Number Of Non-bridging Oxygen Atoms Research Articles

X-ray photoelectron spectroscopy, structural, and radiation shielding properties for transparent borosilicate glasses

The current work investigates the impact of SrO content on the structural, physical, and shielding properties of xSrO-10TiO2–10SiO2-(65-x) B2O3, where (15 ≤ x ≤ 30) glasses. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), and radiation shielding features were utilized to investigate the samples’ features. XRD results affirmed the amorphous behavior. The FTIR values presented many peaks attributed to SiO2 and B2O3. The Sr30B50 sample (3.048 g/cm3) showed the highest density, followed by Sr25B55 (2.936 g/cm3), Sr20B60 (2.720 g/cm3) and Sr15B65 (2.679 g/cm3). The XPS analysis of Ti 2p core level spectra reveals that Ti ions exist in both Ti4+ and Ti3+ oxidation states, with the content of Ti4+ increasing with the SrO ratio in the glass sample. The XPS analysis of O 1s core level spectra revealed that the number of non-bridging oxygen atoms is enhanced with an increase in SrO content, indicating the weakening of the glass structure. Furthermore, neutron and photon shielding properties were calculated theoretically using Phy-X software. The gamma shielding properties were enhanced with increasing SrO, while the neutron attenuation was equivalent to water. For example, the fast neutron removal cross-section (FNRCS) values are 0.101, 0.098, 0.102, and 0.101 cm−1 for Sr15B65, Sr20B60, Sr25B55, and Sr30B50, respectively. The findings suggest that the SrO improved radiation shielding properties while decreasing glass stability.

Cadmium oxide as a substitute for sodium phosphate structural units: structure and properties

Amorphous glasses in the system xCdO-(100-x)(yNa2O + zP2O5), (x = 0, 10, 20, 30, 40, 42.5, 45, y = z) mol% are prepared by a fast quenching technique. Addition of CdO at the expense of equal amounts of both P2O5 and Na2O causes a substantial influence on the distinctive feature of the measured Raman spectra. The concentration of nonbridging oxygen atoms (NBO) rises with increasing CdO content. The numerical data from the deconvolution of Raman spectra revealed that Q3 (branching group) and Q2 (metaphosphate group) decline while Q1 (pyrophosphate group or end group) increases. The rise in the number of NBO in terms of Q1 is supported by the change in molar volume, free volume, and packing density. This result is compatible with Raman and NMR spectroscopic observations. Increased CdO content causes a rise in the O/P ratio, which causes an increase in NBO in the glass network which lowers the glass’s hardness number.

Effect of the SiO2/GeO2 ratio in the Na2O-B2O3-SiO2-GeO2 system on the characteristics of porous glasses

Results from a study of glasses of the Na2O-B2O3-SiO2-GeO2 system and porous materials obtained from them are presented. Conclusions about the appearance of highly coordinated germanium atoms in the network of the initial glasses with a decrease in the SiO2/GeO2 ratio and simultaneous decrease in the number of non-bridging oxygen atoms are drawn according to the results of Raman spectroscopy. The characteristics of the porous materials were determined by the nitrogen adsorption/desorption method. It is noted that the growth of the specific surface area and pore volume depends on the structural features of the initial glass. The porous characteristics of glass are shown to be directly dependent on the number of six-coordinated germanium atoms and inversely dependent on the number of non-bridging oxygen atoms. It is shown that the replacement of silicon oxide with germanium oxide in the Na2O-B2O3-SiO2 system leads to an increase in the pore diameter, which may be due to the absence of a secondary germanium residue.

The structure of glasses M2O-B2O3 (М – Li, Na, K): Estimation of thermodynamic characteristics of alkali borates and physicochemical modeling

The paper presents results of structural calculations carried out on the alkali borate glasses using physicochemical modeling based on Gibbs energy minimisation. Standard heat capacity, entropy and enthalpy of formation values for lithium, sodium and potassium borates are estimated by regression analysis for use as the input data for the models taking into account the error of the initial data. The correction of the physicochemical model was made using results of Raman spectroscopy. The dependence of the maximum of the “borate anomaly” on the number of non-bridging oxygen atoms was shown. It was found that the most obvious changes in the dependence of properties occur in the regions of N1 and N2 compositions, which are characterized by the appearance of asymmetric triangles BØ2O− and BØO22− in glasses, correspondingly.

