JPS62275056A - Manufacture of high purity high strength cordierite sinteredbody - 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] 3. Detailed Description of the Invention The present invention relates to a method for producing a high-purity, high-strength cordierite sintered body, and in particular, a pure cordierite sintered body with excellent properties such as strength. The present invention relates to a method for advantageously manufacturing.

(Prior art and its problems) Cordierite porcelain has traditionally had a composition centered around cordierite (2Mg02Alzox5sioz), and a thermal expansion coefficient of 1 to 3 x 10-'/''
It has a small temperature difference of 250 to 280 degrees Celsius, so it has thermal shock resistance, and its bending strength is 7 to 9 kg/
mm'', it is widely used as engineered ceramics, for example in acid-resistant pumps, cold tanks, etc.

By the way, such cordierite ceraminox is usually made from a mixture of naturally occurring talc and clay, and in order to approximate the composition of cordierite, alumina (A1203) is added to this raw material and then fired. It is manufactured by However, in this conventional manufacturing method, although a liquid phase is generated and sintering progresses, the amount is approximately 40%, and even a small temperature rise generates a large amount of liquid phase, resulting in a dense structure. It is difficult to produce fine porcelain, and the firing temperature range is narrow, making it difficult to manage the firing.

For this reason, in the past, 3 to 10% of feldspar was added in order to adjust the viscosity of the resulting liquid phase and widen the firing temperature range, but due to the presence of this extra component, The thermal, mechanical,
This has a negative effect on electrical properties.

(Solution Means) Here, the present invention was made to solve the conventional problems in the above-mentioned cordierite porcelain (sintered body), and its characteristics are as follows: (a) Magnesium Alcohol with alkoxide and aluminum alkoxide? (b) reacting in a medium to prepare a double alkoxide solution; (b) adding 10-1 to 1 O-2 mol of hydrochloric acid to an alcoholic solution containing silicon alkoxide at a concentration of 10-2 to 1 mol/l; (c) mixing the double alkoxide solution obtained in the above step and the partially hydrolyzed solution; (d) producing an amorphous powder by adding a large amount of water to the mixed solution to carry out hydrolysis and polymerization reactions, and drying the resulting gel having a cordierite composition; After calcining the amorphous dry cordierite composition powder at a temperature of 900°C or lower to remove residual organic matter, moisture, etc., the desired molding is performed, and the obtained molded body is heated at a temperature of 1350°C or lower. The structure was designed to include a step of sintering.

By the way, in the present invention, first, in order to produce a pure and homogeneous fine powder having an easily sinterable cordierite composition,
After mixing an alcohol solution of double salt of magnesium and aluminum alkoxide with an alcohol solution of partially hydrolyzed silicon alkoxide, add sufficient water to perform hydrolysis and polymerization, and dry the resulting gel. However, in order to produce such a pure and homogeneous cordierite composition fine powder, the following conditions are necessary. This was discovered through research by the inventors.

That is, a powder obtained by drying a gel of a composition in which magnesium, aluminum, and silicon alkoxides are simultaneously added to alcohol and mixed at room temperature or under heating, and water is added to precipitate the powder. In calcination at 1000℃ or higher, α-cordierite,
Spinel and crystals of an unknown phase are formed, and a homogeneous fine powder with a single composition of cordierite is not obtained.As will be explained later, a high-strength sintered body cannot be obtained from such powder. It turned out that. The reason for this is that the hydrolysis rate of silicon alkoxide is much slower under the same conditions than the hydrolysis rate of magnesium and aluminum alkoxides.

Therefore, in order to obtain a fine powder having such a homogeneous cordierite composition, first, silicon alkoxide is
An alcohol solution is prepared which is present at a concentration of 1 mol/l, while hydrochloric acid is present at a concentration of 10-1 to 10-3 as a hydrolysis accelerator.
Such alkoxides of silicon can be prepared beforehand by heating in the temperature range preferably from room temperature to the boiling point of the solvent and allowing the reaction to proceed in an inert gas or atmospheric atmosphere under conditions where the silicon alkoxide is present at a concentration of mol/l. After partial hydrolysis, a separately prepared alcoholic solution of magnesium and aluminum alkoxides, in other words, a double alkoxide solution obtained by reacting magnesium alkoxide and aluminum alkoxide in an alcoholic solvent, is added and mixed. By adding water to the mixed solution, a gel-like precipitate was generated, and this precipitate gel was dried to obtain the desired fine powder.

By heat-treating the fine powder obtained in this way, a homogeneous cordierite fine powder consisting of a single phase of α-cordierite as seen by X-rays is obtained, and a sintered body of this fine powder is obtained. It has become clear through studies by the present inventors that this material has high strength.

