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1.
The molecular dynamics computer simulation technique was used to determine the short-time dynamics behavior and resultant structures of ions at the surface of Li20·3SiO2 and Na2O-3SiO2 glasses. Room temperature and elevated temperatures were used. Results are compared with similar studies of the K2O·3SiO2 glass surface and with recent experimental ion-scattering-spectroscopy data. The simulations indicate that a localized surface rearrangement occurs within picoseconds after formation of the free surface, creating a surface excess of alkali in the Na (and K) case, but not in the Li case. Elevated temperatures, even for brief times, enhance the observed surface excess of Na and K. The results correspond to those obtained from the ion-scattering-spectroscopy studies.  相似文献   

2.
The internal friction of R2O·Al2O3·6SiO2 glasses was measured from-180° to 700°C at 0.4 Hz. Glasses containing Li2O or Na2O exhibited only the one internal friction peak characteristic of the stress-induced movement of the alkali ions. Substitution of a second alkali resulted in two significant changes in the internal friction: (1) a rapid reduction in the magnitude of the original alkali peak and (2) the appearance of a new internal friction peak whose magnitude was especially sensitive to the concentration of the second alkali. Each combination of two alkali ions resulted in a new peak, with peaks being observed for the combinations Li-Na, Na-K, and Li-K. A mechanical damping spectrum is predicted for aluminosilicate glasses containing more than two alkali ions.  相似文献   

3.
Clear glasses which included droplet-like microphases were produced when SiO2 in sodium borosilicate glasses was replaced by Sc2O3. Phase separation and/or crystallization occurred after heat treatment. The porous skeleton of leached glasses consisted of hexagonal ScBO3. The specific surface areas and pore radii are comparable to those of porous SiO2 glass. The sintering temperature of porous Sc-based material is higher than that of porous SiO2. Alumina contamination influenced the structure of the porous material.  相似文献   

4.
Clear glasses were produced when SiO2 in sodium borosilicate glasses was replaced by Ga2O3. Phase separation and/or crystallization occurred after heat treatment. The porous skeleton of leached material consisted of monoclinic β-Ga2O3. The specific surface areas and pore radii are comparable to those of porous SiO2. Alumina contamination influenced the structure of the porous product.  相似文献   

5.
Protons were introduced into the surface of an Li2O·Al2O3·2SiO2 glass fiber (0.5 mm in diameter) by ion exchange in NH4HSO4 at 366°C for 21 h. Infrared absorption measurements established that the protons were associated with bridging oxygen ions. After ion exchange, the magnitude of the alkali internal friction peak decreased and a new peak appeared at ∼220°C. This new peak is attributed to the interaction of alkali and hydrogen ions, independent of the presence of nonbridging oxygen ions.  相似文献   

6.
The variation with water content of dc conductivity and Na diffusion coefficient for the Na2O · 4siO2 and Na2O · 2SiO2 glass systems was found to be similar to that of the Na2O.3SiO2 series reported earlier. The conductivity was estimated for the ternary system Na2O-H2O-SiO2 by combining the present results with the previous data on the Na2O · 3SiO2 system. When the conductivity of those glasses with a constant [Na2O] + [H2O] content was plotted against water content, a pronounced mixed "alkali" effect was demonstrated. The Haven ratio, calculated by comparison of the dc conductivity to the Na diffusion coefficient at 100°C for each of the three glass systems, was found to increase toward unity with increasing water content. This suggests that the addition of water reduces the number of sodium charge carriers. The subsequent increase in conductivity beyond the minimum with the introduction of larger amounts of water is, probably, due to an increase in the mobility of the Na+ ions.  相似文献   

