A new generation of thermal shock resistant Al2O3‐C refractories with approximately 30% less residual carbon and functionalized due to nanoscaled additives based on carbon nanotubes (CNTs) and alumina nanosheets (α‐Al2O3) were developed and investigated after coking at 1000 and 1400 °C. With the aid of electron backscatter diffraction analyses (EBSD) on fracture surfaces of the carbon bonded samples, Al3CON was identified on the nanosheet shapes already at 1000 °C coking temperature. The Al3CON new phase based on the reaction between alumina nanosheets and CNTs offers a chemical interconnecting phase for the carbon as well as for the oxide alumina filler. The new refractory composite structure presents excellent thermo‐mechanical properties in spite the lower carbon content. In addition, due to EDS and EBSD analyses amorphous whiskers and platelets within the system of SiO were observed in samples coked at 1000 °C, that were transformed to crystalline β‐SiC‐whiskers in samples coked at 1400 °C.
Components based on carbon‐bonded alumina refractories are widely used in steelmaking industry in terms of submerged entry nozzles, monoblock stoppers, and ladle shrouds. According to the current state of the art, such components are glazed to inhibit oxidation of carbon‐containing refractories. Carbon oxidation leads to a deterioration of the components properties, risking even a detrimental failure and should therefore be prevented. In this paper, alumina–graphite refractories were produced according to standard commercial practice and mechanical, as well as physical properties were determined with special focus on carbon content and the application of nanoscaled additives. The investigations showed a correlation between porous structure and generation of a self‐glaze after heat treatment in air, effectively inhibiting the oxidation process. Moreover, the mechanical and thermo‐mechanical behavior of the tested samples was comparable to commercial components. These newly developed self‐glazed Al2O3‐C refractories could have the potential to replace the currently used components in the near future.
Alumina–tantalum composites are produced in a two‐step synthesis via cold isostatic pressing (CIP) from commercially available raw materials without any addition of organic additives. The highest densification for fine‐grained composites is found with a maximum pressure of 150 MPa, whereby a cyclic pressure increase or at maximum pressure showed no measurable influence. The increase of the sintering temperature from 1600 to 1700 °C led to a higher densification up to a relative density of 75.8%. Aggregates received by jawbreaking show a blocky morphology, rounded corners, and edges with porosities of 6.2−7.3%. The formation of tantalum carbide and the incorporation of oxygen into the tantalum lattice are verified during sintering. The coarse‐grained composites produced from these aggregates show open porosities of 25.3−25.7% and shrinkage <0.5%. Determined splitting tensile strenghts are in the range between 8.4 and 9.1 MPa.
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