Furthermore, from the results of the research conducted by the present inventors, it has been found that when the silicon alkoxide concentration and the hydrochloric acid concentration in the solution deviate from the above conditions during partial hydrolysis, α-cordierite single-phase hypothetical It became clear that a sintered product could not be obtained and the strength of the sintered body was low. As mentioned above, when three types of alkoxide solutions are mixed at the same time, the difference in the hydrolysis rate between silicon alkoxide and other alkoxides causes non-uniformity of the powder composition, and according to the present invention, When using a partially hydrolyzed solution of a silicon alkoxide, if the concentration is high, the polymerization reaction will proceed along with the hydrolysis, resulting in gelation, and the solution will become heterogeneous, and the resulting gel will also be heterogeneous. On the other hand, if the concentration is too low, the yield will decrease. In addition, if the concentration of hydrochloric acid added is too high, the hydrolysis rate will be too high, promoting the polymerization reaction and causing problems such as non-uniformity; It became clear that this was causing problems.

In addition, in the present invention, magnesium and aluminum alkoxides used to prepare the double alkoxide solution, and silicon that is partially hydrolyzed in advance (
Various known alkoxides can be used as the alkoxide of silicon (silicon), but -i may include aliphatic alcohols such as methanol, ethanol, propatool, isopropanol, and butanol, especially lower aliphatic alcohol groups. The introduced alkoxide will be suitably used. Further, as the alcohol for dissolving these alkoxides, aliphatic alcohols such as methanol, ethanol, propatool, butanol, and especially lower aliphatic alcohols are preferably used.

Next, since the powder gel obtained in this way contains organic substances such as water and alcohol, the sintering process is necessary to obtain the desired high-strength cordierite sintered body. It is necessary to remove them by calcination beforehand. According to research conducted by the present inventors, in order to remove such water, organic matter, etc. from a powder gel (dried cordierite composition powder) without crystallizing the powder gel, 900
It has become clear that it is necessary to carry out the calcination at a temperature not exceeding 800°C, preferably at a temperature not exceeding 800°C.

Note that if the calcination temperature is too high, the powder will crystallize from the gel, making it difficult to obtain a sufficiently dense sintered body when sintering is performed later. The specific surface area of the body becomes smaller, which also has a negative effect on sinterability. Furthermore, if the calcination temperature is too low, it will take a long time to remove water and organic matter, so the lower limit temperature is generally about 700°C. Calcination is then carried out in such a temperature range for a predetermined period of time, but in the present invention, generally, 800°C
The temperature and time in each case will be determined using the 2-hour calcination condition as a guide.

The thus obtained calcined powder with a large specific surface area is then molded into a desired shape according to the desired shape of the sintered body according to a known method, and then the molded body is sintered. The bending strength of the cordierite sintered body thus obtained was found to be maximum at a sintering temperature of 1300°C, as a result of studies by the inventors. did. The reason for this is that densification is not sufficient at low temperatures, and grain growth becomes extremely large at higher temperatures, resulting in a rapid decrease in the strength of the sintered body. Therefore, in the present invention, the sintering of the molded body obtained from the calcined product of the dried cordierite composition powder is carried out at a temperature of 1350° C. or lower, preferably 1330° C. or lower, where crystal growth is not significant. Further, the lower limit of the sintering temperature is generally about 1200°C.

(Effect of the invention) As is clear from the above explanation, if the method of the present invention is followed,
Compared to conventional cordierite porcelain made from natural raw materials,
It is possible to advantageously obtain a fine powder with a cordierite composition that allows pure cordierite porcelain to be produced at a relatively low temperature. The light sintered body can guarantee heat resistance, low thermal expansion, thermal shock resistance, and high strength, and this is where the great industrial significance of the present invention lies.

(Examples) Below, some examples of the present invention will be shown to clarify the present invention more specifically, but the present invention is not limited in any way by the description of such examples. It goes without saying that it is nothing.

In addition to the following examples and the above-mentioned specific description, the present invention includes various changes, modifications, and changes based on the knowledge of those skilled in the art, as long as they do not depart from the spirit of the present invention.
It should be understood that improvements and the like may be made.

Example 1 Ethyl silicate (Si(OCzHs)4), magnesium ethoxide (Mg(o CzHs)z) and aluminum isopropoxide A!! were used as reaction raw materials silicon alkoxide, magnesium alkoxide, and aluminum alkoxide, respectively. (OCR(C
H3)2)3 was used. Among these alkoxides, partial hydrolysis of ethyl silicate can be carried out in an ethanol solvent at a concentration of 1 mol/l of ethyl silicate and a concentration of 10-'' mol/l of hydrochloric acid in the atmosphere. 70℃
This was done by refluxing at a temperature of 50 hours. On the other hand, by reacting magnesium ethoxide and aluminum isopropoxide using an isobutyl alcohol solvent under reflux at a temperature of 90 ° C. for 12 hours,
A double alkoxide solution was prepared.

