JPH051228B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for joining ceramics. [Prior Art] Ceramics are generally bonded by applying a bonding agent that melts at high temperatures, abutting the bonded surfaces, and heating the bonded portion. Electric furnaces and gas burners are commonly used heating means. Since heating in an electric furnace is performed by placing the entire ceramic in the electric furnace, not only the joints but also the entire ceramic is exposed to high temperatures. Heating with a gas burner involves blowing gas burners (generally a plurality of gas burners) onto the joint and igniting the joint with a gas flame. In the heating method using a gas burner, temperature unevenness tends to occur at the joint, so in order to suppress this, it is necessary to periodically change the position where the gas flame hits, and a moving (or rotating) device to the ceramic side or the gas burner side is required. is provided. The present inventors have also proposed a method for joining ceramics by passing current through the bonding agent portion while heating the bonding portion with a gas burner, and melting the bonding agent by the Joule heat generated by the energization. (Tokugansho
61−78697). In this bonding method, a bonding agent that is conductive at high temperatures is used. [Problems to be Solved by the Invention] When heating using the electric furnace described above, the entire ceramic is exposed to high temperatures, which causes significant thermal contraction and thermal distortion, leading to problems such as thermal deterioration of the base material. . When heating with a gas burner, it is difficult to control the temperature of the joint, and the positional temperature difference or temporal temperature change at the joint may become excessive.This causes considerable thermal stress to be applied to the joint, causing the joint to fail. Cracks may occur in the parts. In addition, in the method of heating the bonded portion with a gas burner while passing electricity through the bonding agent portion to heat the bonded portion with Joule heat, the bonding agent must be electrically conductive at high temperatures. An object of the present invention is to provide a method for joining ceramics that has small thermal shrinkage, thermal distortion, thermal deterioration, etc., does not cause problems due to thermal stress, and can be used even with a bonding agent that does not have conductivity at high temperatures. It's about doing. [Means for Solving the Problems] A bonding agent having a dielectric loss greater than that of ceramics is used, this bonding agent is interposed between the bonding surfaces of the ceramics, and the bonding surfaces are abutted against each other. Next, a high frequency electric field in a short wave band or a microwave band is applied to the vicinity of the joint part or to the entire ceramic, and dielectric heating is used to heat and melt the bonding agent, thereby bonding the ceramics. [Operation] A dielectric placed under an alternating electric field generates dielectric loss and heats up. If the loss generated per unit volume of the dielectric is P (w/cm ³ ), it is given by P=(5/9)fE ² eεtanδ×10 ⁻¹² . Here, f, E, ε, and tan δ are frequency (Hz), electric field strength (V/cm), relative dielectric constant, and dielectric power factor, respectively. Further, εtanδ is called a loss coefficient and indicates the degree of loss generated in a dielectric, and a substance with a larger loss coefficient generates a larger dielectric loss. When bonding ceramics, use a bonding agent with a loss coefficient larger than that of the ceramics in order to bring the bonded part to the highest temperature. The frequency of the heating power source is a short wave band or a microwave band, and the usable frequencies are determined by the Radio Law. The frequencies allocated for industrial, chemical, and medical purposes in Japan are 13.56, 27.12, and 27.12 in the shortwave band.
40.68MHz, and in the microwave band, 2450,
5800MHz, etc., so select the frequency you want to use from among these. When a short wave power source is used, the ceramics to be bonded are placed between plate-shaped electrodes near the joint, and when a microwave power source is used, the ceramics to be bonded are housed in a metal box that is irradiated with microwaves. In such an arrangement, by applying a high-frequency voltage between the plate-shaped electrodes or by irradiating high-frequency power into the metal box, a high-frequency electric field is applied to the vicinity of the ceramic joint or the entire ceramic, and the above equation is satisfied. Produces fever as shown. Since the loss coefficient of the bonding agent is larger than that of the ceramics, the bonding agent part will be heated more strongly than the ceramic part.
Selective heating occurs in the so-called bonding agent portion. In this way, the bonding agent portion can be efficiently heated and melted to bond ceramics. Note that the dielectric constant (ε) and dielectric power factor (tan δ) of a dielectric usually change depending on temperature and frequency even if the material and composition are the same. Therefore, the loss coefficient (εtanδ) also usually changes depending on temperature and frequency, and it is desirable to use a bonding agent with these behaviors in mind. [Example] An example of the present invention will be described with reference to the drawings. FIGS. 1A and 1B are schematic diagrams showing a bonding apparatus for carrying out the method of the present invention, showing a plan view and a front view, respectively. In this embodiment, a case will be described in which rectangular ceramics 1a and 1b are vertically butt-jointed obliquely. The surfaces of the ceramics 1a and 1b to be bonded are inclined with respect to the thickness direction, and the ceramics 1a and 1b are butted together with a bonding agent 2 interposed therebetween. The loss coefficient of the bonding agent needs to be larger than the loss coefficient of the objects to be bonded, so a material with a large loss coefficient is mixed into the powder of the material components of ceramics 1a and 1b, and other suitable auxiliaries and water are added. etc. and knead it to form a sheet or pellet to obtain the bonding agent 2. Materials that increase the loss coefficient include KAlSi ₃ O ₈ , NaAlSi ₃ O ₈ ,
_Li2O , _SiO2 , MgO, _TiO2 , BaO, _{Al2O3 ,} ZnO,
There are B ₂ O ₃ , etc., and from these, suitable types,
The loss coefficient of the bonding agent 2 can be made several times to several tens of times larger than the loss coefficient of the ceramics 1a and 1b by mixing the same amount of material. Tables 1 and 2 show examples of dielectric properties of ceramics, glasses, etc.

