Permeability of hydrogen in amorphous Pd(1−x)Six alloys at elevated temperatures

Hydrogen permeabilities of amorphous Pd_(1−x)Si_x (x=0.15, 0.175, 0.2) alloys in the form of ribbon, which were prepared with a single roller spinning technique, were measured at elevated temperatures up to 390°C. It was found that the hydrogen permeability of the amorphous alloys, strongly depending on the Si content, decreased with an increase in the Si content. The amorphous alloys possessed 3–5 times higher hydrogen permeability than the corresponding crystallized ones. The pressure dependence of hydrogen permeability in the amorphous alloys could be described by the simple n-th power equation, which was derived in this study.     

Effect the conditions of the acid–thermal modification of clinoptilolite have on the catalytic properties of palladium–copper complexes anchored on it in the reaction of carbon monoxide oxidation

The dependence of the physicochemical and structural–adsorption properties of natural and acid–thermal modified clinoptilolite, and of Pd(II)–Cu(II) catalysts based on them, on the duration of acid–thermal modification is investigated. The samples under study are described via XRD and thermal gravimetric (DTG and DTA) analysis, IR, DR UV–Vis, EPR spectroscopy, and water vapor adsorption. Values of both the specific surface area (S_sp) and pH of aqueous suspensions are determined. The resulting catalysts are tested in the reaction of low-temperature carbon monoxide oxidation with air oxygen. A conclusion is drawn about the nature of surface bimetallic Pd(II)–Cu(II) complexes. The greatest catalytic activity is shown by complexes based on clinoptilolite and modified with 3 M HNO₃ for 0.5 and 1 h.     

Simulating infrared spectra and hydrogen bonding in cellulose Iβ at elevated temperatures

We have modeled the transformation of cellulose Iβ to a high temperature (550 K) structure, which is considered to be the first step in cellulose pyrolysis. We have performed molecular dynamics simulations at constant pressure using the GROMOS 45a4 united atom forcefield. To test the forcefield, we computed the density, thermal expansion coefficient, total dipole moment, and dielectric constant of cellulose Iβ, finding broad agreement with experimental results. We computed infrared (IR) spectra of cellulose Iβ over the range 300-550 K as a probe of hydrogen bonding. Computed IR spectra were found to agree semi-quantitatively with experiment, especially in the O-H stretching region. We assigned O-H stretches using a novel synthesis of normal mode analysis and power spectrum methods. Simulated IR spectra at elevated temperatures suggest a structural transformation above 450 K, a result in agreement with experimental IR results. The low-temperature (300-400 K) structure of cellulose Iβ is dominated by intrachain hydrogen bonds, whereas in the high-temperature structure (450-550 K), many of these transform to longer, weaker interchain hydrogen bonds. A three-dimensional hydrogen bonding network emerges at high temperatures due to formation of new interchain hydrogen bonds, which may explain the stability of the cellulose structure at such high temperatures.     

Effect of copper addition on glass transition of silicate–phosphate glasses

Glass transformation effect of mixed SiO₂?CP₂O₅?CK₂O?CMgO?CCaO?CCuO glasses was studied by DSC, XRD, SEM, and Raman spectroscopy methods. The relationship between the parameters characterizing glass transformation effect and an amount of phosphorous and copper forming the glassy structure was discussed. It was shown that an increasing content of phosphorous increased solubility of copper in the structure of the studied glasses which was the result of P?CO?CCu bonds formation. Degree of changes of T _g, ?c _p, and time of relaxation values were higher in glasses with higher content of P₂O₅ and CuO. The observed relations were explained on the basis of the local atomic interactions in the structure of glass.     

