GROUND-GLASS JOINTS LEAKPROOF TO CORROSIVE CHEMICALS LOUIS D. QUIN and ROBERT 8. GREENLEE Westvaco Chemical Division, Focd Machinery and Chemical Corporation, South Charleston, West Virqinia
I x LIBORATORY work with highly corrosive chemicals, the use of glassware with ground joints is often complicated by attack of the chemicals on lubricants required to obtain a good joint seal. This attack usually results in leaks through the joint during an operation and in severe sticking of the joint. The loss of material through leaking from a process is undesirable in any case, but particularly so where corrosive chemicals are concerned, because of the resulting contamination of the atmosphere. Wit,h certain corrosive chemicals, the attack on the ordinary lubricants is so severe that a prolonged operation such as rectification cannot be completed without one or more time-consuming shutdowns for repair of the joint. The recently introduced Teflon-coated joints provide a partial solution to the problem, but it has been our experience that, on repeated use, the coating tears or otherwise deteriorates, and the joint is rendered worthless. I n addition, the necessity for using special equipment for work with corrosive chemicals is obviously undesirable. We have found that a joint sealed with molten Saran (Dow Chemical Company's vinylidene chloride polymer) is quite resistant to leaking for periods of as much as 240 hours or more when used with certain corrosive chemicals a t reflux. These chemicals include rhlorosulfonic acid, sulfuryl chloride, thionyl chloride, fuming nitric acid, phosphorus oxychloride, phos-
phorus triehloride, phosphorus trihromide, and various organophosphorus halides. Effectiveness of the seal with other untested materials is probable. The seal is prepared as follows. Small pieces of Saran tubing are partially melted on a metal spatula and placed on the clean male joint. The joint is heated in a flame, and the molten plastic is evenly spread over the surfare with the spatula. It is then rapidly inserted into the female joint, and, while the plastic is solidifying, it is turned several times with pressure to obtain a uniformly coated, tight-fitting seal. To open the sealed joint, it is warmed with a flame and separated when the plastic has softened. The joint is rleaned by thorough wiping while the plastic is molten. Scruhbing with a detergent and hot water will destroy and remove any adhering film. This sealing procedure has been used with standard taper as well as hall and socket joints. The seal is effertive when used in an operation a t a temperature above the softening point (about 120°C.) of the plastir. We have used the seal for work a t both atmospheric and subatmospheric pressures. This type of seal is quite versatile in that it can be applied as needed t o practically any piece of ordinary ground-glass equipment. Although Saran is the only commercial plastic we have used, it is possible that other chemically resistant thermoplastic polymers may be similarly useful.
