System Overview

The following figure shows the block diagram for a Critical Pitting Temperature system that uses a TDC4 Temperature Controller. This figure is the basis of the following discussion.

A Gamry Instruments' Potentiostat/Galvanostat/ZRA (the system potentiostat) is connected to the host computer via USB. The system potentiostat's cell connector is attached directly to the electrochemical cell under test. You can use various cell designs. Gamry's Flex Cell Kit is a particularly useful cell because its unique design avoids the crevices found in other cell designs. This permits pitting to be studied without complications from crevice corrosion.

The temperature of the electrochemical cell is controlled by the TDC4 Temperature Controller. The TDC4 is a PID-controller able to maintain the cell's temperature to within 1°C. The cell temperature set points are all controlled via the RS-232/USB communications, which connect the TDC4 directly to the computers.

The cell temperature is measured by the TDC4 using a platinum RTD. The TDC4 sends the temperature to the computer. The system always checks that the requested temperature is reached before it takes a measurement. This closed-loop control allows experiments to be performed as rapidly as possible, without temperature errors.

In the above figure, a cartridge heater directly heats the cell. The TDC4 can also control a recirculating bath. The advantage of the bath is that it allows experiments to run below room temperature.

The Critical Pitting Test software runs in the system computer. It automates the control and data-acquisition process.