JP2019061946A - Heating element, heating device and method of manufacturing silicon carbide - Google Patents

Heating element, heating device and method of manufacturing silicon carbide Download PDF

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JP2019061946A
JP2019061946A JP2018060761A JP2018060761A JP2019061946A JP 2019061946 A JP2019061946 A JP 2019061946A JP 2018060761 A JP2018060761 A JP 2018060761A JP 2018060761 A JP2018060761 A JP 2018060761A JP 2019061946 A JP2019061946 A JP 2019061946A
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heating element
heating
specific gravity
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silicon carbide
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JP6940444B2 (en
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石田　弘徳
Hironori Ishida
弘徳 石田
増田　賢太
Kenta Masuda
賢太 増田
潔 野中
Kiyoshi Nonaka
潔 野中
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Taiheiyo Cement Corp
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Abstract

To provide a heating element which can prevent the heating element from being gradually blown away by a gas generated from a processed material without being heated at a low voltage for a long time, a heating device, and a method of manufacturing silicon carbide.SOLUTION: A heating element 17 for heating a processing object 20 accompanied by generation of gas at a time of heat treatment with Joule heat is formed of a graphitic powder having a bulk specific gravity of 0.16 or more. As a result, since the specific gravity of the heating element is sufficient, it is possible to prevent the heating element from being gradually blown away by the gas generated from the processing object 20 without heating at a low voltage for a long time. A heating device 10 includes: a container 11 for accommodating the processing object, whose vertically upper end face is open to the atmosphere; electrodes 15a, 15b formed on an inner wall of the container 11 and to which a voltage is applied; and a heating element 17 embedded in the processing object 20 and connected to the electrodes 15a, 15b.SELECTED DRAWING: Figure 1

Description

本発明は、加熱処理時にガスの発生を伴う処理物をジュール熱で加熱するための発熱体、これを用いた加熱装置および炭化珪素の製造方法に関する。   The present invention relates to a heating element for heating, with Joule heat, a treatment product accompanied by gas generation during heat treatment, a heating apparatus using the same, and a method of manufacturing silicon carbide.

従来、処理物を加熱する加熱方法としては、高周波やレーザを用いる方法があるが、ジュール熱により発熱体を用いる方法が用いられている。このような発熱体には、黒鉛質の発熱体が挙げられる。黒鉛質の発熱体は、加熱炉に使用されることが多く、そのような加熱炉の一つにアチソン炉がある。これは、炉の中心に発熱体を配置し、その周囲に処理物を配置する構造の炉である。発熱体には電気的な抵抗体を用い、通電することでジュール熱を発生させる。工業的には、黒鉛や炭化珪素、炭化ホウ素の製造に用いられる。   Conventionally, as a heating method for heating a processing object, there is a method using a high frequency or a laser, but a method using a heating element by Joule heat is used. Such heating elements include graphitic heating elements. Graphite heating elements are often used in furnaces, one such furnace being the Acheson furnace. This is a furnace having a structure in which a heating element is disposed at the center of the furnace and a workpiece is disposed around the heating element. An electrical resistor is used as the heating element, and Joule heat is generated by energizing. Industrially, it is used for the production of graphite, silicon carbide and boron carbide.

アチソン炉に関しては様々な技術が開示されている。例えば、特許文献１には、アチソン炉で高割合の粗結晶状炭化珪素を製造する方法が開示されている。特許文献２には、多数の炭素焼成体をアチソン炉の炉長方向に直配列して黒鉛化する方法が開示されている。特許文献３には、複数の炭素材をアチソン炉の炉長方向に直配列してパッキング材で被包する黒鉛化構造が開示されている。特許文献４には、底壁または側壁の内側面のうち近い内側面と外周面が接する円筒形領域の外側と炉本体との間の領域に、耐熱温度が１５００℃以上の高耐火性部材を備える炉構造が開示されている。   Various techniques have been disclosed for Atchison furnaces. For example, Patent Document 1 discloses a method of producing a high proportion of coarse crystalline silicon carbide in an Atchison furnace. Patent Document 2 discloses a method of graphitizing a large number of fired carbon bodies by arranging them in the furnace length direction of an Acheson furnace directly. Patent Document 3 discloses a graphitized structure in which a plurality of carbon materials are aligned in the longitudinal direction of an Acheson furnace and encapsulated with a packing material. Patent Document 4 discloses a high fireproof member having a heat-resistant temperature of 1500 ° C. or higher in the region between the furnace body and the outside of the cylindrical region where the inner surface and the outer peripheral surface are in contact. A furnace structure is disclosed.

