Chemistry: physical processes – Physical processes – Crystallization
Patent
1983-11-08
1985-06-25
Lacey, David L.
Chemistry: physical processes
Physical processes
Crystallization
23301, 23305A, 156619, B01D 902
Patent
active
045251711
DESCRIPTION:
BRIEF SUMMARY
Crystals are grown from various inorganic or organic liquids. For industrial use it is mainly desired to achieve a high purity for the utilization of physical effects. For the production of doubles in the precious stone trade it is desired to obtain grown products which have a proper form, which is as similar as possible to natural products and has undamaged, naturally grown crystal surfaces.
All known growing processes require seed crystal holders of mechanical type unless microseeds are used or macroseeds are used in conjunction with rotating magnetic fields or the processes are carried out in an extraterrestrial environment.
It may be possible to grow crystals from gel or vapor phases and the like without a need for a crystal holder but in that case the resulting crystals grow on and adhere to solid surfaces and will certainly be damaged when they have been detached. This applies also to crystals which form spontaneously as a result of supersaturation; this is due to the fact that with a critical radius r.sub.k or a smaller radius of the nucleus the surface tensions of the solutions of molten materials predominate over the weight of the nucleus so that said micronuclei will always float on the surface of the solvent regardless of the density ratio of the nucleus to the solvent.
Owing to the light weight of such nuclei, they will spontaneously form at the locations at which a supersaturation exists rather then at the "top" or "bottom".
For all nuclei which are larger than r.sub.k it has previously been necessary to precisely locate them so that they
(a) will not fall down or
(b) will not float on the meniscus of the solvent, depending on whether their density (d.sub.k) is higher or lower than the density (d.sub.s) of the solvent or molten material Su represent the lower portion of the growing region, Sm represents the middle portion of the growing region and So represent the upper portion of the growing region
For this reason it is an object of the invention to provide a process which enables a growing operation in which one or more seeds can be used without seed holders. This object is accomplished in that the growing is effected in a solvent having a density which is equal or approximately equal to the density of the grown crystal at the instantaneous temperature and under the instantaneous pressure employed in the growing process (d.sub.k.sup..perspectiveto. d.sub.s =d.sub.L) so that the seeds float in the mass, in the feed solution or the like, d.sub.L being the density of the solution.
A gradient process can be performed by which crystals having the quality of precious stones can be grown in a terrestrial environment whereas gravitation is entirely or almost entirely inhibited. Because the density of liquid solvents will always exhibit a much higher dependence on temperature than the density of solids (nuclei), it can be assumed that in a gradient process the lower portion of the growing region will be somewhat warmer than the middle portion and the upper portion will be somewhat cooler than the middle portion (t.sub.su >t.sub.so).
When the feed substance is established in the lower, warmer portion then t.sub.n =t.sub.sm +.sup..DELTA.t, wherein t.sub.n is the temperature of the solution (molten material) in the feeding region in .degree.C., .DELTA.t is the temperature gradient in the solution (molten material) in .degree.C., t.sub.sm is the temperature of the solution (molten material) in the middle growing region in .degree.C., t.sub.su is the temperature of the solution (molten material) in the lower growing region in .degree.C. and t.sub.so is the temperature of the solution (molten material) in the upper growing region in .degree.C.
Because the temperatures are held most precisely constant in all gradient processes, the fact that t.sub.su >t.sub.sm >t.sub.so permits for the densities of the liquid solvent in the growing region (if liquid salt mixtures having positive coefficients of expansion are used) the conclusion that d.sub.su <d.sub.sm >d.sub.so, i.e., the densities (d.sub.s)
REFERENCES:
patent: 2875108 (1959-02-01), Pfann
patent: 3148023 (1964-09-01), Ploss
patent: 3714329 (1973-01-01), Arnaud
patent: 3758705 (1973-09-01), Schmid
patent: 3788818 (1974-01-01), Madjid et al.
patent: 3819335 (1974-06-01), Daniels et al.
Grenz Hans J.
Knischka Paul O.
Kelman Kurt
Knischka Rubine Gesellschaft m.b.H
Lacey David L.
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