KR101456374B1 - Method of joining ceramic by liquid-phase sintering - Google Patents

Abstract

The present invention relates to a method of joining alumina ceramics using liquid phase sintering, and it is possible to manufacture a complex polymorphic ceramic structure by joining ceramics of simple shape through the above-mentioned joining method. In order to minimize the machining amount of the dense ceramics Complex polymorphic ceramics can be manufactured as simple-shaped parts and bonded together to produce complex ceramics parts at an efficient price without using special equipment. In addition, when the alumina ceramics are bonded by using the liquid-phase sintering method, the bonding site forms a stronger bonding structure by the diffusion of the dissolved alumina, and the additional pressure supplied from the outside during the bonding process It is not necessary.

Description

TECHNICAL FIELD The present invention relates to a method of joining alumina ceramics using liquid phase sintering,

The present invention relates to a method for manufacturing an intermediate layer material used for bonding ceramics and bonding a simple shape ceramic with an intermediate layer material to produce a polymorphic ceramic structure. More particularly, The present invention also relates to a method of joining ceramics by means of heat sintering in a state of being interposed between ceramics to be bonded to each other by liquid phase sintering.

Generally, compact ceramics sintered bodies have very high hardness, so diamond tools must be used to process them into specific shapes, and the time required for machining is very long, which greatly affects the cost of production in production costs have. Therefore, joining is a way to reduce processing costs in the production of ceramics parts. Ceramics can be made into a simple shape, such as metal welding, and then joined together to produce complex polymorphic parts. However, due to the high melting temperature and brittleness of ceramics materials, it is impossible to melt-bond (weld) like metal, and a ceramics joining method in a manner different from the joining of metals is being developed. The core of ceramics joining technology is to develop a method for economically manufacturing ceramic parts of complex structure. It is used for adhesive bonding, cement bonding, glass frit bonding, active metal brazing, Diffusion bonding, and simultaneous sintering (green body bonding).

Korean Patent Laid-Open Publication No. 1997-0033380 relates to a brazing method which is used in a plurality of ways, and shows low yield strength, high ductility and high tensile strength, which are indispensable for successful bonding between ceramic and metal, Ni-Cr-Fe based bonding alloys useful for bonding between ceramics and metals due to their high bonding performance.

However, conventional joining by the active metal brazing method tends to cause cracks due to generation of stress between the base materials to be bonded, and there remains a heterogeneous structure of metal components which are disadvantageous in heat resistance and oxidation resistance, etc., at the bonding interface after brazing.

Therefore, by interposing an intermediate layer made of a joining agent of a material such as heat resistance, corrosion resistance, and oxidation resistance of the joint, which is similar to the base material, they are homogenized by similar components as the base material, There is a need for a simpler bonding process technique that can produce a precise and complex polymorphic structure because there is no deformation.

An object of the present invention is to provide a ceramic structure having a complex shape by joining ceramics having a simple shape, and more particularly, to a method of manufacturing an intermediate layer to be inserted into a joint surface and bonding a ceramic base material, There is a purpose.

In order to accomplish the above object, the present invention provides a method for producing an anodic oxide powder, comprising the steps of: (a) preparing an anorthite powder which enables liquid phase sintering of alumina; Mixing the anorthite powder, alumina and a solvent to prepare a slurry (second step); Applying the slurry to both surfaces of alumina ceramics to be bonded, drying the slurry in an overlapping manner, or inserting and bonding a tape-shaped intermediate layer casting the slurry by a tape casting method (third step); And bonding the bonded assembly through liquid phase sintering (fourth step). The present invention also provides a method of joining alumina ceramics using liquid phase sintering.

The anorthite powder may be prepared by adding an alcohol including a dispersant to calcium oxide, alumina, and silicon oxide powder and ball milling the powder, drying and pulverizing and granulating the ball milled powder, and granulating the granular powder in a crucible Followed by calcination.

In addition, CaO-Al ₂ O ₃ -SiO ₂ ternary anorthite (CaAl ₂ Si ₂ O ₈ [CAS ₂ ]) is the most commonly used liquid forming powder for the sintering of alumina. The anosite (CAS ₂ ) may be a powder obtained by mixing 15 to 25% by weight of calcium oxide, 35 to 45% by weight of alumina and 35 to 45% by weight of silicon oxide.