特開昭５８−２１７４１５号公報Japanese Patent Application Laid-Open No. 58-217415 特開昭６２−０９１４１１号公報Japanese Patent Application Laid-Open No. 62-091411 実開平０１−０７８１３５号公報Japanese Utility Model Publication No. 01-078135 特開２０１６−０９９１０２号公報JP, 2016-099102, A

上記のようなアチソン炉では、例えば炭化珪素を製造できる。炭化珪素は、原料の珪石とコークスを２２００℃以上で焼成して製造できる。この場合の発熱体には、劣化が軽微で２３００℃以上に昇温できる材質として黒鉛が好適である。特に商用生産においてはコストが重視されることからコークスが用いられる。   For example, silicon carbide can be produced in the above-described Acheson furnace. Silicon carbide can be produced by firing raw materials silica and coke at 2200 ° C. or higher. In the heating element in this case, graphite is preferable as a material which is slightly deteriorated and can be heated to 2300 ° C. or higher. Especially in commercial production, coke is used because cost is important.

しかしながら、炭化珪素の製造では、焼成中に原料が反応しガスが発生する。そのガスが発熱体を通過する際、発熱体を噴いてしまうことがある。このようなガスの噴出が生じるとその部分の抵抗が局所的に下がり異常発熱する。また、最悪の場合は発熱体が断線してしまい焼成が不可能になる。   However, in the production of silicon carbide, the raw materials react during firing to generate a gas. When the gas passes through the heating element, the heating element may be sprayed. When such gas ejection occurs, the resistance of the portion locally decreases and abnormal heat is generated. Further, in the worst case, the heating element is disconnected and the firing becomes impossible.

反応時に発生するガス量を抑制するために、発熱体に投入される電力を低く制御する方法を採ることも考えられる。しかしながら、この方法で焼成すると、焼成に要する時間が長くなる。生産性を上げるためには高電力を印加して焼成することが望まれる。   In order to suppress the amount of gas generated at the time of reaction, it is also conceivable to adopt a method of controlling the power supplied to the heating element to be low. However, if it bakes by this method, the time which baking requires will become long. In order to raise productivity, it is desirable to apply and bake high electric power.

本発明は、このような事情に鑑みてなされたものであり、低電圧で長時間加熱しなくても処理物から生じるガスで徐々に発熱体が吹き飛ばされるのを防止できる発熱体、加熱装置および炭化珪素の製造方法を提供することを目的とする。   The present invention has been made in view of such circumstances, and a heating element, a heating device, and a heating element capable of preventing the heating element from being gradually blown away by a gas generated from a processed material without being heated at low voltage for a long time An object of the present invention is to provide a method of manufacturing silicon carbide.

（１）上記の目的を達成するため、本発明の発熱体は、加熱処理時にガスの発生を伴う処理物をジュール熱で加熱するための発熱体であって、かさ比重０．１６以上の黒鉛質の粉体で形成されることを特徴としている。これにより、十分に発熱体の比重があるため、低電圧で長時間加熱しなくても処理物から生じるガスで徐々に発熱体が吹き飛ばされるのを防止できる。   (1) In order to achieve the above object, the heating element of the present invention is a heating element for heating a treated product accompanied by generation of gas at the time of heat treatment by Joule heat, and graphite having a bulk specific gravity of 0.16 or more It is characterized by being formed of quality powder. Accordingly, since the specific gravity of the heat generating body is sufficient, it is possible to prevent the heat generating body from being gradually blown away by the gas generated from the processing object even without heating at a low voltage for a long time.

（２）また、本発明の発熱体は、かさ比重が０．４以下であることを特徴としている。このように発熱体の比重が大きすぎないため、処理物から発生するガスが抜けやすくなる。その結果、局所的にガスが通過する箇所が生じず、発熱が集中したり、断線したりする危険性を低減できる。   (2) Moreover, the heat generating body of this invention is characterized by bulk specific gravity being 0.4 or less. As described above, since the specific gravity of the heating element is not too large, the gas generated from the processed material is easily released. As a result, there is no local passage of gas, which can reduce the risk of concentration of heat generation or disconnection.

（３）また、本発明の加熱装置は、鉛直上端面が大気開放され、前記処理物を収容する容器と、前記容器の内壁に形成され、電圧が印加される電極と、前記処理物内に埋設され、前記電極に接続される上記（１）、（２）の発熱体と、を備えることを特徴としている。このように発熱体の周囲に処理物が配置されガスの影響を受けやすい構成において、発熱体が吹き飛ばされ、発熱体が断線するのを防止することができる。   (3) Further, in the heating device of the present invention, the vertically upper end face is open to the atmosphere, a container for containing the treated product, an electrode formed on the inner wall of the container, to which a voltage is applied, and It is characterized by including the heating element of the above (1) and (2) which is embedded and connected to the electrode. As described above, in the configuration in which the object to be treated is disposed around the heating element and susceptible to the influence of gas, it is possible to prevent the heating element from being blown off and disconnection of the heating element.