7.
Fibers of Li2O.Al2O3.2SiO2 glass were ion-exchanged for 1 to 300 min in an NaNO3 bath at 366°C. The internal friction and the Li and Na concentration profiles were measured. As Na progressively replaced Li, the alkali internal friction peak became smaller while a new peak (mixed-alkali peak) appeared and increased in magnitude. These changes in internal friction are similar to those that occur when a second alkali is added to glasses prepared by conventional melting. The magnitudes of both internal friction peaks in the ion-exchanged glass depended on the overall composition of the glass; that of the alkali peak depended on the composition of the unexchanged glass core, whereas that of the mixed-alkali peak depended on the composition of the exchanged layer on the glass surface. When the exchanged surface layer was dissolved, the original alkali peak was restored, and the mixed-alkali peak disappeared. Changing the alkali distribution did not affect the mixed-alkali peak much; however, it caused the alkali peak to shift to higher temperatures and become smaller. The height of the alkali peak can be used to determine the maximum depth of penetration of the second alkali.  相似文献   

8.
The effect of zirconium ions on glass structure and proton conductivity was investigated for sol-gel-derived P2O5–SiO2 glasses. Porous glasses were prepared through hydrolysis of PO(OCH3)3, Zr(OC4H9)4, and Si(OC2H5)4. Chemical bonding of the P5+ ions was characterized using 31P-NMR spectra. The phosphorous ions, occurring as PO(OH)3 in the ZrO2-free glass, were polymerized with one or two bridging oxygen ions per PO4 unit with increased ZrO2 content. The chemical stability of these glasses was increased significantly on the addition of ZrO2, but the conductivity gradually decreased from 26 to 12 mS/cm at room temperature for 10P2O5·7ZrO2·83SiO2 glass. A fuel cell was constructed using 10P2O5·5ZrO2·85SiO2 glass as the electrolyte; a power of ∼4.5 mW/cm2 was attained.  相似文献   

9.
Bulk physical properties such as elastic moduli, thermal expansions, and moduli of rupture were measured for a series of 0.98Li2O-1.0ALO3- n SiO2 glasses and the corresponding keatite solid-solution-phase glass-ceramics. The SiO2 content ranged from n =4 to 12. The magnitude of the elastic properties of the glasses changed monotonically with increasing SiO2 content. The properties of keatite-phase glass-ceramics depended almost linearly on SiO2 content, but their behavior differed qualitatively from that of the glasses.  相似文献   

10.
Phase equilibrium studies of compound formation and liquidus and solidus surfaces of the system K2O-BaO-SiO2 are presented. The system contains 3 ternary compounds: K4BaSi3O9, K8BaSi10O25, and K2Ba3Si8O20. Both high and low polymorphs of the third have fields on the ternary liquidus surface. Solid solution with SiO2 depresses the high-low inversion from 1030°C at K2Ba3Si8O20 to 835°C at 70.2 mol% SiO2. Data for 20 liquidus invariant points were found; 8 are thermal maxima and 12 are eutectics or peritectics. The isofracts of quenched glasses were determined.  相似文献   

11.
Phase-equilibrium relations on the liquidus surface in the system Ba0-A12O3-SiO2 have been investigated by the quenching method. The compositions investigated within the ternary area were those containing less than 30%, A12O3 and more than 20% SiO2 by weight. Petrographic and X-ray techniques were employed in the determination of the crystalline phases.
The crystal phases that separate from melts within the area investigated are barium orthosilicate (2BaO. SiO2,), barium metasilicate (BaO 2SO2,), solid solutions, sanbornite (BaO 2SiO2), tridymite and cristobalite (SO2), mullite (3A12O3 2SiO2), and celsian (BaO A12O3.2SiO2). Diagrams show the isotherms and indices of refraction of the glasses.
Five quintuple points and eleven boundary curves have been determined within = .5yo compositional variations. The liquidus-surface temperatures have been obtained within limits of ± 125°C.  相似文献   

12.
The radial distribution functions of ZnO–K2O–SiO2 glasses with 7 and 10 wt% ZnO are compared with that of the corresponding K2O–SiO2 matrix leading to "difference distribution curves'representative of the zinc structural arrangement. Analysis of the curves indicates that Zn2+ ions are prevalent (65% to 80%) in the glasses in tetracoordinated form.  相似文献   

