JP2006117472A - Silicon carbide tool material for firing and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-priced silicon carbide tool material for firing capable of improving energy saving in firing and productivity and uniformly reaction-treating an article to be fired, and its manufacturing method. <P>SOLUTION: The silicon carbide tool material for firing is composed of a silicon carbide substrate having an apparent porosity of ≥20% and an apparent specific gravity of ≤3.20, and a silicon dioxide layer is formed on the surface of the silicon carbide crystal in the surface layer of the silicon carbide substrate. Its manufacturing method is also provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a silicon carbide-based firing tool material, and more particularly, to a silicon carbide-based firing tool material in which a silicon dioxide layer is formed on a silicon carbide crystal surface of a silicon carbide-based substrate surface layer.

  In recent years, ceramics are widely used as electronic materials. For example, ferroelectric ceramics such as barium titanate are used as ceramic capacitors, and piezoelectric ceramics such as soft ferrite (Mn-Zn series, Ni-Zn series, etc.) It is used as a constituent material for electronic parts such as ceramic transformers.

Such ceramics for electronic parts are generally heat-treated or fired in a temperature range of 1000 to 1700 ° C. For this reason, Al ₂ O ₃ —SiO ₂ quality, Al ₂ O ₃ —SiO ₂ quality—MgO quality, MgO quality—Al ₂ O ₃ —ZrO ₂ quality, SiC quality are used as tool materials for heat treatment of ceramics for electronic parts. Such ceramics having excellent heat resistance are used. Among these, in particular, SiC ceramics are considered to be suitable materials because they are excellent in heat resistance and creep resistance.

When a workpiece is placed directly on a SiC ceramics heat treatment tool material, depending on its components, it reacts with the constituent materials of the heat treatment tool material during heat treatment, and the characteristics of the workpiece May change. When CO gas is generated by the oxidation reaction of SiC (SiC + 3 / 2O ₂ → SiO ₂ + CO ↑), the CO gas and the object to be fired react.

In order to prevent the reaction as described above, a tool material whose surface is composed of ceramics such as ZrO ₂ having excellent release reactivity is used. For example, when heat-treating barium titanate (BaTiO ₃ ), a ZrO ₂ ceramic material is used, and when heat-treating soft ferrite (Mn—Zn, Ni—Zn, etc.), Al Ceramics having the same composition as ₂ O _3, ZrO ₂ or the object to be processed, or those obtained by coating a SiC ceramic substrate with these ceramics are used.

  In the case of obtaining the coating material, for example, a desired ceramic slurry is applied and then formed by using a method of baking at a high temperature, a CVD method, a thermal spraying method, or the like. Among these, the thermal spraying method is a method of performing physical adhesion using the anchor effect, and is frequently used because the coating is difficult to peel off.

As such a covering material, for example, a heat-treating member in which Al ₂ O ₃ , mullite, ZrO _{2 and the} like are thermally sprayed on a SiC ceramic base material having excellent heat resistance and creep resistance has been proposed (Patent Document). 1, 2).

  However, since the firing tool materials described in Patent Documents 1 and 2 use a dense base material with a low porosity, it becomes difficult for the reaction gas to flow uniformly through the base material through the base material. It is difficult to carry out a uniform reaction treatment of an object, and a coating of a material different from the base material is sprayed or formed on the base material, which makes the manufacturing process complicated and expensive, and there is room for improvement.

In addition, there are demands for firing tool materials that make efficient use of the furnace space, increase production efficiency through rapid heating, and save energy. To meet these demands, the firing tool materials are made thinner and have a lower heat capacity. In order to achieve this, it is necessary to improve the bending strength in order to reduce the thickness of the substrate.
JP 2001-278865A JP 2003-306392 A

  The present invention has been made in consideration of the above-described circumstances, and is an inexpensive silicon carbide-based firing tool capable of improving energy saving, improving productivity, and uniformly reacting the material to be fired. The purpose is to provide materials.

  Also, manufacture of silicon carbide-based baking tool materials that can improve the energy saving at the time of the baking object, improve the productivity, and can manufacture an inexpensive silicon carbide-based baking tool material that can uniformly react the baking object. It aims to provide a method.

