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1.
Myoung Youp Song Young Jun Kwak Hye Ryoung Park Daniel R. Mumm 《Materials Research Bulletin》2011,46(11):1887-1891
Pure Mg was employed as a starting material instead of MgH2 in this work. The magnesium prepared by mechanical grinding under H2 (reactive mechanical grinding) with transition elements or oxides showed relatively high hydriding and dehydriding rates when the content of additives was about 20 wt.%. Ni, Fe and Ti were chosen as metallic transition elements to be added. Fe2O3 was selected as an oxide to be added. Samples Mg–14Ni–2Fe2O3–2Ti–2Fe were prepared by reactive mechanical grinding, and their hydrogen storage properties were examined and compared with those of a pure Mg sample prepared by reactive mechanical grinding under the same conditions. The Mg–14Ni–2Fe2O3–2Ti–2Fe sample showed much better hydrogen storage properties than the pure Mg sample. The as-milled Mg–14Ni–2Fe2O3–2Ti–2Fe sample did not require the activation. This sample absorbs 4.26 wt.% H for 5 min, and 4.41 wt.% H for 10 min, and 4.56 wt.% H for 60 min at n = 2. It desorbs 1.13 wt.% H for 10 min, 2.67 wt.% H for 30 min, and 3.32 wt.% H for 60 min at n = 2. 相似文献
2.
Carina Börrnert Jens Zosel Annette Polte Roswitha Wenzel Ulrich Guth Hubert Langbein 《Materials Research Bulletin》2011,46(11):1955-1962
In order to investigate the catalytic properties, V2,38Nb10,7O32,7, VNb9O25 and solid solutions of V2O5 in TT-Nb2O5 were prepared by thermal decomposition of freeze-dried oxalate precursors. The samples were characterised by X-ray diffraction and surface area determination. The crystalline samples are capable of the intercalation of sodium and lithium ions from solution. Above a temperature of about 500 °C, in dependence on the oxygen partial pressure a reversible release and uptake of oxygen without a structural variation takes place. The catalytic properties have been evaluated for the oxidative dehydrogenation (ODH) of propane and propene. There are only small differences in the catalytic activity of the different crystalline samples. Because of the relative high starting temperature, a selective catalytic oxidation of propane to propene is hardly observed. 相似文献
3.
Tsveta Mandzhukova Jean-Louis Bobet Maria Khrussanova Pavel Peshev 《Materials Research Bulletin》2009,44(10):1968-1972
The effect of the mechanical activation medium on the hydrogen absorption–desorption properties of MgH2 with NiCo2O4 additives is investigated. The composite 90 wt.% MgH2–10 wt.% NiCo2O4 mechanically activated for 180 min under hydrogen reaches a higher absorption capacity as compared to the composite ground for the same time in an argon medium. At T = 573 K and P = 1 MPa the composite activated mechanically in a reactive medium shows a value of 5.67 wt.% while for the composite ground under argon the value is 4.36 wt.% only, both samples preserving a high absorption capacity at temperatures below 573 K. Addition of nickel cobaltite is found to have a favorable effect on the hydriding kinetics of magnesium. In order to elucidate this effect, a composite containing a large amount of NiCo2O4 (50 wt.%) is also investigated. 相似文献
4.
Stoichiometric lead magnesium niobate, Pb(Mg1/3Nb2/3)O3 (PMN), perovskite ceramics produced by reaction-sintering process were investigated. Without calcination, a mixture of PbO, Nb2O5, and Mg(NO3)2 was pressed and sintered directly. Stoichiometric PMN ceramics of 100% perovskite phase were obtained for 1, 2, and 4 h sintering at 1250 and 1270 °C. PMN ceramics with density 8.09 g/cm3 (99.5% of theoretical density 8.13 g/cm3) and Kmax 19,900 under 1 kHz were obtained. 相似文献
5.
