共查询到20条相似文献,搜索用时 15 毫秒
1.
Yang-Il Jung Byoung-Ki Lee Suk-Joong L. Kang 《Journal of the American Ceramic Society》2004,87(4):739-741
A structural transition of Ba6 Ti17 O40 /BaTiO3 interfaces from faceted to rough was induced by reducing oxygen partial pressure in the atmosphere. As the oxygen partial pressure decreased, the number densities of {111} twins and abnormal grain decreased. TEM observation showed that the twin formation was governed only by the faceting of the interface. Experimental evidence of {111} twin-assisted abnormal growth of faceted BaTiO3 grains was also obtained. 相似文献
2.
Derrick J. Rockosi Edward P. Gorzkowski Patrick T. King † Adam M. Scotch Helen M. Chan Martin P. Harmer 《Journal of the American Ceramic Society》2004,87(7):1339-1342
The growth of abnormal grains of PMN–35PT containing Σ3 twin boundaries was compared with that of untwinned abnormal grains of PMN–35PT. It was thought that the twinned abnormal grains might have a growth advantage because of the presence of reentrant edges. The aforementioned types of grains were embedded in a PMN–35PT polycrystalline matrix with 3 vol% excess PbO, and grown by annealing in an oxygen atmosphere at 1150°C for varying times. It was found that abnormal grains containing Σ3 boundaries showed a comparable degree of growth to that of the untwinned grains. Furthermore, for the twinned seed crystals, the extent of growth was independent of whether there was any initial entrapped porosity within the abnormal grain. 相似文献
3.
Calcium aluminosulfate (Ca4 Al6 O16 S or C4 A3 ̄) was prepared by direct synthesis from calcium and aluminum nitrates, and aluminum sulfate. CaAl4 O7 (CA2 ) formed as an intermediate at 900°C, and C4 A3 ̄ was the main phase after calcination at 1100°C. The specific surface areas after calcination at 1100° and 1300°C were ∼2.5 and 1 m2 /g, respectively. Hydration was investigated using XRD, DSC, SEM, conduction calorimetry, and solid-state 27 Al MAS-NMR spectroscopy. Calorimetry showed that the induction period was longer than that of a sample prepared using conventional solid-state sintering, and this was attributed to the formation of amorphous coatings. Crystalline hydration products, principally calcium monoaluminosulfate hydrate and aluminum hydroxide, appeared subsequently. Although the induction period was very long, complete hydration occurred as early as 3 d in the sample calcined at 1100°C and was 91% complete in the sample calcined at 1300°C. 相似文献
4.
Beta C2 S was hydrated at room temperature with and without added CaCl2 or C2 H5 OH by methods previously studied for the hydration of C3 S, i.e. paste, bottle, and ball-mill hydration. The amount of reacted β-C2 S, the Ca(OH)2 concentration in the liquid phase, the CaO/SiO2 molar ratio, and the specific surface area of the hydrate were investigated. A topochemical reaction occurs between water and β-C2 S, resulting in the appearance of solid Ca(OH)2 and a hydrated silicate with a CaO/SiO2 molar ratio of ≃1. As the liquid phase becomes richer in Ca(OH)2 , the first hydrate transforms to one with a higher CaO/SiO2 ratio. Addition of CaCl2 increases the reaction rate and the surface area of the hydrate but to a much lesser extent than in the hydration of C3 S, whereas C2 H6 OH strongly depresses the hydration rate of β-C2 S, as observed for C3 S hydration. 相似文献
5.
Sang-Yeup Park Kyoon Choi Suk-Joong L. Kang Duk N. Yoon 《Journal of the American Ceramic Society》1992,75(1):216-219
When sintered Al2 O3 is annealed with CaMgSiAlO glass at 1600°C, polyhedral MgAl2 O4 grains form and glass pockets are entrapped within the grains. After annealing for 13 h at 1600°C, the liquid pockets show a regular octahedron shape which is expected to represent the equilibrium shape. All grain surfaces in contact with the glass matrix show the same shape. The small grains, which must be shrinking, thus have the equilibrium shape, because their shrinkage shape is is identical to the equilibrium and growth shape. However, the octahedral shape also represents the growth shape for the growing large grains. The grains also form grain boundaries with neighboring grains. 相似文献
6.
