JP6889062B2 - Manufacturing method of cathode electrode of UV sensor and UV sensor - Google Patents

Description

The present invention relates to a method for manufacturing a cathode electrode of an ultraviolet sensor that detects ultraviolet rays based on a current generated by a discharge between an anode electrode and a cathode electrode, and an ultraviolet sensor.

Conventionally, in various industrial furnaces such as drying furnaces for painting lines of automobile bodies and parts, melting furnaces for aluminum and zinc die casting, and heat treatment furnaces for quenching metal parts, ultraviolet rays have been used as flame detection sensors for combustion safety devices. A sensor is used.

The configuration of the ultraviolet sensor used as the flame detection sensor will be described with reference to FIG. 15 (see, for example, Patent Documents 1 and 2).

In FIG. 15, reference numeral 11 denotes a glass package made of borosilicate glass. In the glass package 11, a special mixed gas (mixed gas of Ne and H2) is sealed in the internal space at a constant pressure. Further, a top plate 12 is provided on the upper surface of the glass package 11, and glass capable of transmitting ultraviolet rays is used for the top plate 12. Further, inside the glass package 11, a disc-shaped cathode electrode 13 and an anode electrode 14 are provided so that their surfaces (electrode surfaces) face each other with a predetermined gap between them.

One end of a plurality of conductive columns 15 (15-1 to 15-3) that support the anode electrode 14 from the direction in which the cathode electrode 13 is provided is laser-welded to the anode electrode 14. The other end of the sex column 15 (15-1 to 15-3) is pulled out to the outside of the glass package 11. Further, a plurality of through holes 14a are formed in a mesh shape in the anode electrode 14.

Similar to the anode electrode 14, the cathode electrode 13 is also laser-welded at one end of a plurality of conductive columns 16 (16-1 to 16-3) that support the cathode electrode 13, and the conductive columns 16 (16-1 to 16-3) are laser-welded. The other end of 16-1 to 16-3) is pulled out to the outside of the glass package 11.

In the ultraviolet sensor 1 configured in this way, when the ultraviolet rays that have passed through the top plate 12 reach the cathode electrode 13 through the through holes 14a of the anode electrode 14, electrons are emitted by the photoelectric effect, and then the enclosed gas / voltage is generated. Causes an electron avalanche to start discharging. That is, a current flows between the anode electrode 14 and the cathode electrode 13, and based on the current flowing between the anode electrode 14 and the cathode electrode 13, only the ultraviolet rays having a specific wavelength that have passed through the top plate 12 are the ultraviolet sensor 1. Detected by.

The photoelectric effect is a phenomenon in which internal electrons are excited when a substance absorbs light, and the electrons are ejected accordingly. In this photoelectric effect, the energy required to extract one electron from the surface of the substance is called the work function. The energy of the incident light is hν, the work function is w, and the kinetic energy of the electrons ejected from the substance is E. In the case (see FIG. 16), it is expressed as E = hν-w.

Japanese Unexamined Patent Publication No. 2012-255730 JP-A-2015-115228

In the conventional ultraviolet sensor, tungsten (W) is used as the electrode material of the cathode electrode. With this W electrode type ultraviolet sensor, there are fields (reaction furnaces in chemical plants, sulfur recovery furnaces in refineries, waste liquid treatment plants, etc.) where flames cannot be detected. In such a field, it is desired to change the electrode material of the cathode electrode to expand the critical sensitivity wavelength (cutoff wavelength), for example, 260 nm to 300 nm.

The critical sensitivity wavelength of the ultraviolet sensor is determined by the work function of the cathode electrode, and the work function is determined by the material and plane orientation of the electrode. FIG. 17 shows the work function and the critical sensitivity wavelength defined for each type of metal. Even for the same metal, the work function and the critical sensitivity wavelength do not have a single value, but have a variation range.

This has a plurality of metal plane orientations such as (200), (220), and (111), and takes a predetermined value in which the work function and the critical sensitivity wavelength differ for each plane orientation (see FIG. 18). Since the (200) plane, the (220) plane, the (111) plane, etc. are randomly mixed in the metal, the mixing condition (distribution) of the plane orientations of the same type of metal is different, resulting in different values. Because it becomes. In the plane orientations (200) and (220), the atomic densities are the same as the plane orientations (100) and (110), and the work function and the critical sensitivity wavelength are also the same values as the plane orientations (100) and (110). Become.