New quenched-in fluorite-type materials with composition (BiO1.5)0.94−x(LaO1.5)0.06(PbO)x, x = 0.02, 0.03, 0.04 and 0.05, were synthesised by solid state reaction. The new materials undergo a number of phase transformations during heating between room temperature and 750 °C, as indicated by differential thermal analysis. Variable temperature X-ray diffraction performed on the material (BiO1.5)0.92(LaO1.5)0.06(PbO)0.02 revealed that the quenched-in fcc fluorite-type material first undergoes a transformation to a β-Bi2O3-type tetragonal phase around 400 °C. In the range 450-700 °C, α-Bi2O3-type monoclinic, Bi12PbO19-type bcc and β1/β2-type rhombohedral phases, and what appeared to be a ?-type monoclinic phase, were observed, before a single-phase fluorite-type material was regained at 750 °C. 相似文献
6.
K. Yasuda 《Materials Research Bulletin》2010,45(9):1278-11034
Pt/CeO2-ZrO2-Bi2O3 catalysts for catalytic combustion of acetaldehyde, which is one of volatile organic compounds (VOCs), were prepared by a wet impregnation method in the presence of polyvinylpyrrolidone K25 (PVP). The addition of PVP in the preparation process was effective to enhance the specific surface area and the Pt2+ ratio on the surface. Additionally, the pore volume and size of the catalysts were modified by the PVP addition. The Pt/CeO2-ZrO2-Bi2O3 catalysts are specific for the total acetaldehyde oxidation and CO and any acetaldehyde-derivative compounds were not observed as by-products. The catalytic activity of the Pt/CeO2-ZrO2-Bi2O3 catalysts was significantly promoted by the PVP addition and the total oxidation temperature decreased. By the optimization of the amount of platinum, the complete oxidation of acetaldehyde was realized at a temperature as low as 140 °C on a 10 wt%Pt/CeO2-ZrO2-Bi2O3 catalyst. 相似文献
7.
Brendan J. Kennedy Paul J. Saines Chiharu Minakata Kenichi Kato 《Materials Research Bulletin》2007,42(11):1875-1880
The structure of the cation-ordered double perovskite Ba2HoTaO6 was examined using synchrotron X-ray powder diffraction at fine temperature intervals over the range of 90-300 K. Ba2HoTaO6 has a cubic structure in space group at room temperature. A proper ferroelastic phase transition to I4/m tetragonal symmetry occurs near approximately 260 K. Analysis of the spontaneous tetragonal strain versus temperature indicated that the phase transition is second order in nature. 相似文献
8.
La modified Pb(Mg1/2W1/2)O3 were prepared by solid-state reaction process, and the sintering behavior, microstructure and microwave dielectric properties were investigated by X-ray powder diffraction (XRD), Raman scattering and HP network analyzer in this paper. A series of single phase perovskite type solid solutions with A-site vacancies (Pb1−3x/2Lax(Mg1/2W1/2)O3 (0 ≤ x ≤ 2/3)) were formed. The solid solution took cubic perovskite type structure (Fm3m) with random distribution of A-site vacancies when 0 < x < 0.5, and tetragonal or orthorhombic structure with the ordering of A-site vacancies when 0.5 ≤ x ≤ 2/3. The dielectric constant and temperature coefficient of resonant frequency decrease with increasing La content. Relatively good combination microwave dielectric properties were obtained for x = 0.56: ?r = 28.7; Q × f = 18098; and τf = −5.8 ppm/°C. 相似文献
9.
Bi2YVO8 was prepared by solid-state reaction for the first time. The structural and photocatalytic properties of Bi2YVO8 were studied. The results showed that this compound has the tetragonal crystal system with space group I4/mmm. The band gap of Bi2YVO8 was estimated to be about 2.09 eV by plotting (αhν)2 versus hν and obtaining the hν axis intercept value according to Tauc's equation. For the photocatalytic water splitting reaction, H2 or O2 evolution was observed from pure water with Bi2YVO8 as the photocatalyst under ultraviolet light irradiation (wavelength = 390 nm). Degradation of aqueous methylene blue photocatalyzed by this compound was investigated under visible light irradiation. Bi2YVO8 showed higher photocatalytic activity compared to Bi2YTaO7, Bi2InTaO7 or TiO2 (P-25). Complete removal of aqueous methylene blue was achieved after visible light irradiation for 170 min. The decrease of the total organic carbon and the formation of inorganic products such as SO42− and NO3− revealed the continuous mineralization of aqueous methylene blue during photocatalytic reaction. 相似文献
10.
