JPH07172905A - Production of alumina ceramics - Google Patents

Abstract

PURPOSE:To improve sliding characteristics, mechanical strengths and heat and impact resistance by molding and baking mixed powders consisting of a given amount of a sintering assistant, Al2O3 powder and SiO2 powder. CONSTITUTION:A 0<=TiO2<=95wt.% TiO2 powder having 0.2-20mum average size, 5<=B2O3<=80wt.% B2O3 powder having 0.5-50mum average size and 0<=CaO<=50wt.% CaO powder having 0.5-50mum average size are compounded to obtain a sintering assistant. Then, to 85-94wt.% Al2O3 powder having 0.2-25mum average size and 2-7.5wt.% SiO2 which is a sub-component having 0.2-25mum average size, the this sintering assistant is mixed as the sintering assistant so that 2-13wt.% sum of TiO2, B2O3 and CaO powders are contained to obtain mixed powders. Then, the mixed powders are molded and baked to produce alumina ceramics having 5-500mum open pore.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing alumina ceramics, and more particularly to a method for producing alumina ceramics that can be used in ceramic substrates, thermocouple protection tubes, faucet valves for mixing hot and cold water, and the like.

[0002]

2. Description of the Related Art Alumina ceramics, which are widely used as various industrial materials, use SiO _{2 as a} raw material for Al ₂ O _3.
2 , a sintering aid such as CaO, MgO, etc. was added and fired at a high temperature, and usually contains Al ₂ O _{3 in an amount} of 80% by weight or more.

Since this alumina ceramic is excellent in electrical insulation, mechanical properties, corrosion resistance, heat resistance, etc., it is used as a hybrid IC substrate, a ceramic tool, an ignition plug for an internal combustion engine, etc., and has an excellent thermal shock resistance. It is also used as a thermocouple protection tube, mechanical seal parts, etc., by utilizing its properties and sliding characteristics.

As an alumina ceramic used for such an application, first, ZrO ₂ powder, TiO ₂ powder, and silicate flux component are mixed in a predetermined ratio with Al ₂ O ₃ powder as a main component, and the mixture is fired to obtain alumina. JP-A-1-320264 discloses a dispersion of tetragonal zirconia in the vitreous binder phase at the crystal grain boundary.
Alumina ceramics obtained by this manufacturing method,
It is described that the bending strength is high and the thermal shock resistance is excellent.

Further, in Japanese Patent Laid-Open No. 61-291450, Al ₂ O ₃ powder, which is the main component, is added to SiO ₂ powder and Ti.
After blending O ₂ powder and CaO powder in a predetermined ratio, 1
Alumina ceramics that are fired at 450 ° C. or lower are disclosed. It is described that this alumina ceramic is also excellent in mechanical strength and thermal shock resistance and can be used for various machine parts.

Further, in Japanese Patent Publication No. 61-56184, a method for producing a low-expansion porcelain composition in which mullite powder, Al ₂ O ₃ powder and B ₂ O ₃ powder are mixed at a predetermined ratio, molded, and fired Is disclosed. It is described that the porcelain composition containing alumina and mullite as constituent components obtained by this production method has excellent thermal shock resistance and can be used as a protective tube for a thermocouple.

[0007]

However, the above-mentioned Japanese Patent Laid-Open Nos. 1-320264 and 61-291450.
The alumina ceramics disclosed in JP-B No. 61-56184 and JP-B No. 61-56184 are manufactured for the purpose of improving thermal shock resistance, segregation strength and the like, and thus have good properties as described above. When it is used for a sliding member that uses a lubricant as a medium, its sliding characteristics are not satisfactory. The sliding characteristics of alumina ceramics will be described below.

A specific example of using alumina ceramics as a sliding member is an example of using alumina ceramics as a valve for mixing hot water. In this hot water mixing plug, two disc-shaped valve bodies are slidably brought into contact with each other so that fluid passages formed in the respective valve bodies are connected or disconnected.

FIG. 1 (a) is a vertical sectional view schematically showing the hot water mixing stopper, and FIG. 1 (b) is a sectional view taken along the line bb of the hot water mixing stopper shown in FIG. 1 (a).

