JPS62171960A - Manufacture of thermal shock-resistant ceramics - 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 2. Field of Industrial Application The present invention is directed to ceramics that have a small coefficient of thermal expansion, excellent thermal shock resistance, and a large specific surface area, such as ceramics used in exhaust gas purification catalysts. Regarding manufacturing methods.

2. Description of the Related Art Conventionally, cordierite ceramics, lithium ceramics, aluminum titanate ceramics, and the like are well known as ceramics having a small coefficient of thermal expansion and excellent thermal shock resistance. Coop Yerai I ceramics is a ceramic consisting of Mg0-A7205-sio2 series. Cordierite is manufactured by mixing talc, kaolin, and alumina (k120.) in any ratio, mixing, dehydrating, molding, drying, and sintering. By the way, the sintering temperature is about 1400'C for 4 to 5 days (
Special Publication No. 54-1564, Special Publication No. 51-20358
Publication No.). In addition, aluminum titanate ceramics is made of titanium oxide (anatase type) and α-mu1 with good purity.
20. It is produced by firing equimolar metal preparations at 160°C to 170°C using 300°C as a raw material (Ceramic Engineering Handbook P, 1274). The specific surface area of each is 1 m2/9 or less.

Problems to be Solved by the Invention These conventional thermal shock-resistant ceramics do not require high-temperature sintering, and the synthesized ceramics may not yield a dense sintered body, or the heat of the constituent crystals may There were problems with grain boundary cracks caused by the large anisotropy of expansion and thermal shock resistance. Furthermore, it could not be used in applications that require a specific surface area, such as exhaust gas purification catalysts. The present invention has been made in view of these points, and an object of the present invention is to provide a ceramic having excellent thermal shock resistance and a large specific surface area.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a mixture containing at least the three essential components of alumina sol, alkali titanate, and fused silica.
Ceramics are obtained by firing at 0°C.

Effect: According to the present invention, a ceramic having excellent thermal shock resistance and a large specific surface area can be obtained.

The alumina sol used in the present invention is a colloidal liquid of alumina hydrate (boehmite type) using water as a dispersion medium, and has No;, a6-, t, CH3C as a stabilizer.
OO- etc. are commonly used.

Next, the alkali titanate salt has the general formula M20・nTio
2 (wherein M represents an alkali metal atom selected from lithium, sodium, potassium, rubidium, cesium, barium, strontium, and calcium, and n is an integer of 1 or more).

Next, fused silica has a thermal expansion coefficient of 0.5X10-6/d
eg (room temperature to 100°C), which is the smallest among substances, and is generally known as a material that reduces thermal expansion. However, fused silica is also a glass-forming oxide and, in the coexistence of other substances such as alkaline components such as Na) IJ, potassium, calcium, alumina, titania, etc., can be used at temperatures above 100°C and above. When heat treated, cristobalite.

Alternatively, crystals such as trichimanite are formed, and the thermal expansion coefficient is 4 to 5 x 10-'/deg (room temperature to 500℃
), and for this reason, it has not been used as a thermal shock-resistant refractory.

In addition to the aluminazonopetitanate alkali salt and fused silica, molding aids such as carboxymethyl cellulose, methyl cellulose, polyvinyl alcohol, etc., and plasticizers such as glycerin and vaseline may also be added.

Example ゛　　The present invention will be explained in detail below.

Example 1 50 parts by weight of alumina sol (A-520 from Nikichi Kagaku ■) with an alumina content of 20% by weight, potassium titanate (K2
5 parts by weight of O.eTio2), 85 parts by weight of fused silica, 4 parts by weight of methyl cellulose as a molding aid, and 2 parts by weight of glycerin as a plasticizer are added. This mixture was kneaded for 10 minutes using a scree kneader, and then fed to a scree type extrusion group 6-page type machine with an outer diameter of 100 mm and a length of 80 mm.
It was formed into a cylindrical honeycomb shape having a wall thickness of 0.25 mm and a square opening with a negative side of 1.5 mm. This molded body is 1
The temperature was raised to 1000°C at a heating rate of 00°C/hour, and 1
It was baked at 000°C for 1 hour. Table 1 shows the physical properties of the honeycomb structure thus obtained.

No comparison yet, α-A120 instead of alumina sol
Comparison using 3 powders Comparative Example B using recompatible alumina Comparative Example C using titanium oxide (anatase type TiO2) instead of potassium titanate C9 Cordierite powder was used instead of fused silica For comparative examples, honeycomb-shaped ceramics were also manufactured in the same manner as in the examples. Also, do you compare commercially available cordierite catalyst carriers?
! IIE. These physical properties are also shown in Table 1.

Furthermore, the honeycomb-shaped ceramic obtained in this way was used as a catalyst carrier, platinum and rhodium were used as rhodium nitrate, and a mixed solution of both was impregnated into the carrier, and after drying, the carrier was dried in a hydrogen atmosphere containing nitrogen. 5
The catalyst heat-treated at 00°C and used as an exhaust gas purification catalyst was evaluated as follows.

(1) Using the above exhaust gas purification catalyst, the catalyst temperature is 200
The CO purification rate after the Co inlet heat treatment was measured at a space velocity of 20,000 hr-'/c.

