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Structure and microstructure of the glasses from NaCaPO4–SiO2 and NaCaPO4–SiO2–AlPO4 systems
Journal of Molecular Structure xxx (2015) 1e16
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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Structure and microstructure of the glasses from NaCaPO4eSiO2 and NaCaPO4eSiO2eAlPO4 systems A. Wajda a, *, K. Bułat a, b, M. Sitarz a a b
AGH University of Science and Technology, Faculty of Materials Science and Ceramics, 30-059, Krakow, Al. Mickiewicza 30, Poland Jagiellonian University, Faculty of Chemistry, 30-060, Krakow, Ingardena 3, Poland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 10 November 2015 Received in revised form 30 November 2015 Accepted 1 December 2015 Available online xxx
Structure and microstructure of silico-phosphate glasses belong to NaXPO4-SiO2 and NaXPO4-SiO2-AlPO4 (where X ¼ Ca or/and Mg) systems were investigated. Scanning electron microscopic studies combined with EDX were made it possible to show the occurrence of phase separation in the obtained materials. It was found that alumina has a homogenising effect on the microstructure of silico-phosphate glasses. Addition of a small amount of alumina (5 mol. % of AlPO4) causes the chemical compositions inversion of the matrix and the inclusions. Structural investigations of the obtained glasses as well as of the corresponding crystalline materials showed that the studied glasses exhibit domain composition. Structure of the domains is close to that of the corresponding crystalline phases. Spectroscopic investigations involving spectra decomposition into component bands were made it possible to establish the homogenising effect of aluminium on the structure of silicate-phosphate glasses. Presence of alumina leads to elimination of P]O bonds as well as replacement of SieOeP by the AleOeP ones. © 2015 Elsevier B.V. All rights reserved.
Keywords: Silico-phosphate glasses Glass structure Glass microstructure Biomaterials FTIR spectroscopy
1. Introduction Phosphorous e containing glasses, due to their specific properties (relatively large thermal expansion coefficients, low optical dispersion, low glass transition temperatures etc.) find the growing field of applications [1e5]. Glasses from NaCaPO4eSiO2 system are well-known bioactive materials, which have an ability to form strong chemical bonds with living tissue [e.g. Refs. [6e16]]. The use of glass as a biomaterial allows to take advantage of the amorphous state. As it can, for example, obtain practically any shape, control properties by adequate choice of chemical composition, it has the possibility to apply various processing methods as well as isotropic properties. The main disadvantages of these materials are their fragility and low chemical stability. Hence, their practical applications in implants exposed to high mechanical loads are limited. Therefore, the continuous research aims to improve the abovementioned properties of glassy biomaterials. It can be achieved by the introduction of appropriate ions into their structure (e.g. Al3þ, B3þ, Mg2þ and others) and/or by their partial devitrification. Partial glass devitrification allows to obtain glass-crystalline
* Corresponding author. E-mail address: [email protected] (A. Wajda).
materials, which combine advantages of glassy (above-mentioned) and crystalline states (primarily mechanical strength) [e.g. Refs. [17,18]. However, appearance and uncontrolled growth of crystalline phase can usually lead to the rapid decrease of the glass bioactivity [19] or even to the conversion of bioactive glass into inert material [20]. While taking into consideration the direct glass crystallization (apart from thermal properties) the understanding of the glassy precursor structure is crucial as glass devitrification is based on domains reorientation during heating [21]. The domains shall be understood as a kind of ‘crystallization nuclei’, which may determine the type of crystallizing phase [22]. Therefore, it is necessary to identify the domains structure as it allows to predict the type of crystallizing phase during crystallization process. Considering the above, we have decided to introduce magnesium and aluminum ions into the silico-phosphate glasses structure from NaCaPO4eSiO2 system. The literature data indicates that presence of these ions in the glass structure improves the mechanical properties and chemical stability of the glass [e.g. Refs. [23,24]. The main aim of this study was the most accurate description of microstructure and structure of silico-phosphate glasses from NaXPO4eSiO2 and NaXPO4eSiO2eAlPO4 systems (where X ¼ Ca and/or Mg). The knowledge of microstructure and structure of the glass provides the opportunity to correctly plan direct
http://dx.doi.org/10.1016/j.molstruc.2015.12.003 0022-2860/© 2015 Elsevier B.V. All rights reserved.
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A. Wajda et al. / Journal of Molecular Structure xxx (2015) 1e16
crystallization process in order to obtain glass-crystalline materials with premeditated phase composition and crystallite size. Consequently, it is possible to obtain the material with desired functional properties.
component bands to the starting spectra (low value of c2 parameter) was reached.
2. Experimental
To confirm the amorphousness of the obtained materials XRD and FIR studies were performed. There were no sharp bands in the FIR spectra and any reflections in the X-ray diffraction patterns, what unequivocally confirm the amorphous state of the prepared materials. The opacity of the obtained materials must arise due to liquation phenomenon. The same result has been confirmed in our previous research on the glass microstructure from NaCaPO4eSiO2 system [27]. It was found out that liquation phenomenon occurs e the clear spherical inclusions dispersed in the rest of the matrix. It was also demonstrated that small addition of aluminum ions (5mol.% AlPO4) to glass from NaCaPO4eSiO2 system leads to homogenization of their microstructure [28]. Moreover, the addition of aluminum ions causes rapid change in the chemical composition of both the matrix and the inclusions (EDX) [27,28]. In the case of glasses from NaCaPO4eSiO2eAlPO4 system with a low content of NaCaPO4 (to 25mol.%), the spherical inclusions are calcium phosphate phase, but the matrix is almost pure silicate phase e opposite to the glasses from the NaCaPO4eSiO2 system. The increase of NaCaPO4 to more than 25mol.% leads to re-inversion of the matrix and inclusions composition e the inclusions become silico phase and the matrix calcium-silico-phosphate phase [29,30]. The morphology and composition of the glasses were analysed by scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (EDX). This study shows that lack of transparency of the obtained glasses is effectively connected with the liquation phenomenon. The analysis of SEM images of glasses from NaCaPO4eSiO2 and NaCaPO4eSiO2eAlPO4 systems [27,28], together with glasses after partial (Na(Ca,Mg)PO4eSiO2 (Fig. 1a) and Na(Ca,Mg)PO4eSiO2eAlPO4 (Fig. 1b) systems) and total (NaMgPO4eSiO2 (Fig. 1c) and NaMgPO4eSiO2eAlPO4 (Fig. 1d) systems) replacement of calcium ions by magnesium ions allows to determine the effect of magnesium ions on the microstructure of the selected silico-phosphate glasses. Complete replacement of calcium ions by magnesium ions in the structure of glasses from the NaCaPO4eSiO2 [27,28] system causes the increase of the inclusions diameters (Fig. 1c). The even larger size of the inclusions was observed after the introduction of two cations to the glass composition (Fig. 1a). It can be also seen that the microstructure of the glass containing magnesium ions is heterogeneous (a large number of inclusions with different sizes). This is due to the inhomogeneous liquation, which makes in both the matrix and the inclusions subsequent phase separation (particularly evident in the samples from the MgCa series e Fig. 1c). The addition of aluminum ions into the structure of glasses containing Mg2þ leads to
Glasses (and their composition) selected for the studies are given in Table 1. The composition was selected to compensate the negative charge of [PO4]3- and [SiO4]4- by couples of Naþ and X2þ cations. The standard solegel method was chosen to obtain the materials of the highest possible homogeneity. TEOS (SiO2), Ca(NO3).24H2O (CaO), Na3PO.412H2O (Na2O), Mg(NO3).26H2O, Al(NO3).33H2O (Al2O3) 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 80 C. Solegel method was selected to provide the highest possible homogeneity and to reduce the volatility of the individual components. To obtain the glassy samples the gels were melted in platinum crucible in the temperature of 1730 C and rapidly cooled on the cast iron plate. The gels were heated with 5 C/min heating speed till 1730 C and then stabilized in the same temperature for 2h. All obtained glasses were not transparent, what indicated that liquation occurred or the materials were not completely amorphous. To obtain crystalline materials the dried gels were heated at 1380 C. Scanning electron microscopy (SEM) of the materials was conducted using FEI Nova NanoSEM 200 scanning microscope and the measurements were performed under low vacuum. X-Ray powder diffraction studies were performed using Philips X'Pert Pro MD diffractometer. The used radiation was Cu Ka1 line monochomatized by Ge(111) monochromator. Standard BraggBrentano geometry with Q-2Q setup was applied (0.008 step size and 5o-90 2Q range). IR spectroscopic investigations (MIR e middle infrared and FIR e far infrared) of the materials were made with a Bio-Rad FTS 60V spectrometer. MIR: transmission technique, samples as KBr pellets. Spectra were collected after 256 scans at 4 cm1 resolution. FIR: polyethylene pellets. Spectra were collected after 2000 scans at 4 cm1 resolution. Spectra deconvolution was carried out according to the method of Handke et al. and a minimization of component bands was applied as the basic rule [25,26]. For the deconvolution Spectra Calc™ software was used, which provides the best fitting of complex band envelopes with the curves of the predetermined belltype functions (mixed Gaussian/Lorentians). The process of decompositions was carried out until a high fitting degree of the
3. Results and discussion
Table 1 Composition of the selected glasses [mol. %]. MgCa series
Na(Mg,Ca)PO4 e SiO2 system
1MgCa 2MgCa 3MgCa 4MgCa 5MgCa
90%SiO2 80%SiO2 70%SiO2 60%SiO2 50%SiO2
Mg Series
NaMgPO4 e SiO2 system
1 2 3 4 5
90%SiO2 80%SiO2 70%SiO2 60%SiO2 50%SiO2
Mg Mg Mg Mg Mg
. . . . .
