The iron absorbs carbon through contact with the coke, which melts owing to its decreased melting point. Equation combines with equations 8 and 9 in a cycle which effectively regenerates CO. Owing to the highly endothermic nature of equation 7, the gases cool as they rise in the furnace. Equation, reduction by CO, is referred to as indirect reduction. The combination of equations 7 and 8, solution loss and indirect reduction, is referred to as direct reduction, because it amounts to reduction of the wustite direcdy by carbon to form iron and CO. This direct reduction is not the same terminology used in direct reduction processes, which in fact often rely on indirect reduction reactions (see Ironbydirectreduction).  [c.416]

Reduction of magnetite and hematite (upper shaft) as more and more CO and H2 are converted to CO2 and H2O, the ascending gases eventually become too weak in concentration to reduce wustite to iron. Eigure 3a and b shows the regions of stabiUty for the Ee—C—O and the Ee—H—O systems, respectively. The boundary lines represent the equiUbrium conditions for the various reduction reactions as shown. The gases, too weak to reduce wustite, are strong enough to reduce magnetite to wustite  [c.416]

Only the slightest amounts of CO 01 are requited to reduce hematite to magnetite, which is why in Figure 3 the regions of magnetite stability are shown extending all the way down to the bottoms of the graphs. Owing to the excess CO generated by the wustite reduction reactions, hematite reduction is also driven to the top of the furnace. The reduction of hematite to magnetite and magnetite to wustite is so fast that hematite, magnetite, and wustite may all be found in the same pellet, owing to the topochemical (occurring at boundaries which progress from surface to center) nature of the reactions. In this zone the gas temperature falls off rapidly because of cooling by the incoming materials, evaporation of moisture, and the net endothermic nature of the reduction reactions.  [c.417]

Fretting corrosion occurs because of oscillating relative motion between touching surfaces. As little as 3 x 10 meter lateral movement is required. The amount of damage increases as the normal force between the surfaces is increased. In dry conditions, the corrosion product is usually the oxide. In the case of steel, this is wustite. This is otherwise the high-temperature form of the oxide, which infers that locally high temperatures are created on the fretting surfaces. The surfaces weld together in the high stress conditions at points of contact and are torn apart by the relative motion of fretting surfaces.  [c.896]

Fig. 7.8 Relative thickness of wustite, magnetite and haematite on mild steel as a function of Fig. 7.8 Relative thickness of wustite, magnetite and haematite on mild steel as a function of
Fig. 7.10 Kinetics of wustite growth on mild steel and low-chromium alloy steels in air and Fig. 7.10 Kinetics of wustite growth on mild steel and low-chromium alloy steels in air and
Melting (fusion) 2one and final reduction of wustite the and CO rise through the burden, contact wustite [17125-56-3] formed from previous reduction reactions in the upper part of the furnace, and reduce it to iron.  [c.416]

The processes being developed by the American Iron and Steel Institute and the Department of Energy (AISI-DOE) in the United States and the Japan Iron and Steel Federation (JISF) in Japan share similar features in the smelter, but differ in prereduction approaches. In the AISI-DOE process, pellets are prereduced to wustite, about 30% prereduction, in a shaft furnace. In the JISF process, called direct iron oxygen smelting (DIOS), iron ore fines are prereduced to between 30 and 60% in one or more fluidi2ed beds in series. For both, the prereduced ore and coal are charged into a vertical vessel containing a molten bath, and oxygen is injected to generate CO and heat. Additional oxygen is provided to post-combust the CO to CO2, thereby improving the energy efficiency of the process.  [c.420]

The reduction of iron ore is accompHshed by a series of reactions that are the same as those occurring in the blast furnace stack. These include reduction by CO, H2, and, in some cases soHd carbon, through successive oxidation states to metallic iron, ie, hematite [1309-37-17, Fe202, is reduced to magnetite [1309-38-2], Fe O, which is in turn reduced to wustite [17125-56-3], FeO, and then to metallic iron, Fe. The typical reactions foUow.  [c.425]

The rate of oxidation of iron is then governed by the stabilities of the various phases, which are in turn a function of the temperature and oxygen partial pressure of the environment. Examination of the Fe-Oz phase diagram (Fig. 7.2) reveals that the principal solid oxide phases below 570°C will be Fej04 (magnetite) and FejOj (haematite). Above 570°C, FeO (wustite) appears as a third phase within the scale. These phases are present within the scale as individual layers, with the layer sequence dictated by the equilibrium oxygen partial pressure ( 2) for phase stability prevailing at the given temperature. Hence, the oxide phase stable at the lowest pO (FeO at >570°C) is found closest to the metal substrate, whereas the phase stable at the highest pOj (FejOj) is found closest to the oxidising environment. If, however, the pO, of the environment is low enough, only FeO will be formed. At intermediate values of the pO, Fej04 will also form and, for most industrial environments, the pOj is sufficient for the formation of an outer layer of Fe20j. Whilst these observations are true for bulk scales, FeO has also been found to be stable in very thin films at temperatures down to 400°C and within narrow cracks at 5()0°C .  [c.967]

As a result of this lack of mobility of certain alloying elements, a new phase layer appears in the scale. This new layer grows inward from the original metal surface, is in intimate contact with the substrate alloy and has an alloying element composition approximately 1.5 times that of the original metal . Moreau S identified this inward growing layer on Fe-Cr steels as FeCr204 globules within a wustite matrix. Further, Rahmel determined that the inner layer of four layered scales grown on iron alloys containing Cr, Mo, V and Si consisted of FeO containing (Fe, 2O3O4 where X is Cr, Mo, V or Si. The oxygen transport through the inner layer is thought to take place via pores within the inner layer, since solid-state diffusion of oxygen through the magnetite lattice is five orders of magnitude too low"", and grain boundary diffusion is also too low, to account for the observed growth rates. The oxygen pathways are now thought to comprise grain boundary triple points and transient microvoids, continuously created and rearranged by creep  [c.972]

Of all of the alloying elements added to steels, Cr has been the most used for improving the corrosion properties. In terms of high-temperature oxidation, steels containing approximately 10% Cr are capable of forming a continuous, highly protective film of CrjOj . Significant reductions in the oxidation rate are realised at lower Cr concentrations due to the formation of FeCr spinels and the suppression of FeO formation to temperatures in excess of 570°C. At 700°C FeO exhibits a very narrow stability range on the Fe-Cr-O phase diagram (Fig. 7.6) for Cr up to 6% . The wustite stability range is almost negligible on Fe-0.5%Cr due to the high reactivity of Cr towards Oj at 1 000°C. However, whilst Cr20j is normally protective on steels in air or O2 up to approximately 900°C, volatile CrOj may form at higher temperatures . Whilst the addition of Cr to steels is normally considered beneficial, Dewanckel et al found that low quantities (<500 ppm Cr) were detrimental to the breakaway performance of low-alloy and carbon steels.  [c.978]

See pages that mention the term Wustite : [c.1074]    [c.1074]    [c.416]    [c.417]    [c.166]    [c.75]    [c.973]    [c.976]    [c.983]    [c.986]    [c.290]   
The Nalco Guide to Cooling Water System Failure Analysis (1993) -- [ c.75 ]