Self-glazing SiC-andalusite Refractories for High Temperature Gasification Applications

The combination of SiC and andalusite with calcium aluminate binder for castables in high corrosive gasifying environments is a promising alternative refractory system for many different slag systems. After sintering,a glassy protective layer has been identified. Beside the interactions of the refractories with intermediate slag also the thermomechanical properties,the thermal shock performance and the microstructure have been evaluated as a function of different binder systems.

Pressure Slip Casting of Graded Coarse Grained Oxide Ceramics for Refractory Applications

In the present study the fabrication of graded coarse grained ceramic bodies for refractory applications was investigated using a pressure filtration cell,which uses pressurized air as the pressure medium. The pressure filtration cell was used to examine the influence of different ceramic raw materials,two dispersants,and of the particle size distribution on the filtration behavior and on the filter cake surface quality. Pressure slip casting of spinel based slips resulted in crack-free filter cakes,while alumina based slips resulted in filter cakes,which always stuck on the used PMMA filter medium. Furthermore,citric acid as an electrostatic dispersant resulted in a much lower filtration cake resistance and hence shorter filtration times than an electrosteric dispersant. A broader particle size distribution with a higher addition of the finest particle fraction caused an increase in the filter cake resistance but also yielded much better surface qualities. Finally,graded filter cakes with three layers of alumina rich magnesium aluminate spinel with a maximum grain size of 3 mm,1 mm,and 0. 5 mm,respectively,were fabricated. The computed X-ray analyzes indicated a perfect bonding between the three layers,which is a significant improvement to previous studies. However,the graded filter cakes exhibited frequently cracks at the bottom,which was probably caused by tensile stresses from the friction of the filter cakes with the pressure filtration cell. This will be further investigated in subsequent studies. The achieved results demonstrate thefeasibility to produce coarse grained oxide ceramics for refractory applications by pressure slip casting,which eventually allows the production of composites with tailored compositions,microstructure and functionality.

Clean Steel Technologies Based on Interactions of Refractory Filtering Materials with Steel Melt

New carbon bonded filters with “active and reactive coatings ” for higher filtration efficiency of alumina based inclusions as well as nano-engineered filters with nano-scaled additives are explored with the aid of impingement tests and are evaluated according to their cold crushing strengths at room temperature. The combination of carbon nanotubes and alumina nanosheets additives leads to in situ formation of Al3 CON. Both the nanoscaled additives as well as the extra alumina “active”coating lead to improved mechanical performance of the carbon bonded filters and open the horizon for filter macrostructures with higher filtration capacities in means of bigger dimensions. In a further step MWCNT（ multi walled carbon nanotubes） in combination with a synthetic pitch have been used as a functional coating on the surface of alumina carbon bonded filters. These filters have then been evaluated also with uncoated filters in a special casting simulator and the interactions between steel and filtering material have been investigated.

Tensile strength and damage of open-cell ceramic foams under cylindrical splitting test

To widen the understanding of tensile failure of reticulated ceramic foams and expand the available mechanical method,a cylindrical splitting test is developed in the present study based on alumina open-cell foams of three different pore densities.The biaxial method is validated by characterization of mechanical parameters,and the in-situ fracture process is validated by a digital image correlation,followed by a formula correction for effective tensile strength with consideration of discrete crack paths.For experimental setup curved loading platens,compliant pad and intermediate quasi-static loading rate are proposed for guaranteeing tensile failure under a radial compressive load.Tensile strength,fracture energy,and brittleness increase with the foam pore density,and the fracture behavior is a balanced result of materials and foam structural support strength.An analytical model of splitting tensile strength with structural parameters is derived,which implies its dependence on cell size and critical stress intensity factor of strut materials.