13.
Ultrasonic interferometry was used to measure elastic-wave velocities and moduli in six Na2O-TiO2-SiO2 glasses; three glasses contained 20 mol% TiO2 and three 25 mol% TiO2. The elastic moduli and their pressure derivatives varied systematically with the SiO2/Na2O molar ratio of the glasses. In the group of glasses which contained 20 mol% TiO2, dK/dP ( K =bulk modulus) decreased linearly from 4.85 to 2.59 as the SiO2/Na2O ratio increased; in the other group, dK/dP decreased from 4.00 to 3.05. Similarly, dμ/dP (μ=shear modulus) decreased with the SiO2/Na2O ratio, but somewhat non-linearly. The extrinsic and intrinsic contributions to the temperature dependencies of the elastic moduli are evaluated in light of the measured pressure dependencies of these moduli.  相似文献   

14.
An examination was conducted to determine the mechanism of peeling of fire-clay brick in the low-temperature region of a blast furnace where 3 to 10% K2O is the principal contaminant. In laboratory tests, as-received high-duty and superduty fire-clay brick and 70% alumina brick treated with KCl-K2CO3 mixtures showed no peeling at a temperature of 1600°F. Cracks were found in high-duty brick that were treated with KCN at 1500°F. under partially reducing conditions. X-ray diffraction studies of mixtures of crushed brick and K2CO3 indicated the formation of leucite (K2O.Al2O3.4SiO2) and kaliophilite (K2O.-Al2O3.2SiO2) at temperatures below 1700°F. These latter data, confirmed by specimens from used blast-furnace linings, showed that silica is the first constituent attacked by alkali. Since the formation of leucite and kaliophilite in fire-clay brick is the probable cause of peeling, the increased reaction of silica, in a dense Al2O3.SiO2 refractory of higher silica content than fire-clay brick, should confine the alkali attack to the surface of the brick in low-temperature applications.  相似文献   

15.
The electrical relaxation associated with alkali diffusion in Na2O·3SiO2 glass was studied from 0.2 Hz to 700 kHz at –1° to 163°C. A formalism for analysis of electrical relaxation in conducting dielectrics which associates the nonexponential decay of the electric field to zero and the dispersions in the dielectric constant and the conductivity with a distribution of relaxation times for the electric field was developed and is shown to be in qualitative accord with current molecular theories of electrical relaxation in alkali silicate glasses. A relation between the dc conductivity, the limiting high-frequency dielectric constant, and the average electric field or conductivity relaxation time was derived and is verified experimentally for the Na2O·3SiO2 glass. The distribution of electric-field relaxation times for the glass is broad, asymmetric on a logarithmic scale, and weighted in favor of the shorter relaxation times; the distribution narrows with increasing temperature. A reduced electrical relaxation curve which can be used to compare electrical and mechanical relaxations in Na2O·3SiO2 glass was generated.  相似文献   

16.
A series of La2O3–HfO2–SiO2 glasses, approximately along the join 0.73SiO2–0.27( x HfO2–(1− x )La2O3), 0< x <0.3), was prepared using containerless processing techniques (aerodynamic levitation combined with laser heating in oxygen). The enthalpy of formation and enthalpy of vitrification at 25°C were obtained from drop solution calorimetry of these glasses and appropriate crystalline compounds in a molten lead borate (2PbO–B2O3) solvent at 702°C. The enthalpy of formation from crystalline oxides was exothermic and became less exothermic with increasing HfO2 content. Heat contents were measured by transposed temperature drop calorimetry and depended linearly on the HfO2 content. Differential scanning calorimetry showed that both the onset glass transition and the onset crystallization temperature of these glasses increased with increasing HfO2 content. Upon slow cooling in air, the glasses crystallized to a mixture of baddeleyite, cristobalite, lanthanum disilicate, and hafnon.  相似文献   

