Добірка наукової літератури з теми "Aluminothermic reactions"

Understanding the reaction thermochemistry as well as formatting the empirical data about element distribution in gas-metal-slag phases is essential for creating a good model for aluminothermic and carbothermic reaction. In this paper modeling of material and energy balance of these reactions is described with the algorithm. The software, based on this model is basically made for production of high purity ferro alloys through aluminothermic process and then extended for some carbothermic process. Model validation is demonstrated with production of FeTi, FeW, FeB and FeMo in aluminothermic and reduction of mill scale, pyrite cinders and magnetite fines in carbothermic process.

The aluminothermic process provides a cost-reduced production method for titanium and titanium alloys by reduction of TiO2 with subsequent refining by electroslag remelting The aluminothermy involves high heating rates, high temperatures and short reactions times combined with a self-propagating behaviour of the reaction. By co-reduction of TiO2 and oxides of alloying elements such as vanadium pentoxide, direct synthesis of a titanium alloy is possible. The use of rutile ore concentrates causes a further reduction of process steps. In order to charge rutile ore complex thermodynamic calculations are required taking enthalpy input of various bycomponents into account. The aluminothermic reduction is conventionally enhanced by a highly heatproviding reaction based on the reduction of KClO4. In order to minimize the use of chlorine-based products extensive studies are made to investigate the feasibility of using mechanically activated rutile as input material for the aluminothermic process. Due to the mechanical activation the intrinsic enthalpy of the reaction is increased thus facilitates a process with reduced amount of KClO4. A major challenge represents the determination of a compromise between low activation duration and reduced KClO4 amount. In order to define the process window parameters like intrinsic chemical energy (enthalpy of the reaction mixture), equilibrium temperature and physical properties (particle size and mixing degree) were optimized. After adjusting the process parameters it is possible to save up to 42 % KClO4 for the ATR reaction with 2h activated input material. This reduction of KClO4 material affects a decrease of the produced gaseous compounds and the subsequent off-gas cleaning system.

Thermite welding (TW) is now widely used all over the world to weld, maintenance and modernization railway and tram rails [1]. The main materials from the thermite composition (TC), results from manufacturing scraps, which can be retrieved all over the country. Exothermic welding (EW) which is based on the exothermal reaction between iron oxides (FeO, Fe2O3 and Fe3O4) and aluminium powder, takes place at temperatures up to 3500 °C and during casting rail ends are melted in order to be welded.In was studied the thermal effects of the aluminothermic reduction reactions of the iron oxides, which were dosed in different percentages. The aluminothermic reaction efficiency is given by strictness in the ratio of the TC selection and mainly in the iron oxides types. Their correct dosage makes possible the control the exothermic reaction (ER) effect. Also it is revealed the effect of particle size from thermite powder (TP) on the thermite dynamics reactions. Is also presented a model of optimization and control the thermite kits (TK) for aluminothermic welding (AW). Finally, the TK composition can be calculated from "QUARK1" Diagram, as function of the heat amount necessary for the welding.

High-nitrogen austenitic steels are promising materials, combining high strength, plasticity and corrosion resistance properties. However, to produce high-nitrogen steel by conventional metallurgical methods under high nitrogen pressure, powerful and complex metallurgical equipment is required. From energy-saving viewpoint, an alternative and simpler method for producing high-nitrogen steels can be aluminothermy (reduction of metal oxides by metallic aluminum) under nitrogen pressure. Thermodynamic modeling of aluminothermic reactions in a nitrogen atmosphere was carried out by the authors. Aluminothermy under nitrogen pressure was used to produce high-nitrogen nickel-free Cr – N and Cr – Mn – N stainless steels with a nitrogen content of about 1 %. Microstructure (X-ray diffraction, metallography and transmission electron microscopy techniques) and mechanical properties were examined. Thermodynamic analysis has shown that the aluminothermic reduction reactions do not go to the end. The most important parameter of the synthesis is the ratio of Al and oxygen in the charge, the correct choice of which provides a compromise between completeness of oxides reduction, content of aluminum and oxygen in steel (the degree of deoxidation), and its contamination with aluminum nitride. Cr – N steel ingots in the cast state had the structure of nitrogen perlite (ferrite-nitride mixture), and Cr – Mn – N steel – ferrite-austenite structure with attributes of austenite discontinuous decomposition with Cr2 N precipitations. Quenching resulted in complete austenization of both steels. The compliance of the austenite lattice parameter obtained from the diffractograms for quenched Cr – Mn – N steel with the parameter predicted from the known concentration dependence for Cr – Mn – N austenitic steels indicated that all alloying elements (including nitrogen) were dissolved in austenite during aging at quenching temperature and fixed in the solid solution by quenching. Study of the mechanical properties of quenched Cr – Mn – N steel has shown a combination of high strength and ductility. It is concluded that by the aluminothermic method a high-nitrogen steel can be obtained, which, by mechanical properties, is not inferior to industrial steel – analog manufacted by electroslag remelting under nitrogen pressure.

