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Structural studies of the NaCaPO4–SiO2 sol–gel derived materials
Journal of Molecular Structure 651–653 (2003) 489–498 www.elsevier.com/locate/molstruc
Structural studies of the NaCaPO4 –SiO2 sol–gel derived materials M. Sitarza,*, M. Rokitaa, M. Handkea, E. Galuskinb a
University of Mining and Metallurgy (AGH), Faculty of Materials Science and Ceramics al Mickiewicza 30, 30 059 Krakow, Poland b University of Silesia, Museum of Earth, Department of Earth Science ul Be¸dzin´ska 60, 41-200 Sosnowiec, Poland Received 25 November 2002; accepted 16 December 2002
Abstract Structural studies of the NaCaPO4 – SiO2 materials have been carried out. Amorphous materials from this system, after controlled crystallization process, can be used as potential nanomaterials. Structural studies of nanomaterials are of fundamental importance in view their future applications. Materials of different [PO4]32/[SiO4]42 tetrahedra proportion have been prepared. Naþ and Ca2þ cations have compensated the negative charge of the lattice. Amorphous and crystalline materials have been obtained by sol – gel as well as conventional melting methods. The XRD phase identification has enabled amorphous and crystalline materials identification and suggests the separation of phosphorus and silicate crystalline phases. The obtained materials were examined using the electron scanning microscope and EDX spectrometer. Analysis of electron scanning microscope maps shows considerable inhomogeneity of crystalline samples. Fluctuations in ions distribution, in case of amorphous materials, have been noted too. DTA investigations have enabled to find the probable characteristic temperatures of glass crystallization. Detailed infrared spectroscopy measurements have been carried out. The spectra of obtained materials have been compared with the spectra of cristobalite. Spectroscopic studies confirm the inhomogeneity of materials. q 2003 Elsevier Science B.V. All rights reserved. Keywords: Phospho-silicate materials; IR spectra; Nanomaterials
1. Introduction Glassy and glassy-crystalline materials from the NaCaPO4 – SiO2 system are commonly known as biomaterials [1,2]. The first bioactive glasses from the SiO 2 – CaO – P 2O 5 system with different additions, capable to create the bonds with the tissue, were designed by Hench [3 –6]. Such glasses, * Corresponding author. Tel.: þ48-12-172232; fax: þ 48-12331593. E-mail address: [email protected] (M. Sitarz).
known as Bioglassw contain up to 55 mol% of SiO2, to 50 mol% of CaO and to 40 mol% of P2O5. To design new bio-glass or bioceramics materials, especially nanomaterials, it is necessary to experience their structure. In the present work the attempt of crystalline and amorphous materials of systematically changing contents of NaCaPO4 (0 – 50 mol%.) and SiO 2 (100 – 50 mol%.) was undertaken. The analysis of the amorphous materials structure is very difficult because of the lack of long-distance order. The main disadvantage is the uselessness
0022-2860/03/$ - see front matter q 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0022-2860(03)00113-3
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of the X-ray methods in analyze of amorphous materials structure. On the other way the vibrational spectroscopy is the method sensitive on the shortrange order and it can be successfully used in this case. Obtaining of the glassy and crystalline NaCaPO4 – SiO2 materials and detail structure analyze was the main aim of the present work.
the resulting materials were made with a Bio-Rad FTS 60V spectrometer. Spectra were collected after 256 scans at 4 cm21 resolution. Samples were prepared by the standard KBr pellets method. Spectra decomposition has been carried out according to the method of Handke et al [7].