（４）また、本発明の炭化珪素の製造方法は、上記（４）の加熱装置を用いた炭化珪素の製造方法であって、前記容器内に前記処理物として珪酸質原料および炭素質原料が混合された混合材料を充填するとともに、前記処理物内に前記発熱体を埋設する工程と、前記発熱体に電圧を印加し通電する工程と、を含むことを特徴としている。これにより、通電による加熱時に珪酸質粒子と炭素質粒子とが反応し、一酸化炭素や一酸化珪素がガスとして発生する際に発熱体が吹き飛ばされ断線するのを防止できる。   (4) The method for producing silicon carbide according to the present invention is a method for producing silicon carbide using the heating device according to (4), wherein a siliceous raw material and a carbonaceous raw material are contained in the container as the treated product. The method is characterized in including the steps of: filling the mixed material mixed, embedding the heat generating body in the processed material, and applying a voltage to the heat generating body to conduct electricity. Thereby, when the siliceous particles and the carbonaceous particles react at the time of heating by energization, and carbon monoxide or silicon monoxide is generated as a gas, it is possible to prevent the heating element from being blown and broken.

本発明によれば、低電圧で長時間加熱しなくても処理物から生じるガスで徐々に発熱体が吹き飛ばされるのを防止できる。   According to the present invention, it is possible to prevent the heating element from being blown off gradually by the gas generated from the processing material even if it is not heated at a low voltage for a long time.

（ａ）、（ｂ）それぞれ加熱装置を示す側断面図および正断面図である。(A), (b) is a side sectional view and a front sectional view showing a heating device, respectively. 実験の条件と評価結果を示す表である。It is a table | surface which shows the conditions and evaluation result of experiment.

本発明者らは、鋭意研究の結果、十分なかさ比重を有する黒鉛質の粉体で発熱体を形成することで、加熱時間を長くしなくても、電流制御が容易で、断線のリスクを低減できる発熱体を発明した。以下に、本発明の実施形態について説明する。   As a result of earnest research, the inventors of the present invention form a heating element from a graphitic powder having a sufficient bulk specific gravity, thereby facilitating current control without reducing heating time and reducing the risk of disconnection. Invented a heating element capable of Hereinafter, embodiments of the present invention will be described.

［加熱装置の構成］
図１（ａ）、（ｂ）は、それぞれ加熱装置を示す側断面図および正断面図である。加熱装置１０は、容器１１、電極１５ａ、１５ｂ、発熱体１７を備えており、処理物をジュール熱で加熱する。加熱装置１０は、いわゆるアチソン炉であることが好ましい。 [Configuration of heating device]
1 (a) and 1 (b) are a side sectional view and a front sectional view showing a heating device, respectively. The heating device 10 includes a container 11, electrodes 15a and 15b, and a heating element 17, and heats the processing object by Joule heat. The heating device 10 is preferably a so-called Acheson furnace.

（容器の構成）
容器１１は、鉛直上端面が大気開放され、内壁面に電極１５ａ、１５ｂを備え、処理物２０を収容する。容器１１の形状は特に問わないが、平行な対向する二面を有することが好ましく、直方形に形成されていることが好ましい。容器１１の材質は特に問わないが、通電時に黒鉛粉末原料からの伝熱により壁面が高温になるため、充填材と接触する部分には耐火性の高い材料を使うことが望ましい。例えば、高アルミナ質耐火れんが、珪酸カルシウムボード等が好適である。容器１１は、反応ガスが過剰に発生した際にガスを抜き、その濃度を適度に保つためのスリットを有してもよい。 (Configuration of container)
The container 11 is open to the atmosphere at the vertically upper end surface, provided with the electrodes 15 a and 15 b on the inner wall surface, and accommodates the processing object 20. Although the shape of the container 11 is not particularly limited, it is preferable to have two parallel opposite faces, and it is preferable that the container 11 be formed in a rectangular shape. The material of the container 11 is not particularly limited, but the wall surface becomes high temperature due to heat transfer from the graphite powder raw material at the time of current application, so it is desirable to use a highly fireproof material for the part in contact with the filler. For example, high alumina refractory bricks, calcium silicate boards and the like are suitable. The container 11 may have a slit for degassing the reaction gas when an excessive amount of reaction gas is generated and for maintaining the concentration appropriately.

（電極の構成）
電極１５ａ、１５ｂは、容器の内壁に形成され、電圧が印加される。電極１５ａ、１５ｂは、容器内側の対向する両端面に設けられていることが好ましい。電極１５ａ、１５ｂは、発熱体１７に接触し、電圧印加により発熱体１７は通電する。電極１５ａ、１５ｂは、発熱体１７からの伝熱の影響を受けることから、高温にも耐性のある黒鉛成型体が好適である。 (Configuration of electrode)
The electrodes 15a, 15b are formed on the inner wall of the container and a voltage is applied. The electrodes 15a, 15b are preferably provided on the opposite end surfaces inside the container. The electrodes 15a and 15b are in contact with the heating element 17, and the heating element 17 is energized by voltage application. Since the electrodes 15a and 15b are affected by the heat transfer from the heating element 17, a graphite molded body that is resistant to high temperatures is preferable.

