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1.
Yasuo Hikichi Toshio Sasaki Kyouhei Murayama Tsuyoshi Nomura Masaaki Miyamoto 《Journal of the American Ceramic Society》1989,72(6):1073-1076
It is reported that, on mechanochemical treatment, weinschenkite-type RPO4 ·2H2 O (R = Dy, Y, or Er) gradually transforms into rhabdophane-type RPO4 · nH2 O (n = 0.5 to 1) and weinschenkite-type YbPO4 ·2H2 O into xenotime-type YbPO4 , at room temperature in air. Rhabdophane-type YPO4 ·0.8H2 O and ErPO4 ·0.9H2 O obtained by grinding weinschenkite-type RPO4 ·2H2 O (R=Y or Er) are new. The new rhabdophane-type YPO4 ·0.8H2 O and ErPO4 ·0.9H2 O gradually transform to xenotime-type YPO4 and ErPO4 when heated above 900°C (R = Y) and 700°C (R = Er) in air. 相似文献
2.
Hisanori Yamane Kazuhiro Ogawara Mamoru Omori Toshio Hirai 《Journal of the American Ceramic Society》1995,78(9):2385-2390
Lattice parameters of RE4 Al2 O9 (RE = Y, Sin, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) prepared at 1600–1800°C and those of RE4 Ga2 O9 (RE = La, Pr, Nd, Sm, Eu, and Gd) prepared at 1400–1600°C were refined by Rietveld analysis for the X-ray powder diffraction patterns. The parameters increased linearly with the ionic radius of the trivalent rare-earth elements ( r RE ). High-temperature differential calorimetry and dilatometry revealed that both RE4 Al2 O, and RE4 Ga2 O, have reversible phase transitions with volume shrinkages of 0.5–0.7% on heating and thermal hystereses. The transition temperatures (7tr ) decreased from 1300°C (Yb) to 1044°C (Sm) for RE4 A12 O9 , except for Y4 Al2 O9 ( Ttr = 1377°C), and from 1417°C (Gd) to 1271°C (La) for RE4 Ga2 O, with increasing ionic radius of the rare-earth elements. These transition temperatures were plotted on a curve against the ionic radius ratio of Al3+ or Gd3+ and RE3+ ( r A1 Ga /rRE ) except for Y4 Al2 O9 . 相似文献
3.
Yasuo Hikichi Toshitaka Ota Keiji Daimon Tomotoshi Hattori Masatoshi Mizuno 《Journal of the American Ceramic Society》1998,81(8):2216-2218
Xenotime-type RPO4 (R = Y, Er, Yb, or Lu) powder was dry-pressed into disks and bars. The disks and bars could be sintered to a relative density of greaterthan equal to98% in air without cracking at 1300° (R = Yb or Lu) or 1500°C (R = Y or Er), depending on the grain size. The linear thermal expansion coefficient (at 1000°C), thermal conductivity (at 20°C), and bending strength (at 20°C) of the xenotime-type RPO4 ceramics were 6.2 10-6 /°C, 12.02 W(mK)-1 , and 95 ± 29 MPa for R = Y; 6.0 10-6 /°C, 12.01 W(mK)-1 , and 100 ± 21 MPa for R = Er; 6.0 10-6 /°C, 11.71 W(mK)-1 , and 135 ± 34 MPa for R = Yb; and 6.2 10-6 /°C, 11.97 W(mK)-1 , and 155 ± 25 MPa for R = Lu. The xenotime-type RPO4 ceramics did not react with SiO2 , TiO2 , Al2 O3 , ZrO2 , or ZrSiO4 , even at 1600°C for 3 h in air, and were stable in aqueous solutions of HCl, H2 SO4 , HNO3 , NaOH, and NH4 OH at 20°C. 相似文献
4.
