WO2015080577A1 - Large pressure range hydrogen sensor - Google Patents

Large pressure range hydrogen sensor Download PDF

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Publication number
WO2015080577A1
WO2015080577A1 PCT/NL2014/050805 NL2014050805W WO2015080577A1 WO 2015080577 A1 WO2015080577 A1 WO 2015080577A1 NL 2014050805 W NL2014050805 W NL 2014050805W WO 2015080577 A1 WO2015080577 A1 WO 2015080577A1
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Prior art keywords
hydrogen
metal
alloy
layer
optical
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PCT/NL2014/050805
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French (fr)
Inventor
Christiaan BOELSMA
Bernard Dam
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Technische Universiteit Delft
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Publication of WO2015080577A1 publication Critical patent/WO2015080577A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/0005—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes
    • C01B3/001—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof
    • C01B3/0031—Intermetallic compounds; Metal alloys; Treatment thereof
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/55—Specular reflectivity
    • G01N21/552—Attenuated total reflection
    • G01N21/553—Attenuated total reflection and using surface plasmons
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/005—H2
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/17—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on variable-absorption elements not provided for in groups G02F1/015 - G02F1/169
    • G02F1/178—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on variable-absorption elements not provided for in groups G02F1/015 - G02F1/169 based on pressure effects
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • G01N21/7703—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator using reagent-clad optical fibres or optical waveguides
    • G01N2021/7706—Reagent provision
    • G01N2021/7709—Distributed reagent, e.g. over length of guide
    • G01N2021/7716—Distributed reagent, e.g. over length of guide in cladding
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • G01N21/7703—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator using reagent-clad optical fibres or optical waveguides
    • G01N2021/7706—Reagent provision
    • G01N2021/772—Tip coated light guide
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • G01N21/7703—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator using reagent-clad optical fibres or optical waveguides
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2202/00—Materials and properties
    • G02F2202/34—Metal hydrides materials
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/32—Hydrogen storage

Definitions

  • the present invention relates to a thin-film device, to a method for producing a thin-film device, to an alloy for hydrogen absorption, to a method for producing a hydrogen absorption alloy, to use of a hydrogen absorption alloy for detecting a chemical species such as hydrogen, to a hydrogen sensor, to an apparatus for detecting hydrogen and to an electro-magnetic transformer comprising said sensor.
  • a prior art thin-film device comprises a substrate, an active sensing layer whose optical properties change depending on hydrogen content and a protective layer on the active sensing layer .
  • WO2007/126313 discloses a switchable mirror device comprising an active layer, wherein said active layer changes its optical properties upon addition or removal of hydrogen and comprises a hydrogen and oxygen permeable and water impermeable layer, wherein said layer is liquid water impermeable and water vapour permeable and has hydrophobic surface properties.
  • the present invention therefore relates to a thin-film device and further aspects thereof, which overcomes one or more of the above disadvantages, without compromising functionality and advantages.
  • the invention relates to a thin-film device according to claim 1, comprising the present alloy.
  • the present invention provides controlled and reliable absorption, specifically of hydrogen, over a large range of hydrogen pressures, with a large optical contrast over the whole pressure range, which optical contrast is built up slowly or slow enough, instead of e.g. instantaneously at a given threshold.
  • a means for monitoring a (varying) hydrogen concentration over a large range of pressures is provided.
  • the present optical system is much safer to use and to handle compared to e.g. electrical (conducting) sensors, especially in environments where a large electro-magnetic field may be present.
  • the present thin thin-film device comprises a substrate, an active sensing layer whose optical properties change continuously as a function of hydrogen content, a Pd cap layer to dissociate hydrogen which acts simultaneously as a protective coating for the sensing layer, and a protective lay ⁇ er coating the Pd which protects this cap layer.
  • a person of skill in the art is able to identify many suitable substrate materials upon which a thin-film device such as the thin-film device of the invention can be constructed.
  • suitable substrate materials include glass, guartz, indium-tin oxide, etc.
  • the substrate material is preferably optically transparent (more than 95%) , at least over a proportion of the visible, UV and/or IR regions of the electromagnetic spectrum (200 nm- 3000 nm) . Such provides for use of white light, IR-light, UV-light, a laser with a specific wavelength, and combinations thereof.
  • optical sensing layers with variable optical properties depending on e.g. a hydrogen content of the layer, comprising an alloy
  • the sensing layer is the pre ⁇ sent alloy.
  • the alloy comprises at least a first metal and a second metal.
  • characteristics of a metal are that they may oxidize, may form a cation, may be an electrical con ⁇ ductor, etc.
  • the first and second metal have an eguilibrium pressure (Pa) for hydrogen absorption.
  • Pa eguilibrium pressure
  • Such an equilibrium pressure per se can be measured with means known to a person skilled in the art. Typically it is measured at ambient temperature (300 K) .
  • the hydrogen equilibrium pressure (Pa) of the first metal is at least 5*10 3 times as large as the hydrogen equilibrium pressure (Pa) of the second metal, preferably at least 10 4 times, more preferably at least 5*10 4 times, even more preferably at least 5*10 5 times, such as 10 6 -10 15 times.
  • a few examples of such alloys are: A x B y C z , with A being selected from alkaline earth-metals (Group II), preferably from Mg, and Ca, B being selected from Zr, Hf, Nb, Y, La, and Ta, preferably Zr, Hf and La, and C being selected from a period 4 transition metal (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) , preferably Sc, Ti, Ni and V,_with ranges preferably as follows:
  • the alloy from doped MgZr alloy, a doped MgHf alloy, a doped MgV alloy, a doped MgNb alloy, a doped MgTa alloy a doped MgY alloy, and a doped MgLa alloy. These alloys provide the advantages in particular.
  • first and second hydrogen pressures of more than 10 s is possible.
  • an additional or ⁇ der of magnitude (10 7 ) is possible, especially when a fourth metal is used.
  • detectable pressures may be expanded by including in the alloy a metal having a significant lower, or. higher, hydrogen, equilibrium, pressure, compared to the first and second metal. It is noted that as the equilibrium pressures are taken with respect to one and another, e.g. a pressure of a first and a second metal, it is in principle less relevant by what exact way of measurement individual pressures are determined .
  • the alloy comprises a metal providing the alloy X-ray amorphous- ness, i.e. as identified by X-ray diffraction techniques.
  • This metal may relate to a third metal, being different from the first and second metal, or it may be the same as any of the first and second metal.
  • An indication of presence of amorphous- ness is given by taking an X-ray measurement of an alloy, and identifying presence or absence of amorphousness ; for the pre ⁇ sent alloy presence is required. The identification of presence or absence of X-ray amorphousness is considered an objective determination.
  • an amorphous or non-crystalline solid relates to a solid that lacks long-range order characteristic of a crystal.
  • the alloy of the optical sensing layer has a distribution of interstitial sites.
