Water dissolution ultra-precision continuous polishing of potassium dideuterium phosphate (DKDP) crystal

Abstract

Traditional potassium dideuterium phosphate (DKDP) polishing techniques, such as single-point diamond flycutting (SPDF), magnetorheological polishing (MRF), and ion beam computation (IBF), are prone to edge collapse, subsurface damage, and small removal rates. In the study, the mechanism of crystal deliquescence is investigated based on the nature of DKDP crystal that are susceptible to deliquescence, and a method of water dissolution ultra-precision continuous polishing of DKDP crystal is proposed, with the corresponding water-in-oil solution configured as a polishing solution. The polishing solution proposed in the paper includes nonylphenol polyoxyethylene ether as a surfactant, glycerol monooleate as an oil phase, n-octanol as a cosurfactant, and pure water as an aqueous phase. The water nucleus in the polishing solution is squeezed, rubbed, and then deformed and ruptured by the action of the polishing pad and the rough peaks on the surface of the DKDP crystal, and the water molecules inside the ruptured water nucleus flow out and dissolve the surface of the crystal, resulting in the polishing of the DKDP crystal. The experimental results show that the water dissolution ultra-precision continuous polishing method can well alleviate the problems of subsurface damage and small removal rate of DKDP crystal brought by the conventional processing. DKDP crystal have surface roughness (Ra) of less than 12 nm and face shape accuracy (RMS) of less than 15 nm.