Dependency of thermal and electrical conductivity on temperature and composition of Sn in Pb–Sn alloys

The variations of thermal conductivity with temperature for Pb–Sn alloys were measured using a radial heat flow apparatus. The variations of electrical conductivity with the temperature for same alloys were determined from the Wiedemann–Franz law by using the measured values of thermal conductivity. According to present experimental results, the thermal and electrical conductivity of Pb–Sn alloys linearly decrease with increasing temperature but exponentially increase with increasing the composition of Sn. The enthalpy of fusion and the change of specific heat for Pb–Sn alloys were also determined by means of differential scanning calorimeter (DSC) from heating trace during the transformation from eutectic liquid to eutectic solid.     

Pt–Sn/Al2O3 catalyst for the selective hydrodeoxygenation of esters

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The density and surface tension of In–Sn and Cu–In–Sn alloys

Abstract  

The density and surface tension of binary In–Sn and ternary Cu–In–Sn alloys have been measured by a sessile-drop method. Decrease of the density and of the surface tension was observed with rising temperature. With increased Sn content in the alloys, the density increased while the surface tension reduced slightly. Addition of Cu could significantly increase the density and surface tension in the Cu–In–Sn system. The surface tension of the Cu–In–Sn alloys was also calculated by means of Butler’s equation, and compared with experimental values, showing good agreement.     

Synthesis and structure of tin tetrachloride adducts with crown ether: Crystal structure of [Sn(H2O)2Cl4] · 18C6 and [Sn(H2O)2Cl4] · 18C6 · 2H2O

Tin coordination compounds [Sn(H₂O)₂Cl₄] · 18C6 (I) and [Sn(H₂O)₂Cl₄] · 18C6 · 2H₂O (II) were synthesized and identified by IR spectroscopy, CH analysis, and X-ray powder diffraction. The crystal structures of compounds I and II were determined. The crystals of I and II are orthorhombic; a = 16.871(1) ?, b = 7.7305(7) ?, c = 16.939(1) ?, Z = 4, space group Cmca for I; a = 14.206(2) ?, b = 20.376(3) ?, c = 8.319(1) A, Z = 4, space group Pna21 for II. The structural units of I and II are [Sn(H₂O)₂Cl₄] · 18C6 complex molecules (in II, also water molecules of crystallization). The coordinated water molecules in I are trans and those in II are cis to each other. The structural units in the crystals of I and II are combined only by hydrogen bonds between water molecules and the crown-ether oxygen atoms with the formation of the chain structure. Complex I was tested as the precursor of tin dioxide in a chemical vapor deposition (CVD) process. The morphology of the obtained film was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and the composition was studied by laser mass spectrometry for elemental analysis.     

Preparation and Double-Helix Icosahedra Structure of δ-Co2Zn15

The first known example of a regular face-sharing icosahedra helix is presented in the novel crystal structure of δ-Co₂Zn₁₅, solved and refined from single-crystal X-ray and neutron powder diffraction data. The compound δ-Co₂Zn₁₅ is also the first example of an intermetallic compound crystallizing in the acentric hexagonal space group P6₂. The parameters from the single crystal refinement are a=11.292(2) Å, c=7.750(1) Å, Z=4, and R_w=0.025.     

Preparation and Characterization of Storage and Emission Functional Material of Cs2O-doped 12CaO·7Al2O3

We provides a novel approach to generate low-temperature atomic oxygen anions (O^-) emis-sion using the cesium oxide-doped 12CaO·7Al₂O₃ (Cs₂O-doped C12A7). The maximal emis-sion intensity of O^- from the Cs₂O-doped C12A7 at 700 oC and 800 V/cm reached about 0.54 μA/cm², which was about two times as strong as that from the un-doped C12A7(0.23 μA/cm²) under the same condition. The initiative temperature of the O^- emission from the Cs₂O-doped C12A7 was about 500 oC, which was also much lower than the initiative temperature from the un-doped C12A7 (570 oC) in the given field of 800 V/cm. High pure O^- emission close to 100% could be obtained from the Cs₂O-doped C12A7 under the lower temperature (<550oC). The emission features of the Cs₂-doped C12A7, including the emis-sion distribution, temperature effect, and emission branching ratio have been investigated in detail and compared with the un-doped C12A7. The structure and storage characteristics of the resulting material were also investigated via X-ray diffraction and electron paramag-netic resonance. It was found that doping Cs₂ to C12A7 will lower the initiative emission temperature and enhance the emission intensity.     

