JPH01278479A - Whisker compound ceramic and production thereof - Google Patents

Abstract

PURPOSE:To produce products of complicated shape and to manufacture high- density products by normal-pressure sintering by orientating whiskers in the direction perpendicular to compression direction of molded article of ceramic. CONSTITUTION:The whisker compound ceramic is a ceramic wherein whiskers are uniformly dispersed in a fixed plane direction in a matrix. In order to produce the compound ceramic, a polymer electrolyte is used as a dispersant of whisker, the surface of the whiskers is mechanically and electrically covered with the electrolyte during dispersion and electrically repulsion force is given between the whiskers. The whiskers are mutually repulsed by the repulsion force during molding such as pressing, injection or extrusion molding, readily orientated in a fixed plane direction and high-density molded articles are obtained. Polyethyleneimine is used as the dispersant of the polymer electrolyte and the pH thereof is preferably 10-13.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a whisker composite ceramic suitable as a structural ceramic or a ceramic for electronic parts, and a method for producing the same.

[Conventional technology]

Generally, as whisker composite ceramics, A j!
2L-S+C+74 Shu-complex, Auiha S+3
Na-SiC whisker composites have been mainly studied, and most of them use the hot pressing method as the sintering method (513N4 reinforced with rsic whiskers).
“Fracture toughness of ceramics”, Ceramics Association Journal 94(9)1
986. pp. 55-59). The main reason for this is that the length of the whiskers is several tens of micrometers and the diameter is several micrometers, making it difficult to disperse compared to general raw material powder (~several micrometers). This is because a ceramic sintered body cannot be obtained (“5interedA j2zos-
3iC-Whisker Composites”,
Am, Ceram.

Soc, Bull, 66 (:2)pp, 33
9-342 (1987)).

[Problem that the invention seeks to solve]

In the hot press manufacturing method described above, since the sample is uniaxially pressed during firing, the shape of the product that can be manufactured is a simple shape such as a disk, and there is a problem that the manufacturing cost is high.

Therefore, it is an object of the present invention to provide a method for inexpensively manufacturing whisker composite ceramics that can be formed into complex shapes and have high density by pressureless sintering, and to provide whisker composite ceramics obtained by the method. It is.

[Means for solving problems]

The present invention provides a whisker composite ceramic in which the whiskers are uniformly dispersed in a certain in-plane direction within the matrix, and a method for manufacturing the same.

The present invention will be explained in detail below.

In the present invention, by uniformly dispersing the whiskers in a certain in-plane direction, the matrix material, such as Al2O3, Si, and Na, is fired at high density during firing without being hindered by the whiskers. If the whiskers are insufficiently dispersed and not well aligned in a certain in-plane direction, the whiskers will form three-dimensional structures or aggregates, and the matrix material will shrink sufficiently and become denser due to these structures or aggregates. This prevents the production of high-density whisker composite ceramics.

The present invention is characterized in that a polymer electrolyte is used as a dispersant for such whiskers.

In the present invention, by using a polymer electrolyte as a dispersant, the polymer electrolyte covers the whisker surface mechanically and electrically during dispersion, and provides electrical repulsion between each whisker. Due to this repulsive force, the whiskers repel each other during molding by pressing, injection molding, extrusion molding, etc., and are more likely to be arranged in the in-plane direction, resulting in a high-density molded product.

The present invention is particularly characterized in that polyethyleneimine is used as a dispersant for the polymer electrolyte. Furthermore, the pH of the polymer electrolyte used is 10 to 13, preferably 10.5 to 1.
It is characterized by being in the range of 1.5.

In the present invention, polyethyleneimine and p
By using the polymer electrolytes H1o to H13, the dispersibility and arrangement of whiskers are further improved, and whisker composite ceramics with higher density can be manufactured.

As a preferred example of the present invention, a method for manufacturing AR, O, -3iC whisker composite ceramics will be described.

Al2O powder is used as the raw material for the matrix, and SiC whiskers are used as the whiskers.

First, we will describe the dispersion characteristics and precipitation characteristics when a polymer electrolyte is used as a dispersant. To investigate the dispersion and precipitation properties, 0.5 g of SiC whiskers were dispersed in a 10-polyelectrolyte/deionized water solution in a 12rn1 glass tube. The concentration of the polymer electrolyte in each solution is as follows.

polyethyleneimine
ne, PEI): 0.5.1.0.3.0.5.0.
7.5 wt% polyvinylpyrrolidone (polyvin
ylpyrolidone.

PVP): 0.5.2.5.5.0.7.5.1
0.0 wt% polyacrylamide (polyacr
ylamide, PA): 0.2.0.4 wt% DarvanC: 5.10.15.20.25.3
0.35.40゜5Q wt% Also, for comparison, polystyrene-methyl methacrylate copolymer (polystyrene-methyl methacrylate copolymer)
thacrylate) (copolymer, P
A 1% by weight toluene solution of S-PIJMA) was also measured. Although PS-PMMA is a type of polymer electrolyte, its degree of ionization is very weak, and it can be considered as a normal dispersant.

