Reusable Thermal History Sensing via Oxidation of a Divalent Rare Earth Ion-Based Phosphor Synthesized by the Sol–Gel Process

Abstract

Temperature measurements in harsh environments, such as those present in gas turbines, are of great importance but very hard to obtain. Sometimes, on-line measurements are not possible, and instead, the temperatures during operation are recorded using so-called thermal history sensors and read off-line. Although thermal paints have been used for many years as thermal history sensors, they present some disadvantages. Recently, a new method based on irreversible changes in the emission properties of phosphor materials when they are exposed to high temperatures has been proposed. It has been demonstrated that the process of oxidation from Eu²⁺ to Eu³⁺ is temperature sensitive up to 1400°C. In this paper, we describe the manufacture of BaMgAl₁₀O₁₇:Eu (BAM:Eu) using a sol–gel process, and report optical properties interrogated after heat treatments in air and argon atmospheres, which confirm that after treatment in argon, the oxidation process can be reversed. This suggests a promising reusability of the phosphor as a thermal history sensor. A temperature-dependent measurand based on the change of optical properties with temperature has been defined with a dynamic range from 700°C to 1100°C. The effect of exposure time to a certain temperature on this measurand has also been addressed.

NOMENCLATURE

BAM	=	barium magnesium aluminate
CCD	=	charged-coupled device
FWHM	=	full width at half maximum
ICDD	=	International Centre for Diffraction Data
Nd:YAG	=	neodymium-doped yttrium aluminum garnet
PDP	=	plasma display panel
VUV	=	vacuum ultraviolet
XRD	=	x-ray diffraction

Additional information

Notes on contributors

Álvaro Yáñez González

Álvaro Yáñez González is a Ph.D. candidate in mechanical engineering at Imperial College London. He has a licenciate degree (B.Sc. + M.Sc.) in mechanical engineering (2011) from Polytechnic University of Madrid, Spain. The study of BAM:Eu as a thermographic phosphor is the main subject of his thesis, and his research interests lie in combustion sciences and thermometry.

Stephen Skinner

Stephen Skinner joined Imperial College in 1998 and was promoted to Reader in 2011. His research interests are in materials for new energy technologies, and he is primarily concerned with the chemical and physical properties of potential solid oxide fuel cell electrolytes and electrodes and encompasses the electrical and structural characteristics of materials. His previous experimental experience includes the use of x-ray diffraction and spectroscopy, Mössbauer spectroscopy, and materials synthesis.

Frank Beyrau

Frank Beyrau, after receiving a degree in physics from Oldenburg University in Germany, did his Ph.D. studies in engineering thermodynamics at the University of Erlangen–Nuremberg with the focus on laser spectroscopy for combustion analysis. After leading the “combustion technology” group at the same institute for 3 years, he moved to Imperial College in 2008. The main focus of his research activities lies in the development and application of advanced laser diagnostics for the investigation of complex, reactive flows. Besides fundamental research in this field, he also performs more applied investigations in cooperation with industry for the development of technical combustors, internal combustion engines, and gas turbine processes.

Andrew L. Heyes

Andrew L. Heyes studied mechanical engineering at the University of Manchester. He obtained a B.Eng. degree in 1989, graduating with first class honors. He then went on to obtain an M.Sc. in 1991 and Ph.D. in 1994, also from Manchester, for development of the laser-based Doppler global velocimetry optical flow diagnostic technique and the application of optical techniques for three-dimensional velocimetry in the vortical flow around a lifting delta wing at supersonic speeds. In 1992 he joined Rolls Royce plc working in the Applied Science Laboratory on the development of optical diagnostic techniques for high temperature and reacting flows and on the gas dynamics of power station circuit breakers. In 1995 he moved to Imperial College London, joining the Department of Mechanical Engineering as a lecturer in thermofluids. He left Imperial in July 2013 as a reader in heat transfer, deputy director of the Energy Futures Laboratory, and director of the Sustainable Energy Futures master's program.