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1.
The alkali resistance and structure of CaO---Al 2O 3---SiO 2 glasses are studied in this paper. The change of coordination number of aluminum ions in the glasses, caused by corrosion from the cement extract aqueous solution, was determined by means of X-ray fluorescence spectra and infrared absorption spectra. The interrelationship between glass compositions, structure, and alkali resistance is discussed. 相似文献
2.
This paper deals with the relationship between phase separation and crystal morphology in the Li 2O---ZnO---Al 2O 3---SiO 2 system glasses, and investigates the effect of the nucleating agent on the microstructure of glass-ceramics, and the effects of heat treatment temperature on the properties of the microstructure. 相似文献
3.
The effect of alumina on the phase separation and the crystallization of the glasses of composition (mol%) 18ZnO·30B 2O 3·52SiO 2 and O-40 Al 2O 3 was studied using an electron microscope and IR spectroscopy. The main crystalline phase appears in the microphase for which the compositions are not nearer to the crystal stoichiometry than the mean. The addition of Al 2O 3 suppresses the immiscibility but enhances the crystallizability. 相似文献
4.
11B Fourier transform spectra have been used to study the structure of Na 2O---B 2O 3---SiO 2 glasses of mid-alkali content. Based on the measurements of the fraction N4 of four-coordinated borons, it has been found that for K = mol.% SiO 2/mol.% B 2O 3 8 and R = mol.% Na 2O/mol.% B 2O 3 = 1, N4 is obviously smaller than 1 rather than equal to 1 as assumed in the relevant literature. Only when R reaches a value appropriately greater than 1, can the case where N4 = 1 occur. A structural model suggested in this paper can satisfactorily explain the fact. 相似文献
5.
Alkoxide derived gels were prepared in the system Na 2O---B 2O 3---SiO 2. The gel compositions were situated in the liquid-liquid immiscibility area of the phase equilibrium diagram. Hydrolytic resistance tests were performed on the gels heat-treated at temperatures ranging between 120 to 850 °C. The Na2O, B2O3 and SiO2 extracted from the attack gels were analyzed. The experimental results indicate that the amount of B2O3 has a significant influence on the chemical durability of the heat-treated gels. At temperatures of 850 °C the greater the B2O3 mol% the greater are the amounts of Na2O and B2O3 extracted. Different behaviour was observed for gels heat-treated at 600 °C where the amounts of B2O3 and Na2O extracted slightly increases as the B2O3 mol% increases. Small amounts of extracted SiO2 were always observed. These results are complemented with other measurements so that an explanation of the controlling mechanism is given. 相似文献
6.
We report the infrared and Raman studies of titanium doped vitreous silica glasses for a number of titanium concentrations. The vibrational modes associated with the randomly oriented chains of SiO 4 tetrahedra show broadenings and shifts. The LO-TO splitting of some Raman active modes decreases with increasing titanium concentration. This is attributed to the decrease in long-range coulomb fields associated with the chains of SiO 4 tetrahedra which are broken by the titanium atoms. The results are discussed in the context of random network models. An increase in the average intertetrahedral angle of the SiO 4 network is calculated from the data. This explains the anomalous decrease in the density of TiO 2---SiO 2 glasses with increasing titanium content. We identify two new modes associated with the distorted titanium tetrahedra. A polarized Raman mode at 1115 cm −1 which is infrared inactive and an unpolarized Raman mode at 945 cm −1 which is infrared active are observed. 相似文献
7.
A glass rod of the PbO---K 2O---B 2O 3---SiO 2 system having a radial gradient of refractive index has been prepared by the sol-gel process using aqueous solutions of lead acetate and potassium nitrate as the sources for index-modifying cations. A gel prepared by gelatinizing a sol from the mixture of tetramethoxysilane, tetraethoxysilane, and the aqueous solutions of boric acid and lead acetate was placed in an aqueous solution of potassium nitrate to form the concentration gradient of modifier cations by diffusion through the micropores of the gel. The glass rod of about 7 mm in diameter obtained by drying and sintering the gel had a refractive index of parabolic profile changing from the center toward the perimeter with a maximum difference of about 0.04. 相似文献
8.
Appropriate glass compositions of the Na 2O---Al 2O 3---SiO 2 system and glass melting technology were investigated. The dependence of some factors, such as composition of molten salts, time and temperature of ion exchange treatment on the modulus of rupture was studied. As expected, the coefficient of interdiffusion is a function of concentration and has the mixed-alkali effect. The order of the interdiffusion coefficient is 10 −6 cm 2/s. The effect of binary and ternary salt baths on the surface controlled crystallization was reported. The experimental data showed that there is a series of technological advantages from applying molten salts of the ternary system Li 2SO 4---Na 2SO 4---K 2SO 4 in comparison with the binary system Li 2SO 4---Na 2SO 4. 相似文献
9.