Effect of hydrogen reduction temperature on the microstructure and magnetic properties of Fe–Ni powders

The effect of hydrogen reduction temperature on the properties of Fe–Ni powders was described. The mixed powders of Fe-oxide and NiO were prepared by chemical solution mixing of nitrates powders and calcination at 350 °C for 2 h in air. The calcined powders formed small agglomeration with an average particle size of 100 nm. The microstructure and magnetic properties were investigated by using X-ray diffractometry, thermogravimetry, differential thermal analyzer, and vibrating sample magnetometer. Microstructure and thermal analysis revealed that the Fe-oxide and NiO phase were changed to FeNi₃ phase in the temperature range of 245–310 °C, and by heat-up to 690 °C the FeNi₃ phase was transformed to γ-FeNi phase. The reduced powder at 350 °C showed saturation magnetization of 76.3 emu/g and coercivity of 205.5 Oe, while the reduced powders at 690 °C exhibited saturation magnetization of 84.0 emu/g and coercivity of 14.0 Oe. The change of magnetic properties was discussed by the observed microstructural features.

     

Thermodynamic properties of liquid copper–lanthanum alloys

Mixing enthalpies of alloys in the Cu–La system are measured using isoperibolic calorimetry method over the ranges 0 < x _La < 0.185 at 1400–1430 K and 0.659 < x _La < 1 at 1370 K. They have moderate exothermic values over the whole concentration range and agree with literature data. Activities of the components, enthalpies and entropies of formation of intermetallics in this system, and its phase diagram are optimized using an ideal associated solution (IAS) model, and agree with most literature data. The updated thermodynamic properties can be used in further investigation of multicomponent systems based on the binary Cu–La.     

Effect of substituents on the solubilities of alkyl-substituted β-diketone copper chelates

The solubilities of alkyl-substituted β-diketone copper chelates were measured in a number of common organic solvents and an aqueous solution, in order to establish the effect of substituents. Using these data and the respective molar volumes of the chelate, the solubility parameters were calculated. The molar volumes for the chelates were in direct proportionality to the additional carbon atoms in the molecule and the solubility parameters were proportional to the reciprocal of them. The constancy of the calculated values was taken as evidence of the adequacy of the regular solution concept for explaining the observed solubility trends in the solvents studied. The distribution coefficients which can be calculated on the basis of the solubility parameter and the molar volume of copper chelates were in fair agreement with those obtained by an extraction method. The higher the solubilities of the chelates were in the organic solvent, the higher the distribution coefficients of the chelates were also. The relationship between the distribution coefficients and the solubilities of the chelates is discussed.     

Study of phase transformation temperatures of alloys based on Fe–C–Cr in high-temperature area

Three alloys based on Fe–C–Cr were studied. These alloys contained carbon in a range of 0.308–0.380 mass% and chromium 1.058–4.990 mass%. Temperatures of solidus (onward used as T_S), liquidus (onward used as T_L) and peritectic transformation (onward used as T_P) were studied in the high-temperature region. These temperatures were obtained using two thermal analysis methods: differential thermal analysis (onward used as DTA) and simple thermal analysis (onward used as TA). The Setaram Setsys 18_TM was used for experiments with employment of the DTA method. All measurements were taken in an inert atmosphere of pure argon at heating rate of 10 °C min^?1, and simple TA method was used for the experiments with the use of the Netzsch STA 449 F3 Jupiter. Measurements were taken in inert atmosphere of pure argon at a heating and cooling rate of 5 °C min^?1. Phase transformation temperatures were obtained by heating and cooling process and were approximated to “equilibrium conditions” (DTA method: zero heating rate and sample mass, standard, TA method: only standard) (?aludová et al. in J Therm Anal Calorim 112:465–471, 2013a. doi: https://doi.org/10.1007/s10973-012-2847-8; J Therm Anal Calorim 111:1203–1210, 2013b. doi: https://doi.org/10.1007/s10973-012-2346-y). The experimental data were compared and discussed with the calculation results using IDS (solidification analysis package) software (onward used as SW) Thermo-Calc and the TCFE8 (Thermo-Calc Fe-based alloys) database. The results of the two alloys were compared with those published for similar steels. The experimentally obtained transition temperatures were close to the calculated values. The solidus, liquidus and peritectic transformation temperatures were lowered with increasing carbon (range 0.308–0.380 mass%) and chromium content (range 1.058–4.990 mass%). The smallest difference between the experimental results and theoretical calculations was observed at the liquidus temperature for all alloys. Nonetheless, the difference measured for the solidus temperatures was much greater.     

