Exothermic welding

Résumé

Exothermic welding, also known as exothermic bonding, thermite welding (TW), and thermit welding, is a welding process that employs molten metal to permanently join the conductors. The process employs an exothermic reaction of a thermite composition to heat the metal, and requires no external source of heat or current. The chemical reaction that produces the heat is an aluminothermic reaction between aluminium powder and a metal oxide. Overview In exothermic welding, aluminium dust reduces the oxide of another metal, most commonly iron oxide, because aluminium is highly reactive. Iron(III) oxide is commonly used: :\mathrm{Fe_2O_3 + 2 \ Al \longrightarrow 2 \ Fe + Al_2O_3} The products are aluminium oxide, free elemental iron, and a large amount of heat. The reactants are commonly powdered and mixed with a binder to keep the material solid and prevent separation. Commonly the reacting composition is five parts iron oxide red (rust) pow

Source officielle

https://en.wikipedia.org/wiki/Exothermic_welding

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The theoretical background and practical aspects of heterogeneous reactions including the basic knowledge of heterogeneous catalysis are introduced. The fundamentals are given to allow for the use of chemical reactors to study reaction kinetics and test various mechanistic assumptions.

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Study of highly exothermic reaction in microstructured reactors: cyclization of pseudoionone as a case study

Olivier Détraz

2010

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The mechanism and kinetics of rapid and exothermic reactions is difficult to study using conventional offline techniques. This paper deals with experimental investigations of highly exothermic and fast model reaction (cyclisation of pseudoionone) using slug flow (micro-batches) microstructured reactor (MSR). The slug flow was obtained using a cross-junction and identifying suitable inert carrier fluid (perfluorohexane) immiscible with the species participating in the reaction. MSR provided short reaction time in a continuous slug-flow that allowed catching intermediates and monitoring the kinetics. The small reaction volumes suppress the temperature rise by removing the reaction heat. The kinetics has been studied under isothermal conditions and more reliable reaction network has been proposed. Finally, the mixing within the slugs and its influence on the obtained results was accessed. This methodology has a generic nature and can be applied for a wide variety of fast exothermic homogeneous reactions. (C) 2012 Elsevier B.V. All rights reserved.

Elsevier2013

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Biphasic Model Describing Soybean Oil Epoxidation with H2O2 in Continuous Reactors

Albert Renken

Epoxidized soybean oil (ESBO) is produced in industry by reacting soybean oil, at 60-70 degrees C, with hydrogen peroxide in the presence of formic or acetic acid. A small amount of sulphuric or phosphoric acid is necessary to catalyze the oxidation of the carboxylic acid to the corresponding per-carboxylic acid. Per-carboxylic acid, formed in situ, migrates from the aqueous phase to the oil phase where it spontaneously reacts with the double bonds to give an oxirane ring. This reaction is extremely exothermic (Delta H = -55 kcal/mol) and must be kept under thermal control. Two undesired side reactions can occur: the oxirane ring-opening and the hydrogen peroxide decomposition. In a previous work, a biphasic kinetic model for describing the epoxidation of soybean oil in fed or pulse-fed-batch reactors has been developed and the parameters of the model have been determined by mathematical regression analysis. In the present paper, the model has been adapted to simulate also kinetic runs performed in two continuous tubular reactors of different sizes, filled with spheres of stainless steel (AISI 316) used as static mixer. The agreement found, in simulating the continuous runs, validates the developed biphasic kinetic model. This model constitutes a valid base for the design of a continuous process and for promoting the process intensification.

2012

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