Preparation of W-Y2O3 Nano Composite via APT and the Effect of Hydrogen Ion Concentration

Tungsten-based materials are widely used in various field for their unique properties such as high melting points, tensile and creep strength, corrosion and wear resistance, electrical and thermal conductivity. W-Y2O3 nano composite powders were synthesized by wet chemical route using APT as raw materials. The hydrogen ion concentration (ρ(H+)) was controlled to investigate its effect on the grain size and morphology of W-Y2O3 nano composite powders.

The synthesis process of W-Y2O3 composite powders by wet chemical route is as below:

Firstly, 20 g ammonium paratungstate (APT) was added to the yttrium nitrate aqueous solution which consists of 120 ml deionized water and 2.5733 g Y(NO3)3·6H2O (AR, Aldrich). Secondly, different amounts of nitric acid were added to the suspension to investigate the ρ(H+) on the final product, the quantity range of nitric acid is 10 ml,12 ml, 15 ml, 17 ml, 20 ml, 25ml, 30 ml. Then, the suspension was left to react for 30 min.   The whole period of reaction was carried out under stirring and ultrasonic process. Then ethanol was added and the suspension was stirred for another 3 h. The suspension was filtered after the whole reaction, then the collected precipitates were washed by ethanol for several times and dried in a vacuum drying oven for 24 h.

The collected precursors were reduced in a tube furnace under hydrogen atmosphere. The reduction process included three steps: First, the precursors were heated at 500 °C in argon gas for 1 h. Then the temperature was increased to 600 °C and the atmosphere was changed into pure hydrogen. After 3 h, the temperature was raised to 800 °C while the reduction atmosphere is still hydrogen. The heating rate is 5 °C/min and the flow rates of argon and hydrogen gas were maintained at around 120 ml/min during the whole reducing progress. The samples were cooled to room temperature in the furnace under a flow of pure hydrogen gas.

The morphology and crystal structures of the powders were analyzed by field emission scanning and transmission electron microscopes with energy dispersive spectrometers (EDS) respectively. X-ray powder diffractometer with Cu Kα radiation was employed to analyze phase composition of the samples.

In summary, it was found that the sample with 15g nitric acid added, where ρ(H+) is 0.16 mol L−1, has the minimum average grain size, which is about 17 nm, but also the best grain size uniformity with no bimodal structure. It is concluded that the morphology and microstructure of W-Y2O3 composite nanopowders can be effectively controlled by adjusting the hydrogen ion concentration in the chemical reaction process.

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