Investigation of radiation of alumina particles injected into water-argon plasma jet and measurement of particle temperature by optical pyrometry

Particle temperature and particle impact velocity are main parameters that determine quality of plasma sprayed coatings. One of common methods of determination of powder particles temperature in plasma jet is optical pyrometry. This paper describes new method of temperature measurement that utilizes several oblique filters for separation of particle images in different spectral ranges. From images recorded by CCD-camera the temperature changes during particle motion can be determined. Evaluation of temperature is complicated by plasma radiation and by non-continuum radiation of some powder components or substances adsorbed on particles. This radiation substantially changes the spectral characteristics of emitted light. The spectra of light emitted by alumina particles injected into plasma jet generated in hybrid water-argon plasma torch are examined. On the basis of the analysis a correction based on measurement of light intensity in three spectral ranges is suggested. Way of obtaining of additional information about admixture component from the same observation is proposed.