Crystal Aluminum Research Articles

Research in the area of obtaining of activated alumina. Part 7. Production of reactive alumina with controlled particle size distribution

The key technological factors determining the formation of granulometric composition of highly dispersed alpha-alumina powders in the process of thermal treatment of feedstock have been researched. The decisive influence of temperature modes of synthesis and concentration of Cr2O3 additive on phase transformations and structural and morphological characteristics of reactive alumina is shown. The fact of formation of thermodynamically stable primary crystals of alpha aluminum oxide with a characteristic mode of 0.5 μm has been established for the first time. Technological principles of thermal synthesis of reactive alpha-alumina with predictable particle size distribution have been developed.

Dislocation Emission Model of Kinked Cracks in Aluminum Crystal under the Condition of Hydrogen Filling

Dislocation Emission Model of Kinked Cracks in Aluminum Crystal under the Condition of Hydrogen Filling

Bimodal Visual Sensors Based on Mechanoluminescence and Biosensing for Artificial Intelligence‐Assisted Orthodontics

AbstractFlexible visual sensors hold great potential for application in wearable electronics and health monitoring. However, the separate acquisition of various visual signals without mutual interference and their functional integration in internal biomedical devices remains a significant challenge. Here, a functional material that integrates mechanoluminescent units with biosensing units through supramolecular interactions, enabling bimodal non‐interfering visual detection of orthodontic force and bacterial infection is presented. The orthodontic force induces fluorescence by facilitating the release of electrons from trapped energy levels, caused by the disruption or rearrangement of defect structures within strontium aluminate crystals. Meanwhile, the seamlessly integrated biosensing component can effectively detect lactic acid in a dose‐dependent manner, underscoring its multifunctional capabilities in biosensing applications. Moreover, the development of a cloud‐based deep learning server can achieve a 97.7% accuracy in the precise decoupling of visual signals, facilitating remote monitoring and enabling early intervention during orthodontic treatment. The proposed artificial intelligence‐enhanced bimodal visual sensors represent a new paradigm for orthodontic monitoring, suitable for a wide range of biomedical applications.

Buried depressed cladding waveguides in neodymium-doped yttrium aluminate crystals fabricated by femtosecond laser writing: Raman properties and laser performance

Buried depressed cladding waveguides in neodymium-doped yttrium aluminate crystals fabricated by femtosecond laser writing: Raman properties and laser performance

Diode-pumped Kerr-lens mode-locked ytterbium-doped compositional mixed calcium aluminate laser.

A diode-pumped Kerr-lens mode-locked laser generating 25 fs pulses at 1080 nm is demonstrated with an Yb3+-doped compositional mixed calcium aluminate crystal. The Yb:Ca(Gd,Y)AlO4 laser, which operates at a repetition rate of 65.6 MHz via soft-aperture Kerr-lens mode-locking, is pumped by a spatially single-mode, fiber-coupled diode laser. To the best of our knowledge, this is the first Kerr-lens mode-locked laser that utilizes an Yb3+-doped compositional mixed calcium aluminate crystal as the gain medium.

Evolution of microstructure and defects in sintering of tape-cast alumina laminates observed by synchrotron X-ray multiscale tomography

Processing-induced defects affect the performance and reliability of multilayered ceramics. They are introduced from the raw powder, or during tape casting, drying, thermo-compression, binder burnout, and sintering. Using synchrotron X-ray multiscale tomography, we investigated how the microstructural heterogeneities and various defects evolve in the sintering of tape-cast alumina laminate. The strength-limiting defects were identified as large defects at the layer interface and peculiar crack-like defects formed around large inclusions contained in the raw powder. Although a slurry might be uniform in colloidal processing, the particle packing in the tape was heterogeneous. This heterogeneity determined the spatial distribution of pores and formed complex pores in later stages. Moreover, we found the formation of flake-like sheets in slurry due to the self-assembly of polyhedral alumina crystals. This phenomenon has the potential to be applied in the manufacture of 2D micro-sheets controlled to the thickness of a single particle.

