Solid solutions of hydrogen

Strictly a-solid solution of hydrogen in a metal catalyst studied. 

Another technique involving photolysis which is often effective involves exposure of a solid containing a trace of some photosensitive compound which absorbs in a region of lower energy than the onset of absorption by the solvent . Typically, dilute solid solutions of hydrogen peroxide in a wide range of solvents can be photolysed with a medium-pressure mercury arc. Early studies of this sort, described in Section III, involved the use of alcohols and it was shown that radicals characteristic of the alcohols were trapped. No evidence for trapped hydroxyl radicals was forthcoming and it was concluded that a secondary reaction occurred such as ... 

The transition metal hydrides exhibit such wide variations from stoichiometric compositions that they have often been considered interstitial solid solutions of hydrogen in the metal. This implies that the metal lattice has the same structure in the hydride phase as in the pure metal. That this is not the case can be seen in Table I, where of 28 hydrides formed by direct reaction of metal and hydrogen, only three (Ce, Ac, Pd) do not change structure on hydride formation. Even in these three cases, there is a large discontinuous increase in lattice parameter. The change in structure on addition of hydrogen plus the high heats of formation (20 to 50 kcal. per mole) (27) indicates that the transition metal hydrides should be considered definite chemical compounds rather than interstitial solid solutions,... 

The body-centered cubic Group VA metals dissolve a considerable amount of hydrogen before distorting to either a b.c. tetragonal or orthorhombic structure. These behave somewhat more like solid solutions of hydrogen in metal than do the more definite hydrides previously discussed. They appear to have the stoichiometric formula MH, but this has never been reported, the maximum being about... 

The theoretical conclusion of Isenburg (17) that H should ionize to H+ in metals applies, under the assumptions used, only to dilute and undistended solid solutions of hydrogen. This conclusion may also mean that the field of the proton under these conditions is completely screened by the conduction electrons. Additional work is needed to show that this condition indeed implies lack of a bound state rather than what amounts to a o- orbital or helium-like distribution of electrons around the proton in an actual hydride. 

Almost thirty years before the date of Moissan s work, a very unstable, crystalline, silver-white compound was described by Troost and Hautefeuille.2 They obtained it by sorption of hydrogen by means of sodium above 300° C., the metal sorbing 237 times its volume of the gas. That their product was a definite chemical compound is doubtful it was probably a solid solution of hydrogen in sodium, analogous to that formed by palladium. 

Figure 4.1 (a) Schematicof a pressure-composition isotherm, a isthe solid solution of hydrogen... 

The preparation of TcH occurs at 300°C and 1.9 GPa Hj with the composition TcHg j. Both TcHp,3 and the hydrogen-free metal have an hep metal lattice, which makes it difficult, without extensive x-ray work showing the dependence of lattice parameters on composition, to determine whether TcHq is a hydride phase or just a solid solution of hydrogen in Tc. However, from the behavior of the electrical resistance of TcH as a function of composition, it can be deducted that a hydride phase is formed below 300°C. 

Hydrogen reacts with metal borides, carbides, silicides, nitrides, phosphides, oxides, sulfides, and halides to form a solid solution of hydrogen in the compound with... 

The theory that hydrogen overvoltage is due to more or less stable hydrides on the metal surfaces has been supported principally by New-bery.23 Although hydrides, and solid solutions of hydrogen, are undoubtedly formed on the surface of some metals during hydrogen evolution, they appear, to this writer at least, to be the result rather than a cause of overvoltage. 

A solid solution of hydrogen in technetium metal is formed during the electrodcpo-sition of technetium from acid aqueous solutions of pcrtechnctate. The maximum hydrogen content of the amorphous phase corresponded to TcHo.27 [6]. 

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