Magnetite forms

Thin adherent Dims of magnetite form on the steel surfaces in the initial stages of operation of the system, but in troublesome situations the magnetite becomes non-adherent and in extreme cases can lead to pump blockages. 

In 1925, Welo and Baudisch found that magnetite formed upon bringing a solution with Fe /Fe - 2, i.e. the ratio of magnetite, up to pH 9-10. Misawa et al. 

For Model II all organic matter has been used up after Reaction 2 has taken place at the same time almost all iron (III) has been consumed. For Model I, 0.112 mole organic matter still remains, which can react in the following ways with sulfate and magnetite (formed by Reaction 2) ... 

The protective oxide on ferritic steel consists of two layers, which are porous to carbon dioxide. The inner layer consists of crystallites of Cr and Si and the outer layer Fe304 (magnetite) formed by the reaction of metallic iron and C02 and the product CO giving elemental carbon. 

This adsorption probably takes place with the hydrocarbon end of the Triton molecule toward the oleate, and the ethylene oxide groups toward water. The amount of non-ionic surfactant adsorbed was 10-2(j)g based on the stoichiometric amount of magnetite formed. 

The transformation of the jointly precipitated (Step I) mixture of ferrous and ferric hydroxides to magnetite (Step II) was studied by the continuous measurement of the magnetic moment. It was found that at large excess ammonia, added in Step I, magnetite forms at a fast rate and the transformation is complete. At small excess ammonia the transformation is slow and incomplete. The application of Avrami s theory to the data indicated grain boundary nucleation in the former case and grain boundary nucleation after saturation followed by diffusion controlled growth in the latter case. Mechanisms are proposed for both cases. 

Tc(VII) as TcOA Possible reductive sorption to reduced minerals (e.g., magnetite), forms insoluble reduced oxides and sulfides Eh, and, if Eh is low, sulfide levels. 

The authors hypothesized that at low O2 partial pressure under the biofilm a passive film of magnetite formed that would not have formed without the microorganisms. The proposed explanations are not completely satisfactory since corrosion inhibition was not observed with killed cells but was observed when respiration was reduced in stressed cells. The absence of Pseudomonas after a six-week exposure in natural seawater may indicate competition from other microorganisms once the controlled corrosion-inhibiting biofilms are introduced into natural environments. 

Another work describes the synthesis of magnetic nanocontainers (i.e., hollow spheres) of magnetite formed using PS particles obtained by emulsion polymerization as sacrificial core [179]. The coating procedure involved the controlled hydrolysis of aqueous solution of FeCb in the presence of the PS latex, urea, and PVR The particles coated with hematite (non-magnetic) that were obtained after aging at 95°C were then heated to 500°C to provide hollow hematite spheres. 

Before performing WGS reaction the prepared catalysts which are in hema-titic form have to be activated to magnetite form by controlled reduction in a stream of process gas such as CO, CO2, H2 and H2O vapour. The ratios of water... 

The yield of retained fraction in the case of irregularly shaped particles was found to be 1.3-1.5 times that for particles with a rounded shape. In crushing operations, for example, particles of barite, quartz, feldspar, and magnetite form rounded particles, decreasing their adhesion. The wastes from low grades of asbestos contain irregularly shaped mineral dust particles, which adhere to the drum surface and are separated as the retained fraction [137]. 

The solid solution formed with iron oxides impacts the reduction rate, for example, addition of 1%-10% CaO increases the reducibility, with the product of the reduction of CaO and a-Fe sponge. CaO and magnetite form CaxFe3 x04, which affects both the thermodjmamics and kinetics together, and Ca2Fe205 has the lowest rate of reduction (Fig. 5.21). ... 

According to this model, the proportion of the sample accessible by photoemission should be reduced to metal within a short period of time, i.e., UPS should detect metallic iron shortly after the surface has reached the reaction temperature of ca 700 K. This was not observed. Instead, the gas-solid interface only becomes metallic after reduction in the bulk of the sample has terminated. The core level data, on the other hand, showed the expected behavior, with an early formation of iron metal nuclei and subsequent growth to form particles large enough to exhibit the spectral parameters of bulk iron. It is therefore concluded that the reduction process produces two interfaces the one, an outer gas-solid interface which remains in the magnetite form until the reaction on the other, an inner metal-metal oxide interface, is completed. For catalytic activity, only the gas-solid interface is relevant. The catalyst therefore only becomes active if the whole of the bulk is converted from oxide to metal, although the majority of the material is still not involved in catalysis. 

Carbon monoxide also reacted with magnetite forming carbides which catalyzed the production of hydrocarbons by Fischer-Tropsch reactions. It has since been shown that both reactions can be suppressed by the addition of copper to the existing iron-chromium catalyst. This has allowed operation of HTS catalysts in existing plants down to a steam ratio as low as 0.4 compared with about 0.6 in the early single stream plants. 

The third application was to define the orientation relationships between various phases, i.e. relationships between the wustite phase and the steel substrate, precipitated magnetite and parent wustite phase, magnetite layer and wustite layer, and magnetite layer and hematite layer. It was found that pro-eutectoid magnetite, formed either at the base of the wustite phase or inside the wustite layer, had the same orientation as its patent wustite phase. 

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