Structure Formation and Mechanical Properties of Wire Arc Additively Manufactured Al4043 (AlSi5) Components

In the current paper, the correlation between the physical size of additively built wire arc specimens and their structure and properties is studied. For the purpose of this work, two oval shaped specimens of different lengths were manufactured under the same technological conditions. The specimens have a length of 200 mm and 400 mm and will be referred to as L200 and L400. The microstructure of the samples was studied using X-ray diffraction analysis (XRD), optical microscopy, and scanning electron microscopy (SEM). The microhardness, yield strength (YS), and ultimate tensile strength (UTS) were determined and their correlation with the technological conditions of specimen build-up was clarified. The results of the carried out experiments indicated that the crystallographic structure of both specimens is similar. The scanning electron microscopy images show a higher concentration of irregularly shaped micro-pores formed near the edge of the αAl grains in the structure of the L400 specimen compared to the L200 one. An increase in the size of the αAl solid solution grains in the case of the L200 specimen towards its top section was noticed using optical microscopy. A slightly lower magnitude change was noticed concerning the L400 specimen. The increase in the size of the aluminum crystals was determined to be the increasing interpass temperature. Due to the much smaller thermal dissipation capacity of the smaller specimen, the interpass temperature of the same increased faster compared to the larger specimen. All of the above-mentioned factors led to a decrease in the microhardness of the specimens at higher stages of build-up. Since the specimens were deposited using similar layer deposition conditions, the resultant YS and UTS data are also highly comparable.

Growth, spectroscopy and SESAM mode-locking of a "mixed" Yb:Ca(Gd,Y)AlO4 disordered crystal.

We present the growth, spectroscopy, continuous-wave (CW) and passively mode-locked (ML) operation of a novel "mixed" tetragonal calcium rare-earth aluminate crystal, Yb3+:Ca(Gd,Y)AlO4. The absorption, stimulated-emission, and gain cross-sections are derived for π and σ polarizations. The laser performance of a c-cut Yb:Ca(Gd,Y)AlO4 crystal is studied using a spatially single-mode, 976-nm fiber-coupled laser diode as a pump source. A maximum output power of 347 mW is obtained in the CW regime with a slope efficiency of 48.9%. The emission wavelength is continuously tunable across 90 nm (1010 - 1100 nm) using a quartz-based Lyot filter. With a commercial SEmiconductor Saturable Absorber Mirror to initiate and maintain ML operation, soliton pulses as short as 35 fs are generated at 1059.8 nm with an average output power of 51 mW at ∼65.95 MHz. The average output power can be scaled to 105 mW for slightly longer pulses of 42 fs at 1063.5 nm.

Tunable laser operations on Nd-doped strontium and lanthanum aluminate crystals

We reported on tunable laser operations in a disordered Nd-doped strontium-lanthanum aluminate (Nd:ASL) crystal, corresponding to the formula Sr1-xNdyLax-yMgxAl12-xO19. We conducted tunable laser experiments in a V-fold cavity with a birefringence filter within the resonator for the first time. The Nd:ASL laser operating at three peak wavelengths (1050, 1062, and 1074 nm) was demonstrated. The results indicated that the wavelength tuned in two separate ranges: 1049.59–1054.43 nm and 1059.71–1078.18 nm. The multi-wavelength feature was also observed in the experiments.

Significant improvement of slag corrosion resistance and thermal shock resistance of corundum‐based dry vibratable refractory by addition of Fe–Si3N4

AbstractFe–Si3N4 was introduced to improve the service performance of corundum‐based dry vibratable refractories in the casting industry, specifically enhancing their thermal shock resistance and resistance to slag corrosion. The study analyzed the effects of Fe–Si3N4 powder content on the refractories’ mechanical properties, phase compositions, slag corrosion resistance, and microstructures. The addition of Fe–Si3N4 facilitated the production of magnesium aluminate spinel in the refractory matrix, while also decreasing the wettability between the molten slag and refractory. Increasing the Fe–Si3N4 content resulted in accelerating the replacing Mg2+ (0.072 nm) with Al3+ (0.053 nm) in the spinel. Simultaneously, Fe3+ (0.055 nm) was effectively dissolved into the alumina crystals. The bulk density, compressive strength, and slag corrosion resistance of the refractories were improved. However, the thermal shock resistance initially increased but then decreased. In industrial tests, a corundum‐based dry vibratable refractory with a 1 wt.% Fe–Si3N4 content effectively prolonged the lifespan of an induction melting furnace when used as a lining refractory. Importantly, the refractory did not spall or generate cracks in the matrix after induction melt furnace industrial test.