Influence of the gradual increase of TiO2-impurities on the structural and optical properties of some calcium sodium borate glasses

The influence of the gradual increase of TiO2-impurities on the structural and optical properties of some calcium sodium borate glasses was studied to estimate its possibility to use for optoelectronic applications. Where a set of samples were prepared by the fast cooling method, then XRD, and FTIR were used for the characterization and identification of the internal structures of those samples, which exhibited the short-range order structure of the amorphous solids. The introduction of TiO2 caused BO3 to convert to BO4, increase the bulk density of the samples, increase the number of non-bridging oxygen atoms, increase the optical absorbance, and decrease the volume energy loss function. The optical band gaps for the allowed electronic transitions of the study samples showed an anomalous behavior when the Ti-content increase, where the value of the optical bandgap for direct transition increased while that of indirect transition decreased. UV–vis spectral analysis showed the absence of any absorption peaks, which requires that all Ti-cations should be of tetrahedral coordination and have an empty d-subshell.

Dielectric properties of CaO–B2O3–SiO2 glass-ceramic systems in the millimeter-wave frequency range of 20–60 GHz

The dielectric and structural properties of the as-quenched melts of three CaO–B2O3–SiO2 compositions (denoted CBS-1, CBS-2, and CBS-3) were investigated to determine their suitability for use in millimeter-wave applications. The CBS-1 glass-ceramic exhibited the lowest coefficient of thermal expansion (CTE = 3.2 ppm/°C), lowest dielectric constant (εr = 4.04) at 60 GHz, and highest dielectric loss (tan δ = 0.0029) at 60 GHz, which were attributed to the presence of quartz (SiO2) as the major phase. In contrast, as the major phase constituent of the CBS-2 and CBS-3 glass-ceramics was β-CaSiO3, they presented relatively high CTEs (6.6 and 5.9 ppm/°C, respectively), relatively high dielectric constants at 60 GHz (6.29 and 7.61, respectively), and relatively low dielectric losses at 60 GHz (0.0020 and 0.0012, respectively). The CBS-1 glass-ceramic exhibited the highest dielectric loss because of the presence of SiO2 as the major phase constituent as well as lattice scattering induced by the high glassy phase content. The thermal conductivities (κ) of the CBS-1, CBS-2, and CBS-3 glass-ceramics were determined to be 2.43, 1.06, and 0.82 W/mK, respectively. Structural analysis using Raman and Fourier transform infrared spectroscopy revealed an absence of nonbridging oxygen in the CBS-1 glass-ceramic, while the high CaO content (>40 mol%) of the CBS-2 and CBS-3 glass-ceramics triggered the formation of nonbridging oxygen in the tetrahedral silicate units. The increase in CaO content of the glass-ceramics increased the number of nonbridging oxygen atoms, thereby resulting in the relaxation of the structure. Consequently, the CBS-2 and CBS-3 glass-ceramics exhibited low thermal conductivity. All the prepared glass-ceramics presented high electrical resistivities of greater than 5 × 1011 Ω cm. The CBS-1 glass-ceramic displayed the highest breakdown strength of 15.20 kV/mm. Overall, the excellent microwave dielectric properties and thermal properties of the CBS glass-ceramics will facilitate the utilization of these materials in millimeter-wave applications.

