Argon: atomic area

Analysis of the diffraction pattern of Ar adsorbed on powdered Co3047 produced values for the surface areas of each of the different faces by which the crystals were terminated. The data were shown to be consistent with a surface area for the 110 face of 11 m2 g-1 and a surface area for the 111 face of 27 m2 g 1. In addition the average area occupied by a single argon atom on each face was shown to be 0.216 and 0.189 nm2 respectively. Both these values are significantly higher than the conventional cross-sectional area of an argon atom, 0.152 nm2, used in gas-adsorption estimates of the surface area of a solid. 

This ratio was determined from the number of metal atoms per unit area, from crystallographic data, to the number of adsorbate molecules per unit area, from the adsorption data. It is the number of nitrogen molecules and of argon atoms per unit area. 

That diameter is 13 A, or 3.4 argon atom diameters, which seems reasonable. The surface area is then... 

The volume of argon gas (measured at STP) required to form a complete mono-layer on a metal surface is 134.5 cm g L Calculate the surface area per gram of the metal if each argon atom occupies 1.58 x 10 20 m. ... 

Bishop [75] determined barium in seawater by direct injection Zeeman-modulated graphite furnace atomic absorption spectrometry. The V203/Si modifier added to undiluted seawater samples promotes injection, sample drying, graphite tube life, and the elimination of most seawater components in a slow char at 1150-1200 °C. Atomisation is at 2600 °C. Detection is at 553.6 nm and calibration is by peak area. Sensitivity is 0.8 absorbance s/ng (Mo = 5.6 pg 0.0044 absorbance s) at an internal argon flow of 60 ml/min. The detection limit is 2.5 pg barium in a 25 ml sample or 0.5 pg using a 135 ml sample. Precision is 1.2% and accuracy is 23% for natural seawater (5.6-28 xg/l). The method works well in organic-rich seawater matrices and sediment porewaters. 

A plant for this purpose comprises a vacuum chamber with ancillary equipment. The articles to be plated are mounted on a water-cooled cathode and, following evacuation of the chamber and filling with argon to a pressure of 0.002 Torr, direct current from a supply in the range 2000 to 5000 V is applied—to give a glow discharge in the area of the cathode. The article or articles mounted there thus are cleaned by ionic bombardment. Next, the evaporation source is excited, and the atoms of source material are deposited on the work pieces. 

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