Complex chromic

Oxalato-diethylenediamino- Diehloro-dietliyfenediamino- Dibromo-diethylcncdianiino-chromic complex. chromic complex. chromic complex . 

The best electrodeposits of chromium are obtained from solutions of chromic acid containing small amounts of certain anions, particularly the sulfate ion. There is little doubt that the nature of the deposit is influenced by the formation of a complex chromic chromate diaphragm on the cathode. The function of the anion appears to be to affect the nature of this diaphragm in such a manner so that it does not block the cathode completely it thus does not prevent access of ions, yet it is suflftciently adherent to interfere with the growth of crystal nuclei. 

Actually we should expect Beer s law to be valid for dilute solutions since, on the basis of modern views, strong electrolytes are completely dissociated. As early as 1909, N. Bjerbum had concluded from the behavior of complex chromic salt solutions that these salts dissociated completely into ions. 

Chromic acid strontium salt Chromic acid strontium salt (1 1). See Strontium chromate Chromic acid, zinc salt. See Zinc chromate Chromic anhydride. See Chromium trioxide Chromic chloride. See Chromium chloride (ic) Chromic chloride stearate. See Stearatochromium chloride complex Chromic fluoride. See Chromium fluoride (ic) Chromic hydrate Chromic hydroxide Chromic (III) hydroxide. See Chromium hydroxide (ic) Chromic nitrate. See Chromium nitrate Chromic oxide. See Chromium oxide (ic) Chromic oxide hydrated. See Chromium hydroxide green... 

Chromium(IH) chloride, chromic chloride, CrClj. Violet solid (Cr plus CI2, hydrate plus SOCI2) only soluble in water in presence of Cr. Forms many complexes including the hydrates [Cr(H20)6]Cl3 - violet, [Cr(H20)jCl]Cl2,H20 - green, [Cr(H20)4Cl2]Cl,2H20 - green. 

Sihcone products dominate the pressure-sensitive adhesive release paper market, but other materials such as Quilon (E.I. du Pont de Nemours Co., Inc.), a Werner-type chromium complex, stearato chromic chloride [12768-56-8] are also used. Various base papers are used, including polyethylene-coated kraft as well as polymer substrates such as polyethylene or polyester film. Sihcone coatings that cross-link to form a film and also bond to the cellulose are used in various forms, such as solvent and solventless dispersions and emulsions. Technical requirements for the coated papers include good release, no contamination of the adhesive being protected, no blocking in roUs, good solvent holdout with respect to adhesives appHed from solvent, and good thermal and dimensional stabiUty (see Silicon COMPOUNDS, silicones). 

Chromic Acid Electrolysis. Alternatively, as shown in Figure 1, chromium metal may be produced electrolyticaUy or pyrometaUurgicaUy from chromic acid, CrO, obtained from sodium dichromate by any of several processes. Small amounts of an ionic catalyst, specifically sulfate, chloride, or fluoride, are essential to the electrolytic production of chromium. Fluoride and complex fluoride catalyzed baths have become especially important in recent years. The cell conditions for the chromic acid process are given in Table 7. 

In 1979, a viable theory to explain the mechanism of chromium electroplating from chromic acid baths was developed (176). An initial layer of polychromates, mainly HCr3 0 Q, is formed contiguous to the outer boundary of the cathode s Helmholtz double layer. Electrons move across the Helmholtz layer by quantum mechanical tunneling to the end groups of the polychromate oriented in the direction of the double layer. Cr(VI) is reduced to Cr(III) in one-electron steps and a colloidal film of chromic dichromate is produced. Chromous dichromate is formed in the film by the same tunneling mechanism, and the Cr(II) forms a complex with sulfate. Bright chromium deposits are obtained from this complex. 

Chromia—alumina catalysts are prepared by impregnating T-alumina shapes with a solution of chromic acid, ammonium dichromate, or chromic nitrate, followed by gentie calciaation. Ziac and copper chromites are prepared by coprecipitation and ignition, or by thermal decomposition of ziac or copper chromates, or organic amine complexes thereof. Many catalysts have spiael-like stmctures (239—242). 