Next, the two solutions thus obtained, namely the partially hydrolyzed ethyl silicate solution and the double alkoxide solution, were mixed to give the theoretical composition of cordierite, and the mixed solution was aged for 3 hours. , by adding commercially available water at a 20-fold molar ratio to the alkoxide to completely hydrolyze the water required for hydrolysis of all alkoxides, and then drying by evaporating the solvent, amorphous A fine powder was obtained. Furthermore, the fine powder was calcined at a temperature of 800'C for 12 hours, and the calcined product was
According to a conventional method, the molded body was molded under a pressure of 3 ton/cm into a predetermined shape corresponding to the shape of the desired cordierite sintered body, and the molded body was sintered at a temperature of 1300°C for 2 hours. As a result, a cordierite sintered body having approximately theoretical density was obtained.

The coefficient of thermal expansion of the sintered body thus obtained is 10 to 15.
X 10-'/'C1 thermal shock resistance ΔT,,,=400~
700℃, Young's modulus near 0-85GPa, bending strength (4
Point bending test): 90-110MPa, fracture toughness value:
3 M pJ/m"".

Example 2 When producing a cordierite sintered body in the same manner as in Example 1, the conditions for partial hydrolysis of ethyl silicate were varied as shown in Table 1 below. By repeating experiments with various alkoxide (ethyl silicate) concentrations, various amorphous powders (gels) were obtained.
was manufactured.

It should be noted that all of the powders obtained by calcining and crystallizing these powders at a temperature of 1000° C. were homogeneous with a single phase of α-cordierite based on X-rays.

Next, each of the various powders obtained in this way was calcined at 80°C for 12 hours, and then the calcined product was molded into a desired shape, and the resulting molded body was heated at 80°C for 12 hours.
The desired cordierite sintered body was obtained by sintering at a temperature of 00°C for 2 hours. Furthermore, the bending strength (four-point bending test) of each of the obtained sintered bodies was measured, and the results are shown in Table 1 below, and all had excellent bending strength.

For comparison, ethyl silicate was partially hydrolyzed under the hydrolysis conditions (hydrochloric acid concentration, alkoxide concentration) shown in Table 2 below, and this was used to perform various drying methods. Cordierite M powder was produced in the same manner as in Example 1.

Each of the powders obtained in this way was calcined at a temperature of 1000°C, and all of them contained crystals estimated to be α-cordierite, spinel, and other complex silicates based on X-ray analysis. However, it was a mixture of heterogeneous crystals. Each of the powders was calcined at 800°C for 12 hours, and the calcined product was used to form a molded body into a desired shape.
All of the samples sintered at 00°C for 2 hours had cracks and had such low strength that it was impossible to measure their strength.

? Room 4FAI'? Ten/l01711 +) Cordierite sintered in a predetermined shape in the same manner as in Example 1, except that the calcination conditions (temperature and time) or sintering conditions (temperature and time) were varied as shown in the table below. manufactured a body. Then, the bending strength (4-point bending test) of the obtained cordierite sintered body was measured, and the results are shown in Tables 3 and 4 below, respectively, along with the calcination conditions and sintering conditions. Ta.

As is clear from the results in Tables 3 and 4, the calcination temperature exceeds 900°C, and the sintering temperature exceeds 1400°C.
It is understood that when the temperature reaches ℃, crystal phases other than cordierite appear, and the bending strength of the sintered body decreases significantly.

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Claims (1)

[Claims] A step of preparing a double alkoxide solution by reacting magnesium alkoxide and aluminum alkoxide in an alcoholic solvent, and an alcoholic solution containing silicon alkoxide at a concentration of 10^-^2 to 1 mol/l. Add hydrochloric acid to 10^-^1~1
A step of preparing a partially hydrolyzed solution in which the silicon alkoxide is partially hydrolyzed by adding it at a concentration of 0^-^3 mol/l, and a double alkoxide solution and a partially hydrolyzed solution obtained in the above step. and adding a large amount of water to the mixed solution to carry out hydrolysis and polymerization reactions, and drying the resulting cordierite composition gel to produce an amorphous powder; After calcining the amorphous dry cordierite composition powder at a temperature of 900°C or lower to remove residual organic matter, moisture, etc., the desired molding is performed, and the obtained molded body is heated at a temperature of 1350°C or lower. A method for producing a high-purity, high-strength cordierite sintered body, comprising the steps of: