Note: Descriptions are shown in the official language in which they were submitted.
METHOD AND DEVICE FOR DETERMINING HYDROGEN FLUX
The present invention relates to a method and a device for deter-
mining hydrogen flux through a rnetal membrane.
TECHNICAL BACK(iROUND
5 In some chemical process industries, corrosion of steel components
may occur under conditions which give rise to hydrogen-induced
cracking or blistering. A typical and technically important example is
corrosion of pipes and pressure vessels for natural gas containing a
condensed liquid phase containing water and hydrogen sulphide ~along
10 with other substances). This condensate is slightly acidic, and will
corrode steel by the generation of hydrogen. The presence of hydro-
gen sulphide inhibits the formation of molecular hydrogen, and a
significant part of the hydrogen permeates into the steel where it may
cause damage in the form of cracking or blistering.
15 It is possible to reduce the hydrogen damage in several ways, e.g.
by avoiding condensation, by removal of hydrogen sulphide or by ad-
ding inhibitors which may perform their function in several ways,
e.g. by neutralizing the liquid phase or by forming a protective film.
In order to be able to monitor the effect of these precautions, the
20 hydrogen uptake or rate of hydrogen uptake in an exposed area of
the steel component in question should be measured. This can be
done in accordance with several known measuring principles, most of
which are based on the fact that the hydrogen which permeates into
the exposed entry side of a steel wall, will diffuse through the steel
25 wall and be liberated in gaseous (molecular) form on the side of the
steel wall opposite to the entry side. The rate of hydrogen generation
on said opposite side of the steel wall may be measured by means of
known techniques, e.g. by measuring the development of pressure in
a closed cavity or by measuring the displacement of a liquid drop in a
P~V F2719 j~ 323345 HSN/KWF 1983 02 23
~9~
glass tube having a calibrated inner wall. The amount Qf hydrogen
may also be analysed in various ways, e.g. by gas phase chromato-
graphy .
To carry out the measurement of the rate of hydrogen generation in
5 accordance with the above-mentioned physical measuring principles
several hydrogen measuring probes have been proposed. However,
these hydrogen measuring probes suffer from various drawbacks.
Some of them are rather primitive and have low sensitivity, while
others need constant supervision and are not suited for automated
10 datalogging. Others are more sensitive and accurate, but are quite
costly and delicate.
An electrochemical measuring principle bàsed on electrochemical oxi-
dation of hydrogen which permeates to the side of the steel wall op-
posite to the entry side is also known. This technique was first de-
15 scribed by N.A.V. Devanathan and Z. Stachorski (Reference 1) . Ahydrogen probe or hydrogen cell constructed in accordance with these
principles is known as a Devanathan-cell.
In this cell an iron or steel sheet forms a wall or membrane between
two compartments. A first compartment constitutes an experimental
20 compartment in which the iron or steel material of the wall is exposed
to corrosive forces or other experimental influences which are likely
to produce hydrogen in the iron or steel material. A second compart-
ment contains a de-aerated alkaline solution, e.g. 1 molar potassium
hydroxide. The surface of the iron or steel wall facing the second
25 compartment is covered with a thin coating of electrodeposited palla-
dium which is permeable to hydrogen and stable in the alkaline solu-
tion. A platinum counterelectrode is arranged opposite to the iron or
steel wall, and a reference electrocle is also arranged in the second
compartment having its tip arranged in close proximity to the palla-
30 dium-covered membrane. In order to maintain a constant potential of
the palladium-coated iron or steel wall in the alkaline solution, a
potentiostat is used. Generally, a potential of EH = +100 mV is used.
At this potential, the palladium coating and the iron or steel material
of the wall are passive. Therefore, the passive current density is
P~V F2719 jG 323345 HSN/KWF 1983 02 23
~3957~
quite small, typically between 0.01 and 0.1 llA per cm2. Any hydro-
gen diffusing through the iron or steel wall and the palladium coating
thereof is oxidi~ed at the side of the palladium coatiny opposite to the
entry side of the iron or steel wall in accordance with the following
5 equation:
H ~ OH -~ H2O + e .
Consequently, an increase of anodic current in excess of the passive
background current is equivalent to a hydrogen flux through the
wall. The hydrogen flux through a unit area of the iron or steel wall
10 of a given thickness is a product of the hydrogen activity at th0
external side of the wall and the diffusion admittance through the
wall, assuming that the potential is capable of maintaining a hydrogen
activity at approximately zero at the opposite, i.e. the internal palla-
dium-coated side of the wall. If the diffusion admittance is known,
15 the hydrogen activity in the first compartment may be calculated on
the basis of the anodic current of the cell. The diffusion admittance
is determined by having a controlled electrochemical environment in
the ~irst compartment or by introducing a hydrogen atmosphere of
known pressure into the first compartment, the external side of the
20 iron or steel wall being coated with palladium which renders the cell
sensitive to molecular hydrogen.
Another laboratory measuring device based on the Devanathan measur-
ing principle is described in Reference 2. In this measuring device, a
steel plate constitutes a part of a wall of a cell containing an electro-
25 Iyte solution, a reference electrode and a counterelectrode. Further-
more, a potentiostat is needed to operate the device.