Edward M. Sabolsky Gary L. Messing Susan Trolier-McKinstry 《Journal of the American Ceramic Society》2001,84(11):2507-2513
Single-crystal layers of 0.65Pb(Mg1/3 Nb2/3 )O3 ·0.35PbTiO3 (PMN-35PT) were grown heteroepitaxially on {001}-BaTiO3 template crystals. A {001}-BaTiO3 crystal was embedded in a fine-grained matrix of PMN-35PT containing excess PbO and heated between 950° and 1150°C for 0–5 h. The initial growth of the PMN-35PT on the {001} surface and the growth of the matrix grains both displayed a t 1/3 dependence which is characteristic of diffusion-controlled growth. Growth was limited to ∼100–150 μm due to the significantly reduced driving force at longer times because of matrix coarsening and porosity evolution. 相似文献
7.
8.
John Gerard Fisher Min-Soo Kim Ho-Yong Lee Suk-Joong L. Kang 《Journal of the American Ceramic Society》2004,87(5):937-942
Abnormal grain growth in Pb(Mg1/3 Nb2/3 )O3 –35 mol% PbTiO3 (PMN-35PT) ceramics doped with Li2 O and PbO has been investigated. Replacing the PbO dopant with up to 2 mol% Li2 O caused an increase in the number of abnormal grains. For the composition containing 2 mol% Li2 O and 6 mol% PbO, the amount of abnormal grain growth decreased with increasing sintering temperature. Single crystals of ∼6 mm × 6 mm × 2 mm thickness were grown from the 2 mol% Li2 O, 6 mol% PbO-containing composition via the templated grain growth method. Grain growth behavior with temperature is explained in terms of the effect of Li2 O on interface-reaction-controlled grain growth and the critical driving force. 相似文献
9.
Effect of Grain Coalescence on the Abnormal Grain Growth of Pb(Mg1/3 Nb2/3 )O3 -35 mol% PbTiO3 Ceramics
Ui-Jin Chung Jong-Keuk Park Nong-Moon Hwang Ho-Yong Lee Doh-Yeon Kim 《Journal of the American Ceramic Society》2002,85(4):965-968
Abnormal grain growth (AGG), which occurred during the heat treatment of Pb(Mg1/3 Nb2/3 )O3 -35 mol% PbTiO3 (PMN-35PT) with excess PbO, was investigated. AGG has been suggested to be the consequence of grain coalescence that results in the formation of Σ3 coincidence site lattice and low angle grain boundaries. Because of reentrant edges appearing at the ends of these boundaries, the coarsening rate of grains was significantly enhanced and AGG occurred. 相似文献
10.
Ui-Jin Chung Jong-Keuk Park Nong-Moon Hwang Ho-Yong Lee Doh-Yeon Kim 《Journal of the American Ceramic Society》2002,85(12):3076-3080
Pb(Mg1/3 Nb2/3 )O3 -35 mol% PbTiO3 (PMN-35PT) specimens with a 5 mol% excess PbO were prepared by excessive heat treatment at 1150°C to induce abnormal grain growth. Through electron backscatter diffraction analysis and the observation of a three-dimensional morphology, the abnormally grown PMN-35PT grains were found to be twinned crystals with penetration characteristics. The morphology of the PMN-35PT twinned crystal was crystallographically analyzed. The abnormal grain growth of PMN-35PT is suggested to be due to preferential growth at the reentrant angles formed by twins. 相似文献
11.
Hirotsugu Takizawa Kyota Uheda Tadashi Endo 《Journal of the American Ceramic Society》2000,83(9):2321-2323
(In0.67 Fe0.33 )2 O3 with the bixbyite structure was synthesized via 28 GHz microwave irradiation, using multimode microwave heating equipment. Indium sesquioxide strongly absorbs 28 GHz microwaves, and this strong coupling with microwave energy can be used to drive a reaction with iron sesquioxide. A mixture of In2 O3 and α-Fe2 O3 powders (In:Fe ratio of 2:1) was irradiated with microwaves at a frequency of 28 GHz. The mixture was heated to 1400°C during the microwave irradiation. The formation of a solid solution was completed within a minute, which indicated a drastic enhancement of the reaction rate. Scanning electron microscopy revealed remarkable grain growth under microwave irradiation. 相似文献
12.
