JPH02153861A - Ceramic material for internal chill and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title material free from cracking during internal chill, having excellent heat resistance and thermal shock resistance, by specifying content of aluminum titanate as crystal phase and average particle diameter of the crystal, respectively and prescribing content and Young's modulus of glass phase containing a rare earth element, respectively. CONSTITUTION:Powder comprising a raw amterial source of Al2O3 having <=96wt.% Al2O3 component and >=3mum average particle diameter and a raw material source of TiO2 having <=3mum average particle diameter and blended with 1.8wt.% calculated as oxide of a rare earth element such as Y, Ce or La is molded. Then the molded article is calcined at 1,450-1,650 deg.C, especially 1,500-1,600 deg.C. Crystal of aluminum titanate is sufficiently grown by the calcination until the crystal becomes 10mum average particle diameter. Consequently, content of the rare earth element is 0.5-16wt.% calculated as oxide. A ceramic material for internal chill having <=20 volume glass phase and 50-2,000kgf/mm<2> Young's modulus is obtained.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to ceramic materials used when hollow tubular ceramics are cast with molten metal such as aluminum or cast iron, and particularly to boat liners for gasoline engines, diesel engines, etc. The present invention relates to a ceramic material for heat-insulating castings used for exhaust manifold liners, piston cavities, cylinder top plates, etc., and a method for manufacturing the same.

(Prior Art) In recent years, environmental pollution caused by automobile exhaust gas has become an important social problem, and methods of removing harmful substances from automobile exhaust gas using catalysts have become the main method. Reducing the amount of precious metals used as catalysts, such as Pt5Rh, has become an issue due to resource and cost issues.Furthermore, in 4-valve engines, which have been on the rise in recent years, catalyst purification performance has declined due to lower exhaust gas temperatures. is a problem.

One of the ways to solve these problems is to line the inner surface of the engine's exhaust port and exhaust manifold with a port liner made of ceramic with a low Young's modulus, and increase the exhaust gas temperature due to its insulation effect.
This is proposed in Japanese Patent No. 236759. Furthermore, the addition of rare earth elements to aluminum titanate, which is the object of the present invention, is disclosed in Japanese Patent Publication No. 3629/1982 and Japanese Patent Application Laid-open No. 92164/1982.

(Problems to be Solved by the Invention) However, the material disclosed in JP-A No. 63-236759 has a problem in that its strength deteriorates and it breaks due to the cooling and heating cycles caused by changes in exhaust gas temperature during use. was there.

Also, Japanese Patent Publication No. 57-3629 and Japanese Patent Publication No. 56-92
In each of the inventions of No. 164, a dense and low-expansion sintered body is obtained by adding a predetermined amount of oxides of Y, La, and Ce to aluminum titanate. However, both had a problem in that they had a high Young's modulus and could not be used as casting materials.

The present invention solves the above-mentioned conventional problems, and has excellent heat resistance, thermal shock resistance, and heat insulation properties, and there is no risk of cracking due to compressive force generated during casting, and it can be used in cold and hot cycles during use. The object of the present invention is to provide a ceramic material for castings with a low Young's modulus that also has durability against the effects of oxidation, and a method for producing the same.

(Means for Solving the Problems) The ceramic material for castings of the present invention contains 65% by volume or more of aluminum titanate as a crystalline phase, the average grain size of the crystals is 10 μm or more, and rare earth elements are oxidized. Glass phase containing 0.5 to 16% by weight in terms of solids is 20% by volume or less and Young's modulus is 50 to 2000 kg
f/+nm".

In addition, the method for producing a ceramic material for castings of the present invention uses, as the A1□03 source material, a raw material in which the A1□03 component is 96% by weight or less and the average particle size is 3 μm or more, and Ti[12
It is characterized by molding and firing a powder having a predetermined composition containing a raw material with an average particle size of 3 μm or less and a predetermined rare earth element in an amount of 1.8% by weight or less in terms of oxide as a source material. .

(Function) The coefficient of thermal expansion in each axial direction of aluminum titanate crystal is a
, the b-axis is positive and the c-axis is negative, and the difference between them is very large, so that distortion occurs in the grain boundaries due to changes in temperature such as during cooling and heating cycles. This distortion is not much of a problem with conventional materials composed of fine grained crystals, but in particular aluminum titanate crystals with an average of 10
It has been found that in the case of casting materials that have been grown to a diameter of .mu.m or more and have a low Young's modulus, this strain becomes extremely large, and as a result, the spacing between grain boundaries widens due to heating and cooling cycles, resulting in a decrease in strength.