Metals are classified into a body-centered cubic structure (W: tungsten, etc.) and a face-centered cubic structure (Cu, Ni: copper, nickel, etc.) according to the crystal structure. The metal of the body-centered cubic structure and the metal of the face-centered cubic structure differ in the magnitude relationship of the work function on each of the (200) plane, (220) plane, and (111) plane, and the metal of the body-centered cubic structure. The magnitude relation of the work function of is (111) plane <(200) plane <(220) plane, but the magnitude relation of the work function of the metal having a face-centered cubic structure is (220) plane <(200) plane < (111) plane.

Further, when a strong process such as rolling is performed, the plane orientation of the metal is oriented to a specific plane orientation (see FIGS. 19A and 19B). This structure is called a rolled texture. The plane orientation of the rolled texture of Cu or Ni is (220). When heating is performed, recrystallization occurs and the plane orientation is oriented to another plane orientation (see FIGS. 19 (b) and 19 (c)). This structure is called a recrystallized texture. The plane orientation of the recrystallized texture of Cu and Ni shows (200).

From the relationship shown in FIG. 18, if Cu is used as the electrode material of the cathode electrode and Cu is used as the rolled texture ((220) plane), the critical sensitivity wavelength can be set to 277 nm. However, in reaction furnaces of chemical plants, sulfur recovery furnaces of refineries, waste liquid treatment plants, etc., there is a demand for further expansion of the critical sensitivity wavelength.

The present invention has been made to solve such a problem, and an object of the present invention is to provide an ultraviolet sensor capable of expanding the critical sensitivity wavelength to 280 nm or more.

In order to achieve such an object, the present invention presents a method for manufacturing a cathode electrode of an ultraviolet sensor (1) that detects ultraviolet rays based on a current generated by a discharge between an anode electrode (14) and a cathode electrode (13). In addition, a rolling step (S101) of rolling the first metal and a second metal having a work function smaller than that of the first metal are formed on the surface of the first metal rolled by the rolling step. It is characterized by including a film forming step (S102) for forming a film and a grain boundary diffusion step (S103) for diffusing the first metal to the second metal formed by the film forming step.

In the present invention, for example, the first metal is nickel and the second metal is copper. That is, copper is formed on nickel. In this case, nickel is diffused at the grain boundaries to the formed copper by the grain boundary diffusion step. When two substances with different work functions are brought into contact with each other, electrons move from a substance having a small work function to a substance having a large work function. In the case of copper and nickel, copper has a smaller work function, so electrons move from copper to nickel. As a result, the amount of electron exudation of copper in the portion in contact with nickel is reduced, the barrier of electron emission from copper is reduced, and the work function is reduced. This makes it possible to expand the critical sensitivity wavelength to 280 nm or more. The first metal may be an alloy of nickel and copper (cupronickel), and the nickel in the cupronickel may be diffused to the formed copper by the grain boundary diffusion step. Cupronickel is easier to obtain than nickel.

In the above description, as an example, the components on the drawing corresponding to the components of the invention are indicated by reference numerals in parentheses.

As described above, according to the present invention, the first metal is rolled, and a second metal having a work function smaller than that of the first metal is formed on the surface of the rolled first metal. Then, the first metal is diffused at the grain boundary to the formed second metal. Therefore, for example, when the first metal is nickel and the second metal is copper, the nickel is granulated on the copper. By making it field diffuse, it is possible to reduce the barrier of electron emission from copper and expand the critical sensitivity wavelength to 280 nm or more.