Characteristic studies on Ag2O-Al2O3-P2O5 glasses and glass ceramics

Glass structure comprising (0–20) mol% Al2O3–(20–40) mol % Ag2O-and 60 mol % P2O5 was examined using a 27Al, 31P MAS- NMR and FTIR spectroscopy. The structural changes within the complicated ternary phosphate glasses were correlated with that of a simple binary silver phosphate. Results show that aluminum acts primarily as intermediate ions, while silver acts as a potent modifier. The number of non-bridging oxygen atoms (NBO) on average in the structure of silver aluminophosphate (SAP) glasses decreases with increasing Al2O3 content. The aluminum ions in the SAP glass system occur in the coordinations of both Al (6) and Al (4). The Al (6) fraction rises with rising concentration of Al2O3. Al (6) is more than Al (4) in the glass containing more Al2O3 than that of 20 mol of Al2O3. The glass was transformed into a glass-ceramics by the effect of thermal heat treatment at 600 °C for 4 h.

Oxygen fugacity and melt composition controls on nitrogen solubility in silicate melts

Knowledge of N solubility in silicate melts is key for understanding the origin of terrestrial N and the distribution and exchanges of N between the atmosphere, the silicate magma ocean, and the core forming metal. To place constraints on the incorporation mechanism(s) of N in silicate melts, we investigated the effect of the oxygen fugacity (fO2) and melt composition on the N solubility through N equilibration experiments at atmospheric pressure and high temperature (1425 °C). Oxygen fugacity (expressed in log units relative to the iron-wüstite buffer, IW) was varied from IW –8 to IW +4.1, and melt compositions covered a wide range of polymerization degrees, defined by the NBO/T ratio (the number of non-bridging oxygen atoms per tetrahedrally coordinated cations). The N contents of the quenched run products (silicate glasses) were analyzed by in-situ secondary ion mass spectrometry and bulk CO2 laser extraction static mass spectrometry, yielding results that are in excellent agreement even for N concentrations at the (sub-)ppm level. The data obtained here highlight the fundamental control of fO2 and the degree of polymerization of the silicate melt on N solubility. Under highly reduced conditions (fO2 = IW –8), the N solubility increased with increasing NBO/T from 17.4 ± 0.4 ppm·atm−1/2 in highly polymerized melts (NBO/T = 0) to 6710 ± 102 ppm·atm−1/2 in depolymerized melts (NBO/T ∼ 2.0). In contrast, under less reducing conditions (fO2 > IW –3.4), N solubility is very low (≤2 ppm·atm−1/2), irrespective of the NBO/T value. Our results provide constraints on N solubility in enstatite chondrite melts and in the shallow part of a planetary magma ocean. The nitrogen storage capacity of an enstatite chondrite melt, which may approximate that of planetesimals that accreted and melted early in the inner Solar System, varies between ∼60 and ∼6000 ppm at IW –5.1 and IW –8, respectively. In contrast, a mafic to ultra-mafic magma ocean could have incorporated ∼0.3 ppm to ∼35 ppm N under the fO2 conditions inferred for the young Earth (i.e., IW –5 to IW). The N storage capacity of a reduced magma ocean (i.e., IW –3.4 to IW) in equilibrium with a N-rich atmosphere is ≤1 ppm, comparable to the N content of the present-day mantle. However under more reducing conditions (i.e., IW –5 to IW –4), the N storage capacity is significantly higher (∼35 ppm); in this case, Earth would have lost N to the atmosphere and/or N would have been transported into and stored within its deep interior (i.e., deep mantle, core).

Effect of Gamma Irradiation on Structural and Optical Properties of Zirconium Incorporated Sodium Borate Glasses

ABSTRACT The effects of gamma irradiation in the dose rate of 25 kGy on the structural and optical properties of ZrO2 doped sodium borate glasses were studied. Glassy nature confirmed by XRD and all the physical parameters were calculated. IR spectra revealed the characteristic vibrational and stretching bands due to trigonal and tetrahedral borate network. Slight changes were caused by gamma irradiation in the intensities of the characteristic infrared borate bands and zirconium bands. Irradiated samples developed a noticeable absorption band similar to the F-band familiar in alkali halide crystals which clearly indicated that successive irradiation produced defects in the glass material. Substitution of ZrO2 to the glass matrix suppressed the formation of visible absorption band formed by irradiation whereas no extra peak was observed in the spectral regions. A nonlinear trend was ascribed in the energy band gap values due to the creation of more number of non-bridging oxygen atoms. Emission spectra showed five emission bands corresponding to the zirconium ions which decreased to a very low intensity with a red shift after irradiation. Matching the colour co-ordinates bright blue emission was found for 5 mol% ZrO2 in both irradiated and non irradiated sample.

