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 (Km), 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 Km = 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 (Rq) and arithmetic mean roughness (Ra) of the KDP crystal were reduced from 1.67 nm and 1.19 nm to 1.58 nm and 1.15 nm, respectively.