Investigation of the network structure of niobium borate glasses

Some structure parameters of niobium borate glasses have been determined with the analytical data of X-ray diffraction and IR spectra. On the basis of experimental results, the model of the Nb₂O₅---B₂O₃---K₂O (NBK) glass network was inferred to be framed by circular structural units which are composed of six-membered and four-membered groups of NbO₆, BO₄ and BO₃ polyhedra in the glasses.     

Structural distribution and rigidity of the glass network determined by EPR of Cu

The linewidth-broadening of the EPR spectra of Cu²⁺ in silicate, borate and phosphate glasses was analyzed in terms of the distribution of g_| and A_| (δ_| and δA_|) and related to the distribution of the rigidity of the network structure. X- and K-band spectra were measured for the glasses doped with ⁶³Cu²⁺ (93% abundance). The linewidth of the HFS shoulders with parallel orientation to H increased linearly with increasing m or microwave frequency. δg_| and δA_| showed a marked dependence on glass composition. For example, in Na₂O---B₂O₃ glasses, on going from x (mol% of Na₂O) being small through intermediate to large, δg_| varied from small through large to negligibly small. In contrast to these glasses δg_| was extremely large for 75PbO · 25B₂O₃ glass. The large δg_| for the Na₂O---B₂O₃ glassesof intermediate x was attributed to the coexistence of various borate groups competitively coordinating to Cu²⁺. Negligibly small δg_| for 70Na₂O · 30B₂O₃ glass and extremely large δg_| for 75PbO ·25B₂O₃ glass, both with a narrower structural distribution, reflect regidity of the glass network. The Pb---O bonding is strong enough to distort the coordination of Cu²⁺-complex. The situation is the reverse in Na₂O---B₂O₃ glasses.     

Viscosity and IR investigations in the Li2O---B2O3 system

The high viscosity in melts of the Li₂O---B₂O₃ system makes it very difficult to grow large crystals of lithium triborate. The viscosity and IR characteristics of molten li₂O---B₂O₃ system are reported in this paper. When the temperature increases the viscosity of li₂O---B₂O₃ system decreases and follows an Arrhenius-type relationship. With an increasing 13203 ratio in Li₂O---B₂O₃ melts, the viscosity rises gradually to a maximum with a composition Li₂O: 3.513203 then it falls rapidly. In order to find active agents to reduce the viscosity, Na₂O, NaCl, LiF, P205, M003, W03 etc oxides were added to Li₂O---B₂O₃ samples respectively and investigated using the orthogonal method. The experimental results show that the addition of acidic oxides can significantly decrease the viscosity in the Li₂O---B₂O₃ system. For Li₂O: 4.513203, an ideal additive agent is 20wt% Li₂O:: 2MoO₃. Near the composition for crystal growth, the percentage reduction of viscosity is 62.2%. The IR spectra of Li₂O---B₂O₃ system revealed that the BO₄⁻/NO₃⁻ ratio is reduced in the melt using Li₂O: 2MoO₃ as an additive. It is proposed that the M003 reduced the concentration of bridging oxygen atoms of BO₄⁻. The change of structure explains the decline in the viscosity. In the crystal structures of lithium triborate, the matrix spaces are so small that larger other cations than Li+ are very difficult to enter the crystal matrix. So the use of additive agents to reduce the viscosity is a possible method if no new phase appears.     

Glass formation and optical properties of glasses in the systems (R2O or R''O)-Ta2O5---Ga2O3

Gallate glasses containing no conventional glass formers were obtained in the systems (Na₂O, K₂O or Cs₂O)-Ta₂O₅---Ga₂O₃ and (Sr or BaO)-Ta₂O₅---Ga₂O₃ by an ordinary crucible-melting technique. The glasses showed high optical transmission in the infrared as well as in the visible region. Infrared spectroscopic analysis suggested that the Ga³⁺ ions are tetrahedrally coordinated in the glasses. The glass-forming tendency of the melt and the infrared transmission of the glasses are discussed in terms of the glass structure.     

Mössbauer studies on some glasses and crystals in the Na2O---Fe2O3---SiO2 system

Mössbauer absorption measurements have been made at room temperature on ⁵⁷Fe in iron sodium silicate glasses containing 3–15 mol% Fe₂O₃ and various iron alkali silicate crystals in order to study the state of iron in these glasses. The spectra of all the glasses gave one doublet with a quadrupole splitting varying from 0.73–0.78 mm s⁻¹, while those of Na₂O · Fe₂O₃ · 4 SiO₂ and 5 Na₂O · Fe₂O₃ · 8 SiO₂ crystals showed much smaller quadrupole splitting, 0.28 mm s⁻¹ and 0.10 mm s⁻¹, respectively, and an asymmetrical doublet of much narrower linewidth. When sodium was replaced by other alkali metals of larger size, such as K and Cs, in MFeSi₂O₆ and MFeSi₃O₈ crystals, the quadrupole splitting became wider and approached to 0.73 mm s⁻¹. Such a variation was not observed for glasses. These results suggest that a larger number of non-identical sites exist in iron sodium silicate glasses than in the corresponding crystals.     

