Study On Oxidation Properties Of Diamond Particles

In this paper,the initial oxidation temperature,macroscopic oxidation kinetic parameters of diamond particles and the effects of crystal surface and surface properties on the oxidation characteristics of diamond particles were studied by comprehensive thermal analysis(TG-DSC)and high temperature oxidation experiments.The oxidation mechanism of diamond particles was deduced by means of optical microscope(OM)and scanning electron microscope(SEM),laser Raman spectroscopy(Raman),temperature programmed desorption(TPD).The results show that:(1)The initial oxidation temperature of diamond powder particles increases with the increase of particle size:the initial oxidation temperatures of diamond powder particles with the particle size of 0.25?m,0.75?m,1?m,2.5?m are 619?,609?,622?and 639?.(2)The weight loss rate of diamond powder particles increases with the increase of particle size:the weight loss rates of diamond powder particles with a particle size of 0.25?m,0.75?m,1?m,2.5?m are 88%,96%,90%and 92%.(3)The apparent reaction order n of the oxidation reaction of diamond particles is 0.52,which is independent of the particle size.The reaction activation energy(E_a)of diamond powder particles with a particle size of 0.25?m,0.75?m,1?m,2.5?m is 66.51 kJ/mol,59.03 kJ/mol,53.21 kJ/mol and 52.38 kJ/mol,and the pre-exponential factor A is 164.02,54.60,36.60 and 33.12.With the increase of grain size,the values of E_a and A decreased with the decrease of particle size,but the degree of decrease is gradually decreasing.(4)The(111)surface of the diamond is easier to be oxidized than the(100)surface:the weight loss rates of the cubic,octahedral and hexahedron diamond single crystal particles are 5.35%,10.82%and 7.02%.It is also found that the oxidation corrosion of(111)surface is more severe than that of(100)surface.(5)Surface treatment will affect the oxidation rate of diamond particles:surface hydrogenation and oxidation treatment can inhibit the oxidation of diamond,surface nitridation will aggravate the oxidation of diamond,and there is the same pattern for diamond powder and single crystal.Hydrogenation and oxidation will reduce the sp~2phase of diamond particles,while nitrogen treatment will increase the sp~2 phase of diamond particles.Therefore,it is assumed that the existence of sp~2 phase promotes the oxidation reaction.