Phosphosilicate Glasses Research Articles

Development of New Glass Composite Membranes and their Properties for Low Temperature H2/O2 Fuel Cells

A new glass electrolyte formed by constant amounts of titanium oxide (TiO2) and various amount of phosphotungstic acid (PWA) doped P2O5-SiO2 is prepared using the sol-gel process. The structural formation is confirmed by Fourier infrared spectroscopy (FTIR) and from thermogravimetric and differential thermal analysis (TG/DTA) measurements, the glasses display good thermal stability. Further characterisation is undertaken by N2 adsorption/desorption measurements, proton conductivity and hydrogen permeability analyses and a H2/O2 fuel cell test is also performed. The glass materials with large pores and specific surface area are suitable for use as the electrolyte in H2/O2 fuel cells. The effect of TiO2 processing with constant amount of PWA in phosphosilicate glasses, is investigated and discussed. The hydrogen permeability is 1.57x10(-11) mol cm(-1) s(-1) Pa(-1) at 110 degrees C for 0.8 mm thick glass; a power density of 46.3 mW cm(-2) at 125 mA cm(-2) and a current density of 175 mA cm(-2) is obtained (T=28 degrees C, relative humidity).

The formation of nanoscale structures in soluble phosphosilicate glasses for biomedical applications: MD simulations

The occurrence of chain-like fragments and rings in phosphosilicate glasses of known bioactivity was examined using classical molecular dynamics simulations, in order to reveal the possible effect of such nanostructures on the bioactive behaviour. Highly bioactive compositions display a large fraction of non-crosslinked, nonlinear chains of tetrahedra, which are not present in bio-inactive compositions. The low(er) energetic cost associated with the direct release of these silicate fragments into solution can assist the fast partial dissolution observed for bioactive glass compositions. Loss of bioactivity when the silicate content increases is accompanied by the transformation of these chains into small closed rings (3- to 8-membered), which appear to protect the silicate network from fast dissolution.

The Structure of Bioactive Silicate Glasses: New Insight from Molecular Dynamics Simulations

The structural properties of three compositions of phosphosilicate glasses are investigated by means of molecular dynamics computer simulations using a new potential model incorporating polarization effects. Structural features of the three compositions are compared in order to highlight the effect of the composition on the different known bioactivities of these materials. Changes in the coordination environment, network connectivity, and ion aggregation with the silica content are discussed, as they enable us to draw a microscopic model of the glasses, which supports the interpretation of experimental data and provides new insight into the special physicochemical behavior of these materials. The transition from highly bioactive to bioinactive compositions is characterized by a marked increase in the connectivity of the silicate network and by an increasing fraction of phosphate groups involved in P−O−Si cross-links. Our analysis also highlights a possible correlation between the loss of bioactivity and a...

High Performance of H2/O2 Fuel Cells using Pt/C Electrodes and P2O5-SiO2-PMA Glasses as an Electrolyte in Low Temperature

Heteropolyacid containing phosphosilicate glasses were prepared by the sol-gel technique and were studied in relation to their structural, thermal, and textural properties. These glasses are mechanically, thermally, chemically stable and have proton conductivity. It was found to be a suitable potential electrolyte for H2/O2 fuel cells. The average pore size of up to 3 nm was observed from a N2 adsorption-desorption analysis. The electrical conductivity was measured under humidity and temperature conditions. The glasses showed the proton conductivity values in the order of 10-3-10-2 S cm-1, especially, 9.8×10-2 S cm-1 at 90°C and 70% RH. The cell performance is mainly determined by the higher conductivity characteristics of the electrolyte. We have successfully achieved a high power density value of 17.2 mW/cm2 using P2O5-SiO2-PMA (7-89-4 mol%) glasses as an electrolyte and 0.1 mg/cm2 of Pt/C loaded on the electrode at 30°C and RH 30%.

