Ceramics-Silikáty 64, (1) 1 - 6 (2020)

The surface properties of G338 ionomer glass powder, both in as-received and heat-treated, have been studied in order to identify the reason that heat-treatment gives a cement that sets quicker but is weaker. Samples of G338 glass were analysed by X-ray fluorescence spectroscopy and the density determined by gas pycnometry. As-received and heat-treated (at 240 °C) glass powders were examined by Scanning Electron Microscopy. Specific surface area (BET) and pore volume were determined with low temperature nitrogen sorption, using eight individual powder samples. Thermo-gravimetric analysis was carried out on as-received G338 in the range 30-900 °C ramped at 10 °C/min in an inert atmosphere. Results showed the appearance of the as-received and heat-treated G338 powders to be the same, as were the specific surface areas and pore volumes. The density was found to be 2.6438 (±0.0093) g/cm³ and the XRF results were consistent with the known composition of the glass. Thermo-gravimetric analysis showed that the glass powder lost mass four steps, which were attributed to variations in states of water-binding on the surface of the glass. These findings lead to the conclusion that the observed differences in the setting properties of the glass G338 with poly(acrylic acid) and the strength of the resulting cements are not due to physical differences between the powders but to variations in the amount and state of surface water. Specifically, these variations are between differences in water binding to silanol groups that occur on glass surfaces.