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Electrochemical Machining of Lanthanum Hexaboride

IP.com Disclosure Number: IPCOM000075632D
Original Publication Date: 1971-Oct-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 44K

Publishing Venue

IBM

Related People

Wardly, GA: AUTHOR

Abstract

Lanthanum hexaboride is a hard refractory material, which is difficult to machine with EDM (electron-discharge machining) and abrasive methods. The electrochemical machining method described subsequently has been found to be effective for making pointed tips on LaB(6) rods.

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Electrochemical Machining of Lanthanum Hexaboride

Lanthanum hexaboride is a hard refractory material, which is difficult to machine with EDM (electron-discharge machining) and abrasive methods. The electrochemical machining method described subsequently has been found to be effective for making pointed tips on LaB(6) rods.

Referring to the figure, a rod of LaB(6) is maintained at a positive potential in the electrolyte relative to the cathode, which is a corrosion resistant material such as stainless steel. An electrolyte of 25% HCl has been found to effect the job of electrolytically removing LaB(6) in a rapid manner. This electrolyte has been used to make sharp tips on rods of sintered and arc-melted material, both of which are valuable as electron emitters. The general tip making procedure is as follows: 1) Preclean rod by electrochemical means (5 volts) briefly. 2) Rinse in water 3) Dry 4) Coat rod with glycol pthalate or mount rod in current-density limiting jig. 5) Rough etch at 5 volts after immersing area to be removed. 6) Clean tip with water. 7) Reimmerse rod into electrolyte and reduce cell voltage for final removal of material (1 1/2 - 2 volts) 8) Turn off cell potential when the rod is pinched through leaving a prepared tip.

The rate of removal of material in chosen areas is controlled by the applied cell voltage. The cell voltage also controls the resultant surface finish. Areas which are not to be attacked are passivated by coatings of glycol pthalate, which are easily removed by acetone rinses.

Cylindrically symmetric points have been electrolytically machined from both arc-melted and sintered materials, the arc-melted material being considerably more difficult.

The electrochemical action is quit...