Oxidation Of Aluminum Powders Research Articles

Thermal enhancement of the oxidation layer of micron-sized aluminum powder and its anti-oxidation performance

Micron-sized aluminum powder, with its typical core-shell structure, exhibits oxidation behavior upon slow heating in an oxidative atmosphere that is related to the particle size of the aluminum powder. A particle size-dependent thermal response mechanism for micron-sized aluminum powder is established: a "shell-breaking eruption" thermal response mechanism. The oxide layer is thermally enhanced, and the anti-oxidation reaction behavior mechanism of the enhanced samples is studied. Aluminum powder samples, heated slowly to specific temperatures to obtain changes in the oxide layer structure, are analyzed using a thermal analyzer to compare the slow heating response behavior of aluminum powder before and after the oxidation layer changes. It was found that after thermal enhancement of the aluminum powder oxidation layer, which changed from amorphous to γ-phase and whose thickness increased to twice the original thickness, the slow oxidation process of micron-sized aluminum powder was inhibited, and the aluminum powder was completely deactivated in the slow heating response.

Improved Combustion Performance of Fluororubber-Coated Micro-Nano Composite Aluminum Powder

In order to improve the reaction rate and reaction degree of aluminized explosives, the micro-nano composite aluminum powder was fabricated by a new method of in situ electro-explosion. The combustion performances of the composite aluminum powder were studied. The results showed that the micro-nano composite aluminum powder was like a “sea urchin structure” with many nano-sized powders around a single micro-sized aluminum particle. The heat of combustion was 25.67 MJ/kg at 3 MPa oxygen pressure, and the rising rate of pressure was particularly obvious. The ignition performance in an air environment was much better than the micro-sized aluminum powder. At the same time, the reaction process of the micro-nano composite aluminum powder was analyzed. The reaction can be divided into three stages, the decomposition of fluororubber between 500 and 600 °C, then melting, and the first step of the oxidation of aluminum powder occurred between 600 and 700 °C. In the third stage, the micro-nano composite aluminum powder reacted violently around 1000 °C and the released energy reached 3779 J/g. The micro-nano composite aluminum powder had excellent combustion performance and a good application prospect in high-power energy storage materials.

Influence of modified natural zeolite on the thermal stability of epoxy based composites

The effect of modified natural zeolite of the Shivyrtuysky deposits on the thermal behavior of epoxy composites at the heating was studied. The modification of the zeolite particles with aluminum oxyhydroxide (AlOOH) nanofibers was made. AlOOH nanofibers were obtained at the heating and oxidation of aluminum powder by water. The parameters of thermal-oxidative and thermal destruction of the samples with a filler concentration of 1, 2, 5, and 10 wt. % were determined. The limiting oxygen index was determined by the calculation method.

Preparation and oxidation of aluminum powders with surface alumina replaced by iron coating

ABSTRACT Aluminum powders are well known for excellent release of energy during oxidation upon heating. However, this release of energy becomes limited due to formation of dense oxide (Al2O3) layer on powder surface. In this study, reactivity of aluminum particles was improved by replacing oxide layer with metallic shell of iron using electroless plating technique. Three different bath compositions were selected for deposition of iron on aluminum particles. The surface morphology of prepared Al/Fe core–shell composite powder was characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Further, iron content in the composite powder was measured quantitatively using helium gas pycnometer while elemental analysis was performed by X-ray diffraction (XRD). Finally, thermo-physical behavior of the composite powder was investigated using simultaneous thermogravimetry–differential scanning calorimetry (TG–DSC). The results showed that the synthesized Al/Fe core–shell composite powder exhibits higher energy release in comparison to the uncoated aluminum powder upon heating in air (up to 1180 °C). The powder with the densest iron coating released the highest energy.

Synthesis of core-shell Al/Al2O3 composite through aluminum powder oxidation in hot water and its characterization

Simple and potentially energy efficient way for synthesis of Al/Al2O3 composites is described. Synthesis method is based on aluminum powder oxidation in water at 100-200 °C and following drying and calcination at 600 °C. Aluminum powder with average size of about 40 urn that is currently applied in additive manufacturing was used. Present work was devoted to the study of oxidation degree of aluminum and so the propagation depth and structure of Al2O3 shell in composite’s matrix. AI/Al2O3 composites were produced in different regimes with different maximum temperature and duration of the process of aluminium oxidation in water. Aluminum oxidation degree and aluminium content in obtained Al/Al2O3 were changed in the range from 5.5 % and 90.1 % to 21.3 % and 66.2 % respectively. The size of single crystals of Al2O3 in shell was changed from about 6 nm to 200 nm and the thickness of Al2O3 shell was changed from about 400 nm to 1000 nm by changing the regime for Al/Al2O3 composite production. Experimental results showed that Al2O3 shell was well clutched with aluminum core. Shell structure had cracks aroused by calcination process. Size distribution for obtained composites was very close for that of initial aluminum powder. All of these characteristics recommend the obtained Al/Al2O3 composites for additive manufacturing.

