共查询到20条相似文献,搜索用时 15 毫秒
1.
M.L. Braunger C.A. Escanhoela I. Fier L. Walmsley E.C. Ziemath 《Journal of Non》2012,358(21):2855-2861
The effects of substituting Si by M4 + cations in soda-lime silica glasses were analyzed by impedance spectroscopy in the frequency range of 1 Hz–1 MHz. The glass composition was (mol%) 22Na2O·8CaO·65SiO2·5MO2, M = Si, Ti, Ge, Zr, Sn, and Ce. Although the Na+ concentration in the glasses is constant, the Zr-containing glass exhibits the highest dc conductivity and the lowest activation energy, while the Ce-containing glass exhibits the lowest conductivity. The activation energies obtained experimentally agree with those obtained by a theoretical equation proposed by Anderson and Stuart. The differences in electrical conductivity presented by the several M-containing glasses are attributed to the effect that the M4 + ion has on the mobility of the diffusing Na+ ion. 相似文献
2.
《Journal of Non》2005,351(8-9):623-631
Na2O–CaO–ZrO2–SiO2 glass compositions with ZrO2 contents of up to 20 mol% were melted. Up to 12.3 mol% ZrO2 could be dissolved into the glasses. Melting temperatures ⩾1450 °C were required to remove seed and produce a melt that could be cast. Addition of ZrO2 caused an increase in the glass transition and crystallization temperatures. Glasses crystallized at temperatures ⩾1050 °C with Keldyshite and Parakeldyshite (Na2O · ZrO2 · 2SiO2) as the crystalline phases. Addition of up to 4.6 mol% ZrO2 caused an increase in the hydrolytic resistance of the glass, with further additions having little effect. The suitability of these glasses as hosts for ZrO2-containing radioactive wastes is discussed. 相似文献
3.
《Journal of Non》2007,353(24-25):2459-2468
This paper deals with a systematic study of crystal nucleation and growth kinetics in a 14.6Na2O–34.0CaO–51.4SiO2 mol% glass, which is close to the CaO · SiO2–Na2O · SiO2 pseudo-binary section, just left of the stoichiometric Na2O · 2CaO · 3SiO2 (N1C2S3) compound. We show that crystallization begins with nucleation of a Na4+2xCa4−x[Si6O18] (0 < x < 1) solid solution that is enriched in sodium as compared with both parent glass and the N1C2S3 compound; while a fully crystallized sample is composed only by a solid solution that is stable at very high temperatures, but is metastable in the temperatures under investigation. We thus confirm a continuous compositional change of the crystals during the course of crystallization. 相似文献
4.
Thermal conductivity of glass is one of the fundamental properties of it. However, that has not been studied enough. That of only less than 20 compositions has been measured below the room temperature. In this study, we measured the thermal conductivity of xNa2O · (100 ? x)SiO2 and (33 ? y)Na2O · yCs2O · 67SiO2 glasses by a transient heating method in the temperature range from about 150 K to room temperature. The conductivity of xNa2O · (100 ? x)SiO2 is found to decrease with the increase in alkali content. The dominant factor of this behavior is the decrease in phonon mean free path, which is due to the increase of non-bridge oxygen. Thermal conductivity of (33 ? y)Cs2O · yNa2O · 67SiO2 is decreased with the increase in Cs2O/(Na2O + Cs2O) ratio. The dominant factor of this behavior is the decrease of sound velocity. However, composition dependence of the phonon mean free path also affects the thermal conductivity. Phonon mean free path of 33Cs2O · 67SiO2 glass is longer than that of 33Na2O · 67SiO2 glass, and should be related to the change in distribution of structural unit in glass. In addition, phonon mean free path of mixed alkali glasses are shorter than that of single alkali glasses. 相似文献
5.