Concentration Dependent Spectroscopic Properties of Terbium Ion Doped Lead-Borate Glasses and Vitroceramics

Terbium ions doped lead borate glasses and vitroceramics with the composition of xTb4O7·(100-x)[4PbO·B2O3] where x is from 0 to 25 mol % Tb4O7 were prepared by the use of a melt-quenching protocol. Their structural and spectroscopic properties were characterized by x-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman and ultraviolet-visible spectroscopies. The XRD patterns reveal the amorphous nature of the samples with low Tb4O7 content up to x equal to 1 mol % Tb4O7. Above this concentration, the analysis of XRD measurements indicates the presence of new crystaline phases in the vitroceramic samples. The FTIR and Raman measurements indicate that the addition of the rare earth oxides in the host network is realized by the deformation of the Pb-O-Pb or O-Pb-O angles, the formation of varied borate units and a large number of non-bridging oxygen atoms. The compositional evolution is conducted at the formation of crystalline phases of the terbium and lead atoms. The terbium atoms have a pronounced affinity toward the borate units while the lead atoms are attracted toward the oxygen atoms. Structural investigations by ultraviolet-visible spectroscopy show the presence of larger bands due to the f-f electron transitions of the Tb3+ ions and 6 s2 → 6s 6p transitions of Pb2+ ions, respectively. The optical gap energy values are dependent upon the concentration of the dopant level.

Water Resistances of Ag₂O-, BaO-, and CuO-Doped V₂O5-P₂O5-TeO₂ Glass Sealants.

V₂O5-P₂O5-TeO₂, a low-temperature vanadate-based glass sealant, was doped with metal oxides (MO = Ag₂O, BaO, or CuO), which generate Ag, Ba, and Cu ions, respectively, to strengthen the glass structure and improve its water resistance. These ions reduce the number of nonbridging oxygen atoms in the glass structure by forming V-O-M or P-O-M crosslinks in the V₂O5-P₂O5 glass system. Structural analysis using Fourier-transform infrared spectroscopy indicated that the numbers of P-O-P, V═O, and V-O-V bonds decreased with increasing metal oxide content. Thermal property analyses revealed that the glass transition temperatures increased by approximately 2-30 °C and that the coefficients of thermal expansion only varied within approximately ±10×10-7 K-1 among all the glass samples. The contact angles were measured to quantify the wetting properties of the doped glasses. The contact angle increased from 11 to 36° with increasing metal oxide content at 410 °C. As an indication of the water resistances of the doped glasses, the dissolution rates of the 9 mol% Ag₂O-doped and pure glasses were 0.078 and 0.523 g cm-2, respectively.

Production of sodium silicate powder from waste glass cullet for alkali activation of alternative binders

A simple process to produce sodium silicate powder from glass cullet has been developed. A mixture of glass powder, sodium hydroxide powder, and water was heated at temperatures of 150 to 330 °C. The effects of glass to NaOH ratio, temperature and duration, inclusion of water and fineness of NaOH were investigated. Fly ash and fly ash/GGBS blends were the precursors for alkali activated binder (AAB) mortars produced with this sodium silicate. Compressive strengths were similar to or better than those obtained with commercially available sodium silicate and sodium hydroxide solutions. FT-IR tests suggested that the reactivity of the glass derived sodium silicate powder was related to the number of non-bridging oxygen atoms in the silicate structure. Cost comparison between AAB and Portland cement concretes gave similar results for normal strength concretes (35 MPa). AAB concretes with higher strengths (50 and 70 MPa) can be cheaper than equivalent traditional concrete.

