Amorphous Alumina Research Articles

Vibrational and thermal properties of amorphous alumina from first principles

Vibrational and thermal properties of amorphous alumina from first principles

Fluoride leaching from tuff breccia and its removal by natural and commercial adsorbents

In Japan, the concentration of fluoride (F−) leached from rocks, such as tuff breccia, excavated in tunnel construction projects often exceeds the Japanese environmental standard of 0.8 mg/L. Because of this, proper disposal methods are necessary for managing F−-bearing excavated rocks. One effective solution based on circular economy is the use of an adsorption layer system. This system can simultaneously prevent the migration of F− released from excavated rocks and allow the recycling of this construction waste material. To determine the most suitable material for the disposal of excavated F−-bearing tuff breccia from a tunnel construction in Hokkaido, Japan, four types of natural geological materials (S-1, S-2, S-3, and S-4) obtained near the tunnel construction site, as well as three types of commercial adsorbents (calcium (Ca), magnesium (Mg), and CaMg adsorbents) were selected for evaluation. The batch adsorption test results showed that S-1 and S-4 had high adsorption capacities for F−, and the adsorption process followed the Langmuir isotherm. The adsorption of F− to the natural adsorbents was strongly influenced by the pH and the presence of bicarbonate ions (HCO3−), but unaffected by chloride (Cl−) and sulfate (SO42−). There was also a strong positive correlation between the abundance of amorphous aluminum (Al) and iron (Fe) extracted and the adsorption of F−, indicating the importance of ion exchange reactions associated with surface OH− in immobilizing F−. Meanwhile, the Mg-bearing adsorbent exhibited the highest adsorption affinity for F− among the commercial adsorbents. This was attributed to adsorption through electrostatic interactions and coprecipitation with magnesium hydroxide (Mg(OH)2) formed during the hydration of magnesium oxide (MgO). To effectively incorporate these adsorbents into the adsorption layer system, parameters such as permeability and residence time need to be determined in order to maximize the retention of F− through adsorption, ion exchange and coprecipitation reactions.

Transferrable Alumina Membranes as High‐Performance Dielectric for Flexible 2D Materials Devices

Abstract2D materials have shown great promise for novel electronic functionality. A common challenge for 2D materials‐based transistors is forming a high‐performance gate terminal due to the challenges of depositing a dielectric of sufficient quality and controllable thickness. Herein the van‐der‐Waals integration of a free‐standing Al2O3 dielectric membrane is demonstrated as a facile, scalable, and powerful gate dielectric. A process is developed that permits the wet transfer of an amorphous alumina layer with a finely adjustable equivalent oxide thickness (EOT) in the single nanometer range. Electrical characterization demonstrates the high breakdown field and low leakage of the dielectric and integration into 2D materials transistors reveals a high performance. The wafer‐scale uniformity of the dielectric membrane permits the formation of large‐scale flexible devices that exhibit good robustness and long‐term stability.

Adsorption of lead and chromium ions from electroplating wastewater using plantain stalk modified by amorphous alumina developed from waste cans

Waste beneficiation is key to environmental protection and the realisation of a circular economy. Herein, amorphous alumina (a-Al2O3) derived from aluminium waste cans (AWC) was used to modify plantain stalk as an adsorbent for sequestration of lead (II) and chromium (VI) ions from electroplating wastewater. Raw plantain-stalk (RPS) and amorphous-alumina modified plantain stalk (APS) developed as adsorbents were characterised using various equipment such as x-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET). The FTIR revealed that the adsorbents are rich in functional groups that could promote the adsorption process which includes carboxyl, hydroxyl, and aliphatic groups. Also, the BET analysis showed a substantial increase in the surface area of APS (174.448 m2/g) compared to that of RPS (40.531 m2/g) which could be due to the effect of modification by the a-Al2O3. The batch adsorption studies revealed that the APS achieved 99.38% and 98.33% removal of Cr(VI) and Pb(II), respectively, which is superior to RPS adsorption efficiency. Also, the estimated and experimental data for the APS compared well under all the kinetic models studied with R2 > 0.88. This suggested that chemisorption is the most plausible adsorption mechanism of Cr(VI) and Pb(II) onto the APS. Further analysis showed that the Cr(VI) and Pb(II) adsorption followed the Langmuir model with the RL value of 0.038 and 0.999, respectively, which indicated that the two metal ions were effectively adsorbed onto the APS. Therefore, this work demonstrated that the modification of plantain-stalk with amorphous-alumina derived from AWC enhanced the characteristics of the APS and favoured its adsorption of the selected heavy metals.

