JPH02229760A - Production of low-expansion ceramics - Google Patents

Abstract

PURPOSE:To enhance airtightness by preparing a raw material consisting of MgO, Al2O3, SiO2 and P2O5 sources, molding and calcining the raw material and thereafter performing heat treatment so that the main component of crystal phase consists of cordierite phase and the ceramic is regulated to the specified opening porosity, thermal expansion coefficient and the rate of change in dimension. CONSTITUTION:The MgO, Al2O3 and SiO2 sources selected from among brucite having <=5mum average particle size, magnesite, talc, clay and alumina and P2O5 source such as aluminum phosphate are prepared so that chemical composition is regulated to 7.5-20wt.% (hereinafter %) MgO, 22-44.3% Al2O3, 37-60% SiO2 and 2-10% P2O5. This mixture is molded and then calcined at 1250-1450 deg.C for 2-20 hours and thereafter heat-treated at 1150-1350 deg.C. Thereby such low expansible ceramics is obtained that the main component of crystal phase consists of cordierite phase and the expansile ceramics is regulated to <=15% opening porosity, <=2.0X10<-6>/ deg.C thermal expansion coefficient at 25-800 deg.C and <=+ or -0.05% rate of change in dimension after this expansible ceramics has been held at 500-1200 deg.C for 1000 hours.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to a method for producing low-expansion ceramics. The present invention relates to a method for producing cordierite-based dense, low-expansion ceramics that have excellent properties.

(Prior Art and Problems to be Solved) With the progress of industrial technology in recent years, there has been an increasing demand for materials with excellent heat resistance and thermal shock resistance. 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 Boisson's ratio, as well as the size and shape of the product, as well as heating and cooling conditions, that is, heat transfer rate. be done.

Among these factors that affect thermal shock resistance, the contribution rate of the thermal expansion coefficient is particularly large.In particular, it is known that when the heat transfer rate is high, it is greatly influenced only by the thermal expansion coefficient. There is a strong desire to develop low-expansion materials with excellent properties.

Cordierite has been known as a relatively low-expansion ceramic material, but cordierite is generally difficult to sinter into dense sintering, and its thermal expansion coefficient from room temperature to 800°C is particularly low. For cordierite substrates that exhibit low expansion properties such as OX 10-'/'C or less, it is necessary to limit the amount of impurities that serve as fluxing agents such as calcia, alkali, potash, and soda to an extremely small amount. Very little phase and becomes porous.

In particular, cordierite honeycomb structures, which have been used as catalyst carriers for automobile exhaust gas purification in recent years, are
Since the coefficient of thermal expansion up to 00℃ is required to be less than 1.5X10-''/℃, raw materials with few impurities such as talc, phosphorus, and alumina are used, and the porosity of the cordierite sintered body is At best, only a range of 25-45% can be obtained.

Therefore, when such cordierite ceramics is applied to a rotating regenerative heat exchanger with a honeycomb structure, for example, its open porosity is large, so that the pores on the surface of the partition wall that form the through holes of the honeycomb structure, especially the communicating holes, are Fluid leaks between the heating fluid and the heat recovery fluid,
It has the serious drawback of reducing the heat exchange efficiency and the efficiency of the entire system in which the heat exchanger is used. Furthermore, when applied to the housing exhaust manifold of a turbocharging rotor, etc., the open porosity is large, causing high pressure air to leak, resulting in a serious drawback. For these reasons, there has been a strong desire for low-expansion, dense cordierite ceramics that have excellent thermal shock resistance.

Furthermore, in high-temperature structural materials exposed to such high temperatures,
Dimensional stability is required, and the dimensional change rate during actual use is ±0.
It is desired that it be less than 0.05%.

