Manganese Phosphates

A zinc phosphate solution tends to produce coatings more quickly than iron or manganese phosphate solutions, and dissociation of primary zinc phosphate proceeds rapidly through reaction 15.2 to 15.3 or directly to tertiary zinc phosphate via reaction 15.4. Even so, a processing time of 30 min is usual with the solution near boiling. 

Manganese phosphate coatings heated in the absence of air lose their corrosion resistance at between 200 and 218°C. At these temperatures, between 75 and 80% of the water of hydration is lost and it is assumed that this results in a volume decrease of the coating which causes voids and thereby lowers the corrosion resistance. Fig. 15.4 shows the loss of water of hydration from zinc, iron and iron-manganese phosphate coatings. 

Fig. 15.4 Effecl of heating on phosphate coatings for 16 h at various temperatures, showing loss of water of hydration. Curve A zinc phosphate, B iron phosphate and C iron manganese phosphate (courtesy y./.S./., 170, II (1952))...

C9H12N3OsP Mn 2.5 H20 Cytidine 5 -(manganese phosphate), hydrate MNCYTP 37 434... 

Manganese phosphate coatings are not used in coil coating operations because they are relatively slow in forming and, as such, are not amenable to the high production speeds of coil coaters. 

The magnetic susceptibility, measured with a vibrating sample magnetometer (Foner), calibrated with nickel (purity 99.99% — specific susceptibility at 293°K 55 cgs/g) at 293 0.2°K with a magnetic field of 17,700 G, is 101.39 0.20 10"6 cgs/g. This value may be compared with 101.65 0.20 10 6 cgs/g for manganese diphosphate prepared by thermal decomposition of the ammonium manganese phosphate. The value calculated from Reference 7 is 101.96 0.20 cgs/g. 

One of the best finishes for firearm steel is phosphatizing (Parkerizing) but few manufacturers offer this finish other than if required for military or police markets. The process deposits a crystalline layer of phosphates on the metal surface by immersion in a bath of iron, zinc, or manganese dioxide and phosphoric acid. Of these, a manganese phosphate finish is preferred for military use. 

Nitriding of steels is not in itself beneficial to bonded film performance, but Kawamura et al showed an interesting synergistic effect of soft nitriding and manganese phosphating on the wear life of a bonded molybdenum disulphide coating on an annealed steel. 

Recently, there has been reference in the literature has to further phosphate-based pigments, such as barium phosphate, manganese phosphate, lead phosphate, and chromium phosphate. Utilization of such products has been limited, due to economical aspects [5.71]. 

Manganese phosphates with an open framework are very scarce, but the chemistry of new phases in this area is emerging with some recent reports of organically-templated, layered manganese phosphates [82, 83] and a three-dimensional system with narrow channels, NH4MnP04, which orders ferro-magnetically at - 17 K [84]. 

Examples of this relatively rare approach, which was not covered in CHEC-I, include vapor-phase pyrolysis of the dioxanedione (396) over alumina or manganese phosphate/carbon which... 

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