Reactive Aluminum Research Articles

Growth and Characterization of Reactive DC Magnetron Sputtered Aluminum Titanate Thin Films

Aluminum titanate (Al2TiO5) films were deposited on to unheated p-silicon and quartz substrates by reactive DC magnetron sputtering of Al67Ti33 target at an oxygen flow rate of 8 sccm and at sputter pressure of 2x10-3 mbar. The as-deposited films were annealed in oxygen ambient at 600°C. The as-deposited and annealed films were characterized for chemical composition core level binding energies, crystallographic structure and optical properties. The as-deposited films were amorphous in nature while those annealed in oxygen were of polycrystalline with orthorhombic structure. Atomic force micrographs confirmed the fine grain growth of the films and the size of the grain increased in annealed films. The films showed optical transmittance of above 85 % in the visible region. The optical band gap of the films decreased from 4.58 eV to 4.50 eV.

Growth and Characterization of Reactive DC Magnetron Sputtered Aluminum Titanate Thin Films

Aluminum titanate (Al2TiO5) films were deposited on to unheated p-silicon and quartz substrates by reactive DC magnetron sputtering of Al67Ti33 target at an oxygen flow rate of 8 sccm and at sputter pressure of 2x10-3 mbar. The as-deposited films were annealed in oxygen ambient at 600°C. The as-deposited and annealed films were characterized for chemical composition core level binding energies, crystallographic structure and optical properties. The as-deposited films were amorphous in nature while those annealed in oxygen were of polycrystalline with orthorhombic structure. Atomic force micrographs confirmed the fine grain growth of the films and the size of the grain increased in annealed films. The films showed optical transmittance of above 85 % in the visible region. The optical band gap of the films decreased from 4.58 eV to 4.50 eV.

Self-hardening of fly ashes from a bubbling fluidized bed combustion of peat, forest industry residuals, and wastes

More and more biomass fly ash is produced because of the increasing usage of renewable energy sources. Therefore, novel applications in which biomass fly ashes can be utilized efficiently are needed. One interesting option is to use biomass fly ashes in hardening applications such as earth construction. In this study, the self-hardening of fly ashes from a bubbling fluidized bed combustion of peat, sludges from the papermaking industry, forest industry residuals, and other wood wastes was investigated. The self-hardening compressive strength of fly ashes after 28days and one year of hardening was measured for four different fly ash samples. The compressive strength for self-hardening samples was dependent on reactive calcium, aluminum, silicate, and sulfate content, but calcium (Ca) and aluminum (Al) seemed to be the most important components. According to the X-ray diffraction measurements, the main reaction products are ettringite, hydrocalumite, monocarboaluminate, and various types of Ca–Al phases.

Reactive Plasma-Sprayed Aluminum Nitride-Based Coating Thermal Conductivity

Recently, thick aluminum nitride/alumina (AlN/Al2O3) composite coatings were successfully fabricated through the reactive plasma spraying of fine Al2O3/AlN mixture in the N2/H2 atmospheric plasma. The coatings consist of AlN, Al5O6N, γ-Al2O3, and α-Al2O3 phases. This study will evaluate the thermal conductivity of these complicated plasma-sprayed coatings and optimize the controlling aspects. Furthermore, the influence of the process parameters on the coatings thermal conductivity will be investigated. The fabricated coatings showed very low thermal conductivity (2.43 W/m K) compared to the AlN sintered compacts. It is attributed to the phase composition of the fabricated coatings, oxide content, and porosity. The presence of Al2O3, Al5O6N and the high coating porosity decreased its thermal conductivity. The presence of oxygen in the AlN lattice creates Al vacancies which lead to phonon scattering and therefore suppressed the thermal conductivity. The formation of γ-Al2O3 phase in the coating leads to further decrease in its conductivity, due to its lower density compared to the α-phase. Moreover, the high porosity of the coating strongly suppressed the conductivity. This is due to the complicated microstructure of plasma spray coatings (splats, porosity, and interfaces, particularly in case of reactive spray process), which obviously lowered the conductivity. Furthermore, the measured coating density was lower than the AlN value and suppressed the coating conductivity. In addition, the spraying parameter showed a varied effect on the coating phase composition, porosity, density, and therefore on its conductivity. Although the N2 gas flow improved the nitride content, it suppressed the thermal conductivity gradually. It is attributed to the further increase in the porosity and further decrease in the density of the coatings with the N2 gas. Furthermore, increasing the arc did not show a significant change on the coating thermal conductivity. On the other hand, the influence of spray parameters was optimized by investigating the effect of simple heat treatment (at 1100 °C) as a function of the arc current and N2 gas flow. The heat treatment improved the coating thermal conductivity at the different spray parameters. Thus, after heat treatment, the coating porosity, γ-Al2O3, Al5O6N strongly decreased and therefore the conductivity improved. On the other hand, the N2 gas flow and/or arc current did not show any difference on the conductivity after heat treatment. Therefore, using higher N2 gas flow and higher arc current is economically useless. Finally, although the obtained conductivity of the coating was not so high (compared to the AlN value), the main factors that govern the conductivity of such complicated plasma-spraying composite coating was realized. Herein, in order to fabricate high thermal conductivity AlN plasma spray coating, adjusting the phase composition, oxide content, porosity, and microstructure (at low N2 gas flow rate and low arc current) through the post-heat treatment is the key factor.