Radiation-induced luminescence from sol-gel silica glasses and phosphosilicate glasses by 1 MeV H+ and 3 MeV Zr2+ irradiations

Radiation-induced luminescence (RIL) spectra have been applied to the study of photon emission from sol-gel silica glasses and phosphosilicate glasses. For the silica glass specimen, the irradiation of 1MeV H+ and 3MeV Zr2+ are investigated with the Red band at 1.9eV and the Blue band at 2.7eV, respectively. For the phosphosilicate glass specimen, the effects of ion irradiation are restrained by the peculiar defects.

Raman and optical reflection spectra of germanate and silicate glasses

Germanate and phosphosilicate glasses made in oxygen surplus conditions were studied by Raman and optical reflection methods. We found that the optical reflection spectra of the germanate glasses are quite similar to the one those of a GeO2 crystal with the α-quartz structure. The reflection of phosphosilicate glasses is very close to silica glass-related spectra. Hence, the determining influence of the tetrahedral structure on reflection spectra is revealed. The Raman spectra of germanate samples are similar to those reported the one known in the literature. Octahedral entities, namely bands similar to stishovite vibration modes, were difficult to detect in phosphosilicate glasses through Raman spectroscopy.

Stability of Luminescent Trivalent Cerium in Silica Host Glasses Modified by Boron and Phosphorus

Ce-doped borosilicate (BSG), phosphosilicate (PSG), and borophosphosilicate (BPSG) glasses (B:P:Si molar ratios 8:0:92, 0:8:92, and 8:8:84; Ce:Si molar ratio 1 x 10(-)(4) to 1 x 10(-)(2)) were prepared by the sol-gel method. High-resolution transmission electron microscopy (HRTEM), (31)P, (29)Si, and (11)B magic angle spinning nuclear magnetic resonance (MAS NMR), electron paramagnetic resonance (EPR), and UV-vis absorption investigations demonstrated that, in PSG and BPSG, Ce(3+) ions interact with phosphoryl, [O=PO(3/2)], metaphosphate, [O=PO(2/ 2)O](-), and pyrophosphate, [O=PO(1/2)O(2)](2)(-), groups, linked to a silica network. This inhibits both CeO(2) segregation and oxidation of isolated Ce(3+) ions to Ce(4+), up to Ce:Si = 5 x 10(-)(3). In BSG, neither trigonal [BO(3/2)] nor tetrahedral [BO(4/2)](-) boron units coordinate cerium; thus, Ce(3+) oxidation occurs even at Ce:Si = 1 x 10(-)(4), as in pure silica glass (SG). The homogeneous rare-earth dispersion in the host matrix and the stabilization of the Ce(3+) oxidation state enhanced the intensity of the photoluminescence emission in PSG and BPSG with respect to BSG and SG. The energy of the Ce(3+) emission band in PSG and BPSG matrixes agrees with the phosphate environment of the rare earth.

Structure and formation mechanism of six-fold coordinated silicon in phosphosilicate glasses

The local structure of sixfold oxygen coordinated silicon $(^{[6]}\mathrm{Si})$ in sodium phosphosilicate glasses has been investigated using MAS NMR spectroscopy and ab initio quantum-chemical techniques. It has been demonstrated that $^{[6]}\mathrm{Si}$ is interconnected by six $\mathrm{P}{\mathrm{O}}_{4}$ tetrahedral units by sharing only their corners, forming a nearly regular ${[\mathrm{Si}{\mathrm{O}}_{6∕2}]}^{2\ensuremath{-}}$ octahedral site. Alkali cations behave as charge compensators of the doubly charged $^{[6]}\mathrm{Si}$ species and hence play an indispensable role in stabilizing the peculiar octahedral coordination in the glasses.

