Sintering direct

Fabrication techniques include compaction and sintering, direct compression molding, hot stamping, forging, and hot plate or spin welding (13). 

Mold-halves and kernels can be sintered directly from foundry sands. 

Becher, P.F., Somers, J.H., Bender, B.A., and MacFarland, B.A. (1978) Ceramics sintered directly from sol-gels, in Processing of Crystalline Ceramics, Materials Science Research, vol. 11 (eds... 

Some ceramics and metals may be sintered directly, taking advantage of the high laser power output offered by spedal SLS equipment. Ceramic powders for direct sintering indude... 

The drying agent was filtered off on a sintered-glass funnel and rinsed with some THF. The solution was transferred into a 500-ml wide-necked flask and concentrated in a water-pump vacuum. In order to remove the last traces of THF and some water the flask was connected directly (without a column) to a condenser and a receiver, cooled at -190°. The flask was evacuated by means of a mercury pump (p < 0.1 mmHg) and heated for 1.5 h at 85°C. The greater part of the mono-... 

MCVD process (Fig. 7) the reactants enter the tube, are reacted in the hot 2one of the torch, deposit therm oph oretically downstream of the torch, and are subsequendy sintered to a clear glass as the torch passes over the deposited particulate layer. Once the desired stmcture has been deposited, the direction of the torch is reversed and the tube is collapsed to form a soHd preform. 

Eree-sintered articles do not have the same dimensions as the mold cavity because they shrink at right angles to the direction of the preform pressure and grow in the direction of the appHed pressure. 

The matte can be treated in different ways, depending on the copper content and on the desired product. In some cases, the copper content of the Bessemer matte is low enough to allow the material to be cast directly into sulfide anodes for electrolytic refining. Usually it is necessary first to separate the nickel and copper sulfides. The copper—nickel matte is cooled slowly for ca 4 d to faciUtate grain growth of mineral crystals of copper sulfide, nickel—sulfide, and a nickel—copper alloy. This matte is pulverized, the nickel and copper sulfides isolated by flotation, and the alloy extracted magnetically and refined electrolyticaHy. The nickel sulfide is cast into anodes for electrolysis or, more commonly, is roasted to nickel oxide and further reduced to metal for refining by electrolysis or by the carbonyl method. Alternatively, the nickel sulfide may be roasted to provide a nickel oxide sinter that is suitable for direct use by the steel industry. 

Reactive aluminas have enabled 85, 90, and 95% -AI2O2 ceramics to be upgraded (16,17), because they could be sintered without fluxes in the temperature range of about 1723—2023 K, rather than 2073—2123 K. Advances in microminiaturization of components for the electronic, computer, and aerospace industries have been directly related to the development of low soda and reactive aluminas (18). 

Barium carbonate also reacts with titania to form barium titanate [12047-27-7] BaTiO, a ferroelectric material with a very high dielectric constant (see Ferroelectrics). Barium titanate is best manufactured as a single-phase composition by a soHd-state sintering technique. The asymmetrical perovskite stmcture of the titanate develops a potential difference when compressed in specific crystallographic directions, and vice versa. This material is most widely used for its strong piezoelectric characteristics in transducers for ultrasonic technical appHcations such as the emulsification of Hquids, mixing of powders and paints, and homogenization of milk, or in sonar devices (see Piezoelectrics Ultrasonics). 

The properties of siHcon carbide (4—6) depend on purity, polytype, and method of formation. The measurements made on commercial, polycrystalline products should not be interpreted as being representative of single-crystal siHcon carbide. The pressureless-sintered siHcon carbides, being essentially single-phase, fine-grained, and polycrystalline, have properties distinct from both single crystals and direct-bonded siHcon carbide refractories. Table 1 Hsts the properties of the hiUy compacted, high purity material. 

A typical converter is made up of multiple furnaces, each of which contains 8 to 10 reactors. Each reactor is made up of 10 to 30 sintered alumina tubes lined with platinum. The furnaces are direct fired with natural gas to 1200—1300°C. A typical furnace can produce about 125 t per month of hydrogen cyanide. Catalyst life is approximately 10,000 h. 

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