Analysis of intermetallic compound formation in the reactions at liquid Ga/ solid Pd interface

Interfacial reactions between liquid Ga and solid Pd were investigated in two different temperature ranges: 120-180 degrees C and 250-350 degrees C. In the low-temperature range (120-180 degrees C), Ga5Pd intermetallic compounds (IMCs) grew at the reaction interfaces, with irregular consumption of the Pd substrates. The time exponents for Ga5Pd IMC growth were 1.04, 1.22, and 1.72 at 120, 150, and 180 degrees C, respectively, with an activation energy of 71.0 KJ/mol. In the high-temperature range (250-350 degrees C), the Ga7Pd3 IMCs grew as the reaction progressed, whereas the Ga5Pd IMCs precipitated on the Ga7Pd3 layer during the cooling process. In this case, the time exponents for Ga7Pd3 growth were 0.96, 1.40, and 1.38 at 250, 300, and 350 degrees C, respectively, with an activation energy of 68.6 KJ/mol. The low time exponent values determined in this study are attributed to the porous microstructures of the IMC layers, which provide effective pathways for Ga-Pd interdiffusion. Growth of the rodtype Ga5Pd (or Ga7Pd3) IMCs was presumed to be governed by interface reaction-controlled kinetics, where the reaction species were abundantly available in numerous channels between the IMC grains. The results have prospectively important implications for interconnection between Ga and Pd in the fabrication of future flexible electronic devices.