Chemical Durability and Structural Properties of Al₂O₃-CaO-Na₂O-P₂O₅ Glasses Studied by IR Spectroscopy, XRD and SEM

摘要

Various characterization techniques were used to study the composition of the glass series xAl₂O₃-(40 - x)CaO-10Na₂O-50P₂O₅ (with 0 ≤ x ≤ 10) in terms of chemical durability, X-ray diffraction, IR spectroscopy and scanning electron microscopy (SEM). The improved chemical durability was attributed to the replacement of easily hydrated P-O-P bonds by covalent and resistant Ca-O-P and Al-O-P bonds. However, the change in the dissolution rate (D_R) versus time showed a marked decrease in chemical durability with increasing the Al₂O₃ content to the detriment of the CaO content. The X-ray diffraction analysis of glasses annealed at 550 style="white-space:nowrap;">°C and 660 style="white-space:nowrap;">°C for 48 hours indicated the presence of pyrophosphate phases and predominant metaphosphates or cyclic metaphosphate phases when the Al₂O₃ content was ≤7.5 mol%. Nevertheless, both, X-ray diffraction and IR spectroscopy confirmed the structural tendency change from metaphosphate (Q2) and pyrophosphate structural units (Q1). Toward short isolated orthophosphate units (Q0) when the Al₂O₃ content above 7.5 mol%. SEM micrographs illustrated that the number of crystallites increased in the glass network when the Al₂O₃ content increased at the expense of the CaO content. An increase in the Al₂O₃ content to 10 mol% led to the formation of a larger number of crystallites of different sizes, dominated by small crystallite sizes assigned to short isolated orthophosphate groups. This phenomenon led to a decrease in chemical durability and seems to be a favorable factor for the formation of the apatite layers which enclose the glass, in a SBF solution test, able of regenerating bone tissue in biomedical application.