Kiyoshi Okada Tomoki Yanagisawa Yoshikazu Kameshima Akira Nakajima 《Materials Research Bulletin》2007,42(11):1921-1929
TiO3 powders were prepared by acid treatment of BaTiO3 and their properties were investigated. The BaTiO3 powder was subjected to HNO3 in concentrations ranging from 10−3 to 8 M at 90 °C for 0.5-6 h. Dissolution of BaTiO3 and precipitation of TiO2 occurred at acid concentrations of 2-5 M. BaTiO3 dissolves completely to form a clear solution at reaction times of 0.5-1 h, but a rutile precipitate is formed after 2 h of acid treatment. By contrast, anatase is precipitated by adjusting the pH of the clear solution to 2-3 using NaOH or NH4OH solution. The rutile crystals were small and rod-shaped, consisting of many small coherent domains connected by grain boundaries with small inclination angles and edge dislocations, giving them a high specific surface area (SBET). With increasing HNO3 concentration, the SBET value increased from 100 to 170 m2/g while the crystallite size decreased from 25 to 11 nm. The anatase crystals obtained here were very small equi-axial particles with a smaller crystallite size than the rutile and SBET values of about 270 m2/g (higher than the rutile samples). The photocatalytic activity of these TiO2 was determined from the decomposition rate of Methylene Blue under ultraviolet irradiation. Higher decomposition rates were obtained with larger crystallite sizes resulting from heat treatment. The maximum decomposition rates were obtained in samples heated at 500-600 °C. The photocatalytic activity of the TiO2 was found to depend more strongly on the sample crystallite size than on SBET. 相似文献
11.
Synchrotron powder diffraction has been used to examine the crystal structure of the TiF3 between 20 and 450 K with emphasis on the cubic to rhombohedral structural phase transition near 370 K. This transition involves an apparently continuous reduction in the tilts of the TiF6 octahedra. A remarkable difference in the thermal expansion coefficients in the two phases is observed. 相似文献
12.
Marko Hrovat Tadej Rojac Andreja Ben?an Janez Holc Marija Kosec 《Materials Research Bulletin》2004,39(11):1723-1728
The subsolidus phase equilibria in air for the Al2O3-CeO2-PbO and Al2O3-CeO2-RuO2 systems were studied with the aim of obtaining information on possible interactions between a CeO2-based solid electrolyte in solid-oxide fuel cells (SOFCs) and other oxides. No ternary compound was found in either of the systems. The tie line in the Al2O3-PbO-CeO2 system is between Al2Pb2O5 and the CeO2. 相似文献
13.
In order to obtain CO2-absorbents to eliminate CO2 concentration locally, Bi2O3-La2O3 mixed powders were prepared by mechanical alloying (MA) method using a planetary ball-milling machine. CO2-absorption and desorption properties were checked by TG-DTA for the obtained powder samples. As a result, the sample shown by (Bi2O3)1−x(La2O3)x [x≤0.50] was found to form α-Bi2O3-solid solution with repeated CO2-adsorption and desorption around 400- 500 °C. Absorbed and desorbed CO2 contents varied with MA time: the 72 h MA’ed sample had a larger CO2 content than the 24 h MA’ed sample. The performance depended on the sample composition, and (Bi2O3)0.70(La2O3)0.30 was found to have the highest performance in the present system. 相似文献
14.
Nanorod alumina-supported Ni-Zr-Fe/Al2O3 catalysts were prepared by co-impregnation, characterized by TEM, TPR, XRD, XPS, and TPD-pyridine, and tested in auto-thermal reforming of ethanol. The characterization results indicate that, with iron and zirconia promotion, the NixFe1−xAl2O4 mixture spinel forms, the valence of the surface Ni species is modified, and the acidity decreases. As a result, during a 30-h test over the Ni-Zr-Fe/Al2O3 catalyst, sintering is restrained, and the selectivity to hydrogen remains around 85.79% without obvious loss, while the un-promoted Ni/Al2O3 shows poor stability and selectivity. 相似文献
15.
