Reactive Aluminum Research Articles

Characterisation of the activation and reaction behaviour and determination of the emissivity of reactive nickel-aluminium particles with regenerated fibre Bragg gratings

Reactive particles represent a customisable heat source for joining applications as each reactive particle is able to undergo an exothermic, self-sustaining reaction. Microwaves are used to homogeneously initiate this reaction and allow the resulting temperature-time profiles to be influenced. The possibility to derive cause-effect relationships between the different particle structures, the activation energy, and the resulting maximum temperatures is essential for developing a resource-efficient, tailored heat source in production engineering. The reaction of reactive nickel and aluminium particles generates heat and thus temperatures up to 1500 K within milliseconds. A promising temperature measurement method despite an unknown emissivity are optical fibre sensors. These feature high frame rates, a compact design, and resistance to high temperatures as well as to electromagnetic waves. In this paper, the investigation of the use of regenerated fibre Bragg gratings (RFBG) as a new, innovative approach to characterise reactive particles is described. Experimental studies with an infrared camera and RFBG demonstrated that RFBG retain their functionality while being exposed to microwaves and high temperatures. The good accordance of the recorded RFBG-based temperature evolutions with infrared thermography data confirmed the suitability of RFBG as a sophisticated characterisation method and for determining the emissivity of reactive metal particles.

Multinuclear Magnetic Resonance Study on Aluminium Sec-butoxide Chelated with Ethyl Acetoacetate in Various Amounts

Reactive aluminum alkoxide (ASB, aluminium sec-butoxide) was chelated using β-diketone (EAA, ethyl acetoacetate) in order to gain control over rapid hydrolysis in the course of the sol-gel process. Derived chelates were analysed using several NMR spectroscopic techniques: one-dimensional 1H, 13C, 27Al NMR and two-dimensional COSY, HSQC and DOSY. The NMR analysis enabled identification of the formed chelate species, as well as determination of their quantitative relationships. Several complexation products were observed: tris-chelated monomer, Al(EAA)3, bis-chelated dimmer, Al2(OnBu)4(EAA) 2, tris-chelated dimmer, Al2(OnBu)3(EAA)3, tetra-chelated dimmer, Al2(OnBu)2(EAA)4, and monochelated trimer, Al3(OnBu)8(EAA). Of the formed oligomer compounds, this is the first evidence of Al2(OR)3L3 in any alkoxide and β-ketoester or β-diketone combination. Aluminium sec-butoxide and ethyl acetoacetate complexes Al2(OnBu)4(EAA) 2 and Al2(OnBu)2(EAA)4 were also observed for the first time. With the increase of the EAA/ASB ratio the coordination of aluminium shifts towards six, whereas above the EAA/ASB ratio of 2.5 solely six-coordinated aluminium exists.

Mesoporogen-free synthesis of hierarchical sodalite as a solid base catalyst from sub-molten salt-activated aluminosilicate

A rapid and environmentally friendly approach to synthesize hierarchical sodalite from natural aluminosilicate mineral without the involvement of any mesoporogen or post-synthesis treatment was developed. This strategy involves three important steps: the first is the depolymerization of an aluminosilicate mineral into highly reactive silicon and aluminum species with ideal meso-scale structures through activation of a sub-molten salt. The second step is the hydrolysis and condensation of the activated aluminosilicate mineral into zeolitic precursors that also have a meso-scale structure. The third is the rapid zeolitization of the zeolitic precursors through the reversed crystal growth route at room temperature and ambient pressure to form hierarchical sodalite. The physicochemical properties of the as-synthesized sodalite were systematically characterized, and the formation mechanism of the hierarchical pore structure was discussed. When used as a solid base catalyst for Knoevenagel condensation, the as-synthesized sodalite and its potassium ion-exchanged product with hierarchical micro–meso–macroporous structure both exhibited high catalytic activity and product selectivity.