Elements of modelling the use of particles in solid-propellant rocket motors

Important elements of the framework for numerically evaluating the usage of reactive aluminum particles in solid-propellant rocket motors are brought forward, and where possible, predicted model re...

Co-sputtered amorphous Nb–Ta, Nb–Zr and Ta–Zr coatings for corrosion protection of cyclotron targets for [18F] production

Protective corrosion resistant coatings serve for decreasing the amount of ionic contaminants from Havar® entrance foils of the targets for [18F] production. The corrosion damage of coated entrance foils is caused mainly by the diffusion of highly reactive products of water radiolysis through the protective film toward Havar® substrate. Since amorphous metal alloys (metallic glasses) are well-known to perform a high corrosion resistance, the glass forming ability, microstructure and diffusion barrier efficiency of binary alloys containing chemically inert Nb, Ta, Zr were investigated. Nb–Ta, Nb–Zr and Ta–Zr films of different alloy composition and ∼1.5μm thickness were co-deposited by magnetron sputtering. Diffusion barrier efficiency tests used reactive aluminum underlayer and protons of acid solution and gallium atoms at elevated temperature as diffusing particles. Though co-sputtered Nb–Ta and Nb–Zr alloy films of different contents were crystalline, Ta–Zr alloy was found to form dense amorphous microstructures in a range of composition with 30–73% atomic Ta. The diffusion barrier efficiency of Nb–Zr and Nb–Ta alloy coatings decreased with increase of Nb content. The diffusion barrier efficiency of sputtered Ta–Zr alloy coatings increased with the transition from nanocrystalline columnar microstructure to amorphous for coatings with 30–73at.% Ta.

Development of low-friction and wear-resistant surfaces for low-cost Al hot stamping tools

In this study, advanced surfaces and coatings have been developed using plasma thermochemical treatment, PVD coating, electroless Ni-BN plating and duplex surface engineering to produce low-friction and wear-resistant surfaces for cast iron stamping tools. Their microstructural and nano-mechanical properties were systematically analysed and the tribological behaviour of these new surfaces and coatings were evaluated. The experimental results have shown that under dry sliding condition, the tribological behaviour of aluminium differed great from that of steel regardless of the counterpart material. Highly reactive aluminium had a strong tendency to solder with tool surfaces during dry sliding. However, the lubricity of gray cast irons can be significantly improved by Ni-BN and DLC coatings. The coefficient of friction reduced from about 0.5 for untreated cast irons to about 0.2 sliding against aluminium. Duplex treatment combining plasma nitrocarburising with low- friction coatings showed superior durability than both DLC and Ni-BN coatings.

Hydroalumination of Alkenes and Alkynes by Primary Aluminum Hydrides under Mild Conditions

The reactions of the sterically crowded primary alane (ArPri8AlH2)2 (ArPri8 = C6H-2,6(C6H2-2,4,6-Pri3)2-3,5-Pri2) with alkynes and alkenes are described. It is shown that hydroalumination of the terminal alkynes HCCSiMe3 and HCCPh readily occurs under mild conditions via the cis-addition of the Al–H moiety across the CC triple bond with no evidence of hydrogen elimination. Hydroalumination was observed also with a range of terminal olefins, but no reactivity was observed with internal alkenes or alkynes. The relatively high reactivity of (ArPri8AlH2)2 was attributed to the steric crowding of the large terphenyl substituent, which favors dissociation of the alane and increases the availability of the more reactive three-coordinate aluminum site in the monomer. In keeping with this view, studies of the reactions of the three primary alanes (ArPri8AlH2)2, (ArPri4AlH2)2 (ArPri4 = C6H3-2,6(C6H3-2,6-Pri2)2), and (ArMe6AlH2)2 (ArMe6 = C6H3-2,6(C6H2-2,4,6-Me3)2) with alkenes showed that the reaction rates are inv...

