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101.
耐高温高表面氧化铝的制备及性质──添加钡及钡与镧的协同作用对氧化铝热稳定性的影响 总被引:7,自引:0,他引:7
氧化铝是高温催化反应中常用的载体材料. 高于1 000 ℃时, Al2O3通过表面活性原子的迁移和表面羟基脱水发生烧结, 并向α相转变[1,2], 同时随着比表面积剧烈下降, 导致催化剂活性组分聚集, 催化剂活性下降等. 大量研究表明, 稀土元素, 硅及碱土元素可明显改善氧化铝的热稳定性[3~8]. 本文以溶胶-凝胶法单独引入Ba元素, 考察了Ba添加量对Al2O3热稳定性的影响. 还采用溶胶-凝胶与表面浸渍相结合的方式共同引入La和Ba, 考察了两元素协同作用对Al2O3热稳定性的影响. 相似文献
102.
将不同剂量的La、Tb和Yb的EDTA络合物注入种蛋,研究了育成雏鸡的畸变和稀土在脏器组织中的分布,提出胚胎对稀土敏感。 相似文献
103.
张俊芬 《光谱学与光谱分析》1992,(3)
本文采用中阶梯光栅光谱仪,直流等离子体光谱法测定高纯(99.99%)氯化镧、氧化钇中稀土杂质元素,由于仪器具有很高的色散率,因而方法具有灵敏度高、干扰少的特点。 相似文献
104.
杂多阴离子的NMR和ESR研究:Ⅱ磷钼钒杂多酸及其镧盐的NMR 总被引:1,自引:0,他引:1
具有Keggin结构的磷钼钒杂多酸及其盐是有效的氧化剂.本文通过磷钼钒杂多酸及其镧盐的~(31)p,~(51)V,~(139)La,~(17)O及~1H的NMR测定,并结合红外和差热分析,说明镧的引入对Keggin结构没有影响,但镧对水分子有强的作用力,使阴离子之间存在更多的水分子,从而对催化氧化活性产生了影响. 相似文献
105.
Gianina Dobrescu Daniela Berger Florica Papa N. I. Ionescu 《Applied Surface Science》2003,220(1-4):154-158
Fractal dimensions of three different samples of lanthanum ferrite were computed using single adsorption method. The fractal Dubinin–Radushkevitch isotherm was used to fit directly the experimental nitrogen adsorption data. Avnir–Jaroniec method for fractal dimension determination was also used. Low and intermediate fractal dimensions were obtained according to BET specific surface areas. 相似文献
106.
The main factor governing the oxygen ionic conductivity in apatite-type La10−xSi6−yAlyO27−3x/2−y/2 (x=0-0.33; y=0.5-1.5) is the concentration of mobile interstitials determined by the total oxygen content. The ion transference numbers, measured by modified faradaic efficiency technique, vary in the range 0.9949-0.9997 in air and increase on reducing oxygen partial pressure due to decreasing p-type electronic conduction. The activation energies for ionic and hole transport are (56-67)±3 kJ/mol and (57-100)±8 kJ/mol, respectively. Increasing oxygen content leads to higher hole conduction in oxidizing atmospheres and promotes minor oxygen losses from the lattice when the oxygen pressure decreases, although the overall level of ionic conductivity is almost constant in the p(O2) range from 50 kPa down to 10−16 Pa. Under reducing conditions at temperatures above 1100 K, silicon oxide volatilization from the surface layers of apatite ceramics results in a moderate decrease of the conductivity with time. This suggests that the operation of electrochemical cells with silicate-based solid electrolytes should be limited to the intermediate-temperature range, such as 800-1000 K, where the ionic transport in most-conductive apatite phases containing 26.50-26.75 oxygen atoms per unit formula is higher than that in stabilized zirconia. The average thermal expansion coefficients of apatite ceramics, calculated from dilatometric data in air, are (8.7-10.8)×10−6 K−1 at 300-1300 K. 相似文献
107.
Giovana G. Nunes Gulaim A. Seisenbaeva Vadim G. Kessler 《Journal of Sol-Gel Science and Technology》2007,43(1):105-109
Niobium isopropoxide, Nb(OiPr)5, is an attractive precursor of simple and complex niobium oxides in sol-gel technology. This compound cannot, unfortunately,
be obtained by alcohol interchange starting from linear chain homologues such as Nb(OMe)5 or Nb(OEt)5. The equilibrium in the latter reaction favours formation of mixed-ligand complexes, [Nb2(OR)2(OiPr)8], R = Me, Et. In particular, [Nb2(OMe)2(OPri)8] (1) has been isolated in high yield from repeated treatment of Nb2(OMe)10 with excess of isopropanol. The X-ray single crystal study reveals a dinuclear structure containing a pair of edge-sharing
octahedra with methoxide ligands in the bridging position. Infrared (IR) and mass spectroscopy (MS) studies confirmed the
incomplete ligand substitution. The 1H-NMR spectra suggest equilibrium between different molecular forms in solution. Solvothermal interaction of 1 with La chips in toluene/isopropanol media results in formation of a mixture of LaNb2(OiPr)13 and La2Nb4(μ4−O)4(OH)2(μ−OiPr)8(OiPr)8 (2).
Electronic Supplementary Material The online version of this article (doi: ) contains supplementary material, which is available to authorised users. 相似文献
108.
109.
[La(NO3)3(OH2)2(phen)] · 15-crown-5 is hexagonal,P65, witha=10.955(2),c=43.769(9), andD
calc
=1.668 g cm–3 for Z=6. In the complex, two nitrogen atoms (from phen) and eight oxygen atoms (six from three bidentate nitrate anions and two from water molecules) are coordinated to the central La(III) ion, forming a coordination polyhedron which is approximately a bicapped square antiprism. The coordinated water molecules donate hydrogen bonds to the oxygen atoms of the crown ether, forming polymeric hydrogen bonded chains which wrap helically along the unit cell directionc. 相似文献
110.
Solid-solute phase equilibria in aqueous solutions,VIII: The standard gibbs energy of La2(CO3)3·8H2O
Anh Mai Nguyen Erich Königsberger Harald Marhold Heinz Gamsjäger 《Monatshefte für Chemie / Chemical Monthly》1993,124(10):1011-1018
The solubilities of lanthanum carbonate La2(CO3)3·8H2O in solutionsS
0([H+]=H mol kg–1, [Na+]=(I–H) mol kg–1, [ClO
4
–
]=I mol kg–1) at various fixed partial pressures of CO2 have been investigated at 25.0 °C. The hydrogen ion molality and the total molality of La(III) ion in equilibrium with the solid phase were determined by e.m.f. and analytical methods, respectively. The stoichiometric solubility constants
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