Crystal Aluminum Research Articles

Effect of nitriding atmosphere on the morphology of AlN nanofibers from solution blow spinning

High purity AlN fiber is a promising thermal conductive material. In this work, AlN fibers were prepared using solution blow spinning followed by nitridation under N2 or NH3 atmosphere. Soluble polymer, such as polyaluminoxane, and allyl-functional novolac resin were adopted as raw materials to form homogeneous distribution of Al2O3 and C nanoparticles within the fibers, which could inhibit the growth of alumina crystal and promote their nitridation process. The effect of nitriding atmosphere on the fiber morphology was investigated. XRD results showed that complete nitridation was achieved at 1300 °C in the NH3 or at 1500 °C in the N2 atmosphere. Hollowed fiber structure was observed when fiber was nitrided in N2 at high temperature, which was caused by gaseous Al gas diffusion, and this phenomenon was eliminated in NH3 atmosphere. The nitridation mechanisms in different atmosphere were analyzed in detail. It was demonstrated that the nitridation of Al2O3 fibers in the NH3 atmosphere offered the favored AlN morphology and chemical quality. Flexible AlN fiber with O content of 0.7 wt% was achieved after nitriding in NH3 at 1400 °C. The high quality AlN can be used in thermal conductive composite materials.

Femtosecond-Laser-Written S-Curved Waveguide in Nd:YAP Crystal: Fabrication and Multi-Gigahertz Lasing

We report on the design and fabrication of straight and S-curved waveguides in neodymium-doped yttrium aluminate (Nd:YAP) crystal by using direct femtosecond laser writing. These S-curved channel waveguides are based on the hexagonal optical-lattice-like and depressed cladding geometry. For each type waveguide, S-curves with three lateral offsets of 50 μm, 100 μm, and 150 μm are implemented. These waveguides are with good guiding properties and low bending losses. With S-curved waveguide as laser cavity, dual-wavelength, 31.6 GHz waveguide laser operating at 1064 nm and 1079 nm have been demonstrated based on MoS2 as a saturable absorber. This work paves the way to develop new on-chip ultrafast laser sources based on femtosecond laser inscribed S-curved waveguides.

Comparative study on utilization of different types of municipal solid waste incineration bottom ash for clinker sintering

In this study, two types of municipal solid waste incineration (MSWI) bottom ash (BA) (MSWI-BA-A, water quenched, MSWI-BA-B, natural cooling), are utilized as alternative materials for clinker sintering. Fixed clinker modulus (lime saturation ratio = 0.90 ± 0.01, silica modulus = 2.6 ± 0.1 and alumina modulus = 1.5 ± 0.1), designed gradient addition ratio of MSWIBA (0, 3%, 6%, 9% and 12%) and same sintering temperature (1723.15 K) are adopted to conduct the experiments. Raw materials are characterized by XRF, X-ray diffraction and differential thermal analysis. Clinkers are analyzed and evaluated by XRF, X-ray diffraction, petrographic analysis, compressive and flexural strength tests and toxicity characteristic leaching procedure. The major difference of the two types of MSWIBA is LOI value which is supposed to be the most probable reason for huge difference between liquid phase formation temperature variation and incremental introduction of MSWI. MSWI-BA-A increases liquid phase formation temperature. Liquid phase formation temperatures and MSWI-BA-B samples addition ratios nearly present negative linear correlation. All clinkers sintered with addition of MSWIBA slightly reduce water demand for normal consistency. MSWIBA addition poses relatively obvious influence on initial setting time and little effect on final setting time. There is an increase in initial strength and a decrease in 28-day strength of clinkers sintered with MSWIBA, 28-day compressive strength decreases with the incremental introduction of MSWIBA. Distinct characteristics, such as free lime, periclase, orthorhombic tricalcium aluminate (C3A) crystal and secondary Belite crystal, are observed by petrographic analysis. MSWIBA is significant source of free lime and periclase in clinkers. Incremental input of alkali introduced by MSWIBA influences clinker sintering and mineral crystallinzation, further results in orthorhombic C3A crystal and indistinct Alite edge caused by corrosion. Leaching concentration of heavy metals from mortars prepared with the sintering clinkers is lower than corresponding concentration of the Chinese National Standard GB 30760-2014.

