Temperature sensor element and temperature sensor

Abstract

An object is to provide a temperature sensor element that can suppress the reduction reaction of a heat-sensitive body even when used in a strong reducing gas environment for a long time. The temperature sensor element (1) includes: a heat-sensitive body (11) whose resistance changes according to temperature; a first covering layer (20) that covers the periphery of the heat-sensitive body (11); a pair of lead wires (15, 15) that are connected to the heat-sensitive body (11) and are led out toward the rear end side through the first covering layer (20); a second covering layer (25) that covers the periphery of the pair of lead wires (15, 15) led out through the first covering layer (20); and a third covering layer (30) that covers the periphery of the first covering layer (20) and the second covering layer (25); the second covering layer (25) is composed of a mixture of at least one of chromium oxide, manganese oxide, ruthenium oxide powder, iridium oxide powder, and platinum oxide and glass.

Description

Technical Field

[0001] The present invention relates to a temperature sensor element including a heat-sensitive body such as a thermistor whose electrical characteristics change corresponding to a temperature change. Background Art

[0002] As a temperature sensor element, for example, it includes a thermistor made of a conductive oxide sintered body, a covering layer covering the periphery of the thermistor, and a set of lead wires connected to the thermistor and penetrating through the covering layer and led out.

[0003] If this temperature sensor element is used in a reducing gas environment, the reducing gas invades the thermistor through the interface between the covering layer and the lead wire. Since the thermistor is an oxide, it is reduced by the invading reducing gas, and there is a case where the temperature detection accuracy of the temperature sensor element decreases.

[0004] Regarding the above problems, Patent Document 1 has, in addition to a first covering layer covering the periphery of the thermistor, a second covering layer that surrounds the extending portion of the lead wire on the outer surface of the first covering layer and is mainly formed of an oxygen supply oxide. The oxygen supply oxide in Patent Document 1 contains at least one oxide of Cr, Mn, Fe, Co, Ni, Ce, Pr. Patent Document 1 can suppress the reduction reaction even when the thermistor is exposed to a strong reducing gas environment by providing the second covering layer containing the oxygen supply oxide even when there is a gap at the interface between the lead wire and the first covering layer.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-12696 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, in Patent Document 1, if the use in a strong reducing gas environment is continued for a long time, there is a concern that the oxygen supply oxide will be depleted.

[0010] Therefore, an object of the present invention is to provide a temperature sensor element that can suppress the reduction reaction of the heat-sensitive body even when the use in a strong reducing gas environment is continued for a long time by improving the wettability at the interface between the lead wire and the first covering layer.

[0011] Means for Solving the Problems

[0012] The temperature sensor element of the present invention is characterized by comprising: a heat-sensitive body whose resistance changes according to temperature; a first covering layer that covers the periphery of the heat-sensitive body; a pair of lead wires that are connected to the heat-sensitive body and are led out toward the rear end side through the first covering layer; a second covering layer that covers the periphery of the pair of lead wires led out through the first covering layer; and a third covering layer that covers the periphery of the first covering layer and the second covering layer.

[0013] The second covering layer of the present invention is composed of a mixture of at least one of chromium oxide, manganese oxide, ruthenium oxide powder, iridium oxide powder, and platinum oxide and glass.

[0014] In the present invention, preferably, the lead wire comprises: a core wire made of platinum; and a plating covering layer that covers the periphery of the core wire and is composed of one or both of titanium oxide and ruthenium oxide.

[0015] In the present invention, preferably, the core wire is made of a platinum alloy containing iridium.

[0016] In addition, in the present invention, preferably, the first covering layer is composed of a first oxide powder or a mixture of the first oxide powder and glass; the third covering layer is composed of a mixture of a third oxide powder and glass.

[0017] In the present invention, preferably, the first oxide powder is composed of the powder of the thermistor constituting the heat-sensitive body.

[0018] In addition, in the present invention, preferably, the second covering layer covers the periphery of the pair of lead wires led out through the first covering layer and covers the first covering layer between the first covering layer and the third covering layer.

[0019] Furthermore, in the present invention, the following form can be made: the second covering layer defines covering the periphery of the pair of lead wires led out through the first covering layer; the first covering layer and the third covering layer are directly in contact.

[0020] Furthermore, the present invention provides a temperature sensor including the temperature sensor element described above.

[0021] Advantages of the Invention

[0022] According to the present invention, it is possible to provide a temperature sensor element that can suppress the reduction reaction of the heat-sensitive body even when used in a strong reducing gas environment for a long time by improving the wettability of the second covering layer provided around the lead wires. Description of the Drawings

[0023] Figure 1 It is a longitudinal sectional view showing the schematic structure of the thermistor element according to the first embodiment.

