T. Aylmer Wood Organic Chemicals Department E. I. Du Pont De Nemours and Company Wilmington, Delaware
A Thermostatic Bath for Temperatures Between 90" and 300°K
A
simple, precisely controlled, variable temperature bath has been constructed for gaseous adsorption studies. Temperatures between the boiling point of liquid oxygen and room temperature are attainable. This bath has been successfullyused in studies of adsorption on low energy surfaces.' The bath is a stirred liquid, contained in a Dewar flask, cooled by liquid nitrogen drawn through a copper coil immersed in the liquid. The flow of liquid nitrogen is controlled by a gas thermometer which activates a Themnocap" relay, Niagara Electron Laboratories, which in turn closes a Fisher electro hosecock on a vacuum bleed. The Thermocap relay is set for high sensitivity, and the vacuum source is adjusted to a low volume in order not to pull too much liquid nitrogen into the coil, overcooling the bath. Only the steep portion of the vapor pressure curve is used where the effect of a small temperature change causes a large vapor pressure change. Temperature ranges of pure gases for use in the gas thermometer are: propane, 195°-235"Ii; propene, 185'-225'K; trifluorochloromethane (CClF,), 175"240°K; ethane, 150°-1850K; ethylene, 140'-175OK; perfluoromethane (CFS, 120"-150°K; methane, 90'llOOIi. Temperature ranges of some liquids for use in the bath are: perfluoromethane (CF,), 90"-145°K; dichlorodifluoromethane (CClzF3, 115'-243'K; petroleum ether, 140'-300°K. Temperature control better than +0.0l0C was attained between 145" and 160°1i when such a bath filled with pet,roleum ether and controlled by an ethylene gas thermometer was used. =TO
A 2-1 dewar flask, 110 mm id X 250 mm deep, was fitted with a ring of 3/4-in. polymethacrylate sheeting which was sealed to the flask with Apiezon Wax. A cover plate of 3/4-in.polymethacrylate sheeting was fabricated to support a 6-ft coil of '/,-in. od copper tubing, a glass bearing for a 5/rin. aluminum shaft with 3-in. slit blade propeller, a gas thermometer bulb, a sample holder, and a Mylar" polyester film agitation draft tube. The draft tube encloses the cooling coil and t,he agitator shaft and blade, snugly fitting the blade. The agitat,ion circulates liquid from the top of the bath down over the cooling coil to the bottom. The agitator was driven by a synchronous motor, Model 10034SY, 300 rpm, Amphenol-Borg Electronics Corp. The sample holder and gas thermometer bulb were placed equidistant from t,heMylar shield and eachother and nearthe center of the bath. A gasket of plastic belting was used between the cover and ring, and a drying tube was attached to the vent. All leads through the cover plate7 were glass except the agitator shaft which had a Delrina polyacetal insert to prevent heat loss. Seals between the inserts and cover plate were made with Leak Lock" from High Side Chemicals, Inc., Clifton, X . J.
' GRAHAM,DONALD P., J . Phys. Chem., 66, 1815 (1962). ALUMINUM SHAFI
/ 6- SPACED AROUND HEAD
2
PLASTIC
VACUUM SOURCE
\
SEALED WITH APIEZON WAX
/2L.
ALUMINUM DISC CUT GIVE 8 BLADES
DEWAR FLASK
m
Figure 1. A, liquid N2 storage; B, vacuum-jacketed transfer line; C, liquid N2 cooling coil; M, mercury manometer; P. gor thermometer bulb; 4, sample holder; TC, movoble clamp for temperature control.
Figure 2.
"
SZSPMPLE HOLDER P: GAS THERMOMETER BULB
Bath details.
Volume 44, Number 7, July 1967
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