Refractories

   

Refractory materials play a key role in many areas such as metal, glass and cement production. In order to minimize wear, the material must be optimally adapted to the mechanical, thermomechanical and corrosive loads. In recent years, the requirements have increased considerably as a result of increased operating temperatures and more stringent operating requirements. The working group is engaged in the development and optimization of refractory materials to meet the growing problem.

 

Influence of grain shape on the high temperature properties of alumina-based refractory concretes

Copyright: © GHI Thermal shock furnace with two separate furnace chambers for the simulation of cyclic high temperature changes

Refractory castables are composed of many different pre-treated components. Therefore, a detailed characterization of the respective materials prior to their use is decisive for the material behavior at the intended place of use. Small differences in raw material properties can also influence the suitability of the material for certain applications. The aim of this basic research area is to investigate the influence of the grain shape of the industry-relevant raw material tabular alumina for use in refractory concretes. Various destructive and non-destructive test methods are used to prove changes in thermomechanical and thermoelastic behavior.

 

Corrosion and property changes of refractory materials in non-ferrous metallurgy

Copyright: © GHI Hot stage microscope for the investigation of corrosive attacks

The growing demand and the high complexity of aluminum products are increasing the demands placed on refractory materials. Despite the comparatively low temperatures, the refractory linings in non-ferrous metallurgy can also be subject to rapid wear. Infiltration followed by chemical reactions contributes significantly to the degradation of furnace linings. In addition, alloy constituents increasingly penetrate the material as well via the gas phase. The changes in the physical state and phase transitions also lead to volume changes and failure in the form of spalling. The aim of this application-oriented research area is to evaluate the effects of individual alloying elements on refractory materials.

 

Coupling of slag infiltration and resulting mechanical property changes

Slag corrosion is the main wear mechanism for refractories. Examining the relationships between the micro-structural damages caused by slag infiltration and by thermal shock helps to get a better understanding of the process. Therefore, the mechanical and elastic properties are monitored in-situ with thermal and chemical load, getting closer to industrial conditions for a better classification of suitable material according to the exposure. Furthermore, the microstructural characterization should help to identify the impact of the wear conditions (thermal gradient, slag viscosity. etc.) and their interactions on the refractory behavior.

 

Experimental-numerical analysis of thermo-mechanical fatigue degradation in refractories

In applications with batch production nature, the refractory lining is frequently subjected to cyclic loads. The loads may not degrade the lining immediately, but the gradual accumulation of damage may lead to its failure. To select an optimal refractory it is vital to predict the in-service degradation process of candidate refractories. To accomplish this, lab experiments and numerical modeling tools are mutually utilized. Cyclic mechanical and thermal experiments are designed and conducted according to load scenarios occurring in service. Then the registered damage in lab is translated to actual wear occurring in service with numerical modeling tools. The current case studies are the permanent lining of steel ladle and the silica lining of Coke ovens.

 

Thermo-mechanical characterisation and monitoring of gradual fatigue due to thermal cycling

Thermal spalling is one of the main reasons for refectory lining degradation and failure. Therefore, the thermo-mechanical behavior and microstructure development under thermal-cycling conditions constitute the fundamental research focus to prevent material degradation in service. Crack healing and stress relaxation phenomena triggered by materials exposure to high temperatures have great potential to extend materials performance. Comprehensive studies including crack healing ability, efficiency and mechanisms will provide an essential foundation for refractory material design with enhanced self-healing capabilities. Complementary understanding of microstructural alterations taking place in the material exposed to thermal cycling conditions may be provided by in-situ monitoring of Young’s modulus, Damping and Acoustic Emission temperature dependency.

 

Change of properties of refractory casting compounds during sintering

Unshaped refractory mixes offer the advantage of simple and fast lining of aggregates. The high-temperature resonance frequency damping analysis is ideally suited for analysing the processes in refractory casting compounds during sintering. High alumina-containing refractory concretes serve as the basis. The influence of different chemical compositions and the binder system is investigated. The results are correlated with other investigation methods such as differential thermal analysis (DTA) or thermogravimetry (TG). Thus, the phase development known from DTA/TG can be linked with the elastic properties. This allows conclusions to be drawn about both the sample and the sensitivity of the measurement system.