Mechanism of aluminum hydroxide layer formation by surface modification of aluminum

In this study, a new, relatively simple and rapid fabrication method for forming an Al(OH)₃ film on Al substrates was demonstrated. This method, i.e., alkali surface modification, is simply comprised of dipping the substrate in a 5 × 10⁻³ M NaOH solution at 80 °C for 1 min and then immersing it in boiling water for 30 min. After alkali surface modification, an Al(OH)₃ film was formed on Al substrate, and its chemical state and crystal structure were confirmed by XPS and TEM. The Al(OH)₃ layer was composed of three regions: an amorphous-rich region, a region of mixed amorphous and crystal domains, and a crystalline-rich region near the Al(OH)₃ layer surface.     

Optical conductivity of aluminum

Energies and wave functions obtained from a recent band calculation are used in a computation of the interband optical conductivity of aluminum. The results are combined with a Drude term and compared with experiment.     

Ultrasonic butt welding of aluminum,aluminum alloy and stainless steel plate specimens

Welding characteristics of aluminum, aluminum alloy and stainless steel plate specimens of 6.0 mm thickness by a 15 kHz ultrasonic butt welding system were studied. There are no detailed welding condition data of these specimens although the joining of these materials are required due to anticorrosive and high strength characteristics for not only large specimens but small electronic parts especially. These specimens of 6.0 mm thickness were welded end to end using a 15 kHz ultrasonic butt welding equipment with a vibration source using eight bolt-clamped Langevin type PZT transducers and a 50 kW static induction thyristor power amplifier. The stainless steel plate specimens electrolytically polished were joined with welding strength almost equal to the material strength under rather large vibration amplitude of 25 microm (peak-to-zero value), static pressure 70 MPa and welding time of 1.0-3.0 s. The hardness of stainless steel specimen adjacent to a welding surface increased about 20% by ultrasonic vibration.     

Assembling of hydrogenated aluminum clusters

The electronic and atomic structure of Al₁₃H has been studied using Density Functional Theory. Al₁₃H has closed electronic shells. This makes the cluster very stable and suggests that it could be a candidate to form cluster assembled solids. The interaction between two Al₁₃H clusters was analyzed and we found that the two units preserve their identities in the dimer. A cubic-like solid phase assembled from Al₁₃H units was then modeled. In that solid the clusters retain much of their identity. Molecular dynamics runs show that the structure of the assembled solid is stable at least up to 150 K. A favorable relative orientation of the clusters with respect to their neighbors is critical for the stability of that solid. Received 21 November 2000     

Electronic charge density of aluminum

The valence electronic charge density is calculated for aluminum from wave-functions obtained via Ashcroft's pseudopotential. A contour plot of the charge density is presented in the (100) plane. The Fourier transform of the charge density is used to calculate the atomic form factors which are compared with experimental X-ray form factors. The accuracy of the wavefunctions are further tested by comparing calculations of the imaginary part of the frequency dependent dielectric function with and without the effect of core states.     

Pyrophoricity of nano-sized aluminum particles

The temperature histories are calculated for spherical nano-sized aluminum particles with no protective oxide shell inserted in air at 300 K. In calculations, initial particle temperatures varied and the minimum initial temperature leading to the particle ignition was determined. The particle, initially without any oxide coating, was assumed to react adiabatically forming a monomolecular oxide coverage; the following oxidation was assumed to be governed by the Cabrera–Mott reaction mechanism. Convection and radiation heat losses were considered. Convection was accounted for using a transition regime heat transfer model by Fuchs. Aluminum particles with diameters less than about 68 nm are predicted to be pyrophoric, e.g., ignite without appreciable initial pre-heating.     

Elastic properties of aluminum nitride

The elastic moduli and their temperature and pressure derivatives for sintered, isotropic, polycrystalline aluminum nitride ceramic have been determined. The temperature derivatives of the elastic moduli are somewhat smaller than those of other wurtzite structure semiconductors, and the pressure derivative of the shear modulus is very small. The mode Grüneisen gamma of the shear mode is essentially zero, while the elastic Grüneisen constant agrees well with the thermodynamic Grüneisen constant. Both the bulk and shear modulus conform to the Keyes relationship.     