FIG. 1 is a process diagram for explaining an embodiment of a method for manufacturing a cathode electrode of an ultraviolet sensor according to the present invention. FIG. 2 is a diagram showing the results of X-ray diffraction measurement of rolled cupronickel. FIG. 3 is a diagram showing a cross-sectional image of the rolled cupronickel. FIG. 4 is a diagram showing the results of X-ray diffraction measurement of the surface of copper-plated cupronickel. FIG. 5 is a diagram showing a cross-sectional image of copper-plated cupronickel. FIG. 6 is a diagram showing a work function of copper plane orientation (111) and a critical sensitivity wavelength. FIG. 7 is a diagram showing the results of X-ray diffraction measurement of the surface of copper-plated cupronickel after heat treatment. FIG. 8 is a diagram showing a cross-sectional image of copper-plated cupronickel after heat treatment. FIG. 9 is a diagram showing the work function of the plane orientation (200) of copper and the critical sensitivity wavelength. FIG. 10 is a diagram schematically showing a state in which nickel in cupronickel is diffused at grain boundaries to copper plating. FIG. 11 is a diagram illustrating the transfer of electrons from copper plating to nickel. FIG. 12 is a diagram illustrating how electrons are seeping out from the surface of the metal. FIG. 13 is an image diagram of a change in the amount of electron exudation in a state where nickel (Ni) is diffused at grain boundaries in copper (Cu). FIG. 14 is a diagram showing the results of spectroscopic measurement of the Cu electrode as the surface (220) of the present application. FIG. 15 is a perspective view showing a main part of the ultraviolet sensor. FIG. 16 is a diagram for explaining the relationship between the kinetic energy of electrons ejected by the photoelectric effect, the energy of incident light, and the work function. FIG. 17 is a diagram illustrating a work function and a critical sensitivity wavelength defined for each type of metal. FIG. 18 is a diagram illustrating a work function and a critical sensitivity wavelength taken by each plane orientation for each metal material. FIG. 19 is a diagram showing a change in crystal structure from an untreated state to a rolled texture and a recrystallized texture.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In this embodiment, as shown in FIG. 1, cupronickel (an alloy of nickel and copper (in this example, nickel (30%) and copper (70%)) is rolled as the first metal (step S101). ), Next, copper is formed on the surface of the rolled cupronickel as a second metal having a work function smaller than that of cupronickel (step S102), and the formed copper (copper plating) is formed. ), The nickel in the cupronickel is diffused at the grain boundary (step S103).

In the present embodiment, the first metal is cupronickel, but nickel may be used. In this embodiment, cupronickel is used as the first metal because it is more easily available than nickel.

When the cupronickel is rolled in step S101, the plane orientation of the cupronickel is oriented to (220). FIG. 2 shows the X-ray diffraction measurement results of the rolled cupronickel. As can be seen from the X-ray diffraction measurement result, (220) is the maximum plane orientation of the rolled cupronickel.

FIG. 3 shows a cross-sectional image of the rolled cupronickel. In this figure, the rolled cupronickel is indicated by reference numeral 21. The rolling process of cupronickel may be performed before delivery of cupronickel. That is, it may be performed by the manufacturer that supplies cupronickel.

In step S102, the surface of the rolled cupronickel 21 is plated with copper (10 μm). FIG. 4 shows the results of X-ray diffraction measurement on the surface of copper-plated cupronickel. As can be seen from the X-ray diffraction measurement result, (111) is the maximum plane orientation of the surface of the copper-plated cupronickel. FIG. 5 shows a cross-sectional image of copper-plated cupronickel. In this figure, the copper plating applied to the surface of cupronickel 21 is indicated by reference numeral 22.

As shown in FIG. 6, the plane orientation (111) of copper has a work function of 4.94 and a limit sensitivity wavelength of 252 nm. Therefore, if cupronickel is plated with copper, the limit sensitivity is limited. No expansion of wavelength can be expected.

In step S103, the nickel in the cupronickel 21 is diffused to the copper plating 22 at the grain boundary, and heat treatment is performed before the grain boundary diffusion to make the cupronickel 21 a recrystallized texture. This heat treatment is performed at 1000 ° C. for 0 minutes. That is, under the conditions of 1000 ° C. and 0 minutes, the mixture is rapidly heated and then rapidly cooled to room temperature.

By this heat treatment, the plane orientation of the cupronickel 21 is oriented to (200), and the surface orientation of the copper plating 22 is (200) due to the influence. FIG. 7 shows the X-ray diffraction measurement results of the surface of the copper-plated cupronickel after the heat treatment. FIG. 8 shows a cross-sectional image of copper-plated cupronickel after heat treatment.

Next, in step S103, the heat-treated cupronickel 21 and the copper plating 22 are reheated by electric discharge treatment or heat treatment to diffuse the nickel in the cupronickel 21 to the copper plating 22.

When this reheating is performed by an electric discharge treatment, the spatter particles adhering by the electric discharge are (111), but tend to adhere to the grain boundaries, and (200) formed by the heat treatment remains. The work function is dominated by (200). When the work function of the surface of the copper plating 22 is (200), as shown in FIG. 9, the work function is 4.59 and the critical sensitivity wavelength is 271 nm.

Further, the diffusion of nickel into the copper plating 22 is promoted at the temperature of the plasma (about 500 ° C.) due to this discharge. FIG. 10 schematically shows a state in which the nickel in the cupronickel 21 is intergranularly diffused to the copper plating 22. In FIG. 10, nickel whose grain boundaries are diffused to the copper plating 22 is indicated by reference numeral 23.

