Function Of Aluminum Research Articles

Insights into the Inducing Effect of Aluminum on Cu–ZnO Synergy for Methanol Steam Reforming

Methanol is considered an attractive hydrogen carrier for fuel cells via steam reforming reaction. The industrial Cu/ZnO/Al2O3 catalyst is widely used for its excellent activity in various reactions. The function of aluminum was deemed to be indispensable for catalytic activity and stability. However, the promotion mechanism of aluminum on the Cu/ZnO catalyst for methanol steam reforming reaction remains ambiguous. Herein, a series of aluminum-modified Cu/ZnO-xAl and Cu/ZnO + xAl catalysts with various loadings were fabricated. Systematic characterizations (e.g., XRD, TEM, H2-TPR, CO2–N2O titration, CO2-TPD, and XPS) prove that incorporation of Al3+ ions into the ZnO lattice remarkably boosts the activity and stability due to enhanced Cu–ZnO synergy. The properties and chemical environment of Cu NPs were comprehensively investigated, and the Cu surface areas, oxygen vacancies, and ZnOx sites were quantitatively measured. The correlation between turnover frequency and catalyst structure proves that the aluminum-induced Znδ+ or ZnOx sites at the interface between Cu and ZnO play a dominant role in enhancing catalytic performance. This insight into Cu–ZnO synergy induced by aluminum may contribute to the design of high-performance catalysts in the future.

Analysis of the dielectric function of aluminum (Al) in bulk and nanometric states

We model the dielectric function of aluminum (Al). The modeling has been performed on Al in bulk and nanometric states. First, we will model the experimental measurements of the dielectric constant as a function of the pulsation ω by appropriate mathematical functions in an explicit way. In the second part, we will highlight the contributions due to intraband and interband electronic transitions. In the last part, we model the dielectric constant of this metal in the nanometric state using several complex theoretical models such as the Drude Lorentz theory and the Drude two-point critical model. We shall comment on which model fits the experimental dielectric function best.

The diversity of volcanic soils: focusing on the function of aluminum–humus complexes

ABSTRACT Andosols (or Andisols) are the typical soils developed from volcanoclastic materials. They possess several distinctive properties that are rarely found in other groups of soils. These properties are largely due to the dominance of short-range ordered minerals (allophane, imogolite, and ferrihydrite) and/or mineral–humus complexes (Al/Fe–humus complexes). In this review, I survey the diversity of volcanic soils mainly from the viewpoint of the function of Al–humus complexes. Specific topics include the role of Al–humus complexes in organic carbon accumulation, Al solubility and kinetics, Al phytotoxicity to plants, and the suppression of soil-borne diseases. It is shown that Al–humus complexes are heavily involved in the diversity of these properties of volcanic soils.

Effect of Al content on the structural and electrochemical properties of A2B7 type La–Y–Ni based hydrogen storage alloy

LaY1.9Ni10.2−xAlxMn0.5 (x = 0–0.6) hydrogen storage alloys have been prepared using a vacuum induction-quenching furnace and annealed at 1148 K for 16 h. The alloys are composed of Ce2Ni7- and Gd2Co7-type phases and an extra Pr5Co19-type phase appears when x = 0.6. Aluminum tends to enter the inner AB5 slabs of Ce2Ni7- and Gd2Co7-type phases and promotes the generation of new AB5 slabs. The maximum discharge capacity of the alloy electrodes is stable at approximate 375 mA h/g as x increases from 0 to 0.4 and then decreases to 364.2 mA h/g (x = 0.6). The cycling capacity retention rate at the 300th cycle is 59.4%, 62.0%, 62.7% and 58.7% for x = 0, 0.2, 0.4 and 0.6, respectively, indicating that the function of aluminum on improving the cyclic stability of the alloy electrodes is limited. The main reason is that the similar pulverization degrees of the alloys are presented during the charge/discharge cycles.

Comprehensive structural and mechanical characterization of in-situ Al–Al3Ti nanocomposite modified by heat treatment

