EFFECT OF WATER-VAPOR ON THE DETERMINATIO N OF HYDROGEN IN ALUMINUM BY NITROGEN-CARRIER FUSION METHOD

The influence of moisture on the reliability of the determination of h ydrogen in aluminium by the Ne carrier fusion method was studied. It w as found that it is necessary to keep the water vapor in the hydrogen- extraction area at under 10 mg/m(3) in order to lower the surface hydr ogen to less than 0.01 ppm (the instrumental detection limit). The sur face waters on an aluminium sample was 'adsorbed' water liberated by h eating at a temperatures lower than 473 K, and 'combined' water by hea ting above 573 K both of which produced surface hydrogen. The combined water produced surface water much more than the adsorbed one. Essenti ally, although it was difficult to eliminate the influence of surface hydrogen on the determination of hydrogen, the surface water could be reduced to 1 mg/m(2) or below by machining the sample in the cylindric al form under an atmosphere (3000 mg H-2 0/m(3)) with a stream of nitr ogen. As a result, the surface hydrogen could be decreased to 0.01 ppm or less. In real analyses, however, surface hydrogen could also be ac hieved to 0.01 ppm by machining the sample very carefully with an etha nol lubricant at room atmosphere. An analysis of commercial high-purit y aluminium (JIS 1N99), showed an average concentration of 0.092 ppm h ydrogen and a relative standard deviation of 6.0% (n = 30).