mylius thermometric technique. A review of a simple corrosion testing method of wide potentialities

ABSTRACT

Mylius' thermometric technique was developed in 1922 to assess the corrodability of aluminium alloys. Strips of the metals were made to react with known volumes of HCI solutions and the variation of the temperature of the system was followed with time. Following an induction period, the temperature rose to reach a maximum value. The corrodability of the metal was expressed in terms of the integral rate of temperature rise per minute. The Mylius test attracted little attention for almost 40 years. It was revived in the author's laboratory, where it was proposed as a rapid method for evaluating corrosion inhibitors. Since then, the technique underwent rapid development and wide expansion. It was applied to study the dissolution of zinc, iron, copper, nickel, tin and lead in a variety of attacking media. Equi-molar solutions of strong mineral acids do not attack metals to the same extent and this was attributed to anion adsorption on the metal surface. The abnormally high dissolution rate of metals in HNO[3] solutions was attributed to an auto-catalytic process involving the formation of HNO[2]. Substances known to destroy HNO[2] reduced corrosion. The Mylius thermometric technique was successfully applied to study the dissolution of a number of copper-base alloys, and its suitability for the determination of the thickness of zinc and tin coats on the surface of steel was proven. The method proved also to be of value in the study of galvanic [bimetallic] corrosion. The chemical oxidation of organic compounds is mostly an exothermic reaction. Here, too, the Mylius technique proved to be instrumental in elucidating the kinetics of the process. Only two examples are found in the literature describing this type of studies. The field is, however, wide open to examine other types of reaction. The dissolution of iron under conditions of the reaction Fe + 2Fe[3+] = 3Fe[2+] was studied in detail by the Mylius technique, and the results were confirmed potentiometrically and gravimetrically. The above reaction is both thermodynamically and kinetically more feasible than the discharge of protons from acid solutions. Mathematical treatment of the results allowed the conversion of the thermometric data into calorimetric ones, thus allowing thermodynamical computations to be carried out. Finally, suggestions are presented for the automation and computerization of the technique, which allow the simulation compensation of heat losses during measurements