  • the sites being characterized and formed by surrounding atoms of the alloy. In a regular crystal such sites could relate to tetraeder and octaeder sites. Also coordination number and interatomic distance may be taken into account.
  • the present alloy may be largely amorphous, only in very small domains such regular sites may be observed. Most sites however are even then at least partially distorted. The sites are in principle considered suited for hy- drogen absorption.
  • the distribution comprises at least four different (types of) sites, preferably at least 10 different (types of) sites, more preferably at least 100 different (types of) sites, such as at least 10 3 different sites (types of) / ⁇ 3 (i.e. taken per unit volume). It is noted that in an. amorphous structure any first site may be different from any second site; thus an enormous amount .of different sites may be present, such as 10 4 different sites/ ⁇ 3 . A difference may further relate to a (slight) variation with respect to hydrogen absorption energy-
  • An effect of the present alloy is a large gap material forms on hydrogenation of at least one of the constituents, a good (hydrogen) diffusion, and. high (optical) dynamics resulting in a wide range of hydrogen pressures that can be detected.
  • MgTi provides 0.5-1 order of detection, whereas adding Zr to the alloy even 3 orders of detection or more are obtained.
  • Inventors provide a sensing material with a large optical contrast over a wide pressure range.
  • the optical sensing layer may be amorphous, and may be in a sequence of layers or layer stacks or in 2- or 3- dimensional domains. It is preferred to use an amorphous layer, as a broader range of e.g. hydrogen absorption pressures is obtained, more preferably an amorphous zircon comprising layer.
  • a term as "on top” may relate to a se ⁇ quence of e.g. layers, a first layer coating a second layer, a layer provided on an intermediate layer, the intermediate provided on e.g. the sensing layer, etc.
  • the layer may also partly be on top.
  • such terminology is mainly functional of nature.
  • a protective layer is provided, the protective layer not limiting functionality of the optical sensing layer, e.g. being permeable to relevant species, opti ⁇ cal transparent, etc. and protecting the optical layer.
  • Both the catalyst layer (where present) and the protecting layer are permeable to a species to be measured, such as hydrogen, and are optically transparent, at least over a range of the visible, UV and/or IR regions of the electromagnetic spectrum.
  • WO2007/126313 is to provide a layer of Teflon.
  • the protective layer is provided to improve the longevity of the thin-film device through preventing deterioration of the catalyst and/or optical sensing layers and improves the handleability of the device through preventing a user from coming into contact with the optical sensing and/or catalyst layers. It is noted that the nature of Teflon and more specific sputtered PTFE makes it in principle difficult to process.
  • the present device further comprises one or more intermediate layers, wherein the intermediate layer pref ⁇ erably comprises a Period 4 transition metal, such as Ti, even more preferably an alloy of (i) a Period 4 transition metal, such as Ti and (ii) the first metal or second metal.
  • the intermediate layer may comprise TiZr; it is preferred to use a same or similar ratio of Ti:Zr in the in ⁇ termediate layer as in the present alloy, in view of performance of the present device. It is preferred to have at least one intermediate layer between the catalyst and present alloy.
  • the intermediate layer has a thickness in the range of 1.5-500 nm, preferably 3-100 nm, such as 5-30 nm.
  • Control and reliability of e.g. hydrogen absorption is further achieved with the thin-film device of the invention by providing an optical sensing layer according to the invention, e.g. comprising a Zr, Hf, Nb, or Ta doped alloy, or preferably both.
  • an optical sensing layer according to the invention e.g. comprising a Zr, Hf, Nb, or Ta doped alloy, or preferably both. Examples hereof are MgZrTi.
  • Group II transition metal based layers such as Mg-transition metal alloys e.g. Mq-Zr alloys, having optical properties that change depending on hydrogen content, with Zr, Hf, Nb, Y, La or Ta
  • Zr, Hf, Nb, Y, La or Ta can result in improved sensing properties in terms of the range of analytes, e.g. hydrogen, pressures under which they are able to be operated and under which they provide a related output, such as a change in an optical property e.g. the ab- sorbance, transmission or reflectance of the layer.
  • the present alloys provide in an example for a range of hydrogen pressures between 4*10 -1 Pa- 3*10 3 Pa to be detected accurately.
  • Desirable performance of the thin-film device of the invention in terms of control and reliability of hydrogen absorp ⁇ tion can be achieved through either improvement separately or through the combination of improvements.
  • Reliability relates particularly to reliability over time, such as tens of years, and with repeated use.
  • the present invention provides a solution to one or more of the above mentioned problems and overcomes drawbacks of the prior art.
  • the optical sensing layer has a Zr, Hf, Nb, Y, La or Ta content in the range of 10 to 40%, preferably 15 to 35%, more preferably 18 to 30%, such as a con- tent of 20%.
  • a Zr, Hf, Nb, Y, La or Ta content in the range of 10 to 40%, preferably 15 to 35%, more preferably 18 to 30%, such as a con- tent of 20%.
  • An example is Mg x Zr y Ti z z being in the above range, and x, ye [5%-80%] .
  • the alloy comprises 10- 40% Zr and 60-90% Mg.
  • optical sensing layers such as a Pd-Au alloy sensing layer may be used in combination, albeit having a smaller dynamic detection range of e.g. hydrogen.
  • the optical sensing layer has. a thickness ' i the . range of 1.5-5 ⁇ 0- nm, such as 10-100 nm.
  • the protective layer has a thickness in the range of 0.02-200 ⁇ , such as 1 um.
  • a catalyst layer to enhance absorption is present, typically on top of the optical layer, either directly or with one or more intermediate layers.
  • the invention relates to the present alloy for use in an optical sensing layer.
  • the invention in a third aspect, relates to a method of for producing a thin-film device comprising providing a substrate, depositing an optical sensing layer on the substrate, the optical sensing layer comprising the present alloy, depositing a catalyst layer on the optical sensing layer, and providing a protective layer on the catalyst layer.
  • the invention relates to a method for forming the present alloy, such as a Zr doped Mg(Ti) alloy.
  • Suitable techniques include vacuum, PVD, sputter deposition, laser ablation and deposition, and evaporation and deposition.
  • the invention in a fifth aspect, relates to a use of the present alloy for detecting a chemical species such as hydrogen.
  • a chemical species such as hydrogen.
  • various methods of the prior art are not reliable, not accurate, expensive, and often not applicable at all, especially in complex and/or harsh environments.
  • the present invention provides for detection of species, e.g. hydrogen gas species, in oil, such as transformer oil.
  • the species are an indirect measurement for the quality and/or status of the transformer as a whole and of sub- functionality thereof, such as transformer oil. As a consequence the quality and status of the transformer can now be monitored continuously.
  • the invention relates to a sensor comprising the thin-film device of the invention.
  • the sensor is a hydrogen sensor.
  • the sensor may be provided with an optical transmitter, suc as an optical fiber.
  • Such provides e.g. as advantage that a measurement can take place at a spatial distance of detection.
