JP6580969B2 - Ceramic heater, gas sensor, and method of manufacturing ceramic heater - Google Patents

Description

  The present invention relates to a ceramic heater including a heater body, a metal terminal, and a brazing material, a gas sensor including the ceramic heater, and a method for manufacturing the ceramic heater.

  A heater body having a heating resistor embedded therein and an electrode pad electrically connected to the heating resistor, and a long metal terminal portion serving as a current-carrying path connecting the electrode pad and an external device; There is known a ceramic heater including a brazing material portion that electrically joins an electrode pad and a metal terminal portion.

  In this ceramic heater, the electrode pad of the heater body and the metal terminal part are joined by the brazing material part, but depending on the influence of the usage environment, etc., in an environment containing components that corrode and deteriorate the brazing material part. In some cases, the metal terminal portion and the electrode pad may be disconnected due to corrosion / deterioration of the brazing material portion. On the other hand, some have a coating film (plating layer) that covers the brazing material portion in order to suppress corrosion and deterioration of the brazing material portion.

  A coating film containing Ni as a main component is known, but in order to realize a ceramic heater having excellent corrosion resistance, a coating film containing Cr as a main component is used as a coating film. A technique to be used has been proposed (Patent Document 1).

  On the other hand, a gas sensor including a ceramic heater is known as a heater unit for heating a detection element (Patent Document 1).

JP 2014-013649 A

  However, since the coating film containing Cr as a main component is inflexible and hard, micro cracks (fine cracks) may occur. The micro cracks are formed on the inner surface of the coating film (the boundary surface with the base). ), The corrosion tends to proceed from the inner surface of the coating film where the microcracks have reached.

  By the way, the coating film mainly composed of Cr usually has poor adhesion to the brazing material portion, and there is a case where a base film mainly composed of Ni is formed as a base of the coating film. The base film mainly composed of Ni has excellent adhesion to the coating film mainly composed of Cr and also has excellent adhesion to the brazing material part and the metal terminal part, so that the coating film is directly applied to the brazing material part. Compared with the form to contact, the adhesiveness of a coating film and a brazing | wax material part improves.

  However, when a coating film mainly composed of Cr is provided on the surface of the base film mainly composed of Ni, since the coating film is less ionized than the base film, microcracks are caused by the influence of the corrosion potential. There is a possibility that the corrosion of the formed coating film is accelerated.

  At this time, it is considered that the smaller the number of microcracks in the coating film, the less likely the corrosion from the inner surface of the coating film occurs. Corrosion potential concentrates on the microcracks, and on the contrary, corrosion / deterioration from the inner surface of the coating film is accelerated, and the corrosion resistance by the coating film may not be exhibited in a short time.

  Accordingly, the present invention provides a ceramic heater that facilitates maintaining the corrosion resistance of the coating film even when microcracks are formed in the coating film containing Cr as a main component, and such a ceramic heater. An object of the present invention is to provide a gas sensor including the above and a method for manufacturing such a ceramic heater.

A ceramic heater according to one aspect of the present invention includes a heater main body portion, a metal terminal portion, a brazing material portion, a coating film, and a base film.
The heater body has a heating resistor embedded therein and an electrode pad electrically connected to the heating resistor and provided on the outer surface of the heater body. The metal terminal portion is configured in a long shape that forms a part of a current-carrying path that connects the electrode pad and the external device. The brazing material portion electrically joins the electrode pad and the joint portion of the metal terminal portion. The coating film covers at least a part of the metal terminal part and at least a part of the brazing material part directly or via another member.

  Among these, the coating film is formed mainly of Cr and has a plurality of microcracks extending from its own surface to the inside. The base film is formed mainly of Ni as the base of the coating film. When the number of microcracks intersecting the virtual line on the surface of the coating film is defined as the crack formation density, the ceramic heater covers the joint portion of the metal terminal portion and the brazing material portion of the coating film. The crack formation density in the region is 400 [lines / cm] or more.

  A coating film having such a crack formation density does not have microcracks concentrated in part, but microcracks are formed in a dispersed manner, so that the corrosion potential is concentrated in some microcracks. Can be suppressed. Thereby, acceleration of corrosion / deterioration from the inner surface of the coating film can be suppressed, and the corrosion resistance by the coating film can be easily maintained.

Therefore, this ceramic heater can easily maintain the corrosion resistance of the coating film even when microcracks are formed in the coating film containing Cr as a main component.
In addition, the lower limit value of the crack formation density is as described above, and the upper limit value of the crack formation density is not particularly limited as long as the coating film can be formed.

The ceramic heater described above includes a base film mainly composed of Ni as the base of the coating film.
Thus, by providing the base film mainly composed of Ni, the coating film mainly composed of Cr is hardly peeled off from the metal terminal portion or the brazing material portion.

  In other words, the base film mainly composed of Ni is excellent in adhesion to the coating film mainly composed of Cr and also excellent in adhesion to the brazing material portion and the metal terminal portion. By providing the base film, the adhesion between the coating film and the metal terminal part (or brazing material part) is improved as compared with a mode in which the coating film is in direct contact with the metal terminal part (or brazing material part).

Therefore, according to this ceramic heater, since the coating film mainly composed of Cr is hardly peeled off from the metal terminal portion or the brazing material portion, corrosion / deterioration of the brazing material portion and the metal terminal portion can be suppressed.
Next, a gas sensor according to another aspect of the present invention includes a detection element and a ceramic heater, and includes the above-described ceramic heater as the ceramic heater.

  The detection element is formed in a cylindrical shape extending in the axial direction and has a closed end to detect a component to be measured. The ceramic heater is disposed in the cylindrical hole of the detection element and heats the detection element.

  Since this gas sensor is equipped with the ceramic heater described above, it is easy to maintain the corrosion resistance due to the coating film even when microcracks are formed in the coating film containing Cr as a main component. It becomes easy to maintain the corrosion resistance.

