GB1244675A - Improvements in redox coulometers - Google Patents

Abstract

1,244,675. Electrolytic meters. GENERAL ELECTRIC CO. July 28, 1969 [July 29, 1968], No.37741/69. Heading G1Q. A redox coulometer for use in timing applications is of the type providing a sudden change in voltage in a constant current circuit when a given quantity of current has passed through it and operates without the normal difficulties due to gas evolution or the deposition of particular amounts of solid material. The coulometer incorporates a container defining a chamber which is divided into two parts by an ion exchange membrane, each containing an electrolytic solution containing a redex couple. The membrane is impervious to the redex couple. A chemically inert electrode is positioned in contact with the solution in each part. A conductive lead contacts each electrode. The container is formed from two parts 13, 14 fitted together to define the chamber 12. This is divided in two by an ion exchange membrane 27 of sulphonated polystyrene, and each part contains a supporting electrolyte of 0À5M Na2 HPO4 and 0À5M KH2 PO4 containing a potassium ferrocyanide-ferricyanide redox couple. The inert electrodes 31 may be porous carbon or pyrolytic graphite, with platinum leads 23. As a constant current is passed through the coulometer, the ratio of oxidized to reduced material in each part varies, and the potential across the unit varies. If one of the oxidized or reduced materials is in limited supply, a large change in potential will occur when it disappears and this change can be used to trigger an external circuit, to indicate the conclusion of a timed period and initiate a reversed direction of current flow through the cell, to start a reset period. The reset period may be made different to the timing period by changing the current supplied.