GB1200238A - Method of, and apparatus for, controlling the process of electrolytically thinning metal plates - Google Patents

Abstract

1,200,238. Electrolytic thinning. COMPAGNIE GENERALE D'ELECTRICITE. March 27, 1968 [March 28, 1967], No.14816/68. Heading C7B. An electrolytic process of thinning a metal plate 5 arranged as an anode between two cathodes 2, 8 in an electrolytic tank 1, e.g. in the preparation of specimens for electron microscope examination, is controlled by measuring the electrical resistance between the cathodes, e.g. using an electronic amplifying contact voltmeter 12 associated with a potentiometer 15, and stopping the process as soon as this resistance drops below a predetermined value, indicative of a hole being formed in the plate. As shown Fig. 3, one cathode 8 is directly connected to the current source 4 for continuous electrolysis, while the other cathode 2 is alternately subjected to electrolysis and to measurement, e.g. by a reversing relay 13 controlled by an electronic timer 14, for connecting this cathode either to the source (contact 131) or the terminal 12a of the voltmeter (contact 132 ). When the deflection on the voltmeter is sufficient to open the contact 121 (when a hole forms in the plate), relay 9 is de-energized and the contact 91 opens to interrupt the electrolysis. The tank may be a cavity formed between two insulating blocks 171, 172 Fig.4 and divided by the plate 5 into two separate compartments 181, 182 into which the cathodes 2, 8 extend and through which electrolyte from a reservoir 19 is circulated, e.g. by a pump 21 via a common duct 24, to fall back into the reservoir, which is preferably immersed in a fluid 20 e.g. alcohol to maintain its temperature constant.