D.S. Brauer M.N. Anjum M. Mneimne R.M. Wilson H. Doweidar R.G. Hill 《Journal of Non》2012,358(12-13):1438-1442
Fluorapatite glass-ceramics are osteoconductive, and glass-ceramics containing fluorapatite crystals in a bioactive silicate glass matrix can combine the benefits of fluorapatite with the bone-regenerative properties of bioactive glasses. High phosphate content (around 6 mol% P2O5) bioactive glasses (SiO2–P2O5–CaO–Na2O–CaF2) were prepared by a melt-quench route. Structural investigation using density measurements and calculations confirmed the presence of phosphorus as orthophosphate. Upon heat treatment, the glasses crystallised to mixed sodium calcium fluoride orthophosphates (sodium-containing compositions) and fluorapatite (sodium-free composition). Fluoride suppressed spontaneous crystallisation, allowing formation of glass-ceramics by controlled crystallisation. A notable feature is that silicate network polymerisation and network connectivity did not change during crystallisation, resulting in orthophosphate and fluorapatite crystals embedded within a bioactive glass matrix. By keeping the phosphate content high and the sodium content low, fluorapatite glass-ceramics can be obtained, while not affecting the structure of the bioactive silicate glass phase. 相似文献
6.
《Journal of Non》1999,243(2-3):281-284
The effect of different concentrations of the network modifier Na2O on the position of the Boson peak, observed in the low frequency Raman scattering experiments, is analyzed. Glasses containing 25% Na2O (Na2O · 4SiO2) and 33% Na2O (Na2O · 2SiO2) are compared with pure SiO2 glass. The observed shift of the Boson peak is interpreted in terms of a change of a correlation length, ℓ, corresponding to some medium range order. This length, ℓ, decreases when the amount of sodium oxide increases. 相似文献
7.
Glasses with the base mol% composition xNa2O · 10CaO · (90 ? x)SiO2 with x = 10, 16, 20 and 26 were investigated at high temperatures using square-wave voltammetry. The recorded voltammograms exhibit two peaks. That at less negative or (depending on temperature and glass composition) even positive potential is attributed to the reduction of Cu2+ to Cu+, while that observed at more negative potential is caused by the reduction of Cu+ to metallic copper. For both redox steps, the peak potentials decrease linearly with temperature. Those of the composition with 10 mol% Na2O show the most negative values. The diffusion coefficients can be fitted to Arrhenius equation. If referenced to the same viscosity, the diffusion coefficients decrease with increasing Na2O-concentration. The effect of composition on the thermodynamics as well as on diffusivities is explained by the incorporation of the copper ions into the melt structure. 相似文献
8.
《Journal of Non》2006,352(38-39):4082-4087
Liquids with the base compositions (16 − x/2)Na2O · xNaF · 10CaO · 74SiO2 (x = 0, 1, 3, and 4) and (10 − x/2) · Na2O · xNaF · 10CaO · yAl2O3 · (80 − y)SiO2 (x = 0, 1, 3, 5 and y = 5 and 15) doped with 0.25 mol% Fe2O3 were studied by means of square-wave voltammetry in the temperature range from 1000 to 1500 °C. With increasing temperature, the redox equilibria were shifted to the reduced state. Also while increasing the alumina concentration, the Fe2+/Fe3+-redox equilibrium is shifted to the reduced state. In the soda-lime–silica melt the addition of fluoride shifts the equilibrium to the oxidized state, while in the aluminosilicate melts with 15 mol% Al2O3, the equilibrium is shifted to the reduced state. In the aluminosilicate melts with 5 mol% Al2O3, the equilibrium was not affected by the fluoride concentration. This is explained by the structure of the respective glass compositions. 相似文献
9.
《Journal of Non》2003,315(1-2):77-88
The crystallisation of CaO–ZrO2–SiO2 glasses doped with V2O5 (0.1–5 mol%) has been investigated in terms of microstructure and thermal parameters. Results indicate that crystallisation is predominantly controlled by a surface nucleation mechanism, even though a partial bulk nucleation has been encountered in compositions containing more than 2 mol% of doping oxide. As detected from differential thermal analysis curves, glass transition temperature and crystallisation temperature, are strongly dependent upon V2O5 content varying from 0.0 to 2.0 mol%, while the crystallisation activation energy values decrease with a parabolic trend from B-glass (0.0 mol% V2O5 content, 495±7) to V-0.7 (0.7 mol% V2O5 content, 420±6) composition, increasing again to 442±5 kJ/mol K with higher amount of V2O5. The microstructure of the glass-ceramic materials clearly showed a marked dependence upon the amount of V2O5, also due to the presence of phase separation for content higher than 0.7 mol%. Wollastonite, CaO·SiO2, and a calcia–zirconia–silicate, 2CaO·4SiO2·ZrO2, are the main crystalline phases whose ratio slightly varies with vanadium oxide content. The glass ceramics obtained from the studied materials are greenish and bluish coloured, so it is possible to use the studied glasses as coloured frits for tile glazes. 相似文献
10.
