Hydrogen hydride elements

Metal hydride element is a complex physical item, which can be described by the continuum theory equations. There are three basic processes i) process of hydrogen filtration through a porous hydride matrix and heat-conducting inserting, ii) processes of heat application and heat abstraction from a space of hydrogenation and iii) chemical processes accompanying hydrogen sorption - desorption. 

IS. An element forms a basic oxide with the formula XO and a hydride with the formula XH2. The hydride reacts with water to give hydrogen. The element X could be... 

Second-phase particles, dispersed in the matrix of the intermetallic compounds, are able to promote as well as to retard activation (Sandrock, 1978). Second-phase particles richer in the hydrogen-attracting element than the main phase will usually promote activation since they form sites favourable to hydride nucleation. They may also serve as canals by means of which the hydrogen enters the bulk of the main phase. Furthermore, if the presence of the second-phase particles leads to an increase in the brittleness of the alloy, the major activation cracks will form more easily and activation can proceed much more rapidly. 

There are many compounds in existence which have a considerable positive enthalpy of formation. They are not made by direct union of the constituent elements in their standard states, but by some process in which the necessary energy is provided indirectly. Many known covalent hydrides (Chapter 5) are made by indirect methods (for example from other hydrides) or by supplying energy (in the form of heat or an electric discharge) to the direct reaction to dissociate the hydrogen molecules and also possibly vaporise the other element. Other known endothermic compounds include nitrogen oxide and ethyne (acetylene) all these compounds have considerable kinetic stability. 

Since the hydrogen-element bond energy decreases from sulphur to tellurium they are stronger acids than hydrogen sulphide in aqueous solution but are still classified as weak acids—similar change in acid strength is observed for Group Vll hydrides. 

Binary Compounds of Hydrogen. Binary compounds of hydrogen with the more electropositive elements are designated hydrides (NaH, sodium hydride). 

Hydrogen reacts direcdy with a number of metallic elements to form hydrides (qv). The ionic or saline hydrides ate formed from the reaction of hydrogen with the alkali metals and with some of the alkaline-eartb metals. The saline hydrides ate salt-like in character and contain the hydride, ie,, ion. Saline hydrides form when pure metals and H2 react at elevated temperatures (300—700°C). Examples of these reactions ate... 

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