The slurry is composed of 30 to 70% by weight of anorthite powder and 30 to 70% by weight of alumina, and 13 to 29.1% by weight of the anorthite powder, 12.5 to 31.5% by weight of alumina and a residual solvent are mixed to prepare a slurry .

The thickness of the intermediate layer may be 20 to 100 탆.

According to the method of joining alumina ceramics using liquid phase sintering according to the present invention, a complicated polymorphic ceramics structure can be manufactured by bonding ceramics having a simple shape. In order to minimize the amount of machining of compacted ceramics, complicated polymorphic ceramics can be manufactured as simple parts and bonded together to produce complex ceramics parts at an efficient price without using special equipment.

1 is a graph showing an XRD pattern measured on an anosite (CAS ₂ ) powder obtained by calcining a raw material mixed powder at three different temperatures.
Figure 2 is a CAS ₂ This is an SEM image showing the microstructure of an alumina ceramic joint bonded using an intermediate layer material.
FIG. 3 is a graph of bonding strength measured by sintering 100 μm-thick intermediate layers at different temperatures.
4 is a graph showing the bonding strength of the alumina ceramic bonded by sintering the Al ₂ O ₃ -CAS ₂ composite intermediate layer material at 1650 ° C for 1 hour.
FIG. 5 is an SEM image of a bonded portion of the alumina ceramic bonded by sintering the Al ₂ O ₃ -CAS ₂ composite intermediate layer material at 1650 ° C. for 1 hour.
6 is a graph showing the bonding strength of alumina ceramics bonded by sintering at 1650 ° C for 1 hour using an intermediate layer material having a weight ratio of alumina: CAS ₂ of 5: 5.
7 is an SEM image of an alumina ceramic bonded by sintering at 1650 ° C for 1 hour at different thicknesses of an intermediate layer material having a weight ratio of alumina: CAS ₂ of 5: 5.

Hereinafter, a method of joining alumina ceramics using liquid-phase sintering according to an embodiment of the present invention will be described in detail. However, it should be understood that the present invention is not limited by the following examples.

First, calcium oxide (CaO), alumina (Al ₂ O ₃ ) and silicon oxide (SiO ₂ ) are mixed to produce anorthite (CAS ₂ ') powder.

In one embodiment, 20.15 wt.% Calcium oxide, 36.65 wt.% Alumina and 43.2 wt.% Silicon oxide are mixed and the mixture is incorporated into ethyl alcohol at a percent by volume of 30 vol.%, Wherein the ethyl alcohol is a phosphate ester salt copolymer Dispersant. The powder mixed slurry is ball-milled, dried, ground and granulated. Then, the granular powder is calcined in a crucible to prepare a powder for a liquid phase type.

To prepare a slurry by mixing the CAS ₂ powder, alumina and a solvent, a polyvinyl butyral binder is added and ball milled for a predetermined time to form a slurry. More specifically, the CAS ₂ powder is 13.5 to 29.1 wt%, the aluminum oxide is 31.5 to 12.5 wt%, and the slurry can be prepared by mixing with the remaining solvent.

At this time, the slurry may be composed of 30 to 70 wt% of CAS ₂ powder and 30 to 70 wt% of alumina.

The slurry is reduced in pressure to remove gas, the slurry is applied to both surfaces of the alumina ceramic to be bonded, and the slurry is dried in a state in which the slurry is in contact with each other or a tape-shaped intermediate layer material cast by the tape casting method is inserted, Bonded by means of liquid phase sintering.

According to the present invention, the CAS ₂ powder contained in the intermediate layer material is melted at the beginning of the heat treatment step of the bonding process to form a liquid phase, and solid phase (alumina) particles present in the intermediate layer together with a partly molten mixture Respectively. At this time, these solid-liquid mixture causes viscous flow to wet both joint surfaces of the base material, and makes direct contact with both sides of the joint surface of the base material, thereby enabling material transfer between the joint surfaces by solution-reprecipitation .

Further, the viscous flow of the intermediate layer due to the liquid phase also provides the effect of preventing the generation of stress due to the difference in plastic contraction ratio with the base material, which is caused by the densification of the intermediate layer, and the prevention of the occurrence of cracks.

