PL174315B1 - Method of obtaining a coherent layer of refractory on a surface and premixed composition therefor - Google Patents

Abstract

1. A mixture for forming a cohesive surface refractory mass based on a silicon compound, comprising a main component of the mixture in the form of refractory particles of one or more substances containing one or more silicon compounds, such as silicon carbide and silicon dioxide, and additional particles of a substance selected from the group consisting of an oxide magnesium, calcium oxide, iron (II) oxide and/or additional particles of a non-metallic compound selected from the group consisting of peroxide, silicate, nitride and carbide, characterized in that it contains combustible silicon particles and optionally flammable aluminum particles, wherein the combustible silicon particles in an amount not more than 15% by weight of the mixture and additional particles of a non-metallic compound in an amount up to 25% by weight of the mixture. Patent Office of the Republic of Poland PL PL PL PL

Description

The present invention relates to a mix for producing a cohesive refractory mass on a surface.

A refractory mass is produced on a surface using a method called ceramic welding as disclosed in British Patent Nos. 1,330,894 and 2,170,191. A cohesive refractory mass is formed on a surface by applying a mixture of refractory particles and combustible particles to the surface in the presence of oxygen. Combustible particles are particles whose composition and graininess are such that they react exothermically with oxygen to form refractory oxide and release the heat needed to melt, at least on the surface, the refractory particles. Examples of such combustible substances are aluminum and silicon.

It is known that silicon can actually be classified as a semi-metal, and since silicon behaves similar to some metals and is capable of undergoing significant exothermic oxidation with the formation of refractory oxide, these combustible substances are referred to for simplicity as metallic combustible substances. Typically, it is preferable to apply the particles in the presence of a high concentration of oxygen, for example using industrial grade oxygen as the carrier gas. In this way, a cohesive refractory mass is formed which adheres to the surface onto which the particles are applied. As a result of the very high temperatures in the ceramic welding reaction, the mass may penetrate the slag which may be present on the surface of the treated refractory material and may soften or fuse the surface so that a good bond is formed between the treated surface and the newly formed refractory mass.

The refractory mass is used to make a refractory product, e.g. a block having a particular shape, and is commonly used to form coatings or for

174 315 repairing bricks or walls and in the repair or reinforcement of existing refractory structures, for example in the repair of walls or refractory linings such as the walls of a coke oven or glass furnace. This operation is usually carried out while the refractory structure is hot. It will enable the repair of eroded refractory surfaces while the equipment remains substantially at operating temperature and in some cases even while it is operating.

The refractory mass is also produced on the surface using the flame spray method. It consists in directing the flame to the place where the refractory mass is to be produced and spraying the refractory powder through the flame. The flame is generated by the combustion of gaseous or liquid fuel, or even powdered coke. Efficient use of the flame spray technique requires the fuel to be completely burned in order to produce a flame at the highest possible temperature. Typically, the temperature of the flame in a flame spraying process is not as high as that which can be achieved with a ceramic welding technique. As a result, the cohesion of the refractory mass produced is not so good, and since the bond between the new refractory mass and the surface of the refractory structure is formed at a lower temperature, the bond is not so strong. Moreover, such a flame is less capable than the ceramic welding reaction of penetrating the slag into the refractory surface to be treated.

The composition of the mixture used in the ceramic welding process is usually selected so as to obtain a repair compound with a chemical composition similar or close to that of the base refractory material. This helps to ensure the homogeneous mixing and adhesion of the new material and the base material on which it is produced.

However, problems exist in the repair of some types of refractory structures, even when a refractory mass is produced with a chemical composition similar to that of the base refractory mass. For example, the repair of silicon carbide-based refractory surface structures with a mixture consisting primarily of silicon carbide particles as well as metallic combustible particles such as aluminum and silicon particles does not always ensure that the produced refractory mass adheres sufficiently to the base refractory material.

Silicon carbide refractory components are used in metallurgical equipment, particularly in blast furnaces for steel smelting or in zinc distillation columns. During the operation of this equipment, certain parts of the refractory structures may have a relatively low minimum operating temperature, for example of the order of 700 ° C, and may be subject to significant changes in ambient temperature. The refractory masses produced by known techniques on these parts of the refractory structure do not always adhere sufficiently to the base refractory mass and in some cases, especially when the refractory block or wall is being repaired at a low temperature, the new refractory mass separates completely from the base refractory mass, often during equipment work.

Similar problems arise in the repair of high-density silicon dioxide refractories, which are different from the traditional low-density silicon dioxide structures used in some coke ovens. Although a refractory mass can be produced with a similar chemical composition to the base refractory mass, the new mass does not always adhere sufficiently and may even rapidly separate from the base refractory mass when the furnace is in operation.