The effect of hydration on the kinetic fragility of soda-lime-silica glasses was investigated by viscometry in the glass transition range. Water-bearing glasses were prepared from industrial float glass (FG) and a ternary model glass (NCS = 16Na2O 10CaO 74SiO2 in mol%) by bubbling steam through the melt at 1480 °C and up to 7 bar. Additionally, a sodium borosilicate glass (NBS = 16Na2O 10B2O3 74SiO2 in mol%) was hydrated under equal conditions. As detected by infrared spectroscopy water dissolves in the glasses exclusively as OH-groups. The hydration resulted in a total water content CW up to ≈ 0.2 wt% for FG, NCS and NBS glasses. Kinetic fragility, expressed by the steepness index m, was determined from the temperature dependence of η at the glass transition. Viscosity data from previous studies on hydrous float glasses (CW > 1 wt%) were surveyed together with literature data on the (H2O)–Na2O–CaO–SiO2, (H2O)–Na2O–SiO2 and (H2O)–SiO2 systems to expand the range of water concentration and bulk composition. We could demonstrate that m decreases for all glasses although water is dissolved as OH and should depolymerize the network. An empirical equation of the general type m = a ? b logCW where a, b are fitting parameters, enables m to be predicted, for each glass series as function of the water content CW. The enlarged data base shows that the parameter B of the Arrhenius viscosity-temperature relation decreases much stronger than the isokom temperature at the glass transition. 相似文献
11.
《Journal of Non》2007,353(18-21):1941-1945
The effect of uranium oxide on the structure of sodium borosilicate host glasses has been studied by neutron diffraction. The samples were prepared by quenching the melted mixtures of composition 70 wt% [(65 − x)SiO2 · xB2O3 · 25Na2O · 5BaO · 5ZrO2] + 30 wt% UO3 with x = 5, 10 and 15 mol%. It was found, that the U-loaded glasses posses good glass and hydrolytic stability. An enhanced probability for inter-mediate atomic correlations at around 4.8 Å has been established. The RMC simulation of the neutron diffraction data is consistent with a model where the uranium ions are incorporated into interstitial voids in the essentially unmodified network structure of the starting host glass. The U–O atomic pair correlation functions show a sharp peak at around 1.7 Å, and several farther distinct peaks are at 2.8, 3.6 and 4.1 Å. The uranium ions are coordinated by six oxygen atoms in the 1.6–3.4 Å interval. 相似文献
12.
Glasses with nominal composition 34SiO2–(45 ? x) CaO–16 P2O5–4.5 MgO–0.5 CaF2–x Fe2O3 (where x = 5, 10, 15, 20 wt.%) have been synthesized by melt quench technique. These have been investigated for structural features by using Fourier transform infra-red (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Results have shown an increase in fraction of non‐bridging oxygen in glasses with an increase in iron oxide content up to 15 wt.% and subsequently decreases with further increase in iron oxide content to 20 wt.%. These effects are originated by the incorporation of Fe2O3 into the silica network. Iron oxide behaves as a network modifier at low concentration and stabilizes the glass network at higher content. The glass-ceramics exhibit an increase in the formation of magnetite phase with an increase in iron oxide. The glass phase in the glass-ceramics matrix, controls the surface dissolution, which in turn decides the response of the material in-vitro. The glass-ceramics with 15 wt.% iron oxide has shown optimum response in simulated body fluid. 相似文献
13.
