Surface etching of diamond powders with electroless Ni-P coating according to phosphorus content

Ni-P coatings with different P content were deposited on the surface of diamond powders with a particle size of about 200 μm by electroless plating. The Ni-Pcoated diamond powders were then annealed at 900 °C in vacuum for 1 h followed by cleaning. The etching properties of the coated diamond powders were investigated. The amount of the Na₂H₂PO₄·H₂O reductant was adjusted to obtain Ni-P coating layers with a P content of 5 and 7 wt%. After the coating for 5, 15, and 60 min, the vacuum annealing and coated layer removal processes were carried out. In each process, the microstructure of the coatings was examined using field emission scanning electron microscopy. The elemental compositions of the coating surfaces were examined using energy dispersive X-ray spectroscopy. Ni-P coating layers were evenly coated on the entire surface of the diamond powders, and the coating thickness was proportional to the root square of the coating time. The thickness of the coatings with high P content was two times higher than that of the coatings with low P content for the same coating time. The surface analysis results after annealing revealed that the coatings layer was initially consisted of spherical grain size of 3um. With an increase in the reductant content and coating time, Ni aggregation was observed along with the formation of Ni-Sn-P intermetallic compounds. With an increase in the P content and coating time, the thickness of the Ni-P coating layers increased. However, the etching ratio of the diamond surface decreased, while the etching depth increased. Therefore, the diamond etching profile could be controlled by Ni-P coating process condition.