Trajectory sampling and finite-size effects in first-principles stopping power calculations

Real-time time-dependent density functional theory (TDDFT) is presently the most accurate available method for computing electronic stopping powers from first principles. However, obtaining application-relevant results often involves either costly averages over multiple calculations or ad hoc selection of a representative ion trajectory. We consider a broadly applicable, quantitative metric for evaluating and optimizing trajectories in this context. This methodology enables rigorous analysis of the failure modes of various common trajectory choices in crystalline materials. Although randomly selecting trajectories is common practice in stopping power calculations in solids, we show that nearly 30% of random trajectories in an FCC aluminum crystal will not representatively sample the material over the time and length scales feasibly simulated with TDDFT, and unrepresentative choices incur errors of up to 60%. We also show that finite-size effects depend on ion trajectory via “ouroboros” effects beyond the prevailing plasmon-based interpretation, and we propose a cost-reducing scheme to obtain converged results even when expensive core-electron contributions preclude large supercells. This work helps to mitigate poorly controlled approximations in first-principles stopping power calculations, allowing 1–2 order of magnitude cost reductions for obtaining representatively averaged and converged results.

Electron-ion-plasma surface modification of hypereutectic silumin

In this study, an integrated treatment approach was employed to modify hypereutectic silumin. This method involved electroexplosive alloying of the surface layer with yttrium oxide powder, followed by irradiation with a pulsed electron beam. The experimental data obtained demonstrate that this integrated treatment results in the formation of a submicron-nanocrystalline structure characterized by high-speed cellular crystallization of aluminum within the surface layer. This structure is composed of crystallization cells enriched with aluminum atoms, indicating the creation of a solid solution based on aluminum. The nanocrystalline layers, formed by silicon particles and yttrium oxide, are positioned at the cell boundaries. The study reveals that, as a consequence of integrated treatment with an electron beam energy density of 25 J/cm2 , the wear parameter of the modified samples increases by 7.9±0.6-fold, and the friction coefficient decreases by 1.7±0.15-fold compared to the initial state. Additionally, the microhardness of the modified silumin surface layer increases by 1.5±0.12-fold compared to the initial state. When the electron beam energy density is elevated to 35 J/cm2, the wear parameter of silumin is enhanced by 2.1±0.21-fold, while the friction coefficient increases by 1.13±0.1-fold. However, the microhardness decreases by 1.3±0.13-fold, while still surpassing the specified characteristics of untreated silumin. This investigation postulates that the substantial increase in the wear parameter during integrated treatment may be attributed to the presence of silicon inclusions in the surface layer that did not dissolve during the modification process. These inclusions are surrounded by the high-speed cellular crystallization structure mentioned earlier.

Optimizing the Solution Annealing of Additively Manufactured AlSi10Mg

Abstract Laser-based powder bed fusion of metals exhibit process-induced anisotropy and residual stresses, making post-manufacturing heat treatment occasionally beneficial. For AlSi10Mg, a T6 heat treatment (solution annealing, quenching, artificial aging) is recommended. Nevertheless, mechanical strength decreases as (1) the eutectic Si network dissolves, (2) the amount of dissolved Si in the Al grains decreases, and (3) the size of the silicon particles and aluminum crystals increases during solution annealing. This changes the mechanical characteristics directly or by influencing the formation of precipitation during the aging process. The success of solution annealing is affected by the annealing duration and the part’s temperature at the moment of quenching. Short annealing durations dissolve a sufficient amount of Si and Mg in the Al matrix. Therefore, both the annealing temperature’s holding duration and the heating process significantly impact the resulting microstructure. In this study, samples of different shape and size where subjected to a T6 heat treatment with different solution annealing temperatures and durations. The influence on mechanical properties after quenching and aging was investigated by hardness and tensile tests. Maximum strength is achieved by quenching promptly upon reaching the solution annealing temperature, while longer durations reduce strength as explained by the Larson-Miller parameter.