Molecular dynamics simulations of the effects of annealing on the micro residual stress induced by vacancy defects in aluminum crystal

Micro residual stress induced by vacancy defects in aluminum crystals was studied by molecular dynamics. The effects of different sizes of vacancy defects on the initial configuration (stable configuration after energy minimization) are analyzed, which are reflected by the changes of atomic potential energy, atomic displacement and atomic stress. The influence of annealing on the lattice structure of atoms near the vacancy defects and the evolution of the defects in the annealing process are also analyzed. After annealing, the vacancies are filled and the atomic lattice structures near the vacancy also change, adding a HCP lattice structure. The atomic distributions are more uniform and more regular. When the voids are small, the atomic stress decreases obviously after annealing. However, when the voids are large, the atomic stress increases after annealing. The influence range of vacancy defects on the micro residual stress is a spherical space with the center of the void as the center of the sphere, and the radius of the sphere is linear relationship with the radius of the voids. When the void radius is small, the annealing heat treatment method can effectively eliminate or reduce the micro residual stress. When the void radius exceeds threshold value, the micro residual stress increases after annealing. A single annealing heat treatment method cannot effectively eliminate the residual stress, which may need to be combined with other methods to eliminate or reduce the residual stress.

Radiation furnace for synchrotron dark-field x-ray microscopy experiments.

We present a multi-purpose radiation furnace designed for x-ray experiments at synchrotrons. The furnace is optimized specifically for dark-field x-ray microscopy (DFXM) of crystalline materials at beamline ID06 of the European Synchrotron Radiation Facility. The furnace can reach temperatures above 1200 °C with a thermal stability better than 10 °C, with heating and cooling rates up to 30 K/s. The non-contact heating design enables samples to be heated either in air or in a controlled atmosphere contained within a capillary tube. The temperature was calibrated via the thermal expansion of an α-iron grain. Temperature profiles in the y and z axes were measured by scanning a thermocouple through the focal spot of the radiation furnace. In the current configuration of the beamline, this furnace can be used for DFXM, near-field x-ray topography, bright-field x-ray nanotomography, high-resolution reciprocal space mapping, and limited powder diffraction experiments. As a first application, we present a DFXM case study on isothermal heating of a commercially pure single crystal of aluminum.

Molecular Statics Analyses of Thermodynamics and Kinetics of Hydrogen Cottrell Atmosphere Formation Around Edge Dislocations in Aluminum

Aluminum alloys are being explored as lightweight structural materials for use in hydrogen-containing environments. To understand hydrogen effects on deformation, we perform molecular statics studies of the hydrogen Cottrell atmosphere around edge dislocations in aluminum. First, we calculate the hydrogen binding energies at all interstitial sites in a periodic aluminum crystal containing an edge dislocation dipole. This allows us to use the Boltzmann equation to quantify the hydrogen Cottrell atmosphere. Based on these binding energies, we then construct a continuum model to study the kinetics of the hydrogen Cottrell atmosphere formation. Finally, we compare our results with existing theories and discuss the effects of hydrogen on deformation of aluminum-based alloys.

Interaction of edge dislocation with copper atoms in an aluminum crystal

In this work, the interaction of the moving edge dislocation with obstacles in form of copper atoms is studied using the molecular dynamics simulations. The samples are aluminum monocrystals of 52 × 60 × 15 nm3 with axes oriented along directions [110], [111], [112]. The structure of copper solid solution is reproduced with following procedure: aluminum atoms are randomly selected and replaced by copper atoms. The concentration of copper atoms varies from 0.25% to 1%. The dislocation movement occurs under action of shear deformation. It is found that zones with a low concentration of copper atoms only slow down dislocation in an aluminum matrix, and the zones with a high local concentration of copper atoms not only produces stronger resistance to dislocation movement, but also they cause the change in the slip plane of the dislocation segment. When a significant part of a dislocation line moves to a neighboring slip plane, the complete transition of the dislocation to this slip plane can occur. It is also noted that such transitions of dislocation segments from one slip plane to another are accompanied by the formation of vacancies. Also the maximum value of the shear stress σxy is estimated-its value is approximately 250 MPa.

