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MoO3 as a structure modifier of glasses from P2O5–SiO2–K2O–MgO–CaO system
Materials Letters 135 (2014) 147–150
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
MoO3 as a structure modifier of glasses from P2O5–SiO2–K2O–MgO–CaO system Magdalena Szumera n Department of Ceramics and Refractories, Faculty of Materials Science and Ceramics, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Kraków, Poland
art ic l e i nf o
a b s t r a c t
Article history: Received 28 March 2014 Accepted 26 July 2014 Available online 4 August 2014
Infrared spectroscopy and density are advantageous tools for the investigations of glasses and they have been used to obtain information concerning the local structure of phosphate–silicate glasses from P2O5– SiO2–K2O–MgO–CaO system modified with the addition of MoO3. It has been found that MoO3 plays the network modifier role in the studied glasses which follows from the gradual breakage of oxygen bridges, i.e. P–O–P, Si–O–Si and/or Si–O–P, and the following formation of connections such as Mo[MoO4]–O–Si and/or Mo[MoO4]–O–P. In summary, it is concluded that the increase of MoO3 content in the structure of glasses of P2O5–SiO2–K2O–MgO–CaO system results in weakening of the structure, resulting in their frameworks depolymerisation. & 2014 Elsevier B.V. All rights reserved.
Keywords: Molybdenum ions Phosphate–silicate glasses FTIR spectroscopy Density
1. Introduction The structure and properties of phosphate glasses containing transition metal ions have attracted considerable interest because of their various applications [1–3]. It is known that molybdenum ions in phosphate glass structure form stable glasses over a wide range of compositions from 0 to 83 mol% MoO3 content [4,5]. Alkali-oxides, when added to oxide glasses of the system (MoO3– P2O5), act as network modifiers by giving rise to non-bridging oxygens in the structure [6]. Simultaneously, literature data [7,8] reports that [MoO6] octahedral and [MoO4] tetrahedral units exist in molybdenum phosphate glasses. The properties of the phosphate glasses can be modified by the addition of oxides of the alkali, alkaline earth and transition elements (e.g. Mn, Mo, Fe, Zn, and Cu) into the glass structure. The knowledge of structural changes is important for the understanding and finding some new possible applications of phosphate glasses. Molybdenum is a chemical element from the group of d transition metals and due to its characteristics it has found many applications in various industries. It is also a microelement—necessary for proper development of plants—possible to use it in glassy fertilizers, as one of its components. The idea to familiarise with the structure of phosphate glass from P2O5–SiO2–K2O–MgO–CaO appeared while carrying out intensive research on silicate–phosphate glass that was applied as a new type of mineral fertilisers [9,10]. For n
Tel.: þ 48 12 617 24 80; fax: þ48 12 633 46 30. E-mail address: [email protected]
http://dx.doi.org/10.1016/j.matlet.2014.07.159 0167-577X/& 2014 Elsevier B.V. All rights reserved.
elucidation of the structural evolution of the model glasses from P2O5–SiO2–K2O–MgO–CaO system modified with the addition of MoO3, as a function of composition and other properties, such as density and molar volume, are investigated. The structural changes were studied using FTIR spectroscopy.
2. Experimental Glass samples of composition (40.7–41.2) P2O5–(5.2–6.5) SiO2– (5.7–6.9) K2O–(10.0–28.8) MgO–(7.2–18.2) CaO–(0.0–29.5) MoO3 [mol%] were synthesised by a conventional melt quenching method. Appropriate amounts of the constituent oxides were mixed and melted at about 1200 1C. The melts were rapidly quenched on a steel plate to obtain glass samples of the desired composition. Chemical composition of the glasses was determined by the XRF spectroscopy using an ARL ADVANT'XP spectrometer and is presented in Table 1. Amorphous state of the analysed phosphate glasses was confirmed by the X-ray diffraction method and it was presented in our previous work [5]. Density of the samples was measured by a helium pycnometry technique using a Micromeritics AccuPyc II 1340 Gas Pycnometer apparatus. The density was determined with an accuracy of 0.0001 g/cm3. Measurement was repeated 30 times to ensure precision. Before the measurement the sample was purged with helium 70 times to remove impurities and stabilise its temperature and volume.