GB Patent No. 1.585.070 discloses an electrochemical cell for determi-
ning the concentration of hydrogen in a fluid, which electrochemical
cell is based on the principles of the Devanathan measuring tech-
30 nique. The cell comprises a container for an electrolyte solution, aworking electrode constituting a wall part of the container and being
adapted to be exposed to a fluid under test, and a platinum/platinum
oxide reference electrode having an area comparable to the working
electrode and being arranged close to and parallel to the working elec-
P~V F2719 jG 323345 HSN/KWF 1983 02 23
5~
trode. In one embodiment of the cell, a counterelectrode, means formaintaining the working electrode at a fixed potential relative to the
reference electrode, and means for determining the current flowing
through the working electrode are provided. This embodiment has to
5 be used in combination with electronic means for maintaining the
working electrode at a fixed potential. In ano-ther embodiment of the
measuring cell, the electronic means, the counterelectrode and the
current determining means are omitted. Instead, the working electrode
and the reference electrode are connected to potential measuring
means. According to the disclosure of GB Patent No. 1 385 070, a
potential difference between the electrodes is related to the concen-
tration of hydrogen at the working eiectrode. However, the specifi-
cation explains that a stable reading is obtainable only at low hydro-
gen activities.
From GB Patent No. 1.524.017, another hydrogen measuring cell
based on the same measuring principles is known. The cell (a so-
called "Patch Cell") is adapted to be secured in fluid-tight engage-
ment with an outer surface of a steel or iron wall, the interior side of
which is exposed to corrosion. The celi responds quantitatively to all
20 hydrogen escaping from the outer surface of the steel or iron wall,
thus measuring the amount of hydrogen produced on the inner sur-
face of the steel or iron wall.
In an article by F. Mansfeld et al. (reference 5), a measuring system
based on the above described Devanathan measuring principle is
25 disclosed. The system comprises a rneasuring cell consisting o~ a cell
body which is press-fitted into a cylindrical magnet assembly serving
fixation purposes when brought into contact with a metal sample
body. The cell body contains a cavity which opens into the side of
the cell body, which is adapted to be brought into contact with the
30 surface of the metal sample body. In the cavity of the cell body, a
Ni-NiO counterelectrode is arranged together with an additional
Ni-NiO e~ectrode which serves to check the potential of the counter-
electrode and the presence of a sufficient amount of electrolyte. The
electrolyte is also arranged in the cavity and is absorbed in a cellu-
35 lose sponge which is positioned in the cavity of the cell body. The
P~V F2719 jG 3233~5 HSN/KWF 1983 02 23
9~
ceilulose sponge constitutes a carrier body for the electrolyte whichon one hand is in direct contact with the Ni-NiO counterelectrode and
on the other hand is brought into direct contact with the surface of
the metal sample body when the cell is arranged in contact therewith.
5 In this measuring cell, the reference electrode, the potentiostat and
the counter electrocle of the above described Devanathan-cell are
combined into a single Ni-NiO counterelectrode. The measuring system
further comprises an electronic measuring and timing circuit including
a current follower, an instrument panel and four timers. The entire
10 system is powered by batteries having a six-hour operation capacity.
The measuring system is intended to be used for determination of
hydrogen concentration in steels, based on the electro-chemical per-
meation technique. As stated in the article, the current generated in
the measuring cell contains transient contributions having their origin
15 in a passivation process immediately after the cell has been
assembled. While the permeation current itself is a function of t 1/2,
these transient contributions decay with t 1. The sensitivity of the
cell is approximately 1 11A/cm2. While the first and the second timers
of the electronic measuring and timing circuit serve the purpose of
20 elirnination of the above transient passivation contributions, the third
and the fourth timers control a digital integrator which carries out a
digital integration of the current supplied from the measuring cell
within a predetermined time period determined by said third and
fourth timers. As stated in the article, the integration of the current
supplied from the measuring cell within a predetermined time period
may be employed for determination of the original concentration of
hydrogen in the metal sample body. As will be understood from the
above, the system is merely adapted to provide a single determination
of an original hydrogen concentration of a metal sample body, and is
not adapted to provide continuous monitoring on an actual measuring
site for a long period of time. Furthermore, the system has to be
assembled prior to use and, consequently, is not a permanently
sealed, ready-to-use system. The system also relies on a highly
elaborate electronic measuring and timing circuit.
- P~V F2719 jG 323345 HSN/KWF 1983 02 23
57C~
BRIEF DESCRIPTION OF THE INVENTION
The method and device of the present invention permit a stable and
reliable measurement of hydrogen flux by means of units, which may
be produced at low cost, and which require no maintenance and use
5 simple and reliable external measuring equipment.
The invention provides a device for determining hydrogen flux
through a metal membrane, which is selectively permeable to hydro-
gen, from a hydrogen entry side, comprising the metal membrane, an
electrolyte solution communicating electrolytically with the side of the
10 membrane opposite to the hydrogen entry side, a metal/metal oxide
cathode communicating electrolytically with the electrolyte, the cathode
being capable of oxidizing hydrogen into hydrogen ions, the electro-
lyte and the cathode being contained in a housing of which the metal
membrane constitutes a wall portion, and leads for electrical connec-
15 tion to external current measuring squipment, the device being adapt-
ed to be maintained in a substantially short-circuited condition by
direct connection between the leads or by connection to a current
measuring system with low internai impedance. The measuring prin-
ciple utilized according to the present invention is the above-de-
20 scribed Devanathan principle. However, according to the invention,the functions of the reference electrode, the potentiostat and the
counterelectrode have been combined into one single component, i . e.
the metal/metal oxide cathode.
Thus, the measuring device of the invention only involves the use of
25 two electrodes, one of which is constituted by the membrane, which
renders it possible to make a compact, simple and accurate measuring
unit. For carrying out the measurement, the only external equipment
required is an am-meter. For the sake of proper functioning of the
device according to the invention, it is of mandatory importance that
30 the device be always kept in a short-circuited state, whether in use
(short-circuiting through the am-meter) or not in use (short-cir-
cuiting through a direct connection between the leads).