Optical and Structural Evaluation of Lithium Strontium Borate Glasses Doped with Copper Ions

Background: The alkali borate glasses containing transition metal ions are of great interest for opto-electronic applications. However, there is no systematic study on the lithium strontium borate glasses doped with CuO. Objectives: The aim of this study is to present a complete structural and optical view of this glass system and the influence of CuO content on these parameters. Methods: Li2O-SrO-B2O3 glasses containing different concentrations of CuO were prepared using the melt quenching technique. The prepared glasses have been investigated by measuring physical properties like density and molar volume, structural properties using FTIR spectroscopy and Raman spectroscopy, optical properties using UV-Vis spectroscopy and the compositional effects on spin-Hamiltonian parameters using EPR spectroscopy. Results: The X-ray diffraction patterns of all the studied samples revealed the amorphous nature. The density, molar volume and refractive index, optical band gap energy and Urbach energy vary with the concentration of CuO. The IR and Raman spectroscopic studies revealed that copper ions lead to structural rearrangements through the conversion of three-coordinated boron into four-coordinated boron and thereby reducing the number of non-bridging oxygen atoms. The electron paramagnetic resonance spectra of all the studied glasses exhibit resonance signals characteristic of Cu2+ ions. The values of spin- Hamiltonian parameters indicate that the Cu2+ ions are present in the distorted octahedral sites. Conclusion: The analysis of these results indicated that majority of the copper ions exist in Cu2+ state in these glasses up to 0.8 mol% of CuO and above this concentration some of these ions may convert into Cu+ state. The dependency of various physical, structural and optical properties on the concentration of copper ions shows good application prospective of this glass system for different applications.

Structural and electrochemical properties of recycled active electrodes from spent lead acid battery and modified with different manganese dioxide contents

Samples of MnO2 incorporated into active electrodes structure of the disassembled car batteries were prepared by classical melt-quenching method. The effect of MnO2 concentration on host network were investigated by X-ray diffraction (XRD) analysis, InfraRed (IR), UltraViolet-Visible (UV–Vis), Photoluminescence (PL) and Electron Paramagnetic Resonance (EPR) spectroscopy, measurements of Cyclic Voltammetry (VC).X-ray diffractograms show the presence of the metallic lead in the cubic structure and small amounts of PbO2 crystalline phase with the orthorhombic structure in the metallic samples.Combining all of the outputs from different characterizations, we can conclude that the amount of MnO2 incorporated into structure of the recycled active electrodes has effect on the number of non-bridging oxygen atoms that determines the role of MnO2 as a modifier/network former. At lower MnO2 contents, the doping breaks PbOPb bonds producing the formation of [MnO6] structural units in which the Mn+2 ions are in octahedral symmetry, gap energy value increases and the effect of luminescence is quenched. At higher MnO2 content, MnO2 plays a network former role, joins the vitroceramic network as [MnO4] and [MnO6] structural units and the PL intensity increases.The sample doped with small MnO2 content (x = 5mol%) used as working electrode in the measurements of cyclic voltammetry shows a good reversibility of the voltammogram, also improved the electrochemical properties, namely an increased stability in acidic electrolyte environments and offers an alternative for obtaining of electrodes for rechargeable batteries.

Structural influence of mixed transition metal ions on lithium bismuth borate glasses

