Detection and identification of corrosion products of sodium aluminoborosilicate glasses by Na-23 MQMAS and H-1 -> Na-23 CPMAS NMR

Na-23 multiple-quantum (MQ) MAS NMR is applicable for monitoring the chemic al and structural changes resulting from atmospheric exposure of a series o f alkali aluminoborosilicate glasses with compositions RNa2O: 1B(2)O(3):1Si O(2):0.25Al(2)O(3) (where R = 0.5 - 2.5). Glasses with high alkali concentr ations possess greater numbers of nonbridging oxygens within the bulk struc ture and presumably at the initial surface of a fresh sample, and for three samples with R greater than or equal to 1.5 sharp resonances are revealed in the isotropic dimension of an MQMAS NMR experiment conducted after prolo nged atmospheric exposure. The MQMAS NMR experiments, combined with H-1 --> Na-23 cross-polarization magic-angle spinning (CPMAS) NMR measurements, in dicate that these resonances arise from sodium cations no longer participat ing in the glass network. Two new phases are formed as corrosion products a nd have been identified as an anhydrous Na2CO3 phase and a NaBO2. 1H(2)O ph ase through comparison with Na-23 MQMAS and H-1 --> Na-23 CPMAS NMR spectra of crystalline samples. Due to an inherent difficulty with direct quantifi cation of populations based on MQMAS spectra, a simplified approach for qua ntification of the amount of the new carbonate phase is presented. Values a re then calculated for relative amounts of corrosion product formation for different exposure times and bulk glass compositions.