Effect Of Carbon Phase Structure And Oxygen-containing Functional Groups On Oxidation Characteristics Of Diamond Powder

In order to explore the oxidation activity sites of diamond,the effects of carbon phase structure and oxygen-containing functional groups on the oxidation properties of diamond power were studied.The initial oxidation temperature,macroscopic oxidation kinetic parameters,programmed thermal desorption spectra of diamond particles with different particle sizes of 30 nm-50μm.The changes of carbon phase structure and oxygen-containing functional groups on the surface of diamond powders before and after oxidation of micron and nano diamond materials were compared.The changes of the surface structure of diamond particles before and after oxidation were compared.The carbon structure and oxygen-containing functional groups on the surface of diamond particles were changed by heat treatment at 550℃in the atmosphere of Ar and Ar-H2 respectively.The oxidation characteristic parameters of diamond particles after surface modification were tested.The results show that:（1）The initial oxidation temperature,activation energy and desorption temperature of CO₂ of diamond powder decrease with the decrease of particle size:For example,the initial oxidation temperature of diamond powder with particle size of30nm and 0.25μm is 520℃and 592℃,activation energy is 100.93 kJ/mol and 234.04kJ/mol,CO₂ desorption temperature is 578℃and 750℃,respectively.（2）Compared with micron diamond powders,nano-diamond powders have more sp² hybrid carbon and oxygen-containing functional groups on the surface,which mainly include C-OH,C-O-C and C=O.The sp² hybrid carbon on the surface of nano-diamond powder will increase after oxidation,indicating that the sp² hybrid carbon will be generated in the oxidation process.After oxidation,the oxygen content on the surface of diamond powder increases,and the content of carbon and oxygen functional groups,especially C-O bond,increases obviously.（3）After heat treatment in Ar and Ar-H2 atmospheres,the sp² hybrid carbon on the surface of diamond powder increases,and the content of carbon and oxygen functional groups decreases.For example,XPS results show that the C-O content of30nm raw material is 33.74%,the C=O content is 11.28%,and the initial oxidation temperature is 520℃.After heat treatment in Ar atmosphere,the carbon content of sp²phase is 24.06%,the C-O content is 7.57%,the C=O content is 6.38%,and the initial oxidation temperature is 529℃.After heat treatment in Ar-H2 atmosphere,the carbon content of sp² phase is 23.12%,the C-O content is 6.33%,the C=O content is 5.92%,the initial oxidation temperature is 554℃,the initial oxidation temperature increases,the activation energy increases,the desorption temperature of CO₂ increases.The lower the content of carbon and oxygen functional groups,especially C-O,the higher the initial oxidation temperature,the higher the activation energy and the higher the desorption temperature of CO₂.（4）The relationship between surface structure and oxidation characteristics of diamond powder before and after comprehensive oxidation and surface treatment,and the content of the sp² hybrid carbon is not the main factor affecting the oxidation characteristic of the diamond,and the oxygen-containing functional group,especially the C-O bond,is the oxidation activity of the diamond.