[0024] Figure 2It is a flowchart showing the order of manufacturing the thermistor element according to the first embodiment.

[0025] Figure 3 Except Figure 2 It is a diagram showing the manufacturing process of the thermistor element according to the first embodiment other than

[0026] Figure 4 Next Figure 3 It is a diagram showing the manufacturing process of the thermistor element according to the first embodiment.

[0027] Figure 5 It is a longitudinal sectional view showing the schematic structure of the thermistor element according to the second embodiment.

[0028] Figure 6 It is a diagram showing the manufacturing process of the thermistor element according to the second embodiment. Detailed implementation mode

[0029] Hereinafter, while referring to the attached Figure 1 The embodiments of the present invention will be described.

[0030] The temperature sensor element 1 according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0031] The temperature sensor element 1 according to the present embodiment, as Figure 1 shown, includes a thermistor element 3 and a covering layer 5. The thermistor element 3 includes a heat-sensitive body 11 whose electrical characteristics, such as resistance value, change according to temperature, a pair of electrodes 13, 13 formed on opposite side surfaces of the heat-sensitive body 11, a pair of lead wires 15, 15 respectively connected to the electrodes 13, 13, and connection electrodes 17, 17 that electrically connect the electrodes 13, 13 to the lead wires 15, 15. In addition, the covering layer 5 includes a first covering layer 20 that covers the heat-sensitive body 11 and a part of the lead wires 15, 15, a third covering layer 30 that covers the outside of the first covering layer 20, and a second covering layer 25 sandwiched between the first covering layer 20 and the third covering layer 30.

[0032] The temperature sensor element 1 is provided with the second covering layer 25 between the first covering layer 20 and the third covering layer 30, and this second covering layer 25, to be specific, undertakes the effect of improving wettability described later. The temperature sensor element 1 can suppress the change rate of the resistance value of the heat-sensitive body 11 to be small in a reducing gas environment, such as a gas environment containing hydrogen.

[0033] In addition, although specific descriptions are omitted here, the temperature sensor element 1 may be used by being housed inside a protective tube made of a metal with excellent heat resistance and oxidation resistance, such as stainless steel or Ni superalloy.

[0034] Hereinafter, after explaining each element of the temperature sensor element 1, the operation and effects of the temperature sensor element 1 will be described.

[0035] [Heat-sensitive body 11]

[0036] In the heat-sensitive body 11, a thermistor sintered body is used. A thermistor is an abbreviation of "thermally sensitive resistor" and is a metal oxide that measures temperature by utilizing the change in resistance value according to temperature.

[0037] Thermistors are classified into NTC (negative temperature coefficient) thermistors and PTC (positive temperature coefficient) thermistors, but either type of thermistor can be used in the present invention.

[0038] In the heat-sensitive body 11, an oxide sintered body having a typical spinel structure as an NTC thermistor, such as manganese oxide (Mn 3 O 4 ) as a basic composition, can be used. In the heat-sensitive body 11, an oxide sintered body having a composition of MxMn 3－x O 4 in which M element (one or more of Ni, Co, Fe, Cu, Al, and Cr) is added to the basic composition can be used. Further, one or more of V, B, Ba, Bi, Ca, La, Sb, Sr, Ti, and Zr can be added.

[0039] In addition, as an NTC thermistor in the heat-sensitive body 11, a composite oxide having a typical perovskite structure, for example, an oxide sintered body having a basic structure of YCrO 3 , can be used. As this NTC thermistor, most typically, a sintered body having at least one of the Y 2 O 3 phase, Y(Cr, Mn)O 3 phase, YCrO 3 phase, and YMnO 3 phase is used.

[0040] [Manufacturing method of thermistor sintered body]

[0041] The heat-sensitive body 11 composed of a thermistor sintered body is manufactured through processes of weighing raw material powder, mixing raw material powder, drying raw material powder, calcination, post-calcination mixing-crushing, drying-granulation, forming, and sintering. Hereinafter, taking a thermistor sintered body having a Y 2 O 3 phase and a Y(Cr, Mn)O 3 phase as an example, each process will be described.

[0042] [Weighing of raw material powders]

[0043] Weigh the raw material powders of yttrium oxide (Y 2 O 3 ), chromium oxide (Cr 2 O 3 ), manganese oxide (MnO, Mn 2 O 3 , Mn 3 O 4 etc.) and calcium carbonate (CaCO 3 ) to achieve the above chemical composition.

[0044] In addition, in this embodiment, the powder is composed of multiple particles.

