Tungsten Blue Oxide TBO

Industrial Production. TBO is formed by calcination of APT under slightly reducing conditions. The conversion can be performed either in multitube push-type furnaces or in 

FIGURE 5.18. SEM image of WO3. The size and shape of the APT crystals are maintained, but the pseudomotphs consist of agglomerates of very small oxide crystals with sizes between 0.1 and 0.5 pm. 

Temperature may vary between 400 and 900 C. Literature values can be misleading, because some are related to the real temperature of the powder layer while others are furnace temperatures measured at the wall of the heating compartment or tube. These temperatures can differ considerably, due to the overall endothermic behavior of the APT — TBO decomposition reaction. The exposure time in a rotary kiln is usually much shorter than in the pusher, and the decomposition temperature is therefore higher for obtaining a similar degree of thermal decomposition. 

The oxygen index (molar ratio 0/W) is commonly used to characterize the degree of reduction of TBO. However, since most TBOs also contain ammonia and water in addition to W and O, a more complete description is given by x(NH3) XH2O) WO . 

Qualitative and quantitative X-ray analyses of the same samples revealed quite a large scatter in composition tungsten bronzes, 0-45% WO3, 0-45% WO2.9, 5-20% WO2.72, 0-25%, and amorphous, 30-55%. 

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