CN110140044B - Sensor element for sensing at least one property of a measurement gas in a measurement gas chamber - Google Patents
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- CN110140044B CN110140044B CN201780081448.2A CN201780081448A CN110140044B CN 110140044 B CN110140044 B CN 110140044B CN 201780081448 A CN201780081448 A CN 201780081448A CN 110140044 B CN110140044 B CN 110140044B
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- 238000005259 measurement Methods 0.000 title claims abstract description 58
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 claims abstract description 16
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 144
- 229910052742 iron Inorganic materials 0.000 claims description 71
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical group [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 66
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 34
- 239000002245 particle Substances 0.000 claims description 34
- 238000000034 method Methods 0.000 claims description 20
- 239000000126 substance Substances 0.000 claims description 20
- 229910052751 metal Inorganic materials 0.000 claims description 18
- 239000002184 metal Substances 0.000 claims description 18
- 238000004519 manufacturing process Methods 0.000 claims description 14
- 238000010438 heat treatment Methods 0.000 claims description 9
- 239000004020 conductor Substances 0.000 claims description 7
- 239000004071 soot Substances 0.000 claims description 6
- 238000009529 body temperature measurement Methods 0.000 claims description 5
- 229910010293 ceramic material Inorganic materials 0.000 claims description 3
- 239000007789 gas Substances 0.000 description 101
- 239000010410 layer Substances 0.000 description 35
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 22
- 229910052697 platinum Inorganic materials 0.000 description 22
- 229910052698 phosphorus Inorganic materials 0.000 description 20
- 239000011574 phosphorus Substances 0.000 description 20
- 239000000523 sample Substances 0.000 description 17
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 10
- 229910052760 oxygen Inorganic materials 0.000 description 10
- 239000001301 oxygen Substances 0.000 description 10
- 238000002485 combustion reaction Methods 0.000 description 8
- 239000000203 mixture Substances 0.000 description 8
- -1 platinum group metals Chemical class 0.000 description 8
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 6
- 238000005247 gettering Methods 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 6
- 230000008569 process Effects 0.000 description 6
- 230000002411 adverse Effects 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 238000001878 scanning electron micrograph Methods 0.000 description 5
- 239000012790 adhesive layer Substances 0.000 description 4
- 230000032683 aging Effects 0.000 description 4
- 239000011248 coating agent Substances 0.000 description 4
- 238000000576 coating method Methods 0.000 description 4
- 150000001875 compounds Chemical class 0.000 description 4
- 238000011068 loading method Methods 0.000 description 4
- 238000002844 melting Methods 0.000 description 4
- 230000008018 melting Effects 0.000 description 4
- 229910044991 metal oxide Inorganic materials 0.000 description 4
- 150000004706 metal oxides Chemical class 0.000 description 4
- 239000010948 rhodium Substances 0.000 description 4
- 238000005245 sintering Methods 0.000 description 4
- 239000002344 surface layer Substances 0.000 description 4
- 239000000589 Siderophore Substances 0.000 description 3
- 238000002679 ablation Methods 0.000 description 3
- 239000000919 ceramic Substances 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 229910052729 chemical element Inorganic materials 0.000 description 3
- 239000011159 matrix material Substances 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- 230000001681 protective effect Effects 0.000 description 3
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 2
- 238000009825 accumulation Methods 0.000 description 2
- 230000004888 barrier function Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 239000012777 electrically insulating material Substances 0.000 description 2
- 229930195733 hydrocarbon Natural products 0.000 description 2
- 150000002430 hydrocarbons Chemical class 0.000 description 2
- 238000005470 impregnation Methods 0.000 description 2
- 229910052741 iridium Inorganic materials 0.000 description 2
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 2
- MVFCKEFYUDZOCX-UHFFFAOYSA-N iron(2+);dinitrate Chemical compound [Fe+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O MVFCKEFYUDZOCX-UHFFFAOYSA-N 0.000 description 2
- 238000000608 laser ablation Methods 0.000 description 2
- 239000002346 layers by function Substances 0.000 description 2
- 238000003754 machining Methods 0.000 description 2
- 229910000510 noble metal Inorganic materials 0.000 description 2
- 229910052762 osmium Inorganic materials 0.000 description 2
- SYQBFIAQOQZEGI-UHFFFAOYSA-N osmium atom Chemical compound [Os] SYQBFIAQOQZEGI-UHFFFAOYSA-N 0.000 description 2
- NDLPOXTZKUMGOV-UHFFFAOYSA-N oxo(oxoferriooxy)iron hydrate Chemical compound O.O=[Fe]O[Fe]=O NDLPOXTZKUMGOV-UHFFFAOYSA-N 0.000 description 2
- 229910052763 palladium Inorganic materials 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 229910052703 rhodium Inorganic materials 0.000 description 2
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 2
- 229910052707 ruthenium Inorganic materials 0.000 description 2
- 238000007650 screen-printing Methods 0.000 description 2
- 230000007704 transition Effects 0.000 description 2
- 238000004220 aggregation Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- YWEUIGNSBFLMFL-UHFFFAOYSA-N diphosphonate Chemical compound O=P(=O)OP(=O)=O YWEUIGNSBFLMFL-UHFFFAOYSA-N 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 239000002003 electrode paste Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 150000002505 iron Chemical class 0.000 description 1