Dispersions were prepared by tumbling a solution of SiC whiskers and polyelectrolyte for 1 day, and dispersion height was measured at various intervals over 4 hours to evaluate dispersion properties. Here, the dispersion height is defined as the distance between the boundary between the dispersion section and the supernatant liquid and the bottom surface of the tube. Therefore, the higher the dispersion height, the better the dispersibility.

The sedimentation characteristics were determined from the heights of the supernatant liquid, fine sediment portion, coarse sediment portion, etc. after the sample was left stationary for 5 days after measuring the dispersion characteristics.

After examining the dispersion and precipitation characteristics, each polymer electrolyte/
The S i C whisker mixture was redispersed by ultrasound and its pH was measured with a Koningen pH meter 125.

To investigate the effect of pH on dispersion and precipitation, NH
The pH of the 0.5 wt % PH1 solution was adjusted to 9.4, 10, 8, 12.2 and 11.5 by adding 40) 1, and the resulting dispersion and precipitation properties were evaluated. In addition, the dispersibility of Al2O powder in a 5% by weight PE1l aqueous solution was investigated using the same method used for SiC whiskers.

Experimental results of dispersion characteristics are shown in FIGS. 1 to 5.

Note that FIG. 1 shows typical dispersion characteristics of the above-mentioned dispersants. PH1 (1), PVP (2), FAA
In polymer electrolytes such as (3) and DarvanOC (4), the dispersibility of SiC whiskers has been affected for a long time;
In the case of the general dispersant PS-PMM^(5), the dispersion area decreases to one half in about 20 minutes and to 25% after 60 minutes.

It can thus be seen that the effect of the polymer electrolyte is remarkable. In particular, the dispersibility of PE is good. This is because the viscosity of the solution is slightly higher in P^^, and the density of the precipitate in the aqueous solution is lower in PVP.

From FIG. 1, it can be seen that although PvP did not have very good sedimentation properties (a large amount of coarse precipitate was formed), it had good dispersibility. Although the sample of 0.5% by weight aqueous PVP solution did not form a coarse precipitate, the amount of precipitate was twice as much as with other dispersants.

The pH of the PVP/water/S i C whisker dispersion ranged from 7.2 to 10.2 for the 0.5 wt% PVP sample.
It ranged from 5.1 to 5.1 for the 0 wt% PVP sample.

Although the PA sample exhibited good dispersion properties, it had a fairly high viscosity even in 0.2 wt.% and 0.4 wt.% aqueous solutions. The pH readings of these two dispersions each were 8.
0 and 8.8.

The dispersion properties of DarvanOC were not very good.

The sediment height of all samples decreased to 60% of the gold body after 3 hours and the supernatant liquid was very clear. The pH of the dispersion was 8.
It was in the range of 5 to 8.7.

FIG. 2 shows the dispersibility of SiC whiskers in the P-1 aqueous solution and the PS-PMMA/)luene solution. PH1 shows good dispersibility, especially 3-8wt
% solution has excellent dispersion properties. In this case, the dispersion height decreases by only 10% even after 3 hours. On the other hand, P
The S-PMMA dispersion precipitated within 10 minutes.

Note that even a PH1 solution of 3 wt% or more has excellent dispersion properties, but considering the removal of the binder in the subsequent ceramic forming process, the lower the concentration of the dispersant, the better, and 3 to 8 wt% is sufficient.

Figure 2 also shows the effect of pH. pH of 1035-11.5 for dispersion of SiC whiskers in water
is most preferred.

Figure 3 shows PEI at each concentration and 1 wt% PS-
This figure shows the precipitation characteristics of PMMA. In PEI, the amount of coarse sediment 11 decreases as the concentration increases, indicating that the density of the sediment becomes high.A layer of fine sediment 120 is formed on each coarse sediment 11, but the The height increases very slowly.In PS-PMMA, precipitation progressed rapidly as seen in Figure 2, and the particle size of the precipitate also became fine.

FIG. 4 shows the influence of pH on the dispersibility of SiC whiskers. In addition, pH adjustment is 0.5wt%
This was done by adding N)140H to a PH1 solution of. PTT unadjusted 0.51% Pal (6) (pH
= 9.4) After adjusting the pH by 10 to 13 degrees (7) P
BI 114), α, QED Tel;! It can be seen that the dispersion characteristics are improved. For reference, p without dispersant
The dispersion characteristics of pure water α power with H adjusted to 11.2 are also shown.

