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1.
Toshihiro Kasuga Takafumi Kimata Akiko Obata 《Journal of the American Ceramic Society》2009,92(8):1709-1712
A calcium titanium phosphate glass–ceramic for use as a dental material with excellent chemical durability was derived from a mother glass with a small amount of fluorine. The laser Raman spectroscopic analysis showed that 35CaO–10CaF2 –30P2 O5 –25TiO2 glass, as the nominal composition, consists of ortho-, pyro-, and meta-phosphate groups. On heating the glass at 865°C, orthophosphate crystals, such as fluorine-containing oxyapatite (Ca10 (PO4 )6 (O,F2 )) and the Nasicon-type phase (CaTi4 (PO4 )6 ), were preferentially precipitated; the apatite particles of several tens of nanometers in size were embedded in the CaTi4 (PO4 )6 phase. The pale bluish color of the glass–ceramic indicated that titanium ions were included in the residual glassy phase. When the glass–ceramic was treated with dilute hydrochloric acid, only the apatite particles at the surface were leached out, while no CaTi4 (PO4 )6 phase was etched; the dissolution of the glass–ceramic was effectively controlled. Almost no dissolution of ions from the glass–ceramic occurred in water. It was suggested that the behavior is a result of the microstructure of the glass–ceramic, which consists of crystalline and glassy phases with excellent chemical durability. 相似文献
2.
Kousuke Yamamoto Toshihiro Kasuga Yoshihiro Abe 《Journal of the American Ceramic Society》1997,80(3):822-824
A novel porous glass-ceramic with a skeleton of CuTi2 (PO4 )3 was prepared by controlled crystallization of a glass and subsequent chemical leaching of the resulting dense glass-ceramic. A volume-crystallized dense glass-ceramic composed of CuTi2 (PO4 )3 and Cu3 (PO4 )2 whose surface was covered by a CuO thin layer was prepared by reheating a glass with a nominal composition of 50CuO·20TiO2 30P2 O5 (in mol%) glass in air. When the resultant glass-ceramic was leached with dilute H2 SO4 , Cu3 (PO4 )2 and CuO phases were dissolved out selectively, leaving a crystalline CuTi2 (PO4 )3 skeleton. The specific surface area and the average pore radius of the porous glass-ceramic obtained were approximately 45 m2 g-1 and 9 nm, respectively. The porous glass-ceramic showed catalytic activity in the conversion reaction of propene into acrolein. 相似文献
3.
Stress in Leached Phase-Separated Glass 总被引:2,自引:0,他引:2
When a phase-separated glass is leached, stresses develop because of release of thermal stresses, creation of surface area, ion exchange, and hydration. Analyses are presented for the thermal stresses, including the portion that develops on cooling from the heat-treatment temperature to the setting temperature of the less viscous phase. During leaching, the interfacial energy of the residual phase increases, so that phase tends to contract. A more important effect is the contraction caused by removal of alkali and B2 O3 from the residual phase during leaching. The extent of removal of B2 O2 decreases with heat-treatment time, tH , because the scale of the microstructure increases as t1/3 H . The change in residual B2 O2 content with tH is shown to be consistent with diffusion-controlled ion exchange. The dependence of stress on tH in partially leached glasses, measured by Drexhage and Gupta, results principally from the change in extent of ion exchange; the reduction in surface area with increasing tH also has a significant effect on the stresses. 相似文献
4.
