Ferrous hydroxide

Add about 0 2 g. of ferrous sulphate crystals to the first portion of the filtrate contained in a boiling-tube. An immediate dark greenish-grey precipitate of ferrous hydroxide should occur if the mixture remains clear, add a few ml. of sodium hydroxide solution. Now boil the mixture gently for a few minutes to ensure formation of the ferrocyanide, cool under the tap, add one drop of ferric chloride solution, and then acidify... 

The ferrous hydroxide may react to form ferric hydroxide ... 

The ferrous hydroxide then combines with oxygen and water to produce ferric hydroxide, Fe(OH)2, which becomes common iron mst when dehydrated to Fe202. 

Ferrous hydroxide in the presence of alkaline hydroxides or carbonates reportedly reduces carbon tetrachloride to methylene chloride (29). 

A solution of sodium cyanide shaken with freshly precipitated ferrous hydroxide is converted to a ferrocyanide ... 

The ferrous ions that dissolve from the anode combine with the hydroxide ions produced at the cathode to give an iron hydroxide precipitate. The active surface of ferrous hydroxide can absorb a number of organic compounds as well as heavy metals from the wastewater passing through the cell. The iron hydroxide and adsorbed substances are then removed by flocculation and filtration. The separation process was enhanced by the addition of a small quantity of an anionic polymer. 

More reduced forms of oxide are present beneath the rust layer. Hydrous ferrous oxide (Fe0 nH20), that is, ferrous hydroxide [Fe(OH)2l... 

Outer crust. A friable outer crust forms atop the tubercle. The crust is composed of ferric hydroxide (hematite), carbonates, silicates, other precipitates, settled particulate, and detritus. Ferrous ion and ferrous hydroxide generated within the tubercle diffuse outward through fis-... 

Core. Friable core material is present beneath the magnetite shell (Fig. 3.6). The core consists mostly of ferrous hydroxide formed by Reaction 3.3 ... 

The corroded floor usually is covered with porous friable corrosion product containing ferrous hydroxide, which may form in place by conversion of the steel surface. If acidity is significant, the thickness of this corrosion product layer is slight. 

The corrosion-product layer that forms due to oxygen corrosion is discussed in Chap. 3, Tuherculation. However, the initial corrosion product is ferrous hydroxide [Fe (OH)2l (Reaction 5.4) ... 

The ferrous hydroxide is rapidly oxidized to ferric hydroxide in oxygenated waters (Reaction 5.5) ... 

Ferric and ferrous hydroxide usually contain water of hydration. A layer of hydrated magnetite sometimes forms between the ferric and ferrous hydroxides (see Fig. 3.2). The threefold layer of corrosion products is usually called rust. The bulk of rust is the ferric hydroxide layer. (In tubercles, however, ferrous hydroxide often is the major component see Chap. 3.)... 

Sulfides are intermixed with iron oxides and hydroxides on carbon steels and cast irons. The oxides are also produced in the corrosion process (Reaction 6.6). Although theoretical stoichiometry of 1 to 3 is often suggested between sulfide and ferrous hydroxide, empirically the ratio of iron sulfide to ferrous hydroxide is highly variable. Sulfide decomposes spontaneously upon exposure to moist air. Additionally, corrosion-product stratification is marked, with sulfide concentration being highest near metal surfaces. 

Geothite is produced by air oxidation of alkaline suspension of ferrous hydroxide (Sada etal., 1988). As a starting material for ferrous oxide, the preparation of fine particles with prescribed size, size distribution and shape is required in its application to magnetic materials for recording tapes and disks. With increasing oxidation rate, the crystal size decreases and the size distribution becomes sharper (Sada etal., 1988). The first step of the reaction. 

Sada, E., Kumazawa, H. and Aoyama, M., 1988. Reaction kinetics and controls of size and shape of geothite fine particles in the production of ferrous hydroxide. Chemical Engineering Fundamentals, 71, 73-82. 

Eisen-hydrozyd, n. ferric hydroxide, iron(III) hydroxide, -hydroxydul, n. ferrous hydroxide, iron(II) hydroxide. -jodid,n. iron iodide, specif, ferric iodide, iron(III) iodide, -jodiir, n. ferrous iodide, iron(II) iodide, -jodiirjo-did, n. ferrosoferric iodide, iron(II,IIl) iodide, kalium, n. potassium ferrate, -kaliumalaun,... 