Aluminum-Al3Ti reinforced MMCs were produced with a large amount (up to ~30 vol%) of Al3Ti phase via mechanical alloying, hot extrusion and heat treatment (as a supplementary process) of the Al–Ti elemental powder mixture, respectively. Samples in each stage were studied precise and comprehensive by field emission electron microscope, energy dispersive spectroscopy, X-ray diffraction, differential scanning calorimetry, densitometry, macro and micssro hardness, nanoindentation and tensile tests. The results indicated that after 4-h vibratory milling, the aluminum crystallite size reached 63 nm and Al3Ti phase formed in powder mixture. After hot extrusion, the volume percentage of Al3Ti increased by the formation of new Al3Ti nanoparticles, and a densed structure was achieved. As the milling time increased and crystallite and particle sizes of aluminum and titanium become smaller, the mechanical behavior of the hot extruded nanocomposites was improved. After heat treatments, the amount of Al3Ti phase significantly increased, and by thickening the Al3Ti layers around the titanium microparticles at high temperatures and long time periods, the voids in the structure proliferated. Increase in Al3Ti content can improve the mechanical properties, provided that volume exchanges originating from its formation do not cause widespread formation of voids in the structure. Mechanical properties varied as a function of aluminum and titanium crystallite and particle sizes and amount of Al3Ti phase and voids in the final samples. Aluminum crystallites growth during heat treatment reduces the hardness and increases the matrix ductility, and reinforcement particles growth brings faster failure for the samples.

Effect of Scandium Additions on the Temperature Dependences of the Heat Capacity and Thermodynamic Functions of Aluminum–Manganese Alloys

Abstract—The “cooling” method based on the Newton–Richmann law is used to measure specific heat capacity. It is shown that, as the manganese concentration in aluminum—magnesium alloys and temperature increase, the specific heat capacity of the alloys increases; as the scandium concentration increases, the heat capacity slightly decreases. As the temperature increases, the specific enthalpy and entropy of the alloys increase, whereas the specific Gibbs energy decreases. Scandium additions almost do not affect changes in thermodynamic functions of the alloys.

Initial-Stage Oxidation of Ni3Al(100) and -(110) from Ab Initio Thermodynamics

The microscopic mechanisms of the initial-stage oxidation of the Ni3Al(100) and Ni3Al(110) surfaces are comparatively studied using ab initio calculations based on density-functional theory and thermodynamics considerations. The surface energies of the two surfaces as functions of aluminum and oxygen chemical potentials are constructed and show that the formation of any antisite defects is not favorable at the Ni3Al(100) surface, whereas Al antisite defects are favorable at the Ni3Al(110) surface. The surface phase diagrams of the Ni3Al(100) and -(110) surfaces with different antisite defects and at the various oxygen coverages are determined. These results show that oxygen adsorption enhances Al surface segregation at the initial stage of oxidation for both surfaces and that the Ni3Al(100) surface is thermodynamically more favored to oxidize completely at a lower oxygen coverage than the Ni3Al(110) surface.

Function of aluminum in crystal structure of rare earth–Mg–Ni hydrogen-absorbing alloy and deterioration mechanism of Nd0.9Mg0.1Ni3.5 and Nd0.9Mg0.1Ni3.3Al0.2 alloys

We investigated in detail the effect of incorporating Al in the crystal structure of rare earth–Mg–Ni hydrogen-absorbing alloys, which were developed as candidate materials for the metal hydride (MH) negative electrode in commercial Ni–MH batteries, using synchrotron powder X-ray diffraction. Partially substituting the Ni part with Al changes the lattice parameter of the major A2B7 phase, eliminating a mismatch between the AB2 units and the AB5 units. The change of the lattice parameter in the alloy leads to good hydrogen reversibility and good durability. Furthermore, we observed the alloy after 30 hydrogen absorption–desorption cycles using a scanning transmission electron microscope image. Consequently, we found that the surface layer of the Nd0.9Mg0.1Ni3.5 alloy had an amorphous state, while the surface layer of the Nd0.9Mg0.1Ni3.3Al0.2 alloy did not. We confirmed that the deterioration mechanism of the Nd0.9Mg0.1Ni3.3Al0.2 alloy was due to partial expansion of the AB2 unit along the c-axis; the local area of deterioration expanded during the cycling period.

Electromagnetic scattering characteristic of aluminous targets in the terahertz and far infrared region

In the terahertz and far infrared region, aluminum is in a state of transition from conductor to dielectric, and the research of the interaction between aluminous target and electromagnetic wave is meaningful for scattering prediction of targets. With the available error criterion model, dielectric function of aluminum is determined by fitting to experimental data in the terahertz and far infrared region. The transmitted parameters in aluminum are deduced by considering different loss mechanisms. Reflection and transmission characteristics on the interface of aluminum are investigated, and the reflection coefficients are given as a function of frequency. Results show that the transmitted parameters in aluminum keep their continuity and coherency from microwave to terahertz frequency. RCS (radar cross-section) results of aluminum plates computed by IBC method demonstrate that the increased wave impedance of aluminous targets has little impact on its backscattering, and the polished aluminous plate or sphere can still be treated as a perfect electrical conductor and used as a reference for RCS calibration.