- 229910000398 iron phosphate Inorganic materials 0.000 description 1
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- DLYUQMMRRRQYAE-UHFFFAOYSA-N phosphorus pentoxide Inorganic materials O1P(O2)(=O)OP3(=O)OP1(=O)OP2(=O)O3 DLYUQMMRRRQYAE-UHFFFAOYSA-N 0.000 description 1
- 230000008929 regeneration Effects 0.000 description 1
- 238000011069 regeneration method Methods 0.000 description 1
- 239000007784 solid electrolyte Substances 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/403—Cells and electrode assemblies
- G01N27/406—Cells and probes with solid electrolytes
- G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
- G01N27/4075—Composition or fabrication of the electrodes and coatings thereon, e.g. catalysts
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/06—Investigating concentration of particle suspensions
- G01N15/0656—Investigating concentration of particle suspensions using electric, e.g. electrostatic methods or magnetic methods
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/403—Cells and electrode assemblies
- G01N27/406—Cells and probes with solid electrolytes
- G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
- G01N27/4073—Composition or fabrication of the solid electrolyte
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/403—Cells and electrode assemblies
- G01N27/406—Cells and probes with solid electrolytes
- G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
- G01N27/4077—Means for protecting the electrolyte or the electrodes
Landscapes
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Health & Medical Sciences (AREA)
- Physics & Mathematics (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Molecular Biology (AREA)
- Dispersion Chemistry (AREA)
- Measuring Oxygen Concentration In Cells (AREA)
Abstract
The invention proposes a sensor element (110) for sensing at least one property of a measurement gas (112) in a measurement gas chamber. The sensor element (110) comprises at least one electrode (114) which can be at least partially loaded by the measuring gas (114). The region (124) of the sensor element (110) facing the measuring gas (112) is ferrous.
Description
Background
Sensor elements for sensing at least one property of a measured gas are known from the prior art. In particular, a sensor element for sensing at least one parameter of the measured gas, in particular at least one property of the exhaust gas of the internal combustion engine, for example the content of a component of the exhaust gas, in which there is a content of oxygen, nitrogen oxides and/or gaseous hydrocarbons, is associated. Other characteristics that can be sensed by such sensor elements may relate to measuring the particle load, temperature and/or pressure of the gas.
Such a sensor element may in particular be a lambda probe. The lambda probe may preferably be installed in the exhaust system of an internal combustion engine, for example in order to sense the oxygen content in the exhaust gas. The lambda probe is described, for example, in Sensoren im Kraftfahrzeug, second edition, springer Vieweg,2012, pages 160 to 165 of Konrad Reif (editor). The lambda probe, in particular the universal lambda probe, balances the two material flows, in particular the oxygen flow, between the electrode cavity in the sensor element and the measuring gas chamber. Here, one of the streams is driven past the diffusion barrier by a concentration difference. The other material flow is driven through the solid electrolyte and the two electrodes, in particular the two pump electrodes, preferably an external pump electrode which can be acted upon by the measuring gas and an internal pump electrode which is controlled by the applied pump current. The pump current can be set in such a way that a constant and very low oxygen concentration occurs in the electrode cavity. The concentration profile via the diffusion barrier is determined unambiguously by a constant setpoint voltage, in particular a constant setpoint voltage, which is generated in the oxygen concentration, in the electrode cavity and by the oxygen concentration on the exhaust gas side. The supply of oxygen molecules from the measuring gas chamber to the electrode cavity is regulated in accordance with the defined concentration profile and in accordance with the regulated pump current. The pump current can thus be used as a measurement value for measuring the oxygen concentration in the gas chamber, in particular for the oxygen concentration present on the exhaust gas side.
However, such a sensor element can also be a sensor element for sensing particles of a measuring gas, in particular carbon black particles or dust particles, in a measuring gas chamber. Particle sensors are known, for example, from DE 101 49 A1, DE 103 19 664A1, DE 103 53 a 860 A1, DE 10 2004 046 882 A1, DE 10 2005 053 120 A1, DE 10 2006 042 362 A1 or WO 2003/006976 A2, in which one or more metal electrodes are applied to an electrically insulating carrier. The particles that accumulate under the effect of the voltage form, during the aggregation phase of the sensor element, conductive bridges between the electrodes of the interdigitated electrodes, which are, for example, shaped as comb-like fits to one another, and thus short-circuit these electrodes. In the regeneration phase, the electrodes are typically self-cleaning burned by means of an integrated heating element. In general, particle sensors analyze the electrical characteristics of the processing electrode structure that change due to particle accumulation. For example, a reduced resistance or an increased current can be measured with a constant applied voltage.
