Reactive Aluminum Research Articles

Global Distributions of Reactive Iron and Aluminum Influence the Spatial Variation of Soil Organic Carbon.

Organic carbon persistence in soils is predominantly controlled by physical accessibility rather than by its biochemical recalcitrance. Understanding the regulation of soil iron (Fe) and aluminum (Al) (hydr)oxides, playing a dominant role in mineral protection, on soil organic carbon (SOC) would increase the reliable projections of the feedback of terrestrial ecosystems to global warming. Here, we conducted a continental-scale survey in China (341 sites) and a global synthesis (6786 observations) to reveal the global distributions of Fe/Al (hydr)oxides and their effects on SOC storage in terrestrial ecosystems. We generated the first global maps of soil Fe/Al (hydr)oxides with high accuracy (with R2 more than 0.74). The variance decomposition analysis showed that Fe/Al (hydr)oxides explained the most proportion of variance for topsoil (0-30 cm) and subsoil (30-100 cm) SOC. Therefore, soil Fe/Al (hydr)oxides play a stronger role in explaining the spatial variation of SOC than well-studied climate, edaphic, vegetated, and soil depth factors in both topsoil and subsoil. Collectively, the planetary-scale significance of soil Fe/Al (hydr)oxides for SOC highlights that soil Fe/Al (hydr)oxides should be incorporated into Earth System Models to reduce the uncertainty in predicting SOC dynamics.

Protective role of reactive aluminum phases to stabilize soil organic matter against long-term cultivation in the humid tropics under volcanic influence

ABSTRACT Cultivation can cause rapid depletion of soil organic matter (SOM), particularly in the humid tropics. Understanding the factors controlling SOM storage is a key step toward effective soil management for sustainable crop production. While clay + silt content is known to be an important factor for soil organic carbon (SOC) storage, recent studies have shown greater importance of oxalate-extracted Al (Alo; roughly corresponds to short-range-order aluminosilicate minerals and organo-Al complexes) and Fe (Feo). However, the extent to which these mineralogical factors control the response of SOM pool to land-use changes remains unclear, especially in the tropics. This study aimed to clarify the factors regulating SOM content in croplands compared to secondary forests or home gardens in Negros Occidental, Philippines. Along two line transects having a wide range of Alo contents, soil samples were collected at a depth of 0 − 10 cm from sugarcane sites (n = 33; long-term continuous cultivation of >70 years) that were paired with either secondary forests (n = 10) or home gardens (n = 20). Sugarcane sites had significantly lower SOC and total nitrogen (N) contents than secondary forest and home garden sites, whereas there was no clear difference between the latter two land uses. Both SOC and total N contents showed significant positive correlations with Alo content and, to a much less extent, with Feo content, but not with clay + silt content. The slope of the regression line between SOC and Alo was indifferent between sugarcane and the other two land uses, while the intercept was significantly lower in the sugarcane sites. These results suggest the protective role of Alo phases in both agricultural and forest soils and the presence of unprotected SOM (e.g. plant litter) in the latter sites. Furthermore, δ13C analysis suggested that the proportion of forest (C3 plant) derived carbon remaining in the sugarcane soils ranged between 10% and 50% and increased with Alo content. Together, our study showed indirect evidence of Alo-induced stabilization of SOM against long-term cultivation under the humid tropical environment.

Aluminum droplets on Ni substrates: Evaluating high-temperature oxidation at the liquid/gas interface

In reactive wetting aluminum (Al)/nickel (Ni) systems, oxides at liquid/gas (L/G) interfaces received less attention compared to intermetallic compounds forming at liquid Al/solid Ni interfaces yet potentially significantly influencing wetting properties. Between 900 and 1250 °C, we observed that the shape of sessile Al droplets with dense oxides at the L/G interface and intense interactions at liquid Al/solid Ni interfaces deviates from a spherical cap and can be used as a way to characterize the oxide evolution. This approach reveals a critical temperature of 1100 °C under a PO2 level of 3.9 × 10−9 atm and a vacuum level of ∼2 × 10−2 mbar. Above it, Al2O3 oxides at the L/G interface are eliminated as Al2O gas, while at lower temperatures, they develop as a mixture of Al2O3 oxides and Al-Ni intermetallic compounds with Ni being dissolved from the substrate. At high temperatures (above 1200 °C), despite oxide-free L/G interfaces, non-spherical cap shapes were also obtained due to the formation of sharp edges at the contact line triggered by the growth of intermetallic compounds. The coupling between the droplet shapes and the interfacial interactions is further confirmed by in-situ observation of oxides, analysis of quenched samples and thermodynamic calculations. The proposed method can be potentially applied to multiple reactive wetting systems (e.g. Sn/Cu, Al/Fe, Mg/Ni systems), which are crucial for high-temperature processes such as soldering, coating, and processing of metal matrix composites.

