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Electrochemical Timing Switch

IP.com Disclosure Number: IPCOM000042763D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Finch, WF: AUTHOR

Abstract

This switch is an electrical device which has a high resistance between its two terminals (1012 ohms or greater) in its initial state, as fabricated. Upon application of a potential difference across the terminals, the resistance remains high for a fixed time (depending on construction parameters) and then switches to a low resistance of about 5 ohms or less. The time to actually switch from about 1012 ohms to about 5 ohms is roughly a few seconds. The time between application of potential to the terminals and switching can be varied by the device design parameters to be from just a few seconds to 10 years or greater. As shown in the drawing, the device comprises an envelope of borosilicate glass tubing. The glass to electrode seal is a conventional glass to metal seal. The electrode has three requirements.

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Electrochemical Timing Switch

This switch is an electrical device which has a high resistance between its two terminals (1012 ohms or greater) in its initial state, as fabricated. Upon application of a potential difference across the terminals, the resistance remains high for a fixed time (depending on construction parameters) and then switches to a low resistance of about 5 ohms or less. The time to actually switch from about 1012 ohms to about 5 ohms is roughly a few seconds. The time between application of potential to the terminals and switching can be varied by the device design parameters to be from just a few seconds to 10 years or greater. As shown in the drawing, the device comprises an envelope of borosilicate glass tubing. The glass to electrode seal is a conventional glass to metal seal. The electrode has three requirements. It must conduct, it must seal to glass and it must contact the electrolyte. Typical construction could be KOVAR* or nickel- plated molybdenum tinned with 10% Sn 90% Pb solder. The electrolyte composition is dioxane and water in a closely packed silica powder or sponge. In operation, when the electrodes are biased above a threshold voltage (the threshold is the overvoltage of the system of interest, typically 1.5 to 2 volts), metal is ionized at the anode, migrates through the electrolyte, and deposits on the cathode. The mass transported is predicted by Faraday's law which states that 96,500 coulombs will produce a chemical change (ionization) of 1 gram- equivalent at the electrodes. For example, 96,500 coulombs (amp-seconds) will ionize 107.9 grams of silver or 63.5 grams (1/2) of divalent copper. In general: M=KIT where M=mass transported I=current T=time K=materials constant Two factors are essential to this switch. They are conductivity modulation (to control time for a given bias voltage) and dendritic deposition at the cathode. In general, m...