JP2589511B2 - SiC structural material for steam resistant atmosphere - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is directed to a steam-resistant atmosphere for extending the life of a recrystallized SiC or reactive sintered SiC structural material, especially in an atmosphere having a large amount of moisture. Related to SiC structural materials for industrial use.

[Conventional technology]

Structural materials used in industrial furnaces in the temperature range of 900 ° C to 1400 ° C are required to have high-temperature strength, corrosion resistance, thermal shock resistance, and the like. For such conditions, SiC has attracted attention.In particular, recrystallized SiC and reactive sintered SiC have recently been used because they satisfy the above characteristics and can sufficiently cope with cost. became. Incidentally, the oxidation resistance of recrystallized SiC or reactive sintered SiC can be said to be good in a general oxidizing atmosphere because a SiO ₂ protective film is formed on the surface.

However, in in juicy atmosphere, SiO ₂ is filled into the structural member cavity portion causes a reaction of _{SiC + 4H 2 O → SiO 2} + CO 2 + 4H 2, the organization cracked by the pressure, oxidation proceeds at an accelerated pace. Further, H ₂ generated by the above reaction becomes H ₂ O by O ₂ in the atmosphere, and H ₂ O repeats a vicious cycle of acting on SiC again, thereby accelerating oxidation. The above reaction is 900 ℃ -1400 ℃
It is particularly remarkable in the temperature range of In addition, due to the presence of water vapor, the protective film formed on the surface of SiC becomes porous, and the effect that oxidation proceeds is also observed.

[Problems to be solved by the invention]

Conventionally, various countermeasures have been taken to compensate for the above-mentioned disadvantages. For example, generally, there is a method of coating with a eucalyptus containing low-melting glass as a main component.

However, in the above-mentioned method, the alkali in the Yu-Yu medicine may have an adverse effect on the oxidation resistance, and some of them have a shorter life than structural materials not coated on the surface.

Further, there is a method of coating chemically stable alumina by a method such as plasma spraying. However, a major drawback of this method is that the difference in physical properties between SiC and Al ₂ O ₃ , for example, the coefficient of thermal expansion is large.

That is, the coated Al ₂ O ₃ often peels off during use, so that great expectation cannot be made.

The object of the present invention is to thoroughly consider the above-mentioned circumstances, and as a result, on the surface of recrystallized SiC or reactive sintered SiC structural material, silicon dioxide, iron oxide and further Si and Fe, Mo, Ni silicide. An object of the present invention is to provide a stable and long-life SiC structural material in an atmosphere having a large amount of water vapor by coating and baking a mixture of one or more kinds.

[Means for solving the problem]

That is, the present invention relates to a recrystallized SiC used in an industrial furnace.
Alternatively, at least 75 to 95% by weight of silicon dioxide, 1 to 3% by weight of iron oxide, or one or two or more of silicides of Si, Fe, Mo, Ni are formed on the surface of the reaction sintered SiC structural material. A composition containing 20% by weight of the three components is coated and baked at a temperature of 1300 ° C. or more.
In the case of the method using the above-mentioned low melting point glass method such as plasma spraying of alumina, complete protective coating of the SiC structural material could not be performed, whereas in the present invention, the pores are filled with silicon dioxide and metal silicon or silicide A very dense coating film can be obtained because it exists in such a form.

In addition, the presence of metal silicon or silicide improved the adhesive strength between the SiC structural material body and its coating film, and did not cause any peeling, resulting in a very stable and long-life surface coated SiC structural material.

The SiC structural material according to the present invention is particularly suitable for use in an atmosphere having a lot of water vapor, which has been a problem in the past.

The degree of adhesion of the structural material main body is a coating film that is simply empirically bonded only with silicon dioxide. In an atmosphere with a lot of water vapor, peeling occurs at, for example, a furnace temperature of 1200 ° C. and an experimental time of about 700 H.

