Hydrogen Detector for Gas and Fluid Media

Abstract

A hydrogen detector for gas and fluid media is disclosed. The detector includes a selective membrane and a housing. Within the housing is a potential measuring unit and a ceramic sensing element made of a solid electrolyte. A standard electrode is located within a cavity of the ceramic sensing element and a porous platinum electrode is applied to an external layer of the ceramic sensing element. A potential measuring unit passes through a sealed lead-in at the upper end of the housing and is brought out to the standard electrode. The selective membrane, which is attached to a hole in the end of the lower bushing, is closed with a plug. The cavity limited by the inner surface of the lower bushing, the external part of the bottom of the ceramic sensing element and the inner surfaces of the selective membrane and the plug is leak-tight.

Claims

1. The hydrogen detector for gas and fluid media comprises a selective membrane and a housing with a potential measuring unit inside, a ceramic sensing element made of solid electrolyte, the cavity of which contains a reference electrode, a porous platinum electrode, applied on the external layer of the ceramic sensing element, a sealed lead-in tightly fixed inside the housing above the ceramic sensing element, a potential measuring unit that passes through the central core of the sealed lead-in and the lower bushing, wherein the ceramic sensing element is designed as a cylinder interlinked with the bottom located in the lower part of the cylinder. The external cylindrical surface of the ceramic sensing element is tightly connected to the inner side surface of the housing. The standard electrode is located in the inner cavity of the ceramic sensing element. The external part of the bottom of the ceramic sensing element is covered with a layer of the porous platinum electrode. The end of the central core of the potential measuring unit is brought out to the standard electrode, thus the electrical contact is provided between the standard electrode and the lower part of the central core of the potential measuring unit. The lower bushing designed as a tube is connected to the lower part of the housing on the side of the ceramic sensing element. The lower end of the lower bushing has a bottom with a center hole with an attached selective membrane made of at least one tube. The lower free end of the selective membrane is tightly closed with a plug. The cavity limited by the inner surface of the lower bushing, the external part of the bottom of the ceramic sensing element and the inner surfaces of the selective membrane and the plug are leak-tight. The detector is equipped with an upper bushing installed in the upper part of the potential measuring unit, wherein the ring-shaped cavity between the inner surface of the upper bushing wall and the external surface of the potential measuring unit is filled with glass-ceramic sealant.

2. A detector according to claim 1, wherein the glass ceramic consists of silicon oxide (SiO.sub.2)—50 weight %, aluminum oxide (Al.sub.2O.sub.3)—5 weight %, boric oxide (B.sub.2O.sub.3)—20 weight %, titanium oxide (TiO.sub.2)—10 weight %, sodium oxide (Na.sub.2O)—12 weight %, potassium oxide (K.sub.2O)—1 weight % and magnesium oxide (MgO)—2 weight %.

3. A detector according to claim 1, wherein its upper bushing is made of stainless steel.

4. A detector according to claim 1, wherein its selective membrane is made of at least one tube.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention is illustrated with a FIGURE that shows a general view of the longitudinal axial cross-section of the detector.

EMBODIMENT OF INVENTION

[0029] The hydrogen detector comprises a selective membrane 1 and housing 2. A potential measuring unit 3, a ceramic sensing element 4 made of solid electrolyte are located inside the housing 2. The sensing element cavity contains a reference electrode 5, a porous platinum electrode 6 applied to the external layer of the ceramic sensing element 4. A sealed lead-in 7 is tightly fixed inside the housing 2 above the ceramic sensing element 4. The detector comprises upper 8 and lower 9 bushings, sealant 10, central core of the potential measuring unit 11 and a plug 12.

[0030] The sealant 10 fills the ring-shaped cavity between the inner surface of the upper bushing wall 8 and the external surface of the central core of the potential measuring unit 11.

[0031] The potential measuring unit 3 passes through the center core of the sealed lead-in 7.

[0032] The ceramic sensing element 4 is located in the lower part of the detector and designed as a cylindrical part interlinked with the bottom.

[0033] The external cylindrical surface of the ceramic sensing element 4 is tightly connected to the inner side surface of the housing 2.

[0034] The reference electrode 5 is located in the inner cavity of the ceramic sensing element 4.

[0035] The external part of the bottom of the ceramic sensing element 4 is covered with porous platinum electrode 6.

[0036] The end of the central core of the potential measuring unit 3 is brought out to the standard electrode 5.

[0037] Electrical contact is provided between the reference electrode 5 and the lower part of the potential measuring unit central core 11.

[0038] The lower bushing 9 designed as a tube is connected to the lower part of the housing 2 from the side of the ceramic sensing element 4.

[0039] The lower end of the bushing 9 has a bottom with a center hole to which a selective membrane 1 made of at least one tube is attached.

[0040] The lower free end of the selective membrane 1 is tightly closed with a plug 12.

[0041] The cavity limited by the inner surface of the lower bushing 9, the external part of the bottom of the ceramic sensing element 4 and the inner surfaces of the selective membrane 1 and the plug 12 is leak-tight.

