共查询到20条相似文献,搜索用时 15 毫秒
1.
Debao Zhang Baoyu Chen Zhuping Liu Shunguang Li Lili Hu 《Journal of the American Ceramic Society》2004,87(12):2228-2231
Er3+ -doped sodium lanthanum aluminosilicate glasses with compositions of (90− x )(0.7SiO2 ·0.3Al2 O3 )· x Na2 O·8.2La2 O3 · 0.6Er2 O3 ·0.2Yb2 O3 ·1Sb2 O3 (in mol%) ( x = 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ω t ( t = 2, 4, 6) decreases with increasing Na2 O. Ω2 decreases rapidly with increasing Na2 O while Ω4 and Ω6 decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na2 O. Fluorescence spectra of the 4 I 13/2 to 4 I 15/2 transition have been measured and the change with Na2 O content is discussed. It is found that the full width at half-maximum decreases with increasing Na2 O. 相似文献
2.
A. C. D. CHAKLADER 《Journal of the American Ceramic Society》1961,44(4):175-180
The effect of additions of 0.22, 0.44, 0.88, and 1.76% A12 O3 (Si4+ /A13+ ratio of 200:1, 100:1, 50:1, and 25:1) on the transformation of Brazilian quartz to cristobalite was studied at 1500°, 1530°, and 1570°C. The smaller percentages of A12 O3 (0.22 and 0.44%) catalyzed the transformation of quartz and the formation of cristobalite considerably. The rates of transformation of quartz with 0.88 and 1.76% A12 O3 were slower than with 0.22 or 0.44%, indicating a critical A13+ /Si4+ ratio where the catalytic effect was found to be maximum. This appeared to occur at about 0.5% A12 O3 . The transformation rate of quartz indicated that the reaction was first order. Cristobalite, however, showed two different rates; the initial rapid growth was followed by a slower rate. The point of changeover was found to be at about 30 ± 5% cristobalite. The critical nature of the A13− /Si4+ ratio at about 0.01 (or A12 O3 /SiO2 ± 0.005) may have some bearing on the properties of silica refractories with more or less than 0.5% A12 O3 . 相似文献
3.
Woon Jin Chung Jae Ryoung Yoo You Song Kim Jong Heo 《Journal of the American Ceramic Society》1997,80(6):1485-1490
Blue up-conversion fluorescence from the Tm3+ :1 G 4 →3 H 6 (480 nm) transition has been observed from calcium aluminate glass codoped with Tm3+ /Nd3+ . The mechanism for the up-conversion process consists of a two-photon process. An excitation beam with a wavelength of 791 nm first excites Tm3+ to the 3 H 4 level, where Tm3+ again absorbs the 1060 nm emission from Nd3+ :4 F 3/2 →4 I 11/2 to attain the Tm3+ :1 G4 level. Lifetime and intensity variations with compositions suggest the presence of an efficient energy transfer from Nd3+ to Tm3+ . The highest 480 nm emission intensity has been obtained from the glass with 0.1 mol% of Nd2 O3 and 0.2 mol% of Tm2 O3 . 相似文献
4.
Yangyang Ji Jingkui Liang Sishen Xie Yude Yu 《Journal of the American Ceramic Society》1995,78(3):765-768
The "subsolidus" phase relations at room temperature in the system CaO-B2 O3 -BaO are investigated. Specimens of various compositions were prepared from appropriate ratios of CaCO3 , B2 O3 , and BaCO3 , and fired from 780° to 1040°C according to their melting points. There are three ternary compounds in this system. The crystal structures of these compounds were determined by X-ray diffraction (XRD). CaBa2 (BO3 )2 and Ca5 Ba2 B10 O22 are monoclinic structures. The lattice constants a = 14.221 Å, b = 4.569 Å, c = 11.926 A, β= 99.947°, and V = 763.4 å3 for CaBa2 (BO3 )2 and a = 15.714 å, b = 6.184 å, c = 10.204 å, β= 93.954°, and V = 989.29 å3 for Ca5 Ba2 B10 O22 are obtained. The third compound, CaBa2 (B3 O6 )2 , is isostructural with the high form of BaB2 O4 with lattice constants a = 7.167 å and c = 35.298 å. Powder second harmonic generation efficiencies of these ternary compounds were measured using a homemade apparatus. 相似文献
5.