Such a sensor element comprises at least one electrode for providing its respective function, which electrode can be loaded for measuring a gas, wherein it can often be advantageous to provide the electrode in the form of a surface having as large a surface as possible. The external pump electrode of the lambda probe or the interdigital electrode of the particle sensor or the resistive conductor track for temperature measurement, in particular in the particle sensor or the temperature sensor, are thus exposed in particular to the exhaust gas flow. However, the electrode surfaces of the sensor element are, as a function of the function, exposed to the measuring gas, such as the exhaust gas of the internal combustion engine, either directly and unprotected, or via a gas-permeable cover layer, to a large extent, irrespective of the actual configuration of the sensor element and the installation region provided, in particular at high operating temperatures of the internal combustion engine, for a longer period of time.
The exhaust gases of internal combustion engines, in particular diesel engines or gasoline engines, may contain the chemical element phosphorus (P), in particular in the form of chemical compounds, which can decompose at high operating temperatures of the internal combustion engine. An example for this is phosphorus pentoxide P 4 O 10 . Thus, the phosphor may have an influence on the chemical composition and/or the spatial structure of the electrode surface when loading the surface of the electrode of the sensor element exposed to the measurement gas. For example, the phosphorus contained in the measurement gas forms a mixed phase with at least the metal component present in the electrode surface, to which metal platinum (Pt) may particularly belong. The metallic platinum has a melting point of 1768.3 ℃, and the mixed phase so produced may have a melting point significantly lower than that of metallic platinum.For example, mixed-phase platinum phosphide Pt 20 P 7 Has a melting point of only 588 ℃. The melting point of the mixed phase may even be lower than the operating temperature of 600 ℃ to 1300 ℃ of the sensor element, so that the surface of the electrode of the sensor element exposed to the measuring gas may have a significantly reduced heat resistance. Furthermore, the temperature-driven aging process in this mixed phase proceeds faster than the aging process in the same environment in pure platinum.
Alternatively or additionally, the electrode surfaces of the sensor element may already undergo changes in particular in terms of chemical composition and/or spatial structure during the production thereof, which changes are not always to be expected. Preferably, the interdigital electrodes of the particle sensor or the resistive conductor tracks for temperature measurement, in particular in the particle sensor or the temperature sensor, can be produced in particular in a combined process comprising screen printing, sintering and laser ablation. For this purpose, the entire surface made of platinum can first be applied to a carrier and sintered, after which the interdigitated electrodes are produced by means of a laser, in particular by ablating the material between the webs of the electrode fingers. The method for producing the interdigitated electrodes can cause a change in the surface, which can prove to be detrimental to the measurement signal forming the sensor element. In principle, at least the platinum located in the electrode surface can exhibit a catalytically active state after the production process, which can promote early soot burning and thus adversely affect the measurement signal.
Disclosure of Invention
Within the framework of the invention, a sensor element for sensing at least one property of a measuring gas in a measuring gas chamber is therefore proposed. Within the framework of the invention, a sensor element is understood to be any device which is suitable for qualitatively and/or quantitatively sensing a selected property of a measuring gas and which can in particular generate an electrical measurement signal, such as a voltage or a current, corresponding to the selected property of the measuring gas. The selected properties of the measurement gas may preferably relate to the content of components of the measurement gas, in particular the content of oxygen, nitrogen oxides and/or gaseous hydrocarbons, the particle loading of the measurement gas, the temperature and/or the pressure.
The sensor element can be provided in particular for use in a motor vehicle. The measuring gas can in particular be exhaust gas of a motor vehicle. Other gases and gas mixtures are in principle also possible. The sensor element may preferably be a lambda probe, in particular a broadband lambda probe, or a particle sensor, in particular a soot particle sensor, which can be exposed to the exhaust gas flow. However other types of sensor elements are equally possible.
The measuring gas chamber may in principle be any, open or closed chamber which is provided for receiving the measuring gas and/or through which the measuring gas flows. The measuring gas chamber can be, for example, an exhaust gas line of an internal combustion engine, for example, a combustion motor.
A sensor element for sensing at least one property of a measurement gas in a measurement gas chamber comprises at least one electrode having a surface which can be at least partially influenced by the measurement gas. For this purpose, the at least one electrode may be arranged in the sensor element such that the surface may be directly or indirectly exposed to the measuring gas. The concept "directly" here indicates an arrangement in which the outer surface of the electrode is applied to the outer surface of the sensor element which is accessible for loading by the measuring gas, irrespective of whether the sensor element is received in the at least one protective tube. The term "indirect" in turn indicates an arrangement of electrodes in which the outer surface of the electrode is provided with at least one further layer which may be at least partially spanned by the measuring gas first in order to reach the electrode surface.
