Novel abrasive-free jet polishing mechanism for potassium dihydrogen phosphate (KDP) crystal

Traditional potassium dihydrogen phosphate (KDP) polishing methods, such as magnetorheological finishing (MRF), ion-beam figuring (IBF), and chemical mechanical polishing (CMP), are limited by either hard-to-remove residual particles, unavoidable heating effects, or an applicability restricted to large-sized KDP. In this paper, we present a novel abrasive-free jet polishing (AFJP) mechanism that can be implemented for abrasive-free and no-residue polishing on KDP surfaces. KDP AFJP makes use of a thermodynamically and kinetically stable ionic liquid (IL) microemulsion that contains nanometer range water droplets evenly dispersed in the non-aqueous carrier liquid. The sprayed out nanoscale water droplets can remove material through dissolution. The feasibility of this approach has first been analyzed through several experiments, namely compatibility tests and assessments of removal controllability and uniformity of the IL microemulsion. The material removal mechanisms in contact removal and slipping removal were then studied. KDP AFJP experiments were then conducted to validate the polishing performance. The experimental results show that an IL microemulsion as an abrasive-free jet can indeed improve the quality of a KDP surface, leaving no residue.