Effect of the Addition of Aluminum Recycling Waste on the Pozzolanic Activity of Sugarcane Bagasse Ash and Zeolite

The pozzolanic activity of aluminum recycling waste (AW) was evaluated along with sugarcane bagasse ash (BA) and zeolite (ZE) to give a more sustainable use. These materials were characterized and submitted to the pozzolanic activity test by a modified Chapelle test and the compressive strength of mortars prepared with limestone Portland cement (LPC). The final solids were characterized again to determine the hydrated products. The main reactive chemical components of AW are Al2O3 and MgO, which are in the form of hydroxides, such as nordstrandite (Al(OH)3), meixnerite ([Mg5Al3(OH)16][(OH)3·(H2O)4]), brucite (Mg(OH)2) and magnesium chloride hydroxide hydrate (Mg3(OH)5Cl·4H2O). All of the studied materials were classified as pozzolans by the modified Chapelle test, and the main hydrated products formed in the AW sample were katoite, ettringite, talc and amesite. When mixed with BA and ZE, C-A-S-H and C-S-H phases were also formed. The C-S-H phases and portlandite were detected only in the solids of the modified Chapelle test of BA and ZE. Calcite was present in all samples, indicating that part of the Ca(OH)2 was consumed by the carbonation process. The compressive strength test of mortars revealed that only ZE is a pozzolan. In mortars containing AW the production of ettringite and calcium carboaluminate increased due to the reactions of aluminum, respectively, with gypsum and calcite present in LPC. In addition to portlandite, C-S-H was formed only in the BA and ZE mortars. Although hydration reactions were not sufficient to form C-S-H in AW mortar, reactive aluminum favors the formation of primary ettringite.

Aluminum(III) Halide Complexes based on a Bis‐(benzoxazol‐2‐yl)methane Ligand

Low‐valent aluminum(I) heterocycles that are specified as metal carbenes can be applied as catalysts and in small molecule activation. Thus, the synthesis of new types of metal carbenes is a rewarding task we set out to contribute. The reactive aluminum compounds should be obtained by reduction of an aluminum(III) halide precursor coordinated to a suitable ligand. The bis(benzoxazol‐2‐yl)methanide ligand HCBOX2 (BOX = benzoxazol‐2‐yl) mimics the beneficial features of the omni‐present nacnac ligand. Two new aluminum halide complexes [(HCBOX2)AlX2] (X = Cl, I) were synthesized in a salt elimination reaction with the corresponding metal halide and the lithiated ligand [(HCBOX2)Li(Et2O)2], derived from H2CBOX2 [bis‐(benzoxazol‐2‐yl)methane]. The complexes [(HCBOX2)AlCl2] (1) and [(HCBOX2)AlI2] (2) were characterized by NMR spectroscopy from solution, mass spectrometry and single‐crystal X‐ray diffraction. 1 crystallizes in the monoclinic space group P21/n and crystals of complex 2 were obtained in the triclinic crystal system with space group P1. Especially [(HCBOX2)AlI2] (2) is a promising precursor for the synthesis of new low‐valent aluminum(I) compounds because especially the Al–I bond is prone to reduction.

Laser Polishing of Cold Work Steel AISI D2 for Dry Metal Forming Tools: Surface Homogenization, Refinement and Preparation for Self-Assembled Monolayers

Liquid lubrication guarantees high precision and surface quality of workpieces in industrial forming processes. In the case of aluminum cold extrusion, wear and cold welding due to direct contact of tool and workpiece are usually prevented by the extensive use of lubricants. Since the use of lubricants is economically and ecologically unfavorable, surface treatments of tools by, e.g. laser polishing and/or coatings are in the focus of current investigations to substitute these lubricants and establish so called “dry metal forming” processes. The material AISI D2, a ledeburitic 12% chromium steel which is known to have a significant amount of chromium carbide precipitations, is widely used in cold extrusion for forming tools. The large fraction of chromium carbide precipitations, however, hinder the formation of a dense self-assembled monolayer (SAM) that is necessary to avoid direct contact of reactive aluminum with surface oxides of the tool. Therefore, a homogeneous distribution of the chemical elements with a smaller fraction or no chromium carbides in the steel matrix, particularly in the tool surface, is aimed for. Using laser polishing, the surface layer is molten by continuous or pulsed laser radiation. Within the melt pool, the elementary distribution is homogenized as a result of thermal convection and diffusion processes, as well as a smoothed surface and a grain refinement are achieved. Consequently, the effects of the surface treatment by laser polishing on the area coverage of self-assembled monolayers are investigated. Thus, a combined surface treatment by laser polishing and functionalization with a dense self-assembled monolayer shall reduce overall adhesive wear. For this investigation, several specimens of conventional manufactured and powder metallurgical molten AISI D2 are laser polished using continuous or pulsed laser radiation or a combination of both. The resulting surfaces are investigated by microscopy and spectroscopic techniques to analyze the surface topography and the elemental distribution near to the surface. These results are compared to those of conventionally hand-polished specimens. Furthermore, the influence of the element homogenization and grain refinement on the area coverage of self-assembled monolayers is explored. First results show that laser polishing of AISI D2 is suitable to achieve a reduction of grain size and a more homogeneous distribution of chromium carbides within the surface layer.

