US EPA

6664868 

Journal Article 

Thermionic determination of hydrofluoric acid in the pickling baths 

Macor, B; Gilberti, L; Piccinini, S 

1970 

752-758 

INSPEC:289980 

Austenitic stainless steels, after annealing and solution- heat treatment, are pickled using an acid bath, which is formed by the classic nitre-hydrofluoric mixture. As the activity of the bath is in function of the temperature, of the nitric and hydrofluoric acid concentration and of the content of dissolved substances it is indispensable to determine at any time and as soon as possible, the value of those parameters. All pickling lines are arranged to determine, at regular intervals, the total bath acidity and the content of substances in solution. To determine the percentage content of nitric and hydrofluoric acid samples are sent to the chemical laboratory. This method, however, causes rather complicate manual operations, which are difficult to carry on in the shops. The problem has been finally solved in a quiet satisfactory way by means of the thermometric analysis, measuring the rising of temperature, which in controlled and reproducible conditions, is caused by the heat arising during the chemical change: 6HF+SiO2=H2SiF6+2H2O In order to carry out this method by the pickling lines, where it is impossible to make use of precision thermometers and thermostats, a special electronic instrument has been planned and built with particular basis specifications.