《Journal of Non》2007,353(22-23):2237-2243
We investigated the kinetics of crystal nucleation, growth, and overall crystallization of a glass with composition close to the stoichiometric 1Na2O · 2CaO · 3SiO2. The nucleation and subsequent growth of sodium-rich crystals in this glass decreases the sodium content in the glassy matrix, drastically hindering further nucleation and growth. Compositional changes of the crystals and glassy matrix at different stages of the crystallization process were determined by EDS. These compositional variations were also monitored by electrical conductivity measurements, carried out by impedance spectroscopy, in glassy, partially, and fully crystallized samples. The electrical conductivity of both crystalline and glassy phases decreases with the increase of the crystallized volume fraction. Starting at a crystallized volume fraction of about 0.5, the crystalline phase dominates the electrical conductivity of the sample. This behavior was corroborated by an analysis of the activation energy for conduction. We show that electrical conductivity is highly sensitive and can indicate compositional shifts, changes in the spatial distribution of mobile ions in the glassy matrix. Conductivity measurements are thus a powerful tool for the investigation of complex heterogeneous systems, such as partially crystallized glasses and glass-ceramics. 相似文献
14.
《Journal of Non》2005,351(43-45):3503-3507
Lead-free glasses in the SiO2–B2O3–Bi2O3–ZnO quaternary system were studied. The glass formation region, as determined by XRD patterns of bulk samples, was limited to glasses having more than 40 mol% of the glass-forming oxides SiO2 and B2O3. Crystalline phases of Zn2SiO4 (willemite) were detected in compositions of 30SiO2 · 10B2O3 · 20Bi2O3 · 40ZnO and 20SiO2 · 10B2O3 · 25Bi2O3 · 45ZnO. Glass transition temperatures (Tg), dilatometric softening points (Td) and linear coefficients of expansion in the temperatures range of 25–300 °C (α25–300) were measured for subsystems along the B2O3 join of 10, 20 and 30 mol%. For these subsystems, Tg ranged from 411 to 522 °C, and Td ranged from 453 to 563 °C, both decreasing with increasing Bi2O3 content. The measured α25–300 ranged from 53 to 95 × 10−7 °C−1, with values increasing with increasing Bi2O3 content. The ZnO content had the opposite effect to the Bi2O3 content. It appears that Bi3+ acts as a glass-modifier in this quaternary system. 相似文献
15.
Adama Tandia K. Deenamma Vargheese John C. Mauro Arun K. Varshneya 《Journal of Non》2012,358(2):316-320
Chemically strengthened glasses are of increasing technological importance for personal electronic devices, tablet computers, and a variety of other applications. However, there are many unexplained phenomena associated with the physics of the ion exchange process used for strengthening. One of the most puzzling of these is the anomalous behavior of the network dilation coefficient, i.e., the parameter governing the amount of linear strain of the glass per unit of alkali ions exchanged, which is inevitably a factor of 2–4 higher for as-melted glasses as compared to chemically strengthened versions of the same glass compositions prepared via ion exchange. In this paper, we investigate the atomistic origin of this discrepancy between as-melted and ion-exchanged glasses based on molecular dynamics simulations of a series of alkali tetrasilicate glasses, viz., xNa2O·(20 ? x)K2O·80SiO2 (mol%). The network dilation coefficient of the ion-exchanged glasses is dependent on composition and ranges from 30% to 54% of the ideal value obtained from the as-melted glasses. This anomalous behavior of the network dilation coefficient is explained in terms of different local environments between sodium and potassium sites in the glass network and a two-stage relaxation process of the local potassium environment after ion exchange. 相似文献
16.
