Refractory Advances and Applications
The opening session included invited speakers that discussed key issues pertinent to the refractories industry. R. Gutierrez from DeAcero (a steel/wire company) predicted that the world steel production for 2001 would be 1.5% higher than in 2000. He talked about the crisis in the steel industry, noting that more steel company bankruptcies can be expected if no changes are made, and suggested that an international agreement to reduce the excess steel capacity globally would be desirable. T. Richter, RHI America, gave an overview of the refractories industry, emphasizing that refractories are strategic materials that can’t be replaced by other materials. Competitive pressures will continue due to numerous factors, such as increased raw materials prices, a continuing decrease in the refractory consumption rate, and no increase in product prices due to the effect of imports from China and East Europe. A serious overcapacity problem exists, as only 25 million tons of the 40 million ton worldwide capacity is being used. Further consolidation of the refractories industry should include centralization and reduction of capacity, and the trade laws between countries need to be liberalized. Also, more attention should be paid to environmental issues and recycling.
Special RecognitionBased on their contributions to refractories technology and their promotion/support of UNITECR, four new Distinguished Life Members were named: Dr. Robert E. Moore (USA), Dr. Axel Eschner (GRA), Sadame Asano (TARJ), and Roberto Olvera Pena (ALAFAR). Alcoa presented an Innovation Award to Norwegian authors from Norsk Hydro ASA, Borgestad Fabrikker and SINTEF Mater.Technology, for their work “Refractories for Molten Aluminum Contact – Part I.” Their study showed that Al can reduce more stable oxides through the formation of inter-metallic phases, and that silica is reduced to Si and corundum in contact with molten Al, irrespective of the type of silica, i.e., free silica, glassy phase or a silica-containing phase. Even for samples with almost no porosity (less than 0.6%), the silica will react with Al. The aluminum resistance of refractories generally a) improves with increased alumina content and the addition of anti-wetting chemicals, and b) decreases with increased silica content, higher pre-firing temperature, and higher exposure temperature. The authors concluded that the consideration of refractories for aluminum applications should include knowledge of the refractory mineralogy and microstructure, in addition to the chemical composition and physical properties.
Overview of the Technical ProgramThe general breakdown of papers in the Proceedings is given in Table 1. A closer review showed that 46% of the papers applied to the steel industry, as other pertinent papers were included under other headings. About 22% of the papers dealt with monolithic refractories, although they were not shown as a separate topic. Selected information from some of the UNITECR’01 papers is presented below to provide a general overview of refractories technology in 2001.
Given the importance of MgO-C brick in steelmaking, they were the subject of numerous papers, ranging from technical and thermodynamic works to practical results from field service. It was reported that preheating MgO-C bricks containing Al could benefit steel chemistry/quality by enhancing the oxidation of Al and formation of secondary spinel in the bricks. The development of MgO-8%C bricks with pitch-coated aggregate has revealed lower thermal conductivity and improved thermal shock resistance, with practical benefits in ladle service. The production of stainless-steel fiber-reinforced MgO-C bricks was reported. Because of the increased strength, toughness and fracture energy, the steel fiber-containing bricks had longer life than bricks with no fibers in ladles and basic oxygen furnace (BOF) impact areas. A new carbo-resin, which has extremely low emissions and toxic potential, has been developed for C-bonded MgO-C bricks. This bond has very high oxidation resistance and excellent stress-absorbing capabilities.
Other papers dealt with blast furnaces, ladles, tundishes, slide gates and steel flow control devices, to name a few. The discussion of lining design in ladles revealed that the practices are varied, with the use of numerous refractory types (bricks and/or castables), such as MgO-C, Al2O3-MgO-C, spinel, Al2O3-spinel, alumina and others. Given the improvement and increased use of castables in steelmaking (and all industries), research was reported on alumina and magnesia castables containing carbon/graphite for ladle slaglines. With the continuing improvement of castables for ladle slaglines, they have shown increased service life, and that trend is expected to continue.
New Developments and Applications
Several papers dealt with thermo-mechanical testing and modeling, which are increasingly being used to obtain critical technical information that will provide practical benefits. Modeling (3-D nonlinear finite element analysis [FEA]) of the behavior of a brick ladle lining was described, and the information illustrated that increasing use of the technique will aid in the optimization of lining design, material selection and operating conditions. Another study, based on FEA, documented that preheat and operation changes in a BOF provide an increased output of steel without any significant detrimental effect on the lining life.
The study of microstructure continues to be a valuable tool in the optimization of refractories. Microstructure analysis was included in many of the papers involving alumina, cordierite, MgO-C, nitride-bonded SiC, porous materials, magnesia-chrome, MgO-spinel and other refractories. A new method of advanced microstructure analysis for refractories using fractal geometry was discussed. Use of the method for several refractory applications revealed that more (and new) information can be gleaned from the microstructure than by conventional microstructure analysis.
A silica-free, spinel-bonded spinel brick has been developed for use in highly alkaline applications as an alternative to chromia-containing products. The development included the use of fused spinel aggregate, a controlled matrix composition, and optimization of the firing cycle, grain size distribution and pressing procedure.
The technology and use of monolithic refractories continues to advance and increase worldwide—35 papers were presented on diverse aspects of the subject, including raw materials, additives/ binders, cements, mixing/rheology, dryout, installation, repairs, modeling and testing/properties. New testing capabilities that provide valuable information about castables include a permeameter for measuring permeability up to 800?C and a sonic device for monitoring hardening. The use of exothermic profiling to monitor phase development and differences therein, as well as the effect of additives, quality control and other functions, were discussed as tools for optimizing castables.
Given the major importance of grain sizing in monolithic refractories, there was discussion of superground aluminas, spinel and a new matrix alumina, as well as mono-, bi- and multi-modal types. The development of a super-abrasion-resistant castable, which uses a new bonding system known as pseudo-hydraulic chemical bond (PHCB), was also reported.
Historically, China has played a vital role in supplying raw materials for the refractories industry. Prof. X. Zhong from the High Temperature Ceramics Institute at Zhengzhou University in Zhengzhou, China (Henan Province), indicated that China now supplies 60% of the bauxite, 30% of the magnesite and 80% of the graphite used by the world’s refractory companies. Zhong predicted that China will develop more synthetic raw materials (high quality and high performance) based on the natural Chinese raw materials, as well as more non-oxide materials.
Consideration of the refractory practices and operations in a copper converter in Peru resulted in a decrease in refractory consumption from 4 to 2 kg/ton of blister copper, and the number of refractory repairs decreased from 17 in 1997 to 10 in 2000. Another study showed that the development and use of low cement castables resulted in a significant decrease in the refractory consumption for copper casting wheels and launders.
The study of mullite formation, using mixes of kyanite with attrition-milled kyanite or aluminum, was also reported. Good mullite resulted, and both the kyanite decomposition expansion and the decomposition temperature were reduced.
Other topics that were discussed included the recycling of refractories (with examples); refractory development using post-mortem analyses; low density, fiber- and silica-free ceramic shapes; degradation of glass tank silica crown bricks; and the mineralogy, mining and beneficiation of kyanite.