A Study On The Preparation And Performances Of Magnesium Aluminate Spinel And Yttrium Aluminate Garnet Powders

This work is a study on the following three fields.Firstly, we research the synthesis of the metal alkoxides-the synthesis techniques of aluminium alkoxide, magnesium alkoxide, magnesium aluminium double-metal alkoxide, yttrium alkoxide, yttrium aluminium double-metal alkoxide. The catalyzing mechanism and distilling process are discussed.The reacting systems of isopropyl alcohol and the aluminum are researched in this paper, the reaction dynamics formula of isopropyl alcohol and the aluminum has been obtained according to amounts of H2 in the reaction process. By studying the aluminum’s response behavior in isopropyl alcohol, we obtain that the reaction is the pitting reaction, even the galvanic battery reaction. By studying the alkoxide density-time and the density-temperature reciprocity, we obtain the alkoxide density-temperature mathematical relation equation. Contrasting the catalytic effect of different catalyst to the aluminium isopropoxide synthesis, the aluminium isopropoxide autocatalysis function effect is better that the others, and the best catalyzed density is from 3.8mol/L to 4.5mol/L. The cupric chloride is used as the catalyst to the aluminium isopropoxide synthesis for the first time. By studying the different chlorides catalytic effects to the synthesis, we obtain that the different chloride catalytic effects base on the different catalyzing mechanisms. HgCl2 catalytic effects bases on oxidation of Hg2+ and Cl-,I2 catalytic effect bases on its strong oxidation and the aluminum chloride catalytic effect is because of alcoholysis, which produces HCl in system.The reacting systems of isopropyl alcohol and the magnesium are also researched in this paper. We find that the reaction doesn’t go on eventually and solid or semisolid alkoxide is produced, which is different from isopropyl alcohol aluminum alkoxide. The reacting systems of isopropyl alcohol and the aluminum and magnesium are also researched, showed that it can react well with the aluminum and magnesium and some kinds of alcohol. The result shows that double-metal alkoxide is produced and the high pure from double-metal alkoxide can be obtained by the mothod of vacumm distillation. N-butanol magnesium-aluminum alkoxide can be prepared at 10mmHg and 350℃while iso-butanol magnesium-aluminum alkoxide can be prepared at 9 mmHg and from 252℃to 282.℃. Double-metal alkoxide have some better properties than single-metal alkoxide, such as thermal stability.Otherwise, the experiment and IR spectrum show that the minimal concentration of aluminium chloride in the isopropanol which is the best catalyst in the preparation of yttrium isopropoxide can be obtained. At the same time the productive ratio accounts to 92%. Yttrium and aluminum double metal alkoxides are attained by the reaction of Yttrium isopropoxide and aluminium, but low effective and non-stoichiometric composition.Secondly, we research the synthesis of high performance magnesium aluminate spinel. The synthesis techniques are the most in research of high property magnesium aluminate spinel.Magnesium aluminate spinel has good characters such as corrosion resistance, wear resistance, chemical stability, insulating property, the small thermal expansion and the high hardness. Therefore, to product the high performance MAS powder is the key element to obtain high quality MAS spinel material. The size and diffusion of powders have an inference on the application in the high technology fieldsIn this paper, two preparation methods of high quality MAS powders are solid phase reaction and alkoxide hydrolysis. In solid-state reaction, the elements like materials, the reaction temperature, holding time and mineralizer are considered to affect the preparation temperature of reaction and morphology. In addition, in alkoxide hydrolysis the factors such as the mount of water, pH, the temperature of hydrolysis, dispersant, surfactant are affecting the particles of colloid, and mineralizer can take changes in the morphology and structure of powders, otherwise hydrothermal technology also have influences on the final powders in the hydrolysis of alkoxide.In solid-state reaction, AlOOH can take place of the Al2O3 in order to promote the reaction. The main crystal phase was formed in 1100℃, and then the perfect crystal phase appeared in 1400℃. The mineralizers such as NH4、AlF3、AlCl3 are added in the mixture in order to finish the reaction. The pure phase of spinel structure was obtained at 1000℃with 1% AlF3. There are two roles for AlF3 in the solid-state reaction process. One is its carrier role of gas mixture. The other is that it possess a function that low the melting temperature to a lower. The property and hydrolyzing mechanism of magnesium aluminium double alkoxides were discussed. Through controlling all kind of factors which affected the performance of the powders, such as the concentration of the double metal alkoxides, the hydrolyzing temperature (65℃), the amount of water (1:200), the speed of adding water, the adding of chelator, some single factor experiments had been done. Then the production was dried by different methods, and microwave drying got the advantage of high efficiency and small granularity. The spinel phase occurred while calcined at 700℃, while the perfect spinel phase was formed at 1000℃.At last, the synthesis of YAG powder is investigated by solid phase reaction and alkoxide hydrolysis. Yttrium Aluminum Garnet (YAG) is a promising material used as host for phosphors and solid-state laser because of its excellent mechanical, thermal and optical properties. Since there are many disadvantages of the traditional methods adopted to prepare the powders such as the more complex techniques, the higher sintered temperature, the bigger granularity; the applications of powders are limited. A new method to synthesize YAG is becoming more and more important.The solid-state mixing method is used to synthesize the pure-phase YAG powder in this paper, and pure-phase YAG powder is synthesized by the alkoxide method and the wet grinding hydrothermal method successfully. Analyzing the phase transformation of different temperature, Contrasting the different temperature roasting effect, obtains the best roasting temperature is 1400℃. The wet grinding hydrothermal method reduces the roasting temperature and the temperature is lower 250℃than the traditional high temperature solid-state reaction. By controlling all kinds of factors which affect the performance of the powders, such as the amount of water, the concentration of the alkoxides, the hydrolyzed temperature, some single factor experiments have been done during the hydrolyzing process of the alkoxides. Then the production is dried through four methods including nature drying, oven drying, and microwave drying, direct heating drying. After drying, the powders are calcined at different temperature and the yttrium aluminium powders are prepared.The performances of the powders have been investigated with TG-DTA, XRD, SEM, TEM, and FTIR. The results show that the optimal amount of water [the alkoxide/the water (molar ration)] is 1:5. The optimal concentration of the alkoxide is 0.2mol/L. The speed of adding water is 10mL/min. The optimal hydrolyzing temperature is 22℃, with the ultrasonic adopted as the milling method. The result of FTIR indicated that there is -Y-O-Al- group structure in the product of alkoxide hydrolysis. The optimal method of drying is the microwave drying. The optimal sintered temperature should be at 1100℃.