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40532-B10
Hydrogen Absorption/Desorption Cycling for the Manipulation of the Mechanical Properties of Metals and Alloys
Our laboratory efforts have continued on the project dealing with the effects of hydrogen absorption/desorption cycling on the mechanical (strength and hardness) properties of palladium. Picking up where last year's report left off, we continued to carry out microhardness testing and strength testing on palladium samples that had been subjected to multiple hydrogen absorption/desorption cycles at 50 degrees C. We also continued carrying out microhardness and strength tests on palladium samples that were subjected to a single hydrogen absorption/desorption cycle at varying temperatures (in the range from 50 degrees C to 350 degrees C).
With regard to the samples exposed to multiple cycles, different samples of palladium were subjected to the absorption/desorption cycling 1, 2, 3, 4, 5, and 10 times, respectively. Our results indicate that the strength of the palladium more than triples (compared to well-annealed palladium) as a result of the first absorption/desorption cycle. A second absorption/desorption cycle gives a more modest additional increase in strength of roughly 15% while further cycling is found to have very little additional effect on the strength of the palladium. These findings are echoed by the microhardness results that also show a marked increase in hardness because of the first absorption/desorption cycle and only modest additional effects due to further cycling. The increases in strength and hardness of the palladium are accompanied by a pronounced embrittlement of the palladium. As expected from the observed strength and hardness behavior of palladium, the greatest degree of embrittlement results from the first hydrogen absorption/desorption cycle that the palladium is exposed to.
The results of our variable temperature cycling studies have been equally interesting. Once again we found that a single hydrogen absorption/desorption cycle significantly increases the strength and hardness of palladium as well as cause significant embrittlement of the metal. Surprisingly, we have found that temperature has little influence on the observed strengthening and embrittlement. Our results indicate that very little difference in strengthening and embrittlement results whether the cycle occurs at 50 degrees C or 200 degrees C (or any temperature in between). We are continuing these studies on samples subjected to higher temperatures during cycling. It will be quite interesting to see if the insensitivity to temperature during absorption/desorption cycling continues up to 350 degrees C.
The project certainly has generated very useful information that will be of value as the search for safe storage media for hydrogen continues. The use of hydrogen as an important alternative to fossil fuels will occur; it's just a matter of time. It is very rewarding to know that our research is helping to advance the use of hydrogen. Knowing that my research contributes to a vital area such as alternative energies is a great motivator. This aspect of my research has not been lost on my student assistants. The students involved in the project worked throughout the academic year as well as the summer. That level of commitment and enthusiasm allowed the past year to be very fruitful.