Effect of structural and thermodynamic factors on the sorption of hydrogen by metal–organic framework compounds

The characteristics of the sorption of hydrogen by metal–organic framework compounds (MOF) were examined, and the structural and thermodynamic factors that favor the sorption of H₂ by such substances were determined. The effect of the structure of the MOF and the size and geometry of the pores on the sorption characteristics was analyzed. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 2, pp. 67-87, March-April, 2009.     

Activity of copper–cerium–zirconium catalysts in oxidation of hydrogen

We have studied the catalytic properties in oxidation of hydrogen for copper–cerium oxide systems deposited on supports obtained by calcination of yttrium-stabilized zirconium dioxide at 300–1000 °C. We have shown that the catalytic activity of the samples obtained depends on the specific surface area of the original supports and the amount of reduced copper within the composition of the catalyst. In samples whose support has high specific surface area, the content of reduced metallic copper is greater and the catalytic activity is higher.     

Electrochemical and electrocatalytic behaviour of platinum–palladium nanoparticle alloys

The electrochemical and electrocatalytic behaviour of Pt/Pd nanoparticles prepared in water-in-oil microemulsion was reported. The catalytic activity of the nanoparticles was studied by using the reactions of dissociative adsorption of methanol and formic acid. The use of these surface probe reactions allowed the detection of palladium at the surface of the nanoparticles. The electrochemical stability of the particles was also investigated by voltammetry and electrochemical quartz crystal microbalance (EQCM). We shown that EQCM technique may be quantitatively used to correlate mass and area modifications when the electrochemical conditions produce corrosion of the elements of the alloy.     

The surface oxidation behavior of Ni–45.16%Ti shape memory alloys at different temperatures

The isothermal oxidation behavior of Ni–45.16%Ti (composition in atomic percent) alloy was investigated by thermogravimetric analysis, and differential scanning calorimeter (DSC) methods. It was found that Ni-rich NiTi alloy exhibits a different oxidation behavior at temperatures above 400 °C in oxygen atmosphere. The alloy was exposed to oxygen atmosphere isothermally, i.e., between 400 and 800 °C, for 1 h. A gravimetric method was used to determine the oxidation kinetics and it was seen that the oxidation constant increases significantly with isothermal temperature. The activation energy of oxidation reaction for NiTi alloy was determined to be 65.47 kJ mol^?1. According to DSC measurements, the transformation temperature of alloy (M _s, M _f, A _s and A _f) was increased and also R phase disappeared above 500 °C. The formal oxides were determined by means of SEM–EDX measurements and obtained oxides are TiO and TiO₂ oxides.     

Effect of copper source on the structure–activity of CuAl2O4 spinel catalysts for CO hydrogenation

Due to the complexity of the structure–activity relationship of the CuAl₂O₄ spinel catalyst, optimization of the catalyst structure is a great challenge. In this paper, three different CuAl₂O₄ spinel catalysts were prepared by the solid-phase method using copper hydroxide, copper nitrate, and copper oxide as the copper source, respectively, to study the difference in the structure of CuAl₂O₄ spinel catalysts induced by the raw materials and the catalytic behavior for CO hydrogenation. The structure of CuAl₂O₄ spinel catalyst was characterized by XRD, BET, SEM, TEM, H₂-TPR and XPS. The activity of CO hydrogenation over the CuAl₂O₄ spinel catalyst without pre-reduction was evaluated in the slurry reactor. The results demonstrated that different copper sources had obvious influence on the CuAl₂O₄ spinel texture properties, surface enrichment degree, as well as decomposition and reduction ability, which further regulated the ratio of Cu⁺/Cu⁰ and thus affected the catalytic performance, especially the alcohol distribution. The CuAl₂O₄ spinel, employing copper hydroxide as the copper source, showed better selectivity of C₂₊OH, which was assigned to a higher ratio of Cu⁺/Cu⁰, along with larger pore size and pore volume. Moreover, the synergistic effect between Cu⁰ and γ-Al₂O₃ improved the selectivity of dimethyl ether.     