Masao Morishita Alexandra Navrotsky Martin C. Wilding 《Journal of the American Ceramic Society》2004,87(8):1550-1555
The relative partial molar enthalpies, Δ SiO2 , of SiO2 in SiO2 –M2 O (M = Li, Na, K and Cs) binary and SiO2 –CaO–Al2 O3 ternary melts were directly measured by drop-solution calorimetry at 1465 K and 1663 K. Δ SiO2 changes from exothermic to endothermic as silica content increases, confirming the tendency toward immisciblity seen from activity measurements. It is concluded that Δ SiO2 is negative due to acid-base reactions and charge-coupled substitutions when the melt is composed of fewer Q 4 and more Q 3 and Q 2 species, but positive due to structural strain when the melt is composed of mostly Q 4 species. The Δ SiO2 obtained by calorimetry is a useful measure of basicity, when comparing different alkali and alkaline earth oxides. 相似文献
6.
Excitation of Tm3+ to 3 H 4 using the 791 nm pump source showed the frequency up-converted blue emission (∼480 nm) due to the Tm3+ :1 G 4 →3 H 6 transition in Tm3+ /Nd3+ codoped CaO·Al2 O3 glasses. Intensity and lifetime changes with rare-earth concentrations suggested the efficient energy transfer of Tm3+ :3 H 4 → Nd3+ :4 F 5/2 and Nd3+ :4 F 3/2 → Tm3+ :1 G 4 . The latter transfer enabled Tm3+ to reach its 1 G 4 level, and the blue emission became possible through the 1 G 4 →3 H 6 transition. Quantitative analysis with rate equations proved that these two transitions were the most efficient among all the possible energy transfer routes between Tm3+ and Nd3+ . Calculated up-conversion efficiency of the Tm3+ /Nd3+ combination in CaO·Al2 O3 glass was 6.6 × 10−3 , and it was ∼4 orders of magnitude larger than those reported for other oxide glasses. 相似文献
7.
Kiyoshi Okada Akiyoshi Hattori Taketoshi Taniguchi Akihiko Nukui Rathindra Nath Das 《Journal of the American Ceramic Society》2000,83(4):928-932
The effect on the γ-Al2 O3 -to-α-Al2 O3 phase transition of adding divalent cations was investigated by differential thermal analysis, X-ray diffractometry, and surface-area measurements. The cations, Cu2+ , Mn2+ , Co2+ , Ni2+ , Mg2+ , Ca2+ , Sr2+ , and Ba2+ , were added by impregnation, using the appropriate nitrate solution. These additives were classified into three groups, according to their effect: (1) those with an accelerating effect (Cu2+ and Mn2+ ), (2) those with little or no effect (Co2+ , Ni2+ , and Mg2+ ), and (3) those with a retarding effect (Ca2+ , Sr2+ , and Ba2+ ). The crystalline phase formed by reaction of the additive with γ-Al2 O3 at high temperature was a spinel-type structure in groups (1) and (2) and a magnetoplumbite-type structure in group (3). In groups (2) and (3), a clear relationship was found between the transition temperature and the difference in ionic radius of Al3+ and the additive (Δ r ): The transition temperature increased as Δ r increased. This result indicates that additives with larger ionic radii are more effective in suppressing the diffusion of Al3+ and O2− in γ-Al2 O3 , suppressing the grain growth of γ-Al2 O3 , and retarding the transformation into α-Al2 O3 . 相似文献
8.
