Al Crystals Research Articles

Ti promotes the reaction of Al alloy with water to rapidly generate hydrogen

Al-3Ga-3In-3Sn alloy activated by Ti was prepared using a smelting and casting method. The microstructures and phase composition were investigated by means of scanning electron microscope (SEM) with energy dispersive x-ray spectrometer (EDX) and x-ray diffraction (XRD). The melting point of the grain boundary phase was measured using a differential scanning calorimeter (DSC). The results showed that with adding 0.3 wt% Ti, particles of the Al alloy are refined and changed from the original column shape to an equiaxed shape, and particle size reduced from 70 μm to 30 μm. The grain boundary phase is more uniformly distributed in the Al-3Ga-3In-3Sn-0.3%Ti alloy than in the Al-3Ga-3In-3Sn alloy. In the Al-3Ga-3In-3Sn alloy, in addition to the GIS phase (Ga–In–Sn eutectic) low-melting point grain boundary phase, there is an endothermic peak caused by the reaction of Al and In3Sn. However, the peak caused by the reaction of Al and In3Sn in the Al-3Ga-3In-3Sn-0.3%Ti alloy disappears, and only the presence of the GIS phase promotes the reaction of the Al alloy. The reaction of Al splitting water is carried out at 20 °C, 40 °C, 60 °C respectively. As the reaction temperature increases, hydrogen production and reaction rate increases. When the content of the Ti is 0.3 wt% of the weight of the Al alloy ingot, the grain size of the Al crystal is reduced, the uniform distribution of the grain boundary phase, and the transformation of the low melting point phase promote the reaction of the Al alloy.

Luminescence of (ZnSe:Al):Yb Сrystals at 4.2 K

It is established that the doping of ZnSe:Al crystals with ytterbium from the vapor phase brings about the appearance of two new bands in the low-temperature luminescence spectra. Emission in the energy range 1.15–1.35 eV is defined by transitions in Yb3+ ions, and the edge band is defined by the LO-phonon-assisted transitions of free electrons to acceptor levels of uncontrollable Li impurities.

Theoretical study on the aggregation of aluminium clusters on a silicone oil surface

By using Amsterdam Density Functional (ADF) program based on first-principles, we have in detail investigated the formation mechanism of the aluminium (Al) nanoparticles (NPs) on a silicone oil surface. Our investigation shows that two moving Al clusters on liquid substrate meet to form a random initial structure. Collisions and interactions may make it become a more compact, more stable structure. As the deposition density increases, a discshaped morphology would be formed because of isotropy on the silicone oil surfaces. The structures built on the Face-Centered Cubic (FCC) units are not stable. Both atomic displacement and adsorption can almost destroy them. It is difficult to form Al crystals on the silicone oil surfaces.

Synthesis and characterization of Al@MOF materials

Abstract The potential impregnation of Al(0) nanoparticles in the pores of three different metal-organic frameworks (MOFs), MIL-53-Al, HKUST-1, and UiO-67, was investigated through the suspension of the MOFs in AlH3·NMe2Et (1), followed by filtration, toluene wash, and heating to 150 °C under vacuum. Calculations based on the ratios of molecular and pore volumes provided idealized, benchmark impregnation capacities. Three successive impregnation cycles were performed to provide maximum incorporation of Al in the pores, and the materials were characterized after each impregnation cycle by ICP elemental analysis, BET surface area, and pore volume measurements. For MIL-53-Al, about half of the calculated amount of Al was incorporated into the MIL-53 pore structure, and PXRD data indicated a loss of crystallinity after the third incorporation cycle. Little Al incorporation was observed with HKUST-1, and the large decrease in surface area and pore volume, without significant change in the PXRD pattern, is attributed to pore blockage. Reaction of a large excess of 1 with UiO-67 was highly exothermic and evolved gas, likely from reaction with the μ3-OH groups in the UiO-67 structure. The resulting material was amorphous apart from metallic Al(0) crystals approximately 30 nm in size and larger than the UiO-67 pores, as determined by PXRD and 27Al MAS NMR spectroscopy. This material exhibited no apparent reaction with air or water and exposure to air gave little change in the 27Al MAS NMR spectrum. The Al(0) crystals thus appear to be protected from oxidation, presumably by the remaining UiO-67 framework.

