Sintering behavior of combusted iron powder in a packed bed reactor with nitrogen and hydrogen

Abstract

Sintering behavior of micron-sized combusted iron powder is studied in a packed bed reactor, at various temperatures under inert (nitrogen) and reducing (hydrogen) conditions. Compression tests are subsequently used to quantify the degree of sintering. A sintering model, based on the formation of a solid bridge through solid state surface diffusion of iron atoms, matches the experimental results. Sintering of combusted iron occurs at temperatures ≥575°C in both nitrogen and hydrogen atmospheres and increases exponentially with temperature. The observed decrease in reduction rate at high temperatures is not caused by the sintering process but by the formation of wüstite as an intermediate species, leading to the formation of a dense iron layer. Iron whiskers form at high temperatures (≥700°C) in combination with low reduction rates (≤25 vol% H2), leading to the production of sub-micron fines.