3. Results and discussion 2. Experimental The description of these kinds of materials, of very complicated composition, requires the systematic structural studies. It enables to investigate the structural changes with the change of chemical composition. The NaCaPO4 – SiO2 materials of changed NaCaPO4/SiO2 proportion (0 – 50 mol% NaCaPO4/100 – 50 mol% SiO2) have been selected (Table 1). The sol – gel method was selected to obtain the materials of the highest possible homogeneity. TEOS (SiO2), Ca(NO3)2·4H2O (CaO), Na3PO4·12H2O (Na2O) and H3PO4 (P2O5) were used to introduce particular oxides. The obtained gels were dried at room temperature (30 days) and then at the temperature of 60 8C. After drying process all the gels were heated at 1380 8C to obtain crystalline materials. The attempts of glassy samples obtaining on the way of progressive heating of gels were unsuccessful. Finally the gels were melting in platinum crucible in the temperature of 1700 8C and rapidly cooled on the cast iron plate. X-ray measurement of all samples were carried out using FPM Seifert XRD 7 with a step of 0,01 deg and collecting time—5 s. EDX spectra were measured on a JEOL 5400 scanning microscope with microprobe analyser LINK ISIS (Oxford Instrument). IR spectroscopic measurements of Table 1 Composition of the samples (mol%) Sample number
NaCaPO4 –SiO2 system
I Ia Ib Ic Id Ie
100% SiO2 90% SiO2, 10% NaCaPO4 80% SiO2, 20% NaCaPO4 70% SiO2, 30% NaCaPO4 60% SiO2, 40% NaCaPO4 50% SiO2, 50% NaCaPO4
The X-ray measurements of samples obtained by gels melting show that all samples are amorphous (the only broad, flat X-ray band in the region of 10– 308—2u). However, in case of the samples with the highest contents of NaCaPO4 (Id and Ie) there are some very weak peaks (of several cps intensity) on the X-ray patterns. The amorphous state of the samples was confirmed by the IR spectroscopy analysis in the FIR region. The lack of bands is the evidence of the lack of long-range order (amorphism of samples). In case of Id and Ie samples one can see some clear bands in the FIR region, what confirm some kind of long-range order (presence of crystalline phases) (Fig. 1). Scanning microscopy measurements, connected with X-ray microanalysis, complemented X-ray measurements. The analysis of glassy (samples Ia –Ic) and glasscrystalline (samples Id and Ie) materials reveals distinct liquation in all samples (Fig. 2). The most interesting results were obtained for the Ib and Ic samples. In case of mentioned samples the spherical inclusions have nanometric size. EDX measurements showed that inclusions contained almost only calcium silicate phase. In comparison with inclusions, the matrix is enriched with phosphorus, calcium and sodium. The amount of sodium, calcium and phosphorus increase with the increasing amount of NaCaPO4 in samples (Figs. 3 and 4). The multistage crystallization process was detected in case of samples Ib and Ic (Fig. 5) on the base of DTA results. This fact is clear in the light of mentioned microscopic results; there are at least two different ‘glassy phases’ in those materials and each phase should have different crystallization temperature. It is possible to obtain the glasscrystalline materials of planned composition and size of crystallites, for example obtaining the only,
M. Sitarz et al. / Journal of Molecular Structure 651–653 (2003) 489–498
491
Fig. 1. FIR spectra of glassy (I–Ic) and glass-crystalline (Id –Ie) samples.
defined crystal phase in the controlled crystallization process. Obtaining of glass-crystalline nanomaterials could be especially interested; the process seems to be possible in case of Ib and Ic samples. Planning of such a process needs detailed knowledge about material structure. The analysis of the structure of glass, which is the precursor of
glass – ceramic material, can be based on the spectroscopic studies. However, the direct interpretation of glass spectra is almost impossible, because they are complex and complicated. The interpretation can be realized by the comparison with analogous crystalline materials spectra. The statement of the amorphous samples MIR spectra has been presented on the Fig. 6.
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Fig. 2. SEM microphotograph of samples (Ia–Ie).
The characteristic broadening of bands, in comparison with the bands of crystalline materials, is clearly visible. However, some sharp bands are present on the Id and Ie sample spectra. This fact confirms the results of previous measurements; these materials contain some amount of crystalline phase. Performed spectroscopic studies of the crystalline NaCaPO4 – SiO2 materials and pure NaCaPO4 enabled for identification the bands connected with P – O and Si – O vibrations. The statement of MIR spectra of
obtained crystalline materials is shown on Fig. 7. With the increasing contents of NaCaPO4 a constant increase of the intensity of the bands due to P – O vibrations can be observed (Ia –Ie spectra; the bands at 574, 598, 960 cm21 and the group of bands in the region of 1020 – 1080 cm21). In the same time the decrease of the characteristic for cristobalite bands intensities (at 622, 795, 1200 cm21 and the group of bands in the region of 1020 – 1080 cm21; Si – O vibrations) is visible. In case of Id sample spectrum
M. Sitarz et al. / Journal of Molecular Structure 651–653 (2003) 489–498
Fig. 3. EDX spectra of Ia –Ie samples (inclusions).