Within the framework of the invention, an electrode is understood to be an electrical conductor which is suitable for current measurement and/or voltage measurement and/or which can be subjected to a voltage and/or current to at least one element which is in contact with the electrode. In order to achieve the highest possible electrical conductivity and a high corrosion resistance, at least the surfaces of the electrodes of the sensor element that are exposed to the measuring gas preferably have noble metals, in particular platinum group metals. In addition to the metal platinum (Pt), other elements of groups 8 to 10 of the fifth and sixth periods of the periodic table of the chemical elements also belong to the platinum group metals. Here, the platinum group metals ruthenium (Ru), rhodium (Rh), and palladium (Pd) of the fifth cycle may also be referred to as "light platinum group metals" and the platinum group metals osmium (Os), iridium (Ir), and platinum (Pt) of the sixth cycle may also be referred to as "heavy platinum group metals". The sensor element is illustrated with an example of metallic platinum (Pt) without limiting versatility; however, the remaining platinum group metals are likewise possible for the use of the sensor element and the associated production method.
The shape of the electrodes is in principle irrelevant, however, the at least one electrode can preferably be configured in the shape of a planar electrode or electrode finger. The concept of a planar electrode here relates in principle to any form of electrode whose dimensions in two dimensions are significantly larger, for example by at least a factor of 2, preferably by at least a factor of 10, particularly preferably by at least a factor of 100, than in the other dimension.
The term electrode is understood to mean in principle any form of electrode whose dimensions in one dimension are significantly larger, for example by at least a factor of 2, preferably by at least a factor of 3, particularly preferably by at least a factor of 5, than in at least one other dimension. In this case, a plurality of electrode fingers can preferably be provided, which can be fitted to one another, in particular comb-shaped. Alternatively, the plurality of electrode fingers may have a structure selected from the group consisting of a fishbone structure, a zigzag structure, and a winding structure.
The at least one electrode may preferably be applied on a carrier. Within the framework of the invention, a carrier is in principle understood to be any substrate which is suitable for carrying the at least one electrode and/or on which the at least one electrode can be applied. The carrier may comprise at least one electrically insulating material, in particular at least one ceramic material. The carrier may have a carrier surface. Within the framework of the invention, a carrier surface is understood to mean, in principle, any layer which separates the carrier from its surroundings and to which electrodes of the sensor element which can be acted upon by the measuring gas are applied.
The invention proposes that the region of the sensor element facing the measuring gas is configured in such a way that it is iron-containingA kind of electronic device. The term "iron-containing" here indicates in principle the content of iron atoms, iron ions or iron complexes present in the region of the sensor element. In a particularly preferred configuration, the iron-containing region of the sensor element may comprise iron oxide and/or iron mixed oxide. In this case, a stoichiometric phase can occur as iron oxide, such as the ferric oxide Fe 2 O 3 Ferrous and ferric oxides, fe 3 O 4 Or a non-stoichiometric phase. Here, the concept "iron mixed oxide" indicates an iron oxide into which other metals are introduced, a nonferrous metal oxide additionally having iron atoms or iron ions introduced therein, or a compound formed of an iron oxide and a nonferrous metal oxide. An example for this is the iron mixed oxide AlFeO 3 。
In a particularly preferred configuration, the iron-containing region of the sensor element facing the measurement gas has an iron content of 0.1% by weight, preferably 1% by weight, up to 10% by weight, preferably up to 5% by weight.
Irrespective of the manner in which iron is actually present in the region of the sensor element facing the measuring gas, iron can suffice to achieve a so-called "gettering function" or "trapping function" in the sensor element, in particular in the lambda probe or particle sensor. Without limiting the versatility, this can be achieved in that the iron present in the region, in particular in the form of iron oxide, can be provided for the purpose of combining phosphorus (P) in the region of the sensor element, which phosphorus can be supplied to the sensor element by means of a measuring gas flow, as described before, after which the phosphorus (P) can form a mixed phase (Pt-P) with platinum (Pt). And such that iron (Fe) may form iron phosphate with phosphorus (P), whereby said phosphorus is no longer provided for a mixed phase, which may comprise at least iron and platinum. In this way, the adverse effects that phosphorus can have on the chemical composition and/or the spatial structure and thus on the functionality of the electrodes of the sensor element can be suppressed as far as possible. This enables a significantly increased stability of the electrode with respect to phosphorus, which can be manifested in particular by a higher quality of the sensor measurement signal and a slower aging process.
Alternatively or additionally, the presence of iron in the region of the sensor element has the following advantages: in which the change in chemical composition and/or spatial structure of the surface of the electrode can already be at least partially suppressed during the production of the sensor element. In particular, it can be prevented in part that platinum located in the electrode surface can assume a catalytically active state after the production method, which can promote early soot burning and thus adversely affect the measurement signal.
Preferably, the iron-containing region of the sensor element may comprise at least one outer layer of the sensor element, which outer layer directly faces the measuring gas and/or which outer layer adjoins a further outer layer of the sensor element, which further outer layer directly faces the measuring gas. The concept "directly" here indicates the arrangement of the at least one outer layer of the sensor element, which outer layer is contactable for loading by the measuring gas, irrespective of whether the sensor element is received in the at least one protective tube.
