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678. A non-crucible vacuum induction installation
Classified Abstracts 676---678 the change in filament emission in the presence of oxygen is the mechanism of detection. The direct filament heating current is regulated by a series transistor and stabilized, and the anode supply potential is also stabilized, being high enough to ensure temperature-limited conditions. The anode current is passed through a resistor, and the metering circuit is arranged to detect changes in this current. With the emission in the range 5 to 0.5 mA, a 20 per cent change gives full-scale deflection ; in the range 500 to 5/~A, a 100 per cent change is needed. M. D. A.
D. Allenden, J. Sci. Instrum., 38 (12), Dec. 1961, 512-513.
28.
Heating Equipment and Thermometers
329
28 677. Casing for thermocouples. U.S.S.R. Thermocouples employed in metallurgy are usually fitted with a protecting sheath or casing made of some ceramic material. Such casings are fragile and often crack when subjected to thermal shock. Workers at the Institute of Powder Metallurgy, U.S.S.R., recommend a refractory consisting of a triple layer of zirconium boride and aluminium oxide as representing a marked improvement. The outer layer of boride protects the thermocouple tip against chemical a t t a c k ; a n intermediate layer made of a mixture of the two powders has a reasonable thermal conductivity, whilst the inner layer of fused aluminium oxide ensures a rapid response. The protecting sheath can moreover be made gas-tight, w.s.s. Anon., New Scientist, 15 (302), 30 Aug. 1962, 459.
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676. Crystal-pulling furnace for gallium arsenide.
678. A non-crucible vacuum induction installation.
Great Britain. The design and operation of equipment for pulling single crystals of gallium arsenide are described. Features of the design include a demountable quartz system with rapidity of set-up and ease of operation, close control of the arsenic pressure in the tube, and very good vision during the crystal growing cycle. The heating element is of resistance heated graphite and is traversable. (Author) R. Wickham, J. Sci. lnstrum., 38 (10), Oct. 1961, 396--399.
U.S.S.R. For producing high-quality castings, use is made of the proposed non-crucible vacuum induction installation with 2 inductors, one of which is employed for levitation melting of the billet and the other for mixing the molten metal and refining the grain structure in the casting with industrial-frequency currents (in Russian). Z. A. Oreshnikov, V. P. Grechin, B. F. Milyayev and E. D. Sal'nikov, U.S.S.R. Patent, 133593, 25 Nov. 1960.
D. Allenden, J. Sci. Instrum., 38 (12), Dec. 1961, 512-513.
28.
Heating Equipment and Thermometers
329
28 677. Casing for thermocouples. U.S.S.R. Thermocouples employed in metallurgy are usually fitted with a protecting sheath or casing made of some ceramic material. Such casings are fragile and often crack when subjected to thermal shock. Workers at the Institute of Powder Metallurgy, U.S.S.R., recommend a refractory consisting of a triple layer of zirconium boride and aluminium oxide as representing a marked improvement. The outer layer of boride protects the thermocouple tip against chemical a t t a c k ; a n intermediate layer made of a mixture of the two powders has a reasonable thermal conductivity, whilst the inner layer of fused aluminium oxide ensures a rapid response. The protecting sheath can moreover be made gas-tight, w.s.s. Anon., New Scientist, 15 (302), 30 Aug. 1962, 459.
28 : 37
28
676. Crystal-pulling furnace for gallium arsenide.
678. A non-crucible vacuum induction installation.
Great Britain. The design and operation of equipment for pulling single crystals of gallium arsenide are described. Features of the design include a demountable quartz system with rapidity of set-up and ease of operation, close control of the arsenic pressure in the tube, and very good vision during the crystal growing cycle. The heating element is of resistance heated graphite and is traversable. (Author) R. Wickham, J. Sci. lnstrum., 38 (10), Oct. 1961, 396--399.
U.S.S.R. For producing high-quality castings, use is made of the proposed non-crucible vacuum induction installation with 2 inductors, one of which is employed for levitation melting of the billet and the other for mixing the molten metal and refining the grain structure in the casting with industrial-frequency currents (in Russian). Z. A. Oreshnikov, V. P. Grechin, B. F. Milyayev and E. D. Sal'nikov, U.S.S.R. Patent, 133593, 25 Nov. 1960.