铬铁矿中三氧化二铬测定结果不确定度的评定

讨论了影响铬铁矿中三氧化二铬测定结果不确定度的各种因素,并评定了地质样品中三氧化二铬测定结果的不确定度.结果表明,采用硫酸亚铁铵溶液滴定方法,当样品三氧化二铬的含量为43.78％时,其扩展不确定度U=0.32％.     

Adsorption of hydrogen on reduced copper chromite

Temperature programmed desorption and volumetric methods in static conditions were used to study hydrogen adsorption on the surface of metallic copper particles produced by the partial reduction of copper chromite CuCr₂O₄ with hydrogen. In the temperature range 300-573 K and in the range of medium surface coverages by hydrogen, the main state of adsorbed hydrogen reveals the heat of adsorption q= 78 kJ/mol and activation energy of adsorption E _a = 69 kJ/mol. In the temperature range 77-300 K, an adsorption state with lower heat and activation energy was found, indicating a non-uniformity of the copper surface within ca. 8% of the total number of surface sites. This revised version was published online in June 2006 with corrections to the Cover Date.     

Theoretical Study of NO Dimer Adsorption and Dissociation on the CuCr2O4 （100） Surface

Theoretical simulation of the adsorption and dissociation of two NO molecules at the Cu^2＋, Cr^3＋ and bridge Cr^3＋ sites （b-Cr^3＋） on the normal spinel CuCr2O4 （100） surface has been carried out by density functional theory calculations. The results show that the formed N-down and O-down NO dimers are negatively charged. The formation of stable O-down dimers on the surface leads to the great elongation of N-O bond, which contributes to the NO reduction. The transition-state calculations indicate that the decomposition of O-down NO dimer at the b-Cr^3＋ site is most favorable and N2O is the major reduction product.     

Selective synthesis of isobutanol by means of the Guerbet reaction: Part 2. Reaction of methanol/ethanol and methanol/ethanol/n-propanol mixtures over copper based/MeONa catalytic systems

The synthesis of isobutanol via the Guerbet condensation between methanol and ethanol was studied by using sodium methoxide (MeONa) as soluble basic component and copper-based catalysts as heterogeneous dehydrogenating/hydrogenating metal species. The effect of the nature of the catalyst and the relative amount of its individual components with respect to the reacting alcohols as well as of temperature on productivity and selectivity of the process was investigated. The collected data indicated that the copper chromite/MeONa was more active than Cu-Raney/MeONa system. The reaction was shown to proceed with the formation only of n-propanol and isobutanol. Ethanol conversion up to 61% with selectivity to isobutanol up to 98.4% was obtained. The same catalytic systems were also employed in the reaction of the methanol/ethanol/n-propanol ternary mixture. Again copper chromite/MeONa resulted more active than the Cu-Raney/MeONa system. Finally, experiments were carried out on methanol/n-propanol mixtures in the presence of the copper chromite/MeONa catalytic system by recycling both the recovered solid copper component and the liquid reaction mixture for evidencing eventual copper leaching by MeONa. On the basis of the obtained results it was concluded that in the Guerbet reaction copper chromite works as heterogeneous catalyst.     

Analysis of the chromite inclusions found in nephrite minerals obtained from different deposits using SEM‐EDS and LRS

Scanning electron microscopy with energy dispersive spectrometer (SEM‐EDS) and laser Raman spectroscopy (LRS) were used to analyse the chromite inclusions found in four samples of the mineral nephrite that were obtained from Taiwan (one), Manasi in China (two) and New Zealand (one). The chromite inclusions found in sample HL‐1 (Taiwan) contain low contents of Mg and Al, as well as a characteristically high Zn content. The most significant finding, however, was that HL‐1 could also be distinguished from the other samples by the lower wavenumbers of the positions of the peaks that belong to the A_1g, F_2g⁽¹⁾ and E_g modes. Compared to the difference in compositions, the difference in the positions of the peaks in the Raman spectra of the chromite inclusions, as revealed by LRS, can more easily be used to distinguish between samples of nephrite that have been obtained from different deposits, and in particular to identify the provenance of the raw material used in ancient nephrite artefacts, in view of the fact that LRS is non‐destructive and easy to apply. Copyright © 2011 John Wiley & Sons, Ltd.     

