Solid State Reaction Sintering of Zirconium Tungstate

At present, the main methods for preparing zirconium tungstate are solid phase reaction sintering, sol-gel method, hydrothermal method, co precipitation method, microwave synthesis method, combustion method, laser sintering method, spray drying method, etc. Among them, the preparation cycle of sol gel method is too long to be used. The reaction principle of hydrothermal method is complex and the time is long. The coprecipitation process is cumbersome and difficult to control. The solid phase reaction sintering method has the advantages of simple principle, simple operation and limited conditions. Therefore, at present, solid-state reaction sintering method can rapidly and effectively prepare zirconium tungstate.

The preparation of negative expansion material zirconium tungstate by solid state reaction sintering can be carried out in the following steps:

1.Ingredients: Zirconia powder and tungsten oxide powder are mixed in the proportion of 1:3.5-4 to obtain the mixture. Then the mixture, zirconia spherulite and distilled water are added to the ball mill in the proportion of 1:2-5:0.5-2 to the mass ratio.

2.Ball milling: The ball mill in step 1 is placed in a fast ball mill or planetary ball mill, and the average particle size of the mixture is less than 1 micron. Then the pulp is removed after 5 minutes of ball milling with polyvinyl alcohol as binder.

3.Drying slurry: The slurry obtained in step 2 is passed through 40 target quasi-sieves, then dried in an air-blast drying box at 85-100 C for 14-16 hours, then crushed with a mortar and passed through 60 target quasi-test sieves to obtain powder;

4.Obsolescence: Add distilled water to the powder obtained in step 3, mix evenly and pack it for 24 hours.

5.Die forming: the stale powders in step 4 are moulded in the pressure range of 110-140 MPa with a tablet press and used as samples.

6.Sintering: The sample is placed in a sealed SiC crucible, discharged in a muffle furnace at 500 ℃, heated to 600 ℃ at the heating rate of 200 ℃/h for 1 h, then heated to T at the heating rate of 300 ℃/h, of which 1105 (< T < 1260) for 2 h, and finally cooled to room temperature by air or water cooling, that is, the negative expansion material zirconium tungstate is obtained.

Among them, the air cooling and water cooling methods can well inhibit the eutectoid Decomposition Phase Transformation of ZrW₂O₈ and maintain a high yield of ZrW2O8. The yield of ZrW₂O₈ can reach more than 80%. The yield of ZrW₂O₈ can be increased to about 95% by process improvement and adding proper amount of phase change inhibitor catalyst.

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