Effects of zirconium diboride addition on porosity reduction in laser metal deposition of tungsten carbide–cobalt cermet material

Laser metal deposition of tungsten carbide–cobalt (WC-Co) cermet material is a promising means of improving the wear resistance of metal products. However, laser metal deposition of WC-Co has constraints on its practical use because a clad bead of WC-Co often includes numerous gas pores. Earlier studies have found CO gas generation in a molten pool by reaction of carbon and oxygen to be the main cause of gas porosity in a WC-Co clad bead. Preventing the gas reaction is important to obtain clad beads with few pores. The addition of elements with strong affinity for oxygen, such as aluminum, was found to be effective for porosity reduction in a clad bead. However, the addition of highly reactive pure aluminum particles on WC-Co powder presents some difficulties for industrial use. For this study, zirconium diboride (ZrB2), a chemically stable compound, was used as an additive to WC-Co powder. After WC-Co powder with adhered ZrB2 particles was prepared using a wet granulation process, laser metal deposition was conducted. Zirconium stemming from the dissolution of ZrB2 in the molten pool was found to have the effect of trapping oxygen elements as solid zirconium oxides. Consequently, gas generation in the molten pool by the reaction of carbon and oxygen was restrained. Clad beads having few pores and fine microstructures were obtained. Observations of the molten pool behavior taken using a high-speed camera indicated that ZrB2 addition drastically improves process stability compared to processes using conventional WC-Co powder.

How do reactive aluminum and iron phases control soil organic carbon and phosphate adsorption capacity in agricultural topsoils across Japan?

ABSTRACT The growing number of studies suggests that the prediction of soil organic carbon (SOC) storage and persistence can be improved by accounting for variations in soil reactive metal phases. Nevertheless, the dataset on reactive metals is often limited at a national scale. In Japan, the phosphate adsorption coefficient (PAC) has been measured for agricultural soils nationwide. PAC is known to be strongly controlled by reactive metals, and hence, it can be used as a surrogate for reactive metal content. However, the relationships between SOC, reactive metals and PAC across a wide range of agricultural soils remain unclear. We thus examined these relationships using agricultural topsoils taken from 115 sites across Japan, covering two major soil great groups, Andosols and Lowland soils, as well as various land uses and soil temperature regimes (7.2–19.1°C). For the whole dataset, PAC was strongly correlated with oxalate-extractable metals (Alox + 0.5Feox: Metalox, r = 0.83) and moderately with pyrophosphate-extractable metals (Alp + 0.5Fep: Metalp, r = 0.68). These results suggest a stronger contribution of short-range-order (SRO) minerals to PAC as the former parameter reflects the content of both SRO minerals and organically complexed metals, while the latter reflects only that of organo-metal complexes. Moreover, Metalp was the best predictor of SOC contents in both Andosols (r = 0.79) and Lowland soils (r = 0.65). When only soils at near neutral soil pH range were considered, the exchangeable Ca content also co-varied with SOC in Lowland soils (n = 17). Of the two metallic elements, reactive Al phases better explained the variation of SOC and PAC in Andosols, whereas reactive Fe phases also showed similar explanatory power for PAC in Lowland soils. Our analyses also suggested that soil group (esp. erosion intensity) and land use likely impacted the SOC-Metalox relationship in Andosols, whereas environmental factors such as soil temperature and soil redox regime affected those relationships in Lowland soils. Overall, we showed that PAC is a useful surrogate for SRO minerals and organo-metal complexes and, with careful considerations of the environmental and pedogenic factors, it is potentially useful to estimate the amounts of SOC stabilized by reactive metal phases in agricultural soils across Japan.

