共查询到20条相似文献,搜索用时 31 毫秒
1.
Young-Min Kim Seong-Hyeon Hong Doh-Yeon Kim 《Journal of the American Ceramic Society》2000,83(11):2809-2812
The effect of TiO2 /SiO2 addition on the grain growth of alumina was reinvestigated. TiO2 promoted the grain growth, but there was no abnormal grain growth. However, codoping of TiO2 and SiO2 resulted in a duplex microstructure consisting of large platelike grains, ∼800 μm long and ∼100 μm thick, and fine matrix grains. The observed anisotropic abnormal grain growth was explained in terms of liquid formation during heat treatment. 相似文献
2.
Yoshikazu Suzuki Naoki Kondo Tatsuki Ohji 《Journal of the American Ceramic Society》2003,86(7):1128-1131
Porous CaZrO3 /MgAl2 O4 composites were synthesized in air by pressureless reactive sintering of an equimolar mixture of dolomite (CaMg(CO3 )2 ), monoclinic zirconia ( m -ZrO2 ), and α-alumina powders, with a 0.5 wt% lithium fluoride additive. The reaction behavior of the mixed powders (with/without LiF additive) was studied using high-temperature X-ray diffraction. A bulk porous composite resulted from sintering at 1300°C for 2 h (in a nearly closed container, so as to increase the LiF-doping effect), which consisted of fine grains (CaZrO3 and MgAl2 O4 , ∼0.5–1 μm) and well-grown idiomorphic ones (MgAl2 O4 octahedra ∼ 2–4 μm). The idiomorphic spinel grains were located around the inner walls of relatively large pores. The composite showed appreciably high bending strength (σf = 110 ± 8 MPa for a porosity of 31%). The porous CaZrO3 /MgAl2 O4 composites can be applied as high-temperature filters and lightweight structural components. 相似文献
3.
Porous Cr3 C2 grains (∼300 to 500 μm) with ∼10 wt% of Cr2 O3 were prepared by heating a mixture of MgCr2 O4 grains and graphite powder at 1450° to 1650°C for 2 h in an Al2 O3 crucible covered by an Al2 O3 lid with a hole in the center. The porous Cr3 C2 grains exhibited a three-dimensional network skeleton structure. The mean open pore diameter and the specific surface area of the porous grains formed at 1600°C for 2 h were ∼3.5 (μm and ∼6.7 m2 /g, respectively. The present work investigated the morphology and the formation conditions of the porous Cr3 C2 grains, and this paper will discuss the formation mechanism of those grains in terms of chemical thermodynamics. 相似文献
4.
The fracture strengths of sintered Al2 O3 containing 20 and 40 vol% ZrO2 (12 mol% CeO2 )—zirconia-toughened alumina (ZTA)—composites along with the fracture resistance can be increased (e.g., to ∼900 MPa and >12 Mpa·m1/2 , respectively), by increasing the mean grain size of the t -ZrO2 (and the Al2 O3 ) from ∼0.5 μm to ∼3 μm. At these lower t -ZrO2 contents, the fracture strength-fracture resistance curves show a continuous rise as opposed to the strength maxima observed in polycrystalline t -ZrO2 (12 mol% CeO2 ), CeTZP, and ZrO2 (12 mol% CeO2 ) ceramics containing ≤20 vol% Al2 O3 . The toughened composites also exhibit excellent damage resistance with fracture strengths of 500 MPa retained with surfaces containing ∼150- N Vickers indentations which produce cracks of ∼160-μm radius. Greater damage resistance correlates with an increase in the apparent R -curve response of these composites. 相似文献
5.
Shinobu Hashimoto Shaowei Zhang William Edward Lee Akira Yamaguchi 《Journal of the American Ceramic Society》2003,86(11):1959-1961
Spinel platelets were formed from a powder mixture of 3–5 μm wide and 0.2–0.5 μm thick α-Al2 O3 and 1–8 μm (average 3 μm) MgSO4 heated 2 h at 1200°C. The hexagonal platelet shape of the original α-Al2 O3 platelet was maintained in the spinel, although their size was slightly increased and their surface roughened. When a mixture of α-Al2 O3 platelets and MgO powder was heated 3 h at 1400°C, the spinel formed lost the platelet morphology of the alumina. 相似文献
6.