There is known from the international patent application WO 90/03848 a method of repairing, for example, refractory linings of a furnace, in which an inert carrier gas and particles of refractory oxide and oxidizing combustible material are supplied to a flame spraying device, in which oxygen under high pressure sucks and accelerates the mixture of carrier gas and particles. This method is used for the repair of refractory blocks and bricks in the nozzle line of a copper smelting converter as well as for the repair of silicon carbide trough columns. This specification discloses a blend comprising 79% silicon carbide, 16.25% silicon, 4% aluminum and 0.75% magnesium sprayed through an air-oxygen system onto a silicon carbide trough column. Magnesium powder use 4

The disadvantage of this method is disadvantageous, at least because the magnesium is relatively volatile and therefore there is uncertainty about the composition of the refractory lining produced.

There is known a composition for the production of a cohesive refractory mass on a surface based on a silicon compound, comprising the main component of the mixture in the form of refractory particles of one or more substances containing one or more silicon compounds, such as silicon carbide and silicon dioxide, and additional particles of a substance selected from the group consisting of an oxide magnesium, calcium oxide, iron (II) oxide, and / or additional particles of a non-metallic compound selected from the group consisting of peroxide, silicate, nitride and carbide.

The blend according to the invention comprises combustible silicon particles and optionally combustible aluminum particles, the combustible silicon particles in an amount not exceeding 15% by weight of the mixture, and additional non-metallic compound particles in an amount up to 25% by weight of the mixture.

The additional particles are less than or equal to 500 µm.

Preferably, the additional particles are at least 10 µm in size.

Preferably the blend comprises 79 to 82 wt% SiC, 8 wt% Si, 5 wt% Al and 5 to 8 wt% MgO.

Preferably the blend comprises 80.5 wt% SiO ₂ , 11.1 wt% Si, 1 wt% Al and 7.4 wt% MgO.

Preferably the blend comprises 80 wt.% SiO ₂ , 8 wt.% CaO · SiO ₂ , 8 wt.% Si and 4 wt.% Al.

An advantage of the invention is that the composition according to the invention is useful in the production of high-quality refractory masses used for the repair of silicon compound-based surfaces, for example the construction of refractory furnaces, as well as for welding components together. The invention provides a refractory mass that adheres perfectly to the base refractory mass, even when the surface is subject to changes in thermal conditions during operation of the equipment and / or when repair is made on a surface whose temperature is relatively low, for example between 600 ° C and 1000 ° C. although the invention is applicable to surfaces having a temperature outside this range.

The refractory masses obtained from the composition according to the invention provide a thermal expansion at the interface of the primary element and the refractory mass formed, different from the thermal expansion that would be obtained if the initial mixture did not contain any substances for introducing into the crystal lattice of the silicon dioxide produced by the combustion of silicon. Due to this property, the refractory masses adapt well to the tested refractory structures.

The aluminum particles added to the combustible silicon particles are rapidly oxidized, releasing a significant amount of heat and forming refractory oxides, leading to an improvement in the quality of the refractory masses.

Due to the content of not more than 15% by weight of silicon in the blend according to the invention, the amount of unreacted silicon that would remain in the produced refractory mass and deteriorate its quality is limited. A homogeneous mass is obtained with the presence of refractory particles of at least 70% by weight. The use of refractory particles larger than 4 mm facilitates the formation of a regular stream of powder. By selecting the size of the additional particles, a high quality of the refractory mass is obtained, since particles that are too large do not perform their function effectively, and particles that are too small volatilize during the reaction.

The presence of magnesium oxide in the mixture ensures the correct heat resistance of the produced refractory mass. The presence of a cordierite crystal lattice in the produced refractory mass provides excellent resistance to thermal shocks of this mass. The presence of a crystal lattice with a forsterite structure and / or a spinel structure improves the heat resistance of the refractory mass produced.

The invention is particularly useful for repairing silicon carbide refractory members or silicon dioxide high density refractory members. As a result, it is preferable to perform ceramic welding with a mixture the main part by weight of which is silicon carbide or silicon dioxide. The invention is also useful for the repair of other types of compound-based refractories

174 315 silicon than previously mentioned, such as normal silicate bricks and silicate-clay bricks.

The substance or substances which constitute the main part of the mixture corresponds to the composition of the refractory element in need of repair or is a different substance. In the latter case, a refractory mass is produced which has properties that are different and ideally improved relative to the refractory element to be repaired, for example improved abrasion or refractive strength.

