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Methane Decomposition Reaction on a ZrNi Alloy

Takao Kawano, Yoichi Sakuma, Masatoshi Ohta, Toshiki Kabutomori, Mamoru Shibuya

Fusion Science and Technology / Volume 41 / Number 3P2 / May 2002 / Pages 981-987

Purification and Chemical Process / Proceedings of the Sixth International Conference on Tritium Science and Technology Tsukuba, Japan November 12-16, 2001 /

A method of decomposing hydrogen compounds was developed by employing a zirconium nickel (ZrNi) alloy. This method enables all tritium compounds (HTO, CH3T, C2H5T, etc.) in an exhaust gas to be decomposed into their respective elements, and the tritium itself to be removed in the form of hydrogen gas (HT). The method was developed through a series of experiments using methane. Using previous study results, a chemical reaction equation of methane decomposition on a ZrNi alloy is proposed and discussed. To ascertain the mechanism of methane decomposition on a ZrNi alloy, alloy samples were examined based on X-ray diffraction spectra and SEM electronographies before, during, and after the experiments. It was found that, as the decomposition time elapsed, peaks attributed to a pure ZrNi alloy gradually disappeared and new ones appeared in the X-ray spectra. The new peaks were attributed to the presence of ZrC, pure Ni, and a simple carbon substance. This indicates that the Zr in a carbon-bound alloy results in ZrC generation that releases Ni metal, and part of the C generated from the methane decomposition remains as a simple, as-grown substance. From these results, the decomposition reaction of methane using a ZrNi alloy can be represented by an equation involving the alpha value. The equation shows that one ZrNi molecule decomposes (1+ α) molecules of methane and generates 2(1+α) molecules of hydrogen. The alpha value was estimated based on the volume of decomposed methane and the weight of the ZrNi alloy used in the experiments. It is known that the alpha value is strongly dependent on the experimental conditions and can be used as an index to evaluate the decomposition condition.

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