JPH0345583A - Heat-resistant coating material for preventing oxidation of carbonaceous material - Google Patents

Abstract

PURPOSE:To obtain the subject coating material sustaining gastightness even at high temperature and having excellent effect of prevention from oxidation by dispersing respectively fixed amounts of alumina fine powder, silica fine powder and silicon phosphate fine powder into colloid solution comprising water and dispersed silica ultrafine particles. CONSTITUTION:20-60 pts.wt. alumina fine powder, 5-30 pts.wt. silica fine powder and 2-20 pts.wt. silicon phosphate for obtaining coating layer respectively having suitable thickness are dispersed in a colloid solution composed of water and dispersed silica ultrafine particles. Said silicon phosphate fine powder is used for giving the coating layer gastightness and adhesion to parent material. Heat- resistant coating material for preventing oxidation of carbonaceous material obtained by said method is applied to refractory material such as nozzle for continuous casting or graphite electrode using in electric furnace and dense coating layer is formed to prevent breaking with oxidation.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a heat-resistant oxidation-resistant coating material, and particularly to a oxidation-preventing coating material for carbon, carbide, graphite-containing refractories, graphite electrodes, etc. .

[Conventional technology]

Nozzles used for continuous casting of steel are mainly composed of alumina-graphite materials and zirconia-graphite materials, and oxidation becomes a problem when used at high temperatures.

Further, graphite electrodes used in electric furnaces are also used at high temperatures, and wear and tear occurs due to oxidation during use. In order to prevent such wear and tear, conventionally water glass-based or frit (glaze)
Materials from the system are used.

[Problem to be solved by the invention]

However, the operating conditions in continuous casting are that the temperature of the molten steel is 1500 to 1600℃, and the outer surface of the nozzle is 12
The temperature can reach 00-1300℃. However, when the temperature of the conventional coating material exceeds about 800° C., the material foams and airtightness is lost, or the coating layer melts and evaporates, losing its antioxidant effect. Such temperature conditions are the same for graphite electrodes, and conventional coating materials have little oxidation-preventing effect on graphite electrodes as well.

Furthermore, although there are coating materials for high temperatures of 800° C. or higher, most of the refractory materials are intended for heat insulation, and most of them do not have airtightness, so they hardly function as antioxidants. This invention was proposed in view of the above-mentioned conventional circumstances, and its purpose is to provide a coating material for carbonaceous materials that maintains airtightness even at high temperatures of 800°C or higher and has great effects such as preventing oxidation. shall be.

[Means to solve the problem]

In order to achieve the above object, this invention adds 20 to 60 parts by weight of a colloidal solution of ultrafine silica particles dispersed in water, 20 to 60 parts by weight of alumina fine powder, 5 to 30 parts by weight of silica fine powder, and silicon phosphate fine powder. I try to disperse 2 to 20 parts by weight.

[Effect]

In the above, if the colloidal solution is 20 parts by weight or less, it becomes mortar-like and cannot be applied to the carbon material.

On the other hand, if the amount is 60 parts by weight or more, the coated layer is likely to crack. Fine powder is used to obtain a coating layer of appropriate thickness. If the alumina fine powder is less than 20 parts by weight, the fire resistance of the coating layer will be lowered, and if it is more than 60 parts by weight, the coated layer will tend to crack.

Fine silica powder is also used along with fine alumina powder to obtain a coating layer of appropriate thickness. This silica fine powder is 5
If it is less than part by weight, the strength in the temperature range of 800 to 1000°C will deteriorate. Further, if the amount is 30 parts by weight or more, cracks tend to occur in the coating layer.

Furthermore, silicon phosphate fine powder is used to provide the coating layer with airtightness and adhesion to the base material.

If the silicon phosphate fine powder is less than 2 parts by weight, the coating layer will have many pinholes, and if it is more than 20 parts by weight, the coating layer will crack.

〔Example〕

As shown in Example 1 in Table 1, 30 parts by weight of a silica colloid solution is added to 50 parts by weight of alumina fine powder, 10 parts by weight of silica fine powder, and 10 parts by weight of silicon phosphate fine powder and stirred to obtain a liquid coating material. Further, as shown in Example 2, by adding 20 parts by weight of the silica colloid solution, a paste-like coating material can be obtained.

In this way, liquid and paste types are used depending on the required thickness of the coating layer.

Precast refractories and refractory bricks have pores (
For refractory surfaces with many hollows, replace 10 to 20 parts by weight of 50 parts by weight of Altansu fine powder with one with a consistency of 0°074 to 0.1. The coating material can easily enter the open pores of the coating material, making it possible to form a dense coating layer without pinholes.

The coating material of Example 1 or Example 2 was coated on a immersion nozzle specimen for continuous casting, and heated at 900°C in an electric furnace.
As shown in Table 1, Examples 1 and 2 had an oxidized layer of 1n or less, whereas Comparative Example, which is a conventional anti-oxidation coating material, had an oxidized layer of less than 1n. was more than 10 minutes.

In addition, when tested by coating it on a graphite electrode (size 30φ x 500mm) used in an arc-type slag test machine, it was found that in Examples 1 and 2, the weight 1i11 & fraction was less than 30%, while in the comparative example it was more than 40%. Met.

In the arc type slag test machine, the furnace temperature is 1800 to 19
00°C, the area near the electrode holder is exposed to the atmosphere, and the most oxidized area is 800-1300°C.

In the comparative example, most of the coating material evaporated and the coating layer disappeared, but in Examples 1 and 2, it remained over more than half the length of the graphite electrode.

Below is a margin [Effects of the Invention] Oxidation of carbon components has become a major problem in graphite electrodes used in continuous casting nozzles, electric furnaces, etc. By applying the coating material of the present invention to these refractories to form a dense coating layer, breakage due to oxidation can be prevented.

Claims (1)

[Claims] [1] Colloidal solution 20 in which ultrafine silica particles are dispersed in water
A heat-resistant oxidation-resistant coating for a carbonaceous material, characterized in that 20 to 60 parts by weight of fine alumina powder, 5 to 30 parts by weight of fine silica powder, and 2 to 20 parts by weight of fine silicon phosphate powder are dispersed in ~60 parts by weight. Material.