JPH05330945A - Method for manufacturing microwave absorption heating element - Google Patents

Abstract

(57) [Summary] [Purpose] A microwave absorption heating element that generates heat with high heat generation efficiency by absorbing microwaves with little penetration of the heating element and efficiently absorbing heat and heat resistance. Provided is a microwave absorption heating element having excellent heating characteristics. [Structure] Silicon carbide is deposited on the inner and outer surfaces of the pores of porous carbon obtained by carbonizing a resin foam by a CVD method, and then the carbon is oxidized and eliminated to form a silicon carbide porous body. A silicon layer is formed on one side of the body. [Effect] Since the obtained SiC porous body is composed of fine and uniform pores, it has good microwave absorption and heat generation characteristics.
Since it is made of a SiC porous body having a high porosity, it has excellent gas diffusibility, and also has good heat convection and thermal shock resistance. Moreover, since the heat capacity is small, the heat generation efficiency is remarkably high. Furthermore, since the silicon layer is formed, there is almost no transmission of microwaves, and the absorption and heat generation characteristics are extremely good.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a microwave absorbing heating element, and more particularly to a microwave absorbing heating element which absorbs microwaves and self-heats, and which has an excellent effect of suppressing transmission of microwaves. The present invention relates to a method for producing a microwave absorption heating element which has remarkably high heat generation efficiency and has significantly improved thermal shock resistance and heat generation characteristics.

[0002]

2. Description of the Related Art Conventionally, timber, cloth, plastic, etc. are dried and processed by utilizing the phenomenon that a substance is heated by absorbing microwaves. These utilize dielectric heating in which dipoles mainly present in a substance are oscillated by an alternating electric field caused by microwaves and heat is generated by friction between molecules.

Most of such microwave heating is based on water molecules having an electric dipole function existing in an object to be heated as a basis of heat generation. Therefore, microwave heating generally contains water. Used for heating and drying substances.

However, with such heating of water molecules, it is impossible to heat the object to be heated to 100 ° C. or higher due to latent heat of vaporization, and when the water in the object to be heated disappears due to evaporation, a heat source is generated. Since there is no water, the heating phenomenon is reduced and the temperature of the heated object does not rise. That is, heating to a temperature of 100 ° C. or higher is not possible simply by irradiating a heated object containing water with microwaves.

Therefore, conventionally, a dielectric or magnetic material that absorbs microwaves and self-heats is used as a heating element, and an object to be heated is heated to a high temperature by contact with or radiation from the heating element.

Conventionally, as such a heating element, a heat-resistant porcelain such as lead titanate porcelain or ferrite porcelain has been used.

[0007]

However, in the above-mentioned conventional heating element, since some of the irradiated microwaves pass through the heating element, the heating efficiency is poor, so that improvement of the heating characteristics is desired. There is.

The present invention has been made in view of the above-mentioned conventional circumstances, and the microwave is efficiently absorbed without being substantially transmitted through the heating element, so that the microwave generates heat with high heating efficiency. It is an object of the present invention to provide a method for manufacturing a microwave absorption heating element which is an absorption heating element and has good thermal shock resistance and heat generation characteristics.

[0009]

According to a first aspect of the present invention, there is provided a method of manufacturing a microwave absorption heating element, wherein silicon carbide is deposited on the inner and outer surfaces of pores of porous carbon obtained by carbonizing a resin foam by a CVD method. After that, the carbon is oxidized and eliminated to form a silicon carbide porous body, and then a silicon layer is formed on one surface of the silicon carbide porous body.

According to a second aspect of the present invention, there is provided the method for producing a microwave absorption heating element according to the first aspect, wherein the porosity of the silicon carbide porous body is 40 to 95%.

According to a third aspect of the present invention, there is provided a method of manufacturing a microwave absorbing heating element according to the first or second aspect, wherein the silicon layer is
It is characterized in that it is formed to a film thickness of 30 to 300 μm by a thermal spraying method.

The present invention will be described in detail below.

In the method of manufacturing a microwave absorption heating element of the present invention, first, silicon carbide (SiC) is formed by the CVD method.
Porous carbon that serves as a base for deposition is produced by heat treating a resin foam such as urethane foam to carbonize it.

Next, SiC is deposited on the inner and outer surfaces of the pores of this porous carbon by the CVD method. In this case, the amount of SiC deposited is not particularly limited, but in general, it is preferable that the amount of SiC deposited is such that the porosity of the porous carbon serving as the substrate is reduced by 10 to 20% by the deposition of SiC.

After depositing SiC, the porous carbon of the substrate is oxidized and disappeared to obtain a SiC porous body.

In the present invention, the porosity of this SiC porous body is preferably 40 to 95%. This SiC
When the porosity of the porous body is less than 40%, the thermal shock resistance is insufficient and the gas diffusion is poor. Also, the porosity is 95%
If it exceeds, the strength is insufficient and it is not practical.

