JPH0725662A - Aluminum titanate ceramic powder and production of sintered product therefrom - Google Patents

Abstract

PURPOSE:To obtain a sintered compact improved in mechanical strength and thermal decomposition characteristics without impairing the high melting point and low thermal expansibility inherent therein by molding aluminum titanate ceramic powder containing SiO2 and Al2O3 followed by baking. CONSTITUTION:The aluminum titanate ceramic powder can be obtained by incorporating (A) aluminum titanate with (B) 0.3-5.6wt.% of SiO2 and (C) 0.7-14.4wt.% of Al2O3. The powder is then incorporated, where appropriate, with a deflocculant, dispersant, defoaming agent, binder, sedimentation inhibitor, etc., followed by conducting a mixed molding and then drying and defatting. The resultant molded form is baked in the atmosphere, in a vacuum, reductive atmosphere or inert atmosphere, thus obtaining the other objective ceramic sintered compact 1-20wt.% in mullite content.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic powder and a sintered body thereof, and in particular, an aluminum titanate fired product having a high melting point and a low thermal expansion property, and further having excellent mechanical strength and thermal decomposability. We propose a method for producing a bound body and its raw material powder.

[0002]

2. Description of the Related Art Generally, aluminum titanate (Al ₂
The TiO ₅ ) sintered body has a high melting point (1850 ° C.), is excellent in heat insulation and low in thermal expansion, and is one of the ceramics excellent in thermal shock resistance. For example, it is an exhaust manifold of an automobile engine. When used as an exhaust boat material or the like, it has been praised for its effective action in effectively reducing the emission of hydrocarbons.

As described above, one of the characteristics of the aluminum titanate sintered body is its low thermal expansion property. The mechanism of this low thermal expansion is the peculiar function of aluminum titanate, that is, the direction of each crystal direction. It is said that this is due to a marked difference in the coefficient of thermal expansion. That is, since the thermal expansion is absorbed by the cracks entering the crystal grain boundaries, the thermal expansion apparently becomes small. However, regarding the mechanical strength of this aluminum titanate sintered body, It is usually low due to cracks, and there is also a problem that it decomposes into rutile (TiO ₂ ) and corundum (Al ₂ O ₃ ) below about 1250 ° C.

Mullite (3Al ₂ is a conventional technique for overcoming such problems of aluminum titanate.
An aluminum titanate sintered body which has high strength and is stable against thermal decomposition by adding (O ₃ .2SiO ₂ ) has been conventionally known (for example, Toyohiko Yano, Nobuaki Nagai,
Kiyohara Masakatsu, Saito Shoichi, Otsuka Nozomu, "Thermal and Mechanical Properties of Aluminum Titanate-Mullite Composite Sinters", Journal of Ceramic Industry, 94, 970-976 (1986)).

[0005]

The particle shape of mullite is acicular. When the cast molding method is used, the needle-shaped particles in the sludge tend to incline in the direction perpendicular to the mold surface. Therefore, when the aluminum titanate-mullite sludge is used for molding, the mullite of acicular particles is oriented perpendicularly to the inking surface, resulting in a non-homogeneous molded body. Since a non-homogeneous molded body shrinks non-uniformly by firing, it becomes a non-homogeneous sintered body and a product having a target dimension cannot be obtained.

[0006] Therefore, an object of the present invention is to develop a ceramic powder and a sintered body thereof which can overcome the problems which the above-mentioned conventional techniques need to solve. That is, mechanical strength and thermal decomposition characteristics are simultaneously improved without impairing the high melting point and low thermal expansion properties, which are the advantages of the aluminum titanate sintered body, and moreover, mass production is easy without causing heterogeneity of the molded body. To establish a possible manufacturing technology.

