Chromium oxide, hydrous

Formula Cr(0H)3 3H20 MW 157.06 occurs only as hydrates Synonyms chromic hydroxide chromic oxide hydrous chromic oxide gel chromium hydrate chromic hydrate. 

Giacomelli, C.E. et al.. Some physicochemical properties of the chromium(III) hydrous oxide-aqueous solution interface, J. Colloid Interf. Sci., 169, 149, 1995. 

Chromic Hydroxide. Chromium hydroxide, chromic oxide gel chromic oxide, hydrous. CrH3Oj mol wt 103.03. Cr 50.48%. H 2-93%, O 46.59%. Cr(OH)j. Occurs only as hydrates. Prepn Ruthroff, Inorg. Syn. 2, 190 (1946) Hein, Herzog in Handbook of Preparative Inorganic Chemistry vol. 2, G- Brauer, Ed, (Academic Press, New York, 2nd ed- 1965) pp 1345-1346. 

Hydrous chromium oxide was precipitated from a 0.1 JV solution of chromic nitrate by the slow addition with stirring of 0.1 AT ammonia water. The filtered, washed gel was then slowly dehydrated in an atmosphere of hydrogen, the temperature being gradually raised over a period of weeks until dehydration was substantially complete. 

Surface complexation description of the dissolution of chromium(III) hydrous oxides by oxalic acid, Inorg. Chem. Vol. 36, 6423-6430, 0020-1669. 

Synonyms Chromic acid sol n. Chromic hydrate Chromic hydroxide Chromic (III) hydroxide Chromic oxide, hydrous Chromium hydrate Chromium hydroxide Chromium (3+) hydroxide Chromium tri hydroxide Empirical CrHaOs Formula Cr(OH)3... 

When sufficient hydroxide is added to an aqueous solution of the trivalent chromium ion, the precipitation of a hydrous chromium (ITT) oxide,... 

Cr2 03 - 112 0, of indefinite composition occurs. This compound is commonly misnamed as chromic or chromium (ITT) hydroxide [1308-14-1], Cr(OH)2. A tme hydroxide, chromium (ITT) hydroxide trihydrate [41646-40-6], Cr(OH)2 3H20, does exist and is prepared by the slow addition of alkaU hydroxide to a cold aqueous solution of hexaaquachromium(III) ion (40). The fresh precipitate is amphoteric and dissolves in acid or in excess of hydroxide to form the metastable Cr(OH). This ion decomposes upon heating to give the hydrous chromium (ITT) oxide. However, if the precipitate is allowed to age, it resists dissolution in excess hydroxide. 

Chromium (ITT) oxide, Cr203, may be prepared by heating the hydrous chromium (ITT) oxide to completely remove water, as the final product of the... 

Excess NaOH is used to start the reaction and not over 35% of the chromium is added as dichromate. At the end of the reaction, the thiosulfate is removed by filtration and recovered. The hydrous oxide slurry is then acidified to pH 3—4 and washed free of sodium salts. On calcination at 1200—1300°C, a fluffy pigment oxide is obtained, which may be densifted and strengthened by grinding. The shade can be varied by changes in the chromate dichromate ratio, and by additives. 

When produced by such dry methods it is frequently unreactive but, if precipitated as the hydrous oxide (or hydroxide ) from aqueous chromium(III) solutions it is amphoteric. It dissolves readily in aqueous acids to give an extensive cationic chemistry based on the [Cr(H20)6] ion, and in alkalis to produce complicated, extensively hydrolysed chromate(III) species ( chromites ). 

Gardner, W.K. Parbery, D.G. Barber, D.A. (1982) The acquisition of phosphorus by Lu-pinus albus L. I. Some characteristics of the soil/root interface. Plant Soil 68 19-32 Garg, A. Matijevic, E. (1988) Preparation and properties of uniform coated colloidal particles. II. Chromium hydrous oxide on hematite. Langmuir 4 38-44 Garg, A. Matijevic, E. (1988) Preparation and properties of uniform coated colloidal parti-... 

Fig. 1.1.8 Scanning electron micrographs (SEM) of (A) aluminum (hydrous) oxide particles. obtained by aging at 100°C for 72 h a solution containing I X 10-3 mol dm-3 A1(CI04)3 and 1 X 10-3 mol dm-3 AINHjfSO.,. (B) TEM of chromium (hydrous) oxide particles, obtained by aging at 75 C for 24 h a 4.0 X 10-4 mol dm-3 solution of CrK(S04)2.

