Quartz crystal growth

Claim 2

A process for growing high quality single crystals of a nutrient substance that can undergo phase transformation from the amorphous to the crystalline state in an appropriate solvent, said process comprising: (a) charging the substance, seed crystals of the substance, and the solvent in an autoclave having a lower dissolution zone connecting with an upper crystallization zone; (b) allowing the closed charged autoclave to stand at ambient temperature for a time sufficient to reach internal equilibrium; (c) gradually heating the autoclave at a rate such that a very small temperature differential (ΔT) is maintained between the cooler upper zone and the warmer lower zone until the nutrient substance has undergone transformation to the crystalline phase; and (d) increasing the heating rate to achieve and maintain a larger temperature differential (ΔT) between the zones sufficient to allow increased material transport between the zones and rapid controlled crystal growth.

Claim 3

The process of claim 1 wherein the nutrient substance is solid fused silica and the solvent is an aqueous caustic solution containing lithium carbonate.

Claim 4

The process of claim 2 wherein the fused silica is in the form of solid pea size lumps and the solvent is an aqueous 1.OM NaOH+0.025M Li 2 CO 3 solution.

Claim 5

The process of claim 3 wherein the charged autoclave is held allowed to stand at ambient temperature and pressure for a period of at least 16 hours.

Claim 6

The process of claim 3 wherein the charged autoclave is subjected to the following heating regime, after standing at ambient temperature and pressure for a period of 16 to 20 hours: (a) in an 8 to 12-hour period, the temperature of the autoclave is continuously increased from ambient temperature to an upper zone temperature of 200°±25° C. while maintaining a ΔT within the range of about 0.25° to 3° C; (b) the temperature of 200°±25° C. and ΔT=0.25 to 3° C. conditions are kept for a period of 15 to 20 hours; (c) in another 8 to 12-hour period, the temperature of the autoclave is continuously increased from an upper zone level of 200°±25° C. to 250°±25° C., while maintaining ΔT=about 0.25°-3° C.; (d) the temperature of 250°±25° C. and ΔT=0.25° to 3° C. conditions are kept for a period of 15 to 20 hours; (e) in a 45 to 50-hour period, the temperature of the autoclave is continuously increased from an upper zone level of 250 ±25° C. to 350 ±25° C., while maintaining ΔT=about 0.25°-3° C.; (f) in a 120 to 144-hour period, the temperature of the lower zone of the autoclave is continuously increased to achieve ΔT=50°±10 20 C.; (g) the upper zone temperature of 350°±25° C. and the lower zone temperature necessary to maintain ΔT=50°±10° C. are held until crystal growth is substantially completed; (h) in a 20 to 30-hour period, the temperature of the upper and lower zones are reduced at a rate such that they reach ambient temperature simultaneously.

Claim 7

The process of claim 5 wherein the heating regime comprises: (a) ambient temperature to 200° C. in upper zone in 8 hours with ΔT=2° C.; (b) 16 hours at 200° C. with ΔT=2° C.; (c) 200° to 250° C. in upper zone in 8 hours with ΔT=2° C.; (d) 16 hours at 200° C. with ΔT=2° C.; (e) 250° C. to 350° C. in upper zone in 48 hours with ΔT=2° C.; (f) lower zone temperature increased to obtain ΔT=50° C. in 144 hours; and (g) 350° C. in upper zone with ΔT=50° C. until crystal growth is substantially complete.