148
M. Szumera / Materials Letters 135 (2014) 147–150
Table 1 Chemical composition of analysed glasses from P2O5–SiO2–K2O–CaO–MgO–MoO3 system. No
0Mo41P 2Mo41P 4Mo41P 8Mo41P 15Mo41P 30Mo41P
Content of components/mol% P2O5
SiO2
K2O
MgO
CaO
MoO3
40.7 40.8 41.9 40.8 40.6 41.2
6.5 6.0 5.2 5.7 6.2 5.8
5.7 5.7 6.9 6.2 6.2 6.3
28.8 27.8 25.5 22.9 19.1 10.0
18.2 17.8 16.6 16.4 12.8 7.2
0.0 1.9 3.9 8.0 15.1 29.5
Table 2 Physical parameters of glasses from P2O5–SiO2–K2O–CaO–MgO–MoO3 system.
0Mo41P 2Mo41P 4Mo41P 8Mo41P 15Mo41P 30Mo41P
Density g/cm3
Standard deviation g/cm3
Molar value cm3/mol
OPD g atm/l
2.4685 2.5294 2.6063 2.6445 2.6597 2.6785
0.0041 0.0066 0.0028 0.003 0.0061 0.0219
35.99 35.90 36.18 39.72 39.02 44.21
277.92 362.21 359.45 354.08 330.69 294.09
Middle infrared (MIR) spectroscopic measurements of the glasses were conducted with a Bruker Vertex 70v spectrometer using the transmission mode. The samples had the form of pellets made of the glasses mixed with KBr. Spectra were collected after 124 scans with 4 cm 1 resolution. Positions of bands on the MIR spectra were determined automatically by Win-IR software. Spectra decomposition has been carried out according to the mathematical self-deconvolution method using the minimisation of the number of the bands rule, proposed by Handke et al. [11].
is also oxygen packing density, which is helpful in determining the compactness of the glass network. It should be emphasised that the mere introduction to the structure of glass containing in its composition MoO3 causes significant increase in OPD, from the value of 277.92–362.21 g atm/l. The obtained data (Table 2) are consistent with the literature [12,18–20]. This indicates that the structure becomes loosely packed with an increase in the MoO3 concentration. Infrared absorption spectra: The effect of MnO2 addition on the structure of analysed silicate–phosphate glasses is illustrated by the FTIR spectra in the middle infrared range (Fig. 1). The spectra of the aforementioned glasses are characterised by the presence of four main absorption bands with the maxima located in the 1400– 1200, 1200–850, 850–700 and 400 cm 1 wavenumber regions. Due to the complex and broad character of absorption spectra of the investigated glasses, a process of their decomposition into separate bands was carried out (Fig. 2). Wavenumbers range: 1400–1200 cm 1: In this range a single band, located at about 1280 cm 1 was registered and it was assigned to the characteristic stretching mode of the P¼O bond [21]. Several previous studies [22–24] also showed that the asymmetric stretching vibration of O–P–O groups, can be found in this frequency region. This band is well visible for both glass 0Mo41P not containing MoO3 and glass modified by its supplementation. It was stated that locations of bands shifted towards lower wavenumbers (1286-1280 cm 1), which may suggest that MoO3 has a depolymerising effect on the phosphate bonding. Wavenumbers range: 1200–850 cm 1: In this range of wavenumbers, the presence of three absorption bands was observed; the conducted process of FTIR spectra decomposition enabled determining, in their scope, additional bands lying in the following wavenumber ranges: 1200–1040 and 1000–850 cm 1 (Fig. 2). The first is assigned to the asymmetric stretching vibration of the
3. Results and discussion Density and molar volume: The density is a powerful tool, capable of reflecting the effect of structural changes in glass. The glass structure can be also expressed in terms of the molar volume, as the former deals the spatial distribution of ions forming the glass structure [12,13]. From the structural point of view, the molar volume V ¼ M=ρ, where M ¼ ∑xi M i is the mean molecular weight of analysed glasses and ρ is the mass density; M i is the molecular weight of component i and xi is the mole fraction of component i [14]. A parameter estimated from density is also the oxygen packing density (OPD) and it was calculated using the following expression: OPD ¼ 1000ρ½O=M, where [O] is the number of oxygen atoms in the composition [15]. The measured values of these parameters for all analysed phosphate–silicate glasses are presented in Table 2. It was found that the density of analysed glasses increased gradually with increasing content of MoO3. Such an effect was expected in connection with introducing to the glass structure a component with a higher molecular weight in relation to the molecular weight of MgO and CaO. Molar volume values calculated by taking into account the measured densities were found to range from 35.99 to 44.21 cm3/mol and exhibited an increase with the substitution of MgO and CaO by MoO3. This behaviour may be attributed to the increase in the quantity of non-bridging oxygen (NBOs) [16,17] which can cause the expansion of the network of the system. It is probably also related to the fact that the MoO3 reticulates the vitreous network and this allows for contracting the arrangement of nonbridging oxygen ions. An important parameter
Fig. 1. FTIR spectra of phosphate–silicate glasses from the P2O5–SiO2–K2O–CaO– MgO–MoO3 system.
