New methods for the determination of hydrogen content of aluminum and its alloys: Part I. Improvements in the vacuum ext
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T H E p r e s e n c e of s m a l l amounts of hydrogen in a l u m i num and its a l l o y s can s u b s t a n t i a l l y modify the p r o p e r t i e s of the m e t a l in the s o li d state.1 All a n a l y t i c a l methods d e s c r i b e d in the l i t e r a t u r e for hydrogen c o n tent d e t e r m i n a t i o n a r e b a s e d on e x t r a c t i o n f r o m the m e t a l by diffusion at high t e m p e r a t u r e . In p r a c t i c e , the use of such m et h o d s a r e long and d e l i c a t e for the following r e a s o n s : - - h y d r o g e n contents a r e v e r y low, g e n e r a l l y in the r a n g e 0.05 to 0.50 m l / 1 0 0 g (or ppm) - - a l u m i n u m and m a g n e s i u m f r o m the alIoys can r e act with t r a c e s of m o i s t u r e and p r o d u c e r e l a t i v e I y high amounts of s p u r i o u s hydrogen, - - h y d r o g e n is not a c o m m o n i m p u r i t y which can be e a s i l y i n t r o d u c e d in known amounts into the m e t a l - for p r e p a r a t i o n of s t a n d a r d s a m p l e s , for instance. The hydrogen content depends actually on the previous interactions of the metal with hydrogenated contaminants: moisture, hydrocarbons, hydrated crucibles, and so forth. The method which best overcomes these difficulties of the aluminum-hydrogen system and which seems to give the most reliable results is based on vacuum extraction from solid samples and was first proposed by Ransley. 2 However, this method has been criticized on several points: 1) For alloys containing volatile elements such as magnesium or zinc, the formation of metallic films able to trap hydrogen lost by the sample could lead to low results (getter effect). 3-4 2) The time required for a hydrogen content deterFRANCIS DEGREVE is Research Engineer, JEAN-CLAUDE. CARLE and NORBERT GONZALEZ are Members of the Service Etudes Analytiques et Mesures, Centre de Recherches, Aluminum Pechiney, BP24,38340, Voreppe, France. Manuscript submitted October 21, 1974. METALLURGICAL TRANSACTIONS.B
mination is too long for routine work when numerous data are needed. 3) The hydrogen extraction from the specimen in the solid state could perhaps be not complete. Some modifications of this method have been proposed 3-~ in o r d e r to at t en u at e o r e l i m i n a t e as much as p o s s i b l e t h e s e d i s a d v a n t a g e s . With the sco p e of p r o v i d i n g a r e f e r e n c e l a b o r a t o r y method able to check o t h e r methods, q u i c k e r or d ir e c t l y a p p l i c a b l e in the foundary, the points mentioned h e r e above have been i n v e s t i g a t e d in d e t a i l using an i m p r o v e d a p p a r a t u s . 7 Particularly, a m a s s s p e c t r o m e t e r as gas d e t e c t o r allows the r e c o r d i n g of each g a s eous s p e c i e s e x t r a c t e d f r o m the s a m p l e . Becau se its solubility and diffusion c o e f f i c i e n t in a l u m i n u m a r e quite s i m i l a r to hydrogen, d e u t e r i u m m a k e s an e x c e l lent t r a c e r to d e t e r m i n e the o r i g
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