Therefore, it is important to solve this problem
This is the most important issue for obtaining C structural materials.

At least 75-95% by weight silicon dioxide as described above,
A composition containing 1 to 3% by weight of iron oxide and one or more silicides of Si, Fe, Mo and Ni and containing 3 to 20% by weight and baked at a temperature of 1300 ° C or more Thus, the addition of the above-mentioned iron oxide, which provided a coating film having the best oxidation resistance, reduced the melting temperature of the coating film, so that the wettability between the coating film and the structural material body was improved. Further, iron oxide also has the effect of uniformly diffusing Si and silicide throughout the coating film.

When the amount of the silicon dioxide exceeds 95% by weight, pores of the coating are excessively filled with silicon dioxide, and oxidative expansion of the silicon dioxide causes cracks. 75% by weight
If the amount is smaller, the pores of the coating film increase, and the effect cannot be obtained.

If the amount of the iron oxide is less than 1%, the wettability of the coating film is poor, and if it exceeds 3%, the structure of the coating film itself changes, resulting in two layers, and the outer layer is peeled off. To go.

The baking temperature must be 1300 ° C. or higher. This is because when baked at a temperature lower than 1300 ° C., the coating film has no gloss and peels off during use, so that no effect is obtained.

If the content of Si or silicide exceeds 20% by weight, a dense coating film is not formed. If the content is less than 3% by weight, the adhesive strength between the coating film and the structural material body is not improved, which is not preferable.

〔Example〕

 The present invention will be described with reference to examples.

An aqueous solution of an organic binder is added to a mixture of 82% of silicon dioxide of 200 mesh or less, 11% of metallic silicon of 350 mesh or less, 5% of molybdenum silicide of 200 mesh or less, and 2% of iron oxide. Crushed and mixed.

The slurry-like mixture thus obtained is recrystallized by a spray method. SiC structural material: (outer diameter φ50 mm, inner diameter φ35 mm, length 50 m
m), dried and baked at 1350 ° C.

In order to confirm the effect of the coating film obtained above, two box electric furnaces (width 300 mm, height 100 mm, depth 200 mm) were used, and the furnace temperature was set to 900 ° C and 1400 ° C, respectively. .

Furthermore, 300cc / h from outside the furnace to make a steam atmosphere
, And continuous operation was started.

To confirm the effect of the coating film, the weight increase rate was measured every 1000 hours.

The SiC structural material for a steam resistant atmosphere of the present invention has a furnace temperature of 900 ° C. and a weight gain of 0.8% at a furnace temperature of 8000 hours, and a furnace temperature of 1400 ° C. has a weight gain of 1.0% and a resistance to oxidation. A considerable effect was obtained.

For comparison, Table 1 shows the measured values of the rate of weight increase in the case of no coating under the same conditions as in the example, and in the case of the coating with a drug.

16.3% of those with a furnace temperature of 900 ° C in 8000 hours
As shown in the table, those with a furnace temperature of 1400 ° C that are not coated show a 18.3% weight increase rate.
Both those at 900 ° C and those at 1400 ° C turned into white powder and collapsed.

According to the present invention, a very stable coating film is formed with respect to other examples, and the rate of weight increase over a long time is extremely small.

〔The invention's effect〕

Innovative Si that can be used stably according to the present invention in an atmosphere with a lot of water vapor that could not be used for a long time
C structure material could be provided. That is, the present invention is very effective in industry and its application is wide.

Claims (1)

(57) [Claims] 1. A recrystallized SiC or reaction sintered SiC structural material used in an industrial furnace at a temperature range of 900 ° C. to 1400 ° C., wherein at least 75 to 95% by weight of silicon dioxide is present on the surface of the structural material. 1% or more of Si or Fe, Mo, Ni silicides. A composition containing 3 to 20% by weight of 3 components is coated and baked at a temperature of 1300 ° C or more. SiC structural material for steam resistant atmosphere.