Experimental evidence is presented that the growth of tungsten whiskers in the process of the NiWO 4 reduction by carbon oxide occurs in accordance with the vapor-liquid-solid mechanism. A liquid phase appears at 940 °C owing to the melting of the NiWO 4 -Na 2 WO 4 eutectic regions which are perhaps results of segregation of sodium impurities included in the reagents used. The presence of the liquid phase ensures for both Ni and W the comparable rates of allocation from the nickel tungstate crystal lattice leading to the formation of the R-W + NiW two-phase regions. The oriented growth of tungsten whiskers during the further reduction of the melt tungstate zones is associated with the W accumulation on the growth surfaces of the W single crystals in the two-phase regions. The result demonstrates that the reactivity of NiWO 4 increases with addition of CuO and Na 2 WO 4 which are capable to form easy-melting phases in the reactive system.
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