Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including specific material of construction
Patent
1988-07-20
1990-09-18
Chaudhuri, Olik
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including specific material of construction
156608, 1566171, 1566201, 1566205, 156DIG61, 156DIG88, C30B 1534
Patent
active
049577131
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to the field of growing crystals from melts and deals with apparatus for growing single crystals of high melting transparent metal compounds, and more particularly, with an apparatus for growing shaped single crystals.
PRIOR ART
Very stringent requirements are imposed upon quality of profiled single crystals. The main quality characteristics are dimensional accuracy, electrical breakthrough strength, integral light transmission, crystallographic disorder of orientation of single crystal blocks, and mechanical strength. Thus it is specified for a tubular single crystal of that it should have a dimensional tolerance of .+-.0.2 mm in diameter, electrical breakthrough strength of -50 kV/mm and integral light transmission more than 92%.
The main factor influencing the quality of single crystals is the character of a temperature field in the melt/single crystal system which depends on the configuration and relative position of thermal shields ensuring thermal screening of the single crystal.
Known in the art is an apparatus for growing shaped single crystals of high-melting transparent metal compounds (P. I. Antonov et al. Producing Shaped Single Crystals by the Stepanov Method. 1981, Nauka, Leningrad, pp. 137-142), comprising a sealed chamber accommodating a heat insulating untit having a heater in the form of a sleeve in which there is mounted a crucible which is installed for axial reciprocations in the sleeve, a shape-imparting member in the form of a cylinder having through capillary orifices for supplying melt from the crucible into the single crystal crystallization zone located above the upper end of the shape-imparting member which is configured to have the cross-sectional shape of the single crystal being grown and which is disposed below the upper extremity of the heater, and planoar hyorizontally extending thermal shields having coaxila openings for the passage of the single crystal being grown therethrough.
The thermal shields are designed for providing a desired temperature gradient lengthwise of the single crystal during both growing and cooling. In addition, the thermal shields are designed for making temperature distribution uniform in the zone of crystallization of the single crystal.
The planar thermal shields are made of a high-melting material in the form of rings each 0.5 to 1 mm thick and are stacked, with 10 to 20 pieces in one stack. A clearance between adjacent shields is at least 5 times as great as their thickness. About one half of the shields are disposed inside the heater, the rest of the shields being installed above the heater. The amount of clearances between the shields and the heater and the single crystal, repectively, does not exceed two times the thermal shield thickness. A temperature gradient of 20.degree. to 30.degree. C./cm can be ensured in an apparatus for growing shaped single crystals using such thermal shields.
This temperature gradient lengthwise of the grown portion of a single crystal lowers the stability of the pulling process, i.e. even under low temperature fluctuations in the crystallization zone the height of the melt column deviates from the desired value so as to cause a change in the cross-sectional dimensions of the single crystal being grown, thus lowering the yield of normal-grade crystals.
It should be noted that it is practically impossible to ensure a constant temperature both in the crystallization zone of a single crystal and at the upper end of the shape-imparting member using such thermal shields owing to inaccurcies in the assembly and installation of the stack of thermal shields before each production cycle of growing of a new single crystal. In addition, the extremities of the planar thermal shields which are located adjacent to the heater surface are overheated. This results in warping of the thermal shields and also in undesired physico-chemical reactions between the metal, e.g. molybdenum of which components of the apparatus are made and carbon evaporating from the heater surface and also i
REFERENCES:
patent: 2890139 (1959-06-01), Shockley
patent: 2956863 (1960-09-01), Goorissen
patent: 3298795 (1967-01-01), Hamilton et al.
patent: 3715194 (1973-02-01), Plooster
patent: 3716345 (1973-02-01), Grabmaier
patent: 3822111 (1974-07-01), Suzuki et al.
patent: 3953174 (1976-04-01), LaBelle
patent: 4000030 (1976-12-01), Ciszek
patent: 4267010 (1981-05-01), Bates et al.
patent: 4267153 (1981-05-01), Taylor
patent: 4325917 (1982-04-01), Pelts et al.
Alishoev Alexandr L.
Averyanov Viktor V.
Egorov Leonid P.
Freiman Efim A.
Kravetsky Dmitry Y.
Chaudhuri Olik
Kunemund Robert M.
LandOfFree
Apparatus for growing shaped single crystals does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for growing shaped single crystals, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for growing shaped single crystals will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1571518