Studies of silicophosphate derivatives by 31P→ 29Si CP MAS NMR

We show that it is possible to efficiently transfer magnetization from 31P to 29Si, using variable amplitude CP MAS experiment. This experiment is demonstrated by using Si 5O(PO 4) 6, the synthesis protocol of which is described. From the obtained results, we show that the experiment allows the spectral edition of 29Si spectra from 31P→ 29Si CP, enabling the studies of derivatives involving Si–O–P linkages, such as phosphosilicate glasses, microporous silicoaluminophosphates (SAPO) and bioactive phosphosilicates.

Synthesis of High Surface Area Phosphosilicate Glasses by a Modified Sol−Gel Method

High surface area phosphosilicate glasses were synthesized by a new sol−gel method and characterized for structural, textural, and acid properties by X-ray diffraction, thermogravimetry/differential thermal analysis, IR spectroscopy (Fourier transform and diffuse reflectance Fourier transform), solid state 31P and 29Si NMR spectroscopy, N2 adsorption, and NH3 temperature programmed desorption. The glasses were synthesized by a sol−gel route hydrolyzing the precursors in an almost solely aqueous environment. Microstructural changes occurring during the conversion of the gels into the corresponding glasses were investigated. For all dried gels (383 K), the elimination of organic residues was complete at 673 K. After this heat treatment, ca. 80% of the phosphorus was present as free phosphoric acid except for the sample with the highest P content for which the percentage dropped to ca. 47%. Textural properties of samples treated at 673 K were greatly influenced by the composition. Surface area decreased and ...

Interaction of molecular hydrogen with the doped silica core of an optical fiber at elevated temperatures

Optical fibers with cores made of germanosilicate, phosphosilicate, and nitrosilicate glasses are loaded by molecular hydrogen at a pressure of 10 MPa and room temperature. Then, preloaded fibers are kept in a hydrogen atmosphere at the same pressure and various fixed temperatures up to 700°C and the transmission spectra of the fibers are measured in situ at a constant temperature with equal time intervals. The kinetics of the chemical interaction between hydrogen and the silica is determined by analyzing an increase in the optical absorption at the overtones of OH and NH groups.

Early Steps of Orthophosphate Crystallisation in a Ca-Mg-K Phosphosilicate Glass Frit

Abstract. An investigation on the crystallisation of a whitlockite type orthophosphate phase in a calcium phosphosilicate glass frit with the molar composition (3CaO.P 2 O 5 ) 20 (SiO 2 ) 35 (MgO) 38.354 (K 2 O) 6.646 was made. Isothermal heat treatments at different temperatures combined with XRD and SEM analysis of the glass ceramics have shown that in glass frits of this composition the whitlockite type orthophosphate phase, Ca 9 MgK(PO 4 ) 7 develops from earlier crystalline phosphate phase precursors, namely from oxyapatite (OAp), the ideal composition being Ca 5 (PO 4 ) 3 O. This OAp phase seems to evolve from a previous tricalcium phosphate phase, Ca 3 (PO 4 ) 2 (TCP). Introduction Devitrification of calcium-phosphosilicate glasses can lead to several Ca-phosphate phases, either crystalline or amorphous. The TCP to OAp conversion has already been reported for a few phosphosilicate glasses [1-3]. Taking into consideration the results previously reported we focus the OAp to Ca

Radiation-induced luminescence and photoluminescence from sol–gel silica glasses and phosphosilicate glasses by 1 MeV H + irradiations

Radiation-induced luminescence (RIL), photoluminescence (PL) and PL excitation (PLE) spectra have been applied to the study of photon emission from sol–gel silica glasses and phosphosilicate glasses. The photoemissions from oxygen excess-related defects are observed at about 1.98 eV by PL and RIL. The irradiation of 1 MeV H + is investigated with the excitation bands at 2.11 and 2.13 eV by PLE. The effects of ion irradiation on the glass samples show that the defects were increased in the silica glass and decreased in the phosphosilicate glass.

