共查询到20条相似文献,搜索用时 31 毫秒
1.
Shiro Torizuka Kaoru Sato Hiroaki Nishio Teruo Kishi 《Journal of the American Ceramic Society》1995,78(6):1606-1610
Compacts of TiB2 with densities approaching 100% are difficult to obtain using pressureless sintering. The addition of SiC was very effective in improving the sinterability of TiB2 . The oxygen content of the raw TiB2 powder used in this research was 1.5 wt%. X-ray photoelectron spectroscopy showed that the powder surface consisted mainly of TiO2 and B2 O3 . Using vacuum sintering at 1700°C under 13–0.013 Pa, TiB2 samples containing 2.5 wt% SiC achieved 96% of their theoretical density, and a density of 99% was achieved by HIPing. TEM observations revealed that SiC reacts to form an amorphous phase. TEM-EELS analysis indicated that the amorphous phase includes Si, O, and Ti, and X-ray diffraction showed the reaction to be TiO2 + SiC → SiO2 + TiC. Therefore, the improved sinterability of TiB2 resulted from the SiO2 liquid phase that was formed during sintering when the raw TiB2 powder had 1.5 wt% oxygen. 相似文献
2.
Parjaree Thavorniti Yuichi Ikuhara Taketo Sakuma 《Journal of the American Ceramic Society》1998,81(11):2927-2932
The microstructures of 5 wt% SiO2 -doped TZP, 5 wt% (SiO2 + 2 wt% MgO)-doped TZP, and 5 wt% (SiO2 + 2 wt% Al2 O3 )-doped TZP are characterized by high-resolution electron microscopy, energy-dispersive X-ray spectroscopy, and electron energy loss spectroscopy. An amorphous phase is formed at multiple grain junctions but not along the grain-boundary faces in these three materials. A small addition of MgO and Al2 O3 into the SiO2 phase results in a marked reduction in tensile ductility of SiO2 -doped TZP. This reduction seems to correlate with segregation of magnesium or aluminum ions at grain boundaries and a resultant change in the chemical bonding state. 相似文献
3.
Differential thermal analysis, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, and transmission electron microscopy were used to study the crystallization of a glass with a composition of 11.2 wt% MgO, 40.5 wt% CaO, 33.3 wt% SiO2 , and 15 wt% P2 O5 . A two-phase "composite," which was composed of apatite and an intermediate phase (H-phase), was formed under appropriate heat-treatment conditions. The spherulitic morphology of apatite phase transformed from "open sheaf" into ellipsoidal as samples were heated to a higher temperature. These phenomena were due to the intermediate H-phase becoming unstable at this temperature so that the retardation effect on the apatite dendritic growth disappeared. 相似文献
4.
Takashi Harada Hiromichi Takebe Makoto Kuwabara 《Journal of the American Ceramic Society》2006,89(1):247-250
The glass transition temperature increases and the thermal expansion coefficient and density decrease with increasing B2 O3 concentration in a series of (100− x )(50BaO–50P2 O5 )− x B2 O3 where x =0–10 mol% for bulk samples. According to Raman spectroscopy, the bulk BaO–P2 O5 –B2 O3 (BaP–B) glasses consist of metaphosphate Q 2 units with ring-type metaborate, diborate, and PO4 –BO4 groups. X-ray photoelectron spectroscopy results reveal qualitatively that P–O–B bonds are formed at the surface of BaP–B glass samples ground in laboratory air over 6 mol% B2 O3 only. The P–O–B bonds are related to the suppression of the crystallization of powdered BaP–B glasses with >6 mol% B2 O3 during differential thermal analysis. 相似文献
5.
The crystallization of MgO-Al2 O3 -SiO2 -ZrO2 glasses at 1000°C was studied. Isothermal heat treatments of a cordierite-based glass (2MgO.2Al2 O3 .5SiO2 = Mg2 Al4 Si5 O18 ) with 7 wt% ZrO2 produced surface crystallization of α-cordierite and tetragonal ZrO2 ( t -ZrO2 ). These phases advanced into the glass by cocrystallization of t -ZrO2 rods in an α-cordierite matrix with a well-defined orientation relation. The t -ZrO2 rods were unstable with respect to diffusional breakup (a Rayleigh instability) and decomposed into rows of aligned ellipsoidal and spheroidal particles. The t -ZrO2 was very resistant to transformation to monoclinic symmetry. With a similar glass containing 15 wt% ZrO2 , surface crystallization of α-cordierite and t -ZrO2 was accompanied by internal crystallization of t -ZrO2 dendrites. Transformation of the dendrites to mono-clinic symmetry was observed under some conditions. 相似文献
6.