（発熱体の構成）
発熱体１７は、処理物２０内に埋設され、電極１５ａ、１５ｂに接続され、黒鉛質の粉体で形成されている。加熱装置１０の構成上、発熱体１７の周囲に処理物２０が配置されているため、発熱体１７は処理物２０から生じるガスの影響を受けやすい。しかし、発熱体１７を形成する黒鉛質の粉体は、かさ比重０．１６以上であるため、低電圧で長時間加熱しなくても処理物から生じるガスで徐々に発熱体が吹き飛ばされるのを防止できる。また、抵抗の変化が小さいため、電流制御が容易で、断線のリスクを低減できる。その結果、発熱体に高電流（電圧）を印加することが可能になることで、焼成時間を短縮し、生産性の向上をもたらす。 (Composition of heating element)
The heat generating body 17 is embedded in the processing object 20, connected to the electrodes 15a and 15b, and formed of a graphitic powder. In the configuration of the heating device 10, the processing object 20 is disposed around the heating element 17, so the heating element 17 is easily influenced by the gas generated from the processing object 20. However, since the graphitic powder forming the heat generating body 17 has a bulk specific gravity of 0.16 or more, the heat generating body is gradually blown away by the gas generated from the processed material without being heated at a low voltage for a long time It can prevent. In addition, since the change in resistance is small, current control is easy and the risk of disconnection can be reduced. As a result, it becomes possible to apply a high current (voltage) to the heating element, thereby shortening the firing time and improving the productivity.

一方で、発熱体１７のかさ比重は、０．４以下であることが好ましい。このように発熱体１７の比重が大きすぎないため、処理物２０から発生するガスが抜けやすくなる。その結果、ガスが通過する箇所が分散し、局所的な発熱が発生し難くなり、断線する危険性を低減できる。また、発熱体のかさ比重が上記の範囲にあるために、投入電力を大きくすることができる。投入電力を大きくすることができれば、処理に要する時間を短くできる。なお、投入電力とは、発熱体の単位表面積当りの熱量（制御的には電源の電圧・電流の積）を指す。なお、発熱体のかさ比重は、０．１６〜０．４の範囲はＪＩＳ Ｒ １６２８、それより大きい範囲はＪＩＳ Ｋ ２１５１に基づいて測定可能である。   On the other hand, the bulk specific gravity of the heating element 17 is preferably 0.4 or less. As described above, since the specific gravity of the heating element 17 is not too large, the gas generated from the processing object 20 is easily released. As a result, the points through which the gas passes are dispersed, local heat generation hardly occurs, and the risk of disconnection can be reduced. In addition, since the bulk specific gravity of the heating element is in the above range, the input power can be increased. If the input power can be increased, the time required for processing can be shortened. The input power refers to the amount of heat per unit surface area of the heating element (controllably the product of the voltage and current of the power supply). The bulk specific gravity of the heat generating element can be measured based on JIS R 1628 in the range of 0.16 to 0.4 and JIS K 2151 in the larger range.

黒鉛質の粉体は、コークスに由来する材料で形成されていることが好ましい。これにより、発熱体を形成するコストを低減できる。なお、コークスに由来するとは、発熱体として何度か焼成に用いたコークスも含むことを意味する。コークスのかさ比重は、０．６〜０．９程度である。アチソン炉で炭化珪素を製造するにあたり、発熱体にコークスを使用すると、使用毎に発熱体のかさ比重が減少する。その理由は以下の３点による。   The graphitic powder is preferably formed of a material derived from coke. Thereby, the cost of forming the heating element can be reduced. In addition, originating in coke means that the coke used for several baking as a heat generating body is also included. The bulk specific gravity of coke is about 0.6 to 0.9. In the production of silicon carbide in an Acheson furnace, if coke is used as the heating element, the bulk specific gravity of the heating element decreases with each use. The reason is based on the following three points.

すなわち、（１）発熱体のコークスが昇華する。（２）発熱体のコークスが酸化する。（３）発熱体のコークスが珪石との反応し炭化珪素となり（処理物と発熱体の界面で起きる現象）、それがさらに分解し、低い鱗片状の黒鉛が生成する。鱗片状黒鉛は流動性に乏しいため、これが増えると発熱体のかさ比重が小さくなる。かさ比重を０．１６以上にすることで、発熱体それ自体の温度上昇に伴う抵抗の変化に加えて、先に述べたコークスの減少の３点と同じく発熱体が減少することで抵抗が上昇するものの制御容易な状態を維持できる。   That is, (1) the coke of the heating element sublimes. (2) The coke of the heating element is oxidized. (3) The coke of the heating element reacts with silica to form silicon carbide (a phenomenon that occurs at the interface between the treated product and the heating element), which is further decomposed to form low scale graphite. Since scaly graphite has poor fluidity, the bulk specific gravity of the heating element decreases as this increases. By setting the bulk specific gravity to 0.16 or more, in addition to the change of the resistance with the temperature rise of the heating element itself, the resistance increases by the reduction of the heating element as in the three points of the reduction of coke mentioned above It is possible to maintain an easy-to-control state of

かさ比重が減少した発熱体を使用して次の焼成を行なうことは可能である。しかし、常に同状態、同条件での製造が望まれる工業生産において、ロット毎にまちまちな物性（かさ比重）の発熱体を使用することは好ましくない。そこで、新たなコークスを追加し、かさ比重を調整することが好ましい。   It is possible to carry out the subsequent firing using a heating element of reduced bulk specific gravity. However, in industrial production where production under the same conditions and conditions is desired at all times, it is not preferable to use heating elements with different physical properties (bulk specific gravity) from lot to lot. Therefore, it is preferable to add new coke and adjust bulk specific gravity.

