| Analysis and calculation of chemical thermodynamics during the solid phasereaction process of MgAl2O4indicated that high temperature and high energyconsumption was necessary in the synthesize of MgAl2O4. And the conventionalmethods for preparation of MgAl2O4consumed a large amount of energy and time.However, microwave sintering provide a better way to prepare MgAl2O4because ofits so many advantages as high heating rates, reduced processing time, low powerconsumption,less environmental hazards and promotion of uniform phase structure.During microwave sintering, large amount of heat may be generated for a lossymaterial throughout the volume, whereas for conventional heating, the material isheated via an external heat source and subsequent radiative transfer.In this paper, firstly, the RF module, the heat transfer analysis module and thestructure analysis module in the finite element software HFSS and COMSOL wereconducted to establish a reasonable mathematical model and physical control equation,and the temperature characteristic curve of microwave sintering of MgAl2O4was got;Secondly, component of MgAl2O4matrix composites ceramics was designed, andpreparation of fine powders, powder compacts and microwave sintering wereconducted; Finally, characterization of MgAl2O4and MgAl2O4matrix composites byXRD, SEM was conducted. The results showed that:1. The part of theory calculation, for2.45GHz frequency microwave, thecoupling between the microwave electromagnetic field and temperature field wasmade clear, that is, the strongest electric field intensity of microwave sinteringappeared at the geometric center of the cavity, and the cavity was suitable for sinteringof cylindrical specimen. The temperature characteristic curve of microwave sinteringof MgAl2O4showed that temperature rised more slowly at the early step, however, thetemperature showed an exponential increase after a short later time.2. MgAl2O4phase could be synthesized by microwave sintering andconventional sintering, however, the MgAl2O4grains synthesized by microwavesintering appeared fine, smooth, regular and uniform shape, and because of theincrease of the lattice ion mobility, the increase of diffusion and sintering speed, so,the reduce of the sintering activation energy and the reduce of the sinteringtemperature was resulted. For MgO and Al2O3powder material system, the optimalparameters of microwave sintering of MgAl2O4phase with2.45GHz frequencymicrowave was as follows: the output power was1600W, the sintering time was30 min.3. With the adding of SiC and SiO2, MgAl2O4matrix composites was synthesized.It was showed that the impurity phase could be avoided because of the side reactionwas restricted in a very short sintering time. And the samples holded macroscopicregular shape with no deformation happened. For composites powder material system,the optimal parameters of microwave sintering of MgAl2O4matrix composites with2.45GHz frequency microwave was as follows: the output power was between1800W, the sintering time was30min.In short, in the system of MgAl2O4matrix composites, SiC could improve themicrowave characteristics of mixed material compacts in microwave field; On the onehand, SiO2could help form MgAl2O4in situ, and on the other hand, it could make upthe particle gap at the molten state, so, it was conducive to improve the density andtoughness of MgAl2O4based composite. So, it will appear good wear and corrosionresistance, high temperature performance, and it could become a kind of new ceramiccomposites materials in the refractory material field and ceramic surface modificationof metal field. |
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