Preparation Of Hercynite By Molten Salt Method

The hercynite is synthesized by molten salt method,and the effects of reaction temperature,holding time,the sort of molten salt,and raw materials on the synthesis of hercynite are investigated.Additionally,the reaction mechanism of synthesized hercynite by chlorine-based and sodium sulfate molten salt is studied.Finally,the platelet hercynite is synthesized by using the reaction mechanism of inorganic powder synthesized with molten salt method.The following conclusions are drawn from above researches:1.In the chlorine-based molten salt system,the hercynite synthesized by the molten salt method is dominated by the"template growth"mechanism.The hercynite phase occurs in product powders when the reaction temperature is 800℃ and the holding time is 3 hours.With the increase of temperature,the content of hercynite gradually increases in product powders,and only the diffraction peak of hercynite is observed in the phase analysis at 1000℃ and 1100℃ for 3 hours.Secondly,the hercynite is synthesized by molten salt,when industrial alumina and iron concentrate powder are used as raw materials,it is found that the reduction in the particle size of raw materials mixed powder not only promotes the synthesis of hercynite but also inhibits the formation of sodalite in the product.Thirdly,composite molten salt NaCl-KCl is more suitable as the molten salt medium to synthesize hercynite.The average particle size of hercynite is 52.83μm,and most of hercynite particle sizes are concentrated in 37-54μm.Compared with the single molten salt NaCl or KCl,the composite molten salt NaCl-KCl is more conducive to control the grain size,because its particle size is more concentrated than the single molten salt（25-55μm）.2.In the sodium sulfate molten salt system,the mechanism of the synthesis of hercynite is"dissolution-precipitation"mechanism.The hercynite phase appears in product powders at 900℃ for 3 hours,but the temperature increasing is not conducive to the synthesis of hercynite.At the same time,it is found that when the smaller particle size and higher activityγ-Al₂O₃is used as the raw material,the synthesis amount of synthetic hercynite is higher than that of industrial alumina andα-Al₂O₃.Secondly,prolonging the holding time is benefited to synthesize hercynite,when the aluminum source and temperature are the same.Finally,the most suitable synthesis conditions in the sulfate system are usedγ-Al₂O₃and Fe₂O₃as raw materials,and sintering at 900℃ for 6 hours in a nitrogen atmosphere.3.The synthesis of platelet hercynite is achieved by the"template growth"mechanism of synthesizing hercynite with chloride-based salt.The platelet hercynite can be synthesized at 1000-1100℃ for 3 hours.Meanwhile,it is found that synthesis temperature increasing is benefited for the synthesis of platelet hercynite and the elimination of residual Al₂O₃,when the temperature increases from 1000℃ to 1100℃.In addition,only the diffraction peak of hercynite is observed in the phase analysis when the holding time is prolonged from 3 hours to 4.5 hours at 1100℃.However,if the temperature is kept at 1100℃ for 6 hours,an impurity phase will be generated,which is not conducive to the synthesis hercynite.