[0045] Y 2 O 3 powder contributes to the formation of the Y 2 O 3 phase. Y 2 O 3 powder, Cr 2 O 3 powder and manganese oxide powder (Mn 3 O 4 powder) contribute to the formation of the Y(Cr, Mn)O 3 phase. CaCO 3 powder not only acts as a sintering aid but also becomes Ca and dissolves in Y(Cr, Mn)O 3 phase, contributing to the reduction of the B constant.

[0046] The raw material powders are powders with a purity of 98% or more, preferably 99% or more, and more preferably 99.9% or more in order to obtain a thermistor sintered body with high characteristics.

[0047] In addition, the particle size of the raw material powders is not limited as long as calcination can be carried out, and the particle size (d50) can be selected in the range of 0.1 - 6.0 μm.

[0048] [Mixing of raw material powders - Ball milling]

[0049] Mix the Y 2 O 3 powder, Cr 2 O 3 powder, Mn 3 O 4 powder and CaCO 3 powder weighed in a specified amount. The mixing can be, for example, in a slurry form with water added to the mixed powder and carried out using a ball mill. Other mixers than the ball mill can also be used in the mixing.

[0050] [Drying of raw material powder]

[0051] Preferably, the mixed slurry is dried / granulated using a spray dryer or other equipment to form a mixed powder for calcination.

[0052] [Calcination]

[0053] The dried mixed powder for calcination is calcined. By performing calcination, from Y 2 O 3 powder, Cr 2 O 3 powder, Mn 3 O 4 powder and CaCO 3 powder, a calcined body with a composite structure having a Y 2 O 3 phase and a Y(Cr, Mn)O 3 phase is obtained.

[0054] Calcination is carried out by putting the mixed powder for calcination into, for example, a crucible and holding it in the atmosphere in the temperature range of 800 to 1300 °C. When the calcination temperature is less than 800 °C, the formation of the composite structure is insufficient. In addition, if it exceeds 1300 °C, there may be a decrease in sintering density or a decrease in the stability of the resistance value. Therefore, the holding temperature of calcination is set in the range of 800 to 1300 °C.

[0055] The holding time of calcination should be appropriately set according to the holding temperature, but as long as it is within the above temperature range, the purpose of calcination can be achieved with a holding time of about 0.5 to 100 hours.

[0056] [Mixing - Crushing - Ball Milling]

[0057] The calcined powder is mixed and crushed. Mixing - Crushing can be carried out in the same manner as before calcination, adding water to make it into a slurry state, and using a ball mill.

[0058] [Drying - Granulation]

[0059] The crushed powder is preferably dried - granulated using a spray dryer or other equipment.

[0060] [Forming]

[0061] The calcined granulated powder is formed into a specified shape.

[0062] In addition to pressure forming using a metal mold, cold isostatic pressing (CIP: Cold Isostatic Press) can also be used for forming.

[0063] The higher the density of the green compact, the easier it is to obtain a sintered body with a high density. Therefore, it is desirable to increase the density of the green compact as much as possible. For this purpose, it is preferable to use CIP that can achieve a high density.

[0064] [Sintering]

[0065] Next, the obtained green compact is sintered.

[0066] Sintering is carried out by holding in the atmosphere in the temperature range of 1400 to 1650 °C. When the sintering temperature is less than 1400 °C, the formation of the composite structure is insufficient. In addition, if it exceeds 1650 °C, the sintered body melts or reacts with the crucible for sintering or the like. The holding time for sintering should be appropriately set according to the holding temperature, but as long as it is within the above temperature range, a dense sintered body can be obtained with a holding time of about 0.5 to 200 hours.

[0067] For the obtained thermistor sintered body, in order to stabilize its thermistor characteristics, it is preferable to perform annealing (annealing: toughening). Annealing is carried out, for example, by holding in the atmosphere at 1000 °C.

[0068] [Electrodes 13, 13 and connecting electrodes 17, 17]

[0069] The electrodes 13, 13 are formed in a film shape, respectively, over the entire front and back surfaces of the plate-shaped heat-sensitive body 11 as shown. The electrodes 13, 13 are made of a noble metal, typically platinum (Pt). Figure 1 The electrodes 13, 13 are formed as thick films or thin films. The thick film electrodes 13, 13 are formed by applying a paste prepared by mixing platinum powder and an organic binder on the front and back surfaces of the thermistor sintered body and sintering after drying. In addition, the thin film electrodes can be formed by vacuum evaporation or sputtering.

[0070] The heat-sensitive body 11 formed with the electrodes 13, 13 is processed into a specified size.

[0071] The connecting electrodes 17, 17 are each composed of a metal film formed on the surface of the electrodes 13, 13. The connecting electrodes 17, 17 are also made of a noble metal, typically platinum (Pt).