M. Szumera / Materials Letters 135 (2014) 147–150
149
Wavenumbers range: 800–700 cm 1: In this range of wavenumbers, the presence of two constituent bands was observed at about 780 and 712 cm 1. Bands in this range of wave numbers with increasing content of MoO3 in the glass composition gradually disappear. This band is due to the symmetric stretching vibration of P–O–P linkages, vs(P–O–P) and/or the stretching vibration of P–O–Mo bond [22,27,28]. Wavenumbers range: 450–500 cm 1: On the basis of decomposition of FTIR spectra, the presence of 3 constituent bands was observed, at about 620, 550 and 483 cm 1. The first is characteristic of Si–O vibrations [29], while two subsequent ones may be assigned either to the harmonics of P–O–P bending vibration or to the characteristic frequency of the pyrophosphate (P2O47 ) group [22,27]. A small shift of locations of bands towards lower wavenumber ranges was observed (509-504 cm 1), proving the increasing degree of glass structure depolymerisation.
4. Conclusions The impact of molybdenum ions on density as well as structure of glass from the P2O5–SiO2–K2O–MgO–CaO–MoO3 system was examined. Infrared spectra of the investigated glasses showed absorption bands related to the characteristic phosphate and molybdate bonds especially: P¼O, P–O–P, P–O–Mo and Mo–O– Mo. On the basis of the results of tests on density and structure of analysed glass, it was stated that the introduction of larger quantities of MoO3 at the expense of reducing the content of MgO and CaO causes gradual glass structure depolymerisation, and molybdenum ions in the analysed glass matrix act as modifying cations.
Acknowledgements
Fig. 2. The decomposition of FTIR spectra of phosphate–silicate glasses from the P2O5–SiO2–K2O–CaO–MgO–MoO3 system containing: (a) 3.9 mol% MoO3 and (b) 29.5 mol% MoO3.
The author want to express their thanks to Prof. Irena Wacławska, for help in density discussion to Prof. Krzysztof Haberko and in FTIR spectroscopy to Prof. Maciej Sitarz of Faculty of Materials Science and Ceramics, AGH University of Science and Technology in Cracow. The work was supported by Faculty of Materials Science and Ceramics AGH – University of Science and Technology (2014) No. 11.11.160.603. References
metaphosphate groups, vas(PO3) [22]. It was stated that introduction to the structure of analysed glass of increasing content of MoO3 affects the position of these bands shifted towards lower wavenumbers (1105-1043 cm 1), which may suggest that MoO3 has a depolymerising effect on the phosphate network. In the second range, bands located at about 960–1020 cm 1 can be attributed to the symmetric stretching vibration of metaphosphate groups, vs(PO3) [22]. However, according to [23], band at about 963 cm 1 could be also ascribed to the Mo–O stretching vibration in bridging Mo–O–Mo linkages. The location of these bands also shifts towards lower wavenumbers, which would confirm the previous presumptions. The conducted process of spectra decomposition made it possible to state the presence of bands at about 917 cm 1 (Fig. 2). Literature data [24–26] suggest that the presence of these bands is characteristic of stretching vibrations of [Mo–O6] groups. This suggests the presence of structural units such as [MoO6] [MoO6] and/or [MoO6] [PO4] [25], in the structure of analysed phosphate glass, thus gradually building molybdenum ions into the phosphate sub-network and causing its gradual depolymerisation.