The colorless and transparent glasses in the Al 2O 3---B 2O 3---SiO 3 system with high B 2O 3 and SiO 2 content were prepared from gels at low temperature. Their IR spectra not only revealed the evolution of the gel to glass conversion, but also showed that the formation of mixed bonds in the glasses obtained did not show any effect due to the B 2O 3 content. The accuracy of the glass composition is dependent upon the SiO 2/B 2O 3 molar ratio. The higher the ratio, the less the deviation of the analyzed compositions of the resulting glasses from their original calculated values. It is obvious that the higher the ratio, the lower the thermal expansion coefficient and the higher the transformation temperature of the glass, and the temperature at which the thermal contraction reaches an equilibrium is higher. 相似文献
10.
The behavior of copper ions in the Cu 2O·Al 2O 3·4SiO 2 (in moles) glass on heating in air at temperatures up to 500°C was studied. When the glass, in which about 90% of Cu was present as Cu + ions, was heated in air above 300°C, a CuO layer was formed on the surface. The amount of CuO was increased with heating temperature and time, corresponding to the decrease in weight of the glass. Furthermore, the fraction of Cu 2+ ions in the glass increased. These observations suggest that oxygens do not diffuse into the glass, but Cu + ions migrate to the surface from the interior to balance the surplus positive charge produced by the oxidation of Cu + to Cu 2+ ions inside the glass. The following reaction scheme for the formation of the CuO layer was proposed; 2Cu +(interior) + 21O 2(surface) → Cu 2+(interior) + CuO(surface). 相似文献
11.
Lead chloroantimonite glasses form stable binary glasses that may accommodate numerous oxides or halides as a third component. Molybdenum trioxide is a glass progenitor leading to molybdate glasses. Ternary glasses have been synthesized and studied in the Sb 2O 3-PbCl 2-MoO 3 system. Compositional limits of glass formation are reported and two series of glass samples have been prepared corresponding to the general formulas: (90 − x)Sb 2O 3-xPbCl 2-10MoO 3 and (90 − x)Sb 2O 3-xMoO 3-10PbCl 2. Glass transition temperature is close to 290 °C at high Sb 2O 3 content and decreases as antimony oxide is substituted by MoO 3 or PbCl 2. Position, width and intensity of crystallization peak suggest that devitrification rate is small in some composition ranges. The evolution of density, thermal expansion, refractive index and microhardness has been studied as a function of composition parameter x. Deviations from linearity are observed. They suggest structural changes in the case of the MoO 3/Sb 2O 3 substitution while it appears that molar volume increases linearly versus lead content in the other series of glasses. Refractive index is close to 2.04. Optical transmission ranges from 550 nm in the visible spectrum to 5.5 μm in the infrared. It is limited by extrinsic absorption bands arising from hydroxyls and silicon impurities. Young's, bulk and shear moduli have been measured for the two series of samples. 相似文献
12.
Mössbauer absorption measurements have been made at room temperature on 57Fe in iron sodium silicate glasses containing 3–15 mol% Fe 2O 3 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 Na 2O · Fe 2O 3 · 4 SiO 2 and 5 Na 2O · Fe 2O 3 · 8 SiO 2 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 MFeSi 2O 6 and MFeSi 3O 8 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. 相似文献
13.
Er 2O 3-doped Bi 2O 3-B 2O 3-Ga 2O 3 glasses were prepared by the conventional melt-quenching method, and the Er 3+: 4I 13/2 → 4I 15/2 fluorescence properties are studied for different Er 3+ concentrations. when the Er 2O 3 concentration increases from 0.03 to 3.0 mol%, the measured lifetime of Er 3+: 4I 13/2 level decrease from 2.24 to 0.9 m s, and from 0.25 to 0.20 m s for the Er 3+: 4I 11/2 level. The fast energy migration among Er 3+ ions cause the reduction of lifetime of the 4I 13/2 level, whereas the change in the 4I 11/2 level is mainly due to a cooperative upconversion process ( 4I 11/2, 4I 11/2) → ( 4F 7/2, 4I 15/2). Based on the dipole-dipole interaction theory, the interaction parameter, CEr,Er, for the migration rate of Er 3+: 4I 13/2 ↔ 4I 13/2 was calculated to be 32 × 10 −40 cm 6 s −1. 相似文献
14.
Glasses in the system Na 2O/B 2O 3/Al 2O 3/In 2O 3 were melted and subsequently tempered in the range from 500 to 700 °C. Depending on the chemical composition, various crystalline phases were observed. From samples without Al 2O 3, In 2O 3 could not be crystallized from homogeneous glasses, because either spontaneous In 2O 3 crystallization occurred during cooling, or other phases such as NaInO 2 were formed during tempering. The addition of alumina, however, controlled the crystallization of In 2O 3. Depending on the crystallization temperature applied, the crystallite sizes were in the range from 13 to 53 nm. The glass matrix can be dissolved by soaking the powdered glass in water. This procedure can be used to prepare nano-crystalline In 2O 3-powders. 相似文献
15.
Homogeneous glass powders were prepared from multicomponent silicate gels in the BaO---Al 2O 3---SiO 2 system. Gels synthesized from TEOS, Al-sec-butoxide, and Ba-acetate were characterized by TGA, DSC, and single-point BET analysis. Amorphous oxide powders of controlled composition were obtained through an appropriate drying and heat treatment schedule. Inclusion-free clear oxynitride glasses were also prepared by co-melting gel synthesized oxide powders with silicon nitride powders. 相似文献
16.