S. Kamakshi Sundaram Jen-Yan Hsu Robert F. Speyer 《Journal of the American Ceramic Society》1994,77(6):1613-1623
The corrosion resistance of molybdenum, molybdenum disilicide, and a SiC(p) /Al2 O3 composite to molten soda-lime-silicate glass was studied. The ASTM-C621–84 corrosion test method was modified because of inherent inaccuracies in the method and Si attack of platinum crucibles. Specimen-glass interfacial regions were characterized using XRD, SEM, and EDS. After 48 h of exposure at 1565°C, the half-down corrosion recessions of Mo, MoSi2 , and SiC(P) /Al2 O3 were 0.11, 0.316, and 0.26 mm, respectively. Mo oxidized to form a MoO2 surface scale which cracked, allowing glass seepage and further oxidation. Silicon was leached out of MoSi2 into the glass, leaving a Mo5 Si3 interface and particles of Mo near the interface. For the SiC(P) /Al2 O3 composite, bubbles observed at the interfacial regions formed from oxidation of SiC to form CO. Thermodynamic modeling corroborated these experimental observations. 相似文献
5.
Woon Jin Chung Bong Je Park Hong Seok Seo Joon Tae Ahn Myung-Hyun Lee Yong Gyu Choi 《Journal of the American Ceramic Society》2005,88(5):1205-1208
Selenide glass optical fibers were fabricated for Ge30 Sb10 Se58 S2 and Ge20 Sb10 Se70 glasses. Their transmission loss has been measured and compared with the theoretical attenuation loss that was calculated taking into account the electronic transition absorption, Rayleigh scattering, and multiphonon absorption. A low attenuation loss of the Ge20 Sb10 Se70 glass composition in 1.2–1.7 μm range has been expected due to its high optical band gap energy compared with the Ge30 Sb10 Se58 S2 glass. However, the measured attenuation loss of the Ge30 Sb10 Se58 S2 glass fiber was ∼13 dB/m at 1.5 μm while Ge20 Sb10 Se70 glass showed ∼82 dB/m. An enhanced weak absorption tail due to the localized states of the Ge20 Sb10 Se70 glass was responsible for this behavior. Structural defects are related to the localized states and discussed for the present glass compositions. 相似文献
6.
A novel porous glass-ceramic with a skeleton of a NASICON-type copper(II) titanium phosphate was prepared via the controlled crystallization of a glass and the subsequent chemical leaching of the resulting dense glass-ceramic. A volume-crystallized dense glass-ceramic comprised of CuTi2 (PO4 )3 and Cu3 (PO4 )2 , whose surface was covered by a thin layer of CuO, was prepared by reheating a glass with a nominal composition of 50CuO20TiO2 30P2 O5 (in mol%) in air. When the resulting glass-ceramic was leached with dilute HCl, the Cu3 (PO4 )2 and CuO phases were dissolved out selectively, and a cuprous NASICON crystal of CuTi2 (PO4 )3 was converted to its cupric type, CuTi4 (PO4 )6 , which was left as a skeleton of the porous materials. The specific surface area and the average pore radius of the porous glass-ceramic obtained were ∼70 m2 /g and ∼7 nm, respectively. The porous glass-ceramic showed high catalytic activities for the dehydration of 2-propanol. 相似文献
7.
Clear glasses which included droplet-like microphases were produced when SiO2 in sodium borosilicate glasses was replaced by Sc2 O3 . 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
8.
A glass with the eutectic composition 3MnO1.5 –2SiO2 was used to simulate the formation of a liquid phase during sintering of BaTiO3 . Two oxide additives (Mn2 O3 and SiO2 ) performing various functions of the properties of BaTiO3 were investigated for their crystallization and thermal characteristics at temperatures ≤1400°C. The wetting behavior of the glass, the dissolution of BaTiO3 in glass melt, the identification of newly formed phases, and the sequential reaction kinetics of the glass/BaTiO3 system, especially when isothermally treated at 1150°C, were investigated by electron microscopy with quantitative X-ray energy dispersive spectroscopic (Q-EDS) analysis. The evolution of the interfacial reaction of the glass/BaTiO3 at 1150°C is reported and discussed. 相似文献
9.
The Rayleigh scattering of the mixed-alkali glass system K2 O–Na2 O–MgO–SiO2 (KNMS) was investigated, both experimentally and theoretically. The lowest Rayleigh scattering coefficient (38% of that for pure SiO2 glass) was obtained when the glass composition was 22K2 O–8Na2 O–10MgO–60SiO2 (in mol%). These values are equal to or less than the minimum values reported for the ternary sodium silicate glass Na2 O–MgO–SiO2 . The Rayleigh scattering caused by concentration fluctuation was believed to have been reduced greatly in this KNMS glass, because the mobility of the alkali-metal ions was reduced by the mixed-alkali effect. 相似文献
10.
Aran Rafferty Anton Clifford Robert Hill David Wood Bisserka Samuneva Margarita Dimitrova-Lukacs 《Journal of the American Ceramic Society》2000,83(11):2833-2838
The nucleation and crystallization of a series of glasses based on 4.5SiO2 ·3Al2 O3 ·1.5P2 O5 ·(5 − z )CaO · z CaF2 with a Ca:P ratio corresponding to apatite were studied. In these glasses, the objective was to investigate the influence of fluorine content and z was varied from 3 to 0. All the glasses studied crystallized to fluorapatite (FAP) and mullite with the exception of the glass containing no fluorine, which crystallized to β-tricalcium phosphate (Ca3 (PO4 )2 ) and anorthite (CaAl2 Si2 O8 ). Glasses that contained sufficient fluorine to form FAP bulk nucleated to give FAP without a nucleation hold. Thermal gravimetric analysis demonstrated a significant weight loss corresponding to the crystallization of mullite, which increased with the fluorine content of the glass and also with decreased particle size. The loss was attributed to volatile SiF4 . The glass transition temperature decreased with increased fluorine content of the glass. 相似文献
11.
Christina Scheu Gerhard Dehm Wayne D. Kaplan 《Journal of the American Ceramic Society》2001,84(3):623-630
The microstructure of copper–alumina (Cu-Al2 O3 ) composites that have been prepared via the melt infiltration of liquid copper into porous alumina preforms was studied in detail, using various transmission electron microscopy (TEM) techniques. Two different samples—with open pore diameters of 0.2 and 0.8 μm—were investigated. For both specimens, a single crystalline copper network that extended throughout the open porosity of the alumina preform was observed. An amorphous glass phase that contained silicon and calcium was observed at the Al2 O3 /Cu/Al2 O3 triple junctions. The diameters of these amorphous pockets, which were strongly faceted along the Al2 O3 grains, were up to 20 and 100 nm for the initial pore sizes of 0.2 and 0.8 μm, respectively. A glass phase that contained silicon and calcium also was present at the Cu/Al2 O3 interfaces, whereas the Al2 O3 boundaries remained dry. Detailed high-resolution transmission electron microscopy investigations have shown that the interfacial glass phase at the Cu/Al2 O3 interfaces exhibited a uniform equilibrium film thickness along the interface region. However, the interfacial film thickness was dependent on the orientation of the Al2 O3 grain, and its value varied from 0.4 nm for Al2 O3 rhombohedral-plane termination ((1¯012)) up to 1 nm for Al2 O3 basal-plane termination ((0001)). 相似文献
12.
Takahiro Takada Sea Fue Wang Shoko Yoshikawa Sei-Joo Jang Robert E. Newnham 《Journal of the American Ceramic Society》1994,77(7):1909-1916
The effect of glass addition on the properties of BaO–TiO2 -WO3 microwave dielectric material N-35, which has Q = 5900 and K = 35 at 7.2 GHz for samples sintered at 1360°C, was investigated. Several glasses including B2 O3 , SiO2 , 5ZnO–2B2 O3 , and nine other commercial glasses were selected for this study. Among these glasses, one with a 5 wt% addition of B2 O3 to N-35, when sintered at 1200°C, had the best dielectric properties: Q = 8300 and K = 34 at 8.5 GHz. Both Q and K increased with firing temperature as well as with density. The Q of N-35, when sintered with a ZnO–B2 O3 glass system, showed a sudden drop in the sintering temperature to about 1000°C. The results of XRD, thermal analysis, and scanning electron microscopy indicated that the chemical reaction between the dielectric ceramics and glass had a greater effect on Q than on the density. The effects of the glass content and the mixing process on the densification and microwave dielectric properties are also presented. Ball milling improved the densification and dielectric properties of the N-35 sintered with ZnO–B2 O3 . 相似文献
13.