In a preferred configuration, the ferrous region of the sensor element facing the measurement gas may comprise at least one surface of the electrode of the sensor element facing the measurement gas. The electrodes can be selected from the group consisting of lambda probes, in particular the outer electrodes of broadband lambda probes, the interdigital electrodes of particle sensors, in particular the resistive conductor tracks for temperature measurement in particle sensors or temperature sensors. Thus, in this configuration, the volume of the electrode is ferrous or only the surface layer of the electrode facing the measurement gas is ferrous.
In a particularly advantageous manner, the electrode in this configuration fulfills the "gettering function" described above in order to combine the phosphorus (P) brought about by the measuring gas, since the surface of the electrode can be contacted in a particularly simple manner for the phosphorus (P) coming together with the measuring gas.
Alternatively or additionally, the iron-containing region of the sensor element facing the measurement gas may comprise at least one layer adjoining to the electrode. Thus, in this configuration, it is preferred that the at least one layer directly adjoining the electrode is ferrous. In a particularly preferred embodiment, the iron-containing layer adjoining the electrode can be arranged on the surface of the electrode that can be at least partially acted upon by the measuring gas, independently of whether the electrode itself contains iron. Alternatively or additionally, the adhesive layer with respect to the layer adjoining the electrode may be configured as an iron-containing region. The iron-containing layer applied to the electrode surface can thus capture phosphorus (P) coming together with the measuring gas in a particularly simple manner and thus also in a particularly advantageous manner realize the "gettering function" described above for the purpose of combining phosphorus (P) brought about by the measuring gas.
Alternatively or additionally, the iron-containing region of the sensor element comprises a ceramic matrix adjoining at least one insulating layer or a metal-containing, in particular platinum-containing, functional layer on the electrode. In particular, iron can be used as AlFeO 3 In the form of an insulating layer or ceramic matrix, which has Al present there 2 O 3 Is particularly high in miscibility.
Alternatively or additionally, the ferrous region of the sensor element may comprise a heater arranged to heat the electrode, the ferrous component being additionally introduced into the conductive material of the heater.
In another aspect of the invention, a method for manufacturing a sensor element for sensing at least one property of a measurement gas in a measurement gas chamber is presented. The region of the sensor element facing the measuring gas is provided with an iron-containing substance, wherein the application of the iron-containing substance can be carried out according to at least one of the methods described in more detail below.
In the first method, the iron-containing material may be impregnated by means of impregnationApplied to the sensor element. For this purpose, the sensor element may be introduced completely or partially into the ferrous solution, wherein the ferrous substance is then preferably fixed by heating the sensor element into the region of the sensor element that is introduced into the solution.
In a further method, the iron-containing substance can be applied by means of a doping (Versetzen) paste to the region of the sensor element facing the measuring gas, wherein the paste comprises iron-containing particles, in particular iron oxide particles. The application of the paste may here comprise a direct application to the electrode facing the measuring gas and/or to at least one layer adjoining the electrode, wherein the layer adjoining the electrode may preferably be arranged on the surface of the electrode that can be at least partially loaded by the measuring gas.
In a further method, the iron-containing substance can be realized by applying an iron-containing layer to the area of the sensor element facing the measuring gas. The iron-containing layer can be applied here preferably directly to the electrode facing the measuring gas.
Alternatively or additionally, the iron-containing layer may comprise a ceramic matrix comprising a metal-containing, in particular platinum-containing, functional layer adjoining the electrode, or an adhesive layer with respect to the layer adjoining the electrode.
In a special configuration of the method, the spatial structure can be introduced into the surface of the at least one electrode with a surface that can be at least partially loaded with the measuring gas by means of a structuring method, such as laser stripping. In this configuration, the structure of the iron-containing platinum electrode that is subsequently subjected to a temperature treatment, in particular a heating process, can be improved by: the crystal structure of the platinum component of the electrode layer is optimized. Furthermore, platinum-containing regions on the electrode surface that have an amorphous structure after the application of a structuring method, such as laser stripping, can be forced back into the crystalline structure of the particles. In this way, the sensor element thus manufactured can have a relatively high signal quality of the sensor measurement signal.
The method can be used in particular for producing a sensor element according to the invention, i.e. according to one of the embodiments mentioned above or according to one of the embodiments described in further detail below. Accordingly, reference may be made to the description of the sensor elements as far as possible for definition and alternative configurations. However, other configurations are in principle also possible.