- P~V F2719 jG 323345 HSN/KWF 1983 02 23
A particular aspect of the present invention is a low cost and compact
device for determining hydrogen flux through a metal membrane,
which is selectively permeable to hydrogen, from a hyclrogen entry
side, comprising the metal membrane, an electrolyte solution commu-
5 nicating electrolytically with the side of the membrane opposite to tl1ehydrogen entry side, and a metal/metal oxide cathode communicating
electrolytically with the electrolyte, the cathode being capable of
oxidizing hydrogen into hydrogen ions, the electrolyte and the catho-
de being contained in a housing of which the membrane constitutes a
10 wall portion, the housing being permanently sealed. In this aspect of
the present invention, a measuring device having extremely small
dimensions, including small internal volume, may be provided. Due to
the permanent sealing, a permanent high standard of purity and
reproducibility may be obtained by finishing the measuring device in
15 a factory under controlled conditions, and no mainterance is re-
quired, as contrasted to known hydrogen measuring devices.
The invention also relates to a method for determining hydroyen flux
through a metal membrane, which is selectively permeable to hydro-
gen, from a hydrogen entry side, comprising:
20 providing a housing, arranging a metal/metal oxide cathode and an
electrolyte solution in the housing, which cathode is capable of
oxidizing hydrogen into hydrogen ions and communicates electrolyt-
ically with the electrolyte solution, arranging in the housing the metal
membrane so that it constitutes a wall portion thereof, contacting the
25 side of the metal membrane opposite to the hydrogen entry side with
the electrolyte solution, sealing the metal membrane in the housing,
short-circuiting the metal membrane at the metal/metal oxide cathode,
and measuring the electrical current generated as the result of oxida-
tion of hydrogen passing through the membrane.
30 Another aspect of the present invention relates to a method for
determining hydrogen flux through a metal membrane, which is
selectively permeable to hydrogen, from a hydrogen entry side
comprising:
providing a housing, arranging a metal/metal oxide cathode and an
35 electrolyte solution in the housing, which cathode i5 capable of
P~V F2719 jG 323345 HSN/KWF 1983 02 23
7~
oxidizing hydrogen into hydrogen ions and communicates
electrolytically with the electrolyte solution, arranging the housing in
contact with the metal membrane so that at least part of the metal
membrane constitutes a wall portion of the housing, contacting the
5 side of the metal membrane opposite to the hydrogen entry side with
the electrolyte solution, sealing said part of the metal membrane
relative to the housing, short-circuiting the metal membrane and the
metal/metal oxide cathode, and continuously measuring the electrical
current generated as the result of short-circuiting the metal
10 membrane and the metal/metal oxide cathode. In this aspect of the
present invention, the escape of hydrogen from the side of the metal
membrane opposite to the hydrogen entry side is determined con-
tinuously by continuousiy measuring the electrical current. On the
basis of escape of hydrogen, the hydrogen flux through the metal
15 membrane may be determined.
When carrying out the method according to the invention, the above
device according to the invention may advantageously be employed
providing highly reproduceable and accurate measuring results.
DETAILED DESCRIPTION OF THE INVENTION
20 The metal membrane used according to the invention should be of a
metal which is selectively permeabie to hydrogen. in practice, useful
metals for this purpose are steel/iron, and palladium. For many
purposes, the metal membrane is made of a sheet of steel/iron which
is coated with palladium on one or both sides. The thickness of the
25 membrane determines the measuring response time of the device. A
palladium membrane or coating is normally in the ran~3e of 0.05-10 llm,
preferably 0.1-0.5 llm, while a steel membrane may be considerably
thicker, typically from about 20 llm to about 1 mm.
The metal/metal oxide cathode used according to the present invention
30 should be of a kind which is able to oxidize hydrogen into hyclrogen
ions, but which will not give rise to any undesired oxidation reactions
with other components present. Thus, preferred cathodes used accor-
ding to the invention have an oxidation potential which is between 200
P~V F2719 jG 323345 HSN/KWF 1983 02 23
5~7C~
and 1200 mV above the equilibrium potential of the hydrogen electrode
at the pH of the electrolyte solution, in particular ~00-1200 mV above
the equilibrium potential of the hydrogen electrode at the pH of the
electrolyte solution. In the embodiments preferred at present, the
5 oxidation potential of the cathode is about 900 mV above the equili-
brium potential of the hydrogen eletrode at the pH of the electrolyte
sol ution .
Subject to this, the metal oxide of the cathode may be selected from,
e.g., silver oxide, mercury oxide, and manganese dioxide. The metal
10 of the metal/metal oxide cathode only serves as an electrical conduc-
tor, but should be of a kind which is substantially chemically inert in
relation to the metal oxide and the electrolyte solution. Hence, the
metal may suitably be selected from nickel, nickel-coated steel, silver,
and noble metals such as gold, palladium, and platinum.
15 The potential of the metal/metal oxide cathode may also be expressed
with reference to the range required for anodic oxidation of hydrogen
on the metal membrane, preferably in the range of -100 to ~300 mV
EH ~
The cathode should be designed so that it is able to supply current
20 to the metal membrane in sufficient quantity to oxidi~e all hydrogen
passing throu~h the membrane under normal conditions of application,
while still remaining in the acceptable potential range.
Also, the total capacity of the cathode should preferably exceed the
normal useful life of the metal membrane.
25 The electrolyte solution used according to the invention and communi-
cating with the metal membrane and the metal oxide of the cathode
should be an electrolyte which is suitably adapted to the type of the
metal oxide. As examples of electrolyte solution may be mentioned
aqueous alkaline solutions such as sodium or potassium hydroxide,
30 normally in concentrations in the range of 0.1-14N. For some appli-
cations, e.g. when the measurement is to be performed at high tem-
peratures, it may be preferred to use an acidic electrolyte solution in
P~V F2719 jG 323345 HSN/KWF 1903 02 23
9~
combination with an appropriate metal oxide, e.g., sulphuric acid in
combination with lead oxide.
