Potassium Iodide-Phosphoric Acid Method

This is a surface treatment process based on the oxidation of the steel to produce a continuous epsilon oxide (Fc203). It is reported to give strong durable bonds and to improve the salt-spray and humidity resistance of polymer-coated steel. The steps are 

Alkaline clean in a solution containing 3% trisodium phosphate and 3% sodium carbonate for 5 min at 82 °C 

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Schnepfe [83] has described yet another procedure for the determination of iodate and total iodine in seawater. To determine total iodine 1 ml of 1% aqueous sulfamic acid is added to 10 ml seawater which, if necessary, is filtered and then adjusted to a pH of less than 2.0. After 15 min, 1 ml sodium hydroxide (0.1 M) and 0.5 ml potassium permanganate (0.1M) are added and the mixture heated on a steam bath for one hour. The cooled solution is filtered and the residue washed. The filtrate and washings are diluted to 16 ml and 1ml of a phosphate solution (0.25 M) added (containing 0.3 xg iodine as iodate per ml) at 0 °C. Then 0.7 ml ferrous chloride (0.1 M) in 0.2% v/v sulfuric acid, 5 ml aqueous sulfuric acid (10%) - phosphoric acid (1 1) are added at 0 °C followed by 2 ml starch-cadmium iodide reagent. The solution is diluted to 25 ml and after 10-15 min the extinction of the starch-iodine complex is measured in a -5 cm cell. To determine iodate the same procedure is followed as is described previously except that the oxidation stage with sodium hydroxide - potassium permanganate is omitted and only 0.2 ml ferrous chloride solution is added. A potassium iodate standard was used in both methods. 

This method of integration was used by W. Hederlin (Zeit. phys. Chem., 41, 565, 1902) in his study of the reaction between phosphorous acid, potassium iodide, and potassium persulphate and by R. Wegscheider (Zeit. phys. Chem., 41, 52, 1902) for the saponification of the sulphonic esters. 

Sulfuric and phosphoric acid concentrations up to 70% can be inhibited by methods similar to those used for hydrochloric acid. Concentrations of sulfuric acid higher than 70% are strongly oxidizing, attack steel slowly, and do not require inhibition. Fertilizer-grade phosphoric acid (73% black acid) attacks steel readily and usually is inhibited with potassium iodide. Organic inhibitors are not effective... 

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