As shown in FIG. 1A, the movable valve body 11 and the fixed valve body 12 are arranged inside the tubular member 16 in a state of being in contact with each other at the sliding contact surfaces 11a, 12a. This movable valve body 1
A concave portion 14 is formed on the upper part of 1, and the concave portion 14 has
In order to move the movable valve body 11, one rounded end of the rod-shaped body 15 is inserted. The rod-shaped body 15 is supported at one point of the movable valve body 11 so that it can be easily operated by using a lever, and the other end of the rod-shaped body 15 is connected to the lever 13.

Further, as shown in FIG. 1B, the tubular member 1
Three passages 16a, 16b, 16c are formed in the inside of 6, and the hot water and the cold water flow in from the passages 16a, 16b, while the inflow and mixed liquids flow out from the passage 16c. There is.

As can be seen from FIGS. 1 (a) and 1 (b),
By moving the lever 13 up and down, left and right, the movable valve body 1
1 can be freely moved in a state of being in contact with the fixed valve body 12 within the sliding contact surface 12a. Therefore, this allows passage 1
6a, 16b and 16c can be connected to and cut off from each other, and the flow rate of the liquid flowing from the passages 16a and 16b can be controlled.

When the above-mentioned alumina ceramics is used as the valve body of such a hot water mixing plug, a lubricant such as silicone grease is applied to the sliding contact surfaces 11a and 11b of both the movable valve body 11 and the fixed valve body 12. Although the sliding characteristics must be maintained, when the above-mentioned alumina ceramics are used, the lubricant leaks out during long-term use, the sliding friction becomes large, and the lever 13 cannot be operated easily. There is a problem in that the sliding characteristics of the alumina ceramics are deteriorated, such as being damaged or worn.

In order to prevent such a lubricant from flowing out, it has been proposed to use a porous ceramics sintered body having open pores of a three-dimensional mesh structure made of, for example, silicon carbide as a material of the valve body. Has been made (Japanese Patent Laid-Open No. 61-
(JP-A-206875, JP-A-61-244980, JP-A-62-37517).

In these porous materials, the lubricant, resin, etc. are permeated and retained in the open pores, so that these lubricants, etc. do not flow out even after long-term use, and the sliding characteristics are maintained. It has been described that it has the advantage of being able to.

However, since these materials are composite materials, the manufacturing cost is high, and in terms of performance, wear resistance and deterioration of material strength become problems when used for a long time, which is not practical. There was a problem.

The present invention has been made in view of these problems, and is excellent in sliding characteristics, mechanical strength, and thermal shock resistance, and particularly excellent sliding characteristics can be maintained for a long period of time. It is an object of the present invention to provide a method for producing alumina ceramics.

[0018]

In order to achieve the above object, the alumina ceramics according to the present invention comprises 85 to 94% by weight of Al ₂ O ₃ powder as a main component and Si as an auxiliary component.
The powder contains ₂ to 7.5% by weight of O ₂ powder, and further contains _{2 to 3} powders of TiO ₂ , B ₂ O ₃ and CaO as a sintering aid in total.
A mixed powder containing 13% by weight, wherein the content of each component in the sintering aid is 0 ≦ TiO ₂ ≦ 95% by weight, 5 ≦
It is characterized in that a mixed powder in the range of B ₂ O ₃ ≦ 80 wt% and 0 ≦ CaO ≦ 50 wt% is molded and fired.

In the method for producing alumina ceramics according to the present invention, the main component Al ₂ O ₃ powder has an average particle size of 0.2 to 25 μm, more preferably 0.5 to 10 μm. The amount is preferably in the range of 85 to 94% by weight.

If the average particle size of the Al ₂ O ₃ powder is less than 0.2 μm, the shrinkage during firing becomes too large, and warpage is likely to occur, and the size of the particles in the sintered body becomes uneven. Therefore, the mechanical strength is lowered, and on the other hand, if the average particle diameter exceeds 25 μm, densification becomes difficult and the mechanical strength is lowered.

The content of Al ₂ O ₃ powder is 85% by weight.
If it is less than A, the hardness is lowered and the wear resistance is also lowered.
If the content of the l ₂ O ₃ powder exceeds 94% by weight, the thermal shock resistance is deteriorated.