[1] Brow RK. J Non-Cryst Solids 2000;263:1–28. [2] Stoch P, Ciecińska M. J Therm Anal Calorim 2012;108:705–9. [3] Novajra G, Lousteau J, Milanese D, Vitale-Brovarone C. Mater Lett 2013;99:125–7. [4] Khattak GD, Salim MA, Al-Harthi AS, Thompson DJ, Wenger LE. J Non-Cryst Solids 1997;212:180–91. [5] Szumera M, Wacławska I. J Therm Anal Calorim 2012;109:649–55. [6] Koudelka L, Mosner P. Mater Lett 2000;42:194–9. [7] Boudlich D, Haddad M, Nadiri A, Berger R, Kliava J. J Non-Cryst Solids 1998;224:135–42. [8] Bih L, Allali N, Yacoubi A, Nadiri A, Boudlich D, Haddad M. (Hammamet, Tunise). 5emes Journ Maghreb des Sci des Mater 1996;3:3. [9] Szumera M, Wacławska I, Mozgawa W, Sitarz M. J Mol Struct 2005;744:609–14. [10] Szumera M, Wacławska I. J Therm Anal Calorim 2007;88:151–6. [11] Handke M, Mozgawa W, Nocuń M. J Mol Struct 1994;325:129–36. [12] Chanshetti UB, Shelke VA, JAdhav SM, Shankarwar SG, Chondkekar TK, Shankarwar AG, et al. Fact Univ Phys Chem Technol 2011;9(1):29–36. [13] Sanad AM, Moustafa AG, Moustafa FA, El-Mongy AA. Cent Glass Ceram Res Bull 1985;32(3):53–6. [14] Walter G, Hoppe U, Barz A, Kranold R, Stachel D. J Non-Cryst Solids 2000;263&264:48–60. [15] Vasantharani P, Vijayalakshmi M. Int J Recent Sci Res 2011;2(1):14–7. [16] Chimalawong P, Kaewkhao J, Limsuwan P. Energy Rec J 2010;1(2):176–81. [17] Abdel-Baki M, Abdel-Wahab FA, Radi A, El-Diasty F. J Phys Chem Solids 2007;68:1457–70.
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Hoppe U. J Non-Cryst Solids 1996;195:138–47. Celikbilek M, Ersundu A E, Aydin S. J Non-Cryst Solids 2013;378:247–53. Fredholm YC, Karpukina N, Law RV, Hill RG. J Non-Cryst Solids 2010;356:2546–51. Abbas L, Bih L, Nadii A, Elamraui Y. J Therm Anal Calorim 2007;90:453–8. Marzouk S, Abo-Naf S M, Hammam M, El-Gendy Y A, Hassan NS. J Appl Sci Res 2011;7(6):935–46. [23] Šubčik J, Koudelka L, Mošner P, Montagne L, Revel B, Gregora I. J Non-Cryst Solids 2009;355:970–5.