De-alloying corrosion in the heat-affected zone in Mn-Al bronze weld

This study reports on de-alloying corrosion in a heat-affected zone (HAZ) of marine propeller Mn-Al bronze. The HAZ consisted of α, β∗ phases and a 2–5 μm thick α/β∗ interface layer. The β∗ phase having high aluminium content was expected to corrode first, it found that the de-alloying initiated from the α/β∗ interface layer. TEM diffraction patterns and images showed Cu3Mn2Al and orthorhombic L-J precipitates in Cu2MnAl matrix plus numerous dislocations and strain fields, which caused the layer to be corroded first. This study suggests that microstructure is a critical factor for corrosion more than the highly reactive aluminium content.

Alkali-activated materials from different aluminosilicate sources: Effect of aluminum and calcium availability

The present study aims to determine the influence of aluminum and calcium availability from two different aluminosilicate sources (COx argillite and sediment), thermally treated at 750 °C, on the formation, the structure and the working properties of the resulting alkali-activated materials. Despite their similar chemical composition, some differences in terms of aluminum coordination, amorphous phase and calcium availability were detected between the two studied aluminosilicate sources. Indeed, sediment sample exhibits higher reactive aluminum and lower reactive calcium compared to argillite sample. Moreover, FTIR spectroscopy has revealed that available calcium interacts with free silicon and aluminum and alkali cation in excess (sodium or potassium) leading to the formation of several networks (SiOAl and SiOCa bonds). For both aluminosilicates, the calcium content (0.33 < Ca/Si < 0.36) seems to be not sufficient to produce C-S-H hydrated phases. It was also demonstrated that the low availability of aluminum in addition to the high availability of calcium favor the precipitation of secondary reaction products in the detriment of the geopolymer network. These products fill the voids inducing a decrease of the porosity and the pore size but also lead to higher heterogeneity that decreases the mechanical properties of the final material. However, the higher availability of aluminum and the lower availability of calcium in presence of high alkaline conditions favor the polycondensation reaction.

Seasonal quantitative dynamics and ecology of pelagic rotifers in an acidified boreal lake

Lake Gjerstadvann is a dimictic, oligotrophic, slightly acidified boreal lake in southern Norway (northwest Europe). The planktonic rotifer community of this lake was studied quantitatively during one year in order to investigate the impacts of the local environment and biotic interactions on seasonal succession and habitat selection. Pure suspension feeders (mainly Keratella spp., Conochilus spp., and Kellicottia longispina) together with raptorial graspers or specialised feeders (mainly Polyarthra spp. and Collotheca spp.) dominated the rotifer community over prolonged periods, whereas carnivorous/omnivorous species (mainly Asplanchna priodonta) were extremely uncommon. Low bicarbonate buffering capacity resulted in a distinctive seasonal oscillating pH between 5.0 and 5.6, defining a special acid-transition lake category. The pH values were highest in the productive period during summer, and lowest during ice break-up coinciding with the peak reactive aluminium concentrations of 250-300 mg L-1. As in typical Norwegian boreal perch lakes, the most abundant cladoceran was Bosmina longispina due to perch predation on the genus Daphnia. Rotifer community structure was significantly related to temperature and oxygen (P=0.001 and P=0.022), illustrating the important effects of the seasonal cycle and vertical density stratification. The most significant competition indicator species were B. longispina and Eudiaptomus gracilis (both with P=0.001). A variance partitioning indicated that 14% of the total community composition variance could only be explained by biotic interactions, while 19% of the variance could be attributed to environmental gradients. Of the variance, 23% could not be resolved between biotic interactions and environmental gradients, while a residual of 44% was not explainable by any of the variables. Acid conditions alone cannot account for all the observed changes in the rotifer community of this lake with low humic content, since resource limitation and food competition are also important factors shaping rotifer population dynamics and the community structure.

