The effect of TiO 2 additions and oxygen potential on liquidus temperatures of some CaO-Al 2 O 3 melts
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I.
INTRODUCTION
TITANIUM dioxide, though a minor constituent of the slag, can have an extremely detrimental effect on slag properties. TiO2 has been considered to be the cause of gumminess in slags and has been blamed for the malfunctioning of furnaces in various pyrometallurgical processes. 1,2 During the casting of titanium- and aluminum-deoxidized steels, a fine network of solid oxide inclusions may form and clog the nozzle through which the steel is flowing. 3 The result is the heat must be aborted with a corresponding loss of production. TiO2 is also used as a binder in some calcium-aluminate cements, The determination of the liquidus surfaces for the CaO-A1203-TiO2 system is, therefore, important because of its implications in metallurgical and ceramic applications. Liquidus temperatures were determined in this investigation by hot-wire microscopy. It is known from the literature4 7 that hot-wire microscopy is a very accurate, reproducible, and reliable method for determining the liquidus temperature of high melting point slags. A brief description of the experimental technique is presented, as complete details have been previously published. 6'7 The procedure for data analysis and the construction of liquidus surface diagrams follows.
II. EXPERIMENTAL The success of hot-wire microscopy depends upon manufacturing a large number of homogeneous samples of known composition. A brief description of the sample preparation technique, experimental apparatus, and procedure follows. Sample Preparation. Samples of known composition were prepared by melting thoroughly mixed CaO-A1203 master slags in inductively heated graphite crucibles. A known weight of homogeneous master slags was obtained by holding the melts at several hundred degrees Kelvin N. NITYANAND, formerly a Research Assistant at the University of Kentucky, is now a Graduate Student in the Department of Metallurgicat Engineering and Materials Science, Carnegie-Mellon University, Pittsburgh, PA 15213. H. ALAN FINE is Associate Professor with the Department of Metallurgica~ Engineering and Materials Science, 763 Anderson Hall, University of Kentucky, Lexington, KY 40506. Manuscript submitted May 6, 1982.
METALLURGICALTRANSACTIONS B
above the temperature at which they began to melt for about an hour. Samples in the CaO-AI203-TiO2 system were then made by stirring in a preweighed quantity of the unfused master slag which contained a known amount of TiO:, holding at temperature for about thirty minutes, and sampling. Samples were taken by dipping a graphite rod into the melt. The precise weight of the sample and remaining melt were then determined and the procedure repeated until the desired number of samples was obtained. Samples were then crushed to - 1 0 0 mesh, placed in an alumina boat, and decarburized by heating to 1300 K for 24 hours in air. Experimental Apparatus. Liquidus temperature measurement by hot-wire microscopy entails the direct observation of the formation of the first crystal from a melt during cooling or the melting of the last crystal
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