JPH02311359A - Production of mullite-based sintered compact - Google Patents

Abstract

PURPOSE:To obtain the subject sintered compact excellent in dimensional accuracy with a suppressed baking shrinkage, by mixing a specified amount of a thermosetting resin and a slurry of inorganic powder containing Al2O3, SiO2 and iron oxide at a specified weight ratio followed by forming, curing and then baking at specified temperatures. CONSTITUTION:Firstly, a slurry of inorganic powder comprising (A) 63 to 75wt.% of aluminum oxide, (B) 22 to 32wt.% of silicon oxide and 0.5 to 7wt., of iron oxide in terms of wt.% Fe2O3 is prepared. Second, the slurry is mixed with 5 to 15 pts.wt., per 100 pts.wt. of the inorganic powder, of a thermosetting resin (e.g. epoxy resin). Thence, the resultant mixture is formed and cured and then baked at 1400 to 1700 deg.C, thus obtaining the objective mullite-based sintered compact. Thereby, the baking shrinkage can be suppressed to ca.<=2%, leading to the objective sintered compact excellent in dimensional accuracy suitable for crucibles, heat exchangers, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a mullite-based sintered body that has high firing dimensional accuracy and is suitable for manufacturing large-sized sintered bodies.

(Prior Art) There are many known methods for molding ceramics, such as a dry press method, an extrusion molding method, an injection molding method, and a cast molding method. The so-called doctor blade method is also frequently used as a representative example of a method in which ceramic powder is made into a slurry with a curable resin, this slurry is shaped, and then hardened to form a green body.

Many ceramic materials have been put into practical use, including alumina, zirconia, silicon carbide, silicon nitride, etc., and mullite (3A#tOa・25i (h)) has its features such as low thermal expansion and high strength. It is used extensively.

Ceramic products are manufactured by molding ceramic powder and then firing it at a high temperature to sinter the ceramic particles together. During this sintering process, the distance between the particles becomes shorter, usually accompanied by firing shrinkage of about 5 to 25%. It is no exaggeration to say that the higher the firing shrinkage rate, the higher quality sintered body that is denser and stronger can be obtained.

, -,, -□ However, it is virtually impossible to cause shrinkage during firing uniformly and with good reproducibility throughout the sintered body due to temperature irregularities during firing, compositional irregularities in the grease body, etc. The dimensions after firing cannot be precisely controlled from the dimensions before firing. That is, the dimensional accuracy after firing is generally extremely poor, and there is a problem in that post-processing such as grinding is required after firing in order to obtain a ceramic product with excellent dimensional accuracy. Furthermore, this firing shrinkage becomes an obstacle when producing large sintered bodies. In other words, when firing a large green body, the length of contraction during firing becomes large, and stress is generated due to friction with the firing jig and differences in shrinkage rates at various parts, resulting in shortening during the contraction process. There is a problem of cracks forming. In order to solve these problems associated with firing shrinkage, methods have been used to use a particle-sized blended raw material in which coarse particles are intentionally blended as raw material ceramic powder, or to lower the firing temperature. However, the strength of the obtained sintered body is low. In non-oxide ceramics,
It is known that when silicon carbide or silicon nitride is manufactured using a reactive sintering method using metallic silicon as a raw material, the firing shrinkage is extremely small, but in oxide ceramics such as mullite, Since it is difficult to reduce the firing shrinkage, the purpose is to provide a method for manufacturing a mullite-based sintered body that has a small firing shrinkage, has high firing dimensional accuracy, and is suitable for manufacturing large sintered bodies. It is in.

(Means for Solving the Problems) The above purpose is to produce a sintered body by molding and curing a slurry of inorganic powder containing a curable resin, and then firing it to produce a sintered body. amount% aluminum oxide,
22-32% heavy silicon, converted to Fe2O3 0
A slurry of inorganic powder consisting of 5 to 7% iron oxide and 5 to 15 parts by weight of a curable resin are used as the main raw materials per 100 parts by weight of the inorganic powder, and fired at 140o to 1yoo'c. This is achieved by a method for producing a mullite-based sintered body characterized by the following.

31 In the present invention, a mullite-based sintered body refers to a sintered body in which a single phase of a mullite crystal phase and a sintered body mainly composed of a mullite crystal phase and either or both of a corundum phase and a silica phase such as quartz are mixed. .

Aluminum oxide and silicon oxide are mullite (chemical composition 3A
It is the main component that makes up 120g/25if2).

In the present invention, it is preferable to use crystalline corundum as the aluminum oxide raw material. It is not preferable to mix a large amount of γ-alumina or aluminum hydroxide, and the mixing ratio of these is preferably 20% or less of the total aluminum oxide raw material in terms of corundum. The content of aluminum oxide is 63-75% by weight. If it deviates from the above range, firing shrinkage will increase and the amount of mullite produced will further decrease.