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Fig. 4. EDX spectra of Ia– Ie samples (matrix).
M. Sitarz et al. / Journal of Molecular Structure 651–653 (2003) 489–498
495
Fig. 5. DTA of Ib sample.
the two of mentioned bands, at 1199 and 622 cm21, are even invisible. The most characteristic for cristobalite band at 795 cm21 (due to bending vibrations of the silico– oxygen bridge [8]), shifts to the lower wavenumbers (with the decrease of intensity) in the Ia –Id series. It is characteristic that one can observe more intensive band in this region, on the spectrum of the Ie sample. The similar changes can be seen in case of the band at 487 cm21 due to bending Si – O – Si vibrations. These changes are caused by lowering amount of crystallizing cristobalite and in the same time, arising amount of tridymite. The bands characteristics for tridymite are analogous to these for cristobalite but they are located at little lower wavenumbers [9]. These results are compatible with X-ray diffraction results (Table 2.), which showed the constant decrease of crystallizing cristobalite in the Ia – Id series (and the lack of cristobalite in case of Ie sample) with the coincident increase of tridymite amount. The intensity and positions of the bands at about 790 and 480 cm 21 can be influenced by the crystallizing phospho-silicate Na2Ca4(PO4)2SiO4.
The comparison of amorphous materials spectra together with their crystal analogous spectra (Ib and Ic) has been presented on the Fig. 8. Despite of differences in bands intensity and width the similarity of spectra are clear. The kind of crystallizing phases in glass-crystalline samples Id and Ie (Fig. 6) was qualified as phosphate phase on the base of IR bands positions (the bands at 958, 597, 574 cm21 and the group of bands in the region of 1080 –1020 cm21). On the base of spectra similarities one can suppose that the short-range order in glasses will be in a close relation to the crystalline phases (Table 2). The amorphous materials (Ia – Ic) spectra decomposition into component bands enabled to state that mentioned materials have cristobalite-like structure.
4. Conclusion 1. The amorphism of obtained materials was confirmed using X-ray analysis and infrared spectroscopy in the FIR region. The analysis of FIR spectra suggests arrangement of domains.
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Fig. 6. MIR spectra of glassy (I –Ic) or glass-crystalline (Id–Ie) samples.
2. Performed microscope measurements enable to observe distinct nanoliquation-samples IIb and IIc. 3. EDX measurements showed that the matrix, in comparison with inclusions, is enriched with phosphorus, calcium and sodium. 4. DTA measurements of glassy samples enable to estimate the region of glass devitrification as 800 –1000 8C, in case of IIb and IIc sample the process of devitrification is multistage. 5. MIR spectra of the series of NaCaPO4 – SiO2 materials were compared with the spectra of low
temperature cristobalite and NaCaPO4. The systematic increase of the intensity of bands due to phospho – oxygen vibrations with the decrease of SiO2 contents was observed. The bands due to P – O vibrations (574, 598, 960 and the group in the range of 1020 –1080 cm21) as well as Si – O vibrations (487, 622, 795, 1094 and 1200 cm21) were separated. In case of bands at c.a. 470 – 490 and 795 –790 cm21 the decrease of SiO2 contents causes initially decrease and then increase with simultaneous shift into lower wavenumbers is observed. It is connected with
M. Sitarz et al. / Journal of Molecular Structure 651–653 (2003) 489–498
497
Fig. 7. MIR spectra of crystalline (I–Id) samples. Table 2 X-ray phase analysis (crystalline samples)
disappearance of cristobalite phase (the bands at 622 and 1200 cm21 disappear too) and appearance of phospho –silicate phase. 6. The comparison of amorphous and crystalline materials spectra enabled to show the similarity in their structures. 7. Mathematical process of decomposition enabled to state that these materials (samples Ia – Ic) have cristobalite-like structure.
