Yasser B. Saddeek

Relaxation of longitudinal ultrasonic waves in some tellurite glasses

The longitudinal ultrasonic absorption in binary (100x)TeO2–xNb2O5 and ternary (100x)TeO2–0.5xNb2O5–0.5xLi2O, tellurite glass systems, was measured using pulse echo technique at ultrasonic frequencies 2, 4, 6 and 8 MHz in the temperature range from 200 to 280 K. The relaxation spectra or the shape of maximum peaks showed the presence of well-defined broad peaks at various temperatures depending upon the glass composition and operating frequency. The maximum peaks shift to higher temperatures with increasing frequency suggesting some kind of relaxation process. This process has been interpreted as a thermally activated relaxation process which arise when ultrasonic waves disturb the equilibrium of an atom moving in a double-well potential in the glass network. Results showed that the mean activation energy of the process is strongly dependent on the modifier content. The dependence of the maximum peaks on composition was analyzed in terms of an assumed loss of standard linear solid type, with low dispersion, and a broad distribution of Arrhenius type relaxation with temperature independent relaxation strength. The relaxation strength and deformation potential were determined experimentally and theoretically.

Effect of B2O3 on the structure and properties of tungsten–tellurite glasses

The elastic properties and Debye temperatures of xB2O3–70TeO2–(30–x)WO3, (0 ≤ x ≤ 30 mol%) glasses have been investigated using sound velocity measurements at 4 MHz. Ultrasonic and thermal parameters, combined with the results of IR spectroscopic analyses, were employed to explore the effect of B2O3 on the structure of tungsten–tellurite glasses. According to IR analysis, there is competition between WO6 and TeO4 units to form BO4 units, and the vibrations of the tellurite structural units are shifted towards lower wavenumbers on the formation of non-bridging oxygens. It is assumed that B2O3 acts as a modifier by decreasing the glass-transition temperature T g and increasing both the thermal stability and glass formation range of the tellurite glasses. The change in density and molar volume with B2O3 content reveals that the borate units are less dense than the tellurite structural units. The observed compositional dependence of elastic moduli is interpreted in terms of the effect of B2O3 on the coordination number of the tellurite units. A good correlation was observed between experimentally determined elastic moduli and those computed with the Makishima–Mackenzie model.

Effect of WO3 on the glass transition and crystallization kinetics of borotellurite glasses

Tellurite glasses of the system xWO3–75TeO2–(25 − x)B2O3 (0 ≤ x ≤ 25 mol. %) were prepared and studied by differential thermal analysis to explore the effect of WO3 on their glass transition and crystallization kinetics. The crystallization kinetics was studied under non-isothermal conditions using the formal theory of transformations for heterogeneous nucleation. The crystallization results were analyzed and both the activation energy of the crystallization process and the crystallization mechanism characterized. The phases into which the glass crystallizes were identified by X-ray diffraction. Diffractograms of the transformed material indicate the presence of microcrystallites of α-tellurite, Te0.95W0.05O2.05, Te2W and B2O3 in the amorphous matrix.

Thermal analysis and infrared study of Nb2O5–TeO2glasses

Tellurite glasses of the xNb2O5–(100–x) TeO2, (3 ≤ x ≤ 20 mol%) system have been prepared and studied by IR spectroscopy and differential thermal analysis to explore the role of Nb2O5 on their structure. IR analysis indicates that NbO6 transforms TeO4 units into tellurite structural TeO3 units, with a shift of lattice vibrations towards higher wavenumbers. The stretching force constant of the tellurite structural units increases with Nb2O5 content, a feature that is attributed to the higher bond strength and higher coordination number of Nb2O5 relative to TeO2. The crystallization kinetics has been studied under non-isothermal conditions using the formal theory of transformations for heterogeneous nucleation. The crystallization results are analyzed, and both the activation energy of the crystallization process and the crystallization mechanism are characterized. The thermal stability of these glasses are characterized in terms of characteristic temperatures, such as the glass-transition temperature, T g, the temperature of onset of crystallization, T in, the temperature corresponding to the maximum crystallization rate, T p, and two kinetic parameters, K(T g) and K(T p). The results reveal that thermal stability increases with increasing Nb2O5 content. XRD diffraction of the studied glasses indicates the presence of microcrystallites of α-tellurite, γ-telluride, Nb2Te4O13 and an amorphous matrix.

Crystallization kinetics of the TeO2-BaO glass system

Tellurite glasses of the system (100–x)TeO2–xBaO, with x = 05, 10, 15 and 20 wt%, have been prepared and studied by differential scanning calorimetry (DSC). The crystallization kinetics of the glasses were investigated under non-isothermal conditions, applying the formal theory of transformations for heterogeneous nucleation to the experimental data obtained by DSC, using continuous-heating techniques. In addition, from the dependence of the glass-transition temperature (T g) on heating rate, the activation energy for the glass transition was derived. Similarly, the activation energy of the crystallization process was determined and the crystallization mechanism characterized. The thermal stability of these glasses are considered in terms of the characteristic temperatures, T g and T in (the onset temperature of crystallization), via ΔT = T in−T g and a kinetic parameter K(T g). The results confirm that thermal stability decreases with increasing BaO content. The phases into which the glass crystallizes have been identified by X-ray diffraction. Diffractograms of the transformed material indicate the presence of microcrystallites of α-TeO2, γ-TeO2 and BaTeO3 in the remaining amorphous matrix.