The C3 A compacts were hydrated and the reaction was studied by DTA, X-ray diffraction, mercury porosimetry, and volume change analysis. The hexagonal hydroaluminates C2 AH8 and C4 AH19 formed at 2°, 12°, and 23°C by a direct mechanism between C3 A and H2 O. The hydration reaction at 52° and 80°C was stopped by formation of C3 AH6 around the C3 A grains. The rate of conversion of the hexagonal hydrates to cubic C3 AH6 increased with temperature. Volume change analysis confirmed that C3 AH6 grows epitaxially on the surface of the C3 A grain. The reaction at this surface and the passage of water through the layer of hexagonal hydroaluminates control the overall reaction rate. The conversion of the hexagonal hydrates to C3 AH6 accelerates the reaction by removing the layer of products from around the C3 A grain by a solution mechanism. At 52° and 80°C, C3 AH6 may form without the intermediate formation of the hexagonal hydrate. 相似文献
5.
Above 755°C, compounds along the spinel join LiFe5 O8 -Li4 Ti5 O12 form a complete solid solution and below that temperature a two-phase region separates the ordered LiFe5 O8 and the disordered spinel phase. At 800° and 900°C, cubic LiFeO2 ( ss ) and monoclinic Liz Ti03 ( ss ) exist on the monoxide join LiFeO2 -Li2 TiO3 . The distributions of cations in both the spinel and monoxide structures were calculated as a function of equilibrium temperature and composition. Sub-solidus equilibria in the system Li2 O-Fe2 O3 -TiO2 at 800° and 900°C were determined for compositions containing ∼50 mol% Li2 O. 相似文献
6.
A MgAl2 O4 (MA) spinel layer was synthesized on Ti3 AlC2 substrate through the molten salt synthesis (MSS) method. The Ti3 AlC2 substrate was immersed in MgCl2 ·6H2 O powders and treated at 800°, 850°, and 900°C for 4 h in air. A continuous and 10-μm-thick MgAl2 O4 layer was obtained at 900°C, by which the surface hardness of Ti3 AlC2 can be effectively improved. The combined scanning electron microscopy observations and crystal morphology simulation further revealed that the as-formed MgAl2 O4 presents tetragonal bipyramids morphology with (400)-orientation. 相似文献
7.
Osamu Yamaguchi Msami Morimi Hidenao Kawabata Klyoshi Shimizu 《Journal of the American Ceramic Society》1987,70(5):97-C-
A compound tentatively denoted as Zn2 Ti,3 O8 is determined to be a low-temperature form of ZnTiO3 . At a heating rate of 10°C·min−1 the low-temperature form crystallizes at 600° to 765° C from an amorphous material prepared by the simultaneous hydrolysis of zinc acetylacetonate and titanium isopropoxide. It has a cubic unit cell with a =0.8408 nm. The cubic-to-hexagonal transformation occurs slowly above 820°C; during transformation ZnTiO3 decomposes into Zn2 TiO4 and TiO2 (rutile) at 965° to 1010°C. A single phase of the hexagonal form can be prepared by heating for 5 h at 900°C. The structure of both forms consists of octahedral TiO6 groups. 相似文献
8.
Phase relations in the system Na2 O· Al2 O3 -CaO· Al2 O3 -Al2 O3 at 1200°C in air were determined using the quenching method and high-temperature X-ray diffraction. The compound 2Na2 O · 3CaO · 5Al2 O3 , known from the literature, was reformulated as Na2 O · CaO · 2Al2 O3 . A new compound with the probable composition Na2 O · 3CaO · 8Al2 O3 was found. Cell parameters of both compounds were determined. The compound Na2 O · CaO-2Al2 O3 is tetragonal with a = 1.04348(24) and c = 0.72539(31) nm; it forms solid solutions with Na2 O · Al2 O3 up to 38 mol% Na2 O at 1200°C. The compound Na2 O · 3CaO · 8Al2 O3 is hexagonal with) a = 0.98436(4) and c = 0.69415(4) nm. The compound CaO · 6Al2 O3 is not initially formed from oxide components at 1200°C but behaves as an equilibrium phase when it is formed separately at higher temperatures. The very slow transformation kinetics between β and β "-Al2 O3 make it very difficult to determine equilibrium phase relations in the high-Al2 O3 part of the diagram. Conclusions as to lifetime processes in high-pressure sodium discharge lamps can be drawn from the phase diagram. 相似文献
9.
