One-step synthesis of pure γ-FeNi alloy by reaсtive sol–gel combustion route: mechanism and properties

Abstract

A pure crystalline γ-FeNi alloy powder was fabricated through the one-step process of sol–gel combustion. An experiment was conducted in inert atmosphere with the hexamethylenetetramine (HMTA) used as an oxygen-free fuel and metal nitrites as oxidizers. It was demonstrated that fuel-to-oxidizer ratio is a critical parameter to produce pure γ-FeNi alloy. A concentration of the fuel necessary for the alloy synthesis is three times higher (φ = 3) than at the stochiometric molar ratio. The ~1100 K maximum temperature, 830 K/s heating and 170 K/s cooling rates and the total reaction time of ~3 s are characteristics of the optimized sol–gel combustion synthesis of the γ-FeNi alloy powder. A mechanism of the alloy formation through the coordination metals—HMTA complex was proposed and experimentally verified. Microstructural and magnetic properties of the synthesized material are also investigated and discussed.