Optical Hydrogen Sensor Based on the Elastic Clamping Effect

V. Palmisano, A. Baldi, M. Slaman, H. Schreuders and B. Dam

Department of Chemical Engineering, Delft University of Technology, Delft, The Netherlands Email: vpalmis@few.vu.nl

The development of fast, reliable and cheap hydrogen sensors is crucial for the social acceptance of hydrogen as a clean energy carrier. There are four important parameters related to the performance of a hydrogen detector: reliability, sensitivity, response time and lifetime. Hydrogen sensors based on fiber optics allows working in explosive environments thanks to the possibility of separating the sensing point from the electrical read-out.

Following the discovery of the switchable mirror effect [1] we developed an optical hydrogen detector [2] based on the change in the optical reflectance of a thin layer of Mg0.7Ti0.3 upon hydrogenation. The fiber optic hydrogen detector represents a unique combination of small dimensions, low cost and safety, however it only indicates whether the hydrogen pressure is above or below a certain threshold level.

We have shown that the thermodynamics of hydrogen absorption of thin Mg layers is strongly influenced by the chemical nature of the “cap” layer and that plateau pressures can be increased by a factor 300 respect to bulk Mg [3]. We exploit this effect in order to engineer a multistep sensor made by a thin film multilayer. To be able to detect different ranges of hydrogen concentrations the multilayer consists of various Mg layers sandwiched between different buffer materials. In particular we show a multilayer which can distinguish three ranges of hydrogen pressure: between 30 and 200 Pa; between 200 and 10000 Pa; higher than 10000 Pa. Another way to tune the equilibrium pressure is by varying the Mg thickness of clamped Mg thin films: we use this effect in order to make a device with a continuous measurement range between 200 and 4000 Pa. The device consists of a wedge of Pd-capped Mg: the hydrogen pressure is measured by the lateral progression of the portion of the film which undergoes the M-H transition. The clamping effect may also be exploited in multifiber hydrogen sensors by depositing the capped Mg wedge on a bunch of fibers. The main problem associated with the use of Pd-capped Mg layers is the low reproducibility upon cycling due to alloying at the interface between Mg and Pd [4]. Mg shows low hydrogenation kinetics at room temperature. To solve these inconveniency we are exploiting Mg alloys as alternative sensing materials. Furthermore, research of clamping materials with a Young modulus higher than Pd allows us to extend the measurement range.

References

1. J.N. Huiberts, R. Griessen, J.H. Rector, R. J. Wijngaarden, J.P. Dekker, D.G. de Groot, N.J. Koeman, Nature 380, 231 (1996).

2. M. Slaman, B. Dam, M. Pasturel, D.M. Borsa, H. Schreuders, J.H. Rector, and R.

Griessen,Sensors and Actuators B123, 538 (2007).

3. A. Baldi,M. Gonzalez-Silveira, V. Palmisano, B. Dam, and R. Griessen, Phys. Rev. Lett.

102, 226102 (2009).

4. Baldi A,V. Palmisano, M. Gonzalez-Silveira, Y. Pivak, M. Slaman, H. Schreuders, B.

Dam, and R. Griessen, Appl. Phys. Lett. 95 071903 (2009).

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Magnetocaloric Effects in Y

R

Fe

M

(H,D)

Compounds (R= Gd, Tb, Er; M=Al)

V. Paul-Boncour¹, T. Mazet², M. Phejar¹, O. Isnard³, C.V. Colin³

1Chimie Métallurgique des Terres Rares, ICMPE, CNRS et Université Paris XII, 2-8 rue H. Dunant, 94320 Thiais Cedex, France

2 Institut Jean Lamour, Département P2M, Nancy Université, UMR 7198, BP 70239, 54506 Vandœuvre-lès-Nancy Cedex, France

3Institut Néel, CNRS et université Joseph Fourier, BP 166, 38042 Grenoble Cedex 9, France

