JPS6047229B2 - Coating agent for ceramics - Google Patents

Description

[Detailed description of the invention] The present invention relates to a coating agent for ceramics.

In the present invention, the coating agent for ceramics is an adhesive for refractories such as silicon nitride bricks, silicon carbide bricks, carbon bricks, and carbon blocks, joint fillers, or surface coatings for preventing oxidation, as well as carbon electrodes or carbon resistors. Adhesives and joint fillers for ceramics used at high temperatures, such as surface coating agents for preventing oxidation of carbon products such as bodies, carbon crucibles and containers.
This is a general term for coating materials, etc.

Conventionally, there has been no suitable adhesive for silicon carbide refractories, and carbonaceous cement, which is used to bond carbon bricks and the like, whose binder carbonizes and produces carbon when heated,
So-called carbon cement was used as a substitute.

Carbon cement is usually a mixture of carbon powder such as anthracite, coke, or graphite, and a binder such as coal tar or pitch, or liquid phenol resin or liquid furan resin to provide appropriate fluidity for application. After application, the binder of such carbon cement carbonizes when heated, forming a strong bond and strongly adhering the bricks together.

However, the disadvantage of carbon cement is that because it is carbonaceous, oxidative consumption occurs at temperatures above about 500° C. in atmospheres containing oxygen, water vapor, or carbon gas. For this reason, although silicon carbide bricks exhibit considerable oxidation resistance, the bonded portions are consumed by oxidation, resulting in a decrease in bond strength. This also applies when it is used for refractories other than silicon carbide bricks.

For example, carphone bricks are subject to oxidation and wear and tear, but the bonded parts are particularly susceptible to oxidation, and even though the bricks themselves are still usable, the structure as a whole becomes unusable due to the oxidation of the bonded parts. There is also. As described above, carbon products including carbon bricks are generally consumed by oxidation in an oxidizing atmosphere at high temperatures, and various measures have been proposed to prevent this.

For example, it is known to impregnate or coat carbon products with silica, alumina, etc., or to coat them with glass component powder. However, the effect has not yet been fully demonstrated. It is difficult to apply a strong, impermeable film such as silica or alumina, and glass materials have poor heat resistance. When Silica 5 is used, it reacts with the carbon of the base material to form silicon carbide at high temperatures, but it is difficult to form a dense coating. The present invention was developed under these circumstances, and is suitable as an adhesive, joint filler, or repair agent for ceramics used at high temperatures, and is also suitable as a coating agent for ceramic products that are easily oxidized at high temperatures. The purpose of the present invention is to provide a coating agent for ceramics suitable for.

The characteristics of the first invention are that metal silicon powder or ferrosilicon powder is blended into the liquid thermosetting resin, and the second invention
In the invention, ultrafine particulate silica is added to the first invention in order to improve the workability of the coating agent and further enhance the effect. The present invention will be explained in detail below.

The silicon powder or ferrosilicon powder is used by crushing commercially available metal silicon or ferrosilicon.

The particle size is suitable for joint fillers and adhesives to be about 60 mesh or less, and for coatings to be about 200 mesh or less. It is desirable for ferrosilicon to have a high silicon concentration, and JI
It is preferable to use silicone with a silicon concentration higher than S-filtered product (Sl: about 75%). The thermosetting resin used is an initial condensate of phenol resin, furan resin, urea resin, etc., which is liquid at room temperature.

If necessary, a solvent is added to these to adjust the viscosity depending on the degree of condensation. As the solvent, alcohols such as ethylene glycol, aromatics such as penzole, coal tar, etc. are used. Among the resins, phenol resins are preferred because they have a high carbonization rate and are inexpensive. These silicon powders or ferrosilicon powders and liquid thermosetting resin are mixed to form a coating agent, but the ratio is preferably in the range of 300 to 700 boads at 20°C, taking into consideration workability and other aspects. .

At that time, dilute with the above solvent as necessary. Further, within the above-mentioned viscosity range, it is possible to add silicon carbide powder, silica powder, carphone powder, molasses powder, etc. within a certain limit, and some of them are even preferable in small amounts. For example, β-type silicon carbide can be easily obtained in fine particles, so adding a small amount of silicon carbide has the effect of making the heated coating layer denser. In addition, molasses has the function of alleviating the odor of phenolic resin, so it is desirable to include it during construction. Carbon powder can be used to replace part of the resin46. However, in the coating agent of the present invention, silicon and carbon react at high temperatures to produce silicon carbide to increase the strength of the coating layer, so it is undesirable to use too much silicon carbide powder or silica powder. According to the inventor's experiments, even if a large amount of silicon carbide is added to the coating agent from the beginning or silicon carbide is generated as in the present invention, if silicon carbide is generated by a reaction between silica and carbon, It was found that the strength of the coating layer was inferior to that produced by the reaction between silicon and carbon. When a large amount of carbon powder is used, the amount of resin used decreases accordingly, and such a coating agent has poor adhesion to ceramics and poor performance. For this reason, in the present invention, it is desirable that the amount of components other than ferrosilicon or ferrosilicon and the resin in the coating agent excluding the solvent is 5% by weight or less. The quantitative ratio of resin and silicon is determined based on the stoichiometric ratio of silicon carbide production.

