Experimental investigation of magnesium combustion in steam

Abstract

This paper presents a summary of the experimental results and studies of magnesium combustion in steam. The major subject of these studies was to measure the temperature of magnesium particles after the particles had been ejected from an exploding wire. The distribution of particle temperature along the track was measured by the two-color photo-pyrometry method (TC-PPM). A scanning microdensitometer served as a major data reduction tool in analyzing the film density due to the particle tracks as recorded on calibrated film. The initial temperature of the particle ejection from the plasma and at the beginning of combustion is 3430 K + or - 9.1%. At the initial phase of combustion, the particle consists of pure magnesium with spectral emissivity of about 0.25. During the combustion process, magnesium oxide is formed locally on the particle surface. The oxide is in liquid state with emissivity of 0.9. In the second stage of combustion there are changes on the particle surface in correlation with optical density variation and explained by emissivity variations due to peeling of the oxide film and exposure of the pure magnesium surface. Solidification of the particle, which is magnesium oxide, is observed at the measured temperature of 3125 K + or - 5.7%. The spearpoint effect, which is known in the literature as the Blick Effect, was observed at the end of the particle track. The particle supercools below the normal freezing point and then suddenly crystallizes.