Utilizing the Adsorbability of Pseudoboehmite for Tailoring the Stability of an Aluminum Sulfate Alkali-free Accelerator for Shotcrete.

Shotcrete is widely used in tunnels, bridges, culverts, and other large-scale projects. The accelerator is an additive employed to expedite the setting time of shotcrete. Previous research primarily concentrated on enhancing the early strength of accelerators, whereas their long-term stability has been inadequately investigated. In this study, pseudoboehmite (PB) and amorphous aluminum hydroxide (AAH) were incorporated into the accelerator to enhance its stability over a period of 90 days without any signs of crystallization or delamination. Furthermore, the accelerator exhibited an initial setting time of 170 s, a final setting time of 550 s, and a compressive strength of 11.58 MPa after 1 day. The mechanism of effects was studied by isothermal calorimetry, FTIR, XRD, TG-DTG, and SEM analysis. The enhancement in stability is attributed to the distinctive adsorption and thixotropic properties of PB, which facilitate the formation of an electrical double-layer structure in acidic solutions. The expedited setting and hardening are primarily due to the equilibrium between Al3+, SO42-, and Ca2+ ions, which accelerates the hydration process of cement. This research offers a methodology for developing a high-performance, alkali-free liquid accelerator.

Ultrastrong and Deformable Aluminum-Based Composite Nanolaminates with Transformable Binary Intergranular Films.

Nanostructured metals with conventional grain boundaries or interfaces exhibit high strength yet usually poor ductility. Here we report an interface engineering strategy that breaks the strength-ductility dilemma via externally incorporating graphene oxide at lamella boundaries of aluminum (Al) nanolaminates. By forming the binary intergranular films where graphene oxide was sandwiched between two amorphous alumina layers, the Al-based composite nanolaminates achieved ultrahigh compressive strength (over 1 GPa) while retaining excellent plastic deformability. Complementing experimental results with molecular dynamics simulation efforts, the ultrahigh strength was interpreted by the strong blocking effect of the binary intergranular films on dislocation nucleation and propagation, and the excellent plasticity was found to originate from the stress/strain-induced crystalline-to-amorphous transition of graphene oxide and the synergistic deformation between Al nanolamellas and the binary intergranular films.

