F. Legarda

Diffusive transport parameters and surface rate constants of deuterium in Incoloy 800

Abstract A gas permeation technique has been used to obtain the complete set of deuterium transport parameters in Incoloy 800 with deuterium driving pressures ranging from 10 4 to 1.5×10 5 Pa and temperatures from 427 to 780 K. The deuterium diffusive transport parameters obtained are: D ( m 2 s −1 )=3.87×10 −7 exp (−47.8 ( kJ mol −1 )/RT) , K s ( mol m −3 Pa −1/2 )=0.102 exp (−7.8 ( kJ mol −1 )/RT) , Φ ( mol m −1 s −1 Pa −1/2 )=3.94×10 −8 exp (−55.6 ( kJ mol −1 )/RT) . The deuterium surface rate constants for a non-oxidized surface has been evaluated as: σk 1 ( mol m −2 s −1 Pa −1 )=2.67×10 −10 exp (−40.1 ( kJ mol −1 )/RT) , σk 2 ( mol −1 m 4 s −1 )=2.58×10 −8 exp (−24.5 ( kJ mol −1 )/RT) , and for an oxidized surface: ( σk 1 ) ′ ( mol m −2 s −1 Pa −1 )=4.14×10 −6 exp (−44.3 ( kJ mol −1 )/RT) , ( σk 2 ) ′ ( mol −1 m 4 s −1 )=4.00×10 −4 exp (−28.6 ( kJ mol −1 )/RT) .

Deuterium transport in SiCf/SiC composites

Abstract A time-dependent gas-phase isovolumetric desorption technique has been used over a temperature range of 675–1029 K and driving pressures ranging from 13 to 101 kPa, to obtain the deuterium transport parameters diffusivity, D, and solubility, S, in a 3-D SiCf/SiC composite. The values obtained are: D(m2s−1)=1.1×10−4 exp[−107.7 (kJ/mol)/RT], S( mol m −3 )=1.9×10 3 exp[−30.2(kJ/mol)/RT]. The set of measurements performed at the same temperature, 871 K, and different loading pressures 13, 33, 60, 101 kPa, has evidenced a power relationship of solubility versus loading pressure with exponent 0.22, departing from Sieverts’ law. These results are compared with the parameters previously obtained for different types of monolithic SiC, and explained on the basis of the physico-chemical phenomena foreseen within its particular structure. The same experiment has been performed with two sets of specimens manufactured using different variants of the hybrid CVI/PIP technique; a negligible variation of transport parameters has been accounted between both groups of specimens.

Characterisation of deuterium transport in the fibres and matrix of a 3D-SiCf/SiC composite

A non-stationary heterogeneous transport model has been used to simulate a series of deuterium absorption–desorption tests carried out with two sets of 3D-SiCf/SiC composite specimens over a temperature range of 675–1029 K and driving pressures ranging from 13 to 101 kPa. The deuterium transport parameters corresponding to each phase of the composite have been derived showing the following Arrhenius tendencies for the diffusivity and solubility in the matrix: Dm (m2 s−1)=9.0×10−8 exp(−39.0 (kJ mol−1)/RT), Sm (mol m−3)=1.9×105 exp(−70.7 (kJ mol−1)/RT), and the fibre: Df (m2 s−1)=1.6×10−11 exp(−91.0 (kJ mol−1)/RT), Sf (mol m−3)=2.1×101 exp(−28.5 (kJ mol−1)/RT), the solubilities being referred to 105 Pa. The different manufacturing procedures followed in the preparation of the specimens have not provoked a noticeable variation of the deuterium transport characteristics of the matrix or the fibres. The results are compared with the parameters previously obtained for different types of silicon carbide and the same material with a homogeneous transport model. The differences found are explained on the basis of the physico–chemical phenomena foreseen within its particular structure.