  In order to achieve the above-described object, the silicon carbide-based firing tool material according to the present invention has a silicon carbide-based substrate having an apparent porosity of 20% or more and an apparent specific gravity of 3.20 or less, and the silicon carbide-based substrate. A silicon dioxide layer is formed on the surface of the silicon carbide crystal surface.

  Preferably, the silicon dioxide layer is formed by an oxidation process.

Preferably, at least one of ZrO ₂ and Al ₂ O ₃ is coated on at least a portion of the silicon carbide base material on which the object to be fired is placed.

Preferably, at least one of the ZrO ₂ and Al ₂ O ₃ is coated by thermal spraying.

  Preferably, the bending strength of the silicon carbide base material is 60 Mpa or more.

  Preferably, the silicon carbide base material has an apparent porosity of 30% by mass or more and a bending strength of 35 Mpa or more.

  In the method for producing a silicon carbide based firing tool material according to the present invention, an organic binder is added to a silicon carbide raw material such as SiC powder so that a residual carbon ratio after sintering is 0 to 5.0 mass%. Then, water is added to the mixture and kneaded, and the porous molded body obtained by molding is sintered at 1500 ° C. to 2400 ° C., and the obtained sintered body is subjected to an oxygen atmosphere with an oxygen concentration of 2% or more. Baking is performed at 1400 ° C. to 1500 ° C. for 2 to 6 hours.

  According to the silicon carbide-based firing tool material according to the present invention, the material to be fired can be fired at a high yield from the beginning of use, the number of times of use can be improved, and further, the production efficiency and energy saving can be improved. It is possible to provide a silicon carbide-based firing tool material that can be used.

  Further, according to the method for manufacturing a silicon carbide-based firing tool material according to the present invention, it is possible to improve the energy saving at the time of the firing object, improve the productivity, and uniformly subject the firing object to a low-cost carbonization. It is possible to provide a method for manufacturing a silicon carbide-based baking tool material capable of manufacturing a silicon-based baking tool material.

  Hereinafter, an embodiment of a silicon carbide-based firing tool material according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a longitudinal sectional view of a silicon carbide-based firing tool material according to the present invention.

  As shown in FIG. 1, a silicon carbide-based firing tool material 1 according to the present invention comprises a silicon carbide base material 2 having an apparent porosity of 20% or more and an apparent specific gravity of 3.20 or less. Silicon dioxide layer 2 is formed on the surface of silicon carbide crystal on the surface of substrate 1. The silicon dioxide layer 2 is preferably formed by oxidation treatment. Thereby, a silicon dioxide layer can be formed easily and firmly. Moreover, it is preferable that the silicon carbide-based firing tool material has a bending strength of 60 Mpa or more. Thereby, even if the thickness is reduced, sufficient strength can be obtained. Further, when the apparent porosity of the silicon carbide base material is 30% or more, the bending strength is preferably 35 Mpa or more. Thereby, the intensity | strength which is practically unhindered is obtained, obtaining a large apparent porosity.

  With the silicon carbide firing tool material according to the present invention, there is no change over time due to repeated use. That is, there is no generation of CO gas, and the properties of the object to be fired do not change (especially in the initial use). In addition, when the surface of the SiC substrate is coated, there is no change in physical properties due to oxidation of the SiC substrate at the interface between the SiC substrate and the coating layer, and the coating layer is not cracked or peeled off. .

Furthermore, the bending strength increases (unoxidized: 50 MPa or less, the present invention: 60 MPa or more). Although the reason for this has not been fully elucidated, a phenomenon has been confirmed in which the bending strength is increased due to the presence of amorphous SiO ₂ on the SiC crystal surface of the substrate surface layer. This makes it possible to reduce the weight by increasing the porosity of the base material, and further to reduce the thickness by increasing the strength, thereby reducing the heat capacity of the base material. A large amount of heat is not required for heating, and since the object to be fired can be fired from the initial use of the tool material, energy saving can be improved, and further, the productivity of firing the object to be fired can be improved. Further, by increasing the porosity, the flow of the reaction gas through the substrate can be improved, and the object to be fired can be uniformly reacted.