Conventionally, as a method for obtaining dense cordierite ceramics, a method is known in which a batch mixture of cordierite composition is melted, molded, and then subjected to crystallization treatment to form glass ceramics. for example,? Topping and Marsui's paper published in Volume 46 of the Journal of the Canadian Ceramic Society, published in 1977, states that within 20% of the SiO in cordierite can be treated with AIPO.
．． We are proposing a replacement with . According to the same paper, A
IPO. Cordierite glass is produced by melting and cooling the raw material main component to which is added at 1600°C, and then reheating and cooling to produce cordierite crystals. The resulting cordierite is dense, or the orientation of the precipitated cordierite crystal phase cannot be controlled, so even if the coefficient of thermal expansion is small, it will be 2. It still has a big drawback of 15X 10-"/"C.

JP-A-59-13741 and JP-A-59-9294
In the invention of Publication No. 3, B203 and/or P205 are added to the main raw material component to which Y203 or ZnO is added, and the crystallized glass component obtained by firing is finely pulverized to 2 to 7 μm to form a glass frit. We are proposing a crystallized glass body that is formed by molding and then fired and crystallized again. This material has a large drawback of having a coefficient of thermal expansion of 2.4 to 2.6 XIO-'/'C.

The reason why cordierite ceramics exhibits low expansion is that
For example, U.S. Patent No. 3,885 entitled "Anisotropic Cordierite Monolith" was granted to Irwin M. Latchman et al. on May 27, 1975. As disclosed in Specification No. 977 (corresponding Japanese application: JP-A-50-75611),
This is because cordierite ceramics are oriented and formed after firing due to the planar orientation caused by plate clay and laminated clay.For this reason, dense cordierite formed into glass ceramics has a 2. It has a high coefficient of thermal expansion of OX 10-@/''C or more.

Furthermore, no description regarding dimensional stability is found in these conventional examples.

The object of the present invention is to solve the above-mentioned problems and improve the coefficient of thermal expansion. Dense cordierite ceramic with low expansion of OX 10-'/'C or less, open porosity of 15% or less, and dimensional change rate of less than ±0.05% after being held at 500 to 200℃ for 1000 hours. The aim is to provide a manufacturing method.

? (Means to Solve the Problems) The manufacturing method of the low expansion ceramics of the present invention is based on the chemical composition or Mg
07.5-20.0% by weight, AI20. 22.0-4
4.3% by weight, SiO ■ 37.0-60 weight 945, P
20. 2.0~IO. 0 weight. preparing a hatch with fA O6, molding the batch, firing the molded body, and heating the fired body to 1150°C.
Heat treated at -1350℃, the main component of the crystal phase is cordierite phase, the porosity is 15% or less, 25-8
Thermal expansion coefficient between 00℃ or 2. The present invention is characterized by obtaining a ceramic having a dimensional change rate of 0.times.x10-'/'C or less and a dimensional change rate of ±0.05% or less after being maintained at 500 to 1200°C for 1000 hours.

P205 contained in cordierite is converted to AIPO during firing.
．． It forms a solid solution by replacing SiO in the cordierite crystal, producing a cordierite solid solution with a slightly lower melting point than cordierite ceramics, increasing the liquid phase generated during sintering, and making cordierite easier. It makes it more precise. Furthermore, after sintering, most of this liquid phase crystallizes into a cordierite solid solution during cooling, which is different from cordierite ceramics that are densified using fluxing agents such as calcia, alkali, potash, and soda. , the coefficient of thermal expansion does not increase. Also, after sintering, 1150
By heat treatment at a temperature of ~1350°C, the remaining glass phase is also completely crystallized;
Even after being maintained at ~1200°C for 1000 hours, the dimensional change rate is ±0.05% or less.

Furthermore, the raw materials used in conventional cordierite are talc, clay, alumina, brucite, magnesite,
By selecting from aluminum hydroxide, cordierite crystals can be oriented, so that the coefficient of thermal expansion is 2. It is possible to obtain a low-expansion, dense cordierite-based ceraminocus with OXIO-'/''C or less.

The total pore volume of pores with a diameter of 5 μm or more is usually 0. 04
cc/g or less.

Mg in cordierite phase is 1 with Zn and/or Fe
It may be iron cordierite or iron-zinc cordierite substituted with 0 mol% or less.

