Comparative studies of etching mechanisms of CR-39 in NaOH/H2O and NaOH/ethanol

The bulk etch rate for CR-39 in NaOH/ethanol was faster than those in aqueous solution of NaOH (NaOH/H2O). Furthermore, a layer of precipitate always accumulates on the surface of CR-39 detector during etching in NaOH/ethanol, which is absent during etching in NaOH/H2O. In the present work, mass spectrometry results have shown that the same etched products are present in the etchants of NaOH/H2O and NaOH/ethanol after etching of CR-39. This shows that CR-39 has the same etching mechanism in both etchants. These etched products support the etching mechanism of scission of the carbonate ester bond in CR-39 by the hydroxide ion through basic hydrolysis of ester. The difference in the bulk etch rates can be explained in terms of the solubility of the etched products in the etchants. FTIR analyses of the solute formed from the etchants show the formation of allyl alcohol and carbonate during etching in both etchants. The FTIR spectra of the precipitate formed at the surface of CR-39 detectors during etching in NaOH/ethanol has also shown that sodium carbonate is present in the precipitate. Finally, XRD analyses of the solute formed from the etchants show the formation of sodium bicarbonate and sodium carbonate in the etchant of NaOH/H2O after etching and the formation of the mineral natrite and thermonatrite in the etchant of NaOH/ethanol as well as in the layer of precipitate on the surface of the CR-39 detector formed during etching in NaOH/ethanol.