With the manufacturing industry transitioning towards high-end production, the rapid development of clean energy fields, and growth in the semiconductor and photovoltaic industries, the demand for diamond tools with high efficiency and high precision processing capabilities is increasing. However, synthetic diamond micron powder, the most important raw material for diamond tools, faces issues such as weak bonding with the base material and premature carbonization, leading to shorter tool life. To address these problems, the industry commonly uses the technology of coating metal materials on the surface of diamond micron powder to improve its surface properties and durability, thereby enhancing the overall quality of the tools. This article will introduce the process of chemical plating on diamond micron powder.
Chemical plating on diamond micron powder involves placing pre-treated diamond micron powder into a chemical plating solution, where the metal ions in the plating solution are catalytically reduced and deposited on the diamond surface by the action of a reducing agent in the solution, forming a dense metal coating. Currently, nickel-phosphorus (Ni-P) binary alloy chemical plating, commonly referred to as electroless nickel plating, is the most widely used method for chemical plating on diamond.
The sodium hypophosphite system for chemical plating requires the substrate to have certain catalytic activity, but the diamond surface itself does not have catalytic active centers. Therefore, pre-treatment is necessary before chemically plating the diamond micron powder. Traditional pre-treatment processes for chemical plating include degreasing, roughening, sensitizing, and activating.
Degreasing and Roughening
Degreasing is primarily to remove grease, stains, and other organic contaminants on the diamond micron powder surface, ensuring tight adhesion and good performance of the subsequent plating layers. Roughening creates tiny pits and cracks on the diamond surface, increasing surface roughness, which aids in the adsorption of metal ions, facilitating subsequent chemical and electroplating processes. It also forms steps on the diamond surface, providing favorable conditions for the growth of the deposited metal layer during chemical or electroplating.
Typically, alkaline solutions like NaOH are used for degreasing, while acidic solutions like nitric acid are used for roughening the diamond surface. Additionally, these steps are often paired with an ultrasonic cleaner to improve the efficiency of degreasing and roughening, saving time and ensuring better results.
Sensitizing and Activating
Sensitizing and activating are the most crucial steps in the entire chemical plating process, directly affecting whether the chemical plating can proceed. Sensitizing involves adsorbing easily oxidized substances onto the diamond micron powder surface, which inherently lacks self-catalytic abilities. Activation involves adsorbing catalytically active metal ions (such as palladium) on the diamond micron powder surface, to expedite the reduction of nickel ions and the oxidative action of sodium hypophosphite, accelerating the deposition rate of the plating layer on the diamond micron powder surface.
Generally, if the sensitization and activation treatment time is too short, fewer palladium particles will form on the diamond surface, resulting in weak adhesion of the plating layer, making it prone to peeling or difficult to form a complete plating layer. On the other hand, if the treatment time is too long, it leads to wastage of palladium particles. The optimal time for sensitization and activation is 20-30 minutes.
Chemical Nickel Plating
The process of electroless nickel plating is influenced not only by the composition of the plating solution but also by its temperature and pH value. Traditional high-temperature electroless nickel plating generally operates at 80-85°C. Exceeding 85°C can cause the plating solution to decompose, while higher temperatures within this range increase the reaction rate. As for pH, an elevated pH increases the deposition rate of the plating layer but also leads to the formation of nickel salt precipitates, inhibiting the chemical reaction rate. Therefore, it is necessary to optimize the composition and ratio of the plating solution and the process conditions to control and improve the deposition rate, density, corrosion resistance, and compactness of the plating layer, producing diamond micron powder that meets industrial development needs.
As the primary raw material for diamond tools, the surface modification of diamond micron powder is a key method to enhance bonding with the base material and extend tool life. The application of chemical plating technology to diamond micron powder can significantly improve the lifespan of tools.
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