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1.
The internal friction of R2 O·Al2 O3 ·6SiO2 glasses was measured from-180° to 700°C at 0.4 Hz. Glasses containing Li2 O or Na2 O 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
2.
Toshinobu Yoko Toshio Nishiwaki Kanichi Kamiya Sumio Sakka 《Journal of the American Ceramic Society》1991,74(5):1112-1116
The ion-exchange mechanism between copper and alkali ions, when 20R2 O · 10Al2 O3 · 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 CuSO4 ─2 SO4 , 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
3.
Compositions in the system ThO2 -YO1.5 were coprecipitated as oxalates and converted to oxides. Disks were pressed and sintered in oxygen at 1400° to 2200°C. Densities of the sintered disks were 96 to 98% of theoretical. Solid solutions with the fluorite-type structure were formed up to 20 to 25 mole % YO1.5 at 1400°C and up to 45 to 50 mole % YO1.5 at 2200°C. Density data showed that these solid solutions correspond to Th1— x Y x O2—0.5 x , having a complete cation sub-lattice filled by Th4+ and Y3+ ions, and vacancies in the anion sublattice. The observed increase in electrical conductivity with increase in YO1.5 content is consistent with charge transport by oxygen ions through a vacancy mechanism. Approximately 7 mole % ThO2 is soluble in YO1.5 at 2200°C. Density results indicate an anion interstitial structure for the Y2 O3 phase. Transference number measurements indicate that the electrical conductivities are only partly due to ions. 相似文献
4.
Stoichiometric NiAl2 O4 , CuAl2 O4 , and ZnAl2 O4 spinels were prepared and equilibrated at temperatures from 600° to 1400°C. The parameters u and x , denoting the oxygen position and fraction of divalent cations on tetrahedral sites, respectively, were determined from a detailed X-ray diffraction analysis. In NiAl2 O4 , x increased from 0.07 at 595° to 0.26 at 1391°C; in CuAl2 O4 , x decreased from 0.68 at 613° to 0.64 at 1195°C; and in ZnAl2 O4 , x decreased from 0.96 at 905° to 0.94 at 1197°C. The form of the temperature dependence of x could not be described using theoretically based equations advanced in the literature. A more general equation which allows for a non-distributional contribution to the configurational entropy was derived and observed to properly describe the temperature dependence; the results indicate that short-range order is of definite significance in these intermediate aluminate spinels. 相似文献
5.
Fibers of Li2 O.Al2 O3 .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
6.
Phase equilibria in the system MnO–CoO–Cr2 O3 were investigated at 1300°C under controlled oxygen partial pressures by using the gas equilibration technique. The CoO activities in various phase assemblages of the system were measured by determining the partial pressures of oxygen in the gas phase for coexistence with metallic cobalt. The activity data revealed that at 1300°C, MnO–CoO and MnCr2 O4 –CoCr2 O4 solid solutions exhibit mild positive departures from ideal behavior. The activities in the stoichiometric spinel solutions were found to be in good agreement with those predicted from a model based on cation distribution equilibria. The standard free energy of formation of the compound CoCr2 O4 from its oxide components at 1300°C was determined as −37 636 J/mol, while that for MnCr2 O4 was found as −44 316 J/mol. 相似文献
7.
Activities of NiO were measured in the oxide and spinel solutions of the system MnO–NiO–Al2 O3 at 1300° and 1400° C with the aim of deriving information on the thermodynamic properties of the spinel phases. Synthetic samples in selected phase assemblages of the system were equilibrated with metallic nickel and a gas phase of known oxygen partial pressures at a total pressure of 1 atm. The data on NiO activities and directions of conjugation lines between coexisting oxide and spinel phases were used to establish the activity–composition relations in spinel solid solutions at 1300° and 1400°C. The MnAl2 O4 –NiAl2 O4 solid solutions exhibit considerable negative deviations from ideality at these temperatures. The free energy of formation of MnAl2 O4 from its oxide components (MnO + Al2 O3 ) at 1300° and 1400°C is calculated to be −24.97 and −26.56 kJ. mol−1 , respectively. The activities determined in the stoichiometric spinel solid solutions are more negative as compared with those predicted from cation distribution models. 相似文献
8.
Equilibrium phase diagrams for the systems NdCl3 –CaCl2 and NdCl3 –NaCl were determined by differential thermal analysis. A simple eutectic was observed at 59 ± 1 mol% CaCl2 and 600°± 2°C in the NdCl3 –CaCl2 system. A compound NaCl.3NdCl3 which melts incongruently at 545°± 5°C to NdCl3 and a liquid containing approximately 47 mol% NaCl, and a eutectic at 68 mol% NaCl and 439°± 2°C were found in the NdCl3 –NaCl system. On the basis of agreements between the activities calculated by the Clausius–Clapeyron equation and Temkin's model using the present data for the NdCl3 –CaCl2 system and the literature data for the PrCl3 –CaCl2 system, the melts in the former system consist of Nd3+ , Ca2+ , and Cl− ions and in the latter system of Pr3+ , Ca2+ , and Cl− ions. The above approach indicates the presence of Na+ , Cl− , and NdCl2- 5 ions in the NaCl-rich melts and Nd3+ , Cl− , and NdCl− 4 in the NdCl3 -rich melts in the NdCl3 –NaCl system. Analogous ions were indicated in the melts of the PrCl3 –NaCl system. 相似文献
9.
