Adsorption of Nitrogen, Argon, and Neon on Sintered Copper and of Neon on Argon-Coated Sintered Copper at Low Temperatures

The results of measurements of adsorption isotherms are given for nitrogen, argon, and neon on bare sintered copper and on sintered copper covered with a monolayer of argon. The temperatures employed where 77.3 K for the N-2 and argon, and 17.26, 20.22, 22.64, 25.71, and 27.00 K for the neon, and the pressure range was from 0.25 to 200.Torr. The sintered copper specimen was of mass 170 g,made with powder (Alcan Metal Powders, Inc., "Druid Copper," grade MD60), which had an average particle size of 2 x 2 x 0.5 mu. The sintering was done at 650 degrees C for 0.5 h. The bare surface area Sigma in m(2)/g, of the sintered copper specimen was found from the N2 adsorption isotherms at 77.3 K. This gave Sigma = 0.41 m(2) /g, based on a molecular area of N-2 of 13.8 angstrom(2) (solid N-2). The N-2 and argon isotherms on the bare sintered copper at 77.3 K yielded values of the monolayer coverage of V-m. = 0.11 cm(3)(STP),Ig for N-2 and V. = 0.11 cm(3)(STP)Ig for argon. The neon results showed that at any given pressure and temperature the mass of neon adsorbed was less when the adsorption was on argon-coated copper than on bare copper. Calculations were made of the isosteric heat of adsorption Q(st) for neon, and the results are presented graphically as functions of the coverage. For neon adsorption on the bare copper, Q(st)/R had a maximum value of about 390 K at a coverage of about 0.2 cm(3)(STP)/m(2), and it decreased to about 275 K at 0.5 cm3(STP)/m(2). For neon on the argon-coated copper, Q/R had a maximum value of about 320 K, at the lowest coverages and fell to about 245 K at 0.5 cm(3)(STP)/m(2). The shape of the (L/R curve vs. coverage for neon indicated that the argon-coated copper was more homogeneous from an adsorptive point of view than the bare copper. The Q/R vs. coverage curves allowed an assessment to be made of the monolayer coverages V., which were 0.38 cm(3)(STP)/m(2) for neon on the bare sintered copper and 0.34 cm(3)(STP)/m(2) on the argon monolayer coated on the sintered copper. This indicated that the effective area for adsorption on the argon monolayer was 0.37 m(2)/g, which was 10% less than that for the bare copper. In addition, the Q(st)/R values at monolayer coverage were found to be 306 K on the bare copper and 275 K on the argon monolayer.