  Next, a method for manufacturing a ceramic heater according to another aspect of the present invention is a method for manufacturing a ceramic heater including a heater main body portion, a metal terminal portion, a brazing material portion, and a coating film. A coating film forming step for forming the base film, and a base film forming step for forming the base film.

  The heater body has a heating resistor embedded therein and an electrode pad electrically connected to the heating resistor and provided on the outer surface of the heater body. The metal terminal portion is configured in a long shape that forms a part of a current-carrying path that connects the electrode pad and the external device. The brazing material portion electrically joins the electrode pad and the joint portion of the metal terminal portion. The coating film covers at least a part of the metal terminal part and at least a part of the brazing material part directly or via another member.

Among these, the coating film is formed mainly of Cr.
In the coating film forming step, at least a part of the metal terminal part and at least a part of the brazing material part are immersed in an electrolytic plating solution mainly composed of Cr to perform an electrolytic plating process to form a coating film.

  In addition, the base film forming process is a process executed before the coating film forming process. In the base film forming step, a base film mainly composed of Ni covering the metal terminal portion and the brazing material portion is formed as the base of the coating film.

  The electrolytic plating solution is mainly composed of chromic anhydride, and sulfuric acid and sodium fluorosilicate are added. The concentration of sulfuric acid in the electrolytic plating solution is 1.2 ± 0.4 g / L, and the concentration of sodium fluorosilicate in the electrolytic plating solution is 6.0 ± 2.0 g / L.

According to this method for manufacturing a ceramic heater, the number of microcracks in the coating film can be adjusted within a predetermined range.
In this way, the coating film in which the number of microcracks is adjusted does not have microcracks concentrated in a part, but is formed by dispersion of microcracks. Concentrating on can be suppressed. Thereby, acceleration of corrosion / deterioration from the inner surface of the coating film can be suppressed, and the corrosion resistance by the coating film can be easily maintained.

  Therefore, according to this method for manufacturing a ceramic heater, it is possible to manufacture a ceramic heater that easily maintains the corrosion resistance of the coating film even when microcracks are formed in the coating film containing Cr as a main component.

  Note that “mainly containing chromic anhydride” means that chromic anhydride is the most among the components contained in the electrolytic plating solution. The concentration of chromic anhydride in the electrolytic plating solution is, for example, 250 ± 50 g / L.

  Also, in the above-described ceramic heater manufacturing method, before the coating film forming step, as a base of the coating film, a base film is formed by forming a base film mainly composed of Ni covering the metal terminal portion and the brazing material portion. The process is performed.

As a result, a ceramic heater having a base film mainly composed of Ni can be manufactured as the base of the coating film, and the coating film mainly composed of Cr is hardly peeled off from the metal terminal portion or the brazing material portion.
In other words, the base film mainly composed of Ni is excellent in adhesion to the coating film mainly composed of Cr and also excellent in adhesion to the brazing material portion and the metal terminal portion. By providing the base film, the adhesion between the coating film and the metal terminal part (or brazing material part) is improved as compared with a mode in which the coating film is in direct contact with the metal terminal part (or brazing material part).

  Therefore, according to this method for manufacturing a ceramic heater, it is possible to manufacture a ceramic heater in which a coating film mainly composed of Cr is hardly peeled off from the metal terminal portion or the brazing material portion, and corrosion and deterioration of the brazing material portion and the metal terminal portion are prevented. A ceramic heater that can be suppressed can be manufactured.

According to the ceramic heater of the present invention, it is easy to maintain the corrosion resistance of the coating film even when microcracks are formed in the coating film containing Cr as a main component.
According to the gas sensor of the present invention, even when micro cracks are formed in the coating film containing Cr as a main component in the ceramic heater, the corrosion resistance due to the coating film can be easily maintained. It becomes easy to maintain sex.

  According to the method for manufacturing a ceramic heater of the present invention, it is possible to manufacture a ceramic heater that easily maintains the corrosion resistance of the coating film even when microcracks are formed in the coating film containing Cr as a main component.

It is a perspective view showing the appearance of a ceramic heater. It is a disassembled perspective view showing the internal structure of the ceramic heater. It is a fragmentary sectional view in the circumference part of an electrode part seen from a direction of an arrow in dashed-dotted line A-A 'among ceramic heaters shown in FIG. It is a flowchart showing the order of each process performed with the manufacturing method of a ceramic heater. It is explanatory drawing showing the connection state at the time of an electrolytic plating process. It is the table | surface which showed the conditions of Cr plating liquid at the time of forming a chromium plating film. It is a schematic block diagram of the measuring apparatus for investigating the correlation with the crack formation density and corrosion resistance (corrosion resistance) in the chromium plating film | membrane of a ceramic heater. It is the SEM photograph which image | photographed the surface state of two types of chromium plating films from which crack formation density differs. It is explanatory drawing which shows the investigation result of the correlation with the crack formation density and corrosion resistance (corrosion resistance) in the chromium plating film | membrane of a ceramic heater. It is sectional drawing explaining the whole structure of the gas sensor which concerns on 2nd Embodiment. It is explanatory drawing which shows the structure of a gas detection element.

Embodiments to which the present invention is applied will be described below with reference to the drawings.
In addition, this invention is not limited to the following embodiment at all, and it cannot be overemphasized that various forms may be taken as long as it belongs to the technical scope of this invention.

[1. First Embodiment]
[1-1. overall structure]
An embodiment of a ceramic heater and a ceramic heater manufacturing method to which the present invention is applied will be described with reference to the drawings.

  In addition, the ceramic heater of this embodiment can be used for the use etc. which heat a sensor element to activation temperature. In addition, as a sensor element to be heated, a gas sensor that detects a specific gas (oxygen) in a measurement target gas (exhaust gas) for use in various controls (for example, air-fuel ratio feedback control) in an automobile or various internal combustion engines. An element etc. are mentioned.