Charles A. Bateman Lijie Zhang Helen M. Chan Martin P. Harmer 《Journal of the American Ceramic Society》1992,75(5):1281-1283
It is experimentally observed that the peritectic reaction, 211 + liquid → 123, can be driven essentially to completion in 1 h at an undercooling of only ∽30°C. The kinetic data, together with the observed microstructures, are inconsistent with the normal mechanism of the peritectic reaction. It is proposed that the mechanism of the reaction involves dissolution of 211 particles into the liquid and precipitation of solid 123. The aligned grain structure is explained through sympathetic nucleation of new 123 grains on existing grains. 相似文献
13.
Kun'ichi Miyazawa 《Journal of the American Ceramic Society》2002,85(5):1297-1299
C70 whiskers with submicrometer diameters (C70 nanowhiskers, or C70 NWs) have been successfully fabricated by forming liquid/liquid interfaces in systems that involve a toluene solution of C70 and isopropyl alcohol. Transmission electron microscopy observations show that the C70 NWs have a 〈110〉 growth axis and that the intercluster distance of C70 molecules in the C70 NWs are shortened by ∼3%, compared with that of face-centered cubic C70 crystals in the 〈110〉 close-packed growth direction, which indicates the formation of strong chemical bonds between the C70 molecules. It is suggested that the C70 molecules are polymerized, with their short axis parallel to the growth axis of the C70 NWs, from observation via high-resolution transmission electron microscopy. 相似文献
14.
Reactive-Templated Grain Growth of Bi1/2 (Na,K)1/2 TiO3 : Effects of Formulation on Texture Development
In this paper we report the effects of formulation on texture development for the "reactive-templated grain growth" (RTGG) of Bi1/2 (Na,K)1/2 TiO3 (BNKT). The solids formulation for BNKT was systematically varied by prereacting to well—defined alkali and bismuth titanates (Na2 Ti3 O7 (N2 T3 ), K2 Ti2 O5 (K2 T2 ), and Bi2 Ti4 O11 (B2 T4 )). Use of these precursors in different BNKT formulations determined that the amount of expansion associated with reacting dry-pressed compacts at 600−800°C could be influenced by formulation. Lotgering factors ( F 00 l ) derived from Θ/2Θ X-ray diffraction scans indicated that the formulation route strongly affected the {00 l } texture development in tape-cast and sintered specimens. Prereacting alkali carbonates with TiO2 to form N2 T3 and K2 T2 inhibited texture development in RTGG-processsed BNKT. However, when Bi2 O3 was prereacted to form B2 T4 , the measured F 00 l increased from 0.5 to 0.7. 相似文献
15.
Myung-Koo Kang Young-Sung Yoo Doh-Yeon Kim Nong M. Hwang 《Journal of the American Ceramic Society》2000,83(2):385-390
Two different types of BaTiO3 seed particles, normal and twinned seeds of ∼30 μm on the average, were prepared from crushed sintered specimens. Normal seeds were obtained from the usual BaTiO3 sintered compacts, while twinned seeds containing a double twin were obtained from BaTiO3 compacts sintered with 2 mol% of SiO2 . The BaTiO3 powder compacts were again prepared with 5 wt% of seed grains and sintered under various conditions. The microstructural evolution was quite different in the two cases: the growth of normal seed grains was ultimately limited but that of the twinned seeds continued extensively. The observed difference is discussed in terms of the growth mechanism and the atomic structure of interfaces. 相似文献
16.
C3 S and C3 S+2% CaCl2 were hydrated for varied times; the degree of hydration and zeta potential were determined. In the absence of CaCl2 , the duration of the induction period was 5 h, whereas when CaCl2 was added, an induction period of 1 h was observed. The zeta potential was positive, maximum, and constant during induction . 相似文献
17.