Sub-nanometer scale depth patterning on sapphire crystal by femtosecond soft x-ray laser pulse irradiation.

Damage thresholds and structures on a metal aluminum and an aluminum oxide crystal induced by the soft x-ray free electron laser irradiations were evaluated. Distinctive differences in damage thresholds and structures were observed for these materials. On the aluminum oxide crystal surface, in particular, a novel, to the best of our knowledge, surface processing, which we suggest defining as "peeling," was recognized. Surface structures formed by peeling had extremely shallow patterning of sub-nanometer depth. For the newly observed peeling process, we proposed a scission of chemical bond, i.e., binding energy model, in the crystal.

Al-40Sn ALLOY PRODUCED BY SELECTIVE LASER MELTING OF A MIXTURE OF ELEMENTARY POWDERS

Al-40Sn alloy was synthesized by selective laser melting (SLM) of a mixture of elemental powders. In the structure of the alloy, traces of a semi-elliptical melt are observed, the boundaries of the melt regions are decorated with pores and inclusions of tin. The internal structure of melt traces consists of finely crystalline regions with identically oriented columnar Al crystals separated by thin layers of tin. With an increase in laser power, the rate of crystallization of the melt decreases, and the cells of aluminum crystals increase, and with them the thickness of the tin interlayers separating them also increases. The porosity of the alloy decreases slowly with increasing power, and to minimize it, a change in the parameters of the SLM process is required.

The isothermal Boltzmann–Gibbs entropy reduction affects survival of the fruit fly Drosophila melanogaster

To the best of our knowledge, this is the first experimental evidence of the effect of isothermal changes in entropy on a living organism. In greater detail, the effect of the reduction of the total Boltzmann–Gibbs entropy (S) of the aquatic environment on the survival rate and body mass of the fruit fly Drosophila melanogaster was investigated. The tests were carried out in standard thermodynamic states at room temperature of 296.15 K and ambient atmospheric pressure of 1 bar. Two variants of entropy reduction (ΔS) were tested for ΔS = 28.49 and 51.14 J K−1 mol−1 compared to the blind and control samples. The entropy level was experimentally changed, using the quantum system for isothermal entropy reduction. This system is based on quantum bound entanglement of phonons and the phenomenon of phonon resonance (interference of phonon modes) in condensed matter (Silicon dioxide (SiO2) and single crystals of Silicon (Si0), Aluminum (Al0) plates (“chips”), glass, and water). All studied organisms were of the same age (1 day). Mortality was observed daily until the natural death of the organisms. The investigations showed that changes in the Boltzmann–Gibbs entropy affected the survival and body mass of the fruit flies. On the one hand, the reduction in entropy under isothermal conditions in the aquatic environment for ΔS = 28.49 J K−1 mol−1 resulted in an extension of the lifespan and an increase in the body mass of female fruit flies. On the other hand, the almost twofold reduction in this entropy for ΔS = 51.14 J K−1 mol−1 shortened the lives of the males. Thus, the lifespan and body mass of flies turned out to be a specific reaction of metabolism related to changes in the entropy of the aquatic environment.

Anomalous bluish-green light emitting features of europium doped barium aluminate (BaAl2O4:Eu2+) phosphor

