Effects of chemical etching with nitric acid on glass surfaces

Glass slides were chemically etched with nitric acid using five different methods. We investigated the effects of chemical etching treatments on such properties as chemical composition, surface roughness, transmittance, and thermal stability of the glass. Sodium, calcium, and aluminum atoms in the surface of the glass are effectively reduced by chemical etching with nitric acid. Especially, boiling the glass in a 70% nitric acid solution for 30 min is more effective in the reduction of sodium, calcium, and aluminum atoms at the surface of the glass than other etching methods with nitric acid. The surface morphologies of the glasses were very similar regardless of the chemical etching treatments with nitric acid etchant. Root-mean-square surface roughness of the bare glass was 0.58 nm but that of the glass etched with nitric acid was ranged from 5.4 to 6.8 nm. Sodium concentration at the glass surface was largely reduced from 2.44% to 0.25%. In order to investigate the thermal stability of the glass, the bare glass and the glass samples boiled for 30 min in a 70% HNO3 solution were annealed in air at 300, 400, 500, and 600 deg. C for 1 h. Sodium, aluminum, and calcium at the surface of the glass increased with an annealing temperature regardless of chemical etching with nitric acid, but the Na, Al, and Ca content at the surface of the glass boiled in 70% HNO3 for 30 min was greatly reduced relative to that of the surface of the bare glass at an annealing temperature of 500 deg. C