Incorporation of metal-organic framework amino-modified MIL-101 into glycidyl methacrylate monoliths for nano LC separation.

Metal-organic frameworks consisting of amino-modified MIL-101(M: Cr, Al, and Fe) crystals have been synthesized and subsequently incorporated to glycidyl methacrylate monoliths to develop novel stationary phases for nano-liquid chromatography. Two incorporation approaches of these materials in monoliths were explored. The metal-organic framework materials were firstly attached to the pore surface through reaction of epoxy groups present in the parent glycidyl methacrylate-based monolith. Alternatively, NH2 -MIL-101(M) were admixed in the polymerization mixture. Using short time UV-initiated polymerization, monolithic beds with homogenously dispersed metal-organic frameworks were obtained. The chromatographic performance of embedded UV-initiated composites was demonstrated with separations of polycyclic aromatic hydrocarbons and non-steroidal anti-inflammatory drugs as test solutes. In particular, the incorporation of the NH2 -MIL-101(Al) into the organic polymer monoliths led to an increase in the retention of all the analytes compared to the parent monolith. The hybrid monolithic columns also exhibited satisfactory run-to-run and column-to-column reproducibility.

Люминесценция кристаллов ZnSe<Al> : Yb при 4.2 K

AbstractIt is established that the doping of ZnSe:Al crystals with ytterbium from the vapor phase brings about the appearance of two new bands in the low-temperature luminescence spectra. Emission in the energy range 1.15–1.35 eV is defined by transitions in Yb^3+ ions, and the edge band is defined by the LO-phonon-assisted transitions of free electrons to acceptor levels of uncontrollable Li impurities.

Выращивание объёмных кристаллов AlN и GaN сублимационным сандвич-методом

The review of the results of growth of bulk Al and Ga nitride crystals on foreign substrates by the sublimation sandwich method (SSM) is presented. The kinetics and the mechanism of sublimation and condensation nitrides depending on the growth conditions, structure of the vapor phase, crystal orientation and the distance between the source and the seed are analyzed. It is experimentally established that by joint annealing of AlN and SiC the rate of AlN sublimation significantly increases due to formation of a liquid phase on the crystal surface. Non-uniform distribution of the liquid phase localized mainly near structural and morphological defects results in the selective nature of the surface etching, and also is the reason of deterioration of the growing crystal quality. The process of bulk AlN crystals growth with simultaneous evaporation of the seed allowing to grow crystals without cracks and with the improved parameters is realized. On SiC seeds bulk AlN crystals from 0.5 to 2 inch in diameter are grown.

Effect of Cd and Al Coincorporation on the Structures and Properties of Goethite

Goethite is one of the most common and active Fe oxyhydroxide minerals in soils. Although single metal substitution for Fe in goethite is extensively studied, investigation is rare on simultaneous incorporation by Al and Cd, which is more common in some metal-polluted ecosystems. In this study, a series of Al and Cd cosubstituted goethite crystals were synthesized at room temperature and characterized by powder X-ray diffraction, Rietveld structure refinement, wet chemical analysis, transmission electron microscopy, and infrared spectroscopy. The highest substitution levels of Al and Cd for Fe are ∼7.8 and ∼9.9 mol %, respectively. Increasing Cd concentration in goethite is accompanied by decreasing crystal size and crystallinity. Incorporation of Cd into the goethite structure is hardly affected by Al, but the incorporation of Al is greatly inhibited by Cd. Rietveld structure refinement analysis shows a significantly positive relationship among unit-cell dimensions, crystal density, and Cd concentration....