WILLIAM C. HAGEL P. J. JORGENSEN D. S. TOMALIN 《Journal of the American Ceramic Society》1966,49(1):23-26
Since the difference between oxygen-ion and cation diffusion coefficients is greater for α-Cr2 O3 than for α-Fe2 O3 or α-Al2 O3 , a study of initial-sintering kinetics was undertaken to show unequivocally which species is rate controlling. Fine powders of α-Cr2 O3 , obtained by thermal decomposition of reagent-grade (NH4 )2 Cr2 O7 , were lightly compacted and their isothermal rates of shrinkage were determined between 1050° and 1300°C. Resultant data follow volume-diffusion sintering models, and calculated diffusion coefficients agree with, those measured for oxygen ions in α-Cr2 O3 . There is little evidence that oxygen diffusion along grain boundaries becomes so enhanced that chromium ions are left in control of the process. 相似文献
10.
Ken Ando Yasumichi Oishi Hiroyuki Hase Koichi Kitazawa 《Journal of the American Ceramic Society》1983,66(12):222-C
Self-diffusion coefficients of the oxygen ion in single-crystal Y2 O3 were determined by the gas-solid isotope exchange technique. The results in the range 1100° to 1500°C are described by D=7.3 X 10-6 exp [-19l(kJ/mol)/RT] cm2 /s. Comparison of the results with those for oxides with the fluorite-type structure indicates that the regularly arranged vacant anion sites in the C-type structure do not contribute eflectively to oxygen ion diffusion . 相似文献
11.
B. D. ROITER 《Journal of the American Ceramic Society》1964,47(10):509-511
Phase relations in the spinel region of the system FeO-Fe2 O3 -Al2 O3 were determined in CO2 at 1300°, 1400°, and 15000°C and for partial oxygen pressures of 4 × 10−7 and 7 × 10−10 atmospheres at 15OO°C. The spinel field extends continuously from Fe3 O4-x to FeAl2 O4+z . 相似文献
12.
An intimate Ba-Al-Al2 O3 -SiO2 powder mixture, produced by high-energy milling, was pressed to 3 mm thick cylinders (10 mm diameter) and hexagonal plates (6 mm edge-to-edge width). Heat treatments conducted from 300° to 1650°C in pure oxygen or air were used to transform these solid-metal/oxide precursors into BaAl2 Si2 O8 . Barium oxidation was completed, and a binary silicate compound, Ba2 SiO4 , had formed within 24 h at 300°C. After 72 h at 650°C, aluminum oxidation was completed, and an appreciable amount of BaAl2 O4 had formed. Diffraction peaks consistent with hexagonal BaAl2 Si2 O8 , BaAl2 O4 , β-BaSiO3 , and possibly β-BaSi2 O5 were detected after 24 h at 900°C. Diffraction peaks for BaAl2 O4 and BaAl2 Si2 O8 were observed after 35 h at 1200°C, although SEM analyses also revealed fine silicate particles. Further reaction of this silicate with BaAl2 O4 at 1350° to 1650°C yielded a mixture of hexagonal and monoclinic BaAl2 Si2 O8 . The observed reaction path was compared to prior work with other inorganic precursors to BaAl2 Si2 O8 . 相似文献
13.
Masayuki Nogami Naoya Hayakawa Naoya Sugioka Yoshihiro Abe 《Journal of the American Ceramic Society》1996,79(5):1257-1261
Samarium ions (Sm2+ ) incorporated into aluminosilicate glasses by a sol-gel process showed persistent spectral hole burning at room temperature. Gels of the system Na2 O-Al2 O3 SiO2 synthesized by the hydrolysis of Si(OC2 H5 )4 , Al(OC4 H9 )3 , CH3 COONa, and SmCl3 ·6H2 O were heated in air at 500°C, then reacted with H2 gas to form Sm2+ ions. Whereas Al3+ ions effectively dispersed the Sm3+ ions in the glass structure, Na+ ions were not effective. The Al2 O3 -SiO2 glasses proved appropriate for reacting the Sm3+ ions with H2 gas and exhibited the intense photoluminescence of Sm2+ ions. The reaction of Sm3+ ions with H2 in the Al2 O2 -SiO2 glasses was determined by first-order kinetics, and the activation energy equaled 95 kJ/mol. At 800°C, the maximum photoluminescence of the Sm2+ ions was achieved within 20 min. 相似文献
14.
The subsolidus phase equilibrium diagram for the pseudobinary join MgAl2 O4 -Ga2 O3 was determined. The shape of the exsolution boundary was obtained by heat-treating samples pre- equilibrated at 1600°C. Crystalline solubility of Ga2 O3 in MgAl2 O4 decreased from 73 mole % at 1600°C to 55 mole % at 1200°C. The crystalline solution was formed by the replacement of Mg2+ ions by Ga3+ ions to produce a cation defect spinel. The phase precipitated was the mono-clinic δ-Ga2 O3 (=δ-Al2 O3 structure). Changes in the ratios of relative X-ray diffraction intensities indicated that the crystalline solutions also disorder with temperature. 相似文献
15.