かさ比重が０．１６〜０．４０の発熱体は、コークスそのものより空隙が多く、焼成中に発生するガスは、発熱体を均等に通過しやすい。これに対し、コークスを主成分とする発熱体では、空隙が少なく発生したガスの溜まりが生じ、そこから急激にガスが抜けることで、発熱体を吹き飛ばす。かさ比重が０．１６〜０．４４（０．２０〜０．４４）である黒鉛質の発熱体においても、焼成毎にかさ比重が減少する。発熱体にコークスや黒鉛粉を添加することでかさ比重を上げることができる。なお、発熱体のかさ比重は、実際には焼成中に除々に低減する。これは焼成中の発熱体の抵抗が上昇することから分かる。   A heating element having a bulk specific gravity of 0.16 to 0.40 has more voids than coke itself, and gases generated during firing tend to pass through the heating element evenly. On the other hand, in the case of a heating element mainly composed of coke, a small amount of voids is generated and a gas accumulation occurs, from which the heating element is blown off by the rapid removal of the gas. Even in the case of a graphitic heating element having a bulk specific gravity of 0.16 to 0.44 (0.20 to 0.44), the bulk specific gravity decreases with each firing. The bulk specific gravity can be increased by adding coke or graphite powder to the heating element. In addition, the bulk specific gravity of a heat generating body is gradually reduced during baking. This can be seen from the increase in resistance of the heating element during firing.

［処理物の加熱方法］
（処理物）
処理物は、加熱処理時にガスの発生を伴うものである。このような処理物には無機珪酸質原料および炭素質原料の混合材料が挙げられる。この場合、全体の系としては、以下の反応が生ずる。
ＳｉＯ２（ｓ）＋３Ｃ（ｓ）→ＳｉＣ（ｓ）＋２ＣＯ（ｇ） [Method of heating processed material]
(Processed item)
The processed matter is accompanied by the generation of gas at the time of heat treatment. Such treated products include mixed materials of inorganic siliceous raw materials and carbonaceous raw materials. In this case, the following reaction occurs as a whole system.
SiO 2 (s) + 3C (s) → SiC (s) + 2CO (g)

しかし、実際には反応は以下のように段階的に生じている。
ＳｉＯ２（ｓ，ｌ）＋Ｃ（ｓ）→ＳｉＯ（ｇ）＋ＣＯ（ｇ）
ＳｉＯ２（ｓ）＋２Ｃ（ｓ）→ＳｉＣ（β）＋ＣＯ（ｇ）
ＳｉＣ（β）→ＳｉＣ（α）
ＳｉＯ（ｇ）＋ＳｉＣ（ｓ）→２Ｓｉ（ｌ，ｇ）＋ＣＯ（ｇ）
２Ｓｉ（ｌ，ｇ）＋ＣＯ（ｇ）→ＳｉＣ（α，β）＋ＳｉＯ（ｇ）
（ｓ、ｌ、ｇは固体、液体、気体を示し、α、βは粒子の結晶構造を示す） However, in practice, the reaction occurs in stages as follows.
SiO 2 (s, l) + C (s) → SiO (g) + CO (g)
SiO 2 (s) + 2 C (s) → SiC (β) + CO (g)
SiC (β) → SiC (α)
SiO (g) + SiC (s) → 2Si (l, g) + CO (g)
2Si (l, g) + CO (g) → SiC (α, β) + SiO (g)
(S, l, g indicate solid, liquid, gas, and α, β indicate crystal structure of particle)

これらの式から、混合材料を加熱している際にはガスが常に発生していることが分かる。ガスが発生すると、発熱体が吹き飛ばされることによるその抵抗の上昇という１つの事象に留まらず、発熱体や処理物の自重で吹き飛ばされた部分が埋まる動きが発生する。その結果、秒〜分単位で抵抗の変動が生じる。そして、ガスにより発熱体が吹き飛ばされる現象が生じると、発熱体の抵抗が変動し、明らかな異常発熱が発生することもある。   From these equations, it can be seen that gas is always generated when heating the mixed material. When gas is generated, the heating element is blown away and it does not stop in one event of the rise of the resistance, but the movement of the portion blown off by the weight of the heating element or the treated material is buried. As a result, resistance fluctuations occur in seconds to minutes. And when the phenomenon that a heat generating body blows off with gas arises, the resistance of a heat generating body will fluctuate, and a definite abnormal heat generation may generate | occur | produce.