In view of the advantages of such a liquid phase, many past studies have attempted to form an intermediate layer only of a composition forming a liquid phase, for example, bonding a glass-frit joining ceramic material. However, as shown in FIGS. 2 and 3, cracks due to the difference in thermal expansion coefficient between the liquid composition and the base material of the intermediate layer and the low strength of the intermediate layer liquid composition itself cause a high bonding strength No junctions can be made.

Therefore, in the present invention, an intermediate layer material of a solid-liquid composite composition is prepared by adding not only the liquid forming composition but also the constituent component particles of the base material at the time of manufacturing the intermediate layer material, and attempting to bond the ceramic using such an intermediate layer material. When the intermediate layer material of the liquid-solid mixture composition is used, the material flow between the bonding surfaces due to the wetting of the base material bonding, dissolution-re-precipitation by the viscous flow of the liquid-solid mixture at the initial stage of the heat treatment, And the generation of stress between the base material and the intermediate layer due to plastic shrinkage of the liquid-solid mixture can be eliminated by the viscous flow. In addition, when the composite composition intermediate layer material is used, the chemical composition of the bonding region becomes a mixed composition of the liquid phase and the alumina particles due to the anosite present in the intermediate layer material at the early stage of the bonding heat treatment as the bonding process heat treatment proceeds, In the end of the bonding heat treatment process, the chemical composition of the bonding layer is made up of a small amount of liquid phase and a large number of alumina particles, thereby inducing a chemical composition and bonding strength similar to those of the liquid phase sintered alumina monolith by allowing the liquid phase to permeate into the base material. This is a key element of the present invention.

Particularly, in order to prevent the occurrence of cracks due to the difference in plastic contraction ratio between the base material and the intermediate layer occurring in the bonding heat treatment process, there is no need to apply pressure as in the normal bonding process, and the viscous flow viscous flow), it is not necessary to supply additional external pressure during the bonding process. In addition, the alumina dissolved in the liquid phase through the liquid phase existing on the joint becomes a channel for diffusion for mass transfer, and a stronger bonding structure can be formed. Therefore, there is no need for a special expensive equipment or process for applying pressure, and it is advantageous in that a ceramic joint body of high strength can be easily obtained economically.

Hereinafter, a method for bonding alumina ceramics using liquid-phase sintering will be described in detail as a concrete example of the above-described method.

≪ Example 1 > Preparation of anorthite powder

The anosite (CAS ₂ ) powder was used as a liquid phase powder in an oxide interlayer. That is, the CAS ₂ powder contains 20.15 wt% of calcium oxide (Extra pure, Daejung Chemicals & Metals Co., Ltd.), 36.65 wt% of alumina (AES-11, Sumitomo Chemical Co., Daejung Chemicals & Metals Co., Ltd.) were each weighed and mixed in ethyl alcohol at a solid volume fraction of 0.3. At this time, the ethyl alcohol contained a phosphate ester salt copolymer dispersant.

The mixed powder mixture was ball milled using alumina balls for 24 hours, dried at 60 DEG C overnight, pulverized and sieved with a 100 mesh sieve to obtain granules. The granular powder was sintered in an alumina crucible at a temperature of 1450 ° C for 1 hour to prepare a CAS ₂ powder through a solid phase reaction. Sintered at different temperatures of 1350 ° C, 1400 ° C and 1450 ° C to find the optimum conditions for the solid phase reaction (see FIG. 1).

< Example  2> Tape type Intermediate layer material  Produce

60% by weight of toluene and 40% by weight of ethanol were mixed in order to prepare an azeotropic mixture used as a solvent for the liquid medium for ball milling and the tapping process.

Alumina and CAS ₂ powder were mixed in an azeotrope mixture of 44 vol.% As a solvent and the azeotropic mixture contained 2 wt.% Of a copolymer dispersant (DISPERBYK-103, BYK Chemie GmbH) relative to the powder. During the mixing process, the amounts of CAS ₂ were adjusted to 1.0, 0.7, 0.5 and 0.3 by weight, respectively, to prepare powders for producing the Al ₂ O ₃ -CAS ₂ composite intermediate layer having different compositions.