Hideo Hosono Zhibo Zhang Yoshihiro Abe 《Journal of the American Ceramic Society》1989,72(9):1587-1590
A porous glass-ceramic in the CaO–TiO2 —P2 O5 system has been prepared by crystallization and subsequent chemical leaching of the corresponding glass. By applying a two-step heat treatment to 45CaO · 25TiO2 · 30P2 O5 glasses containing a few mol% of Na2 O, volume crystallization results in the formation of dense glass-ceramics composed of CaTi4 (PO4 )6 and β-Ca3 (PO4 )2 phases. By leaching the resultant glass ceramics with HCI, β-Ca3 (PO4 )2 is selectively dissolved out, leaving a crystalline CaTi4 (PO4 )6 skeleton. The surface area and mean pore radius of the porous glass-ceramics were approximately 40 m2 /g and 13 nm, respectively. 相似文献
14.
Bing Zhang Qi Chen Li Song Huiping Li Fengzhen Hou 《Journal of the American Ceramic Society》2008,91(6):2036-2038
The influence of 0–16 mol% Sb2 O3 substitution for P2 O5 on the properties of ZnO–P2 O5 glasses has been investigated. It was shown that Sb2 O3 could participate in the glass network and thermal stability of the glasses decreased with increasing Sb2 O3 content. Glass transition temperature T g , softening temperature T s , and water durability all decreased firstly (up to 6 mol% Sb2 O3 added) and then increased. Substitution of 12 mol% Sb2 O3 led to a 16°C decrease in T g and 30°C decrease in T s , and weight loss of the glass was only 0.42 mg/cm2 , which is ∼11 times lower than that of the glass without Sb2 O3 after immersion in deionized water at 90°C for 1 day. The glass containing 12 mol% Sb2 O3 might be a substitute for Pb-based glasses in some applications. 相似文献
15.
Takashi Yamaguchi Hiroko Ayaki Lika Asai 《Journal of the American Ceramic Society》1993,76(4):993-997
Interfacial and powder reactions between CaTiO3 and 90PbO–10B2 O3 and 75PbO–25SiO2 binary glasses were studied. The reaction has been analyzed as the effect of B2 O3 and SiO2 additions on the interaction between CaTiO3 and PbO, and discussed from thermodynamic and kinetic points of view. For a fixed CaTiO3 /PbO ratio2 the product perovskite phase became enriched with lead as the amount of additives increased, which is more pronounced with B2 O3 addition. The reaction of CaTiO3 with the lead–boron glass was controlled by a dissolution-precipitation mechanism, and that with the lead-silica glass by a diffusion mechanism. 相似文献
16.
Daniel Caurant Odile Majérus Edward Fadel Marion Lenoir Christel Gervais Olivier Pinet 《Journal of the American Ceramic Society》2007,90(3):774-783
Crystallization of the poorly durable Na2 MoO4 phase able to incorporate radioactive cesium must be avoided in SiO2 –Al2 O3 –B2 O3 –Na2 O–CaO glasses developed for the immobilization of Mo-rich nuclear wastes. Increasing amounts of B2 O3 and MoO3 were added to a SiO2 –Na2 O–CaO glass, and crystallization tendency was studied. Na2 MoO4 crystallization tendency decreased with the increase of B2 O3 concentration whereas the tendency of CaMoO4 to crystallize increased due to preferential charge compensation of BO4 − entities by Na+ ions. 29 Si MAS NMR showed that molybdenum acts as a reticulating agent in glass structure. Trivalent actinides surrogate (Nd3+ ) were shown to enter into CaMoO4 crystals formed in glasses. 相似文献
17.
