Tungsten–Samarium Oxide Composite Prepared by Ammonium Paratungstate

Nuclear fusion is one of the very few options promising to solve the currently looming energy crisis, and the materials technology plays a critical role in determining the technological realization of the fusion power source. Plasma Facing Materials (PFMs) is one of the key materials in ITER which will work in harsh conditions, including complex thermal, mechanical, and chemical loads as well as strong irradiation.

Tungsten (W) is a promising material to be used as PFMs for its many unique advantages. However, some inherent defects such as the embrittlement, high DBTT of tungsten material restrict its application on PFMs and PFCs. So, it is required to develop modified tungsten materials with improved mechanical properties. Second-phase particles (such as La2O3, Y2O3, TiC, and HfC) can play a major role in mitigating these problems. Rare-earth oxide particles are particularly effective, because they can gather solutes owing to strong rare-earth–oxygen interactions. For example, rare-earth–oxygen can refine the grains by promoting grain nucleation and hindering grain growth. A commonly used method to produce nanosized oxide dispersion-strengthened (ODS) tungsten powders is mechanical milling (MM).

Thus, a novel wet chemical method for the synthesis of highly uniform ODS–W powders had been introduced, in which a precursor of tungsten and metal oxides is prepared by the reaction of tungsten (W) and samarium (Sm) salts in aqueous solution at room temperature. Tungsten–samarium oxide composite (Sm2O3/W) has been prepared by ammonium paratungstate (APT), the tensile strength values of it is much higher than pure W samples. The doped precursor was reduced in hydrogen atmosphere and the reduced powders were then sintered into W–Sm2O3 composites by SPS. The synthesis process of is as below:

Firstly, ammonium paratungstate hydrate (APT) was suspended in an aqueous solution of samarium nitrate hexahydrate to synthesize samarium doped tungsten precursors with samarium content corresponding to W–1 wt% Sm2O3. About 30 g of APT (H42N10O42W12·xH2O) and 0.56 g of samarium nitrate (SmN3O9·6H2O) was dissolved in sequence in 150 ml of deionized water under vigorous stirring at room temperature. The solution was filtered after 24 h reaction to ensure complete reaction between APT and Sm ions and the obtained powder was dried at 60 °C for 2 h. The powder was then calcined under nitrogen atmosphere at 450 °C for 1 h whereby the powder is transformed into oxide mixture. Next, the precursor was reduced by high purity hydrogen in a single-tube electrically heated furnace. The boat containing the precursor was placed in the central section of the furnace tube and heated to 800 °C at a of 5 °C/min in a gas flow, then maintained at that temperature for 6 h. After that, the sample was cooled to room temperature, still under a hydrogen flow. Finally the consolidation of the samples was carried out through SPS (FCT Group, SE-607, Germany) technique.

In conclusion, Tungsten–samarium oxide composite has been prepared by ammonium paratungstate (APT) by a wet chemical method, the tensile strength values of it is much higher than pure W samples. Sm2O3/W composite was successfully sintered by SPS technique in much shorter time than those in conventional sintering methods which avoided substantial grain growth. Sm2O3 particles are homogeneously distributed in the tungsten matrix. The grain size and relative density of the W–1 wt% Sm2O3 composite samples were 4 μm, 97.8%, respectively. The tensile strength values of Sm2O3/W samples were higher than those of pure W samples. As the temperature rises from 25 to 800 °C, the thermal conductivity of pure W and W–1 wt% Sm2O3 composites decreased with the same trend, and the thermal conductivity of both samples was above 160 W/m K at room temperature.

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