JP5187579B2 - Method for manufacturing end portion of silicon carbide heating element - Google Patents

Description

The present invention relates to a method for manufacturing an end portion of a silicon carbide heating element.

  The silicon carbide heating element is configured by joining a heating part made of silicon carbide and an end part made of a composite material of silicon carbide and silicon at a high temperature using an adhesive made of SiC, C, and a binder. (See Patent Document 1). Silicon in the composite material constituting the end portion melts in the bonding step, and reacts with the heat generating portion at the interface between the heat generating portion and the end portion to form a good bonding surface.

  In such a silicon carbide heating element, if the resistance value of the end portion is higher than the resistance value of the heat generating portion, power loss increases, which is a problem in terms of energy saving. Is done. As a method for lowering the resistance value, a method is known in which a silicon carbide molded body is heated and fired in a nitrogen gas atmosphere, and at the same time densified and nitrogen is dissolved (dope) to impart conductivity (Patent Document). 1), and a method of lowering the resistance value by performing secondary firing in which a silicon carbide molded body is heated in vacuum or in an inert atmosphere and then reheated in a pressurized nitrogen gas atmosphere. (See Patent Document 2)

The end portion of the silicon carbide heating element is also resistant by reacting and sintering a silicon carbide molded body containing silicon, and then heating to a temperature of, for example, 1800 ° C. or higher in a nitrogen gas atmosphere to dissolve nitrogen in a solid solution. Although the process of lowering the value has been performed, such an extra step causes an increase in manufacturing cost and a decrease in productivity, and hence improvement is desired.
Japanese Patent No. 3932405 JP 2001-110553 A Japanese Examined Patent Publication No. 61-56187

The present invention has been made to answer the above-mentioned demands, and its purpose is to have a low resistance value, reduce the power loss of the silicon carbide heating element, enable energy saving, and reduce the manufacturing cost. Another object of the present invention is to provide a method for manufacturing an end portion of a silicon carbide heating element that is advantageous in terms of surface.

A method for manufacturing an end portion of a silicon carbide heating element according to claim 1 for achieving the above object is a method for manufacturing an end portion of a silicon carbide heating element formed by joining an SiC heating portion and an end portion made of SiC-Si. In this case, silicon carbide and carbon are mixed, and 1.2 to 24% by weight of silicon nitride is added to the total amount of silicon carbide and carbon, and the resulting mixed powder compact is obtained in the presence of silicon. And it heats to the temperature of 1450-1700 degreeC under pressure reduction of 150-1500 Pa, and carries out reaction sintering , and obtains the silicon carbide heating element edge part whose specific resistance value is less than 0.003 ohm-cm .

According to the present invention, there is provided a method for manufacturing an end portion of a silicon carbide heating element that has a low resistance value, can reduce power loss of the silicon carbide heating element, enables energy saving, and is advantageous in terms of manufacturing cost. Is done.

  The manufacture of the silicon carbide heating element end according to the present invention is performed by adding a binder to a mixed powder containing silicon carbide powder, carbon powder and silicon nitride powder, drying, calcining at a temperature of about 500 ° C, The obtained calcined body is encased in silicon powder and heated in a reaction sintering by heating to a temperature of 1450-1700 ° C. in the presence of silicon and under a reduced pressure of 150-1500 Pa. Is called.

  By the reactive sintering, a composite sintered body of silicon carbide and silicon is obtained. Nitrogen decomposed from silicon nitride during the reactive sintering is dissolved (doped) in the composite sintered body, and the specific resistance value is 0. An end portion of a silicon carbide heating element having a low resistance of less than 003 Ωcm is obtained. When silicon nitride is not added, the specific resistance value of the composite sintered body is 0.003 Ωcm or more.

  In the case where silicon nitride is not added, in order to make the specific resistance value of the composite sintered body less than 0.003 Ωcm, it is necessary to perform the treatment at a temperature of 1800 ° C. or higher in a nitrogen gas atmosphere of 1 atm. As the temperature of the processing furnace rises, the consumption of the furnace material is accelerated, the power consumed by the processing furnace is increased, the processing time is increased, the amount of silicon blown out from the processed material is increased, and the processing time in the subsequent process is increased. Such a problem occurs and the manufacturing cost increases.

