JPS60118681A - Manufacture of porous mulite 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 has a particularly low thermal conductivity and a 1f
This invention relates to a method for producing porous mullite porcelain.

Low thermal conductivity is required for high-temperature insulation materials.

Ceramic 7 fibers of 0.0001 Cal /Cl1l -sec -℃ class are known, but fibers with irregular shapes and low mechanical strength are inconvenient for practical use, so they exhibit low thermal conductivity due to their regular shape. Ceramics are requested.

In addition, thermal shock resistance is required for high-temperature structural materials including the above-mentioned high-temperature insulation materials, but since the thermal shock resistance is approximately proportional to thermal conductivity, medium-expansion ceramics, which have low thermal conductivity, are required. However, it has been difficult to impart high heat resistance and impact resistance.

The present invention provides a mesh-like porous mullite porcelain that has a low thermal conductivity that is approximately equal to that of the above-mentioned ceramic fiber, and a thermal shock resistance that is equivalent to that of cordierite or β-spodumene porcelain, which is said to have a high value among ceramics. That is.

Practical example: Metallic silicon (98% purity, 150 meshes, Mitsuwaka $)
) 200° alumina (purity 99.9%, Taimicron AG.

Daimei Chemical) 1092g Methyl ethyl ketone (solvent) '120y dibutyl phthalate (EJI plasticizer) 80g Ionet 5-20 (
Dispersant, Sanyo Chemical>, By or more with an internal volume of 31! After mixing and pulverizing for 24 hours in an alumina porcelain ball mill, 120 g of polyvinyl butyral was added as a binder and mixing was continued for another 24 hours.

The obtained slurry was formed into a sheet on a polyester film by a doctor blade method and air-dried for 15 hours to obtain a green sheet with a thickness of 4 shoulders.

This sheet with a thickness of 4rrrm is fired under various conditions - (1
Table 1 shows the properties of the samples obtained after holding the ceramic composition for a long time, together with the general properties of other ceramic compositions.

As is clear from the preceding table, according to the present invention, 'N
The samples '44Nα1 to 6 and Nα11 to 16 actually had a porous mullite structure with a porosity of 55% or more.

The porous structure is similar to that of samples NQ2 and No.
As shown in Figures 1 and 2, which are micrographs (X5000) of No. 14, needle-shaped crystals are formed spatially in a network shape, and have the high heat resistance inherent to mullite and the low heat resistance almost comparable to ceramic fibers. It has high mechanical strength while being conductive (insulating).

Therefore, in addition to the above characteristics, high-temperature insulation materials such as furnace materials, burner nozzles, arc insulation plates, etc. have thermal shock resistance equivalent to low-expansion porcelain such as cordierite and β-subodumene, so they can be used to protect against external damage. The compressed air is preheated to a high temperature before being introduced into the combustion chamber.

After fuel is injected and burned in the combustion chamber to operate the turbine, a portion of the thermal energy of the high-temperature exhaust gas is recovered into the compressed air introduced into the combustion chamber and released into the atmosphere.Especially when the temperature difference is large. It is highly effective as a material for various heat exchangers, including the honeycomb structure type of gas turbines, and the mesh structure, which has a porosity of up to 92%, is used as a furnace material and bioceramic as a biochemical reaction catalyst carrier. , is effective in a wide range of applications such as adsorption sheets for liquid chromatography, but samples Nα7 and Nα17 have hydrogen gas and ammonia decomposition gas dew points exceeding 10°C even if the starting materials are the same.
exhibited a granular crystal structure and exhibited various characteristic values close to those of the mullite porcelain cited as a reference example.

In the present invention, metallic silicon Si is used as a 5s02 source which reacts with Al2O3 to produce mullite.

The reason for firing in a reducing atmosphere with a water vapor dew point of 10°C or less is that the starting material, metallic silicon, is oxidized by the water vapor in the firing atmosphere into SiO and 5i02, the latter 5i0
2 reacts with At203 to produce mullite, but if the dew point is lowered, 5i02 reacts with Al2O3 at a low concentration, so the reaction takes time to produce mullite with a network crystal structure, which is in equilibrium with 5i02. As Si02 is reduced by A12036 reaction, 5io2. This reacts with free Al 20 a one after another to produce mullite with a network crystal structure, and this reaction occurs when the water vapor dew point is 10°C.
This is because it has been experimentally confirmed that it can be obtained by limiting the following.

Therefore, the lower limit of the water vapor dew point is about 15°C from the standpoint of mass production.

In the previous table, metallic silicon and alumina were used as starting materials and were weighed to obtain the theoretical composition of mullite. Free Al2O3, Si
The presence of O2 is permissible as long as it is within 8%5 of mullite.

In addition, as a starting material, metal silicon Si cannot be used as a source of SiO□, but alumina sol can be used as a source of Al2O3.

An aluminum compound such as aluminum hydrate can be used, and the firing gas may also be a reducing gas such as a mixed gas of carbon monoxide gas and nitrogen gas.

Furthermore, the example shows the case where the powder of the starting material is made into a slurry and a green sheet is manufactured using the doctor blade method. A molding method can be selected depending on the purpose, such as press molding performed by granulation.

[Brief explanation of drawings]

The drawings are micrographs (X5000) of the mesh-like porous mullite porcelain obtained by the present invention, and FIG. 1 is the sample Nα2. Figure 2 is the same (Sample Nα14 in Table 1 is shown as a representative example. Patent applicant: NGK Spark Plug Co., Ltd. Agent Imai d1° (None) Figure 2 Procedures Amendment (Method) Date of March 1, 19801, Case description, 1982 Patent Application No. 223948, 2 Name of the invention, Process for manufacturing porous mullite porcelain a. Person making the amendment Relationship to the incident Patent applicant address 14-18 Takatsuji-cho, Mizuho-ku, Nagoya Name (45
4) NGK Spark Plug Co., Ltd. Representative Shujio Ogawa Agent Address Postal Code 46'l In the specification subject to the G amendment, the column "Brief explanation of drawings" and "Drawings"
. 7. Inclusion of amendments (1) The brief explanation of the drawings column on page 8, line 5 of the specification is corrected as follows. "Figure 1 is an electron micrograph (magnification: 5000x) of the crystal structure of porous mullite porcelain according to the present invention, and Figure 2 is an electron micrograph (magnification: (2) Figures 1 and 2 of the drawings will be corrected as shown in the attached sheet. Procedural amendment (voluntary) Indication of the case dated June 79, 1988 Patent application No. 228948 2 Name of the invention Process for manufacturing porous mullite porcelain ) NGK Spark Plug Co., Ltd. Representative Shujio Ogawa (467) Column for detailed explanation of the invention in the specification subject to the five amendments. Contents of the G amendment (1) gA Specification, page 2, line 8 to line 4 of the same page are corrected as follows. ``It has been considered difficult to impart high thermal shock resistance to ceramics.''

Claims (1)

[Claims] A method for producing mesh-like porous mullite porcelain, characterized by firing a molded body mainly composed of a mixed powder of metallic silicon and an aluminum compound in a reducing atmosphere such as hydrogen gas or ammonia decomposition gas with a dew point of 10°C or less. .