Mechanical and microstructural characterization of one-part binder incorporated with alkali-thermal activated red mud

The traditional production of silicate cement is associated with substantial carbon emissions and environmental degradation. In contrast, cementless alkali-activated binders, derived from solid waste and industrial byproducts, have garnered significant interest for their reduced material costs, energy efficiency, and environmental benefits. This research investigates the application potential of an advanced mixture of anhydrous sodium silicate and red mud in one-part alkali-activated binders. It is assessed through various analytical techniques, including compressive strength, X-ray diffraction, fourier transform infrared, thermogravimetric analysis, digital image correlation, and scanning electron microscopy with energy dispersive spectroscopy. Findings demonstrate that the synergy between red mud and anhydrous sodium silicate markedly enhances the early strength of one-part alkali-activated binders incorporated with alkali-thermal activation. The increment in sodium silicate content is pivotal for bolstering binder performance. A 40 % red mud admixture results in a compressive strength of 40 MPa, achieving an optimal carbon-to-strength ratio. The inclusion of polypropylene fiber significantly influences the mode of compression failure in alkali-activated binders. Alkali-thermal activation of red mud elevates the levels of active silicon and aluminum, markedly augmenting the reactive silica and aluminum content. This modification fosters the disintegration and reorganization of Si-O and Al-O bonds in silica-aluminum materials, culminating in a denser structure. This structure is characterized by the generation of amorphous ((N, C)-A-S-H) gels, contributing to the material's enhanced properties.

Revisited Synthesis of Trispyrazolylborate Aluminum Halides Suban Kundu, Raju Chambenahalli, Alex P. Andrews and Ajay Venugopal*

Tris(3,5‐dimethylpyrazolyl)borate aluminum dihalides TpMe2AlX2 (X=Cl, Br and I) can be potential precursors for preparing highly electrophilic dications as well as low oxidation state aluminum compounds. However, the coordinative unsaturation in TpMe2AlX2 makes them susceptible to rearrangement to [Tp2Al][AlX4]. In this work, we revisited the synthesis of TpMe2AlX2 by isolating the solvent‐stabilized tris(3,5‐dimethylpyrazolyl)borate aluminum dihalides TpMe2AlX2(L) (X=Cl, Br; L = THF, HPMA). Efforts to isolate TpMe2All2 resulted in the ring opening of THF revealing the mediation of a highly reactive cationic aluminum species. The monocationic, [TpMe2AlCl(THF)2][B{C6H3(CF3)2}4] was prepared from TpMe2AlCl2(THF) via silver salt metathesis. Attempts to prepare the dicationic species [TpMe2Al(THF)3]2+ resulted in the instantaneous ring‐opening polymerization of THF.

Nature of instability in flow-driven porous anodic oxide.

Self-organized porous anodic oxide films are formed by the electrochemical oxidation of reactive metal aluminum in acidic solutions in which the oxide is soluble. Recently, viscous flow models have shown using linear stability analysis that the instability results from a trade-off between the destabilizing effect of viscous flow of oxide and the stabilizing effect of oxide formation, which provides the wavelength selection mechanism for pattern formation. Anion adsorption on surface growth sites causes nonuniform compressive stress at the oxide-solution interface, which drives the flow. This anodic instability is analogous to the classical Marangoni instability induced by surface tension gradients. In this work, nature of the instability beyond the stability threshold is determined using a weakly nonlinear analysis. For the growth of well-developed pores beyond the threshold, a subcritical nature of the instability is essential. However, our weakly nonlinear analysis shows that the solutions emerging from neutral stability are supercritical in nature at all wavenumbers for the practical range of anodizing control parameters investigated. We also determine the region where the model is Hadamard stable, a necessary condition for well-posedness.