First, the structure of the ceramic heater 100 will be described with reference to FIGS.
FIG. 1 is a perspective view showing the appearance of the ceramic heater 100. FIG. 2 is an exploded perspective view showing the internal configuration of the ceramic heater 100.

  In the ceramic heater 100 of the present embodiment, of the both ends in the longitudinal direction, the side provided with the heat generating portion (the side where the heat generating portion 142 described later is formed) is referred to as the “tip side”, and the opposite end The part is described as “rear end side”.

  The ceramic heater 100 includes a round bar (substantially cylindrical) ceramic base 102 having a heating resistor 141, an electrode pad 121 provided on the outer surface of the ceramic base 102 and electrically connected to the heating resistor 141, and a melting point. And a metal terminal portion 130 joined to the electrode pad 121 by a conductive brazing material portion having a temperature of 900 ° C. or higher.

  The ceramic heater 100 is configured such that the heat generating resistor 141 generates heat by energizing the heat generating resistor 141 from an external device (power supply device) via an electrode pad 121 provided on the rear end side of the ceramic base 102. It is. Note that the heat generating portion 142 (see FIG. 2) of the heat generating resistor 141 is disposed on the tip side of the ceramic substrate 102. That is, the ceramic heater 100 is configured to heat the sensor element when the tip side of the ceramic base 102 generates heat.

  As shown in FIG. 2, the ceramic heater 100 is manufactured by winding green sheets 140 and 146 made of alumina ceramic with high insulating properties around the outer periphery of a round rod-like alumina ceramic tube 101 and firing them. .

  On the green sheet 140, a heating resistor 141 mainly composed of a tungsten-based material as a heat pattern is formed. The heat generating resistor 141 includes a heat generating part 142 formed on the front end side, and a pair of lead parts 143 connected to both ends of the heat generating part 142.

  In addition, two through holes 144 are provided on the rear end side of the green sheet 140. The pair of lead portions 143 are electrically connected to the two electrode pads 121 formed on the outer surface of the ceramic heater 100 through the two through holes 144.

The green sheet 146 is a sheet that is pressure-bonded to the surface of the green sheet 140 on which the heat generating resistor 141 is formed.
Alumina paste is applied to the surface of the green sheet 146 opposite to the pressure contact surface in contact with the green sheet 140, and the green sheets 140 and 146 are wound around the tub tube 101 and pressed inward from the outer periphery with the applied surface facing inside. As a result, a ceramic heater molded body is formed. Thereafter, the ceramic heater molded body is fired to form the ceramic heater 100.

  Next, as shown in FIGS. 1 and 2, the ceramic heater 100 is formed with two electrode pads 121 on the anode side and the cathode side. The electrode pads 121 are provided at two positions on the outer surface of the green sheet 140 corresponding to the two through holes 144 (see FIG. 2). The conduction between the heat generating resistor 141 and the lead portion 143 is performed through a conductive paste filled in the through hole 144. Note that a metal layer (a plating film 122 for pads shown in FIG. 3) by plating described later is formed on the surface of the electrode pad 121.

  The metal terminal portion 130 is made of a long nickel member, and includes a bonding portion 133 bonded to the electrode pad 121 by a brazing material portion, a crimped portion 135 cut out in a flat plate shape, and a bonding portion 133. And a connecting portion 134 that connects the caulking portion 135.

  The distal end portion of the connecting portion 134 is bent stepwise in the thickness direction, and is formed so as to be connected to the joint portion 133. In addition, the metal terminal portion 130 is twisted so that a connection region of the connecting portion 134 with the caulking portion 135 rotates around the central axis in the longitudinal direction of the connecting portion 134.

  The metal terminal portion 130 is connected to an external circuit (external power supply device) via a lead wire or the like by caulking and fixing a lead wire or the like for connecting an external circuit (not shown) to the caulking portion 135. .

  The two metal terminal portions 130 configured as described above are joined to the two electrode pads 121 and function as an anode side terminal and a cathode side terminal when a voltage is applied to the ceramic heater 100.

  FIG. 3 is a partial cross-sectional view of the surrounding portion of the ceramic heater 100 shown in FIG. 1 as viewed from the direction of the arrow along the one-dot chain line A-A ′. In FIG. 3, a direction from the metal terminal portion 130 toward the central axis of the ceramic heater 100 (downward in the drawing in the drawing) is a downward direction, and a direction away from the central axis (upward in the drawing in the drawing) is an upward direction. explain.

  As shown in FIG. 3, the electrode pad 121 is formed on the outer surface (upper surface in FIG. 3) of the green sheet 140 wound around the outer periphery of the soot tube 101, and the inner surface (see FIG. 3) through the through hole 144. 3 is connected to the lead portion 143 of the heating resistor 141 formed on the lower surface).

  The electrode pad 121 is a pad-like metal layer containing 80% by weight or more of a main material containing at least one element selected from tungsten and molybdenum. Tungsten and molybdenum are suitable for the composition of the electrode pad 121 because they have good bonding properties to the copper-based brazing material portion 124 and have a high melting point and excellent heat resistance.

  The metal terminal part 130 is comprised with the nickel member which contains nickel 90weight% or more. As shown in FIG. 3, the metal terminal portion 130 is joined to the electrode pad 121 covered with the pad plating film 122 by the brazing material portion 124. A nickel plating film 125 mainly composed of nickel (Ni) and a chromium plating film mainly composed of chromium (Cr) are further formed on the metal terminal portion 130 and the electrode pad 121 joined together by the brazing material portion 124. 126 is formed. A chromium plating film 126 is formed on the upper side of the nickel plating film 125, and the nickel plating film 125 and the chromium plating film 126 are provided to prevent corrosion of the brazing material portion 124 and the metal terminal portion 130 due to oxidation. .

  And the brazing material part 124 which joins the electrode pad 121 and the metal terminal part 130 contains the quantity of copper exceeding 50 weight%. In the present embodiment, the electrode pad 121 and the metal terminal portion 130 are brazed using a brazing material portion 124 of 100% by weight of copper.

