Papers by Keyword: Exothermic Reaction

Abstract: The problem of unsteady non – Newtonian flow past a vertical porous surface in the presence of thermal radiation is investigated. Using the theory of boundary layer analysis, the flow of micropolar fluid in the presence of exothermic and endothermic kind of chemical reaction is considered. It is assumed that the relationship between the flow rate and the pressure drop as the fluid flows over a porous medium is non – linear. Using local similarity transformation, the governing partial differential equations of the physical model are reduced to ordinary differential equations. The corresponding boundary value problem is solved numerically using shooting method along with Runge-Kutta Gill method together with quadratic interpolation. It is found that increase in micro-rotation parameter increases the velocity while the micro- rotation decreases across the flow region. Maximum micro-rotation of tiny particles is guaranteed at higher values of suction parameter. Local heat transfer rate decreases with an increase in exothermic /endothermic parameter.

Abstract: In view of the demand for electrified long-range vehicles, the performance of traction batteries has to be improved. To achieve a high power density, the battery cells must be interconnected with low electrical resistance within the joints. The joining process has to fulfill specific requirements, as the battery cells may only be exposed to very low mechanical and thermal impacts. Joining by using reactive aluminum-nickel nanofoils represents an innovative technology meeting the abovementioned requirements. These foils are multilayered systems consisting of several hundred alternating monolayers of aluminum and nickel, each with a thickness in the nanometer range. Their unique ability is that they can react with temperatures up to 1500 °C for a duration of a few milliseconds upon external ignition. This thermal reaction energy serves as a heat source in the joining process, melting the materials in the interfacial surface. Subsequently, the joining partners solidify and form an adhesive bond when compressed properly. However, these advantageous characteristics are contrasted by complex reaction mechanisms and an unknown interaction of the process parameters. For the industrial application of the joining technology, the requirements for initiating the exothermic reaction must be known. Therefore, the process window and the mechanism of ignition have to be scrutinized. For this purpose, an experimental test setup was developed to generate and monitor short circuit currents to ignite the nanofoils. The amperage as well as the layer composition of the nanofoils were varied within a parameter study. Two independent process windows for a stable ignition were identified for all analyzed nanofoils.

Abstract: Conventional recycling methods of industrial waste such as ferrous and non-ferrous chips and broken graphite are ineffective. In this paper we investigate exothermic remelting of industrial waste. Parameters of the most effective recycling conditions which result in a maximal yield of reduced metal and high efficiency of steel casting have been determined. The influence of the aluminothermic mixture density, a fraction and a granulometric composition of the mixture initial components on the metallic yield is shown in the paper. The possibilities of reducing the material content in the thermite mixture are also discussed. The most productive process of steel casting with the use of industrial waste which makes it possible to reduce the overall dimensions of casting molds and the bulk of molding materials is proposed.

Abstract: Self-propagating exothermic formation reactions have been intensively studied in a variety of reactive multilayer films, which typically include alternating layers of two or more reactants. Here, we introduce a reactive multilayer film which contains a thermite reaction between Ni and Al.Al/Ni multilayer films which were composed of alternate Al and Ni layers were prepared by DC magnetron sputtering.The total thickness of each films was approximately 1.2 μm having bilayer thicknesses of 60, 100, 150 nm. Each bilayer consisted of an aluminum layer and a nickel layer in a 3:2 thickness ratio to maintain an overall 1:1 atomic composition.Meanwhile, Al/Ni multilayer films with the bilayer thickness of 60 nmwas prepared. In each bilayer, the thickness ratio of Al to Ni was maintained at 1:2 to obtain an overall 1:3 atomic composition.The total thickness of Al/Ni multilayer films was around 1.2 μm.DSC curves show that the values of heat release in Al/Ni multilayer films with bilayer thicknesses of 60 (Al:Ni), 100 (Al:Ni), 150 (Al:Ni) and 60 (Al:3Ni) nm are 324.63 Jžg^-1, 348.51 Jžg^-1, 400.45 Jžg^-1 and 69.85 Jžg^-1, respectively. XRD measurements show that the final products of exothermic reactions with Al:Ni atomic ratio of 1:1 and 1:3 are the compound of AlNi and AlNi₃, respectively.

Abstract: Utilization of industrial waste in foundry engineering is one of approaches for decrease of production cost price. This technological process may be based on exothermic oxidation-reduction reaction with the resulting formation of iron from dross. Initial charge mixture consists of dispersed aluminum, iron dross and admixtures. This paper is concerned with mathematical modeling of thermite steel production. Presented model takes into account thermal, mechanical and kinetic processes occurring in aluminothermic method of steel melt production.

Abstract: Exothermic reaction in thermite charge of casting pattern was investigated by estimated and experimental techniques. Thermophysical properties of steel mouldings production in graphitic shell molds were determined.

Abstract: In this article, a new technique for controlling crack position and its propagation direction in solder-bonding using Al/Ni exothermic reaction is described. Sputtered Al/Ni multilayer film is able to produce heat instantly by its self-propagating exothermic reaction, and the reactive film can be used as heat source for solder-bonding. During the reaction, however, volume reduction by approximately 12% occurs due to crystal structural change from fcc to bcc and lattice-spacing reduction. Consequently, cracks are produced in the reacted NiAl structure. The cracks negatively affect the strength of the bonded system. We have found a new technique for controlling crack position and its propagation direction. Multiple ignitions for reaction demonstrated that cracks in reacted NiAl film can be controlled. When applying the flash heating technique to wafer-level bonding, cracks are probably produced. If cracks can be fabricated on dicing cut lines by using the simultaneous multiple reactions technique, crack-less solder-bonded Si hermetic packages would be realized.

Abstract: This paper describes evaluation of the strength in Ag-Sn-jointed Si specimens heated by Al/Ni film’s exothermic reaction. The reaction generates heat enough to melt Ag-Sn film for soldering. To measure the strength, four-point micro-bending test technique has been developed. The rectangular-solid Si specimens having a Ag-Sn/AlNi/Ag-Sn section were prepared by dicing the bonded Si-wafer under various pressure loads. A higher pressure yielded a better contact condition between Al/Ni and Ag-Sn so that heat-conduction improved; consequently Ag-Sn was melted sufficiently. Al/Ni reactive film has a potential as a micro-heater in soldering for MEMS.

Abstract: Post-reaction sintering as a technique for the fabrication of Si3N4 ceramics has received much attention as a cost-effective process due to the use of cheap Si powder as a raw material. In this method, the rapid exothermic nitridation of Si results in local melting of Si to cause its agglomeration, which is expected to be a flaw after densification. Therefore, control of the exothermic reaction is needed to improve the reliability of post-reaction sintered Si3N4 ceramics. In this study, Si3N4 ceramics were fabricated by post-reaction sintering with Si3N4 or SiO2 powders in order to control the exothermic reaction. As a result, the microstructure and bending strength of Si3N4 ceramics was changed by adding these additives. In particular, the addition of SiO2 resulted in the high strength of Si3N4 ceramics. Consequently, it was found that Si3N4 and SiO2 particles played the role of diluents, and SiO2 was effective in post-reaction sintering as an oxygen donor.

Abstract: A 3-D transient heat transfer finite element (FE) analysis was performed to simulate the curing process of thick thermoset composites. The simulated temperature was compared with the available experimental data to check the validity of the analysis. The influence of thickness of composite laminates on the temperature distribution was investigated, and how the size of laminates affects the inside temperature was also discussed. The results indicate that the laminate thickness rather than the laminate size has a significant influence on temperature distribution, and the 3-D analysis offers more accurate predictions than the 1-D analysis.