Chromium molybdate, method

For formation of anticorrosive and adhesion-improving protective layers on metals the cleaned surface is treated with aqueous acidic solution containing molybdate, chromium fluoride, phosphate, acetate, and Zn ions. As dispersant a mixture of 60% alkali salt of a phosphate ester, 20% alkylpolyglucoside, and 20% fatty alcohol ethoxylate was applied. This method passivates the metal surface by formation of an anticorrosive and protective layer that improves adhesion of subsequent coatings. 

Many of the finishes applied to other types of metal products can also be applied to zinc die castings, although some differences in formulation as well as occasional differences in method of application may be desirable. The types of finishes applicable to zinc die castings include mechanical finishes (buffed, polished, brushed, and tumbled) electrodeposited finishes (copper, nickel, chromium, brass, silver, and black nickel) chemical finishes (chromale, phosphate, molybdate and black nickel) and organic finishes (enamel, lacquer, paint and varnish, and plastic finishes). Electrodeposited coatings of virtually any metal capable of electrodeposition can be applied to zinc die castings. 

A simple and rapid method for the iodometric determination of microgram amounts of chromium(ni) in organic chelates is based on the oxidation of chromium(III) with periodate at pH 3.2, removal of the umeacted periodate by masking with molybdate and subsequent iodometric determination of the liberated iodate . Iodometric titration was also used for determination of the effective isoascorbate (see 2) concentration in fermentation processes . The content of calcium ascorbate can be determined with high sensitivity by complexometric titration with edta, which is superior to iodometry. The purity of /3 -diketonate complexes of Al, Ga, In and Ni was determined by complexometric titration with edta at pH 5.5-3, with RSD < 0.01 for determining 5-30% metal ion. Good analytical results were obtained by a similar procedure for the metal content of 15 lanthanide organic complexes. ... 

One other notable method has been used in the preparation of mixed transition metal molybdates, amongst many other oxide systems. This novel method(TT) involves preparation of the mixed metal oxides via an amorphous precursor such as a citrate salt of the appropriate metals, and then thermal decomposition of the complex to yield the resulting mixed oxides. The experimental procedures are described in four French patents(78-81), giving details of many different preparations including a proposed M0O3 rich, chromium doped iron molybdate, prepared as a possible selective oxidation catalyst. 

By far the most successful method of preparation was via an amorphous organic precursor to the required mixed molybdates, following the method of Delmon et al.(jrT). The method has proved successful for the pure iron, chromium and aluminum molybdates, and also for the mixed phases. A detailed outline of the method taking the example of FeCr(Mo0i )3 is as follows ... 

A very rapid oxidative disintegration of chromium-bearing minerals, rocks and alloys is obtained by fusing or sintering the finely pulverized material with potassium bifluoride (platinum spoon). Potassium chromate results and may be detected by means of the diphenylcarbazide reaction. The fluoride disintegration is particularly recommended for the detection of chromium in steels or special alloys, which are likely to contain molybdenum. The latter, in the form of molybdate ions, reacts with diphenylcarbazide to yield a red-violet color and thus impairs the test for chromium. However, the fluoride method yields no M0O4" ions, but instead complex [M0O3F2] ions, which do not react with diphenylcarbazide. 

One of the methods of preparing metal quinoxalinoporphinazines involves the thermolysis of quinoxaline 65a with dry manganese and chromium chlorides at 220 °C, which leads to 129 (R = R = R = R = H, X = Mn, CrCl) in 80-84% yields (1997RUP2074188,1996RUP2052464). Similarly, heating quinoxaline 65j with the acetates of zinc, cobalt, or copper at 220° C without any solvent, but in the presence of ammonium molybdate as a catalyst resulted in corresponding metal complexes of the macrocycles 129 (R = R = R = H, R = f-Bu, X = Zn, Co, Cu) in 57-74% yields (2008ZOB1214). 

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