JP3070742B1 - Heating element mainly composed of MoSi2 and method of manufacturing the same - Google Patents

Abstract

An object of the present invention is to improve the durability of a heating element containing MoSi ₂ as a main component and to suppress the occurrence of defects during a manufacturing process. SOLUTION: In the heating element containing 70% or more of MoSi ₂ , the average density of the entire heating element and 1/1/1 of the diameter of the heating element.
A heating element having MoSi ₂ as a main component having a density difference (true density ratio) of 5% or less, and preferably 3% or less from a central portion corresponding to 5 and a heating rate were appropriately adjusted in a pre-sintering process. A method for manufacturing the heating element that is sintered in a temperature pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating element containing 70% or more of MoSi ₂ (molybdenum silicide) (including a heating element and a material in which all components constituting the heating element are MoSi _2.) , "Heating element" and "heating element material"
Are used in this sense. ) And a method for producing the same, particularly, a central portion corresponding to １ ／ of the average density of the entire heating element and the heating element material (base material) and 1/5 of the diameter of the heating element (“central section” in the following description). Means a central portion corresponding to 1/5 of the diameter of the heating element, unless otherwise specified.) And a heating element in which the entire substrate is uniformly sintered, and the production thereof. About the method.

[0002]

_2. Description of the Related Art In the production of a heating element containing MoSi ₂ as a main component, a raw material (MoSi ₂ ) powder adjusted to a predetermined particle size is first formed with a molding aid such as clay mineral (bentonite, etc.), water and an organic binder. And extruded into a predetermined shape, for example, a rod. Next, water, organic binders, etc., which become unnecessary after molding, are removed from the molded body by a drying or degreasing process. The true density ratio of the compact at this time is usually 5
0 to 70%. Temporary sintering (also called primary sintering) in neutral and reducing atmospheres to prevent oxidation of this compact
To increase the true density ratio of the molded body to 70 to 95%. The temporary sintered body thus obtained is heated in a oxidizing atmosphere (including the atmosphere) by applying a current to the temporary sintered body itself (electrical sintering). By this electric current sintering, an oxide film is usually formed on the surface of the sintered body and the true density ratio is 90 to 90.
It is raised to 100%, and is finally finished into a member constituting a heating element. Thereafter, the heat-generating portion and the terminal portion, which are usually made of the same material, are connected by current welding to be put to practical use.

[0003] In the prior art, the relationship between the internal / external difference in the density of the rod-shaped heat generating material and the performance of the heat generating material is not sufficiently clarified. A method for making the density of the sintered body uniform in a process performed continuously is not disclosed. The present inventors have obtained the following findings as a result of earnest studies.
In general, the influence (density difference) is small if the diameter of the rod-shaped body is less than 9φ, but the uniformity of sintering does not proceed with a large-diameter heat generating material of 9φ or more, and the density difference starts to increase gradually. Problem becomes extremely prominent. Although the heating element has a large diameter of 24φ, the increase in the density difference tends to increase as the diameter increases. In this way, the base material that once had a density difference due to temporary sintering does not shrink even if sintering is further advanced in the electric sintering process, so that the density difference remains in the final product that is a heating element. The result was to do. A heat-generating material having a difference in density between the central portion and the peripheral portion of the temporary sintered body (primary sintered body) may generate a porous portion called a "nest" at the center portion during electric sintering, There was a problem that cracks were caused by distortion due to expansion difference.
In addition, when base materials having the same diameter are welded, there is a problem that cracks occur at a welded portion due to a difference in hardness between a central portion and a peripheral portion. In addition, since the low-density central portion is not sufficiently resistant to low-temperature oxidation, once mixed with oxygen, it is easily oxidized and powdered, which is a cause of breakage when used in the grip portion of the heating element. Was.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention is to solve the above drawbacks, heating element density difference at the central portion and the peripheral portion of the heating element is composed mainly of MoSi ₂ with excellent very small durability And a method for producing the same, and in a series of manufacturing steps of forming a heating element by provisional sintering and current sintering of a heating element material, a porous portion called a “nest” is generated at the center,
The problem that cracks occur due to distortion due to the difference in expansion of the heat generating material is reduced. Another object of the present invention is to suppress the occurrence of cracks during welding of the heating element and to prevent the heating element from collapsing due to low-temperature oxidation at the center.