In one embodiment of the device according to the invention, the metal
membrane is supported on a plastic foil. In this embocliment, the metal
5 membrane may be a steel/iron membrane having a palladium coating on
one or both sides, or may be constituted by a palladium coating on
the plastic foil. In this embodiment, -the plastic foil may advantageous-
ly be arranged so as to constitute an outer face of the device pro-
viding a mechanical protection of the metal membrane, and in order to
10 provide access for hydrogen to the metal membrane, the plastic foil
may be perforated or raay be made of a hydrogen-permeable plastic
material. When providing a perforation of the supporting plastic foil,
any plastic material which is not affected by the actual corrosive
forces may be employed, such as a foil made of e.g. Mylar(~. Alter-
15 natively, the hydrogen permeable plastic foil may be made of, e. g .,polytetraflouroethylene (Teflon(9).
In this embodiment of the device according to the invention, the
metal/metal o~ide cathode may also be supported on a plastic foil,
preferably a hydrogen-impermeable plastic foil, constituting a wall
20 portion of the housing. The metal/metal oxide cathode supporting
plastic foil is preferably made of a strong, inelastic and pliable plastic
material, such as Mylar~. When providing the metal membrane and the
metal/metal oxide cathode supported on respective plastic foils, the
supporting foils may be kept in a spaced-apart relationship by means
25 of a separator and be joined and sealed to one another along an outer
rim portion. In this embodiment, a so-called "Patch Cell" is provided
which is adapted to be mounted on an outer surface of a steel or iron
wall, the corrosive influences on which are to be determined. In this
so-called "Patch Cell", the electrolyte solution may be a layer of an
30 electrolyte paste which is arranged on the side of the metal membrane
opposite to the hydrogen entry side, and, consequently, concealed
within the space defined between the metal membrane supporting foil
and the metal/metal oxide cathode supporting foil.
P~V F2719 jG 323345 HSN/ICWF 1983 02 23
11
In a further embodiment of the invention, the device comprises a first
device part and a second device part, both having any of the above
characteristics, wherein the first device part constitutes an active
sensing element, and the second device part, which is sealed so as to
S exclude hydrogen, constitutes a reference element. In this embodi-
ment, the second device part is adapted to respond to any environ
mental influences other than the corrosive forces or influences which
are being measured by means of the first device part. Thus, the
second device part may constitute a temperature responsive sensor.
10 When connected to appropriate measuring equipment, environmental
influences other than the corrosive influences which are to be deter-
mined by means of the measuring results provided by the first device
part, may be compensated for by means of measuring results provided
by the second device part. Such environmental influences other than
15 corrosive influences may be e.g. temperature variations.
In an important embodiment of the method according to the invention,
the hydrogen flux is generated as a result of a chemical or electro-
chemical reaction between the entry surface of the membrane and an
exterior fluid medium such as a liquid or gas with which the surface
20 of the membrane reacts chemically or electrochemically. This makes it
possible to use the membrane material as a model for any object made
of the same material and subjected to chemical or electrochemical
reaction, so that the hydrogen flux measured by the method of the
invention will be representative of the hydrogen flux to which the
object made of the same material will be subjected when exposed to
the environment in question.
Thus, in one embodiment, the entry side of the membrane is exposed
to a fluid which corrodes the surface metal of the membrane with
generation of a hydrogen flux into the membrane. An important exam-
ple of this is where the membrane is made of a sample of a steeltype, the hydrogen corrosion of which, when subjected to chemical or
electrochemical treatments in a cleaning solution, in pickling, phos-
phating, stripping or metalplating baths, or in other electrogalvanic
processes, is to be judged. The membrane may also b~ made of steel
35 being subjected to corrosion in a process stream of a chemical plant
P~V F2719 jG 323345 HSN/KWF 1983 02 23
1~9~7~
12
or a power plant, or when measuring or processing natural gas, oil,
or geothermal steam.
I t is also possible to provide the membrane with an outer protective
coating or layer, the protective effect of which is to be studied when
5 subjected to corrosive or other influences. Alternatively, the metal
membrane may be provided with an outer coating or layer of a mate-
rial, the corrosive influence of which on the metal membrane is to be
studied .
Also, the method of the invention may be utilized for determining
10 hydrogen uptake in steel subjected to corrosion in natural environ-
ments, ranging from atmospheric exposure to natural waters and
soils, including exposure to or in building materials, such as con-
crete, thermally insulating materials, wood, etc.
According to the invention, the metal membrane may be exposed to
15 the said environments or materials, also including the case where
solid materials are applied to the membrane, and the case where the
device is built into or applied onto a material the hydrogen influence
of which on the steel is to be monitored.
The membrane may be provided with surface coatings corresponding
20 to the simulation desired, including chemically corrosive layers,
paints, metal coatings, anticorrosive protective layers, including
paints, etc., the hydrogen uptake of which or the influence of which
on the hydrogen uptake of the membrane metal is to be investigated
or monitored.
25 The size and shape of the membrane exposed may be adapted to suit
the purpose in question, e.g., to simulate the functions of an engi-
neering component.
The membrane may also be subjected to additional electrochemical
control or bimetallic contact in order to make it possible to study the
30 effect of cathodic protection, galvanic action, or any other m~ans of
control .
P~V F2719 jG 323345 HSN/KWF 1983 02 23
~B~57
13
Furthermore, the method of the invention may be used for controlling
(testing and/or standardizing) test solutions in which stress corrosion
or hydrogen embrittlement tests are carried out.