Moreover, it is preferable that at least a portion of the silicon carbide-based firing tool material on which the material to be fired is placed is coated with Al ₂ O ₃ or ZrO ₂ by thermal spraying. As a result, the manufacturing process becomes the same level as before, but the amorphous SiO ₂ on the surface layer of the base material is coated with Al ₂ O ₃ and ZrO ₂ , thereby reducing the thickness of the firing tool material and accompanying this. Not only can the heat capacity be reduced, it also has excellent release reactivity. In addition, since the silicon dioxide layer on the surface of the silicon carbide crystal can be formed by oxidation treatment regardless of thermal spraying or other film forming steps, an inexpensive baking tool material can be obtained.

  According to the silicon carbide-based firing tool material of the above-described embodiment, the silicon carbide-based firing tool is inexpensive and capable of improving energy saving, improving productivity, and uniformly reacting the fired product. The material is realized.

  Next, a method for producing a silicon carbide-based firing tool material according to the present invention will be described.

  In the method for producing a silicon carbide based firing tool material according to the present invention, an organic binder is added to a silicon carbide raw material such as SiC powder so that a residual carbon ratio after sintering is 0 to 5.0 mass%. The porous molded body obtained by adding water to the mixture and kneading and molding is sintered at 1500 ° C. to 2400 ° C. The obtained sintered body is fired in an oxygen atmosphere having an oxygen concentration of 2% or more, 1400 ° C. to 1500 ° C., for 2 to 6 hours.

  The silicon carbide raw material is not particularly limited, and a raw material made of silicon carbide powder known per se, which is usually used in the production of this kind of silicon carbide ceramics, may be used. Examples of such silicon carbide raw material powder include commercially available SiC powder having a purity of about 90% or more and an average particle diameter of about 0.1 to 200 μm, and those having a purity of 95% or more are preferably used. The In particular, from the viewpoint of preventing reaction with the object to be fired, it is necessary to use a high-purity one, and it is usually preferable to use powder having a purity of 99% by mass or more. Further, a mixed powder in which fine powder and coarse powder are mixed at an appropriate ratio may be used.

  The organic binder is, for example, phenol resin, and the amount of addition is such that the residual carbon ratio after sintering is 0 to 5.0% by mass. When it exceeds 5.0 mass%, the amount of oxidation increases and it takes time for the oxidation treatment. This is not particularly limited and is generally used as an organic binder, for example, an aromatic resin binder such as phenol-formaldehyde resin, phenol-furfural resin, polybenzimidazole resin, polyphenylene, polyvinyl alcohol, methylcellulose, carboxymethylcellulose, Aliphatic resin binders such as polyvinyl chloride, polyvinylidene chloride, and polyacrylic resins, and various organic binders such as silicone resins and tar pitch can be used.

  As a forming method, a normal press, rubber press, extrusion, slip casting, or the like can be used.

  The oxygen atmosphere preferably has an oxygen concentration of 2% or more, and if it is lower than 2%, a required silicon dioxide layer cannot be formed. Moreover, a calcination temperature is 1450 degreeC and 1400-1500 degreeC is preferable. When the temperature is lower than 1400 ° C., it takes a long time to form a necessary silicon dioxide layer. Furthermore, the firing time is 2 to 6 hours. If it is shorter than 2 hours, a necessary silicon dioxide layer cannot be formed, and if it is longer than 6 hours, it is economically disadvantageous.

  A normal thermal spraying method can be applied to the thermal spraying. The sprayed film may be formed on the entire surface of the base material, but may be formed on a part of the base material including a portion on which the object to be fired is placed. The thickness of the sprayed film is preferably 50 to 1000 μm. The raw material particle size of the thermal spray material is preferably 70 to 130 μm. Further, a mixed powder of raw materials finer than these raw materials may be granulated to 70 to 130 μm and sprayed.

In the case of forming a zirconia sprayed film, plasma spraying, particularly water plasma spraying is preferred in view of the melting point of zirconia. Thermal spraying is a method of performing physical adhesion using the anchor effect, and is preferable because the coating is difficult to peel off. In the case of a zirconia sprayed film, it is preferable to mix unstabilized zirconia and stabilized or partially stabilized zirconia. There is no need to limit the mixing ratio. In order to make it difficult to peel off the ZrO ₂ coating layer, it is preferable that the stabilized or partially stabilized zirconia is 30 to 60% by mass and the unstabilized zirconia is 70 to 40% by mass.