. . . . .
10%Na(Mg,Ca)PO4 20%Na(Mg,Ca)PO4 30%Na(Mg,Ca)PO4 40%Na(Mg,Ca)PO4 50%Na(Mg,Ca)PO4
10%NaMgPO4 20%NaMgPO4 30%NaMgPO4 40%NaMgPO4 50%NaMgPO4
AlMgCa series
Na(Mg,Ca)PO4 e SiO2 e AlPO4 system
1AlMgCa 2AlMgCa 3AlMgCa 4AlMgCa 5AlMgCa
90%SiO2 80%SiO2 70%SiO2 60%SiO2 50%SiO2
AlMg Series
NaMgPO4 e SiO2 e AlPO4 system
1AlMg 2AlMg 3AlMg 4AlMg 5AlMg
90%SiO2 80%SiO2 70%SiO2 60%SiO2 50%SiO2
. . . . .
. . . . .
5%Na(Mg,Ca)PO4 . 5%AlPO4 15%Na(Mg,Ca)PO4 . 5%AlPO4 25%Na(Mg,Ca)PO4 . 5%AlPO4 35%Na(Mg,Ca)PO4 . 5%AlPO4 45%Na(Mg,Ca)PO4 . 5%AlPO4
5%NaMgPO4 . 5%AlPO4 15%NaMgPO4 . 5%AlPO4 25%NaMgPO4 . 5%AlPO4 35%NaMgPO4 . 5%AlPO4 45%NaMgPO4 . 5%AlPO4
Please cite this article in press as: A. Wajda, et al., Structure and microstructure of the glasses from NaCaPO4eSiO2 and NaCaPO4eSiO2eAlPO4 systems, Journal of Molecular Structure (2015), http://dx.doi.org/10.1016/j.molstruc.2015.12.003
A. Wajda et al. / Journal of Molecular Structure xxx (2015) 1e16
homogenization of the microstructure e it becomes more homogeneous. Comparison of the SEM photographs of the glasses from NaMgPO4eSiO2eAlPO4 (Fig. 1d) and Na(Mg,Ca)PO4eSiO2eAlPO4 (Fig. 1b) systems with the photographs of glasses from NaCaPO4eSiO2eAlPO4 system [27,28] demonstrates similarity of the microstructure of this glasses, the only difference is that presence of magnesium ions causes increase in inclusions size. In order to determine the effect of magnesium ions on the chemical composition of the matrix and inclusions, glasses of each series were studied by EDX (Figs. 2 and 3). The complete (Figs. 2 and 3c) and partial (Figs. 2 and 3a) substitution of calcium ions by magnesium ions does not cause significant changes in the chemical composition of the inclusions and matrix in the glasses without aluminum ions (except of course the conversion of calcium ions to magnesium ions). The matrix in this glasses is silico-phosphate phase and with the increase of NaMgPO4 (Fig. 2c) or Na(Mg,Ca) PO4 (Fig. 2a), the matrix is increasingly enriched with phosphorus ions. The presence of a significant amount of magnesium, sodium and/or calcium ions is also observed. On the other hand, the inclusions in all glasses are nearly pure silica phase with a very small amount of magnesium, sodium and/or calcium ions (Fig. 3c and a). In glasses from NaMgPO4eSiO2eAlPO4 (Figs. 2 and 3d), Na(Mg,Ca)PO4eSiO2eAlPO4 (Figs. 2 and 3b) and NaCaPO4eSiO2eAlPO4 [27,28] systems the chemical composition inversion of the matrix and inclusions can be observed. The inclusions from NaMgPO4eSiO2eAlPO4 (Fig. 3d) system with the lower content of NaMgCaPO4 (less than 35mol.%) are almost pure phosphate phase, whereas the matrix (Fig. 2d) is just pure silica phase. The chemical composition inversion of the matrix and inclusions takes place only above 35mol.% of NaMgPO4. The matrix becomes phosphate phase and the inclusions become silica phase (Figs. 2 and 3d). The same situation occurs in the glasses of the Na(Mg,Ca)PO4eSiO2eAlPO4 system (Figs. 2 and 3b). The EDX spectra comparison of these glasses systems with the glasses from NaCaPO4eSiO2eAlPO4 [27,28] clearly indicates that the total or partial substitution of calcium by magnesium ions moves the boundary of the chemical composition inversion of the matrix and inclusions. The inversion in the glasses from NaCaPO4eSiO2eAlPO4 system appears only above 25% mol. of NaCaPO4 [27,28], while in the case of glasses from NaMgPO4eSiO2eAlPO4 (Figs. 2 and 3d) and Na(Mg,Ca)PO4eSiO2eAlPO4 (Figs. 2 and 3b) systems after exceeding 35mol.% of NaMgPO4 or Na(Mg,Ca)PO4. While considering glass-crystalline biomaterials obtainment, the liquation phenomenon seems to be beneficial as it may help to limit the problem associated with the uncontrolled growth of crystalline phases during devitrification. Phase boundary between inclusions and matrix should be a barrier, which can limit growth of crystals. Different chemical composition of inclusions and matrix should cause e upon the appropriate thermal treatment e the separate crystallization of the matrix or inclusions. It can be assumed that by carrying out direct crystallization process aimed at crystallizing only inclusions, the growth of crystallizing phase will be limited to the inclusions size. As it was mentioned, in the planning of direct crystallization process of the glass, precise knowledge of the glass-crystalline precursor structure is required. Due to the lack of long-range order in glasses, only spectroscopic methods provide information about their internal structure. The understanding of the glasses structures with complex compositions containing various network modifiers (Naþ, Kþ, Ca2þ, Mg2þ) and various glass-forming ions (Si4þ, P5þ, Al3þ) firstly requires to carry out detailed spectroscopic studies of glasses and their crystalline counterparts. It is generally accepted that in areas with short-range order of glasses, the structure corresponds with their crystalline counterparts [e.g. Refs. [31,32]. Hence, in order to proper MIR spectra interpretation, it
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is necessary to compare the spectra of the glasses with those corresponding to relevant crystalline materials and decompose the spectra into component bands. The noticed homogenizing influence of aluminum ions on the texture of silico-phosphate glasses was also observed in the case of crystalline materials of the NaCaPO4eSiO2 system [33]. The introduction of 5% mol. AlPO4 to these materials, significantly reduces the amount of crystallizing phases e in all MIR spectra of crystalline materials from NaCaPO4eSiO2eAlPO4 system fewer amount of bands can be seen in comparison with MIR spectra of the materials from NaCaPO4eSiO2 system [33]. In the MIR spectra of aluminum containing devitrified glasses with a high amount of SiO2 virtually are invisible characteristic bands of the phosphate phase at 597 and 574 cm1 (MIR spectrum NaCaPO4). These bands become visible after exceeding 25 mol. % of NaCaPO4 - after chemical composition inversion of matrix and inclusions. Our previous structural studies revealed the existence of solid solutions AlPO4 in SiO2 until 20e25 mol. % content of AlPO4 [34]. It was ascertained that a similar range of solid solutions are found in the NaCaPO4eSiO2eAlPO4 system, but after exceeding 20e30 mol.% content of NaCaPO4 phosphate phase separation takes place [27,28]. The studies on model glasses and crystalline materials help to ensure that in the case of materials without aluminum ions, we can discuss total separation of the silicate and phosphate phases. However, by the adding aluminum ions to the materials from NaCaPO4eSiO2 system phosphate phases become “dissolved” [33]. Figs. 4e7 present MIR spectra of the glasses and their crystalline counterparts from systems: NaMgPO4eSiO2 (Fig. 4), Na(Mg,Ca) PO4eSiO2 (Fig. 5), NaMgPO4eSiO2eAlPO4 (Fig. 6) and Na(Mg,Ca) PO4eSiO2eAlPO4 (Fig. 7). The spectra have three characteristic bands at: around 480 cm1, 850 - 600 cm1 and in the range of 1200e900 cm1 (see Table. 