  • the invention may relate to a combination of optical sensing layers, such as a stack of layers.
  • Each layer or stack of layers may be optimised to sense a species, such as hydrogen, oxygen, nitrogen, carbon monoxide, carbon dioxide, etc.
  • a layer or stack of layers may be optimised to determine a species in a first concentration range, and a further layer or stack of layers for determining a species in a second concentration range.
  • the senor may comprise one or more of the above, e.g. layers for various species and layers for various concentrations of one or more species.
  • other materials may be used in combination with the present optical layer to extend e.g. a pressure range and to incorporate further species being measurable.
  • the invention relates to an electromagnetic transformer comprising the hydrogen sensor of the invention. Therewith behaviour and status of the transformer can be monitored. Even further, an automatic signal may be provided, indicating malfunction or risk of malfunction, based on the hydrogen concentration measurement. The transformer can then be replaced or serviced, as required.
  • the invention in an eighth aspect relates to an apparatus for detecting hydrogen comprising a sensor, the sensor being located at a longitudinal side of an optical transmitter, the optical transmitter comprising a central transmitting element, such as a quartz core, a transducer layer, preferably having a surface plasmon resonance frequency, an alloy according to the invention, and optionally a protection layer, preferably according to the invention, and a frequency shift detector.
  • a central transmitting element such as a quartz core
  • a transducer layer preferably having a surface plasmon resonance frequency
  • an alloy according to the invention and optionally a protection layer, preferably according to the invention, and a frequency shift detector.
  • the above apparatus relates to a new design of a fiber optic Surface Plasmon Resonance (SPR) sensor using e.g. Palladium as a' sensitive layer for . hydrogen detection, or likewise an alloy according to the present invention.
  • a trans ⁇ ducer layer is deposited on the outside of a multimode fiber, after removing the optical cladding thereof.
  • the transducer layer is a multilayer stack made of a silver, a silica and the sensing layer (e.g. the alloy, the Pd-alloy and the protective coating) .
  • Spectral modulation of light transmitted by the fiber allows detecting the presence of hydrogen in the environment.
  • the sensor is only sensitive to a Transverse Magnetic polarized light and Traverse Electric polarized light can be used therefore as a reference signal. A more reliable response is expected for the fiber SPR hydrogen sensor based on spectral modulation instead of on intensity modulation.
  • the multilayer thickness defines the sensor performance.
  • the silica thickness tunes the resonant wavelength, whereas the Silver and Palladium thickness determine the sensor sensitivity.
  • a resonant wavelength is shifted over 17.6 nm at a concentration of 4% Hydrogen in Argon for the case of the 35 nm Silver/100 nm Silica/3 nm palladium multilayer.
  • the invention in a ninth aspect relates to a switching de ⁇ vice, such as for use in a display, in an optical switching element, in an electrical switching element, in an indicator, in an optical recording medium, and in a mirror with variable reflection and transmission, comprising a substrate, a switching film layer on the substrate, the switching film layer comprising an alloy according to the invention, the alloy having at least one reversible hydrogen phase transition, each phase having different optical properties, the phase transition occurring at a hydrogen equilibrium pressure, wherein the hydrogen equilibrium pressure is tuneable by addition of the alloying element, optionally a protective layer provided on the optical sensing layer either directly or through an adhesive layer; and optionally a catalyst layer between the optical sensing layer and the protective layer.
  • Figure 1 is a schematic representation of hydrogen pressure versus hydrogen content.
  • Figure 2 is a measurement of hydrogen pressure as a function of relative transmittance .
  • Figure 3 is a measurement of hydrogen pressure as a function Of relative transmittance.
  • Figure 4 shows hydrogen pressures and optical response for various MgTi alloys.
  • Figure 1 is a schematic representation of hydrogen pressure (vertical axis) versus hydrogen content and relates to prior art systems.
  • one or more phase may be present, namely an a-phase, a ⁇ - phase and a mixed ⁇ + ⁇ -phase.
  • the hydrogen content can be measured as natural logarithm of a relative transmittance at a given pressure.
  • a dynamic range is limited, typically to about one order of magnitude hydrogen concentrations (e.g. from 10 ⁇ 2 to 10 "1 Pa).
  • Figure 2 is a measurement of hydrogen pressure (PH 2 in Pa) as a function of transmittance (ln(T/T 0 ).
  • a present sensor comprising a quartz substrate of 10x10x1 mm 3 , a first 10 nm thick Tio.45Zro. 55 layer on the substrate, a 80 nm Mgo.51Tio.22Zro.27 sensing layer on the first TiZr layer, a second 10 nm thick Tio.45Zro.55 layer on the sensing layer, and a 10 nm Pd layer on the second TiZr layer, is used to measure hydrogen pressure. It can be seen that it is now possible to measure the hydrogen pressure over approximately 5 orders of magnitude
  • Figure 3 is a measurement of hydrogen pressure (PH 2 in Pa) as a function of transmittance (In (T/To) for Ti and Mg, respectively.
  • H hydrogen pressure
  • In transmittance
  • Figure 3 shows hydrogen pressures (PH 2 in mbar (100Pa)) and op- tical response for various prior art Mg y Tii_ y alloys. Even the
  • Pd thin films with a thickness of 60 nm were deposited at room temperature on quartz substrates in an ultrahigh-vacuum (UHV) DC/RF magnetron sputtering system (base pressure 10 ⁇ 8 mbar, Ar deposition pressure 0.003 mbar).
  • UHV ultrahigh-vacuum
  • Alloy thin films of e.g. Mg(Ti)Zr with a thickness of 80 nm were co-deposited in a similar DC magnetron sputter system using quartz substrates.
  • the thin films show a significant (In (T/TO) >0.5) optical response that is linear over almost 4 orders of magnitudes of hydrogen pressure (from 0.4 Pa to 2000 Pa) at 120°C. On deposition the films are crystalline, which decays on cycling with hydrogen.

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Abstract

The present invention relates to a thin-film sensor, to a method for producing a thin-film device, to an alloy for use in an optical sensing layer, to use of an alloy for sensing a chemical species such as hydrogen, to a sensor, to an apparatus for detecting hydrogen, to an electro-magnetic transformer comprising said sensor and to a switching device.

Description

Large pressure range hydrogen sensor
FIELD OF THE INVENTION
The present invention relates to a thin-film device, to a method for producing a thin-film device, to an alloy for hydrogen absorption, to a method for producing a hydrogen absorption alloy, to use of a hydrogen absorption alloy for detecting a chemical species such as hydrogen, to a hydrogen sensor, to an apparatus for detecting hydrogen and to an electro-magnetic transformer comprising said sensor.