Selective laser melting of aluminum-alumina powder composites obtained by hydrothermal oxidation method

Selective laser melting of Al-Al2O3 core–shell composite with 10 wt.% of alumina was studied. The initial powder was obtained by hydrothermal oxidation of aluminum powder. A matrix of parameters was selected for selective laser melting of composites, including laser power from 180 to 220 W, scanning speed from 180 to 220 mm/s, and hatch spacing from 0.13 to 0.18 mm. The type of microstructure, relative density, and hardness of synthesized objects were determined. The influence of the laser’s areal energy density on the properties of synthesized objects was studied. Depending on the EDa used, different types of microstructure were formed. The EDa within the range 7–8 J/mm2 was found to be optimal for SLM of Al-10 wt.% Al2O3 core–shell powder composites. Beyond this range, uncomplete powder melting as well as boiling of the aluminum leads to the low density and formation of microcracks after solidification. The hardness of the finest synthesized sample (58.3 ± 0.9 HB) and uniform distribution of alumina was obtained at EDa = 7.69 J/mm2 with the following SLM parameters: P = 220 W; h = 0.13; V = 220 mm/s. Based on the obtained results, further research using SLM with double exposure of the layer with a laser beam was suggested.

The role of bound water in the process of low-temperature oxidation of aluminum powders

The processes of oxidation of aluminum powders with various particles size (micron and submicron samples) when heated in air were studied using differential thermal analysis. It was found that decreasing of particle size leads to an increase in the content of bound water in the form of hydroxides in the aluminum particles shells. The (hydr)oxides decompose with the release of water vapor when heated, and there is a local loss of continuity of the protective shells of Al particles, which contributes to the initiation of the metal oxidation process. In the temperature range of 350-600 °C, water vapor interacts with the surface of Al particles, resulting in the presence of hydrogen in the gas released from the thermal analyzer furnace. Based on a combination of data from thermal analysis, mass spectrometry and electron microscopy, it was shown that the main cause of the onset of oxidation of submicron Al particles was destruction of the (hydr)oxide shells due to intense gas formation at the metal core/shell interface due to the release of water vapor and hydrogen.

Mechanochemical Oxidation of Aluminum: Formation of the Porous Structure of Aluminum Hydroxides and Oxides

The main characteristics of aluminum oxides and hydroxides obtained by mechanochemical oxidation of aluminum powder, both in the initial state and after their heat-treatment in the interval 150 – 1100°C, are compared. The conditions for obtaining pseudoboehmite by thermal activation of mechanically oxidized product were established. The structure, morphology, and texture of the pseudoboehmite structure of aluminum hydroxide synthesized from mechanically oxidized product and aluminum oxides obtained on its basis in the temperature interval 450 – 1100°C are characterized.

Characterization of Shivirtui Zeolite Modified with Aluminum Oxyhydroxide Nanofibers

Natural zeolite of Shivirtui deposit (Russia) was modified with nanofibers of aluminum oxyhydroxide AlOOH. Aluminum oxyhydroxide nanofibers were produced at the heating and oxidation of aluminum powder with water. The properties of modified zeolite were investigated by means of X-ray diffraction, transmission electronic microscopy, scanning electronic microscopy, low-temperature nitrogen adsorption, thermal analysis, and Fourier transform infrared spectroscopy. It was found that water content in the modified sample of zeolite was about 15 %. Based on the study of the physical and chemical properties, shivirtui zeolite modified with nanofibers of aluminum oxyhydroxide can be proposed for use as a flame-retardant additive to polymers.

Effect of organic coatings of nanoaluminum on the burning rate of mixed compositions

Mixed compositions based on ammonium perchlorate, inert fuel-binder and nanosized aluminum, encapsulated with organic compounds, have been experimentally studied. The study of aluminum powders using scanning electron microscopy and transmission electron microscopy was carried out. The oxidation of aluminum powders was investigated by differential thermal and thermogravimetric methods. The chemical composition of the condensed products was determined by X-ray diffraction. The laws of mixed composition combustion were determined in a wide pressure range. The possibility of controlling the burning rate and the content of condensed combustion products by using encapsulated nanoaluminum is shown.

