0° C./min to 300° C. (top) and 200° C. (bottom) and held for 0.5 hours. In Step 8, the hot ampoule is removed from the furnace, submerged in a room temperature water bath for 6 seconds to quench the glass melt forming a solid glass ingot. The ampoule containing the solid glass ingot is then placed in another furnace at 195° C. for 10 hours to anneal the solid glass and reduce stress due to quenching. FIGS. 10A-10C shows the results of this example. FIG. 10A shows a photo of a 3.0 inches thick glass Ge.sub.xAs.sub.ySe.sub.zTe.sub.(100-x-y-z) ingot 83. FIG. 10B shows an IR-image of a hot steel grating 52 viewed through the 55 mm diameter, 3.0 inches thick Ge.sub.xAs.sub.ySe.sub.zTe.sub.(100-x-y-z) glass cylinder 83 with both faces polished showing no striae in the uniform bulk glass. FIG. 10C shows a human hand and fingers 62 viewed through the 55 mm diameter, 3.0 inches thick Ge.sub.xAs.sub.ySe.sub.zTe.sub.(100-x-y-z) glass cylinder 83 with both faces polished showing no striae in the uniform bulk glass.

[0046] This invention has been demonstrated using Ge.sub.xAs.sub.yS.sub.(100-x-y-z)Se.sub.z and Ge.sub.xAs.sub.ySe.sub.zTe.sub.(100-x-y-z) glasses in the above example but can also be applied to other two-component and multi-component chalcogenide glasses such as but not limited to, arsenic, sulfur, selenium and tellurium based glasses and other multi-component chalcogenide and chalcohalide glasses containing antimony, gallium aluminum, indium, bismuth, tin, iodine, bromine, chlorine, fluorine, lanthanum and other elements. The present invention could also be applied to the fabrication of other glasses (for example silicates, borates, fluorides, phosphates and others) or processing of viscous liquids (for example polymer melts, metals, salts and other liquids) where homogeneity is desired.

[0047] The above descriptions are those of the preferred embodiments of the invention. Various modifications and variations are possible in light of the above teachings without departing from the spirit and broader aspects of the invention. It is therefore to be understood that the claimed invention may be practiced otherwise than as specifically described. Any references to claim elements in the singular, for example, using the articles “a,” “an,” “the,” or “said,” is not to be construed as limiting the element to the singular.