The perovskite solid solution composition Sr(Ti0.5Zr0.5)O3 (STZ (ss)) has been synthesized from the mixture of SrCO3, TiO2 and ZrO2 powders through solid-state reaction. The phase formation mechanism and kinetics were investigated using TG/DSC, XRD. SrCO3 in the precursor decomposes at relatively lower temperature than pure powder decomposition, due to the presence of acidic TiO2. Upon calcinations of the precursor SrTiO3 (ST) and SrZrO3 (SZ) were formed separately in the system. Then ST defuses in to SZ to form STZ (ss). ST formation started at lower temperature (800 °C) with lower activation energy (47.274 kcal/mol) than SZ. SZ formation started at 1000 °C with high activation energy (65.78 kcal/mol). STZ (ss) formation started from 1500 °C with very high activation energy (297.52 kcal/mol). It is concluded that solid solution formed coherently with SZ lattice by the diffusion of Ti in to the SZ. 相似文献
16.
Chun Huy Wang 《Materials Research Bulletin》2004,39(6):851-858
In this work, the piezoelectric ceramic system of Pb[(Zr1−xTix)0.74(Mg1/3Nb2/3)0.20(Zn1/3Nb2/3)0.06]O3, 0.47≤x≤0.57, with composition close to the morphotropic phase boundary, was studied. From the results of X-ray diffraction and piezoelectric measurement, ceramics near x=0.51 were found at the morphotropic phase boundary (MPB) between the tetragonal and pseudocubic perovskite. The planar coupling factor (kp=0.72) is high at compositions near the MPB, but the mechanical quality factor (Qm=75) is low. The calculation of the diffuseness of phase transition shows that the region of phase coexistence of this system is broader than that of the ternary system. 相似文献
17.
A new phase diagram is reported for the CaOAl2O3SiO2H2O (CASH) system at 200 °C. This system is rare in nature but has applications in cementing geothermal and deep oil wells. The phase diagram was constructed by synthesising a range of hydroceramics with CASH assemblages from oilwell cement, silica flour (quartz) and alumina (corundum). A hydroceramic is defined as any ceramic material incorporating water as H2O or OH. At 200 °C, gyrolite, hillebrandite, jaffeite, portlandite, quartz, 11 Å tobermorite, xonotlite, hibschite and katoite were observed as product phases. The mineral assemblages produced the following three-phase triangles in the CaOAl2O3SiO2 diagram: Gyr + Qtz + Xon; Crn + Tob + Xon; Crn + Hib + Xon; Crn + Hib + Jaf; Crn + Jaf + Kat; Hib + Jaf + Por; Hib + Jaf + Xon; and two reactions are found to be in progress at 200 °C. When alumina is present in the reaction mixture, the thermal stability of tobermorite is extended to higher temperature, and the crystallinity of tobermorite and xonotlite enhanced. 相似文献
18.
R.V.K. Mangalam 《Materials Research Bulletin》2009,44(3):576-36
The ferromagnetic metallic oxide, SrRuO3 (TC ∼ 165 K) undergoes structural, magnetic and metal-insulator transitions upon substitution of Cu at the Ru-site. For x = 0.2 in SrRu1−xCuxO3, the structure becomes a tetragonal with the space group I4/mcm and there is a signature of both ferromagnetic (TC = 65 K) and antiferromagnetic (TN = 32 K) ordering due to possible magnetic phase separation. The antiferromagnetism arises due to short range ordering of Cu- and Ru-moments. Jahn-Teller distortion of (Ru,Cu)-O6 octahedra indicates that the copper ions are in 2+ oxidation state with 6t2g3eg electronic configuration. For x ≥ 0.1, narrowing of Ru-4d bandwidth by the substitution of Cu ions results in semiconducting behavior. For x = 0.3, the ac and dc susceptibility measurements indicate a spin glass behavior. The origin of spin glass behavior has been attributed to competing ferromagnetic and antiferromagnetic interactions. 相似文献
19.
Marko Hrovat Andreja Ben?an Janez Holc Tadej Rojac Marija Kosec 《Materials Research Bulletin》2011,46(1):98-100
Subsolidus equilibria in air in the RuO2-Bi2O3-ZrO2 system were studied with the aim of obtaining information on possible interactions between a Bi2Ru2O7-based cathode and a ZrO2-based solid electrolyte in solid-oxide fuel cells (SOFCs). No ternary compound was found in the system. The tie lines are between Bi2Ru2O7 and ZrO2, and between Bi2Ru2O7 and gamma-Bi2O3—the ZrO2 stabilised Bi2O3 phase, stable at temperatures over 710 °C. 相似文献