JPS6230656A - Manufacture of low expansion ceramic - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing low expansion ceramics having low expansion, high melting point, and high strength.

In recent years, with the progress of industrial technology, the demand for materials with excellent heat resistance and thermal shock resistance has increased. The thermal shock resistance of ceramics is affected by the material's properties such as coefficient of thermal expansion, thermal conductivity, strength, modulus of elasticity, and Poisson's ratio, as well as the size and shape of the product, as well as the heating and cooling conditions, that is, the rate of heat transfer. Ru. Among these characteristics that affect thermal shock resistance, the coefficient of thermal expansion is particularly important, and in particular, when the rate of heat transfer is significant, it is known that it is greatly influenced by the coefficient of thermal expansion alone. There is a strong desire to develop low-expansion materials with excellent thermal shock resistance.

Conventionally, the coefficient of thermal expansion between 25℃ and 800℃ is 5 to 20.
Cordierite (1, IAS), lithium aluminum silicate (LAS), etc. are ceramic materials with relatively low expansion of about X10-7 (1/℃).
The former has a melting point of 1450°C and the latter 1423°C. For example, in the case of ceramic honeycomb used as a catalyst carrier in an automobile catalyst purification system, the mounting position of the catalytic converter is changed from the conventional underbed to the engine engine in order to improve the catalyst purification efficiency. Due to design changes such as installing a turbocharger for the purpose of improving fuel efficiency and improving engine efficiency, the exhaust gas temperature will rise compared to before, and the catalyst bed temperature will rise by 100 to 200 degrees Celsius. It has been found that even cordierite honeycomb carriers with a high melting point can cause clogging due to melting, and there is a strong desire to develop a low-expansion material with excellent heat resistance and thermal shock resistance equal to or higher than that of cordierite. Ta.

On the other hand, in general, ceramics with low expansion properties have a large difference in coefficient of thermal expansion depending on the direction of the crystal axes of the crystals that make up the ceramic, and thermal stress occurs inside the ceramic and this exceeds the strength limit of the constituent crystals and grain boundaries. Microscopic cracks occur within the grains and at grain boundaries, resulting in weak strength. For example, in the case of ceramic honeycombs used as catalyst carriers in automotive catalytic purification equipment, breakage occurs when the ceramic honeycombs are press-fitted into catalytic converters. However, there is a problem that cracks or breakage are likely to occur due to vibration or mechanical impact during actual running, and there has been a strong desire to develop a material with high strength and low expansion.

The method for producing low expansion ceramics of the present invention solves these conventional drawbacks and problems, and is made of magnesia, alumina, titania, silica, and iron oxide, which have low expansion properties, high melting points, and high strength. It is a manufacturing method for obtaining ceramics, and the chemical composition is 1.2 to 20% by weight.
%MgO, 6,5-68% Al2O3, titanium is T
19 to 80% in terms of in2, 1 to 20%5in2 and 0.5 to 20% by weight of iron in terms of Fe2O3, and preferably a chemical composition of 2 to 17% by weight, MgO111 to 62%.
A1□03, titanium is 25-75% in terms of TiO2
, 2-15% Sin□ and iron is 2-15% in terms of Fe2O3
The steps include preparing a patch consisting of 10% by weight, plasticizing and molding this patch if necessary, drying this molded body, and firing this molded body at a temperature range of 1300 to 1700°C to remove the crystalline phase. It is a solid solution whose main components are magnesium oxide, aluminum oxide, titanium oxide, silicon oxide, and iron oxide, and the second phase of the crystalline phase is rutile,
20% by weight of at least one type of crystal selected from the group consisting of corundum, mullite and cordierite
Thermal expansion coefficient between 25 and 800℃ is 20X1, including:
0-7 (1/°C) or less, the four-point bending strength of the test piece is 50 kg/am2 or more at room temperature, and the melting point is 1500°C or more. . Note that although Ti can form a non-stoichiometric compound with oxygen, it is difficult to separate it, so it was assumed that Ti is tetravalent.

Note that although Ti can form a non-stoichiometric compound with oxygen, it is difficult to separate it, so it was assumed that Ti is tetravalent.

Next, the method for producing the low expansion ceramics of the present invention will be explained in more detail.