The role of aluminium in alkali-activated bentonites

In the pursuit of new sources of aluminosilicates for alkaline cement manufacture, the present paper reports on the compositional and mineralogical assessment of the reactive potential of several types of bentonites. A number of factors affect strength development in these materials, in particular their potentially reactive silica and aluminium content. While bentonites normally have a high SiO2 content, the amount of reactive Al2O3 present is not always sufficient for the purpose at hand. The present study consequently also explored the effect of adding aluminium correctors (commercial sodium aluminate and bauxite) to the mix. The findings showed that de-hydroxylated bentonite reacted with an alkaline activator, yielding materials with cementitious properties. The addition of 10 % sodium aluminate raised mechanical strength, which was unaffected by the inclusion of bauxite. The primary reaction product was consistently found to be a (N,C)–A–S–H gel, with zeolites as the secondary products.

Activated aluminum powders for space propulsion

Aluminum powders are commonly used in solid propellants to enhance the performance of space propulsion systems. During combustion, a fraction of the fuel metal particles, which emerge from the bulk, tends to merge into aggregates. These structures eventually leave the combustion surface in the shape of partially molten agglomerates which can reach the size of hundreds of microns. These condensed combustion products partake in nozzle expansion and hinder the delivered specific impulse of the rocket unit. The enhancement of original particle reactivity improves combustion quality and may reduce sensibly agglomerate size and relevant losses.More reactive aluminum fuel can be obtained by activation of micron-sized powders, without resorting to the use of nano-metals. One of the methods consists of a chemical treatment with a processing solution which alters the standard oxide layer at the surface of the particles. Such modifications grant lower ignition temperature and faster propellant burning rates but deplete a fraction of the active metal content, as a result of the chemical reaction.The present paper compares the features of three batches of aluminum particles which were treated with fluorine-based activating solutions of different concentrations. The batches were supplied in the frame of HISP FP7 European Project. The characterization focused on physical, chemical and thermal properties, looking at the reactivity of the samples and at the alterations introduced by the chemical processing. Finally, activated aluminum batches were tested in lab-scale propellants, monitoring the variation of ballistic properties with respect to a reference formulation.

Crystal growth, structure and magnetic properties of Sm3Ni5Al19: A compound in the Sm2n+mNi4n+mAl15n+4m homologous series

Sm3Ni5Al19 was obtained as large rod shaped single crystals from reactive aluminium flux. Single crystal X-ray diffraction suggests that Sm3Ni5Al19 crystallizes in the Gd3Ni5Al19 structure type, orthorhombic space group Cmcm and lattice constants a = 4.0974(1) Å, b = 16.0172(6) Å and c = 27.0774(10) Å. Sm3Ni5Al19 is a member of the Sm2n+mNi4n+mAl15n+4m series with n = 1 and m = 1. The crystal structure of Sm3Ni5Al19 consists of SmNiAl4 and Sm2Al4Al15 slabs intergrown along the b-axis. Magnetic susceptibility data on Sm3Ni5Al19 confirms the paramagnetic nature with a complicated magnetic ordering below 18 K. The inverse susceptibility data follows modified Curie-Weiss law above 150 K with effective magnetic moment 1.3 μ B/Sm atoms suggests trivalent Sm atoms. Sm3Ni5Al19 was obtained as large rod shaped single crystals from reactive aluminium flux. It is a member of the Sm2n+mNi4n+mAl15n+4m series with n = 1 and m = 1. Magnetic susceptibility data on Sm3Ni5Al19 confirms the paramagnetic nature with complicated magnetic ordering below 18 K.

Influence of the surface roughness of the bottom electrode on the resistive-switching characteristics of Al/Al2O3/Al and Al/Al2O3/W structures fabricated on glass at 300 °C

Resistive-switching devices based on Metal–Insulator–Metal (MIM) structures have shown promising memory performance characteristics while enabling higher density of integration. Usually, these MIM devices are fabricated using different processing conditions including high temperature thermal treatments that could lead to undesirable chemical reactions in the insulator material and at its interface with the metals involved. In this work, we compare the electrical characteristics of MIM devices (fabricated on glass at 300°C) that use aluminum or tungsten as bottom electrode (BE) in order to study the influence of a highly reactive (aluminum) or inert (tungsten) metal electrode on the memory characteristics. We found that the switching characteristics of Al2O3 (from a high-resistance state HRS to a low-resistance state LRS and vice versa), are highly dependent on the surface roughness of the BE, the thickness of Al2O3 and the current compliance (CC) which limits the electron density flowing through both top/bottom electrodes.

