Thorium oxide, sintered

Thorium oxide, has the highest melting point of the usual ceramic materials (3390°C). It is used to form ceramics, Th02, as the so-called meta-Th02, freshly prepared by low temperature decomposition of thorium oxalate it is fairly soluble in acids and tends (especially in the presence of nitrate ions) to form colloidal solutions which can be dried to form stable gels that can be sintered to give high-density ceramic bodies. 

Ceramic infrared light sources are used in some spectrometers. A ceramic stick is heated by a metallic conductor, made from platinum or a platinum alloy, and wound around the ceramic stick. The conductor is surrounded with a sintered layer of aluminum, thorium oxide, zirconium silicate or a similar material. The heating conductors made from chrome nickel or tungsten wire are preferably suitable for short-wave spectral analysis. 

The thorium oxide catalyst of the iso-synthesis cannot be poisoned by sulfur or sulfur compounds. The activity of this catalyst slowly declines only in cases when carbon covers its surface. A periodical treatment with oxygen containing gases restores the activity of the high melting oxide catalysts without activity decline by sintering. 

Thorium oxide. The major portion of studies on corrosion-erosion characteristics of high-temperature aqueous slurries has been carried out using thorium oxide [110-111]. Most preparations have used the calcination product of thorium oxalate precipitated under various conditions, with calcination temperatures from 450 to 1600°C having been used. Thoria prepared by other procedures, such as formate precipitation, has also beeti examined. Thoria calcined at temperatures in the vicinity of 1600°C has low surface area, crystallite sizes approaching particle size, less tendency to degrade, and exhibits a greater tendency to produce abrasive sintered particles consequently, certain of such thoria products have been... 

The fuel was a mixture of oxides of thorium and uranium-235 (THUD fuel), a material expected to have high physical and chemical stability in a reactor atmosphere, and to offer possibilities of breeding in a boiling water power system. Small cylinders of this mixture were pressed, sintered and stacked inside aluminum to form a fuel pin 60 inches long and -q inch ta diameter. Two versions of this fuel were available in quantity, the first having a thorium to uranium-235 atomic ratio of 25 1 the second an atomic ratio of 50 1. ... 

Although some of these saltlike nitrides have high melting points (for instance, thorium nitride 2820"C uranium nitride 2800°C plutonium nitride 2550 beryllium nitride 2200 C barium nitride 2200"C), they are sensitive to hydrolysis and react readily with water or moisture to give ammonia and the corresponding metal oxide or hydroxide. Consequently, they do not meet the refractory requirements as interpreted here. Some of these nitrides are useful industrial materials particularly as sintering additives for the production of silicon nitride, aluminum nitride, and cubic boron nitride (see Ch. 14). 

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