Ferric chromates, basic

Numerous basic double ferric chromates have been prepared,8 namely —... 

Chemical shifts for iron(III) chromate, basic chromate, and arsenate have been reported [121]. Ferric phosphate, FeP04, is like Fe2(S04)3 in that it is partially converted to an Fe species by applicatidn of high pressure [9]. Typical spectra are shown in Fig. 6.22. Iron(III) dichromate, Fe2(Cr207)3, is also converted to an Fe " " species by pressure. 

Persian red inorg chem Red pigment made from basic lead chromate or ferric oxide. por-zhon red ... 

Ferrous chromate does not appear to be capable of existing. When solutions of ferrous sulphate and chromic acid, or its alkali salts, are mixed at low temperatures, the iron is oxidised, basic ferric sulphates resulting, the chromium being correspondingly reduced. If the ferrous sulphate is in excess, ferroso-ferric sulphate results. 

Ferric oxide Pigment green 8 Ultramarine blue Wollastonite pigment, ceramic coatings Lead chromate pigment, ceramic glazes Cadmium Cadmium sulfide Lead carbonate basic... 

This evidence of the uptake of inhibitive anions into oxide films forms the basis of the chemical or pore plugging theory of inhibition, associated originally with Evans etal. In this theory the rdle of the inhibitive anion is to promote the repair of weak points or pores in the oxide film, where corrosion has started, by reacting with dissolving iron cations to form insoluble products of separate phase, which plug the gaps. These insoluble products may contain the inhibitive anion either as a salt, e.g. phosphate, or a basic salt, e.g. azeiate , or as an insoluble oxide, e.g. CrjOj from chromate Precipitation of such solid products is favoured if the pH in the region of the pores does not become acid. Thus, on the basis of this theory, inhibition by anions such as phosphate, borate, silicate and carbonate, is enhanced by their buffer properties which serve to prevent a fall in pH in the anodic areas. Since ferric salts are usually more insoluble than... 

Perrit. A support, made of heat-resisting alloy, designed to carry vitreous enamel-ware through an enamelling furnace. Persian Blue. See Egyptian blue. Persian Red. Pigments of ferric oxide and basic lead chromate. 

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