Y1-xRxFe2(H,D)4.2 compounds (R= Gd, Tb, Er) display a giant isotope effect (H,D) on the magnetic transition temperature (T_M) between a ferromagnetic (FM) and an antiferromagnetic (AFM) structure on the Fe sublattice [1]. This first order transition exhibits an itinerant electron metamagnetic behaviour. The FM-AFM transition temperature TM is very sensitive to the volume change, the (H,D) isotope content and the application of an external or internal field. The investigation of the magnetocaloric properties of YFe2D4.2

compound has shown an entropy variation at the transition (TM = 84 K, –ΔSM = 10.83 J.K^-

1.kg^-1 for a field variation of 5 T) close to that of Gd [2]. These compounds are interesting since they form a new family showing promising magnetocaloric properties. Their magnetic and magnetocaloric properties can be tuned by the chemical substitution of Y and Fe atoms but also by D for H substitution. The influence of the substitution of R for Y and Al for Fe has been investigated using magnetic and neutron diffraction measurements. Both types of substitution induce different changes on the magnetic structure. The aim of this study is to increase both the transition temperature and the magnetic entropy variation, in the purpose of magnetic refrigeration applications.

References

1. V. Paul-Boncour, M. Guillot, G. Wiesinger, G. André, Phys. Rev. B, 72 (2005) 174430 2. V. Paul-Boncour, T. Mazet, J. Appl. Phys., 105 (2009) 013914

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V-W Alloy Membranes for Hydrogen Purification

H.Yukawa¹, T.Nambu², M.Matsumoto³, M.Morinaga¹

1Department of Materials Science and Engineering, School of Engineering, Nagoya University, Japan

2Department of Materials Science and Engineering, Suzuka National College of Technology, Japan

3Department of Mechanical Engineering, Oita National College of Technology, Japan Email: hiroshi@numse.nagoya-u.ac.jp

Mass production of high purity hydrogen gas is necessary for the future clean energy systems. Hydrogen permeable membranes are important materials for hydrogen separation and purification technologies. Nb- and V-based alloys are ones of the most promising materials for hydrogen permeable membranes because of their lower cost and higher hydrogen permeability than currently used Pd-based alloys. However, there is a still large barrier to the practical application due to their poor resistance to hydrogen embrittlement.

Recently, a concept for alloy design of Nb-based hydrogen permeable membrane has been proposed [1]. Following this concept, Nb-based alloys with high hydrogen permeability and strong resistance to hydrogen embrittlement have been designed and developed. For example, designed Nb-5mol%W alloy possesses more than 4 times higher hydrogen permeability than Pd-26mol%Ag alloy without showing any hydrogen embrittlement [2].

In this study, the concept is further applied to V-based alloys. The mechanical properties of pure vanadium in hydrogen atmosphere are investigated by the in-situ SP test method in hydrogen atmosphere at 637~773K. It is found that the ductile to brittle transition occurs drastically at the hydrogen concentration around H/M=0.23. These results suggest that the resistance to hydrogen embrittlement will be improved by reducing the hydrogen concentration less than this critical value. For this purpose, the alloying effects on the hydrogen solubility and the resistance to hydrogen

embrittlement are investigated for V-based alloys. The hydrogen solubility is found to decrease by the addition of tungsten into vanadium. For example, V-5mol%W alloy absorbs only 0.2 (H/M) of hydrogen even in the hydrogen pressure of 0.3MPa at 773K.

On the other hand, the hydrogen fluxes, J, through the membrane are measured by the conventional gas permeation method at 673~773K. It is evident that V- 5mol%W alloy possesses more than 7 times higher permeability than Pd-26mol%Ag alloy without showing any evidence of hydrogen embrittlement, as shown in Fig.1.

References

1. H. Yukawa, T. Nambu, Y. Matsumoto, N. Watanabe, G.X. Zhang, and M. Morinaga,. Materials Transactions, 49 (2008), 2202-2207.

2. N. Watanabe, H. Yukawa, T. Nambu, Y. Matsumoto,

G.X. Zhang, and M. Morinaga, J. Alloys and Compounds, 477 (2009), 851-854.

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