2). The band at 480 cm1 is characteristic for bending OeSieO vibrations. The bands in the range of 850e600 cm1 are assigned to symmetric stretching SieOeSi vibrations [4,5,32]. For silico e phosphate glasses, in this range also bands connected with bending OePeO vibrations occur [4,5,34]. The bands in the range of 1200e900 cm1 are characteristic for asymmetric stretching SieO(Si) (bridging bonds) and SieO- (nonbridging bonds) vibrations. In addition, in the same range the bands connected with stretching vibrations of PeO and AleO (coordination number of aluminum ions ¼ 4) and bands related to stretching vibrations of Si]O and P]O are visible [4,5,35,36]. High MIR spectra similarity of the obtained glasses and crystalline materials allows to assume that the glasses domains have the same structure as in the corresponding crystalline materials [33]. Such assumption is equivalent to the conclusion that in the studied glasses, domains with various types of arrangement occur at the same time. It is obvious that in the liquation glasses such domains exist because matrix and inclusions have a different chemical composition and certainly have a different character of local arrangement. MIR spectra analysis of the glasses and the corresponding crystalline materials of NaMgPO4eSiO2 system (Fig. 4) allows to determine that the complete substitution of calcium ions by magnesium ions causes homogenization of these glasses structure. The domains from 1 Mg to 2 Mg glasses are only crystobalite type. The bands at 598 and 574 cm1 related to phosphate phase become visible for amorphous and crystalline materials with a lower amount of SiO2 (3 Mg e 5 Mg). The partial substitution of calcium ions by magnesium ions decreases homogenizing influence of magnesium ions on the silicophosphate glasses structure. Only one the MIR spectrum of devitrified glasses with the lowest content of Na(Mg,Ca)PO4 (Fig. 5), the typical bands of phosphate phase cannot be observed. A large number of bands, which appear in the spectra of crystalline
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A. Wajda et al. / Journal of Molecular Structure xxx (2015) 1e16 Fig. 1. a. SEM microphotographs of the glasses from Na(Mg,Ca)PO4eSiO2 system. b. SEM microphotographs of the glasses from Na(Mg,Ca)PO4eSiO2eAlPO4 system. c. SEM microphotographs of the glasses from NaMgPO4eSiO2 system. d. SEM microphotographs of the glasses from NaMgPO4eSiO2eAlPO4 system.
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Fig. 1. (continued).
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A. Wajda et al. / Journal of Molecular Structure xxx (2015) 1e16 Fig. 2. a. EDX spectra of the glasses from Na(Mg,Ca)PO4eSiO2 system (matrix). b. EDX spectra of the glasses from Na(Mg,Ca)PO4eSiO2eAlPO4 system (matrix). c. EDX spectra of the glasses from NaMgPO4eSiO2 system (matrix). d. EDX spectra of the glasses from NaMgPO4eSiO2eAlPO4 system (matrix).
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Fig. 2. (continued).
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Fig. 3. a. EDX spectra of the glasses from Na(Mg,Ca)PO4eSiO2 system (inclusions). b. EDX spectra of the glasses from Na(Mg,Ca)PO4eSiO2eAlPO4 system (inclusions). c. EDX spectra of the glasses from NaMgPO4eSiO2 system (inclusions). d. EDX spectra of the glasses from NaMgPO4eSiO2eAlPO4 system (inclusions).
8 A. Wajda et al. / Journal of Molecular Structure xxx (2015) 1e16
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Fig. 3. (continued).
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Fig. 4. MIR spectra of glassy and crystalline samples form NaMgPO4eSiO2 system.
materials is associated with the formation of calcium and magnesium phosphate. It can be concluded that the domains in these glasses are of various types. The modification of glasses structure from NaMgPO4eSiO2 and Na(Mg,Ca)PO4eSiO2 systems by aluminum ions increases its homogeneity. Based on the MIR spectra of glasses and their crystalline counterparts from those systems (Figs. 4 and 5), it can be noticed that there are a smaller number of bands associated with the
phosphate phases. It is particularly evident in the MIR spectra of crystalline materials containing both calcium and magnesium ions - typical phosphate bands become apparent for samples: 4AlMgCa and 5AlMgCa. A large half-width bands makes MIR spectra of all studied glasses to be almost practically the same (except for slight shifts bands) (Figs. 4e7). Effect of magnesium and aluminum ions in the structure of silico-phosphate glasses is visible only after the
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Fig. 5. MIR spectra of glassy and crystalline samples from Na(Mg,Ca)PO4eSiO2 system.
decomposition of the glass MIR spectra into component bands (Figs. 8 and 9). The analysis of these MIR spectra decompositions of glasses containing aluminum ions (Fig. 9) shows that there are fewer bands. In addition, the introduction of aluminum ions into the glasses structure causes a rapid decrease of the bands intensity connected with structural defects, i.e. the bands associated with the vibrations: Si]O, P]O (1180e1232 cm1) and SieO-(Naþ,Ca2þ) (944e961 cm1). With simultaneous intensity increase of bands which are characteristic for stretching vibrations of SieO(Si),
SieO(P) and SieO(Al). This is due to the replacement of SieOeP vibrations by AleOeP ones e connection the tetrahedrons of [PO4]3- and [SiO4]4 by tetrahedrons [AlO4]5- [37]. To obtain glass-crystalline materials, besides the understanding of the microstructure and glass structure, it is necessary to know its thermal parameters, especially temperature of devitrification (TD) at which individual phases crystallize. For this purpose, DSC studies of selected glasses (NaMgPO4eSiO2 (Fig. 10) and Na(Ca,Mg) PO4eSiO2 (Fig. 11)) were carried out. The interpretation of the
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Fig. 6. MIR spectra of glassy and crystalline samples from NaMgPO4eSiO2eAlPO4 system.
presented results of glasses thermal studies is very complicated. The both of DCS curves have four exothermal peaks, what proves that four different phases crystallize. This is due to ascertained heterogeneity of glass microstructure and structure of matrix and inclusions e the presence of domains of different nature [38]. The liquation is heterogeneous and in both inclusions and matrix, phase separation are observed, what may explain the existence of several exothermal effects. The introduction of aluminum ions into the glasses effects in that crystallization running in two stages. The DSC
curves present exothermal peaks at 713 C (4AlMgCa e Fig. 12) and 752 C (4AlMg e Fig. 13) related to matrix crystallization and 950 C (4AlMgCa), 953 C (4AlMg) related to inclusions crystallization. Such weak exothermal peaks associated with the inclusions crystallization are the consequence of a homogenizing influence of aluminum ions on the microstructure and the structure of silicophosphate glasses. The introduction of Al3þ causes noticeable reduction of inclusions amounts. Probably there are not enough of them to see visible exothermal peak on DCS curve, which could be
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Fig. 7. MIR spectra of glassy and crystalline samples from Na(Mg,Ca)PO4eSiO2eAlPO4 system.
