Abstract: In the invention pickling process, steel and nickel or chromium alloys are pickled with an acidic pickling solution employing an oxidant, particularly hydrogen peroxide, and in which liquor is recirculated through inlets comprising a nozzle feeding liquor into a diffuser such that liquor is withdrawn from the bath and the volume of liquor flowing through the diffuser is a multiple of flow through the nozzle. Steel or the alloys are pickled with an acidic solution containing iron and free hydrogen peroxide at a concentration of up to 0.1 gpl. The process can operate effectively at a free fluoride concentration of from 20 to 30 gpl and a sulphuric acid concentration of from 80 to 110 gpl. The lifetime of the bath before it needs to be replaced can be lengthened by the process compared with using an air agitation system.

Abstract: In the invention pickling process, steel and nickel or chromium alloys are pickled with an acidic pickling solution employing an oxidant, particularly hydrogen peroxide, and in which liquor is recirculated through inlets comprising a nozzle feeding liquor into a diffuser such that liquor is withdrawn from the bath and the volume of liquor flowing through the diffuser is a multiple of flow through the nozzle. Steel or the alloys are pickled with an acidic solution containing iron and free hydrogen peroxide at a concentration of up to 0.1 gpl. The process can operate effectively at a free fluoride concentration of from 20 to 30 gpl and a sulphuric acid concentration of from 80 to 110 gpl. The lifetime of the bath before it needs to be replaced can be lengthened by the process compared with using an air agitation system.

Abstract: Aqueous acidic solutions of hydrogen peroxide used for metal surface treatments suffer from an increased decomposition rate of the hydrogen peroxide, caused by the dissolved metals such as iron, copper or titanium. A method is provided wherein stabilization can be achieved by employing a combination of a) a hydroxybenzoic acid, preferably p-hydroxybenzoic acid; b) a hydrotropic sulphonic acid, preferably p-toluene sulphonic acid; and c) a hydrophobic alkaryl sulphonic acid, preferably dodecylbenzene sulphonic acid.

Abstract: Aqueous acidic solutions of hydrogen peroxide used for metal surface treatments suffer from an increased decomposition rate of the hydrogen peroxide, caused by the dissolution of metals such as iron, copper, or titanium. Stabilization can be achieved by employing a combination of a) hydroxybenzoic acid, preferably p-hydroxybenzoic acid; b) a hydrotropic sulphonic acid, preferably p-toluene sulphonic acid; and c) a hydrophobic alkaryl sulphonic acid, preferably dodecylbenzene sulphonic acid.

Abstract: Production of peroxomonosulphuric acid (Caro's acid) by reaction between concentrated hydrogen peroxide and sulphuric acid solutions can be impaired substantially when substoichiometric amounts of sulphuric acid are employed.The problem is ameliorated or removed by first forming a body of sulphuric acid-rich fluid (usually the smaller volume) and thereafter introducing into that body of fluid the hydrogen peroxide solution (usually the larger volume). The reaction mixture progressively becomes sulphuric acid-lean. The body of fluid is advantageously either concentrated sulphuric acid itself, or a premix formed by reaction between hydrogen peroxide and at least an equimolar amount of sulphuric acid. The process is particularly suitable for making Caro's acid when from 0.02 to 0.5 moles of sulphuric acid is employed per mole of hydrogen peroxide.