Temperature and Oxygen Partial Pressure Dependences of the Surface Tension of Liquid Sn–Ag and Sn–Cu Lead-free Solder Alloys

Summary. Temperature dependence of the surface tension of liquid Sn–Ag and Sn–Cu base lead-free solder alloys and oxygen partial pressure dependence of liquid Sn–Ag alloy were evaluated using the experimental data obtained, respectively, by the constrained drop method and the sessile drop method in the previous studies [1, 2]. The temperature dependences of the surface tension have maximum positive values when the mol fraction of Ag and Cu is about 0.7, while those for pure liquid Sn, Ag, and Cu have negative values. The calculated values based on Butler’s equations were found to be in reasonable agreement with those of the experimental data. The oxygen partial pressure dependences of the surface tension of liquid Sn–Ag alloys at 1253 K have a minimum value when the mol fraction of Ag is about 0.9 and the oxygen partial pressure is less than about 10⁻¹³ atm. From this, it is considered that the oxygen adsorption increased by adding Ag to Sn when the mol fraction of Ag is less than 0.9.     

Static atomic displacements of Sn in disordered NiAs/Ni2In type HT-Ni1+δSn

The crystal structures of the intermediate solid solution HT (high temperature) Ni_1+δSn with δ=0.28, 0.52 and 0.61 (refined Ni contents) have been analyzed in detail by X-ray diffraction on single crystals. The previously reported basic atomic arrangement, i.e., a NiAs/Ni₂In structure type (P6₃/mmc, Ni(1) on 2a, 0 0 0, Ni(2) with an occupancy δ on 2d, and Sn on 2c, ), is confirmed. However, strong anisotropic atomic displacements occur for Sn within the a-b plane of the hexagonal unit cell, which require a Gram-Charlier expansion of the probability density function of Sn in order to obtain a good fit to the diffraction data. Direction, magnitude and the concentration dependence of the displacements can be interpreted in terms of the geometrical requirements of the different local atomic configurations in the planes z=±1/4, so that the displacements can be identified as static ones.     

Sn and Y co-doped BaCo0.6Fe0.4O3-δ cathodes with enhanced oxygen reduction activity and CO2 tolerance for solid oxide fuel cells

Applying mixed oxygen ionic and electronic conducting（MIEC） oxides as the cathode offers a promising solution to enhance the performance of solid oxide fuel cells（SOFCs）. However, the phase instability in CO₂-containing air and sluggish oxygen reduction activity of MIEC cathodes remain a long-term challenge for optimizing the electrochemical performance of SOFCs. Herein, a heterovalent co-doping strategy is proposed to enhance the oxygen reduction activity and CO₂ tolerance...     

Synthesis and characterization of dinuclear p-, m- and o-xylyl bridged complexes of molybdenum and tungsten. The crystal structures of μ-p-xylyl- bis(η-pentamethyl-cyclopentadienyltri- carbonylmolybdenum) and μ-m-xylyl-bis(η- pentamethylcyclopentadienyltricarbonyltungsten)

The reactions of (M = Mo, W) with α,α′-p-, m- and o-dichloro-xylenes yielded p-, m- and o-xylyl bridged dinuclear complexes of in high yields. All of such new complexes are stable to air and water, even stable in dilute acids and bases.     

Effect of oxygen non-stoichiometry on the structural and magnetotransport properties of LaMn0.85Cr0.15O3+δ

Thermogravimetry, X-ray diffraction (XRD), d.c. magnetization, high-temperature susceptibility and electrical resistivity measurements were performed for LaMn_0.85Cr_0.15O_3+δ perovskites with accurate control of the oxygen content (0?δ?0.11). For 0?δ<0.09, three orthorhombic structures (Pnma) are found: for 0?δ<0.045, the O′ phase (b/√2<c<a), for 0.045?δ<0.06, the O″ (b/√2<a<c) and for 0.06?δ<0.09, the O^? (a<b/√2<c). For 0.09?δ?0.11, a rhombohedral symmetry coexists with O^? in a biphasic field. Magnetic measurements revealed the ferromagnetic interactions (FM) character of the Mn³⁺-O-Cr³⁺ interaction, but also the intricate magnetic phase diagram due to the presence of multiple interactions (Mn^3+,4+-O-Mn^3+,4+, Cr³⁺-O-Mn³⁺, etc.). The comparison of the results for LaMn_0.85Cr_0.15O_3+δ with those of LaMn_0.9Cr_0.1O_3+δ allows discuss the role of Cr³⁺ on the structural, magnetic and magnetotransport properties of the LaMn_1−xCr_xO_3+δ perovskites.     