Paul F. Becher Kathleen B. Alexander Alan Bleier Shirley B. Waters Wilbur H. Warwick 《Journal of the American Ceramic Society》1993,76(3):657-663
Based on experimental and modeling studies, the rate of increase in the martensite start temperature M s for the tetragonal-to-monoclinic transformation with increase in zirconia grain size is found to rise with decrease in ZrO2 content in the zirconia-toughened alumina ZTA system. The observed grain size dependence of M s can be related to the thermal expansion mismatch tensile (internal) stresses which increase with decrease in zirconia content. The result is that finer zirconia grain sizes are required to retain the tetragonal phase as less zirconia is incorporated into the alumina, in agreement with the experimental observations. At the same time, both the predicted and observed applied stress required to induce the transformation are reduced with increase in the ZrO2 grain size. In addition, the transformation-toughening contribution at temperature T increases with increase in the M s temperature brought about by the increase in the ZrO2 grain size, when T > M s . In alumina containing 20 vol% ZrO2 (12 mol% CeO2 ), a toughness of ∼10 MPa. √m can be achieved for a ZrO2 grain size of ∼2 μm ( M s ∼ 225 K). However, at a grain size of ∼2 μm, the alumina–40 vol% ZrO2 (12 mol% CeO2 ) has a toughness of only 8.5 MPa. √m ( M s ∼ 150 K) but reaches 12.3 MPa. ∼m ( M s ∼ 260 K) at a grain size of ∼3 μm. These findings show that composition (and matrix properties) play critical roles in determining the ZrO2 grain size to optimize the transformation toughening in ZrO2 -toughened ceramics. 相似文献
7.
Formation and Densification Behavior of Magnesium Aluminate Spinel: The Influence of CaO and Moisture in the Precursors 总被引:1,自引:1,他引:0
Ibram Ganesh Kolli Archana Teja Natarajan Thiyagarajan Roy Johnson Benjaram Mahipal Reddy 《Journal of the American Ceramic Society》2005,88(10):2752-2761
Different grades of stoichiometric and non-stoichiometric dense magnesium aluminate spinel (MgAl2 O4 ) grains were prepared by a conventional double-stage firing process using two types of alumina and four types of magnesia raw materials. The MgAl2 O4 spinel formation was found to be highly influenced by CaO and moisture present in the precursor oxides as confirmed by thermogravimetry (TG), differential thermal analysis (DTA), and X-ray diffraction (XRD) techniques. The Fourier transform-infrared spectroscopy (FTIR) study of the precursor oxides revealed the presence of moisture. Influence of alumina and magnesia composition on the densification behavior of MgAl2 O4 spinels was assessed by characterizing bulk density (BD), apparent porosity (AP), water absorption (WA) capacity, and the microstructures of the stoichiometric, the magnesia-rich, and the alumina-rich spinels sintered at 1650°C for 1 h. Sintering studies indicate that to obtain dense stoichiometric spinel grains with >3.35 g/mL BD, <2.0% AP, and <0.5% WA, the spinel powder should possess a median particle size of <2 μm, CaO content of >0.9%, compact (green) density of >1.95 g/mL, and spinel content of >90%. Among various spinels synthesized, the magnesia-rich spinels exhibited superior properties in terms of high BD, low percentage of AP, and low WA capacity, whereas alumina-rich spinels showed inferior properties. Stoichiometric spinels exhibited an average grain size of 10 μm whereas alumina-rich spinels with 90% alumina had an average grain size of 20 μm. The increase in holding time at higher temperatures enhanced the sintering properties of the spinels, particularly the magnesia-rich spinels. Further, raw mixtures having >0.9% CaO exhibited better sintered properties as compared with others. 相似文献
8.