[0072]

[0073] [Leads 15, 15]

[0074] Figure 1 As shown, one end side of the leads 15, 15 is electrically and mechanically connected to the electrodes 13, 13 via the connecting electrodes 17, 17. The other end side of the leads 15, 15 is connected to a detection circuit (not shown) outside. The leads 15, 15 are made of wire materials having heat resistance, such as platinum or an alloy of platinum and iridium (Ir). The leads 15, 15 are made of wire materials having heat resistance, such as platinum or an alloy of platinum and iridium (Ir).

[0075] Connect the lead wires 15, 15 to the electrodes 13, 13 as follows.

[0076] Pre-coat a paste containing platinum powder for forming the connection electrodes 17, 17 on one end side of each of the lead wires 15, 15. Dry the platinum paste in a state where the platinum paste-coated sides of the lead wires 15, 15 are in contact with the electrodes 13, 13, and then sinter the platinum powder.

[0077] [First covering layer 20]

[0078] Next, the first covering layer 20 will be described.

[0079] The first covering layer 20 functions as a buffer member that directly applies the stress generated by the thermal expansion of the third covering layer 30 to the heat-sensitive body 11 for relaxation. In other words, the first covering layer 20 bears the thermal stress brought by the third covering layer 30.

[0080] In addition, the first covering layer 20 realizes stable electrical and mechanical connections by fixing the connection portions of the heat-sensitive body 11 and the lead wires 15, 15.

[0081] In a preferred form, the first covering layer 20 of the present embodiment is composed of a mixture of glass and oxide powder (first oxide powder).

[0082] In the first covering layer 20, the glass acts as a binder that binds the oxide powders to maintain the shape of the first covering layer 20.

[0083] The ratio of the glass to the oxide powder is not limited as long as it can obtain a desired linear expansion coefficient and act as a binder.

[0084] As the glass constituting the first covering layer 20, either or both of crystalline glass and amorphous glass can be used, but preferably crystalline glass that is stable at high temperatures is used. As the crystalline glass, for example, it can be applied with a composition consisting of SiO 2 : 30 to 60 wt%, CaO: 10 to 30 wt%, MgO: 5 to 25 wt%, Al 2 O 3 : 0 to 15 wt%.

[0085] As the oxide powder constituting the first covering layer 20, alumina (Al 2 O3), magnesia (MgO), calcium oxide (CaO), yttrium oxide (Y 2 O 3 ), zirconia (ZrO 2 ), etc. can be cited. In addition, as the oxide powder, the thermistor powder constituting the heat-sensitive body 11 can be used.

[0086] As the thermistor powder, a powder having the same composition as the thermistor sintered body constituting the heat-sensitive body 11 can be used. The so-called same composition means that in both the heat-sensitive body 11 and the thermistor powder contained in the first inner layer form, for example, the chemical compositions of Cr, Mn, Ca, and Y other than the above-mentioned oxygen are included in the composition ranges of Cr: 3 to 15 mol%, Mn: 5 to 15 mol%, and Ca: 0.5 to 8 mol%. This includes the case where the thermistor powder and the thermistor sintered body constituting the heat-sensitive body 11 have the same composition.

[0087] Regarding the first covering layer 20 of the present embodiment, it is allowed to be composed only of oxide powder as another preferred form.

[0088] [Third covering layer 30]

[0089] Next, the third covering layer 30 will be described.

[0090] The main function of the third covering layer 30 is to provide airtightness for hermetically sealing the heat-sensitive body 11 from the surrounding gas environment. In addition, the third covering layer 30 imparts mechanical strength to protect the heat-sensitive body 11 from external forces.

[0091] The third covering layer 30 can be composed of the same oxide powder as the first covering layer 20. In addition, the third covering layer 30 can also be composed of a mixture of the same glass as the first covering layer 20 and oxide powder (third oxide powder). As the oxide powder, alumina (Al 2 O 3 ), magnesium oxide (MgO), yttrium oxide (Y 2 O 3 ), calcium oxide (CaO), zirconium oxide (ZrO 2 ), strontium oxide (SrO), titanium oxide (TiO), and lanthanum oxide (La 2 O 3 ) of one or more kinds can be used.

[0092] Although the required thickness and state can be obtained by a single-layer third covering layer 30 formed in one time, the third covering layer 30 can also be made into multiple layers. In the case of making the third covering layer 30 into multiple layers, the thickness of each layer can be equal or unequal.

[0093] [Second covering layer 25]

[0094] Next, the second covering layer 25 will be described.

[0095] The second covering layer 25 is provided between the first covering layer 20 and the third covering layer 30. In addition to covering the first covering layer 20, it also covers the outer peripheral surface of the lead wire 15 led out from the first covering layer 20. The periphery of the second covering layer 25 covering the lead wire 15 is covered by the third covering layer 30.