ELLEN L. MOCHEL MARTIN E. NORDBERG THOMAS H. ELMER 《Journal of the American Ceramic Society》1966,49(11):585-589
Removal of soda from a glass surface at high temperature can, on cooling, give appreciable strengthening due to lowering of the expansion coefficient at the surface. Soda depletion has been accomplished previously by treating a high-expansion soda-lime glass with SO2 in the presence of oxygen and water. The depletion rate can be doubled by using dispersed platinum to catalyze the oxidation of SO2 to SO3 before the gas reacts with soda from the glass. The data are consistent with the soda depletion being Fickian both with and without the catalyst. Alumina in the glass composition markedly increases the strength which can be attained by sulfur oxide treatment. Although the percentage of soda retained in the leached layer increases, the total amount of soda removed from the glass also increases as alumina increases. It must follow that the depth of the layer is increased. 相似文献
18.
Beata Zalinska Mehdi Mirsaneh Ian M. Reaney 《Journal of the American Ceramic Society》2009,92(9):1981-1985
The effect of a bespoke glass sintering aid, 0.3Bi2 O3 –0.3Nb2 O5 –0.3B2 O3 –0.1SiO2 (BN1), developed from the base ceramic composition, BiNbO4 (BN), on the sinterability, microstructure, and microwave (MW) dielectric properties of BN ceramics has been investigated. Densities >97% theoretical could be achieved at 1020°C for samples with up to 15% BN1 additions. The resulting microstructure was composed of BN laths surrounded by a residual glass phase that contained small fibrous crystals. Some evidence of dissolution of BN crystals was observed. Optimum properties were exhibited for samples with 15 wt% of glass addition sintered for 4 h at 1020°C with a relative permittivity ɛr =38, a MW quality factor Q × f 0 =17 353 at 5.6 GHz, and a temperature coefficient of resonant frequency τf =−10 ppm/°C. The high Q × f 0 , ɛr , and low τf , coupled with a relatively low sintering temperature, suggest that the use of bespoke glass sintering aids of this type may have great potential for the fabrication of MW ceramics. 相似文献
19.
Hee-Kyun Shin Hyunho Shin Seo-Yong Cho Kug Sun Hong 《Journal of the American Ceramic Society》2005,88(9):2461-2465
Effects on phase evolution caused by the addition of a new sintering agent, lithium borosilicate, Li2 O·B2 O3 ·SiO2 (LBS) glass to 0.9MgTiO3 –0.1CaTiO3 ceramic and resultant dielectric properties were investigated. The added LBS glass, a liquid phase sintering agent, significantly lowered the densification temperature from 1300° to about 950°C, while yielding decomposition of MgTiO3 into MgTi2 O5 and Mg2 TiO4 . At the same time, the by-products of the decomposition reaction, MgO and TiO2 , were dissolved into the glass network. Such phase evolution partly compensated the influence of deleterious glass addition so that the specimen demonstrated fairly good apparent dielectric properties. 相似文献
20.
Masahide Okamoto Hironori Kodama Kazuo Shinozaki 《Journal of the American Ceramic Society》2008,91(4):1110-1114
The sintering of a composite of MgO–B2 O3 –Al2 O3 glass and Al2 O3 filler is terminated due to the crystallization of Al4 B2 O9 in the glass. The densification of a composite of MgO–B2 O3 –Al2 O3 glass and Al2 O3 filler using pressureless sintering was accomplished by lowering the sintering temperature of the composite. The sintering temperature was lowered by the addition of small amounts of alkali metal oxides to the MgO–B2 O3 –Al2 O3 glass system. The resultant composite has a four-point bending strength of 280 MPa, a coefficient of thermal expansion (RT—200°C) of 4.4 × 10−6 K−1 , a dielectric constant of 6.0 at 1 MHz, porosity of approximately 1%, and moisture resistance. 相似文献