Permeable Alloys Research Articles

Phase Equilibria of the V-Ti-Fe System and Its Applications in the Design of Novel Hydrogen Permeable Alloys.

The precise liquidus projection of the V-Ti-Fe system are crucial for designing high-performance hydrogen permeation alloys, but there are still many controversies in the research of this system. To this end, this article first uses the CALPHAD (CALculation of PHAse Diagrams) method to reconstruct the alloy phase diagram and compares and analyses existing experimental data, confirming that the newly constructed phase diagram in this article has good reliability and accuracy. Second, this obtained phase diagram was applied to the subsequent development process of hydrogen permeation alloys, and the (Ti65Fe35)100-xVx (x = 0, 2.5, 5, 10, 15, 25) alloys with dual-phase {bcc-(V, Ti) + TiFe} structure were successfully explored. In particular, the alloys with x values equal to 2.5 at.% and 5 at.% exhibit relatively high hydrogen permeability. Third, to further increase the H2 flux permeation through the alloys, a 500-mm-long tubular (Ti65Fe35)95V5 membrane for hydrogen permeation was prepared for the first time. Hydrogen permeation testing showed that this membrane had a very high H2 flux (4.06 mL min-1), which is ca. 6.7 times greater than the plate-like counterpart (0.61 mL min-1) under the same test conditions. This work not only indicates the reliability of the obtained V-Ti-Fe phase diagram in developing new hydrogen permeation alloys, but also demonstrates that preparing tubular membranes is one of the most important means of improving H2 flux.

Phase Equilibria, Solidified Microstructure, and Hydrogen Transport Behaviour in the V-Ti-Co System.

At present, the V-Ti-Co phase diagram is not established, which seriously hinders the subsequent development of this potential hydrogen permeation alloy system. To this end, this article constructed the first phase diagram of the V-Ti-Co system by using the CALculation of PHAse Diagrams (CALPHAD) approach as well as relevant validation experiments. On this basis, hydrogen-permeable VxTi50Co50-x (x = 17.5, 20.5, …, 32.5) alloys were designed, and their microstructure characteristics and hydrogen transport behaviour were further studied by XRD, SEM, EDS, and so on. It was found that six ternary invariant reactions are located in the liquidus projection, and the phase diagram is divided into eight phase regions by their connecting lines. Among them, some alloys in the TiCo phase region were proven to be promising candidate materials for hydrogen permeation. Typically, VxTi50Co50-x (x = 17.5-23.5) alloys, which consist of the primary TiCo and the eutectic {bcc-(V, Ti) and TiCo} structure, show a high hydrogen permeability without hydrogen embrittlement. In particular, V23.5Ti50Co26.5 exhibit the highest permeability of 4.05 × 10-8 mol H2 m-1s-1Pa-0.5, which is the highest value known heretofore in the V-Ti-Co system. The high permeability of these alloys is due in large part to the simultaneous increment of hydrogen solubility and diffusivity, and is closely related to the composition of hydrogen permeable alloys, especially the Ti content in the (V, Ti) phase. The permeability of this alloy system is much higher than those of Nb-TiCo and/or Nb-TiNi alloys.

A novel method to design Nb(W)–Ti–Co(Fe) alloy membrane with high hydrogen permeability and strong resistance to hydrogen embrittlement

A hydrogen permeable Nb43W5Ti27Co20Fe5 alloy membrane was designed and its microstructure and hydrogen transportation performances were systematically studied. W mainly dissolves into primary body-centered cubic (bcc)-(Nb) phases, while Fe is captured in eutectic structures. Substituting Nb with W leads to a substantial reduction in hydrogen solubility and substituting Co with Fe negligibly affects hydrogen solubility. The W and Fe substitutions contribute to an enhanced intrinsic hydrogen diffusion coefficient D∗. The designed Nb43W5Ti27Co20Fe5 alloy membrane exhibits lower hydrogen solubility and higher hydrogen permeability at temperatures below 623 K than that of the original Nb48Ti27Co25 alloy membrane. No hydrogen-induced failures were found for the designed Nb43W5Ti27Co20Fe5 alloy membrane during cooling to room temperature and under long-term hydrogen permeation at 673 K for 72 h, whereas the original alloy membrane failed at 444 K during cooling to room temperature and after 19 h during hydrogen permeation at 673 K. The designed Nb43W5Ti27Co20Fe5 alloy membrane exhibits high hydrogen permeability and strong resistance to hydrogen embrittlement.