connected with inclusions crystallization. 4. Conclusions 1. Partial or complete substitution of calcium ions by magnesium ions in the structure of silico-phosphate glasses from NaCaPO4eSiO2 system leads to an increase of the inclusions sizes and heterogeneity of liquation e in the matrix and the inclusions appear phase separations. Additional introduction of aluminum
ions causes rapid homogenization of the microstructure (SEM). 2. The chemical analysis (EDX) of the glasses from NaMgPO4eSiO2eAlPO4 and Na(Mg,Ca)PO4eSiO2eAlPO4 systems indicated chemical composition inversion of the matrix and inclusions. The inversion takes place after exceeding 35 mol.% of NaMgPO4 or NaMgPO4eSiO2. It means that introduction of magnesium ions moves the boundary of the chemical composition inversion of the matrix and inclusions (to compare to the glasses from NaCaPO4eSiO2eAlPO4 system e 25% NaCaPO4). It can be concluded that
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Table 2 Bands assignment of MIR spectra of silicophosphate glasses [4,5,27,29]. Group of bands
Kind of vibrations
480 cm1 850e600 cm1 1200e900 cm1
Bending OeSieO Symmetric stretching SieOeSi and OePeO Asymmetric stretching SieO(Si,Al) (bridging bonds), SieO- (non-bridging bonds), stretching PeO, stretching Si]O and P]O
the introduction of magnesium ions in place of calcium ions in the studied systems expands the formation range of the solid solutions. 3. Based on spectroscopic study (MIR) it was shown that complete substitution of calcium ions by magnesium ions causes glasses structure homogenization. However, partial (50/50) substitution of calcium ions by magnesium ions decrease the
homogenizing influence of magnesium ions on the silicophosphate glasses structure. It was also demonstrated that the domains in these glasses are of various types. The introduction of additional aluminum ions into the glass structure significantly increases its homogeneity. 4. Decomposition of the selected MIR spectra into component
Fig. 8. Decomposition of the MIR spectrum of 3MgCa glass.
Fig. 9. Decomposition of the MIR spectrum of 3AlMgCa glass.
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A. Wajda et al. / Journal of Molecular Structure xxx (2015) 1e16
Fig. 10. DSC of 3Mg glass.
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Fig. 13. DSC of 4AlMg glass.
crystalline materials by direct crystallization process. These materials can have amorphous matrix and crystalline inclusions or vice versa. Considering the chemical composition inversion of inclusions and matrix in the glasses containing aluminum ions, the studied glass are very promising precursors to a variety of glasscrystalline material. Acknowledgements This work was supported by NCN project ‘Functional layers of black glasses based on ladder-like silsesquioxanes 2014/15/B/ST8/ 0282’. References
Fig. 11. DSC of 3MgCa glass.
Fig. 12. DSC of 4AlMgCa glass.
bands showed that the homogenizing effect of the aluminum ions on the glass structure results from the replacement of SieOeP bonds by AleOeP, what means that the tetrahedrons [PO4]3- and [SiO4]4- are connected by tetrahedrons [AlO4]5-. 5. Thermal analysis (DSC) indicated that crystallization of all studied glasses is multistage - the matrix and inclusions crystallize separately. It can be concluded that it is possible to obtain glass-
[1] D.B. Dingwell, R. Knoche, S.L. Webb, Eur. J. Min. 5 (1993) 133. [2] L.L. Hench, J. Am. Ceram. Soc. 74 (1991) 1487. [3] G. Volksch, T. Hoche, I. Szabo, W. Holand, Glas. Ber. Glass Sci. Technol. C71 (1998) 500. [4] A.M. Abdelghany, H.A. ElBatal, J. Mol. Struct. 1024 (2012) 47e53. [5] A.M. Abdelghany, H.A. ElBatal, J. Mol. Struct. 1067 (2014) 138e146. [6] L.L. Hench, J. Am. Ceram. Soc. 74 (1991) 1487e1510. [7] R.D. Rawlings, Clin. Mater 14 (1993) 155e179. [8] P. Li, I. Kangasniemi, K. Groot, T. Kokubo, A.U. Yli-Urpo, J. Non Cryst. Solids 168 (1994) 281e286. [9] L.L. Hench, R.J. Splinter, T.K. Greenlee, W.C. Allen, J. Biom. Res. Symp 2 (1971) 117e141. [10] L.L. Hench, H.A. Paschall, J. Biom. Res. Symp. 4 (1973) 25e42. [11] G. Piotrowski, L.L. Hench, W.C. Allen, J. Biom. Res. 9 (1975) 47e61. [12] R.G. Hill, A. Stamboulis, R.V. Law, A. Clifford, M.R. Towler, C. Crowley, J. Non Cryst. Solids 336 (2004) 223. [13] G. Lusvardi, G. Malavasi, L. Menabue, M.C. Menziani, A. Pedone, U. Segre, J. Eur. Ceram. Soc. 27 (2007) 499. [14] G. Lusvardi, G. Malavasi, L. Menabue, V. Aina, C. Morterra, Acta Biomater. 5 (2009) 3548. [15] D.S. Brauer, M. Mneimne, R.G. Hill, J. Non Cryst. Solids 357 (2011) 3328. [16] A. Goel, R.R. Rajagopal, J.M.F. Ferreira, Acta Biomater. 7 (2011) 4071. [17] W. Cao, L.L. Hench, Bioact. Mater. Ceram. Int. 22 (1996) 493e507. [18] W. Bonfield, M. Wang, K.E. Tanner, Acta Mater. 46 (1998) 2509e2518. [19] O.P. Filho, G. Torre, L.L. Hench, J. Bio. Mater. Res. 30 (1996) 509e514. [20] P. Li, F. Zhang, T. Kokubo, J. Mater. Sci. Mater. Med. 3 (1992) 452e456. € rlich, Glassy State, AGH, 155AGH Publisher, Cracow, 1989 in Polish. [21] E. Go [22] M. Sitarz, M. Szumera, J. Therm. Anal. Cal. 91 (2008) 255e260. [23] U. Gross, V. Strunz, J. Biomed. Res. 19 (1985) 251e271. J. Mol. Struct. [24] O.H. Andersson, K.H. Karlsson, K. Kagasniemi, A. Yli-Urpo, Glas. Ber. 61 (1988) 300e305. [25] A.M. Abdelghany, Silicon 2 (2010) 179e184. [26] M. Handke, W. Mozgawa, M. Nocun, J. Mol. Struct. 325 (1998) 129e136. [27] M. Handke, M. Sitarz, M. Rokita, E.W. Galuskin, J. Mol. Struct. 651e653 (2003) 39e54. [28] M. Sitarz, M. Rokita, M. Handke, E.W. Galuskin, J. Mol. Struct. 651e653 (2003) 489e498. [29] M. Sitarz, J. Mol. Struct. 887 (2008) 237e248. [30] M. Sitarz, Spectrochim. Acta Part A 79 (2011) 739e742. [31] S. Brawer, Phys. Rev. B11 (1975) 3173e3194.
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[32] M. Sitarz, Vibrational Spectroscopy of Crystalline and Amorphous Silicates Containing Rings of Various Numbers of Members, Ph.D. Thesis, AGH University of Science and Technology, 1998. [33] M. Sitarz, M. Rokita, M. Handke, J. Mol. Struct. 614 (2002) 289e295. [34] M. Handke, M. Rokita, W. Mozgawa, Vib. Spectrosc. 19 (1999) 419e423.
[35] M. Sitarz, Z. Fojud, Z. Olejniczak, J. Mol. Struct. 924e926 (2009) 107e110. [36] W. Jastrze˛ bski, M. Sitarz, M. Rokita, K. Bułat, Spectrochim. Acta Part A 79 (2011) 722e727. [37] L. Stoch, Glass Phys. Chem. 27 (2001) 167e174. [38] M. Sitarz, K. Bułat, M. Szumera, J. Therm. Anal. Calorim. 109 (2012) 577.