SiO ₂ powder, which is an accessory component, is Al ₂ O ₃
The appropriate amount of mullite (3Al ₂ O
₃ : 2SiO ₂ ) and has an average particle size of 0.2 to 25 μm, further 0.5.
The content of the SiO ₂ powder in the raw material powder is preferably in the range of _{2 to} 7.5% by weight.

If the average particle size of the SiO ₂ powder is less than 0.2 μm, it becomes difficult to uniformly disperse the primary particles during mixing, while the average particle size of the SiO ₂ powder is 25 μm.
When it exceeds m, the particle size is too large, which makes uniform mixing difficult, and it becomes difficult to form an appropriate amount of mullite.

When the content of SiO ₂ powder is less than 2%, mullite is less produced and the thermal shock resistance is inferior.
If the content of the iO ₂ powder exceeds 7.5%, the amount of mullite produced becomes too large and the mechanical strength decreases.

[0025] In the production method of alumina ceramics according to the present invention, in addition to SiO ₂ in the raw material powder, but is blended powder TiO _2, B ₂ O ₃ and CaO as a sintering aid, which is SiO ₂ Along with this, a glass phase is formed in the grain boundary to enable low temperature firing and to secure thermal shock resistance, and the content is 2-1.
3% by weight is preferred.

If the total amount of these sintering aids is less than 2% by weight, low-temperature firing becomes difficult, while if the content of these sintering aids exceeds 13% by weight, the mechanical strength decreases.

The TiO ₂ powder, which is a component of the sintering aid, is added to promote the synthesis of mullite from Al ₂ O ₃ and SiO ₂ and to achieve low thermal expansion.
The average particle diameter is preferably 0.2 to 20 μm, and the content thereof is preferably in the range of 0 ≦ TiO ₂ ≦ 95% by weight with respect to the whole sintering aid.

[0028] In the mean particle size of the TiO ₂ powder is less than 0.2 [mu] m, uniform dispersion due to aggregation or the like of the primary particles upon mixing becomes difficult and an average particle diameter of the other TiO ₂ is more than 20μm when TiO ₂ component Segregation deteriorates properties such as mechanical strength.

If the amount of the TiO ₂ powder with respect to the total amount of the sintering aid exceeds 95% by weight, it becomes difficult to form a glass phase,
Low temperature firing becomes difficult.

B ₂ O ₃ in the sintering aid is used to form a glass phase to lower the firing temperature, and to volatilize the glass phase by the subsequent firing to form open pores inside the sintered body. The average particle size is 0.5 to
50 μm is preferable, and the content thereof is preferably in the range of 5 ≦ B ₂ O ₃ ≦ 80 wt% with respect to the whole sintering aid.

If the average particle diameter of the B ₂ O ₃ powder is less than 0.5 μm, it becomes difficult to uniformly disperse the primary particles during mixing, while the average particle diameter of B ₂ O ₃ exceeds 50 μm. And segregation of B ₂ O ₃ components deteriorates properties such as mechanical strength.

If the B ₂ O ₃ powder content is less than 5% by weight, the glass phase formed during firing is less likely to volatilize and open pores are not formed in the sintered body, while the B ₂ O ₃ powder is fired. If the amount with respect to the total amount of the auxiliary agent exceeds 80% by weight, the volatilization amount of the glass phase becomes too large, the void amount in the sintered body becomes too large, and the mechanical strength decreases.

CaO in the above-mentioned sintering aid is added to promote sintering, and its average particle size is 0.5 to 0.5.
50 μm is preferable, and the content thereof is preferably in the range of 0 ≦ CaO ≦ 50% by weight with respect to the entire sintering aid.

If the average particle size of the CaO powder is less than 0.5 μm, it becomes difficult to uniformly disperse the primary particles during the mixing, while if the average particle size of CaO exceeds 50 μm, the CaO component is segregated. Characteristics such as mechanical strength are deteriorated.

If the amount of CaO powder with respect to the total amount of the sintering aid exceeds 50% by weight, the thermal shock resistance deteriorates.

