Silicon carbide (SiC) porous substrates are prepared by pressureless sintering of SiC powders under an inert atmosphere of argon. The porous SiC substrates were characterized by measuring their porosity, pore size distribution, surface characteristics, and structure. Their transport characteristics were investigated using N 2 and He as the test gases. Three different starting powders and four different sintering aids, Al 2 O 3 , B 4 C, carbon black, and phenolic resin, either by themselves or in combination, were investigated in terms of their ability to prepare good quality substrates. It was found that the porosity, pore size distribution, and transport characteristics of the resulting SiC-sintered bodies depend on the nature of the original powder, the particle size in the green SiC samples, and the type and molar ratio of the sintering aid utilized. Depending on the preparation technique, both mesoporous and macroporous materials could be prepared. These supports are currently utilized for the preparation of microporous membranes.

An interferometric technique has been used to determine the thermooptic coefficient (dn/dT) of polycrystalline ZnSe and ZnS at 0.6328 microm, 1.15 microm, 3.39 microm, and 10.6 microm; polycrystalline CdTe and TI-20 glass at 1.15 microm, 3.39 microm, and 10.6 microm; polycrystalline CaF(2) and BaF(2) at 0.6328 microm, 1.15 microm, and 3.39 microm, and pure and europium-doped single crystal KCl at 0.6328 microm, 1.15microm, 3.39 microm, and 10.6 microm. The values were obtained over the temperature range of 25-65 degrees C and were calculated using the observed change in optical path of the samples as they were heated. Some difficulties in thermometry were encountered in the standard configuration of sample and thermocouple probe, so measurements were made in an oil bath at the shortest wavelength at which the sample was transparent to provide temperature correction factors for each sample. An empirical dispersion relation for dn/dT has also been found for the semiconductor materials. This dispersion relation is of the form dn/dT = aR(b), where R is defined as lambda(2)/(lambda(2) - lambda(g)(2)), lambda(g) is the short wavelength cutoff associated with the energy gap, and a and b are constants which are different for each material.

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Articles you may be interested inRoom temperature dielectric and magnetic properties of Gd and Ti co-doped BiFeO3 ceramics Room-temperature ferromagnetism in Co-doped CeO2 nanospheres prepared by the polyvinylpyrrolidone-assisted hydrothermal methodThe room temperature Gd3+ EPR spectrum in SrF2 containing Ce3+ as a second dopant exhibits three types of symmetry sites: cubic, trigonal, and tetragonal. Relative intensities of the spectra from these sites have been determined as a function of the Ce3+ codopant level in crystals having nominally 0.1 molar % of Gd3+. At low Ce3+ concentrations «0.1 molar %), the tetragonal-to-trigonal intensity ratio is 1.85± 0.25, with the cubic site intensity accounting for less than one tenth of the total observed intensity. At higher Ce3+ concentrations (up to 0.8 molar %), the cubic site intensity grows and the intensity of both axial sites decreases. This increase of cubic intensity is at variance with the generally accepted model of nonlocalized cubic compensation of the Gd3+, and a phenomenological explanation based on a local cubic phase in which rare earth ions are essentially surrounded with interstitial compensating fluorines is presented.

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