【table】

[Table] Ceramics 1a and 1b are held in place by a support jig (not shown). Electrodes 3a and 3b are disposed facing each other on the left and right sides of the joint near the joint, and are held in place by a support jig (not shown). The electrodes 3a and 3b are made of extremely heat-resistant metal (eg, molybdenum, etc.) so as to withstand high temperatures. The lengths of the electrodes 3a, 3b in the vertical direction and the length in the front-rear direction are larger than the lengths of the ceramics 1a, 1b in the vertical direction and the lengths of the longitudinal joints of the ceramics 1a, 1b, respectively. The electrodes 3a and 3b are
The ends in the front and rear directions are opened in a flap shape, so that the distance between the opposing electrodes increases. The purpose of this is to reduce the heat generation density by making the electric field strength lower in the part farther away from the joint in the front-rear direction than in the joint part, and to smooth the temperature distribution in the front-rear direction of the ceramics during joining. It is. The high-frequency power generator 4 is composed of a self-excited oscillator, etc., and rectifies a commercial frequency alternating current into a direct current, and further performs frequency conversion and voltage conversion of the high frequency, and connects the electrodes 3a, 3b to an application line 5 using a coaxial line or the like. Apply a high frequency voltage to. The frequency to be used is selected from among the frequencies approved for use under the Radio Law as shown in the above [Operation] section. The outline of the ceramic bonding procedure is as follows. A bonding agent 3 is interposed between the bonding surfaces of the ceramics 1a and 1b, and the bonding surfaces are pressed and fixed together using a support jig (not shown). The electrodes 3a and 3b are placed on the left and right sides of the joint between the ceramics 1a and 1b, with a gap of about 2 to 3 mm between the electrodes and the ceramics at the center of the electrodes, and fixed in place using a support jig (not shown). A high frequency voltage is applied from the power generator 4 between the electrodes 1a and 1b. An electric field is applied between the electrodes 1a and 1b, and dielectric heating occurs at the ceramic bonding area, causing a temperature rise with the bonding agent 2 being the highest temperature area. After several minutes to more than 10 minutes after energization, the temperature suitable for bonding (temperature at which the bonding agent melts, generally 1,000-odd degrees) is reached, so at this point the energization is stopped and the heated part is allowed to cool naturally. In addition, at the final stage of energization, ceramics 1
Pressure is applied to a and 1b in the direction of pressing them against each other (pressure in the normal direction on the joint surface is 0.05 to 2 Kg/mm ² ).
By discharging the excess bonding agent and voids to the outside, a thin and dense bonding metal is formed, so that the bonding strength can be increased. In addition, it is possible to perform intermittent control of energization, and perform slow cooling by reducing the energization rate until the final energization is stopped, thereby making it possible to further reduce the bonding stress. Further, dielectric heating may be performed in the vicinity of the bonding portion and the electrode under an inert gas atmosphere. In this way, oxidative deterioration of the ceramics due to high temperatures during bonding can be prevented, and the appearance of the bonded portion can also be improved. Other Examples Preheating method using auxiliary heat source Generally, the loss coefficient of a dielectric tends to be smaller at room temperature than at high temperature. In such a case, dielectric heating alone causes problems such as a slow rise in temperature, but these problems can be solved by preheating the joint using an auxiliary heat source. As an auxiliary heat source, use a radiant heat radiation type electric heater as shown in Figure 1B.
