Topics in..
.
I
Chemical Instrumenfation Edited by GALEN W. EWING, Seton Hall University, So. Orange, N. J. 07079
These articles are intended to serurve the readers of THIB JOURNAL by calling attention to new developments i n the theory, design, or availability of chemical laboratory instrumentation, or by presenting useful insights and eznlanations of ton& that are of nractical i m = ~ t a n c eto those who use. M teach ;he use of, mod.& instrumeniakm and in&mental techniques. The editor invites correspondence from prospective contn'but~s.
LV. Analysis of Gases in Metals: Fusion and Extraction Methods JOHN ROBOZ, 123 Phelps Ave., Cresskill, New Jersey 0 7 6 2 6 Table 1. Techniques of Gas Analysis
INTRODUCTION The expression "gas analysis in metals" refers to the determination of hydrogen, nitrogen, and oxygen content in metals and alloys, usually a t trace levels, i.e., below a few hundred parts per million (ppm) by weight. The information req u ~ r e dmay either be the tot,al quantity of the gas(es) present, or t.he quantity released under given experimental condition:, such as various heat treatments. The determination of gases as major components, such as in pure hydrides, nitrides, oxides, glasses, ores, and minerals, usually demands macro rather than trace tecbniques. Hydrogen, nitrogen, and oxygen are commonly present in metals in four form^: (a) inclusions of a. second phase, such as bydrides, nitrides, m d oxides; this is the most frequent kind, ( b ) gaseous elements in solid solution, ( c ) molecular gases in bubbles or crevices trepped during solidification (inhomogeneously distributed), (d) adsorbed gases on surfaces; in highpurity metals this may be the dominant source. I n powder samples, where the surface-to-volume ratio is large, analysis a t low levels may become meaningless. The presence of these impurities results in profound effects on the mechanical, thermal, and electrical properties of the host metals. Transition metals, for example, can he deformed satisfactorily only if their gas content is below certain limits. A well-known problem is hydrogen emhrittlement in steel, in welded structures, in massive parts which can retain hydrogen, and in corrosive environments. I n hiehitrenglh w l d i n ~ , lrsr exnmplc, rercnr g o v c r ~ ~ ~ nscpn w t i f i c ~ ~ ii ~m&~r w. hydrogen conte!nt of L l r than :
