NON-ISOTHERMAL KINETIC STUDY ON THE THERMAL DEHYDRATION OF SODIUM TUNGSTATE DIHYDRATE

１ＩＮＴＲＯＤＵＣＴＩＯＮＳｏｄｉｕｍｔｕｎｇｓｔａｔｅｄｉｈｙｄｒａｔｅｉｓｕｓｅｄｉｎｔｈｅｐｒｅｐａｒａｔｉｏｎｏｆｃｏａｔｅｄｅｌｅｃｔｒｏｄｅｓｆｏｒｅｌｅｃｔｒｏｃａｔａｌｙｓｉｓ［１］ａｎｄａｓｆｉｒｅｒｅｔａｒｄａｎｔｆｏｒｆａｂｒ...

The thermal dehydration of sodium tungstate dihydrate has been studied by using differential scanning calorimetry (DSC). It was found that the dehydration takes place in a single thermal step at heating rates β =2～15 K/min, and the enthalpy change is (100.4±1.9)kJ/mol. In the main decomposition range of α =0.05～0.95 when β =2～5 K/min, α =0.05～0.80 when β =10 K/min and α =0.05～0.75 when β =15 K/min, the fittest kinetic equation was deduced, and from this equation the calculated activation enegy E was 184.3 kJ/mol. According to this equation, the mechanism of dehydration should be the formation and the plate like growth of randomly distributed nuclei. When β ≥10 K/min, the dehydration obeys at least two kinetic equations.