Pozzolanic activity of FCC catalyst waste slag (CWS) for cement and geopolymer production

Catalyst waste slag (CWS) is generated in large amounts when fabricating the catalyst required in the fluid cracking catalyst (FCC) process used for oil refining. Currently, CWS is landfilled. This paper characterizes the CWS and measures its pozzolanic activity. It determines whether the CWS can be used as partial Portland cement (PC) replacement for the first time in the literature. CWS is primarily composed of Al2O3 and CaO. It contains a negligible quantity of heavy metals that can be immobilised in a matrix. The raw CWS is totally amorphous and extremely reactive which results in flash set. Calcination is an effective method to control the reactivity of CWS. Reactivity increased when CWS was calcined between 300 and 600 °C and it peaked at 500 °C, but this caused flash set. Calcination at 800 °C lowers reactivity (as the highly disordered aluminium phases achieve a greater order) which allows for proper handling. Temperatures over 800 °C caused partial crystallization significantly lowering reactivity.The 800°C-calcined CWS reached high mechanical index (6.25), comparable to other pozzolans such as fly ash and red mud, and greater than alum sludge. CWS combines lime profusely and develops more abundant cementing hydrates than similar pozzolans such as calcined alum sludge. The pozzolanic reaction of the 800°C-calcined CWS provides abundant cementing minerals including AFt and AFm phases, calcium aluminium carbonate hydrates and calcium aluminium hydrates.The high reactivity of CWS and its prolific production of cementing phases in pozzolanic reactions indicate that it can be used as a supplementary cementitious material in PC and lime systems; and that it can be used as a precursor to produce low-carbon and geopolymer cements. CWS constitutes a reactive aluminium source which, in a PC system, participates in hydration reactions and can enhance the properties of the resultant materials.

Thermal pre-treatment of reactive aluminium alloy waste powders

AbstractThis study focussed on assessing the efficiency of thermal pre-treatment of Al alloy waste powders to facilitate their subsequent treatment and disposal. Five samples originating from aluminium surface finishing industries underwent thermogravimetric analyses and were subjected to a laboratory tub furnace. Four set temperatures (450, 475, 500, 525 °C) for the tubular furnace were selected based on the TG results. Using sequential images of the sample inside the tubular furnace, the ignition delay time was calculated. In addition, the efficiencies of medium-temperature thermal pre-treatment were determined using the gas volume method. The shot blasting samples (S1 and S2) exhibited shorter ignition delay times compared to the sandblasting (S3) and one of the polishing samples (S4). The influence of ZnO alloy content on the ignition delay time was investigated, revealing that the ignition delay time decreased with an increase in ZnO alloy content. The raw and pre-treated materials were analysed for morphology, composition and reactivity. The pre-treatment efficiency of the samples improved, especially with a retention time longer than the ignition delay of the samples. Recommendations for the storage and handling of pre-treated products were provided.

Improving sulfate and chloride resistance in eco-friendly marine concrete: Alkali-activated slag system with mineral admixtures

This study investigates the effects of various mineral admixtures, such as fly ash, metakaolin, and limestone powder, on the mechanical, chloride, and sulfate resistance properties of alkali-activated slag (AAS). The resistance of alkali-activated concrete (AAC) to chloride and sulfate is evaluated using the rapid chloride migration (RCM), wetting-drying cycles, SEM and XRD, TG/DTG. The results reveal that introducing fly ash improves workability but degrades the strength and durability of AAS. The 15% slag substitution by metakaolin is recommended to improve durability. Incorporating 15% limestone powder increases the compressive strength and reduces porosity due to filling and nucleation effects. The replacement ratio of 30% for each mineral admixture induces a considerable Ca2+ dilution, resulting in reducing the strength and durability of AAC. Under short-term wetting-drying cycles, the continued hydration of raw materials under MgSO4 erosion and the subsequent production of gypsum, hydrotalcite, and brucite from the matrix initially increase the AAC strength. However, the continued substitution of calcium in the C-(A)-S-H gel by magnesium and precipitation of gypsum under excessive cycles adversely deteriorates the compressive strength. The chloride migration degree in AAC is closely related to the porosity. Although the porous gel N-A-S-H facilitates chlorine migration in accelerated tests, it prevents further chlorine penetration by adsorbing chloride ions in large quantities, exhibiting the dominant effect on chloride immobilization. The formation of Friedel's salt, stemming from the chemical bonding of chloride, is present only in the high-calcium specimen G100 and the highly reactive aluminum specimen G85M15. Improvements in the gel chemistry and porosity are key factors in bolstering the durability of AAC. The findings of this study contribute to advancing the application of eco-friendly AAC in marine environments.