Advanced lignin-acrylamide water treatment agent by pulp and paper industrial sludge: Synthesis, properties and application

A novel flocculant LA (lignin-acrylamide polymer), which was used as aid for aluminum sulfate and polyaluminum chloride in this study, was prepared by grafting acrylamide onto lignin that deriving from pulp and papermaking sludge. Physicochemical properties of LA were measured by X-ray photoelectron spectroscopy and scanning electron microscopy. The experimental outcome indicated acrylamide was grafted onto the lignin backbone successfully. The effects of LA addition were evaluated on coagulation performance and floc characteristics as a function of aluminum (Al) dosage, such as floc size, growth rate, strength and recoverability. Effects of different dosing sequences, Al dosed first and LA dosed first, were also investigated. LA used as coagulant aid markedly enhanced the removal efficiency of turbidity and dissolved organic carbon, especially at low Al dosages. The dissolved organic carbon removal efficiencies of aluminum sulfate and polyaluminum chloride at the Al dosage range selected in this study were improved more than 30% and 5% by LA, respectively. LA dramatically enlarged floc size and it was in the order: Al dosed first > LA dosed first > Al. Floc strength and recoverability were also improved by LA. LA played a significant role in charge neutralization, adsorption and bridging in floc formation.

ESTUDO TERMODINÂMICO DE INCLUSÕES NÃO-METÁLICAS EM AÇO ACALMADO AO ALUMÍNIO E TRATADO COM CÁLCIO

The main goal was the study of non-metallic inclusion formation in the continuous casting (CC) for Al-killed, calcium treated steel (SAE 8620). The specific goals were: 1) To obtain the phases and compounds formed in the inclusions as a function of composition and casting temperature adopted for the SAE 8620 steel. 2) To establish conditions of steel chemical composition for the formation of less harmful inclusions to the SAE 8620 castability. Based in the literature and previous work of the authors, were carried out simulations using the software FactSage and databases. The simulations were realized using the global chemical composition of SAE 8620 steel in the CC tundish. The results were steel and non-metallic inclusions (oxides and sulphites) composition in the aimed temperature. The results showed the formation of different solid oxides and the formation of liquid phase in the inclusions by the variation of calcium content in the steel. It was possible to determine the inclusion composition as a function of aluminum and calcium content of SAE 8620 steel. For the specific composition and temperature of SAE 8620 steel, it was possible to establish a range of calcium content were the inclusions are formed by predominant liquid phase. It was possible to calculate the percent of liquid and solid phase in the inclusions, as well the composition in terms of oxides.

Thermodynamic study of non-metallic inclusion formation in SAE 1141 steel

The main purpose of this paper is the thermodynamic study of non-metallic inclusion formation in the CC tundish for SAE 1141 steel. The specific purposes are: 1) obtaining inclusions as function of steel composition and casting temperature. 2) establishing steel chemical composition to form less harmful inclusions to the SAE 1141 steel castability. Simulations using the commercial software FactSage and databases were carried out. Results showed both different solid oxides and liquid phase formation in inclusions by varying calcium content in the steel. Thus, it was possible: 1) to determine both the inclusion composition as a function of aluminum and calcium content of SAE 1141 steel. 2) to establish a range of calcium content in which inclusions are formed predominantly by liquid phase. 3) to calculate percentage of liquid and solid phases in inclusions, and oxides composition as well.

ATP Binding Modulates the Nucleic Acid Affinity of Hepatitis C Virus Helicase

The helicase of hepatitis C virus (HCV) unwinds nucleic acid using the energy of ATP hydrolysis. The ATPase cycle is believed to induce protein conformational changes to drive helicase translocation along the length of the nucleic acid. We have investigated the energetics of nucleic acid binding by HCV helicase to understand how the nucleotide ligation state of the helicase dictates the conformation of its nucleic acid binding site. Because most of the nucleotide ligation states of the helicase are transient due to rapid ATP hydrolysis, several compounds were analyzed to find an efficient unhydrolyzable ATP analog. We found that the beta-gamma methylene/amine analogs of ATP, ATPgammaS, or [AlF4]ADP were not effective in inhibiting the ATPase activity of HCV helicase. On the other hand, [BeF3]ADP was found to be a potent inhibitor of the ATPase activity, and it binds tightly to HCV helicase with a 1:1 stoichiometry. Equilibrium binding studies showed that HCV helicase binds single-stranded nucleic acid with a high affinity in the absence of ATP or in the presence of ADP. Upon binding to the ATP analog, a 100-fold reduction in affinity for ssDNA was observed. The reduction in affinity was also observed in duplex DNA with 3' single-stranded tail and in RNA but not in duplex DNA. The results of this study indicate that the nucleic acid binding site of HCV helicase is allosterically modulated by the ATPase reaction. The binding energy of ATP is used to bring HCV helicase out of a tightly bound state to facilitate translocation, whereas ATP hydrolysis and product release steps promote tight rebinding of the helicase to the nucleic acid. On the basis of these results we propose a Brownian motor model for unidirectional translocation of HCV helicase along the nucleic acid length.