The powder was ball milled with zirconia balls, and 6.25 parts by weight and 12.5 parts by weight of a polyvinyl butyral binder B-76 (molecular weight 90,000 to 120,000; Kuraray Co., Ltd.) and B -98 (molecular weight: 40,000 to 70,000; Kuraray Co. Ltd.) was added thereto to prepare a slurry.

16.25 parts by weight of dioctyl phthalate (Samchun Pure Chemical Co., Ltd.), which is a plasticizer, was added to 100 parts by weight of the slurry of the mixed powder,

The slurry was ball-milled again for 24 hours, degassed for 15 minutes at a pressure of 160 torr, introduced into a tape casting process to produce a tape-type intermediate layer and moved at a rate of 44 cm / min, 탆, RS21G, SKC Co., Ltd.). During the casting process, the thickness of the intermediate layer was controlled by the height of the blade of the tape casting machine. In order to measure the bond strength according to the thickness of the intermediate layer, samples were prepared with thicknesses of 20, 50 and 100 μm.

After the tape casting step, it was exposed to air at room temperature and dried for 12 hours to complete a tape-type intermediate layer material.

< Example  3> Alumina Ceramic Of base metal  join

An interlayer was inserted between the two dense alumina ceramic base materials to be bonded. The intermediate layer has a different composition depending on the amount of CAS ₂ and is cut according to the size of the base material.

The combined alumina ceramic matrix was heat treated in air at 1650 ° C for 1 hour. The results of sintering temperature were prepared by heat treatment at different temperatures of 1550 ℃, 1600 ℃ and 1650 ℃. Here, the temperature was increased at a low rate of 2 ° C / min at a temperature range of 25 ° C to 600 ° C and maintained at a constant temperature of 160 ° C, 350 ° C and 600 ° C for 1 hour, Burned.

In order to measure the strength of the joint, the bonded ceramic base sample was made of 4 × 3 × 40 mm ³ rod. The center of each rod was used as a joint, and the outer surface of the measurement specimen was polished using a diamond paste having a size of 6 μm.

The test specimens were tested with 6 specimens (Autograph 500, Shimadzu Co., Ltd.) with a span of 10 mm inside and 20 mm external to the 4-point flexual strength was measured.

In order to observe the change of bonding strength and microstructure according to the thickness of the intermediate layer, the thickness of the intermediate layer was changed to 20 ㎛, 50 ㎛ and 100 ㎛ and SEM images were taken.

Experimental Example 1 Analysis of Anorthite Powder and Intermediate Layer

CAS ₂ The formation process of the anothite phase, the residue and the unreacted phase was analyzed using an X-ray diffractometer (XRD, D / Max-2200).

In addition, the bonded part using the intermediate layer was subjected to thermal etching at 1450 ° C. for 1.5 hours to observe the microstructure using a scanning electron microscope (SEM, S-4800, Hitachi High-technologies Co., Ltd.) Respectively.

1. Bonding at the boundary layer Generation behavior  Confirm

1 is a CAS ₂ And XRD patterns obtained by calcining the powder at three different temperatures. Sintered at different temperatures of 1350 ℃, 1400 ℃ and 1450 ℃ to confirm the XRD patterns. As a result, a small amount of residues and unreacted powder were observed. However, through the solid phase reaction between the raw powders, CAS ₂ Phase was successfully generated.

FIG. 2 is an SEM image showing the microstructure of the bonded alumina ceramic joint using the intermediate layer produced using only CAS _2. FIG. (A) and (b) were sintered at 1,550 ° C, (c) and (d) at 1600 ° C, and (e) and (f) were sintered at 1,650 ° C for 1 hour, respectively. As expected, the CAS ₂ The liquid phase derived from the alumina ceramic completely wet the two alumina ceramic base joints and penetrated between the wetted alumina grains. Furthermore, it was confirmed that the liquid permeates the interface of the particles between the alumina particles and permeates into the alumina ceramic matrix. This can be clearly seen from the decrease in the thickness of the liquid phase layer at the junction, as can be seen in Figures 2 (e) and 2 (f).

