High-temperature mechanical behavior of compact carbon-bonded alumina based on a pitch-free lactose-tannin binder system.

Compact cylinders and prismatic bars of carbon-bonded alumina based on an environment-friendly lactose-tannin binder system with lactose to tannin mass ratios of 5:1, 4:1 and 3:1, completely free of the conventional but harmful pitch binder, were prepared by slip casting and uniaxial pressing, respectively. The specimens were characterized by their physical properties (density, porosity), residual carbon content as well as microstructural analysis. In addition, the rheological behavior of the slurries was studied in order to prepare the compacts by slip casting. Mechanical tests at room temperature and, in particular, at high temperatures up to 1400 °C under bending, compression and creep loading, were performed. The results showed a brittle-to-ductile transition at temperatures between 1100 °C and 1300 °C. The bending strength of the bars was significantly lower compared to previously reported pitch-based ones. Early hardening of the powder before pressing could greatly decrease the bending strength. During heating at 1500 °C, cracks occurred unexpectedly on bars to be tested, and some dark grey droplets were observed as well after cooling down. A possible reason is a synergetic interaction between structural change of the carbonaceous matrix and overheating triggered by the electromagnetic field of the inductive heating. [ABSTRACT FROM AUTHOR]