Does the low expansion ceramic of the present invention have a chemical composition of MgO? ．． 5
~20 weight? 6, A1203 22.0-44.3 weight 06, SiO ■ 37, 0-60 weight%, P206 2
．． 0-10. A hatch with a concentration of 0% by weight is prepared, and the prepared batch is formed into a molded body of any shape by casting such as slip casting, plastic molding such as extrusion molding, and pressure forming such as press molding, and this molded body is dried. After, 1250~l45
It is manufactured by firing at 0°C for 2 to 20 hours and heat-treating at a temperature of 1150 to 1350°C to further crystallize the remaining glass phase.

P20. The raw material is preferably a combination of one or more selected from aluminum phosphate, magnesium phosphate, zinc phosphate, iron phosphate, and MgO, Al203, Si
O. Preferably, the source material is mainly selected from brucite, magnesite, talc, clay, and alumina.

In addition, lil such as brucite, magnesite, talc, etc.
By reducing the average particle size of the gO source material to 5 μm or less,
Is it possible to obtain dense cordierite ceramics that suppress the diameter of remaining open pores to 5 μm or less and have sufficient airtightness even with an open porosity of 15% or less? You can do something like that.

(Function) The present invention has P20. 2 to 10% by weight, AIPO. By binding and forming a solid solution, the open porosity is 15% or less and the coefficient of thermal expansion is between 25 and 800℃.
．． This is due to the new discovery that dense, low-expansion cordierite ceramics with a temperature of OX10-6/'C or less can be obtained. The reason why P20 is limited to 2% by weight or more is that if it is less than that, a liquid phase sufficient for densification will not be generated and densification will not occur.The reason why P20a is limited to 10% by weight or less is that if it is less than that, P20, is AIP
O. This is because the solid solubility limit is exceeded and the expansion becomes high. The reason why the dimensional change rate after holding at 500-1200°C for 1000 hours was set to less than ±0.05 is because the dimensional change would have been greater than this when used as a mechanical part.
This is because it poses a problem in actual use.

The chemical composition is Mg07.5-20% by weight, AI20.
22.0-44.3% by weight, SiO■37.0-60% by weight, P20. The reason why it is limited to 2.0 to 10.0% by weight is that if it exceeds this range, the cordierite phase will not be sufficiently produced, resulting in high expansion.

If the firing temperature is below 1250°C, the cordierite phase will not be sufficiently formed, and if the firing temperature is higher than 1450°C, it will be softened and deformed. Similarly, if the firing time is shorter than 2 hours, the cordierite phase will not be sufficiently formed, and if the firing time is longer than 20 hours, deformation will occur depending on the temperature or due to softening.

The reason why the diameter of the remaining open pores or the total pore volume of 5 μl'r1 or more was limited to 0.04 cc/g or less is as follows.
Depending on the amount of leakage of pressurized gas or the total pore volume of pores with a diameter of 5 μm or more, by reducing the amount to 0.04 cc/g or less, the amount of leakage can be suppressed to less than half that of conventional cordierite. This is because it is possible.

Also cordierite phase 2MgO・2Al20s・5Si
Mg in O2 is up to 10 mol%, Zn and/or F
Even if it is substituted with e, it is possible to obtain cordierite ceramics having the same characteristics as the cordierite ceramics defined in the present invention.

The reason why the heat treatment temperature was limited to 1150-1350℃ is 1.
At temperatures below 150°C, the rate of crystallization of the remaining glass phase?
This is because the heat treatment is slow and requires a very long heat treatment, and the residual glass phase does not crystallize at temperatures higher than 1350°C.

The reason why the P205 source is one or a combination of two or more phosphate compounds selected from aluminum phosphate, magnesium phosphate, zinc phosphate, and iron phosphate is that phosphoric acid is difficult to mix because it is a liquid, and it is difficult to mix. This is because it becomes uniform. In addition, phosphoric acid locally melts at a low temperature below the formation temperature of cordierite, creating huge bores, so it is difficult to add it in the form of a phosphate compound, which has a relatively high melting point and is insoluble in water, etc. desirable.

