Decomposition Process Of Hafnia Scrap Via Alkali Fusing

The utilization rate of hafnium oxide wafer target during coating process is low(generally no more than 10%), the industry production remaining years wastes a large number of hafnia material, in the process of preparation of the target, the density of target material can be close to 90% of its physical density through high temperature sintering processing, the density of residual target is high after preparation of hafnium oxide thin films by electron beam evaporation, magnetron sputtering and atomic layer deposition method. So the recycling of the target material is difficult.The paper mainly studies process conditions and reaction mechanism of the alkali decomposition process to provide theoretical guidance to the recycling of hafnia scrap. The research contents and conclusions are as follows:(1)selecting of alkali decomposition agentThe alkali decomposition contrast experiment is performed using HfO2 with KOH, NaOH and LiOH under the same conditions. The results show when selecting KOH as the decomposition, the decomposition rate of hafnium oxide is significantly higher than other two kinds of decomposition agent within the scope of the reaction temperature 500℃~800℃, Finally potassium hydroxide is selected as the decomposition agent.(2)process conditions study of alkali decompositionThe effects of reaction temperature, mole ratio of alkali to hafnium oxide, particle size and alkali fusion time on the decomposition of hafnium oxide is primarily investigated in this study, he investigation shows that the decomposition rate is over 96% with the condition that KOH/HfO2 molar ratio of 2.7:1,particle size of hafnia of 45~53 μm at 800℃ for 2 h.According to the results of XRD, the study of effects of molar ratio(KOH/HfO2) on decomposition rate with the conditions of particle size of hafnia of 38~45 μm at 800℃ for 2 h. shows when KOH/HfO2 molar ratio is 3:1 higher than the theoretical value(2:1), react: HfO2+2KOH= K2HfO3; when the KOH/HfO2 molar ratio is 1:1, in the initial stages of reaction, the reaction of potassium hydroxide and hafnia generates K2HfO3, K2HfO3 is wrapped in particle surface and continue to react with hafnia : K2HfO3+ HfO2= K2Hf2O5.(3)kinetics study of alkali decompositionThe decomposition kinetics of hafnia scrap in molten KOH is studied, results shows that the shrinking core model with chemical reaction controlled process is the most applicable for the decomposition process with the scope of the reaction temperature 650 ℃ ~800 ℃, KOH/HfO2 molar ratio of 2.5:1.