SiO2 (cristobalite) I Ia Ib Ic Id Ie
*** *** ** ** **
NaCaPO4
* * * ** **
SiO2 (tridymite)
* ** ** *
Na2Ca4(PO4)2·SiO4
*
Estimated amount of phases: *** a predominated phase, ** a phase of considerable amount, * a small amount of phase.
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Fig. 8. The comparison of the spectra of crystalline and glassy Ib and Ic samples.
Acknowledgements This work is supported by Polish Committee for Scientific Research under grant no. PBZ/KBN013/T08/34.
References [1] R.D. Rawlings, Clinical Materials 14 (1993) 155. [2] P. Li, I. Kangasniemi, K. Groot, T. Kokubo, A.U. Yli-Urpo, Journal of Non-Crystalline Solids 168 (1994) 281.
[3] L.L. Hench, R.J. Splinter, T.K. Greenlee, W.C. Allen, Journal of Biomedical Research Symposium 2 (1971) 117. [4] L.L. Hench, R.J. Splinter, W.C. Allen, T.K. Greenlee, Journal of Biomedical Research 5 (1972) 117. [5] L.L. Hench, H.A. Paschall, Journal of Biomedical Research Symposium 4 (1973) 25. [6] G. Piotrowski, L.L. Hench, W.C. Allen, Journal of Biomedical Research 9 (1975) 47. [7] M. Handke, W. Mozgawa, M. Nocun´, Journal of Molecular Structure 450 (1998) 229. [8] M. Sitarz, M. Handke, W. Mozgawa, Spectrochimica Acta Part A 56 (2000) 1819. [9] E. Gorlich, K. Blaszczak, M. Handke, Mineralogica Polonica 14 (1983) 3.
Structural studies of the NaCaPO4 –SiO2 sol–gel derived materials M. Sitarza,*, M. Rokitaa, M. Handkea, E. Galuskinb a
University of Mining and Metallurgy (AGH), Faculty of Materials Science and Ceramics al Mickiewicza 30, 30 059 Krakow, Poland b University of Silesia, Museum of Earth, Department of Earth Science ul Be¸dzin´ska 60, 41-200 Sosnowiec, Poland Received 25 November 2002; accepted 16 December 2002
Abstract Structural studies of the NaCaPO4 – SiO2 materials have been carried out. Amorphous materials from this system, after controlled crystallization process, can be used as potential nanomaterials. Structural studies of nanomaterials are of fundamental importance in view their future applications. Materials of different [PO4]32/[SiO4]42 tetrahedra proportion have been prepared. Naþ and Ca2þ cations have compensated the negative charge of the lattice. Amorphous and crystalline materials have been obtained by sol – gel as well as conventional melting methods. The XRD phase identification has enabled amorphous and crystalline materials identification and suggests the separation of phosphorus and silicate crystalline phases. The obtained materials were examined using the electron scanning microscope and EDX spectrometer. Analysis of electron scanning microscope maps shows considerable inhomogeneity of crystalline samples. Fluctuations in ions distribution, in case of amorphous materials, have been noted too. DTA investigations have enabled to find the probable characteristic temperatures of glass crystallization. Detailed infrared spectroscopy measurements have been carried out. The spectra of obtained materials have been compared with the spectra of cristobalite. Spectroscopic studies confirm the inhomogeneity of materials. q 2003 Elsevier Science B.V. All rights reserved. Keywords: Phospho-silicate materials; IR spectra; Nanomaterials
1. Introduction Glassy and glassy-crystalline materials from the NaCaPO4 – SiO2 system are commonly known as biomaterials [1,2]. The first bioactive glasses from the SiO 2 – CaO – P 2O 5 system with different additions, capable to create the bonds with the tissue, were designed by Hench [3 –6]. Such glasses, * Corresponding author. Tel.: þ48-12-172232; fax: þ 48-12331593. E-mail address: [email protected] (M. Sitarz).
