Etching studies on {100} faces of MgO crystals in H3PO4 acids

The effect of temperature (20–100°C) and concentration of H₃PO₄ etching solutions on the etching behaviour of {100} faces of MgO crystals in investigated. It is observed that the formation of etch pits and pyramids and the values of dissolution rate depend on the etching conditions. The density of the pyramids in 33.08 N H₃PO₄ solution was found to be maximum at 20°C. From the plots of logarithm of dissolution rate versus inverse of absolute temperature, the values of activation energy and pre-exponential factor for the dissolution process are computed. It is found that for H₃PO₄ concentrations upto 22.05 N the value of the activation energy remains constant but that of pre-exponential factor increases with acid concentration. At higher concentrations, the activation energy decreases. The results are systematically described and discussed.