Identification and characterization of tephra for geopolymer precursor

Abstract Volcanic ash and pumice are products of volcanic eruptions characterized by a high amount of amorphous silica and alumina. They can potentially serve as a source of raw materials for the production of geopolymers. Geopolymers are more environmentally friendly compared to conventional cement. However, there is a requirement for aluminosilicate for creating geopolymers. This study aims to identify the mineralogical composition and chemical properties of the volcanic ashes and pumices that are potentially used as geopolymers precursor materials. Tephra and pumice samples were collected from several volcanoes in Indonesia. The samples include two tephras from recently erupted volcanoes in Java and one pumice material from West Sumatra. Tephras were collected one week after the eruptions of Mt. Tangkuban Perahu (26th July 2019). Another source of tephra was collected from Mt. Kelud, which erupted on 13th February 2014. Pumice samples of Mt. Maninjau were collected at Sungai Limau district, 30 km from the Maninjau caldera, a product of the Holocene (52K) volcanic eruption of Mt. Maninjau. Mineralogy of the tephra and pumice samples was identified with XRF and XRD. Chemical properties characterized include pH, exchangeable cations, cation exchange capacity (CEC), potential-P, and available-P. Results showed that crystalline feldspar minerals and amorphous volcanic glass dominated volcanic ash and pumice. The SiO2 content is higher in pumice, followed by tephras from Mt. Tangkuban Perahu and Mt. Kelud (74.97%-60.28%). But the Al2O3 content is higher in Mt. Kelud compared to pumice and Mt. Tangkuban Perahu (23.57%-4.03%). The pH is very acidic to slightly acidic (2.35–6.1). Mg is higher than Ca, Na, and K. The potential-P and available-P were considered very low. Among the samples, Mt. Kelud volcanic ash has the highest available P compared to Tangkuban Perahu volcanic ash and pumice. The SiO2/Al2O3 ratio are 4.35, 8.00, and 26.38 for samples of Mt. Kelud, Mt. Maninjau pumice, and Mt. Tangkuban Perahu, respectively. The optimum ratio of geopolymer is between 2.5–5; thus, volcanic ash Mt. Kelud is the most suitable option. Nevertheless, the exchangeable basic cations of volcanic ash and pumice indicated that they are more suitable for plant nutrition.

Fault-tolerant structures against breakdown in heterogeneous ferroelectric PbZr0.52Ti0.48O3 thin films based on adaptive self-repairing effects

The design of fault-tolerant structures against the breakdown of heterogeneous ferroelectric films is essential to enhance the breakdown strength. Based on the self-repairing theory, heterogeneous ferroelectric PbZr0.52Ti0.48O3 (PZT) film capacitors with a fault-tolerant structures against breakdown were synthesized by utilizing dielectric/electrolytic dual characteristics of the amorphous aluminum oxide film (AmAO). The PZT/AmAO composite films with Au top electrodes exhibited significant weak breakdown at low voltages, whereas the breakdown in the composite films with Al top electrodes have been repaired and no longer occurred. Compared to PZT(100 nm)/AmAO(120 nm) composite films with Au top electrodes, breakdown strength of PZT(100 nm)/AmAO(120 nm) composite films with Al top electrodes improves from 278 MV/m to 477 MV/m, energy storage density increased from 14.3 J/cm3 to 22.5 J/cm3, since the heterogeneous interface and structural defects have been repaired by adaptive anodizing of Al electrode under high electric field. Cross-sectional SEM images have confirmed the formation of fresh aluminium oxide films (AAO) at the interfaces of AmAO/Al and PZT/AmAO during the application of an electric field. Defects have been effectively repaired, resulting in an increase in breakdown strength. This study establishes a theoretical and technical foundation for the design of fault-tolerant structures against breakdown in heterogeneous ferroelectric films.

Surface Enhanced Raman Spectroscopy Application of Aluminum Nanofilm in Improving the Performance of Optical Telescopes

Optical telescopes play a crucial role in exploring the universe, and understanding various aspects of the Earth and the universe. However, traditional optical telescopes have problems with high noise in the optical signal, which is not conducive to material analysis. To improve the performance of optical telescopes, this study utilized surface enhanced Raman spectroscopy technology of aluminum nanofilms for spectral analysis. The experimental results demonstrated that the amorphous aluminum film prepared by UV annealing exhibited Raman spectral enhancement effect at different laser wavelengths. The optimal effect can be achieved by using excitation light with a wavelength of 670 nm. The transmittance curve modified by aluminum nanofilm met the requirements of a day blind ultraviolet detector. Moreover, the bandgap energy gap was approximately 5 eV. The detector with a 7 nm aluminum deposition had the best performance improvement. The modification of aluminum nanoparticles improves the photoelectric response and reduces the time constant of the slow response stage. This study provides a foundation for further exploration and application of surface enhanced Raman spectroscopy technology in improving the performance of optical telescopes.

