RU2548374C2 - Solid electrolyte detector of oxygen concentration in gas media - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: invention relates to measurement equipment. A solid electrolyte detector of oxygen concentration in gas media comprises a ceramic sensitive element (3), tightly placed in a metal body (4), a comparison electrode (8), a potential collecting lead (5), a measurement electrode (2), applied onto the external part of the ceramic sensitive element (3). The measurement electrode (2) represents a double-layer current-conducting coating, the first layer comprises a mixture of a powder of noble metal and zirconium dioxide, the second one consists of a noble metal powder. The ceramic sensitive element (3) is made from solid electrolyte in the form of a cylindrical element and a part of a sphere coupled to each other. The upper external cylindrical surface of the ceramic sensitive element (3) is connected to an internal side surface of the body (4) by means of a connecting material (7). The ceramic sensitive element (3) is additionally equipped with a plug (6) from metal oxide with a hole that covers the cross section of the cavity of the ceramic sensitive element (3). The comparison electrode (8) is located in a cavity formed by the internal surface of the ceramic sensitive element (3) and the surface of the plug (6), occupies its part and contacts with the internal part of the sphere and at least with a part of the internal cylindrical surface of the ceramic sensitive element (3). The comparison electrode (8) comprises a lower and at least one subsequent layer, the free end of the potential-collecting lead (5) facing the part of the sphere is taken out into the volume of the comparison electrode (8) via a hole in the plug (6), at the same time there is electric contact between the potential-collecting lead (5) and the lower layer of the comparison electrode (8). The free end of the potential-collecting lead (5) facing towards the part of the sphere is taken out into the comparison electrode volume (8) via the hole in the plug (6). At the same time there is an electric contact between the potential-collecting lead (5) and the lower layer of the comparison electrode (8). At least a part of the sphere of the ceramic sensitive element (3) protrudes beyond the limits of the body (4). Materials of the body (4), the ceramic sensitive element (3) and the connecting material (7) have a close coefficient of temperature expansion. The free part of the body (4) is connected to a tight lead of useful signal (1) with the help of welding, the cavity formed by the ceramic sensitive element (3), the body (4) and the tight lead of useful signal (1), is tight in respect to the environment.

EFFECT: invention provides for the possibility to expand area of application and reduction of detector cost.

9 cl, 1 dwg

Description

A device for measuring the concentration of oxygen in gases is described in the patent for the invention [Patent for the invention of the Russian Federation No. 2107906, class. G01N 27/409, priority 1993], comprising a cylindrical body, an elongated cylindrical element, closed with a separate tip made of stabilized zirconia, the cylindrical element is made of heat-resistant material other than zirconia, while the tip of zirconia is made with an annular a part covering the end of the cylindrical element and which the tip is hermetically attached to the elongated cylindrical element using glass ceramics.

A disadvantage of the known device is its autonomy, i.e. the need for communication with the external environment, for example, using a gas line, which imposes restrictions on its scope. A disadvantage of the known device is also low resistance to high pressures and rapid changes in temperature of the analyzed medium.

Closest to the claimed technical solution is a device for measuring oxygen in gases, described in the patent for the invention [RU No. 2339028, class. G01N 27/417 Priority 2007]. The specified device contains a solid-electrolyte cell, an insulator, a metal shell, a current collector from the reference electrode, two layers are deposited in series on the smaller base of the solid-electrolyte cell and on the combined large bases of the electric insulator and solid-electrolyte cell, the first is a mixture of noble metal powder and zirconia, the second is made of powder noble metal, on the basis of the current collector at the place of its contact with the solid electrolyte cell, a foil of the same noble metal is applied, Azores between the mating surfaces of the electrical insulator and the metallic shell is filled with the amorphous foil of an alloy containing 25-30% titanium, the rest - copper.

The disadvantage of this device is the air is not tight relative to the external environment of the reference electrode, which limits the scope of its use by the need for constant delivery of air to the reference electrode.

The proposed technical solution allows you to:

- expand the scope due to the autonomy of the design;

- to increase resistance to pressure and rapid temperature changes of the analyzed medium due to the design of the ceramic sensitive element.

The technical result consists in expanding the scope and reducing the cost of the sensor.

