Solution Precursor Plasma Spraying of Cr-Doped Al 2 O 3 Thermochromic Coatings
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Solution Precursor Plasma Spraying of Cr-Doped Al2O3 Thermochromic Coatings Tomas Tesar1,2 • Radek Musalek1 • Frantisek Lukac1 • Jan Medricky1,2 Jan Cizek1 • Stefan Csaki1 • Ondrej Panak3 • Marketa Drzkova3
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Submitted: 28 June 2019 / in revised form: 18 October 2019 ASM International 2019
Abstract Solution precursor plasma spraying (SPPS) presents a modern route to deposit coatings directly from liquid feedstock. In this study, unique ability of SPPS to intermix different precursors on the atomic scale was employed to deposit pure and Cr-doped Al2O3 (technically, synthetic ruby) from several mixtures of aluminum and chromium nitrates. Highly porous coatings ([ 60% porosity) were deposited by high-enthalpy WSP-H torch. Homogeneous distribution of Cr atoms in Al2O3 resulted in coatings color ranging from pink to grayish-green correlated with increasing Cr content and change of lattice parameters as observed by x-ray diffraction. High content of over 80 wt.% of a-alumina phase was reached for all coatings. For the Cr-doped Al2O3 coatings, distinct and fully reversible thermochromic behavior was observed by temperature-resolved colorimetry. Further increase in aphase content (up to 95 wt.%) and coating densification were achieved by additional surface remelting by plasma torch. This article is an invited paper selected from presentations at the 2019 International Thermal Spray Conference, held May 26-29, 2019 in Yokohama, Japan and has been expanded from the original presentation. & Tomas Tesar [email protected] 1
Department of Materials Engineering, Institute of Plasma Physics CAS, v.v.i, Za Slovankou 3, 182 00 Prague, Czech Republic
2
Department of Materials, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Trojanova 13, 120 00 Prague, Czech Republic
3
Department of Graphic Arts and Photophysics, Faculty of Chemical Technology, University of Pardubice, Studentska 95, 532 10 Pardubice, Czech Republic
Keywords Alumina hybrid plasma torch mixtures oxides phase composition solution precursor spraying
Introduction Plasma spraying is a steadily growing family of technologies used for fabrication of functional coatings on the surfaces of broad range of industrial components. The coatings are used for protection against demanding operational conditions such as high temperatures (gas turbines, jet and rocket engines), oxidizing atmosphere (boilers, engines), friction or contact wear (paper rolls, engines), or for improvement in surface biocompatibility with living tissues (bone implants) (Ref 1-5). The vast application scope of plasma spray technologies stems from the versatility of the deposition process enabling processing of various materials, such as metals, ceramics, cermets, and their combinations (Ref 6). For the deposition, feedstock materials can be supplied in the form of a dry coarse powder (typical particle size in tens of micrometers), suspension of fine powder in a carrier liquid—solvent (typical particle size from tens of nanometers
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