On the other hand, it has been found that adding a small amount of rare earth elements such as Y, Ce, and La can prevent strength deterioration due to cooling and heating cycles. This is thought to be due to the fact that the added rare earth element aggregated in the grain boundary glass phase, improving the strength of the glass phase and the bonding force between the glass phase and the aluminum titanate crystals.

That is, the present invention was completed based on such knowledge, and the main crystal phase is aluminum titanate having a predetermined crystal grain size, and a predetermined amount of rare earth element is added to the grain boundaries of the aluminum titanate crystals. It has been found that a ceramic material having a structure in which a glass phase containing the above is present can achieve the low Young's modulus that is the object of the present invention, and also has thermal cycle durability.

In addition, as a method for manufacturing a ceramic material having this crystal structure, coarse grained Al2O, source material and fine grained Tie2
By using the raw material and a predetermined amount of rare earth elements, the above material contains 65% by volume or more of aluminum titanate as a suitable crystalline phase, and the average grain size of the crystals is 1.
0 μm or more, and Young's modulus of 50 to 2000 kgf/
It is possible to obtain a ceramic material for castings having a compressive strength of 5 to 40 kgf/+nm2 and a porosity of 5 to 35%.

In addition, the reason for limitation and the preferable range of each component in the ceramic material of the present invention are as follows. The reason for limiting the aluminum titanate to 65% by volume or more and the average grain size of its crystals to be 10μm or more is that if the values are less than 65% by volume and less than 10μm, the Young's modulus will be 2000%.
This is because cracks will occur during casting if the amount of the glass phase exceeds 20% by volume, and the Young's modulus will exceed 2000 kgf/mm'. % or less.Furthermore, the rare earth element in the glass phase is 0.5% by weight in terms of oxide.
If it is less than 1, the deterioration rate of bending strength due to heating and cooling cycles will be 1.
If it exceeds 6% by weight, Young's modulus will be 2000kgf/mm2.
Therefore, the content of rare earth elements in the glass phase was limited to 0.5 to 16% by weight in terms of oxides.

Furthermore, the preferred range is based on the following reasons. Compressive strength is 5
kgf/mω2 or less and/or bending strength is 0.2
If it is less than 40 kgf/mm', there is a risk of deformation during casting, which may cause problems in handling, and if the compressive strength exceeds 40 kgf/mm' or the bending strength is 2.0
When exceeding kgf/w2, Young's modulus is 2000 kgf/m
m' may be exceeded. In addition, if the porosity is less than 5%, sufficient insulation effect cannot be obtained, and if the porosity exceeds 35%, the strength
Young's modulus may fall outside the numerical range of the present invention. The Young's modulus is most preferably set to 50 to 200 kgf/mm2, but if the rare earth element in the glass phase exceeds 10% by weight in terms of oxide, the Young's modulus becomes 200 kgf/mm2.
kgf/mm'. Furthermore, the composition of the ceramic material is Al20340~65% by weight, Ti0230
It is preferable to set the amount to ~60% by weight, because with other compositions, it is difficult for the crystal content of aluminum titanate to exceed 65% by volume, and at least one of SiO□, MgO1Fe, and O should be contained in a total amount of 10% by weight or less. The reason why it is preferable is that if it exceeds 10% by weight, the amount of aluminum titanate crystals will be difficult to exceed 65% by volume, and the crystal grain size may not exceed 10 μm. Furthermore, the ceramic material of the present invention has a 2.0×1O−
6 (40~800℃) or less, and has a coefficient of thermal expansion of 0.
, 8-5. OX 10-' cal/Cm-5ec
- A thermal conductivity of t is suitable for a port liner that comes into direct contact with high-temperature exhaust gas.

Next, the reasons for limiting the Al2O3 source material and the TiO2 source material in the production method of the present invention are as follows. A1□G, #When the purity of the raw material is higher than 96% and the average particle size is 3 μm or more, the reactivity of the Al2O3 source raw material is low, so there are many unreacted residues, and the Young's modulus is 2000 k
gf/mm2, and there is a risk of cracking due to aluminum casting. In addition, when the average particle size of the A12[1, source material is smaller than 3 μm, the average particle size of aluminum titanate is 10 μm regardless of the purity of the Al2O3 source material.
m or less, and the Young's modulus exceeds 2000 kgf/mm2. Furthermore, if the impurities contained in the AI, 03 source material exceeds 510220% by weight, Fe, 0°20%, or the total of SlO□, Fe2O, exceeds 20%,
There are cases where the crystal grain size of aluminum titanate is not 65% or more and the crystal grain size is not 10 μm or more.

