JPS5857391B2 - Silicon carbide refractory mixture - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The chemical components of the present invention are mainly 80 to 95 wt% of 5iC and 3 to 17 wt% of Si, and the total amount of SiC and Si is 92 wt%.
% or more and has a porosity of 8% or less (hereinafter referred to as special silicon carbide raw material), and is used as a monolithic refractory or as a fired refractory with low porosity and hot strength. , relates to a silicon carbide refractory mixture having excellent corrosion resistance and alkali resistance.

The silicon carbide raw material used for conventional silicon carbide refractories is a mixture of silica sand, coke, etc.
Heating to 200-2500℃, SiO2+3C→SiC
It is produced by a gas phase reaction expressed by the reaction formula +2CO↑, and the chemical component is mainly SiC80-99wt%.
, 3 to 17 wt% of Si, 8 wt% or less of other impurities, and a fine crystal aggregate having a porosity of 8 to 25%.

With such porous conventional silicon carbide raw materials, coarse particles of SiC single crystals with a size of 3 or more can hardly be obtained, and therefore, silicon carbide refractories using this as an aggregate have a particle size composition of coarse particles. Moreover, since the porosity of the raw material itself is high, it is extremely difficult to reduce the porosity of the entire refractory to 14% or less.

For this reason, metallic silicon is generally added to the formulation of conventional silicon carbide refractories, and free carbon in the silicon carbide raw material, carbon powder added at the same time, and carbon such as tar, pitch, and phenolic resin as binders are added. Although attempts have been made to strengthen the matrix by converting Si+C to βSiC using a substance and sintering in a reducing atmosphere, no substantial improvement has been achieved as the characteristics of the aggregate itself remain unchanged.

The present invention was developed as a result of various researches to solve the above-mentioned conventional problems.
The present inventors have discovered a special silicon carbide raw material that has a low porosity of 8% or less and can produce coarse particles, and has completed the present invention.

This special silicon carbide raw material used in the present invention can be obtained from a by-product deposited at the bottom of an electric furnace that mixes silica stone with coke and produces metallic silicon through the reduction reaction of 5i02+2cm+si+2co↑.

This by-product is a miscellaneous product containing carbon and metal silicon, so
Conventionally, the Si-rich portion has been used only as a second grade silicon metal, and the rest has only been used as a deoxidizer or carburizer for hot metal or molten steel, and has never been used as a raw material for refractories.

In the present invention, from among these by-products, those whose chemical components mainly consist of 80 to 95 wt% of SiC and 3 to 17 wt% of Si, and whose coarse particles of 1 m1 rL or more have a porosity of 8% or less are selected and used.

The selection method can be easily carried out by once confirming the location in the electric furnace where a by-product with this chemical component ratio is produced, and then collecting it from the same location next time.

It can also be done by visually judging the color and degree of crystal development.

The special silicon carbide used in the present invention is not limited to the above-mentioned byproducts,
It can also be obtained by impregnating conventional silicon carbide with molten metallic silicon at high temperatures.

This impregnation is performed, for example, by immersing a lump of silicon carbide in metal silicon melted at 2000° C. or lower.

The soaking time depends on the size of the lump, but for example, 10Cr71
It will take about 1 hour.

After impregnation, the mass is cooled and ground to the desired particle size for use.

As mentioned above, conventional silicon carbide raw materials are aggregates with a porosity of 8% or more due to the manufacturing method, and for this reason, when the porosity is 1 mm or more, coarse particles of SiC single crystal cannot be obtained, and coarse particles Even if it is crushed to 11n11L or less, the porosity will be 8% or more.

The special silicon carbide raw material used in the present invention contains 3 to 17 wt of Si.
%, and this Si fills the voids between SiC crystal grains, lowering the porosity and making it possible to obtain coarse particles of 1 mm or more. It improves properties such as corrosion resistance, alkali resistance, and hot strength of refractories.

Note that conventional silicon carbide raw materials also contain Si, but this Si remains because it cannot be converted into SiC, and is not intended for quality control of silicon carbide raw materials.

Therefore, the proportion thereof is as small as 2.0 wt% or less, and the characteristics of the refractory of the present invention cannot be obtained at this level.

The reason why the ratio of chemical components and the porosity of special silicon carbide are limited in the present invention is as follows.

If SiC is less than 80wt%, the corrosion resistance, alkali resistance and hot strength of SiC cannot be fully exhibited;
% or more, Si will not reach the desired proportion.

If Si is less than 3wt%, it is insufficient to fill the voids between SiC grains, and if it is more than 17wt%, Si
is undesirable because it flows out from between the SiC crystal grains and promotes melting loss, and the most suitable content is 10 to 14 wt%.

The reason why the porosity of the coarse particles of 1 pore or more is set to 8% or less is that if the porosity is more than 8%, the effect will not be different from that of the conventional one.

The reason for blending 20 to 60 wt % of coarse particles with a size of 1 mm or more is to increase the filling properties of the silicon carbide refractory, lower the porosity, and increase the strength.

