Synthesis Of Calcium Aluminate Powder Containing Carbon Element By Combustion Method And Combustion Mechanism

Calcium aluminate powder containing carbon element was prepared with CaO₂,Al,Al₂O₃ and organic acid calcium including calcium oxalate?CaC₂O₄?,calcium stearate(CaC₃₆H₇₀O₄),calcium gluconate(CaC₁₂H₂₂O₁₄)and calcium citrate(Ca₃C₁₂H₁₀O₁₄)as raw material by a combustion synthesis method.The resultant powder was characterized by X-ray diffraction,Raman spectroscopy,carbon sulfur measurement,scanning electron microscopy and energy dispersive spectroscopy,high-resolution transmission electron microscopy,respectively.The effects of type organic acid calcium and their addition amounts as well as ferrous oxalate with different addition amounts on the phase compositions and microscopic morphology of combustion products also the content and order of carbon were investigated.In addition,the mechanism of combustion synthesis for calcium aluminate powder containing carbon element was analyzed by a combustion front quenching method.The results showed that the main phase compositions of combustion products for calcium oxalate system were monocalcium aluminate?CaO·Al₂O₃,CA?,calcium dialuminate?CaO·2Al₂O₃,CA₂?and the residual aluminum?Al?.The actual carbon content was 0.04 wt%when the content of calcium oxalate was 13.6 wt%.The main phase compositions of combustion products for calcium gluconate system,calcium stearate system and calcium citrate system were CA and CA₂.The diffraction peak intensity of CA increased while that of CA₂ decreased the increase of calcium stearate in calcium stearate system,the actual carbon content was 0.26 wt%when the content of calcium stearate was 2.31 wt%.The diffraction peak intensity of CA and CA₂ first increased and then decreased while the actual carbon content has been incresing with the increase of calcium citrate in the calcium citrate system.The actual carbon content reached a maximum which was 0.40 wt%when the content of calcium citrate was 9.71wt%.The diffraction peak intensity of CA and CA₂ as well as the actual carbon content first increased and then decreased with the increase of calcium gluconate in calcium gluconate system.The diffraction peak intensity of CA was the strongest when the content of calcium gluconate was 6.66 wt%,the actual carbon content also reached a maximum which was 0.80 wt%.The carbon with the circular lattice stripe exists in calcium aluminate containing carbon powder.According to the selected area of the diffraction patterns,the lattice planes,including?002?,Which can be calculated to be the lattice spacing of 0.33 nm of the carbon.The order of carbon first increased and then decreased the increase offerrous oxalate in calcium gluconate system,carbon had the highest degree of order when the content of ferrous oxalate was 0.75 wt%.Initially,CaO₂ was decomposed into CaO and O₂ in the preparation of calcium aluminate powder containing carbon element.Then the fused Al reacted with O₂ to produce Al₂O₃,Al₂O₃ react with CaO to produce 12CaO·7Al₂O₃(C₁₂A₇).As the same time,CaC₁₂H₂₂O₁₄4 was decomposed into CaCO₃ and C,which were wrapped by molting of Al and Al₂O₃.Furthermore,CaCO₃ was decomposed into CaO and CO₂,a large amount of heat was released during the aluminum heat reduction reaction which promote C₁₂A₇ phase transition to CA.Last C₁₂A₇ and CA transition to CA₂.The retained carbon in combustion products were attributed to the high temperature pyrolysis of calcium gluconate in the combustion wave zone and aluminum heat reduction reaction in the reaction zone and product zone.