Iron oxide or hydroxide

Oxygen Tubercles. Similar to crevice attack, it is encouraged by the deposit of a layer, semipermeable to oxygen (porous layer of iron oxide or hydroxide). 

Acid Pickling This process is widely used for removing rust and millscale from steel, or for removing internal scales from boilers. The objective of the process is the dissolution of iron oxides or hydroxides or hardness scales, but at the same time the iron will also tend to corrode in the acid, with hydrogen... 

Not all iron oxides are available for reduction. Some iron minerals are solid crystals or even entire iron grains, which makes them resistant to microbial reduction (Lovley, 1991 Postma, 1993 Heron et al., 1994b). Other iron oxides or hydroxides are amorphous and readily reducible. Over time, even some crystalline minerals such as goethite and hematite may be reduced in the complex environment in leachate (Heron and Christensen, 1995). This indicates that the importance of iron as a redox buffer controlling the size of plumes is not given just by the amount of iron oxides present. The composition and microbial availability of iron for reduction are key parameters. Methods for the actual quantification of the microbial iron reduction capacity have, however, not been developed. 

The raw material for the manufacture of aluminum hydroxide is bauxite, a mineral with ca. 45 to 60% AI2O3 in the form of hydrargillite (gibbsite), bdhmite and diaspore with iron oxides or hydroxides, silica (as kaolinite) and titanium dioxide as minor constituents. The largest deposits are to be found in Africa and Australia. 

We have completed experiments label the ionic domains. We have found evidence of a precipitation phenomenon of particles of iron oxide or hydroxide when an iron form of membrane was exchanged by different other ions like K+, Na+, etc. We therefore have analyzed these particles by different techniques -like X rays, Mossbauer spectroscopy, magnetic measurements and electron microscopy- with two goals in mind. First of all the formation of ultra thin particles is very important in different domains and especially in catalysis when these membranes are used in the solid polymer electrolyte process. Second, we expect some correlation between the sizes and distribution of precipitates with the starting ionic domains. 

Oxidized root channels have been observed for few species, including rice (0. saliva), cattails, reeds, Spartina sp., Carex sp., and Potomogeton sp. (see review by Mendelssohn et al., 1995). The iron-em-iched plaques essentially consist of FeOOH minerals (Bacha and Hossner, 1977). Iron plaque may be amorphous or crystalline, in the forms of iron such as ferric hydroxides, goethite, lepidocrocite, and siderite. Iron oxides or hydroxides in rhizosphere have high affinity for metals and metalloids. 

As has already been pointed out on page 10, colloids can be divided into the two classes, reversible and irreversible, depending upon whether or not they leave a soluble residue on evaporation. The irreversible can be still further divided into two groups. 1. To the first class belong those that coagulate in dilute solution, and precipitate in the form of a powder rather than a jelly. Examples of these are the colloidal metals in a pure state (colloidal metals that are not rendered impure by the presence of any other colloid). 2. The second class consists of those that may be considerably concentrated before coagulation sets in and whose precipitates are decidedly jelly-like, such as colloidal silicic acid, stannic acid, clay, iron oxide or hydroxide. 

Paramagnetic fractions produce quadrupole doublets (QS) in the spectrum. Their parameters are close to those of hydroxides (e.g., lepidocrocite, y-FeOOH) or to small superparamagnetic particles of iron oxides or hydroxides with a mean diameter of about 10 nm. It should be noted that it is not difficult to distinguish among different magnetically ordered phases when they are present in a well-ordered crys-... 

Chloride ions in the pore solution, having the same charge as OH ions, compete with these anions to combine with the Fe + cations. The resulting iron chloride complexes are thought to be soluble (unstable) therefore, further metal dissolution is not prevented, and ultimately the buildup of voluminous corrosion products takes place. Chloride ions also tend to be released from the unstable iron chloride complexes, making these harmful ions available for further reaction with the reinforcing steel. As the iron ultimately precipitates out in the form of iron oxide or hydroxide corrosion products, it can be argued that the consumption of hydroxide ions leads to localized pH reduction and therefore enhanced metal dissolution. 

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