Steels continued oxidation

Metals vary greatly in their corrosion-resistance - chromium and titanium have good resistance, while steel readily corrodes. The oxide film formed on chromium and titanium closely adheres to the surface and protects the metal from further oxidation. In the case of steel, the oxide film in the form of rust is loose, allows moisture to be retained, and promotes further corrosion. If corrosion is allowed to continue, the steel will eventually be completely consumed, i.e. the metal will have returned to the condition of the ore from which it was extracted. 

On the publication of his work on steel in 1722 Reaumur was given a pension of 12,000 livres by the Duke of Orleans, but he made it over to the Academy for the perfection of the arts. He also introduced the manufacture of tinplate into France, showing that the iron sheets must be very clean and free from oxide before they are dipped in the bath of melted tin covered with tallow. 2 The nature of steel continued to be obscure till the work of Berthollet and Guyton de Morveau (see p, 530). In 1779 Jean Demeste, a Liege surgeon who made chemistry a hobby, thought that ordinary iron contains zinc, which is removed when it is converted into steel. ... 

C A state of surface dealloying with no continuous oxide, e.g., gold alloys in many aqueous solutions [75,99]. Dealloying may also occm within localized corrosion sites in passive alloys such as austenitic stainless steels. 

A continuous oxide layer without defects is considered as protective and hinders direct contact between the bare T91 steel and the liquid metal, therefore reducing the risk for a degradation of the mechanical properties of the steel. 

United States, LaSalle, IH. 1918 continuous Hquid-phase oxidation (since ca 1961) K MnO separation from Hquid phase is without prior dilution continuous electrolysis of filtered electrolyte in bipolar ceUs Monel anodes, mild steel cathodes, vacuum crystallization 14,000 ... 

The essential protective film on the 2inc surface is that of basic 2inc carbonate, which forms in air in the presence of carbon dioxide and moisture (Fig. 1). If wet conditions predominate the normally formed 2inc oxide and 2inc hydroxide, called white mst, do not transform into a dense protective layer of adhesive basic 2inc carbonate. Rather the continuous growth of porous loosely adherent white mst consumes the 2inc then the steel msts. 

Naphthalene (qv) from coal tar continued to be the feedstock of choice ia both the United States and Germany until the late 1950s, when a shortage of naphthalene coupled with the availabihty of xylenes from a burgeoning petrochemical industry forced many companies to use o-xylene [95-47-6] (8). Air oxidation of 90% pure o-xylene to phthaUc anhydride was commercialized ia 1946 (9,10). An advantage of o-xylene is the theoretical yield to phthaUc anhydride of 1.395 kg/kg. With naphthalene, two of the ten carbon atoms are lost to carbon oxide formation and at most a 1.157-kg/kg yield is possible. Although both are suitable feedstocks, o-xylene is overwhelmingly favored. Coal-tar naphthalene is used ia some cases, eg, where it is readily available from coke operations ia steel mills (see Steel). Naphthalene can be produced by hydrodealkylation of substituted naphthalenes from refinery operations (8), but no refinery-produced napthalene is used as feedstock. Alkyl naphthalenes can be converted directiy to phthaUc anhydride, but at low yields (11,12). 

Ladle metallurgy, the treatment of Hquid steel in the ladle, is a field in which several new processes, or new combinations of old processes, continue to be developed (19,20). The objectives often include one or more of the following on a given heat more efficient methods for alloy additions and control of final chemistry improved temperature and composition homogenisation inclusion flotation desulfurization and dephosphorization sulfide and oxide shape control and vacuum degassing, especially for hydrogen and carbon monoxide to make interstitial-free (IF) steels. Electric arcs are normally used to raise the temperature of the Hquid metal (ladle arc furnace). 

Figure 1.6 Dark oxide and deposit lobes on a copper continuous caster mold from a steel-making operation. Since heat transfer is high, even small amounts of deposit are unacceptable.

Figure 5.9 Wall of steel tank, originally V2 in. (1.3 cm) thick, that was entirely converted to oxide. It was continuedly exposed to oxygenated water mist at about 180°F (82°C).

The triggering mechanism for the corrosion process was localized depassivation of the weld-metal surface. Depassivation (loss of the thin film of chromium oxides that protect stainless steels) can be caused by deposits or by microbial masses that cover the surface (see Chap. 4, Underdeposit Corrosion and Chap. 6, Biologically Influenced Corrosion ). Once depassivation occurred, the critical features in this case were the continuity, size, and orientation of the noble phase. The massive, uninterrupted network of the second phase (Figs. 15.2 and 15.21), coupled... 

Polished steel substrates primed with plasma polymerized acetylene films were immersed into a stirred mixture of these materials at a temperature of 155 5°C to simulate the curing of rubber against a primed steel substrate. During the reaction, the mixture was continuously purged with nitrogen to reduce oxidation. At appropriate times between 1 and 100 min, substrates were removed from the mixture, rinsed with hexane ultrasonically for 5 min to remove materials that had not reacted, dried, and examined using RAIR. The RAIR spectra obtained after reaction times of 0, 15, 30, and 45 min are shown in Fig. 13. 

The use of equipment close to the temperature at wliich the material was diffusion treated will result in continuing diffusion of chromium, aluminum etc., into the substrate, thus depleting chromium with consequent loss in oxidation and corrosion resistance. For aluminum, this effect is noticeable above 700°C in steels, and above 900°C in nickel alloys. For chromium, the effect is pronounced above 850°C for steels and above 950°C for nickel alloys. 

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