発熱体に接続される電源には、設定値にあわせて出力を自動調整するものを使用できる。上記のような変動が生じると電源の自動調整が追いつかない。特に、工業生産で使用される長さがメートル単位の加熱装置では上記のようなガスの発生に起因する挙動は好ましくない。また、三方を壁で囲うような容器構造を有するアチソン炉の場合、発熱体より下方の処理物から発生するガスの大半は炉の上方に放出されるため、この現象が特に生じやすい。なお、処理物は、上記の例に限られず、例えばホウ素化合物原料および炭素質原料の混合材料（炭化ホウ素の製造原料）であってもよい。   The power source connected to the heating element can be one that automatically adjusts the output according to the set value. If the above fluctuation occurs, the automatic adjustment of the power supply can not catch up. In particular, in a heating device having a length of meters used in industrial production, the behavior caused by the generation of the gas as described above is not preferable. Further, in the case of an Acheson furnace having a container structure that encloses three sides with a wall, this phenomenon is particularly likely to occur because most of the gas generated from the processed material below the heating element is released to the upper side of the furnace. The treated product is not limited to the above example, and may be, for example, a mixed material of boron compound raw material and carbonaceous raw material (raw material for producing boron carbide).

（方法の具体的手順）
発熱体１７の埋設は、無機珪酸質粒子および炭素質粒子が混合された処理物２０の内部に容器１１内の電極１５ａ、１５ｂ間を接続するように行なう。 (Specific procedure of the method)
The heating element 17 is embedded in such a manner that the electrodes 15a and 15b in the container 11 are connected to the inside of the processed material 20 in which the inorganic siliceous particles and the carbonaceous particles are mixed.

以下に、加熱装置１０を用いた処理物の加熱方法の一例として、炭化珪素の製造方法を説明する。この場合、いずれも粉体の珪酸質原料および炭素質原料が混合された混合材料を処理物として用いる際に発熱体が吹き飛ばされ断線するのを防止できる。   Hereinafter, a method of manufacturing silicon carbide will be described as an example of a method of heating a processed object using heating apparatus 10. In this case, when using a mixed material in which powdery siliceous raw material and carbonaceous raw material are mixed as the processing material, it is possible to prevent the heating element from being blown and broken.

無機珪酸質原料には、化学式ＳｉＯ２で表される物質一般が使用できる。ＳｉＯ２で表される物質には、例えば、珪砂、石英粉末、結晶質シリカ粉末、非晶質シリカ粉末、シリカゲル等が挙げられる。上記ＳｉＯガスの発生は非晶質のＳｉＯ２を使用した方が起こりやすいことから、非晶質シリカ粉末、シリカゲルは特に好適である。 As the inorganic siliceous raw material, a general substance represented by a chemical formula SiO 2 can be used. Examples of the substance represented by SiO 2 include silica sand, quartz powder, crystalline silica powder, amorphous silica powder, silica gel and the like. Amorphous silica powder and silica gel are particularly preferable because the generation of the SiO gas is more likely to occur when using amorphous SiO 2 .

炭素質原料には、結晶質の黒鉛、非晶質のカーボンブラックの両方を使用できる。いずれも形態は問わず、例えば土状、鱗片状等であってもよい。発熱体の黒鉛により多くの電流を流すことがエネルギーコストの面で望ましいため、炭素質原料には電導性の小さい非晶性のカーボンブラック粉末が特に適している。   Both crystalline graphite and amorphous carbon black can be used as the carbonaceous material. Any form may be used, for example, it may be earth-like, scaly, or the like. Since it is desirable from the viewpoint of energy cost to pass more current to the graphite of the heating element, non-crystalline carbon black powder with low conductivity is particularly suitable for the carbonaceous material.

処理物２０に発熱体１７を埋設し終えたら、電極１５ａ、１５ｂに通電する。その結果、充填された発熱体１７が通電により発熱する。次第に伝熱により発熱体１７から周囲の処理物２０に熱が伝わり、徐々にＳｉＯガスの発生が起こる。   After the heating element 17 is embedded in the workpiece 20, the electrodes 15a and 15b are energized. As a result, the filled heating element 17 generates heat by energization. Heat is gradually transferred from the heating element 17 to the surrounding processing object 20 by heat transfer, and generation of SiO gas gradually occurs.

反応が進んでいくと、次第に、発熱体１７の周囲の炭素質原料と無機珪酸質原料が溶融あるいは反応し、ガラス質の組織や反応によって生じた炭化珪素結晶が生じる。処理物が無機珪酸質粒子および炭素質粒子の混合物であり周囲に余分な電流が生じ難いことから、エネルギー効率を向上できる。   As the reaction proceeds, the carbonaceous raw material and the inorganic siliceous raw material around the heating element 17 are melted or reacted gradually to produce a vitreous structure or silicon carbide crystals produced by the reaction. Energy efficiency can be improved because the treated product is a mixture of inorganic siliceous particles and carbonaceous particles, and it is difficult for excess current to occur in the surroundings.