This is because if the content is less than 20 wt% or more than 60 wt%, close packing cannot be obtained and the corrosion resistance decreases.

The silicon carbide refractories of the present invention can be used regardless of whether they are fixed or unshaped, such as bricks for lining blast furnaces, gutter materials for blast furnaces, mud for closing tapholes in blast furnaces, monolithic refractories for lining blast furnaces, and hot blast furnaces. It can be applied to lining bricks, refractories for soaking furnaces and heating furnaces, and repair materials for various furnaces.

Therefore, other raw materials and binders to be combined with the special silicon carbide raw material are also adjusted from known ones to suit the refractory.

The proportion of other refractory raw materials that can be used in combination with special silicon carbide is 80% or less, and if it is more than that, no significant effect can be obtained by blending the special silicon carbide raw material.

Other refractory raw materials include ordinary silicon carbide, alumina, alumina-silica, magnesia, zircon, and zirconia.
More than one species is used.

Further, the amount of organic binders such as tar, pitch, phenol resin, water, and pulp waste liquid added is 10 to 2 wt%, and the amount of other additives such as carbon, metal silicon, and ferrosilicon is 20 to 5 wt%.

The refractory mixture of the present invention is produced by blending carbon powder among additives such as carbon, metal silicon, ferrosilicon, etc. alone or in combination with other refractory raw materials, so that this carbon powder can be added to the Si + C in the special silicon carbide raw material. → Strengthen the bond with Mar-IJ lux aggregate by βSiC reaction,
It increases the strength of refractories and improves their resistance to slag and alkali vapor.

A preferred example is one in which metal silicon, ferrosilicon, etc. are added in addition to carbon powder to further enhance the above reaction and further improve the physical properties of the refractory.

Next, examples of the present invention will be shown together with conventional examples for comparison, and the results of measuring physical property values for each will be shown.

The quality of silicon carbide used in this example and the conventional example is shown in the following table.

In Examples 1, 2.3 and Conventional Example 1 shown in Table 2, the mixing ratio was 500 kg/cI! 114×230 at the pressure of
The green bricks obtained by press molding between X65 and air drying for 24 hrs and heat drying at 140° C. for 24 hrs were placed in a pod, filled with coke and sealed, and subjected to reduction firing at 1450° C.

As a result, both Examples 1 and 2.3 of the present invention have lower porosity than Conventional Example 1, have higher structural strength in compressive strength and hot bending strength, and have excellent corrosion resistance and alkali resistance. The results were shown.

Example 3 contains 20 wt% of special silicon carbide, and some effects are observed.

Examples 4 and 5 and Conventional Examples 2 and 3 shown in Table 3 are monolithic refractories for vibration molding, and in order to measure the physical properties, these formulations were kneaded and vibrated in a mold to obtain a molded product of 114 x 230 x 65 mm. After molding, air drying for 120 hrs, and heating drying at 115° C. for 48 hrs, it was packed in a pod, filled with coke, sealed, and subjected to reduction firing at 1450° C. to obtain a test piece.

As shown in the table, the physical properties of Example 4 of the present invention are those of Conventional Example 2.
It has a lower porosity and higher compressive strength and bending strength than that of the steel, and good results were obtained in terms of corrosion resistance and alkali resistance.

As described above, it is clear that the silicon carbide refractory of the present invention has various physical property values superior to those manufactured using conventional silicon carbide raw materials.

In other words, in conventional products, the raw material, silicon carbide, is Si.
It has a structure that has voids between the C crystal grains and is easily attacked by foreign components.

In addition, due to the high porosity, coarse particles of 31 nN or more cannot be obtained, and a dense refractory cannot be obtained because a particle size structure containing coarse particles cannot be obtained.

On the other hand, the refractory of the present invention has a special silicon carbide compound that fills the voids between SiC crystal grains with metallic silicon, making it dense and preventing erosion of foreign components, and the special silicon carbide has a porosity of 8%. Due to the following denseness, coarse particles with a size of 3 or more can be obtained, making it possible to create a dense particle size structure with a coarse particle mixture.
As a result, hot strength, corrosion resistance, alkali-resistant porosity reduction, etc. are significantly improved compared to conventional materials.

Although only the special silicon carbide raw material is used as the aggregate in the above embodiments, it may be combined with conventional silicon carbide raw materials and other known refractory raw materials.

Further, additives such as metal silicon and carbon powder, and binders are not limited to those in the examples.

Claims (1)

[Claims] In a silicon carbide refractory mixture consisting of 11 or more plates of 20 to 60 wt% of dense silicon carbide and the remainder being a refractory raw material,
Said 1ml! The porosity of the dense silicon carbide particles is 8
% or less and the chemical components are 5iC80-95wt%, Si
A silicon carbide refractory mixture characterized in that the total amount of SiC and Si is 92 wt% or more in a range of 3 to 17 wt%.