Mechanism of tungsten strengthening hydrogen transportation in Nb48Ti27Co25 hydrogen permeable alloy membrane

Substitution of Nb by W in Nb48Ti27Co25 dual phase hydrogen permeable alloy was carried out. The elemental W replacing Nb mainly dissolved into the primary body-centered cubic (bcc)-(Nb) phase to modify its composition and crystal lattice. The W alloying effect on hydrogen transportation was systematically discussed based on hydrogen chemical potentials and first principle calculations. The substitution of Nb by W reduced the hydrogen solubility, and led to an improved intrinsic hydrogen diffusion coefficient, especially at temperature below 573 K, which promoted the hydrogen permeation flux of Nb48Ti27Co25 alloy membrane at 523 K. According to the theoretical study based on density function theory of the Nb–W system, the reduced hydrogen solubility can be attributed to the weakened binding strength between hydrogen atoms and the bcc-(Nb) lattice and the reduced charge gained by hydrogen atoms after W substitution for Nb. In addition, the W occupying the Nb sublattice can change the diffusion path of hydrogen atoms in the bcc-(Nb) lattice, thereby reducing the diffusion energy barrier for high hydrogen diffusivity.

Microstructure and hydrogen transport properties of (V90Cr5Al5)90Cu10 alloy membranes

Our newly developed V90Cr5Al5 hydrogen permeable alloy has been extended to enhance malleability by Cu alloying. The resulting (V90Cr5Al5)90Cu10 consists of bcc-(V) and fcc-(Cu) phases and can be cold rolled into a thin membrane with a thickness of 0.1 mm due to the introduction of the ductile copper phase. After rolling and annealing, (V90Cr5Al5)90Cu10 contains finer grains and a higher percentage of special grain boundaries compared to the as-cast case. The rolled/annealed (V90Cr5Al5)90Cu10 exhibits a lower hydrogen diffusivity than the as-cast one, but a significantly improved hydrogen permeation flux due to the reduced membrane thickness and the inverse relationship of flux and thickness. Typically, a pronounced high hydrogen flux of ∼72 cc H2 cm−2min−1 was achieved at a hydrogen pressure difference of 0.6 MPa at 673 K. In comparison with V90Cr5Al5, Cu alloyed membranes exhibit enhanced resistance against hydrogen embrittlement and enhanced long-term hydrogen permeation stability at 673 K.

Regenerative effect tissue engineering scaffold based on fibrous permeable TiNi-based alloy

The aim of this study was to explore the in vivo applicability of intracorporeal constructions with hepatocytes cultured in the fiber TiNi-based scaffold (FTNS). We also sought to determine whether application of hepatocytes cultured in the FTNS was superior to simple hepatocyte injection in terms of restoration of liver functions and survival time in a CCl4-induced hepatitis rat model. In investigation 200 animals were assigned to explore the experimental groups as follows: Group I – control; Group II – animals with CCl4-induced hepatitis; Group III – animals with toxic hepatitis followed by implantation of cell-free FTNS (sham-surgery); Group IV – animals with toxic hepatitis followed by infusion of hepatocytes only (20 × 106 cells/ml); Group V – animals with toxic hepatitis followed by implantation of hepatocytes cultured in the FTNS. In terms of restoration of liver function, Group V showed a significant reduction of serum alanine aminotransferase level compared to Group II. Group IV also showed a significant decrease in ALT level at 15 days. However, the level of ALT increased at 30 days, and the level was similar with results of the Group II. This probably was caused by a short-term effect of hepatocyte injection only. The change patterns of serum protein, lactate, albumin, fibrinogen, and total bilirubin levels were similar to the results of ALT. The survival time of animals was significantly longer in Group V. These findings showed possible abilities of the FTNS as a scaffold to support the hepatocellular metabolism. Using 12 animals, image analysis of SEM data of in vivo hepatocyte evolution in the FTNS was carried out. In the SEM analysis, hepatocytes demonstrated good adhesion and proliferation in the pore space of the FTNS. Moreover, mature tissue comprising both colloidal and fibrous components filled the pore body by 95% in 28 days. Overall, this study sheds a light on how the implantable «auxiliary liver» by engrafting the cultured FTNS substitutes the missing hepatic function without the need to replace the whole liver.

