JP2022174406A - MoSi2 HEATER AND TERMINAL MEMBER FOR THE HEATER, AND METHOD OF MANUFACTURING MoSi2 HEATER AND METHOD OF MANUFACTURING TERMINAL MEMBER FOR THE HEATER - Google Patents

Abstract

To provide a MoSi2 heater in which peeling of a metal film formed on an electrode portion is prevented, which therefore can be long-lived, and to provide a terminal member for use in the heater.SOLUTION: An MoSi2 heater is provided, comprising: a heat generating portion; a terminal portion; and an electrode portion provided at one end of the terminal portion. The electrode portion is constituted by covering the surface of the MoSi2 base material with a metal film. The diameter of the terminal portion: the diameter of the base material of the electrode portion are 1:0.91-0.98.SELECTED DRAWING: None

Description

The present invention relates to a _MoSi2 heater, a terminal member for the heater, a method for manufacturing the _MoSi2 heater, and a method for manufacturing the terminal member for the heater.

Since MoSi ₂ (molybdenum disilicide) heaters have excellent oxidation resistance, they have long been used as ultra-high temperature heaters for use in the air or in an oxidizing atmosphere, and have been used in a wide range of applications up to now. This heater contains MoSi ₂ as a main component, and an insulating oxide such as SiO ₂ is sometimes added to increase the electrical resistance. In the present disclosure, a MoSi ₂ heater refers to one made of a material containing 70 wt % or more of MoSi ₂ .

Currently, _MoSi2 heaters used in the glass industry, ceramics firing, and many other fields have U-shaped (Fig. 1(a)), L-shaped (Fig. 1(b) ), W-shaped or multi-U-shaped (Fig. 1(c)), three-dimensional U-shaped (Fig. 1(d)), multi-circumferential U-shaped (Fig. 1(e)), thermal insulation embedded type ( There are various shapes and sizes, such as FIG.

FIG. 2 shows a schematic diagram of a conventional U-shaped heater. Although there are various shapes of heaters, basically, they are composed of a heating portion 23 and terminal portions 21 at both ends, and an electrode portion 22 connected to an external power supply is provided at one end of the terminal portion. there is When the heater is energized, the high-resistance, thin-diameter part becomes hot and plays the role of a heat-generating part. play the role of The diameter of the heat generating portion and the diameter of the terminal portion have a relationship of about 1:2.

Currently commercially available MoSi ₂ heaters have diameters of the heating part and the terminal part of 3 mm/6 mm, 4 mm/9 mm, 6 mm/12 mm, 9 mm/18 mm, 12 mm/24 mm, etc., respectively. The length of the electrode part is 25 mm (diameter of terminal part: 6 mm, 9 mm), 45 mm (diameter of terminal part: 12 mm), 75 mm (diameter of terminal part: 18 mm), 100 mm (diameter of terminal part: 24 mm). , etc. In this way, there are industry standard values for the combination of the thickness of the heating portion and the thickness of the terminal portion, or the length of the electrode portion.

FIG. 3 shows an example of how the _MoSi2 heater is connected to an external power source. An aluminum braided wire 31 is connected to the electrode portion 33 and fixed with a metal fitting (clamp) 32, and power is supplied from an external power supply to the terminal portion 34 via the electrode portion. A bundle of the aluminum braided wire and the clamp is also called a connecting band. FIG. 3(a) is a photograph of a state in which the connecting band is attached to the heater. In the photograph, the connecting band is attached only on one side for convenience of explanation. A belt is attached. FIG. 3(b) is a schematic diagram (front view) of a case where a connection band is attached to the electrode portion of the heater, and FIG. 3(c) is a top view (plan view) of FIG. 3(b). be.

