238
RICHARD B. BERNSTEIN AND DANIEL CUBICCIOTFI CONCLUSION
It would seem from our results that no discontinuity exists in the dielectric constant t's. concentration curve for polystyrene in toluene. The dielectric constant varies linearly with concentration in such a way as to extrapolate to the dielectric constant of the solid polymer. Impurities and the influence of handling of the samples have been shown to lead to experimental results which, if not interpreted carefully, might suggest the existence of a break in the curve. REFERENCES (1) SMYTH, C. P.: Dielectric Constant and Molecular Strncfiue, p. 60.The Chemical Catalog
Company, Inc., New York (1931). (2) VOET,A , : J. Phys. & Colloid Chem. 53,597 (1949).
T H E PERMEABILITY OF ZIRCO1\'IPlI TO HYDROGEK' RICHARD B. BERNSTEIN A N D DASIEL CUBICCIOTTI Department of Chemistry, Illinois Institute of Technology, Chicago, IIlinois Received February 6 , 1950
Zirconium is known to dissolve hydrogen appreciably over a wide range of temperatures (3). Hall, Martin, and Rees (8) hare made a careful study of the solubility of hydrogen in the metal. Their results indicated that the absorption and desorption of hydrogen occurred reversibly for clean zirconium. The present study reports measurements of the rate of permeation of hydrogen through zirconium at elevated temperatures. Zirconium reacts with many gases a t high temperatures (6); above 500°C. it is readily oxidized by most oxygen-bearing gases, forming a black oxide which, under certain conditions, may diffuse and dissolve in the metal phase (4).The oxygen-rich metal dissolves less hydrogen under given conditions than the pure metal (8). The reaction with impure nitrogen forms a gold-yellow phase which is also soluble in the metal (6). Guldner and Wooten (7) have studied the low-pressure gas reactions of zirconium at elevated temperatures. One of the major experimental problems in this study of the hydrogen permeability of zirconium was the need for exclusion of foreign gases from the zirconium specimens. Smith (9) has reviewed the literature on the zirconium-hydrogen system, indicating some of the experimental difficulties associated with studies involving this active metal. EXPERIMENTAL
Figure 1 is a schematic diagram of the apparatus used in this investigation. The system consists of a hydrogen purification train, a stainless-steel holder 1 This research was done under the sponsorship of the Office of Saval Research, United States Xavy Department.
239
PERMEABILITY OF ZIRCONIUM TO m E O Q E N
for zirconium sheet, and a vacuum-type collection buret for measuring the quantity of hydrogen diffused through the zirconium in a given time interval. Associated components of the apparatus are also indicated in the figure.
The specimen holder 4 detailed sketch of the zirconium disc holder is given
ia the insert of figure
1. I t consisted of two stainless-steel (303) flanges bolted together by means of
six t-in.-20 steel bolts, clamping a disc of zirconium slightly less than 4 in. in diameter into a groove 4 in. in diameter and & in. deep. The exposed portion of the disc was # in. in diameter. An annealed and polished copper gasket in the
TOEPLCR WYP WPE OOLLV.TlOl IU(IET
STAINLESS STEEL S U R E HOLDER
ISCALE I+
FIQ.1 . Apparatus for the study of the permeability of zirconium
l"4l
t o hydrogen
form of a cylindrical ring in. long, 4 in. O.D., and j in. I.D. was placed adjacent to the specimen so that the specimen was in the downstream side of the holder. Under the usual compressions employed, the gaskets showed appreciable deformation but at no time did the two stainless-steel flange faces meet. Each flange was welded to an %in. length of stainless-steel tubing which extended outside the furnace. -4Kovar-to-Pyrex seal joined the all-glass hydrogen inlet system to the holder; the downstream side of the holder was waxed into the Pyrex collection and vacuum system. The U-tube trap cooled in liquid nitrogen was intended to remove traces of condensibles such as hydrocarbon and mercury vapors which were presumably present in the inlet section of the manifold. After the specimen was mounted in the holder, the asaembly was inserted in the vacuum line at the spherical ball-joints indicated in hgure 1. Each mounting \vas
240
RICHARD B. BERNSTEIN AND DANIEL CUBICCIOTTI
subjected to a high-vacuum test, first at room temperature and then at about 200°C. Mountings which were leak-tight under these conditions generally remained tight up to 900°C. The holder was heated in a tubular resistance furnace, 23 in. I.D., 6 in. O.D., and 6 in. long. Two chromel-alumel thermocouples were placed in holes drilled in the body of the flanges. The uncertainty in temperature was estimated to be approximately & 5°C. A slow stream of nitrogen was passed through the furnace during the run, serving to minimize corrosion of the holder at the high temperatures. The nitrogen also reduced the possibility of an inleak of oxygen, which reacts more rapidly than nitrogen with zirconium.
The vacuum system A two-stage mercury diffusion pump with liquid-nitrogen trap was used to evacuate the apparatus. Pressures below lo-‘ mm. were easily attainable. The combined rates of outgassing and inleak of the holder and manifold were seldom greater than 2 microns per minute, or about IO-* cc. atm. per minute. In several overnight tests, the pressure rise was