Thermal analysis of gel-derived bioactive phospho-silicate glasses

Thermal reactions of model phospho-silicate gels of simple composition has been studied. The investigations demonstrate that the kind of compounds introducing P2O5 into the gel silicate network, H3PO4, PO(OC2H5)3, POCl3 influence the course and temperature and the xerogel formation. The amount of interstitial water and xerogel porosity is dependent on the cations, amorphous structure modifiers (Ca, Na) used. Thermal analysis curves appear the convenient carriers of informations about the processes in gel pores and the formation of xerogel and glass.

Synthesis and characterization of cerium-doped glasses and in vitro evaluation of bioactivity

The results of preparation, characterization and in vitro bioactivity evaluation of phosphosilicate glasses based on Bioglass ® 45S5 (SiO 2 45; Na 2O 24.5; CaO 24.5; P 2O 5 6 wt%) doped during melting with (1.5–13.5 wt%) cerium dioxide (CeO 2), has been reported. The choice of cerium was related to its low toxicity associated with bacteriostatic properties; cerium-doped bioactive glasses could be useful when implantation concerns local infected areas. The maximum value that permitted forming a homogeneous glass was 13.5 wt% and enabled us to get a better insight into CeO 2 effect on the chemical behaviour of glasses. The as-quenched glasses were characterized by means of magnetic and spectroscopic measurements that revealed the prevailing presence of cerium (III). The bioactivity of the glasses was tested by soaking them in a simulated body fluid at 37 °C, under continuous stirring. ICP measurements were carried out for ion concentration determinations and the solution/glass interface was investigated by scanning electron microscopy equipped with energy dispersive analyzer (SEM/EDS technique) to check morphological modifications; the solids were investigated by means of X-ray powder diffraction and IR techniques. The results indicated that at low cerium content the glass degradation and repolymerization gave rise to an internal silicon-based layer and an external calcium-phosphate-based layer formed on the glass surface; high cerium content retards the glass degradation and gave rise to cerium–phosphate layer instead of calcium one. The cerium was never found in solution. For the reacted glasses, in the external layer, at 10% and 13.5% CeO 2 contents the molar ratio Ca/P were ≈1 and 0.8 respectively and the molar ratio Ce/P was ≈0.3 in both cases. On the surface of the glasses with the highest cerium content it could distinguish new regular aggregates mainly formed by cerium and phosphate (Ce/P≈3.5, Ca/P≈0.6). In the cerium-free glass and with low cerium content (1.5 wt%) the calculated Ca/P ratio was 1.67, as calculated for pure hydroxyapatite. At low cerium content (BG-1.5 Ce) the glass behaviour was strictly similar to that of Bioglass ® 45S5.

Solid state 1H NMR study, humidity sensitivity and protonic conduction of gel derived phosphosilicate glasses

1H Magic Angle Spinning (MAS) NMR and 1H T1 and T1ρ relaxation times measurements were used to investigate structural aspects of gel derived glasses of composition 10P2O5·90SiO2 (10P) and 30P2O5·70SiO2 (30P), with the aim of understanding the different humidity sensitive behaviour observed for films of the same composition. The experimental evidence suggests that 10P and 30P gel samples heat treated at 100 °C have a similar POH environment while further heating causes a different structural evolution of POH units. In particular, the 30P sample heat treated at 400 °C shows a single 1H resonance while a number of resonances are seen in the 1H spectrum of the 10P sample heat treated at 400 °C. Further evidence of the different structure of 10P and 30P samples was given by the NMR relaxation times measurements, the gels were found to be heterogeneous on a nanometric scale. Domains, about 60 nm in size, related to 1H resonance in POH were evenly distributed in the matrix of both gels, only in the 10P gel also larger domains (about 700 nm) were found that can be related to 1H resonance in SiOH groups. Finally, MAS in combination with variable temperature static NMR spectra provided detailed information on the network structural features present in the 30P sample heat treated at 300 °C as well as in the 10P sample heat treated at 400 °C and allowed investigation of the dynamic processes taking place in these samples.