An X-ray diffraction study of the structure of B2O3---Cs2O liquids

The short range structures of B₂O₃ (90 mol%)---Cs₂O (10 mol%) and B₂O₃ (80 mol%)---Cs₂O (20 mol%) liquids were analyzed at 973 and 1053 K, respectively, by an X-ray diffraction method, and the effects of Cs₂O addition on the boron-oxygen bonding were investigated. The existence of BO₃ triangles, which form the so-called boroxol ring structure, was confirmed in B₂O₃---Cs₂O liquids, as well as in B₂O₃ liquid, but some fraction of the BO₃ triangles was thought to be converted to BO₄ tetrahedra. Similar results have previously been observed also in B₂O₃---Cs₂O glasses. A Cs atom was found to be surrounded by six O atoms; four Cs---O interatomic distances were about 3.2 Å but the other two were at 3.8–3.9 Å. These distances indicate that distorted Cs---O octahedra may exist in these B₂O₃---Cs₂O liquids.     

Nuclear magnetic resonance studies of alkaline earth phosphosilicate and aluminoborosilicate glasses

The ¹¹B, ²⁷Al, ²⁹Si and ³¹P magic angle spinning (MAS) NMR spectra of MO–P₂O₅, MO–SiO₂–P₂O₅ and MO(M^′₂O)–SiO₂–Al₂O₃–B₂O₃ (M=Mg, Ca, Sr and Ba, M^′=Na) glasses were examined. In binary MO–P₂O₅ (M=Ca and Mg) glasses, the distributions of the phosphate sites, P(Q_n), can be expressed by a theoretical prediction that P₂O₅ reacts quantitatively with MO. In the ternary 0.30MO–0.05SiO₂–0.65P₂O₅ glasses, the 6-coordinated silicon sites were detected, whose population increases in the order of MgOxCaO–0.05SiO₂–(0.95−x)P₂O₅ glasses, its population increases with an increase in f (=([P₂O₅]−[MO]−[B₂O₃]−[Na₂O])/[SiO₂]) and has maximum at f=9. The signal due to the 5-coordinated silicon atoms is also observed when x is smaller than 0.45. When three network-forming oxides such as SiO₂, Al₂O₃ and B₂O₃ coexist, Al₂O₃ reacts preferably with MO. The populations of 4-coordinated boron atoms, N₄, are expressed well with r/(1−r), where r=([Na₂O]−[Al₂O₃])/([Na₂O]−[Al₂O₃]+[B₂O₃]). The correlation of the Raman signal at 1210 and 1350 cm⁻¹ with the NMR signal of Si(Q₆) at −215 ppm is also seen.     

Alkali diffusion and electrical conductivity in sodium borate glasses

The diffusion coefficient of sodium, ²²Na, and silver, ¹¹⁰Ag, and electrical conductivity for sodium borate glasses (4–24 mol% Na₂O) has been measured from 100°C to slightly below the glass transition temperature, T_g. Unlike silicate glasses where the self-diffusion coefficient is much larger than the impurity diffusion coefficient, D_Na and D_Ag had close to the same magnitude in the sodium borate glasses. In some glasses, D_Ag was slightly larger than D_Na. Na₂O-Ag₂O-B₂O₃ glasses show a relatively small mixed alkali effect, despite the significant mass difference between Ag(≈108) and Na(≈23). It is concluded that the mixed alkali effect is more dependent upon the difference in ionic radii rather than differences in mass.     

Structural and thermal properties of some tellurite glasses

Tellurium oxide glasses were prepared by the hammer and anvil technique. The glass systems are (0.85TeO₂ + 0.15Z), where Z = K₂O, TiO₂, V₂O₅, MnO, Fe₂O₃, CoO, NiO or CuO. A second group is a ternary system 0.85TeO₂+(0.15 − x)TiO₂ + xFe₂O₃) with x=0.0, 0.05, 0.1, 0.15 mol. X-ray diffraction, infrared spectroscopy and differential thermal analysis measurements were carried out. The present study showed the different glass-forming groups, the glass transition and crystallization temperatures as well as the crystallization processes.     