A fluorescence turn “on-off” imaging probe for sequential detection of Al3+ and L-Cysteine in HeLa cells

At this “Aluminum Age”, exposure to aluminum (metallic or ionic form) is inevitable and inestimable. The presence of aluminum in biological systems is evident but more often aluminum toxicity is less understood. Therefore, the presence of biologically reactive aluminum needs to be identified and quantified. Alongside metals, L-cysteine, an essential amino acid, plays a pivotal role in the homeostasis of cellular oxidative and reductive stress. However, excess (<7g) could be lethal and can lead to death. Thus, in-situ selective detection of aluminum and L-cysteine is of larger interest. Here we report a fluorogenic probe (R) for the sequential selective detection and quantification of Al3+ and L-cysteine in a semi-aqueous medium (3:7; water: DMSO). The probe (R) was synthesized by a one-step acid-mediated condensation reaction between pyridine-3,4-diamine and 2-hydroxy-1-napthaldehyde. The synthesized probe was characterized using 1H and 13C NMR, and HR-Mass spectroscopic techniques. The probe (R) is non-emissive in nature, but on recognition of Al3+, the probe R showed “turn-on” emission (bright yellow colour) showing two emission maxima (522 nm and 547 nm), and no naked eye observable color change. Other competing cations do not show any noticeable fluorescence outcome. The R + Al3+ ensemble can specifically detect L-cysteine among all the essential amino acids by showing a fluorescence “turn-off” response. The sensing mechanism of Al3+ is obeying the chelation-enhanced fluorescence (CHEF) effect. The binding constant of R + Al3+ is 0.3 × 104 M−1. The limit of detection (LoD) for Al3+ and L-cysteine are 2.02 × 10-7 M and 0.5 × 10-5 M respectively. The probe (R) can show maximum efficiency within the pH range (7.0–10.0). The probe is found non-toxic (>80 % cell viability with 15 µM concentration) and employed for the in-vitro fluorescence imaging in the HeLa cell.

Reductive Coupling of a Diazoalkane Derivative Promoted by a Potassium Aluminyl and Elimination of Dinitrogen to Generate a Reactive Aluminium Ketimide.

The reaction of 9-diazo-9H-fluorene (fluN2 ) with the potassium aluminyl K[Al(NON)] ([NON]2- =[O(SiMe2 NDipp)2 ]2- , Dipp=2,6-iPr2 C6 H3 ) affords K[Al(NON)(κN1 ,N3 -{(fluN2 )2 })] (1). Structural analysis shows a near planar 1,4-di(9H-fluoren-9-ylidene)tetraazadiide ligand that chelates to the aluminium. The thermally induced elimination of dinitrogen from 1 affords the neutral aluminium ketimide complex, Al(NON)(N=flu)(THF) (2) and the 1,2-di(9H-fluoren-9-yl)diazene dianion as the potassium salt, [K2 (THF)3 ][fluN=Nflu] (3). The reaction of 2 with N,N'-diisopropylcarbodiimide (iPrN=C=NiPr) affords the aluminium guanidinate complex, Al(NON){N(iPr)C(N=CMe2 )N(CHflu)} (4), showing a rare example of reactivity at a metal ketimide ligand. Density functional theory (DFT) calculations have been used to examine the bonding in the newly formed [(fluN2 )2 ]2- ligand in 1 and the ketimide bonding in 2. The mechanism leading to the formation of 4 has also been studied using this technique.

Energy-Intensive Materials with Mechanically Activated Components

The production and study of highly dispersed aluminum-based powders represents one of contemporary science’s priority fields. This is primarily driven by the practical necessity to develop new materials, a feat that, in some cases, can only be achieved through the utilization of powdered components. This article presents the results of the mechanochemical treatment method employed to obtain highly reactive aluminum particles. It also includes a comparative analysis of aluminum particles generated through various methods and their respective properties. Furthermore, the application of these highly reactive aluminum particles in energy-intensive materials is discussed.

Soil acidification suppresses phosphorus supply through enhancing organomineral association

It has long been assumed that soil acidification increases reactive iron and/or aluminum (Fe/Al) oxides and promotes Pi sorption onto mineral surfaces, resulting in a decrease in Pi. However, this assumption has seldom been tested in long-term field experiments. Using a 12-year acid addition experiment in a tropical forest, we demonstrated that soil acidification increased the content of noncrystalline Fe and Al oxides by 16.3 % and 27.7 %, respectively; whereas it did not alter the absorbed Pi pool and Pi sorption capacity. Furthermore, soil acidification increased the Fe/Al-bound organic matter content by 82.5 %, causing a 54.9 % reduction in Pi desorption, a 42.3 % decrease in soluble Pi content, and a 9.2 % increase in occluded Pi content. Our findings demonstrate that soil acidification reduces Pi bioavailability by repressing Pi desorption rather than enhancing Pi sorption. These results could be attributed to the enhanced organomineral association, which competes for sorption sites with Pi and promotes the Pi occlusion. However, the interactions between organomineral-Pi have not been incorporated into global land models, which may overestimate ecosystem productivity under future acid rain scenarios.

Enhanced microbial contribution to mineral-associated organic carbon accrual in drained wetlands: Beyond direct lignin-iron interactions

Drainage poses a major threat to the tremendous soil organic carbon (SOC) reservoir in wetlands. However, drainage-induced carbon loss may be mitigated by the accumulation of mineral-associated organic carbon (MAOC) via both microbial processes and iron (Fe)-organic matter (especially lignin) interactions, which remains under-investigated in wetlands. Here using a novel analytical approach, we quantitatively examined the response of MAOC to drainage and the driving mechanisms in four distinct wetlands. Contrary to the prevailing assumption, MAOC consisted a significant fraction (7%∼91%) of wetland SOC, and increased with mineral-bound (microbial-dominated) sugars, but decreased with Fe-bound lignin phenols in SOC assessed after removal of reactive soil minerals. Furthermore, mineral-bound sugars increased with clay and reactive aluminum instead of Fe, and overrode Fe-bound lignin regarding contribution to MAOC after long-term drainage. These results indicate that microbial processes leading to microbial sugars accumulation played a prominent role in wetland MAOC accrual after long-term drainage, especially in soils rich in reactive Al and clay. Our study highlights the prevalent yet under-investigated microbial regulation on MAOC accrual in wetlands during long-term drainage. Given the large stock and persistence of MAOC in wetlands, its increase may partly compensate for particulate organic carbon loss during drainage, and may underpin wetland SOC stabilization in the long term.

Alkali fusion of bauxite refining residue (red mud-RM) to produce low carbon cements

This paper creates hydraulic binders using waste and a low energy input. Cements are produced with a bauxite refining residue (red mud-RM), blended with limestone and lime, and fused at temperatures from 600 to 1200 °C. The Saudi RM investigated has significant Al and Si but low Ca. Therefore, lime (CaO) and limestone (CaCO3) are used, as a source of calcium, to harvest cementing hydrates.When calcining RM alone, reactive aluminium phases begin to form at c.300 °C. However, at c.900 °C, they turn into crystalline corundum (Al2O3), a more stable and less reactive phase. It is hoped that the Ca provided by the lime/limestone will react with the Al in the RM during fusion, to form reactive silicates and aluminates rather than inert corundum. Both types of fusion produced calcium silicates and aluminates with cementing properties. However, lime fusion required higher temperature. Limestone fusion produces cementing phases at lower temperature than lime fusion, due to the lower decomposition temperature of CaCO3 when compared to CaO. High temperature is required to break down CaO (melting point = 2572 °C), whereas CaCO3 decomposes at 600 °C and disappears at 850 °C. Despite the top alkali fusion temperature being much lower than the CaO melting point, the results demonstrate that calcium was released from the lime and entered reactions forming calcium silicates and aluminates. This is probably due to the high alkali content of the RM acting as a flux and lowering the decomposition temperature of the CaO.