17.
The devitrification kinetics and mechanism of a low-dielectric, low-temperature, cofirable K2O–CaO–SrO–BaO–B2O3–SiO2 glass-ceramic have been investigated. Crystalline phases including cristobalite (SiO2) and pseudowollastonite ((Ca,Ba,Sr) SiO3) are formed during firing. Activation energy analysis shows that the nucleation of the crystalline phases is controlled by phase separation of the glass. The crystallization kinetics of both cristobalite and pseudowollastonite obey Avrami-like behavior, and the results show an apparent activation energy close to that of the diffusion of alkaline and alkali ions in the glass, suggesting that diffusion is rate limiting. The above conclusion is further supported by analysis of measured growth rates.  相似文献   

18.
This paper focused on the effects of various phases of SiO2 additives on the γ-Al2O3-to-α-Al2O3 phase transition. In the differential thermal analysis, the exothermic peak temperature that corresponded to the theta-to-α phase transition was elevated by adding amorphous SiO2, such as fumed silica and silica gel obtained from the hydrolysis of tetraethyl orthosilicate. In contrast, the peak temperature was reduced by adding crystalline SiO2, such as quartz and cristobalite. Amorphous SiO2 was considered to retard the γ-to-α phase transition by preventing γ-Al2O3 particles from coming into contact and suppressing heterogeneous nucleation on the γ-Al2O3 surface. On the other hand, crystalline SiO2 accelerated the α-Al2O3 transition; thus, this SiO2 may be considered to act as heterogeneous nucleation sites. The structural difference among the various SiO2 additives, especially amorphous and crystalline phases, largely influenced the temperature of γ-Al2O3-to-α-Al2O3 phase transition.  相似文献   

19.
The ion-exchange mechanism between copper and alkali ions, when 20R2O · 10Al2O3· 70SiO2 (R = Li, Na, and K) glasses are immersed in divalent copper-containing molten salts in air and nitrogen at 550°C, has been investigated. In molten CuCl2, the ion-exchange behavior in both air and nitrogen was very close to that in molten CuCl in air reported previously. This is explained by assuming that CuCl2 decomposes into CuCl and Cl2 at 550°C and the Cu+ ions thus formed mainly diffuse in glasses to replace alkali ions, where Cl2 acts as an oxidizing agent just like oxygen. In the case of molten CuSO42SO4, a small amount of Cu+ which is present in the molten state plays a primary role in the Cu ⇌ R+ ion exchange process, although the contribution of direct Cu2+⇌ 2R+ ion exchange cannot be ignored.  相似文献   

20.
Amorphous lithium electrolyte thin films, xLi2O·ySiO2·zP2O5, were deposited by rf magnetron sputtering of pure and mixed-phase lithium silicate, lithium phosphate, SiO2, Li2O, and Li2CO3 targets, and their compositions were determined using proton-induced y -ray emission spectroscopy, energy-dispersive X-ray analysis, Rutherford backscattering spectrometry, and atomic-emission spectroscopy. The deposition conditions were chosen to assure thermalization of the sputtered flux, which proved to be necessary in order to obtain a homogeneous distribution of Si and P in the films. Optical absorption and ac impedance measurements showed that glass-in-glass phase separation occurred in a large SiO2-rich domain of the composition diagram. In contrast to bulk glasses, all of the Li2O–SiO2 films were phase-separated, including those with lithia contents larger than lithium disilicate. High-performance liquid chromatography measurements revealed that, analogous to bulk glasses, the addition of SiO2 to Li2O-P2O5 compositions reduced the number of phosphate anion dimers, trimers, and higher anion polymers in the films through the formation of -Si-O-P-bonds. However, in contrast to bulk glasses, the distribution of phosphate anion polymers followed closely the Flory distribution, with the fraction of anion polymers decreasing monotonically with increasing chain length.  相似文献   

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