Production of UHTC Complex Shapes and Architectures

In spite of the difficult sinterability of Zr and Hf borides and carbides, recent results highlight that these ceramics can be produced with full density, fine microstructure, and controlled mechanical and thermal properties, through different procedures: pressureless sintering and hot pressing with proper sintering aids, reactive synthesis/sintering procedures starting from precursors, and field assisted technologies like spark plasma sintering. More recently, the use of near net shaping techniques and the development of UHTC porous components open the way to further and innovative applications, where the performances, fixed the material, are linked to 2D or 3D architectures and the high ratio of specific surface area to volume of the component and to the features of the porosity itself. Structural lightweight parts, insulator panels, filters, radiant burners, and solar absorbers are some of the possible applications.

Mullite Formation in Al2O3/SiO2/SiC Composites for Processing Porous Radiant Burners

ABSTRACTUse of porous ceramic burners for natural gas combustion is an optimum alternative to enhance energy efficiency and decrease emission of pollutant gases per generated power. Materials requirements for the operation of such porous burners are mainly thermal shock and chemical resistance and those can be reached with cellular ceramics. Mullite was theoretically identified among the best materials for this application; however, its potential was not properly explored yet. Even though mullite can be synthesized from different compounds and processing routes, control of final material characteristics is complicated mainly due to the formation of amorphous phase. In this work, using a technological approach mullite burners were processed by the replication method starting from different mixtures of Al2O3/SiO2/SiC. Rheological study of the slurries has given additives content for the coating of the polyurethane sponges. After varying sintering temperatures up to 1600 °C and isotherm times for 12 h, microstructural aspects and product phases of the final composites were characterized in order to understand the influence of Al2O3/SiO2/SiC ratios in the formation of mullite phase and amorphous content.