Oxidation of Powdered Aluminum after Surface Modification with Mn, Fe, Co, and Ni Formates

The effect of small additives of manganese, iron, cobalt, and nickel oxides on the oxidation of aluminum powder of ASD-4 grade while heating in air is studied. Composites of Al/MOx were prepared by impregnating the metal powder with saturated solutions of M(HCOO)2 ⋅ 2H2O (M = Mn, Fe, Co, and Ni) formates and thermal treatment of the mixtures in air with a maximum annealing temperature of 375°C. It has been established that the effect of modifiers on the intensity of oxidation depends on the nature of the interfacial interaction on the surface of particles. The formation of a liquid phase in the interaction of aluminum oxides and iron leads to the loss of the protective properties by the barrier layer of oxidation products and acceleration of the process.

In situ high-temperature X-ray diffraction, FT-IR and thermal analysis studies of the reaction between natural hydroxyapatite and aluminum powder

The present work focuses on the study of the effects of mechanical activation on the reaction between hydroxyapatite (HAp) and aluminum metal powder using Algerian phosphate (natural HAp) as a starting raw material. Aluminum metal powder was used to obtain reinforced (HAp) composites materials with alumina. The alumina phases result from the oxidation of aluminum powder at high temperature. The reactions and phase transformations between HAp and aluminum powder were studied using thermal techniques (DTA/TG), X-ray diffraction (in situ HTXRD and standard), infrared spectroscopy (FT-IR) and SEM analysis. After mechanical treatment for different milling time, no new phases were formed from HAp and Al after 40 h of milling at room temperature. However, all mixture powders were milled for different time showing the formation of several alumina transitions during heat treatment. The oxidation of Al powder, the formation of alumina transitions (χ and κ-Al2O3), α-alumina, HAp crystallization and tricalcium phosphate (β-TCP and α-TCP) formation were affected by ball milling time. After 40 h of ball milling, the aluminum was not detected at 673 K, which confirms the solid-state oxidation of aluminum at low temperatures. The results showed the formation of high amount of α-TCP at 1173 K in the samples milled for 40 h.

Partial oxidation of aluminum powder for obtaining a controlled amount of aluminum oxide on the surface of aluminum

This work is devoted to the study of the process of partial oxidation of aluminum powder with hydrogen generation and the production of a metal-ceramic product that can be used in the production of various manufacturers such as additive manufacturing (AM) engineering technologies, machine building and so on. The released hydrogen can be effectively used in the form of an energy carrier that will contribute to reducing the cost of production and reduce the cost of the final product.

Nanostructured Disaggregated Aluminum Hydroxide and Oxide Powders

Results are provided for an experimental study of disaggregation of aluminum hydroxide (boehmite) powder prepared by hydrothermal oxidation of aluminum powder. The effect of heat treatment temperature, drying with heated steam, milling in ball and knife mills, treatment in rotary pulsating equipment, addition of surfactant on original powder disaggregation and preparation of nanostructured boehmite and aluminum oxide, are studied. Process parameters are determined for preparing nanostructured powders.

Mechanochemical Oxidation of Aluminum for Production of Its Oxides, Hydroxides and Hydrogen

The mechanochemical synthesis of aluminum oxides and hydroxides is studied by means of X-ray diffraction, volumetry, and thermogravimetry. Kinetic aspects of metallic aluminum powder oxidation depending on time and the method of mechanical activation are investigated. The basic kinetic patterns of the process of the mechanical activation of metallic aluminum powder in an aqueous medium are established.

Initial stages of oxidation of aluminum powder in oxygen

Oxidation of aluminum powders is known to include several stages, corresponding to growth of different polymorphs of alumina. The initial oxide layer is amorphous, which transfers to γ-Al2O3 at elevated temperatures and greater oxide thicknesses. This work focuses on quantitative characterization of oxidation for thin initial oxide layers occurring at relatively low temperatures. The experiments include different types of thermo-gravimetric (TG) measurements with increased amounts of powder loaded for greater sensitivity. Modulated and isothermal TG measurements were found to be less useful than constant heating rate measurements. Results were processed using both, an explicit oxidation model and a model-free isoconversion method. The latter approach was more productive in identifying the activation energy of oxidation. Using the activation energy as a function of reaction progress, the pre-exponent was also determined as a function of reaction progress assuming a diffusion-limited reaction mechanism. The reaction kinetics was validated by comparison between predicted and measured oxidation rates for nanoaluminum powders reported in the literature. Finally, the oxidation model was combined with a heat transfer model to describe ignition of aluminum particles exposed to a heated oxidizing environment. A sharp increase in the ignition temperature from 850 to 2260 K is predicted as the particle size increases from 0.3 to 1.2 µm. The results are found to be sensitive to the assumed initial oxide thickness (2.5 nm); they are also somewhat affected by the value of thermal accommodation coefficient used in the heat transfer model.

