Transient Self-Exothermic Reaction and Pore Evolution Process of Porous Ni-Al Compounds

Ni-Al porous compounds without macroscopic defects were synthesized from Ni and Al elemental powders via transient self-exothermic reaction. Observations reveal that this reaction occurs simultaneously throughout the entire powder compact, causing the compact to change from gray to incandescent within 10 s. This process yields a pure NiAl3 phase characterized by a uniform microscopic pore structure. The high-temperature gradient rapid cooling rate are the unique synthesis conditions and distinguishing features of this reaction. Small pores formed between the product particles, while large pores developed within the skeletons, eventually connecting to form pore channels. The maximum porosity of 51.2% was achieved at 700°C, which is closely related with the eutectic reaction (Al-NiAl3) initiated by the remaining liquid phase Al. After cyclic oxidation at 650°C for 192 h, the oxide layer formed on the surface of the porous Ni-Al compound was thin and continuous, with a maximum weight gain rate of only 0.75%, indicating that porous NiAl3 exhibits excellent high-temperature oxidation resistance. The permeability of the porous Ni-Al sintered billet decreased from 52.6 to 38.5 m3/(h·kPa·m2) as the oxidation time increased from 0 to 192 h meeting the requirements for long-term and reliable applications such as high-temperature filtration.