known as Bioglassw contain up to 55 mol% of SiO2, to 50 mol% of CaO and to 40 mol% of P2O5. To design new bio-glass or bioceramics materials, especially nanomaterials, it is necessary to experience their structure. In the present work the attempt of crystalline and amorphous materials of systematically changing contents of NaCaPO4 (0 – 50 mol%.) and SiO 2 (100 – 50 mol%.) was undertaken. The analysis of the amorphous materials structure is very difficult because of the lack of long-distance order. The main disadvantage is the uselessness
0022-2860/03/$ - see front matter q 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0022-2860(03)00113-3
490
M. Sitarz et al. / Journal of Molecular Structure 651–653 (2003) 489–498
of the X-ray methods in analyze of amorphous materials structure. On the other way the vibrational spectroscopy is the method sensitive on the shortrange order and it can be successfully used in this case. Obtaining of the glassy and crystalline NaCaPO4 – SiO2 materials and detail structure analyze was the main aim of the present work.
the resulting materials were made with a Bio-Rad FTS 60V spectrometer. Spectra were collected after 256 scans at 4 cm21 resolution. Samples were prepared by the standard KBr pellets method. Spectra decomposition has been carried out according to the method of Handke et al [7].
3. Results and discussion 2. Experimental The description of these kinds of materials, of very complicated composition, requires the systematic structural studies. It enables to investigate the structural changes with the change of chemical composition. The NaCaPO4 – SiO2 materials of changed NaCaPO4/SiO2 proportion (0 – 50 mol% NaCaPO4/100 – 50 mol% SiO2) have been selected (Table 1). The sol – gel method was selected to obtain the materials of the highest possible homogeneity. TEOS (SiO2), Ca(NO3)2·4H2O (CaO), Na3PO4·12H2O (Na2O) and H3PO4 (P2O5) were used to introduce particular oxides. The obtained gels were dried at room temperature (30 days) and then at the temperature of 60 8C. After drying process all the gels were heated at 1380 8C to obtain crystalline materials. The attempts of glassy samples obtaining on the way of progressive heating of gels were unsuccessful. Finally the gels were melting in platinum crucible in the temperature of 1700 8C and rapidly cooled on the cast iron plate. X-ray measurement of all samples were carried out using FPM Seifert XRD 7 with a step of 0,01 deg and collecting time—5 s. EDX spectra were measured on a JEOL 5400 scanning microscope with microprobe analyser LINK ISIS (Oxford Instrument). IR spectroscopic measurements of Table 1 Composition of the samples (mol%) Sample number
NaCaPO4 –SiO2 system
I Ia Ib Ic Id Ie
100% SiO2 90% SiO2, 10% NaCaPO4 80% SiO2, 20% NaCaPO4 70% SiO2, 30% NaCaPO4 60% SiO2, 40% NaCaPO4 50% SiO2, 50% NaCaPO4
The X-ray measurements of samples obtained by gels melting show that all samples are amorphous (the only broad, flat X-ray band in the region of 10– 308—2u). However, in case of the samples with the highest contents of NaCaPO4 (Id and Ie) there are some very weak peaks (of several cps intensity) on the X-ray patterns. The amorphous state of the samples was confirmed by the IR spectroscopy analysis in the FIR region. The lack of bands is the evidence of the lack of long-range order (amorphism of samples). In case of Id and Ie samples one can see some clear bands in the FIR region, what confirm some kind of long-range order (presence of crystalline phases) (Fig. 1). Scanning microscopy measurements, connected with X-ray microanalysis, complemented X-ray measurements. The analysis of glassy (samples Ia –Ic) and glasscrystalline (samples Id and Ie) materials reveals distinct liquation in all samples (Fig. 2). The most interesting results were obtained for the Ib and Ic samples. In case of mentioned samples the spherical inclusions have nanometric size. EDX measurements showed that inclusions contained almost only calcium silicate phase. In comparison with inclusions, the matrix is enriched with phosphorus, calcium and sodium. The amount of sodium, calcium and phosphorus increase with the increasing amount of NaCaPO4 in samples (Figs. 3 and 4). The multistage crystallization process was detected in case of samples Ib and Ic (Fig. 5) on the base of DTA results. This fact is clear in the light of mentioned microscopic results; there are at least two different ‘glassy phases’ in those materials and each phase should have different crystallization temperature. It is possible to obtain the glasscrystalline materials of planned composition and size of crystallites, for example obtaining the only,
M. Sitarz et al. / Journal of Molecular Structure 651–653 (2003) 489–498
491
Fig. 1. FIR spectra of glassy (I–Ic) and glass-crystalline (Id –Ie) samples.