A very important example of determination of hydrogen uptake in
steel or iron subjected to corrosion in natural environments is the
determination of hydrogen uptake in a steel or iron wall of a pipe or
vessel. In this case, the metal membrane is arranged adjacent to the
outer surface of the steel or iron wall, and the flux of hydrogen
escaping from an outer surface of the steel or iron wall is deter-
10 mined.
BRIEF DESCRIPTION OF THE DRAWING
The invention will now be further described with reference to the
drawing, wherein
Fig. 1 is a vertical, sectional view of a first embodiment of a hy-
drogen probe or hydrogen monitoring cell according to the invention,
Fig. 2 is an illustration of a possible application of the hydrogen
monitoring cell shown in Fig, 1,
Fig. 3 is a vertical, sectional view of a prototype of a measuring cell
constructed in accordance with the principles of the present inven-
20 tion,
Fig. 4 is a diagramme showing the current plotted versus time in atest application of the prototype shown i Fig. 3,
Fig. 5 is a partly sectional view of a second embodiment of a hydro-
gen probe or hydrogen monitoring cell according to the invention,
Fig. 6 is a partly sectional view of a third embodiment of a hydrogen
probe or hydrogen monitoring cell according to the invention,
Fig. 7 is a partly sectional view of a fourth embodiment of a hydro-
gen probe or hydrogen monitoring cell according to the invention or a
"PATCH CELL",
30 Fig. 8 is an exploded view o~ the embodiment or "PATCH CELL"
shown in Fig. 7, and
Fig. 9 is a partly sectional view of a fifth embodiment of a hydrogen
probe or hydrogen monitoring cell according to the invention.
P~V F2719 jG 323345 HSN/KWF 1983 02 23
3S7~
14
DETAILED DESCRIPTION OF THE DRAWING
Fig. 1 shows a first embodiment of a hydrogen monitoring cell ac-
cording to the invention designated 10 in its entity. The cell 10 is
constructed as a button-shaped power cell (a mercury battery) of the
5 kind commonly used in watches, pocket computers, hearing aids or
the like. The cell 10 comprises two main components, a bottom part
and a top part designated 11 and 12, respectively. The top part 12
constitutes a membrane wall of the measuring cell and is made from
steel sheet comprising pure iron or steel plate of the kind commonly
10 used for fabrication of tinplate in the canning industry. The interior
surface of the top part 12, i.e. the surface facing the interior of the
measuring cell, is provided with a coating of palladium. The bottom
part 11, together with a metal oxide filling 14, constitutes a metal/-
metal oxide cathode of the hydrogen monitoring cell. The metal/metal
15 oxide caihode may be constructed in several ways using several
combinations o~ metals and oxides, all of which are known from the
construction of alkaline batteries. The bottom part 11 is made of a
metal which is not or only very slowly oxidized in a solution at the
potential of the cathode, such as nickel or nickel-coated steei, stain-
20 less steel, or a noble metal such as silver, gold or palladium or acoating of these metals on steel or another suitable carrier. The metal
oxide may be manganese dioxide, silver oxide, mercury oxide, and
other oxides either alone or in combination with metal powders, mer-
cury or other additives serving to give conductivity, to increase the
25 effective area or to improve the performance of the cathode in other
ways known from the construction of cathodes in alkaline power
generating cells. The metal oxide filling 14 is press-fitted into the
bottom part 11 in order to obtain good contact between the metal and
the metal oxide.
30 The two components, i.e. the bottom part 11 and the top part 12 are
sealed together, a sealing compound 15 being provided within the
in-turned edge of the top part 12. The thickness of the top part 12
is mainly determined by the ability of the material to be formed in the
turned-in edge. However, the thickness of the material also deter-
35 mines the useful life of the measuring cell and the response time
P~V F2719 j~ 323345 HSN/KWF 1983 02 23
357~
thereof. As will be appreciated, a more heavy metal sheet provides alonger useful life time, but reduces the response time of the moni-
toring cell. A sheet thickness of 0.25 mm commonly used in the can-
ning industry provides satisfactory results relating to these above
5 mentioned factors. The thickness of the palladium coating of the
interior surface of the top part 12 may be within the range of O.OS to
10 ,um, preferably 0.1 to 0.5 llm.
Within the hydrogen monitoring cell 10, in a space defined between
the palladium coating 13 and the upper surface of the metal oxide
filling 14, an electrolyte 16 and a separator 17 are provided. The
electrolyte 16 may be a pure solution of alkali hydroxide, preferably
sodium or potassium hydroxide in a concentration of 0.1 to 14 molar,
preferably 1 molar. The separator 17 serves to prevent particles of
metal oxide from getting into contact with the palladium coating and
15 may be made of polymer fibres, e.g. polypropylene fibres commonly
used as separators in alkaline batteries.
In Fig. 2 the first embodiment of the hydrogen probe or hydrogen
monitoring cell is shown mounted at the end of a tube 18 and in
electrically conductive connection therewith. The tube 18 may be made
20 of, e.g., steel or iron and is provided with an interior flange part
19. The bottom part 11 of the measuring cell 10 is insulated relative
to the tube 18 by means of a insulating annular sealing 20 which is
mounted in the interspace between the interior surface of the tube 18
and the exterior surface of the bottom part 11. In a central bore 21
25 of the flanged part 19, a spring contact 22 is mounted in an insu-
lating sealing 23. Through a soidered joint 24, the contact 22 is
connected to an insulated wire 25 for establishing connection to ex-
ternal current measuring equipment also connected to the tube 18 (not
shown). Surrounding the tube 18, a corrosive resistant tube 26
30 having a turned-in flange 27 is mounted. The tube 26 is insulated
relative to the measuring cell 10 by means of an insulating annular
sealing 28 which is mounted between the flange 27 and the top sur-
face of the membrane 12 of the measuring cell. Furthermore, an
insulating sealing (not shown) may be provided within the space
35 between the two tubes 18 and 26 in order to keep the tubes in
P~V F2719 jG 323345 HSN/KWF 1983 02 23
~39570
16
spaced-apart relationship. The measuring cell mounted at the end of
the tube 18 may thus be introduced or withdrawn from a measuring
environment in a manner known per se through one or more ball
va I ves .