Explosion hazards of aluminum finishing operations

Metal dust deflagrations have become increasingly common in recent years. They are also more devastating than deflagrations involving organic materials, owing to metals' higher heat of combustion, rate of pressure rise, explosion pressure and flame temperature.Aluminum finishing operations offer a particularly significant hazard from the very small and reactive aluminum particles generated, and thus require high attention to details of operation and explosion safety management.This paper presents available statistics on metal dust explosions and studies the specific explosion hazards of aluminum finishing operations. The analysis of seven case studies shows that the proper design, monitoring and maintenance of dust collection systems are particularly important. Furthermore, the isolation of deflagrations occurring in dust collection systems, as well as good housekeeping practices in buildings, are critical safeguards to avoid the occurrence of catastrophic secondary explosions.

Cenozoic global cooling and increased seawater Mg/Ca via reduced reverse weathering

Authigenic clay minerals formed on or in the seafloor occur in every type of marine sediment. They are recognized to be a major sink of many elements in the ocean but are difficult to study directly due to dilution by detrital clay minerals. The extremely low dust fluxes and marine sedimentation rates in the South Pacific Gyre (SPG) provide a unique opportunity to examine relatively undiluted authigenic clay. Here, using Mg isotopes and element concentrations combined with multivariate statistical modeling, we fingerprint and quantify the abundance of authigenic clay within SPG sediment. Key reactants include volcanic ash (source of reactive aluminium) and reactive biogenic silica on or shallowly buried within the seafloor. Our results, together with previous studies, suggest that global reorganizations of biogenic silica burial over the Cenozoic reduced marine authigenic clay formation, contributing to the rise in seawater Mg/Ca and decline in atmospheric CO2 over the past 50 million years.

Study of the heat affected zone within metals joined by using reactive multilayered aluminum–nickel nanofoils

The combustive feature of reactive multilayered nanofoils can be harnessed to produce lightweight components in multi-material design. However, the intended use of nanofoils serving as a heat source requires the knowledge of the shape and the depth of the heat affected zone (HAZ) within the joining partners in order to prevent any material damage. This study addresses the experimental and numerical investigation of the HAZ within metallic joints produced by reactive aluminum–nickel nanofoils with varying layer structures. For the first time, the HAZ within reactively joined materials was metrologically quantified due to the use of a specific low-melting alloy. Furthermore, a new modeling approach was developed in order to compute the transient temperature field within the joining partners during and after the exothermic reaction of the ignited nanofoil. The simulation model was validated by using the experimental findings of the HAZ. The review of the predictive accuracy confirmed a good agreement with the experimental data.

Distribution of reactive aluminum under the influence of mesoscale eddies in the western South China Sea

To understand the distribution of aluminum (Al) under the influence of mesocale eddies in the western South China Sea (SCS), sea level anomaly, geostrophic current, environmental parameters and reactive Al were investigated in the western SCS in August 2013. The highest reactive Al concentration ((180±64) nmol/L) was observed in the surface waters, indicating a substantial atmospheric input. Vertically, the reactive Al decreased from the surface high concentration to the subsurface minima at the depth of chlorophyll a (Chl a) maxima and then increased again with depth at most of the stations. The average concentration of reactive Al in the upper 100 m water column was significantly lower in the cyclonic eddy ((137±6) nmol/L) as compared with that in the noneddy waters ((180±21) nmol/L). By contrast, the average concentrations of Chl a and silicate in the upper 100 m water column were higher in the cyclonic eddy and lower in the anticyclonic eddy. There was a significant negative correlation between the average concentrations of reactive Al and Chl a in the upper 100 m water column. The vertical distribution of reactive Al and the negative correlation between reactive Al and Chl a both suggest that the reactive Al in the upper water column was significantly influenced by biological removal processes. Our results indicate that mesoscale eddies could regulate the distribution of reactive Al by influencing the primary production and phytoplankton community structure in the western SCS.