  The content of silicon nitride in the mixed powder is preferably 1 to 25% by weight, and if it is less than 1% by weight, the effect of lowering the resistance value is not sufficient. Is undesirable because it is expensive and disadvantageous in terms of cost.

  The pressure during reaction sintering is preferably 150 to 1500 Pa, and the heating temperature is preferably 1450 to 1700 ° C. When the pressure is less than 150 Pa, the evaporation of silicon becomes intense, and the silicon necessary for the reactive sintering becomes insufficient. If the pressure exceeds 1500 Pa, a phenomenon that reaction sintering becomes difficult to proceed occurs. If the heating temperature is less than 1450 ° C., reaction sintering is difficult to proceed, and if it exceeds 1700 ° C., excess silicon melts and adheres to the sintered body, and it takes time and effort to remove it, resulting in high costs.

  Examples of the present invention will be described below in comparison with comparative examples to demonstrate the effects. In addition, these Examples show one embodiment of this invention, and this invention is not limited to these.

Example Powders of silicon carbide (SiC), carbon (C), and silicon nitride (Si ₃ N ₄ ) were blended in the proportions shown in Table 1 to obtain mixed powders. However, the addition amount of silicon nitride is a ratio to the total amount of silicon carbide and carbon. Binder and water are added to and mixed with the mixed powder, molded into the end of the silicon carbide heating element (outer diameter: 20 mm, inner diameter: 10 mm, length: 300 mm), dried and calcined at a temperature of 500 ° C., The calcined body was covered with silicon powder, heated to 1650 ° C. under a reduced pressure of 1300 Pa, and subjected to reaction sintering to obtain silicon carbide heating element ends (test materials 1 to 5) made of SiC—Si.

  Silicon carbide (SiC) powder is combined by adding a binder and water, and formed into a heating part (outer diameter: 20 mm, inner diameter: 10 mm, length: 300 mm) of a silicon carbide heating element, dried, and then in a nitrogen gas atmosphere Sintering was performed at a temperature of 2300 ° C. to obtain a SiC heating part.

  The ends made of SiC-Si are welded to both ends of the obtained heat generating part using an adhesive made of SiC, C, and a binder at a pressure of 1300 Pa and a temperature of 1500 ° C. for 3 hours to weld silicon carbide. A heating element was produced. Table 1 shows specific resistance values of the end portions (test materials 1 to 5).

Comparative Example Silicon carbide (SiC) and carbon (C) were blended at a ratio shown in Table 1 to obtain a mixed powder. Silicon nitride (Si ₃ N ₄ ) powder is not added. As in the example, the mixed powder was mixed with a binder and water, molded into the end of the silicon carbide heating element (outer diameter: 20 mm, inner diameter: 10 mm, length: 300 mm), dried, and then at a temperature of 500 ° C. The calcined body is encapsulated with silicon powder, heated to 1650 ° C. under a reduced pressure of 1300 Pa, and subjected to reaction sintering to form a silicon carbide heating element end (test material 6) made of SiC-Si. Obtained.

  In the same manner as in the examples, the ends of the heat generating part were welded by using an adhesive composed of SiC, C and binder at the ends, heat-treated at a pressure of 1300 Pa and 1500 ° C. for 3 hours, and then heated. Was made. Table 1 shows specific resistance values of the end portions (test material 6).

  As shown in Table 1, any of the test materials 1 to 5 according to the present invention can have a specific resistance value as low as 0.0021 to 0.0026 Ωcm and a silicon carbide heating element with little power loss at the end. It is accepted.

  On the other hand, in the test material 6 to which no silicon nitride was added, the specific resistance value was as large as 0.0034 Ωcm. Before the test material 6 was joined to the heat generating part, it was heated in a nitrogen gas atmosphere of 1 atm to 2000 ° C. for 3 hours and then joined to both ends of the heat generating part. The specific resistance value decreased to 0.0025 Ωcm.

Claims (1)

In a method for manufacturing an end portion of a silicon carbide heating element formed by joining an SiC exothermic portion and an end portion made of SiC-Si , silicon carbide and carbon are mixed, and 1.2% relative to the total amount of silicon carbide and carbon. -24% by weight of silicon nitride was added, and the resulting mixed powder compact was heated to a temperature of 1450-1700 ° C. in the presence of silicon and a reduced pressure of 150-1500 Pa to react and baked. And obtaining a silicon carbide heating element end having a specific resistance value of less than 0.003 Ωcm .