MICHAEL GREBIEN FLORIAN HABEREY KURT SAHL 《Journal of the American Ceramic Society》1984,67(10):195-C
The pseudobinary system Ga2 O3 -Bi2- x 3+ Bi x 5+ O3+ x 2- was studied in view of its importance for growth of SrGa12 O19 crystals from a bismuth oxide flux. A subsolidus transition of γ*-Bi2 O3 to a β'-phase and a strictly stoichiometric 1:2 phase with 33.3 mol% bismuth oxide were found. The single-crystal data for the compound indicated space group P21 21 2, with lattice constants a=0.79180±0.0003 nm, b =0.8288±0.0003 nm, and c =0.5889±0.0003 nm; the measured density was 7.1±0.3 g/cm3 and the cell content (Z) 2. 相似文献
9.
Dai Guiqin Lin Wei Zheng An Huang Qingzhen Liang Jingkui 《Journal of the American Ceramic Society》1990,73(8):2526-2527
Thermal expansion of the low-temperature form of BaB2 O4 (β-BaB2 O4 ) crystal has been measured along the principal crystallographic directions over a temperature range of 9° to 874°C by means of high-temperature X-ray powder diffraction. This crystal belongs to the trigonal system and exhibits strongly anisotropic thermal expansions. The expansion along the c axis is from 12.720 to 13.214 Å (1.2720 to 1.3214 nm), whereas it is from 12.531 to 12.578 Å (1.2531 to 1.2578 nm) along the a axis. The expansions are nonlinear. The coefficients A, B , and C in the expansion formula L t = L 0 (1 + At + Bt 2 + Ct 3 ) are given as follows: a axis, A = 1.535 × 10−7 , B = 6.047 × 10−9 , C = -1.261 × 10−12 ; c axis, A = 3.256 × 10−5 , B = 1.341 × 10−8 , C = -1.954 × 10−12 ; and cell volume V, A = 3.107 × 10−5 , B = 3.406 × 10−8 , C = -1.197 × 10−11 . Based on α t = (d L t /d t )/ L 0 , the thermal expansion coefficients are also given as a function of temperature for the crystallographic axes a , c , and cell volume V. 相似文献
10.
M. F. YAN 《Journal of the American Ceramic Society》1980,63(7-8):443-447
Sintering and microstructural evolution were studied in Fe3 O4 as a model system for spinel ferrites. Fe3 O4 powder, purified by the salt-crystallization method, was sintered to ∼99.5% density in a CO-CO2 atmosphere. The p O2 Of the sintering atmosphere drastically affects the microstructure (grain size) of sintered Fe3 O4 without significantly affecting density. The measured grain-boundary mobilities, M , of Fe3 O4 fit the equation M=M 0 ( T ) p O2 −1/2 with M 0 ( T ) = 2.5×105 exp[-(609kJ·mol-1 / RT ](m/s)(N/m2 )−l . The grain-boundary migration process appeared to be pore-drag controlled, with lattice diffusion of oxygen as the most likely rate-limiting step. 相似文献
11.
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
12.
A phase diagram of the system A12 O3 -A14 C3 is proposed. Two intermediate oxycarbides, A14 O4 C and A12 OC, were established. Eutectic melting between alumina and A14 O4 C occurred at 1840° C. No other low melting was observed. The alumina phase was not corundum but was similar to delta-alumina. Because of the high reactivity of aluminum carbide and all the intermediate compounds with moisture and oxygen, use of refractories based on the system A12 O3 -A14 C3 must be limited to applications where these agents are excluded. The behavior of high-alumina refractories in the presence of carbon is explained. 相似文献
13.