Effect of vanadium-containing activating additives on the oxidation of aluminum powders

The effect of vanadium-containing activating additives on the oxidation of an ASD-4 aluminum powder subjected to low-rate heating in the air is studied. The tests are conducted for a number of activators introduced by impregnating the metal powder with vanadium-containing gels with the following compositions: Li2V12O31 · nH2O, Na2V12O31 · nH2O, Na2MoV11O31 · nH2O, V2O5 · nH2O, and 6V2O5 · B2O3 · nH2O. A gel-preparation method based on the instantaneous cooling of melts of the respective reagents in cold water is proposed. It is found that the oxidation of the activated powders is shifted to a low-temperature region.

Non-Isothermal Kinetic Analysis of Oxidation of Pure Aluminum Powder Particles

Non-isothermal kinetic analysis of oxidation of aluminum powder particles (100–200 μm) was investigated by simultaneous thermogravimetry (TG) and differential thermal analysis under linear temperature programming (ranging from 25 to 1,400 °C) at different heating rates (10, 20 and 30 °C/min). In addition, the rate of oxidation reaction (rate of thermogravimetry; RTG) was obtained by the RTG curves. It was found that the oxidation of aluminum powders took place over several stages and the complete oxidation process did not occur even up to 1,400 °C. Among different stages, the temperature ranging from 1,000 to 1,150 °C was identified as the main stage for oxidation process. Hence, kinetic analysis of non-isothermal was determined to be carried out in this region only. Therefore, non-isothermal kinetic analysis of oxidation of pure aluminum powder particles was performed using isoconversional methods (Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, Friedman ), Markworth and Coats–Redfern methods. Also, the empirical kinetic triplets [Ea, A, and f(α)] have been calculated.

Reaction Interface for Heterogeneous Oxidation of Aluminum Powders

Heterogeneous oxidation of aluminum is rate limited by diffusion through a growing aluminum oxide layer. If inward diffusion of oxygen ions is faster than outward diffusion of aluminum, the reaction will occur at the inner interface of the oxide. Conversely, the reaction will occur at the outer oxide surface if outward diffusion of aluminum is faster. The location of the heterogeneous reaction is identified processing results of thermogravimetric measurements for two oxidizing spherical aluminum powders with different but overlapping particle size distribution. For each experiment, the measured weight gain is distributed among particles of different sizes assuming that the rate of oxidation is proportional to the reactive interface area. Different models are considered to determine the interface area. For a ductile oxide shell, when there is no void between oxide and aluminum, two cases with the reaction occurring at both inner and outer surfaces of the shell were evaluated. In addition, a case with the reaction at the outer surface of a rigid oxide shell is considered, for which a void inside the particle forms when the aluminum core is shrinking. Oxidation weight gains for the same size particles present in different aluminum powders are expected to be identical to each other when the calculated reactive interface area reflects the true oxidation mechanism. It is concluded that the reaction at the outer surface of a rigid oxide shell describes the experiments most accurately. Thus, the outward diffusion of aluminum ions controls the rate of heterogeneous oxidation of aluminum in a wide range of temperatures of approximately 400–1500 °C. The conclusion is further supported by the electron microscopy of particles quenched at different temperatures, showing oxide surface features consistent with the identified reaction mechanism.

The Oxidation Mechanism of Pure Aluminum Powder Particles

The oxidation mechanism of aluminum powder particles was studied by simultaneous TG–DTA analysis (under air atmosphere) at different heating rates (10, 20 and 30 °C/min) and from an ambient temperature up to 1,400 °C. Also, the rate of oxidation reaction (rate of weight gain; RTG) was obtained by the differentiation of weight gain (TGG) curve. Additionally, SEM and X-ray diffraction analysis (XRD) studies were performed on each of the above samples for their structural and phase studies. The results obtained from TG–DTA and RTG curves; microstructure and phase analysis studies indicated that the oxidation of aluminum powders occurred during five stages. On the other hand, according to the results obtained from XRD and TGG curves, aluminum particles after the thermal analysis test, even heated up to 1,400 °C, were not entirely oxidized (i.e. less than 10 %).