Masayoshi Ohashi Yasuo Iida Hisashi Morikawa 《Journal of the American Ceramic Society》2002,85(1):270-272
CuAlO2 is a delafossite-type compound and is a known p -type semiconductor. Transparent CuAlO2 thin films were prepared using a sol–gel technique. The films with an Al/Cu atomic ratio of 1.0 consisted of CuAlO2 , Cu2 O, and CuO after heat treatment at 800°–900°C in nitrogen gas. The electrical resistivity of the film heated at 800°C was 250 Ω·cm. 相似文献
10.
An intimate Ba-Al-Al2 O3 -SiO2 powder mixture, produced by high-energy milling, was pressed to 3 mm thick cylinders (10 mm diameter) and hexagonal plates (6 mm edge-to-edge width). Heat treatments conducted from 300° to 1650°C in pure oxygen or air were used to transform these solid-metal/oxide precursors into BaAl2 Si2 O8 . Barium oxidation was completed, and a binary silicate compound, Ba2 SiO4 , had formed within 24 h at 300°C. After 72 h at 650°C, aluminum oxidation was completed, and an appreciable amount of BaAl2 O4 had formed. Diffraction peaks consistent with hexagonal BaAl2 Si2 O8 , BaAl2 O4 , β-BaSiO3 , and possibly β-BaSi2 O5 were detected after 24 h at 900°C. Diffraction peaks for BaAl2 O4 and BaAl2 Si2 O8 were observed after 35 h at 1200°C, although SEM analyses also revealed fine silicate particles. Further reaction of this silicate with BaAl2 O4 at 1350° to 1650°C yielded a mixture of hexagonal and monoclinic BaAl2 Si2 O8 . The observed reaction path was compared to prior work with other inorganic precursors to BaAl2 Si2 O8 . 相似文献
11.
Phase equilibria have been determined in the system CaO-Al2 O3 -H2 O in the temperature range 100° to 1000°C. under water pressures of up to 3000 atmospheres. Only three hydrated phases are formed stably in the system: Ca(OH)2 , 3CaO·Al2 O3 ·6H2 O, and 4CaO·3Al2 O3 -3H2 O. Pressure-temperature curves delineating the equilibrium decomposition of each of these phases have been determined, and some ther-mochemical data have been deduced therefrom. It has been established that both the compounds CaO·Al2 O3 and 3CaO·Al2 O3 have a minimum temperature of stability which is above 1000°C. The relevance of the new data to some aspects of cement chemistry is discussed. 相似文献
12.
Melting Temperatures of Monazite and Xenotime 总被引:1,自引:0,他引:1
The melting temperatures of natural and synthetic monazite and xenotime (rare-earth ortnophosphates) were measured, using a heliostat-type solar furnace. The results obtained are as follows: natural monazite from Japan (2057°40°C), synthetic monazite RPO4 (R=La, 2072°20°C; R=Ce, 2045°20°C; R=Pr, 1938°20°C; R=Nd, 1975°20°C; R=Sm, 1916°20°C), and synthetic xenotime RPO4 (R=Y, 1995°20°C; R=Er, 1896°20°C). 相似文献
13.
