Key words diamond nickel plating | 2020-01-15 09: 32: 52 | Source Technology Forum
1 Overview
Nowadays, artificial diamond is widely used in the field of optical devices and the electronics industry. Its hardness and abrasion resistance are high, so it can be used for grinding, cutting and dressing.
Although its characteristics are superhard abrasives, it is affected by temperature and other factors in actual work. It is a metastable crystal state at normal temperature and pressure, has 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 artificial diamond cannot be effectively exerted in practical applications, which hinders the life and processing efficiency of artificial diamond.
Studies have found that electroplating nickel on the surface of artificial diamond can further improve its characteristics. In addition to enhancing its high hardness, it also effectively protects the binding capacity existing at the interface between the diamond and the substrate, and achieves oxygen barrier protection purpose.
2.Plating nickel experiment
1Equipment, raw materials and formula used in electroplating experiment
1) The instruments used are: JRl artificial 120/140 mesh diamond, thermostatic water tank, electronic balance, electric stirrer, barrel plating machine.
2) Raw materials used: deionized water, sodium hypophosphite, nickel chloride hydrochloric acid, nickel stannous sulfate and sodium hydroxide.
3) Electroplating bath formula: Concentration / g.L-1 where H3BO3 and NiSO4.NiCl2 are 30-50g.L-1, 200-300gL-1, 20-40g.L-1.
2 electroplating process and operation
1) Operation: In the actual electroplating, the diamond needs to be placed in the plating bottle, and the plating bottle should be placed at a certain angle to facilitate the plating work.
Among them, nickel is used as the anode and copper wire is used as the cathode. Both the anode and the cathode are placed from the bottle mouth of the plating bottle, and the cathode and the anode are placed in the plating solution from the mouth of the bottle. The anode must be suspended, and 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 properly rolled, but the cathode and anode of the plating must be kept in a stationary state. Then select the appropriate plating equipment. The maximum flow of the ammeter is 10A, the maximum range of the voltmeter is 30V, and the parameters of the barrel plating machine are 23r / min.
2) Diamond plating process: After degreasing → washing with water → hydrophilization → water washing again → sensitization treatment → water washing → activation treatment → water washing again → chemical nickel plating → nickel plating → performance Detection.
Among them, the diamond is degreased, mainly with a dilute nitric acid solution, and rinsed with deionized water for half an hour, so as to completely remove the surface grease, so that the bonding 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 in order to increase hydrophobicity and provide a reliable guarantee for sensitization treatment. Sensitization was carried out with a mixture of SnCl2.HCl and water. The activation was performed with a mixture of PdC2, HCl and water for catalysis. The sensitization process and the activation process are the key steps in the diamond plating process, which are directly related to the success of nickel plating.
3. Results
1 Comparison of surface morphology and microstructure of artificial diamond after nickel plating
When diamond is not electroplated with nickel, its surface structure is smooth and its edges and corners are clear. It was found that the surface structure was rough after nickel plating, and the degree of roughness was directly related to the weight gain of the coating.
The study found that the rough surface structure of artificial diamond is caused by a large amount of residual metal ions, which causes the concentration of the main salt to increase, and the coating is rough after electroplating.
The surface morphology of the electroplated diamond was heat-treated at 400 ℃ for half an hour in a pot increase resistance furnace. At 400 ℃, the surface morphology of the artificial diamond does not change after nickel plating, which indicates that 400 ℃ does not affect the surface morphology of the artificial diamond.
2 Analysis of electroplated diamond phase by X-ray traveling method
After half an hour of heat treatment of the electroplated diamond under 400C environment, the phase of the electroplated diamond was analyzed by X-ray diffraction, and the blue shift of the peak position of diamond and nickel appeared. The reason is that when the artificial diamond is electroplated with nickel, its crystals will expand at a certain temperature, which will increase the value of the lattice constant and the corresponding distance value. According to the calculation formula,
The peak position of the obtained diamond and nickel appeared blue shift.
3 Compressive strength test of artificial diamond after nickel plating
By comparing the nickel plating of different grades of diamond plating, the average single particle compressive strength of artificial diamond is not significantly different from that before electroplating, but the compressive strength is increased when the nickel plating is thin. In the case of thicker nickel plating, the average single particle compressive strength of artificial diamond is significantly different from that before electroplating. The compressive strength measured by the compressive strength tester is significantly higher than that before electroplating.
And the average compressive strength of diamond treated at 400 ℃ showed an increasing state with the increase of the coating. The above shows that the compressive strength of artificial diamond is increased after nickel plating. This is because the cracks and pores of artificial diamond are effectively eliminated and reduced after electro-nickel treatment, which increases the compressive strength.
4 Conclusion
According to the above experiments, the compressive strength of artificial diamond increased significantly after the electroplating process. 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, the cathode and the anode are placed in the plating solution from the bottle mouth, and the anode must be suspended. Focus on the sensitization process and activation process, because this step is directly related to the success of nickel plating.
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