[0005]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, by controlling the density of the heat-generating material as follows, It is clear that durability can be improved. The control method was clarified. 1 In a heating element containing 70% or more of MoSi ₂ ,
A heating element containing MoSi ₂ as a main component, wherein a density difference (true density ratio) between an average density of the entire heating element and a central portion corresponding to 1/5 of a diameter of the heating element is 5% or less. (2) The difference in density (true density ratio) between the average density of the entire heating element and the central portion thereof is 3% or less.
Heating element containing MoSi ₂ as a main component 3 Heating element material containing 70% or more of MoSi ₂ at least in the range of 1350 ° C. to 1650 ° C.
The temperature is gradually raised over 5 hours so that the density difference (true density ratio) between the average density of the entire heating element material and the center corresponding to 1/5 of the diameter of the heating element material is 5% or less. The density difference (true density ratio) between the average density of the entire heating element and the central portion corresponding to 1/5 of the diameter of the heating element is characterized by 5% or less. MoS characterized by being
Method for Manufacturing Heating Element Mainly Containing i ₂ 4 The average density of the heating element material after provisional sintering and the average density of the heating element after electric sintering and the density difference (true density ratio) between the center and 3 are 3
% Or less, MoSi _{2 according to} 3 above,
For producing a heating element containing as a main component

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION A heating element material mainly composed of MoSi ₂ is heated to 1400 to 1650 ° C. to perform temporary sintering (primary sintering). The cause of the density difference between the central portion and the peripheral portion of the body originates from the fact that the peripheral portion of the heating element material to which heat is easily transmitted starts sintering before the central portion. If only the peripheral portion precedes and sinters in the preliminary sintering process, a donut-shaped hard layer is formed in the cross section of the preliminary sintered body, which causes a bridging phenomenon and makes it difficult to shrink the sintering to the central portion. Become. As a result, the density does not increase as the center portion of the base material becomes closer to the peripheral portion, resulting in a difference in density. As described above, in the temporary sintered body once having the density difference due to the temporary sintering, the density difference does not shrink even if the sintering is promoted by electric current sintering (resistance heating) having different heating methods. Therefore, in order to solve this, sintering is performed so that bridging does not occur in temporary sintering.

Generally, in powder sintering, densification progresses with shrinkage in the order of neck formation (shrinkage: small) → neck growth (shrinkage: large) → diffusion to the outside. However, as the diameter of the sintered body increases, a temperature difference occurs between the peripheral portion (near the surface) and the central portion due to the effect of heat transfer, and as a result, the shrinkage speed changes. For example, when the formation of the neck has finally started at the center of the temporary sintered body, the growth of the neck has already progressed at the periphery. Therefore, in the conventional temporary sintering of a simple temperature pattern (constant speed heating, constant temperature holding, etc.),
This tendency was particularly pronounced in a large-diameter sintered body, and bridging was likely to occur. In order to suppress this phenomenon, it is necessary to supply only the minimum necessary energy in accordance with the progress of sintering as needed so as not to cause an undesirable substance transfer (only the peripheral portion is significantly shrunk). I made it. That is, a heating element material containing 70% or more of MoSi ₂ is heated to 1000 to 1300 ° C. in a relatively short time, and then heated from 1350 ° C. to 1650 ° C.
The temperature was gradually raised to the range of ° C over 5 to 15 hours, and the material of the heating element was pre-sintered so that the density difference (true density ratio) between the center and the periphery of the cross section was 5% or less.

[0008] As a result, it is considered that the steps of sintering are uniform on the entire surface of the base material, and sintering shrinkage occurs uniformly in the center direction. Therefore, the present inventors performed sintering in a temperature pattern in which the temperature raising rate was appropriately adjusted in the preliminary sintering, so that even in a large-diameter temporary sintered body, the density was reduced at the center and the peripheral portion of the temporary sintered body. A sintered body with a very small difference was obtained. That is, the density difference (true density ratio) between the central portion and the peripheral portion of the temporary sintered body cross section is 5% or less, and the density difference (true density ratio) is 3%.
% Or less was obtained. As described above, the central portion means the central portion corresponding to 1/5 of the diameter of the heating element. To measure the density of the central portion, fix the central portion and grind the peripheral portion with a lathe. Iki, 1/5 of the original size
(If the original diameter is φ9, φ1.8 becomes the average density) is defined as the density at the center (true density). The density is measured by the ordinary Archimedes method. It was found that when the temporary sintered body thus obtained was electrically sintered at about 1700 ° C., the density of the entire sintered body was uniformly increased, and the resulting heating element was excellent in durability. In the heating element thus obtained, cracks due to the density difference between the central part and the peripheral part may occur even when welding the rod-shaped heating element without generating nests and cracks in the manufacturing process. Absent. In addition, the inside of the heating element (especially when nests are generated) is selectively oxidized during use, and powdering progresses, and the problem of collapse from the inside of the heating element is eliminated.

