JP3019378B2 - Bonding agent for electrical bonding of ceramics - Google Patents

Description

The present invention relates to a bonding agent for electrical bonding of ceramics used in an electrical bonding method.

<Prior Art> Ceramics are superior to metals in high-temperature strength, thermal shock resistance, abrasion resistance, and the like, and are being applied to gas turbines, automobile engines, heat exchangers, and the like.

In order to fully utilize the functions of ceramics for the various uses described above, it is necessary to join these ceramics together in the manufacturing process.

Therefore, various bonding agents for increasing the bonding strength have been proposed. For example, as shown in JP-A-62-65986, for joining particularly by heating only the joint, A ₂ O _3, SiO ₂
An electrically conductive bonding agent is used which contains a glass component as a main component and a metal oxide, a rare earth oxide or the like mixed with a fluoride such as CaF ₂ or NaF. At the time of joining, an electric current is passed in the direction crossing this joining agent, and the ceramics are joined by the Joule heat generated at that time. In many cases, development for confirming the compatibility of the ceramics to be joined to the material and increasing the high-temperature strength, stability, reproducibility and the like after the joining are continued.

By the way, among the conductive components, it is known that a bonding agent containing CaF ₂ and NaF in particular has obtained good results in terms of the reproducibility and stability of the bonding layer.

<Problems to be solved by the invention> However, when joining is performed using a conventional joining agent,
Since the Ca and Na elements contained in the bonding agent remain in the bonding layer, they cause various properties of the bonded body to deteriorate.
For example, regarding the bonding strength, Ca ²⁺ or Na ⁺ in the bonding layer lowers the bonding strength at a high temperature to lower the viscosity of the bonding layer at a high temperature. For example, in the case of a Si ₃ N ₄ ceramics joined body, if the temperature exceeds 1000 ° C., the strength is significantly reduced.

<Means for Solving the Problems> Under such circumstances, the present inventor has sought to improve the disadvantages of the prior art and to join ceramics that maintain necessary high-temperature strength when using a ceramic molded body as a high-temperature member. Research was conducted for the purpose of developing technology, and a bonding agent for electric bonding suitable for this purpose was found.

That is, the present invention comprises ScF ₃ as a main component, or
It is characterized by a bonding agent for electric bonding mainly comprising ScF ₃ and at least one of A ₂ O ₃ and SiO ₂ .

 Hereinafter, the present invention will be described in detail.

Compounding ratio of the bonding agent of the present invention, in ScF ₃ is 15 wt% or more, A
_At least one of ₂ O ₃ and SiO ₂ is the remainder. The reason for this limitation is that when ScF ₃ becomes 15 wt% or less,
The resistance value of the bonding agent becomes high, and it becomes impossible to supply electricity. Even if electricity can be supplied, the generation of Joule heat generated here is not uniform, so that an unmelted portion is partially generated, and a good bonded body cannot be obtained.

By the way, if there is at least one of A ₂ O ₃ and SiO ₂ , which are wettability components, the wettability with the ceramic to be bonded at the time of bonding is improved, so that a better bonded body can be obtained.

However, a good bonded body can be obtained even when ScF _{3 is set} to approximately 100 wt%. The reason is, for example, when joining Si ₃ N ₄ ceramics, SiO ₂ and a base material sintering aid component generated by an oxidation reaction of the base material at the time of joining enter the bonding agent,
Acts as a wetting component.

The bonding agent of the present invention is obtained by mixing each powder of ScF ₃ , A ₂ O ₃ , and SiO _{2 at} a predetermined mixing ratio, and then uniformly kneading the powder with an organic solvent such as acetone or toluene to form a paste. The thickness of the bonding agent is determined as appropriate according to the composition of the bonding agent, the conditions for applying electric current and heating, the formation of the member, etc., but it is about 0.01 to 0.1 g, more preferably about 0.05 to 0.1 g per cm ^{2 of} the bonding area. What should I do?

At the time of joining, irrespective of the bonding agent of the present invention, depending on the shape of the ceramic or the work having relatively poor thermal shock, there is a possibility that the ceramic or work may be damaged by thermal shock generated during heating and cooling. In this case, it is desirable to control the heating source at the time of preheating heating, control the electric power at the time of energization, and gradually heat and gradually cool.

<Function> The reason why the bonding strength of the bonding agent of the present invention is improved, particularly the high-temperature strength, is presumed as follows.

