Carbon Thermometer-Heaters for Use at Low Temperatures. Effects of Particle Size and Adsorption of Hydrogen or Helium

Abstract

Measurements of the electrical resistance of carbon blacks have been made for various particle sizes, from 1° to 295°K. The smaller sizes have larger resistances and larger negative temperature coefficients of resistance. The effect of magnetic fields at liquid helium temperatures is very small in all cases but increases somewhat as particle size decreases. The effect of adsorption of helium gas on the electrical resistance is very small at the temperatures of liquid hydrogen. At the temperatures of liquid helium the resistance at first increases, and then decreases below the original value, as the amount of helium absorption is increased to saturation. A similar effect is observed when hydrogen is adsorbed at liquid hydrogen temperatures. When adsorbed hydrogen or helium gases are pumped off, the effect is found to be reversible within the small limit of error.