MgO, Al203, S+0■ The reason why we chose the sources from brucite, magnonsite, talc clay, alumina, and aluminum hydroxide is that cordierite ceramics made from these raw materials have particularly low expansion. Alternatively, the MgO source may be selected from magnesium oxide, Sin, and the source may be selected from silica.

The reason why the average particle size of the MgO source material is set to 5 μm or less is that in cordierite ceramics, the MgO source material particles remain after sintering, causing open pores.
By limiting the average particle size of the source material to 5 μm or less,
This is because open pores larger than 5 μm can be suppressed, and cordierite ceramics with high airtightness, which is the object of the present invention, can be obtained.

(Example) Examples of the present invention will be described below.

Brucite, magnesite, talc, alumina, aluminum hydroxide, clay, aluminum phosphate, magnesium phosphate, and iron phosphate whose particle sizes had been adjusted in advance according to the proportions listed in Table 1 were mixed. Table 2 shows the chemical analysis values of the raw materials used.

To 100 parts by weight of this mixture, 5 to 10 parts by weight of water and 1 part by weight of 20 parts of starch paste (80% moisture) were added, thoroughly kneaded in a kneader, and then molded using a vacuum extruder to form a plate with a pitch of 1.0 and a thin wall thickness. sa0
．． It was extruded into a honeycomb columnar body having a triangular cell shape of 10 mm and a length of 65 squares or 120 mm. After drying, this honeycomb molded body was fired under the firing conditions listed in Table 1.
Furthermore, heat treatment is performed at a high temperature of 1150'C-1350°C,
Cordierite ceramic honeycombs of Examples 1-13 and Reference Examples 15-29 of the present invention were obtained.

For the various cordierite-based ceramic honeycombs shown in Table 1, the cordierite crystals were determined by powder X-ray diffraction, and the thermal expansion coefficient, open porosity, and mercury intrusion borosimeter in the temperature range of 25°C to 800°C were determined in the ceramic honeycomb thin wall. The total volume of pores with a diameter of 5 μm or more and the amount of pressurized air leaking from the thin walls were measured and compared. The amount of pressurized air leaking from the thin wall is 20 mm at the center of one end face of the cordierite ceramic honeycomb.
Attach a 65x65mm rubber packing with a square hole of 20mm x 20mm, and attach a 65x65mm rubber packing with no hole on the other end.
A 65mm rubber packing is attached and sealed, and pressurized air of 1.4 kg/ctl is introduced into the hole of the rubber packing, and the flow rate of the pressurized air is measured to determine the amount of leakage per unit area and per unit time. (kg/m2sec). Furthermore, 1 ceramic honeycomb sample of 5 mm x 5 mm x 50 L was added.
The dimensional change rate after holding at 200°C for 1000 hours was measured using a micrometer. The results are shown in Table 1. Also, the * mark for talc in Table 1 indicates the average particle size of 2.0
Those with μm and ** indicate average particle diameters of 10.0 μm, and the average particle diameters of all others are 5.0 μm.

? Based on the results of Examples 1 to 13 and Reference Examples 15 to 29 shown in Table 1, and the results thereof P20 in the composition is 2.0 to IO. 0
When it is contained by weight%, the target open porosity of the present invention is 1.
5% or less and a thermal expansion coefficient of 2.5% or less between 25 and 800°C. A low-expansion ceramic with O
AI20, 22.0-44.3% by weight, SiO■j7.
0-60. It can be seen from Table 1 that a range of ci weight % is preferred.

The low expansion ceramic of the present invention can also be obtained by partially replacing MgO in the cordierite phase with Zn or Fe.