Generally, the electrode portion of the MoSi ₂ heater is formed with a metal film (such as an Al sprayed film) on its surface in order to improve electrical connection. In the process of forming a metal film by thermal spraying, first, blasting is performed for the purpose of removing the insulating oxide film on the surface of the base material to ensure conductivity, and for the purpose of improving the adhesion of the thermal spraying film. or electric thermal spraying. In order to prevent deterioration of the electrode portion of the heater, it is possible to form a metal film on the portion of the electrode portion from which the oxide film has been removed, and to overlap the portion of the terminal portion from which the oxide film has not been removed with the metal film. (Patent Document 1).

JP-A-2000-48937

The present invention provides a _MoSi2 heater capable of preventing peeling of a metal film formed on an electrode portion and enabling a longer life of the heater, a terminal member used for the heater, a method for manufacturing the _MoSi2 heater, and the heater. An object of the present invention is to provide a method for manufacturing a terminal member.

One embodiment of the present invention is a _MoSi2 heater comprising a heat generating portion, a terminal portion, and an electrode portion provided at one end of the terminal portion, wherein the electrode portion is a _MoSi2 substrate surface coated with a metal film. and the diameter of the terminal part: the diameter of the base material of the electrode part= ₁ :0.91 to 0.98.
Another aspect of the present invention is a terminal member for a _MoSi2 heater comprising a terminal portion and an electrode portion provided at one end of the terminal portion, wherein the electrode portion covers the surface of the _MoSi2 base material with a metal film. and the diameter of the terminal part: the diameter of the substrate of the electrode part= ₁ :0.91 to 0.98.

EFFECTS OF THE INVENTION According to the present invention, in a _MoSi2 heater, it is possible to prevent peeling of the metal film formed on the electrode portion and to extend the life of the heater.

Fig. 4 is an illustration of the geometry of the _MoSi2 heater; FIG. 2 is an illustration of a conventional MoSi ₂ heater (in the case of U-shape); FIG. 4 is an explanatory view showing attachment of a connecting band to a heater electrode; ₂ is a SEM photograph showing a cut surface (perpendicular to the axial direction) of a MoSi2 material. It shows the relationship between the diameter of the substrate and the thickness of the low-density layer in the electrode portion. FIG. 4 is an explanatory diagram showing an example of the processing order of the MoSi ₂ heater (in the case of U-shape) of the present embodiment; It is a SEM photograph of a cut surface (perpendicular to the axial direction) of bar A. 4 is a SEM photograph of a cut surface (perpendicular to the axial direction) of bar material B; 4 is SEM photographs for observing the presence or absence of peeling of the metal films of Example 1 and Comparative Example 1. FIG. 4 is SEM photographs for observing the presence or absence of peeling of the metal films of Example 2 and Comparative Example 2. FIG. It summarizes the results of the peeling test of the metal films of the examples and the comparative examples.

The terminal part of the MoSi ₂ heater has a smaller resistance heating than the heat generating part, but the electrode part provided at one end of the terminal part (hereinafter also referred to as the terminal electrode part) has a high temperature from the heat generating part. Heat conduction increases the temperature. Further, depending on the structure of the furnace, the electrode portion may be a closed space. Generally, it is recommended that the temperature of the electrode portion of the MoSi ₂ heater be 300° C. or less, but it may be used at a temperature higher than 300°C.

MoSi ₂ causes simultaneous oxidation of Mo and Si at low temperatures (300° C. to 800° C.). This is the so-called plague phenomenon. _In general, the electrode part is coated with a metal film by spraying a metal such as aluminum. Oxygen reaches up to At this time, simultaneous oxidation of Mo and Si in _MoSi2 occurs at the interface between the _MoSi2 base material and the metal film, creating a gap at the interface that expands with time, and eventually the metal film peels off. be. If the metal film is peeled off, the electrical resistance increases at that portion, and the terminals are disconnected due to abnormal heat generation or sparks, and the life of the heater ends.

When the present inventor observed the structure of the cross section perpendicular to the axial direction of the _MoSi2 substrate, as shown in FIG. We discovered the existence of a low-density layer that A detailed investigation also confirmed that the thickness of the low-density layer varied with the diameter of the _MoSi2 substrate, as shown in FIG.