In the case of ferrosilicon, the silicon content is the standard. When the resin is heated, it carbonizes and its fixed carbon reacts with the silicon. The fixed carbon content of the resin varies depending on the type of resin, and if heated in an oxidizing atmosphere, a portion will burn, so this must also be taken into consideration when formulating the resin. Furthermore, when carbon powder is added, it also takes part in the silicon carbide production reaction. Taking these things into consideration, we determine the quantitative ratio of silicon content and resin, but it is not a fatal flaw even if some carbon content, silicon content, or iron content remains in the coating agent after application and heating, so it must be strictly determined. There is no need for stoichiometric proportions of silicon carbide formation. In general, liquid thermosetting resin has a silicon content of 200 to 25 parts per 10 parts of (1 resin amount + carbon powder) because about 114 parts of it remains carbonized.
The weighing section is appropriate. Even when silica is added, as long as the amount is within the above-mentioned limits, it is sufficient to select the one with the least amount of silicon in this quantitative ratio. Note that the liquid part has a much lower specific gravity than aggregates such as metal silicon powder, so if you leave it for a long time, the two will separate, so you can increase the viscosity of the liquid resin, or... It is desirable to stir the mixture well before processing.

Next, a second invention, a coating agent containing ultrafine particulate silica, will be explained.

This second invention aims to improve the workability of the coating agent of the first invention and also to improve the coating effect.

Ultrafine particulate anhydrous silica has a particle size of 50 to 300A, and has SlOH groups in some places on the surface of the particles, and in the static 5 state, the particles form weak hydrogen bonds with each other, which acts to prevent the particles from spreading. However, when these particles are suspended in a solvent or the like and placed under a state of movement such as stirring, the hydrogen bonds are broken and they become easy to flow, that is, they have thixotropic properties. The second invention applies this unique property to a coating agent to develop a coating agent whose viscosity decreases during application, and whose viscosity increases and stabilizes its shape in the static state after application. The specific gravity of liquid thermosetting resin or these resin liquids diluted with a solvent is approximately 1, whereas the specific gravity of metallic silicon powder, which is an aggregate, is approximately 2.3, and that of ferrosilicon (75% Si) is approximately 1. 3.7, P-silicon carbide is about 3.7.
2, if the viscosity of the resin liquid is low, sedimentation and separation of the aggregate will occur if the mixture of the resin liquid and aggregate is allowed to stand still. However, when a small amount of the ultrafine anhydrous silica powder is added to a resin liquid and dispersed uniformly, even when powders of substances with high specific gravity such as metal silicon and ferrosilicon are mixed, the sedimentation and separation of these powders becomes significant. Reduced. Therefore, there is no need to stir the compound before installation, making it easy to handle, and when the compound is applied to the adhesive surface and bonded, dripping of the adhesive and separation and outflow of the resin liquid are almost completely eliminated. It can be prevented. Further, when the compound is applied by spraying or brushing onto the surface of a carbon product for the purpose of preventing oxidation, a thick coating layer can be obtained. The appropriate amount of ultrafine anhydrous silica in the coating agent is 0.5 to 0.5% by weight, but from an economic standpoint, 0.5% to 0.5% by weight is appropriate.
5 to 3% is preferred.

If it is less than 0.5%, the effect will not be sufficient; if it is 3%, a fairly sufficient effect will be obtained; if it exceeds 10%, the fluidity will decrease;
This is because coating becomes difficult.

Even when ultrafine anhydrous silica is added, as in the first invention, silicon carbide other than metallic silicon or ferrosilicon,
The content of aggregate components such as silica, including ultrafine anhydrous silica, is preferably 5% or less in the total amount of the coating agent. This ultrafine anhydrous silica can be produced, for example, by burning silicon tetrachloride.

Further, ultrafine silica generated as gusto when metal silicon or ferrosilicon is smelted in an electric furnace can also be used. Since the coating agent of the present invention reacts with silicon and carbon to produce silicon carbide, approximately 140%
It is necessary to heat it to 0°C or higher.