Like aluminum oxide, it is preferable to use crystalline quartz, cristobalite, and tridymite as the silicon oxide raw material. It is not preferable to mix a large amount of amorphous silicon oxide, such as silica glass or diatomaceous earth, and it is preferable that the mixing ratio of these is 30% or less of the total silicon oxide raw material. The content of silicon oxide is 22-32% by weight. Outside this range, firing shrinkage will increase and the amount of mullite produced will further decrease.

In the present invention, iron oxide is added to promote the reaction of aluminum oxide and silicon oxide to form mullite at high temperatures, but excessive addition significantly increases firing shrinkage. Iron oxide is FearFe20g, F8g0
It may be added in the form of any of the oxides of 4. The content of iron oxide is 0.5 to 1% by weight, preferably 2 to 4% by weight in terms of Fe2Oδ. If it is less than 0.5% by weight, the amount of mullite produced will be small, while if it exceeds 7% by weight, firing shrinkage will increase.

In the present invention, oxides other than the above-mentioned components may be added as additives for improving molding and firing workability, or as unavoidable impurities, within a range that does not impede the purpose of the present invention. These components include Li2O, Na2O, K20
etc. 7Jl/potassium metal oxide, OaO, MgO, 8rO
, alkaline earth metal acid supra such as BaO, Or20g,
MnO, ZrO2, NiO, 5n02, Sb20
Examples include oxides such as gBi2O3 and 0e02.

These may be blended alone or in any form such as hydroxide, carbonate, or double oxide. The total content of these is 1
It is desirable that the content be 0% by weight or less.

It is desirable that the raw material powder used in the present invention is easily sinterable, and for this purpose, the particle size is preferably small. The particle size is preferably 50μ or less, more preferably 10μ or less, and most preferably 5μ or less.

In the present invention, ceramic powder is mixed with a curable resin and a dispersion medium, and shaped into a slurry state.

In the present invention, the curable resin refers to both a cross-linked resin whose molecular structure becomes three-dimensional through a cross-linking reaction, and a film-type resin which forms a film and hardens when a dispersion medium or solvent evaporates. It is.

As cross-linked m fingers, epoxy, phenol, melamine,
Examples include resins such as urea. When these are used together with a curing agent, a crosslinking reaction occurs.

On the other hand, film-type resins include vinyl-type resins such as polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polystyrene, polyacrylic ester, polymethacrylic ester, polyvinyl alcohol, polybutyral, nylon, 16mm 8F of polyester, polyurethane, etc.! , hydroxyethyl cellulose, hydroxymethyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, and other cellulose resins. These may be used alone, as a copolymer, or as a mixture, and may also be used in the form of a solution or a dispersion.

The curable resin contains 5 to 100 parts by weight of inorganic powder.
It is 15 parts by weight. If the amount is less than 5 parts by weight, the dry state after molding, ie, the strength of the green body, will be low and workability will be poor.

Hardened marine fat is removed by incineration during the ceramic manufacturing process of degreasing and firing, and adding more than 15 parts by weight is economically disadvantageous.

In the present invention, either water or an organic solvent may be used as the dispersion medium. Examples of the organic solvent include methyl alcohol, ethyl alcohol, toluene, xylene, ethyl acetate, butyl acetate, etc. alone or in mixtures. The type and amount of dispersion medium depend on the molding equipment and method used,
It is selected as appropriate, taking into account the curable resin and the like.

The inorganic powder slurry of the present invention is prepared using a mixing device such as a ball mill or attritor. The inorganic powder slurry contains a dispersant to improve the dispersibility of the inorganic powder, an antifoaming agent to improve the molding workability of the slurry, a viscosity modifier, a lubricant, a drying regulator, and a green material. A plasticizer or the like that improves flexibility can be added as appropriate.

The sintered body of the present invention is formed into an appropriate shape using a slurry of inorganic powder by a doctor blade method or a casting method, the dispersion medium is removed by air drying or forced heating, and the resulting green body is cured. Manufactured by degreasing and firing using a known method.

The firing temperature in the present invention is 1400 to 1700°C, preferably 1500 to 1650°C.

If the temperature is less than 1400°C, the amount of mullite synthesized will be small, making it impossible to obtain the sintered body that mullite originally has. On the other hand, if the temperature exceeds 1100°C, it becomes impossible to fire in a firing furnace using ordinary refractory materials, and a special high-temperature furnace is required, making it impossible to produce the product at low cost industrially.

(Effects of the Invention) The mullite ceramics of the present invention can be used as a material in a high-temperature atmosphere for various heat treatments such as shelves, crucibles, pipes, and protective tubes, by taking advantage of its properties such as low thermal expansion due to firing shrinkage and high-temperature strength. Suitable for members; or heat-resistant parts such as burners, heat exchangers, and heat insulators. Further, by forming a porous body or a honeycomb structure, it is suitable for molten metal filters, automobile exhaust gas filters, high-temperature gas filters, catalyst carriers for catalytic combustion, and the like.

Furthermore, by making use of mullite's excellent electrical properties and making it into a thin plate, it is suitable as a substrate for electronic components.

The present invention will be specifically explained below with reference to Examples.