The crystallization behavior of an Li2 O-Zn0-SiO2 glass with a ZnO content of −28.5 wt% and nucleated with P2 O5 was investigated by infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. A three-stage process, consisting of the nucleation, crystallization, and transformation of Li3 Zn0.5 Si04 and the emergence of a silica phase, occurs during heat treatment of this system. A small addition of K2 O varies the sequence of crystallization and the phase composition of the resulting glass-ceramic. 相似文献
7.
The crystallization behavior of a glass with a composition of 40 wt% 3CaO · P2 O5 −60 wt% CaO · MgO · 2SiO2 was investigated. The primary crystalline phase was apatite with a dendritic form and ellipsoidal shape. β-(3CaO · P2 O5 ) and CaO · MgO · 2SiO2 were crystallized as samples heated to 990°C, and a three-layer structure was obtained. The development and morphology of this construction were explained by both the surface crystallization of the apatite and CaO · MgO · 2SiO2 and the bulk crystallization of apatite and the CaO · MgO · 2SiO2 -β-(3CaO · P2 O5 ) composite. 相似文献
8.
Bertha Alicia Vázquez Ángel Caballero Pilar Pena 《Journal of the American Ceramic Society》2005,88(7):1949-1957
Solid-state compatibility and melting relations of MgAl2 O4 in the quaternary system Al2 O3 –CaO–MgO–SiO2 were studied by firing and quenching selected samples located in the 65 wt% MgAl2 O4 , plane followed by microstructural and energy dispersive X-ray analysis. A projection of the liquidus surface of the primary crystallization volume of MgAl2 O4 was constructed from CaO, SiO2 and exceeding Al2 O3 , not involved in stoichiometric MgAl2 O4 formation; those three amounts were recalculated to 100 wt%. The temperature and character of six invariant points, where four solids co-exist with a liquid phase, were defined. One maximum point was localized and the positions of the isotherms were tentatively established. The effect of CaO, SiO2 , and Al2 O3 impurities on the high temperature behavior of spinel materials was also discussed. 相似文献
9.
Crystallization Kinetics and Properties of Nonstoichiometric Cordierite-Based Thick-Film Dielectrics 总被引:1,自引:0,他引:1
Yong S. Cho † Walter A. Schulze Vasantha R. W. Amarakoon 《Journal of the American Ceramic Society》1999,82(11):3186-3192
Dielectric thick films based on a nonstoichiometric cordierite (2.4MgO·2Al2 O3 ·5SiO2 , containing 3 wt% B2 O3 , 3 wt% P2 O5 , and 3 wt% PbO) were investigated, in regard to their microstructure, crystallization kinetics, and properties. A stable glass-ceramic thick-film microstructure that was formed on a 96% alumina substrate was observed after firing at a temperature of 915°C for 30 min in a nitrogen atmosphere. No µ-cordierite was observed in the X-ray diffraction (XRD) patterns of the thick film. The crystallization kinetics were studied via quantitative XRD analysis using the Avrami equation, and the rate constant increased as the temperature increased. The decreasing tendency of the Avrami parameter, relative to temperature, suggested a change in growth directionality during crystallization. The activation energy for crystallization of the thick film was determined to be ~83 kcal/mol (~350 kJ/mol). The coefficient of thermal expansion (CTE) and the dielectric constant of the glass phase were evaluated using the bulk-sample data. For the case of a 3-wt%-PbO sample fired at 950°C for 30 min in a nitrogen atmosphere, the remaining glass was estimated, using the parallel mixing rule, to have a dielectric constant of 15.3 at 1 MHz. The dielectric constant of the remaining glass was dependent on the PbO content and the heat-treatment temperature. The estimated CTE of the remaining glass for the 3-wt%-PbO sample was 19 × 10-6 /°C. 相似文献
10.