Stability and oxygen-storage characteristics of Al-substituted YBaCo4O7+δ

A series of Al-substituted YBa(Co_1−xAl_x)₄O_7+δ samples was synthesized and characterized with respect to the capability to store large amounts of oxygen at low temperatures (at 200-400 °C) and the phase decomposition upon heating under oxidizing conditions at higher temperatures (above 550 °C). It was revealed that increasing the Al-substitution level up to x≈0.10 boosts up the phase-decomposition temperature from ∼550 to ∼700 °C, while the unique oxygen absorption/desorption characteristics remain nearly the same as those of the pristine YBaCo₄O_7+δ phase. The maximum amount of excess oxygen absorbed by the Al-substituted YBa(Co_1−xAl_x)₄O_7+δ samples was determined to be as large as δ≈1.45 for x=0.10 (in 100 atm O₂ at 320 °C). Isothermal annealing experiments carried out for the same x=0.10 phase at 300 °C revealed that it could be reversibly charged and discharged with 1.2 oxygen atoms per formula unit by switching the gas flow from N₂ to O₂ and vice versa.     

Theoretical study of the energies and activation barriers of elementary reactions of hydrogenation of the Ti-doped closo-aluminide cluster Al@TiAl11 and its anion Al@TiAl 11?

The potential energy surfaces, energies E, and activation barriers h of elementary reactions of addition of an H₂ molecule to the Ti-doped closo-aluminide cluster Al@TiAl₁₁ and its anion Al@Ti₁₁⁻ with an icosahedral and marquee structure in the states with different multiplicity were calculated within the B3LYP approximation of the density functional theory using the 6–31G* and 6–311+G* basis sets. The results were compared with the data calculated at the same level of theory for the related reactions of hydrogenation of bare closo-aluminides Al₁₃ and Al₁₃⁻ and their B-, C-, Si-, and Ge-doped derivatives. The computations demonstrated that, depending on the structure, charge, and multiplicity of the Al@TiAl₁₁ cluster, the hydrogenation energy varies in the range 15–23 kcal/mol. At the first stage of addition (chemisorption) of H₂, a μ-H₂ complex at the Ti atom (intermediate) forms with the distance R(Ti-H₂) ∼ 1.9–2.0 ?, which is accompanied by an energy decrease of ∼4–10 kcal/mol. The H-H bond in the μ-H₂ complex is ∼0.1 ? longer and the stretching vibration frequency V_val(HH) is ∼700–1500 cm⁻¹ (or more) lower than the corresponding characteristics of the isolated H₂ molecule. In the transition state with an imaginary frequency of ∼600i–1100i, the H₂ molecule is coordinated to the attacked edge Ti-Al_r, and its length increases to ∼0.9–1.1 ?. The activation barrier height h varies from a few kcal/mol to ∼8–10 kcal/mol when measured from the μ-H₂ complex and is within 18–22 kcal/mol when measured from the product (dihydride Al@TiAl₁₁H₂). The latter barrier (to the reverse reaction of dehydrogenation) is considerably higher than the barriers to migration of hydrogen atoms around the metal cage in the Al@TiAl₁₁H₂ dehydrides. There is a correlation between the energies E and barriers h of hydrogenation reactions and the structure, external charge, and multiplicity of the Al@TiAl₁₁ cluster. In all cases, the hydrogenation should occur significantly more readily than dehydrogenation. It was shown that these reactions can be both irreversible (for example, for an icosahedron in the singlet state) and reversible (for a marquee in the triplet state and others). The conclusion was drawn that the elementary reactions of hydrogenation and dehydrogenation for Ti-doped aluminides should occur considerably faster and under milder conditions than for bare aluminides or their analogues doped with main-group atoms. Original Russian Text ? V.K. Charkin, O.P. Kochnev, N.M. Klimenko, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 8, pp. 1345–1354.     

Enthalpies of solution and standard enthalpy of formation of crystalline NaVO3 · 2H2O

The enthalpies of solution of sodium metavanadate dihydrate in aqueous solutions of sodium perchlorate at ionic strength I = 0.3, 0.5, and 1.0 mol/L were calorimetrically measured at 298.15 K. The resulting experimental data were used to calculate the standard enthalpy of formation of crystalline NaVO₃ · 2H₂O.     

High resolution and in situ neutron powder diffraction study of the crystal structure and the stability of Ba4CaCu3O8+δ

The crystal structure and stability of Ba₄CaCu₃O_8+δ have been investigated by neutron powder diffraction, differential thermal analysis and thermogravimetry. It is found that the phase is not stable below 1065 K in p(O₂)=1 bar and decomposes according to the eutectoid reaction Ba₄CaCu₃O_8+δ+x O₂⇒Ba₂CuO_3.4+CaO+2BaCuO₂. However, the equilibrium with the outer gas is not reached for sintered ceramics so that Ba₄CaCu₃O_8+δ can be obtained in a metastable state after normal cooling conditions. In this case, the crystal structure is cubic (Im-3m, , δ=0.68, Z=2, R_wp=2.5%, R_Bragg=5.4%) as reported in the literature. In reduced oxygen partial pressure (p(O₂)<10⁻⁶ bar), Ba₄CaCu₃O_8+δ is stable down to room temperature and has a tetragonal structure with a significant lower oxygen content (P4/mmm, , , δ=-0.81, Z=2, R_wp=2.8%, R_Bragg=5.1%). The difference between the two crystal structures is discussed in terms of oxygen content, copper formal valence and cation coordination. The influence of the oxygen pressure on the stability of Ba₄CaCu₃O_8+δ is also discussed.     