Normally, when forming a metal film on the electrode part, blasting is performed to remove the oxide film of the _MoSi2 base material and improve the adhesion of the sprayed film, but the removed area is at most about 20 μm. Therefore, it is not removed up to this low density layer, and therefore metal film deposition is performed on this low density layer. However, the inventors of the present invention removed this low-density layer, applied a normal blasting treatment, and then formed a metal film. Found it.

Based on the above findings, the MoSi ₂ heater in one embodiment of the present invention is a MoSi ₂ heater including a heat generating portion, a terminal portion, and an electrode portion provided at one end of the terminal portion, wherein the electrode portion is MoSi ₂ The surface of the base material is covered with a metal film, and the diameter of the terminal part: the diameter of the base material of the electrode part=1:0.91 to 0.98.
In the electrode part, the low-density layer is removed, the diameter of the base material of the electrode part is made smaller than the diameter of the terminal part, and then the metal film is coated, so that the interface between the MoSi ₂ base material and the metal film Simultaneous oxidation of Mo and Si is suppressed, and peeling of the metal film at the electrode portion is less likely to occur. Since the metal film is less likely to peel off, disconnection at the electrode portion is eliminated, and the life of the heater itself can be extended.

The low-density layer has a thickness of 60 to 220 μm (nominal substrate diameter: 6 mm) and a thickness of 75 to 250 μm (nominal substrate diameter: 9 mm) from the outermost surface of the MoSi ₂ substrate toward the inside (axis center). , with a thickness of 180-520 μm (nominal substrate diameter: 12 mm). The thickness of this low-density layer is 0.9 to 3.7% (nominal substrate diameter: 6 mm), 0.8 to 2.8% (nominal substrate diameter: 9 mm), This corresponds to 1.5-4.5% (nominal substrate diameter: 12 mm). Since the base material is ground for the purpose of removing this low-density layer, the diameter of the base material of the electrode portion becomes smaller than the diameter before grinding (corresponding to the diameter of the terminal portion). The amount of grinding can be determined in consideration of the diameter of the substrate and the thickness of the low-density layer to be formed.

When the density of the outer peripheral layer of the _MoSi2 substrate is low, oxygen that reaches the interface is widely supplied to the outer peripheral layer through the pores, and the presence of the pores increases the specific surface area of _{MoSi2 .} The plague phenomenon is more likely to occur than when the outer peripheral layer of the substrate has a high density. Therefore, by removing the low-density layer existing on the outer periphery of the electrode portion and setting the diameter of the terminal portion: the diameter of the base material of the electrode portion = 1: 0.91 to 0.98, the low-density layer is removed. By forming a metal film on the base material having been coated, the plague phenomenon can be suppressed, and peeling of the metal film can be prevented.

For example, when the nominal base material diameter is 12 mm, the diameter of the base material of the electrode portion after grinding is 10.92 mm to 11.64 mm (the diameter ratio of the base material of the terminal portion to that of the electrode portion is 1:0.91 to 0.91 mm). 97). This corresponds to reducing the diameter of the base material of the electrode portion by 0.36 mm to 1.08 mm by setting the substantial grinding amount of one side of the base material to 0.18 mm to 0.54 mm. This grinding will remove the low density layer (0.18-0.52 mm). Since the thickness of the low-density layer varies depending on the diameter of the substrate, it is preferable to change the amount of grinding according to the diameter.

_Usually , the _MoSi2 base material is produced by molding and firing a raw material powder containing _MoSi2 as a main component. It is processed. Therefore, the glass component (oxide) located at the outer periphery of the _MoSi2 substrate evaporates during high-temperature firing, generating a large number of pores in the outer peripheral layer and forming a low-density layer. The region (thickness) in which the low-density layer is formed varies depending on the composition and particle size of the raw material, the firing conditions, the diameter of the substrate, and the like. Therefore, using SEM images etc. in advance, the thickness at which the low density layer is formed is grasped, the amount of grinding is determined so that the low density layer is removed, and the MoSi ₂ substrate after grinding (that is, , the substrate from which the low-density layer has been removed) is used as a base layer to form a metal film, the effect of the present invention can be obtained. However, it is not necessary to grind beyond the removal of the low density layer, as too much grinding may increase the resistance and reduce the strength.