On the structure of phosphosilicate glasses

Vibrational spectra of phosphosilicate glasses with P 2O 5 concentrations up to 15 mol% are investigated by the methods of Raman spectroscopy and quantum-chemical modeling. We have found that the Raman band at 1320 cm −1 characteristic for such glasses is not simple and may be decomposed into two components with frequencies at ≈1317 and ≈1330 cm −1 caused in our opinion by single phosphorus centers (OPO 3 tetrahedra surrounded by SiO 4 ones) and by double phosphorus centers (pairs of OPO 3 tetrahedra bonded by a common oxygen atom). In the investigated phosphosilicate glasses manufactured by MCVD and SPCVD methods the ratio of concentrations of single and double centers varies from 1:5 to 1:2. A novel interpretation of the Raman bands distinct from the traditional one is suggested. The approach to the Raman spectra analysis developed in this article can be applied for control and optimization of manufacturing process of phosphosilicate and similar glasses as well as optical fibers.

Investigation of the medium range structure of phosphosilicate glasses by cw-EPR, 1D-ESEEM and HYSCORE spectroscopies

6Li 2O 3P 2O 5 6SiO 2 and 6Na 2O 3P 2O 5 6SiO 2 glasses were exposed to 60Co γ-ray irradiation for the production of paramagnetic states that were studied by continuous wave(cw)-EPR, 1D-electron spin echo envelop modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) spectroscopies. The cw-EPR signal consisted of a doublet separated by ≈47 G. This doublet was assigned to the Q n=2 -type center (POHC-defect). The analysis of the 1D-ESEEM peaks determined the A iso and T ⊥ parameters. Using the point dipole approximation for T ⊥, the r(P–O–P)-distance was estimated to be ≈2.83 and ≈3.49 Å while the P–O–P bond angle was determined to be ≈107° and ≈168° for Li and Na containing glasses, respectively. HYSCORE spectroscopy unveiled the presence of alkali metal ions in close proximity to the phosphorus oxygen hole center (POHC). The experimental findings together with SCF-HF calculations suggested the existence of the POHC–POHC–Li/Na complex (Q 2–Q 2–Li/Na-structure) in the glasses. It has been demonstrated that the advanced EPR techniques extend the spatial resolution of the cw-EPR spectroscopy to the medium range structure of the amorphous state.

Thermochemistry of Biologically Active Glasses

Mutual relation between thermal activity and biochemical activity of the phospho-silicate glasses which are used as controlled rate release fertilisers and bioglasses for medical applications, has been observed. Analysis of the local atomic interactions in the structure of glass is used to explain this relation.

Solid state 29Si and 31P NMR study of gel derived phosphosilicate glasses

Solid state 29Si and 31P MAS NMR have been used to investigate the microstructural changes occurring in phosphosilicate gels during their conversion from a gel to the corresponding gel-derived glasses by heating. The studied gels have the molar compositions 10P2O5·90SiO2 and 30P2O5·70SiO2. It was found that the dried gels (100 °C) have very similar structures formed by a siloxane framework containing silanol groups and including trapped molecules of orthophosphoric acid along with a very small amount of pyrophosphoric acid. In spite of this initial similarity further heating causes markedly different structural rearrangements of their glassy matrices. Namely, the co-polymerisation of phosphate and silicate tetrahedra takes place at 300 °C for the gel with the higher phosphorus content whereas this occurs only after heat treatment for 30 minutes at 400 °C for the gel with the lower phosphorus content. Moreover, the presence of six-coordinated silicon in the glassy matrix of the 30P2O5·70SiO2 gel has been observed. The different evolution of the investigated gel microstructures mirrors their different crystallization behaviour: 10P2O5·90SiO2 keeps its amorphous nature up to 1000 °C while for 30P2O5·70SiO2 crystallization starts after heat treatment for 30 minutes at 400 °C.