Reactions between Synthetic Mica and Simple Oxide Compounds with Application to Oxidation-Resistant Ceramic Composites 总被引:1,自引:0,他引:1
Reaction-couple experiments have been pursued in order to evaluate the potential of a phyllosiiicate to act as a chemically protective, fracture-deflecting, oxidation-resistant interphase for oxide fiber–oxide matrix composites. The synthetic mica fluorophiogopite (KMg3[AlSi3]O10F2) was reacted with single-phase substrates of alumina (Al2O3), mullite (3Al2O3·2SiO2), forsterite (Mg2SiO4), or enstatite (MgSiO3). X-ray spectroscopy, X-ray diffraction, and scanning electron and transmitted polarized light microscopy were applied to the analysis of the reaction couples. Fluorophlogopite reacts strongly with alumina, mullite, and enstatite, resulting in substantial damage to the substrate as well as the breakdown of the mica. The chemical reactions between mica–alumina and mica–mullite are examined critically. In the case of alumina, the reaction results in the formation of a planar spinel (MgAl2O4) layer separating the substrate from the breakdown products of the mica. This unvarying result suggests, therefore, that a spinel diffusion barrier would prove effective in protecting alumina from fluorophlogopite. Experiments revealed such effectiveness: local equilibrium is established in the layer sequence alumina–spinel–fluorophlogopite; i.e., planar interfaces are established amongst these phases that are stable under conditions of high temperature and high oxygen fugacity. A similar chemical approach for protection of mullite is not obvious. Based on an understanding of its intrinsic fracture energy, the fluoromica interphase is expected to be effective in mechanically protecting adjacent oxides from propagating cracks, a behavior qualitatively demonstrated by indentation experiments on the kinetically persistent alumina–spinel–fluorophlogopite–spinel–alumina laminates. 相似文献
9.
Quench studies of in-house melted glasses were used to study the microstructural evolution in Macor-type and Corning Code 9606-type glass–ceramics to elucidate the microstructures of the commercial products. They reveal that phase separation initiates crystallization in both systems which then proceeds via formation of several phases at different scales of size, the first phases to form being those containing the most rapidly diffusing species. This study highlights the concept of crystallization hierarchies whereby crystals form, sometimes simultaneously, sometimes sequentially, on heating glasses, but at different length scales . This is illustrated by the simultaneous nucleation of μ-cordierite nanocrystals and ∼0.2 μm MgAl2 Ti3 O10 rosettes in Corning 9606-type compositions and of ∼0.3 μm chondrodite and 3–4 μm fluorophlogopite laths in Macor-type compositions. 相似文献
10.
Tamer El-Raghy Michel W. Barsoum Antonios Zavaliangos Surya R. Kalidindi 《Journal of the American Ceramic Society》1999,82(10):2855-2860
In this article, the second part of a two-part study, we report on the mechanical behavior of Ti3 SiC2 . In particular, we have evaluated the mechanical response of fine-grained (3–5 μm) Ti3 SiC2 in simple compression and flexure tests, and we have compared the results with those of coarse-grained (100–200 μm) Ti3 SiC2 . These tests have been conducted in the 25°–1300°C temperature range. At ambient temperature, the fine- and coarse-grained microstructures exhibit excellent damage-tolerant properties. In both cases, failure is brittle up to ∼1200°C. At 1300°C, both microstructures exhibit plastic deformation (>20%) in flexure and compression. The fine-grained material exhibits higher strength compared with the coarse-grained material at all temperatures. Although the coarse-grained material is not susceptible to thermal shock (up to 1400°C), the fine-grained material thermally shocks gradually between 750° and 1000°C. The results presented herein provide evidence for two important aspects of the mechanical behavior of Ti3 SiC2 : (i) inelastic deformation entails basal slip and damage formation in the form of voids, grain-boundary cracks, kinking, and delamination of individual grains, and (ii) the initiation of damage does not result in catastrophic failure, because Ti3 SiC2 can confine the spatial extent of the damage. 相似文献
11.
A Catalytic Process for Mullite Whiskers 总被引:2,自引:0,他引:2
Mixtures of alumina and silica react with SiF4 above 600°C to form fluorotopaz. Pyrolysis of fluorotopaz gives a stoichiometric yield of interlocked whiskers of mullite and SiF4 , which is recovered for reuse. The diameter of whiskers (aspect ratio ∼15) can be controlled from a maximum of ∼100 μm to less than 1 μm. 相似文献
12.