BACKGROUND OF THE- INVENTION
In a more ..generic perspective in an economy with hy¬ drogen as a major energy carrier, the development of affordable, reliable, sensitive and selective hydrogen sensors is in- - dispensable. Several types of hydrogen sensors are currently available, which exploit the following detection mechanisms: catalytic, electrochemical, mechanical, optical, acoustic, thermal conductivity, resistance and work function. In principle, Pd-based optical fibre sensors could meet requirements if cross-contamination effect of a Pd surface by oxygen, moisture or carbon monoxide, for example, can be prevented. Such sensors can also be used for detecting hydrogen in other environments. Since hydrogen detection often takes place in an explosive environment, cf. for leak detection or hydrogen-concentration measurements in gas streams, use of optical hydrogen sensors has a major advantage of being intrinsically safe due to the lack of electric leads in a sensing area. In addition known, fibre-optic, Pd-based thin-film hydrogen sensors represent a relatively cheap and reliable solution to this problem since they also allow for continuous sensing via remote hydrogen-gas detection, a key for personal and material safety. However, it is well known that Pd-based sensors have a highly non-linear optical response, depending strongly on the applied hydrogen pressure .
A prior art thin-film device comprises a substrate, an active sensing layer whose optical properties change depending on hydrogen content and a protective layer on the active sensing layer .
Such thin-film devices are known from the prior art. As an example, WO2007/126313 discloses a switchable mirror device comprising an active layer, wherein said active layer changes its optical properties upon addition or removal of hydrogen and comprises a hydrogen and oxygen permeable and water impermeable layer, wherein said layer is liquid water impermeable and water vapour permeable and has hydrophobic surface properties.
Similar devices are also disclosed in Slaman et al. "Optical hydrogen sensors based on metal-hydrides", Photonic Applications for aerospace, Transportation, and Harsh environment III, SPIE, Vol. 8368, No. 1, May 11, 2012 (p. 1-8), Slaman et al. "Fiber optic hydrogen detectors containing Mg-based metal hydrides", Sensors and Actuators B: Chemical: Int. J. Devoted to Research, and Development of Physical and Chemical Transducers, Elseviers, Vol. 123, No. 1, March 30, 2007 (p. 538-545), Perroton et al . "A distributed optical fiber sensor for hydro- gen detection based on Pd, and Mg alloys", Proc. SPIE, Vol.
7675, April 19, 2010 (p. 76750F-76750F-8 ) , Perroton et al. "Fiber optic Surface Plasmon Resonance sensor based on wavelength modulation for hydrogen sensing", Optic Express, Vol. 19, No. S6, November 7, 2011 (p. A1175) , Westerwaal et al . "Microstruc- tural origin of the optical black state in Mg2NiHx thin films", J. of Alloys and Compounds, Elsevier Sequoia, Vol. 404-406, December 8, 2005 (p. 481-484), Gremaud et al. "Chemical short- range order and lattice deformations in MgyTii-yHx thin films probed by hydrogenography", Phys . Rev. B, Vol. 77, No. 14, April 1, 2008, Gonzalez-Silveira et al. "Effect of H-induced microstructural changes on pressure-optical transmission isotherms for Mg-V thin films", Int. J. Hydrogen Energy, Elsevier, Vol. 35, No. 13, May 5, 2010 (p. 6959-6970), R.J. Westerwaal, et al . , Nanostructured Pd-Au based fiber optic sensors for probing hydrogen concentrations in gas mixtures, Int. J.
Hydrogen Energy, 38 (2013) 4201, Shanhu Bao et al . "Switchable mirror based on MgZrH thin films", J. of Alloys and Compounds, Elsevier Sequoia, Vol. 513, October 29, 2011 (p. 495-498), and US 2002/044717 Al . The latter paper only shows a relative large optical contrast as such.
In this respect it is observed that there is a principle difference between a detector and a sensor. The detector is only capable of detecting presence of a physical/chemical entity, whereas the sensor is capable of determining a quantity of the physical/chemical entity, in other words the sensor responds to a stimulus of the physical/chemical entity and provides a result in the form of another (variable) physical/chemical entity that is representative for the quantity. For a sensor it is important that for instance an optical contrast obtained as a result of changing concentration of e.g. hydrogen is built up gradually in order to precisely determine the concentration.
Thin-film devices of the prior art suffer a number of disadvantages in particular with regards to achieving controlled and reliable absorption of a species such as hydrogen, such as over a broad range of hydrogen pressures. It remains important to have a protective coating of Pd-based hydrogen sensors that does1 not compromise its favourable properties such as low detection limits and response time, relatively easy and affordable fabrication, low weight and portability, etc.
Most of the above prior art devices show threshold behav¬ iour: a large optical contrast over a small pressure range (or just a large optical contrast but no reference to an actual pressure) . In Pd-alloys such as PdAu the threshold behaviour is suppressed, however the remaining optical contrast is very poor. Only in MgTi a reasonable optical contrast was obtained allowing for the measurable pressure range to extend over 1-2 orders of magnitude. Also stability (such as for the MgV alloy) is insufficient for practical purposes.
The present invention therefore relates to a thin-film device and further aspects thereof, which overcomes one or more of the above disadvantages, without compromising functionality and advantages.
SUMMARY OF THE INVENTION
It is an object of the invention to overcome one or more limitations of the thin-film devices of the prior art and at the very least to provide an alternative thereto.
In a first aspect, the invention relates to a thin-film device according to claim 1, comprising the present alloy.
It is noted that the present invention provides controlled and reliable absorption, specifically of hydrogen, over a large range of hydrogen pressures, with a large optical contrast over the whole pressure range, which optical contrast is built up slowly or slow enough, instead of e.g. instantaneously at a given threshold. As the mechanism of absorption is in principle reversible, also controlled and reliable desorption is provid- ed. In an example a means for monitoring a (varying) hydrogen concentration over a large range of pressures is provided. It is noted that the present optical system is much safer to use and to handle compared to e.g. electrical (conducting) sensors, especially in environments where a large electro-magnetic field may be present.
In an example the present thin thin-film device comprises a substrate, an active sensing layer whose optical properties change continuously as a function of hydrogen content, a Pd cap layer to dissociate hydrogen which acts simultaneously as a protective coating for the sensing layer, and a protective lay¬ er coating the Pd which protects this cap layer. In the- following sections various elements of the present device are further elucidated .
A person of skill in the art is able to identify many suitable substrate materials upon which a thin-film device such as the thin-film device of the invention can be constructed. Examples of suitable substrate materials include glass, guartz, indium-tin oxide, etc. The substrate material is preferably optically transparent (more than 95%) , at least over a proportion of the visible, UV and/or IR regions of the electromagnetic spectrum (200 nm- 3000 nm) . Such provides for use of white light, IR-light, UV-light, a laser with a specific wavelength, and combinations thereof.
