The aluminium effect on the phospho-silicate materials

https://doi.org/10.1016/S0022-2860(02)00263-6Get rights and content

Abstract

Because of the noted phase separation in phospho-silicate materials with sodium and calcium the attempt of homogenization by the addition of aluminium has been undertaken. Constant amount of aluminium equal to 5 mol% of AlPO4 was added whereas the proportion of NaCaPO4/SiO2 was changed.

X-ray diffraction (XRD) measurements made it possible to identify amorphous and crystalline samples. The amount of crystalline phases in comparison with the analogous NaCaPO4–SiO2 materials decreased. We used energy-dispersive X-ray analysis (EDX) to evaluate chemical composition and scanning electron microscopy (SEM) to find out the chemical elements distribution. It was found that the addition of aluminium caused more uniform distribution of all elements.

Fourier transform infrared spectroscopy (FTIR) measurements as well as computer decomposition of the obtained spectra into component bands were performed. The decomposition made it possible to connect bands with the groups of phospho-oxygen, silico-oxygen and lattice vibrations.

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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