Chemical composition is 1.2-20% by weight L4go, 6.5
~68% Al2O3, titanium is 19 in terms of TiO2
Magnesia, magnesium carbonate, magnesium hydroxide, curcum, alumina, aluminum hydroxide, bauxite, anatase type titanium oxide so that ~80%, 1-20% Sin□ and iron are 0.5-20% by weight in terms of Fe2O3. , rutile type titanium oxide, metallic iron, α type 2,3 iron oxide, T type 2,3 iron oxide, hydrated iron oxide, titanium steel, clay, calcined clay, fired clay, waxite, mullite, sillimanite, kyanite A molding aid is added to this mixture as necessary to make a deformable plastic patch, and this plasticized patch is processed by extrusion molding, press molding, slip casting, injection molding, etc. After molding using a ceramic molding method such as a molding method, it is dried.

Next, this dried product is fired at a heating rate of 5°C/hour to 300°C/hour and a firing holding temperature in the range of 1300°C to 1700°C, preferably for 0.5 to 48 hours, thereby producing the low expansion ceramic of the present invention. is obtained.

Note that the raw materials used in the method for producing the low expansion ceramics of the present invention are not limited to the above-mentioned raw materials, and various natural raw materials can be used as long as they mainly have the above-mentioned chemical composition. As mentioned above, the low expansion ceramics of the present invention can be applied to any method of molding ceramics, and there are no limitations on the shape of the product, such as triangular, square, hexagonal, circular shapes, etc. or a combination thereof, with any geometrical cross-sectional shape, forming a number of open holes extending from one end to the other)
It can be applied to products with any structure and shape, such as honeycomb structures with IJ hooks, complex products with three-dimensional three-dimensional shapes, thick-walled products, and various blocks.

The reasons for the limitations in the present invention are as follows.

(1) Mg01.2-20% by weight, Al2O36.0
~68% by weight, titanium is 19-80 in terms of TiO2
Weight %: The MgO-Al2O3 two-component ceramic forms spinel crystals and has a melting point of 2000°C or higher, making it extremely effective as a component for improving heat resistance. However, although it varies depending on the composition, the coefficient of thermal expansion is approximately 60 to 8.
It is extremely large at 0xlO-7 (1/°C). In the present invention, a low expansion ceramic having a coefficient of thermal expansion of 20×10 −7 (1/° C.) or less is required. For this purpose, MgO・A
When 19-80% of TiO2 is added to 1□03, the first
As shown in the figure, the coefficient of thermal expansion is 20xlO-7 (1/℃)
and the melting point does not fall below 1500°C.

When more than 80% TiO2 is added, the melting point increases with the increase in TiO2, but the thermal expansion coefficient also increases from 20 to 80X10.
It is not preferable because it increases rapidly to -7 (1/°C). Also Ti
When the amount of O2 added is 19% or less, the melting point will be 1700~
Although it increases to 2000℃, the coefficient of thermal expansion is also 20 to 8fl
Since it rapidly increases to XlO-7 (1/'l:), Tin□ is another component Fe2O.

and at least 19 taking into account the addition of 5in2
% or more is necessary.

(2) Fe2030゜5~20% by weight;
The reason why the value is 0.5 to 20% by weight in terms of O3 is due to changes in the coefficient of thermal expansion that occur in this range, especially when subjected to long-term constant temperature or repeated thermal B history at about 1000 to 1200°C for more than 2000 hours. 25
The coefficient of thermal expansion between ℃ and 800℃ is 20xlO-7 (1/
This is because ceramics can be obtained that have a low expansion of less than 1500°C and a high melting point of 1500°C or more. Especially if the amount of iron contained is less than 0.5% by weight in terms of Fe2O3,
The change in thermal expansion coefficient that occurs when subjected to long-term constant temperature or repeated thermal history at 000 to 1200°C for more than 2000 hours becomes large, and when it exceeds 20% by weight, the melting point decreases to 1.
The temperature is less than 500℃, and the heat resistance decreases, and 2
The coefficient of thermal expansion between 5℃ and 800℃ is 20X10-7 (
1/°C), the thermal shock resistance decreases.

(3) 5i021 to 20% by weight; The reason why the amount of 5102 is set to 1 to 20% in the chemical composition of the present invention is that, as is clear from Fig. 2, when SiO□ is less than 1%, the four-point bending strength This is because if it is less than 50 kg/am2, the effect of increasing the strength of low-expansion ceramics will not be sufficient.On the other hand, if 5i02 exceeds 20%, the strength will be high, but more heterogeneous crystal phases will be formed.
This is not preferred because the coefficient of thermal expansion exceeds 20 x 1 O-7 (1/°C), resulting in poor thermal shock resistance. For the above reasons, S
iO□ was limited to 1 to 20% by weight.