As mentioned above, optical sensing layers, with variable optical properties depending on e.g. a hydrogen content of the layer, comprising an alloy, are known in the prior art. In an example of the present invention the sensing layer is the pre¬ sent alloy. The alloy comprises at least a first metal and a second metal. Typically characteristics of a metal are that they may oxidize, may form a cation, may be an electrical con¬ ductor, etc. In the present alloy the first and second metal have an eguilibrium pressure (Pa) for hydrogen absorption. Such an equilibrium pressure per se can be measured with means known to a person skilled in the art. Typically it is measured at ambient temperature (300 K) . In the present alloy the hydrogen equilibrium pressure (Pa) of the first metal is at least 5*103 times as large as the hydrogen equilibrium pressure (Pa) of the second metal, preferably at least 104 times, more preferably at least 5*104 times, even more preferably at least 5*105 times, such as 106-1015 times.
In table 1 various metals and equilibrium pressures (Pa, @273 K) (as calculated/estimated) are given.
Mg 1.1*10°
Ti 6.1*10~15
Zr 1.2*1(Γ23
Hf 1*1(Γ5
Ta 1*10~13
Inventors have discovered that in principle metals having any ratio of pressures can be combined (into alloys) . If the ratio is relatively large, e.g. more than 106, it' is preferred to introduce a third--- metal , having with respect to the first and second metal an intermediate hydrogen equilibrium pressure. A few examples of such alloys are: AxByCz, with A being selected from alkaline earth-metals (Group II), preferably from Mg, and Ca, B being selected from Zr, Hf, Nb, Y, La, and Ta, preferably Zr, Hf and La, and C being selected from a period 4 transition metal (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) , preferably Sc, Ti, Ni and V,_with ranges preferably as follows:
xe [0.1-0.95] , ye[0.1-0.4], ze [0.05-0.6] , and preferably y : xe [ 0.7-0.9] . Examples of suitable alloys are given below:
MgxZryTiz, MgxZryVz, MgxZryScz, MgxZryNiz, MgxZryCrz, MgxZryCoz, MgxZryMnz, MgxZryFez, MgxZryCuz, MgxZryZnz, MgxHfyTiz, MgxHfyVz, MgxHfyScz, MgxHfyNiz, MgxHfyCrz, MgxHfyCoz, MgxHfyMnz, MgxHfyFez, MgxHfyCuz, MgxHfyZnz, MgxNbyTiz, MgxNbyVz, MgxNbyScz, MgxNbyNiz,
MgxNbyCrz, MgxNbyCoz, MgxNbyMnz, MgxNbyFez, MgxNbyCuz, MgxNbyZnz, MgxLayTiz, MgxLayVz, MgxLayScz, MgxLayNiz, MgxLayCrz, MgxLayCoz, MgxLayMnz, MgxLayFez, MgxLayCuz, MgxLayZnz, MgxYyTiz, MgxYyVz,
MgxYyScz, MgxYyNiz, MgxYyCrz, MgxYyCoz, MgxYyMnz, MgxYyFez, MgxYyCuz, MgxYyZnz, MgxTayTiz, MgxTayVz, MgxTayScz, MgxTayNiz, MgxTayCrz,
MgxTayCoz, MgxTayMnz, MgxTayFez, MgxTayCuz, MgxTayZnz, CaxZryTiz, CaxZryVz, CaxZryScz, CaxZryNiz, CaxZryCrz, CaxZryCoz, CaxZryMnz, CaxZryFez, CaxZryCuz, CaxZryZnz, CaxHfyTi , CaxHfyVz, CaxHfyScz, CaxHfyNiz, CaxHfyCrz, CaxHfyCoz, CaxHfyMnz, CaxHfyFez, CaxHfyCuz, CaxHfyZnz, CaxNbyTiz, CaxNbyVz, CaxNbyScz, CaxNbyNiz, CaxNbyCrz,
CaxNbyCoz, CaxNbyMnz, CaxNbyFez, CaxNbyCuz, CaxNbyZnz, CaxLayTiz, CaxLayVz, CaxLayScz, CaxLayNiz, CaxLayCrz, CaxLayCoz, CaxLayMnz, iz, CaxYyCrz, CaxYyCoz, CaxYyMnz, CaxYyFez, CaxYyCuz, CaxYyZnz, Cax- TayTiz, CaxTayVz, CaxTayScz, CaxTayNiz, CaxTayCrz, CaxTayCoz, Cax- TayMnz, CaxTayFez, CaxTayCuz, and CaxTayZnz,
with xe [0.4-0.6] , ye[0.2-0.3], ze [0.05-0.45] , and preferably y : xe [0.7-0.9] . It is preferred to select the alloy from doped MgZr alloy, a doped MgHf alloy, a doped MgV alloy, a doped MgNb alloy, a doped MgTa alloy a doped MgY alloy, and a doped MgLa alloy. These alloys provide the advantages in particular.
In other words a ratio of first and second hydrogen pressures of more than 10s is possible. Likewise an additional or¬ der of magnitude (107) is possible, especially when a fourth metal is used. Likewise detectable pressures may be expanded by including in the alloy a metal having a significant lower, or. higher, hydrogen, equilibrium, pressure, compared to the first and second metal. It is noted that as the equilibrium pressures are taken with respect to one and another, e.g. a pressure of a first and a second metal, it is in principle less relevant by what exact way of measurement individual pressures are determined .
Inventors have identified that it is preferred that the alloy comprises a metal providing the alloy X-ray amorphous- ness, i.e. as identified by X-ray diffraction techniques. This metal may relate to a third metal, being different from the first and second metal, or it may be the same as any of the first and second metal. An indication of presence of amorphous- ness is given by taking an X-ray measurement of an alloy, and identifying presence or absence of amorphousness ; for the pre¬ sent alloy presence is required. The identification of presence or absence of X-ray amorphousness is considered an objective determination. In condensed matter physics and materials science, an amorphous or non-crystalline solid relates to a solid that lacks long-range order characteristic of a crystal.
In an example the alloy of the optical sensing layer has a distribution of interstitial sites. The sites being characterized and formed by surrounding atoms of the alloy. In a regular crystal such sites could relate to tetraeder and octaeder sites. Also coordination number and interatomic distance may be taken into account. As the present alloy may be largely amorphous, only in very small domains such regular sites may be observed. Most sites however are even then at least partially distorted. The sites are in principle considered suited for hy- drogen absorption. The distribution comprises at least four different (types of) sites, preferably at least 10 different (types of) sites, more preferably at least 100 different (types of) sites, such as at least 103 different sites (types of) /μπι3 (i.e. taken per unit volume). It is noted that in an. amorphous structure any first site may be different from any second site; thus an enormous amount .of different sites may be present, such as 104 different sites/μιη3. A difference may further relate to a (slight) variation with respect to hydrogen absorption energy-
An effect of the present alloy is a large gap material forms on hydrogenation of at least one of the constituents, a good (hydrogen) diffusion, and. high (optical) dynamics resulting in a wide range of hydrogen pressures that can be detected. In an example MgTi provides 0.5-1 order of detection, whereas adding Zr to the alloy even 3 orders of detection or more are obtained. Inventors provide a sensing material with a large optical contrast over a wide pressure range.
