^00C-S3D t^ O^f/ rppc^ -^3^ V MDDC - 830 N UNITED STATES ATOMIC ENERGY COMMISSION EMISSIVITY AND TEMPERATURE SCALE FOR VACUUM HEATED URANIUM by H. B. Wahlin Argonne National Laboratory oTSepoHI^^ Manuscript Date: September 12, 1944 Date Declassified: AprU 7, 1947 Its issuance does not constitute authority for declassification of classified copies of the same or similar content and title and by the same author. Technical Information Division, Oak Ridge Operations AEC, Oak Ridge, Tenn., 10-29-48—850-12533 Printed in U.S.A. PRICE 5 CENTS I EMISSIVITY AND TEMPERATURE SCALE FOR VACUUM HEATED URANIUM By H. B. Wahlin In this investigation the true and apparent temperatures were determined for uranium which had been heated in a vacuum of 10"^ mm or lower for a period of 300 hours or more. The procedure was to take flat strips of the metal and roll them into hollow cylinders about 3 mm in diameter and 12 cm long. A hole 1/2 mm in diameter was drilled in the side of the cyl- inders. These were then mounted in a tube connected to a pumping system and evacuated. During the heat treatment continuous pumping was carried on. At the start the emissivity, calculated from the temperatures of the metal surface and the temperature of the hole (which gives the true temperature), was higher than the final value. Con- tinuous heating at temperatures between 1250 and 1300°K will clean the surface and lower the emis- sivity. This cleaning, it seems, may be speeded up by turning the heating current off and allowing the cylinder to cool through the recalescence points. The emissivity (E) was calculated from the equation 14384 1 1 en E .6705 T,p T^ where Trp is the true and T is the apparent temperature, .6705 is the mean wavelength transmitted by the red glass used in the eyepiece of the optical pyrometer. As will be seen from the accompanying plot of emissivity against true temperature, there is a sudden change in emissivity between the temperatures 1321 and 1323° K. The cause of this change is unknown although it may be a third crystal structure change. Such a change in emissivity with crystal structure has been observed in iron. The question naturally arises as to whether the metal surface is free of oxide after prolonged heat treatment. While this cannot be answered definitely from the data, it seems that an oxide sur- face will give a much higher emissivity. The value of .453 observed below 1321° K is lower than the .46 obtained for clean tungsten. The optical pyrometer readings were taken by Dr. Frances Johnson and Miss Monica Bainter, both instructors in the Department of Physics at the University of Wisconsin. Both observers were found to have excellent "pyrometer eyes." MDDC - 830 ^ ^ 2 ] MDDC - 830 Below are listed the true and apparent temperatures calculated from the emissivity data above. It must be emphasized, however, that this temperature scale is only applicable to clean uranium surfaces. True Apparent True Apparent temperature temperature temperature temperature 1180 1130.7 1290 1231.4 1190 1139.9 1300 1240.5 1200 1149.1 1310 1249.6 1210 1158.3 1320 1258.7 1220 1167.4 1325 1256.7 1230 1176.6 1330 1261.2 1240 1185.7 1340 1270.2 1250 1194.9 1350 1279.2 1260 1204.0 1360 1288.2 1270 1213.1 1370 1297.1 (?) 1280 1222.2 END OF DOCUMENT UNIVERSITY OF FLORIDA 3 1262 08910 9887 Hill H