From the above, the Al2O3 source material has a purity of 96% by weight.
Below, the average particle size must be 3 μm or more, preferably the amount of impurities is 51020~20%, l”e2030~
20% or 0 to 20 in total of 5i02, Fe, 03
% is preferable.

Furthermore, if the average particle size of the TiO2 source material is larger than 3 μm, there will be a large amount of unreacted residue, and the Young's modulus will be 2000 kg.
If f/ll1ff12 is exceeded, there is a risk of cranking due to aluminum casting. Therefore, the TiO7 source material must have an average particle size of 3 μm or less.

By setting the addition amount of rare earth elements such as Y, La, and Ce to 1.8% by weight or less, Young's modulus of 2000 kgf/m
m'' or less, more preferably less than 0.3% by weight, the Young's modulus can be 200 kgf/mm2 or less.

(Example) To produce the ceramic material of the present invention, first, alumina, calcined bauxite, purified rutile, crude rutinopeanatase type titanium, ilmenite, red ferrite, fused magnesium, magnesite, fused spinel, kaolin, From quartz, fused silica, certain rare earth elements, etc.
Chemical composition is Al in weight%, 0.40-65%, Tl07
The raw materials are selected so that the total content of at least one of 5in2, MgO, and Fe2O is 30 to 60% and 10% or less.

At this time, A1. (13 Source raw materials ^ Raw materials with an I2O3 component of 96% by weight or less and an average particle size of 3 μm or more, and Ti
It is necessary to mix raw materials with an average particle size of 3 μm or less as O2 source raw materials.

Rare earth elements can also be added in the form of nitrates, oxides, and other compounds, but in order to obtain the effect with addition in a small amount, it is preferable to uniformly disperse them using fine particle raw materials.

To this, 0.1 to 1.0% of a deflocculant selected from water glass, polycarboxylic acid ammonium salt, amines, sodium pyrophosphate, etc. is added, and further PVA, MCSCMC,
A binder selected from acrylates and the like is used in a range of 1.0-5.
Add 0% and mix thoroughly with 15-40% water using a trommel, pot mill, etc. to make 200-1000 cp.
Adjust the viscosity of the slurry. Such a slurry is formed into a cylindrical shape or a boat liner shape by a casting method, and then dried and fired. As a result, it has heat resistance, thermal shock resistance, and heat insulation properties that contain 65% or more of aluminum titanate as a crystal phase and 20% or less of a glass phase that contains 0.5 to 16% of rare earth elements in terms of oxides. In addition, an aluminum titanate sintered body having excellent thermal cycle durability can be obtained, but it may also contain one or more crystals among rutile, corundum, and mullite as other crystal phases. In the present invention, the firing conditions are, for example, 1,450 to 1,650°C, preferably 1,500 to 1,500°C.
By heating at 600° C. for about 1 to 16 hours, crystals of aluminum titanate are grown sufficiently until the average particle size becomes 10 μm or more.

As a result, the Young's modulus is 50 to 2000 kgf/+++
m2, preferably compressive strength 5-40 kgf/m2, bending strength 0.2-2, 0 kgf/mm", porosity 5
It can have physical property values of ~35%. Ceramic materials with such a low Young's modulus can shrink together with the metal material when the metal material in which they are cast shrinks, and in particular, conventional high-strength, high Young's modulus ceramics can break due to stress concentration. No cracks occur even in complex shapes.

Therefore, as well as a cylindrical boat liner, it has two boats 2 on the cylinder side for a 4-valve engine as shown in Figures 1 and 2, and a single exhaust port 1 on the exhaust manifold side. It is also suitable for a boat liner 3 having a complicated shape or an exhaust manifold liner as shown in FIG. In addition, the microcracks in this sintered body lower the thermal conductivity, and a sufficient heat insulation effect is exhibited even if the porosity is relatively small.

Since aluminum titanate has a melting point of over 1700℃, there are no particular restrictions on the molten metal for casting, and it can be used for casting made of gray cast iron, spheroidal graphite cast iron, white cast iron, aluminum alloy, copper alloy, magnesium alloy, and zinc alloy. can.

In addition, by having a small amount of rare earth elements present in the glass phase, the grain boundary glass phase is firmly bonded to aluminum titanate, making it durable for cold and hot cycles without impairing the above-mentioned properties suitable for low Young's modulus castings. A material with both properties can be obtained.

An actual example will be explained below.

A1°0. shown in Table 1 below in Examples. The raw materials were prepared using the TlO ,
An elliptical cylindrical test piece with 36 short diameters was prepared.

Each test piece was fired under the conditions shown in Table 3, and various properties were measured on the resulting fired body.

Next, each fired body was filled with anti-sand and then cast with aluminum to produce a metal-ceramic composite with an aluminum wall thickness of 7 mm. It was confirmed whether or not cracks had occurred in the test piece after sand protection was removed. 3rd result
Shown in the table.

In Table 1, the cooling/thermal cycle test was conducted before and after repeating the cooling/thermal cycle of holding room temperature for 10 minutes and holding at 900°C for 20 minutes 50 times, as shown in Figure 4, which shows the schedule of cooling/heating cycles and the actual sample temperature. The rate of strength deterioration was measured. Further, the amounts of aluminum titanate and glass phase were determined as volume % determined from the respective area ratios in the SEλ1 photograph. Additionally, the amount of rare earth elements in the glass phase was determined using EDX analysis with a transmission electron microscope.

In addition, in order to make it easier to confirm the changes due to the thermal cycle for the materials of the present invention and the comparative example, Fig. 5(a) shows an electron micrograph of the fired product and the fired product after conducting the above-mentioned thermal cycle test up to 600 cycles. (b) and Figure 6 (a)
) and (b) respectively. That is, FIG. 5(a)
, (b) shows the crystal structure of the fired body of the present invention before and after cooling and heating cycles, and FIG. From FIG. 5(a), (b) and FIG. 6(a), et al., it can be seen that in the material of the comparative example, the grain boundary interval widens due to the thermal cycle, but in the material of the present invention, No significant difference was observed before and after.

From the results in Table 3, it can be seen that in the ceramic materials obtained in the examples of the present invention, no cracks due to casting were observed, and there was less deterioration due to the thermal cycle test compared to the comparative examples.

(Effects of the Invention) As is clear from the above description, according to the ceramic material for castings and the manufacturing method thereof of the present invention, predetermined coarse-grained Al2O3 source raw materials, fine-grained TiO□ source raw materials, and rare earth elements are used. By doing so, a glass phase containing 65% by volume or more of aluminum titanate as a crystal phase, the average grain size of the crystals being 10 μm or more, and 0.5 to 16% by weight of rare earth elements in terms of oxides is obtained. As a result, it has a low Young's modulus, excellent heat resistance, thermal shock resistance, and heat insulation properties, and there is no risk of cracking due to the compressive force generated during casting. It is also possible to obtain a ceramic material for castings that has both cold and heat cycle durability.

[Brief explanation of the drawing]

Figure 1 1;! A perspective view of a port liner for a 4-valve engine, Fig. 2 is a sectional view of the boat liner after being cast into the engine head, Fig. 3 is a sectional view of the exhaust manifold liner after being cast, and Fig. 4 is an evaluation method of the present invention. Graphs showing the schedule of the cooling and heating cycles in FIGS.
a) and (b) are 38M photographs showing the crystal structure of the fired body of the comparative example before and after the thermal cycle. Patent applicant Nippon Insulator Co., Ltd. Figure 1 Time Figure 5 (al Figure 6 (a) tb) Procedural amendment December 1989

Claims (2)

[Claims] 1. Contains 65% by volume or more of aluminum titanate as a crystal phase, and the average grain size of the crystals is 10 μm or more,
and 0.5 to 16% by weight of rare earth elements in terms of oxides.
A ceramic material for castings characterized by containing a glass phase of 20% by volume or less and having a Young's modulus of 50 to 2000 kgf/mm^2. 2. As an Al_2O_3 source raw material, a raw material with an Al_2O_3 component of 96% by weight or less and an average particle size of 3 μm or more;
As a TiO_2 source raw material, raw materials with an average particle size of 3 μm or less and specified rare earth elements are 1.8% by weight in terms of oxides.
A method for manufacturing a ceramic material for castings, which comprises molding and firing a powder having a predetermined composition as described below.