Nanoporous Hybrid Electrolytes for High‐Energy Batteries Based on Reactive Metal Anodes

Successful strategies for stabilizing electrodeposition of reactive metals, including lithium, sodium, and aluminum are a requirement for safe, high‐energy electrochemical storage technologies that utilize these metals as anodes. Unstable deposition produces high‐surface area dendritic structures at the anode/electrolyte interface, which causes premature cell failure by complex physical and chemical processes that have presented formidable barriers to progress. Here, it is reported that hybrid electrolytes created by infusing conventional liquid electrolytes into nanoporous membranes provide exceptional ability to stabilize Li. Electrochemical cells based on γ‐Al2O3 ceramics with pore diameters below a cut‐off value above 200 nm exhibit long‐term stability even at a current density of 3 mA cm−2. The effect is not limited to ceramics; similar large enhancements in stability are observed for polypropylene membranes with less monodisperse pores below 450 nm. These findings are critically assessed using theories for ion rectification and electrodeposition reactions in porous solids and show that the source of stable electrodeposition in nanoporous electrolytes is fundamental.

Coating of unreactive and reactive surfaces by aluminosilicate binder

Currently, many applications require the assembly of different materials to improve their properties in use. This work focuses on the production of a geopolymer binder coating based on metal or agglomerated sand. For this, several compositions based on sodium or potassium and different reactivities of metakaolin and their interactions in the presence of different types of support were studied. The interactions between the binder and substrate were analysed by measurements of the wetting angles. Coating trials conducted over tin-plated copper and bonded sand highlighted the influences of the binder composition and the drying and deposition parameters. Scanning electronic and optical microscopy observations confirm the chemical adhesion between the various components. FTIR spectroscopic analyses have also identified the parameters for obtaining a geopolymer network such as the reactive aluminium concentration (5a.u.) and the molar Si/Al and M/Al (M=K or Na) ratios (2 and 1.2, respectively). It is therefore possible, by determining the wetting angle, to control the deposition on either a metal or silica sand.

Predictive tools to control the structure and the properties of metakaolin based geopolymer materials

Geopolymers are innovative mineral binders. These materials are still under research development in order to better understand the formation mechanism, the local structure and the final working properties. The aim of this study is to provide predictive tools permitting to control the geopolymerisation reaction. At first, it is important to determine the parameters responsible of raw materials reactivity. For alkaline solutions, the siliceous species distribution and connectivity control the reactivity. Concerning metakaolins, the Si/Al molar ratio, the wettability value, the amorphous phase content and the amount of reactive tetrahedral aluminum are responsible of metakaolin reactivity. Moreover, the reactivity of raw materials was proven to determine the geopolymer existence domains in the Si–Al–M/O ternary diagram. Thermal analysis during and after curing give informations about the amount of water consumed during the reaction and trapped in the final structure as well as the energy required for oligomer formation which seem to be directly related to raw materials reactivity. The pores distribution and size are also influenced by raw materials reactivity. Reactive precursors, especially reactive alkaline solutions, induce higher densification rate and, therefore, lower porosity and larger pore size. Furthermore, reactive precursors favor the formation of geopolymer network. This fact was evident by 29Si NMR. As a consequence, the increase of geopolymer phase in the structure improves the mechanical strength while the competition of different networks is source of weakness.

Determination of the pozzolanic activity of mortar’s components by thermal analysis

Historic lime mortars are complex multicomponent system whose mineralogical and chemical composition changes over time. With age, hydraulic phases are converted by carbonation process to calcium carbonate and reactive silicon and aluminium oxides. The consolidation of lime mortars is usually based on the dotation of the Ca(OH)2 into its matter so pozzolanic reaction may possibly take place. The study was aimed to explore pozzolanic potential of sand grains and degraded binder with respect to renewal of hydraulic phases which could contribute to mortar’s mechanical strength and therefore prolong its durability. For this purpose, pastes of mortar components with lime hydrate were prepared and stored in wet conditions (RH = 99 ± 1 %, T = 30 ± 1 °C) for 180 days. Pozzolanic reaction products were studied at different ages using thermal analysis and X-ray diffraction. With respect to sand grains pozzolanic activity, both methods confirmed the presence of newly formed monocarboaluminate as an only hydraulic phase; moreover, CSH and hydrocalumite have been found in degraded binder pastes. CSH, stratlingite and monocarboaluminate were detected as products of pozzolanic reaction of silicate and metakaolin with calcium hydroxide.