In the examples, "parts" means "parts by weight", and the measurements and evaluations of physical properties in the examples were carried out by the following methods.

Firing shrinkage rate: The firing shrinkage rate was determined from the following formula, with the dimensions before and after firing being lo and Ilt, respectively.

Amount of mullite synthesized: Hiroshi Okuda -- 0 volumes of chemically engineered hair "Inorganic synthetic materials and their applications" V
ol, 14 No. 8. The amount of mullite synthesized was measured by the chemical analysis method described in P219 (1970).

Example 1 For 100 parts of inorganic powder having the composition shown in Table 1, pure components were 10 parts of epoxy resin binder, 0.26 parts of polycarboxylic acid type dispersant, 3 parts of propylene glycol, and 1 part of water.
2.76 parts were mixed and dispersed in a ball mill for 24 hours to obtain a ceramic slurry.

In addition, among the epoxy resin binders, the curing agent was mixed immediately before the slurry casting operation described below.

The slurry was poured into a polypropylene container, and after curing, the green body was demolded and dried. Using an electric furnace, 400°C
The temperature was increased at a rate of 0.5°C/min until then and at a rate of 10°C/min thereafter, and the green body was fired at 1600°C for 1 hour. The fired body was cut to a predetermined size, polished, and then its physical properties were evaluated according to the method described above. The results are shown in Table 1. In addition, the particle diameter of the inorganic powder is as follows. Corundum 2.8μ, α As shown in Table 1, by setting the contents of aluminum oxide and silicon oxide in appropriate amounts, it is possible to obtain a sintered body with a low firing shrinkage rate and a high synthesis amount of mullite. Aluminum oxide content is 63-76% by weight
, preferably 67 to 71% by weight.

On the other hand, the content of silicon oxide is 22 to 32% by weight, preferably 26 to 28% by weight.

Example 2 As shown in Table 2, the ratio of aluminum oxide and silicon oxide was taken as the theoretical composition ratio of mullite, and the amount of F820g added was varied to produce a sintered body according to Example 1, and its physical properties were evaluated. evaluated. Note that the firing temperature here was 1550°C. The results are shown in Table 2.

As shown in Table 2, the addition of 20 g of Fe has the effect of significantly accelerating the mullite synthesis reaction, but excessive addition is undesirable because it increases the firing shrinkage rate.

FetOail is 0.5 to 7!1 ffi1%, preferably 2 to 4 ffi amount%.

Example 3 An aqueous slurry having the composition shown in Table 3 was mixed and dispersed in a ball mill for 24 hours to prepare 100 parts of the inorganic powder having the No. 12 composition of Example 2. The optimum value of the water μ' was determined based on the fluidity of the slurry.

A thin film sheet with a width of 300 mm, a length of 0.0 mm, and a thickness of 0.5 mm was prepared from the obtained slurry using a doctor blade device. After air drying, the green sheet was degreased and fired in accordance with Example 1, and then sintered. I got a body. 3rd result
Shown in the table. Here, the properties of the green sheet were evaluated based on the following criteria.

It has excellent flexibility and strength and can produce good samples. ○〃
Although it is inferior to the above, it is possible to prepare a sample. Inferior to △〃, sample cannot be prepared. × If the content of the curable resin is 5 parts per 100 parts of the inorganic powder, the properties of the green sheet will be poor, and 5 parts or more is required. Furthermore, excessive addition is economically disadvantageous.

Example 4 Corundum (particle size 1.2μ), α-quartz (particle size 4.0μ
] and 10 g of Fe (particle size 2.7 p) and 100 parts of inorganic powder with the composition shown in Table 4, a mixture of 10 parts of butyral resin, 2 parts of tung oil, 3 parts of fish oil, and 1 part of methanol/toluene. 20 parts of a solvent was added and mixed and dispersed in a ball mill for 24 hours to prepare a ceramic slurry. Using the obtained slurry, a thin film-like sheet having a width of 300 mm, a length of 500 mm, and a thickness of 1 mm was prepared using a doctor blade device and air-dried to obtain a green sheet.

The green sheets were fired according to Example 1 at various temperatures for 6 hours. The results are shown in Table 4.

When the firing temperature is less than 1400°C, the amount of mullite synthesized is extremely small, and no significant improvement is seen even with the addition of a large amount of Fe5O12. A slight increase in shrinkage is observed if the firing temperature is too high. Furthermore, it is unsuitable for industrial production. It can be seen that the firing temperature is 1400 to 1700°C, preferably 1500 to 1650°C.

Claims (1)

[Claims] Molding and molding slurry of inorganic powder containing hardening resin
In a method of manufacturing a sintered body by firing after hardening,
A slurry of inorganic powder consisting of 63 to 75% by weight of aluminum oxide, 22 to 32% by weight of silicon oxide, and 0.5 to 7% by weight of iron oxide in terms of Fe_2O_3 and 100 parts by weight of the inorganic powder. , 5 to 15 parts by weight of a curable resin as the main raw material, and firing at 1400 to 1700°C.