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Structure and microstructure of the glasses from NaCaPO4eSiO2 and NaCaPO4eSiO2eAlPO4 systems A. Wajda a, *, K. Bułat a, b, M. Sitarz a a b
AGH University of Science and Technology, Faculty of Materials Science and Ceramics, 30-059, Krakow, Al. Mickiewicza 30, Poland Jagiellonian University, Faculty of Chemistry, 30-060, Krakow, Ingardena 3, Poland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 10 November 2015 Received in revised form 30 November 2015 Accepted 1 December 2015 Available online xxx
Structure and microstructure of silico-phosphate glasses belong to NaXPO4-SiO2 and NaXPO4-SiO2-AlPO4 (where X ¼ Ca or/and Mg) systems were investigated. Scanning electron microscopic studies combined with EDX were made it possible to show the occurrence of phase separation in the obtained materials. It was found that alumina has a homogenising effect on the microstructure of silico-phosphate glasses. Addition of a small amount of alumina (5 mol. % of AlPO4) causes the chemical compositions inversion of the matrix and the inclusions. Structural investigations of the obtained glasses as well as of the corresponding crystalline materials showed that the studied glasses exhibit domain composition. Structure of the domains is close to that of the corresponding crystalline phases. Spectroscopic investigations involving spectra decomposition into component bands were made it possible to establish the homogenising effect of aluminium on the structure of silicate-phosphate glasses. Presence of alumina leads to elimination of P]O bonds as well as replacement of SieOeP by the AleOeP ones. © 2015 Elsevier B.V. All rights reserved.
Keywords: Silico-phosphate glasses Glass structure Glass microstructure Biomaterials FTIR spectroscopy
1. Introduction Phosphorous e containing glasses, due to their specific properties (relatively large thermal expansion coefficients, low optical dispersion, low glass transition temperatures etc.) find the growing field of applications [1e5]. Glasses from NaCaPO4eSiO2 system are well-known bioactive materials, which have an ability to form strong chemical bonds with living tissue [e.g. Refs. [6e16]]. The use of glass as a biomaterial allows to take advantage of the amorphous state. As it can, for example, obtain practically any shape, control properties by adequate choice of chemical composition, it has the possibility to apply various processing methods as well as isotropic properties. The main disadvantages of these materials are their fragility and low chemical stability. Hence, their practical applications in implants exposed to high mechanical loads are limited. Therefore, the continuous research aims to improve the abovementioned properties of glassy biomaterials. It can be achieved by the introduction of appropriate ions into their structure (e.g. Al3þ, B3þ, Mg2þ and others) and/or by their partial devitrification. Partial glass devitrification allows to obtain glass-crystalline
* Corresponding author. E-mail address: [email protected] (A. Wajda).
materials, which combine advantages of glassy (above-mentioned) and crystalline states (primarily mechanical strength) [e.g. Refs. [17,18]. However, appearance and uncontrolled growth of crystalline phase can usually lead to the rapid decrease of the glass bioactivity [19] or even to the conversion of bioactive glass into inert material [20]. While taking into consideration the direct glass crystallization (apart from thermal properties) the understanding of the glassy precursor structure is crucial as glass devitrification is based on domains reorientation during heating [21]. The domains shall be understood as a kind of ‘crystallization nuclei’, which may determine the type of crystallizing phase [22]. Therefore, it is necessary to identify the domains structure as it allows to predict the type of crystallizing phase during crystallization process. Considering the above, we have decided to introduce magnesium and aluminum ions into the silico-phosphate glasses structure from NaCaPO4eSiO2 system. The literature data indicates that presence of these ions in the glass structure improves the mechanical properties and chemical stability of the glass [e.g. Refs. [23,24]. The main aim of this study was the most accurate description of microstructure and structure of silico-phosphate glasses from NaXPO4eSiO2 and NaXPO4eSiO2eAlPO4 systems (where X ¼ Ca and/or Mg). The knowledge of microstructure and structure of the glass provides the opportunity to correctly plan direct
http://dx.doi.org/10.1016/j.molstruc.2015.12.003 0022-2860/© 2015 Elsevier B.V. All rights reserved.
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A. Wajda et al. / Journal of Molecular Structure xxx (2015) 1e16
crystallization process in order to obtain glass-crystalline materials with premeditated phase composition and crystallite size. Consequently, it is possible to obtain the material with desired functional properties.
component bands to the starting spectra (low value of c2 parameter) was reached.
2. Experimental
To confirm the amorphousness of the obtained materials XRD and FIR studies were performed. There were no sharp bands in the FIR spectra and any reflections in the X-ray diffraction patterns, what unequivocally confirm the amorphous state of the prepared materials. The opacity of the obtained materials must arise due to liquation phenomenon. The same result has been confirmed in our previous research on the glass microstructure from NaCaPO4eSiO2 system [27]. It was found out that liquation phenomenon occurs e the clear spherical inclusions dispersed in the rest of the matrix. It was also demonstrated that small addition of aluminum ions (5mol.% AlPO4) to glass from NaCaPO4eSiO2 system leads to homogenization of their microstructure [28]. Moreover, the addition of aluminum ions causes rapid change in the chemical composition of both the matrix and the inclusions (EDX) [27,28]. In the case of glasses from NaCaPO4eSiO2eAlPO4 system with a low content of NaCaPO4 (to 25mol.%), the spherical inclusions are calcium phosphate phase, but the matrix is almost pure silicate phase e opposite to the glasses from the NaCaPO4eSiO2 system. The increase of NaCaPO4 to more than 25mol.% leads to re-inversion of the matrix and inclusions composition e the inclusions become silico phase and the matrix calcium-silico-phosphate phase [29,30]. The morphology and composition of the glasses were analysed by scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (EDX). This study shows that lack of transparency of the obtained glasses is effectively connected with the liquation phenomenon. The analysis of SEM images of glasses from NaCaPO4eSiO2 and NaCaPO4eSiO2eAlPO4 systems [27,28], together with glasses after partial (Na(Ca,Mg)PO4eSiO2 (Fig. 1a) and Na(Ca,Mg)PO4eSiO2eAlPO4 (Fig. 1b) systems) and total (NaMgPO4eSiO2 (Fig. 1c) and NaMgPO4eSiO2eAlPO4 (Fig. 1d) systems) replacement of calcium ions by magnesium ions allows to determine the effect of magnesium ions on the microstructure of the selected silico-phosphate glasses. Complete replacement of calcium ions by magnesium ions in the structure of glasses from the NaCaPO4eSiO2 [27,28] system causes the increase of the inclusions diameters (Fig. 1c). The even larger size of the inclusions was observed after the introduction of two cations to the glass composition (Fig. 1a). It can be also seen that the microstructure of the glass containing magnesium ions is heterogeneous (a large number of inclusions with different sizes). This is due to the inhomogeneous liquation, which makes in both the matrix and the inclusions subsequent phase separation (particularly evident in the samples from the MgCa series e Fig. 1c). The addition of aluminum ions into the structure of glasses containing Mg2þ leads to
Glasses (and their composition) selected for the studies are given in Table 1. The composition was selected to compensate the negative charge of [PO4]3- and [SiO4]4- by couples of Naþ and X2þ cations. The standard solegel method was chosen to obtain the materials of the highest possible homogeneity. TEOS (SiO2), Ca(NO3).24H2O (CaO), Na3PO.412H2O (Na2O), Mg(NO3).26H2O, Al(NO3).33H2O (Al2O3) 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 80 C. Solegel method was selected to provide the highest possible homogeneity and to reduce the volatility of the individual components. To obtain the glassy samples the gels were melted in platinum crucible in the temperature of 1730 C and rapidly cooled on the cast iron plate. The gels were heated with 5 C/min heating speed till 1730 C and then stabilized in the same temperature for 2h. All obtained glasses were not transparent, what indicated that liquation occurred or the materials were not completely amorphous. To obtain crystalline materials the dried gels were heated at 1380 C. Scanning electron microscopy (SEM) of the materials was conducted using FEI Nova NanoSEM 200 scanning microscope and the measurements were performed under low vacuum. X-Ray powder diffraction studies were performed using Philips X'Pert Pro MD diffractometer. The used radiation was Cu Ka1 line monochomatized by Ge(111) monochromator. Standard BraggBrentano geometry with Q-2Q setup was applied (0.008 step size and 5o-90 2Q range). IR spectroscopic investigations (MIR e middle infrared and FIR e far infrared) of the materials were made with a Bio-Rad FTS 60V spectrometer. MIR: transmission technique, samples as KBr pellets. Spectra were collected after 256 scans at 4 cm1 resolution. FIR: polyethylene pellets. Spectra were collected after 2000 scans at 4 cm1 resolution. Spectra deconvolution was carried out according to the method of Handke et al. and a minimization of component bands was applied as the basic rule [25,26]. For the deconvolution Spectra Calc™ software was used, which provides the best fitting of complex band envelopes with the curves of the predetermined belltype functions (mixed Gaussian/Lorentians). The process of decompositions was carried out until a high fitting degree of the
3. Results and discussion
Table 1 Composition of the selected glasses [mol. %]. MgCa series
Na(Mg,Ca)PO4 e SiO2 system
1MgCa 2MgCa 3MgCa 4MgCa 5MgCa
90%SiO2 80%SiO2 70%SiO2 60%SiO2 50%SiO2
Mg Series
NaMgPO4 e SiO2 system
1 2 3 4 5
90%SiO2 80%SiO2 70%SiO2 60%SiO2 50%SiO2
Mg Mg Mg Mg Mg
. . . . .