The toxicity of aluminium in humans

We are living in the 'aluminium age'. Human exposure to aluminium is inevitable and, perhaps, inestimable. Aluminium's free metal cation, Alaq(3+), is highly biologically reactive and biologically available aluminium is non-essential and essentially toxic. Biologically reactive aluminium is present throughout the human body and while, rarely, it can be acutely toxic, much less is understood about chronic aluminium intoxication. Herein the question is asked as to how to diagnose aluminium toxicity in an individual. While there are as yet, no unequivocal answers to this problem, there are procedures to follow to ascertain the nature of human exposure to aluminium. It is also important to recognise critical factors in exposure regimes and specifically that not all forms of aluminium are toxicologically equivalent and not all routes of exposure are equivalent in their delivery of aluminium to target sites. To ascertain if Alzheimer's disease is a symptom of chronic aluminium intoxication over decades or breast cancer is aggravated by the topical application of an aluminium salt or if autism could result from an immune cascade initiated by an aluminium adjuvant requires that each of these is considered independently and in the light of the most up to date scientific evidence. The aluminium age has taught us that there are no inevitabilities where chronic aluminium toxicity is concerned though there are clear possibilities and these require proving or discounting but not simply ignored.

Can biochar increase the bioavailability of phosphorus?

A large proportion of phosphate (P) fertilizer applied to Andosols reacts with reactive aluminum (Al) and iron (Fe) to become unavailable for plant uptake. We investigated whether biochar could enhance plant growth by (i) mobilizing soil P through changing soil pH or facilitating the growth of arbuscular mycorrhizal fungi (AMF), and/or (ii) introducing additional P. We grew Lotus pedunculatus cv barsille in two Andosols of contrasting P status amended with three biochars (with distinct porosity, nutrient and liming properties) at a dose of 10 t ha-1 for 32 weeks. The growth medium was divided into a root and a hyphal zone through a nylon mesh and a tephra layer that allowed the P in the hyphal zone to be transferred only by AMF hyphae. The addition of a relative nutrient-rich biochar (e.g. made from willow woodchips) with liming properties to the root zone of the P-deficient soil increased plant growth by 59% and P uptake by 73%. Pine-based biochar provided no extra nutrient acquisition and no plant-growth stimulation when added to the root zone of the P-deficient soil. However,when hyphae of those plants had access to a P-rich soil patch, the presence of pine biochar in the soil patch greatly enhanced P uptake and plant growth (e.g., by 76% and 40% when using biochar produced at 450oC compared to the absence of it). None of the tested biochars conferred advantages in the root zone of a high-P soil. We concluded that the benefits from biochar addition to nutrient uptake and plant growth are biochar- and soil-specific. Thus, biochars need to be tailored-made for certain soils by optimizing feedstock and pyrolysis conditions before application.

The Use of Forced Gas Rodent Burrow Fumigation Systems and the Potential Risk to Humans

Author(s): Eisemann, John D.; Moulton, Rachael S.; Witmer, Gary W. | Abstract: The use of fumigants has been commonly practiced for decades to manage burrowing rodent populations in both agricultural and urban habitats. Stories abound about farmers and ranchers illegally fumigating rodent burrows by inserting toxic gas-producing road flares into burrow openings or by simply piping automotive exhaust into burrows systems. Legal fumigant technology includes incendiary devices such as gas cartridges that produce carbon monoxide, and highly reactive magnesium and aluminum phosphide pellets that produce toxic gasses by reaction with the atmosphere. These devices rely on passive diffusion of the toxic gasses through the burrow system. Recently, products have been introduced to the market that force toxic gasses into burrow systems by using blowers or pressurized gas systems. The effectiveness of fumigation systems where toxic gasses, such as carbon monoxide, are allowed to passively infiltrate burrow systems are limited in their geographical range, and as a result are limited in the potential risk to humans or other organisms. Regardless, these products have traditionally had use restrictions based on the proximity to structures and other inhabited areas. The use of systems where toxic gasses are forcefully blown into burrow systems present a greater hazard potential. This manuscript examines the potential risk, in terms of US EPA Standards, for carbon monoxide exposure; published data on carbon monoxide levels in burrow systems; burrow morphology of various burrowing species; and suggests safe distance standards for burrow fumigation activities conducted around structures and other human-occupied habitats.