■) Idl- of a car equipped with a 2800 cc engine
One gas purification catalyst is installed in each gas path, and the air-fuel ratio is set to 1.
C
O.

The purification rate of hydrocarbons (HC) and nitrogen oxides (NOx) was measured after a 50-hour bench durability test.1. Ta.

Table 2 shows the results of evaluation method (1), and evaluation method (2).
The results are shown in Table 3. Table 3 is calculated from the representative graph in Figure 2 obtained from evaluation method (2), and shows the purification rates A and B at the points where the NOx curve intersects with the Co and HC curves, and the NOx at a purification rate of 80%. -00,NOx-)-(in any air-fuel ratio of C (window 1)) Evaluation was made at the narrower of G and D.

As is clear from Table 1, Table 3, and Table 1, Comparative Examples A-
E has a low coefficient of thermal expansion, poor thermal shock resistance, and a small specific surface area.

However, as is clear from Table 2, the catalysts of the comparative examples showed extremely high thermal deterioration compared to the catalysts of the examples.

Similarly, in the engine bench durability test results shown in Table 3, Comparative Example Catalysts E were CO and IC.

The NOx component gas purification rate and the window width are also inferior to the catalysts of the examples.

1 o vane Example 2 A 1 o vane with the same composition and the same shape as in Example 1,
The sample was prepared by increasing the temperature at a temperature increase rate of 00° C./hour and cooling for another 1 hour. Table 4 shows the results of measuring the compressive strength, thermal shock temperature, and specific surface area of these samples.

As is clear from Table 4, the firing temperature is between 1000℃ and 13℃.
A temperature in the range of 00°C is excellent; outside this range, physical properties such as pressure resistance, thermal shock resistance, and specific surface area are unsuitable.

Page 11 Example 3 Various mixing ratios of alumina sol, potassium titanate, and fused silica were added, and molding aids, plasticizers, and water were added in the same manner as in Example 1 to form a honeycomb shape. I did it. As a result, the composition range with excellent compressive strength and thermal shock resistance was the area surrounded by the line connecting points a, b, c, and d in FIG. 1 (hatched area). The composition ranges at each point a, b, c, and d are as shown in Table 5.

In areas other than the shaded area above in Table 5, the thermal expansion/contraction ratio was as shown in Figure 3, and sufficient specific surface area and pressure resistance were not obtained. The thermal expansion and contraction coefficient of the ceramic according to the present invention is the third
It looked like curve B in the figure.

The curved figure is thought to be due to the formation of some crystals such as cristopalite and trichimanite from fused silica.
It is presumed that the coefficient of thermal expansion was particularly large at low temperatures, resulting in a decrease in thermal shock resistance. Similar results were obtained for other alkali titanate salts.

Example 4 50 parts by weight of alumina sol (A-520 manufactured by Nissan Chemical ■) with an alumina content of 20% by weight, various alkali titanate salts 6
A honeycomb-shaped ceramic was prepared in the same manner as in Example 1 using a mixture of 86 parts by weight of fused silica, 4 parts by weight of methylcellulose, 2 parts by weight of glycerin, and 32 parts by weight of water as raw materials. The physical properties of this product are shown in Table 6.

(Margin below) As is clear from Table 6 on page 13 and 14, ceramics made of alumina sol, various alkali titanates, and fused silica have a large specific surface area and are excellent in pressure resistance and thermal shock resistance. Among them, those using potassium titanate are particularly excellent in specific surface area and thermal shock resistance.

Example 4 Table 7 shows the physical properties when each alkali titanate salt in Example 3 is a whisker.

(Hereinafter, blank) 15B-2 From Table 1, the alkali titanate salt has a large root specific surface area as a whisker, and is also excellent in compressive strength and thermal shock resistance.

Effects of the Invention As described above, according to the present invention, it is possible to obtain a practical ceramic having excellent thermal shock resistance, a large specific surface area, and excellent pressure resistance. The ceramic according to the present invention is particularly useful as a catalyst carrier for exhaust gas purification.

[Brief explanation of drawings]

Figure 1 is a diagram showing the preferred composition range of the solid content of the raw material for producing the ceramics of the present invention, Figure 2 is a diagram showing the relationship between the air-fuel ratio and purification rate of the exhaust gas purification catalyst, and Figure 3 is the thermal expansion of the ceramics. It is a diagram comparing shrinkage rates. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure to zo so 4
゜Alumina (vehicle volume, 2nd ward, 9 furnaces,] -b

Claims (4)

[Claims] (1) A mixture consisting of at least alumina sol, alkali titanate, and fused silica is heated at 1000 to 1300°C.
A method for producing thermal shock-resistant ceramics characterized by firing. (2) The solid content in the mixture is 5 to 30% by weight of alumina, 1 to 10% by weight of alkali titanate, and 60 to 94% by weight of fused silica contained in the alumina sol. A method for producing the thermal shock resistant ceramics described. (3) The method for producing thermal shock-resistant ceramics according to claim 1 or 2, wherein the alkali titanate salt is potassium titanate. (4) The method for producing thermal shock-resistant ceramics according to claim 1 or 2, wherein the alkali titanate is a whisker.