[0096] It can be known that during the use of the temperature sensor element 1 in the high temperature range, the second covering layer 25 closely contacts the boundary surface with the lead wire 15 by improving the wettability with the lead wire 15. By this improvement in wettability, the minute gap between the lead wire 15 and the second covering layer 25 is reduced, thereby improving the reduction resistance of the temperature sensor element 1.

[0097] It can be known that because the second covering layer 25 is composed of a mixture of at least one of chromium oxide (Cr 2 O 3 ) powder, manganese oxide (Mn 3 O 4 ) powder, ruthenium oxide (RuO 2 ) powder, iridium oxide (IrO 2 ) powder, and platinum oxide (PtO 2 ) powder and glass, it can improve the wettability of the glass with respect to the lead wire 15. In the present embodiment, chromium oxide, manganese oxide, ruthenium oxide, iridium oxide, and platinum oxide are referred to as wettability-improving oxides.

[0098] Here, the present inventor dissected and analyzed the temperature sensor element having the lead wire 15 formed of platinum and the first covering layer 20 containing the thermistor powder. As a result, a state in which the thermistor powder was strongly connected to the lead wire 15 was observed. It can be known that this is because the wettability of the glass with respect to the lead wire 15 is improved by containing the thermistor powder. As a technique for improving the bonding strength / wettability between a metal material and an oxide material containing glass, there are a mechanical bonding technique for improving the mechanical bonding strength and a chemical bonding technique for improving the chemical bonding strength. Although the effect of improving the reduction resistance was confirmed by performing mechanical processing on the surface of the lead wire 15 in order to improve the glass bonding effect, good results were not obtained. However, among the materials widely used as chemical bonding materials, transition metal oxides (Mn−O, Cr−O, Fe−O, Ti−O, etc.) can be cited. In the thermistor powder material of the present invention, yttrium oxide (Y 2 O 3) and Y-Ca-Cr-Mn oxides. Therefore, in the following examples, the present inventors confirmed the effect on the reducibility resistance in a high temperature range by making the second covering layer 25 contain monomer oxides of chromium oxide and manganese oxide. As a result, an improvement in reducibility resistance was confirmed in any of the oxide powders. By observing the cross section, the optimal particle size and addition amount of the added particles were studied, and this improvement in wettability played a role during the firing process of the glass. As a result, needless to say for the glass, the thermistor powder was also in close contact with the lead wire 15, and it was possible to suppress the intrusion of reducing gases, especially hydrogen, along the lead wire 15.

[0099] In order to find other oxides other than chromium oxide and manganese oxide that can achieve an improvement in reducibility resistance, an exploration of materials that can form a firm bond on the surface of the lead wire was carried out. As chemical bonding materials, in addition to ruthenium oxide used for high-temperature metal materials, indium oxide used for in-vehicle spark plugs, etc., which has a relatively high oxygen-binding force, i.e., relatively strong reducibility resistance, was used, and platinum oxide, etc., which utilizes the anchor effect brought about by mechanical bonding techniques, was used. Oxides with higher heat resistance than chromium oxide and manganese oxide and stronger binding force with oxygen were used, and the reducibility resistance was confirmed. As a result, as can be seen from the following examples, it was confirmed that the reducibility resistance was improved by being composed of a mixture of at least one of ruthenium oxide powder, iridium oxide powder, and platinum oxide powder and glass.

[0100] Based on the above, the second covering layer 25 is composed of a mixture of reducibility resistance-improving oxide powder and glass, and the reducibility resistance-improving oxide powder is composed of at least one of chromium oxide powder, manganese oxide powder, ruthenium oxide powder, iridium oxide powder, and platinum oxide powder. The glass in the second covering layer 25 can be the same glass as that used in the first covering layer 20.

[0101] The content of the reducibility resistance-improving oxide powder in the second covering layer 25 due to the improvement in wettability is selected from the range of 0.5 to 30% by mass, and the remainder is glass. When it is less than 0.5% by mass, there may be a case where the effect of improving the reducibility resistance is insufficient. In addition, if it exceeds 30% by mass, the amount of glass relatively decreases, and the airtightness of the covering itself deteriorates.

[0102] The preferred content of the reducibility resistance-improving oxide powder is in the range of 1 to 25% by mass, and the more preferred content of the reducibility resistance-improving oxide powder is in the range of 2 to 20% by mass.

[0103] [Manufacturing method of the temperature sensor element 1]

[0104] Next, the manufacturing method of the temperature sensor element 1 will be described.