Synthesis and properties of MoO3–V2O5–PbO glasses

Lead vanadate glasses of the system xMoO3–50V2O5–(50-x)PbO (0 ≤ x ≤ 25 mol. %) were synthesized and studied by FTIR and ultrasonic spectroscopy and differential scanning calorimetry to investigate the role of MoO3 content on their atomic structure. The elastic properties and Debye temperatures of the glasses were investigated using sound velocity measurements at 4 MHz. The activation energy for the glass transition was derived from the dependence of the glass-transition temperature (Tg ) on the heating rate. Similarly, the activation energy of the crystallization process was also determined. According to the IR analysis, the vibrations of the vanadate structural units are shifted towards higher wavenumbers on the formation of bridging oxygens. The change of density and molar volume with MoO3 content reveals that the molybdinate units are less dense than the lead oxide units. The observed compositional dependence of the elastic moduli is interpreted in terms of the effect of MoO3 on the coordination number of the vanadate units. A good correlation was observed between the experimentally determined elastic moduli and those computed according to the Makishima–Mackenzie model. It is assumed that MoO3 plays the role of a glass former by increasing the activation energy for the glass transition and the activation energy for crystallization and by increasing both the thermal stability and the glass formation range of the vanadate glasses.

Study of rigidity of semiconducting vanadate glasses and its importance in use of coatings

The elastic moduli of some multicomponent vanadate based glasses were analysed in terms of the bond compression model by some physical parameters such as, the density, average stretching force constant and average atomic ring size. These parameters were calculated for all the glass series and for all the glass composition to estimate the rigidity of these glasses. The results showed that the average force constant and the elastic moduli of these glasses are sensitive to the decrease in PbO content. This behaviour was attributed to the increase in the molar volume and the role of different modifiers. These parameters along with the coordination number of the glasses affect the glass transition temperature. The correlation between the elastic moduli and thermal properties of these samples showed that 0·25MoO3–0.25PbO–0·5V2O5 glass is the most rigid and has an applicable glass transition temperature for coating.

FTIR spectroscopic features of γ-ray influence on new cement kiln dust based glasses

A harmful environmental problem such as cement kiln dust (CKD) was considered as a source of CaO and SiO2, which are useful oxides for the glass industry. So, Na2O, B2O3, Bi2O3, PbO and CKD were used to fabricate new borate based glasses. The structure of the prepared glasses was studied by FTIR before and after gamma irradiation at doses up to 120 kGy. Analysis of FTIR before irradiation revealed that CKD split the characteristic broad band of the vibrations of BO3 structural units into two bands and created two effective ranges of concentrations which were confirmed by N4 calculations. After gamma irradiation, the intensity of the FTIR bands decreased and the structure of glass was weakened when 0 ≤ CKD ≤ 23.5 mol% as a result of energy transferred by gamma rays. Increasing CKD beyond this limit created bridging oxygens, more covalent bonds and interlinked the structural groups of the glass network which may resist the irradiation effects. The glass containing 32 mol% of CKD showed higher resistance for radiation effects which was attributed to its strong covalent bonds and to [BiO6] and [PbO6] structural units.

Theoretical analysis of constants of elasticity of lead calcium alumino-borosilicate glass system

This paper reports on the constants of elasticity of xPbO-RNa2B4O7-(100 − R − x) CAS with 0 ≤ x ≤ 50, and 50 ≤ R ≤ 75 mol % glass system (CAS is calcium alumino silicate glasses). The constants of elasticity were calculated in terms of the bond compression model and Makishima-Mackenzie model. The average cross-link density, the number of network bonds per unit volume, the average stretching-force constant, and the ratio of the estimated bulk modulus (Kbc) to the experimentally determined (Ke), have been calculated and discussed in terms of the bond compression model to analyze the role of PbO. Young’s modulus, the packing density and dissociation energy have been calculated and analyzed according to the Makishima-Mackenzie model. The dimensionality of the glassy network has been calculated in terms of the d ratio (4C44/C12) and discussed in terms of the cross-link density of these glasses. C12 = C11−2C44, C11 and C44 are the longitudinal and shear elastic constant. The results show good agreement between the experimental and theoretical data for the representation of the constants of elasticity of borosilicate glasses.

Some Physical Features of Glasses Synthesized from Some Environmental Wastes

New glasses based on wastes of limestone, phosphate, and cement kiln dust besides white sand were manufactured. The structure of the prepared glasses was studied by FTIR, thermal analysis, UV spectroscopy and ultrasonic techniques. The analysis revealed that increasing the content of SiO2 influences the concentrations of the structural units constituting the amorphous network. The values of the physical parameters; the density, ultrasonic velocity, the elastic moduli, the refractive index, the optical band gap and the glass transition temperature increase as the SiO2 content increases, which was attributed to the former role of SiO2 which strengthens the calcium borate network and the conversion of non-bridging oxygens into bridging oxygens. These factors increase the crosslink density and connectivity within the glass network and hence its rigidity.