Low Temperature Synthesis of Negative Thermal Expansion Y2W3O12

The effect of variation of transmission ratio (r) in the pulverisette-4 (P4) ball-milling machine on the synthesis of Y2W3O12 is reported. Y2O3 and WO3 powders have been milled in a P4 planetary ball mill with different r values, i.e., -1.5, -1.75, -2, -2.25, -2.75, and -3, at a disk revolution speed of 300 rpm for 10 h with toluene as the process control agent. Differential thermal analysis results suggest that the reaction temperature of as-mixed powder is 1000 A degrees C. It decreases down to 845 A degrees C with an increase in the r value up to -2.25. However, a further increase in the r value results in an increase in the reaction temperature. The average particle size for different r values varies in similar manner and it is found to be around 65 nm for r = -2.25. XRD analysis of 10 h milled powders with the r value of -2.25, heat treated at different temperatures confirms the formation of Y2W3O12 at 800 A degrees C. The low temperature synthesis leads to retention of finer grain size and hence, helps in good densification and sinterability. The above material shows a negative thermal expansion coefficient of the order of -7.1 x 10(-6)/A degrees C in the temperature range 150-650 A degrees C.