Furthermore, the main component of the crystalline phase constituting the low expansion ceramic obtained by the present invention is a solid solution consisting of magnesium oxide, aluminum oxide, titanium oxide, silicon oxide, and iron oxide, but the second phase of the crystalline phase is rutile, spinel, etc. It can contain at least 20% by weight, preferably 10% by weight or less, of at least one crystal selected from the group consisting of nenovemulite, corundum, and cordierite, and within this range, it has low expansion and high softening and melting temperatures. However, by making the slope of the softening and shrinkage curve gentler from the softening temperature to the melting temperature, it is possible to improve heat resistance and increase strength.

Next, the present invention will be explained in detail.

The raw materials selected to have the chemical compositions of Examples 1 to 5 and Reference Examples 1 to 4 were weighed, and 2 parts by weight of a vinyl acetate binder was added to 100 parts by weight of this mixture, and after thorough mixing, 10mmX at a pressure of 1000 kg/am2
A rod-shaped test piece of 10 mm x 1 O was prepared.

Additionally, 4 parts by weight of methylated rose and 30 to 40 parts by weight of water were added to 100 parts by weight of each of the formulations, thoroughly kneaded in a niegu, extruded into a honeycomb shape with a square cell cross-section using a vacuum extrusion molding machine, and dried. A honeycomb molded body was obtained. This rod-shaped test piece and honeycomb molded body were fired under the firing conditions listed in Table 1, and Examples 1 to 1 of the present invention were used.
5. Ceramics of Reference Examples 1 to 4 were obtained. 2 Regarding the rod-shaped test pieces of Examples 1 to 5 and Reference Examples 1 to 4 of the present invention
The coefficient of thermal expansion and melting point were measured between 5°C and 800°C, and the rod-shaped sample was 4mm wide, 3mm thick,
Four-point bending strength was measured for a sample cut to a length of 45 mm and polished under conditions of an inner span of 10 mm, an outer span of 30+n+n, and a loading rate of 0.5 mm/min.

On the other hand, Examples 1 to 5 and Reference Examples 1 to 2 of the present invention No. 1
A thermal shock test was conducted using an electric furnace on a honeycomb structure having a diameter of 0.00 mmφ x 75 mm, and the temperature difference between rapid heating and rapid cooling without cracking or destruction was determined.

Furthermore, 25.4 m of Examples 1 to 5 and Reference Examples 2 to 4 of the present invention
For a honeycomb structure of mφ×25.4 mmL, 10
Heat treatment was performed for a minute, and the shrinkage rate and softening temperature were measured.

The shrinkage rate was defined as the dimensional change rate when heat treated at a temperature 50°C lower than the melting point. The softening temperature was the temperature at which the shrinkage rate was 10%.

Furthermore, the amount of the second crystal phase was determined using X-rays for the honeycomb structures of Examples 1 to 5 and Reference Examples 1 to 4 of the present invention.

The results are shown in Table 1, and Examples 1 to 1 of the present invention
5 has a thermal expansion coefficient of 20XIO- between 25℃ and 800℃.
It has low expansion of 7 (1/℃) or less, and as a result, as a result of a thermal shock test using an electric furnace, the difference in rapid heating and cooling temperature was large compared to Reference Examples 1 and 2, indicating excellent thermal shock properties. . Furthermore, Examples 1 to 5 of the present invention have a four-point bending strength of 50 kg/am2.
Thus, it had practically sufficient strength and also had a high melting point of 1500° C. or higher.

Furthermore, the present invention, which contains 20% by weight or less of the second crystal phase, has low expansion, low shrinkage at high temperatures, high softening temperature, and a high ratio of softening temperature to melting point, resulting in improved heat resistance. I know what you're doing.

Figure 1 shows 1. It is a characteristic diagram showing the relationship between the amount of TiO2, melting point, and coefficient of thermal expansion in Igo・At203-Tin2 ceramics. Curve A shows the relationship between TiO□ and the melting point of the ceramic, and curve B shows the relationship between T+02M and the ceramic from 25°C. The relationship with the thermal expansion coefficient between 800°C is shown. As is clear from the figure, the addition of TiO2 has a significant effect of lowering the coefficient of thermal expansion.