In this embodiment, the metal film can be formed using methods such as thermal spraying, plating, and ion plating. In particular, an Al or Al alloy film is effective. Also, the metal film is preferably formed to a thickness of 50 μm or more and 300 μm or less. Also, before forming the metal film, it is preferable to perform a blasting treatment in order to remove the oxide film and improve adhesion. Sandblasting etc. are mentioned as a blasting process.

In this embodiment, a metal film is formed on the portion from which the low-density layer has been removed to form the electrode portion. Oxygen easily penetrates in the step portion) due to its structure. Therefore, intrusion of oxygen can be effectively suppressed by forming the metal film so as to overlap the portion where the low-density layer is not removed in the longitudinal direction of the terminal member. In a preferred form, the metal film is preferably formed so as to overlap the portion where the low-density layer is not removed within a range of 0.4 mm or more and 2 mm or less from the boundary to the terminal portion.

An example of the processing procedure of the MoSi ₂ heater (in the case of U-shape) according to this embodiment will be described with reference to FIG. Note that the present embodiment is not limited to this processing procedure, and may be manufactured using other processing methods and processing procedures.
Fig. 6(a): A raw material containing _MoSi2 as a main component is shaped and fired to produce a _MoSi2 bar. This will later become a terminal member. Although the description of the heat generating portion is omitted, a MoSi ₂ bar having a diameter smaller than that of the terminal member is produced. Raw materials, molding, and firing conditions are not particularly limited, and general methods and conditions may be used.

FIG. 6(b): One end of the MoSi ₂ bar is cut as thin as a pen tip. This will be the part where the heat generating part will be attached later. There is an industry standard for the relationship between the thickness of the terminal part and the thickness of the heat generating part, so the diameter of the pen tip can be determined according to it. In addition, the inclination ratio (height: length) from the terminal portion to the heat generating portion can also be determined as appropriate.
Next, at the other end of the MoSi ₂ bar, the low-density layer of the electrode portion is removed. Cutting is a convenient method for removal, but grinding (polishing) can also be used. In addition to the mechanical processing, other methods such as laser processing may be used. At this time, it is preferable to previously observe the cross section perpendicular to the axial direction of the MoSi ₂ material with an SEM image to grasp the thickness of the low-density layer, and grind the thickness accordingly.

FIG. 6(c): The removed portion is thermally sprayed with aluminum. Here, aluminum thermal spraying is used as an example, but since it is sufficient to form a metal film, other metals such as nickel, chromium, and titanium and other film formation methods can be used. Further, in order to increase the adhesion of the aluminum sprayed film (an example of the metal film), it is preferable to roughen the surface of the removed portion by blasting (Fig. 6 (c-1
)). Blasting is an optional step because the oxide film on the _MoSi2 substrate has been removed in the previous step.
Furthermore, it is preferable to form the aluminum sprayed film (an example of the metal film) slightly outside the cut portion (on the terminal portion side including the stepped portion) (FIG. 6(c-2)). As a result of the above removal, a step is formed between the terminal portion and the electrode portion, and MoSi ₂ is exposed, so that oxygen can easily enter. Therefore, in order to prevent oxygen from entering, it is preferable to perform aluminum thermal spraying so as to partially overlap the terminal portion.

FIG. 6(d): MoSi ₂ bar is bent into a U shape. This MoSi ₂ bar will eventually become a heat generating portion, and has a smaller thickness (diameter) than the MoSi ₂ bar (terminal member) described above. In the case of producing a W-shaped heater, three U-shaped bars may be alternately combined in opposite directions to produce a three-dimensional U-shaped or multi-circumferential U-shaped heater. In some cases, it can be produced by three-dimensionally combining a plurality of U-shaped bars. Further, depending on the application, the shape may be linear or curved instead of U-shaped.

