Mechanochemical activation of aluminum: 5. Formation of aluminum carbide upon heating of activated mixtures

The mechanical activation of thermal synthesis of aluminum carbide Al4C3 in Al-15 wt % C and Al-30 wt % C mixtures is studied with differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. It is found that the mechanical treatment of powders results in an essential reduction in the temperature of carbide synthesis. A correlation between the temperature of the onset of synthesis and size L of the coherent scattering region of aluminum is established. When the doses of absorbed mechanical energy exceed 15-20 kJ/g and, as a result, the L value decreases to 20 nm, the synthesis proceeds by a solid-phase mechanism at a temperature significantly lower than the melting point of aluminum and the synthesis temperature reduces by 800 degrees C. The particle size of the formed aluminum carbide and unreacted aluminum after heating to 900 degrees C is 20-40 nm. At doses D = 50-80 kJ/g, the heat of the formation of carbide from activated samples is about two times lower compared to the standard value. The possible sources of this discrepancy are discussed.