HIROSHI HIRASHIMA KOTA NISHII TETSURO YOSHIDA 《Journal of the American Ceramic Society》1983,66(10):704-708
The dc conductivities (σ) of V2 O5 -P2 O5 glasses containing up to 30 mol% TiO2 were measured at T=100° to ∼10°C below the glass-transition temperature. Dielectric constants from 30 to 106 Hz, densities, and the fraction of reduced V ion were measured at room temperature. The conduction mechanism was considered to be small polaron hopping between V ions, as previously reported for V2 O5 -P2 O5 glass. The temperature dependence of σ was exponential with σ = σ0 exp(-W/kT ) in the high-temperature range. When part of the P2 O5 was replaced by TiO2, σ increased and W decreased. The hopping energy depended on the reciprocal dielectric constant which, in this case, increased with increasing TiO2 content. 相似文献
14.
Combined tension/torsion tests were performed on solid A12 O3 rods at principal stress ratios σ2 /σ1 of 0 (pure tension), -0.17, -0.38, -0.78, and -1.0 (pure torsion). The tensile principal stress at fracture σ1 increased with increasing compressive principal stress σ2 , resulting in a higher strength in torsion than uniaxial tension. The ratio σ1 (torsion)σ1 (tension) was 1.31 for A12 O3 , in general agreement with limited torsional data for brittle materials in the literature. Brittle fracture data in the tension-compression quadrant of principal stress space show an interesting dichotomy since strengthening is observed in torsional investigations, whereas weakening is observed for pressurized-tube studies. This difference may be either a pressurized-tube test artifact or a real effect due to the presence of stress gradients. 相似文献
15.
The percent intergranular fracture (PIF) was measured along radii extending from fracture origins in 96% A12 O3 specimens, fractured at various loading rates and temperatures, and plotted vs estimates of stress intensity factors ( K 1 ) at the corresponding crack lengths. Two types of curves were observed. The first was similar to curves previously observed for hot-pressed alumina. In this case the subcritical crack-growth boundary was located approximately where the minimum in the PIF occurred near K 1 =4MPa·m½ , as was also the case for hotpressed alumina. Therefore, the location of this minimum or the projecting grams formed by intergranular fracture as the crack velocity increased can be used as criteria for locating the subcritical crack-growth boundary. The second type of curve lacks the minima in PIF characteristic of the first type and is characterized by a gradual trend toward higher PIF beginning at K 1 =3MPa·m½ . This type of curve may be caused by acceleration of the crack to high crack velocities at values of K 1 approximately equal to or slightly greater than those necessary to cause critical crack growth on the lower fracture-energy planes in sapphire. Assuming that this is the case, the K 1 at which the trend toward higher PIF begins can be used to calculate the radius to the critical flaw boundary for this type of fracture. 相似文献
16.
Mari Lou Balmer Fred F. Lange Vikram Jayaram Carlos G. Levi 《Journal of the American Ceramic Society》1995,78(6):1489-1494
Aqueous mixtures of zirconium acetate and aluminum nitrate were pyrolyzed and crystallized to form a metastable solid solution, Zr1- x Al x O2− x /2 ( x < 0.57). The initial, metastable phase partitions at higher temperatures to form two metastable phases, viz., t −ZrO2 +γ-Al2 O3 with a nano-scale microstructure. The microstructural observations associated with the γ- →α-Al2 O3 phase transformation in the t -ZrO2 matrix are reported for compositions containing 10, 20, and 40 mol% A12 O3 . During this phase transformation, the α-Al2 O3 grains take the form of a colony of irregular, platelike grains, all with a common crystallographic orientation. The plates contain ZrO2 inclusions and are separated by ZrO2 grains. The volume fraction of A12 O3 and the heat treatment conditions influence the final microstructure. At lower volume fractions of A12 O3 , the colonies coarsen to single, irregular plates, surrounded by polycrystalline ZrO2 . Interpenetrating microstructures produced at high volume fractions of A12 O3 exhibit very little grain growth for periods up to 24 h at 1400°C. 相似文献
17.