[0036]

According to the alumina ceramics of the present invention,
85 to 94% by weight of Al ₂ O ₃ powder as a main component, ₂ to 7.5% by weight of SiO ₂ powder as a secondary component, and further powders of TiO ₂ , B ₂ O ₃ and CaO as a sintering aid. It is a mixed powder containing 2 to 13 wt% in total, and the content of each component in the sintering aid is 0 ≦ TiO ₂ ≦ 95.
% By weight, 5 ≦ B ₂ O ₃ ≦ 80% by weight, 0 ≦ CaO ≦ 50
Since the mixed powder in the range of wt% is molded and fired, the addition of B ₂ O ₃ causes the other three components (SiO ₂₎ to be added.
₍₂ , TiO ₂ , CaO), a glass having a much lower melting point is formed at the grain boundaries, and firing at low temperature is realized.
Furthermore, a part of this glass phase formed during firing volatilizes to form large open pores, while this glass phase does not deteriorate the mechanical properties of the sintered body, so sliding properties, mechanical strength, and heat resistance are improved. Alumina ceramics having excellent impact properties are manufactured.

Therefore, this alumina ceramics is used for various members utilizing the above characteristics, but when it is used as a sliding member through a lubricant such as a valve, grease as a lubricant has open pores. It is filled in a large amount inside, and the lubricant gradually exudes to the surface during use, so the initial excellent sliding characteristics are maintained, and in addition it has excellent mechanical strength and thermal shock resistance The mechanical properties do not deteriorate with use.

The diameter of the open pores in this alumina ceramics is usually 5 to 500 μm, and large pores are obtained especially when the firing temperature is raised above the temperature at which the maximum density is obtained (over-fired state). Therefore, a large amount of lubricant such as grease can be retained in the open pores.

On the other hand, in ordinary alumina ceramics, the diameter of the open pores is as small as 0.1 to 5 μm, and even if grease is applied to the surface, the volume for holding this grease is small, so that the surface can be kept in a short time. Drained from.

[0040]

Embodiments of the method for producing alumina ceramics according to the present invention will be described below with reference to the drawings.

The average particle size is 1 μm and the purity is 99.9% by weight.
The above Al ₂ O ₃ powder, silica stone powder having an average particle size of 2 μm,
Table 1 shows a TiO ₂ powder having a reagent grade 1 and an average grain size of 1 μm, a CaCO ₃ powder having a reagent grade 1 and an average grain size of 1 μm, and a B ₂ O ₃ powder having a reagent grade 1 and an average grain size of 5 μm. The mixture was mixed at a ratio of oxide weight, 0.1% by weight of sodium hexametaphosphate was added as a deflocculant, and wet mixing was performed for 10 hours in a pot mill made of alumina.

Next, the slurry obtained by the wet mixing was granulated with a spray dryer and passed through an 80 mesh screen. Then, this powder was molded under a pressure of 1200 Kg / cm ² and fired within a range of 1250 to 1600 ° C. for 2 hours to obtain an alumina ceramics of 10 mm × 50 mm × 50 mm.

Next, the alumina ceramics obtained in the above process was processed into a size of 3 mm × 4 mm × 50 mm by grinding, and various characteristics shown in Table 1 were evaluated. The results are shown in Table 1.

Here, the bending strength was measured by three-point bending in accordance with JIS1601 at a head speed of 0.5 mm / min, and the thermal shock resistance was measured for each sample (3 mm × 4
(mm × 50 mm) is kept at a constant temperature for 1 hour, and then 0
It was dropped in ice water at ℃, and the maximum temperature difference was set so that the sample did not crack.

Next, under the same conditions as those of the above-mentioned respective examples and comparative examples, the hot water mixing valve having the same shape as the movable valve body 11 and the fixed valve body 12 shown in FIG. 1 were manufactured. And
The sliding contact surfaces 11a, 1 of the fixed valve body 11 and the movable valve body 12
1b has a surface roughness of 0.3 μRa and a flatness of 0.3.
The sliding surfaces 11a, 11
Silicon grease was applied to b and the cartridge was attached to a dedicated cartridge. At this time, the tightening torque of the cartridge is 20
It was set to 0 kg · cm.