J.M. LAMEILLE G. GOUTIERE JEAN-CLAUDE PETIT MICHELINE REGOURD 《Journal of the American Ceramic Society》1987,70(8):604-614
The retention of cobalt, cesium, and strontium as trace elements in the hydrates of simple ordinary portland cement components has been investigated. The combined characterization of the solid by SEM, electron microprobe, XRD, and SIMS, as well as the chemical analysis of the solutions, allowed us to identify the likely localization of these trace elements in the solid. In particular, cobalt is dramatically incorporated into the solid during the hydration of C3 S; we show that this is due to the formation of a cobalt oxychloride, a compound which is unstable at temperatures ≥60°C. Cesium is retained in small amounts in the C-S-H and CH mixture. The formation of hydrated aluminates notably increases its retention. Finally, small quantities of strontium are also retained in silicates and, in the presence of gypsum, its retention is markedly higher. This is likely due to the formation of sulfoaluminates. 相似文献
18.
The control of the microstructure of Ce-doped Al2 O3 /ZrO2 componsites by the valence change of cerium ion has been demonstrated. Two distinctively different types of microstructure, large Al2 O3 grains with intragranular ZrO2 particles and small Al2 O3 grains with intergranular ZrO2 particles, can be obtained under identical presintering processing conditions. At doping levels greater than ∼ 3 mol% with respect to ZrO2 , Ce3+ raises the alumina grain-boundary to zirconia particle mobility ratio. This causes the breakaway of grain boundary from particles and the first type of microstructure. On the other hand, Ce4+ causes no breakaway and produces a normal intergranular ZrO2 distribution. The dramatic effect of Ce3+ on the relative mobility ratio is found to be associated with fluxing of the glassy boundary phase and is likewise observed for other large trivalent cation dopants. The ZrO2 second phase acts as a scavenger for these trivalent cations, provided their solubility limit in ZrO2 is not exceeded. 相似文献
19.
Nina Daneu Aleksander Renik Slavko Bernik Drago Kolar 《Journal of the American Ceramic Society》2000,83(12):3165-3171
The effects of adding small quantities of SnO2 to the basic ZnO–Bi2 O3 varistor composition were studied in terms of phase reactions, microstructural development, and the formation of inversion boundaries. Scanning and transmission electron microscopy studies showed that the inversion boundaries, triggered by the addition of SnO2 , cause anisotropic grain growth in the early stages of sintering. ZnO grains that include inversion boundaries grow exaggeratedly, at the expense of normal grains, until they dominate the microstructure. Higher additions of SnO2 lead to an increase in number of grains with inversion boundaries and to a more fine-grained microstructure. The increasing amount of secondary phases is also related to a higher level of SnO2 addition; however, the influence of these phases on ZnO grain growth is subordinate to the role of inversion boundaries. 相似文献
20.
Nakshatra B. Singh Awadhesh K. Singh Shashi Prabha Singh 《Journal of the American Ceramic Society》1990,73(10):3063-3068
Hydration occurring in the system Ca3 Al2 O6 –CaSO4 · 2H2 O–Ca(OH)2 –H2 O has been studied at different temperatures and it was found that the reactions are diffusion controlled. The kinetic data obeyed Jander's equation and the rate of reaction increased with increasing temperature. X-ray diffraction studies and calorimetric measurements show that when gypsum is consumed, ettringite is converted into monosulfate. The rate of this conversion also increased with the increasing temperature and decreased in the presence of citric acid. Spectroscopic studies showed that there was some interaction between citric acid and the cement and that the product of hydration is of colloidal nature. Zeta potential measurements show that retardation of Ca3 Al2 O6 hydration in the presence of gypsum and Ca(OH)2 is not due to SO2− 4 adsorption. Electrical conductivity and thermoelectric potential measurements of solid Ca3 Al2 O6 show that Ca3 Al2 O6 is an n -type semiconductor and contains defects. The retardation of Ca3 Al2 O6 may be due to poisoning of reaction sites by gypsum and Ca(OH)2. 相似文献