Glass - Back to the Future!

Presenting Author:
Carsten Blaeß

article posted 21 March 2016

Carsten Blaeß is at the German Standards Bureau...

Sintering and crystallization of new bioactive glasses

Carsten Blaeß*2, Stefan Reinsch2, Ralf Müller2, Delia S. Brauer1
1 Otto-Schott-Institut für Materialforschung (OSIM), Friedrich-Schiller-Universität Jena, Fraunhoferstr. 6, 07743 Jena, Germany 2 Bundesanstalt für Materialforschung und –prüfung (BAM), Richard-Willstätter-Str. 11, 12489 Berlin, Germany;

Bioglass® 45S5 is mainly used clinically as powders, granules or pastes instead of sintered compacts. This is due to the inherent problem of crystallization during the sintering, which results in poor mechanical properties and reduced bioactivity. Recently, new bioactive glasses with improved crystallization stability have been developed as promising candidates for manufacturing of sintered powder compacts for bone regeneration, which combine improved sintering behavior 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 3 mol% calcium fluoride were added, in order to stabilize the glass against crystallization. The aim of this study was to investigate the sintering and crystallization behavior of these new bioactive glasses.
Sintering and crystallization were characterized by heating microscopy, XRD, FTIR, SEM, and DTA. The results show that a sintered density of 88–99% is achieved in contrast to only 57–67% for Bioglass® 45S5. In addition, FTIR and XRD analyses show that Bioglass® 45S5 crystallized during sintering while for the new glasses no crystalline phases are detected. The thermal properties of all glasses were studied by DTA measurements, and the influence of grain size was characterized. These studies showed that full densification can be attained for particle size < 32 µm, whereas coarser particles progressively increase residual porosity. Observed foaming phenomena, are strongly retarded by crystallization of beta-HAp.