Molecular hydrogen diffusion

The simultaneous analysis of orthophosphate, glycerol phosphates, and inositol phosphates has been achieved by spectrophotometric analysis of the molybdovanadate complexes. Also, a sensitive and selective chemiluminescent molecular emission method for the estimation of phosphorus and sulphur is described, which is based on passing solutions into a cool, reducing, nitrogen-hydrogen diffusion flame. For organic compounds it was usually necessary to prepare test solutions by an oxygen-flask combustion technique. 

At elevated temperatures, molecular hydrogen dissociates into the atomic form, which can readily enter and diffuse through the steel. Under these conditions, the diffusion of hydrogen in steel is more rapid. As discussed in Section 4, Forms of High Temperature Hydrogen Attack, hydrogen may react with the carbon in the steel to cause either surface decarburization or... 

The first step in interstellar chemistry is the production of diatomic molecules, notably molecular hydrogen. Observations of atomic hydrogen in dense clouds show that this species cannot be detected except in a diffuse halo surrounding the cloud, so that an efficient conversion of H into H2 is necessary. In the gas phase this might be accomplished by the radiative association reaction,... 

Shocks were first invoked to explain the unusually high abundance of the radical CH+in diffuse clouds (n 100 cm-3 T = 100 K), where standard chemical models predict far too little of this substance which is reactive both with electrons and with atomic and molecular hydrogen.128 In a high temperature medium, however, the reaction,... 

Figure 2.3 Left, reduction models. In the shrinking core or contracting sphere model the rate of reduction is initially fast and decreases progressively due to diffusion limitations. The nucleation model applies when the initial reaction of the oxide with molecular hydrogen is difficult. Once metal nuclei are available for the dissociation of hydrogen, reduction proceeds at a higher rate until the system comes into the shrinking core regime. Right the reduction rate depends on the concentration of unreduced sample (1-a) as f(a) see Expressions (2-5) and (2-6).

Atomic hydrogen formed as an intermediate in the hydrogen evolution reaction is adsorbed to the surface of the membrane. Molecular hydrogen is formed by one of at least two mechanisms, but parallel to this, a fraction of the atomic hydrogen is absorbed by the metal, eventually leading to an equilibrium between adsorbed and absorbed atomic hydrogen. In the absorbed state, the hydrogen atoms are able to diffuse as interstitials in the metal lattice. 

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