Abstract
Abstract The crystallization process of a bioactive silicate glass with 47.5SiO2-10Na2O-10K2O-10MgO-20CaO-2.5P2O5 molar composition was investigated by using nonisothermal differential t hermal a nalysis (DTA). T he DTA plots recorded at different heating rates exhibited a single crystallization peak. The activation energy for crystallization was estimated by applying the equations proposed by Kissinger and Matusita-Sakka. The Johnson-Mehl-Avrami exponent (n) was assessed by using the Ozawa and Augis-Bennett methods. The analyses suggest that a surface crystallization mechanism with one-dimensional crystal growth is predominant. The activation energy for viscous flow was also assessed (176 kJ/mol) and was found lower than the activation energy for crystallization (271 kJ/mol). This confirms the stability of 47.5B against crystallization and its good sinterability, which is a highly attractive feature for producing glass products of biomedical interest, such as bioactive porous scaffolds for bone repair.
Highlights
Bioactive glasses were invented fifty years ago at the University of Florida by Prof
The crystallization process of a bioactive silicate glass with 47.5SiO2-10Na2O-10K2O-10MgO-20CaO2.5P2O5 molar composition was investigated by using nonisothermal differential t hermal a nalysis ( differential thermal analysis (DTA))
The analyses suggest that a surface crystallization mechanism with one-dimensional crystal growth is predominant
Summary
Bioactive glasses were invented fifty years ago at the University of Florida by Prof. Larry Hench and his team, who developed the famous 45S5 composition (45SiO2-24.5CaO24.5Na2O-6P2O5 wt.%) [1] This glass, trade-named as Bioglass , was initially found able to bond both to bone and to soft collagenous tissues of the body [2]. 45S5 glass cannot be sintered without undergoing devitrification, which has an impact on the kinetics of apatite formation (bioactivity) in vitro and in vivo and, on the bone-bonding capability and osteointegration rate In this regard, Peitl et al [9] showed that the onset time of hydroxyapatite formation on the surface of 45S5 Bioglass increases from 8 to 25 h when the crystalline fraction increases from 0 to 60%; the bioactivity is not totally suppressed and the partially-crystallized material is still potentially suitable for biomedical applications [10,11,12]. Other glasses have been developed with a larger sintering window (e.g. 13-93, 53SiO2-6Na2O-12K2O-5MgO20CaO-4P2O5 wt.%) [15] and/or with the capability of retaining an excellent and fast apatite-forming ability in partially-crystallized forms (e.g. CEL2, 43.8SiO2-15.0Na2O6.1K2O-4.6MgO-23.6CaO-6.9P2O5 wt.%) [16]
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