[24] Hafid M, Jermoumi T, Toreis N, Ghailassi T. Mater Lett 2002;56:486–90. [25] Jastrzębski W, Sitarz M, Rokita M, Bułat K. Spectrochim Acta A 2011;79:722–7. [26] Ghauri MA, Siddigi SA, Shah WA, Ashig MGB, Igbal M. J Non-Cryst Solids 2009;355:2466–71. [27] Sitarz M, Handke M, Fojud Z, Jurga S. J Mol Struct 2005;744–747:621–6. [28] Muthupari S, Rao KJ. J Phys Chem Solids 1996;57:553–61. [29] Handke M, Mozgawa W, Nocuń M. Pol Ceram Soc 1993;43:33.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
MoO3 as a structure modifier of glasses from P2O5–SiO2–K2O–MgO–CaO system Magdalena Szumera n Department of Ceramics and Refractories, Faculty of Materials Science and Ceramics, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Kraków, Poland
art ic l e i nf o
a b s t r a c t
Article history: Received 28 March 2014 Accepted 26 July 2014 Available online 4 August 2014
Infrared spectroscopy and density are advantageous tools for the investigations of glasses and they have been used to obtain information concerning the local structure of phosphate–silicate glasses from P2O5– SiO2–K2O–MgO–CaO system modified with the addition of MoO3. It has been found that MoO3 plays the network modifier role in the studied glasses which follows from the gradual breakage of oxygen bridges, i.e. P–O–P, Si–O–Si and/or Si–O–P, and the following formation of connections such as Mo[MoO4]–O–Si and/or Mo[MoO4]–O–P. In summary, it is concluded that the increase of MoO3 content in the structure of glasses of P2O5–SiO2–K2O–MgO–CaO system results in weakening of the structure, resulting in their frameworks depolymerisation. & 2014 Elsevier B.V. All rights reserved.
Keywords: Molybdenum ions Phosphate–silicate glasses FTIR spectroscopy Density
1. Introduction The structure and properties of phosphate glasses containing transition metal ions have attracted considerable interest because of their various applications [1–3]. It is known that molybdenum ions in phosphate glass structure form stable glasses over a wide range of compositions from 0 to 83 mol% MoO3 content [4,5]. Alkali-oxides, when added to oxide glasses of the system (MoO3– P2O5), act as network modifiers by giving rise to non-bridging oxygens in the structure [6]. Simultaneously, literature data [7,8] reports that [MoO6] octahedral and [MoO4] tetrahedral units exist in molybdenum phosphate glasses. The properties of the phosphate glasses can be modified by the addition of oxides of the alkali, alkaline earth and transition elements (e.g. Mn, Mo, Fe, Zn, and Cu) into the glass structure. The knowledge of structural changes is important for the understanding and finding some new possible applications of phosphate glasses. Molybdenum is a chemical element from the group of d transition metals and due to its characteristics it has found many applications in various industries. It is also a microelement—necessary for proper development of plants—possible to use it in glassy fertilizers, as one of its components. The idea to familiarise with the structure of phosphate glass from P2O5–SiO2–K2O–MgO–CaO appeared while carrying out intensive research on silicate–phosphate glass that was applied as a new type of mineral fertilisers [9,10]. For n
Tel.: þ 48 12 617 24 80; fax: þ48 12 633 46 30. E-mail address: [email protected]
http://dx.doi.org/10.1016/j.matlet.2014.07.159 0167-577X/& 2014 Elsevier B.V. All rights reserved.
elucidation of the structural evolution of the model glasses from P2O5–SiO2–K2O–MgO–CaO system modified with the addition of MoO3, as a function of composition and other properties, such as density and molar volume, are investigated. The structural changes were studied using FTIR spectroscopy.
2. Experimental Glass samples of composition (40.7–41.2) P2O5–(5.2–6.5) SiO2– (5.7–6.9) K2O–(10.0–28.8) MgO–(7.2–18.2) CaO–(0.0–29.5) MoO3 [mol%] were synthesised by a conventional melt quenching method. Appropriate amounts of the constituent oxides were mixed and melted at about 1200 1C. The melts were rapidly quenched on a steel plate to obtain glass samples of the desired composition. Chemical composition of the glasses was determined by the XRF spectroscopy using an ARL ADVANT'XP spectrometer and is presented in Table 1. Amorphous state of the analysed phosphate glasses was confirmed by the X-ray diffraction method and it was presented in our previous work [5]. Density of the samples was measured by a helium pycnometry technique using a Micromeritics AccuPyc II 1340 Gas Pycnometer apparatus. The density was determined with an accuracy of 0.0001 g/cm3. Measurement was repeated 30 times to ensure precision. Before the measurement the sample was purged with helium 70 times to remove impurities and stabilise its temperature and volume.