During brazing, the nickel component of the pad plating film 122 provided on the electrode pad 121 diffuses into the brazing material portion 124.
That is, in the ceramic heater 100 of the present embodiment, as shown in FIG. 3, the pad plating film 122 before brazing has a contour shape indicated by a dashed line 123 at the boundary portion with the brazing material portion 124. After the brazing, a part of the pad plating film 122 is diffused and melted into the brazing material portion 124, and the pad plating film 122 and the brazing material portion 124 are formed in an integrated state. .

[1-2. Production method]
Next, the manufacturing method of the ceramic heater of this embodiment is demonstrated.
FIG. 4 is a flowchart showing the order of each process executed in the method for manufacturing the ceramic heater 100.

  In the ceramic substrate forming process of S110 (S represents a step), first, metal resistor ink (metallized ink) to be the heating resistor 141 and the electrode pad 121 is applied to the green sheet 140 in a predetermined pattern shape ( Printing) and filling the through hole 144 with metallized ink (or conductive paste). Next, the green sheet 146 is pressure-bonded to the green sheet 140, and the green sheet 140 and the green sheet 146 are wound around the soot tube 101 to form a ceramic heater molded body. Subsequently, the ceramic heater molded body is fired to execute a process of forming the ceramic base body 102 in which the green sheets 140 and 146 and the soot tube 101 are integrated.

  The processing so far is the ceramic substrate forming step, and the electrode pad 121 is formed by applying metal resistor ink (metallized ink) to the ceramic substrate 102 while manufacturing the ceramic substrate 102 having the heating resistor 141. It is processing.

Subsequently, in the electrode pad plating forming step of S120, an electrode pad plating forming process for forming a pad plating film 122 covering the electrode pad 121 is performed.
Next, in the bonding step of S130, the brazing material portion and the metal terminal portion 130 are arranged on the pad plating film 122 so as to contact each other. Then, in this state, the brazing material portion is melted by heating to 900 ° C. or more, thereby performing a process of joining the metal terminal portion 130 and the electrode pad 121 by brazing to form the brazing material portion 124.

  In this bonding step, the brazing material portion 124 and the region surrounded by the alternate long and short dash line 123 in the pad plating film 122 are solidified, and the region surrounded by the alternate long and short dash line 123 in the pad plating film 122 is solidified. The phenomenon that melts into.

  Then, in the nickel plating forming step of S140, a process for forming a nickel plating film 125 is performed by performing a nickel plating process by an electroless plating method so as to cover the joint part 133 of the brazing material part 124 and the metal terminal part 130. To do.

Thereafter, in the chrome plating formation step of S150, a chrome plating process is performed by an electrolytic plating method to form a chrome plating film 126 mainly composed of Cr.
Here, the chromium plating formation process using the electrolytic plating method will be described. In addition, in FIG. 5, the explanatory view showing the connection state at the time of an electrolytic plating process is shown.

  In the chromium plating forming process, first, in the ceramic heater 100 (the ceramic base body 102 and the metal terminal part 130) after the nickel plating forming process is completed, the electroconductive part for electrolytic plating with respect to the caulking part 135 of the metal terminal part 130. The cathode 205 is connected.

  Next, in a state where the entire ceramic heater 100 (the ceramic base body 102 and the metal terminal portion 130) is immersed in the Cr plating solution 207 (electrolytic plating solution), the nickel plating film 125 (the brazing material portion 124 and the metal terminal portion) is supplied from the power source 201. The nickel plating film 125) covering 130 is energized to perform electrolytic plating.

  At this time, the Cr plating solution 207 is configured by adding predetermined additives (sulfuric acid, sodium fluorosilicate, trivalent chromium) based on chromic anhydride. In the present embodiment, the electrolytic plating process is performed using a Cr plating solution 207 that satisfies the conditions shown in FIG.

  The energization path from the power source 201 is the path of the anode 203, the Cr plating solution 207, the nickel plating film 125 (the nickel plating film 125 covering the joint portion 133 of the brazing material portion 124 and the metal terminal portion 130), and the cathode 205. By performing energization in such a path, the electroplating process is performed on the nickel plating film 125 and the metal terminal portion 130 covering the brazing material portion 124, the joint portion 133. The current density of the current that is energized at this time is 12.0 [A / dm2].

Thereby, the chromium plating film 126 is formed on the nickel plating film 125 covering the brazing material portion 124 and the metal terminal portion 130.
A plurality of microcracks (also referred to as microcracks) extending from the surface to the inside (nickel plating film 125) are formed in the chromium plating film 126 formed in this way. The micro cracks are not formed concentrated on a part of the chrome plating film 126 but distributed throughout the chrome plating film 126.

  When the number of microcracks that intersect the virtual straight line on the surface of the chrome plating film 126 is defined as the crack formation density, in this embodiment, the joint portion 133 and the brazing material portion of the metal terminal portion 130 in the chrome plating film 126 are used. The crack formation density in the region covering 124 (in other words, the nickel plating film 125) is adjusted to 400 to 1000 [lines / cm]. At this time, the crack formation density can be adjusted by adjusting the chromic anhydride concentration, sulfuric acid concentration, sodium fluorosilicate concentration, and trivalent chromium concentration, respectively.

  By performing the manufacturing method including the steps as described above, the ceramic heater 100 including the chromium plating film 126 in which the crack formation density is adjusted to a predetermined range can be manufactured.

[1-3. Measurement result]
Here, the measurement result which investigated the correlation with the crack formation density and corrosion resistance (corrosion resistance) in the chromium plating film | membrane of a ceramic heater is demonstrated.

