Graphite iron-carbon alloys

Iron/ carbon alloy, poured as a hot molten liquid into a mold. Usually produced as either gray iron (where flakes of graphite are embedded in an iron matrix) or nodular iron (spheroids of graphite in the matrix). 

Fra] Fray, DJ., CMpman, J., The Solubility of Graphite in Fe-Ni and Fe-Co Alloys at 1000°C , Trans. Metall. Soc. AIME, 245, 1143-1144 (1969) (Phase Relations, Experimental, 4) [1969Ruh] Ruhl, R.C., Cohen, M., Splat Quenehing of Iron-Carbon Alloys , Trans. AIME, 245, 241-251 (1969) (Crys. Stiueture, Experimental, Phase Relations, 50)... 

Figure 6.3 The iron-carbon phase diagram showing the alternative production of iron and cementite from the liquid alloy, which occurs in practice, to the equilibrium production of graphite...

Cast irons, although common, are in fact quite complex alloys. The iron-carbon phase diagram exhibits a eutectic reaction at 1 420 K and 4-3 wt.<7oC see Fig. 20.44). One product of this eutectic reaction is always austenite however, depending on the cooling rate and the composition of the alloy, the other product may be cementite or graphite. The graphite may be in the form of flakes which are all interconnected (although they appear separate on a... 

In gray iron, most of the contained carbon is in the form of graphite flakes, dispersed throughout the iron. In ductile iron, the major form of contained carbon is graphite spheres, which are visible as dots on a ground surface. In white iron, practically all contained carbon is combined with iron as iron carbide (cementite). a very hard material. In malleable iron, the carbon is present as graphite nodules. High-alloy irons usually contain an alloy content in excess of 3%. 

For anodic processes the choice of materials for the electrode is much more limited than for cathodic ones, as the anode could bo easily attacked by the products of the electrolysis (chlorine, oxygon etc.), or electrochemioally dissolved. In alkaline solutions the selection will be restricted to the application of platinum (or alloys of platinum with irridium or rhodium), palladium, carbon (or rather graphite) iron and nickel, while for acid solutions only metals of the platinum group and graphite will be suitable in a special case of the electrolysis in sulphuric acid solutions lead has found wide use, it getting coated with a conductive film of lead dioxide. 

E6.2. Predict whether or not galvanic corrosion will cause the following alloys to be subjected to leaching (i) carbon and carbon steel alloys in an oxidizing atmosphere, (ii) steel rivets in aluminum drain gutters, (iii) copper-nickel alloy in refinery condenser tubes, (iii) graphite fiber-reinforced aluminum composites, (iv) brass in water, (v) iron-chromium alloys, and (vi) carbon steel pipe in contact with the weld to stainless steel pipe. 

Chi] Chipman, J., Alfred, R. M., Gott, L. W., Small, R. B., Wilson, D. M., Thomson, C. N., Gue, D.L., The Solubility of Carbon in Molten Iron and Iron-Silieon and Iron-Manganese Alloys , Trans. Amer. Soc. Metals, 44,1215-1232 (1952) (Experimental, Phase Relations, 16) [1952Tho] Thomson, C., Effect of Manganese on the Solubility of Graphite in Liquid Iron , Trans. 

Kag] Kagawa, A., Imaizumi, T., Mizumoto, M., Pressirre-Induced Transition fiom Graphite Eutectic to Carbide Eutectic in Iron-Carbon-Sihcon Alloys , Mat. Trans., 42(7), 1385-1391 (2001) (Experimental, Morphology, Meehan. Prop., 20)... 

Hackett et al. (2007) reported experiments with DCFCs where rods prepared from different carbon materials were used as the anodes. The cathodes were made from iron-titanium alloy. Melts of NaOH at temperatures in the range 600 to 700°C were used as the electrolyte. The most stable operation with high performance figures was obtained with graphite anodes. The OCV value was 0.788 V. At the optimum temperature of 675°C, the voltage was 0.45 V at a current density of 140 mA/cm. Anodes made of other carbon materials had higher OCVs (up to 1.044 V), but exhibited inferior and less stable performance when current was drawn. The equation for the anodic reaction in NaOH melt can be written as... 

Traditional anodic materials such as carbon steel, aluminum, high-silicon cast iron, impregnated graphite, and lead alloys will... 

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