Combustion synthesis of AlN whiskers

Long and coarse AlN whiskers comprising more than 80 vol% of the combustion product have been successfully produced through combustion synthesis. Addition of ammonia halides can accelerate the vaporization of Al, and retard the deposition rate of AlN, with the result that the growth of AlN whiskers is markedly promoted. A growth model for a spiral whisker by a helical screw dislocation mechanism, or a combination mechanism of a helical screw dislocation and the VLS process, is proposed. Periodic interactions of vacancies and the tip of a screw dislocation cause the growth of a spiral whisker in the model. Under an atmosphere of supersaturated “AlN vapor,” the growth of whiskers along the axial direction slows down and gradually arrests, due to the limitation of the diffusion distance. A series of deposition sites are then produced at regular, isolated locations along the center line on the prismatic plane, and eventually cause the formation of dendritic whiskers.