Figure 1.1.8 illustrates the aluminum (39) and chromium (hydrous) oxide (55) particles prepared under conditions given in the legend. Some details of the mechanisms of formation for the chromium system are given in Section 1.1.3.2. 

Figure 1.1.20 shows the differential thermal analysis (DTA) data for the cores, of chromium hydrous oxides particles prepared in the absence of hematite, and of coated particles. It is obvious that the latter behave as the coating material, when alone. This example clearly indicates the possibility of having the surface site characteristics of chromium hydrous oxide induced onto ellipsoidal iron oxide particles. The latter morphology cannot be achieved by diiecl precipitation of the same chromium compound. 

Fig. 1.1.19 (A) TEM of ellipsoidal hematite (a-Fci03) particles and (B) of the same particles coated by chromium hydrous oxide obtained by aging at 85°C for 6 h 40 cm3 of a dispersion containing 30 mg dm-3 of the cores in the presence of 5.0 X 10-4 mol dm-3 chrome alum. (From Ref. 144.)...

Fig. 1.1.20 Differential thermal analysis data for chromium hydrous oxide, hematite, and hematite particles coated with chromium hydrous oxide. Data refer to dispersions as illustrated in Fig. 1.1.19.

The earliest expectations of cupferron being a selective and specific reagent for copper and iron only were not justified as the reagent has been found to precipitate, with the exception of aluminum and chromium,83 almost all the tri- to penta-valent metals which form insoluble hydrous oxides. However, the reagent has acquired permanent value as an aid in separating certain metals, e.g. titanium from aluminum and chromium.84... 

Both positively and negatively charged colloids have been prepared. The former results when the hydrated oxide is pejotised with chromic chloride, or may be formed by hydrolysis of the chloride or nitrate the latter is prepared by peptising the hydrous oxide with sodium or potassium hydroxide, or by adding sodium hydroxide to chromium nitrate solution in presence of arsenious acid and then dialysing. ... 

The name chromium(III) hydroxide, used here for convenience, is more properly hydrous chromium (III) oxide or hydrated chromium(III) oxide. ... 

Garg, A. and Matijevic, E. (1988) Preparation and properties of coated uniform colloidal particles. II. Chromium hydrous oxide on hematite. Langmuir 4 38-44. 

Unfortunately, many precipitates cannot be formed as crystals under practical laboratory conditions. A colloidal solid is generally encountered when a precipitate has such a low solubility that S in Equation 12-1 always remains negligible relative to Q. The relative supersaturation thus remains enormous throughout precipitate formation, and a colloidal suspension results. For example, under conditions feasible for an analysis, the hydrous oxides of iron(lll), aluminum, and chromium(III) and the sulfides of most heavy-metal ions form only as colloids because of their very low solubilities.- ... 

Chromium. So-called stainless steels contain in their alloys elements soeh as Cr, Ni, Co, and Mo) that eventually become incorporated into the passive oxide films. Cr(III), as shown by EXAFS studies with hydrous ferric acxie and goethite (18), forms inner-sphere surface complexes in the form of... 

ELECTRON SPIN RESONANCE SPECTROSCOPY Electron spin resonance (ESR) is a technique that can also be used on aqueous samples and has been used to study the adsorption of copper, manganese, and chromium on aluminum oxides and hydroxides. Copper(II) was found to adsorb specifically on amorphous alumina and microcrystalline gibbsite forming at least one Cu-O-Al bond (McBride, 1982 McBride et al., 1984). Manganese(II) adsorbed on amorphous aluminum hydroxide was present as a hydrated outer-sphere surface complex (Micera et al., 1986). Electron spin resonance combined with electron spin-echo experiments revealed that chromium(III) was adsorbed as an outer-sphere surface complex on hydrous alumina that gradually converted to an inner-sphere surface complex over 14 days of reaction time (Karthein et al., 1991). 

Crawford, R.J., Harding, LH., and Mainwaring, D.E., The zeta potential of iron and chromium hydrous oxides during adsorption and coprecipitation of aqueous heavy metals, J. Colloid Interf. Sci., 181, 561, 1996. 

Magaz, G.E. et al., Electrokinetic behaviour and interaction with oxalic acid of different hydrous chromium(in) oxides, Croat. Chem. Acta, 71, 917, 1998. 

Charlet, L., and A. Manceau. 1992. X-ray absorption spectroscopic study of the sorption of chromium(IH) at the oxide-water interface. II. Adsorption, coprecipitation, and surface precipitation on hydrous ferric oxide. J. Colloid Interf. Sci. 148 443-58. 

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