Seeding a mixture of boehmite (AIOOH) and colloidal ZrO2 with α-alumina particles and sintering at 1400°C for 100 min results in 98% density. The low sintering temperature, relative to conventional powder processing, is a result of the small alumina particle size (∼0.3 μm) obtained during the θ-to α-alumina transformation, homogeneous mixing, and the uniform structure of the sol-gel system. Complete retention of pure ZrO2 in the tetragonal phase was obtained to 14 vol% ZTA because of the low-temperature sintering. The critical grain size for tetragonal ZrO2 was determined to be ∼0.4 μm for the 14 vol% ZrO2 —Al2 O3 composite. From these results it is proposed that seeded boehmite gels offer significant advantages for process control and alumina matrix composite fabrication. 相似文献
13.
Alumina Dissolution into Silicate Slag 总被引:1,自引:0,他引:1
Shaowei Zhang Hamid Reza Rezaie Hossain Sarpoolaky William Edward Lee 《Journal of the American Ceramic Society》2000,83(4):897-903
Dissolution of commercial white fused and tabular Al2 O3 grains into a model silicate slag was investigated after 1 h at 1450° and 1600°C. Formation of CA6 and hercynitic spinel layers was observed at all Al2 O3 /slag interfaces. The spinel layer was not always continuous, and so, compared with the CA6 layer, it had a less-significant effect on the dissolution process. The CA6 layer that formed adjacent to the tabular Al2 O3 was incomplete at both temperatures, so that its dissolution was not a totally indirect process. These incomplete CA6 and spinel layers meant that slag penetrated into the tabular Al2 O3 grains, which, thus, were corroded and disintegrated by the penetrating slag. There was evidence of liquid in the CA6 layer adjacent to the fused Al2 O3 after 1 h at 1450°C, which also enabled direct dissolution. After 1 h at 1600°C, fused Al2 O3 revealed a thick (∼60 μm), continuous and unpene-trated CA6 layer, indicating fully indirect dissolution at this temperature. 相似文献
14.
Ken Hirota Yoshihiro Nakayama Masaki Kato Shingo Nakane Toshiyuki Nishimura 《International Journal of Applied Ceramic Technology》2009,6(5):607-616
Carbon nanofiber (CNF)-dispersed B4 C composites have been synthesized and consolidated directly from mixtures of elemental raw powders by pulsed electric current pressure sintering (1800°C/10 min/30 MPa). A 15 vol% CNF/B4 C composite with ∼99% of dense homogeneous microstructures (∼0.40 μm grains) revealed excellent mechanical properties at room temperature and high temperatures: a high bending strength (σb ) of ∼710 MPa, a Vickers hardness ( H v ) of ∼36 GPa, a fracture toughness ( K I C ) of ∼7.9 MPa m1/2 , and high-temperature σb of 590 MPa at 1600°C in N2 . Interfaces between the CNF and the B4 C matrix were investigated using high-resolution transmission electron microscopy, EDS, and electron energy-loss spectroscopy. 相似文献
15.
MANFRED KAHN 《Journal of the American Ceramic Society》1971,54(9):455-457
Effects of grain size and grain growth in Nb-doped BaTiO3 on temperature and frequency dependencies of the dielectric constant were investigated. When 0.65 μm powder is sintered to an average grain size of 1 μm, two dielectric constant peaks indicate the presence of Nb-free BaTiO3 and of Nb-containing material. Single peaks are observed above room temperature after additional grain growth or when 0.07 μm powder is sintered to an average grain size of 1 μm. The Curie point of pure BaTiO3 with 1 μm grains is 4 to 6°C lower than that of material with grains >10 μm. Thermodynamically, this behavior is accounted for by a phase inversion stress ∼ the room-temperature stress. 相似文献
16.
