Diffusion of Hydrogen through Molybdenum alloy

[alu9]

I have been preforming experiments to study the diffusion of Hydrogen through Molybdenum. According to Sievert's law diatomic molecules would diffuse as atoms. But according to my experiments I notice that the flux of hydrogen is directly proportional to the pressure of hydrogen and not to the Square root of pressure.

1. Why do diatomic molecules disassociate when they get adsorbed on metal surfaces?

2. Is the chemical potential of hydrogen in the inner wall of the metal equal to the chemical potential of H in the outer wall?

3. How do I explain my observations?

 

[Vagn]

I have been preforming experiments to study the diffusion of Hydrogen through Molybdenum. According to Sievert's law diatomic molecules would diffuse as atoms. But according to my experiments I notice that the flux of hydrogen is directly proportional to the pressure of hydrogen and not to the Square root of pressure.

1. Why do diatomic molecules disassociate when they get adsorbed on metal surfaces?

2. Is the chemical potential of hydrogen in the inner wall of the metal equal to the chemical potential of H in the outer wall?

3. How do I explain my observations?

Have you looked at any surface science papers on the adsorption of hydrogen on molybdenum single crystals?
For instance:
http://aip.scitation.org/doi/pdf/10.1063/1.1675105
http://pubs.rsc.org/-/content/articlelanding/2016/cp/c5cp07349a#!divAbstract
http://www.sciencedirect.com/science/article/pii/0039602893901368?via=ihub

 

[Useful nucleus]

2. Is the chemical potential of hydrogen in the inner wall of the metal equal to the chemical potential of H in the outer wall?

Yes, if equilibrium was reached.