Eisenoxydul-hydrat, n. ferrous hydroxide, iron(ll) hydroxide, -oxyd, n. ferrosoferric oxide, iron(II,III) oxide, magnetic iron oxide (FeaOi). -salz, n. ferrous salt, iron(II) salt, -sulfat, n. ferrous sulfate, iron(II) sulfate, -verbindung, /. ferrous compound, iron(ll) compound. 

Ferrous Carbnnsle. Ferrous Hydroxide. Ferrous Oxide. . Ferrous Sulfate. . Ferrous Sulfate. , Ferrous Sulfate.. ... 

Ferrous ions (Fe ) combine with hydroxyl ions (OH") to form brownish red ferrous hydroxide [Fe(OH)2] ... 

Ferrous hydroxide precipitates from solution. Since this compound is unstable in oxygenated solution, it is oxidized to the ferric salt ... 

The hydroxyl ion thus produced combines with ferrous ion produced in the first step and forms ferrous hydroxide (rust), which coats the cathode ... 

This is the common form of cathodic reaction in most environments. The OH ions react with Fe ions to form ferrous hydroxide ... 

The product, ferrous hydroxide, is commonly further oxidised to magnetite (Fej04) or a hydrated ferric oxide (FeOOH), i.e. rust. 

A simple calculation based on the solubility product of ferrous hydroxide and assuming an interfacial pH of 9 (due to the alkalisation of the cathodic surface by reaction ) shows that, according to the Nernst equation, at -0-85 V (vs. CU/CUSO4) the ferrous ion concentration then present is sufficient to permit deposition hydroxide ion. It appears that the ferrous hydroxide formed may be protective and that the practical protection potential ( —0-85 V), as opposed to the theoretical protection potential (E, = -0-93 V), is governed by the thermodynamics of precipitation and not those of dissolution. 

In rusting, the initial corrosion product of iron is ferrous hydroxide. Reacting with oxygen and water, it forms higher oxides, mainly hydrated ferric oxide and magnetite. Rust formed in industrial or marine environments contains corrosion-promoting salts and is particularly dangerous. Rust is not considered a satisfactory base over which to paint and it too must be removed. 

In the presence of oxygen the ferrous hydroxide will be converted into rust, Fe20j.H20. 

Ferrous hydroxide is soluble (9%) in pure water, but slight oxidation renders it appreciably less soluble. Thus in the presence of water and oxygen alone the corrosion product may be formed in close contact with the metal and attack will consequently be stifled. In the presence of an electrolyte such... 

This is considered, however, to proceed in two stages, i.e. the initial production of ferrous hydroxide ... 

The primary reaction in the corrosion of boiler steel is the formation of ferrous hydroxide and its subsequent decomposition to magnetite and hydrogen - the Schikorr reaction (Section 4.4). This is demonstrated by the products of corrosion encountered throughout the whole range of boiler operating pressures, but the details are influenced by other factors, i.e. the water quality, heat flux, and the boiler operating conditions. 

To consider these reactions and the problems caused, it may be useful to refer back to the basic corrosion mechanisms of iron and water as shown in section 4.5.1. It can be seen from the second anodic half reaction that ferrous hydroxide is formed from ferrous ions and hydroxide ion where water (condensate) is present. 

The soluble copper ammonia ion passes through the condensate system and plates out as a cathode on steel surfaces in the deaerator, heaters, economizer, and the boiler itself. A secondary galvanic corrosion process is initiated that damages the surrounding steel by forming ferrous hydroxide and releasing copper and ammonia. The ammonia carries over into the steam, and the entire corrosion process repeats itself. 

In practice, aeration towers using coke or volcanic lava tend not to be as efficient as spray ponds in facilitating the precipitation of ferrous hydroxide consequently, there is usually a requirement for a cationic flocculant to aid the precipitation of the insoluble materials into a larger floe or denser sludge that can be removed by clarification or sand filtration. 

Copperas [green vitriol or ferrous sulfate (FeS04 7H20)] was also employed as an external coagulant (at pH values of approximately 7.7). It forms a turbid precipitate, and when oxygen is present (as is usual), a slimy precipitate of ferrous hydroxide also may form in addition to ferric hydroxide ... 

NOTE It is also apparent that the ferric ion (Fe3+) should chelate most readily. In practice, however, under strongly alkaline conditions, the preferred reaction is to instantaneously form ferrous hydroxide and then to slowly revert to ferric hydroxide (competing anion effect). 

Depending on the condensate temperature and level of oxygen infiltration, other reactions may occur. For example, hot condensate in the absence of oxygen produces ferrous hydroxide. 

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