Fig. 6(e): A U-shaped MoSi ₂ heater is manufactured by joining the terminal member sprayed with aluminum (Fig. 6(c)) and the heat generating part bent into a U-shape (Fig. 6(d)). do. The bonding method is not particularly limited, and a crimping method (also referred to as current welding) using current or induction heating, which is generally performed for MoSi ₂ , can be used. In addition, although a U-shape is shown here as an example, terminal members (FIG. 6(c)) may be welded to both ends of the heat generating portion as a heater, so one or more of the heat generating portions excluding both ends may be appropriately By combining and welding, etc., the shape of the heater can be designed relatively freely.

The processing method of the _MoSi2 heater according to the embodiment of the present invention is as described above, but the terminal member alone as shown in FIG. 6(c) can also be handled. Accordingly, a terminal member for a _MoSi2 heater according to another embodiment is a terminal member for a _MoSi2 heater having a terminal portion and an electrode portion provided at one end of the terminal portion, wherein the electrode portion is It is constructed by covering the surface of a MoSi ₂ base material with a metal film, and is characterized in that the diameter of the terminal portion: the diameter of the base material of the electrode portion=1:0.91 to 0.98.

Hereinafter, description will be made based on examples and comparative examples. It should be noted that this embodiment is merely an example, and the present invention is not limited by this example. That is, the present invention is limited only by the scope of the claims, and includes various modifications other than the examples included in the present invention.

(Production of bar material)
MoSi ₂ powder and SiO ₂ powder were weighed at a ratio of 96:4 (wt%), mixed and pulverized with a pulverizer so that the average particle size was 5 μm, then 10 wt% of a binder was added and mixed with a mixer. gone. Next, this mixture was molded into a bar shape using an extruder, degreased in a nitrogen atmosphere, and sintered in an argon atmosphere. After that, they were taken out from the furnace and subjected to electrical sintering in the atmosphere to obtain bar A (diameter 6 mm) and bar B (diameter 9 mm).
These bars A and B were cut in the axial direction, and the cut surfaces were observed by SEM. The respective tissue images obtained by cross-sectional SEM are shown in FIGS. As shown in FIG. 7, both bar A and bar B had a low-density layer (thickness of 200 μm) in the outer peripheral layer.

(Example 1, Comparative Example 1)
As Example 1, the bar A was cut at a length of 100 mm, and only one side was cut 200 μm from the surface toward the center (axis) in order to remove the low-density layer at a point of 24 mm from one end. The ratio of the diameter of the uncut portion (corresponding to the terminal portion) to the diameter of the cut portion (corresponding to the base material of the electrode portion) was 1:0.93. Next, the cut portions were blasted to a depth of about 20 μm and then plasma-sprayed with aluminum to form a metal film with a thickness of 160 to 200 μm.
On the other hand, as Comparative Example 1, without removing the low-density layer, a metal film having a thickness of 160 to 200 μm was formed by blasting and plasma spraying aluminum on only one side at a distance of 24 mm from one end.
These aluminum-sprayed bars A were held in the air at 450° C. for 1 to 4 weeks, and the presence or absence of peeling of the metal film was observed. FIG. 9 shows cross-sectional SEM photographs of the bar A after each period. In Example ₁ , no peeling of the metal film was observed even after 1 week and 4 weeks. occurring) was observed. In addition, in Comparative Example 1, the test was not performed for 4 weeks because the film was peeled off after one week.