烧成温度对La0.7Ca0.3CrO3/Al2O3导电陶瓷微滤膜支撑体结构与性能的影响

采用高温固相反应烧结法制备La0.7Ca0.3CrO3(LCC)/Al2O3导电陶瓷微滤膜支撑体.研究了烧成温度对制备的LCC/Al2O3支撑体样品的物相组成、微观结构、烧成收缩、孔隙率和孔径分布、电导率、抗弯强度、渗透通量及耐腐蚀性能等的影响.结果表明,高温烧成过程中LCC与Al2O3发生复杂的固相反应,样品主晶相为菱形结构La07Ca0.3Cr1-xAlxO3,并生成了少量LaAl11O18和CaCr2O4等.烧成温度从1350℃提高到1600℃时,样品的烧结程度、电导率、抗弯强度和耐酸腐蚀性能明显提高,而孔隙率明显减小.样品的平均孔径和纯水渗透通量随烧成温度提高,表现出先增大后减小的变化趋势.在1550℃时保温2h烧成制备的LCC/Al2O3支撑体,具有高的孔隙率(43.4;)和抗弯强度(36.9 MPa),其平均孔径(d50)为1.02 μm、纯水通量为2.24 m3/m2·h·bar、电导率为0.11 S/m,且具有良好的耐腐蚀性能.     

Phase Formation Study of Alkaline Earth-doped Lanthanum Chromites

In this paper the influence of alkaline-earth admixtures on the synthesis of lanthanum chromites of La_1–xM_xCrO₃ (x=0; 0.3; M=Ca, Sr, Ca+Sr) type was studied. The formation mechanism as well as the phase composition evolution, under non-isothermal and isothermal conditions, were investigated by thermal analysis and X-ray diffraction. The structure of the compounds and of the solid solutions formed depends on the solute type by means of the structural distortion induced. The crystallinity of the chromites obtained is obviously influenced by both the temperature and the thermal treatment plateau. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electrochemical performance and large positive–negative magnetodielectric coupling in iron chromite spinels

Spinel ferrites with remarkable electrochemical performance and magnetodielectric (MD) coupling are promising candidates for energy storage and spintronic devices. This study focuses on structural phases, dielectric and magnetic polarization along with magnetodielectric (MD) coupling and electrochemical response of Fe-Cr spinels. Low cost sol–gel method is used to synthesize iron chromite nanopowders. Iron to chromium (Fe/Cr) ratio is varied in the range of 0.2–0.65 (with interval of 0.05). XRD patterns confirm the formation of phase pure FeCr₂O₄ at Fe/Cr ratios of 0.45, 0.6 & 0.65. Amorphous behavior is observed at Fe/Cr ratios of 0.2, 0.25, 0.5 & 0.55. Mixed phases are observed at 0.3, 0.35 & 0.4 Fe/Cr ratios. Formation of pure spinel phase at Fe/Cr ratio of 0.45 results in high saturation magnetization of 9.2 emu/g. High grain boundary resistance (189.62kΩ) and high dielectric constant (～83.38 at log f = 5.0) along with low tangent loss (0.00423 at log f = 5) are observed at Fe/Cr ratio of 0.45. Magneto dielectric studies confirm positive magneto dielectric constant (MDC) of synthesized nanopowders at 0.45, 0.6 & 0.65 Fe/Cr ratios. Cyclic voltammetry is performed at constant potential window. Oxidation/reduction process leads to the pseudo-capacitive response of the material. The cyclic voltammetry curves show specific capacitance of 156 Fg^?1, 144 Fg^?1 and 152 Fg^?1 at scan rate of 25 mV/s at Fe/Cr ratios of 0.45, 0.6 & 0.65 of FeCr₂O₄ nanopowders, respectively. The galvanostatic charging/discharging behavior shows capacitive behavior of FeCr₂O₄ nanopowders. The electrochemical results suggest that synthesized nanopowders have potential for energy storage system.     

Theoretical Study of NO Dimer Adsorption and Dissociation on the CuCr204 (100) Surface

Theoretical simulation of the adsorption and dissociation of two NO molecules at the Cu2 , Cr3 and bridge Cr3 sites (b-Cr3 ) on the normal spinel CuCr2O4 (100) surface has been carded out by density functional theory calculations. The results show that the formed N-down and O-down NO dimers are negatively charged. The formation of stable O-down dimers on the surface leads to the great elongation of N-O bond, which contributes to the NO reduction. The transition-state calculations indicate that the decomposition of O-down NO dimer at the b-Cr3~ site is most favorable and N2O is the major reduction product.     

两种有机溶胶法合成铬酸镧超细粉体的对比研究

用两种有机溶胶法——Pechini法和低温燃烧法分别合成了铬酸镧超细粉体。借助红外光谱（ATR）、热分析（TG，DSC）、X射线衍射等手段对制备的凝胶结构、热分解过程、粉体结构和形貌进行对比分析。结果得出，羟基作为最主要的络合基团存在于两种合成方法的凝胶中。虽然两种方法的反应过程相似，但燃烧法只经过一步燃烧就可以迅速合成最终粉体，Pechini法必须经过较长时间煅烧。燃烧法得到的粉体粒径小于Pechini法，分散性也较好。另外，还讨论了两种合成方法反应过程及产物形态差别的原因。