Viscosity, Density, and Refractive Index of Aqueous Sodium and Potassium Aluminate Solutions

The viscosities, densities, and refractive indices of synthetic sodium and potassium aluminate solutions are reported as a function of aluminum and caustic concentration, total caustic to Al(III) molar ratio, and temperature. The influence of hydrogen isotope was also explored through complementary studies on deuterated solutions. A significant alkali metal ion effect on the viscosity and density is indicated, the influence of the other primary variables shown to range from strong to moderate. Under similar solution conditions, the sodium ions display stronger solute interactions and greater solution structure-making ability, reflected in higher solution viscosity (and enhanced density), than do potassium ions. The effect of Al(III) solute concentration, caustic to Al(III) ratio, ionic strength, and hydrogen isotope on the solution bulk properties is discussed and their relevance to speciation and the interactions of species in Bayer liquors is highlighted. Empirical models for viscosity and density are p...

Activities of the Constituents in Spinel Solid Solution and Free Energies of Formation of MgO, MgO Al2O3.

Spinel (MgO·Al2O3) is known as one of the most harmful non-metallic inclusions in steel. However, the technology to avoid spinel formation has not yet been established due to lack of thermodynamic information on the spinel itself. In the present work, the free energies of formation of MgO and MgO·Al2O3, and the activities of the constituents in spinel solid solution have been directly measured by the chemical equilibrium technique. The free energies of formation of MgO and MgO·Al2O3 determined in the present work are expressed by the following equation:Mg(l) + 1/2O2(g) = MgO(s) ΔG°f, MgO = -669350 + 135.0T (J/mol)Al2O3(s) + MgO(s) = MgO·Al2O3(s) ΔG°f, MgO· Al2O3 = -20790 - 15.7T (J/mol)The activity of stoichiometric MgO·Al2O3 exhibits negative deviation from ideality in the spinel solid solution. Phase stability diagram of spinel formation in liquid steel was assessed as a function of aluminum, magnesium and oxygen contents in iron at 1 873 K. The predicted phase boundaries of MgO·Al2O3, MgO and Al2O3 agreed well with previous observations by one of the present authors.

IR spectroscopic study of thermal transformation of the structure of dealuminated Y zeolite

The effect of the relative concentration of framework (AlVI, O), in-framework, and out-of-framework (AlVI, O) aluminum compounds on thermal transformation of the structure was investigated by IR Fourier spectroscopy. It was found that partial reduction of the anion function of aluminum takes place during prolonged exposure and heat treatment of the samples in air due to its transitions from the six-coordinated state in the out-of- and in-framework compounds into the four-coordinated state of the nodal lattice oxygen.

Calculated spectral weight function in aluminum

The spectral weight function of aluminum has been calculated within the local-density approximation. The inclusion of the energy-dependent self-energy has been proved to be important in calculating the single-particle energies, that are in good agreement with experimental data. The main disagreement we found is at theX 1 − level the calculated energy of which is too low. An appreciable lifetime broadening is found with small band dependence and almost parabolic trend as a function of energy.

Influence of aluminum and chromium on the activity of oxygen in nickel based melts at 1600‡C

The activity of oxygen in technically important nickel melts containing 15 wt pct cobalt and 5 wt pct molybdenum has been determined at 1600‡C for various concentrations of chromium ranging from 0 to 30 wt pct and aluminum varying from 0 to 15 wt pct. The activity of oxygen was measured by an electrochemical technique using yttria-doped thoria electrolyte cells. The results obtained are analyzed in terms of activity coefficients of oxygen as a function of aluminum and chromium contents in the melts. Clear positive deviations of the experimentally determined from the calculated activity coefficients of oxygen were found when aluminum was added to Ni-Co-Mo melts with or without chromium. From the results obtained in the range between 1 and 10 wt pct aluminum, the following equilibrium constants for the reaction 2 [Al] + 3 [O] ⇋ Al2O3 in the nickel based melts at 1600‡C were calculated: loga0 =-2/3 log [pct Al] - 3.94 for 0 pct Cr loga0 = -2/3 log [pct Al] - 4.21 for 10 pct Cr loga0 = -2/3 log [pct Al] - 4.81 for 20 pct Cr loga0 = -2/3 log [pct Al] - 5.06 for 30 pct Cr.