JPH089509B2 - Method for manufacturing ceramic three-dimensional mesh structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a method for producing a ceramic three-dimensional network structure used as a preform molded body for forming a composite material with a filter, an adsorption medium, an electrode or a metal. Regarding

(Prior art) Ceramics are superior to metals in terms of slidability, heat resistance, hardness, etc. Especially when composite materials are made with metals or when they are used as filters, etc. It is necessary to make the sintered body of (3) have a three-dimensional network structure.

Conventionally, as a method for producing a sintered body having such a three-dimensional network structure, an organic foam having a three-dimensional network structure is first prepared, and the surface of the organic foam is immersed in a ceramic slurry. A ceramic is adhered to, the ceramic slurry is dried and solidified and then fired, and the organic foam is burned and removed by heat during firing to form a three-dimensional network structure.

(Problems to be Solved by the Invention) The three-dimensional network structure obtained by the above-mentioned conventional method has a coarse structure and a fine structure (pore size is 200 μm or less).
In addition, the combustion temperature of the organic foam is much lower than the sintering temperature of the ceramic, which makes it easy to change the dimensions between the burning of the organic foam and the sintering of the ceramic. If a large amount of a sintering aid is used to prevent this, and the ceramic is sintered at a low temperature, the strength is lowered.

Since the ceramic three-dimensional network structure manufactured by using the organic foam has a coarse structure and insufficient strength, it is liable to be chipped when secondary processing such as electric discharge machining is performed after sintering. Subsequent processing cannot be performed. Further, when electric discharge machining is applied to the ceramic material, the temperature may rise and the ceramic material may be destroyed.

(Means for Solving Problems) In order to solve the above problems, the present invention provides a vitreous pore-forming powder that can be eluted with an acid instead of an organic foam,
An oxide powder for increasing the thermal conductivity was mixed with a ceramic powder to form a molded body, and after firing or calcination of the molded body, the pore-forming powder was eluted with an acid.

(Function) By eluting the pore-forming powder, it is possible to form a three-dimensional network structure having a finer structure than before, and by mixing oxide powder, it is possible to enhance the heat dissipation effect during secondary processing. .

(Example) Below, the Example of this invention is described based on an accompanying drawing. In addition, as an example, a case of manufacturing a conductive ceramic three-dimensional mesh structure that can be subjected to electric discharge machining as a secondary machining is shown.

According to the present invention, as shown in the process chart of FIG. 1, first, a conductive powder, an oxide powder and a pore forming powder are mixed and mixed with a ceramic powder, and the mixed powder is pressure-molded to form a molded body. To manufacture.

Here, as the ceramic powder, for example, Si ₃ N ₄ , Al ₂ O ₃ ,
An insulating material such as ZrO ₂ or sialon is used, and as the conductive powder, one having conductivity from the beginning and one exhibiting conductivity by firing, for example, Ti, Zr, Hf, Ta, W, Mo, C
Carbides such as r, Nb, etc., nitrides, borides, silicides, carbonitrides, and mixtures thereof are used, and the amount added is such that the resistivity of the sintered body after firing is 10 Ωcm or less. Further, as the oxide powder to be added to improve the thermal conductivity, a Group IIa or Group IIIa oxide is used, the amount added for Group IIa oxide is 0.5 to 20 wt%, and for Group IIIa oxide, The addition amount is preferably 0.5 to 50 wt%. This is because if the added amount is less than the above value (0.5), the thermal conductivity becomes insufficient, and if it exceeds the above value (20 or 50), no further effect can be exhibited. Further, as the pore forming powder, an acid-soluble glassy powder having a diameter of about 1 to 5 μm is used, and the specific component ratios are as follows: SiO _{2 20 to} 35 wt% B ₂ O ₃ 35 to 50 wt % Na ₂ O 12 to 25 wt% K ₂ O _{3 to} 10 wt% Al ₂ O _{3 2 to} 12 wt% MgO _{3 to} 14 wt% As a mixing ratio, the final porosity should be 80% or less. In addition to the above powder, TiO ₂ or the like may be added in an amount of 0.1 to ₂ wt% in order to control the size and amount of pores, and the addition amount of the sintering aid is set to be smaller than usual.

Next, after the molded body is dried and degreased, it is calcined. The preliminary firing may be omitted and the main firing may be performed immediately.

When calcination is performed, it is performed at 1000 to 1400 ° C. for about 30 minutes to 2 hours. Then, this calcination melts the vitreous pore-forming powder, takes in the impurities present at the grain boundaries of the ceramic powder into the glass, and also removes the impurities when the pore-forming powder is later eluted with an acid. To do.
Here, the linear shrinkage due to the calcination is 1 to 8%, the hardness after the calcination is 200 to 800 kgf / mm ² in Vickers hardness (HV), and the bending strength is about 40 kgf / mm ² .

When the calcination is completed as described above, the elution treatment with acid is performed. The acid used is HNO ₃ , Hcl or these acids.
A small amount of H ₃ PO ₄ , HF, organic acid, etc. may be added or a mixture thereof may be used.

The three-dimensional network structure obtained by eluting the pore-forming powder in this manner is fired. Firing temperature is 1600-2200
Do it for about 2 hours at ℃. Here, the linear shrinkage due to firing is 1 to 7
%, And the hardness after firing is 600k in Vickers hardness (HV)
The gf / mm ² and bending strength are about 25 kgf / mm ² .