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M. Szumera / Materials Letters 135 (2014) 147–150
Table 1 Chemical composition of analysed glasses from P2O5–SiO2–K2O–CaO–MgO–MoO3 system. No
0Mo41P 2Mo41P 4Mo41P 8Mo41P 15Mo41P 30Mo41P
Content of components/mol% P2O5
SiO2
K2O
MgO
CaO
MoO3
40.7 40.8 41.9 40.8 40.6 41.2
6.5 6.0 5.2 5.7 6.2 5.8
5.7 5.7 6.9 6.2 6.2 6.3
28.8 27.8 25.5 22.9 19.1 10.0
18.2 17.8 16.6 16.4 12.8 7.2
0.0 1.9 3.9 8.0 15.1 29.5
Table 2 Physical parameters of glasses from P2O5–SiO2–K2O–CaO–MgO–MoO3 system.
0Mo41P 2Mo41P 4Mo41P 8Mo41P 15Mo41P 30Mo41P
Density g/cm3
Standard deviation g/cm3
Molar value cm3/mol
OPD g atm/l
2.4685 2.5294 2.6063 2.6445 2.6597 2.6785
0.0041 0.0066 0.0028 0.003 0.0061 0.0219
35.99 35.90 36.18 39.72 39.02 44.21
277.92 362.21 359.45 354.08 330.69 294.09
Middle infrared (MIR) spectroscopic measurements of the glasses were conducted with a Bruker Vertex 70v spectrometer using the transmission mode. The samples had the form of pellets made of the glasses mixed with KBr. Spectra were collected after 124 scans with 4 cm 1 resolution. Positions of bands on the MIR spectra were determined automatically by Win-IR software. Spectra decomposition has been carried out according to the mathematical self-deconvolution method using the minimisation of the number of the bands rule, proposed by Handke et al. [11].
is also oxygen packing density, which is helpful in determining the compactness of the glass network. It should be emphasised that the mere introduction to the structure of glass containing in its composition MoO3 causes significant increase in OPD, from the value of 277.92–362.21 g atm/l. The obtained data (Table 2) are consistent with the literature [12,18–20]. This indicates that the structure becomes loosely packed with an increase in the MoO3 concentration. Infrared absorption spectra: The effect of MnO2 addition on the structure of analysed silicate–phosphate glasses is illustrated by the FTIR spectra in the middle infrared range (Fig. 1). The spectra of the aforementioned glasses are characterised by the presence of four main absorption bands with the maxima located in the 1400– 1200, 1200–850, 850–700 and 400 cm 1 wavenumber regions. Due to the complex and broad character of absorption spectra of the investigated glasses, a process of their decomposition into separate bands was carried out (Fig. 2). Wavenumbers range: 1400–1200 cm 1: In this range a single band, located at about 1280 cm 1 was registered and it was assigned to the characteristic stretching mode of the P¼O bond [21]. Several previous studies [22–24] also showed that the asymmetric stretching vibration of O–P–O groups, can be found in this frequency region. This band is well visible for both glass 0Mo41P not containing MoO3 and glass modified by its supplementation. It was stated that locations of bands shifted towards lower wavenumbers (1286-1280 cm 1), which may suggest that MoO3 has a depolymerising effect on the phosphate bonding. Wavenumbers range: 1200–850 cm 1: In this range of wavenumbers, the presence of three absorption bands was observed; the conducted process of FTIR spectra decomposition enabled determining, in their scope, additional bands lying in the following wavenumber ranges: 1200–1040 and 1000–850 cm 1 (Fig. 2). The first is assigned to the asymmetric stretching vibration of the
3. Results and discussion Density and molar volume: The density is a powerful tool, capable of reflecting the effect of structural changes in glass. The glass structure can be also expressed in terms of the molar volume, as the former deals the spatial distribution of ions forming the glass structure [12,13]. From the structural point of view, the molar volume V ¼ M=ρ, where M ¼ ∑xi M i is the mean molecular weight of analysed glasses and ρ is the mass density; M i is the molecular weight of component i and xi is the mole fraction of component i [14]. A parameter estimated from density is also the oxygen packing density (OPD) and it was calculated using the following expression: OPD ¼ 1000ρ½O=M, where [O] is the number of oxygen atoms in the composition [15]. The measured values of these parameters for all analysed phosphate–silicate glasses are presented in Table 2. It was found that the density of analysed glasses increased gradually with increasing content of MoO3. Such an effect was expected in connection with introducing to the glass structure a component with a higher molecular weight in relation to the molecular weight of MgO and CaO. Molar volume values calculated by taking into account the measured densities were found to range from 35.99 to 44.21 cm3/mol and exhibited an increase with the substitution of MgO and CaO by MoO3. This behaviour may be attributed to the increase in the quantity of non-bridging oxygen (NBOs) [16,17] which can cause the expansion of the network of the system. It is probably also related to the fact that the MoO3 reticulates the vitreous network and this allows for contracting the arrangement of nonbridging oxygen ions. An important parameter
Fig. 1. FTIR spectra of phosphate–silicate glasses from the P2O5–SiO2–K2O–CaO– MgO–MoO3 system.