Dae-Chul Park Toyohiko Yano Takayoshi Iseki Kazuyori Urabe 《Journal of the American Ceramic Society》2000,83(12):2967-2973
A chemical adsorption method in a Si3 N4 slurry that contained a nitrate solution was studied during ball milling, with particular interest in increasing the oxide layer in the Si3 N4 powder and improving the distribution homogeneity of the sintering additives. The nitrate salts Al(NO3 )3 ·9H2 O and Y(NO3 )3 ·6H2 O were selected as sintering additives. The following characterization techniques were used: oxygen–nitrogen analysis, X-ray photoelectron spectroscopy, high-resolution electron microscopy (coupled with energy-dispersive X-ray spectroscopy), and X-ray imaging (using wavelength-dispersive X-ray spectroscopy). The thickness of the amorphous layer and the oxygen content of the Si3 N4 powder were greater for samples that were milled with nitrate additives, which were heat-treated at 600°C, than those of powders that were milled with oxide additives. The chemical composition of the oxygen-containing layer—that is, the amorphous layer that formed and/or changed on the Si3 N4 surface—was similar to Si2 N2 O in heat-treated Si3 N4 powder with nitrate additives, whereas the composition of heat-treated Si3 N4 powder with oxide additives was similar to SiO2 . Furthermore, a homogeneous distribution of the additives was achieved via the incorporation of aluminum and yttrium into the amorphous layer on the Si3 N4 surface. The metal ratio (Y:Al) of the adsorbates was somewhat higher than that of the additives. 相似文献
11.
Influence of Molybdenum Silicide Additions on High-Temperature Oxidation Resistance of Silicon Nitride Materials 总被引:2,自引:0,他引:2
Hagen Klemm Katja Tangermann Christian Schubert Waldemar Hermel 《Journal of the American Ceramic Society》1996,79(9):2429-2435
The influence of additions of molybdenum disilicide (MoSi2 ) on the microstructure and the mechanical properties of a silicon nitride (Si3 N4 ) material, with neodymium oxide (Nd2 O3 ) and aluminum nitride (AIN) as sintering aids, was studied. The composites, containing 5, 10, and 17.6 wt% MoSi2 , were fabricated by hot pressing. All materials exhibited a similar phase composition, detected by X-ray diffractometry. Up to MoSi2 additions of 10 wt%, mechanical properties such as strength, fracture toughness, or creep at 1400°C were not affected significantly, in comparison to that of monolithic Si3 N4 . The oxidation resistance of the composites, in terms of weight gain, degraded. After 1000 h of oxidation at 1400° and 1450°C in air, a greater weight gain (by a factor of approximately three) was obtained, in comparison to that of the material without MoSi2 . Nevertheless, after 1000 h of oxidation, the degradation in strength of the composites was considerably less severe than that of the material without MoSi2 . An additional layer was formed, caused by processes at the surface of the Si3 N4 material, preventing the formation of pores, cracks, or glassy-phase-rich areas, which are common features of oxidation damage in Si3 N4 materials. This surface layer, containing Mo5 Si3 and silicon oxynitride (Si2 ON2 ), was the result of reactions between MoSi2 , Si3 N4 , and the oxygen penetrating by diffusion into the material during the hightemperature treatment. 相似文献
12.
Sean P. Morgan Ian M. Reaney Robert Buckley David Furniss Angela B. Seddon 《Journal of the American Ceramic Society》2000,83(3):617-622
The crystallization of 70Ga2 S3 . 30La2 S3 (mol%) glasses has been studied using X-ray diffraction and transmission electron microscopy. Two of the glasses were prepared from raw materials with nominally different oxide concentrations. The third was prepared from raw materials aged in an oxygen-depleted, argon-flushed glove box for more than 1 yr. Their oxide/hydroxide impurity content was qualitatively ranked using Fourier transform infrared spectroscopy. The lowest oxide content composition (≤0.5 wt%, supplied information) devitrified readily close to the glass transition temperature, T g , forming crystallites of a new (GLS) phase with a monoclinic Bravais lattice and a lathlike internal structure. Ga2 S3 was observed in small quantities between the laths. Samples prepared from nonaged, high oxide (1–3 wt%) content precursors produced the most stable glass. On crystallization, these samples exhibited spherulites composed of intergrown laths of melilite-structured La3.33 Ga6 S14 and the new monoclinic GLS phase. Whiskers of Ga2 S3 were found in the residual glass between crystallites. Samples prepared from aged raw materials produced spherulites of La3.33 Ga6 S14 on crystallization with no identifiable regions of the new GLS phase. 相似文献
13.