Figure 2 shows the low expansion ceramics of Examples 1 to 3 and the ceramics of Reference Examples 1 and 2 obtained by the present invention.
It is a diagram showing the amount of iO7, bending strength, and coefficient of thermal expansion, where curve A is the relationship between the amount of 5102 and the bending strength in 4-point bending of ceramics, and curve B is the relationship between the amount of 5in2 and the bending strength of ceramics at 25 points.
The relationship with the coefficient of thermal expansion between ℃ and 800℃ is shown. Si
Points with 2% O□ amount (AI, B,) are Example 1. Points with 10% (A 2 , B 2) are Example 2. 15% point (
A3. B3) is the data of Example 3, 0% of the amount of Sin□
The point (A4. e4) is the point of 1.22% of the reference example (8 St
as) shows the data of Reference Example 2. As is clear from FIG. 2, the addition of 5102 has a remarkable effect of improving the bending strength.

Figure 3 (A), (B), ([:), (D)
, (E) is the amount of second crystal phase, thermal expansion coefficient, four-point bending strength, shrinkage rate, and softening of the low expansion ceramics obtained by the present invention, Examples 1 to 5, and the ceramics of Reference Example 1.2.4, respectively. It is a figure showing the relationship between temperature and softening temperature/melting point.

It is clear from FIG. 3 that the above-mentioned characteristics of the low expansion ceramic of the present invention are satisfied when the second crystal phase contains 20% by weight or less of at least one crystal among rutile, spinel, mullite, corundum, and cordierite. be.

As described above, the low expansion ceramics obtained by the production method of the present invention have low expansion, high strength, and a high melting point, and have a
It is thermally stable even when subjected to long-term heat treatment at any temperature up to ℃, so it can be used for various ceramic parts that require heat resistance and thermal shock resistance, such as catalyst carriers for automobile exhaust gas purification, carriers for catalytic combustion, and automobiles. Ceramic heat exchangers for industrial use, pistons, cylinder liners, combustion chambers, auxiliary combustion chambers, engine parts such as turbocharger rotors, gas turbine parts such as nostle, rotors, roundabouts, scrolls, frenums, combustors, transition pieces, etc. It is widely used as ceramic T and T14 which require heat resistance, thermal shock resistance, abrasion resistance, corrosion resistance, etc., such as heat-resistant ceramic materials for Taiyo Kogyo Lumber, refractories, and ceramics for the chemical industry. , is extremely useful industrially.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the relationship between the amount of TiO2, melting point, and coefficient of thermal expansion in MgO・A1203-TiO2 ceramics. Figure 2 shows Examples 1 to 3 of low expansion ceramics obtained by the production method of the present invention and for reference. Characteristic diagram showing the amount of 810□, bending strength, and coefficient of thermal expansion in the ceramic of Example 1.2, Figure 3 (A), (B), (C), (D),
(ε) is the amount of the second crystal phase and the coefficient of thermal expansion in Examples 1 to 5 of the low expansion ceramics obtained by the production method of the present invention and the ceramics of Reference Examples 1 and 2.4, respectively.
This is a special graph showing the relationship between four-point bending strength, shrinkage rate, softening temperature, and softening temperature/melting point.

Claims (1)

[Claims] 1. Chemical composition: 1.2 to 20% MgO by weight, 6.5
Preparing a patch consisting of a compound selected such that ~68% Al_2O_3, titanium is 19-80% TiO_2, 1-20% SiO_2 in terms of TiO_2, and iron is 0.5-20% by weight in terms of Fe_2O_3. , a step of plasticizing and molding this patch, a step of drying this molded object, and a step of drying this molded object at 1300 to 17
The main components of the crystal phase are magnesium oxide - aluminum oxide - titanium oxide - silicon oxide -
A solid solution consisting of iron oxide, containing 20% by weight or less of at least one type of crystal selected from the group consisting of rutile, spinel, mullite, corundum and cordierite as the second crystalline phase, between 25°C and 800°C. The coefficient of thermal expansion is 20×10^-^7 (1/℃) or less and 4
A method for producing low-expansion ceramics, comprising the steps of obtaining low-expansion ceramics having a point bending strength of 50 kg/cm^2 or more at room temperature and a melting point of 1500° C. or more. 2. Chemical composition is 2-17% MgO in weight%, 11-62
%Al_2O_3, titanium is 25 in terms of TiO_2
~75%, 2-15% SiO_2 and iron Fe_2O
The method for producing a low expansion ceramic according to claim 1, wherein the amount is 2 to 10% by weight calculated as _3. 3. The method for producing low expansion ceramics according to claim 1 or 2, wherein part or all of the SiO_2 source material is made of mullite. 4. The method for producing low expansion ceramics according to claim 3, wherein the amount of mullite blended is 3.5% to 60% by weight.