The chemisorption of hydrogen on porous graphites at low pressure and at elevated temperature
1991; Elsevier BV; Volume: 182; Linguagem: Inglês
10.1016/0022-3115(91)90418-7
ISSN1873-4820
Autores Tópico(s)Muon and positron interactions and applications
ResumoThe plasma facing components of the vacuum chamber for thermonuclear fusion experiments are clad with graphite. Recycling of gases affects the plasma properties, and the tritium quantity accumulated in the graphite during the operation of Tokamaks with DT must be known. An adsorption isotherm for deuterium on the nuclear grade graphitic Matrix A3-3 was measured by using a volumetric method at 1173 K at pressures < 130 Pa. The data obey a Langmuir type isotherm for dissociative adsorption. The saturation concentration is 140 appm. The adsorption energy at 0 K was estimated as Ec = 2.5 eV/D2 using Fowler's equation. The isotherms calculated for Ec = 2.5 eV/D2 predict saturation of the adsorption sites in graphite at T ⩽ 700 K and PD2 ⩾ 0.1 Pa. At T ⩾ 1173 K and PD2 ⩽ 10−2 Pa the adsorbed quantity is less than 1% of the saturation level. A C-H bond energy Eb ⋍ 3.4 eV/H and an activation energy of desorption Ed ⋍ 4 eV/H2 was estimated from a Lennard-Jones potential energy diagram. The partial pressures of hydrocarbons Cn⩽ 3Hm in equilibrium with graphite were calculated. At total pressures < 10−2 Pa the partial pressures of these hydrocarbons are less than 10−7 Pa in the temperature range 600–1500 K.
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