It is also possible to preheat the ceramic joint by attaching it near the upper or lower surface of the ceramic joint. Furthermore, (or) a contact heating type electric heater may be embedded in the power sources 3a and 3b, and the heat may be transferred from the electrode to the ceramic junction. When the temperature of the ceramic joint reaches several hundred degrees due to these auxiliary heat sources, the input of the auxiliary heat sources is cut off. Next, in order to avoid problems when applying high-frequency voltage, the electric heaters placed on the top and bottom surfaces of the ceramic joint should be separated from the joint surface.
The input lead wire to the electrode-embedded heater is separated from the electrode part, and then dielectric heating is performed. Dielectric heating method in a metal box When using a microwave band frequency, the ceramics to be bonded are placed inside a metal box (one side is approximately several times the wavelength), and high-frequency power is irradiated into the metal box. Ceramics can be bonded using this method. In this method, high frequency power generated by a magnetron is guided through a waveguide or the like, an opening is provided in the metal box, and the high frequency power is irradiated into the metal box from this opening. In this method, it is necessary to pay attention to the structure and arrangement of ceramic supporting jigs (made of metal) so that they do not generate discharge or become a shadow of the power irradiated to the joint. In addition, in order to uniformly heat the joint, it is necessary to avoid fixation of the electric field distribution in the joint, and for this purpose, it is necessary to use a metal starvation fan or to use materials to be joined (ceramics and other materials). measures such as irradiating high-frequency power while rotating the support material, etc.). [Effects of the Invention] According to the present invention, since the bonding agent and its vicinity can be intensively heated, thermal deterioration and thermal deformation of ceramics accompanying bonding can be reduced. Furthermore, since the joint portion is heated uniformly over time, the thermal stress during joining becomes extremely small, and the joint strength improves. Furthermore, even a bonding agent that has low conductivity and cannot be used for electrical bonding using Joule heat can be used as a bonding agent according to the method of the present invention.

[Brief explanation of the drawing]

1A and 1B are a plan view and a front view, respectively, schematically showing a bonding apparatus for carrying out the method of the present invention. 1a, 1b...ceramics, 2...bonding agent,
3a, 3b... Electrode, 4... High frequency power supply device.

Claims (1)

[Claims] 1. A method of joining ceramics by interposing a bonding agent between the bonding surfaces of ceramics, butting the bonding surfaces, heating the bonded portion, and melting the bonding agent,
Using a bonding agent that causes a dielectric loss larger than the dielectric loss of the ceramics, the bonding agent is heated and melted by applying a high frequency electric field in a short wave band or microwave band to the vicinity of the bonded portion or the entire ceramic to dielectrically heat it. Ceramics joining method.