(Example 2, Comparative Example 2)
As Example 2, the bar material B was cut at a length of 100 mm, and only one side was cut 200 μm from the surface toward the center (axis) at a location 24 mm from one end to remove the low density layer. The ratio of the diameter of the uncut portion (corresponding to the terminal portion) to the diameter of the cut portion (corresponding to the base material of the electrode portion) was 1:0.96. Next, the cut portions were blasted to a depth of about 20 μm and then plasma-sprayed with aluminum to form a metal film with a thickness of 160 to 200 μm.
On the other hand, as Comparative Example 2, a metal film having a thickness of 160 to 200 μm was formed by blasting and then plasma spraying aluminum on one side at a distance of 24 mm from one end without removing the low-density layer.
These aluminum-sprayed rods B were held in the atmosphere at 450° C. for 1 to 4 weeks, and the presence or absence of peeling of the metal film was observed. FIG. 10 shows cross-sectional SEM photographs of the bar B after each period. In Example ₂ , no peeling of the metal film was observed even after 2 weeks and 4 weeks. ) was observed. In addition, in Comparative Example 1, the test was not performed after 2 weeks because the film was peeled off after 1 week. FIG. 11 shows a summary of the results of the metal film peeling test described above.

When manufacturing a MoSi ₂ heater as an industrial product, one side (the side on which the metal film is not formed) of a bar material with a diameter of 6 mm or 9 mm is processed into a pen tip shape, and then U-shaped with a diameter of 3 mm or 4 mm. MoSi ₂ material (equivalent to the heat generating part) is welded to finish the U-shaped heater, but the presence or absence of the above welding is irrelevant in confirming the effect of the present invention, so in the examples and comparative examples, welding A peeling test is performed without

Advantageous Effects of Invention According to the present invention, in a _MoSi2 heater, it is possible to prevent peeling of the metal film formed on the electrode part even in a high-temperature environment, thereby achieving an excellent effect of extending the life of the heater. The MoSi ₂ heater according to the present invention is excellent for use as an ultra-high temperature heater and makes technical contributions in the glass industry, ceramics firing, and many other fields.

21 terminal part 22 electrode part 23 heat generating part 31 aluminum braided wire 32 metal fitting (clamp)
33 electrode section 34 terminal 41 outer layer (low density layer)

Claims (8)

A _MoSi2 heater comprising a heat generating portion, a terminal portion, and an electrode portion provided at one end of the terminal portion, wherein the electrode portion is formed by coating the surface of a _MoSi2 base material with a metal film, and the terminal portion is: A MoSi ₂ heater characterized in that the diameter: the diameter of the substrate of the electrode part=1:0.91 to 0.98. 2. The MoSi ₂ heater according to claim 1, wherein the metal film is formed so as to overlap the terminal portion in the longitudinal direction of the terminal portion. 3. The _MoSi2 heater of claim 1 or 2, wherein the metal film is composed of Al or an Al alloy. A terminal member for a _MoSi2 heater comprising a terminal portion and an electrode portion provided at one end of the terminal portion, wherein the electrode portion is formed by coating the surface of a _MoSi2 base material with a metal film, and the terminal portion is: Diameter: A terminal member for a MoSi ₂ heater, characterized in that the diameter of the base material of the electrode part=1:0.91 to 0.98. 5. The terminal member for MoSi ₂ heater according to claim 4, wherein the metal film is formed so as to overlap the terminal portion in the longitudinal direction of the terminal portion. 6. The terminal member for _MoSi2 heater according to claim 4, wherein the metal film is made of Al or an Al alloy. A method for manufacturing a MoSi ₂ heater having a heating portion, a terminal portion, and an electrode portion provided at one end of the terminal portion, wherein the diameter of the terminal portion: the diameter of the base material of the electrode portion=1:0.91- After grinding the base material of the electrode part so that it becomes 0.98, the surface of the base material of the electrode part is coated with a metal film, and a MoSi ₂ bar serving as a heat generating part is joined to the terminal member. A method of manufacturing a _MoSi2 heater characterized by: A method for manufacturing a terminal member for a MoSi ₂ heater having a terminal portion and an electrode portion provided at one end of the terminal portion, wherein the diameter of the terminal portion: the diameter of the base material of the electrode portion=1:0.91- A method for producing a terminal member for a _MoSi2 heater, characterized in that after grinding the base material of the electrode part to a value of 0.98, the surface of the base material of the electrode part is coated with a metal film.

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