As the stabilizer, CaO or Y ₂ O ₃ is preferable. Thereby, even if heating and cooling are repeated as a baking tool material, the residual expansion of the stabilized zirconia is absorbed, and the thermal spray layer is less peeled and durability is improved. The ratio of unstabilized zirconia in the sprayed layer is preferably 30 to 60% by mass.

As a method for coating Al ₂ O ₃ and ZrO _2, a general method such as a thermal spraying method, a method of baking at a high temperature after applying a desired ceramic slurry, or a CVD method may be used.

  According to the method for manufacturing a silicon carbide-based firing tool material of the above-described embodiment, the silicon carbide material is inexpensive and can improve the energy saving at the time of firing, improve the productivity, and uniformly treat the firing object. A baking tool material can be manufactured.

  Test method: A sample was prepared by the method for manufacturing a silicon carbide-based firing tool material of the present invention, and the bending strength at 8 points at measurement positions 1 to 8 as shown in FIG. The apparent porosity, apparent specific gravity, and bulk specific gravity were measured. The substrate used was 270 × 270 mm and had a thickness of 4 mm. The substrate was cut in half before the oxidation treatment, the substrate at measurement positions 1 to 4 was oxidized, and the substrate at measurement positions 5 to 8 was not oxidized. The measuring method of bending strength was based on JIS R2213-1995, and the measuring method of apparent porosity and apparent specific gravity was based on JIS R2205-1992.

Results: shown in Table 1. Each measured value shows an average value of four points.

  As can be seen from Table 1, Examples 1, 2, and 4 can obtain a large value of an average bending strength of 65 MPa or more while maintaining a relatively large apparent porosity, and correspond to an apparent specific gravity. It can be seen that it is smaller and lighter than the comparative example.

  Furthermore, although the average bending strength of Example 3 is relatively small at 39.6 MPa, the maximum apparent porosity of 30.3% is obtained in each Example and Comparative Example.

  On the other hand, it can be seen that each comparative example has a lower average bending strength, a larger apparent specific gravity, and a lower average bending strength relative to the weight of the corresponding example.

The conceptual diagram of the tool material for silicon carbide based baking which concerns on this invention. Explanatory drawing which shows the measurement point of the test using the silicon carbide-like baking tool material of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tool material for silicon carbide type baking 2 Silicon carbide type base material 3 Silicon dioxide layer

Claims (7)

The silicon carbide substrate has an apparent porosity of 20% or more and an apparent specific gravity of 3.20 or less, and a silicon carbide layer is formed on the silicon carbide crystal surface of the silicon carbide substrate surface layer. Quality firing tool material. The silicon carbide-based firing tool material according to claim 1, wherein the silicon dioxide layer is formed by an oxidation treatment. _3. The silicon carbide material according to claim 1, wherein at least one of ZrO ₂ and Al ₂ O ₃ is coated on at least a portion of the silicon carbide substrate on which the material to be fired is placed. Tool material for baking. The silicon carbide based firing tool material according to claim ₃ , wherein at least one of the ZrO ₂ and Al ₂ O ₃ is coated by thermal spraying. The silicon carbide based firing tool material according to any one of claims 1 to 4, wherein the silicon carbide based substrate has a bending strength of 60 MPa or more. The silicon carbide-based firing tool material according to any one of claims 1 to 4, wherein an apparent porosity of the silicon carbide-based substrate is 30% or more and a bending strength is 35 MPa or more. . An organic binder is added to a silicon carbide raw material such as SiC powder and mixed so that the residual carbon ratio after sintering is 0 to 5.0% by mass, and water is added to the mixture and kneaded and molded. The porous molded body thus obtained is sintered at 1500 ° C. to 2400 ° C., and the obtained sintered body is fired in an oxygen atmosphere having an oxygen concentration of 2% or more, 1400 ° C. to 1500 ° C., for 2 to 6 hours. A method for producing a silicon carbide-based firing tool material.

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