Metal fuel : a clean, CO2-free, recyclable source of energy : investigating the sintering mechanisms and kinetics of iron oxide powders after combustion

Details

Supervisors

Jacques, Pascal ; Choisez, Laurine

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil en chimie et science des matériaux, à finalité spécialisée

Abstract

Transitioning from fossil fuels to green fuels is of the uttermost importance nowadays in the context of climate crisis. The use of metal fuel, and in particular iron, is an emerging technology able to energetically compete with fossil fuels. Iron fuel could be a solution regarding a cleaner storage and transport of energy. Combustion of iron is very promising. It has a high enough specific energy and energy density to compete with fossil fuels. Its combustion mode makes the collection of combusted iron possible in a closed loop context, and iron is known to be amongst the most recycled metals. However, losses are observed after combustion, with the apparition of cracks and porosities on the particles. In addition, transport of powder from a combustion plant to a reduction center can also generate losses during handling due to the small size of the powder particles. Sintering of iron oxide powders after combustion is proposed as a way to reduce these losses by agglomerating the particles together and reducing the porosity. In this work, the specific case of solid-state sintering was studied, without reaching a liquid phase. Sintering was conducted in capillaries, cylindrical molds and pre-compacted pellets at three temperature: 900°C, 1000°C and 1100°C. The studied sintering time ranged between 5 min and 2 hours. The influence of atmosphere and particle size was also studied. The mechanical properties were measured, and fracture mechanisms were observed. Two phenomena were observed to take place simultaneously and interact with each other: oxidation and sintering. Because of this interaction, an improvement of the sintering kinetics but also an non-uniform sintering level in samples was observed. The open porosity decreased by more than 20% during intermediate sintering stage, while the internal porosity was already in low content (less than 1%). The resistance to compressive load was recorded as high as 21.2 MPa for the most sintered samples. Particle size and atmosphere were found to be of high importance for sintering, with best results obtained with smaller particles under oxidizing atmosphere.