Eui Yeol Lee Yong-ho Sohn Santosh K. Jha John W. Holmes Richard D. Sisson 《Journal of the American Ceramic Society》2002,85(8):2065-2071
Phase constituents and transformations of plasma-sprayed thermal barrier coatings (TBCs) with CeO2 -stabilized ZrO2 (CSZ; 16–26 wt% CeO2 ) have been investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The as-coated CSZ coatings with 16 and 18 wt% CeO2 consisted only of the nonequilibrium tetragonal ( t ') phase. A mixture of the t ' and the nonequilibrium cubic ( c ') phases was observed for the as-coated CSZ coatings containing 20–26 wt% CeO2 . During 65 min cyclic oxidation at 1135°C (45 min hold time) in air, the t ' or the mixture of the t ' and the c ' phases decomposed to the equilibrium tetragonal ( t ) and the equilibrium cubic ( c ) phases. Some of the t phase transformed to the monoclinic ( m ) phase on cooling. More m phase was observed to develop in the CSZ coating containing 16 wt% CeO2 than in the other coatings. More m phase was observed on the top surface than on the bottom surface of the CSZ coating. Spalling of the plasma-sprayed CSZ coating during thermal cycling occurred after 230 cycles for the CSZ coating containing 16 wt% CeO2 , whereas the lifetime of the CSZ coatings with 18–26 wt% CeO2 ranged between 320 and 340 cycles. 相似文献
14.
Compatibility relations of Al2 03 in the quaternary system Zr02-Al2 03 -Si02 -CaO were studied by firing and quenching followed by microscopy and energy-dispersive X-ray examination. A projection of the boundary surface of the primary crystallization volume of Al2 03 was constructed in terms of the CaO, Si02 , and Zr02 contents of the mixtures recalculated to 100 wt%. Two invariant points, where four solids coexist with a liquid phase, are defined, and the positions of the isotherms were established. 相似文献
15.
Sung Min Rhim Seokmin Hong Heungjin Bak Ok Kyung Kim 《Journal of the American Ceramic Society》2000,83(5):1145-1148
The effects of B2 O3 addition on the sintering behavior and the dielectric and ferroelectric properties of Ba0.7 Sr0.3 TiO3 (BST) ceramics were investigated. The dielectric and ferroelectric properties of a BST sample with 0.5 wt% B2 O3 sintered at <1150°C were as good as those of undoped BST sintered at 1350°C, and the dielectric loss was better. When >1.0 wt% B2 O3 was added to BST, the overdoped B2 O3 did not form a liquid phase or volatilize; it remained in the samples and formed a secondary phase that lowered the sintering behavior and the dielectric and ferroelectric properties of the BST. 相似文献
16.
Cristina Leonelli Tiziano Manfredini Mariano Paganelli Gian Carlo Pellacani Jose Luis Amoros Albaro Jose Emilio Enrique Navarro Maria Jose Orts Silvia Bruni Franco Cariati 《Journal of the American Ceramic Society》1991,74(5):983-987
In order to verify the possibility of using glass-ceramic materials as tile coatings, the devitrification processes of three industrial formulations belonging to the Li2 O─Al2 O3 ─SiO2 glass-ceramic system were investigated by differential thermal analysis, X-ray diffractometry, scanning electron microscopy, and IR spectroscopy. Compositional variations were made by addition of large amounts of MgO or CaO or PbO (ZnO) oxides as well as through smaller additions of other oxides. In these systems the surface crystallization contributes appreciably to the bulk crystallization mechanism. All the systems investigated show a high tendency toward crystallization even at very high heating rates, developing a very close network of interlocked crystals of synthetic β-spodumene-silica solid solutions (LiAlSi4 O10 ). The results of this research are expected to establish the conditions under which these glass-ceramic systems can be practically used as tile glazes. 相似文献
17.
