I think you should look at the papers you quote that I and my fellow authors wrote. The reaction mechanism for bulk uranium that has a clean surface and is well annealed were calculated by John Kirkpatrick with great success. If you check it carefully you will discover that the reaction of bulk U can be calculated without any parameters* over a large range of pressures and temperature.
Notice in this calculation what the mechanism is, that is, the hydrogen penetrates the metal phase, nucleates, grows until it exceed the tensile strength of the metal at which point the surface spalls. For Uranium, this spallation happens at the moving reaction front, but for other metals a dislocation loop punching mechanism as proposed by Trinkaus functions to break up the metal.
At very low pressures and near equilibrium, the mechanism changes to a first order in pressure kinetics. This is the range in which Block and Mintz were making their measurements. In that range the mechanism they proposed required at least 6 parameters and was unable to predict outside the range.
The reaction of water with uranium can be calculated by the same mechanism with some preliminary equilibrium steps, again without parameters. Indeed, with labeled water (O-16 vs O-18) one can actually measure the decay constant of the reaction front which agrees with that predicted from the proposed mechanism.
There are several precautions in making measurements for the hydriding reaction. Firstly, the reaction rate is very dependent upon the residual stress of the samples. Secondly, the presence of oxide on the surface prolong the observed induction time so clean environments and polished samples are needed. Thirdly, oxygen gas is a very effective inhibitor of the reaction. As little as 1 ppm oxygen can inhibit the reaction, which is why the oxygen needs to be scrubbed completely out the the hydrogen. The systems need to be ultra-high vacuum and baked with hydrogen. Check our papers to see what extensive preparations need to be made.
There are also several other metals that follow this reaction mechanism for either the hydride reaction or oxidation. In most cases the loop punching calculations are needed to determine the reaction rate.
*Def: Numbers obtained from source other than the present experiment and not from experiments that measure the same phenomenon, that is, independent of the present type of measure - not fitted.
Sincerely yours,
James Condon
Dear James Condon, thanks for the information, but what should be discussed here?
First thanks Alan Rawle for you snide remark. I am retired and I frankly am not interested in publicity or any other advantage. Furthermore, I don't give a damn if YOU get it right. It's this kind of attitude which gives scientist a bad name and leads to bad engineering.
Frank Edelmann, If you read the publications carefully you would have realized that oxygen does a poor job of inhibiting the reaction. Indeed, in purified H2, < 0.1 ppm O2, the "passivation" breaks down in seconds or minuets. As I recall, you work at LASL. You might want to check some of the classified materials at your disposal.
We had one very expensive problem come up where the engineers kept doing the intuitive thing with this reaction, If they had they kept going it would have costed EXTRAORDINARY expenses. That information may be in the classified patents. It is, however, consistent with the open literature publications.
Since my retirement from the DOE job, I no longer have clearance. Please keep that in mind in our communications. If you want to do private communications we can connect by email.
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