[0009]

[Examples and Comparative Examples] The diameter after heating materials forming and degreased containing MoSi ₂ 70% or more molded article comprising a rod-like body of .phi.11, Atsushi Nobori pattern shown in a~d in Figure 1 - Was temporarily sintered. FIGS. 1A and 1B show Comparative Examples 1 and 2, and FIGS.
d shows Examples 1 and 2 of the present invention. Table 1 shows the average density and the respective densities of the central portion and the density difference between the average density and the central portion when pre-sintering was performed with each of the heating and heating patterns of a to d. Here, a to d in FIG. 1 correspond to a to d in Table 1. In Comparative Examples 1 and 2 of the heating patterns a and b in Table 1 sintered with a simple heating pattern, the average density of the entire pre-sintered body and the density at the center were 5.7% or more. There was a 10.3% density difference. On the other hand, in the heating and heating patterns c to d of Examples 1 and 2 of the present invention in which only the minimum necessary energy was supplied at any time according to the progress of sintering, the density difference was 0.3% to 2%. An extremely small temporary sintered body of 0.8% was obtained.

[0010]

[Table 1]

(Test 1) Next, the state of occurrence of defects when a temporary sintered body having a low sintered density was electrically sintered was examined. A temporary sintered body having a true density ratio of 88% (Example 3) in which the entire body is uniformly sintered, and a temporary sintered body of Comparative Example 1 in which a heating and heating pattern a having a density difference between a central portion and a peripheral portion are obtained. Sintering at 1700 ° C. for 2 minutes. In Example 3 which was uniformly sintered by the preliminary sintering, the sintered body was uniformly sintered by the electric current sintering, and the true density was 9%.
Up to 9%. On the other hand, the temporary sintered body of Comparative Example 1 having a difference in density is sintered so that the material in the central part having a low density is attracted to the peripheral part during electric sintering, and as shown in FIG. Nest 1 has developed. Reference numeral 2 indicates a cross section of the peripheral portion of the pre-sintered rod, and reference numeral 3 indicates a cross section of the central portion. In addition, as is clear from Table 1, the average preliminary sintered density in FIG.
%, And the density of the central portion 3 is 75.7%.

(Test 2) Next, the state of occurrence of defects was examined when a temporary sintered body having a high sintered density was electrically sintered. A temporary sintered body having a true density ratio of 92% (Example 4) in which the entire body is uniformly sintered and a temporary sintered body of Comparative Example 2 in which a heating and heating pattern b having a density difference between a central portion and a peripheral portion are used. Then, current sintering was performed at 1700 ° C. for 2 minutes. Example 4 in which the pre-sintering was uniformly performed was sound even after the electric sintering, but the pre-sintered body of the comparative example 2 having the density difference was different from the central part during the electric sintering. Cracks 4 occurred at the time of temperature decrease as shown in FIG. 3 due to the difference in thermal expansion in the peripheral portion. Reference numeral 5 is a cross section of the periphery of the temporarily sintered rod-shaped body,
Reference numeral 6 indicates a cross section at the center. As is clear from Table 1, the average preliminary sintering density in FIG. 3 is 93.5%, and the density of the central portion 6 is 87.8%.

(Test 3) Next, the state of occurrence of defects when current welding was performed was examined. Temporary sintered body of Example 1 (average preliminary sintered density is 91.2%, center density is 88.4%, and density difference is 2.8%) in which the density difference is relatively small in Table 1c. 2
The book was electrically sintered. In the electric sintering, the above-mentioned “cavities” and cracks did not occur. Therefore, as shown in FIG. 4, in order to manufacture a long heating element using these two rods 8, 9, electric current welding was performed in which both end faces 10 were contacted and pressurized while energizing. In the electric welding, the welding surface was crushed and deformed. At this time, the rod-shaped presintered body having a difference in density had cracks 7 as shown in FIG. On the other hand, when welding was performed using a sintered body after current sintering with a very small density difference (corresponding to Example 2 having a density difference of 0.3% or less), welding was performed without any cracks on the weld surface. did it. As can be seen from the above, in the case of undergoing strong deformation, a relatively small density difference of 2.8% between the peripheral portion and the central portion is insufficient, and the density difference is further small, preferably 2.0%. Is preferably 1% or less.

