The density of liquid iron-carbon alloys
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I.
INTRODUCTION
A C C U R A T E determination of densities in liquid ironcarbon alloys is essential to allow realistic calculations of gravitationally driven and interfacial phenomena; however, there is a large scatter in the reported density values of iron-carbon alloys at 1600 ~ (Figure 1) which can lead to a significant error in any derived value. Thus, the densities of liquid iron-carbon alloys were redetermined using a sessile drop profile method to assess the reliability and accuracy of current literature values.
II.
EXPERIMENTAL
An X-ray radiographic technique was used to image the droplet profile, and then the image was digitized by means of a sophisticated image analyzer developed by the authorsJ 7'8j The droplet volume was calculated from computer generated solutions of the Young-Laplace equation.
A. Experimental Method Figure 2 shows a schematic for the experimental apparatus with the X-ray device. Details for the apparatus and procedure are described elsewhere.tY.8J The iron used in this study was 99.99 pet metallic purity iron (from Noah Technology, San Antonio, TX). Impurities in the iron are summarized in Table I. The Fe-C alloys were made of the iron metal and high-purity grade (99.95 pct) graphite powder (by Johnson Matthey, Ward Hill, MA). The mixture of iron and carbon was heated in the atmosphere-controlled induction furnace at around 1500 ~ for 30 minutes and then quickly cooled by an ultrahigh-purity CO jet in the furnace. Each sample piece was prepared cutting 1 to 1.5 g from the mother alloy. The piece was polished with sandpaper, cleaned with acetone in an ultrasonic washer, and dried. I. JIMBO, Associate Scientist, and A.W. CRAMB, Associate Professor, are with the Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213. Manuscript submitted March 19, 1992. METALLURGICAL TRANSACTIONS B
For each run, a sample crucible (McDanel 998 HighPurity Alumina, Conical, 22-ram top diameter x 33-mm height), which is also the pedestal material, was charged from the top of the furnace tube onto a shallow alumina crucible. An alumina powder layer is placed in the shallow crucible to prevent the sample crucible from cracking by thermal shock and to avoid contamination of the pedestal when the sample crucible breaks by accident. The atmosphere in the furnace was a reducing dehydrated gas mixture of ultrahigh-purity carbon monoxide (99.999 pct) and ultrahigh-purity argon (99.999 pct) (by Matheson Gas Products). The decrease in weight of sample during the experiment was found to be within 0.2 pct of the initial weight. The experimental conditions are shown in Table II. Carbon content for each mother alloy was analyzed by a LECO* Carbon Analyzer. For each condition, at least *LECO is a trademark of LECO Corporation, St. Joseph, MI.
four individual runs were accomplished. For each individual run, at least four X-ray pictures were taken every 20 minutes after confirming that the sample had melted. The equilibrium shape was quickly obtained after the sample melted.
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