[0007]

Means for Solving the Problems As a result of experiments and studies for realizing the above object, the present inventor has found that the shape of the additive and the amount of the additive play an important role in solving the above problem. Based on the findings, the following invention was completed. That is, according to the present invention, SiO ₂ is 0.3% by weight or more and 5.6% by weight or less, and Al ₂ O _{3 is} 0.7% by weight or more and 1% by weight.
Provided is a ceramic powder containing less than or equal to 4.4% by weight and the balance mainly consisting of aluminum titanate. The method for producing a sintered body of an aluminum titanate ceramic according to the present invention includes the above-mentioned SiO ₂ : 0.3 wt% or more and 5.6.
Wt% or less, Al ₂ O ₃ : 0.7 wt% or more and 14.4 wt% or less, the rest is mainly aluminum titanate, the raw material powder is molded, and then fired according to a conventional method to obtain a sintered body. Is a method of producing a sintered body containing mullite in the range of 1% by weight or more and 20% by weight or less, and the balance mainly consisting of aluminum titanate. Further, in this case, it is preferable that the molar ratio of SiO ₂ and Al ₂ O ₃ is substantially 2/3 or more.

[0008]

As described above, the ceramic according to the present invention
Adjust the shape and amount of ceramic powder additive
It is obtained by doing. The present invention
And SiO₂And Al₂O₃The reason for focusing on is both oxidation
Since the shape of the material particles is almost spherical,
Since there is no particle orientation in the inking layer, the powder is evenly dispersed and
This is because a homogeneous molded body can be obtained. In addition, the above Si
O ₂ And Al₂ O₃ Aluminum titanate powder containing
By firing powder, SiO₂And Al₂O₃Is
Reacts at high temperatures and transforms into mullite. As a result
A composite ceramic of aluminum titanate and mullite as a unit
You get a mix. That is, aluminum titanate
By including mullite in the sintered body,
Effectively suppresses the occurrence of cracks at the grain boundaries of the
It can be expected to have the effect of remarkably improving the mechanical strength. Moreover,
By containing mullite, aluminum titanate
Decrease the specific surface area of the sintered body itself to significantly increase the thermal decomposition temperature
It effectively acts to improve and improves the so-called thermal decomposition characteristics.
You can do good.

The SiO ₂ used in the present invention is
The forms of Al ₂ O ₃ and Al ₂ O ₃ do not matter. SiO ₂ has a crystal structure such as quartz, tridymite, cristobalite, or amorphous, and Al ₂ O ₃ has α-Al ₂ O ₃ , γ-Al ₂ O ₃ , η-Al ₂
It has a crystal structure such as O ₃ or is amorphous.

The aluminum titanate ceramic powder of the present invention has a ratio of the amount of metal elements converted to oxides of 0.3.
SiO _{2 in} the range of not less than wt% and not more than 5.6 wt%,
Al in the range of 0.7 wt% to 14.4 wt%
Contains ₂ O ₃ . Such SiO ₂ and Al ₂ O ₃
The content of SiO ₂ is less than 0.3% by weight, and Al ₂ O
_{When 3} is less than 0.7% by weight, that is, in a small amount of less than 1% by weight in terms of mullite, the effect of the above-mentioned addition cannot be sufficiently exhibited. On the other hand, the addition amount of SiO ₂ exceeds 5.6% by weight,
When the amount of l ₂ O ₃ added exceeds 14.4% by weight and exceeds 20% by weight in terms of mullite, sinterability is impaired and densification is impaired, and further cracking of the crystal grain boundaries occurs. The excessive suppression impairs the low thermal expansion property, which is an advantage of aluminum titanate. Therefore, the amounts of SiO ₂ and Al ₂ O ₃ added are 0.3 wt% to 5.6 wt% of SiO ₂ and 0.7 wt% to 14.4 wt% of Al ₂ O ₃ respectively. That is, 1% by weight converted to mullite
It should be 20% by weight or less. Preferably, the amount of SiO ₂ and Al ₂ O ₃ is 1.4 wt% or more and 4.2 wt% or less of SiO ₂ , 3.6 wt% or more and 10.8 wt% or less of Al ₂ O ₃ , and converted to mullite. To 5% by weight or more and 15% by weight or less.

