Some Theoretical and Practical Aspects of Gases 

 in Metals * 



By J. H. SCAFF and E. E. SCHUMACHER 



In this paper there are included a discussion of the theories pertaining 

 to the absorption of gases by metals and descriptions of actual work illus- 

 trating them. Apparatus for the analysis and measurement of gases in 

 metals and for melting metals in vacuum are described. Information is 

 included, also, on commercial vacuum melting methods and the results 

 obtained. 



Introduction 



SINCE Thomas Graham ^ discovered in 1866 that a piece of meteoric 

 iron heated in vacuum yielded 2.8 times its volume of gas,^ the 

 solubility of gases in metals has been the subject of a large number of 

 investigations. While these studies have not as yet afforded more 

 than a partial understanding of the nature of the processes by which 

 gases are dissolved in metals, they have yielded considerable knowledge 

 of those factors which determine the extent of such solubility, and 

 thus of the methods by which the amount of dissolved gas can be 

 increased or diminished. At the same time they have shown the 

 importance of dissolved gases in determining not merely the behavior 

 of metals in casting processes, but also the magnetic, mechanical, and 

 chemical properties of metallic materials. It is proposed to discuss, 

 in this paper, theories of the absorption of gases by metals and to 

 review important work on this subject. 



The Effect of Gases on the Properties of Metals 

 The importance of producing sound metals should interest every 

 metal founder in the effects of dissolved gases. Any gas whose 

 solubility is greater in the liquid than in the solid metal may cause 

 the formation of blowholes. The formation of these blowholes, 

 however, can be reduced or prevented by cooling the metal slowly 

 enough through its freezing range to permit the escape of liberated 

 gases. Iron saturated with hydrogen, for instance, will yield a sound 

 ingot if cooled very slowly through its freezing point, while chill 

 casting not only will make the metal porous but may cause an evolution 

 of gas violent enough to throw metal from the mold. This phenome- 



* Metals and Alloys, January, 1933. 



1 Thomas Graham, Proc. Roy. Soc, 15, 502 (1866). 



2 All gas volumes given in this paper are at N.T.P. 



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