New data obtained on the join Ca2 SiO4 -CaMgSiO4 established a limit of crystalline solubility of Mg in α-Ca2 SiO4 corresponding to the composition Ca1.90 Mg0.10 SiO4 at 1575°C. The α-α'Ca2 SiO4 inversion temperature is lowered from 1447° to 1400°C by Mg substitution in the lattice. α'-Ca2 SiO4 takes Mg into its lattice up to the composition Ca1.94 Mg0.06 SiO4 at 1400°C and to Ca1.96 Mg0.04 SiO4 at 900°C. A new phase (T) reported previously by Gutt, with the approximate composition Ca1.70 Mg0.30 SiO4 , was stable between 979° and 1381°C, and should be stable at liquidus temperatures in multicomponent systems involving CaO–MgO–SiO2 . 相似文献
16.
Konstantin Efimov Mirko Arnold Julia Martynczuk Armin Feldhoff 《Journal of the American Ceramic Society》2009,92(4):876-880
X-ray diffraction and transmission electron microscopy were applied to investigate a sol–gel synthetic process for the mixed oxygen ion and electron conductor La2 NiO4+δ with a K2 NiF4 structure type. The development of the La2 NiO4+δ is elucidated considering the influence of calcination temperatures and dwell times. Following the thermal decomposition of nitrate and organic precursors in an intermediate step, the lanthanum nickel oxide is obtained after a short dwell time above 750°C. This occurs by the transformation of an ultrafinely dispersed powder consisting of lanthanum oxycarbonate, lanthanum oxide, and nickel oxide. The pure La2 NiO4+δ phase was obtained by similar solid-state reactions between nanocrystalline powder particles at just 950°C. 相似文献
17.
Phase equilibria data, obtained both by differential thermal analysis and by quenching, are presented for the system Na2 O-Nb2 O5 . Five compounds corresponding to the formulas 3Na2 O.1Nb2 06 , lNa2 O. 1Nb2 O5 , lNa2 O 4Nb2 O6 , lNaz O.7Nb2 O5 , and lNa2 O. 10Nb2 O6 have been found. The compound 3Naz 0.lNb2 O5 melts congruently at 992°C. The compounds 1Na2 O. 4Nb2 O6 , lNa2 O.7Nb2 O, and 1Na2 O. 1Onb2 O5 melt incongruently at 1265°, 1275°, and 1290°C., respectively. The well-known perovskite structure phase NaNbO3 was found to melt congruently at 1412°C. The transition temperatures in NaNbO5 were checked by thermal analysis and only the major structural changes at 368° and 640°C. could be detected. A new disordered form of NaNbO3 could be preserved to room temperature by very rapid quenching. 相似文献
18.
Concurrent DTA, TGA, and oxygen pressure measurement were used to determine liquidus temperature for compositions near YBa2 Cu3 Ox . Liquidus temperatures were measured for oxygen partial pressures from 2 × 10−4 to 1 bar. Liquidus temperatures decreased for lowered oxygen pressure. The ternary eutectic is 930°C for 1 bar and 854°C for 0.02 bar oxygen pressure. Incongruent melting of YB2 Cu3 Ox occurs at 1034°C for 1 bar and 938°C for 2 × 10−4 bar oxygen pressure. Some implications for processing are also discussed. 相似文献
19.
The quenching technique was used to study subliquidus and subsolidus phase relations in the pseudobinary system Na2 Ti2 Si2 O11 -Na2 Ti2 Si2 O9 . Both narsarukite (Na2 TiSi4 O11 ) and lorenzenite (Na2 Ti2 Si2 O9 ) melt incongruently. Narsarsukite melts at 911°±°C to SiO2 +liquid, with the liquidus at 1016°C. Lorenzenite melts at 910°±5°C to Na2 Ti6 O13 +liquid; Na2 Ti6 O13 reacts with liquid to form TiO2 and is thus consumed by 985°±5°C. The liquidus occurs at 1252°C. 相似文献
20.
The ionic conductivity of cubic solid solutions in the system CaO -Y2 O3 -ZrO2 was examined. Particular Y2 O3 -ZrO2 binary compositions were more conductive at elevated temperatures (>600°C) than either CaO-ZrO2 binary or CaO-Y2 O3 -ZrO2 ternary compositions. The higher ionic conductivity appears to be related to a lower activation energy rather than to the number of oxygen vacancies dictated by composition. Those compositions of highest conductivity lie close to the cubic-monoclinic solid-solution phase boundary. Conductivity-temperature data are presented that indicate a reversible order-disorder transition for Y2 O3 -ZrO2 cubic solid solutions containing 20 and 25 mole % Y2 O3 . The transference number for the oxygen ion at 1000°C for Y2 O2 -ZrO2 cubic solid solutions is greater than 0.99. 相似文献