To eliminate the aforementioned drawbacks in a solid-electrolyte sensor for oxygen concentration in gaseous media containing a ceramic sensitive element hermetically seated in a metal case, a reference electrode, a potential detachable terminal, a two-layer conductive coating is applied to the external part of the ceramic sensitive element, the first layer consists of a mixture of noble metal powder and zirconium dioxide, the second consists of a noble metal powder, offers I have:

- ceramic sensitive element made of solid electrolyte in the form of a pair of two cylindrical elements and part of a sphere;

- connect the upper outer cylindrical surface of the ceramic sensing element to the inner side surface of the housing by means of a connecting material;

- the ceramic sensing element is additionally equipped with a metal oxide plug with an opening overlapping the cross section of the cavity of the ceramic sensitive element;

- place the reference electrode in the cavity formed by the inner surface of the ceramic sensitive element and the surface of the cork, so that it occupies part of it and contacts the inside of the sphere and at least part of the inner cylindrical surface of the ceramic sensitive element;

- the reference electrode is made from the lower and at least one subsequent layer;

- facing the side of the sphere, the free end of the potential removal terminal is brought out into the volume of the reference electrode through the hole in the plug, while ensuring electrical contact between the voltage removal terminal and the lower layer of the reference electrode;

- choose a close coefficient of thermal expansion of the material of the housing, ceramic sensitive element and connecting material;

- connect the free part of the housing with the hermetic output of the useful signal by welding;

- to ensure tightness with respect to the external environment of the cavity formed by the ceramic sensitive element, the housing and the hermetic output of the useful signal.

In special cases, the implementation of the device is proposed:

- as a connecting material, use a glass consisting of silicon oxide (SiO ₂ ) 20-30 wt.%, alumina (Al ₂ O ₃ ) 6-7 wt.%, boron oxide (B ₂ O ₃ ) 20-21 wt. %, zinc peroxide (ZnO ₂ ) 10-12 wt.%, zirconium oxide (ZrO ₂ ) 5-6 wt.%, tin oxide (SnО ₂ ) 5-7 wt.%, calcium oxide (CaO) 15-21 wt.%, sodium oxide (Na ₂ O) 3-4 wt.%, potassium oxide (K ₂ O) 3-4 wt.%;

- ceramic sensitive element made of polycrystalline or monocrystalline partially stabilized zirconia;

- ceramic sensitive element made of polycrystalline or single crystal stabilized zirconia;

- ceramic sensitive element made of polycrystalline or single crystal stabilized hafnium dioxide;

- at least one of the layers of the reference electrode is made of bismuth, lead, indium, gallium, nickel, iron, copper, aluminum, bismuth oxide, lead oxide, indium oxide, gallium oxide from nickel oxide, from iron oxide, from copper oxide, from alumina;

- the body should be made of ferritic-martensitic steel EI-852 (X13M2S2) or of ferritic-martensitic steel EP-823 (16X12MVSFBR);

- the lower part of the potential removable terminal is made of steel 12X18H10T or molybdenum;

- use silver, palladium, platinum or mixtures thereof in the composition of the measuring electrode.

The invention is illustrated in the figure, which shows a longitudinal axial section of the sensor. The following notation is used in the figure: 1 - hermetic output of a useful signal; 2 - measuring electrode; 3 - ceramic sensing element; 4 - case; 5 - potential removal terminal; 6 - cork; 7 - connecting material; 8 - reference electrode.

A solid electrolyte oxygen concentration sensor in gaseous media contains a ceramic sensing element (3) sealed in a metal housing (4), a reference electrode (8), a potential detachment lead (5), a measuring electrode (2) deposited on the outer part of the ceramic sensitive element ( 3).

The measuring electrode (2) is a two-layer conductive coating, the first layer consists of a mixture of noble metal powder and zirconia, the second consists of a noble metal powder.

The ceramic sensing element (3) is made of solid electrolyte in the form of a cylindrical element and part of a sphere conjugated to each other. The upper outer cylindrical surface of the ceramic sensing element (3) is connected to the inner side surface of the housing (4) by means of a connecting material (7).

The ceramic sensing element (3) is additionally equipped with a plug (6) of metal oxide with an opening overlapping the cross section of the cavity of the ceramic sensing element (3).

The reference electrode (8) is located in the cavity formed by the inner surface of the ceramic sensing element (3) and the surface of the plug (6), occupies its part and is in contact with the inner part of the sphere and at least part of the inner cylindrical surface of the ceramic sensing element (3 ), the reference electrode (8) consists of the lower and at least one subsequent layer, the free end of the potential-removing terminal (5) facing the side of the sphere is brought into the volume of the reference electrode (8) through an opening in the box (6), while ensuring electrical contact between the potential removal terminal (5) and the lower layer of the reference electrode (8).

The free end of the potential detachable terminal (5) facing the side of the sphere is brought into the volume of the reference electrode (8) through an opening in the plug (6). In this case, an electrical contact is provided between the potential detachable terminal (5) and the lower layer of the reference electrode (8).