(Test 4) An electrically conductive sintered material of φ18 having a true density ratio of 95.0% (Example 5) in which the whole was uniformly sintered, the average electrically conductive sintered density was 95.2%, and the density of the central part. 83.0%
A low-temperature oxidation resistance test was performed using the current-carrying sintered material (Comparative Example 3). Each substrate was cut to a length of 100 mm, and the temperature cycle (200 ° C. to 480 ° C.) shown in FIG. 5 was repeated in the atmosphere. In this temperature range, since excellent oxidation resistance is not formed and a SiO ₂ film is not formed, simultaneous oxidation of Mo and Si occurs to form a powder. Comparing both base materials after 100 cycles, the base material having a difference in density (Comparative Example 3) has a low density at the center and a large contact area with oxygen, so that oxidation is considerably advanced, and powdering from the inside occurs. It was no longer able to keep its original form. On the other hand, in the high-density base material having no difference in density, although the powdering slightly occurred in the surface layer portion, the inside was healthy without any oxidation. Therefore, assuming that electricity is supplied as a heating element, the conventional base material having a density difference between the central portion and the peripheral portion is broken, but the product of the present invention is not broken and has excellent durability. I understand.

[0015]

According to the present invention, by temporarily sintering at a temperature pattern in which the temperature raising rate is appropriately adjusted, the steps of temporary sintering are uniform over the entire surface of the base material, and shrinkage due to sintering is uniform in the center direction. As a result, even in a large-diameter provisional sintered body, a sintered body having a very small density difference between the central portion and the peripheral portion can be obtained. That is,
The average density difference (true density ratio) from the center of the pre-sintered body section is 5
% Or less, and further a temporary sintered body having this density difference of 3% or less is obtained. This pre-sintered body is subjected to final sintering by electric sintering at about 1700 ° C., and by this electric sintering, the density of the entire sintered body is uniformly increased and a heating element product having excellent durability is obtained. The heating element product obtained in this way has no nests or cracks in a series of manufacturing processes, and cracks due to the difference in density between the center and the periphery when welding a rod-shaped heating element Never do. Furthermore, an excellent feature that the inside of the heating element is selectively oxidized during use (especially when nests are generated), powdering proceeds, and there is no problem of collapse from the inside of the heating element. have.

[Brief description of the drawings]

FIG. 1 is a diagram (graph) showing heating and heating patterns of pre-sintering in Comparative Examples and Examples.

FIG. 2 is an explanatory diagram showing the occurrence of defects “cavities” when a temporarily sintered body having a low sintering density is electrically sintered.

FIG. 3 is an explanatory view showing the occurrence of defects “cracks” when a temporary sintered body having a high sintered density is electrically sintered.

FIG. 4 is an explanatory diagram showing generation of a defect “crack” when two rod-shaped sintered bodies are electrically welded.

FIG. 5 is an explanatory diagram showing a heating temperature cycle (200 ° C. to 480 ° C.) in a low-temperature oxidation resistance test of a sintered heating element.

[Explanation of symbols]

 1 Nest 2,5 Peripheral part 3,6 Central part 4,7 Crack 8,9 Two rods to be welded by electric current 10 End face

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H05B 3/14 B22F 3/14 101 C04B 35/58 106 C04B 35/64 H05B 3/20 H01L 7/02

Claims (4)

(57) [Claims] 1. A heating element containing 70% or more of MoSi ₂ , wherein the average density of the entire heating element and 1/1 of the diameter of the heating element.
A heating element comprising MoSi ₂ as a main component, wherein a density difference (true density ratio) from a central portion corresponding to 5 is 5% or less. 2. A heating element as a main component MoSi ₂ according to claim 1, wherein the density difference between the average density of the whole and the central portion (true density ratio) is 3% or less of the heating element . 3. A heating element material containing 70% or more of MoSi ₂ is gradually heated from at least 1350 ° C. to 1650 ° C. over 5 to 15 hours, and the same as the average density of the entire heating element material. The entire heating element, which is pre-sintered so that the density difference (true density ratio) from the center corresponding to 1/5 of the diameter of the heating element material is 5% or less, and then is electrically sintered. method for manufacturing a heating element as a main component MoSi _2, wherein the difference in density between the central portion corresponding to 1/5 of the diameter of the average density and the heating element (true density ratio) is 5% or less. 4. The density difference (true density ratio) between the central portion and the average density of the entire heating element material after provisional sintering and the heating element after electric sintering is 3% or less. A method for producing a heating element comprising MoSi ₂ as a main component according to claim 3.