APT Prepares Negative Thermal Expansion Material-- Yttrium Tungstate Powder

Negative thermal expansion material means materials which are contrary to the common "thermal expansion" phenomenon, that is to say material shrinking when heated, while cooling down it expanding, which called "negative thermal expansion" effects (Negative Thermal Expansion, shorted for ΝΤΕ). ΝΤΕ material is widely used in precision controlling field, such as: in the aerospace high-precision assembly, all components are faced with extreme cold or hot environments, the use of ΝΤΕ material can eliminate the thermal expansion mismatch which is caused by temperature changes; telescope. Also the ΝΤΕ material is used in laser equipment, optical communication system, microelectronics ect.. Yttrium tungstate as the material with exceptionally NTE properties can be prepared from ammonium paratungstate (APT) and yttrium oxide.

Steps as bellows:
1. Generate tungsten trioxide powder from APT by conventional methods;
2. Uniformly mixing the yttrium oxide and tungsten trioxide powder by molar ratio of 1:3 by wet ball milling, and drying and grinding to obtain the raw material mixture;
3. The raw material mixture was placed in a muffle furnace for calcination treatment at 1100°C for 9 hours, then cooled down with the furnace, crushed and grinded to generate the calcined product;
4. Placing the calcined product in a muffle furnace under the same conditions for secondary firing (1100°C, 9 hours), and crushing, grinding after cooling down with the furnace, thus generate the secondary calcined product;
5. The secondary calcined product selected by a sieve with 300 meshes, then yttrium tungstate powder obtained.

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