Furthermore, as is clear from Figure 2, which shows the correlation between the leakage amount of 1.4 kg/cnr pressurized air from the ceramic honeycomb thin wall and the pore volume with a pore diameter of 5 μm or more,
A high correlation is observed between the amount of leakage and the volume of pores with a diameter of 5 μm or more. Figure 4 shows Example 6 and Reference Example 16.
．． The pore size distribution curve of No. 18 is shown. In Example 6, which has a small total pore volume with a diameter of 5 μm or more, Reference Example 16.
As is clear from FIG. 2, the amount of leakage is significantly lower than that of No. 18. Furthermore, from FIG. 2, by reducing the total pore volume of pores of 5 μm or more to 0.04 cc/g or less, the amount of leakage could be reduced to less than half that of normal cordierite. Furthermore, as is clear from FIG. 3, which shows the time dependence of the dimensional change rate when held at 1200°C, heat treatment at a high temperature of 1150 to 1350°C, which is the range of the present invention, can be performed at 1200°C for 1000 hours. Even after holding, it was possible to achieve a dimensional change rate of ±0.05% or less, which is almost the same as that of cordierite, which was conventionally considered to be small and good.

From the above, according to the ceramics within the scope of the present invention,
In addition to having good airtightness, the coefficient of thermal expansion and rate of dimensional change at high temperatures are on the same level as normal cordierite, so it also has good impact resistance and has extremely excellent properties as a high-temperature structural material.

FIGS. 4 and 5 show the microstructures of Reference Example 16 and Reference Example 18, respectively, and it can be seen that they are porous and have large pores. In addition, Fig. 6 shows Example 4.
It can be seen that the microstructure is dense with fewer large pores compared to the reference example mentioned above. Further, FIG. 7 shows an X-ray diffraction chart using CuKa rays for Example 4, and it can be seen from this chart that the main crystal phase is cordierite phase, and that mullite, corundum, or subinel are present as secondary crystal phases.

(Effects of the Invention) As is clear from the above detailed explanation, according to the method for producing low expansion ceramics of the present invention, a cordierite phase containing 2 to IO weight % of P205 can be further heated to 115 to 10% by weight after firing. By heat-treating at 350°C, it is possible to achieve densification of the base while maintaining low expansion comparable to that of cordierite, and to reduce the rate of dimensional change at high temperatures, which was impaired by the addition of P205, to the same level as cordierite. It is possible to obtain low expansion ceramics.

Therefore, its range of applications is wide and sufficiently practical as a low-expansion material that requires airtightness, such as heat exchangers for heat exchangers, housings for ceramic turbocharger rotors, etc.

[Brief explanation of the drawing]

Figure 1 shows cordierite ceramic honeycomb P20.
Figure 2 shows the relationship between the content, open porosity, and thermal expansion coefficient. Figure 3 is a diagram showing the time dependence of the dimensional change rate when held at 1200°C, Figure 4 is a diagram showing the pore distribution curve, Figures 5 and 6 are conventional Figure 7 is an enlarged photograph showing the crystal structure of the low expansion ceramic of the present invention, Figure 8 is an enlarged photograph of the crystal structure of the low expansion ceramic of the present invention, and Figure 8 is It is a figure which shows a line diffraction chart. Fig. 1 P20 cold t10f quantity%) 0 /00 2tυ300 400 500 600
700 11130 Q00 1000/200'C
5P4Btff'a'fFigure 2 1415) tM Kokugami n NJ JL n &! ftf
JL&# (' %) Fig. 4 8B Mr. (micron 2

Claims (3)

[Claims] 1. Chemical composition is MgO7.5-20.0% by weight, Al_
2O_322.0-44.3% by weight, SiO_237.
0 to 60.0% by weight, P_2O_52.0 to 10.0% by weight, molding the batch, firing the molded body, and heating the fired body at 1150°C to 1350°C. The main component of the crystalline phase is cordierite phase, the open porosity is 15% or less, and the coefficient of thermal expansion between 25 and 800°C is 2.0 x 10^.
A method for producing low expansion ceramics, characterized in that the dimensional change rate after being maintained at -^6/°C or less for 1000 hours at 500 to 1200°C is less than ±0.05%. 2. The P_2O_5 source raw material is a combination of one or more selected from aluminum phosphate, magnesium phosphate, zinc phosphate, iron phosphate, MgO, Al_2O_3, SiO
_2 A method for producing a low expansion ceramic according to claim 1, wherein the source is primarily selected from brucite, magnesite, talc, clay, and alumina. 3. The method for producing low expansion ceramics according to claim 1, wherein the average particle size of the MgO source material is 5 μm or less.