De-oxidation of steels

In modern technical alloys, which almost all consist of a large number of components, the presence or absence of traces of some elements plays an extraordinarily great role in determining the mechanical properties. We have previously seen how it is just in the metals that such a great influence of traces can become manifest. The individual, typically chemical properties of the admixed elements usually play only a minor role in this (compare on the other hand de-oxidation of steel by aluminium or sodium). 

Uses. It is used as a getter it has a relatively low vapour pressure and is very reactive towards H2, 02, N2, C02, H20, etc., even removing inert gases by inclusion. It is used as de-oxidizer for steel, etc. and also as modifying agent of Al-Si eutectic alloys (as Na and Sr). 

CHLORURE de VINYLIDENE (French) (75-35-4) Forms explosive mixture with air (-18°F/-28°C). Inhibitors such as the monomethyl ether or hydroquinone must be added to prevent polymerization. Readily forms explosive peroxides with air or contaminants (a white deposit may indicate the presence of explodable peroxides). Violent polymerization from heat or on contact with oxidizers, chlorosulfonic acid, nitric acid, or oleum or under the influence of oxygen, sunlight, copper, or aluminum. Violent reaction with alkali metals (lithium, sodium, potassium, rubidium, cesium, and francium). Incompatible with ozone. May cause an explosive reaction with trifluorochloroethylene above 356°F/180°C, perchlory fluoride above 212°F/100°C. May be corrosive or unstable in the presence of steel. 

OXICLORURO de FOSFORO (10025-87-3) Fumes in moist air. Contact with water, steam, or alcohols produces hydrochloric acid, phosphoric acid, and phosphine gas, which is pyrophoric, with possible ignition or explosion (may be a delayed reaction). Contact with air produces corrosive fumes. Violent reaction with carbon disulfide, 2,6-dimethylpyiidine-M-oxide, dimethyl sulfoxide, ferrocene-l,l -dicarboxylie acid, pyridine, zinc powder. Reacts, possibly -violently, with acids, alkali metals, alkalis, combustible materials, dimethyl formamide, organic matter, zinc powder. Incompatible with acetic anhydride, iV,A -dimethyl formamide, 2,5-dimethylpyrrole, sodium. Rapid corrosion of steel and most metals, except lead, occurs in the presence of moisture. 

Calcium silicon is used in the iron and steel industry as a de-oxidizer and desul-furizer and for the modification of non-metallic inclusions. A high calcium quicklime is required (e.g. 94 to 97 % CaO) with controlled levels of combined CO2 and water. 

Reaumur, who mentions that Perrault (1613-88) had noticed that a steel wire becomes thicker when heated and quenched, proved that steel increases in volume by in this treatment. His process for converting cast iron into steel is really that described in 1540 by Biringuccio (Vol. II, p. 34), viz. immersing a piece of solid wrought iron in molten cast iron le fer avide des soufres boit une partie de ceux de la font qui en a plus de lui. He also found that cast iron is converted into malleable iron when it is heated embedded in what he calls safran de Mars , an oxide of iron.i ... 

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. ... 

Jean Henri Hassenfratz (Paris 20 December 1755-26 February 1827), from 1795 professor of mineralogy in the Ecole des Mines and from 1797 professor of physics in the Fcole Polytechnique, published on respiration, affinity, metallic acids (tin and iron), the calcination of metals in pure air (oxygen), the distinction between inflammation and combustion, the amoimts of light produced by different combustibles, hydrometry, the oxides of iron, and papers on mineralogy, etc. He put forward the humus theory of vegetation, and published a large work on iron and steel. He and Adet devised a system of symbols in which, e.g., the metals are denoted by capital letters (C cuprum, P plumbum, S stannum, Fe ferrum, Sb stibium) enclosed in circles. ... 

Protection of steels from high temperature oxidation is made by various inorganic coating films such as Si02 film (De Sanctis, 1990), borosilicate film (Guglielmi) and aluminosilicate film (Di Giampaolo Conde, 1992). 

When the operating temperature is about 1000°C, interconnects need to be made of ceramic materials. Although excellent performances of fuel cells based on ceramic interconnects have been proved, costs are still a relevant restriction. At reduced temperature, the use of less expensive materials, like for instance stainless steel, is possible. Several organizations are currently investigating the interaction of different metals with the electrodes (De Jonghe et al. 2004, Zahid et al. 2004, Pedersen et al. 2004). The two main issues to overcome are the oxidation of the metal when in contact with air at the cathode side and the interaction of the chromium vapors with the cathode. 

On the other hand, there are few reports about SOFC stacks, which employ rare earth doped ceria electrolytes, although a high power density has been reported for single cell test (Steele, 2000 Bance et al., 2004). The rare earth doped ceria exhibits isothermal expansion in a reducing atmosphere due to the reduction of cerium ion from tetiavalent (Ce +) to trivalent state (Ce " ") accompaitying the formation of oxygen vacancies, which results in the warping or de-straction of the electrolyte plate. The formation of trivalent cerium ion also causes a decrease of oxide ion transport number, which reduces the efficiency of the cell. 

Thermal oxidizers must be built to provide the residence time and temperatures to achieve the desired destruction efficiency (DE). As such, thermal oxidizers are comparatively larger than catalytic oxidizers since their residence time is two to four times greater. Historical designs of thermal oxidizers were comprised of carbon steel for the outer shell and castable refractory or brick as the thermal liner (a refractory is like a cement, which is put on the inside of the rector shell to act as a thermal insulation barrier). Modern units are designed and built using ceramic fiber insulation on the inside, which is a lightweight material, and has a relatively long life. Old refractory would tend to fail over a period of years by attrition of expansion and contraction. 

Ceilings, P. J. and de Jongh, M. A., Grain Boundary Oxidation and the Chromium-depletion Theory of Intercrystalline Corrosion of Austenitic Stainless Steels , Corros. Sc/., 7,413 (1967) Armijo, J. S., Impurity Adsorption and Intergranular Corrosion of Austenitic Stainless Steel in Boiling HNOj-KjCrjO, Solutions , Corros. Sci., 7, 143 (1967)... 

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