Refractories Review: Refractories Papers at the ACerS Annual Meeting
V. Pandolfelli and R. Pileggi of Federal University of Sao Carlos, Brazil, discussed the development of multifunctional and high performance castables. For a study of high alumina castables, Pandolfelli reported that the correct particle sizing is very important. In fact, if the particle sizing and dispersant are correct, it is not necessary to include micro-silica in the mix, which has been typical in the majority of high-tech castables despite the potential for some decrease in refractoriness. Thorough mixing is essential for realizing the optimum properties, and he suggested adding the water in two steps, i.e., 75% initially, with the remainder at the “turning point” (where the rheology changes).
Pileggi discussed the rheology and particle sizing of pumpable castables. He indicated that a castable must be pseudo-plastic to be pumpable, and that the aggregate and matrix constituents must flow together and not segregate. The pumpability of a castable must be evaluated by a rheometer and not a flow table because of the segregation of components that can occur. Regarding high performance castables, Pileggi discussed the importance of controlling the aggregate (3 to 45 mesh) and matrix content of castables.
Based on the need for MgO-graphite castables in steelmaking, H. He of CIREP, Ecole Polytechnique, Canada, described several different methods—including extruded, coated and granulated—of including graphite in such castables. An extruded form of graphite plus carbon and antioxidant showed promise with a higher temperature of initial oxidation (800°C) than flake graphite (600°C), but evaluation of the slag resistance is still to be done.
B. Headrick, University of Missouri-Rolla, discussed the measurement of modulus of elasticity (MOE) of a range of self-flowing castables, including measurements at elevated temperature. He determined that MOE decreased as the amount of bond decreased, and that it was slightly higher for white fused alumina mixes than tabular alumina mixes.
C. Schacht, consultant, discussed the use of finite element analysis in evaluating the stress state of a brick and mortar lining in steelmaking ladles. And J. Kwong of the U.S. Department of Energy (DOE) Albany Research Center described the development of a model that uses phase equilibrium data to optimize the MgO saturation of slag for electric arc furnaces.
A post-mortem study of used MgO-Cr2O3 refractory from a Zn-containing environment, by G. Oprea, University of British Columbia, revealed the contribution of spinel formation (ZnFe2O4, expansion and ZnCr2O4, shrinkage) to the cracking and spalling of the hot face.
R. Chinn of the DOE Albany Research Center summarized the evaluation of refractories from a slagging gasifier. Based on the deterioration mechanisms determined, a microstructural modification was developed to minimize slag penetration (patent pending).
P. Kleven, Energy & Environmental Research Center, N.D., reported the results of work to compare refractories for use in a slagging gasifier. It was confirmed that (a) a dynamic slag test gave a better indication of service performance than a static cup test, (b) lowering the temperature 100 degrees to 1500°C reduced the refractory corrosion by half, and (c) slag additives (e.g., 3% alumina) can reduce the refractory corrosion up to 60%. She also indicated that an improved slag test furnace had been designed and would be used in further tests to compare candidate refractories.
D. Ellerby, Sandia Labs, Albuquerque, N.M., described the tile (and high-emittance coatings) used on the NASA space shuttle. Conditions on the space shuttle surface vary from 300 to 1650°C, so several tile compositions and coatings have been developed that allow the surface protection to be zoned. Based on the tile and other developments, the number of tiles on the space shuttle has been reduced from 30,000 to 24,000.
Next year, the RCD spring program will be held in conjunction with the St. Louis Section meeting in March, instead of at the spring ACerS meeting. Further information about the 2002 spring RCD meeting can be obtained from Patty Smith, firstname.lastname@example.org.