F. G. BUTTLER L. S. DENT GLASSER H. F. W. TAYLOR 《Journal of the American Ceramic Society》1959,42(3):121-126
Single-crystal X-ray and electron-diffraction studies show the existence in one polymorph of 4CaO.Al2 O3 . 13H2 O of a hexagonal structural element with α= 5.74 a.u., c = 7.92 a. u. and atomic contents Ca2 (OH)7 - 3H2 O. These structural elements are stacked in a complex way and there are probably two or more poly-types as in SiC or ZnS. Hydrocalumite is closely related to 4CaO.A12 O3 .13H2 O, from which it is derived by substitution of CO3 2- for 20H- + 3H2 O once in every eight structural elements; similar substitutions explain the existence of compounds of the types 3CaO Al2 O3 .Ca Y 2 - xH2 O and 3CaO Al2 O3 Ca Y xH2 O. On dehydration, 4CaO.Al2 O3 .13H2 O first loses molecular water and undergoes stacking changes and shrinkage along c. At 150° to 250°C., Ca(OH)2 and 4CaO.3Al2 O3 .3H2 O are formed and, by 1000°C., CaO and 12CaO.7Al2 O8 . The dehydration of hydrocalumite follows a similar course, but no 4CaO.3Al2 O3 .3H2 O is formed. 相似文献
14.
The orthorhombic, low-temperature α-modification of Nb2 C has a structure similar to that of ζ-Fe2 N (a = 12.36 A, b = 10.895 A, c = 4.968 A) and transforms at ∼1200°C into the hexagonal ε-Fe2 N type. A second transition at approximately 2500°C is associated with the destruction of long range order in the carbon sublattice. Alpha-divanadium carbide (orthorhombic, a = 11.49 A, b = 10.06 A, c = 4.55 A) is isostructural with α-Nb2 C and transforms at ∼800°C into the hexagonal high-temperature modification. The structures of α-V2 C and α-Nb2 C are distorted modifications related to the ε-Fe2 N type. 相似文献
15.
Mi-Ri Joung Jin-Seong Kim Myung-Eun Song Jae-Hong Choi Jong-Woo Sun Sahn Nahm Jong-Hoo Paik Byung-Hyun Choi 《Journal of the American Ceramic Society》2009,92(9):2151-2154
Li2 CO3 was added to Mg2 V2 O7 ceramics in order to reduce the sintering temperature to below 900°C. At temperatures below 900°C, a liquid phase was formed during sintering, which assisted the densification of the specimens. The addition of Li2 CO3 changed the crystal structure of Mg2 V2 O7 ceramics from triclinic to monoclinic. The 6.0 mol% Li2 CO3 -added Mg2 V2 O7 ceramic was well sintered at 800°C with a high density and good microwave dielectric properties of ɛ r =8.2, Q × f =70 621 GHz, and τf =−35.2 ppm/°C. Silver did not react with the 6.0 mol% Li2 CO3 -added Mg2 V2 O7 ceramic at 800°C. Therefore, this ceramic is a good candidate material in low-temperature co-fired ceramic multilayer devices. 相似文献
16.
Seiji Shinohara Jong-Gab Baek Tetsuhiko Isobe Mamoru Senna 《Journal of the American Ceramic Society》2000,83(12):3208-3210
Phase-pure perovskite Pb(Zn x Mg1– x )1/3 Nb2/3 O3 solid solution (PZ x M1– x N) is obtained for x ≦ 0.7 by heating a milled stoichiometric mixture of PbO, Mg(OH)2 , Nb2 O5 , and 2ZnCO3 ·3Zn(OH)2 ·H2 O at 1100°C for 1 h. Percent perovskite ( f P ) with respect to total crystalline phase decreases with increasing temperature of subsequent heating then increases to 900°C for the mixtures where x ≦ 0.8 and milled for 3 h. For mixtures with x = 0.9 and x = 1, f P decreases monotonically. Curie temperature increases almost linearly with increasing x up to x = 0.7. The maximum dielectric constant at 1 kHz is 2×104 and 1.7×104 for the mixture with x = 0.4 and x = 0.7, respectively. The stabilization mechanism of strained perovskite is discussed. 相似文献
17.