Effect of nano-Al2O3 particles and of the Co concentration on the corrosion behavior of electrodeposited Ni–Co alloys

Incorporation of nano-Al₂O₃ particles into a Ni–Co alloy by electrodeposition influences the corrosion properties, morphology, and structure of the layers. The resistance against corrosion of Ni–Co/Al₂O₃ composite films deposited on stainless steel was investigated in a 0.1-M NaCl solution by potentiodynamic polarization. The presence of nanoparticles improves the corrosion resistance of Ni–Co/nano-Al₂O₃ deposits when compared to pure Ni–Co alloy. Moreover, by increasing the pH of the electrodeposition bath and the content of Co in the alloy, the resistance against corrosion is furthermore improved. The morphology of the deposits before and after their corrosion was analyzed by scanning electron microscopy. The presence of the embedded alumina particles in the Ni–Co alloys was one of the key factors that limited further propagation of corrosion on the metallic surface. Preferential corrosion attack, in the form of a pitting corrosion, was located mainly at the grain boundaries.     

Liquid Co–Sn alloys at high temperatures: structure and physical properties

The Co–Sn system is an important subsystem for Sn-based anode materials of lithium-ion batteries. Experimental results on the physical–chemical properties of this system in the liquid state, however, are rather sparse. In this work, the atomic structure and structure-sensitive thermophysical properties (viscosity, electrical resistivity, and thermoelectric power) of liquid Co–Sn alloys were investigated in a wide temperature range with special attention to the melting-solidification region. The obtained experimental results were combined with differential thermal analysis (DTA) data in order to verify the liquidus curve in the Sn-rich part of the Co–Sn phase diagram.     

Sol–gel processing at increased temperatures: the formation of polyester nanocomposites

Polyester nanocomposites were prepared using sol–gel precursors, prehydrolyzed sols, or nanoparticles in polyester formulations. The different inorganic components were introduced in the early stages of the esterification reaction and a typical polymerization temperature program was applied leading to temperatures up to 240 °C at low pressures. The structural and physical properties of the final materials depend on the applied method for the introduction of the sol–gel materials. Silicon atoms were incorporated into the polyester chain if silicon tetraalkoxide was used as precursor. The silicon atoms represent branching points in the polymer structure. Prehydrolyzed sols that were prepared under acidic conditions were another source of silicon and formed larger inorganic aggregates in the polymer matrix. Nanoparticles prepared via the Stöber process were the third inorganic species in polyester formation. All three processing pathways produced different kinds of materials depending on the type of silica incorporated in the polyester networks but also with regard to the nanoscale structure of the materials. Both, composition and structure have a major influence on the final polyester nanocomposite properties. Model reactions between silicon tetraalkoxides and diols or diacids using the temperature program for the polyester formation showed that exchange reactions of the alkoxides and the alcohols or acids can occur and the obtained products can carry out side reactions in the polyester formation. The final materials show a homogeneous distribution of the silicon containing moieties in the polyester matrix. The viscosities and the branching degrees of the polymers changed dramatically compared to the pristine polymers by incorporation of the sol–gel precursors.     

Determination of the copper activity of liquid CuLa alloys

The thermodynamic activities of liquid CuLa alloys were obtained at 1549 K by Knudsen effusion experiments. The experimentally known concentration and temperature dependences of thermodynamic properties of liquid CuLa alloys are explained on the basis of an association model. These results are discussed in comparison with the enthalpy of crystallization and the crystallization temperature as well as the enthalpy of melting and the melting temperature of lanthanum-rich glassy and crystalline alloys respectively.     

Effect of sulphur addition on the properties of FeTi alloy for hydrogen storage

Addition of sulphur to the Fe-Ti alloy was found to produce a marked improvement in the properties of the alloy for hydrogen storage. The most effective composition was FeTi_1.05S_0.02, which had a low activation temperature (80–100 °C), a short incubation time (10–30 h) and a good equilibrium plateau pressure over a wide concentration range of absorbed hydrogen. The degree of pulverization for this alloy after the absorption-desorption cycle test was comparatively moderate. The sulphur added to the alloy was converted into Ti₂S which was precipitated in a network structure with strips about 5 μm wide separated by spaces of dimensions about 20–50 μm.