Irene A. Chou Helen M. Chan Martin P. Harmer 《Journal of the American Ceramic Society》1996,79(9):2403-2409
The machining and subsequent annealing behavior of an Al2 O3 -SiC nanocomposite (A12 O3 + 5 vol% 0.2 μm SiC particles) was compared to that of single-phase A12 O3 . The machining-induced residual line force was determined by measuring the extent of elastic bending in thin disk specimens, and the surface roughness was evaluated by profilometry. The results showed that, when the two materials were subjected to the same grinding conditions, they developed compressive residual stresses and surface roughness values of similar magnitude. The maximum thickness of the residual stress layers was estimated to be ∼ 10 μm for the A12 O3 and ∼12 μm for the nanocomposite. A direct linear correlation was observed between the residual force and the surface roughness for different machining treatments. Annealing of the machined samples produced complete relaxation of residual stresses in the single-phase Al2 O3 , whereas only partial stress relaxation occurred for the nanocomposite. 相似文献
17.
Atsushi Kitaoka Ken Hirota Masaru Yoshinaka Yoshinari Miyamoto Osamu Yamaguchi 《Journal of the American Ceramic Society》2000,83(5):1311-1313
NiAl/10-mol%-ZrO2 (3Y) composites of almost full density have been fabricated via spark plasma sintering (SPS) for 10 min at 1300°C and 30 MPa. The former intermetallic compound, which contains a trace amount of Al2 O3 , has been prepared via self-propagating high-temperature synthesis. The composite microstructures are such that tetragonal ZrO2 (∼0.2 μm) and Al2 O3 (∼0.5 μm) particles are located at the grain boundaries of the NiAl (∼46 μm) matrix. Improved mechanical properties are obtained: the fracture toughness and bending strength are 8.8 MPa·m1/2 and 1045 MPa, respectively, and high strength (>800 MPa) can be retained up to 800°C. 相似文献
18.
Yoshihiko Takano Masahiro Hachiya† Masaru Yoshinaka† Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》2000,83(2):448-450
CrN powder consisting of granular particles of ∼3 μm has been prepared by self-propagating high-temperature synthesis under a nitrogen pressure of 12 MPa using Cr metal. Dense pure CrN ceramics and CrN/ZrO2 (2Y) composites in the CrN-rich region have been fabricated by hot isostatic pressing for 2 h at 1300°C and 196 MPa. The former ceramics have a fracture toughness ( K IC ) of 3.3 MPa ·m1/2 and a bending strength (σb ) of 400 MPa. In the latter materials almost all of the ZrO2 (2Y) grains (0.36–0.41 μm) are located in the grain boundaries of CrN (∼4.6 μm). The values of K IC (6.1 MPa · m1/2 ) and σb (1070 MPa) are obtained in the composites containing 50 vol% ZrO2 (2Y). 相似文献
19.
Hanns P. Steier Pilar Pena Jose S. Moya 《Journal of the American Ceramic Society》1995,78(9):2560-2562
A mechanically stable thick layer (∼SO pm) of ZrTiO4 on a rutile substrate has been obtained at 1600°C by reactive coating of zircon. This layer is constituted by ZrTiO, grains of ∼10 μm average size embedded in a silica-rich glassy matrix. The results are discussed in terms of the ZrO2 -SOi2 -TiO2 , equilibrium diagram. 相似文献
20.
Influences of Particle Size of Alumina Filler in an LTCC System 总被引:3,自引:0,他引:3
Yong Jun Seo Jin Hyun Jung Yong Soo Cho Jun Chul Kim Nam Kee Kang 《Journal of the American Ceramic Society》2007,90(2):649-652
A low temperature co-fired ceramics system consisting of a typical calcium aluminoborosilicate glass and alumina filler was used to investigate the effects of four different sizes, 13 nm, 0.5, 3, and 39 μm, of a commercially available alumina filler on the resultant densification, crystallization, and dielectric properties. There was definitely a proper range of alumina particle size, which leads to desirable densification and enhanced dielectric properties. The onset temperatures of densification and crystallization depended strongly on the filler particle size. The 3 μm sample as an optimum filler size exhibited a promising performance of k ∼8.1 and Q ∼160 at a resonant frequency of 14.8 GHz, which results from early densification and intensive crystallization of the anorthite CaAl2 Si2 O8 phase. Particularly, the use of nano-sized alumina (13 nm) retarded both densification by ∼200°C and crystallization by ∼80°C compared with the results of the 3 μm alumina case. The dependence of the filler particle size was postulated as being related to the wetting and connectivity behavior of glass through consequent inter-reactions between glass and ceramic. 相似文献