Electromagnetic and Mechanical Properties of Silica-Aluminosilicates Plasma Sprayed Composite Coatings
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F. Cipri, C. Bartuli, T. Valente, and F. Casadei (Submitted February 27, 2007; in revised form July 3, 2007) The physico-chemical and thermo-mechanical properties of aluminosilicate ceramics (high-melting point, low thermal expansion coefficient, excellent thermal shock resistance, low-density and good corrosion resistance) make this class of materials a good option for high-temperature structural applications. Al2O3-SiO2 compounds show an excellent refractory behavior allowing a wide use as wear-resistant thermal barrier coatings, in metallurgical and glass plants and in high temperature heat exchangers. Moreover, the low values of thermal expansion coefficient and of complex permittivity allow to extend the use of this ceramic for microelectronic devices, radome for antennas and electromagnetic windows for microwaves and infrared. The present article presents the results of an extensive experimental activity carried out to produce thick aluminosilicate coatings by plasma-spray technique. The APS deposition parameters were optimized on the basis of a surface response approach, as specified by design of experiments (DoE) methodologies. Samples were tested for phase composition, total porosity, microstructure, microhardness, deposition efficiency, fracture toughness, and modulus of rupture. Finally, coatings were characterized for their particularly interesting electromagnetic properties: complex permittivity was measured at microwave frequency using a network analyzer with wave guide.
Keywords
air plasma spray, alumina-silica, permittivity, complex permeability
1. Introduction Meta-silicates materials, the main components of the MgO-Al2O3-SiO2 system, are widely applied in the coating and refractory industries. Among the most interesting features of these ceramic materials are very low coefficient of thermal expansion (CTE), good thermal and chemical stability, high mechanical strength and thermal shock resistance and low-complex permittivity (Ref 1). More specifically, aluminosilicate ceramics, such as 3Al2O3Æ2SiO2, present an orthorhombic crystal lattice without any polymorphic transitions up to 1580 C; this
This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007. F. Cipri, C. Bartuli, and T. Valente, Department of Chemical & Materials Engineering, Sapienza University of Rome, Rome, Italy; and F. Casadei, Centro Sviluppo Materiali, Rome, Italy. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
thermodynamical stability prevents any volume change and allows excellent thermal shock resistance and high strength at temperatures as high as 1500 C (Ref 2). Moreover, the presenc
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