Next, by using this hot water mixing stopper, the movable valve body 1
Repeatedly performing the moving operation 1 and after a certain number of times,
Measure the operating torque, water pressure 17.5 kgf / cm ²
Was added for 1 minute, and it was examined whether there was any water leakage.

The results are also shown in Table 1. In Table 1, the evaluation of the operating torque is that the magnitude of the operating torque after 100,000 operations is less than 10 kgf · cm, ○, 10 kgf · c
Those with m or more are marked with x. Also, the water leakage evaluation is 1
The case where there was no water leakage after the operation of 0,000 times was marked with ◯, and the case where water leakage occurred was marked with x.

[0048]

[Table 1]

As is clear from the results shown in Table 1, the alumina ceramics of the examples have excellent mechanical strength and thermal shock resistance, and the operating torque is 10 kgf · cm even after operating the hot water mixing plug 100,000 times. It is less than the practical level and does not leak.

On the other hand, the alumina ceramics having a large amount of alumina components, such as the alumina ceramics according to Comparative Examples 1 and 3, have insufficient mechanical strength. As in the case of Comparative Example 2, the thermal shock resistance is insufficient when the content of the entire sintering aid is less than 2 wt%. As in Comparative Examples 4 to 7, when the proportion of each sintering aid is outside the range of the present invention, the heat resistance is not sufficient, the operating torque is large, or water leakage occurs. In particular, in Comparative Examples 4 and 6, it is considered that since the content of B ₂ O ₃ was small, the pores filled with grease became minute and the operating torque increased. Further, in Comparative Example 7, since the amount of B ₂ O ₃ was too large, the pore diameter became too large, and the operating torque was sufficiently small, but water leakage occurred. In the cases of Comparative Examples 8 and 10, the amount of Al ₂ O ₃ component was small, and in Comparative Example 9, SiO ₂
Since the content of is too large, the mechanical strength is insufficient in all cases.

[0051]

As described in detail above, in the alumina ceramics according to the present invention, Al ₂ O ₃ powder is used as the main component in an amount of 85 to 94% by weight, and SiO ₂ powder is used as an auxiliary component.
~ 7.5 wt% TiO as a sintering aid
_2, B ₂ O ₃ and 2-13% by weight of powder of CaO in total
A mixed powder containing, wherein the content of each component in the sintering aid is 0 ≦ TiO ₂ ≦ 95% by weight, 5 ≦ B ₂ O ₃ ≦
Since a mixed powder in the range of 80% by weight and 0 ≦ CaO ≦ 50% by weight is molded and fired, a glass having a low melting point is generated at the grain boundary by adding B ₂ O ₃ and fired at a low temperature. In addition, open pores can be formed by volatilizing a part of this glass phase formed during firing, while this glass phase does not deteriorate the mechanical properties of the sintered body, so sliding characteristics Alumina ceramics having excellent mechanical strength and thermal shock resistance can be manufactured.

Therefore, the alumina ceramics can be used for various members such as a ceramic substrate and a thermocouple protection tube utilizing the above characteristics, but when it is used as a sliding member through a lubricant such as a valve, it is lubricated. A large amount of grease, etc., as an agent is filled inside the pores, and the lubricant gradually exudes to the surface during use, which makes it possible to maintain the initial excellent sliding characteristics and also to deteriorate the mechanical characteristics. It can be used for a long time without.

[Brief description of drawings]

FIG. 1 (a) is a vertical cross-sectional view schematically showing a hot water mixing stopper, and FIG. 1 (b) is b- in the hot water mixing stopper shown in (a).
It is a b line sectional view.

Claims (1)

[Claims] 1. Al ₂ O ₃ powder as a main component is 85-9.
4% by weight, a mixed powder containing ₂ to 7.5% by weight of SiO ₂ powder as an accessory component, and further containing ₂ to 13% by weight of TiO ₂ , B ₂ O ₃ and CaO powder as a sintering aid in total. And the content of each component in the sintering aid is 0 ≦
TiO ₂ ≦ 95% by weight, 5 ≦ B ₂ O ₃ ≦ 80% by weight, 0
A method for producing alumina ceramics, which comprises molding and firing a mixed powder within a range of ≤ CaO ≤ 50% by weight.