At least part of the sphere of the ceramic sensing element (3) extends beyond the housing (4), the materials of the housing (4), the ceramic sensitive element (3) and the connecting material (7) have a similar coefficient of thermal expansion, the free part of the housing (4) connected to the hermetic output of the useful signal (1) by welding, the cavity formed by the ceramic sensitive element (3), the housing (4) and the hermetic output of the useful signal (1) is sealed against the external environment.

In particular cases, the sensor performs the following: - as a connecting material, a ceramic is used, consisting of silicon oxide (SiO ₂ ) 20-30 wt.%, Alumina (Al ₂ O ₃ ) 6-7 wt.%, Boron oxide (B ₂ O ₃ ) 20-21 wt.%, Zinc peroxide (ZnO ₂ ) 10-12 wt.%, Zirconium oxide (ZrO ₂ ) 5-6 wt.%, Tin oxide (SnO ₂ ) 5-7 wt.%, calcium oxide (CaO) 15-21 wt.%, sodium oxide (Na ₂ O) 3-4 wt.%, potassium oxide (K ₂ O) 3-4 wt.%.

- the ceramic sensing element is made of polycrystalline or monocrystalline partially stabilized zirconia;

- the ceramic sensor is made of polycrystalline or single crystal stabilized zirconia;

- the ceramic sensor is made of polycrystalline or single crystal stabilized hafnium dioxide;

- at least one of the layers of the reference electrode is made of bismuth, lead, indium, gallium, nickel, iron, copper, aluminum, bismuth oxide, lead oxide, indium oxide, gallium oxide from nickel oxide, from iron oxide, from copper oxide, from alumina;

- the case is made of ferritic-martensitic steel EI-852 (X13M2S2) or of ferritic-martensitic steel EP-823 (16X12MVSFBR);

- the lower part of the potential removal terminal is made of steel 12X18H10T or molybdenum;

- silver, palladium, platinum or mixtures thereof are used in the composition of the measuring electrode.

A solid electrolyte sensor for the concentration of oxygen in gaseous media works as follows.

The principle of operation of the sensor is based on the use of an electrochemical method for determining oxygen concentration using an oxygen sensor based on a solid oxide electrolyte.

The essence of the method is to compose a galvanic concentration element: Reference electrode (8) / ceramic sensitive element (3) / measuring electrode (2).

The total potential-forming process is the process of oxygen transfer from the electrode, where its chemical potential is greater, to the electrode, where its chemical potential is less.

The value of the EMF of element (E) is associated with a change in the chemical potential of oxygen and is expressed by the following equation:

- парциальное давление кислорода в исследуемой среде; $$P{"}_{O_2}$$

- парциальное давление кислорода на электроде сравнения.where n = 4 is the number of electrons involved in the electrode reaction; T is the temperature, K; R is the universal gas constant, J / (mol · K); F is the number of Faraday, C · mol ^-1 ; $$P{\text{'}\text{'}}_{O_2}$$

- partial pressure of oxygen in the test medium; $$P{"}_{O_2}$$

- partial pressure of oxygen on the reference electrode.

By measuring the temperature and EMF of an element with the known chemical potential of the reference electrode in the standard state, one can easily determine the partial pressure of oxygen in the medium under study.

An example of a specific implementation of the sensor

Germovy useful signal (1) is made of steel 12X18H10T.

The ceramic sensing element (3) is made of partially stabilized zirconia and protrudes 6 mm beyond the housing.

Case (4) is made of ferritic-martensitic steel EI-852. Case dimensions (4): diameter - 15 mm, length - 220 mm.

The measuring electrode (2) is made of two layers deposited sequentially: the first is from a mixture of platinum and zirconia powders, the second is from platinum powder and has a thickness of 20 μm.

As a potential-removable terminal (5), the central core of the double-sheathed cable of the KNMS 2 C type was used.

Cork (6) is made of zirconia.

The connecting material (12) is a ceramic composed of silicon oxide (SiO ₂ ) - 25 wt.%, Alumina (Al ₂ O ₃ ) - 6 wt.%, Boron oxide (B ₂ O ₃ ) - 20 wt.% zinc peroxide (ZnO ₂ ) - 10 wt.%, zirconium oxide (ZrO ₂ ) - 5 wt.%, tin oxide (SnO ₂ ) - 5 wt.%, calcium oxide (CaO) - 21 wt.%, sodium oxide (Na ₂ O) - 4 wt.% And potassium oxide (K ₂ O) - 4 wt.%.

The reference electrode (8) is made of a mixture of bismuth and bismuth oxide.