Even if SiO ₂ remains in aluminum titanate, the coefficient of thermal expansion is almost the same (Al ₂ TiO ₅ :
Since it is 1 to 1 × 10 ⁻⁶ ° C. ⁻¹ and SiO _{2 is up} to 1 × 10 ⁻⁶ ° C. ⁻¹ , a target low thermal expansion material can be obtained. on the other hand,
When Al ₂ O ₃ remains in aluminum titanate, the difference in thermal expansion coefficient (Al ₂ TiO ₅ : ˜1 × 10 ⁻⁶ ° C. ⁻¹ ,
Al ₂ O ₃ : ~ 8 × 10 ^-6 ° C ^-1 ), the thermal expansion coefficient of the obtained material becomes large. Therefore, even if SiO ₂ remains in the aluminum titanate, the characteristics are not deteriorated, but if Al ₂ O ₃ remains, the characteristics may be impaired. Therefore, the molar ratio of SiO ₂ and Al ₂ O ₃ is 2/3
Or more is preferable.

SiO in aluminum titanate₂ And A
l₂ O₃ At high temperature (> 1400 ℃)
When fired at₂ Because the capillaries melt
Due to the phenomenon, the surface of each powder is SiO₂ Get wet with the liquid phase. Shi
Therefore, SiO in the powder state ₂ And Al₂ O₃ In the powder
SiO even if it is not close₂ And Al₂ O₃ In the molded body
If homogeneously dispersed in₂ Liquid phase wets the powder
By doing this SiO₂ Liquid phase and Al₂ O₃ Is high
Since it reacts at a high temperature, mullite is produced. Therefore,
Low amount of SiO₂ Calcination to sufficiently generate liquid phase even with addition of
Depending on the conditions, equivalent SiO₂ And Al₂ O₃ 
It is possible to react all of the
It

From the above, SiO ₂ and Al ₂ O ₃ are contained in the raw materials.
It is possible to incorporate only the mullite phase into the sintered body by blending so as to become mullite and by adopting the firing conditions such that the liquid phase of SiO ₂ is sufficiently produced. The generated mullite crystals are considered to exist as needles at the grain boundaries of aluminum titanate, but unlike the conventional technology in which mullite was added to aluminum titanate and cast, the mullite of needle-shaped particles was It is not oriented perpendicularly to, and does not become a non-homogeneous sintered body.

SiO ₂ and Al on aluminum titanate
_In addition to the addition of ₂ O ₃ only, if it is a substance that improves the mechanical strength and thermal decomposition temperature of aluminum titanate,
Other substances may be added in addition to O ₂ and Al ₂ O ₃ . As a typical additive, a metal such as titanium, magnesium, manganese, zirconium, or iron, or an oxide thereof, a composite oxide thereof, or a composite oxide of them and aluminum or silicon, MgTi.
₂ O ₅ , spinel (MgAl ₂ O ₄ ), zircon (Zr
SiO ₄ ) and the like.

Next, a method for producing an aluminum titanate sintered body using the powder of the present invention containing aluminum titanate as a main raw material will be described. The production method using the powder of the present invention, according to a conventional method for producing ceramics, it is possible to apply a production process consisting of raw material adjustment and raw material mixing molding, drying, degreasing and firing, but particularly in the molding step, It is desirable to use the casting method. The reason for adopting this casting method is that the microstructure of the product sintered body is homogenized, and the product is enlarged, complicated,
This is because it is well suited for mass production.

In the preparation of sludge containing the aluminum titanate powder of the present invention as a main raw material, a peptizer, a dispersant, and
A defoaming agent, a binder, an anti-settling agent, etc. may be appropriately used as an auxiliary agent. As a firing method for a molded body using the powder of the present invention containing aluminum titanate as a main raw material, a general firing method for ceramics is used. The atmosphere may be air, vacuum (vacuum degree of 1 Pa or less), nitrogen atmosphere, reducing atmosphere (hydrogen, etc.), inert atmosphere (argon, neon, helium, etc.), but preferably in the air. It is firing.