Alumina (Al2O[Formula: see text] coated nano silicon was synthesized by aluminothermic reduction for the first time. It was realized by preoxidation of the nano silicon followed by a aluminothermic reduction that transformed the surface silicon oxide into Al2O3. The thickness of Al2O3 can be controlled by regulating the preoxidized temperature and the processing time. The nano silicon coated with 2–4[Formula: see text]nm Al2O3 showed a more stable cycling performance and a higher coulombic efficiency than the uncoated nano silicon. It is believed that the improved electrochemical performance was benefited from the Al2O3 coating, which could hinder the side chemical reactions during the cycling process. This work provides an alternative method for surface coating on nanomaterials by safe and flexible solid state chemical reaction.

The kinetics of low-temperature (900 – 1180 °C) reduction of iron tantalate (98.2 wt % FeTa2O6, 1.8 wt % Ta2O5, particle size < 0.1 mm) by excess aluminum (particle size < 0.14 mm) at the molar ratio Al:FeTa2O6 = 6 was studied. According to differential scanning calorimetry and X-ray powder diffraction, reduction is almost completed at 1180 °C, the metal products are TaFeAl, TaAl3, and Ta17Al12. Based on the results of thermokinetic calculations (Ozawa – Flynn – Wall and nonlinear regression methods), the formal mechanism of the process is represented by the Bna → CnC model, which includes two consecutive steps controlled by autocatalytically activated reactions. Kinetic parameters of the steps are: 1) Е1 = 429 kJ·mol–1, A1 = 1015.3 s–1; 2) Е2 = 176 kJ·mol–1, A2 = 103.9 s–1 (Ej is the activation energy, Aj is the preexponential factor). Prediction in the Bna → CnC model frames indicates the possibility of obtaining a reaction mixture containing ≥ 98 mol. % the final formal reduction product, with isothermal exposure in the temperature range of 1040 – 1120 °C during 1.5 – 5 minutes. The proposed model can be used to develop scientific foundations and substantiate technological modes for obtaining tantalum alloys from mineral and technogenic raw materials.

Abstract In this work we investigate the mechanism of product formation of the aluminothermic reaction of Fe2O3 in the presence of Al2O3 using Ball Milling and Self-propagating High-temperature techniques. Results obtained by experiments under either argon or air atmosphere are analysed by X-ray diffraction and Mössbauer spectroscopy, together with microstructure observations. It is shown that ball milling products are strongly affected by the kind of atmosphere, while self-propagating high-temperature ones are only weakly influenced. Reaction mechanisms taking place in these cases are proposed. While ball milling involves only solid state reactions, the formation of a melt occurs under self-propagating high-temperature conditions.

The reaction mechanism of MoS2-Fe2O3 aluminothermic reduction in the presence of lime using microwave-assisted combustion synthesis method was surveyed. Achieving technical feasibility in one-step production of ferromolybdenum along with sulfur removing in solid form are the main features of this novel process. Simultaneous Preliminary thermoanalytical investigations DSC/TGA and X-ray diffraction experiments during the heating process of 0.42MoS2 +1.14Al + 0.29Fe2O3 +0.84CaO demonstrated four key sequential endothermic and exothermic reactions at 420, 540, 660, and 810?C. The most noteworthy reactions involve evaporation of moisture and volatile matter, molybdenite roasting, simultaneous production of lateral compounds such as CaMoO4 and CaSO4, aluminum melting transition, and final termite reaction. Kinetics procedure of the system was conducted using a classical model-free approach by Kissinger?Akahira?Sunose (KAS) method. In this study, the activation energy was determined about 106.4 (kJ.mol-1) for thermite reaction in the temperature range of 810 to 918?C.

Vacuum aluminothermic reduction of magnesia is multi-phase chemical reaction and the briquette forming condition has a great influence on the extent of the reactions. This paper focused on the effect of briquette forming condition on the extraction of magnesium from calcined magnesite. Briquettes were prepared at different conditions, including two forming pressures, four briquette thicknesses and two briquette diameters. The reduction ratio was calculated from the weight loss of the briquette before and after thermal reduction. The obtained condensed magnesium and briquette residues were mainly characterized via X-ray diffraction analysis and scanning electron microscopy. It was revealed that the briquette preparation condition had a great influence on the reduction ratio of magnesia and the phase constitution of the briquette residues, but had a minor influence on the morphology of condensed magnesium.