简单金属Al原子链的磁性

使用密度泛函理论下的第一性原理方法,研究了纳米尺度下简单金属Al原子链的磁性．计算结果显示,一维的Al原子链无论是在线性链还是锯齿形的结构下都有可能表现出磁性,但是这些磁性都是在原子键长被拉伸的情况下才会出现．通过原子轨道相互作用的图像,配合电子状态密度的计算和Stoner判据,解释了一维Al原子链磁性产生的原因． 关键词： 磁性 Al原子链 第一性原理计算     

Wear during microscratching of aluminum

The wear and force characteristics have been examined for the scratching of aluminum by single grains of abrasive at speeds between 0.1 and 120 m/sec. The stress decreases as the speed rises up to about 100 m/sec, whereas the fractional volume of metal cut increases. Explanations are proposed.     

Vacancy-solute complexes in aluminum

Several vacancy-solute complexes in the Al matrix are examined theoretically. In particular, these are V-Cu, V-Cd, V-In, V-Sn, V-Si and V-Fe. We concentrate on coincidence Doppler broadening (high momentum) profiles and positron lifetimes that bring complementary information about these defects. Positron calculations are carried out utilizing the atomic superposition method employing realistic atomic configurations obtained using an ab initio pseudopotential method. In this study we inspect to what extent such defects are detectable and differentiable using positron annihilation techniques. The influence of lattice relaxations around defects on the positron properties turns out to be important and is also debated. The obtained results are discussed in connection with experimental data published in literature.     

Theoretical form factors of metallic aluminum

The form factors of metallic aluminum are obtained from two APW calculations of the density in the solid. The first one is a standard self-consistent Kohn-Sham calculation. The second one includes an exact Hartree-Fock core-valence exchange potential and an approximate local valence—valence exchange-and-correlation potential. The second model decreases the valence contribution and increases the core contribution. But the total form factors are nearly equal in the two schemes. The ‘non-muffin-tin’ contributions to the form factors are shown to be important. The results remain too large compared with experiment.     

Deexcitation of sputtered metastable aluminum atoms

An experimental system was set up incorporating pulsed ion beam sputtering, two Nd:YAG pumped dye lasers and an imaging time-of-flight (TOF) analysis system. The system was used to perform state-selective analyses of neutral atoms sputtered from surfaces using resonant one-color and two-color ionization schemes. We have measured, for the first time, TOF mass spectra of Al atoms sputtered into the ground state and first excited state (with an excitation energy of 0.014 eV) from single crystals of Ni₃Al and NiAl. The population ratio of the first excited state to the ground state in the sputtered flux was estimated to be 0.91 for Ni₃Al and 0.95 for NiAl, respectively. This indicates that the magnitude of the excitation energy plays an important role even in the deexcitation rate of sputtered metastable state atoms with an open outer shell.     

Viscosity of aluminum under shock-loading conditions

A reliable data treatment method is critical for viscosity measurements using the disturbance amplitude damping method of shock waves. In this paper the finite difference method is used to obtain the numerical solutions for the disturbance amplitude damping behaviour of the sinusoidal shock front in a flyer-impact experiment. The disturbance amplitude damping curves are used to depict the numerical solutions of viscous flow. By fitting the experimental data to the numerical solutions of different viscosities, we find that the effective shear viscosity coefficients of shocked aluminum at pressures of 42, 78 and 101 GPa are (1500±100) Pa · s, (2800±100) Pa · s and (3500±100) Pa · s respectively. It is clear that the shear viscosity of aluminum increases with an increase in shock pressure, so aluminum does not melt below a shock pressure of 101 GPa. This conclusion is consistent with the sound velocity measurement.     

The conductivity of aluminum nitride ceramics

Based on the analysis of the experimental behavior of the conductivity of highly dispersed aluminum nitride ceramics on temperature and frequency, conclusions are drawn about the existence in polycrystalline AIN of electromigration hopping mechanisms. At low temperatures and for high frequencies, the conductivity can be described within the framework of a two-point model, but as the temperature increases, or as the frequency decreases, a transition is observed through multiple jumps. The electromigration activation mechanisms dominate at temperatures higher than 370 K.Scientific Research Institute on High Voltages, Polytechnical University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 122–14, July, 1992.     

Chemisorption of oxygen on aluminum surfaces

A critical review of the oxygen—aluminum system is presented. The primary emphasis concerns the electronic properties of aluminum surfaces exposed to oxygen. The chemisorption and oxidation aspects are considered. Cluster and slab model calculations are discussed fully and the results are related to relevant experimental data. Some of the unresolved issues are listed. A comprehensive guide to the oxygen—aluminum literature is provided.