Some Photoelectric and Thermionic Properties of Rhodium

A thin ribbon of rhodium was subjected to rigorous heat treatment at 950^∘{}-1450^∘{}C for 1050 hours in a final vacuum of 10^-8 mm of Hg in order to put it in a stable condition for photoelectric and thermionic measurements. During this period the long wave limit shifted from about 2530A to 3150A and then shifted back to 2509A where it remained during the latter 375 hours of heat treatment.The photoelectric current was found to increase about 130% as a result of increasing the temperature of the rhodium from 25^∘{}C to 950^∘{}C. A rather sudden increase took place at about 240^∘{}C.The photoelectric work function at 25^∘{}C was determined from the final long wave limit of 2482-2536A to be 4.92±{}0.06 volts. The long wave limit at 240^∘{}C was 2652-2752A which gave a photoelectric work function of 4.57±{}0.09 volts for this temperature. No further change in long wave limit was observed up to 650^∘{}C.An anomaly was observed at 1100^∘{}C where the thermionic current was irregular and where the rate of change of the resistance of the rhodium with temperature changed on increasing the temperature.The thermionic work function of rhodium, as determined from observations and with Richardson's equation, was 4.58±{}0.09 volts. This value agrees with the photoelectric work function at 240^∘{}C.Pure hydrogen and oxygen were introduced separately into the experimental tube while the rhodium was in its outgassed equilibrium condition. In the case of hydrogen the wave limit was changed from 2482-2536A to 2378-2482A. In the case of oxygen the wave limit was changed from 2482-2536A to a value so low that it could not be determined by the method used in this work.