The survey measurement was performed using a measuring apparatus as shown in FIG.
Specifically, the ceramic terminal 100 is immersed in a water tank 211 filled with a 0.1% nitric acid solution, and is stirred with 0.2 [L / min] air bubbling using an air supply pipe 223. A test voltage (40 [V]) in which the portion 130 was set to a positive potential and the Ni plate 213 as a counter electrode was set to a negative potential was applied. The test voltage was applied from the power supply device 215 to the ceramic heater 100 (metal terminal portion 130), the nitric acid solution, and the Ni plate 213 via the resistance element 217. At this time, using the first voltmeter 219 for detecting the applied voltage, the applied voltage is detected while detecting the applied voltage to the series circuit of the ceramic heater 100 (metal terminal portion 130), the nitric acid solution, and the Ni plate 213. It adjusted so that it might become an appropriate value. Further, the voltage at both ends of the resistance element 217 was detected using the second voltmeter 221, and the current value was adjusted from the resistance value of the resistance element 217 and the voltage across the resistance element so that the current value became an appropriate value. .

  Then, using a plurality of types of ceramic heaters with different crack formation densities of the chrome plating film, the elapsed time from when the test voltage is applied to when the ceramic base 102 is removed from the metal terminal portion 130 in the ceramic heater 100 is measured. Then, the correlation between the crack formation density and the corrosion resistance (corrosion resistance) in the chromium plating film was investigated.

Here, FIG. 8 shows SEM photographs of the surface states of two types of chromium plating films having different crack formation densities.
FIG. 8 shows a 1000 times SEM photograph, one virtual straight line is set, and the number of microcracks that intersect the virtual straight line is indicated by a number.

  In FIG. 8, SEM photograph 1 and SEM photograph 2 represent chromium plating films having different conditions of the Cr plating solution used in the chromium plating forming step. The conditions of the Cr plating solution and the crack formation density for the chromium plating films shown in SEM photograph 1 and SEM photograph 2 are as shown in FIG.

  In addition, the crack formation density is set to four virtual straight lines at random in the SEM photograph, and for each of the four virtual straight lines, the number of micro cracks (fine cracks) intersecting the virtual straight line is counted, and the cross per cm The average value of the number of locations was calculated. In the SEM photograph 1 of FIG. 8, there are three intersections, and in the SEM photograph 2, there are nine intersections.

  The survey measurement was conducted using five ceramic heaters for each of the chromium plating films of seven levels of crack formation density (100, 200, 300, 400, 500, 600, 1000 [lines / cm]). did. When 20 hours have elapsed from the start of application of the test voltage, it is determined that the ceramic heater 100 from which the ceramic base 102 has not dropped from the metal terminal portion 130 is acceptable, while the ceramic base 102 has dropped from the metal terminal portion 130. The ceramic heater 100 was determined to be unacceptable.

  According to the measurement results shown in FIG. 9, the ceramic heater having a chromium plating film with a crack formation density of 300 [lines / cm] or less has a case where the crack formation density is determined while there is a case where it is determined to be rejected. The total number of ceramic heaters having a chromium plating film of 400 [lines / cm] or more is determined to be acceptable.

For this reason, the ceramic heater having a chromium plating film with a crack formation density of 400 [lines / cm] or more has excellent corrosion resistance (corrosion resistance).
[1-4. effect]
As described above, in the ceramic heater 100 of the present embodiment, the chromium plating film 126 is formed mainly of Cr and has a plurality of micro cracks extending from its own surface to the inside. When the number of microcracks that intersect the virtual straight line on the surface of the chrome plating film 126 is defined as the crack formation density, in the ceramic heater 100, the joint portion 133 of the metal terminal portion 130 and the soldering portion of the chrome plating film 126 are used. The crack formation density in the region covering the material part 124 is 400 [lines / cm] or more.

  In the chromium plating film 126 having such a crack formation density, the microcracks are not concentrated and partly formed, but the microcracks are formed in a dispersed manner, so that the corrosion potential is concentrated on a part of the microcracks. This can be suppressed. Thereby, acceleration of corrosion / deterioration from the inner surface of the chromium plating film 126 can be suppressed, and the corrosion resistance by the chromium plating film 126 can be easily maintained. This is supported by the measurement results shown in FIG.

  Therefore, the ceramic heater 100 can easily maintain the corrosion resistance due to the chromium plating film 126 even when microcracks are formed in the chromium plating film 126 containing Cr as a main component.

  Note that the lower limit value of the crack formation density is (400 [lines / cm]) as described above, and the upper limit value of the crack formation density is not particularly limited as long as the coating film can be formed.

Further, the ceramic heater 100 includes a nickel plating film 125 as a base film mainly composed of Ni as a base of the chromium plating film 126.
Thus, by providing the nickel plating film 125 as a base film mainly composed of Ni, the chromium plating film 126 mainly composed of Cr is hardly peeled off from the metal terminal portion 130 and the brazing material portion 124.

  In other words, the nickel plating film 125 is excellent in adhesion to the chromium plating film 126 and also excellent in adhesion to the brazing material portion 124 and the metal terminal portion 130. Compared with the embodiment in which the film 126 is in direct contact with the metal terminal portion 130 (or brazing material portion 124), the adhesion between the chromium plating film 126 and the metal terminal portion 130 (or brazing material portion 124) is improved.

  Therefore, according to the ceramic heater 100, the chromium plating film 126 mainly composed of Cr is difficult to peel off from the metal terminal portion 130 and the brazing material portion 124, so that corrosion and deterioration of the brazing material portion 124 and the metal terminal portion 130 can be suppressed. .

  Next, the manufacturing method of the ceramic heater 100 includes each process as shown in FIG. 4, and among these, as S150, there is a chrome plating forming process (coating film forming process) for forming the chrome plating film 126. is doing.

The chromium plating film 126 is formed mainly of Cr as described above.
In the chrome plating forming step, at least a part of the metal terminal portion 130 and at least a part of the brazing material portion 124 are immersed in a Cr plating solution 207 (electrolytic plating solution) mainly composed of Cr, and an electrolytic plating process is performed to perform the chromium plating film 126 Form.