Improved mechanical properties of GNPs/Al composites by eliminating alumina and obtaining a strong bonded GNPs-Al direct contact interface and Mg-rich phases

The interface between Graphene Nanosheets and Aluminum (GNPs-Al) without carbide and transition layers is referred to as a direct-contact GNPs-Al interface. In this work, the GNPs-reinforced aluminum matrix composites are fabricated by ultrasonic casting process. The interfacial structure of GNPs-Al is investigated using transmission electron microscopy, and the strength of the fabricated direct-contact GNPs-Al interface is analyzed. The results identified the presence of weak amorphous aluminum oxide at the original GNPs-Al interface. The direct contact GNPs-Al interface was obtained by introducing Mg. The migration of Al atoms formed an Al/C mixing zone between GNPs-Al, which led to the enhancement of the interface strength. The average UTS value has improved by about 20.5% due to the optimization of the interface structure. The enhancement of strength at the same toughness is achieved by the load transfer of GNPs, bridging, and the enhancement of dislocation storage capacity by the Mg-rich phase. The present work provides a new reference for the reinforcement of cast aluminum alloys by GNPs.

Effect of mechanical milling on microstructure evolution and mechanical properties of Al–Zn–Mg–Cu–Si alloy fabricated via spark plasma sintering

We investigated the effect of high-energy ball milling (HEBM) on the microstructure and mechanical properties of powders and spark plasma sintered samples of an Al–Zn–Mg–Cu–Si alloy. HEBM produced a nanocrystalline powder with an average grain size of 0.16 μm while increasing the amount of solid solution and the formation of fine amorphous aluminium oxide. The sintered alloy without HEBM consisted of η-Mg(Zn,Cu,Al)2, T-Mg32(Al,Zn)49, β-Mg2Si, and Q-Al5Cu2Mg8Si6 phases. The grain size of the sintered alloy decreased from 2.66 to 0.40 μm due to the application of HEBM. The amorphous aluminium oxide phase in the milled powder was transformed into MgO particles during sintering. The formation of MgO particles caused the depletion of Mg solid solutions, which resulted in the formation of Mg-free phases during sintering. High-energy ball milling (HEBM) improved the microhardness of the sintered alloy from 94 to 134 HV owing to grain refinement and the formation of fine secondary phases and MgO particles.

Combined Experimental and Computational Insight into the Role of Substrate in the Synthesis of Two-Dimensional WSe2.

Synthesis of large-area transition-metal dichalcogenides (TMDs) with controlled orientation is a significant challenge to their industrial applications. Substrate plays a vital role in determining the final quality of monolayer materials grown via the chemical vapor deposition process by controlling their orientation, crystal structure, and grain boundary. This study determined the binding energy and equilibrium distance for tungsten diselenide (WSe2) monolayers on crystalline and amorphous silicon dioxide and aluminum dioxide substrates. Differently oriented WSe2 monolayers are considered to investigate the role of the substrate in the orientation, binding strength, and equilibrium distance. This study can pave the way to synthesizing high-quality two-dimensional (2D) materials for electronic and chemical applications.

Dependence between glass transition and plasticity in amorphous aluminum oxide: A molecular dynamics study

Aluminum oxide (Al2O3) is known to form amorphous structures that exhibit a unique plastic deforming ability at room temperature. However, alumina is considered a poor glass former, and it has been unclear whether alumina undergoes a glass transition during solidification from melt, and what effects such a transition would have on the plastic deform ability of the material. Here, we show using molecular dynamics simulations that a melt-quenched alumina indeed exhibits a glass transition, and that the glass transition greatly affects the observed material ductility. The glass transition temperature is found to positively correlate with the used cooling rate and we observe that maximum stress correlates with varying quench cooling rates in tensile test simulations, indicating that profound structural differences are formed during the glass transition. Significantly, we show that inducing plastic deformation allows erasing the structural memory of the material, and at 50% strain, all samples quenched at different rates shift again to exhibit similar flow stress. Characterizing methods that include medium-range structural information show a better ability to capture the structural differences formed during the glass transition. Our analysis results indicate that lower glass transition temperature imposes deeper potential wells of atoms and, therefore, a ’colder’ structure. The mechanical work input plays a similar role as input thermal energy to the structure. A ’colder’ structure needs more mechanical energy to get activated, thus showing a higher maximum stress. At a steady state flow, all samples show similar flow stress, indicating a similar structure.