Transmission, reflection and/or absorption of light by the layers changes through addition or removal of hydrogen from the layer. Such changes can be measured. Hydrogen absorbs into the alloy material. The optical sensing layer may be amorphous, and may be in a sequence of layers or layer stacks or in 2- or 3- dimensional domains. It is preferred to use an amorphous layer, as a broader range of e.g. hydrogen absorption pressures is obtained, more preferably an amorphous zircon comprising layer.
A catalyst such as in a layer is provided on top of the optical sensing layer, such as coating the optical sensing layer. Examples of such layers include for example Pd-layers. The Pd-layers may comprise pure Pd or mixtures comprising Pd. For example, Ag can be added in a quantity of for example 20-30 mole% . The catalyst may also relate to a complex layer, suited for the present purpose. Such layers serve to facilitate hydrogen absorption by the optical sensing layer.
In an exemplary embodiment, the catalyst layer has a thickness in the range of 1.5-500 nm, preferably 3-100 nm, such as 5-30 nm.
It is noted that a term as "on top" may relate to a se¬ quence of e.g. layers, a first layer coating a second layer, a layer provided on an intermediate layer, the intermediate provided on e.g. the sensing layer, etc. The layer may also partly be on top. In view of the present application such terminology is mainly functional of nature.
On top of the optical sensing layer, or where present, on top of the catalyst (layer) , a protective layer is provided, the protective layer not limiting functionality of the optical sensing layer, e.g. being permeable to relevant species, opti¬ cal transparent, etc. and protecting the optical layer. Both the catalyst layer (where present) and the protecting layer are permeable to a species to be measured, such as hydrogen, and are optically transparent, at least over a range of the visible, UV and/or IR regions of the electromagnetic spectrum. An example of- a'.protecting layer from the aforementioned
WO2007/126313 is to provide a layer of Teflon. The protective layer is provided to improve the longevity of the thin-film device through preventing deterioration of the catalyst and/or optical sensing layers and improves the handleability of the device through preventing a user from coming into contact with the optical sensing and/or catalyst layers. It is noted that the nature of Teflon and more specific sputtered PTFE makes it in principle difficult to process.
In an example the present device further comprises one or more intermediate layers, wherein the intermediate layer pref¬ erably comprises a Period 4 transition metal, such as Ti, even more preferably an alloy of (i) a Period 4 transition metal, such as Ti and (ii) the first metal or second metal. For in¬ stance, when the present alloy (of the optical sensing layer) comprises MgTiZr, the intermediate layer may comprise TiZr; it is preferred to use a same or similar ratio of Ti:Zr in the in¬ termediate layer as in the present alloy, in view of performance of the present device. It is preferred to have at least one intermediate layer between the catalyst and present alloy.
It is preferred to provide two intermediate layers, one between the catalyst and present alloy, and one between the present alloy and substrate.
In an exemplary embodiment, the intermediate layer has a thickness in the range of 1.5-500 nm, preferably 3-100 nm, such as 5-30 nm.
Control and reliability of e.g. hydrogen absorption is further achieved with the thin-film device of the invention by providing an optical sensing layer according to the invention, e.g. comprising a Zr, Hf, Nb, or Ta doped alloy, or preferably both. Examples hereof are MgZrTi.
Examples of coating layers are given in the Dutch Patent Application NL2010031, filed December 20, 2012. Details, teach- ings and examples thereof are incorporated by reference.
Research by the inventors has shown that doping of (i) Group II transition metal based layers such as Mg-transition metal alloys e.g. Mq-Zr alloys, having optical properties that change depending on hydrogen content, with Zr, Hf, Nb, Y, La or Ta can result in improved sensing properties in terms of the range of analytes, e.g. hydrogen, pressures under which they are able to be operated and under which they provide a related output, such as a change in an optical property e.g. the ab- sorbance, transmission or reflectance of the layer. The present alloys provide in an example for a range of hydrogen pressures between 4*10-1 Pa- 3*103 Pa to be detected accurately. Depending on the present alloy much lower pressures (e.g. 10~5 Pa) and much higher pressures (e.g. 107 Pa)may be detected. Upon calibration of the curves larger ranges are envisaged. In compari- son an optimal crystalline MgTi layer provides 1-2 orders of hydrogen pressure to be detected accurately.
Desirable performance of the thin-film device of the invention in terms of control and reliability of hydrogen absorp¬ tion can be achieved through either improvement separately or through the combination of improvements. Reliability relates particularly to reliability over time, such as tens of years, and with repeated use.
The invention also relates to a Zr doped Mg-based alloy, optionally comprising Ti, to a method for producing a Zr doped g(Ti) alloy, to use of a Zr doped Mg(Ti) alloy for detecting a chemical species such as hydrogen, to a protective layer for shielding an oxygen, moisture, hydrogen sulphide and/or carbon monoxide sensitive surface, to a hydrogen sensor and to an electro-magnetic transformer comprising said hydrogen sensor.
The present invention provides a solution to one or more of the above mentioned problems and overcomes drawbacks of the prior art.
Advantages of the present description are detailed
throughout the description. DETAILED DESCRIPTION OF THE INVENTION
In an exemplary embodiment, the optical sensing layer has a Zr, Hf, Nb, Y, La or Ta content in the range of 10 to 40%, preferably 15 to 35%, more preferably 18 to 30%, such as a con- tent of 20%. An example is MgxZryTiz z being in the above range, and x, ye [5%-80%] . In an example the alloy comprises 10- 40% Zr and 60-90% Mg.
In an alternative also known optical sensing layers, such as a Pd-Au alloy sensing layer may be used in combination, albeit having a smaller dynamic detection range of e.g. hydrogen.
In an exemplary embodiment, the optical sensing layer has. a thickness ' i the . range of 1.5-5Ό0- nm, such as 10-100 nm.
In an exemplary embodiment, the protective layer has a thickness in the range of 0.02-200 μτη, such as 1 um.
Also a catalyst layer to enhance absorption is present, typically on top of the optical layer, either directly or with one or more intermediate layers.
In a second aspect, the invention relates to the present alloy for use in an optical sensing layer.
In a third aspect, the invention relates to a method of for producing a thin-film device comprising providing a substrate, depositing an optical sensing layer on the substrate, the optical sensing layer comprising the present alloy, depositing a catalyst layer on the optical sensing layer, and providing a protective layer on the catalyst layer.
It has been found experimentally that for a stable performance a device is first cycled a few times, from a relatively low (hydrogen) pressure to a relatively high (hydrogen) pressure, and back. 2-10 cycles are typically sufficient. It is al- so preferred to cycle at elevated temperature; fewer cycles are required in that case, compared to ambient temperature cycling.
In a fourth aspect, the invention relates to a method for forming the present alloy, such as a Zr doped Mg(Ti) alloy.
