High Quality Zirconium Tungstate/Aluminium Alloy Negative Thermal Expansion Material

Zirconium tungstate (ZrW₂O₈) is a commonly used negative expansion material, which has high coefficient of negative expansion and wide temperature range. Zirconium tungstate can be prepared separately or added to metal matrix, such as copper or aluminium alloy, to reduce the expansion coefficient of the material. However, in the modern process, excessive preparation temperature and holding time will lead to the decomposition of zirconium tungstate or the reaction between zirconium tungstate and metal, so how to control the interface reaction is also a problem that zirconium tungstate metal matrix composites need to face.

To solve the problem that the thermal expansion curve of existing Al-based zirconium tungstate particle composites fluctuates greatly and the thermal expansion value is high, some researchers believe that the method of preparing porous zirconium tungstate/aluminium composites by spark plasma sintering can avoid this trouble. It is accomplished in the following steps:

1.Weighing: 50-60% zirconium tungstate powder and 40-50% aluminium powder are weighed according to volume fraction.

2.Mixing by ball milling: adding zirconium tungstate powder and aluminium powder in turn into polyethylene ball mill tank, then adding agate ball, the ball-to-ball ratio is 1:(1.2-1.5), and finally adding anhydrous ethanol. The volume ratio of zirconium tungstate powder to anhydrous ethanol is 1:(1.5-2). Mixing by sealed ball milling for 12h-24h, the mixture after ball milling is obtained.

3.Drying and sieving: Ball-milled mixture is dried and sifted to obtain mixed powder.

4.Spark plasma sintering: the mixed powder is loaded into graphite mould, then transferred to the chamber of spark plasma sintering furnace, applied 25 MPa-65 MPa axial pressure, then sintered at 550-650 ℃ and under inert gas protection. The sintering time is 5 minutes, and the vacuum in the chamber of spark plasma sintering furnace is 0.1 Pa during sintering process, and then cooled to room temperature with the furnace. Porous zirconium tungstate/aluminium composites were obtained.

Porous zirconium tungstate/aluminium composites were prepared by spark plasma sintering. The sintering temperature was 550-650 ℃, which was much lower than the decomposition temperature of zirconium tungstate (770 ℃). The crystal integrity of zirconium tungstate was effectively guaranteed. At the same time, the holding time is 5 minutes, which effectively prevents the direct interface reaction between zirconium tungstate and aluminium, and regulates the thermal expansion properties of the composites through the axial pressure.

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