5 In Fig. 3 a pro-totype constructed in accordance with the principles of
the present invention is shown. The prototype is designated 30 in its
entity and comprises a housing consisting of a bottom component 31
and a top component 32 made of polymethacrylate. The two compo-
nents 31 and 32 are joined together by means of screw connections 33
10 and 34 and confine a membrane 35 within the interspace between the
two components. The membrane 35 is made of a piece of detinned and
finely polished tin plate with a thickness of 0.25 mm and is coated
with palladium 3n one side, the side facing the interior of the bottom
component 31. The palladium coating is deposited from the following
15 solution:
per liter: 5 9 PdCI2
240 g Na3PO4, aq
55 9 (N~4)3PO4
3.5 g benzoid acid, pll adjusted to 11 with ammonia.
0 Working conditions: Temperature 60-70C,
current density 2 mA/cm2,
time 2-4 minutes.
Thus, a palladium coating of a thickness of approximately 0.1 -0.2 llm
is obtained. The opposite, uncoated side of the steel membrane pro-
25 vides an exposed area of 7 cm2 within a central circular recess of thetop component 32. The membrane 35 is secured and sealed relative to
the interior of the bottom part 31 by means of an annular sealing 37
mounted in an annular recess 38 provided in the top surface of the
bottom component 31. In the interior of the bottom component 31, two
30 co-axically arranged cavities or chambers 39 and 40, respectively, are
provided. The chamber 40 is filled with a metal/metal oxide electrode
41 which is connected to an insulated wire leading through a central
bore 43 of the bottom component 31. The metal/metal oxide electrode
P~V F2719 jG 323345 HSN/KWF 1983 02 23
57~
17
41 is secured in the chamber 40 by means of a sealing 44 also sealing
the chamber 39 relative to the environment. The sealings 37 and 4'1
are made of alkali resistent rubber. The metal/metal oxide electrode is
constituted of a nickel-coated steel shell which is filled with a mixture
of equal weights of mercury oxide and a powder of metallic silver.
The powders are pressed into the shell. The wire 42 is soldered to
the exterior surface or bottom surface of the nickel-coated steel shell.
Within the chamber 39 a 1 N sodium hydroxide electrolyte solution of
high purity is confined.
When assembling the cell 30, the cell is flushed with pure nitrogen
and then placed in a de-aerated electrolyte solution. While immersing
the cell in the electrolyte solution, vacuum is applied, which helps to
remove gasses before closing the cell.
Five cells of the kind shown in Fig. 3 have been constructed in
accordance with the principles described above. They were stored for
24 hours in a short-circuited state. Having been short-circuited for
24 hours, the cells generated currents in the range 0.1-0.5 llA, ty-
pically 0.2 llA. Since the internal area of the membrane is 16 cm2, the
currents thus obtained equal a current density of approximately
0.01-0. 03 ~A/cm2 .
In Fig. 4 a diagramme of current generated in a prototype cell of the
kind shown i Fig. 3 is shown plotted versus time. The zero current
(not shown in Fig. 4) of the cell is approximately 0.2 llA as men-
tioned above. At the time zero, the cell is immersed in a 0.2 molar
H2S04 solution. Within approximately 7 minutes the current generated
in the cell rises to a value (125 ,uA) of approximately 50% of the
maximum current (250 ~A). After having stabilized at the maximum
current, the cell is removed from the solution at the time indicated by
an arrow in Fig. 4. The currect decays fairly rapidly. I lowever, the
30 transient response of the measuring cell may be increased (or de-
creased) by decreasing (or increasing) the thickness of the mem-
brane. Responses identical to the one shown in Fig. 4 were obtained
in three successive measurements. Thus, the cell does not exhibit
hysteresis .
P~V F2719 jG 323345 HSN/KWF 1983 02 23
~8~35~
18
In Fig. 5, a second embodiment of the hydrogen measuring probe or
hydrogen detecting cell i5 shown designated 50 in its entity. The
hydrogen measuring probe 50 comprises a sensing element, i.e. a
membrane, of a short length of a thin-walled steel or iron tube 51
closed at one end 51a. The interior surface of the tube 51 may be
provided with a palladium coating although this is not mandatory to
the proper functioning of the probe. The probe also includes a
metal/metal oxide electrode comprising a rod of a metal/metal oxide
powder mixture 52 which may be of the kind described above in
connection with Fig. 3 and which is pressed around a metal conductor
53 of e.g. nickel. A separator 54 is provided surrounding the
metal/metal oxide electrode 52, 53. The separator may be made of
e. g . propylene fibres . The assembly of metal/metal oxide electrode
52, 53 and separator 54 is fitted into a plastic stopper 55 which is
press-fitted into the open end of the tube 51 after filling the interior
space of the tube with a de-aerated electrolyte solution 56 which may
be of the kind described above in connection with Fig. 3. The metal
conductor 53 projects through the stopper 55 and is connected to an
insulated wire 57. The tube 54 is also connected to an insulated wire
58. The wires 57 and 58 are adapted to be connected to external
current measuring equipment, e.g. a conventional sensitive am-meter.
A plastic jacket 59 is heat-shrinked around the open end of the tube
51 and around the wires 57 and 58.