Quenching distance of flames in hybrid methane–aluminum mixtures

Quenching distances for laminar flames in hybrid methane–aluminum fuel mixtures (16.3%O2/8.1%CH4/75.6% N2/Al) were experimentally measured at different concentrations of aluminum suspensions with the aluminum particles having an average size of about d32=5.6μm. Experiments were performed with freely propagating flames in a 48-mm-inner-diameter Pyrex glass tube. A set of parallel equidistant metal plates was installed at about 50cm from the open tube end, forming parallel channels. The flame was initiated at the upper open tube end and propagated downwards. Benchmark experiments performed with an inert silicon carbide (SiC) powder suspension in the same gaseous mixture have demonstrated a steady increase of the quenching distance from about 3.5mm for an unseeded methane flame to about 9.5mm for a flame seeded with 270g/m3 of SiC. At higher SiC concentrations, the flame failed to propagate down the tube. Coupled aluminum–methane flame fronts only appeared above a threshold aluminum concentration around 300g/m3. Below this concentration, the appearance and quenching behaviors of the methane flame seeded with reactive aluminum and inert SiC dusts were similar. The coupled aluminum–methane flame demonstrated two quenching modes. At concentrations below 400g/m3, the aluminum flame decoupled from the methane flame and quenched while the methane flame still propagated. The quenching of a decoupled methane flame in a narrow channel resembles the quenching behavior of the inert powder-seeded flame. At concentrations above 400g/m3, only a coupled aluminum–methane flame could be observed to propagate, or be extinguished, as a whole and exhibited a weaker dependence of the quenching distance on aluminum concentration. These results were interpreted in terms of models for binary fuel mixtures wherein the second fuel to react is completely decoupled, separated by a fixed distance, or merged with the initial flame front.

Reactivity and self-hardening of fly ash from the fluidized bed combustion of wood and peat

An investigation into the self-hardening of fly ash from the fluidized bed combustion of wood, peat and forest industry residuals shows the self-hardening strength of eight different ash samples after 28days of curing at room temperature followed by 7days at 50°C to be dependent on its reactive calcium, aluminium and sulphate content. The main reaction products were ettringite and hydrocaluminate. Sulphate was found to be the most typical limiting component for ettringite formation.

Aluminum exposure and toxicity in neonates: a practical guide to halt aluminum overload in the prenatal and perinatal periods.

During the last years, human newborns have been overexposed to biologically reactive aluminum, with possible relevant consequences on their future health and on their susceptibility to a variety of diseases. Children, newborns and particularly preterm neonates are at an increased risk of aluminum toxicity because of their relative immaturity. Based on recent original publications and classical data of the literatures, we reviewed the aluminum content in mother's food during the intrauterine life as well as in breast milk and infant formula during lactation. We also determined the possible role of aluminum in parenteral nutrition solutions, in adjuvants of vaccines and in pharmaceutical products. A special focus is placed on the relationship between aluminum overexposure and the insurgence of bone diseases. Practical points of management and prevention are suggested. Aluminum sources that infants may receive during the first 6 months of life are presented. In the context of prevention of possible adverse effects of aluminum overload in fetal tissues during development, simple suggestions to pregnant women are described. Finally, practical points of management and prevention are suggested. Pediatricians and neonatologists must be more concerned about aluminum content in all products our newborns are exposed to, starting from monitoring aluminum concentrations in milk- and soy-based formulas in which, on the basis of recent studies, there is still too much aluminum.

Preparation and Microstructure of Nano ZrB<sub>2</sub> Reinforced Aluminum Matrix Composites

The ZrB2 particulate reinforced aluminum matrix composites were fabricated via melt direct reaction method using Al-K2ZrF6-KBF4 components. 850°C and 30 min were the optimized synthesizing temperature and reaction time separately. The metallurgical thermodynamic and kinetic processes were then analyzed in detail. It reveals that the interphases include Al3Zr, AlB2, [Z and [ atoms. The ZrB2 particulates can be acquired through the molecular combination between Al3Zr and AlB2 or atomic combination between Zr and B atomics. The in situ reaction between reactive salts and molten aluminum takes place spontaneously, which exhibits the character of liquid-liquid reaction. Scanning electronic microscope observation results demonstrate that the sizes of ZrB2 particulates are almost 100-200 nm. The intervals between particles are almost 200-400 nm, demonstrating a unirom status of distribution.

