Illustration of results
Source: BAM, Glass division
Bioactive glasses are similar to natural bone in their chemical composition and can be used as bone replacement material. In contact with aqueous solutions, such as body fluid, bioactive glasses release ions and dissolve without residue during the growth of new natural bone. To create complex shaped bodies, the glasses must also be well processable. This can be impaired by an excessive tendency to crystallization or non-desired foaming during sintering. In contrast to desired foaming during manufacturing of highly porous structures, for example for insulating materials, the non-desired foaming and its causes have rarely been investigated in detail even for other glasses.
This article exemplarily reports on possible causes and influencing factors of this effect using the example of two bioactive glasses of different crystallization tendencies, where glass F3 (44.8SiO2-2.5P2O3-36.5CaO-6.6Na2O-6.6K2O-3.0CaF2) has a high crystallization tendency and glass 13-93 (54.6SiO2-1.7P2O3-22.1CaO-6.0Na2O-7.9K2O-7.7MgO) has a low crystallization tendency. Both glasses were melted, fritted, and processed into powder by milling in CO2 atmosphere or in isopropanol. Initial glasses and powder compacts were then analyzed by heating and electron microscopy, differential thermal analysis, FTIR spectroscopy, vacuum hot extraction, and ToF-SIMS.
Consistent with analogous studies on other glasses, carbon species were found to be the cause of the observed foaming. Powder syntheses by milling in CO2 atmosphere led to the formation of carbonates; milling in isopropanol additionally caused reduced carbon. Both species were found to be sufficiently temperature stable to be trapped in the volume of the sintered bodies. The intensity of foaming was much more pronounced for milling in CO2 and correlated with milling time. Milling in isopropanol, however, resulted in a distinct black coloration of the sintered bodies. Decolorization occurred again while foaming and degassing. Crystallization of glass F3 delayed the foaming by increasing the effective viscosity until the crystal phase(s) melted.
Sintering and foaming of bioactive glasses
Carsten Blaeß, Ralf Müller
published in Journal of American Ceramic Society, pages 1-11, 2022
BAM division Glas