Characterization of High Alumina Refractory Ceramics Treated with Combined Two Laser Surface Processing
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Characterization of High Alumina Refractory Ceramics Treated with Combined Two Laser Surface Processing Johanna R. Bernstein, Dimitris Triantafyllidis1, Lin Li1 and F. Howard Stott Corrosion and Protection Centre, University of Manchester Institute of Science and Technology, Manchester M60 1QD, UK. 1 Department of Mechanical, Aerospace and Manufacturing Engineering, University of Manchester Institute of Science and Technology, Manchester M60 1QD, UK. ABSTRACT Alumina-based refractory materials are extensively used in high-temperature industrial applications, such as for linings in waste and other incinerators. The existence of porosity and material inhomogeneities can promote chemical degradation due to molten slag penetration, while impacting solid or liquid feedstock can cause erosive-wear damage. Previous research has successfully used single laser energy sources to alter the surface properties of similar ceramics, with emphasis on sealing porosity and enhancing degradation resistance. However, this process has resulted in some solidification cracking at the surface due to large temperature gradients developed during processing. In the present, ongoing work, the surface of the refractory ceramic is modified by combining two laser energy sources to control the thermal gradients and cooling rates, with the objective of eliminating crack formation. The surface morphology and microstructures of the laser-treated areas are analyzed. This paper presents some initial results from the programme. INTRODUCTION High alumina refractory ceramic bricks are commonly used for internal linings in waste incineration plants. These materials are able to withstand compressive stresses resulting from the weight of the furnace and its contents, thermal shock from heating/cooling cycle, particle wear from the movement of the incinerator content and degradation by chemical attack [1]. In addition to particulates, the incineration process produces a slag that adheres to the surface of the refractory lining bricks, often containing a high percentage of corrosive salts. Consequently, the lining bricks may suffer from particulate erosion as well as slag penetration and corrosion resulting in a loss of brick thickness. For particularly aggressive conditions, a refractory containing at least 80% alumina and at least 5% chromia is required. Refractory ceramics with this level of alumina and chromia content offer increased slag penetration resistance due to the formation of a dense and pore-free spinel layer between the slag and the surface of the refractory material during service [2]. However, to extend the life of conventional refractory ceramics in the harshest environments and intense erosion areas, a pore-free surface is required. One of the techniques that can produce a pore-free surface is laser treatment. Previous efforts to modify the surface properties of various alumina-based ceramics by applying a single laser energy sources have been partially successful [3-5]. Laser irradiation of brittle ceramics results in the development of the
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