Characterization of equine inflammasomes and their regulation.

Inflammasome, a cytosolic multi-protein complex, assembly is a response to sensing intracellular pathogenic and endogenic danger signals followed by caspase-1 activation, which maturates precursor cytokines such as interleukin (IL)-1β. Most inflammasome research has been undertaken in humans and rodents, and inflammasomes in veterinary species have not been well-characterized. In this study, we observed the effects of well-known inflammasome activators on equine peripheral blood monocytes (PBMCs). The NLRP3 inflammasome triggers include ATP, nigericin, aluminum crystals, and monosodium urate crystals, and NLRP3 activation induces IL-1β secretion in a dose-dependent manner. Activators of NLRC4 and AIM2 inflammasomes include cytosolic flagellin and dsDNA, and their activation induces IL-1β secretion. The bacterial inflammasome triggers Salmonella Typhimurium and Listeria monocytogenes also induce IL-β releases. To elucidate the role of potassium efflux as an upstream signal of NLRP3 inflammasome activation, equine PBMCs were treated with blockers of potassium efflux in the presence of NLRP3 triggers. As a result, the IL-1β secretion stemming from equine NLRP3 inflammasome activation was not completely attenuated by the inhibition of potassium efflux. Taken together, the results indicate that equine PBMCs normally secrete IL-1β in response to well-known inflammasome activators, although equine NLRP3 inflammasome activation might not be dependent on potassium efflux.

Structural state and thermodynamic stability of Al–Cu alloys

It is known that processes occurring in binary system melts affect the crystallization process and the phase composition of alloys. To predict these processes, we should determine the region of thermodynamic stability of the melt. In this paper, the structural properties of hypoeutectic and hypereutectic alloys in Al–Cu system are studied depending on the heating temperature above the liquidus line and aftercooling rate. It is shown that overheating of Al–Cu melts to 150 K above the liquidus line and further cooling leads to complete suppression of the process of formation of primary aluminum crystals in hypoeutectic alloys and [Formula: see text] phase in hypereutectic alloys. For the first time, by accounting in Gibbs energy of binary Al–Cu alloy for the first degree approximation of high-temperature expansion of thermodynamic potential, the dependence of temperature of line of the melt thermodynamic stability on copper content in alloy is obtained.

Dual Wavelength Chirped Pulse Regenerative Amplifier Based on Yb<sup>3+</sup>:LuAlO<sub>3</sub> Crystal for Terahertz Applications

Compact diode-pumped chirped pulse regenerative amplifier systems with pulse repetition rate of hundreds kilohertz based on Yb 3+ -doped crystals are of practical importance for wide range of applications such as materials processing, medicine, scientific research, etc. The aim of this work was to study the Yb 3+ :LuAlO crystal based dual wavelength chirped pulse regenerative amplifier. Perovskite-like aluminate crystals have unique spectroscopic properties that allowed to use amplifier active element gain spectrum as an amplitude filter for amplified pulse spectrum and even obtained dual wavelength amplification without any additional components. In our work a simple way to obtain dual-wavelength operation of chirped pulse regenerative amplifier by using the active medium gain spectrum as an amplitude filter for the formation of the amplified pulses spectrum demonstrated for the first time to our knowledge. Maximum output power of 5.4 W of chirped pulses (3.8 W after compression) and optical-to-optical efficiency of 22.5 % have been obtained for Yb:LuAP E//b-polarization at 200 kHz repetition rate. Compressed amplified pulse duration was about 708 fs while separate spectral components durations were 643 fs and 536 fs at 1018.3 nm and 1041.1 nm central wavelengths, respectively. Performed investigations show high potential of Yb 3+ :LuAP crystals as active elements of compact diode pumped chirped pulse regenerative amplifiers

Thermal History Dependent Al Distribution in Aluminum Substituted Strontium Hexaferrite.