通電は、発熱体１７周辺の温度が１５００℃以上になるように電流等を調整するのが好ましい。この通電による加熱時に珪酸質粒子と炭素質粒子とが反応し、一酸化炭素や一酸化珪素がガスとして発生する。後述の分離を容易にするため、硬質な炭化珪素結晶の生じやすい２２００℃以上になるようにするのが特に好ましい。   It is preferable to adjust the current or the like so that the temperature around the heating element 17 is 1500 ° C. or more. At the time of heating by the energization, the siliceous particles and the carbonaceous particles react with each other to generate carbon monoxide and silicon monoxide as a gas. In order to facilitate the separation described later, it is particularly preferable to set the temperature to 2200 ° C. or higher at which hard silicon carbide crystals are easily generated.

所定時間の通電の後、炭化珪素のガラス質組織または結晶を取り出し、発熱体１７と分離する。炭化珪素の殻ごと発熱体を取り出し、殻をハンマー等で粉砕後、中の黒鉛粉末をかき出し、ふるいで殻を分離することができる。このようにして、炭化珪素を製造できる。   After energization for a predetermined time, the glassy structure or crystal of silicon carbide is taken out and separated from heating element 17. The heating element can be taken out together with the silicon carbide shell, and after crushing the shell with a hammer or the like, the graphite powder inside can be scraped out and the shell can be separated by a sieve. Thus, silicon carbide can be produced.

［実験］
（条件）
上記の加熱装置および処理物の処理方法を基準に実験を行なった。加熱装置として長さ８５０ｍｍ、幅６００ｍｍ、高さ６００ｍｍの箱型で、長手方向に発熱体を配置したアチソン炉を用いた。発熱体はφ１００ｍｍで形成した。平均粒径が１ｍｍより小さい珪石とカーボンブラックを２軸ミキサーで混合し、処理物を作製した。混合比はＣ／Ｓｉ＝３（モル）である。この処理物を炉内（容器内）に８００ｋｇ充填した。そして、電極に電圧を印加し、２時間で５０ｋＷまで電力を上げて、８ｈ保持し、その後０ｋＷまで下げた。この条件で発熱体のかさ比重を変えて焼成を繰り返し行なった。 [Experiment]
(conditions)
The experiment was conducted based on the above-described heating apparatus and the method of treating the processed material. As a heating device, an Acheson furnace was used, which was a box type having a length of 850 mm, a width of 600 mm, and a height of 600 mm, in which heating elements were disposed in the longitudinal direction. The heating element was formed to have a diameter of 100 mm. A treated material was prepared by mixing silica stone smaller than 1 mm in average particle diameter and carbon black with a twin screw mixer. The mixing ratio is C / Si = 3 (mol). The treated product was charged into the furnace (in the container) for 800 kg. Then, a voltage was applied to the electrode, power was increased to 50 kW in 2 hours, held for 8 hours, and then lowered to 0 kW. Baking was repeated while changing the bulk specific gravity of the heating element under these conditions.

このようにして行なった焼成において発熱体の抵抗の変化と断線の有無を評価した。８ｈ保持開始時の発熱体の抵抗をＲ１、８ｈ保持終了時の発熱体の抵抗をＲ２と表わしたとき、Ｒ２／Ｒ１の値によって、各実施例と比較例の発熱体の抵抗の変化を評価した。電源の制御能力の観点でＲ２／Ｒ１は小さい方が好ましい。発熱体の吹き飛ばしが無くても焼成により抵抗が上昇するため、Ｒ２が大きくなることが想定された。また、断線の有無は、断線が生じると発熱体の抵抗が無限大となるため、電源の制御回路により焼成が中止されることを基準に判断した。   In the firing performed in this manner, changes in resistance of the heating element and the presence or absence of disconnection were evaluated. When the resistance of the heating element at the start of holding for 8 h is R1 and the resistance of the heating element at the end of holding for 8 h is R2, the change in resistance of the heating elements of each example and comparative example is evaluated by the value of R2 / R1. did. From the viewpoint of controllability of the power supply, R2 / R1 is preferably smaller. Even if there is no blow-off of the heating element, it is assumed that R2 increases because the resistance increases due to the firing. Further, the presence or absence of the disconnection was judged on the basis that the firing was stopped by the control circuit of the power supply because the resistance of the heating element became infinite when the disconnection occurred.