[0105] The temperature sensor element 1 is as Figure 2 and Figure 3As shown, through the steps of joining the heat-sensitive element 11 to the lead wires 15, 15 ( Figure 2 S100 of Figure 3 (a) thereof), the step of forming the first covering layer 20 on the joined heat-sensitive element 11 ( Figure 2 S200 of Figure 3 (b) thereof), the step of forming the second covering layer 25 around the first covering layer 20 ( Figure 2 S300 of Figure 4 (a) thereof) and the step of forming the third covering layer 30 around the first covering layer 20 and the second covering layer 25 ( Figure 2 S400 of Figure 4 (b) thereof), it is manufactured.

[0106] [S200]

[0107] Regarding the first covering layer 20, for example, the above-mentioned oxide powder, preferably the thermistor powder and the crystalline glass powder are mixed with a solvent to prepare a paste. After forming this paste on the heat-sensitive element 11, through drying, for example, firing treatment of the glass component at 1200 °C, the first covering layer 20 is formed.

[0108] The paste is formed on the heat-sensitive element 11. Preferably, dipping is applied in which a prescribed range from one side of the heat-sensitive element 11 to the lead wire 15 is immersed in the paste and then lifted from the paste. The same applies to the second covering layer 25 and the third covering layer 30.

[0109] In the case where the first covering layer 20 is formed of multiple layers, dipping is performed multiple times and then drying is carried out, for example, firing treatment at 1200 °C. Further, in the case where the first covering layer 20 is formed of multiple layers, although the boundary between adjacent covering layers can be visually recognized, the adjacent covering layers are joined with a force sufficient to ensure the function of the first covering layer 20. This also applies equally to the second covering layer 25 and the third covering layer 30.

[0110] [S300]

[0111] Regarding the second covering layer 25, a paste prepared by mixing a reducing resistance-improving oxide powder and a crystalline glass powder with a solvent is prepared. After forming this paste on the first covering layer 20, through drying, for example, firing treatment of the glass component at 1200 °C, the second covering layer 25 is formed.

[0112] [S400]

[0113] Furthermore, regarding the third covering layer 30, the outer layer glass paste prepared by mixing an oxide powder, a glass powder and a solvent in the same manner as above is also used to form the third covering layer 30 on the second covering layer 25.

[0114] [Second Embodiment]

[0115] Next, with reference to Figure 5 and Figure 6 the temperature sensor element 2 of the second embodiment will be described.

[0116] If the temperature sensor element 2 is described by comparing it with the temperature sensor element 1, as Figure 5 shown, the second cover layer 27 does not cover the first cover layer 20, but selectively covers the peripheries of the lead wires 15, 15.

[0117] That is, the temperature sensor element 2 does not directly contact the first cover layer 20 and the third cover layer 30, and the second cover layer 27 is provided only on the outer peripheries of the lead wires 15, 15. Therefore, the cross-section of the portion where the second cover layer 27 is provided has a structure arranged in the order of the lead wire 15, the second cover layer 27, and the third cover layer 30 from the inside or the center, similar to the first embodiment. Except for this point, as Figure 6 shown, the temperature sensor element 2 is manufactured through the same processes as the temperature sensor element 1.

[0118] The temperature sensor element 2 having a cross-section structure above the periphery of the lead wire 15 can improve the reduction resistance as well as the temperature sensor element 1 of the first embodiment.

[0119] The second cover layer 27 is difficult to form by dipping. For example, paste is applied to this area using a liquid metering and discharging device called a dispenser, and the second cover layer 27 is formed by performing drying and firing processes.

[0120] [First Example]

[0121] Next, an example of the present invention will be described based on a specific example.

[0122] A temperature sensor element 1 having a first cover layer 20, a second cover layer 25, and a third cover layer 30 described below is manufactured, and the change rate of the resistance value is measured.

[0123] [Manufacture of the Heat Sensing Body 11]

[0124] Raw material powder having the following particle diameters (d50) is prepared at the following mixing ratios, and the heat sensing body 11 is manufactured according to the above-described processes. The calcination is carried out at 1300 °C for 24 hours, and the sintering is carried out at 1500 °C for 24 hours, both in the atmosphere.

[0125] Y 2 O 3 : 79.5 mol% Particle diameter: 0.1 μm

[0126] Cr2 O 3 ： 8.5 mol% particle size: 2.0 μm

[0127] CaCO 3 : 3.5 mol% particle size: 2.0 μm

[0128] Mn 3 O 4 : 8.5 mol% particle size: 5.0 μm

[0129] The electrode 13, the lead wire 15, and the connection electrode 17 are all made of platinum (Pt), and the thermistor element 3 is fabricated in the order described in the embodiment.

