Effect Of Different Starting Materials On Synthesis Of Al₄SiC₄and Al₄O₄C By A Carbothermal Reduction Process

In the Al Si C system, there are many compounds, includes Al₄SiC₄, Al4Si2C5, Al4Si4C7,Al4Si3C6and Al8SiC7. Among the compounds, Al₄SiC₄is one of the promisinghigh temperature ceramics for many engineering applications because of its low density（3.03g/cm3）, high melting point （²353K） and excellent oxidation resistance. Recently, severalmethods for synthesis of Al₄SiC₄have been investigated. Most of the methods require relativelydangerous fine metal powders or high cost artificial materials, which limited the industrialapplication of Al₄SiC₄. In terms of economy and efficiency, a carbothermal reduction process isconsidered to be a promising method for the synthesis of the ternary carbide because of theinexpensive and safe starting materials and its simplicity, and Al₄SiC₄synthesized from rawmineral materials can reduce the costs of its industrial application remarkably. Al4O4C formedas intermediate products when the mixture of calcined bauxite, SiC/SiO2and carbon blackstarting materials was heated, and Al4O4C is stable until1890and its oxidation resistance andhydration resistances is very good, so Al4O4C is also very good as high performance refractoryand oxidation protective coatings. The relevant literatures on Al4O4C are little, so it isnecessary to research it.The present study researched the synthesis of Al₄SiC₄by heating a mixture of calcinedbauxite, SiC/SiO2and carbon black through a carbothermic reduction process in order tocontribute a commercial available composition. The high temperature phase reactions duringheating were investigated.The influence of additive amount of SiC/SiO2in synthesis of Al₄SiC₄by carbothermic reduction was investigated. The different for synthesizing Al4O4C frommixtures of alumina and carbon black and alumina, carbon black and aluminum, as startingmaterials, were examined in the present study, and the effect of Al4O4C on anti oxidationbehavior of magnesia carbon bricks were investigated.To determine the formation mechanism of the synthesis of Al₄SiC₄using a mixture ofcalcined bauxite, SiC and carbon black by a carbothermal reduction process, each carbothermalreaction of the oxide constituents should be considered because the main crystalline phases incalcined bauxite are Al2O3and Al2SiO5, and the onsets of reduction reactions of Al2O3andAl2SiO5occur individually, Al₄SiC₄exists as irregular tabular structure,the mechanism of thesynthesis of Al₄SiC₄is believed to be a solid solid reaction. While the mechanism of thesynthesis of Al₄SiC₄using a mixture of calcined bauxite, SiO2and carbon black was observedduring three step reaction calcination: the carbothermic reduction of sillimanite, SiO2and Al2O3.Al₄SiC₄platelets possess a well developed hexagonal characteristic and the surface weresmooth, the mechanism of the synthesis of Al₄SiC₄is believed to be a gas solid reaction. The lack amount of Si addition caused SiC shortage, then Al8SiC7formed. With the increasing ofadditive amount of Si, Al and Si formed in synthesized samples. Al, Si has a low melting point,the liquid Al, Si could coat and bond Al₄SiC₄grains and promote nucleation on the surface ofAl₄SiC₄phase.The mechanism of the synthesis of Al4O4C using a mixture of Al2O3and carbon black isbelieved to be a solid solid reaction, and Al4O4C exists as irregular granules The mechanism ofthe synthesis of Al4O4C using a mixture of Al2O3, Al and carbon black is believed to be agas solid reaction, and Al4O4C exists as granules. The increase of the amount of Al additionpromoted the formation of Al4O4C, while the increase of the amount of C addition promoted theformation of Al2OC. Al4O4C start to oxidized from about809when heated in air, and theoxidation resistance of Al4O4C was good as Al in magnesia carbon bricks.