Similar behavior can be observed even in the case of substituted quinuclideines 170). Neostrychnine (68) serves as an example of more complex compounds which show spectra differing from those of other enamines. The ultraviolet spectrum of this compound exhibits no batho-chromic shift and its basicity is considerably decreased 159,171,172) (pK in methylcellosolve at 20° is 3.8, whereas the analogous saturated compound has a pK under the same conditions of 7.45, and a compound with the double bond further removed, strychnine, has a pK of 7.37). As another example, the ultraviolet spectrum of trimethyl conkurchine (69) shows the same absorption maxima as a saturated tertiary amine (A in ether, about 213 m/i). 

The theoretical aspects of molybdenum s corrosion behaviour are complex and there is as yet no clear cut, generally applicable picture. There are, however, a large number of literature references which include data on polarisation, passivation and potential of molybdenum under widely assorted conditions. The electrode potential of molybdenum depends on its surface condition. For example, some tests showed an of -t-0-66V when the molybdenum was passivated by treatment with concentrated chromic acid and —0-74 V after activation by cathodic treatment in sodium hydroxide. 

The reactions which take place when the mixed etch primer is applied to a metal are complex. Part of the phosphoric acid reacts with the zinc tetroxychromate pigment to form chromic acid, zinc phospliates and zinc chromates of lower basicity. The phosphoric acid also attacks the metal surface and forms on it a thin chromate-sealed phosphate film. Chromic acid is reduced by the alcohols in the presence of phosphoric acid to form chromium phosphate and aldehydes. It is believed that part of the chromium phosphate then reacts with the resin to form an insoluble complex. Excess zinc tetroxy chromate, and perhaps some more soluble less basic zinc chromes, remain to function as normal chromate pigments, i.e. to impart chromate to water penetrating the film during exposure. Although the primer film is hard... 

As an example of the problem of species in solution, consider the case of a solution made by dissolving some potassium chrome alum, KCrfSO s-12H20, in water. On testing, the solution is distinctly acidic. A currently accepted explanation of the observed acidity is based upon the assumption that, in water solution, chromic ion is associated with six H20 molecules in the complex ion, Cr(H20) a. This complex ion can act as a weak acid, dissociating to give a proton (or hydronium ion). Schematically, the dissociation can be represented as the transfer of a proton from one water molecule in the Cr(H20) 3 complex to a neighboring H20 to form a hydronium ion, H30+. Note that removal of a proton from an H20 bound to a Cr+3 leaves an OH- group at that position. The reaction is reversible and comes to equilibrium ... 

The stability of sexivalent chromium, in the chromate ion and related ions, can also be understood. The chromic complexes, involving tervalent chromium, make use of d2sp3 bond orbitals, the three remaining outer electrons of the chromium atom being in three of the 3d orbitals, with parallel spins. The resonance energy of these three atomic electrons in a quartet state helps to stabilise the chromic compounds. However, if all of the nine outer orbitals of the chromium atom were available for bond formation, stable compounds might also be expected... 

When ceric ions were substituted for chromic acid, the reaction was still zero-order with respect to metal ion, the rate of reduction of which was unchanged. The mechanism favoured by the authors depends on formation of a complex of silver ions and hydrogen, viz. 

The kinetics of the oxidation of phenylphosphonous acid (132) to phenylphosphonic acid by chromic oxide have been investigated." The reaction, which is first order in Cr, is catalysed by both acid and pyridine and the mechanism suggested involves the initial formation of a complex between chromic acid and the tervalent form of the starting acid. Ratedetermining decomposition of this complex is followed by rapid oxidation by Cr. ... 

Chromium(III) is a commonly-used crosslinker for preparing profile control gels with polymers having carboxylate and amide functionalities (la,b). Cr(III) is applied in many forms. For example, it can be used in the form of simple chromic salts of chloride and sulfate, or as complexed Cr(III) used in leather tanning (2), or as in situ generated Cr(III) from the redox reaction of dichromate and bisulfite or thiourea. The gelation rate and gel quality depend on which form of Cr(III) is used. 

Metal Complexes as Dyes for Optical Data Storage and Electro chromic Materials... 

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