[0130] [Formation of the covering layer]

[0131] On the above thermistor element 3, a first covering layer 20, a second covering layer 25, and a third covering layer 30 are formed.

[0132] The first covering layer 20 uses crystalline glass and thermistor powder having the same composition as the heat-sensitive body 11 as glass. The mass ratio of the crystalline glass to the thermistor powder is set to 20:80. In addition, an organic binder is used as the binder to make a paste for the first covering layer 20, and a precursor layer of one layer is formed by dipping. Then, heat treatment for drying and firing is performed to form the first covering layer 20 of the example.

[0133] The second covering layer 25 uses crystalline glass and powders of yttrium oxide (Y 2 O 3 ), chromium oxide (Cr 2 O 3 ), and manganese oxide (Mn 3 O 4 ). The particle size is the same as that used by the manufacturer of the heat-sensitive body 11. The mass ratio of the crystalline glass to the oxide powder for improving the reduction resistance is set as shown in Table 1. The powder of yttrium oxide (Y 2 O 3 ) is the oxide powder used in the part corresponding to the second covering layer 25 in the past. In addition, the second covering layer 25 is connected to the lead wire 15 as Figure 1 shown.

[0134] The third covering layer 30 uses crystalline glass and Y as the third oxide powder 2 O 3 . The mass ratio of the crystalline glass to Y of the third oxide powder 2 O 3 is 80:20.

[0135] The second covering layer 25 and the third covering layer 30 are formed as follows. After dipping in the paste for forming the second covering layer 25 to form the precursor layer of the second covering layer 25, dip in the paste for forming the third covering layer 30 to form the precursor layer of the third covering layer 30, and then perform heat treatment for drying and firing to form the second covering layer 25 and the third covering layer 30 of the relevant embodiment.

[0136] For the four temperature sensor elements (Sample Nos. 1 to 4) shown in Table 1, the change rate of the resistance value obtained based on the following conditions was measured. The measurement results are shown in Table 1.

[0137] [First measurement condition]

[0138] Holding temperature: 900 °C

[0139] Gas environment: 5 vol.% hydrogen + 95 vol.% nitrogen

[0140] Holding time: 5 hours, 10 hours

[0141] Resistance value measurement temperature: 25 °C

[0142] [Second measurement condition]

[0143] The change rate of the resistance value was measured under the second measurement condition that is the same as the first measurement condition except that the holding temperature is set to 1050 °C.

[0144] [Table 1]

[0145]

[0146] As shown in Table 1, it can be seen that by using chromium oxide and manganese oxide as the oxide powder of the second covering layer 25, the change rate of the resistance value in a high temperature range such as 900 °C and 1050 °C can be reduced, and the reduction resistance is improved. In particular, the improvement effect of the reduction resistance brought by chromium oxide is more significant.

[0147] [Second embodiment]

[0148] Five temperature sensor elements (Sample Nos. 5 to 9) manufactured in the same manner as in the first embodiment except that the oxide powder in the second covering layer 25 is the substance shown in Table 2 were used to measure the change rate of the resistance value under the first measurement condition and the second measurement condition of the first embodiment. The measurement results are shown in Table 2.

[0149] [Table 2]

[0150]

[0151] As shown in Table 2, it can be seen that in the oxide of titanium (TiO 2) and the oxide of aluminum (Al 2 O 3 ) as a metal element, the rate of change of the resistance value in the high temperature range can be reduced, and the reduction resistance is improved. However, for the surface modification using transition metal oxides, the effect decreases in the temperature range exceeding 1000 °C. From this, it can be seen that in the oxides of iridium and ruthenium (IrO 2 , RuO 2 ) and the oxide of platinum (PtO 2 ) which are noble metal elements the same as platinum constituting the lead wire 15, the rate of change of the resistance value in the high temperature range can be reduced, and the reduction resistance is improved. In particular, the improvement effect of the reduction resistance of the oxide of the noble metal element is larger than that of the oxide of the metal element.

[0152] [Example 3]

[0153] Next, for the purpose of improving the wettability of the lead wire 15 side with respect to glass, a temperature sensor element (sample Nos. 10 to 11) in which the lead wire 15 is covered with a coating of ruthenium and titanium which has been confirmed to have an improvement effect on the reduction resistance in the above examples is used, and the rate of change of the resistance value under the first measurement condition and the second measurement condition of the first example is measured. The measurement results are shown in Table 3. In addition, except for applying the coating, the temperature sensors of sample Nos. 10 to 11 have the same structure as the temperature sensor of sample No. 1.

[0154] [Table 3]

[0155]

[0156] As shown in Table 3, it can be seen that the reduction resistance is improved by forming a layer composed of elements that exhibit the effect of improving the wettability of the lead wire 15 side with respect to glass.

