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

Abstract

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°C. The particle size of the formed aluminum carbide and unreacted aluminum after heating to 900°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.