Investigation of the Cause-Effect Relationships between the Exothermic Reaction and the Microstructures of Reactive Ni-Al Particles Produced by High Energy Planetary Ball Milling

Abstract

Reactive particles consisting of nickel and aluminum represent an adaptable heat source for joining applications, since each individual particle is capable of undergoing a self-sustaining exothermic reaction. Of particular interest are particles with intrinsic lamellar microstructures, as they provide large contact areas between the reactants nickel and aluminum. In this work, the exothermic reaction as well as the microstructure of such lamellar reactive particles produced by high energy planetary ball milling were investigated. Based on statistically designed experiments regarding the milling parameters, the heat of reaction was examined by means of differential scanning calorimetry (DSC). A statistical model was derived from the results to predict the heat of reaction as a function of the milling parameters used. This model can be applied to adjust the heat of reaction of the reactive particles depending on the thermal properties of the joining partners. The fabricated microstructures were evaluated by means of scanning electron microscopy (SEM). Through the development of a dedicated SEM image evaluation algorithm, a computational quantification of the contact area between nickel and aluminum was enabled for the first time. A weak correlation between the contact area and the heat of reaction could be demonstrated. It is assumed that the quantification of the contact areas can be further improved by a higher number of SEM images per sample. The findings obtained provide an essential contribution to enable reactive particles as a tailored heat source for joining applications.

Discrete One-Stage Mechanochemical Synthesis of Titanium-Nitride in a High-Energy Mill

“…In ( 8) and ( 9), the first term determines the rate of accumulation of excess energy, the second term determines the rate of relaxation of excess energy, and the third term in (9) determines the rate of normalization of the solid phase structure due to chemical transformation.…”

“…Mechanochemical synthesis of inorganic substances is widely used to stimulate various solid-phase reactions and is a promising method to obtain superfine powders containing significant amounts of gaseous components. Synthesis stimulated by mechanical action has been the subject of numerous studies [1][2][3][4][5][6][7][8][9][10][11][12][13][14].…”