FIG. 3 is a graph of bonding strength measured by sintering 100 μm-thick intermediate layers at different temperatures. At this time, the maximum bond strength was 47.1 ± 8.4 MPa. This low bond strength is primarily due to CAS ₂ And the low mechanical strength of the Ca-Al-Si-O glass itself formed by eutectic reaction between alumina. In addition, it is believed that the difference in thermal expansion coefficient between alumina and liquid phase causes cracking and residual stress as shown by the arrow in FIG. 3, and thus shows a low bonding strength.

2. Analysis of bond strength of interlayers according to alumina composition

In order to increase the bonding strength, alumina, which is a base material component capable of forming a solid phase component, was added to the intermediate layer material to prepare an intermediate layer material having a liquid - solid phase composition. The coefficient of thermal expansion (CTE) of the joint was expected to be close to the thermal expansion coefficient of the base material as the content of alumina contained in the intermediate layer increased. The addition of alumina also means that most of the liquid phase penetrates into the base material during the heat treatment process and finally forms a joint composed of a small amount of liquid phase and a majority of solid phase particles. By doing so, the bond strength (232 MPa) higher than that of the monolith of the reported liquid sintered alumina could be achieved. The strength of a typical liquid-phase sintered alumina ceramic monolith with sintering of calcium oxide and silicon dioxide is about 180 MPa.

4 is a graph showing the bonding strength of the alumina ceramic bonded by sintering the intermediate layer material at 1650 ° C for 1 hour. The change in bond strength was measured by varying the amount of alumina introduced into the intermediate layer.

Fig. 5 is an SEM image of a junction of an alumina ceramic bonded by sintering the intermediate layer material at 1650 ° C for 1 hour. Here, (a) and (b) have a weight ratio of 3: 7, the weight ratio of (c) and (d) is 5: 5, and the weight ratio of (e) and (f) is 7: 3.

The increase in the bond strength at the same time when the composition of alumina is increased to 50 wt% is attributed to the fact that the alumina solid particles present in the liquid sintered joint serve as a main frame to withstand the load. This can be confirmed by the dotted line and the arrow in the microstructure image of the junction of FIG. Most of the solid alumina particles are bonded by direct contact between the particles, but in some cases they are bonded through the liquid film between the liquid droplets existing at the contact points of the particles and the particles. This is precisely consistent with the microstructure of liquid phase sintering of general alumina ceramics.

Liquid phase additive additives are used in the production of commercial alumina ceramic joints where the additive based on the alumina-calcium oxide-silicon oxide three-component system contains a number of eutectic reactions forming liquid phases below 1400 ° C It has received constant attention. Adding a small amount of a mixture of calcium and silicon oxide to alumina leads to a small amount of liquid phase formation at 1200 占 폚. This wetts the alumina particles, forms a solution during the sintering process and promotes re-precipitation. On the other hand, the presence of silicon and calcium in the liquid film between alumina particles promotes the transfer of material during the heat treatment process.

On the other hand, it was confirmed that an eutectic liquid was formed in the interlayer inserted between the two alumina ceramic base materials to be bonded. In this case, the mass transfer between the alumina base material and the intermediate layer was enhanced through the dissolution-re-precipitation mechanism. In addition, in the heat treatment process for bonding, the CAS ₂ The liquid phase resulting from the phase was made into a solid-liquid mixture with alumina solid particles added in the interlayer material to make the base material interface wet by viscous flow. Due to the viscous flow and fast mass transfer, the interface between the bonded alumina base materials was filled with alumina, re-precipitated alumina, alumina particles grown in the base material, and a small amount of liquid, creating a strong bond between the base materials.

On the other hand, when the weight ratio of alumina in the intermediate layer exceeds 50%, the reduction in the bonding strength is due to the limited viscosity at the interface of the intermediate layer in the heat treatment of the bonding. When the weight ratio of alumina: CAS ₂ was 7: 3, the amount of solid particles was expected to occupy 62 vol% in volume as a whole. In this case, the viscosity of the solid particles and the liquid mixture partially dissolved in the intermediate layer was injected between the voids as shown in Figs. 5 (e) and 5 (f), and was insufficient to fill the gap.

As a condition of the intermediate layer composition, the interlayer material should be compatible with not only chemically but also thermo-mechanically bonded ceramic base materials and should be melted at a temperature lower than the sintering or melting temperature of the ceramic base material, The intermediate layer should wet the ceramic part and promote mass transfer through the ceramic surface to be bonded.