[0017]

EXAMPLE The ceramic powder and the sintered body used in this example are manufactured as follows. The composition ratios of aluminum titanate raw material powder (average particle size 0.5 μm), amorphous silica powder (average particle size 0.4 μm) and corundum powder (average particle size 0.2 μm) are shown in Table 1. After weighing and mixing as described above, ion-exchanged water and a dispersant were added to prepare a slurry. Next, this slurry was adjusted with an auxiliary agent such as a defoaming agent, a binder, and an anti-settling agent, and cast into a predetermined mold to produce a molded body of 100 × 70 × 10 mm. Then, after drying and degreasing according to a conventional method, the temperature was raised to a temperature of 1550 ° C. in the air and baking was performed.

For each of the obtained samples, the bulk density, the four-point bending strength (according to JIS-1601), the coefficient of thermal expansion (2
(0 to 1000 ° C.), and the thermal decomposition rate after holding in the air at 1100 ° C. for 100 hours was measured, and the results are shown in Table 1. Further, aluminum titanate to which mullite (average particle size 0.4 μm) was added, and aluminum titanate to which iron oxide (average particle size 0.5 μm) was added together with SiO ₂ and Al ₂ O ₃ were also prepared. An evaluation test was conducted.

[0019] As is apparent from Table 1, the sintered body according to the present invention (Sample No. 1-5), as compared with the sintered body of Comparative Example (Sample No. 7, 8), SiO ₂ and Al ₂ O _It can be seen that by adding a predetermined amount of ₃ , the mechanical strength is high without impairing the low thermal expansion property, and the thermal decomposition property is extremely good. Further, as is clear from Table 1, even when the sintered body of the present invention (Sample No. 3) was compared with the comparative sintered body added as mullite (Sample No. 9), the low thermal expansion property was not impaired, and It can be seen that the physical strength and the thermal decomposition characteristics are improved in a very balanced manner. In particular, SiO ₂ and Al
The amount of ₂ O ₃ is 1.4% by weight or more of SiO ₂ and 4.2% by weight.
Hereafter, the addition amount of Al ₂ O ₃ of 3.6% by weight or more and 10.8% by weight or less, or 5% by weight or more and 15% by weight or less in terms of mullite, does not impair the low thermal expansion property and the mechanical strength is reduced. It can be seen that the thermal decomposition characteristics and the thermal decomposition characteristics are improved very well.

Further, as is apparent from Table 1, the sintered body of the present invention (Sample No. 3) is compared with the sintered body of the present invention (Sample No. 6) in which iron oxide is added together with SiO ₂ and Al ₂ O _3. Then, it can be seen that the mechanical strength is further improved without impairing the low thermal expansion property. In addition, as a result of quantitatively measuring mullite in the samples of Sample Nos. 1 to 9 by powder X-ray diffraction using a standard calibration curve, the mullite content in the sintered body was as shown in Table 1. As a result of powder X-ray diffraction, only two phases of aluminum titanate and mullite were confirmed in the sintered body of No.

As is apparent from Table 1, it is desirable that the content of mullite in the sintered body is preferably 1% by weight or more and 20% by weight or less.

[0022]

[Table 1]

[0023]

As described above, according to the ceramic powder of the present invention containing a predetermined amount of SiO ₂ and Al ₂ O ₃ with respect to aluminum titanate, the original high melting point and low thermal expansion are not impaired. It is possible to obtain a sintered body having improved mechanical strength and thermal decomposability. Further, by producing a product by casting molding of a slurry using the ceramic powder of the present invention, the components in the product are homogenized, so that the product homogeneity, the improvement of the product yield, and the mass productivity work advantageously. , It establishes industrially simple manufacturing technology and greatly contributes to the practical application of ceramic products.

Claims (3)

[Claims] 1. SiO₂ : 0.3 wt% or more, 5.6 weight
% Or less, Al₂ O ₃ : 0.7% by weight or more, 14.4 weight
Content of less than or equal to%, the balance being mainly aluminum titanate
Aluminum titanate ceramic powder consisting of aluminum. 2. A method for producing an aluminum titanate ceramic sintered body, which comprises firing the powder according to claim 1 to produce a ceramic sintered body containing 1% by weight or more and 20% by weight or less of mullite. Method. _3. The method for producing an aluminum titanate ceramic sintered body according to claim 2, wherein the powder contains SiO ₂ and Al ₂ O _{3 in} a molar ratio of 2/3 or more.