When two substances with different work functions are brought into contact with each other, electrons move from a substance having a small work function to a substance having a large work function. In the state shown in FIG. 10, since the copper plating 22 has a smaller work function than the nickel 23, electrons move from the copper plating 22 to the nickel 23 (see FIG. 11). As a result, the amount of electron exudation of the copper plating 22 in the portion in contact with the nickel 23 is reduced, and the barrier of electron emission from the copper plating 22 is reduced.

FIG. 12 shows how electrons are seeping out from the surface of the metal. In FIG. 12, the figure on the left is a graph of electron distribution in a cross section from the inside of a solid across the surface to a vacuum, and the figure on the right is a graph of the positive charge and electron charge density of nuclei in that cross section. Unlike bulk, electrons near the surface have a weak force to be attracted to positively charged nuclei and exude into a vacuum. Since the electrons seep out from the surface into the vacuum, positive electric dipoles are generated on the solid side and negative on the vacuum side. The work function is affected by the electronic state of the surface because this electric dipole interacts with the electrons coming out of matter. Since the exuding electrons serve as a barrier when extracting internal electrons, the work function becomes large when the amount of exuding is large, and small when the amount of exuding is small.

FIG. 13 shows an image diagram of a change in the amount of electron exudation in a state where nickel (Ni) is diffused at grain boundaries in copper (Cu). Since the exuding electrons are pulled by Ni, the amount of Cu electrons exuding from the portion in contact with Ni is reduced, and the barrier for electron emission from Cu is reduced.

In this way, in the present embodiment, by diffusing the nickel 23 in the cupronickel 21 into the copper plating 22, the amount of electron exudation of the copper plating 22 in the portion in contact with the nickel 23 is reduced. The barrier to electron emission from the copper plating 22 becomes smaller, and the work function becomes smaller. By using the electrode obtained by diffusing nickel 23 in cupronickel 21 into the copper plating 22 as the cathode electrode (Cu electrode) 13 of the ultraviolet sensor 1 shown in FIG. 15, the critical sensitivity wavelength of the ultraviolet sensor 1 can be set. It can be enlarged to 280 nm or more.

FIG. 14 shows the results of spectroscopic measurement of the Cu electrode as the surface (220) of the present application. In FIG. 14, the horizontal axis represents the wavelength (nm), the vertical axis represents the number of discharges, I indicates the spectroscopic measurement result of the Cu electrode of the present application, and II indicates the spectroscopic measurement result of the Cu electrode having the (220) plane. In the Cu electrode having the (220) plane, the limit sensitivity wavelength is 277 nm, but in the Cu electrode of the present application, the limit sensitivity wavelength is 280 nm or more.

The grain boundary diffusion treatment (heat treatment + reheating) in step S103 may be performed in a state where the copper-plated 22-coated cupronickel 21 is incorporated as the cathode electrode of the ultraviolet sensor 1, and may be used as the cathode electrode. It may be performed in the state before incorporating.

[Extension of Embodiment]
Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the structure and details of the present invention within the scope of the technical idea of the present invention.

1 ... UV sensor, 11 ... Glass package, 13 ... Cathode electrode (Cu electrode), 14 ... Anode electrode, 21 ... Rolled cupronickel, 22 ... Copper plating, 23 ... Nickel.

Claims (3)

A method for manufacturing a cathode electrode of an ultraviolet sensor that detects ultraviolet rays based on a current generated by a discharge between an anode electrode and a cathode electrode.
The rolling process of rolling the first metal and
A film forming step of forming a second metal having a work function smaller than that of the first metal on the surface of the first metal rolled by the rolling step.
A method for manufacturing a cathode electrode of an ultraviolet sensor, which comprises a grain boundary diffusion step of diffusing the first metal to the second metal formed by the film forming step. In the method for manufacturing a cathode electrode of an ultraviolet sensor according to claim 1.
The grain boundary diffusion step is
A method for manufacturing a cathode electrode of an ultraviolet sensor, which comprises heat-treating the first metal before diffusing the first metal into the second metal to form a recrystallized texture of the first metal. In the method for manufacturing a cathode electrode of an ultraviolet sensor according to claim 2.
The grain boundary diffusion step is
The cathode electrode of an ultraviolet sensor, which comprises reheating the heat-treated first metal and the second metal to diffuse the first metal to the second metal. Production method.

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