Surface characterization of face-centered cubic crystals

To date, the examination of surface energy and surface layer relaxation has been the subject of several experimental and simulation works, whereas evaluation of surface residual stresses and surface elastic constants has received very little attention. In addition to the fundamental importance of these properties in the understanding of such phenomena as crystal equilibrium shape, surface roughening and segregation, they are also crucial for use in the theoretical studies based on continuum theory of elastic material surfaces. This work focuses on developing a theoretical approach for the calculations of the surface residual stress and surface elastic constants for (100) planes of fcc crystals. This is achieved through inter-relating the corresponding energies obtained from ab initio DFT calculations and from surface elasticity theory which deals with energetic material surfaces enclosing a classical simple elastic bulk material. Moreover, surface layer relaxations and surface energies associated with the (100) planes of Al, Ag, Ni, Pt, and Cu fcc crystals are evaluated using ab initio DFT calculations and compared with the available theoretical and experimental results.

A topologically correct method of dislocations construction for atomistic modeling

We discuss the deep topological reasons why dislocation quadrupoles should be used for the construction of dislocations containing edge components. We demonstrate that contrary to all other currently used methods, this approach exactly preserves the topology of the order parameter field (atomic displacements in a crystal with defects relative to a defect-free crystal) of a dislocation-free crystal with periodic boundary conditions even for small simulation volumes and, thus, restores the verity of the material frame indifference principle, broken in other techniques. Using dislocation quadrupoles for edge and mixed dislocations, we have developed a careful procedure for relaxation of atomic positions around a dislocation core which enables one to achieve arbitrary low dislocation densities characteristic for real crystals. As a demonstration of the method capabilities, we have constructed a simulation volume with as low dislocation density as 1.5·1014m-2, which is realistic in deformed crystals, and one can easily lower this value as desired. All details of dislocation construction process are explicitly specified, making it very easy to reproduce our results. FCC Al crystal is used as a test case.

Mixed ZnSxSe1–x Crystals as a Possible Material for Alpha-Particle and X-ray Detectors

A possibility to use ZnSxSe1−x as a material for the detection of X-rays and alpha particles has been studied. The influence of the sulfur content on the properties of bulk ZnSxSe1−x crystals is analyzed. Six specimens with different component contents were grown, by using the Bridgman–Stockbarger method: ZnS0.07Se0.93, ZnS0.15Se0.85, ZnS0.22Se0.78, ZnS0.28Se0.72, ZnS0.32Se0.68, and ZnS0.39Se0.61. The intensity of X-ray luminescence spectra of ZnSxSe1−x crystals is found to increase with the sulfur content and reaches a maximum for the composition ZnS0.22Se0.78. The luminescence light yield of mixed ZnSxSe1−x crystals is higher than that of commercial ZnSe(Te) and ZnSe(Al) crystals. The advantages of mixed crystals based onZnSxSe1−x over the ZnS(Te) and ZnSe(Al) crystals have been discussed.

Investigation of porous anodic alumina templates formed by anodization of single-crystal aluminum substrates

Ordered porous anodic alumina (PAA) templates are of great interest as they facilitate the future development of nanodevices. The present study focuses on the impact of substrates with different crystallographic orientations on the template's pore structure. Characteristics such as pore diameter, interpore distance, pore regularity, porosity, and circularity are calculated as a function of the anodization potential for three different Al crystal orientations. The presented experiments reveal that the different crystallographic orientations mainly impact the pore ordering, while other structural parameters, such as the pore diameter and interpore distance, are not significantly affected.

Annular dark-field scanning confocal electron microscopy studied using multislice simulations.

Annular dark-field scanning confocal electron microscopy (ADF-SCEM) has been studied using multislice simulations. Thermal diffuse scattering was considered in the calculations. Geometric aberrations of the lenses were introduced. A finite-sized pinhole was taken into consideration, in addition to an ideal point pinhole. ADF-SCEM images of Al crystals aligned along a zone-axis exhibit elongated contrast along the optic axis. Results of simulations suggest that if geometric aberrations of an imaging lens are corrected, depth resolution in ADF-SCEM can be improved by employing a large collection semi-angle of an annular aperture, even with a finite pinhole.

