Development of temperature-sensitive paints for high-temperature aeropropulsion applications

Abstract

Fluorescence from a phosphor coating will indicate the temperature of the substrate to which it is attached, assuming thermal equilibrium is achieved. The goal of this investigation is to identify phosphors for making temperature measurements on aerospace surfaces with temperatures varying from ambient to 1000 C and to identify and test binders/adhesives that may be mixed with thermographic phosphors and sprayed onto surfaces of interest to provide a durable and uniform coating. The surfaces of interest include various high-strength metal alloys, such as stainless steel and nickel with and without thermal barrier coats, ceramics, carbon/carbon composites, and copper. Our initial efforts have concentrated on the most challenging substrates, the high-strength nickel alloy without the thermal barrier coating. Several candidate phosphors have been identified, and we are considering mixing two or more phosphors to cover the full temperature range. The phosphors being considered are Y2O3:Eu, YAG:Eu, YAG:Dy, YAG:Cr, and YPO4:Eu,Dy. The initial results indicate that two binders—Sauereisen’s Thinning Liquid #14 and a mix of ZYP, Inc.’s, LK and HPC will function well on high-strength nickel alloys to 800C. Furthermore, the LK and HPC mix This material is declared a work of the U.S. government and is not subject to copyright protection in the United States. performed well on high-strength stainless steel substrates coated with a thermal barrier coat to a temperature of 1000C. Introduction and Background Phosphor coatings are the basis for a viable means of measuring temperature in a wide variety of situations. A phosphor is a fine powder that efficiently fluoresces when suitably excited by sources such as lasers, light-emitting diodes, ultraviolet lamps, or electron beams. A phosphor is thermographic when the fluorescence characteristics change with temperature. Fluorescence from a thermographic phosphor coating will indicate the temperature of the substrate to which it is attached, assuming thermal equilibrium is achieved. Noel et al. and Grattan and Zhang provide in-depth descriptions of the physical basis and many useful applications. Goal Described in this paper is a recently initiated effort aimed at an application for temperature measurement on aerospace surfaces wherein the temperature may vary over the entire range from ambient to 1000°C. There is a further constraint regarding the method by which a phosphor coating may be applied. Earlier work has indicated that sputtering or E-beam deposition of a pure phosphor onto a surface makes a very useful and