W. ZDANIEWSKI 《Journal of the American Ceramic Society》1975,58(5-6):163-169
Crystallization sequences of glasses with compositions in the tridymite primary phase field of the MgO-Al2 O3 -SiO2 system were studied by DTA, X-ray diffraction, and other techniques. Crystallization was catalyzed by the addition of 7 wt% of either ZrO2 or TiO2 . Up to 10 wt% CeO2 was also added to some glasses. Metastable solid solutions with the high-quartz structure exhibiting varying lattice parameters commonly occurred at low temperatures, transforming into a high cordierite at higher temperatures. Depending on the composition and heat treatment, other phases also appeared, e.g. Ce2 Ti2 O4 (Si2 O7 ). The rate of crystallization was markedly dependent on the catalyst. Colloidal precipitation of the catalyst accompanied by bulk crystallization of the glass was observed with ZrO2 , but no crystalline TiO2 was detected. In the presence of CeO2 , TiO2 was a more effective catalyst than ZrO2 . Although CeO2 lowered the melting temperatures of the glass-ceramics, it increased the stability of the glasses and inhibited volume nucleation, causing coarse structures to form on crystallization. 相似文献
18.
Akihiko Tsuge Hiroshi Inoue Katsutoshi Komeya 《Journal of the American Ceramic Society》1989,72(10):2014-2016
An analysis was made of the Si3 N4 · Y2 O3 crystallization process from a compacted Si3 N4 powder (composition: 5 wt% Y2 O3 and 2 wt% Al2 O3 ) during heat treatment in various powder beds. X-ray diffraction was used to measure the degree of cyrstallization, which was correlated with weight loss. Crystallization and weight loss were affected significantly by the SiO2 content in the packing powder. Crystallization correlated strongly with the weight loss. The dominant loss was attributed to SiO volatilization from the Y-Si-Al-O-N liquid. The crystallization mechanism with the loss of material was interpreted using a solubility—supersolubility diagram at constant temperature. 相似文献
19.
The relative abundance of the cubic ( c ), tetragonal ( t ), monoclinic ( m ), and orthorhombic ( o ) polymorphs of ZrO2 , and the δ phase, Mg2 Zr5 O12 , present in samples of 3.4-wt%-magnesia-partially-stabilized zirconia have been determined by Rietveld analysis of X-ray powder diffraction data. The samples studied correspond to the as-fired (AF), and subetectoid-aged maximum-strength (MS) and thermalshock (TS) states, with their surfaces in the ground or polished condition. The polymorph abundances of the bulk and near-surface regions are discussed in relation to the type of surface treatment. Grinding produces significant quantities of both m - and o -ZrO2 in the near-surface regions of all samples. The m content increases from about 5 wt% in the bulk, to 10, 24, and 33 wt% in AF, MS, and TS material, respectively, while the o content increases from trace amounts to about 11 wt% in all samples. The m and o phases both increase at the expense of t -ZrO2 , and the transformation is accompanied by significant lattice distortion and/or crystal size reduction. Thus, measurement of only the 'ground-surface-monoclinic' content does not give an accurate indication of the total amount of transformable t -ZrO2 in ceramics of this kind. Polishing removes some of the ground-surface m -ZrO2 in MS and TS, and all of the m -ZrO2 in AF material. The o -ZrO2 produced by grinding also declines substantially in AF and MS, but is not removed by polishing of TS. As a result, the bulk composition cannot be guaranteed, in the general case, to be accessible by X-ray analysis of polished surfaces. 相似文献
20.
Peter J. Hayward Eric R. Vance C. Dennis Cann Diane C. Doern 《Journal of the American Ceramic Society》1989,72(4):579-586
The effects of different cooling and reheating rates on the phase constitutions of Na2 O–Al2 O3 –TiO2 –SiO2 glass-ceramics containing up to 20 wt% of simulated nuclear fuel recycle waste have been studied using X-ray diffraction, differential thermal analysis, and scanning and transmission electron microscopy. The metastable formation of a perovskite-structured phase (nominally CaTiO3 , but containing ionic substituents) was observed in samples with up to 15 wt% of simulated waste after cooling from the melt at rates between 0.25 and 50°C/min. When the partially devitrified glass was reheated to 1050°C, incomplete conversion of this phase to sphene (nominally CaTiSiO5 ) occurred by reaction with the silica-rich glass matrix. The conversion was completed by heating further to 1150°C. Waste loadings ⋝10 wt% produced crystallization of powellite (nominally CaMoO4 ) in addition to sphene and perovskite, whereas metastable perrierite (a rare-earth titanosilicate) was also crystallized at waste loadings ⋝15 wt%. New data on elemental partitioning between the crystalline and vitreous phases confirmed earlier results obtained in different atmospheres and with simplified waste compositions and were largely in accord with crystal-chemical predictions. 相似文献