| To investigate the effect of surface free energy difference between plain and cerium-treated cast iron, the wettability between iron and graphite was compared by means of contact angle measurements in the two cases, namely, where cerium was preliminarily coated on the graphite surface, and where not coated. The result was such that a significant difference in the contact angles has been shown to exist between the above two cases, indicating the presence of a minimum wettability at a critical concentration of cerium in the iron-graphite interface. It is further noted from X-ray and Laser microprobe analysis that some compounds of nodulizing elements are formed during the melting of the iron samples and these may have a nucleating influence on the formation of graphite nodules. The foregoing results imply that the nodule formation of the graphite may be due to the increase of interfacial energy between melt and graphite by the adsorption of cerium or magnesium vapour on the graphite surface, or to the nucleation of graphite by some compounds of nodulizing elements formed during melting, or both. |
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