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1.
Fine-particle beta sodium ferrite (β-NaFeO2 ), rather than α-Fe2 O3 , may be responsible for superparamagnetic behavior in a glass of composition (in mole fractions) 0.37Na2 O-0.26Fe2 O3 -0.37SiO2 . The 700°C isothermal section of the phase diagram of the Na2 O-Fe2 O3 -SiO2 system is given, showing a three-phase field bounded by Na2 SiO3 -NaFeO2 -Fe2 O3 ; there is no evidence for the existence (at 700°C) of compounds of molar composition 6Na2 O-4Fe2 O3 -5SiO2 or 2Na2 O-Fe2 O3 -SiO2 . The Moessbauer spectrum of β-NaFeO2 has an internal magnetic field of 487 kOe at room temperature. 相似文献
2.
Günther H. Frischat Wolfgang Krause Horst Hübenthal 《Journal of the American Ceramic Society》1984,67(1):10-C-
Up to 3.3 wt% nitrogen can be incorporated into Na2 O-B2 O3 glass melts. The melting procedure is described, and structure models are given. In contrast to N-containing silicate glasses, the borate glasses were transparent; however, micrographs of their fracture surfaces showed some crystallinity. Properties were determined as a function of the N and Na2 O contents of the glasses. Compared with N-containing silicate glasses, the properties of borate glasses are much less changed by the nitrogen introduced. 相似文献
3.
Chung-Kook Lee Yolande Berta Robert F. Speyer 《Journal of the American Ceramic Society》1996,79(1):183-192
A glass crystallization method was utilized to synthesize nanosized BaO-6Fe2 O3 platelets from a 0.412BaO-0.258B2 O3 -0.330Fe2 O3 batch composition. Quenched ribbons were inhomogeneous, showing microclustering and ∼1 μm hematite crystals. Na2 O substitutions for BaO greatly enhanced the glass-forming tendency of quenched ribbons, though quenched-in ∼0.5 μm barium ferrite crystals were infrequently present. The improved homogeneity with Na2 O substitution was attributed to lower vapor pressure of BaO during batch melting, which increased its retention in the as-quenched ribbons. Quantities of BaO equal to or in excess of Fe2 O3 allowed iron ions to adopt stable network positions in the glass melt. With Na2 O substitution, devitrification of dispersed ∼40 nm barium ferrite particles from phase-separated regions occurred after secondary heat treatment. 5 mol% Na2 O batch substitution showed the lowest crystallinity in the as-quenched ribbons, and the highest crystallinity after secondary heat treatment. After optimum devitrification, the maximum values of saturation magnetization and coercivity were 21.22 emu/g and 2.82 kOe, respectively. 相似文献
4.
ANTHONY R. WEST 《Journal of the American Ceramic Society》1976,59(3-4):124-127
Ternary phase relations have been studied and several modifications made to Kracek's phase equilibrium diagram. These include location of the primary phase fields of Na6 Si8 O19 and Li2 Si2 O5 . Metastable phases and polymorphs were often encountered, notably a primary phase, δ-Na2 Si2 O5 , and a new polymorph of Li2 Si2 O5 . 相似文献
5.
The interdiffusion of ferric oxide and silica between Na2 O-SiO2 and Na2 O-SiO2 -Fe2 O3 melts containing the same mole % Na2 O was studied at 1200°C in air. Values in the range lO−5 to lO−8 cm2 sec−1 were obtained depending on the composition of the binary melt. The results were rationalized on the basis of the changing ionic nature of the iron with the soda-silica ratio of the ternary melt. It is concluded that significant concentrations of iron cations are present in the melt only if the mole fraction of soda is less than 0.3. A cursory examination of the relative electrical conductivity of a binary and a ternary melt tends to confirm this thesis. 相似文献
6.
The phase equilibrium relations in the systems Y2 O3 -Al2 O3 and Gd2 O3 -Fe2 O3 were examined. Each system has two stable binary compounds. A 3:s molar ratio garnet-type compound exists in both systems. The 1:1 distorted perovskite structure is stable in the system Gd2 O3 -Fe2 O3 but only metastable in the system Y2 O3 -AI2 O3 . This interesting example of metastable formation and persistence of a compound with ions of high Z/r values explains the discrepancies in the literature on the structure of the composition YA1O3 . A new 2:1 molar ratio cubic phase has been found in the system Y2 O3 -A12 O3 . Since silicon can be completely substituted for aluminum in this compound, the aluminum ions are presumably in fourfold coordination. 相似文献
7.