In Fig. 6, a third embodiment of the invention is shown. The embodi-
ment of the invention shown in Fig. 6 and designated 60 in its entity
differs only slightly from the embodiment of the invention shown in
Fig. 5. Thus, identical re~erence numerals are designating identical
components of the two embodiments. As distinct from the probe 50,
the probe 60 comprises a tube 61 of a metal impermeable to hydrogen,
e.g. nickel, iron/nickel alloy or stainless steel. The inside of the
tube 61 may be covered with an alkali-resistant enamel. The end of
the tube 61 opposite to the end fitted with the plastic stopper 55 is
provided with a steel or iron disc which is welded to the tube 61.
The disc 62 constitutes the metal membrane of the hydrogen measur-
ing probe in accordance with the principles of the present invention.
The embodiments of the invention shown in Fig. 5 and Fig. 6 are
P~V F2719 jG 323345 ~ISN/KWF 1983 02 23
95~
~9
intended and adapted to be used when measuring in situ, e.g. when
the metal is subjected to an electrogalvanic process. Thus, the probe
is dipped into the electrogalvanic solution to simulate the process
normally performed in the bath (e.g. cleaning, pickling, phospating,
5 stripping, electroplating, electrodeposition etc.) while the tube of -the
hydrogen probe, i . e. the tube 51 of the embodiment shown in Fig . 5
and the tube 61 of the embodiment shown in Fig. 6, respectively, is
connected to external electrogalvanic current/voltage generating
means .
10 The long and slender shape of the hydrogen probe 60 shown in Fig.
6 provides additional useful properties. Thus, the shape of the hy-
drogen probe makes it easily adaptable to an "access fitting". Fur-
thermore, the length of the hydrogen probe when combined with a
tube with low thermal conductivity, e.g. a stainiess steel or iron/-
15 nickel alloy tube, makes it possible to apply cooling to the end of thetube which is provided with the plastic stopper 55, while maintaining
the end of the tube which is provided with the metal disc 62 at a
significantly higher temperature in the galvanic bath. Thus the tem-
perature dependency of the measurement is reduced. The combination
20 of a hydrogen-impermeable metal tube 61 and hydrogen-permeable
metal disc 62 renders it possible to perform measurements on special,
possibly user-supplied iron or steel materials.
In Figs. 7 and 8, a fourth embodiment of the hydrogen measuring
device or a so-called "PATCH CELL" is shown. The "PATCH CELL"
25 shown in Figs. 7 and 8 is designated 70 and adapted to be mounted
on an outer surface of a steel or iron wall which is exposed to cor-
rosion. Thus, the "PATCH CELL" is adapted to detect and measure
hydrogen permeating through the steel wall and liberated from the
outer surface of the iron or steel wall within a measuring area deter-
30 mined by the physical dimensions of the measuring device. Fig. 7 is avertical sectional view of the measuring device 70 when assembled and
ready for use, while Fig. 8 is an exploded view thereof. Thus, iden-
tical reference numerals designate identical parts in Figs. 7 and 8.
The measuring device 70 comprises an outer protective foil 71 of a
35 suitable plastic material which is pliable, strong and inelastic, e.g.
P ~V F2719 j G 323345 H S N/ KWF 1983 02 23
:~8~5~
Mylar~. A thin metal layer 72 is firmly bonded to the plastic foil 71
and constitutes a metal component of a metal/metal oxide electrode of
the measuring device. The metal layer 72 may be made from any
appropriate metal, e.g. nickel or silver. Apart from supporting the
5 metal layer 72, the plastic foil 71 provides protection and insulation to
the metal layer relative to the environment. The metal layer may be
deposited as a thin metal coating on the plastic foil 71. The metal
oxide component of the metal/metal oxide electrode is designated by
the reference numeral 73. The metal ox;de may be made from a mix-
10 ture of metal oxide powder and metal powder which are pressed intoan intimate mixture also containing a binder if desired. The metal
oxide component is appiied to the metal component of the metal/metal
oxide electrode, i.e. the metallic layer 72, e.g. by thick film tech-
nique.
15 Similar to the above-described embodiments of the invention the
measuring device 70 comprises a metal membrane which is constituted
by a foil 77 of a metal permeable to hydrogen, e.g. palladium or iron
coated with palladium on both sides. Similar to the combination of the
plastic foil 71 and the metallic layer 72, the metal foil or membrane 77
20 is firmly bonded to a supporting plastic foil 78. However, the plastic
foil 78 is provided with several holes 79 in order to provide external
access to the membrane 77. Alternatively, the plastic foil may be made
of a material which is permeable to hydrogen, e. g . polytetrafluoro-
ethylene (Teflon6)).
25 The metal oxide 73 of the metal/rnetal oxide electrode is prevented
from coming into contact with the metal membrane 78 by means of a
separator 74. The separator 74 may be made from a sheet of alkali
resistant filter paper, e.g. made from polypropylene fibers. The rim
of the separator 74 is on both sides provided with layers 75 and 76 of
30 a plastic material which permeates the filter material and also func-
tions as a glue and sealing compound when the measuring device is
assembled in a heat-sealing process to be described in further detail
below. The material of the layers 75 and 76 must fulfill two functions,
firstly, the material must be able to permeate and fill the pores of the
35 separator and, secondly, the material must have adhesive properties
P~V F2719 jG 323345 HSN/KWF 1983 02 23
35~0
21
in order to firmly join the metallic layer 72 and the metal membrane 79
together and seai the measuring device.