Direct high-purity hydrogen production from ammonia by using a membrane reactor combining V-10mol%Fe hydrogen permeable alloy membrane with Ru/Cs2O/Pr6O11 ammonia decomposition catalyst

The hydrogen production capabilities of the membrane reactor combining V-10 mol%Fe hydrogen permeable alloy membrane with Ru/Cs 2 O/Pr 6 O 11 ammonia decomposition catalyst are studied. The ammonia conversion is improved by 1.7 times compared to the Ru/Cs 2 O/Pr 6 O 11 catalyst alone by removing the produced hydrogen through the V-10mol%Fe alloy membrane during the ammonia decomposition. 79% of the hydrogen atoms contained in the ammonia gas are extracted directly as high-purity hydrogen gas. Both the Ru/Cs 2 O/Pr 6 O 11 catalyst and the V-10 mol% Fe alloy membrane are highly durable, and the initial performance of the hydrogen separation rate lasts for more than 3000 h. The produced hydrogen gas conforms to ISO 14687–2:2019 Grade D for fuel cell vehicles because the ammonia and nitrogen concentrations are less than 0.1 ppm and 100 ppm, respectively. • Reactor combing V-alloy membrane and Ru catalyst for H 2 production from NH 3 . • High purity H 2 conforming to ISO standards for FCV is produced directly from NH 3 . • NH 3 conversion of Ru catalyst increases 1.7 times by combining with V-alloy membrane. • 79% of the H contained in the supplied NH 3 is directly extracted as high purity H 2 . • The stable H 2 separation flux lasts for more than 3000 h.

Design of Nb-Ti-Fe hydrogen permeable alloys based on the ductile-to-brittle transition-hydrogen concentration region

Nb-based dual-phase alloys are one of the most promising candidates for hydrogen purification. To solve their brittle fracture in hydrogen-containing atmospheres, the ductile-to-brittle transition-hydrogen concentration (DBTC) is a significant reference index, and the dissolved hydrogen concentration should be controlled below the lower limit of the DBTC, i.e., 0.72 H/M (atomic hydrogen to metal ratio). In this study, hydrogen permeable Nb-Ti-Fe alloys were designed and developed by using the above DBTC concept. Four hyper-eutectic Nb-Ti-Fe alloy membranes were prepared, and their hydrogen solubility was systematically analyzed by corresponding pressure-composition isotherms (PCT curves). The results show that all these samples had a linear relationship between the hydrogen concentration and square root of the hydrogen pressure between 0.1 and 0.4 MPa, which is in accordance with the Sieverts’ law. The hydrogen solubility of the specimens containing the primary TiFe phase was lower than 0.72 H/M, but the alloys with the primary Nb phase had a value that was much higher. The latter was completely broken during the test, even if the feed hydrogen pressure was reduced to 0.15 MPa. Based on the above results and DBTC concept, novel insights into the design of Nb-Ti-Fe hydrogen permeable alloys were elucidated; that is, an improvement in both the hydrogen permeability and hydrogen embrittlement resistance can be attained by controlling the hydrogen solubility. Following this concept, a Nb5Ti58Fe35Cu2 alloy was successfully developed that exhibited a high permeability of 4.32 × 10−8 mol H2 m−1 s−1 Pa−0.5 at 673 K, which is 2.7 times than that of a pure Pd membrane under the same test conditions. The present work demonstrated the feasibility and applicability of the DBTC concept in the design of dual-phase Nb-Ti-Fe hydrogen permeable alloy membranes.

Tailoring the hydrogen transport properties of highly permeable Nb51W5Ti23Ni21 alloy membrane by Pd substitution

The substitutions of Ni and Ti/Ni by 5 at% Pd in Nb51W5Ti23Ni21 alloy were performed and the alloying effects of Pd on microstructures and hydrogen transport properties were investigated. The description of hydrogen permeation flux based on hydrogen chemical potentials was applied to depict the dependence of hydrogen permeation flux on hydrogen solubility. Substituting Ni and Ti/Ni by Pd cause the reduced hydrogen solubility, leading to the enhanced resistance to hydrogen embrittlement. The Pd substituting Ni and Ti/Ni induce the decreased hydrogen permeation flux, which can be attributed to the decreased hydrogen solubility and the slightly decreased intrinsic hydrogen diffusion coefficient. The Nb51W5Ti23Ni16Pd5 alloy membranes exhibits strong resistance to hydrogen embrittlement which shows no failure when cooled down to room temperature under hydrogen atmosphere.