The Sc element in ScF ₃ which is the active ingredient of the bonding agent of the present invention and the Ca element in CaF ₂ which is the active ingredient of the conventional bonding agent are both present as Sc ³⁺ and Ca ²⁺ in the bonding layer glass. However, these are so-called network modifying ions which cut the Si-O network structure in the bonding layer and exist in the network.

The single bond strength ε between them and oxygen (when the oxide is MxOy, the MO short bond strength formed by the metal atom M and the oxygen atom O) is obtained from the equation (1). While the maximum value in the modified oxide is 60 Kcal / mol, Ca
The -O bond is only about 32 Kcal / mol, indicating that Sc ³⁺ has a stronger binding force with O.

ε = E _D / n (Kcal / mol) (1) where E _D is the dissociation energy (Kcal) required to completely separate 1 mol of oxide (MxOy), and n is the oxygen of M atom The coordination number.

Furthermore, the melting point of the compound is associated with the lattice energy of the compound, the lattice energy U _L, as shown in equation (2), the ionic radius - is related to the (cationic anionic distance).

However, A is Maderungu constant, Zi, Zj is the valence of the cation and anion, e is the charge, a is the cation - anion distance, N _A is Avogadro's number, [rho is the ion coefficient of restitution.

From this equation, it is expected that the smaller the ionic radius of the constituent ions, the larger the lattice energy and the higher the melting point. Sc ^{3+ has} an ionic radius of 0.68Å and Ca
^{Since 2+} is 1.00 °, the Sc ³⁺ compound seems to have a higher melting point. In fact, the melting point of ScF ₃ is 1515 ° C. and CaF ₂
This is supported by the fact that the temperature is 1360 ° C.

From these facts, compared to the conventional bonding agent CaF ₂ system
Using some form of ScF ₃ based bonding agent appears to be able to obtain a high joint body to a high temperature properties.

<Example> A bonding agent composed of ScF ₃ : 50 wt%, A ₂ O ₃ : 25 wt% and SiO ₂ : 25 wt% was prepared, and the bonding agent was placed between 15 mm × 15 mm × 20 mm silicon nitride ceramic molded bodies. It is interposed so that the 50 mg / cm ^2, keeping the current 0.6～1.0A, continued energization 5-10 minutes while moving at a speed of 5 cm / min, was bonded the whole joining surface.

A 3 mm x 4 mm x 40 mm square bar was cut out from this joined body sample, and a three-point bending test was performed under normal temperature conditions under the conditions of a span of 30 mm and a load speed of 0.5 mm / min. When the strength was determined, a strength of 416 MPa was obtained as shown in the following table, and this strength was maintained at 1050 ° C.

Ceramics that can be used as the object to be bonded are Si
_{In addition to 3} N ₄ , oxide ceramics such as A ₂ O ₃ and ZrO ₂ and non-oxide ceramics such as Sialon can be exemplified.

Also, depending on the mixing ratio, kaolinite (A ₂ O ₃ .2SiO ₂ .2H ₂ O) or mullite (3A ₂ O ₃ .2SiO ₂ ), which is a compound of A ₂ O ₃ and SiO ₂ , can be used instead.

Furthermore, as the bonding agent of the present invention, in addition to the main component or ScF _3, the A ₂ O ₃ and SiO ₂ composed mainly of ScF _3, component or the invention for adding the effect of the other operational effects of the present invention In order to further include N, C in the glass of the bonding layer, a bonding agent to which a nitride such as Si ₃ N ₄ , AN, or a carbide such as SiC, TiN or the like has been added to further improve the effect of Include. In this case, oxynitride vitrification and oxycarbide vitrification improve various properties of the joined body.

<Effects of the Invention> As described above, according to the present invention, ScF ₃ as an active ingredient of a bonding agent used in an electric bonding method is used as a main component, or ScF ₃ is mixed with A ₂ O ₃ and SiO ₂ . By using a bonding agent containing at least one as a main component, bonding strength, particularly strength at high temperatures, can be improved.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-160675 (JP, A) JP-A-3-153577 (JP, A) JP-A-3-199173 (JP, A) JP-A-62-162 65986 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 37/00

Claims (2)

(57) [Claims] A bonding agent used in an electric bonding method for heating a bonding portion by Joule heat caused by passing an electric current through the bonding agent, wherein the bonding agent has ScF _3. A bonding agent for electrical bonding of ceramics whose main component is 2. A is interposed a joining agent having conductive ceramic junction portion, by the Joule heat by passing it through a current to the bonding agent, the bonding agent used in the electric joining method of heating the bonding portion, ScF ₃ And A ₂ O ₃ and SiO ₂
A bonding agent for electrical bonding of ceramics containing at least one of the following as a main component.