Preparation and physical properties of amorphous V2O5 containing TiO2, Na2O or Li2O

V₂O₅ gels containing up to 18 mol% of TiO₂ were obtained through the simultaneous hydrolysis of alkoxides in ethanol solution. V₂O₅ gels containing Na₂O or Li₂O were obtained through the ion exchange method. The crystallization temperature, T_cr, of the gels increased and the H₂O content of the gels decreased by the addition of TiO₂ or Na₂O. These additives seem to stabilize the amorphous state of the gels. On the other hand, T_cr and the H₂O-content slightly varied with the addition of Li₂O. No ionic polarization was observed in coating films of the gels dried at temperatures below T_cr. The dc conductivity of the films was anisotropic, and increased with the addition of Li₂O or Na₂O. However, it decreased with increasing TiO₂ content. The fiber-like structure of gels was observed by TEM. The gels obtained from alkoxides were thin and short in comparison with the gels obtained through the ion exchange method.     

Glass formation, properties and structure of glasses in the P2O5---WO3---K2O---Al2O3 system

Glass formation in the P₂O₅---WO₃---K₂O---Al₂O₃ system was investigated and the glass-forming regions are presented.

the properties of the glasses in the P₂O₅---WO₃---K₂O---Al₂O₃ system (Al₂O₃ 8 mol.%) are reported.

The colouration of glass was studied. It was found that W⁵⁺ ions make glass blue.

Infrared spectra were measured by means of making KBr pills. Results of the investigation suggest that P---O---P, P---O---W, and W---O---W bonds form a continuous network in the phosphate glasses. So we suggest that tungsten trioxide is a glass former.     

Glass formation in the PbBr2–PbCl2–PbF2–PbO–P2O5 system

New glasses in the PbBr₂–PbCl₂–PbF₂–PbO–P₂O₅ system have been prepared and characterized. The glass-forming regions have been explored and the stability of the glasses against crystallization studied. Results show that the PbBr₂–PbCl₂–P₂O₅ ternary system has a broad glass-forming region which extends to 30 mol% P₂O₅. Most of the glasses in this system show strong stability against crystallization and some have glass transition temperatures as low as 146°C. When 5% PbO or 5% PbF₂ is introduced into the PbBr₂–PbCl₂–P₂O₅ system, the glass-forming region becomes smaller and the glass transition temperatures increase. However, the introduction of 2.5% PbF₂ and 2.5% PbO into the ternary system increases the glass transition temperature and broadens the glass-forming region. The introduction of PbF₂ alone improves the glass-forming ability of the system while the introduction of PbO alone lowers the glass-forming ability.     

Hydration of phosphate and borate glasses in an autoclave

Kinetics of hydration of CaO---Al₂O₃---P₂O₅ and Na₂O---CaO---B₂O₃---Al₂O₃ glasses in an autoclave at high temperatures and high pressures has been investigated. The hydration of the phosphate glasses may occur as a result of hydrolysis of glass constituents to form orthophosphate crystals. Cabal glasses which do not contain any alkali oxides have shown a quite high resistance to water. Substitution of sodium for calcium deteriorates the chemical durability of Cabal glasses.     

Raman spectrum studies of the glasses in the system Na2O---Al2O3---P2O5

Raman spectra of ternary sodium aluminosphosphate glasses indicate that for glasses with Al₂O₃/P₂O₅<0.63, the glass network is mainly built up of (PO₃)_n^n- chains and rings or different kinds of phosphate groups and AlO₄ tetrahedra; for glasses with Al₂O₃/P₂O₅>0.63, the glass network is mainly built up of AlPO₄ groups.     

Raman spectroscopic study of bioactive silica based glasses

A study of the structure and bonding configuration of the bioactive glasses in the system Na₂O–CaO–P₂O₅–SiO₂ by Fourier transform Raman spectroscopy is presented. The assignment of the Raman lines, the changes in the Si–O–Si bond environment and the identification of the non-bridging silicon–oxygen groups (Si–O–NBO) for a wide range of silicate glasses are discussed. The frequency shifting and intensity variations of the Raman lines as a function of the bioactive glass composition are attributed to a decrease of the local symmetry originated by the addition of alkali and alkali earth oxides to the vitreous silica network. Correlation plots for the quantification of the Si–O–NBO groups as a function of the glass composition are also presented. These Raman analyses contribute to a better knowledge of the structural role of the network modifiers in the bioactive glasses and, as a consequence, improve the understanding of the bioactive process and the chemical routes of the CaP layer formation when exposed body fluids.     