図２は、実験の条件と評価結果を示す表である。各実施例と比較例の発熱体は以下の様に準備した。まず、発熱体にコークスを用いたアチソン炉で炭化珪素を製造し、発熱体にコークスを追加しないで８０ｋＷを２４ｈ保持する５回の焼成を行なった。上記５回目の焼成が終わった発熱体を用いた焼成が比較例２である。比較例２の焼成が終わった発熱体を用いた焼成が実施例３である。実施例３の焼成が終わった発熱体を用いた焼成が実施例２である。実施例２の焼成が終わった発熱体を用いた焼成が比較例１である。比較例１の焼成が終わった発熱体に市販のカーボンブラック（比重０．６）を添加したものを用いた焼成が実施例１である。   FIG. 2 is a table showing the conditions of the experiment and the evaluation results. The heating element of each example and comparative example was prepared as follows. First, silicon carbide was produced in an Acheson furnace using coke as a heating element, and five firings were performed to maintain 80 kW for 24 hours without adding coke to the heating element. The firing using the heating element after the fifth firing is Comparative Example 2. The firing using the heating element after firing in Comparative Example 2 is Example 3. The firing using the heating element after firing in Example 3 is Example 2. The firing using the heating element after firing in Example 2 is Comparative Example 1. Example 1 shows the firing using the one obtained by adding commercially available carbon black (specific gravity: 0.6) to the heating element after the firing of Comparative Example 1 is finished.

（評価結果）
上記のように評価を行なったところ、実施例１〜３の焼成では、発熱体の抵抗変化が小さく、断線も生じなかった。一方、比較例１の焼成では、発熱体の抵抗変化が大きく、焼成の後半では電源の制御電圧上限での焼成となった。比較例２の焼成では、焼成中に発熱体が断線し、焼成が不可能になった。以上より、発熱体のかさ比重を０．１６以上にすることで断線を防止でき、０．４以下にすることで抵抗変化を電圧制御可能な範囲に収めることができることを確認できた。 (Evaluation results)
When evaluation was performed as mentioned above, in baking of Example 1-3, the resistance change of a heat generating body was small, and disconnection did not arise, either. On the other hand, in the firing of Comparative Example 1, the resistance change of the heating element was large, and in the latter half of the firing, the firing was at the upper limit of the control voltage of the power supply. In the firing of Comparative Example 2, the heating element was disconnected during firing, and firing became impossible. From the above, it was confirmed that the disconnection can be prevented by setting the bulk specific gravity of the heating element to 0.16 or more, and the resistance change can be kept within the voltage controllable range by setting the bulk specific gravity to 0.4 or less.

１０ 加熱装置
１１ 容器
１５ａ、１５ｂ 電極
１７ 発熱体
２０ 処理物
DESCRIPTION OF SYMBOLS 10 heating apparatus 11 container 15a, 15b electrode 17 heating element 20 processed material

Claims (4)

加熱処理時にガスの発生を伴う処理物をジュール熱で加熱するための発熱体であって、
かさ比重０．１６以上の黒鉛質の粉体で形成されることを特徴とする発熱体。 It is a heating element for heating by Joule heat a treated product accompanied by gas generation during heat treatment,
A heating element formed of a graphitic powder having a bulk specific gravity of 0.16 or more. かさ比重が０．４以下であることを特徴とする請求項１記載の発熱体。   The heat generating body according to claim 1, wherein bulk specific gravity is 0.4 or less. 鉛直上端面が大気開放され、前記処理物を収容する容器と、
前記容器の内壁に形成され、電圧が印加される電極と、
前記処理物内に埋設され、前記電極に接続される請求項１または請求項２記載の発熱体と、を備えることを特徴とする加熱装置。 A container which is open to the atmosphere at the vertical upper end face and which accommodates the treated object;
An electrode formed on the inner wall of the container to which a voltage is applied;
The heating element according to claim 1, wherein the heating element is embedded in the workpiece and connected to the electrode. 請求項３記載の加熱装置を用いた炭化珪素の製造方法であって、
前記容器内に前記処理物として珪酸質原料および炭素質原料が混合された混合材料を充填するとともに、前記処理物内に前記発熱体を埋設する工程と、
前記発熱体に電圧を印加し通電する工程と、を含むことを特徴とする炭化珪素の製造方法。 A method of manufacturing silicon carbide using the heating apparatus according to claim 3,
Filling the mixed material in which the siliceous raw material and the carbonaceous raw material are mixed as the treated material in the container, and embedding the heating element in the treated material;
And V. applying a voltage to the heating element and energizing the heating element.
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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6144704A (en) * 1984-08-07 1986-03-04 Sumitomo Metal Ind Ltd Production of high-strength and high-density carbonaceous material
JP2004143652A (en) * 2002-08-29 2004-05-20 Showa Denko Kk Finely graphitized carbon fiber, method for producing the same and use for the same
JP2015157737A (en) * 2014-02-25 2015-09-03 太平洋セメント株式会社 Method for producing silicon carbide powder

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6144704A (en) * 1984-08-07 1986-03-04 Sumitomo Metal Ind Ltd Production of high-strength and high-density carbonaceous material
JP2004143652A (en) * 2002-08-29 2004-05-20 Showa Denko Kk Finely graphitized carbon fiber, method for producing the same and use for the same
JP2015157737A (en) * 2014-02-25 2015-09-03 太平洋セメント株式会社 Method for producing silicon carbide powder

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