From the above comparison, the effect of pH adjustment is clear. however,
The bulk density of the precipitate produced by these dispersants is low, 3.0~
coarse compared to that obtained from 7.5 wt% PBI. In particular, the precipitation height in pure water (deionized water) with a pH of 11.2 was 72% of the total solution height.

This was approximately three times the precipitation height in a 5 wt% PH1 aqueous dispersion.

Figure 5 shows Aj! by 5wt% Pal aqueous solution! This shows the dispersion characteristics of 20* powder. Even 6 hours after dispersion, the height of the dispersed area hardly decreased. Due to this ^
It can be seen that PHI has excellent dispersion characteristics even for β203 powder and SiC whiskers.

Next, an example of manufacturing ^β2Off-SiC whisker composite ceramics will be described.

AL SiC whisker 20. Ball milled in deionized water (pH 11) with grinding media for 68 hours. Ball milling reduced the average length of SiC whiskers and destroyed their agglomerates. After ball milling, the suspension was separated into three parts: precipitate, dispersion (solvent containing dispersed whiskers) and supernatant. Only the dispersion liquid portion was used in the following composite ceramic production. The average length of ball milled SiC whiskers is approximately 2
0 μm, and its average diameter was approximately 0.6 μm.

FIG. 9 shows AL, 0. -3iC whisker composite ceramics are shown.

At 20. Powder at a 1:20 weight ratio of 4% PSI by weight
SiC whiskers were dispersed in a 4 wt % PBI aqueous solution at a 1:200 weight ratio. After sonication and tampling, A1203 dispersion and SiC
Whisker dispersion liquid was mixed in a desired ratio, and AL with a SiC content of 0.5, 10, 15, and 20% by weight, respectively;
03-3iC whisker complexes were formed. 2500r
After centrifugation at pm for 1 hour, the supernatant was removed and deionized water was added into the mixture in an amount equal to half the amount of precipitate. The mixture was then sonicated for 1 hour, cumbling for 24 hours, and colloid pressed for 1 hour at 153 MPa. The binder was burned off in air at 600° C. for 2 hours. Sintering was performed in an argon atmosphere in the following three steps.

(1) Heating to 1555°C for 20 minutes and holding for 10 minutes, (2) Heating to 1650°C for 30 minutes and holding for 20 minutes, and (3) Heating to 1725°C for 30 minutes and holding for 20 minutes. .

The shrinkage rate was determined by the following formula using each dried sample before the binder was burned off and the same sample after sintering.

The density of all samples was determined by the Archimedes method. The sintered samples were coated twice with acrylic spray Krylon (Trademark of Borden) to prevent moisture absorption through surface pores. 1650℃ or 1725℃
15 wt% SiC whiskers sintered with - At, Os
The density of the composite was measured using a modification of STM #C373-72. In this method, uncoated samples were immersed in boiling water for 1 hour and then left in cooling water overnight. The weight of each sample (including absorbed water) was determined the next morning. The weight excluding absorbed water was measured after drying each sample for 12 hours. The volume of each sample (including the volume of absorbed water) is determined by the following formula: Dry weight: Weight after drying in air H, Weight in 0: Weight in water Wet weight: Absorbed water The weight of the rod in the air containing 6 diagrams is 0
．． 5.10.15.20 twt% SiC whisker content ^11203 The fired density of the composite ceramic is expressed as a ratio to the theoretical density. The theoretical density is 3.990 g/crl for 0 wt% SiC whiskers, 3.8608/cffl for 515 wt%, 3.903 g/cut for 10 wt%, and 3.990 g/crl for 15 wt% SiC whiskers. case 3.8608/cat, 2
At 0% by weight, it is 3.8168/cd.

Combustion of composites containing 0, 5, 10, 15 and 20% by weight of SiC whiskers, respectively, was carried out at 1550 °C;
Sintering of other composite plates (15 wt% whiskers) is 1650
or 1725°C. Whisker content from 0 to
It can be seen that the firing density decreases only slightly despite the increase to 2Qwt%. Specifically 0.5
．． Theoretical densities are 88.6.86.8.85. for a SiC whisker content of 10.15.20% by weight, respectively.
They were 5.82.5 and 83.3%.

The sample with 0 wt % SiC whisker content broke into two pieces during sintering, so the density of the larger piece was measured.

15wt%S fired at 1650℃ or 1725℃
The fired densities of the composite ceramic acrylic coated sample with iC whiskers and the substantial remainder Aβ203 were 89.6% and 95.0%, respectively. Note that the SiC whisker content of 15 wt% corresponds to 13.4 vo1%.

References cited earlier (^m, Ceram, Soc, Bu
ll), 2 wt% Y2L, 0.
Despite adding 5 wt% MgD, 170
15 and 20 VOI% by firing at 0~0800℃
The fired densities of the SiC whisker-containing-substantial balance A I 203 composite ceramics are approximately 92 and 81%,
The effect of improving the firing density according to the present invention is obvious.