As will be appreciated, the plastic foil 71, the metallic layer 72 and
the metal oxide component 73 are prepared as one single unit to be
5 joined and sealed with another unit comprising the metal membrane 77
and tlle plastic foil 78 by means of the adhesive rim material 75 and
76 of the separator 74. Before assembling the measuring device, an
electrolyte solution is provided between the metal/metal oxide elec-
trode and the metal membrane 77. The electrolyte solution is a de-
10 aerated alkaline electrolyte preferably made into a paste using tech-
niques known from the manufacturing of batteries. The metal oxide
component-73 and the separator sheet 74 are soaked with electrolyte
solution and, furthermore, a layer of the electrolyte solution is ap-
plied on the metal membrane 77. When assembling the cell, air (oxy-
15 gen) must be excluded from the interspace between the metal/metaloxide electrode and the metal membrane. Furthermore, the electrolyte
solution must be prevented from coming into contact with the adhesive
material 75 and 76. The cell is assembled by means of an appropri-
ately heated tool comprising two parts which are contacted with the
20 rim portions of the plastic foil 71 and 78, respectively, and pressed
together .
The plastic foil 71, the metallic layer 72, the metal membrane 77 and
the plastic foil 78 are provided with flaps 71a, 72a, 77a, and 78a,
respectively. The metal flap 72a is intended to be folded around a
25 metal wire 82 and the metal flap 77a is adapted to be folded around a
metal wire 83, as shown in Fig. 7. Thus, the plastic flap 71a and the
plastic flap 78a insulate the metal flaps relative to one another and
relative to the environment. The metal wires 82 and 83 are intended
to be short-circuited when the measuring device is stored, and to be
30 connected to external current measuring equipment such as a con-
ventional am-meter when in use.
Finally, a cover made of paper or cardboard is applied on the outer
surface of the plastic foil 78 by means of a compressible, flexible
material 80 such as foam rubber or foam plastic with self-adhesive
P~V F2719 jG 323345 HSN/KWF 1983 02 23
surfaces in order to protect the exposed surface areas of the metal
membrane 79 when the measuring cell is not in use. The adhesive
surface of the material 80 facing the cover 81 also serves to apply the
measuring device to a measuring site on a steel or iron wall.
5 In Fig. 9 a fifth embodiment of the hydrogen measuring device ac-
cording to the invention is shown and designated 90 in its entity.
The embodiment of the invention shown in Fig. 9 differs from the
above described embodiments in that the device comprises two ba-
sically identical parts or halves. The first part constitutes the active
10 sensing element, and the second part is neutralized or inactive or
adapted to be neutralized or inactivated so that the second part
constitutes a reference element. Unlike the first part of the measuring
device, the second part or reference element is not intended to be
exposed to corrosive forces or other influences to be measured.
15 Instead, the reference element responds to temperature variations
only. When connected to appropriately calibrated differential measur-
ing equipment, the first part of the measuring device provides cur-
rent measurements while the second part or reference element serve
temperature compensation purposes when supplying current to the
20 measuring equipment.
The measuring device 90 comprises a metal sheet 91, e.g. a nickel or
silver sheet. The metal sheet 91 is common to both the above de-
scribed parts of the measuring device and provides support thereto
and physical strength to the measuring device as a whole. On a first
25 side of the metal sheet on which the active sensing part of the meas-
uring device is constructed, a metal oxide component 92 is applied in
intimate contact with the metal sheet 91. Together, the metal sheet 91
and the metal oxide component 92 constitute a first metal/metal oxide
electrode of the active part of the measuring device. Above the metal
30 oxide component 92, a separator 93 is arranged. Above the separator
93 a metal membrane 94 is arranged. Furthermore, the first part of
the measuring device comprises an electrolyte solution which is en-
closed in the space between the metal/metal oxide electrcde and the
metal membrane 94. Basically, the above described components of the
35 measuring device are identical to the corresponding components of the
P~V F2719 jG 323345 HSN/I~WF 1983 02 23
57~
23
embodiment of the invention shown in Figs. 7 and 8. Thus, a hydro-
gen permeable plastic foil serving protective purposes may also be
arranged so that it covers the metal membrane 94.
The second part o~ the measuring device comprises components ba-
sically identical to the above described components, i.e. a metal oxide
component g5, a separator 96, a metal membrane 97, and an elec-
trolyte solution enclosed in the space between the metal/metal oxide
electrode and the metal membrane 97. Furthermore, the second part of
the measuring device 90 comprises a corrosion resistant foil 98 which
completely seals the second part of the measuring device and protects
the metal membrane 97 when the measuring device is subjected to
corrosive forces. The foil 98 may either constitute an integral part of
the measuring device or be applied by a user. Thus, the foil 98 may
be made of plastic or may be applied as an anticorrosive composition,
paste or the like.
The entire measuring device 90 is assembled in a heat-sealing process
similar to the process described above in connection with Figs. 7 and
8.
The metal sheet 91, the metal membrane 94, and the metal membrane
98 are connected to individual wires 99, 100, 101, respectively, and
the wires 99-101 are enclosed within a common jacket 102.
It is understood that the above described embodiments are merely il-
lustrative of the application of the principles of the present inven-
tion. Numerous other embodiments may be devised by those skilied in
the art without departing from the spirit and scope of the present in-
vention .
P~V F2719 jG 323345 HSN/KWF 1983 02 23
57~
24
REFERENCES
1. M.A.V. Devanathan and Z. Stachurski:
Proceeding of the Royal Society, 1962, Vol A270, p90.
2. M. Meron et al, Metal Progress, July 1981, p.52.
3. GB Patent Specification No. 1 S85 070
4. GB Patent Specification No. 1 524 017
5. G. Mansfeld, S. Jeanjaquet, and D.K. Roe,
Materials Performance, February 1982.
P ~V F2719 j G 323345 H S N / KW F 1983 02 23