A fast crystallization of TUN zeolite via the interzeolite conversion method

Abstract A TUN-type aluminosilicate zeolite was rapidly synthesized via the interzeolite conversion method (IZC) using a MWW-type one as a starting material. It was found that the co-addition of the organic structure direct agent (OSDA) and the seed played a crucial role in accelerating the crystallization of the TUN phase. The TUN zeolite synthesized via the IZC method exhibited comparable physicochemical properties to those of the conventional one crystallized from amorphous silica and alumina materials.

Selective oxidation of methanol to green oxygenates on vanadium-aluminum phosphate based catalysts

The methanol transformation reaction in the presence of oxygen was carried out in the temperature range of 210–310 ºC, over vanadium catalysts based on vanadium oxide (V2O5) and on vanadium-phosphorus oxide (VPO) calcined at 450 ºC in air. Specifically, the vanadium oxide systems with V2O5 loadings below, above or corresponding to the theoretical monolayer (1–34 wt% of V2O5) were obtained by the impregnation of a mesoporous amorphous aluminum phosphate, AlPO4, calcined at different temperatures (from 350 ºC to 650 ºC) with vanadyl oxalate. Additionally, mechanical mixtures of either VPO or V2O5 with AlPO4 were also employed. Under the experimental conditions employed, with a methanol enriched feed (O2/methanol molar ratio=0.6), formaldehyde and dimethoxymethane were the main products obtained with all the catalysts studied. Vanadyl phosphate (VPO) exhibited slightly lower activity than vanadium oxide, formaldehyde being the main product (SFA ≥ 95%). The conversion of both vanadium oxide and vanadyl phosphate appreciably increased when mixed with the AlPO4, also promoting the formation of dimethoxymethane. The interaction of the vanadium species with the aluminum phosphate surface took place preferentially through the surface Al-OH groups, the vanadium species with less development being the most active in the formation of formaldehyde and dimethoxymethane, per at-g of vanadium.

Insights into formation and properties of amorphous mesostructured alumina

Here, using liquid crystals as template, an EISA (evaporation-induced self-assembly) method has been used to synthesize amorphous mesostructured alumina. The effect of the synthesis parameters such as the presence of a chelating agent, the amounts of both porogen agent and alumina precursor on the materials properties have been investigated in details. Under the optimum conditions, after Soxhlet extraction, the obtained Al2O3 presents an HMS (Hexagonal Molecular Sieves) structure and a high specific surface area (≈400 m2/g) with a mesopore size distribution centered around 8.3 nm.Investigation of the thermal stability shows that the crystallization into γ-Al2O3 of the amorphous alumina walls delimiting mesopores begins after heating at 800 °C. We have also demonstrated that half of the carbon present in the as-synthesized material can be removed by washing with water or ethanol at room temperature instead of Soxhlet extraction.On the basis of SAXS, XRD and N2 adsorption-desorption analyses, we have shown that when treated into boiling water or exposed to water vapor the alteration of the mesostructure occurs quickly. Its collapse has been attributed to the crystallization of the amorphous alumina walls into aluminum hydroxides, mainly boehmite, upon the hydration of the alumina.Dual mesoporous alumina have been also obtained from micelles through a cooperative templating mechanism at low P123 amount and in the presence of citric acid. In that case both mesopores networks adopt a wormhole-like mesostructure.