Spectroscopic properties of Er 3+-doped Na 2O-Sb 2O 3-B 2O 3-SiO 2 glasses have been investigated for developing 1.5-μm broadband fiber amplifiers. An intense 1.5-μm near infrared emission with a broad full width at half maximum (FWHM) of 88 nm has been obtained for Er 3+-doped 5Na 2O-20Sb 2O 3-35B 2O 3-40SiO 2 glass upon excitation with a 980 nm laser diode. The obtained emission cross-section of the 4I 13/2 → 4I 15/2 transition and the lifetime of the 4I 13/2 level of Er 3+ ions are 6.8 × 10 −21 cm 2 and 0.36 ms, respectively. It is noted that the product of the emission cross-section and the FWHM of the glass, σe × FWHM, is as great as 598.4 × 10 −21 cm 2 nm, which is comparable or higher than that of Er 3+-doped bismuth-based and tellurite-based glasses. These special optical properties encourage in identifying them as important materials for potential applications in high performance optics and optical communication networks. 相似文献
17.
The optical absorption spectra of xPbO-(100 − x) P 2O 5 glasses where x = 5, 10, 15, 20, 25, and 30 is reported. The spectral absorption of these glasses was measured in the spectral range 300-900 nm at room temperature. Optical absorption spectra show that the absorption edge has a tail extending towards lower energies. The edge shifts nearly linearly towards higher energies with increasing PbO content. The degree of the edge shift was found to depend on the PbO content and is mostly related to the structural rearrangement and the relative concentrations of the glass basic units. The optical energy gap increases, from 2.55 to 3.05 eV by increasing PbO content from 5 to 30 mol%. The width of the localized states is decreased by increasing PbO content. 相似文献
18.
By rapid quenching in a twin roller apparatus, glass was found to occur widely in the systems of Li 2O with Al 2O 3, Ga 2O 3, Bi 2O 3 and in mixed systems. Examination of the resulting flakes by X-ray powder diffraction, differential thermal analysis, and capacitance data revealed the occurrence of glass, glass transitions, crystallization exotherms and the nature of some of the crystallization paths.The log ionic conductivity of the glasses was found to follow a linear relationship with the Li concentration. Evidence was observed for three new metastable crystalline phases, one in the Li 2OAl 2O 3 system and two in the Li 2OBi 2O 3 system. The latter system also showed evidence for the occurrence of two glasses at almost all compositions. 相似文献
19.
Glasses having compositions 40Bi 2O 3-20GeO 2-(40− x)PbO- xMoO 3 (where x = 3, 6, 9, 12 and 15 mol%) were prepared by normal melt quenching technique. The density ( d) decreases gradually with the increase of the MoO 3 content in such glasses. This may be due to the lower molecular weight MoO 3 is substituted by a higher molecular weight PbO. The dc conductivity decreases while the activation energy increases with the increase of the MoO 3 content. The dc conductivity in the present glasses is electronic depends strongly upon the average distance, R, between the Mo ions. Analysis of the electrical properties has been made in the light of small polaron hopping model. The parameters obtained from the fits of the experimental data to this model are reasonable and consistent with glass composition. The conduction is attributed to non-adiabatic hopping of small polaron. Dielectric properties (constant ε, loss tan δ, ac conductivity σac, over a range of frequency 0.12-100 kHz and temperature 325-650 K and frequency exponent s) of these glasses have been studied. 相似文献
20.
The influence of Cr 2O 3 on glass forming characteristics and physical properties of PbO-Fe 2O 3-P 2O 5 glasses has been investigated by Raman and Mössbauer spectroscopies, X-ray diffraction analysis (XRD), Differential Thermal Analysis (DTA), Scanning Electron Microscopy (SEM) and impedance spectroscopy. Glasses of the general composition xCr 2O 3-(28.3-x)PbO-28.7Fe 2O 3-43.0P 2O 5, 0 ≤ × ≤ 10, (mol%) were prepared by conventional melt-quenching technique. The compositions containing up to 4 mol% Cr 2O 3 formed fully amorphous samples and their Raman spectra show systematic increase in the fraction of orthophosphate Q 0 units with increasing Cr 2O 3 content and O/P ratio.On the other hand, compositions containing 8 and 10 mol% Cr 2O 3 partially crystallized during cooling and annealing to Fe 7(PO 4) 6, Fe 2Pb 3(PO 4) 4 and Cr 2Pb 3(PO 4) 4. A high tendency for crystallization of these melts is related to the high O/P (> 4) and Fe 2+/Fe tot (≈ 0.60) ratios.Electrical conductivity of xCr 2O 3-(28.3-x)PbO-28.7Fe 2O 3-43.0P 2O 5, 0 ≤ × ≤ 10, (mol%) compositions is independent of Cr 2O 3 and controlled entirely by the polaron transfer between Fe 2+ and Fe 3+ ions. 相似文献
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