The main characteristics of the sensor.

до 100 об.%, пределы допускаемого относительного отклонения сигнала датчика ±10%, давление среды - до 7 МПа, скорость изменения температуры рабочей среды - не более 100°C/с, температура рабочей среды - от 300 до 650°C, время выхода на рабочий режим при первичной установке датчика в рабочую среду - не более 2 ч, средняя наработка на отказ - не менее 38000 ч, средний срок службы - не менее 6 лет.Range of measurement of oxygen concentration from $$\mathrm{one}\cdot {10}^{-35}$$

up to 100 vol.%, the limits of the permissible relative deviation of the sensor signal ± 10%, the pressure of the medium is up to 7 MPa, the rate of change of the temperature of the working medium is not more than 100 ° C / s, the temperature of the working medium is from 300 to 650 ° C, exit time to the operating mode during the initial installation of the sensor in the working environment - no more than 2 hours, mean time between failures - at least 38,000 hours, average life - at least 6 years.

Overall dimensions of the sensor: length 600 mm, diameter 27 mm, sensor weight - not more than 0.022 kg.

Claims (9)

1. A solid-electrolyte oxygen concentration sensor in gaseous media, containing a ceramic sensitive element hermetically seated in a metal housing, a reference electrode, a potential detachable lead, a two-layer conductive coating is applied to the external part of the ceramic sensitive element, the first layer consists of a mixture of precious metal powder and zirconia, the second consists of a powder of a noble metal, characterized in that the ceramic sensitive element made of solid electrolyte in the form of two cylindrical elements conjugated between each other and part of a sphere, the upper outer cylindrical surface of the ceramic sensing element is connected to the inner side surface of the housing by means of a connecting material, the ceramic sensing element is additionally equipped with a metal oxide plug with an opening overlapping the cross section of the ceramic cavity sensing element, the reference electrode is located in the cavity formed by the inner surface the surface of the ceramic sensing element and the surface of the cork, occupies part of it and is in contact with the inner part of the sphere and at least part of the inner cylindrical surface of the ceramic sensing element, the reference electrode consists of a lower and at least one subsequent layer facing to the side of the sphere part, the free end of the potential detachable terminal is brought out into the volume of the reference electrode through the hole in the plug, while electrical contact is provided between the potential detachable terminal and the bottom with a layer of the reference electrode, at least part of the sphere of the ceramic sensitive element extends beyond the housing, the materials of the housing, the ceramic sensitive element and the connecting material have a similar coefficient of thermal expansion, the free part of the housing is connected to the hermetic output of the useful signal by welding, the cavity formed by the ceramic sensitive element, housing and hermetic output of the useful signal, is tight with respect to the external environment. 2. The sensor according to claim 1, characterized in that the connecting material is a glass metal consisting of silicon oxide (SiO ₂ ) 20-30 wt.%, Alumina (Al ₂ O ₃ ) 6-7 wt.%, Boron oxide (B ₂ O ₃ ) 20-21 wt.%, Zinc peroxide (ZnO ₂ ) 10-12 wt.%, Zirconium oxide (ZrO ₂ ) 5-6 wt.%, Tin oxide (SnO ₂ ) 5-7 wt. %, calcium oxide (CaO) 15-21 wt.%, sodium oxide (Na ₂ O) 3-4 wt.%, potassium oxide (K ₂ O) 3-4 wt.%. 3. The sensor according to claim 1, characterized in that the ceramic sensing element is made of polycrystalline or monocrystalline partially stabilized zirconia. 4. The sensor according to claim 1, characterized in that the ceramic sensitive element is made of polycrystalline or monocrystalline stabilized zirconia. 5. The sensor according to claim 1, characterized in that the ceramic sensing element is made of polycrystalline or monocrystalline stabilized hafnium dioxide. 6. The sensor according to claim 1, characterized in that at least one of the layers of the reference electrode is made of bismuth, lead, indium, gallium, nickel, iron, copper, aluminum, bismuth oxide , from lead oxide, from indium oxide, from gallium oxide, from nickel oxide, from iron oxide, from copper oxide, from aluminum oxide. 7. The sensor according to claim 1, characterized in that the housing is made of ferritic-martensitic steel EI-852 (X13M2S2), of ferritic-martensitic steel EP-823 (16X12MVSFBR). 8. The sensor according to claim 1, characterized in that the lower part of the potential removal terminal is made of steel 12X18H10T or molybdenum. 9. The sensor according to claim 1, characterized in that the composition of the measuring electrode includes silver, palladium, platinum or mixtures thereof.