  The Cr plating solution 207 is mainly composed of chromic anhydride and is added with sulfuric acid and sodium fluorosilicate. The concentration of sulfuric acid in the Cr plating solution 207 is 1.2 ± 0.4 g / L, and the concentration of sodium fluorosilicate in the Cr plating solution 207 is 6.0 ± 2.0 g / L.

According to such a manufacturing method of the ceramic heater 100, the number of microcracks in the chromium plating film 126 can be adjusted to a predetermined range.
In this way, the chromium plating film 126 in which the number of microcracks is adjusted does not have microcracks concentrated in a part, but is formed by dispersion of microcracks. Concentration on cracks can be suppressed. Thereby, acceleration of corrosion / deterioration from the inner surface of the chromium plating film 126 can be suppressed, and the corrosion resistance by the chromium plating film 126 can be easily maintained.

  Therefore, according to the manufacturing method of the ceramic heater 100, even when micro cracks are formed in the chromium plating film 126 containing Cr as a main component, it is possible to manufacture a ceramic heater that can easily maintain the corrosion resistance due to the chromium plating film 126. .

  Note that “mainly composed of chromic anhydride” means that chromic anhydride is the most among the components contained in the Cr plating solution 207. The concentration of chromic anhydride in the Cr plating solution 207 is, for example, 250 ± 50 g / L.

  Further, in the manufacturing method of the ceramic heater 100, Ni covering the metal terminal portion 130 and the brazing material portion 124 is mainly used as a base of the chromium plating film 126 before the chromium plating forming step (coating film forming step). A nickel plating formation step (underlayer formation step, S140) for forming the nickel plating film 125 is performed.

  As a result, the ceramic heater 100 including the nickel plating film 125 as a base film mainly composed of Ni can be manufactured as the base of the chromium plating film 126, and the chromium plating film 126 mainly composed of Cr is used for the metal terminal portion 130 and the brazing material. It becomes difficult to peel off from the portion 124.

  In other words, the nickel plating film 125 is excellent in adhesion to the chromium plating film 126 and also excellent in adhesion to the brazing material portion 124 and the metal terminal portion 130, and therefore includes the nickel plating film 125 as a base film. Thus, the adhesion between the chrome plating film 126 and the metal terminal portion 130 (or brazing material portion 124) is improved as compared with the embodiment in which the chrome plating film 126 is in direct contact with the metal terminal portion 130 (or brazing material portion 124). To do.

  Therefore, according to the manufacturing method of the ceramic heater 100, the ceramic heater 100 in which the chromium plating film 126 is hardly peeled off from the metal terminal portion 130 or the brazing material portion 124 can be manufactured, and the brazing material portion 124 and the metal terminal portion 130 are corroded and deteriorated. Can be manufactured.

[1-5. Correspondence with Claims]
Here, the correspondence of the words in the claims and the present embodiment will be described.
The ceramic substrate 102 having the electrode pads 121 corresponds to an example of a heater main body, the metal terminal portion 130 corresponds to an example of a metal terminal portion, the chromium plating film 126 corresponds to an example of a coating film, and the nickel plating film 125. Corresponds to an example of the base film.

The chromium plating forming process of S150 corresponds to an example of a coating film forming process, and the nickel plating forming process of S140 corresponds to an example of a base film forming process.
[2. Second Embodiment]
As a second embodiment, a gas sensor 1 including a ceramic heater 100 will be described.

In the following description, the same configurations as those of the first embodiment among the configurations of the second embodiment are denoted by the same reference numerals as those of the first embodiment, and description thereof is omitted.
FIG. 10 is a cross-sectional view illustrating the overall configuration of the gas sensor 1 according to the second embodiment.

  A gas sensor 1 to which the present invention is applied is a gas sensor that is fastened to an exhaust passage of an internal combustion engine mounted on a vehicle such as a passenger car and has its tip portion disposed inside the exhaust passage. It is an oxygen sensor that measures the concentration.

  In the following description, in the direction along the axis O shown in FIG. 10, the side on which the protector 80 is attached to the metal shell 60 (the lower side in the figure) is the tip side, and the opposite side (the upper side in the figure). Is described as the rear end side.

  The gas sensor 1 is a sensor including a ceramic heater 100 for heating a gas detection element 10 to be described later. The gas detection element 10 is heated and activated by the heat of the ceramic heater 100 to measure the oxygen concentration in the exhaust gas. To do. This ceramic heater 100 has the same configuration as the ceramic heater 100 of the first embodiment.

  As shown in FIG. 10, the gas sensor 1 includes a gas detection element 10 (detection element 10), a ceramic heater 100, a separator 30, a seal member 40 (elastic member 40), a plurality of terminal fittings 50, leads. A wire 55 (lead member 55), a metal shell 60 covering the periphery thereof, a protector 80, an outer cylinder 90 (outer cylinder member 90), and the like are mainly provided.

FIG. 11 is an explanatory diagram showing a configuration of the gas detection element 10 of FIG.
The gas detection element 10 is formed from a solid electrolyte having oxygen ion conductivity. The gas detection element 10 is formed in a cylindrical shape extending in the direction of the axis O, and is provided on the element main body 11 with the end on the front end side (the lower end in FIG. 11) closed, and on the outer peripheral surface of the element main body 11. The outer electrode 16 and the inner electrode 19 provided on the inner peripheral surface of the element body 11 are mainly provided. On the outer periphery of the central portion of the element body 11, a flange portion 14 that protrudes radially outward is provided in the circumferential direction.

A typical example of the solid electrolyte constituting the element body 11 is ZrO _{2 in} which Y ₂ O ₃ or CaO is dissolved. In addition to this solid electrolyte, a solid electrolyte which is a solid solution of an alkaline earth metal or rare earth metal oxide and ZrO ₂ may be used. Further, a solid electrolyte containing HfO _{2 in} a solid solution of an alkaline earth metal or rare earth metal oxide and ZrO ₂ may be used.