. . . . .
10%Na(Mg,Ca)PO4 20%Na(Mg,Ca)PO4 30%Na(Mg,Ca)PO4 40%Na(Mg,Ca)PO4 50%Na(Mg,Ca)PO4
10%NaMgPO4 20%NaMgPO4 30%NaMgPO4 40%NaMgPO4 50%NaMgPO4
AlMgCa series
Na(Mg,Ca)PO4 e SiO2 e AlPO4 system
1AlMgCa 2AlMgCa 3AlMgCa 4AlMgCa 5AlMgCa
90%SiO2 80%SiO2 70%SiO2 60%SiO2 50%SiO2
AlMg Series
NaMgPO4 e SiO2 e AlPO4 system
1AlMg 2AlMg 3AlMg 4AlMg 5AlMg
90%SiO2 80%SiO2 70%SiO2 60%SiO2 50%SiO2
. . . . .
. . . . .
5%Na(Mg,Ca)PO4 . 5%AlPO4 15%Na(Mg,Ca)PO4 . 5%AlPO4 25%Na(Mg,Ca)PO4 . 5%AlPO4 35%Na(Mg,Ca)PO4 . 5%AlPO4 45%Na(Mg,Ca)PO4 . 5%AlPO4
5%NaMgPO4 . 5%AlPO4 15%NaMgPO4 . 5%AlPO4 25%NaMgPO4 . 5%AlPO4 35%NaMgPO4 . 5%AlPO4 45%NaMgPO4 . 5%AlPO4
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homogenization of the microstructure e it becomes more homogeneous. Comparison of the SEM photographs of the glasses from NaMgPO4eSiO2eAlPO4 (Fig. 1d) and Na(Mg,Ca)PO4eSiO2eAlPO4 (Fig. 1b) systems with the photographs of glasses from NaCaPO4eSiO2eAlPO4 system [27,28] demonstrates similarity of the microstructure of this glasses, the only difference is that presence of magnesium ions causes increase in inclusions size. In order to determine the effect of magnesium ions on the chemical composition of the matrix and inclusions, glasses of each series were studied by EDX (Figs. 2 and 3). The complete (Figs. 2 and 3c) and partial (Figs. 2 and 3a) substitution of calcium ions by magnesium ions does not cause significant changes in the chemical composition of the inclusions and matrix in the glasses without aluminum ions (except of course the conversion of calcium ions to magnesium ions). The matrix in this glasses is silico-phosphate phase and with the increase of NaMgPO4 (Fig. 2c) or Na(Mg,Ca) PO4 (Fig. 2a), the matrix is increasingly enriched with phosphorus ions. The presence of a significant amount of magnesium, sodium and/or calcium ions is also observed. On the other hand, the inclusions in all glasses are nearly pure silica phase with a very small amount of magnesium, sodium and/or calcium ions (Fig. 3c and a). In glasses from NaMgPO4eSiO2eAlPO4 (Figs. 2 and 3d), Na(Mg,Ca)PO4eSiO2eAlPO4 (Figs. 2 and 3b) and NaCaPO4eSiO2eAlPO4 [27,28] systems the chemical composition inversion of the matrix and inclusions can be observed. The inclusions from NaMgPO4eSiO2eAlPO4 (Fig. 3d) system with the lower content of NaMgCaPO4 (less than 35mol.%) are almost pure phosphate phase, whereas the matrix (Fig. 2d) is just pure silica phase. The chemical composition inversion of the matrix and inclusions takes place only above 35mol.% of NaMgPO4. The matrix becomes phosphate phase and the inclusions become silica phase (Figs. 2 and 3d). The same situation occurs in the glasses of the Na(Mg,Ca)PO4eSiO2eAlPO4 system (Figs. 2 and 3b). The EDX spectra comparison of these glasses systems with the glasses from NaCaPO4eSiO2eAlPO4 [27,28] clearly indicates that the total or partial substitution of calcium by magnesium ions moves the boundary of the chemical composition inversion of the matrix and inclusions. The inversion in the glasses from NaCaPO4eSiO2eAlPO4 system appears only above 25% mol. of NaCaPO4 [27,28], while in the case of glasses from NaMgPO4eSiO2eAlPO4 (Figs. 2 and 3d) and Na(Mg,Ca)PO4eSiO2eAlPO4 (Figs. 2 and 3b) systems after exceeding 35mol.% of NaMgPO4 or Na(Mg,Ca)PO4. While considering glass-crystalline biomaterials obtainment, the liquation phenomenon seems to be beneficial as it may help to limit the problem associated with the uncontrolled growth of crystalline phases during devitrification. Phase boundary between inclusions and matrix should be a barrier, which can limit growth of crystals. Different chemical composition of inclusions and matrix should cause e upon the appropriate thermal treatment e the separate crystallization of the matrix or inclusions. It can be assumed that by carrying out direct crystallization process aimed at crystallizing only inclusions, the growth of crystallizing phase will be limited to the inclusions size. As it was mentioned, in the planning of direct crystallization process of the glass, precise knowledge of the glass-crystalline precursor structure is required. Due to the lack of long-range order in glasses, only spectroscopic methods provide information about their internal structure. The understanding of the glasses structures with complex compositions containing various network modifiers (Naþ, Kþ, Ca2þ, Mg2þ) and various glass-forming ions (Si4þ, P5þ, Al3þ) firstly requires to carry out detailed spectroscopic studies of glasses and their crystalline counterparts. It is generally accepted that in areas with short-range order of glasses, the structure corresponds with their crystalline counterparts [e.g. Refs. [31,32]. Hence, in order to proper MIR spectra interpretation, it
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is necessary to compare the spectra of the glasses with those corresponding to relevant crystalline materials and decompose the spectra into component bands. The noticed homogenizing influence of aluminum ions on the texture of silico-phosphate glasses was also observed in the case of crystalline materials of the NaCaPO4eSiO2 system [33]. The introduction of 5% mol. AlPO4 to these materials, significantly reduces the amount of crystallizing phases e in all MIR spectra of crystalline materials from NaCaPO4eSiO2eAlPO4 system fewer amount of bands can be seen in comparison with MIR spectra of the materials from NaCaPO4eSiO2 system [33]. In the MIR spectra of aluminum containing devitrified glasses with a high amount of SiO2 virtually are invisible characteristic bands of the phosphate phase at 597 and 574 cm1 (MIR spectrum NaCaPO4). These bands become visible after exceeding 25 mol. % of NaCaPO4 - after chemical composition inversion of matrix and inclusions. Our previous structural studies revealed the existence of solid solutions AlPO4 in SiO2 until 20e25 mol. % content of AlPO4 [34]. It was ascertained that a similar range of solid solutions are found in the NaCaPO4eSiO2eAlPO4 system, but after exceeding 20e30 mol.% content of NaCaPO4 phosphate phase separation takes place [27,28]. The studies on model glasses and crystalline materials help to ensure that in the case of materials without aluminum ions, we can discuss total separation of the silicate and phosphate phases. However, by the adding aluminum ions to the materials from NaCaPO4eSiO2 system phosphate phases become “dissolved” [33]. Figs. 4e7 present MIR spectra of the glasses and their crystalline counterparts from systems: NaMgPO4eSiO2 (Fig. 4), Na(Mg,Ca) PO4eSiO2 (Fig. 5), NaMgPO4eSiO2eAlPO4 (Fig. 6) and Na(Mg,Ca) PO4eSiO2eAlPO4 (Fig. 7). The spectra have three characteristic bands at: around 480 cm1, 850 - 600 cm1 and in the range of 1200e900 cm1 (see Table. 