Nb35Hf32.5Co32.5 dual-phase alloy: Hydrogen permeability degradation due to the microstructural changes caused by annealing

NbxHf(100-x)/2Co(100-x)/2 (30 ≤ x ≤ 50) alloys are a type of typical dual-phase materials with advantages of excellent hydrogen permeability, high intensity, and low cost, which are at the forefront of the development trends of new materials used for hydrogen separation. However, changes in the microstructure and hydrogen permeability after annealing of the hypereutectic alloys were unknown until now. To this end, the effect of annealing on the microstructure and hydrogen permeability of Nb35Hf32.5Co32.5 alloy is investigated in this paper. The results show that this alloy still possesses a hypereutectic structure after short-time annealing, but the above microstructural characteristics gradually disappear with an increase of annealing time (or temperature), and some new impurity phases (e.g. Co2Nb, Co2Hf and Co6Nb7) are formed. With this change, the alloys show a gradual reduction in hydrogen permeability, which is mainly attributed to the transition of the bcc-(Nb, Hf) phase in the eutectic structure, from a continuous thin layer to discontinuous granules. Furthermore, brittle fracture occurs in the alloy membranes after long-time annealing at various temperatures due to the formation of the above impurity phases. This study demonstrates that annealing cannot improve the hydrogen permeability, and on the contrary, it deteriorates the hydrogen embrittlement resistance of the Nb-Hf-Co hydrogen permeable alloys.

Design of Nb-Ti-Fe Hydrogen Permeable Alloys Based on the Ductile-to-Brittle Transition-Hydrogen Concentration Region

Design of Nb-Ti-Fe Hydrogen Permeable Alloys Based on the Ductile-to-Brittle Transition-Hydrogen Concentration Region

Flexible Hydrogen Sensor Using Ni-Zr Alloy Thin Film

A triple-layered PMMA/Ni64Zr36/PDMS hydrogen gas sensor using hydrogen permeable alloy and flexible polymer layers is fabricated through spin coating and DC-magnetron sputtering. PDMS(polydimethylsiloxane) is used as a flexible substrate and PMMA(polymethylmethacrylate) thin film is deposited onto the Ni64Zr36 alloy layer to give a high hydrogenselectivity to the sensor. The measured hydrogen sensing ability and response time of the fabricated sensor at high hydrogen concentration of 99.9 % show a 20 % change in electrical resistance, which is superior to conventional Pd-based hydrogen sensors, which are difficult to use in high hydrogen concentration environments. At a hydrogen concentration of 5 %, the resistance of electricity is about 1.4 %, which is an electrical resistance similar to that of the Pd77Ag23 sensor. Despite using low cost Ni64Zr36 alloy as the main sensing element, performance similar to that of existing Pd sensors is obtained in a highly concentrated hydrogen atmosphere. By improving the sensitivity of the hydrogen detection through optimization including of the thickness of each layer and the composition of Ni-Zr alloy thin film, the proposed Ni-Zr-based hydrogen sensor can replace Pd-based hydrogen sensors.

Phase composition of macroporous Ni-Al alloys obtained by combustion synthesis

This paper discusses the phase composition of macroporous Ni-Al alloys obtained by self-propagating high-temperature synthesis. The alloys have been synthesized in a nonstationary combustion mode. The combustion wave consists of super adiabatic foci, and macroporous structure is realized under the action of capillary hydrodynamic effects. The influence of reaction mixture composition of aluminium in the range of 13.5-31.5 wt.% is also discussed. The specific requirements to obtain the single phase B2 NiAl and LI2 Ni3Al as well as biphase gas permeable alloys with the average size of structure elements in the range of 1.2-3.15 mm are described in the paper.

Effect of Pd overlayer and mixed gases on hydrogen permeation of Pd/Nb30Hf35Co35/Pd composite membranes

Effect of Pd overlayer and mixed gases on hydrogen permeation of Pd/Nb30Hf35Co35/Pd composite membranes was investigated. The diameter of Pd particle increases with increasing sputtering power. With this change, the membrane shows a signification reduction in hydrogen permeability/or flux, but its durability and stability increases significantly, which can be mainly attributed to a decrease in hydrogen solubility coefficient. In addition, H2S impurity in mixed gases can greatly degrade membrane performance, especially the hydrogen permeability, whereas the Ar impurity content has less effect in the temperature range of 523–673 K. Lowering of permeability caused by the change of gas purity can be attributed to a decrease in hydrogen solubility, which is closely related to the stronger adsorption of H2S molecules to the Pd overlayer of the membrane. Thus, it is concluded that aside from the optimum design for composition of Nb-based hydrogen permeable alloy to improve their permeability, the control of Pd overlayer film on membrane surface and gas purity in the feed gas is important.