When fired at 1650°C and 1725°C, the shrinkage rates of the composite ceramic containing 15 wt% SiC whiskers were 92.1% and 90.1% in the diameter direction, and 82.6% in the thickness direction. It was 72.3%. It shows that there is a large contraction in the thickness direction of the composite, which is also the pressing direction, and there is not much contraction in the radial direction. This is because the SiC whiskers are mainly arranged perpendicular to the pressing direction.

7 and 8 show At20.0 containing 15 wt% SiC whiskers. This is an SEM photograph of a fractured surface of composite ceramics (sintered at 1650°C). FIG. 7 shows the center of the sample, and FIG. 8 shows the vicinity of the top of the sample. In Figure 7, most of the SiC whiskers appear in the longitudinal form;
Moreover, they are arranged perpendicularly from the bottom right to the top left of the photo in the direction of the press. In FIG. 8 the SiC whiskers appear in radial form. The alignment effect of SiC whiskers according to the invention is obvious.

According to the present invention, the dispersibility of whiskers is improved and most of the whiskers are arranged in a plane in a certain direction, so that it is possible to achieve high density of whisker composite ceramics by pressureless sintering, which was previously impossible. As a result, it has become possible to provide whisker composite ceramics with more complex shapes at a lower cost, which was not possible using the hot press method.

In the examples of the present invention, A1□0s-SiC whisker composite ceramics were described, but the matrix material was Al
It is not limited to 2O3 (ceramics and polymers such as Si3N,
A whisker material such as whisker or Si3N4 whisker may also be used. Further, a sintering aid may be added. Injection molding, extrusion molding, etc. may be used as a molding method, and hot isostatic pressing may be performed after pressureless sintering to further improve the density.

Furthermore, it is also possible to use the present invention in a hot press method to produce whisker composite ceramics at lower temperatures and in a shorter time.

Polyelectrolytes are particularly useful in the present invention for dispersing SiC whiskers. SiC whiskers and AI, 03
A 3-5% by weight aqueous solution of polyethyleneimine is particularly good for dispersing the powder. SIC in At 203 matrix with unidirectional colloidal pressing by using 4 wt% polyethyleneimine/water as dispersant/solvent.
The whiskers are oriented and the sintered density of the final composite ceramic is significantly improved.

[Brief explanation of the drawing]

FIG. 1 shows various polymer electrolytes (3 weight f;
! PHI/water, 2.5 wt% PVP/water, 0.4 wt FAA/water, 50 wt% DarvanoC/water and 1 wt% PS-PMMA/)S by luene)
FIG. 2 is a graph showing the dispersion characteristics of iC whiskers, and FIG. 2 is a graph showing the dispersion characteristics of iC whiskers.
5, 1, 3, 5 and 7.5 wt%) and 1 wt% PS-
FIG. 3 is a graph showing the dispersion characteristics of SiC whiskers in a PMM^/toluene solution, and FIG.
5, 1, 3, 5 and 7.5 wt%) and 1 wt% PS-
FIG. 4 is a graph showing the precipitation characteristics of SiC whiskers in a PM&lA/) luene solution; FIG. 5 according to the present invention.
Fig. 6 is a graph showing the dispersion characteristics of Al2O powder by weight% polyethyleneimine aqueous solution; -5iC whisker composite ceramics (SiCO 15, 10, 15, 20%) is a graph showing the firing density at 1550 ° C.
Figures 7 and 8 show A 120. This is a 36M photograph showing the center and the vicinity of the top of the fracture surface of -5iC whisker composite ceramics (SiC 15% by weight), and FIG. 9 is a flowchart showing the manufacturing method of Al2O, -5iC whisker composite ceramics according to the present invention.

Claims (6)

[Claims] (1) A whisker composite ceramic, characterized in that the whiskers are oriented in a direction perpendicular to the compression direction of the ceramic sex molded body. (2) A method for manufacturing whisker composite ceramics, including (a) electrically surface-treating the whiskers, and (b) molding a mixture of the whiskers and matrix ceramics so that the whiskers are oriented in the matrix ceramics. A method characterized by forming a compact, and (c) sintering the compact by a pressureless sintering method. (3) A method according to claim 1, characterized in that the surface treatment of the whiskers is carried out by dispersing the whiskers in a polyelectrolyte solution. (4) The method according to claim 3, wherein the surface treatment is carried out by dispersing the whiskers in an aqueous solution of the polymer electrolyte having a concentration of 3 to 8% by weight. (5) In the method according to claim 4, the aqueous solution is
A method characterized by adjusting H10 to H13. (6) The method according to claim 3, wherein the whiskers are SiC whiskers and the matrix ceramics are Al_2O_3 ceramics.