Refractories Review: Refractories Research and Applications Update
In addition to more than 1000 papers on advanced ceramics and new materials, the program included two symposia on classical ceramics—“Science for New Technology of Silicate Ceramics” and “Refractories: Trends in Research and Applications.” Following are some highlights of the refractories talks and selected posters. (A total of 17 talks and posters were presented at the meeting.)
Slag AttackProfessor W. Lee of the University of Sheffield, UK, discussed the slag attack of refractories, past, present and future. Studies in the early 1900s were mostly simple, static methods, with analysis by optical microscopy in conjunction with phase diagram development and use. The testing has evolved to include dynamic tests, such as the rotary slag test, with analysis by electron microscopy. Testing has shown that the composition of the penetrated liquid may be very different than the bulk slag. Given the wide particle size range of refractories, the localized reactions must be evaluated, and kinetic effects considered.
In the future, it is expected that physical corrosion theory will be incorporated with chemical corrosion theory. Further development of software for the calculation of thermodynamic equilibria in complex systems, as well as improvement of the test/analysis procedures, will contribute to an increased understanding of high-temperature reactions and allow the development of more durable refractories.
Oxidation KineticsProfessor H. Sunayama of Kunamoto University, Japan, described his work on the oxidation kinetics of MgO-C refractories, which is significant because the wear resistance of MgO-C refractories is directly related to the oxidation. His work addressed the need for more reproducible results, which was achieved using cubic samples in a thermal balance. It was speculated that the oxidation is controlled by the diffusion of oxygen through the outer decarburized layer, under 1400 degrees C, in air. Data showed that the effective diffusion coefficient was directly proportional to the open porosity in the decarburized layer.
Thermal Shock ResistanceDr. J. Rodriques of the University of San Carlos in Brazil presented research that addressed the fact that thermal shock resistance parameters, such as R’’’’ and Rst, when calculated using room temperature properties, do not provide good correlation with high-temperature results (lab or field tests) because of the changes that occur in a refractory at high temperature. Data for two high-alumina, low-cement castables illustrated the importance of including properties determined at high temperature to improve the correlation of calculated and actual thermal shock resistance and enhance the capability to predict performance in the field.
Adding Zirconia to Dolomite RefractoriesDr. F. Golestani-Ford of the University of Science and Technology, Iran, discussed research on the addition of zirconia to dolomite refractories for the purpose of improving thermal shock resistance. Results for firing at 1600 degrees C showed that a 4% addition of zirconia resulted in the best retained strength after thermal shock exposure. There was improvement in the retained strength when coarser (0.5-0.63 mm) zirconia particles were added, but this improvement was not evident with finer zirconia particles.
Gasification TechnologyAs reported by J. Bennett of the U.S. Department of Energy, Albany Research Center, Ore., gasification technologies allow the conversion of various feedstocks into electrical power, liquid fuels and chemicals with relatively high efficiency and low environmental impact. But the refractories currently used have unacceptable service life, which limits the widespread commercial development of the technology. The process involves a high flow of slag (5 to 15 tons/hour), so refractories with good resistance to slag penetration, corrosion and spalling are needed. Experiments have shown that high chromia (e.g., 70%) refractories are needed for improved durability. Since such bricks are difficult to manufacture, it is very important to pre-characterize them before use.
Carbon-Containing CastablesCarbon-containing bricks and shapes have been used in steelmaking applications with great success. But the use of carbon-containing castables has been slow to develop because of difficulties in achieving properties comparable to bricks. Professor M. Rigaud of the Ecole Polytechnique, Canada, discussed the development and testing of ultralow- and no-cement alumina and magnesia castables, with added carbon and graphite to improve the resistance to penetration and degradation. Field trials of the castables have been conducted in ladles for molten steel transfer. Further improvement of the castables is continuing for steel ladles and other steel-making applications.
Using AdditivesProfessor A. Yamaguchi, Nagoya Institute of Technology, Japan, reviewed the reactions and benefits of the use of various additions (metals, alloys, carbides, etc.) in carbon-containing refractories. Beyond their role in reducing oxidation, the additions contribute other beneficial effects such as dense zone formation, decreasing porosity and increasing hot strength.
SIDEBAR: Poster TopicsThe following poster titles provide a further indication of the range of refractory topics that are being studied around the world today.
- Algeria—Densification of Kaolin-Dolomite Mixtures
- Argentina—Preparation of Mullite-Zirconia Composites by Slip Casting
- Brazil—Determination of R-Curve of Alumina Castables
- Germany—New Technology for Kaolinite-Based Refractory Bricks
- Poland—Behavior of Calcium Dialuminate-Based Refractory Compositions on Heating
- Romania—Porous Cordierite Ceramics
- Russia—Effect of Raw Materials on Fused MA Spinel Properties
- Yugoslavia—Prediction of Thermal Shock Behavior of Alumina-Based Refractories