JPH0367316B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing carbon heating elements. Specifically, the present invention relates to a method for producing an oxidation-resistant carbon heating element that can be used in air and has free formability. Carbon materials have excellent heat resistance, thermal shock resistance, and corrosion resistance, and are expected to be used as heating element materials, but carbon reacts with gases such as oxygen, carbon dioxide, and water vapor at high temperatures and is oxidized and consumed. This phenomenon is a major obstacle when using carbon as a heating element in air. Therefore, conventional carbon heating elements have the disadvantage that they can only be used in an inert atmosphere. For this reason, in recent years, various methods have been developed to impart oxidation resistance to carbonaceous materials without coating the heat-resistant surface with an oxidation-resistant material. For example, carbon-ceramic composite materials using ground raw coke as the main raw material have been provided, such as the manufacturing method of carbon-ceramic composite materials by Kyukoken (Japanese Patent Application Laid-Open No. 140075/1983), but Since coke is used, there is a drawback that, for example, it is not possible to obtain an oxidation-resistant carbon material having complex and free shapeability such as a coil shape. The inventors of the present application have conducted intensive research to develop a heat-resistant heating element that can be shaped freely and can be used in air, and as a result, they have found that when subjected to air oxidation in a heat-resistant matrix, a uniform glassy structure is formed. By combining metal compounds such as these, the oxidation-resistant film has spontaneous healing properties and prevents oxygen diffusion into the interior, and by using a synthetic resin as a carbon precursor, This research began with the two ideas of uniformly dispersing a metal compound in a synthetic resin, with the idea that it would be possible to perform molding equivalent to ordinary plastic molding. As a result of research, it was found that when a synthetic resin with metal compounds uniformly dispersed is molded into a round rod shape and carbonized, the exposed metal compounds are removed during the process in which the carbon on the surface is oxidized and consumed in an oxidizing atmosphere. By creating a uniform glassy film that undergoes oxidation and preventing oxygen from diffusing into the interior, oxidative consumption of carbon is prevented, and as a result, the carbon heating element stably generates heat without being oxidized even in the air. I found the facts. The present invention was made based on this knowledge, and involves uniformly kneading a composition such as a synthetic resin that has formability and a high carbon residue yield after firing, and a metal compound that forms glass in air oxidation. A molding composition is obtained, this molding composition is shaped into a free shape, it is treated with a carbon precursor in an air oven, and then carbonized and fired in an inert gas atmosphere. Become. The metal compound is preferably boron carbide and/or silicon carbide, and the composition preferably contains carbonaceous powder such as carbon black, graphite, pitch, or coke as a filler. Even when the carbon heating element thus obtained is heated in air at 800°C for 30 hours, there is almost no difference in appearance or weight before and after heating. Next, the present invention will be explained in more detail with reference to Examples. Example 1 200 g of chlorinated vinyl chloride, 175 g of graphite powder with a particle size of 10 μm or less, 75 g of boron carbide powder with a particle size of 10 μm or less
g, 50 g of silicon carbide powder with a particle size of 10 μm or less, and 100 g of diallyl phthalate monomer were mixed for 30 minutes at room temperature in a Henschel mixer, and the resulting mixture was kneaded using two rolls and formed into a film. was extruded into a round bar-shaped wire with a diameter of 2 mm using a plunger. The obtained round rod-shaped wire was formed into a spring shape as shown in Fig. 1, and treated in an air oven at 5°C/hr up to 180°C, and then heated at 5°C/hr in a nitrogen gas atmosphere in a horizontal tube furnace. for 300
The temperature was raised to 1100°C, further raised to 1100°C at a rate of 20°C/hr, held at 1100°C for 3 hours, and then naturally cooled. The coiled carbon heating element obtained through the above steps was subjected to an oxidation resistance test in air using an electric heating method using the apparatus shown in FIG. The results are shown in Table 1. As shown in Table 1, there was almost no change in weight loss or appearance before and after heating. Moreover, during the oxidation resistance test, the heating element
He had a steady fever from beginning to end. Example 2 400g of furan resin, 350g of graphite powder with a particle size of 10μm or less
g, 150 g of boron carbide with particle size of 10 μm or less, particle size of 10 μm
100g of silicon carbide powder with a size of less than m in a Bonnie mixer
After kneading for 30 minutes at room temperature, the resulting kneaded product was further kneaded using two rolls, and then formed into a sheet and extruded into a round bar shape of 2 mmφ using a plunger. The obtained round bar was cut into lengths of 100 mm as shown in Figure 2, and heated at 5°C/hr in an air oven.
Processed to 180℃, then in a horizontal tube furnace.
The temperature was raised to 300°C at a rate of 5°C/hr in a nitrogen gas atmosphere, then the temperature was raised to 1100°C at a rate of 20°C/hr, and the temperature was increased to 1100°C.
It was kept at ℃ for 3 hours. After that, natural cooling was performed. The thus obtained round bar was subjected to an oxidation resistance test using an electric heating method using the apparatus shown in FIG. The results are shown in Table 1. As shown in Table 1,
There was almost no change in weight loss or appearance before and after heating. Moreover, the heating element generated stable heat throughout the oxidation resistance test. 【table】

[Brief explanation of drawings]

FIG. 1 shows a coil-shaped heating element, FIG. 2 shows a rod-shaped heating element, and FIG. 3 is a schematic diagram of an apparatus for an oxidation resistance test. In the figure, 1... heating element, 2... pyrometer, 3...
Recorder, 4... Electrode for supporting heat generation, 5... Electrode, 6
...Insulator block.

Claims (1)

[Claims] 1. A molding composition is obtained by uniformly kneading a synthetic resin that has formability and exhibits a high carbon residue yield after firing, and a metal compound that forms a glassy substance in air oxidation. A method for producing a carbon heating element, which comprises shaping a composition, heating the resulting shaped product in an oxidizing atmosphere to perform a carbon precursor treatment, and then carbonizing and firing it in an inert gas atmosphere. 2. The method for producing a carbon heating element according to claim 1, wherein the metal compound is boron carbide and/or silicon carbide. 3. The method for manufacturing a carbon heating element according to claim 1, wherein the composition contains carbonaceous powder such as carbon black, graphite, pitch, coke, etc. as a filler.