La sélection des matériaux utilisés dans les parties chaudes des moteurs aéronautiques ou dans les centrales de production d’énergie est devenue un enjeu crucial au vu des impératifs écologiques et économiques. L’un des composants critiques de ces systèmes sont les aubes de turbine dont la tenue mécanique est assurée par la nature des substrats employés (aciers et superalliages à base nickel). Cependant, leur tenue environnementale nécessite l’application de revêtements protecteurs source d’Al capables de former de barrières d’oxyde (Al2O3) imperméables à l’attaque externe par oxydation et corrosion aux hautes températures. L’épuisement de l’Al pour former l’oxyde et par interdiffusion avec le substrat conduit inexorablement à la perte de protection. Ainsi, des structures spécifiques de revêtement telles les barrières de diffusion peuvent alors être mises en place pour augmenter la durée des vies des aubes au détriment de leurs propriétés mécaniques et de coûts élevés de fabrication et environnementaux. Durant cette étude, des nouvelles voies originales de synthèse des revêtements de diffusion d’aluminium « autorégénérants » ont été étudiées. Ces revêtements disposent d’une structure composite, avec une matrice de phases intermétallique (NixAly) renforcée par des microréservoirs constitués d’un cœur (NixAly) et d'une paroi en Al2O3 à travers laquelle l’Al du cœur peut ravitailler la matrice et maintenir une concentration globale en Al suffisamment élevée dans la matrice capable de former la couche externe protectrice d’Al2O3.Nos études démontrent que les réactions aluminothermiques entre du NiO et l’Al permettent de former un tel revêtement autorégénerant avec une barrière de diffusion à l’interface substrat/revêtement lorsque le Ni est initialement pré-oxydé à 1100°C pendant 2h. Néanmoins, aucun compromis n’a été trouvé pour former des revêtements sans NiO résiduel qui pourrait compromettre l’adhérence du revêtement au substrat. En revanche, une voie électrochimique permet d’incorporer de microparticules d’Al3Ni2 dans des électrodépots de Ni. A la suite d’un traitement d’aluminisation par barbotine, les microparticules préoxydées s’incorporent de manière homogène dans un revêtement de β-NiAl. Après traitement d’oxydation isotherme à 1000°C durant 48h, ce revêtement par voie électrodéposition + aluminisation présente une teneur en aluminium supérieure à 40 at%, ce qui est supérieur à un revêtement de diffusion absent de microréservoirs démontrant ainsi le caractère autorégénerant des nouveaux revêtements
The selection of materials used in the hot parts of aeronautical turbines or in power plants has become a crucial issue in view of ecological and economic imperative. Turbine blades are amongst the most critical components. Their mechanical resistance is ensured by the substrate itself (steels and Ni alloys and superalloys). However, their low environmental resistance requires the application of protective coatings delivering Al to form oxide barriers blocking the external oxidative and corrosive attack. Upon exposure at high temperatures, Al depletes from the coating by oxidation to grow the oxide scale and by interdiffusion with the substrate’s elements resulting in the loss of protection. Some specific coating structures like the diffusion barriers have been investigated in the past but the overall mechanical properties are lowered and the fabrication and environmental costs are high. Therefore, a pioneering and original investigation has been conducted to synthesize “self-regenerating” aluminum diffusion coatings. These coatings are characterized by a composite structure whereby the matrix made of NixAly intermetallic phases is strengthened with microreservoirs made of NixAly core and an Al2O3 shell through which Al diffuses out to maintain the adequate Al concentration in the matrix, hence to stabilize the external protective Al2O3 scale.Our studies demonstrate that the aluminothermic reactions between NiO and Al lead to the formation of such a self-regenerating coating with an interdiffusion barrier at the coating/substrate interface whenever Ni is preoxidized at 1100°C for 2h beforehand. However, all the coatings sintered through this method possess residual NiO, which may compromise their adherence to the substrate. In contrast, the use of electrochemical methods allows to incorporate Al3Ni2 microparticles in the NI electrodeposits. With a subsequent slurry aluminizing treatment, the preoxidized particles incorporate homogeneously in a β-NiAl coating matrix. After exposure at 1100°C for 48h in air, the Al content in the self-regenerating coatings is greater than 40 at% as opposed to the micro-reservoirs-free aluminide coating allowing to demonstrate the self-regenerating property of these new coatings

Magnesium is considered as impurity element in aluminum recycled for obtaining some cast alloys, with low concentration Mg, because at 0.1 wt% results in fragility, fractures, and defects. This research applies the aluminothermic reduction process to decrease magnesium content in aluminum cans by adding ZnO, to produce reaction products solid-state (Al2O3, MgO and MgAl2O4), and there is a possibility to obtain Al-Zn alloy. The conditions of the process were, melting temperature (750, 800, 850°C) and stirring velocity (200, 250, 300 rpm). The Mg and Zn contents were measured for chemical analysis and scrap generated from every process was analyzed by X-ray diffraction. The results show how the aluminothermic reduction decreased Mg from 0.93 to 0.06 wt% and increased zinc up to 5.52wt % in the molten metal. Therefore, this process can be used to remove Mg and can also prevent the generation of polluting gases into the environment.