A Passive Seal for Ground Glass Joints Indium wire of 0.010 in. diameter can he used for sealing ground glass joints in static applications which normally require the use of grease, rubber O-rings, Teflon sleeves, or precision polished surfaces. Indium resists water, atmospheric and alkali corrosion. It is compatible with liquids normally capable of dissolving grease. Indium will not dry out over long periods of time as Apiezon L or silicones do and it can hold vacuums of 10-8 torr. Because the temperature coefficient of expansion is only ten times that of glass, low clamping forces are required to maintain a high vacuum seal during temperature cycling. Indium is useful from low temperatures to at least 125°C. A standard taper joint is sealed by wrapping a length of 0.010 in. wire once around the cone so the ends overlap. Then the socket is pushed straight onto the cone with care taken to avoid twisting. The pressure on the wire results in a cold welding of the overlapping ends and a plastic flow of material which tenaciously conforms to the surface. The metal can be re-cycled after use by slowly peeling away from the glass surface with a wooden or plastic pry. Indium is rapidly dissolved by HNOJ and slowly by other acids both mineral and organic. The cost of sealing a 24/40 standard taper joint with indium is identical to the cost of properly greasing that same joint with Apiezon L. The most economical source of indium amone twelve sources recentlv surveved is The Indium Cor~orationof America.' 1 The Indium Corporation of America, 1676 Lincoln Avenue, Box 269, Utica, New Yark, 13503. Their minimum order is $45.00 which will purchase 646 feet of 99.9% pure wire.
Charles F. Gay University of California Riverside, California 92502
Volume 50, Number 4. April 1973
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