Lithium bismuth borate glasses containing mixed transition metals having composition 7CoO·23Li2O·20Bi2O3·50B2O3 (CLBB), 7V2O5·23Li2O·20Bi2O3·50B2O3 (VLBB) and x(2CoO·V2O5)·(30 - x)Li2O·20Bi2O3·50B2O3 (x = 0.0 (LBB) and x = 2.0, 5.0, 7.0, 10.0 mol% (CVLBB1-4)) are synthesized via melt quench route. The synthesized compositions are investigated for their physical properties using density (D) and molar volume (Vm), thermal properties by analyzing DSC/TG thermo-graphs, structural properties using IR absorption spectra in the mid-IR range and optical properties using UV–Vis–NIR spectroscopy. The Electron Paramagnetic Resonance (EPR) spectra of vanadyl and cobalt ion have been analyzed to study compositional effects on spin-Hamiltonian parameters. The non linear variations in physical properties depict a strong structural influence of Co/V- oxides on the glassy matrix. The compositional variations in characteristic temperatures (glass transition temperature Tg, glass crystallization temperature Tp and glass melting temperature Tm) reveals that Tg for glass samples CLBB is relatively less than that of pure lithium bismuth borate (LBB) glass sample wherein Tg for sample VLBB is higher than that of LBB. The increase in Tg (as compared with LBB) with an enhanced substitution of mixed transition metal oxides (2CoO·V2O5) shows a progressive structure modification of bismuth borate matrix. These predictions are very well corroborated by corresponding compositional trends of Tp and Tm. FTIR studies reveal that Co2+& VO2+ ions lead to structural rearrangements through the conversion of three-coordinated boron into four coordinated boron and thereby reducing number of non-bridging oxygen atoms. Bismuth is found to exist in [BiO6] octahedral units only, whereas boroxol rings are not present in the glass network. The theoretical values of optical basicity (Λth) and corresponding oxide ion polarizability (αo2−) have also been calculated to investigate oxygen covalency of glass matrix. Trends in both these parameters suggested an increase in ionic bonding on substitution of divalent transition metal cations causing a more bonding compaction in glass structure. The UV–Vis–NIR spectra suggest that cobalt ions exist as Co2+ states in octahedral coordination in glass network. Inter-electronic repulsion parameter and crystal field splitting energy were evaluated to understand the site symmetry around Co2+-ion in glass. X-band EPR spectra suggest that vanadium ions (V4+) exists as VO2+-ions in octahedral coordination with tetragonal compression. Spin Hamiltonian parameters g-values and A-values of VO2+ ions in glass were calculated. For sample CLBB two resonance lines in EPR spectrum attribute to octahedral symmetry around Co2+-ions were observed.

Determination of the ionization coefficient of carbon on an example of silicate glasses analysis by secondary ion mass spectrometry (SIMS)

A method is proposed for the quantitative estimation of the carbon ionization coefficient followed by the determination of its concentration in silicate glasses by secondary ion mass spectrometry (SIMS). The method is based on the calculation of the sputtering ratio of carbon from the surface of silicate glasses. The dependence of the ionization coefficient on the NBO/T parameter (ratio of the number of nonbridging oxygen atoms to the number tetrahedrally coordinated silicon and aluminum ions), corresponding to the structure and composition of the matrix, is shown. The dependences obtained are calibration graphs for the determination of the ionization coefficient and for the subsequent quantitative estimation of carbon in a silicate sample for a particular SIMS instrument and experimental conditions.

Positron annihilation Lifetime and Fourier transform infrared spectroscopic studies on Bi2O3–B2O3 glasses

Bismuth borate glasses with compositions x (Bi2O3)×(100−x) (B2O3) (where x is in mol. % ranging from 25 to 50 in steps of 5) have been prepared by using melt quenching technique. The glass transition temperature (Tg) of the prepared samples has been measured. It was found that the glass transition temperature (Tg) decreases with increasing Bi2O3 content which indicates that the degree of disorder increases.Furthermore, the density, molar volume and oxygen packing density have been studied. It has been found that the density increases as well as the molar volume. However, the oxygen packing density decreases by increasing the Bi2O3 content which gives an indication that the structure becomes loosely packed. Positron Annihilation Lifetime (PAL), Fourier Transform Infra-Red (FT-IR) and X-ray Diffraction (XRD) measurements have been performed to study the amorphous and defect structure as well as the vibrating band structure. PAL results have revealed weak formation of ortho-positronium (o-Ps) at amorphous sites. The correlation between the optical properties deduced from FT-IR spectra, and the positron annihilation lifetime parameters has been investigated. The decrease of the annihilation lifetime τ2 of trapped positrons at defects with Bi2O3, suggests a free annihilation of positrons at non-bridging oxygen (NBO) bonds, which is also evidenced by the positive correlation between I1 and the number of NBO atoms. FT-IR spectra revealed the presence of some bonds, that are assigned to vibrations of Bi–O bonds from [BiO3] pyramidal and [BiO6] octahedral units and B–O bonds from [BO3] and [BO4] units. On the other hand, increasing Bi2O3 have led to increase in the optical basicity or polarizability up to 35% concentration because the ionic radii of Bi2O3 is larger than those of B2O3. Consequently, a decrease in the optical band gap energy (Eg) with Bi2O3 is observed.