[0042] The sealant 10 is a glass-ceramic consisting of silicon oxide (SiO.sub.2)—50 weight %, aluminum oxide (Al.sub.2O.sub.3)—5 weight %, boric oxide (B.sub.2O.sub.3)—20 weight %, titanium oxide (TiO.sub.2)—10 weight %, sodium oxide (Na.sub.2O)—12 weight %, potassium oxide (K.sub.2O)—1 weight % and magnesium oxide (MgO)—2 weight %.

[0043] The sealant is necessary to prevent ingress of oxygen from the air into the inner cavity of the detector and to avoid changes in the standard electrode 5 properties. The specified formula of the sealant was determined during a research. This sealant provides increased resistance to unfavorable operating conditions in corrosive environments at high temperature. Consequently, it provides leak-tightness of the detector for a longer operating life, loss-of-sealing risks decrease and fewer reading errors occur.

[0044] In a specific embodiment of the detector the upper bushing 8 is made of stainless steel.

[0045] The materials of the upper bushing 8 and the potential measuring unit 3 have an equal thermal-expansion coefficient, which allows to keep the detector operable under temperature changes within the range of 0-300° C.

[0046] The lower bushing 9 and the plugging 12 are made of nickel, grade NP0.

[0047] The sealed lead-in 7 and the upper bushing 8 are made of 12KH18N10T steel.

[0048] The ceramic sensing element 4 is made of partially stabilized zirconium dioxide and protrudes beyond the housing 2 for 6 mm.

[0049] The housing 2 is made of EI-852 ferritic-martensitic steel and has the following dimentions: the diameter is 15 mm, the length is 220 mm.

[0050] The porous platinum electrode 6 thickness is 20 μm.

[0051] The KNMS 2S double-clad cable is used as the potential measuring unit 3.

[0052] The selective membrane 1 comprises one tube made of NMg0.08v nickel. The sizes of the selective membrane 1 are the following: the diameter is 6 mm, the length is 40 mm, the wall thickness is 0.15 mm.

[0053] The standard electrode 5 is made of bismuth and bismuth oxide mixture.

[0054] The ratio between the area of the inner side surface of the selective membrane 1 and its voidage is 0.4 mm.sup.−1.

[0055] A Pd protective layer chemically stable in the oxidation atmosphere covers the external and inner parts of the selective membrane.

[0056] The hydrogen detector applies the electrochemical method that allows to determine oxygen concentration by means of oxygen sensor made of solid oxide electrolyte.

[0057] The hydrogen detector functions as follows.

[0058] While placing the hydrogen detector in the test medium hydrogen that is contained in the medium reversibly diffuses through the selective membrane 1 into the steam hydrogen compartment changing the electromotive force of the detector. The steam hydrogen compartment is a cavity limited by the inner surface of the lower bushing 9, the external part of the ceramic sensing element 4 protruding beyond the case 6 and the inner surface of the selective membrane 1.

[0059] The electromotive force of the detector occurs due to differences in partial pressure of oxygen in the electrodes of the concentration cell. The scheme can be presented in the following way:

[0060] Me| the reference electrode (5)∥ZrO.sub.2.Y.sub.2O.sub.3∥ the porous platinum electrode (6)|H.sub.2O, H.sub.2| the selective membrane| the medium.

[0061] The steam hydrogen compartment has fixed partial vapor pressure of water and functions as a converter of hydrogen thermodynamic potential into oxidation potential of steam hydrogen mixture on the porous platinum electrode 6.

[0062] The total electromotive force is a hydrogen pressure function that is defined in the following way:

[00002]$E=E_0-\frac{R.Math.T}{n.Math.F}.Math.\ln .Math.\frac{P_{H_2.Math.O}}{P_{H_2}},$

[0063] where: T is temperature, K; R is the gas constant, J/(mol*K); F is Faraday constant, J/mol; n is the number of the electrons participating in the reaction; P.sub.H.sub.2.sub.O is partial vapor pressure of water in the steam hydrogen compartment, Pa; P.sub.H.sub.2 is partial hydrogen pressure in the test medium, Pa.

[0064] An electrical signal output to be supplied to the secondary instruments is provided by the potential measuring unit 3. Changes in oxygen concentration in the controlled medium result in changes of the value of the electrical signal that ensures its uninterrupted pickup and processing.

[0065] Delay of the detector is connected with hydrogen permeability through the the selective membrane 1 and it can be estimated by the signal delay time:

[00003]${\tau }_{3.Math..Math.\mathrm{an}}=\frac{\mathrm{dV}}{\mathrm{SD}},$

[0066] Where d is the thickness of the selective membrane 1, m; D is the hydrogen diffusion coefficient in the material of the selective membrane 1, m.sup.2/sec, S is the area of the selective membrane surface 1, m.sup.2 and V is the inner voidage of the selective membrane 1, m.sup.3.

INDUSTRIAL APPLICABILITY

[0067] The detector can be commercially manufactured. Moreover, its manufacturing does not require special equipment.