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Chemical variability is a main strength of glass. Glass powders are therefore promising candidates for manufacturing a broad diversity of sintered materials like sintered ¬glass-ceramics, glass matrix composites or glass bonded ceramics with tailored mechanical, thermal, electrical and optical properties and complex shape. Its wide and precise adjustability makes this class of materials, even if it may not be obvious at first sight, a key component of advanced technologies. Manufacture and processing of initial glass powders often allow even more flexibility in materials design. At the same time, however, they can cause additional problems. The lecture illustrates possible consequences of glass powder processing upon glass crystallization and sintering as well as chances for targeted utilization. Simple kinetic models describing the effect of particle size distribution, surface crystallization and rigid inclusions on sintering as well effects of different milling and seeding on sinter crystallization are presented.
Nowadays, the use of bioactive glasses is established for bone regeneration; however glasses are used mostly as powders, granules or in a paste. Sintered scaffolds are not used clinically, because of the inherent problem of crystallization during the sintering process, resulting in poor mechanical properties and reduced bioactivity. Therefore it was the aim to design new bioactive glasses, which combine improved processing and sintering with bioactivity.
Compared with the well-known Bioglass® 45S5 (SiO2-P2O5-CaO-Na2O) the calcium/alkali oxide ratio was increased, sodium oxide was partially replaced by potassium oxide and up to 8 mol% calcium fluoride were added, in order to stabilize the glass against crystallization.
The sintering behavior of the new glasses was characterized by heating microscopy and compared to that of Bioglass® 45S5. Results show that the new glasses achieve a sintered density of 88-99 % in contrast to only 57-67% for Bioglass® 45S5. In addition, FTIR and XRD analyses show that Bioglass® 45S5 crystallizes during sintering while for the new glasses no crystalline phases were detected. The thermal properties of all glasses were studied by DTA and DSC measurements, and the influence of grain size was characterized. These studies showed an increase of sintering temperature and final porosity with increasing particle size. The structure of sintered compacts during and after sintering was examined using light and electron microscopy (SEM).