Precipitation of amorphous iron and aluminum during the weathering of rock dust in soil columns

Precipitation of amorphous iron and aluminum during the weathering of rock dust in soil columns

Synthesis and sintering of 1D Al2O3@MWCNTS ceramic composite with excellent mechanical and electrical properties for advanced engineering applications

A novel strategy was exploited to synthesize one-dimensional (1D) Al2O3 ceramic by using MWCNTs as a template. The prepared amorphous alumina [Al(OH)3] was annealed at high temperatures to convert it into corundum Al2O3. Homogeneous dispersion of MWCNTs was obtained by the deposition of Al2O3 on the MWCNTs surface. Then, the calcined 1D Al2O3@MWCNTs hybrid powder was sintered at 70 MPa and 1300 ˚C for 10 min using spark plasma sintering (SPS). The microstructure analysis confirmed the uniform distribution of MWCNTs in Al2O3 ceramic. The compressive residual stresses on MWCNTs lead to a much stronger grain boundary as well as higher interfacial shear strength between the outer wall of MWCNT and Al2O3 ceramic. As a result, by the addition of only ∼1.27 wt.% MWCNTs, the flexural strength and fracture toughness along with higher electrical conductivity (315 S/m) were simultaneously enhanced up to ∼70% and ∼73%, respectively, with respect to monolithic Al2O3.

In-depth characterization of phosphate intercalated Mg Al Layered double hydroxides and study of the PO4 release properties.

Slow-release fertilizers (SRFs) form the core of innovative strategies in sustainable agriculture. Layered Double Hydroxides (LDH), known for their high capacity to sequester plant nutrients, especially phosphate, are emerging as promising candidates for SRF synthesis. The phosphate release properties of MgAl LDH (with a targeted Mg/Al ratio of 2.0) intercalated with HPO42- anions were assessed in various aqueous environments. A comprehensive analysis, including in-depth chemical and structural characterizations (ICP-OES, XRD, PDF, 27Al NMR, 31P NMR, FTIR, SEM) of the as-prepared phase unveiled a more intricate composition than anticipated for a pure or ideal Mg2Al-HPO4 LDH, encompassing an excess of intercalated phosphate in conjunction with K+. Beyond the intercalated phosphate, solid state 31P NMR speciation identified multiple HxPO4(-3+x) environments, indicating a portion of the phosphate reacting with intralayer Mg2+ to form K-struvite. Additionally, some phosphates were adsorbed onto the surface of amorphous aluminum hydroxide, a side phase formed during MgAl coprecipitation. The phosphate release demonstrated rapid kinetics, occurring within 6 days. Moreover, the released phosphate increased significantly when reducing the Solid/Liquid (S/L) ratio (58%) and further increasing in the presence of carbonate ions (90%). The released phosphate varied from 12% to 90% under different release conditions, transitioning from water to a 3.33 mM NaHCO3 aqueous solution at a low S/L ratio (from 20 mg LDH per mL to 0.02 mg LDH per mL). The simultaneous release of K+, Mg2+, Al3+ indicated the complete dissolution of the K-struvite and partial dissolution of phosphate intercalated MgAl LDH. These results enhanced our understanding of the mechanism governing phosphate release from MgAl LDH, paving the way for potential phosphate recovery by LDH or for the development of LDH-based SRFs.

On the Structure of Oxygen Deficient Amorphous Oxide Films.

Understanding defects in amorphous oxide films and heterostructures is vital to improving performance of microelectronic devices, thin-film transistors, and electrocatalysis. However, to what extent the structure and properties of point defects in amorphous solids are similar to those in the crystalline phase are still debated. The validity of this analogy and the experimental and theoretical evidence of the effects of oxygen deficiency in amorphous oxide films are critically discussed. The authors start with the meaning and significance of defect models, such as "oxygen vacancy" in crystalline oxides, and then introduce experimental and computational methods used to study intrinsic defects in amorphous oxides and discuss their limitations and challenges. To test the validity of existing defect models, ab initio molecular dynamics is used with a non-local density functional to model the structure and electronic properties of oxygen-deficient amorphous alumina. Unlike some previous studies, the formation of deep defect states in the bandgap caused by the oxygen deficiency is found. Apart from atomistic structures analogous to crystal vacancies, the formation of more stable defect states characterized by the bond formation between under-coordinated Al ions is shown. The limitations of such defect models and how they may be overcome in simulations are discussed.