E. F. RIEBLING 《Journal of the American Ceramic Society》1974,57(9):373-377
Ternary Na2 O.Sb2 O3 .GeO2 glasses (with various [Na]/[Na + Sb] ratios) that contained ≥65 mol% GeO2 were prepared. Their densities (volumes), refractive indices, and infrared spectra were determined and their colors noted. The ternary glasses with ≥88 mol% GeO2 exhibit nearly additive volumes, refractivities, and frequencies for the main Ge-O vibration. Ternary glasses with lesser amounts of GeO2 exhibit a variety of behaviors, depending on the [Na]/[Na + Sb] ratio. Small amounts of Sb2 O3 cause significant volume and refraction deviations, as well as changes in νGe-O , that can be associated with gradual elimination of GeO6 octahedra. All the information supports a model for the glasses with 65 to 88 mol% GeO2 that involves a degree of depolymerization that is greater when Na2 O and Sb2 O3 are present together than when either is present alone. 相似文献
8.
Alumina and gallia were substituted separately for Na2 O in amounts of 0.2, 0.5, 1.0, 1.5, 2.0, and 3.0 wt% in three Na2 O-SiO2 glass compositions (82, 84, and 86 wt% SiO2 ) within the immiscibility region. The immiscibility regions for each system extend to ∼1.5 mol% of the added oxide. In general, the addition reduced the immiscibility temperature ( T m ), but at the edge of the immiscibility region (82% SiO2 ) the Na2 O loss effect initially increased T m . A structural model of the miscibility of Al2 O3 added to silicate glasses is presented. 相似文献
9.
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
10.
Different structural models for melts between Na2 SiO3 and Na2 Si2 O5 were tested by comparison of activities computed from the models with activities determined from the calorimetric heat of fusion. Data were used from the liquidus curve of the phase diagram for the system Na2 SiO3 -Na2 Si2 O5 (Kracek and Morey and Bowen). A group model involving (SiO3 )x 2x - rings or chains, with a random distribution of (SiO2.5 )2 pairs which bridge between rings or chains, gives activities in good agreement with those determined from the calorimetric heat of fusion. 相似文献
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12.
Transparent glass-ceramics, in which the major phase was NaNbO3 , were obtained by heat treatment of glasses in the Na2 O-Nb2 O5 -SiO2 system. The structure of the glass and the changes occurring during crystallization as a function of temperature and heating rate were examined by X-ray diffraction, transmission and replication electron microscopy, density, and other measurements. On heating, a rather abrupt formation of uniformly dispersed particles was observed. In the early stages of crystallization, these particles contained NaNbO3 as loose, radially grown dendrites of identical crystal orientation which became dense during later stages of crystallization. The particle sizes ranged from 200 to 10,000 A, depending on the SiO2 content of the glass. Transparency of the crystallized material was dependent on the particle size rather than on the amount of NaNbO3 formed. The temperature at which crystallization occurred increased with the heating rate whereas the viscosity at crystallization decreased. For a given value of the rate of crystal formation per °C of temperature increase, the product (viscosity)n × (heating rate) was constant. The nucleation and growth phenomena which occurred in these glasses was attributed to microheterogeneities of higher Nb2 O5 content which formed part of the glass structure. 相似文献
13.