The proposed sensor element and the proposed method for producing the sensor element have a number of advantages over known sensor elements and associated production methods. The described structure and composition of the sensor element makes it possible to suppress as much as possible the adverse effect of phosphorus on the chemical composition and/or the spatial structure and thus on the functionality of the electrodes of the sensor element. A significantly increased robustness of the electrode with respect to the effect of phosphorus can thereby be achieved, which can be manifested in particular by a higher quality of the sensor measurement signal and a delay in the aging process of the electrode. Furthermore, it is possible to prevent, already in the manufacture of the sensor element, that at least the platinum located in the electrode surface assumes a catalytically active state, which likewise can lead to a higher quality of the sensor measurement signal. The proposed sensor element and the proposed production method can be used, apart from other types of sensor elements, in a wide range of applications, preferably in lambda probes, in particular broadband lambda probes, or particle sensors, in particular soot particle sensors, or temperature sensors.
Drawings
Further optional details and features of the invention result from the following description of preferred embodiments schematically shown in the drawings.
The drawings show:
fig. 1 shows an embodiment of a sensor element according to the invention in a top view;
FIGS. 2A to 2D illustrate different embodiments of the sensor element of FIG. 1 in cross-sectional views; and
a scanning electron micrograph of the surface of a conventional electrode of the sensor element of fig. 3A to 3C after successful laser machining of the surface (fig. 3A, prior art) and a scanning electron micrograph after a successful heating process (fig. 3B, prior art) or a scanning electron micrograph of an electrode according to the invention (fig. 3C).
Detailed Description
Fig. 1 schematically shows an embodiment of a sensor element 110 according to the invention for sensing at least one property of a measurement gas 112 in a measurement gas chamber in a top view. The sensor element 110 can be provided in particular for use in a motor vehicle, preferably as a lambda probe, in particular a broadband lambda probe, or as a particle sensor, in particular a soot particle sensor. For this purpose, the sensor element 110 may comprise, in particular, one or more further functional elements, which are not shown in the figures, such as further electrodes, further electrode leads or contacts, layers, one or more heating elements, electrochemical cells or other elements as disclosed in the prior art mentioned above. Furthermore, the sensor element 110 can be received, for example, in a protective tube, which is likewise not shown here.
The sensor element 110 comprises at least one electrode 114, wherein the electrode 114, in particular a surface 116 of the electrode 114 facing the measurement gas 112, can be at least partially loaded by the measurement gas 112 in order to perform the function of the sensor element 110. The at least one electrode 114 may be, for example, an external electrode of a lambda probe, in particular a broadband lambda probe, or an interdigital electrode of a particle sensor, or a resistive conductor track for temperature measurement, in particular in a particle sensor or a temperature sensor. However other fields of application are possible.
The sensor element may comprise at least one carrier 118, wherein the at least one electrode 114 may in particular be applied to a carrier surface 120 of the carrier 118. However, other arrangements are possible. The carrier 118 may have at least one electrically insulating material, preferably at least one ceramic material. Furthermore, at least one electrode lead 122 to the electrode 114 may be applied on the carrier 118, as schematically shown in fig. 1. However, other embodiments of the electrode lead 122 are possible, such as through a cavity located inside the carrier 118.
The at least one electrode 114 has in particular as high an electrical conductivity as possible and at the same time a high corrosion resistance, in particular with respect to the measurement gas 112, whereby a noble metal, in particular a platinum group metal, in particular platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os) and/or iridium (Ir), with platinum (Pt) being particularly preferred, can be present at least on the surface 116 of the electrode 114 of the sensor element 110 exposed to the measurement gas 112. Thus, the sensor element 110 is illustrated without limiting generality, for example with metallic platinum (Pt); however, the use of the remaining platinum group metals is likewise possible for the sensor element 110.
The sensor element 110 has a region 124 facing the measurement gas, which can be loaded with the measurement gas 112. The measurement gas 112 can be in particular exhaust gas of a motor vehicle. Such exhaust gases may contain the chemical element phosphorus (P), in particular in the form of chemical compounds which can decompose at high operating temperatures. Thus, without further measures, the phosphor can have a possibly adverse effect on the chemical composition and/or the spatial structure of the surface 116 of the electrode 114 exposed to the measuring gas 112 when the region 124 of the sensor element 110 facing the measuring gas 112 is loaded, and in particular forms a mixed phase (pt—p) here with the metallic platinum (Pt) present at least on the surface 116 of the electrode 114.
Thus, the region 124 of the sensor element 110 facing the measurement gas is configured as a ferrous region 126. To this end, the iron-containing region 126 of the sensor element 110 may comprise, in particular, iron oxide or iron mixed oxide. Ferric oxide Fe can be present as iron oxide 2 O 3 Ferrous and ferric oxides, fe 3 O 4 Or a non-stoichiometric phase. The iron mixed oxide may include an iron oxide into which an additional metal element is introduced, a nonferrous metal oxide additionally having an iron atom or ion introduced therein, or a compound composed of an iron oxide and a nonferrous metal oxide, such as AlFeO 3 . However, additional iron mixed oxides are possible. In a particularly preferred embodiment, the iron-containing region 126 of the sensor element 110 can have an iron content of 0.1% by weight, preferably 1% by weight, up to 10% by weight, preferably up to 5% by weight.