Eu doped barium aluminate is an important material for light emitting devices. Here we report structural, optical absorption and emission features of 1–5 % Eu doped barium aluminate phosphor and explore its ‘anomalous’ emission feature. The structural analysis suggests that the undoped sample has a mixture of BaAl2O4 and BaAl12O19. On the other hand, the samples doped with Eu have a mixture of BaAl2O4, Ba(Al2O4) and BaAl12O19 phases. Among these, the major phase in all the samples was BaAl2O4. The undoped sample shows a high absorption peak at around 209 nm followed by three weak intensity peaks apparent at around 250, 288 and 338 nm. In contrast, all the doped samples show three maxima at around 209, 266 and 340 nm. The position and intensity of these absorption maxima are found to vary with the Eu concentration. The optical bandgap of the undoped sample is estimated to be 5.05 eV and it is found to reduce to 4.68 eV after doping of Eu at 5 %. All the samples produce common PL emission peaks centred at ∼405, 428 and 456 nm due to potential oxygen vacancies. The doped samples show additional peaks at around 485, 518 and 657 nm due to Eu2+ and Eu3+ ions. In particular, the sample doped with 2 % of Eu produces a strong anomalous emission band of Eu2+ ion in the bluish-green region. Our study reveals that the broadband bluish-green emission of Eu2+ ions can be achieved when the barium aluminate crystal is doped by 2 % of Eu. When the host is doped by Eu at >2 % or <2 %, the emission band associated with oxygen vacancies dominates over the Eu2+ emission.

Crystal growth and phase formation of high‐entropy rare‐earth monoclinic aluminates

AbstractFor the first time, high‐entropy rare‐earth monoclinic aluminate crystals were grown via directional solidification using the micro‐pulling‐down method. Five high‐entropy compositions were formulated with a general formula RE4Al2O9, where RE is an equiatomic mixture of five rare‐earth elements. The rare‐earth elements included were Lu, Yb, Er, Y, Ho, Dy, Tb, Gd, Eu, Sm, Nd, and La. High‐temperature powder X‐ray diffraction and Rietveld structure refinement indicated that all crystals were a single monoclinic phase and that rare‐earth average ionic radius did not affect phase purity. At room temperature, the refined lattice parameters increased consistently with increasing average ionic radii of the five compositions. One of the crystals had a typical high‐temperature phase transition of single‐RE RE4Al2O9 in the range of 1100–1150°C, which consisted of a lattice contraction upon heating. Differential scanning calorimetry indicated a thermal event corresponding to that phase transition. Electron probe microanalysis revealed Al‐rich inclusions on the surface of the crystals. Crystals containing Tb had dark surface features that became lighter after annealing in a reducing atmosphere, which indicated that Tb4+ may be responsible for the dark features.

Alumina Nucleation, Growth Kinetics, and Morphology: A Review

The reaction between aluminum and the dissolved oxygen in liquid steel yields the precipitation of alumina crystals with characteristic morphologies and size distributions. Alumina precipitation and growth involve a wide spectrum of time, length, velocity, and thermodynamic supersaturation scales throughout the refining processes. The smallest length and time scales are those quantifying the nucleation kinetics and the initial growth at the highest supersaturation. Further growth and crystal morphology depend on the concentration of surface tension elements which inhibit the crystal's faces suffering further modifications due to washing effects provided by turbulent flows. This step involves longer time, velocity, length, and moderate supersaturations. The final step involves the growth of alumina inclusions through collision–agglomeration–sintering, and capillary processes on the surfaces of argon bubbles under low supersaturations. Jumps of supersaturation, due to late aluminum additions or steel reoxidation, lead to alumina crystals changing their morphology to dendritic‐type growth. The present contribution reviews each one of these kinetic phenomena closing with the consequences that alumina precipitation has on the continuous casting process. The content of this review is useful to practitioners and theorists alike.

Finite-temperature effects on the x-ray absorption spectra of crystalline alumina from first principles

By including phonon-assisted transitions within plane-wave density functional theory methods for calculating the x-ray absorption spectrum (XAS), we obtain the Al K-edge XAS at 300 K for two crystalline Al2O3 phases. The 300 K XAS reproduces the pre-edge peak for α-Al2O3, which is not visible at the static lattice level of approximation. Configurations from Monte Carlo sampling of the γ-Al2O3 phase space at the 300 K XAS correctly describe two out of the three experimental peaks. We show that the second peak arises from 1s to mixed s-p transitions and is absent in the 0 K XAS. This letter serves as an insight into the electronic origins of the characteristic peaks in the Al K-edge XAS for alumina crystals.