A Eulerian population balance/Monte Carlo approach for simulating laminar aluminum dust flames

Recently, metal powders have been conceptualized as carbon-free recyclable energy carriers that may form a cornerstone of a sustainable energy economy. The combustion of metal dusts in oxidizing atmospheres is exothermal and yields oxide particles that could, potentially, be retrieved and, subsequently, recharged by conversion to pure metals using green primary energy sources. As a step towards a predictive tool for designing metal dust combustors, we present a fully Eulerian modelling approach for laminar particle-laden reactive flows that is, conceptually, based on a population balance description of the dispersed particles and relies on a stochastic Eulerian solution strategy. While the population balance equation (PBE) is formulated for the number-weighted distribution of characteristic properties among all particles near a spatial location, it is kinetically informed by the rates at which mass, momentum and heat are exchanged between the carrier gas and the particulate phase on the single particle level. Within the scope of the Eulerian Monte Carlo solution scheme, the property distribution is discretely represented in terms of the total number density and a finite number of property samples and the computational work is channelled towards the Eulerian estimation of mean particle properties.For the case of reactive aluminum particles, we combine a kinetic description of the gas-particle heat and mass transfer with a transport-limited continuum formulation to obtain rate expressions that are valid across the entire particle size range from the free molecular through the continuum regime. Besides velocity, the particle properties include only the particle mass, temperature and oxide mass fraction. This set of thermochemical degrees of freedom is retained also as phase transitions due to melting occur, drawing on a smooth blend of the solid and liquid thermodynamic and material properties. The particle-level formulation encompasses aluminum evaporation, surface oxidation, scavenging of oxide smoke, oxide evaporation/dissociation and radiation. After investigating how these effects translate, through the PBE, to the particle population level and affect the combustion in a homogeneous dust reactor, we analyze the combustion of an aluminum dust in a counterflow flame and validate predictions of the particles’ centerline velocity profile and the flame speed by comparison with available experimental data. Concomitantly, nitrogen oxide emissions are investigated along with the particle burnout and outlet size distribution.

Study on phase transformation and reaction behavior of alumina extraction process by calcification of aluminum dross

The aluminum dross generated during the aluminum alloy processing and regeneration process contains a large amount of harmful highly reactive aluminum nitride and salts, which can cause environmental pollution. A novel method for preparing calcium aluminate by dry calcification of aluminum dross is proposed in this paper to extract valuable aluminum resources while achieving efficient detoxification. Detection methods such as XRD, XRF, and standard dissolution procedures have been applied to characterize the phase transition and reaction behavior of the aluminum extraction process. The results indicate that calcium additives can react with aluminum components in aluminum dross to generate 12CaO·7Al2O3 (C12A7), which is soluble in sodium carbonate solution, thereby separating it from other impurities. Under the optimal roasting conditions, the leaching rate of alumina is 87.89%, and the removal rate of nitrogen, chlorine, and soluble fluorine elements exceeds 99%.Excessive sodium carbonate is required to ensure that the hydrolysis product of C12A7 is calcium carbonate, avoiding the formation of hydrated calcium aluminate precipitates. The optimal leaching conditions are sodium carbonate concentration of 80 g L−1, caustic soda concentration of 5 g L−1, liquid-solid ratio of 8 mL g−1, and leaching time of 30 min. The leaching reaction of calcium aluminate conforms to the unreacted core model controlled by internal diffusion, and the apparent activation energy of the reaction is 18.05 kJ mol−1.

Deep insight into reactive chemical structures of Class F fly ash

Reactive amorphous aluminum silicates dominate the reactivity of fly ash in alkali cement; however, the quantitative characterization of valid chemical compositions and structures information is highly challenging due to the heterogeneity and complexity of these phases. To acquire this information, in this work, Class F fly ash was treated with 1% hydrofluoric acid, followed by step-by-step analysis using a scanning electron microscope with an energy dispersive spectrometer (SEM-EDS), solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR), and Fourier transform infrared (FT-IR) spectroscopy. Based on the acidolysis method, along with SEM-EDS statistical analysis, four amorphous aluminum silicate phases with relatively higher reactivity were successfully separated and quantitatively showcased, along with their respective average atomic percentage compositions (i.e., Si, Al, Ca, Fe, Na, K, and Mg%). In addition, the use of MAS-NMR and FT-IR analyses allowed for further quantitative insight into the reactive chemical structures and their associations with reactivity. The proposed characterization techniques have unique advantages for acquiring detailed reactive amorphous chemistries, which are difficult to obtain using conventional analysis procedures in alkali systems.