Next, a silicon layer is formed on one surface of the SiC porous body, that is, on the surface opposite to the surface to be irradiated with microwaves when used as a microwave absorption heating element.

In the present invention, the thermal spraying method is industrially effective as a method for forming the silicon layer. Thermal spraying can be broadly divided into gas type thermal spraying using chemical combustion as a heat source and electric type thermal spraying using electric energy as a heat source. In the present invention, any method is possible, but plasma spraying of electrical type spraying is most suitable. Is.

If the thickness of the formed silicon layer is less than 30 μm, it is difficult to form a uniform silicon layer, and microwaves are partially transmitted through the heating element, resulting in absorption heat generation characteristics. descend. When the film thickness exceeds 300 μm,
In addition to the decrease in heat generation characteristics, peeling from the SiC porous body poses a problem. Therefore, the thickness of the silicon layer is 30 to 300 μm.
It is preferable to form it.

[0020]

In the present invention, since SiC is deposited by the CVD method on the inner and outer surfaces of the pores of the porous carbon obtained by carbonizing the resin foam, the carbon is oxidized and lost to obtain the SiC porous body. Consisting of fine and uniform pores,
A high-strength, heat-resistant SiC porous body having a relatively high porosity can be manufactured. As described above, the fine and uniform high-porosity SiC porous body has extremely good microwave absorption and heat generation characteristics. That is, the gas diffusibility is extremely good, and the convection of heat and the thermal shock resistance are good. In addition, since the heat capacity is small, the heat generation efficiency is remarkably high and the microwave absorption heat generation characteristics are remarkably excellent. In particular, since it is high-purity SiC produced by the CVD method, these characteristics are further excellent. Furthermore, by forming a silicon layer,
There is almost no transmission of microwaves, and the absorption and heat generation characteristics are extremely good.

According to the method of manufacturing a microwave absorption heating element of the present invention, a microwave absorption heating element further excellent in mechanical characteristics such as absorption and heating characteristics, gas diffusivity and strength is provided. According to the method for producing a microwave absorbing heat generating element of the third aspect, a microwave absorbing heat generating element further excellent in the function of preventing transmission of microwaves and having high heat generation efficiency is provided.

[0022]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples.

Examples 1 to 3 Porous carbon was prepared by carbonizing urethane foam having a porosity of 90%. Then, Si and C sources such as methyltrichlorosilane are supplied as raw material gas to the porous carbon kept at 1000 ° C. to generate SiC on the inner and outer surfaces of the pores of the porous carbon by the CVD method, and then the carbon is burned. With 80% porosity by oxidation removal by
A C porous body was obtained. A silicon layer having a film thickness shown in Table 1 was formed on one surface of the SiC porous body by plasma spraying.

Table 1 shows the absorption and heat generation characteristics of the obtained heat generating element. The absorption and heating characteristics are set on the temperature of the porous body when the microwave of output power of 500 W is applied to the surface opposite to the silicon layer formation surface for 2 minutes, and on the side opposite to the porous body (silicon layer formation surface side). The water temperature of 100 ml of water was evaluated. It can be said that the less the microwave is transmitted, the less the water temperature rises.

Comparative Example 1 A SiC porous body was manufactured in the same manner as in Example 1 except that the silicon layer was not formed, and the absorption and heat generation characteristics were similarly examined. The results are shown in Table 1.

From Table 1, it is clear that the present invention makes it possible to manufacture a microwave absorbing heat generating element having a low microwave transmission and a remarkably excellent microwave absorbing heat generating characteristic.

[0027]

[Table 1]

[0028]

As described in detail above, according to the method for producing a microwave absorption heating element of the present invention, the gas diffusivity is extremely good, the thermal shock resistance is excellent, and the microwave transmission is almost nonexistent. Provided is a microwave absorption heating element which is remarkably excellent in wave absorption and heat generation efficiency and heat generation characteristics.

According to the method of claim 2, there is provided a microwave absorption heating element which is further excellent in mechanical characteristics such as absorption and heat generation characteristics, gas diffusivity and strength. According to the method of claim 3, there is provided a microwave absorption heating element which is further excellent in the function of preventing transmission of microwaves and has high heating efficiency.

Claims (3)

[Claims] 1. Silicon carbide is deposited on the inner and outer surfaces of the pores of porous carbon obtained by carbonizing a resin foam by a CVD method, and then the carbon is oxidized and eliminated to obtain a silicon carbide porous body. A method for producing a microwave absorption heating element, characterized in that a silicon layer is formed on one side of a silicon porous body. 2. The porosity of the silicon carbide porous body is 40 to 95%.
The method for manufacturing a microwave absorption heating element according to claim 1, wherein 3. The silicon layer has a thickness of 30 to 30 by a thermal spraying method.
The method for producing a microwave absorption heating element according to claim 1 or 2, wherein the film thickness is 0 μm.