Although the acid elution treatment is performed after the preliminary firing and before the main firing in the examples, the acid elution treatment (pickling) may be performed after the main firing. However, when the acid elution treatment is carried out after the main calcination, the pore diameter becomes slightly larger as is clear from the graph of FIG.

The sintered body having the three-dimensional network structure obtained as described above is subjected to secondary processing such as electric discharge machining, ultrasonic machining, and grinding with a diamond grindstone to obtain a ceramic three-dimensional network structure having a target shape. .

 Next, an experimental example in which specific numerical values are given will be shown.

[Example] Silicon nitride powder (maximum particle size 2 μm, average particle size 0.4 μm) 50
Borided into 0.5 parts by weight of Y ₂ O ₃ (particle size range 0.1 to 1.0 μm, average particle size 0.4 μm) and 0.5 parts by weight of Al ₂ O ₃ (particle size range 0.1 μm, average particle size 0.5 μm). Ten parts by weight of titanium and 39 parts by weight of the above-mentioned glassy powder (maximum particle size 20 μm) were added, and an organic binder and additives were added and mixed well.

After mixing, it was molded at 100 MPa with a dry press to obtain a φ40 × 10 mm test piece.

After being sufficiently dried, it was degreased and then calcined at 1200 ° C. for 2 hours. The shrinkage rate after calcination is 3.5% (linear shrinkage), the hardness is 600 kgf / mm ² in Vickers hardness (HV), and the three-point bending strength is
It was 25 kgf / mm ² .

One of them was pickled (Sample A) and the other (Sample B) was directly subjected to the next step.

The pickling was performed with a 25% HNO ₃ + 0.2% HF solution and irradiation with ultrasonic waves of 16 MHz.

After pickling, it was thoroughly washed with water and dried. After drying, the pore size distribution was measured by the mercury method.

Those pickled (Sample A) and those not picked (Sample B)
Was heated to 1700 ° C. and baked for 1 hour. The shrinkages after firing were 7.5% and 8.0% from the initial state, respectively.

Those that were not pickled were pickled under the same conditions as the conditions of the calcined product to remove all impure components.

After the removal, the above sample was crushed and analyzed for Y in EPMA. It was judged that a component that was contained in an extremely small amount and was not involved in excessive sintering was removed.

On the other hand, SEM observation confirmed that columnar crystals with a diameter of about 0.4 μm and a length of about 5 μm were generated.

The pore size distribution of this product was also taken and summarized in FIG.

In addition, a decrease in pore size was observed due to shrinkage with increasing firing temperature. However, it was found that large pores remained and micropores reduced the amount.

Furthermore, most of the sintering aid components are removed even after calcination,
The fact that grain growth is observed and shrinkage of the compact is observed during the main firing is considered to be a result of the reaction having already progressed to some extent.

On the other hand, crystallographically, the calcined product is an α-Si ₃ N ₄ body,
The amount of β-Si ₃ N ₄ increases after firing.

Also, if pickling is performed after calcination, abnormal grain growth does not occur,
It had a homogeneous structure and most of the particles had the same size.

Furthermore, if the removal component remains until after firing, flaky crystal grains start to be generated. This is given as abnormal grain growth at high temperature, and comparing the above points, the acid treatment after calcination seems to be better.

In both samples A and B, almost no closed pores were found, and the final porosity was 51.2% and 49.6%.

The specific resistance value at this time is 1.3 × 10 ^-2 Ωcm, 0.2 × 10 ^-2
The conductivity was Ω · cm, which was sufficient for electrical discharge machining.

(Effect of the invention) As described above, according to the present invention, the vitreous pore-forming powder is mixed in the ceramic powder, and the pore-forming powder is leached (calcined) and then eluted with an acid. As shown in the graph of FIG. 3, it is possible to obtain a ceramic three-dimensional network structure having a fine structure with most pore diameters of 20 μm or less. Since the oxide is included, the thermal conductivity is improved, heat dissipation during secondary machining can be effectively performed, and a product with accurate dimensions can be obtained by performing electrical discharge machining.

[Brief description of drawings]

FIG. 1 is a block diagram showing the order of steps of the method of the present invention, FIG. 2 is a graph showing the relationship between pore diameter and cumulative percentage, and FIG. 3 is a graph showing the relationship between pore diameter and existence percentage.

Claims (3)

[Claims] 1. A ceramic powder is blended with an oxide powder for increasing thermal conductivity and a pore-forming powder which can be eluted by an acid, and the mixed powder is pressed to form a compact, and the compact is fired. A method for producing a ceramic three-dimensional network structure, characterized in that after the treatment, the sintered body is subjected to an acid elution treatment to elute the pore-forming powder. 2. When the ceramic powder is an insulating substance such as Si ₃ N ₄ , Al ₂ O ₃ , ZrO ₂ or sialon, a powder exhibiting conductivity is mixed into the mixed powder from the beginning or by firing. The method for manufacturing a three-dimensional ceramic network structure according to claim 1, wherein 3. The oxide powder is a Group IIa or Group IIIa oxide, the amount of Group IIa oxide added is 20 wt% or less, and the amount of Group IIIa oxide added is 50 wt% or less. 3. The method for producing a ceramic three-dimensional network structure according to claim 1, wherein the two are used alone or as a mixture.