Study Of Surface Modification Of Fine Diamond Particles With Silane Coupling Agent

Diamond tools are often made by fixing diamonds in different binding matrix such as metal,ceramic and resin.In other to make full use of diamonds,it is required that diamonds must be held firmly and dispersed evenly,especially for fine diamond particles.Because of the strong chemical inertness of diamond,the wettability and holding force between diamonds and binding agents are poor.Diamonds without any surface modification can only be fixed by the mechanical combination with the matrix,which is easy to fall off during the using process of diamond tools,resulting in waste of diamond and significantly reducing the service life of the tools.Therefore,the surface of diamonds(particle size more than 70/80 mesh)is usually coated by the carbide-formed elements of Ti,Cr,W and so on to improve the chemical activity of diamond surface when the diamond tools being prepared at high temperature with ceramic or resin binding agents.The coating metal can significantly improve its wettability to diamonds or form metallurgic bonds with the matrix components to improve the interfacial bonding ability between diamonds and the matrix under the condition of high temperature.Fine diamond powders are often used to prepare resin binding tools.However,for diamond particles with small particle size(less than 325mesh),the existing techniques of diamond surface metallization tends to produce problems such as diamond particle agglomeration,incomplete coating and high coating cost,which makes it difficult to apply this kind of diamond in large-scale industrial production.In addition,due to the low sintering/curing temperature of the resin binder(usually 170-200℃),the metallized diamond cannot play its full role in the resin binder due to their insufficient chemical/metallurgical action.Therefore,based on the consideration of cost-effective factors,the original diamonds(unmodified)are preferred to be used in practical preparation of the resin-bonded tools with high diamond concentration,large production batch and relative low price,such as the diamond abrasives for stone and ceramic grinding,but the service life of abrasives is very short,and this becomes an engineering problem faced by this kind of resin-bonded diamond tools.At the same time,due to the hard and slippery surface of diamond,the phenomenon of diamond segregation will inevitably occur when mixing with resin binder particles,resulting in uneven distribution of diamond particles and thus affecting the performance of the abrasive tools.Therefore,It is of great significance for preparing high-performance diamond tools to develop a new surface modification technique of fine-grained diamond to obtain a functional coated film which can react with the resin agent,and thus improving the binding ability between diamond and resin agent as well as the poor dispersion of diamond in binder matrix.In this work,tetraethyl orthosilicate is used to coat the surface of diamonds,and various methods such as SEM,TEM,XRD and XPS are used to characterize and analyze the coated diamonds.It is proved that a layer of amorphous pure Si O2 film is coated on the diamond surface by its own shrinkage,which can not only increase the electrostatic repulsion between diamond surface but also enhance the effective dispersion ability of diamond in the matrix.At the same time,it also can increase the chemical activity of diamond surface to improve the holding force between diamond and matrix.It is found that when the mixture of the modified diamond and phenolic resin powder are solidified and sintered at 120℃,the diamond surface is wrapped with a dense layer of resin components by the chemical bond,which proves that the holding force of the resin matrix to the modified diamond has been effectively improved.In order to further expand the application field of the as-modified diamond,the modified diamond with additional silicon nano-powder was sintered under the conditions of high temperature and high pressure(HTHP),and a new type of non-SP~3bonded diamond composite with ceramic luster and good structural strength was successfully fabricated.The analysis results show that Si C phase appears on the diamond surface in the as-fabricated samples,and the diamond particles are bonded to a toughening/strengthening grid structure formed by the cross-linked nano Si O2 wire clusters,breaking through the existing technical route of preparation of diamond composites.The new diamond composite with Si O2 as binder phase can be used to develop the ultra-precision grinding tools which has a good engineering application potential.