Single crystals of aluminum substituted strontium hexaferrite SrFe12–xAlxO19 were grown from sodium oxide based flux. The substitution level aimed for was x = 1.2. Annealing experiments performed on single crystals show that the Al distribution on the five iron sites of the hexaferrite structure depends on the annealing time at 900 °C. Single crystal X-ray diffractometry shows that annealing a crystal after the initial synthesis has an impact on the Al content on the octahedrally and tetrahedrally coordinated sites. Furthermore, it was found that heating in a corundum crucible increases the overall Al content. Magnetic measurements show that annealing in a platinum or corundum crucible decreases coercivity and remanence while the saturation magnetization is hardly influenced.

Unifying analyses of the crystal field energy levels and EPR g factors for the trigonal Co2+ tetrahedral center in β˝-alumina

The crystal field energy levels (obtained from the optical spectra) and g factors g//, g⊥ (obtained from EPR spectra) for the Co2+ ion at the trigonal Al3+ tetrahedral site in β˝-alumina crystal are unifiedly analyzed with the full diagonalization (of energy matrix) method founded on the two-spin-orbit-parameter model (which contains the contributions from both the spin-orbit parameters of central dn ion and ligand ion via covalence effect). The results display that by applying only three adjustable parameters, the observed ten spectral data (eight crystal field energy levels and two g factors) can be rationally interpreted, confirming the availability of this full diagonalization method in the united analyses of optical and EPR data. The large impurity-generated angular distortion and hence the large trigonal distortion [which correspond to the large g-factor anisotropy and large ground state splitting ΔE(4A2)] of the Co2+ tetrahedral center in β˝-alumina are also gained. The outcomes are discussed.

STRENGTH CHARACTERISTICS OF HYPEREUTECTIC SILUMIN AFTER ELECTRON BEAM MODIFICATION

Irradiation (SOLO installation, Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences) of hypereutectic silumin specimens of Al-(22-24)Si composition with an intense pulsed electron beam was carried out. The formation of the structure of highspeed cellular crystallization of aluminum (cell size 250-600 nm) was revealed. It was shown that the cell boundaries are strengthened by globular-shaped silicon particles (particles of size 50-70 nm). It was found that the hardness of the silumin specimen surface layer increases by more than 5 times after modification. Tensile tests of plane proportional samples showed an increase in the ductility of irradiated samples while maintaining the tensile strength.

Growing Bulk Aluminum Nitride and Gallium Nitride Crystals by the Sublimation Sandwich Method

The results of the growth of bulk crystals of aluminum and gallium nitrides on foreign seeds by the sublimation sandwich method are reviewed. The kinetics and mechanism of sublimation and condensation are analyzed depending on the growth conditions, vapor phase composition, crystal orientation, and the distance between the source and the seed. It is experimentally found that during joint annealing of aluminum nitride and silicon carbide, the sublimation rate of aluminum nitride substantially increases due to the formation of a liquid phase on the crystal surface. The inhomogeneous distribution of the liquid phase, localized mainly near structural and morphological defects, leads to the selective nature of surface etching and causes a deterioration in the quality of the growing crystal. A process of growth of bulk AlN crystals with simultaneous seed evaporation was implemented, which yields crystals without cracks and with improved parameters. Bulk crystals of aluminum nitride and gallium nitride up to 2 inches in diameter were grown on SiC seeds.

Finite-displacement computation of the electron-phonon interaction within the projector augmented-wave method

A computational method has been developed to compute the electron-phonon interactions using the projector augmented wave method and finite displacements. Aluminium and diamond crystals are considered to test our strategy. It is found that the potential derivatives are quickly convergent with respect to the supercell size. Moreover the method is found to be efficient enough to densely sample the Brillouin zone and compute the Eliashberg function and phonon lifetime without requiring the use to interpolations.

