Research On Synthesis Of Hydroxide Powders And Oxide Powders By Electrolysis Of Aqueous Solution

In this dissertation metal oxide precursor has been prepared by electrochemical process with inert electrode as cathode, aluminum and magnesium as anode. Different morphologies of ultra-fine powder were prepared by hydrothermal treatment of the electrolysis products. The samples prepared under different conditions investigated systemically by XRD, SEM, and differential thermal analysis. The results indicate that:AlOOH can be obtained by electrolyzing aluminum. AlOOH changed into α-Al2O3after calcinating at1200℃for3hours. The as-synthesized products are small granular powders with uniform size. Mg(OH)2can be obtained by electrolyzing magnesium. Mg(OH)2changed into MgO after calcinating at800℃for3hours. The as-synthesized products are flocculent structure with uniform size. A admixture composed by MgAl(OH)14*xH2O、 Mg2Al(OH)7、Mg6Al2(OH)18*4.5H2O and Mg2Al(OH)10*xH2O can be obtained by electrolyzing aluminum and magnesium in proportion. After calcinating at1200℃for3hours the admixture changed into MgAl2O4with cube structure (accompanied by MgO impurity phase).There is a certain relationship between the microscopic size of the electrolysis products and the ratio of alcohol-water. The products have the smallest size by electrolyzing aluminum or magnesium when the alcohol-water ratio is1:2. The magnesium aluminates spinel precursor has the smallest size when the alcohol-water ratio is2:1.Different hydrothermal conditions can significantly improve the morphology and size of the electrolysis products, and the content of adsorbed water and conductive salt can be significantly reduced. The products by electrolyzing aluminum have the smallest microscopic size with the block structure in this condition:the ratio of alcohol-water is2:1, the hydrothermal temperature is200℃, the hydrothermal treatment time is24hours; The products by electrolyzing magnesium have the smallest microscopic size with the flaky structure in this condition:the ratio of alcohol-water is1:2, the hydrothermal temperature is180℃, the hydrothermal treatment time is24hours; The magnesium aluminates spinel precursor has the smallest microscopic size with the flaky structure in this condition:the ratio of alcohol-water is2:1, the hydrothermal temperature is200℃under different hydrothermal time.On the basis of the above studies, Thermodynamic analysis of the magnesium aluminates spinel precursor was analyzed and discussed in this detail. Dehydration of the crystal water is in the range of420-520K; Dehydration of structural water is in the range of520-1000K; When the calcinations temperature reaches1000K, the precursor decomposition reaction is substantially completed. Spinel crystal phase is formed in the range of1000K-1400K. The analysis of the grain growth kinetics indicates that at a low temperature, spinel grain growth by mutual bond between the small grains, it is a simple physical process; at a high temperature, the grain growth process belongs to the grain boundary movement, the movement rate of grain boundary increases with increasing temperature, therefore, at a high temperature, grain growth rate becomes faster.