Ammonium Paratungstate APT

Although a hexahydrate and a decahydrate exist, only the tetrahydrate (NH4)io [H2Wi2042] -4H20 forms under industrial conditions, since the hexahydrate is unstable at temperatures exceeding 96 °C, while the decahydrate crystallyzes only from solutions at room temperature. 

Characterization. The important physical and chemical properties have been already treated in subsection (b) of Section 4.2.7.3. Here, only parameters relevant for the further processing are discussed. 

APT is a white, crystallized powder. The average ciystal size of commercial products ranges between 30 and 100 pm. The SEM image in Fig. 5.16 reveals mainly faceted 

Specially purified APT (by multiple-step liquid extraction of selected, very pure batches under clean-room conditions) for the production of 4N and 6N tungsten sputter targets shows a much lower impurity content (Table 5.8). 

Thermal Decomposition. On heating APT to 300-800 °C, ammonia and water are evolved. The decomposition becomes more complete as the temperature and duration of heating are increased. The final decomposition product is determined by the 

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Scheelite, natural or synthetic, is attacked by hydrochloric add in an autoclave. An almost insoluble residue of WO,-5 1120, contaminated by silicates from the gangue, is obtained. On treatment with ammonia this oxide-hydrate is dissolved to form a colorless solution and purified by filtration. After evaporation a white substance crystallizes, ammonium paratungstate APT (or ammonium parawolframate APW) with the formula (NH ) j H j Wj O g. APT has been an important substance in the worldwide trade in tungsten products. When this compound is ignited pure WO, is formed. 

Ammonium tricarbonatozirconate. See Ammonium zirconyl carbonate Ammonium, trimethyloctadecyl-, chloride. See Steartrimonium chloride Ammonium, trimethylphenyl-, hydroxide. See Tri methyl phenyl ammonium hydroxide Ammonium, trimethyltetradecyl-, bromide. See Myrtrimonium bromide Ammonium tungstate CAS 11120-25-5 EINECS/ELINCS 234-364-9 Synonyms Ammonium paratungstate Ammonium tungstate (VI) Ammonium p-tungstate Ammonium wolframate APT Empirical H40N10O41W12... 

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