Chromium oxyhydroxide

X-ray photoelectron spectroscopic study of the spontaneously passive amorphous Fe-10Cr-13P-7C alloy in 1 N HCl revealed that the passive film consists of Cr, 0 , OH" and HjO, and hence the passive film has been called a passive hydrated chromium oxyhydroxide film (CrO (OH)j Subsequent investigations have revealed that... 

The effect of metalloids on the corrosion resistance of alloys also varies with the stability of polyoxyanions contained in their films. Phosphorus and carbon contained in iron-chromium-melalloid alloys do not produce passive films of phosphate and carbonate in strong acids, and so do not interfere with the formation of the passive hydrated chromium oxyhydroxide... 

Ebbinghaus B.B. (1993) Thermodynamics of gas phase chromium species the chromium oxides, the chromium oxyhydroxides, and volatility calculations in waste incineration processes. Combust. Flame,93, 119-137. 

In contrast, boron-containing alloys require the addition of large amounts of chromium to increase the passivating ability by concentrating the chromium oxyhydroxide in the surface films because the films contain chromium borate . ... 

Figure 3.16 Possible rcacfion mecimnism for ilie formation of chromium oxyhydroxide a-CrOOH and hydroxides M(OH)j of brucile structure...

The passive films formed by the addition of sufficient amounts of valve metals to amorphous nickel-valve-metal alloys are exclusively composed of valve-metal oxyhydroxides or oxides such as TaOjCOH) , Nb02(OH) or TajO,. Consequently, amorphous alloys containing strongly passivating elements, such as chromium, niobium and tantalum, have a very high ability... 

For removing low levels of priority metal pollutants from wastewater, using ferric chloride has been shown to be an effective and economical method [41]. The ferric salt forms iron oxyhydroxide, an amorphous precipitate in the wastewater. Pollutants are adsorbed onto and trapped within this precipitate, which is then settled out, leaving a clear effluent. The equipment is identical to that for metal hydroxide precipitation. Trace elements such as arsenic, selenium, chromium, cadmium, and lead can be removed by this method at varying pH values. Alternative methods of metals removal include ion exchange, oxidation or reduction, reverse osmosis, and activated carbon. 

Peterson, M.L. Brown Jr., G.E. Parks, G.A. (1997) Quantitative determination of chromium valence in environmental samples using XAFS spectroscopy. In Voigt, J.A. Bunker, B.C. Casey,W.H. Wood,T.E. Crossey, L.J. (eds.) Aqueous chemistry and geochemistry of oxides, oxyhydroxides, and related materials. Materials Research Society, Pittsburgh... 

Chemical passivity corresponds to the state where the metal surface is stable or substantially unchanged in a solution with which it has a thermodynamic tendency to react. The surface of a metal or alloy in aqueous or organic solvent is protected from corrosion by a thin film (1—4 nm), compact, and adherent oxide or oxyhydroxide. The metallic surface is characterized by a low corrosion rate and a more noble potential. Aluminum, magnesium, chromium and stainless steels passivate on exposure to natural or certain corrosive media and are used because of their active-passive behavior. Stainless steels are excellent examples and are widely used because of their stable passive films in numerous natural and industrial media.6... 

Nanoparticles of iron and aluminum oxides and oxyhydroxides transport both organic and inorganic contaminants in the environment. The systematics developed here may be applied to understanding such natural nanocomposites. For example, it may be possible to treat coating of amorphous uranium or chromium oxides on nanophase (Fe, Al)OOH particles as a mixture of nanophase end-members from the point of view of energetics. 

Pechenyuk, S.L et al.. Sorption properties of chromium(ni) amorphous oxyhydroxides, Colloids Surf. A, 144,43, 1998. 

Chromium is known to have a strong tendency to form oxyhydroxide compounds, and the presence of chromium in the passive film on Fe-Cr alloys is thought to ensure a somewhat hydrated structure for the oxide [107]. In fact, there have been suggestions that bound water is present in the film, and this helps to facilitate film repair after film breakdown [108] and thus helps Fe-Cr alloys to resist pitting corrosion. The bound water model is still, however, not generally accepted and remains the subject of some speculation. 

Under stronger alkalinization, chromium forms a series of increasingly condensed polycations [3], and then a hydrated hydroxide gel Cr(OH)3(bH2)3 [4]. Different behavior is observed for iron(lll) and aluminum(lll). Aluminum forms the stable hydroxide AlfOH), (gibbsite, bayerite) [5], whereas the Fe(OH)3 hydroxide has never been identified- It transforms very rapidly to an oxyhydroxide through spontaneous dehydration [6j. 

In spite of the structural similarities between their oxides M2O3 and oxyhydroxides MOOH [I2a,b], chromium, iron and aluminum exhibit very different behaviors in solution. 

The difficulties in synthesizing the mixed spinel seem related to both thermodynamic and kinetic issues. Hydroxides (and/or basic salts) of divalent elements are more stable than the ferrite at low temperatures. The large reactivity difference between iron and chromium explains the rapid crystallization of iron oxides or oxyhydroxides compared with the chromium compounds, as well as the segregation of both elements. 

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