Application of Multiwavelength Pyrometry in Microwave Processing of Materials

Abstract

Over the past decade microwave energy has been increasingly used in materials processing, especially for sintering and more recently for the joining of advanced ceramics. However the hostile electromagnetic and plasma environment within a high power (1–6 kW) microwave applicator poses serious problems for very accurate high temperature measurement by precluding the use of existing classes of thermometry. For instance, conventional probe-based thermometry, multiple-wavelength ratio pyrometry and even the more recently developed technologies of optical fibre thermometry by fluoroptics and radiometry, are either incompatible or of restricted application. The main aim of this paper is to propose multiwavelength pyrometry as a viable technique for wide range (500–5000 K) thermometry in hostile electromagnetic and plasma environments. After briefly reviewing the physical basis of its operation, the experimental set up of the multiwavelength pyrometer is outlined, and consists of a comparatively inexpensive low resolving power grating monochromator and a PbS infrared single element detector. Results are presented that compare the measurements during conventional/microwave heating trials, from this multiwavelength pyrometer and from a K-type thermocouple, a double-wavelength ratio pyrometer and a single wavelength pyrometer aimed at a dummy target (carbon/metal).