Design and characterizations of novel Nb-ZrCo hydrogen permeation alloys for hydrogen separation applications

Novel Nb–ZrCo hydrogen permeable alloys are developed as potential membrane materials for hydrogen separation applications. Microstructures, hydrogen permeation behavior and the resistance to hydrogen embrittlement of NbxZr(95-x)/2Co(105-x)/2 (x = 15 … 40) alloys are studied. Three different microstructures are found in these alloys, particularly (a) the primary ZrCo phase and eutectic {bcc-(Nb, Zr) + B2-ZrCo} for x < 25, (b) the fully eutectic for x = 25 and (c) the primary bcc-(Nb,Zr) and eutectic for x > 25. Alloys with Nb content between 20 and 30 at.% present higher permeation results. Increase in Nb content lead to higher hydrogen permeability (Φ), but poorer embrittlement resistance, which can be attributed to an increase in hydrogen solubility. Nb25Zr35Co40 exhibits an appropriate balance between hydrogen permeability and embrittlement resistance. Permeability is improved apparently and hydrogen embrittlement resistance is also further strengthened for directionally solidified (DS) Nb25Zr35Co40, which is mainly attributed to a decrease in hydrogen solubility and the significant increment of hydrogen diffusivity. The present work demonstrates that the newly developed alloys could be used as potential candidate for hydrogen separation applications.

The Effect Infrared and Ultraviolet Radiation in the Development of the Cells in the Porous Permeable Titanium Nickel Based Alloy Scaffold

The respond of the cells to electromagnetic radiation depends on many factors, including microenvironment. Different cells exhibit different behavior when exposed to low-intensity radiation employed in the research. The effect of infrared (IR) and ultraviolet (UV) radiation leads to the reliable change in the number of viable cells. Viable cells of Ehrlich tumor, spleen and bone marrow of C57BL/6 mice placed in a porous permeable TiNi-based alloy scaffold were studied. The level of the radiation effect was determined for different types of cells. A comparative analysis of the viable cells cultured in the porous permeable TiNi scaffold was performed.

Investigation of New Ammonia Synthesis Process Utilizing Vanadium-Based Hydrogen Permeable Alloy Membrane

Investigation of New Ammonia Synthesis Process Utilizing Vanadium-Based Hydrogen Permeable Alloy Membrane

Improvement of Hydrogen Permeability of Pd-Gd Film by Removal of Inclusion Particles – Part 1: Removal of Inclusion Particles

It was hard to make a thinner film of hydrogen permeable alloy by rolling when small nonmetallic inclusion particles with the size of 5 to 30 μm were present in the alloy. For this reason, the removal of nonmetallic inclusion particles from Pd-Gd alloy were examined using various fluoride fluxes. In the experiments on the removal of nonmetallic inclusion particles from Pd-7 to 16 mass% Gd alloys, the lowest total oxygen content was obtained by the addition of GdF3 flux.

Asymmetric layered vanadium membranes for hydrogen separation

Layered alloy membranes, with sub-micron Pd catalyst layers over a highly permeable vanadium alloy core, provide a low-cost alternative to supported Pd-alloy membranes. Despite the minimal Pd consumption, Pd still comprises a significant fraction of the overall membrane costs, and further cost reductions can be achieved by replacing Pd with suitable alternative catalytic layers. Ni is an obvious candidate, exhibiting high catalytic activity for a range of reactions while being relatively inexpensive, but its instability in syngas renders it unsuitable as a feed-side catalyst. The permeate surface of an alloy membrane is exposed to H2 only during operation, making Ni of interest as a permeate-side catalyst.Asymmetric Pd/V/Ni alloy membranes have been fabricated with varying Ni thickness, and hydrogen permeance has been examined over a wide range of pressures and temperatures. Hydrogen permeance increases with decreasing Ni thickness, down to a limiting thickness of 150nm, beyond which permeance degraded due to incomplete Ni coverage. The permeance was 65% that of a symmetrical Pd/V/Pd membrane with 500nm Pd layers. The cost-effectiveness is dependent on raw Pd price and manufacturing costs.

Hydrogen permeation behavior of Nb30Ti35Ni35−xCox (x = 0…35) alloys containing high fractions of eutectic

The hydrogen permeability of cast Nb30Ti35Ni35−xCox (x = 0…35) alloys is found to increase with the Co content, induced by the tailored microstructures containing high fractions of eutectic and less primary phase. Among the cast alloys, Nb30Ti35Co35 consisting entirely of eutectic exhibits the highest permeability, particularly 2.65 × 10−8 mol H2 m−1 s−1 Pa−0.5 at 673 K. This permeability is further increased to 3.58 × 10−8 mol H2 m−1 s−1 Pa−0.5 by aligning eutectic grains perpendicularly to the membrane surface using directional solidification. The high permeability is attributed to the high hydrogen solubility and diffusivity in alloys. Our work demonstrates that hydrogen permeable alloys containing high fractions of eutectic may exhibit high permeability by adequately optimizing morphology, volume fraction and alignment of the bcc-Nb phase in the eutectic as the pathways for hydrogen permeation.