For this purpose, the iron-containing region 126 of the sensor element 110 facing the measuring gas 112 can in a particularly advantageous manner perform the "gettering function" described above to combine the phosphorus (P) brought by the measuring gas 112, since the iron-containing region 126 can be contacted simply for the phosphorus (P) coming with the measuring gas 112.
Fig. 2A to 2D each schematically show an embodiment of the sensor element 110 of fig. 1 in cross-section, wherein in the sensor element 110 the electrodes 114 are each applied to the carrier 118. It is explicitly pointed out in this context that the embodiments of the sensor element 110 shown individually in fig. 2A to 2D can also be combined with one another, for example the embodiments from fig. 2A and 2B, from fig. 2A, 2B and 2C, from fig. 2B and 2C or from fig. 2D in combination with fig. 2A or fig. 2A and 2B and 2C. Other combinations are possible.
In a particularly preferred embodiment according to fig. 2A, the electrode 114 can here have a volume 128 and a surface 116 provided for being acted upon by the measuring gas 112. In this embodiment, the volume 128 of the electrode 114 may assume the function of the ferrous region 126. Alternatively, only the surface layer 130 of the electrode 114 facing the measurement gas 112 can assume the function of the iron-containing region 126. The particularly preferred embodiment according to fig. 2A enables the above-mentioned gettering function to be achieved in a particularly advantageous manner, since the surface 116 of the electrode 114 can be contacted in a particularly simple manner for the phosphorus (P) coming with the measurement gas 112.
In a further preferred embodiment according to fig. 2B, an iron-containing coating 132 can be provided adjacent to the surface 116 of the electrode 114, which can here take on the function of the iron-containing region 126. The preferred embodiment according to fig. 2B also enables an advantageous gettering function, since the iron-containing coating 132 arranged on the surface 116 of the electrode 114 can likewise be contacted in a simple manner for the measuring gas 112 and thus the phosphorus (P) coming together with the measuring gas.
In a further embodiment according to fig. 2C, an iron-containing adhesive layer 136 can be provided between the surface 116 of the electrode 114 and the cover layer 134 applied thereto, which can here also assume the function of the iron-containing region 126 in addition to the function of the adhesive layer. Here, the cover layer 134 may be implemented with or without iron.
In another embodiment according to fig. 2D, a ferrous carrier layer 140 may be provided between the underside 138 of the electrode 114, through which the electrode 114 may be placed on the carrier 118, and the carrier surface 120 of the carrier 118 facing the electrode 114. Here, the siderophore layer 140, the support 118, and/or the near-surface layer 142 of the support 118 may serve the function of the siderophore region 126.
For the production of the sensor element 110, the region 124 of the sensor element 110 facing the measuring gas 112 is provided with an iron-containing substance, wherein the application of the iron-containing substance can be carried out by means of impregnation with the iron-containing substance, coating with an iron-containing paste or application of an iron-containing layer.
For the sensor element 110 to be immersed by means of the iron-containing substance, the sensor element 110 can be introduced completely or partially, for example immersed in an iron-containing solution, for example an iron nitrate solution, wherein the iron-containing substance is subsequently immobilized on the area 124 of the sensor element 110 that is introduced into the solution, in such a way that a stable iron oxide can be formed from the iron nitrate, preferably by heating the sensor element 110.
Alternatively or additionally, the region 124 of the sensor element 110 facing the measurement gas 112 may be provided with a paste, wherein the paste may comprise iron-containing particles, in particular iron oxide particles. The paste may be applied here in particular directly to the electrode 114 facing the measurement gas 112, the cover layer 134 and/or the near-surface layer 142 of the carrier 118.
Alternatively or additionally, the iron-containing substance may be realized by means of applying an iron-containing layer to the region 124 of the sensor element 110 facing the measurement gas 112. Here, the iron-containing coating 132 may preferably be applied directly to the electrode 114 facing the measurement gas 112. Alternatively or additionally, the siderophore layer 140 may be applied directly to the carrier 118, after which the electrode 114 may be applied thereto.
As already mentioned above, the electrodes 114, in particular the interdigital electrodes of the particle sensor, can preferably be manufactured in a combined process comprising screen printing, sintering and laser ablation. For this purpose, it is preferably possible to first apply the entire surface of the electrode made of platinum to the carrier and sinter it, after which the electrode 114 is produced, in particular by ablation of the material by means of a laser. After sintering, the platinum grains condense in a crystalline phase and the surface of the entire electrode is free of defects or impurities such as those generated by droplet accumulation.
The laser process is particularly advantageous for producing electrode structures with small electrode spacings by means of laser processes, which ablate material from the entire surface of the electrode. This ablation can not only cause structuring of the entire electrode surface, but can also alter the surface of individual grains located in the ablation region, wherein the surface of the platinum grains can even undergo a phase transition. The observed phase transition of platinum or the catalytic activity of the electrode can generally be caused entirely by the method of manufacturing the platinum structure, independently of the use of a laser process.