2). The band at 480 cm1 is characteristic for bending OeSieO vibrations. The bands in the range of 850e600 cm1 are assigned to symmetric stretching SieOeSi vibrations [4,5,32]. For silico e phosphate glasses, in this range also bands connected with bending OePeO vibrations occur [4,5,34]. The bands in the range of 1200e900 cm1 are characteristic for asymmetric stretching SieO(Si) (bridging bonds) and SieO- (nonbridging bonds) vibrations. In addition, in the same range the bands connected with stretching vibrations of PeO and AleO (coordination number of aluminum ions ¼ 4) and bands related to stretching vibrations of Si]O and P]O are visible [4,5,35,36]. High MIR spectra similarity of the obtained glasses and crystalline materials allows to assume that the glasses domains have the same structure as in the corresponding crystalline materials [33]. Such assumption is equivalent to the conclusion that in the studied glasses, domains with various types of arrangement occur at the same time. It is obvious that in the liquation glasses such domains exist because matrix and inclusions have a different chemical composition and certainly have a different character of local arrangement. MIR spectra analysis of the glasses and the corresponding crystalline materials of NaMgPO4eSiO2 system (Fig. 4) allows to determine that the complete substitution of calcium ions by magnesium ions causes homogenization of these glasses structure. The domains from 1 Mg to 2 Mg glasses are only crystobalite type. The bands at 598 and 574 cm1 related to phosphate phase become visible for amorphous and crystalline materials with a lower amount of SiO2 (3 Mg e 5 Mg). The partial substitution of calcium ions by magnesium ions decreases homogenizing influence of magnesium ions on the silicophosphate glasses structure. Only one the MIR spectrum of devitrified glasses with the lowest content of Na(Mg,Ca)PO4 (Fig. 5), the typical bands of phosphate phase cannot be observed. A large number of bands, which appear in the spectra of crystalline
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A. Wajda et al. / Journal of Molecular Structure xxx (2015) 1e16 Fig. 1. a. SEM microphotographs of the glasses from Na(Mg,Ca)PO4eSiO2 system. b. SEM microphotographs of the glasses from Na(Mg,Ca)PO4eSiO2eAlPO4 system. c. SEM microphotographs of the glasses from NaMgPO4eSiO2 system. d. SEM microphotographs of the glasses from NaMgPO4eSiO2eAlPO4 system.
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Fig. 1. (continued).
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A. Wajda et al. / Journal of Molecular Structure xxx (2015) 1e16 Fig. 2. a. EDX spectra of the glasses from Na(Mg,Ca)PO4eSiO2 system (matrix). b. EDX spectra of the glasses from Na(Mg,Ca)PO4eSiO2eAlPO4 system (matrix). c. EDX spectra of the glasses from NaMgPO4eSiO2 system (matrix). d. EDX spectra of the glasses from NaMgPO4eSiO2eAlPO4 system (matrix).
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Fig. 2. (continued).
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Fig. 3. a. EDX spectra of the glasses from Na(Mg,Ca)PO4eSiO2 system (inclusions). b. EDX spectra of the glasses from Na(Mg,Ca)PO4eSiO2eAlPO4 system (inclusions). c. EDX spectra of the glasses from NaMgPO4eSiO2 system (inclusions). d. EDX spectra of the glasses from NaMgPO4eSiO2eAlPO4 system (inclusions).
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Fig. 3. (continued).
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Fig. 4. MIR spectra of glassy and crystalline samples form NaMgPO4eSiO2 system.
materials is associated with the formation of calcium and magnesium phosphate. It can be concluded that the domains in these glasses are of various types. The modification of glasses structure from NaMgPO4eSiO2 and Na(Mg,Ca)PO4eSiO2 systems by aluminum ions increases its homogeneity. Based on the MIR spectra of glasses and their crystalline counterparts from those systems (Figs. 4 and 5), it can be noticed that there are a smaller number of bands associated with the
phosphate phases. It is particularly evident in the MIR spectra of crystalline materials containing both calcium and magnesium ions - typical phosphate bands become apparent for samples: 4AlMgCa and 5AlMgCa. A large half-width bands makes MIR spectra of all studied glasses to be almost practically the same (except for slight shifts bands) (Figs. 4e7). Effect of magnesium and aluminum ions in the structure of silico-phosphate glasses is visible only after the
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Fig. 5. MIR spectra of glassy and crystalline samples from Na(Mg,Ca)PO4eSiO2 system.
decomposition of the glass MIR spectra into component bands (Figs. 8 and 9). The analysis of these MIR spectra decompositions of glasses containing aluminum ions (Fig. 9) shows that there are fewer bands. In addition, the introduction of aluminum ions into the glasses structure causes a rapid decrease of the bands intensity connected with structural defects, i.e. the bands associated with the vibrations: Si]O, P]O (1180e1232 cm1) and SieO-(Naþ,Ca2þ) (944e961 cm1). With simultaneous intensity increase of bands which are characteristic for stretching vibrations of SieO(Si),
SieO(P) and SieO(Al). This is due to the replacement of SieOeP vibrations by AleOeP ones e connection the tetrahedrons of [PO4]3- and [SiO4]4 by tetrahedrons [AlO4]5- [37]. To obtain glass-crystalline materials, besides the understanding of the microstructure and glass structure, it is necessary to know its thermal parameters, especially temperature of devitrification (TD) at which individual phases crystallize. For this purpose, DSC studies of selected glasses (NaMgPO4eSiO2 (Fig. 10) and Na(Ca,Mg) PO4eSiO2 (Fig. 11)) were carried out. The interpretation of the
Please cite this article in press as: A. Wajda, et al., Structure and microstructure of the glasses from NaCaPO4eSiO2 and NaCaPO4eSiO2eAlPO4 systems, Journal of Molecular Structure (2015), http://dx.doi.org/10.1016/j.molstruc.2015.12.003
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Fig. 6. MIR spectra of glassy and crystalline samples from NaMgPO4eSiO2eAlPO4 system.
presented results of glasses thermal studies is very complicated. The both of DCS curves have four exothermal peaks, what proves that four different phases crystallize. This is due to ascertained heterogeneity of glass microstructure and structure of matrix and inclusions e the presence of domains of different nature [38]. The liquation is heterogeneous and in both inclusions and matrix, phase separation are observed, what may explain the existence of several exothermal effects. The introduction of aluminum ions into the glasses effects in that crystallization running in two stages. The DSC
curves present exothermal peaks at 713 C (4AlMgCa e Fig. 12) and 752 C (4AlMg e Fig. 13) related to matrix crystallization and 950 C (4AlMgCa), 953 C (4AlMg) related to inclusions crystallization. Such weak exothermal peaks associated with the inclusions crystallization are the consequence of a homogenizing influence of aluminum ions on the microstructure and the structure of silicophosphate glasses. The introduction of Al3þ causes noticeable reduction of inclusions amounts. Probably there are not enough of them to see visible exothermal peak on DCS curve, which could be
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Fig. 7. MIR spectra of glassy and crystalline samples from Na(Mg,Ca)PO4eSiO2eAlPO4 system.