  An outer electrode 16, a longitudinal lead portion 17, and a contact lead portion 18 (outer lead electrode 18) are formed on the outer peripheral surface of the element body 11. The outer electrode 16 is an electrode in which Pt or a Pt alloy (hereinafter referred to as “Pt or the like”) is formed porous on the tip side of the gas detection element 10. The vertical lead portion 17 is a conductive portion extending in the axial direction from the outer electrode 16 and is formed of Pt or the like. The contact lead portion 18 is a conductive portion that is conductively connected to the vertical lead portion 17 provided at the end portion on the rear end side of the vertical lead portion 17 and is formed of Pt or the like. In the present embodiment, the contact lead portion 18 is a portion that is formed in a rectangular shape that covers a part of the outer peripheral surface of the element body 11 in the circumferential direction, and is in electrical contact with a second sensor terminal fitting 52 described later. Note that the shape of the contact lead portion 18 may be rectangular, may be other polygonal shapes, may be circular or elliptical, and is not particularly limited. An inner electrode 19 in which Pt or the like is formed in a porous shape is formed on the inner peripheral surface of the element body 11.

  The plurality of terminal fittings 50 include a first sensor terminal fitting 51 and a second sensor terminal fitting 52 (outer terminal member 52). The plurality of terminal fittings 50 are fittings formed from a nickel alloy (for example, Inconel 750, manufactured by Inconel, UK, registered trademark).

  The first sensor terminal fitting 51 is in electrical contact with the inner electrode 19 of the gas detection element 10 and outputs a detection signal of the gas detection element 10 together with the second sensor terminal fitting 52. The first sensor terminal fitting 51 holds the ceramic heater 100 and presses the tip side of the ceramic heater 100 against the inner surface of the gas detection element 10. On the other hand, the second sensor terminal fitting 52 is electrically connected to the outer electrode 16 of the element body 11.

  The core wires of the lead wires 55 are caulked and connected to the plurality of terminal fittings 50, respectively. In FIG. 10, three lead wires 55 among the four lead wires 55 are illustrated.

  As shown in FIG. 10, the separator 30 is a member disposed between the gas detection element 10 and the seal member 40, and is a cylindrical member formed of an electrically insulating material such as alumina. The separator 30 is provided with an accommodating portion 31 for accommodating a plurality of terminal fittings 50 and the like. The accommodating portion 31 is a through hole formed so as to penetrate the separator 30 in the direction of the axis O, and allows air to flow between the space on the front end side and the space on the rear end side with respect to the separator 30. It is.

  Furthermore, a flange portion 32 that protrudes radially outward is provided on the outer peripheral surface of the separator 30. A holding metal fitting 33 formed in a substantially cylindrical shape is disposed on the outer peripheral surface of the separator 30 on the tip side of the flange portion 32. At this time, the separator 30 is disposed so as to be inserted into the holding metal fitting 33.

  The seal member 40 is a plug member made of an elastic material such as fluorine rubber, and is a member disposed at the rear end of the gas sensor 1. The seal member 40 is a member that closes the rear end of the outer cylinder 90 and is formed in a substantially cylindrical shape with the axis O direction as the height direction. The seal member 40 is fitted into the opening on the rear end side of the outer cylinder 90 so as to contact the surface on the rear end side of the separator 30.

  As shown in FIG. 10, the metal shell 60 is a member formed from a stainless alloy (for example, SUS310S of JIS standard), and is a member formed in a substantially cylindrical shape. The metal shell 60 is provided with a step portion 61 that supports the flange portion 14 of the gas detection element 10 so as to protrude in the circumferential direction from the inner circumferential surface toward the radially inner side.

  A screw part 62 for attaching the gas sensor 1 to an exhaust passage (not shown) of the internal combustion engine and an attachment tool for screwing the screw part 62 into the exhaust passage are associated with the outer peripheral surface on the front end side of the metal shell 60. A hexagonal portion 63 to be joined is provided in the circumferential direction. An annular gasket 64 is disposed between the screw portion 62 and the hexagonal portion 63. The gasket 64 prevents gas from being released from the gap between the gas sensor 1 and the exhaust passage.

  A front end engaging portion 65 to which a protector 80 described later is engaged is formed on the front end side of the metal shell 60 with respect to the screw portion 62. The tip engaging portion 65 is a portion formed with a smaller diameter on the outer peripheral surface than the screw portion 62. Further, the rear end engaging portion 66 engaged with the outer cylinder 90 and the gas detection element 10 are arranged on the metal shell 60 on the rear end side of the hexagonal portion 63 from the hexagonal portion 63 toward the rear end side. A caulking fixing portion 67 for caulking and fixing is formed.

  Inside the metal shell 60, in order from the step portion 61 toward the rear end side, a metal front end side packing 71, a cylindrical support member 72 made of alumina, a metal rear end side packing 73, talc powder A filling member 74, an alumina sleeve 75, and an annular ring 76 are disposed. A step portion is formed on the inner peripheral surface of the support member 72, and the flange portion 14 of the element body 11 is supported by the step portion. The rear end side packing 73 is sandwiched between the support member 72 and the flange 14.

  The ring 76 is disposed between the sleeve 75 and the caulking and fixing portion 67, and a force in the distal direction applied by the caulking and fixing portion 67 being deformed radially inward and on the distal end side, This is transmitted to the filling member 74, the rear end side packing 73, the support member 72, and the front end side packing 71. By this pressing force, the filling member 74 is compressed and filled in the direction of the axis O, and airtightly fills the gap between the inner peripheral surface of the metal shell 60 and the outer peripheral surface of the element body 11.

  The protector 80 protects the gas detection element 10 protruding into the flow path from collision of water droplets or foreign matters contained in the gas flowing in the flow path when the gas sensor 1 is attached to the exhaust flow path. is there. The protector 80 is a member formed from stainless steel (for example, JIS standard SUS310S), and is a protective member that covers the tip of the gas detection element 10. The protector 80 is a cylindrical member extending in the axial direction, and is formed in a shape with a closed end. The rear end edge of the protector 80 is fixed to the front end engaging portion 65 of the metal shell 60 by welding.