Phase equilibria data, obtained both by differential thermal analysis and by quenching, are presented for the system Na2 O-Nb2 O5 . Five compounds corresponding to the formulas 3Na2 O.1Nb2 06 , lNa2 O. 1Nb2 O5 , lNa2 O 4Nb2 O6 , lNaz O.7Nb2 O5 , and lNa2 O. 10Nb2 O6 have been found. The compound 3Naz 0.lNb2 O5 melts congruently at 992°C. The compounds 1Na2 O. 4Nb2 O6 , lNa2 O.7Nb2 O, and 1Na2 O. 1Onb2 O5 melt incongruently at 1265°, 1275°, and 1290°C., respectively. The well-known perovskite structure phase NaNbO3 was found to melt congruently at 1412°C. The transition temperatures in NaNbO5 were checked by thermal analysis and only the major structural changes at 368° and 640°C. could be detected. A new disordered form of NaNbO3 could be preserved to room temperature by very rapid quenching. 相似文献
18.
SHIGERU ITO NOBUO KUBO SHINYA NARIKI NOBORU YONEDA 《Journal of the American Ceramic Society》1987,70(12):874-879
The potassium ions in potassium β-ferrite ((1 + x)K2 O ·11Fe2 O3 ) crystals were exchanged with Na+ , Rb+ , Cs+ , Ag+ , NH4 + , and H3 O+ in molten nitrates or in concentrated H2 SO4 . On the other hand, spinel and hexagonal ferrites were formed by soaking the crystals in the melt of divalent salts. The crystals of K+ , Rb+ , and Cs+ β-ferrites decomposed to form α-Fe2 O3 at high temperatures of 800° to 1100°C. In addition, H3 O+ , NH4 + , and Ag+ β-ferrites decomposed to form α-Fe2 O3 at relatively low temperatures of 350° to 650°C, in accordance with the stabilities of the inserted ions. The electrical properties of some β-ferrites were measured. 相似文献
19.
Yang Xiao Xiang Ming Chen Xiao Qiang Liu 《Journal of the American Ceramic Society》2004,87(11):2143-2146
CaRAlO4 (R = Nd, Sm, Y) ceramics with a K2 NiF4 structure were prepared by a solid-state reaction approach, and their microwave dielectric characteristics were evaluated, along with their microstructures. Dense CaNdAlO4 , CaSmAlO4 , and CaYAlO4 ceramics were obtained by sintering at 1425°–1500°C in air for 3 h, and good microwave dielectric characteristics were achieved: (1) ɛ= 18.2, Qf = 17 980 GHz, τf =−52 ppm/°C for CaNdAlO4 ; (2) ɛ= 18.2, Qf = 51 060 GHz, τf =−3 ppm/°C for CaSmAlO4 ; and (3) ɛ= 18.9, Qf = 39 960 GHz, τf = 6 ppm/°C for CaYAlO4 . 相似文献
20.
Daniele Mazza Mario Vallino Guido Busca 《Journal of the American Ceramic Society》1992,75(7):1929-1934
A morphous solids belonging to the systems Al2 O3 –Me2 O (Me = Na, K) and Al2 O3 –B2 O3 were prepared by nitrate decomposition, introducing boron in the form of boric acid. Crystalline metastable solids with pseudotetragonal symmetry were obtained from thermal treatment at 850° to 900°C for the compositions Al6 Mex O(9+0.5 x ) ( x ≅ 1; Me = Na, K) and Al6- x B x O9 (1 x 3). The resultant solids were stable only within a difinite temperature range and transformed, with further treatment increases, into stable equilibrium phases. The structures of the metastable phases were examined by X-ray diffraction and Fourier transform infrared spectroscopy, and both analyses showed a mullite type of framework, inside of which the atomic coordinates were refined in the Pbam (no. 55) space group. The present results indicate that these silica-free mullite structures are stabilized by two different mechanisms: (1) interstitial occupation of bulky cations (Na+ , K+ ) or (2) substitution of B for Al in some of the tetrahedral positions. 相似文献