Study On The Mechanism Of Carbon Reduction Nitridation Of Alumina

AIN ceramics have outstanding performance in mechanics,electricity and so on,which was widely used in the fields of substrate materials,ceramics,optics and so on.AlN was mainly prepared by carbothermal reduction of Al2O3 consisting of two steps:the carbothermal reduction and the nitridation.There still exist different viewpoints on mechanism of carbothermal reduction and nitriding of Al2O3 due to the differences in the mechanism of the carbothermal reduction of Al2O3.In this paper,the mechanism of carbothermal reduction and nitriding of Al2O3 was studied through experimental and thermodynamic calculations The experiments were divided into three parts:carbothermal reduction nitridation of Al2O3,decomposition and nitridation of the products from Al2O3 carbothermal reduction,effects of CO on the carbothermal reduction of Al2O3.The carbothermal reduction of Al2O3 was studied from four aspects of nitrogen pressure,nitrogen flow rate,reaction time and reaction temperature.Based on the experimental results and thermodynamic calculation,it was demonstrated that Al-containing gases were generated by the reactions of Al2O3 and C in the heating process,which reacted with N2 to form AIN.The nitridation experiments of carbothermal reduction products of Al2O3 consisting of Al4O4C,Al4C3,Al2O3 and C,was studied from four aspects of nitrogen pressure,nitrogen flow rate,reaction time and reaction temperature,and the decomposition of carbonthermal reduction products of Al2O3 were explored.Based on experimental results and thermodynamic calculation,it was demonstrated that Al4O4C and Al4C3 could compose to generate Al-containing gases when heating.Al-containing gases reacted with N2 to form AIN,and reacted with CO to form Al4O4C?Al4C3?Al2O3?CThe effects of CO on the carbothermal reduction nitridation of Al2O3 was explored using Al2O3 as raw material,it was demonstrated that the possibillity of the increasing CO partial pressure inhibited the decompositon of Al2O3 and thus reduction of Al2O3 by CO was less likely.The carbothermal reduction and nitridation of Al2O3 without direct contant with C was investigated.It was demonstrated that the composition of Al2O3 generated AlO,Al2O,Al and O2,and carbon from the graphite units in the vacuum furnace reacted with O2 to form CO,Al2O,AlO,Al,reacted with CO to form Al4C3,Al4O4C,Al2O3,C,reacted with N2 to form AlN.Therefore the gases containing Al formed in the carbothermal reduction of Al2O3 should be generated through the decompositon of Al2O3.