Although it is preferable to heat in an inert atmosphere until the silicon carbide production reaction is almost completed, an oxidizing atmosphere is also possible. Example 1 A resin liquid was prepared by uniformly mixing 10 parts of liquid phenol resin (solid content 87%) (all parts below are based on weight), 45 parts of ethylene glycol, and 5 parts of molasses.

For 15 chants of this resin liquid, A: Metallic silicon powder (200
(under the mesh) 67 parts, B: A further mixed with 3.5 parts of ultrafine anhydrous silica (manufactured by Nippon Aerosil Co., Ltd., trade name Aerosil 200), C: B
2 out of 67 parts of metallic silicon powder? ? ? P-SIC
D: Substituted with ferrosilicon powder (Si content 75%, 2
Five types of coating agents were prepared: E: A mixture of 9 parts of silica powder (under 200 mesh) in place of the metal silicon powder of B, and E: a mixture of 67 parts of silica powder (under 200 mesh). The above five types are summarized in Table 1.Next, these five types of coating agents were tested for oxidation prevention.A test piece cut out from a graphite block (diameter 3
The coating agents A to E were sufficiently applied with a brush to the entire surface of the 0Tfrm, length 6h), and the excess was allowed to fall off naturally. This was cured by raising the temperature from room temperature to 120°C over 6 hours, and then placed in an argon atmosphere. The temperature was raised to 1400° C. in about 5 hours, maintained at that temperature for 1 hour, and then cooled. These respective test pieces and ? The weight of the same comparative test piece without cloth was measured, and then the temperature was raised to 1400°C in air for about 5 hours, and after keeping it at the same temperature for 3 hours, it was immediately taken out of the furnace and left to cool. The weight was measured and the oxidative consumption rate (weight loss rate) was calculated. The results are shown below. Example 2 The above B, . C. ．． D. Those using calcined anthracite (60 mesh or lower) instead of silica powder in E and F, and A″
A coating agent having the same composition as A was prepared except that the composition of the resin liquid was 100 parts of phenol resin, 35 parts of ethylene glycol, and 5 parts of molasses.

These coating agents were tested for dripping properties and adhesive strength. First, from silicon carbide bricks with silicon nitride bonds (4)
After applying a coating agent to one side of each of two test specimens of normal angle and W thickness, they were pasted together so that the gap was about 17 rrft,
Removed excess overflowing agent.

Next, the adhesive surface was stood vertically and left at room temperature for 24 hours. B. containing ultrafine anhydrous silica particles. ．． C.I.D.
．． For ENF, almost no dripping of the coating agent was observed, but for A'', although the viscosity of the resin liquid was increased, approximately 112% of the coating agent in the gap flowed out.Also, for BIC, .D, .E ．．．
F is placed in an air-filled tank and heated from room temperature to 3!120℃ for about 6
Although the temperature was raised over a period of time and the mixture was cured, no outflow of the compound occurred during that time. Next, in order to test the adhesive strength, we used the same silicon carbide bricks as above, measuring 30m square and 70Tn high! n
A test piece was cut out.

The above-mentioned coating agents A to F were applied to the surface of 30×30 Tfn, overlapped, and pressed together with their own weight, so that the excess coating agent protruded from the periphery.

Place the specimen in a constant temperature air bath with the adhesive surface horizontal, raise the temperature from room temperature to 120°C in about 6 hours, and after curing, place it in a graphite crucible for treatment in a non-oxidizing atmosphere, and place it around the test piece. The graphite crucible was filled with coke and inserted into a silicone melt furnace, and the temperature was raised to 1400° C. over about 5 hours, and after being maintained at that temperature for about 1 hour, it was allowed to cool. This test piece was subjected to a Michaelis type bending tester, and the bending strength was measured as a measure of adhesive strength. The results are shown in Table 2. In addition, it was recognized that the adhesive surface of all samples other than F was mainly composed of β-SiC. In addition, in order to examine the strength of the adhesive surface after oxidation, test pieces treated at 1400°C in the same manner as above were heated to 1200°C.
After being treated for 12 hours with air leaking into the lamp, the transverse rupture strength was measured in the same manner as above.

The results are shown in Table 2.

From Table 2, 1'5 at 1200℃! Although the transverse rupture strength of all formulations decreases due to the oxidation treatment, the product of the present invention has a lower transverse rupture strength than the control product. ．． It is noteworthy that F retains its strength after 30 to 4 ruts (K9ld) compared to the case where the transverse rupture strength becomes 0 when the adhesive part is peeled off.

Claims (1)

[Scope of Claims] 1. A coating agent for ceramics comprising silicon powder or ferrosilicon powder and liquid thermosetting resin. 2. A coating agent for ceramics containing silicon powder or ferrosilicon powder, liquid thermosetting resin, and ultrafine particulate silica.