Page 25 - PCMI Summer Journal 2021

The Chemistry and Control of Etching Ferrous Metals with Ferric Chloride Solutions: The Concept of a Constant Etchant Pool Presented by: David M. Allen, Emeritus Professor of Microengineering, Cranfield University, UK
monitoring methods are recommended (Figure 6), it should be noted that manual titration analyis is a necessary back-up and a calibration and reliability check on the automated methods. This is necessary because probes need to be checked periodically over extended periods of use as they can lead to the logging of incorrect data if electrical or electronic faults develop with time due to the aggressive chemical environments in which they are immersed or the probe becomes coated with non-conductive deposits.
Figure 5. Average conductivity v. % HCl (by weight) of virgin ferric chloride solutions (based on readings taken over a 7-day period at 21 ± 1°C) [2].
Figure 6. Application of free HCl monitoring and control.
Issue 137 August 2021 PCMI Journal 25