connected with inclusions crystallization. 4. Conclusions 1. Partial or complete substitution of calcium ions by magnesium ions in the structure of silico-phosphate glasses from NaCaPO4eSiO2 system leads to an increase of the inclusions sizes and heterogeneity of liquation e in the matrix and the inclusions appear phase separations. Additional introduction of aluminum
ions causes rapid homogenization of the microstructure (SEM). 2. The chemical analysis (EDX) of the glasses from NaMgPO4eSiO2eAlPO4 and Na(Mg,Ca)PO4eSiO2eAlPO4 systems indicated chemical composition inversion of the matrix and inclusions. The inversion takes place after exceeding 35 mol.% of NaMgPO4 or NaMgPO4eSiO2. It means that introduction of magnesium ions moves the boundary of the chemical composition inversion of the matrix and inclusions (to compare to the glasses from NaCaPO4eSiO2eAlPO4 system e 25% NaCaPO4). It can be concluded that
Please cite this article in press as: A. Wajda, et al., Structure and microstructure of the glasses from NaCaPO4eSiO2 and NaCaPO4eSiO2eAlPO4 systems, Journal of Molecular Structure (2015), http://dx.doi.org/10.1016/j.molstruc.2015.12.003
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Table 2 Bands assignment of MIR spectra of silicophosphate glasses [4,5,27,29]. Group of bands
Kind of vibrations
480 cm1 850e600 cm1 1200e900 cm1
Bending OeSieO Symmetric stretching SieOeSi and OePeO Asymmetric stretching SieO(Si,Al) (bridging bonds), SieO- (non-bridging bonds), stretching PeO, stretching Si]O and P]O
the introduction of magnesium ions in place of calcium ions in the studied systems expands the formation range of the solid solutions. 3. Based on spectroscopic study (MIR) it was shown that complete substitution of calcium ions by magnesium ions causes glasses structure homogenization. However, partial (50/50) substitution of calcium ions by magnesium ions decrease the
homogenizing influence of magnesium ions on the silicophosphate glasses structure. It was also demonstrated that the domains in these glasses are of various types. The introduction of additional aluminum ions into the glass structure significantly increases its homogeneity. 4. Decomposition of the selected MIR spectra into component
Fig. 8. Decomposition of the MIR spectrum of 3MgCa glass.
Fig. 9. Decomposition of the MIR spectrum of 3AlMgCa glass.
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Fig. 10. DSC of 3Mg glass.
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Fig. 13. DSC of 4AlMg glass.
crystalline materials by direct crystallization process. These materials can have amorphous matrix and crystalline inclusions or vice versa. Considering the chemical composition inversion of inclusions and matrix in the glasses containing aluminum ions, the studied glass are very promising precursors to a variety of glasscrystalline material. Acknowledgements This work was supported by NCN project ‘Functional layers of black glasses based on ladder-like silsesquioxanes 2014/15/B/ST8/ 0282’. References
Fig. 11. DSC of 3MgCa glass.
Fig. 12. DSC of 4AlMgCa glass.
bands showed that the homogenizing effect of the aluminum ions on the glass structure results from the replacement of SieOeP bonds by AleOeP, what means that the tetrahedrons [PO4]3- and [SiO4]4- are connected by tetrahedrons [AlO4]5-. 5. Thermal analysis (DSC) indicated that crystallization of all studied glasses is multistage - the matrix and inclusions crystallize separately. It can be concluded that it is possible to obtain glass-
[1] D.B. Dingwell, R. Knoche, S.L. Webb, Eur. J. Min. 5 (1993) 133. [2] L.L. Hench, J. Am. Ceram. Soc. 74 (1991) 1487. [3] G. Volksch, T. Hoche, I. Szabo, W. Holand, Glas. Ber. Glass Sci. Technol. C71 (1998) 500. [4] A.M. Abdelghany, H.A. ElBatal, J. Mol. Struct. 1024 (2012) 47e53. [5] A.M. Abdelghany, H.A. ElBatal, J. Mol. Struct. 1067 (2014) 138e146. [6] L.L. Hench, J. Am. Ceram. Soc. 74 (1991) 1487e1510. [7] R.D. Rawlings, Clin. Mater 14 (1993) 155e179. [8] P. Li, I. Kangasniemi, K. Groot, T. Kokubo, A.U. Yli-Urpo, J. Non Cryst. Solids 168 (1994) 281e286. [9] L.L. Hench, R.J. Splinter, T.K. Greenlee, W.C. Allen, J. Biom. Res. Symp 2 (1971) 117e141. [10] L.L. Hench, H.A. Paschall, J. Biom. Res. Symp. 4 (1973) 25e42. [11] G. Piotrowski, L.L. Hench, W.C. Allen, J. Biom. Res. 9 (1975) 47e61. [12] R.G. Hill, A. Stamboulis, R.V. Law, A. Clifford, M.R. Towler, C. Crowley, J. Non Cryst. Solids 336 (2004) 223. [13] G. Lusvardi, G. Malavasi, L. Menabue, M.C. Menziani, A. Pedone, U. Segre, J. Eur. Ceram. Soc. 27 (2007) 499. [14] G. Lusvardi, G. Malavasi, L. Menabue, V. Aina, C. Morterra, Acta Biomater. 5 (2009) 3548. [15] D.S. Brauer, M. Mneimne, R.G. Hill, J. Non Cryst. Solids 357 (2011) 3328. [16] A. Goel, R.R. Rajagopal, J.M.F. Ferreira, Acta Biomater. 7 (2011) 4071. [17] W. Cao, L.L. Hench, Bioact. Mater. Ceram. Int. 22 (1996) 493e507. [18] W. Bonfield, M. Wang, K.E. Tanner, Acta Mater. 46 (1998) 2509e2518. [19] O.P. Filho, G. Torre, L.L. Hench, J. Bio. Mater. Res. 30 (1996) 509e514. [20] P. Li, F. Zhang, T. Kokubo, J. Mater. Sci. Mater. Med. 3 (1992) 452e456. € rlich, Glassy State, AGH, 155AGH Publisher, Cracow, 1989 in Polish. [21] E. Go [22] M. Sitarz, M. Szumera, J. Therm. Anal. Cal. 91 (2008) 255e260. [23] U. Gross, V. Strunz, J. Biomed. Res. 19 (1985) 251e271. J. Mol. Struct. [24] O.H. Andersson, K.H. Karlsson, K. Kagasniemi, A. Yli-Urpo, Glas. Ber. 61 (1988) 300e305. [25] A.M. Abdelghany, Silicon 2 (2010) 179e184. [26] M. Handke, W. Mozgawa, M. Nocun, J. Mol. Struct. 325 (1998) 129e136. [27] M. Handke, M. Sitarz, M. Rokita, E.W. Galuskin, J. Mol. Struct. 651e653 (2003) 39e54. [28] M. Sitarz, M. Rokita, M. Handke, E.W. Galuskin, J. Mol. Struct. 651e653 (2003) 489e498. [29] M. Sitarz, J. Mol. Struct. 887 (2008) 237e248. [30] M. Sitarz, Spectrochim. Acta Part A 79 (2011) 739e742. [31] S. Brawer, Phys. Rev. B11 (1975) 3173e3194.
Please cite this article in press as: A. Wajda, et al., Structure and microstructure of the glasses from NaCaPO4eSiO2 and NaCaPO4eSiO2eAlPO4 systems, Journal of Molecular Structure (2015), http://dx.doi.org/10.1016/j.molstruc.2015.12.003
16
A. Wajda et al. / Journal of Molecular Structure xxx (2015) 1e16
[32] M. Sitarz, Vibrational Spectroscopy of Crystalline and Amorphous Silicates Containing Rings of Various Numbers of Members, Ph.D. Thesis, AGH University of Science and Technology, 1998. [33] M. Sitarz, M. Rokita, M. Handke, J. Mol. Struct. 614 (2002) 289e295. [34] M. Handke, M. Rokita, W. Mozgawa, Vib. Spectrosc. 19 (1999) 419e423.
[35] M. Sitarz, Z. Fojud, Z. Olejniczak, J. Mol. Struct. 924e926 (2009) 107e110. [36] W. Jastrze˛ bski, M. Sitarz, M. Rokita, K. Bułat, Spectrochim. Acta Part A 79 (2011) 722e727. [37] L. Stoch, Glass Phys. Chem. 27 (2001) 167e174. [38] M. Sitarz, K. Bułat, M. Szumera, J. Therm. Anal. Calorim. 109 (2012) 577.
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