Suitable techniques include vacuum, PVD, sputter deposition, laser ablation and deposition, and evaporation and deposition.
In a fifth aspect, the invention relates to a use of the present alloy for detecting a chemical species such as hydrogen. It is noted that various methods of the prior art are not reliable, not accurate, expensive, and often not applicable at all, especially in complex and/or harsh environments. Specifi- cally the present invention provides for detection of species, e.g. hydrogen gas species, in oil, such as transformer oil. It is noted that the species are an indirect measurement for the quality and/or status of the transformer as a whole and of sub- functionality thereof, such as transformer oil. As a consequence the quality and status of the transformer can now be monitored continuously.
In a sixth aspect, the invention relates to a sensor comprising the thin-film device of the invention. In a preferred example the sensor is a hydrogen sensor. The sensor may be provided with an optical transmitter, suc as an optical fiber. Such provides e.g. as advantage that a measurement can take place at a spatial distance of detection. Even further the invention may relate to a combination of optical sensing layers, such as a stack of layers. Each layer or stack of layers may be optimised to sense a species, such as hydrogen, oxygen, nitrogen, carbon monoxide, carbon dioxide, etc. Also, a layer or stack of layers may be optimised to determine a species in a first concentration range, and a further layer or stack of layers for determining a species in a second concentration range. Likewise and preferred a combination of various 2-d and 3-D domains may be used. Thereby an enlarged range of concentrations can be determined. Even further the sensor may comprise one or more of the above, e.g. layers for various species and layers for various concentrations of one or more species. Even further, other materials may be used in combination with the present optical layer to extend e.g. a pressure range and to incorporate further species being measurable. An advantage is that the present invention allows for a combination of various optical layers without much extra measures to be taken in order to obtain a functional device.
In a seventh aspect, the invention relates to an electromagnetic transformer comprising the hydrogen sensor of the invention. Therewith behaviour and status of the transformer can be monitored. Even further, an automatic signal may be provided, indicating malfunction or risk of malfunction, based on the hydrogen concentration measurement. The transformer can then be replaced or serviced, as required.
In an eighth aspect the invention relates to an apparatus for detecting hydrogen comprising a sensor, the sensor being located at a longitudinal side of an optical transmitter, the optical transmitter comprising a central transmitting element, such as a quartz core, a transducer layer, preferably having a surface plasmon resonance frequency, an alloy according to the invention, and optionally a protection layer, preferably according to the invention, and a frequency shift detector.
With the optical resonator in combination with the frequency shift detector a resolution in the order of pm is obtained .
The above apparatus relates to a new design of a fiber optic Surface Plasmon Resonance (SPR) sensor using e.g. Palladium as a' sensitive layer for .hydrogen detection, or likewise an alloy according to the present invention. In an example, a trans¬ ducer layer is deposited on the outside of a multimode fiber, after removing the optical cladding thereof. In an example the transducer layer is a multilayer stack made of a silver, a silica and the sensing layer (e.g. the alloy, the Pd-alloy and the protective coating) . Spectral modulation of light transmitted by the fiber allows detecting the presence of hydrogen in the environment. The sensor is only sensitive to a Transverse Magnetic polarized light and Traverse Electric polarized light can be used therefore as a reference signal. A more reliable response is expected for the fiber SPR hydrogen sensor based on spectral modulation instead of on intensity modulation. The multilayer thickness defines the sensor performance. The silica thickness tunes the resonant wavelength, whereas the Silver and Palladium thickness determine the sensor sensitivity. In an optimal configuration (NA = 0.22, 100 μπι core radius and transducer length = 1 cm) , a resonant wavelength is shifted over 17.6 nm at a concentration of 4% Hydrogen in Argon for the case of the 35 nm Silver/100 nm Silica/3 nm palladium multilayer. Amongst others the above results are published in two articles of one of the present inventors (Opt. Soc. America, 7 November 2011, Vol. 19, No. S6, ppA1175-1183 and Proc. SPIE, Vol. 8368, pp. 836804-1-12) .
In a ninth aspect the invention relates to a switching de¬ vice, such as for use in a display, in an optical switching element, in an electrical switching element, in an indicator, in an optical recording medium, and in a mirror with variable reflection and transmission, comprising a substrate, a switching film layer on the substrate, the switching film layer comprising an alloy according to the invention, the alloy having at least one reversible hydrogen phase transition, each phase having different optical properties, the phase transition occurring at a hydrogen equilibrium pressure, wherein the hydrogen equilibrium pressure is tuneable by addition of the alloying element, optionally a protective layer provided on the optical sensing layer either directly or through an adhesive layer; and optionally a catalyst layer between the optical sensing layer and the protective layer.
The invention will hereafter be further elucidated through the following examples which are exemplary and explanatory of nature and are not intended to be considered limiting of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims .
FIGURES
Figure 1 is a schematic representation of hydrogen pressure versus hydrogen content.
Figure 2 is a measurement of hydrogen pressure as a function of relative transmittance .
Figure 3 is a measurement of hydrogen pressure as a function Of relative transmittance.
Figure 4 shows hydrogen pressures and optical response for various MgTi alloys.
DETAILED DESCRIPTION OF FIGURES
Figure 1 is a schematic representation of hydrogen pressure (vertical axis) versus hydrogen content and relates to prior art systems. Therein, depending on the temperature of the system, one or more phase may be present, namely an a-phase, a β- phase and a mixed α+β-phase. The hydrogen content can be measured as natural logarithm of a relative transmittance at a given pressure. For such a system a dynamic range is limited, typically to about one order of magnitude hydrogen concentrations (e.g. from 10~2 to 10"1 Pa).
Figure 2 is a measurement of hydrogen pressure (PH2 in Pa) as a function of transmittance (ln(T/T0). Therein an example of a present sensor, comprising a quartz substrate of 10x10x1 mm3, a first 10 nm thick Tio.45Zro. 55 layer on the substrate, a 80 nm Mgo.51Tio.22Zro.27 sensing layer on the first TiZr layer, a second 10 nm thick Tio.45Zro.55 layer on the sensing layer, and a 10 nm Pd layer on the second TiZr layer, is used to measure hydrogen pressure. It can be seen that it is now possible to measure the hydrogen pressure over approximately 5 orders of magnitude
(from 10_1 Pa to 104 Pa) . It is preferred for best results to perform a few (3-5) cycles from low to high hydrogen concentration and back, at an elevated temperature, to arrive at a "stable" situation wherein behaviour of the present sensor does not change any more over time.