Dynamics of Changes in Optical Absorption Induced By Nanosecond Laser Pulses in the Bi12Tio20:Al Crystal

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Construction, characterization, and environmental testing of a Laue lens prototype using Fe and Al crystals

Laue lenses use Bragg diffraction to concentrate soft γ-rays onto a detector. This decoupling of the collecting area from the detector volume can generate a significant increase in sensitivity for applications in astrophysics and nuclear medicine. A demonstrator lens was constructed at the UC Berkeley’s Space Sciences Laboratory in 2014 by gluing 48 Fe and Al diffracting crystals to an aluminium substrate. The goal was to demonstrate a fast and accurate assembly technique that is compatible with the large number of crystals required to fabricate a Laue lens telescope for astronomical observations. We present here the lens design, the assembly technique we used, and the results of measurements of the angular misalignments before and after curing of the glue and during environmental testing (thermal, vacuum, and vibration). We conclude that our alignment technique is fast enough to assemble a full lens made of several thousand crystals. The achieved alignment accuracy had an average of 32.7′′ and a standard deviation of 44.1′′. The accuracy could be improved by using an alternative glue or by having better control over the asymmetry angle resulting from the crystal cut.

Исследование ширины запрещенной зоны смешанных кристаллов ZnSxSe1–x

Scintillators based on ZnSxSe1–x are promising materials for X-ray and γ-ray detection. For optoelectronic devices, it is better to use semiconductor compounds with a direct-zone energy structure with its spectral range lying in the fundamental absorption region. The band gap in such semiconductors is an important parameter that affects the energy resolution, ionization energy, dark current and other scintillation characteristics. The effect of sulfur content on the optical width of the band gap in mixed crystals ZnSxSe1–x is investigated in this paper. The test samples for this study were grown by Bridgman-Stockbarger in graphite crucibles with the diameter of 25 mm in the Ar atmosphere (PAr = 2∙106 Pa) at a temperature from 1870 to 2000 K, depending on the composition of the initial raw materials. Six samples with different content of components were obtained: ZnS0.07Se0.93, ZnS0.15Se0.85, ZnS0.22Se0.78, ZnS0.28Se0.72, ZnS0.32Se0.68, ZnS0.39Se0.61. The transmittance of the samples in the range from 61 to 67% at 1100 nm (sample thickness 4 mm) indicates a high optical quality of the crystals. It was established that the optical width of the band gap for mixed crystals ZnSxSe1–x increases from 2.59 to 2.78 eV with increasing sulfur content from 0.07 to 0.39 for direct transitions and from 2.49 to 2.70 eV for indirect transitions. A comparison was made between theoretical and experimentally obtained values of the band gap width. It is shown that no new (defective) levels appear in the band gap. The smooth dependence of the optical band gap on the composition indicate a possibility of growing ZnSxSe1–x mixed crystals by directional solidification techniques for X-ray and γ-ray detectors. The wider band gap and higer atomic mass ratio of ZnSxSe1–x crystals, as compared to ZnSe(Te) or/and ZnSe(Al) crystals, extend application areas of such semiconductor material

Effect of rapid Solidification on mechanical properties of free machining lead free aluminum alloys for improved machinability

There have been very few reports describing the free machining lead free aluminum alloys containing minimal amounts of tin and indium melt spun process. Our paper describes the effect of fundamental factors on the machinability of free machining lead free aluminum alloys rapidly solidified from melt. Structural and thermal properties have been investigated by x-ray diffraction (XRD) and differential scanning calorimetry (DSC) techniques. Tensile test machine used in studies the mechanical properties such as ultimate tensile strength, elastic constants, yield strength and critical shear stress for Al-Zn-Sn-In alloys. It is noticed that mechanical and thermal properties attributed to fine grained structure, reduced levels of segregation and presence of new intermetallic compounds (IMC) such as AlZn and SnZn due to high casting rate by rapid solidification processes. The determination of mechanical properties was suggested to be attributed to the gradual increase of α-Al crystals. We evaluated the tensile properties using tensile test machine of the melt-spun ribbons at varied stress-strain rates to determine the underlying deformation mechanisms .Critical shear stress (CSS) was also calculated .It was found that it is equal to 9.29 GPa for annealed ribbons at 262 0C for 9 hrs. The results showed that several combination of tensile strength ,yield strength ,elastic moduli can be generated from Al- 0.1wt% Zn-1.5 wt% Sn- 1.63 wt% In alloys before and after heat treatment at (262 0C for 3,6,9 hrs) to meet the needs of free machining aluminum alloy applications.

