1.1 XRD analysis
Figure 1 is composed of two different materials in the XRD pattern of a sample ratio different temperatures after sintering. The results are shown in Figure 1 holding time is 30min. As can be seen in Al2O3 + C sample as raw materials, at 1500 ℃ and 1700 ℃ primary phase after sintering are Al2O3, higher temperatures can be observed at 1700 ℃ Al4C3. In Al2O3 + Al + C as the sample material, after microwave sintering at 1500 ℃ main phase still Al2O3, while it can be observed Al4C. And Al2OC existence.
Thermodynamic analysis is as follows:
When used as a raw material in Al2O3 and C, the reduction of carbon oxides generated by carbothermal reaction Al2OC for:
Al2O3 + 3C = Al2OC (s) + 2CO (g) (1)
According to the thermodynamic equation:
△ G = △ G ° + RTIn (Pco / P ° ) 2 (2)
When the system can be seen as long as the partial pressure of CO in its equilibrium partial pressure, the reaction can occur. Therefore, to generate a reaction occurs sintering temperature must increase or the resulting CO gas discharged in time. In practice the microwave sintering process, the sample is too small relative to the heating chamber, resulting in large temperature gradients, particularly at very high temperatures and is not conducive to the controlled heating of the reaction, the furnace insulation layer to some extent, this suppressed implications.
But by the graphite layer, high alumina fibers and insulation mullite brick constructed, and greatly hinder the exhaust gas generated CO reaction itself, so although the reaction with hydrogen in the pass, but still can not heating chamber gas measurement composition, the partial pressure of CO can not be controlled to a relatively small value, thus making it difficult to generate the reaction.
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