The aluminium effect on the phospho-silicate materials
Introduction
Crystalline and glassy-crystalline materials from the AlPO4–SiO2 system belong to the berlinite bioactive materials group [1]. They are characterised by high chemical and thermal resistance. Advantageous properties of such materials are connected with their structure. There is no aluminium substitution in the silico-oxygen framework, all aluminium is bound as chemically resistant AlPO4. Previously performed examination of the AlPO4–SiO2 system with the addition of Na+ and Ca2+ cations allowed to find the existence of AlPO4–SiO2 solid solution till the 20 mol% of AlPO4 contents and the homogenizing influence of aluminium on their structure [2], [3], [4]. Besides the function of homogenization aluminium should have advantageous influence on mechanical and chemical properties of the obtained materials. In the same time the addition of aluminium makes it difficult to vitrify materials.
The main aim of the present work was to show the aluminium effect on the NaCaPO4–AlPO4–SiO2 materials.
Section snippets
Experimental
The NaCaPO4–AlPO4–SiO2 materials of constant AlPO4 amount (5 mol%) and changed NaCaPO4/SiO2 proportion (5–45 mol% NaCaPO4/90–50 mol% SiO2) have been selected. The composition was selected to compensate the negative charge of [PO4]3− and [SiO4]4− by couples of Na+ and Ca2+ cations. The sol–gel method was selected to obtain the materials of the highest possible homogeneity. TEOS (SiO2), Al(NO3)3 9H2O (Al2O3), Ca(NO3)2·4H2O (CaO), Na3PO4·12H2O (Na2O) i H3PO4 (P2O5) were used to introduce particular
Results and discussion
Explanation of the observed aluminium effect on the phospho-silicate materials homogenization requires systematic structural studies. This is the reason of selecting the materials of constant AlPO4 contents and systematically changed NaCaPO4 (5–45 mol%) and SiO2 (90–50 mol%) contents (Table 1). Analysis and interpretation of the obtained results is based on the results of previous experiments on the NaCaPO4–SiO2 materials (Table 2).
X-ray analysis of NaCaPO4–SiO2 and AlPO4–NaCaPO4–SiO2 materials
Conclusion
The performed XRD and IR spectroscopy investigations made it possible to show the homogenization influence of aluminium on the AlPO4–NaCaPO4–SiO2 crystalline materials. The small addition of aluminium (5% AlPO4) visibly limited the amount of crystallising phases. Obtained results suggest that NaCaPO4 can form the kind of solid solution in cristobalite (with phosphocristobalite) and the limit of dissolved phase is about. 20–30% of NaCaPO4.
Acknowledgements
This work is supported by Polish Committee for Scientific Research under grant no. PBZ/KBN-013/T08/34
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