This report details the physical properties, bioactivity and biocompatibility of manufactured glasses containing a range of calcium fluoride (CaF2) concentrations. Compositions were based on the following system: SiO2, CaO, Na2O, K2O, P2O5, ZnO and MgO, and in total seven glasses were synthesized using a melt–quench route. The ratio of the base compounds was kept constant, but had increasing CaF2 concentrations (0.00, 2.44, 4.77, 9.11, 10.33, 11.53 and 13.00 mol%). Glasses were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and dilatometery. Density was quantified according to Archimedes method and apatite formation tested following immersion in simulated body fluid (SBF) and Tris-buffer solution. Glass coatings were prepared by enamelling technique using 10 mm in diameter pure titanium disks. XRD demonstrates that all glasses are amorphous and that the sintering window, glass transition and softening temperatures decrease with increasing CaF2 content. In contrast, thermal expansion coefficient and glass density increase with CaF2 content. After 1 week immersion in SBF and Tris, XRD and Fourier transform infrared (FTIR) spectroscopy showed that the surfaces of all glasses underwent structural changes with evidence of surface apatite formation. Fluoride-electrode analysis indicates that the amount of fluoride released was proportional to the original CaF2 content. The survival and growth of osteoblasts on the surface of these glasses is consistent with biocompatible characteristics. 相似文献
17.
《Journal of Non》2006,352(21-22):2254-2258
The aluminum coordination state in bismuth doped silica glass, which has new broad infrared emission at 1.3 μm regions, was investigated by using 27Al NMR, and it is demonstrated that 6-fold coordinated aluminum ions with corundum structure are dominant in bismuth doped silica glass until Bi2O3 concentrations of 1.0 mol% with Al2O3. The aluminum ion efficiently affects the creation of a Bi luminescent center at an intensity of Bi2O3 (1.0 mol%)–Al2O3 (2.3 mol%)–SiO2 (96.7 mol%); the sample is three orders of magnitude larger than the Bi2O3 (1.0 mol%)–SiO2 (99.0 mol%) sample. Aluminum ions with corundum structure in silica glass have a very important role for the configuration of peculiar Bi luminescent centers. 相似文献
18.
《Journal of Non》2007,353(24-25):2415-2430
A structure of 13.9Na2O · 36.0B2O3 · 50.1SiO2 glass heat-treated at 610 °C for 5 h (glass G1) and 10 h (glass G2) was studied by stereological method on the basis of electron microscopy data obtained from plane sections of samples. It has been found that liquid phase separation in the course of heat treatment leads to formation of spherical particles with the volume fractions 0.047 (G1) and 0.065 (G2). It is argued that the stage of growth takes place in the glass G1 and the Ostwald ripening stage occurs in the glass G2. The analyses of pair correlation functions of particle traces on a secant plane indicate elements of ordering in mutual arrangement of particles for the both glasses G1 and G2. This conclusion is confirmed by results of numerical simulation. The experimental data on the pair correlation functions are in agreement with the results of calculations presented in the literature. It is noted that the ordering elements in mutual arrangement of particles play a key role in light scattering and other physical properties of material. 相似文献
19.
Kamel Damak Ramzi Maâlej El Sayed Yousef Abdulla H. Qusti Christian Rüssel 《Journal of Non》2012,358(22):2974-2980
In this work a transparent bulk glass with the mol% composition 76TeO2·10ZnO·9.0PbO·1.0PbF2·3.0Na2O doped with Tm3 + has been synthesized. Results of differential thermal analysis (DTA) indicate a high thermal stability and low tendency to crystallization of this glass. The refractive indices at different wavelengths, the Urbach energy, the optical energy gap, the Sellmeier gap energy and the dispersion energy have been estimated. Spectroscopic quality factor of Tm3 + was evaluated from optical absorption spectra. Electric and magnetic dipole transition probabilities, branching ratios, and radiative lifetimes of several excited states of Tm3 + have been predicted using calculated intensity Judd–Ofelt parameters. The classical McCumber theory has been applied to evaluate the emission cross-sections for 3F4 → 3H6 transition around 1.8 μm. This study shows that TZPPN glass doped with Tm3 + ions is a promising candidate for laser applications. 相似文献
20.
《Journal of Non》2006,352(32-35):3522-3524
The controlled synthesis of PbSe quantum dots in Se-doped glass matrix (SiO2–Na2CO3–Al2O3–PbO2–B2O3) with narrow size distributions was achieved. Quantum dot size can be manipulated by tuning annealing time in the process of thermal treatment. The PbSe QD sizes estimated by 4 × 4 k · p theory were in very good agreement with the measurements of atomic force microscopy. 相似文献