Abstract
The effect of substitution of Nb by Mo in Nb40Ti30Ni30 was investigated with respect to microstructural features and hydrogen dissolution, diffusion and permeation. As-cast Nb40−xMoxTi30Ni30 (x = 0, 5, 10) alloys consist of primary bcc-Nb phase and binary eutectic (bcc-Nb + B2-TiNi). The substitution of Nb by Mo reduces the hydrogen solubility in alloys, but may increase (x = 5) or decrease (x = 10) the apparent hydrogen diffusivity and permeability. As-cast Nb35Mo5Ti30Ni30 exhibits a combined enhancement of hydrogen permeability and embrittlement resistance as compared to Nb40Ti30Ni30. This work confirms that Mo is a desirable alloying element in Nb that can contribute to a reduction in hydrogen absorption and an increase in intrinsic hydrogen diffusion, thus improving embrittlement resistance with minimal permeability penalty.
Highlights
The effect of substitution of Nb by Mo in Nb40Ti30Ni30 was investigated with respect to microstructural features and hydrogen dissolution, diffusion and permeation
Foremost among the possible choices of metallic membrane materials are Pd-based alloys due to their high catalytic surface property, reasonable hydrogen permeability, good durability and tolerance to syngas species. It was reported in refs 9 and 10 that a nominal hydrogen production capacity of 40 Nm3/h and an energy efficiency of 70–76% could be reached by a modern steam reforming system with Pd-based alloy membranes
A higher capability in hydrogen production of 12.3 kg per ton of olive mill wastewater (OMW) was reached by catalytic reforming of the combined OMW and methane in a Pd-Ag membrane reactor[12]
Summary
Calculated hydrogen permeability plotted against the upstream pressure (Pu) for the as-cast Nb40Ti30Ni30 (a), Nb35Mo5Ti30Ni30 (b) and Nb30Mo10Ti30Ni30 (c) alloy membranes at 523...673. The as-cast Nb35Mo5Ti30Ni30 exhibits an attractive hydrogen permeability, 3.13 × 10−8 mol H2 m−1s−1Pa−0.5 at 673 K This is ~1.96 times that of pure Pd. At higher Pu values (>0.4 MPa), the decrease of Φ with increasing Pu indicates a deviation from ideal Sieverts’-type behavior, which is expected from the hydrogen absorption data. The fracture temperature gradually decreases with increasing the Mo content This indicates that the substitution of Nb by Mo improves the HE resistance, which can straightforwardly be attributed to the decrasing hydrogen solubility (see Fig. 3). This alloy has high potential to serve as non-Pd alloy membrane for hydrogen separation
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