Figure 3 is a measurement of hydrogen pressure (PH2 in Pa) as a function of transmittance (In (T/To) for Ti and Mg, respectively. As in figure 2, also results of an example of the present sensor are given. In fig. 3 equilibrium pressures for Mg and Ti are indicated (about 3*102 Pa and 2*10-1 Pa, respectively) . It is noted that likewise an equilibrium pressure of e.g. Zr is found to be about 10~13 Pa. These respective equilibrium pressure are far apart from one and another. Instead of producing well-defined pressure a continuous change in optical transmis- sion is observed. _It is considered that for the present sensor X-ray amorphousness is required. Further, it is considered that many energy levels in the present alloy are present. And it is considered that an elastic coupling between levels is present. Figure 4 shows hydrogen pressures (PH2 in mbar (100Pa)) and op- tical response for various prior art MgyTii_y alloys. Even the
"best" alloy, with y=0.61, provides a sensor with not more than 2 orders of magnitude dynamic range. Also the optical response is relatively small.
EXAMPLES
Experimental
Substrate preparation
Pd thin films with a thickness of 60 nm were deposited at room temperature on quartz substrates in an ultrahigh-vacuum (UHV) DC/RF magnetron sputtering system (base pressure 10~8 mbar, Ar deposition pressure 0.003 mbar).
Alloy thin films of e.g. Mg(Ti)Zr with a thickness of 80 nm were co-deposited in a similar DC magnetron sputter system using quartz substrates. The thin films show a significant (In (T/TO) >0.5) optical response that is linear over almost 4 orders of magnitudes of hydrogen pressure (from 0.4 Pa to 2000 Pa) at 120°C. On deposition the films are crystalline, which decays on cycling with hydrogen.

Claims

1. A thin-film sensor allowing controlled and reliable absorption of hydrogen comprising:
(a) a substrate;
(b) an optical sensing layer on the substrate the optical sens- ing layer comprising an alloy;
(c) a protective layer provided on the optical sensing layer either directly or through an adhesive layer; and
(d) a catalyst layer between the optical sensing layer and the protective layer;
characterised in that
(e) the alloy (bl) comprises at least a first metal, a second metal, and a period 4 transition metal, wherein the first and second metal have a hydrogen equilibrium pressure (Pa), wherein the hydrogen equilibrium pressure (Pa) of the first metal is at least 5*103 times the hydrogen equilibrium pressure (Pa) of the second metal, wherein the first metal is selected from a Group II metal, and wherein the second metal is selected from Zr, Hf, V, Nb, Y, La, and Ta.
2. A thin-film sensor according to claim 1, (b2) wherein the first metal, having a relatively high hydrogen equilibrium pressure (Pa) , has a first phase with metallic properties at (compared to the second phase) relative low hydrogen pressure and has a second phase with low electrical conducting properties at (compared to the first phase) relative high hydrogen pressure, such as semi-conducting or insulating properties and/or wherein (b3) the alloy comprising a metal provides the alloy X-ray amorphousness .
3. A thin-film sensor according to one or more of the preceding claims, wherein the alloy of the optical sensing layer has a distribution of interstitial sites, the sites being characterized and formed by surrounding atoms of the alloy, the sites being suitable for hydrogen absorption, wherein the distribution comprises at least four different sites/μιη3.
4. A thin-film sensor according to one or more of the pre- ceding claims, further comprising one or more intermediate layers, wherein the intermediate layer preferably comprises a Period 4 transition metal, such as Ti, even more preferably an alloy of (i) a Period 4 transition metal, such as Ti and (ii) the first metal or second metal.
5. A thin-film sensor according to one or more of the preceding claims, wherein the alloy has a Zr, Hf, Nb, Y, La or Ta dopant content in the range of 10 to 40%.
6. A thin-film device according to one or more of the preceding claims, wherein the optical sensing layer has a thick¬ ness in the range of 1.5-500 nm, and/or
wherein the protective layer has a thickness in the range of 0.02-200 μπι.■
7. An alloy for use in an optical sensing layer comprising (bl) at least a first metal, a second, metal,, and a period 4 transition metal, wherein the first and second metal have a hy¬ drogen equilibrium pressure (Pa), wherein the hydrogen equilib- rium pressure (Pa) of the first metal is at least 5*103 times the hydrogen equilibrium pressure (Pa) of the second metal, and optionally
(b2) wherein the first metal, has a first phase with metallic properties at relative low hydrogen pressure and has a second phase with low electrical conducting properties at relative high hydrogen pressure, such as semi-conducting or insulating properties ,
wherein the first metal is selected from a Group II metal, and wherein the second metal is selected from Zr, Hf, V, Nb, Y, La, and Ta.
8. Alloy according to any of claims 7, wherein the alloy is a Zr or Hf doped MgTi alloy for use in a thin-film device comprising 10-40% Zr, 35-80% Mg and 5-55% Ti, or wherein the alloy comprises 10-40% Zr and 60-90% Mg.
9. A method for producing a thin-film device comprising providing a substrate, depositing an optical sensing layer on the substrate, the optical sensing layer comprising the alloy according to any of claims 7-8, depositing a catalyst layer on the optical sensing layer, providing a protective layer on the catalyst layer, and optionally cycling the device 1-10 times.
10. Use of an alloy, according to any of claims 7-8 for sensing a chemical species, such as hydrogen.
11. A sensor comprising a device of one or more of claims 1-6, preferably a hydrogen sensor, comprising an optical trans- mitter, such as an optical fiber, wherein the optical sensing layer is located at a top of the optical transmitter and/or wherein the optical sensing layer is located at a longitudinal side of the optical transmitter.
12. An electro-magnetic transformer comprising a hydrogen sensor according to claim 11.
13. An apparatus for detecting hydrogen comprising a sensor, the sensor being located at a longitudinal side of an optical transmitter,
the optical transmitter comprising
a central transmitting element, such as a quartz core, a transducer layer, preferably having a surface plasmon resonance frequency,
an alloy according to any of claims 7-8, and
optionally a protection layer,
and a frequency shift detector.
14. Switching device, such as for use in a display, in an optical switching element, in an electrical switching element, in an indicator, in an optical recording medium, and in a mirror with variable reflection and transmission, comprising a substrate, a switching film layer on the substrate, the switching film layer comprising an alloy according to claim 7 or 8, the alloy having at least one reversible hydrogen phase transition, each phase having different optical properties, the phase transition occurring at a hydrogen equilibrium pressure, wherein the hydrogen equilibrium pressure is tuneable by addition of the alloying element, optionally a protective layer provided on the optical sensing layer either directly or through an adhesive layer; and optionally a catalyst layer between the optical sensing layer and the protective layer.
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CN111257286A (en) * 2020-01-17 2020-06-09 武汉理工大学 Optical fiber hydrogen networking alarm device based on MgTiV-PdCu composite film
CN111257286B (en) * 2020-01-17 2021-06-04 武汉理工大学 Optical fiber hydrogen networking alarm device based on MgTiV-PdCu composite film
WO2022098230A1 (en) 2020-11-03 2022-05-12 Technische Universiteit Delft Optical thin-film hydrogen sensing material based on tantalum or other group v element alloy
NL2026815B1 (en) * 2020-11-03 2022-06-27 Univ Delft Tech (Optical) thin-film hydrogen sensing material based on tantalum or other group V element alloy

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