Hydrochloric acid solvent systems are widely employed by the metalworking and chemical cleaning industries. Inhibitors are generally added to these liquors to minimize pitting and dissolution of the base metal as the acid digests oxidation products or other undesirable mineral deposits on the surface. The chemist concerned with optimizing inhibitor formulations will often evaluate the performance of a combination of ingredients. Occasionally an inhibitor combination will demonstrate an improvement known as synergism. (Syn∙er. gism: joint action of discrete agencies in which the aggregate effect is greater than the sum of their effects when acting independently. Merriam-Webster) To illustrate, if ingredient A) is mixed with ingredient B) in equal proportions, and the singular performance value of A) is designated A and the singular performance value of B) is designated B, then the combination is synergistic if their composite performance exceeds (A/2 + B/2) per equivalent concentration in a given system. The experimentation which follows is directed toward explaining empirically the nature of the synergism evidenced. Although the test conditions employed closely simulate those encountered in the practice of continuous steel strip descaling, the observations made and the concepts rendered have greater scope.
