Acid-containing water-in-oil microemulsions for polishing the subsurface damage layer of the KDP single crystal

Microemulsions formed by water/polyoxyethylene tert-octylphenyl ether (TX-100)/n-hexanol/n-hexane were characterized and applied to polish the subsurface damage layer of the potassium dihydrogen phosphate (KDP) single crystal. Effects of the mass ratio of TX-100-to-n-hexanol (K_m), pH and temperature on the phase behavior of these systems were studied by pseudo-ternary phase diagrams and dynamic light scattering. The size of a single-phase region area was largest when K_m = 3 : 2, pH = 3, at 25 °C. The type of microemulsions and reactivity between KDP and acid in water-in-oil (W/O) microemulsions (MEs) were determined by conductivity. The salt-carrying capacity of W/O MEs was investigated by acid-base titration. The static etching rate (SER) of the KDP crystal was calculated to be 709.6 nm min^-1. The micropolarity of W/O MEs was explored by a solvent chromogenic approach. XRD showed that the excess peaks of the subsurface layer of the KDP crystal (200) and (211) were eliminated after polishing. The root mean square roughness (R_q) and arithmetic mean roughness (R_a) of the KDP crystal were reduced from 1.67 nm and 1.19 nm to 1.58 nm and 1.15 nm, respectively.