Project Details
Projekt
Studies on the nature of primary surface crystallization in bioactive glasses of SiO2-P2O5-CaO-Na2O-K2O-CaF2 composition.
Applicant
Dr.-Ing. Carsten Blaeß
Subject Area
Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
Term
from 2022 to 2023
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 506582091
The processability of bioactive glasses is significantly limited by their high tendency to surface crystallization. The clinical use of individually manufactured three-dimensional bone replacement implants made of bioactive glass has therefore only been established in isolated cases so far. Moreover, because processability and bioactivity, in particular solubility in body fluid, are diametrically opposed. A promising compromise seems to be the fluoride-containing glass "F3" (mol%: 44.8SiO2-2.5P2O5-36.5CaO-6.6Na2O-6.6K2O-3.0CaF2). Preliminary studies have shown that its sintering ability depends on grain size. The competing primary detectable surface crystallization is assigned to Combeit (Na6-2xCac+xSi6O18 (0 ≤ x ≤ 1)). This crystal phase is also typical for the clinically used Bioglass® 45S5 and Biosilicate® and prevents crystallization-free sintering there. The primary surface crystallization is thus the greatest danger for the chemical and physical homogeneity of the sintered body with regard to segregation, depletion of the residual glass phase and irregular residual porosity. However, a crystalline framework forming along the former grain boundaries equally has the potential to freeze sintered additively manufactured green bodies at defined porosity and thus prevent the loss of structural integrity of the specimen bodies or even create a complex, hierarchical, and fine-particle void architecture. To elucidate the fundamental influence factors of these phenomena and their applicative potential, also for comparably crystallizing glass compositions, it is necessary to investigate the mechanism and kinetics of primary surface nucleation in glass F3 in more detail. The underlying nucleation mechanism and the technological possibilities for influencing it, for example in the context of powder production or preparation, are largely unknown to date. Since the primary crystal phase is most likely to be oriented to the composition of the Combeit according to the current findings, the variation of the sodium content in the glass as well as on the glass surface appears to be the most targeted. The influence of the surface sodium concentration on the crystallization, the sintering behavior and the resulting microstructure of the sintered bodies will be investigated by comparing surface chemically leached or enriched as well as fractured, fire-polished, and annealed surfaces. DTA, microscopy, XRD, XPS, spectroscopy (IR, Raman) and NMR will be used for the planned work. The planned investigations will take place on powders as well as on bulk materials.
DFG Programme
WBP Fellowship
International Connection
Brazil