Fe ve Fe - %25 Al için maksimum streslerin (hkl) düzlemlerinde teorik olarak hesaplanması

At room temperature, Fe and Fe-25% Al (Fe 3 Al) crystals are in bcc structure and the experimental lattice parameters (a 0 ) are 2.87 A and 2.8964 A. The physical properties of Fe and Fe 3 Al crystals, whose internal interaction energies are very close to each other, are investigated from many perspectives. The basic physical parameters have different sizes in the (hkl) crystal planes. In this study, the maximum stresses (T hkl ) were investigated from the elastic parameters in the (hkl) planes for both Fe and Fe 3 Al crystals. For this, second order elastic constants (C 11 , C 12 and C 44 ) were calculated first for cubic symmetry by using the Wien2k method. The lattice parameters of the crystals and scattering angles (2θ) were used to find the peak widths (β hkl ). Some elastic parameters calculated with respect to the planes were compared with the results calculated from different equations. The dislocation densities (δhkl) related to crystal dimensions (D hkl ) were also studied in planes (hkl). All the obtained results were interpreted according to (hkl) planes and some [hkl] directions and compared with the results of other close studies. It has been reached that such analytical investigations could be extended to the (222) plane.

Revisiting the Aluminum Trimesate-Based MOF (MIL-96): From Structure Determination to the Processing of Mixed Matrix Membranes for CO2 Capture

A microporous Al trimesate-based metal–organic framework (MOF), denoted MIL-96-(Al), was selected as a porous hybrid filler for the processing of mixed matrix membranes (MMMs) for CO2/N2 postcombustion separation. First, the structural model of MIL-96-(Al) initially reported was revisited using a combination of synchrotron-based single-crystal X-ray diffraction, solid-state nuclear magnetic resonance spectroscopy, and density functional theory (DFT) calculations. In a second step, pure MIL-96-(Al) crystals differing by their size and aspect ratio, including anisotropic hexagonal platelets and nanoparticles of about 70 nm in diameter, were prepared. Then, a combination of in situ IR spectroscopy, single-gas, and CO2/N2 coadsorption experiments, calorimetry, and molecular simulations revealed that MIL-96-(Al) nanoparticles show a relatively high CO2 affinity over N2 owing to strong interactions between CO2 molecules and several adsorption sites such as Al3+ Lewis centers, coordinated water, and hydroxyl gro...

Quality Analysis of AlTi5B1 Master Alloys

Grain refinement in commercial aluminium alloys can be achieved by addition of AlTi5B1 master alloy, containing α aluminium matrix, TiB2 and Al3Ti particles. These particles act as nucleation points for α Al matrix, resulting in a uniform fine, equiaxed as cast microstructure. Current grain-refinement practice involves the addition of master alloy (e.g. Al-Ti-B, Al-Ti-C) before casting introducing inoculants particles to the melt. The final size SDAS in aluminium cast alloys depends on the kinetics of both nucleation and growth of solid in the liquid. As per the classical nucleation theory, the critical activation energy (ΔG*) to form stable nucleus and the critical radius (rkr.) for the nucleus to grow into a crystal with long order atomic arrangement are inversely proportional to the undercooling. In practical instances, nucleation does not occur heterogeneously on solid substrates such as mould walls. Several works, mainly regarding primary foundry alloys, have been carried out on grain refinement revealing how the TiB2 particles present in AlTi5B1 master alloy provide a germ for heterogeneous nucleation; however, these particles become efficient grain refiners only with excess Ti content. This condition can not only increase the nucleating potency of TiB2 particles, but also reduce the grain growth of primary α - Al crystals during solidification. At atomic scale the nucleating potency of TiB2 is dictated by the mismatch between the lattice of this particle and the nucleating phase. The performance of AlTi5B1, well established to be the best grain refiner for cast aluminium alloys as AlSi7Mg0.3 and AlSi12Cu2. Producer of the master alloys as AlTi5B1 guarantee the chemical composition but not size of particles that are very important for solidification process. This review focuses on the quality of five AlTi5B1 master alloys.