Hydrogen in metals, including

Hydrogen in metals is trapped by all maimer of lattice impurities, including other interstitials and lattice defects. Trapping reduces the mobility of hydrogen but its solubility is usually improved. This prevents precipitation, and the crystal degradation that it causes is avoided. 

Hydrogen-in-metal systems ( 6.6) constitute a large fraction of the materials that have been studied by INS. The spectra of many of these are veiy similar consisting of broad lines (because of dispersion) often recorded at low resolution. The field has been extensively documented [1-5] so only the hydrides of relevance to catalysis or those with unusual spectra are included. Note that no hydrogen-in-platinum system is known. 

A review is presented of some recent applications of neutron vibrational spectroscopy to the study of disordered metal-hydrogen systems. The examples discussed cover a range of systems from simple dilute solutions in bcc or fee metals to amorphous alloy hydrides. It is shown that neutron inelastic scattering studies of the vibrational density of states provide a powerful and sensitive probe of the local potentials and bonding sites of hydrogen in metals and often reveal critical information on the novel microscopic physical properties and behavior of disordered metals-hydrogen systems, including those influenced by interstitial or substitutional defects. 

It is easy to reduce anhydrous rare-earth hatides to the metal by reaction of mote electropositive metals such as calcium, lithium, sodium, potassium, and aluminum. Electrolytic reduction is an alternative in the production of the light lanthanide metals, including didymium, a Nd—Pt mixture. The rare-earth metals have a great affinity for oxygen, sulfur, nitrogen, carbon, silicon, boron, phosphoms, and hydrogen at elevated temperature and remove these elements from most other metals. 

Sulfur constitutes about 0.052 wt % of the earth s cmst. The forms in which it is ordinarily found include elemental or native sulfur in unconsohdated volcanic rocks, in anhydrite over salt-dome stmctures, and in bedded anhydrite or gypsum evaporate basin formations combined sulfur in metal sulfide ores and mineral sulfates hydrogen sulfide in natural gas organic sulfur compounds in petroleum and tar sands and a combination of both pyritic and organic sulfur compounds in coal (qv). 

Troublesome amounts of C and Q acetylenes are also produced in cracking. In the butadiene and isoprene recovery processes, the acetylenes in the feed are either hydrogenated, polymerized, or extracted and burned. Acetylene hydrogenation catalyst types include palladium on alumina, and some non-noble metals. 

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