M. Szumera / Materials Letters 135 (2014) 147–150
149
Wavenumbers range: 800–700 cm 1: In this range of wavenumbers, the presence of two constituent bands was observed at about 780 and 712 cm 1. Bands in this range of wave numbers with increasing content of MoO3 in the glass composition gradually disappear. This band is due to the symmetric stretching vibration of P–O–P linkages, vs(P–O–P) and/or the stretching vibration of P–O–Mo bond [22,27,28]. Wavenumbers range: 450–500 cm 1: On the basis of decomposition of FTIR spectra, the presence of 3 constituent bands was observed, at about 620, 550 and 483 cm 1. The first is characteristic of Si–O vibrations [29], while two subsequent ones may be assigned either to the harmonics of P–O–P bending vibration or to the characteristic frequency of the pyrophosphate (P2O47 ) group [22,27]. A small shift of locations of bands towards lower wavenumber ranges was observed (509-504 cm 1), proving the increasing degree of glass structure depolymerisation.
4. Conclusions The impact of molybdenum ions on density as well as structure of glass from the P2O5–SiO2–K2O–MgO–CaO–MoO3 system was examined. Infrared spectra of the investigated glasses showed absorption bands related to the characteristic phosphate and molybdate bonds especially: P¼O, P–O–P, P–O–Mo and Mo–O– Mo. On the basis of the results of tests on density and structure of analysed glass, it was stated that the introduction of larger quantities of MoO3 at the expense of reducing the content of MgO and CaO causes gradual glass structure depolymerisation, and molybdenum ions in the analysed glass matrix act as modifying cations.
Acknowledgements
Fig. 2. The decomposition of FTIR spectra of phosphate–silicate glasses from the P2O5–SiO2–K2O–CaO–MgO–MoO3 system containing: (a) 3.9 mol% MoO3 and (b) 29.5 mol% MoO3.
The author want to express their thanks to Prof. Irena Wacławska, for help in density discussion to Prof. Krzysztof Haberko and in FTIR spectroscopy to Prof. Maciej Sitarz of Faculty of Materials Science and Ceramics, AGH University of Science and Technology in Cracow. The work was supported by Faculty of Materials Science and Ceramics AGH – University of Science and Technology (2014) No. 11.11.160.603. References
metaphosphate groups, vas(PO3) [22]. It was stated that introduction to the structure of analysed glass of increasing content of MoO3 affects the position of these bands shifted towards lower wavenumbers (1105-1043 cm 1), which may suggest that MoO3 has a depolymerising effect on the phosphate network. In the second range, bands located at about 960–1020 cm 1 can be attributed to the symmetric stretching vibration of metaphosphate groups, vs(PO3) [22]. However, according to [23], band at about 963 cm 1 could be also ascribed to the Mo–O stretching vibration in bridging Mo–O–Mo linkages. The location of these bands also shifts towards lower wavenumbers, which would confirm the previous presumptions. The conducted process of spectra decomposition made it possible to state the presence of bands at about 917 cm 1 (Fig. 2). Literature data [24–26] suggest that the presence of these bands is characteristic of stretching vibrations of [Mo–O6] groups. This suggests the presence of structural units such as [MoO6] [MoO6] and/or [MoO6] [PO4] [25], in the structure of analysed phosphate glass, thus gradually building molybdenum ions into the phosphate sub-network and causing its gradual depolymerisation.
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