LIBERTO DE PABLO-GALAN WILFRlD R. FOSTER 《Journal of the American Ceramic Society》1959,42(10):491-498
Beta alumina was once considered to be merely a metastable polymorph of corundum. Its status as a distinct and stable compound (Na2 O.-11Al2 O5 and analogous formulas) is now quite firmly established. Yet the published phase diagram for the system soda-alumina-silica takes no cognizance of its existence. A study of the alumina-rich portion of the system was conducted to determine whether or not beta alumina should be incorporated in the diagram. Conventional methods of investigation were used, with certain innovations designed to overcome difficulties inherent in the system. Solid-state sintering and modified quenching techniques were utilized to minimize soda loss. Sintering was at 1400°C. or thereabout, in platinum envelopes which were immersed in buffering mixtures so as to reduce volatilization. To the same end, extra-large quenching charges were employed, and these were held at 1600°C., far below the liquidus temperatures of most of the mixtures studied. Phase identification was primarily by the X-ray powder method. The results of these studies confirm the status of beta alumina as a discrete compound, and are believed to justify the insertion of an additional tie line, linking beta alumina to carnegieite, in the soda-alumina-silica diagram. A large primary field of beta alumina, occupying a portion of the present corundum field, is also strongly indicated. The phase diagram accordingly has been modified so as to incorporate these latest findings. The revised diagram, although in some respects tentative, is believed to be in fuller accord with technological experience. It is believed also to be in complete agreement with all recent laboratory studies in the system lime-soda-alumina-silica. 相似文献
14.
Immiscibility temperatures of Na2 O-B2 O3 -SiO glasses, with andwithout 1 mol% MoO3 , additions, were determined and the effect of MoO3 additions on the 65O°C immiscibility isotherms was established. In addition, immiscibility temperature and phase-separation morphology of an Na2 O-B2 O3 -SiO2 glass with progressive additions of MoO3 , were investigated. It was found that the addition of small amounts of MoO3 extends the immiscibility boundary of the system and raises the immiscibility temperature by ∼l8°C for each mol % MoO3 , addition. Analysis of phase-separation morphology suggests that the MoO3 , additions do not significantly alter the tie lines of phase separation in the system, although such additions cause a lowering of the viscosities and the glass-transition temperatures of these glasses. 相似文献
15.
Coatings were deposited on Cu0 , Ni0 , and Al0 anodes from aqueous solutions of NaAlO2 and Na2 SiO3 by anodic spark deposition. Some coatings formed at constant current density (1.0 A/cm2 ) were characterized by scanning electron microscopy, electron beam microprobe analysis, X-ray diffraction, and emission spectroscopy. A relation for the current decay during a multiple-spark, constant-voltage process was determined. This relation, which describes the behavior of most of the systems studied, is
where φt , φ0 , and φ∞ are the current densities at time t , at the start of the decay ( t =0), and at the steady state, respectively. K is a constant that is voltage and system dependent. 相似文献
where φ
16.
Hyun-Min Kim Fumiaki Miyaji Tadashi Kokubo Chikara Ohtsuki Takashi Nakamura 《Journal of the American Ceramic Society》1995,78(9):2405-2411
Bioactivities of Na2 O-CaO-SiO2 glasses were evaluated by examining the formation of bonelike apatite, which is responsible for their bonding to living bone, on their surfaces in a simulated body fluid, using thin-film X-ray diffraction and Fourier-transform infrared reflection spectroscopy. It was found that glasses in a wide compositional region in the P2 O5 -free Na2 O-CaO-SiO2 system can show bioactivity, as those in the P2 O5 -containing system. The rate of apatite formation on the surfaces of glasses varied largely with the composition of the glasses. Under a constant SiO2 content of 50 mol%, a glass containing equimole of Na2 O and CaO showed the highest rate of the apatite formation. Variation in the rate of apatite formation with the glass composition corresponded well with the rate of increase in the degree of the supersaturation of the simulated body fluid with respect to the apatite due to dissolution of sodium and calcium ions from the glasses. Little difference was observed in the rates of ion dissolution and of apatite formation between P2 O5 -containing Bioglass 45S5-type and a corresponding P2 O5 -free Na2 O-CaO-SiO2 glass. It is believed that P2 Os -free Na2 O-CaO-SiO2 glasses also show bioactivity as high as that of Bioglass. 相似文献
17.
An investigation was made of the effect of TiO2 on the glassforming region and on the physical properties of glasses in the system Na2 O-B2 O3 -SiO2 TiO2 . Glasses containing up to 45 mole % TiO2 may be formed with an alkali content of 30 mole %. At lower alkali contents (10 mole % Na2 O) glasses may be formed containing up to 22 mole % TiO2 . The way in which the coefficient of linear thermal expansion and the transformation and softening temperatures are affected by TiO2 additions has been determined. 相似文献
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