Study On The Preparation And Kinetics Of Yttria Ultrafine Powders

In this article, nano-yttria powders were prepared by liquid precipitation method, technological conditions, thermal decomposition process of precursor and grain growth kinetics behavior of yttria were studied. The main results are as follows:Precursors of yttria were prepared in aqueous solution with yttrium nitrat which was prepared by dissolving the raw yttria in the concentrated nitric acid as material, ammonia, potassium oxalate, ammonium oxalate as precipitator, and cationic surfactant as additives. Then yttria powders were prepared by calcining precursor in the air.The results showed that yttria powders were prepared by ammonium oxalate more losser exquisite, smaller aggregation, higher purity.Studied the feeding method, reactant temperature, washing and drying technology, calcining temperature and time of precursors were influencing the size and dispersibility of yttria. The results showed that the size of yttria less than 20nm by cocurrent flow method, particle size distrution range and aggregation was low; the aggregate behavior was reduced by organic-alcoho(ethanol, butanol) treating of precursors;strong aggregation was reduced by nonlinear programming drying form room temperature to 110℃. XRD showed that precursors was calcined 1 h at 600℃would formed cubic yttria, the grain size would incresed following calcining temperature and time; but when the calcining time more than 7h, the grain size would decresed .TG-DTA curve showed that thermal decomposition process of yttrium oxalate divided into five stages. Using DTA curve, calculated activation energy of four stages by Kissinger method. We found that: the frist stage was losted adsorbed and crystallization water of precursors, apparent activation energy was 42.13KJ/mol; the second stage was decomposited of yttrium oxalate, apparent activation energy was 111.47KJ/mol; the third stage was oxidation process of thermal decomposition product, apparent activation energy was 94.28KJ/mol; the fouth stage was decomposited of yttrium carbonate, we don't calculated the activation energy because of the endothermic peak was not obvious; the fifth stage was amorphous yttria translated into cubic yttria, apparent activation energy was 195.38KJ/mol.Studied the grain growth kinetics of yttria by XRD, the results showed that the grain growth index n < 0.2 of yttria calcining temperature from 600 to 900℃,rate consant significantly increased following calcining temperature, the temperature will higher, the grain size will bigger; the grain growth activation energy is different, which is 76.33 KJ/mol at the temperature lower than 690℃, and 527.11 KJ/mol at the higher temperature.