GB344404A - Improvements in or relating to processes for preventing the solution of metals in acids - Google Patents

Abstract

The action of acid on metal is inhibited by the addition of an insoluble controlling agent which is introduced into the acid bath in a state of fine subdivision. A condensation product of ammonia or an amine with an aldehyde, e.g. anhydroformaldehyde-aniline, or a derivative of thiocarbonic acid, e.g. thiourea or ortho-, meta-, or para-ditolylthiourea, constitutes a suitable inhibitor which may be mixed with a buoying agent such as evaporated cellulose pulp waste liquor, starch, flour or clay. The inhibitor, with or without the buoying agent, may be ground to a finely divided state before it is added to the bath or it may be dissolved in a solvent miscible with the acid of the bath, e.g. in concentrated sulphuric acid, acetone, alcohol or ether, in which case it is precipitated in a state of fine subdivision on addition of the solution to the bath. Alternatively briquettes of the finely divided inhibitor and a filling agent such as sodium chloride, Glauber's salt or sugar with or without a buoying agent may be added to the acid bath. Reference has been directed by the Comptroller to Specifications 259,200 and 287,911, [both in Class 1 (ii), Inorganic compounds, other than &c.]ALSO:The action of acid on metal, particularly in pickling baths, is inhibited by the addition of an insoluble controlling agent which is introduced into the bath in a state of fine subdivision. A condensation product of ammonia or an amine with an aldehyde, e.g. anhydroformaldehyde-aniline, or a derivative of thiocarbonic acid, e.g. thiourea or ortho-, meta-, or paraditolylthiourea constitutes a suitable inhibitor which may be mixed with a buoying agent such as evaporated cellulose pulp waste liquor, starch, flour or clay. The inhibitor, with or without the buoying agent, may be ground to a finely divided state before it is added to the bath or it may be dissolved in a solvent miscible with the acid of the bath, e.g. in concentrated sulphuric acid, acetone, alcohol or ether, in which case it is precipitated in a state of fine subdivision on addition of the solution to the bath. Alternatively briquettes of the finely divided inhibitor and a filling agent such as sodium chloride, Glauber's salt or sugar with or without a buoying agent may be added to the acid bath. Reference has been directed by the Comptroller to Specifications 259,200 and 287,911, [both in Class 82 (ii), Washing granular &c.].