Discussion: the role of nickel plating on the surface of synthetic diamond

1 Overview

Nowadays, synthetic diamonds are widely used in the field of optical devices and the electronics industry. Its hardness and wear resistance are high, so it can be used for grinding, cutting and dressing. Although its characteristics are super-hard abrasives, it is affected by temperature and other factors in actual work. It is a metastable crystal state under normal temperature and pressure, with brittle characteristics, and its heat resistance is not high. In addition, there are impurities, cracks and pores. The above-mentioned defect factors cause the performance of synthetic diamonds to be unable to be effectively exerted in practical applications, and hinder the service life and processing efficiency of synthetic diamonds.” The study found that the surface of synthetic diamonds is electrically charged.Nickel plating can further improve its characteristics, except In addition to enhancing its high hardness, it also effectively protects the bonding ability existing in the interface between the diamond and the matrix, and achieves the purpose of oxygen barrier protection.

2 Electroplating nickel experiment

1 Apparatus, raw materials and formula used in the electroplating experiment

1) The instruments used are: JRl type artificial 120/140 mesh diamond, constant temperature water tank, electronic balance and electric stirrer, barrel plating machine.

2) Raw materials used: deionized water, sodium hypophosphite, nickel chloride hydrochloric acid, stannous chloride nickel sulfate, sodium hydroxide, etc.

3) Electroplating solution formula: Concentration/g.L-1 for H3BO3 and NiSO4.NiCl2 are 30-50g.L-1, 200-300gL-1, 20-40g.L-1, respectively.

2Plating process and operation

1) Operation: During actual electroplating, diamonds need to be placed in a plating bottle, and the plating bottle should be placed at a certain angle to facilitate the electroplating work. Among them, nickel is used as the anode of electroplating, and the copper wire is used as the cathode of electroplating. The anode and the cathode are placed from the bottle mouth of the plating bottle, the cathode and the anode are placed in the plating solution from the bottle mouth, the anode needs to be in a suspended state, and the conductive part at the bottom of the cathode is directly connected to the diamond. It must be noted that in the actual operation process, the diamond needs to be rolled properly, but the cathode and anode of the electroplating should be kept in a stationary state. Then select the appropriate electroplating device. The maximum flow of the ammeter is 10A, the maximum range of the voltmeter is 30V, and the parameter of the barrel plating machine is 23r/min.

2)Diamond electroplating process: After the diamond is degreasing→cleaned by water→hydrophilized→water cleaning again→sensitization treatment→water cleaning→activation treatment→water cleaning again→electroless platingNickel→Plating nickel→Perform performance testing. The degreasing treatment of diamond is mainly carried out with dilute nitric acid solution, and washed with deionized water after stirring for half an hour in order to completely remove the surface grease, so that the bonding force between the coating and the diamond is further increased. Hydrophilization is treated with dilute nitric acid, mainly with NaOH solution, and rinsed with deionized water after stirring for half an hour to increase the hydrophobicity and provide a reliable guarantee for the sensitization treatment. Sensitization is hydrolyzed with a mixture of SnCl2.HCl and water. The activation is carried out with a mixture of PdC2, HCl and water for catalysis. In the diamond electroplating process, the sensitization process and the activation process are key steps, which are directly related to the success of nickel plating.

3 results

1 Compared with the microstructure of the surface morphology of the artificial diamond after nickel plating, the surface structure of diamond is smoother and the edges and corners are clearer when the nickel is not electroplated. After electroplating nickel, it is found that the surface structure is relatively rough, and the roughness is directly related to the weight gain rate of the coating. Studies have found that the reason for the rough surface structure of synthetic diamond is that a large amount of metal ions appear, which increases the concentration of the main salt, and then the coating is rough after electroplating. After the electroplated diamond is heat-treated for half an hour in a pot-increasing resistance furnace at 400℃, the surface morphology of the electroplated diamond is detected. Under the high temperature condition of 400℃, the surface morphology of the artificial diamond after electroplating nickel did not change, indicating that 400℃ will not affect the surface morphology of the artificial diamond.

2Analyze the phase of electroplated diamond by X-ray radiation method. After heat treatment of electroplated diamond at 400C for half an hour, the phase of electroplated diamond is analyzed by X-ray diffraction method. The peaks of diamond and nickel are obtained. The bit appears blue-shifted. The reason is that when the artificial diamond is electroplated with nickel, its crystal will expand at a certain temperature, which will make the value of the lattice constant increase, and the corresponding spacing value also increases, according to the calculation formula Get diamond and nickel The peak position appears blue-shifted.

3 The compressive strength test of synthetic diamond after nickel plating is obtained by comparing different grades of plated diamond electroplated nickel. In the case of a thinner nickel plating layer, the average single particle compressive strength of synthetic diamond is compared with that before electroplating. The performance is not great, but the compressive strength has increased. In the case of thick nickel plating, the average single particle compressive strength of synthetic diamond is compared with that before electroplating, and there is a big difference. The compressive strength measured by the compressive strength tester is significantly higher than that before electroplating. And the average compressive strength of the diamond treated at 400℃ will increase with the increase of the coating. The above shows that the compressive strength of synthetic diamond increases after electroplating nickel. This is because the defects such as cracks and pores of the artificial diamond after the electro-nickel treatment are effectively eliminated and reduced, which increases the compressive strength.

4 Conclusion

Through the above experiment, the synthetic diamond has gone through the electroplating process After treatment, its compressive strength increased significantly. In the actual electroplating process, it should be noted that both the anode and the cathode are placed from the bottle mouth of the plating bottle, and the cathode and anode are placed in the plating solution from the bottle mouth. It is necessary to focus on the sensitization process and activation process, because this step is directly related to the success of nickel plating.