Role of support nature （γ-Al2O3 and SiO2-Al2O3） on the performances of rhenium oxide catalysts in the metathesis of ethylene and 2-pentene

The metathesis of ethylene and 2-pentene was studied as an alternative route for propylene production over Re2O7/γ-Al2O3 and Re2O7/SiO2-Al2O3 catalysts. Both NH3 temperature-programmed desorption (NH3-TPD) and H2 temperature-programmed reduction (H2-TPR) results showed that Re2O7/SiO2-Al2O3 exhibited stronger acidity and weaker metal-support interaction than Re2O7/γ-Al2O3. At 35 60℃, isomerization free metathesis was observed only over Re2O7/γ-Al2O3, suggesting that the formation of metal-carbene metathesis active sites required only weak acidity. Our results suggest that on the Re2O7/SiO2-Al2O3, hydrido-rhenium species ([Re]-H) were formed in addition to the metathesis active sites, resulting in the isomerization of the initial 1-butene product into 2-butenes. A subsequent secondary metathesis reaction between these 2-butenes and the excess ethylene could explain the enhanced yields of propylene observed. The results demonstrate the potential for high yield of propylene from alternative feedstocks.     

Synthesis and Crystal Structure of Novel Mixed-metal Alkoxide Clusters of Ytterbium and Sodium: Yb4O4（OiPr）16Na12

The mixed-metal cluster Yb4O4(OiPr)16Na12 has been synthesized and structurally determined by IR, elemental analysis, and single-crystal X-ray diffraction. The crystal belongs to the cubic system, space group P23 with a = b = c = 13.9788(3), V = 2731.55(10)3 , Z = 1, Dc = 1.202 g/cm 3 , Mr = 1977.42, = 3.480 mm-1 , F(000) = 972, the final R = 0.0288 and wR = 0.1511 for 1677 observed reflections with Ⅰ > 2σ(Ⅰ). X-ray analysis reveals that Yb4O4 (OiPr)16Na12 is centrosym-metric and the structure contains four ytterbium metals and twelve sodium metals, and each ytterbium atom is coordinated by six oxygen atoms. In addition, an ancillary computational analysis of the optimized molecular unit was provided. The large energy gap (3.31 eV) between HOMO and LUMO indicates that the structure framework is particularly stable.     

Catalytic performance in hydrodesulfurization of thiophene and ir investigation of Co and no adsorption over Co?Mo/Al2O3 and Ru?Co?Mo/Al2O3 catalysts

A new Ru–Co–Mo/Al₂O₃ catalyst has been prepared by impregnation of Ru salt as a secondary promoter onto Co–Mo/Al₂O₃ catalyst, and it was found that the Ru–Co–Mo/Al₂O₃ exhibited higher activity than Co–Mo/Al₂O₃ in hydrodesulfurization of thiophene to hydrocarbons. Ir studies on Ru–Co–Mo/Al₂O₃ revealed that the Co and NO adspecies increased significantly in intesnities and displayed a bathochromic shift in frequencies, as compared with Co–Mo/Al₂O₃.

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Ru–Co–Mo/Al₂O₃ Ru, , Co–Mo/Al₂O₃. Co–Mo/Al₂O₃. CO NO, Co Mo, Co–Mo/Al₂O₃. , Mo , Mo³⁺ Mo³⁺ Co Ru–Co–Mo/Al₂O₃.

     

Calorimetric study and thermal analysis of Al–Sn system

The results of calorimetric study and thermal analysis of binary Al–Sn system are presented in this paper. The Oelsen calorimetry was used in thermodynamic analysis. Following thermodynamic properties were determined at 727 °C: activities, activity coefficients, partial/integral molar Gibbs excess, and mixing energies. The energetics of mixing in liquid Al–Sn alloys has been analyzed through the study of concentration fluctuation in the long-wavelength limit. Thermal analysis of selected alloys in Al–Sn system was done using differential thermal analysis. Defined characteristic phase transition temperatures were used for comparison with calculated phase diagram of investigated system. Good agreement with available literature data was obtained. Structural analysis of selected alloys was done using optic microscopy.