Influence of Heat Treatment on Structure and Corrosion Resistance of 8090 Aluminium Alloy for Ethanol Fuel Tank Application

Investigation was carried out to understand the influence of heat treatment on structure and corrosion resistance of 8090 aluminium alloy in ethanol solution for ethanol fuel tank application. Heat treatments were subjected to solutionizing at temperature 525ºC for 4 hours to infiltrate the aluminium crystal by copper atoms and aging at temperature 190ºC with different time to bring copper and lithium atoms out of aluminium crystal during aging process. X-ray diffraction was performed to investigate the phase of each sample with different aging time. Electrochemical experiments were conducted to investigate the corrosion resistance in 3, 5% and 7% NaCl solution and 70% and 96% of ethanol solution. The results show different corrosion behaviour of this material. Heat treatment on this material shows significant different results.

Formation of Structure and Properties of Silumin on Electron-Beam Processing

The analysis of the gradient structure-phase states and nanohardness of hypoeutectoid silumin at 120 μm depth after the processing by high intensive electron beams in the regime of top layer melting has been carried out. It has been shown that depending on the depth to the surface of irradiation the electron beam processing leads to the dissolution of the primary inclusions of silicon and intermetallides and the formation of structure of high-speed cellular crystallization of aluminium and the grains of plastic eutectic. A 1.5‒2 fold decrease in the concentration of the alloying elements has been detected. The hardness of irradiated silumin changes in a nonmonotonous way and reaches the maximum values exceeding the hardness of the initial state by 3.8‒4.2 times in the layer located at 30–50 μm depth. The interpretation of the observed changes in structure and hardness on irradiation has been given.

Coarse-grain alpha-alumina films with highly ordered porous structure

Abstract Application of porous anodic alumina as membranes and templates is restricted by its rapid degradation in acidic and alkaline media. Chemical stability of the anodic alumina could be strongly enhanced by annealing leading to crystallization of as-prepared amorphous material into a mixture of low-temperature Al2O3 polymorphic modifications and then to α-Al2O3 phase. Here an approach to choosing an annealing protocol for crystallization of porous anodic alumina into the corundum phase preserving its starting morphology is suggested. Formation of corundum films with hexagonally-packed 27-nm-diameter channels by multi-step annealing of anodic alumina prepared in 0.3 М sulfuric acid at 25 V is demonstrated. According to electron backscatter diffraction, α-Al2O3 films consist of porous single-crystalline grains with an average size of ~ 5 ÷ 10 μm. Crystallization of α-Al2O3 phase from amorphous anodic alumina results in the enhancement of its chemical stability by two orders of magnitude in comparison with porous films consisting of low-temperature polymorphic modifications of Al2O3.

Characterization of aluminum oxide nanoparticles using egg white as a trap-matrix

In this article, we add egg white (albumen) to the synthesis of aluminum oxide nanoparticles (Al2O3). Egg white can be used as a trap for the aluminum oxide particle matrix to prevent agglomeration of aluminum oxide particles during the synthesis process. To determine the effect of pH on the characteristics of aluminum oxide crystals formed, variations in pH were carried out starting from 7, 9 to pH 11. The calcination temperature used was 1000°C. We used the results of XRD analysis to determine the crystalline size and crystallinity of aluminum oxide nanoparticles. pH 7 shows the size of the smallest nanoparticles of crystals and the relatively large levels of crystallinity.

Cold bonding of alumina: Fractured and re-bonding under compression

Cold bonding of metals necessitates high normal/frictional loads, or ultrahigh-vacuum treated atomically flat ductile surface. In case of ceramics composed of ionic and/or covalent bonds, the high diffusion barrier of ions or atoms gives them a constraint to bond together at room temperature. However, from this investigation, it has been found that alumina crystals could be well bonded at room temperature under high pressure. Also, it has been noticed that if the pressure is capable of yielding and breaking down alumina crystals, it could then re-bond the fractured crystals by reducing the distance of their surface atoms to meet the condition for bonding. Overall, we demonstrate a process for the cold bonding of alumina under high pressure with grain fracturing and re-bonding.