Hydrogen alloying mills

In a variant of the second method described earlier the premixed metallic powders (or pulverized ingots) are milled under hydrogen atmosphere to directly form an intermetallic hydride. It can be also viewed as hydrogen alloying of metal powders and powder mixtures in hydrogen alloying mills. This method is called a reactive mechanical alloying (RMA) or mechanochemical synthesis (MCS). 

Z.S. Wronski, R.A. Vatin, Ch. Chiu, T. Czujko, Mechanosynthesis of nanocrystaUine MgB ceramic powders in hydrogen alloying mills via amorphous hydride intermediate, Adv. Sci. Technol. 45 (2006) 309-314. 

Z. Wronski, R.A. Varin, C. Chiu, T. Czujko, A. Calka, Mechanochemical synthesis of nanostructured chemical hydrides in hydrogen alloying mills , J. Alloys Compd. 434-435 (2007) 743-746. 

In atomization, a stream of molten metal is stmck with air or water jets. The particles formed are collected, sieved, and aimealed. This is the most common commercial method in use for all powders. Reduction of iron oxides or other compounds in soHd or gaseous media gives sponge iron or hydrogen-reduced mill scale. Decomposition of Hquid or gaseous metal carbonyls (qv) (iron or nickel) yields a fine powder (see Nickel and nickel alloys). Electrolytic deposition from molten salts or solutions either gives powder direcdy, or an adherent mass that has to be mechanically comminuted. 

R.A. Vatin, T. Czujko, Overview of processing of nanocrystaUine hydrogen storage inter-metallics by mechanical alloying/milling, Mater. Manuf. Proc. 17 (2002) 129-156. 

Much more efficient method of the synthesis of metal hydrides is a one-step method of reactive ball milling of elemental metal directly under hydrogen gas. The method of reactive mechanical alloying/milling of either elemental metals or preaUoyed... 

The same alloy milled for 80 h did not absorb hydrogen. It seems that the presence of the FCC phase formed during milling somehow blocks the hydrogen intake but the exact explanation is lacking. 

Bellosta von Colbe, J.M., B. Bogdanovic, M. Felderhoff, A. Pommerin, and F. Schuth, Recording of hydrogen evolution—a way for controlling the doping process of sodium alanate by ball milling, /. Alloys Compd., 370, 104-109, 2004. 

Huot, J., G. Liang, S. Boily, A.V. Neste, and R. Schulz, Structural study and hydrogen sorption kinetics of ball-milled magnesium hydride, /. Alloys Compd., 293-295, 495-500, 1999. 

Wang, P, Orimo, S., Tanabe, K., Fujii, H. 2003. Hydrogen in mechanically milled amorphous boron. J Alloys Comp 350 218-221. 

Milling atmosphere, which is a neutral protective gas (helium or argon) during mechanical milling or hydrogen under pressure up to 0.9 MPa under reactive mechanical alloying processes. 

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