3. In the intermediate layer  Ceramic Of base metal  Bond strength analysis

The bonding strength was measured according to the thickness of the intermediate layer. 6 is a graph showing the bonding strength of alumina ceramics bonded by sintering at 1650 ° C for 1 hour using an intermediate layer material having a weight ratio of alumina: CAS ₂ of 5: 5. 7 is an SEM image of an alumina ceramic bonded by sintering at 1650 ° C for 1 hour at different thicknesses of an intermediate layer material having a weight ratio of alumina: CAS ₂ of 5: 5.

Referring to FIGS. 6 and 7, the bonding strength according to the thickness of the intermediate layer was increased when the bonding was performed by sintering at 1650 ° C for 1 hour. The highest bonding strength of 232 MPa was obtained when the thickness of the intermediate layer material having a weight ratio of alumina: CAS ₂ of 5: 5 was 50 탆. The difference in bond strength according to the thickness of the intermediate layer is due to the required amount of dissolved interlayer material above the critical amount in order to fill all voids of the alumina ceramic joint.

On the other hand, the roughness and unevenness of the joints hinder close contact between the base materials. And the volume of the melted intermediate layer should be larger than the porosity of the base metal. Referring to FIG. 7, since the volume of the binder and plasticizer in the intermediate layer material is 50 vol%, the intermediate layer material having a thickness of 20 μm is melted and reduced to 10 μm or less. 7 (a) and 7 (b), this was not enough to fill the gap between the alumina base materials.

The cross section of the bonded alumina ceramic in FIG. 7 confirms the voids in the joint, but in the intermediate layer having a thickness of 50 μm or more, an intermediate layer material having almost no homogeneous cracks was found in the alumina base material. The final microstructure at the end of the bonding process consists essentially of alumina particles and a small amount of glass. In the initial stage of the bonding process, as the liquid bonding process formed inside the interlayer material progresses, it penetrates between the alumina grain boundaries in the base material, and ultimately, only a small amount of liquid phase remains in the joint portion, and most of the structure is induced to consist of only alumina solid particles. As a result of the decomposition and infiltration process, the composition of the intermediate layer moves in the alumina direction on the phase diagram, and as a result, the coefficient of thermal expansion of the intermediate layer can be brought close to the value of the base material.

The present invention is summarized as follows.

The present invention relates to a method of joining alumina ceramics by liquid-phase sintering of an intermediate layer material for joining ceramics, and can replace the metal brazing method. The prepared intermediate layer exhibited excellent wettability essential for strong ceramic bonding and played an important role in the mass transfer process. The dissolved CAS ₂ causes a chemical reaction such as dissolution and re-precipitation in the alumina base material, and the abundantly dissolved CAS ₂ liquid becomes the passage through which the dissolved aluminum oxide is diffused through the joint.

In addition, the present invention is a further developed technology in that it does not require production cost and special equipment such as vacuum electric furnace as compared with the conventional metal blazing method, and it is the first bonding of alumina ceramics by liquid sintering of CAS ₂ .

The optimum intermediate layer material had a composition ratio of alumina: CAS ₂ of 5: 5, and a sintering temperature of 1650 ° C showed a bonding strength of 232 ± 55 MPa.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. will be. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims (7)

(Step 1) of producing an anorthite powder which enables liquid phase sintering of alumina;
Mixing the anorthite powder, alumina and a solvent to prepare a slurry (second step);
Applying the slurry to both surfaces of alumina ceramics to be bonded, drying the slurry in an overlapping manner, or inserting and bonding a tape-shaped intermediate layer casting the slurry by a tape casting method (third step); And
And joining the bonded assemblies through liquid phase sintering (fourth step). The method of bonding alumina ceramics using liquid-phase sintering according to claim 1, delete delete The method according to claim 1,
Wherein the anolyte is a mixture of 15 to 25% by weight of calcium oxide, 35 to 40% by weight of alumina and 35 to 45% by weight of silicon oxide. delete The method according to claim 1,
Wherein the intermediate layer material comprises 30 to 70% by weight of anorthite powder and 30 to 70% by weight of alumina. The method according to claim 1,
Wherein the thickness of the intermediate layer is 20 to 100 占 퐉.

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