  The protector 80 is formed in a bottomed cylindrical shape that is fixed to the inside of the outer protector 81 and an outer protector 81 in which a peripheral edge portion on the open side that is formed in a bottomed cylindrical shape is fitted to the tip engaging portion 65. An inner protector 82 is provided. In other words, the protector 80 has a double structure composed of the outer protector 81 and the inner protector 82.

  The cylindrical surface of the outer protector 81 and the inner protector 82 is provided with an inlet 83 for introducing gas into the inside. In FIG. 10, only the introduction port 83 of the outer protector 81 is shown, and the introduction port 83 of the inner protector 82 is not shown because of the arrangement. Furthermore, the bottom surface of the outer protector 81 and the inner protector 82 is provided with an outer discharge port 84 and an inner discharge port 85 for discharging water droplets and gas that have entered inside.

  The outer cylinder 90 is a member made of stainless steel (for example, JIS standard SUS304L) different from the metal shell 60, and the rear end engaging portion 66 of the metal shell 60 is inserted into the outer cylinder 90. It is fixed to the metal shell 60. Inside the outer cylinder 90, the rear end of the gas detection element 10 protruding from the rear end of the metal shell 60, the separator 30, and the seal member 40 are disposed.

As described above, the gas sensor 1 of the second embodiment includes the ceramic heater 100 of the first embodiment as a heater for heating the gas detection element 10.
As described above, the ceramic heater 100 can easily maintain the corrosion resistance of the chromium plating film 126 even when microcracks are formed in the chromium plating film 126 containing Cr as a main component. By providing such a ceramic heater 100, corrosion / deterioration of the brazing material portion 124 and the metal terminal portion 130 can be suppressed, so that the gas sensor 1 can easily maintain corrosion resistance.

Therefore, according to the gas sensor 1 of 2nd Embodiment, the gas sensor which can suppress the corrosion and deterioration of the brazing material part 124 and the metal terminal part 130 in the ceramic heater 100 is realizable.
Here, the correspondence of the words in the claims and the present embodiment will be described. The gas detection element 10 corresponds to an example of a detection element.

[3. Other Embodiments]
As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, In the range which does not deviate from the summary of this invention, it is possible to implement in various aspects.

  For example, if the crack formation density of the coating film (chrome plating film 126) is 400 [lines / cm] or more as described above, corrosion / deterioration of the brazing material portion 124 and the metal terminal portion 130 can be suppressed. , 500 [lines / cm] or more, the corrosion / deterioration of the brazing material portion 124 and the metal terminal portion 130 can be further suppressed.

  Further, in the above-described nickel plating formation step of S140, the embodiment in which the nickel plating film 125 is formed by the electroless plating method has been described, but the nickel plating film 125 may be formed by the electrolytic plating method.

  DESCRIPTION OF SYMBOLS 1 ... Gas sensor, 10 ... Gas detection element, 55 ... Lead wire (lead member), 100 ... Ceramic heater, 102 ... Ceramic base | substrate, 121 ... Electrode pad, 124 ... Brazing material part, 125 ... Nickel plating film, 126 ... Chrome plating Membrane, 130 ... metal terminal part, 133 ... joint part, 134 ... connecting part, 135 ... caulking part, 201 ... power source, 203 ... anode, 205 ... cathode.

Claims (3)

A heater body having a heating resistor embedded therein, and an electrode pad electrically connected to the heating resistor and provided on its outer surface;
An elongated metal terminal portion that forms part of a current-carrying path connecting the electrode pad and an external device;
A brazing material part for electrically joining the electrode pad and the joint part of the metal terminal part;
A coating film covering at least a part of the metal terminal part and at least a part of the brazing material part directly or via another member;
A ceramic heater comprising:
The coating film is formed mainly of Cr and has a plurality of microcracks extending from its surface to the inside.
As a base of the coating film, comprising a base film mainly composed of Ni,
When the number of the microcracks that intersect the virtual line on the surface of the coating film is defined as a crack formation density, in the region of the coating film that covers the joint portion of the metal terminal portion and the brazing material portion The crack formation density is 400 [lines / cm] or more.
Ceramic heater. A detection element that is formed in a cylindrical shape extending in the axial direction and whose tip is closed and detects a component to be measured;
A ceramic heater that is disposed in the cylindrical hole of the detection element and heats the detection element;
A gas sensor comprising:
The ceramic heater is the ceramic heater according to claim 1,
Gas sensor. A heater body having a heating resistor embedded therein, and an electrode pad electrically connected to the heating resistor and provided on its outer surface;
An elongated metal terminal portion that forms part of a current-carrying path connecting the electrode pad and an external device;
A brazing material part for electrically joining the electrode pad and the joint part of the metal terminal part;
A coating film covering at least a part of the metal terminal part and at least a part of the brazing material part directly or via another member;
A method of manufacturing a ceramic heater comprising:
The coating film is formed mainly of Cr,
A coating film forming step of forming the coating film by performing electrolytic plating by immersing at least a part of the metal terminal part and at least a part of the brazing material part in an electrolytic plating solution mainly containing Cr;
Before the coating film forming step, as a base of the coating film, has a base film forming step of forming a base film mainly composed of Ni covering the metal terminal portion and the brazing material portion,
The electrolytic plating solution is mainly composed of chromic anhydride, and sulfuric acid , trivalent chromium and sodium fluorosilicate are added,
The concentration of the chromic anhydride in the electrolytic plating solution is 250 ± 50 g / L,
The concentration of the sulfuric acid in the electrolytic plating solution is 1.2 ± 0.4 g / L,
The concentration of the trivalent chromium in the electrolytic plating solution is 1.5 ± 0.5 g / L,
The concentration of the sodium fluorosilicate in the electrolytic plating solution is 6.0 ± 2.0 g / L.
Manufacturing method of ceramic heater.