defined crystal phase in the controlled crystallization process. Obtaining of glass-crystalline nanomaterials could be especially interested; the process seems to be possible in case of Ib and Ic samples. Planning of such a process needs detailed knowledge about material structure. The analysis of the structure of glass, which is the precursor of
glass – ceramic material, can be based on the spectroscopic studies. However, the direct interpretation of glass spectra is almost impossible, because they are complex and complicated. The interpretation can be realized by the comparison with analogous crystalline materials spectra. The statement of the amorphous samples MIR spectra has been presented on the Fig. 6.
492
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Fig. 2. SEM microphotograph of samples (Ia–Ie).
The characteristic broadening of bands, in comparison with the bands of crystalline materials, is clearly visible. However, some sharp bands are present on the Id and Ie sample spectra. This fact confirms the results of previous measurements; these materials contain some amount of crystalline phase. Performed spectroscopic studies of the crystalline NaCaPO4 – SiO2 materials and pure NaCaPO4 enabled for identification the bands connected with P – O and Si – O vibrations. The statement of MIR spectra of
obtained crystalline materials is shown on Fig. 7. With the increasing contents of NaCaPO4 a constant increase of the intensity of the bands due to P – O vibrations can be observed (Ia –Ie spectra; the bands at 574, 598, 960 cm21 and the group of bands in the region of 1020 – 1080 cm21). In the same time the decrease of the characteristic for cristobalite bands intensities (at 622, 795, 1200 cm21 and the group of bands in the region of 1020 – 1080 cm21; Si – O vibrations) is visible. In case of Id sample spectrum
M. Sitarz et al. / Journal of Molecular Structure 651–653 (2003) 489–498
Fig. 3. EDX spectra of Ia –Ie samples (inclusions).
493
494
M. Sitarz et al. / Journal of Molecular Structure 651–653 (2003) 489–498
Fig. 4. EDX spectra of Ia– Ie samples (matrix).
M. Sitarz et al. / Journal of Molecular Structure 651–653 (2003) 489–498
495
Fig. 5. DTA of Ib sample.
the two of mentioned bands, at 1199 and 622 cm21, are even invisible. The most characteristic for cristobalite band at 795 cm21 (due to bending vibrations of the silico– oxygen bridge [8]), shifts to the lower wavenumbers (with the decrease of intensity) in the Ia –Id series. It is characteristic that one can observe more intensive band in this region, on the spectrum of the Ie sample. The similar changes can be seen in case of the band at 487 cm21 due to bending Si – O – Si vibrations. These changes are caused by lowering amount of crystallizing cristobalite and in the same time, arising amount of tridymite. The bands characteristics for tridymite are analogous to these for cristobalite but they are located at little lower wavenumbers [9]. These results are compatible with X-ray diffraction results (Table 2.), which showed the constant decrease of crystallizing cristobalite in the Ia – Id series (and the lack of cristobalite in case of Ie sample) with the coincident increase of tridymite amount. The intensity and positions of the bands at about 790 and 480 cm 21 can be influenced by the crystallizing phospho-silicate Na2Ca4(PO4)2SiO4.
The comparison of amorphous materials spectra together with their crystal analogous spectra (Ib and Ic) has been presented on the Fig. 8. Despite of differences in bands intensity and width the similarity of spectra are clear. The kind of crystallizing phases in glass-crystalline samples Id and Ie (Fig. 6) was qualified as phosphate phase on the base of IR bands positions (the bands at 958, 597, 574 cm21 and the group of bands in the region of 1080 –1020 cm21). On the base of spectra similarities one can suppose that the short-range order in glasses will be in a close relation to the crystalline phases (Table 2). The amorphous materials (Ia – Ic) spectra decomposition into component bands enabled to state that mentioned materials have cristobalite-like structure.