Fig. 3A shows a scanning electron micrograph of the surface of a conventional electrode after successful laser machining of the surface and fig. 3B shows a scanning electron micrograph after a successful heating process. With respect to these photographs depicting a conventional electrode according to the prior art, fig. 3C shows a scanning electron microscope photograph of a surface 116 of an electrode 114 in a sensor element 110 corresponding to the present invention. By mixing the iron oxide into the electrode paste, the carrier layer 140 of the electrode 114 or the cover layer of the electrode 114, the effectiveness of the subsequent temperature treatment for improving the signal quality of the sensor element 110 can be improved or can be effective directly for improved platinum structures.
In further embodiments, the application of the iron-containing species may be effected after the sintering or laser process and replenished by subsequent temperature treatment or subsequent heating process in order to render the iron effective for the platinum structure.
Claims (11)
1. Sensor element (110) for sensing soot particles of a measurement gas (112) in a measurement gas chamber, comprising at least one electrode (114) which can be at least partially loaded by the measurement gas (112), wherein a region (124) of the sensor element (110) facing the measurement gas (112) is ferrous, wherein the sensor element (110) has a carrier (118), wherein the carrier (118) has an electrically insulating ceramic material, wherein a ferrous carrier layer (140) is provided between a lower side (138) of the electrode (114) facing the carrier (118) and a carrier surface (120) facing the electrode (114).
2. The sensor element (110) according to claim 1, wherein the electrode (114) and/or at least one layer adjacent to the electrode (114) is iron-containing.
3. The sensor element (110) according to claim 1 or 2, wherein the region (124) of the sensor element (110) facing the measurement gas (112) is arranged on a surface (116) of the electrode (114) that can be at least partially loaded by the measurement gas (112).
4. The sensor element (110) according to claim 1 or 2, wherein the region (124) of the sensor element (110) facing the measurement gas (112) has an iron content of 0.1 to 10% by weight.
5. The sensor element (110) according to claim 1 or 2, wherein the region (124) of the sensor element (110) facing the measurement gas (112) comprises iron oxide or iron mixed oxide.
6. The sensor element (110) according to claim 1 or 2, wherein the electrode (114) comprises a platinum group metal.
7. The sensor element (110) according to claim 1 or 2, wherein the electrodes (114) are interdigitated electrodes of a particle sensor.
8. The sensor element (110) according to claim 1 or 2, wherein the electrode (114) is a resistive conductor track for temperature measurement in a particle sensor.
9. Method for manufacturing a sensor element (110) according to claim 1, wherein the application of the iron-containing substance is performed according to at least one of the following methods:
a) -impregnating, in which the sensor element (110) is brought at least partially into an iron-containing solution and the fixation of the iron-containing substance is performed;
b) -doping the area (124) of the sensor element (110) facing the measuring gas (112) with a paste, wherein the paste comprises iron-containing particles;
c) An iron-containing layer is applied to the region (124) of the sensor element (110) facing the measurement gas (112).
10. The method according to claim 9, wherein the sensor element (110) comprises at least one electrode (114) having a surface (116) that can be at least partially loaded by the measurement gas (112), and wherein a spatial structure is introduced into the surface (116) of the electrode (114) by means of a structuring method.
11. The method according to claim 10, wherein the application of the iron-containing substance is followed by heating of the spatial structure in the surface (116) of the electrode (114).
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE102016226276 | 2016-12-28 | ||
| DE102016226276.9 | 2016-12-28 | ||
| DE102017205064.0A DE102017205064A1 (en) | 2016-12-28 | 2017-03-24 | Sensor element for detecting at least one property of a sample gas in a sample gas space |
| DE102017205064.0 | 2017-03-24 | ||
| PCT/EP2017/078150 WO2018121907A1 (en) | 2016-12-28 | 2017-11-03 | Sensor element for detecting at least one property of a measuring gas in a measuring gas chamber |
Publications (2)
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| CN110140044A CN110140044A (en) | 2019-08-16 |
| CN110140044B true CN110140044B (en) | 2023-11-28 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN201780081448.2A Active CN110140044B (en) | 2016-12-28 | 2017-11-03 | Sensor element for sensing at least one property of a measurement gas in a measurement gas chamber |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP3563145A1 (en) |
| KR (1) | KR102518560B1 (en) |
| CN (1) | CN110140044B (en) |
| DE (1) | DE102017205064A1 (en) |
| WO (1) | WO2018121907A1 (en) |
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Also Published As
| Publication number | Publication date |
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| KR20190102196A (en) | 2019-09-03 |
| EP3563145A1 (en) | 2019-11-06 |
| DE102017205064A1 (en) | 2018-06-28 |
| CN110140044A (en) | 2019-08-16 |
| KR102518560B1 (en) | 2023-04-07 |
| WO2018121907A1 (en) | 2018-07-05 |
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