Structure and Raman spectra of glasses containing several glass-forming oxides and no glass-modifying oxide

Binary glasses containing no modifying oxides, such as SiO₂---GeO₂, SiO₂---B₂O₃, SiO₂---P₂O₅, GeO₂---B₂O₃, Al₂O₃---P₂O₅ and ternary glasses SiO₂---GeO₂---P₂O₅, Al₂O₃---B₂O₃---P₂O₅, B₂O₃---SiO₂---P₂O₅, Al₂O₃---ZrO₂---P₂O₅ have been prepared by melting and CVD methods. The Raman spectra have also been measured. Structural characteristics of SiO₂, GeO₂, B₂O₃, P₂O₅ in different glass systems are analysed. There exist coordination number changes in B₂O₃- and GeO₂-containing glasses and linkage changes between tetrahedra (SiO₄) and (PO₄) in SiO₂ and P₂O₅ containing glasses. The structure of Al₂O₃ containing glasses is homogeneous and the structure of B₂O₃ containing glasses is inhomogeneous. These experimental results are in coincidence with the X-ray small angle scattering analysis.     

Determination of Na2O activities in silicate melts by EMF measurements

An EMF cell using a Na-β″-alumina electrolyte has been designed for the quantification of the thermodynamic activity of Na₂O (aNa₂O) in a series of sodium-bearing silicate liquids at high temperature. Initial experiments have been performed using Na₂O–0.663WO₃ and Na₂O–0.555MoO₃ as reference liquids. Values of aNa₂O derived for Na₂O–2SiO₂ binary melt are found to be in excellent agreement with data from the literature, confirming the validity of the method. To extend use of this experimental set-up to higher temperature, the aNa₂O of industrial C-glass has been calibrated as a reference liquid at temperatures up to 1263 °C. The influence of additions of CaO, Al₂O₃ and B₂O₃ on the Na₂O activity of binary sodium-silicates has been quantified. For each glass composition, measured values of aNa₂O are a function of temperature, log(aNa₂O) varying as a function of inverse absolute temperature. Activation energies derived from these data are all generally similar with the exception of industrial E-glass, which is rich in Al and poor in Na. At constant temperature, additions of network forming Al₂O₃ and B₂O₃ to a Na₂O–SiO₂ binary melt yield a decrease of the activity of Na₂O, while addition of network modifying CaO results in an increase in (aNa₂O). These changes are qualitatively consistent with predictions based upon expected modifications of melt structure. However, measured values of log(aNa₂O) do not correlate perfectly with theoretical models of glass basicity, suggesting that either sodium activity is decoupled from melt basicity, or that current models are insufficient to calculate that parameter, in particular for the case of liquids poor in Na and rich in Al.     

Low expansion copper aluminosilicate glasses

The thermal expansion coefficients of Cu₂O---Al₂O₃---SiO₂ glasses have been measured. These glasses have very low expansion coefficients similar to that for SiO₂ glass, but their liquids temperatures are much lower. It was possible to reduce the liquids temperature by the addition of 2 mol% of Na₂O while maintaining low expansivity. In order to explain the low expansivity, the effects of cation size, valence, the Cu²⁺/Cu⁺ ratio, bond strength and phase separation were examined. Phase separation was observed in these glasses which probably consisted of a copper-rich dispersed phase and a network former-rich matrix phase. It was concluded that the overall expansion coefficients of the glasses were governed by the low expansion matrix phase.     

Optical absorption and elastic properties of Li2O---(LiCl)2---B2O3---Al2O3 glasses

Ultraviolet transmission, densities, and supersonic velocities of the Li₂O---(LiCl)₂---B₂O₃---Al₂O₃ glasses were measured. Adiabatic compressibilities of all these glasses were calculated. The results were interpreted from the viewpoint of the glass structure.     

Study of PbO films on sodium borate glasses part II: Formation of interdiffusion layers at the glass surface

By selecting carefully controlled conditions for the thermal treatment of sodium borate glasses coated with PbO films, it is possible to prevent Pb²⁺ ions from penetrating deeply into the glass. For low alkali glasses, an interdiffusion layer can be formed, which sub-surface cation profiling (by ion beam induced radiation) shows is a solid solution of Na₂O and B₂O₃ in PbO which acts as solvent. Experiments with 18.0 mol-% Na₂O glass show that it is possible to transform such an interdiffusion layer into a second type in which Na₂O and B₂O₃ together act as solvent and the concentration of PbO solute varies through the layer. For both types of layer the Na₂O : B₂O₃ ratio is different from that of the glass substrate, and for the production of the second type of layer it is shown that an important factor connected with penetration of PbO into the glass surface is a “sweating” process in which thermal treatment of the glass, even in the absence of PbO, results in migration of Na⁺ ions so that the glass surface has a Na₂O content higher than that of the bulk glass. Changes in the UV spectra of the Pb²⁺ ion are correlated with the formation of the interdiffusion layers, and results show that types of layer have optical basicities significantly greater than that of the glass substrate, through either the high PbO or high Na₂O content.