In the presence of a fluorine mineralizer, highly aggregated, <5 μm α-Al2 O3 platelet particles form by vapor transport during the thermal transformation of γ-alumina. Platelet aggregation was determined to occur by platelet inter-growth and by edge nucleation on primary α-Al2 03 platelets. The addition of 1010 α-alumina seed particles/cm3 γ–Al2 O3 resulted in the development of discrete particles during the initial stage of transformation. Impingement of the growing platelets during the latter stage of transformation, however, resulted in intergrowth, a process which was not changed by seeding. Particle size distribution broadening was observed to increase with increasing HF and H2 O concentrations because vapor reactant supersaturation increases the degree of edge nucleation. When initially low HF and H2 O concentrations were used in seeded systems, however, essentially aggregate-free α-Al2 O3 platelets of 10–15 μm were obtained. 相似文献
18.
Xian Feng Setsuhisa Tanabe Teiichi Hanada 《Journal of the American Ceramic Society》2001,84(1):165-171
The thermal stability and spectroscopic properties of Er2 O3 -doped TeO2 –GeO2 –ZnO–Na2 O–Y2 O3 glasses for 1.5 μm fiber amplifiers were investigated. The thermal stability of the 75TeO2 ·20ZnO· 5Na2 O glass was improved by introducing GeO2 and Y2 O3 . The radiative transition and the nonradiative transition have a dominant influence on the 4 I13/2 level lifetime of Er3+ in high- and low-GeO2 regions, respectively. Adding Y2 O3 increases the 4 I13/2 level lifetime of Er3+ significantly. The Judd–Ofelt (J-O) parameter Ω6 shows a strong correlation with the 1.5 μm emission bandwidth; and the larger the Ω6 , the wider the bandwidth. 相似文献
19.
Kiyoshi Okada Akiyoshi Hattori Yoshikazu Kameshima Atsuo Yasumori Rathindra Nath Das 《Journal of the American Ceramic Society》2000,83(5):1233-1236
The effect of monovalent cation addition on the γ-Al2 O3 -to-α-Al2 O3 phase transition was investigated by differential thermal analysis, powder X-ray diffractometry, and specific-surface-area measurements. The cations Li+ , Na+ , Ag+ , K+ , Rb+ , and Cs+ were added by an impregnation method, using the appropriate nitrate solution. β-Al2 O3 was the crystalline aluminate phase that formed by reaction between these additives and Al2 O3 in the vicinity of the γ-to-α-Al2 O3 transition temperature, with the exception of Li+ . The transition temperature increased as the ionic radii of the additive increased. The change in specific surface area of these samples after heat treatment showed a trend similar to that of the phase-transition temperature. Thus, Cs+ was concluded to be the most effective of the present monovalent additives for enhancing the thermal stability of γ-Al2 O3 . Because the order of the phase-transition temperature coincided with that of the formation temperature of β-Al2 O3 in these samples, suppression of ionic diffusion in γ-Al2 O3 by the amorphous phase containing the added cations must have played an important role in retarding the transition to α-Al2 O3 . Larger cations suppressed the diffusion reaction more effectively. 相似文献
20.
Kentaro Terashima Sae-Hoon Kim Toshinobu Yoko 《Journal of the American Ceramic Society》1995,78(6):1601-1605
The third-order nonlinear optical susceptibilities χ(3) of M2 O-B2 O3 (M = Li, Na, K, Rb, Cs, and Ag) binary borate glasses have been measured by the third harmonic generation (THG) method. It is found that the enhancement of χ(3) by the structural change of BO3 units to BO4 units is small, while the enhancement of χ(3) due to the formation of non- bridging oxygen is rather significant. The effects of alkali cations on the χ(3) of alkali borate glasses are discussed in terms of the M-O bond character, focusing on the covalency of Li2 O-B2 O3 glasses. Comparison of the χ(3) values for Cs2 O-B2 O3 and Ag2 O-B2 O3 glasses which contain cations of comparable polarizability reveals that the χ(3) value is much greater for Ag2 O-B2 O3 glasses than for Cs2 O-B2 O3 glasses, which is possibly due to the great contribution of Ag(4 dz2 + 5 s + 5 pz ) hybrid orbitals to the nonlinear optical response. 相似文献