Why do diamond abrasive particles need to be coated with metal
Diamond is recognized as the "king of super-hard", its high hardness makes it widely used in the abrasive industry.However, the high interfacial energy between diamond particles and most metals, alloys, ceramics and even resin binders determines that diamond particles in abrasive tools are only mechanically coated in the binder matrix.
However, if the diamond particles cannot be "rigidly" attached to the matrix, the diamond particles will fall off by themselves due to the loss of the matrix coating when the abrasive tool is subjected to grinding force and the abrasive particles are not exposed to the maximum section, which reduces the service life and efficiency of the diamond tool.
Therefore, in order to improve the service life of abrasive tools, people began to use metal coated diamond particles.After metal plating, the surface energy difference between diamond powder and binder matrix can be reduced, and the bonding force between the two can be strengthened and the shedding of diamond can be reduced, so as to improve the utilization rate of diamond powder material.In addition, it can also play a macro isolation and protection role on the surface of diamond, and play a micro side support role on the diamond structure, which is conducive to prevent the oxidation and graphitization of diamond in the use process.
With the increase of diamond particle size, the weight gain rate (i.e. plating speed) of diamond increases.This is because in the process of electroplating, the ideal total area of abrasive particles in the plating bath is the sum of the surface area of all abrasive particles in the batch, and the surface area is closely related to the particle shape and particle size.The grinding particles are plated in a roller bath, and the current is mostly consumed on the top layer of the grinding particles.For diamond of the same quality, the smaller the particle size is, the larger the total surface area is. With the rolling of the plated bottle, the larger the contact surface with the cathode copper wire is, the higher the current efficiency is, and the faster the reduction rate of nickel ions on the diamond surface is, so the plating speed increases.
Fine-grained diamond particles have greater advantages.However, in China, although the research on the coating of coarse-grained diamond has been relatively mature at present, there are still some problems in the coating of micron diamond, especially the technology of 10-micron coating with fine diamond particles, such as uneven coating and easy agglomeration of the particles after plating.
However, there are still some good results in the current research. For example, lu jing used the method of quasi-atomic layer deposition to deposit titanium on the surface of nano diamond, and used titanium tetrachloride gas and hydrogen gas as the precursor to obtain the coating through cyclic reaction.The experimental results show that the silicon coating on the surface of nano-diamond is very uniform and complete.Ren chunchun used the method of electroless nickel plating to prepare diamond coated particles (5-10 microns). Under the appropriate technological conditions, the diamond coated particles with compact structure, complete coating and good dispersion could be obtained.This proves that even using the traditional electroless nickel plating method, the diamond particles with very large surface area can be plated with nickel under the appropriate process conditions, and a good coating can be obtained.