[0157] [Example 4]

[0158] For the purpose of improving the wettability of the lead wire 15 side, a sensor element (sample No. 12) having a lead wire 15 formed of a platinum alloy containing 20% by mass of iridium which has been confirmed to have an improvement effect on the reduction resistance in the above examples is used, and the rate of change of the resistance value under the first measurement condition and the second measurement condition of the first example is measured. The measurement results are shown in Table 4. In addition, except for forming the lead wire 15 of a platinum alloy, the temperature sensor of sample No. 12 has the same structure as the temperature sensor of sample No. 1.

[0159] [Table 4]

[0160]

[0161] As shown in Table 4, it can be seen that the lead wire 15 contains elements that play an effect of improving wettability, and the reduction resistance is increased.

[0162] [Embodiment 5]

[0163] A temperature sensor element (Sample No. 13) was used, which was a combination of Sample No. 7 of the second embodiment containing iridium oxide powder in the second covering layer 25 and Sample No. 12 of the fourth embodiment with a lead wire 15 formed of a platinum alloy containing 20 mass% of iridium, and the change rate of the resistance value under the first measurement condition and the second measurement condition of the first embodiment was measured. The measurement results are shown in Table 5.

[0164] [Table 5]

[0165]

[0166] As shown in Table 5, by enabling both the lead wire 15 and the second covering layer 25 to have the function of improving the wettability of the interface, a higher improvement effect of reduction resistance was obtained.

[0167] [Embodiment 6]

[0168] Next, research was conducted on the first covering layer 20 in contact with the lead wire 15. That is, a temperature sensor element (Sample No. 14) having a first covering layer 20 that does not contain glass but contains 10 mass% of chromium oxide was used, and the change rate of the resistance value under the first measurement condition and the second measurement condition of the first embodiment was measured. The measurement results are shown in Table 6. In addition, the structure of the temperature sensor element of Sample No. 14 other than the first covering layer 20 is the same as that of Sample No. 1.

[0169] [Table 6]

[0170]

[0171] As shown in Table 6, even if the first covering layer 20 has the function of improving the wettability of the interface, a higher improvement effect of reduction resistance was obtained.

[0172] The preferred embodiments of the present invention have been described above, but as long as the gist of the present invention is not deviated from, the structures exemplified in the above embodiments can be selected, discarded, or replaced with other structures.

[0173] Reference Numeral Explanation

[0174] 1 Temperature sensor element

[0175] 3 Thermistor element

[0176] 5 Covering layer

[0177] 11 Heat-sensitive body

[0178] 13 electrodes

[0179] 15 lead wires

[0180] 17 connecting electrodes

[0181] 20 first covering layer

[0182] 25 second covering layer

[0183] 30 third covering layer

Claims

1. A temperature sensor element, characterized in that, it comprises: a heat-sensitive body whose resistance changes according to temperature; a first covering layer that covers the periphery of the heat-sensitive body; a pair of lead wires connected to the heat-sensitive body and led out toward the rear end side through the first covering layer; a second covering layer that covers the periphery of the pair of lead wires led out through the first covering layer; and a third covering layer that covers the periphery of the first covering layer and the second covering layer, wherein the second covering layer is disposed between the third covering layer and the lead wires, and the second covering layer is composed of a mixture of at least one of ruthenium oxide powder, iridium oxide powder, and platinum oxide and glass.

2. The temperature sensor element according to claim 1, characterized in that, the lead wire comprises: a core wire made of platinum; and a plating covering layer that covers the periphery of the core wire and is composed of one or both of titanium oxide and ruthenium oxide.

3. The temperature sensor element according to claim 2, characterized in that, the core wire is made of a platinum alloy containing iridium.

4. The temperature sensor element according to claim 1 or 2, characterized in that, the first covering layer is composed of a first oxide powder or a mixture of the first oxide powder and glass; the third covering layer is composed of a mixture of a third oxide powder and glass.

5. The temperature sensor element according to claim 4, characterized in that, the first oxide powder is composed of the powder of the thermistor constituting the heat-sensitive body.

6. The temperature sensor element according to claim 1 or 2, characterized in that, the second covering layer covers the periphery of the pair of lead wires led out through the first covering layer and covers the first covering layer between the first covering layer and the third covering layer.

7. The temperature sensor element according to claim 1 or 2, characterized in that, the second covering layer defines and covers the periphery of the pair of lead wires led out through the first covering layer; the first covering layer is in direct contact with the third covering layer.

8. A temperature sensor, characterized in that, it comprises the temperature sensor element according to claim 1 or 2.

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