Claims
- 1. 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 (.DELTA.T) 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 (.DELTA.T) between the zones sufficient to allow increased material transport between the zones and rapid controlled crystal growth.
- 2. The process of claim 1 wherein the nutrient substance is solid fused silica and the solvent is an aqueous caustic solution containing lithium carbonate.
- 3. 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.sub.2 CO.sub.3 solution.
- 4. 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.
- 5. 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.degree..+-.25.degree. C. while maintaining a .DELTA.T within the range of about 0.25.degree. to 3.degree. C;
- (b) the temperature of 200.degree..+-.25.degree. C. and .DELTA.T=0.25 to 3.degree. 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.degree..+-.25.degree. C. to 250.degree..+-.25.degree. C., while maintaining .DELTA.T=about 0.25.degree.-3.degree. C.;
- (d) the temperature of 250.degree..+-.25.degree. C. and .DELTA.T=0.25.degree. to 3.degree. 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.degree. C. to 350 .+-.25.degree. C., while maintaining .DELTA.T=about 0.25.degree.-3.degree. C.;
- (f) in a 120 to 144-hour period, the temperature of the lower zone of the autoclave is continuously increased to achieve .DELTA.T=50.degree..+-.10 20 C.;
- (g) the upper zone temperature of 350.degree..+-.25.degree. C. and the lower zone temperature necessary to maintain .DELTA.T=50.degree..+-.10.degree. 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.
- 6. The process of claim 5 wherein the heating regime comprises:
- (a) ambient temperature to 200.degree. C. in upper zone in 8 hours with .DELTA.T=2.degree. C.;
- (b) 16 hours at 200.degree. C. with .DELTA.T=2.degree. C.;
- (c) 200.degree. to 250.degree. C. in upper zone in 8 hours with .DELTA.T=2.degree. C.;
- (d) 16 hours at 200.degree. C. with .DELTA.T=2.degree. C.;
- (e) 250.degree. C. to 350.degree. C. in upper zone in 48 hours with .DELTA.T=2.degree. C.;
- (f) lower zone temperature increased to obtain .DELTA.T=50.degree. C. in 144 hours; and
- (g) 350.degree. C. in upper zone with .DELTA.T=50.degree. C. until crystal growth is substantially complete.
Government Interests
This invention relates to a process for growing .alpha.-quartz single crystals from a fused amorphous silica nutrient. The U.S. Government has rights in this invention pursuant to Contract No. DE-AC04-76DP00789 between the U.S. Department of Energy and Western Electric Company.
US Referenced Citations (8)
Foreign Referenced Citations (2)
Number |
Date |
Country |
601552 |
May 1948 |
GBX |
792724 |
Apr 1958 |
GBX |