Mechanical activation time of 6B2O3–13Al powder mixture vs. structure and phase composition of SHS products

The paper discusses the time of mechanical activation of the 6B2O3–13Al powder mixture affecting the self-propagating high-temperature synthesis (SHS), exothermic reaction temperature, structure, and phase composition of synthesis products. It is found that the time increase of the mechanical activation up to 180 min leads to a reduction in the average size of aluminum and boron trioxide particles down to 4.8 and 3.5 μm, respectively. Aluminum particles with boron trioxide inclusions are observed on the particle surface and inside their structure. Changes in the particle size and structure in the initial mixture components modify the SHS reaction front from chaotic to by layers. The structure of SHS products consists of the alumina layer (63–68 wt%) with aluminum dodecaboride (AlB12) particles (32–37 wt%) distributed under this layer. After 10 and 60 min of mechanical activation, acicular and elongated AlB12 particles appear in products synthesized from the 6B2O3–13Al powder mixture. Based on the data obtained, the SHS with subsequent mechanical activation is proposed for the fabrication of the Al2O3/AlB12 nanocomposite from the 6B2O3–13Al powder mixture. It is shown that after washing grinded SHS products with hydrochloric acid solution, the synthesized powder contains 100 wt% AlB12.