4. Conclusion 1. The amorphism of obtained materials was confirmed using X-ray analysis and infrared spectroscopy in the FIR region. The analysis of FIR spectra suggests arrangement of domains.
496
M. Sitarz et al. / Journal of Molecular Structure 651–653 (2003) 489–498
Fig. 6. MIR spectra of glassy (I –Ic) or glass-crystalline (Id–Ie) samples.
2. Performed microscope measurements enable to observe distinct nanoliquation-samples IIb and IIc. 3. EDX measurements showed that the matrix, in comparison with inclusions, is enriched with phosphorus, calcium and sodium. 4. DTA measurements of glassy samples enable to estimate the region of glass devitrification as 800 –1000 8C, in case of IIb and IIc sample the process of devitrification is multistage. 5. MIR spectra of the series of NaCaPO4 – SiO2 materials were compared with the spectra of low
temperature cristobalite and NaCaPO4. The systematic increase of the intensity of bands due to phospho – oxygen vibrations with the decrease of SiO2 contents was observed. The bands due to P – O vibrations (574, 598, 960 and the group in the range of 1020 –1080 cm21) as well as Si – O vibrations (487, 622, 795, 1094 and 1200 cm21) were separated. In case of bands at c.a. 470 – 490 and 795 –790 cm21 the decrease of SiO2 contents causes initially decrease and then increase with simultaneous shift into lower wavenumbers is observed. It is connected with
M. Sitarz et al. / Journal of Molecular Structure 651–653 (2003) 489–498
497
Fig. 7. MIR spectra of crystalline (I–Id) samples. Table 2 X-ray phase analysis (crystalline samples)
disappearance of cristobalite phase (the bands at 622 and 1200 cm21 disappear too) and appearance of phospho –silicate phase. 6. The comparison of amorphous and crystalline materials spectra enabled to show the similarity in their structures. 7. Mathematical process of decomposition enabled to state that these materials (samples Ia – Ic) have cristobalite-like structure.
SiO2 (cristobalite) I Ia Ib Ic Id Ie
*** *** ** ** **
NaCaPO4
* * * ** **
SiO2 (tridymite)
* ** ** *
Na2Ca4(PO4)2·SiO4
*
Estimated amount of phases: *** a predominated phase, ** a phase of considerable amount, * a small amount of phase.
498
M. Sitarz et al. / Journal of Molecular Structure 651–653 (2003) 489–498
Fig. 8. The comparison of the spectra of crystalline and glassy Ib and Ic samples.
Acknowledgements This work is supported by Polish Committee for Scientific Research under grant no. PBZ/KBN013/T08/34.
References [1] R.D. Rawlings, Clinical Materials 14 (1993) 155. [2] P. Li, I. Kangasniemi, K. Groot, T. Kokubo, A.U. Yli-Urpo, Journal of Non-Crystalline Solids 168 (1994) 281.
[3] L.L. Hench, R.J. Splinter, T.K. Greenlee, W.C. Allen, Journal of Biomedical Research Symposium 2 (1971) 117. [4] L.L. Hench, R.J. Splinter, W.C. Allen, T.K. Greenlee, Journal of Biomedical Research 5 (1972) 117. [5] L.L. Hench, H.A. Paschall, Journal of Biomedical Research Symposium 4 (1973) 25. [6] G. Piotrowski, L.L. Hench, W.C. Allen, Journal of Biomedical Research 9 (1975) 47. [7] M. Handke, W. Mozgawa, M. Nocun´, Journal of Molecular Structure 450 (1998) 229. [8] M. Sitarz, M. Handke, W. Mozgawa, Spectrochimica Acta Part A 56 (2000) 1819. [9] E. Gorlich, K. Blaszczak, M. Handke, Mineralogica Polonica 14 (1983) 3.