Processing Factors Controlling the Microstructures and Properties of Castable

EPSRC research grant GR/L57852

Summary of the final report

Principal Investigator: Professor W E Lee with Professor B Rand, Department of Materials, University of Leeds

Unshaped monolithic refractories, most commonly installed by gunning or casting, are now used in greater volumes worldwide than shaped bricks in a host of applications in e.g. iron and steel and petrochemical industries. Their ease of installation and properties, which approach those of bricks, along with the fact that they are fired in-situ and so the user meets the heating costs, make them increasing popular with refractories manufacturers. This project linked a raw materials supplier, a refractories producer, a refractories user and a refractories research centre to Sheffield and Leeds Universities in a project aimed at understanding and utilising the basic science underpinning these strategically important materials. Research was focused on commercial and model low cement castables (LCC´s), ultra low cement castables (ULCC´s) and calcium aluminate cement (CAC)-free systems. The hydration of various oxide and other cementitious refractory bonds has been followed by a combination of techniques (XRD, ESEM, DSC, ICC, TGA). Rheology and the influence of water content, deflocculants and temperature has been established. The microstructures of selected dried but unfired castables were examined, in particular for porosity and pore size distribution. Fired microstructures have been examined and correlated to the processing and green microstructure. High-temperature strength and corrosion resistance have been related to the fired microstructures. Systems examined included those in current commercial applications based on alumina grain with alumina and submicron silica binders and simpler model systems. This provides a scientific basis on which castable systems with improved microstructure and properties can be developed. Aggregates examined included alumina, zirconia, spinel, mullite and non-oxides such as SiC.

This project generated results that have a significant impact on our understanding of the complex relation between processing, microstructures and properties of castable refractories. In particular, the improved understanding of the use of phase equilibria in such systems, the link between hydrated microstructures and fired microstructures (such as the low-temperature formation of spinel from hydrotalcite) and development of in-situ spinel, mullite and CA_6- containing refractories will be important.

Contact:

Prof W E Lee (now Imperial College, London),
Department of Engineering Materials,
University of Sheffield,
Mappin Street, Sheffield S1 3JD
Telephone: 0114 222 5502
Fax: 0114 222 5943