High-energy ball milling to enhance the reactivity of aluminum nanopowders

High-energy ball-milling is proven to be an effective technique for manufacturing reactive aluminum nanopowders. The procedure of milling presented in this work allows the elaboration of aluminum powders with specific surface areas around 20m2/g. The particles have platelet morphology and are constituted by a nanocrystalline aluminum core surrounded by a thick amorphous alumina layer of 4.5±0.5nm. The reactivity of the powders is enhanced as compared to nanopowders elaborated with techniques involving vapor phase condensation. The morphology, the microstructure and the initial thickness of the alumina layer are shown to be important parameters that influence the reactivity. The method could be extended to any other ductile metal, provided a hard surface layer is continuously formed during milling.

Alkali-activated blends of calcium aluminate cement and slag/diatomite

Abstract The present study deals with the formulation of new cementitious materials via the alkaline activation of an industrial by-product (blast furnace slag) or a natural rock (diatomite) in the presence of reactive aluminium sourced from calcium aluminate cement (CAC). Two blends, one containing 20% CAC and 80% slag and the other 20% CAC and 80% diatomite, were prepared and activated with sodium sulphate or a sodium hydroxide solution. The hardened materials were characterised with X-ray diffraction (XRD) as well as 27 Al and 29 Si nuclear magnetic resonance (NMR) and tested for their 2-day mechanical strength. The main reaction product was a cementitious gel that precipitated with crystalline phases such as ettringite, U phase and katoite. While the slag blend reacted to generate a C–(A)–S–H-like gel under moderately alkaline conditions, diatomite reactivity proved to be very low under such conditions. The greater reactivity of both slag and diatomite at high pH (high alkalinity) favoured their interaction with CAC.

Differences in benthic macroinvertebrate structure of headwater streams with extreme hydrochemistry

AbstractA synoptic study of acidified mountain streams covering six Czech sites was performed. The aim was to provide biological data from small mountain streams in catchments with historically high acid atmospheric deposition, which have so far been subject of intensive long-term monitoring of hydrology and hydrochemistry only, in order to follow the development of the structure of benthic macroinvertebrates in the course of recovery from acidification. We focused on small headwater streams with minimum human influence in the catchment and relatively low concentrations of dissolved organic matter. The sites were classified according to their water pH status: three of them were strongly acidified (pH 4.07–4.57, concentration of reactive aluminium R-Al 448–1913 μg L−1), two were moderately acidified (pH 5.08–6.38, R-Al 52–261 μg L−1) and one non-acidified (pH 7.63–7.89, R-Al 12–59 μg L−1). The largest biotic difference detected by PCA was in the presence of the caddisflies Drusus, Rhyacophila, and Chaetopteryx villosa and stoneflies Leuctra pseudocingulata and Diura bicaudata. The results indicate that at the most acidified sites (the Lysina and the right branch of the Litavka), the process of biological recovery has not started yet due to an insufficient increase in stream pH. Indeed, MAGIC modelling published earlier shows that significant increases cannot be expected in the following decades. An average pH of at least 4.5 is needed for return of less acid-tolerant taxa such as Diura bicaudata, Leuctra major, L. pseudocingulata, L. pseudosignifera, Drusus or Rhyacophila. However, at the Sklářský potok — Jizerka site,^both the clear-cut of mature spruce plantations in 1984–1990 and the regional drop in SO2 emissions in the 1990s resulted in a decline of acid deposition and rising streamwater pH. Mean annual pH at the Sklářský potok — Jizerka outlet increased from 4.0 (1982–1985) to 5.3 (1990–1994), but episodic acidification has still resulted in a delay in recovery of the biota, particularly acid-sensitive species, which may be expected within a couple decades.

Structural properties of boehmite produced by hydrothermal oxidation of aluminum

The structural properties of boehmite produced by hydrothermal oxidation of aluminum micron powder at 230–360°C and 3–20MPa in experimental flow reactor were studied depending on synthesis temperature. It was found that temperature increasing leads to less-ordered structure, particle agglomeration increasing, average crystal size increasing, specific surface decreasing, micropore volume decreasing and mesopore and macropore volumes increasing that corresponds with each other and correlates with the results of kinetic experiments. It was shown that reaction rate and conversion degree is given not only by temperature factor but also by product structural properties, which influence on the diffusion of water to the surface of reactive aluminum. It was shown an important role of flow reaction system in the providing of high rate of hydrothermal oxidation of aluminum and its conversion degree. The results of analysis of structural properties of boehmite confirmed in general that hydrothermal oxidation of aluminum is a promising method of the production of catalyst carriers and sorbents. It was established the possibility to assign the structural properties of nanocrystalline product by thermodynamic parameters within the experimental reactor. The results of mass spectrometric analysis showed that total impurity concentration in produced boehmite decreases in comparison with initial aluminum powder.