Preparation and Characterization of Tungsten Black Oxides

Hydrazinium oxalate tungstate complicated salts were prepared by using hydrazine , oxalic acid and tungstic acid as raw materials , and tungsten black oxides were prepared by using these complicated salts as precursors under the protection of purified nitrogen .The result from thermogravimetry points out that the thermal decomposition of the precursor completes at about 500 ℃.The ingredient of raw materials composing the precursor affects some properties of the product .The optimal ratio of hydrazine , oxalic acid and tungstic acid was determined to be 1 .0∶4 .0∶0 .5 .Temperature and time of thermal decomposition were experimentally found to affect the properties of the product too .When the precursor with the optimal ratio is thermally decomposed at 650 ℃ and for 30 min , the product is typically black and called model product .The O/W index and content of ammonium ion were determined . The O/W index is very close to that in W18O49 and the ammonium tungsten bronze is not enough to account under the selected condition .The powder XRD pattern of model product reveals that the main phase is a W18O49 one and the WO2 phase takes a little .Of the model product , the specific surface area (BET method)was measured to be12 m2·g-1and the agglomerate diameter (d50)3.68μm.

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