On the dual role of ZnO in zinc-borate glasses

ZnO incorporated borate glass structures have been produced by classical melt-quench technique. The effect of ZnO concentration on the behavior of ZnO in glass network as a modifier or network former has been clearly defined by combining various characterization tools. FT-IR transmittance spectra have been used to study the structure of glass systems. Temperature dependent electrical measurements have been performed to investigate the conduction mechanisms, especially at low temperatures. Activation energies determined by considering classical Arrhenius relation and small polaron hopping mechanism support the comments on the behavior of ZnO in glass network. Optical band gap and Urbach energy values have been calculated using optical measurements. Also, Spectroscopic Ellipsometry technique has been used to determine optical constants (refractive index and extinction coefficient) by Cauchy–Urbach model. Results showed that refractive index of borate glasses can be controlled by the composition of ZnO in the structure. Combining all of the outputs from different characterizations, it has been concluded that the amount of ZnO in borate glass structure has a dramatic effect on the number of non-bridging oxygen atoms that determines the role of ZnO as a modifier/network former. ZnO acted as a network former in samples having more than 5% (weight%) incorporation.

Effect of the Addition of CeO2 to Iron Phosphate Glass for Catalytic Applications.

We investigated the effect of CeO2 content on the catalytic behavior and chemical properties of the (100 - x)(80P2O5-20Fe2O3)-xCeO2 (x = 0, 4, 8, 12, 16, 20 and 24 wt%) glass system. Using thermogravimetric analysis, we confirmed that the catalytic activity increased until a CeO2 content of 16 wt%, beyond which, it decreased. The reasons for the change in the catalytic properties of the glass samples were determined using Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and density analyses. It was confirmed using the FT-IR and XPS-01s spectra that CeO2 acts as a network modifier in iron phosphate glass. When the CeO2 content is above 16 wt%, the number of non-bridging oxygen atoms decreases with increasing CeO2 content. For these reasons, the catalytic properties decrease when the CeO2 content is more than 16 wt%. From the dissolution rate measurements, it can be observed that cerium-iron phosphate has a high water resistance. Also, as we expected, it can be confirmed that the chemical durability is improved with increasing CeO2 content.

Optical and thermal investigations on vanadyl doped zinc lithium borate glasses

Using standard melt-quench technique, transition metal oxide (2 mol% of V2O5) doped glasses having composition xZnO·(30 − x)Li2O·70B2O3 (x = 0, 2, 5, 7 and 10) are prepared. The density (D) is measured using buoyancy and found to be lying between 2.21 and 2.45 g/cm3 with an increasing trend on substituting ZnO contents in place of Li2O. The theoretical optical basicity (Λth) is calculated and found to increase with increasing inclusion of ZnO indicating an increase in the ionic character. The molar refraction (Rm), refractive index (nr) and molar polarizability (αm) are calculated and explained on the basis of structural changes. The optical absorption spectra have been used to evaluate the values of optical band gap (Eopt) and band tailing parameter (B). It is observed that Eopt decreases with the increasing contents of ZnO in base glass matrix. The decrease in Eopt is an evidence of enhancement in the number of non-bridging oxygen atoms (NBOs) thereby increasing the four-coordinated boron atoms. The as-quenched samples in bulk form are subjected to differential thermal analysis (DTA) to assess the glass transition temperature (Tg), which is 476 °C for pure lithium borate glass. The variations suggest that the structure is being modified by the substitution of ZnO.