Combustion-assisted sintering for tunable densification of manganese cobalt oxide layers

Facile sintering of metal oxides and ceramics is essential for energy-efficient manufacturing processes of various engineering systems. It should satisfy the increasing density of the resulting layer packed on the substrate in a mild environment and improve the specific performance through structural changes in the internal grain boundaries. However, conventional sintering inevitably involves maintaining high-temperature conditions for a long duration, resulting in energy inefficiency and unintended element diffusion. Herein, we report a novel composite-fuel-assisted sintering strategy as an alternative to conventional sintering for enhanced densification of manganese cobalt oxide (MCO) spinel. MCO spinels, which are commonly used to form a protective layer for metallic interconnects, are electrophoretically deposited on Cr-containing stainless steel, while the initial porosity and thickness are controlled by regulating the deposition parameters. Then, 2,4,6-trinitrophenol combined with sodium azide as a composite fuel is dropped onto the pre-deposited MCO layer. During air drying, this composite fuel tends to self-assemble into an elongated microwire-shaped structure featuring π-stacked aromatic rings and provides a serial connection between the dried fuel particles, facilitating their penetration into the coated material. The composite fuel enables the implementation of a combustion wave passing through the MCO layer in a mild sintering environment, thereby providing instantaneous thermal energy for densifying the initial MCO layer. The densification efficiency achieved using the optimized composite-fuel-assisted sintering strategy is 93 % higher than that achieved conventional air sintering. This study will pave the way for the development of new hybrid sintering strategies based on versatile composite fuels to achieve high efficiencies under mild environments.