The invention will now be illustrated in more detail with the aid of the following examples:

Example 1. A refractory mass is produced on the wall of a zinc distillation column. The wall comprises silicon carbide bricks. A mixture of refractory particles, particles of combustible substance, which are exothermically oxidized by the formation of refractory oxide, and magnesium oxide particles, is applied to the bricks. The wall temperature is 800 ° C. The mixture is applied in a pure oxygen stream at a rate of 60 kg / h.

The mixture has the following composition:

SiC 79 wt.%

Si 8% by weight

Al 5% by weight

MgO 8% by weight

The silicon particles have dimensions below 45 [mu] m and a specific surface area between 2500 and 8000 cm ² / g. The aluminum particles have dimensions below 45 µm and a specific surface area of between 3500 and 6000 cm ² / g. The dimensions of the silicon carbide particles are less than 1.47 mm, with 60% by weight being from 1 to 1.47 mm, 20% from 0.5 to 1 mm and 20% below 0.125 mm. The MgO particles have an average size of approximately 300 µm, with the average size being a size such that 50% by weight of the particles are smaller than the average size.

The new refractory mass adheres permanently to the wall repaired in this way, although it is subject to considerable changes in the ambient temperature.

The structure of the mass produced was examined under a microscope. An excellent continuity was observed between the refractory mass deposited and the refractory mass of the substrate, the silicon dioxide produced by the combustion of silicon being introduced into the crystal lattice of forsterite, cordierite and aluminum spinel.

For comparison, a mixture containing no magnesium oxide was applied to the surface under the same conditions.

The composition of this mixture was as follows:

SiC 87 wt.%

Si 12 * 1? scales

Al 1% by weight.

The refractory mass produced rapidly detached from the wall and detached as solid blocks if the zinc distillation column was still operating.

The mixture is also used, for example, to repair the bottom of a coke oven made of normal silicate bricks and ce ^^ ieT siiii ^ iatto ^^ and ^^^^ J ^ in ^^^ wyich. The result is a repair compound with good abrasion resistance, well adhering to the wall, and subject to significant temperature fluctuations.

Example 2. A mix with a composition similar to that of Example 1 was used, namely with the following composition:

SiC 82 wt%

Si 8%% agowgch

Al 5%% agαwggy

MgO 5 %% agowgch

The wall to be repaired consists of silicon carbide bricks and has a temperature of 700 ° C.

The obtained refractory mass also adheres permanently to the wall.

Example 3. Refractory mass is produced on a coke oven wall made of high-density silicate bricks. While the apparent density of ordinary silicate bricks is in the order of 1.80, the apparent density of high density bricks is around 1.89.

174 315

Such bricks are already available on the market and have better gas permeability and thermal conductivity properties compared to conventional silicate bricks.

A wall whose temperature is around 750 ° C is repaired with the following mixture:

SiO2 80.5% by weight

Si 11.1% by weight

Al 1% by weight

MgO 7.4% by weight

The SiO2 particles are smaller than 2 mm, with a maximum of 30% by weight of the SiO2 particles being from 1 to 2 mm and less than 15% by weight of the SiO2 particles being less than 100 gm.

The produced refractory mass adheres permanently to the wall.

In contrast, the application of a similar mixture under the same operating conditions, but not containing the magnesium oxide, provides a refractory mass which easily separates from the wall when the wall is subject to different thermal conditions during the operation of the furnace.

Example 4. A refractory mass is produced on the wall of a coke oven, made of a silicon-based refractory substrate, which is subject to significant changes in ambient temperature and whose temperature does not exceed 900 ° C. A wall with a temperature of about 750 ° C is repaired with the following mixture:

SiO2 80% by weight

CaO · SiO2 (wollastonite) 8% by weight

Si 8% by weight

Al 4 ¹ % by weight

The average size of the wollastonite particles is approximately 300 gm. The particle size of the metal is given in Example 1 and the particle size of the silicon dioxide is given in Example 3.

The produced refractory mass adheres permanently to the wall.

Publishing Department of the UP RP. Circulation of 90 copies. Price PLN 2.00

Claims (6)

Patent claims A silicon compound based cohesive surface refractory composition comprising the main component of the mixture being refractory particles of one or more substances containing one or more silicon compounds, such as silicon carbide and silicon dioxide, and additional particles of a substance selected from the group consisting of an oxide magnesium, calcium oxide, iron (II) oxide and / or additional particles of a non-metallic compound selected from the group consisting of peroxide, silicate, nitride and carbide, characterized in that it comprises combustible silicon particles and optionally combustible aluminum particles, the combustible silicon particles in an amount of no more than 15% by weight of the blend, and additional non-metallic particles up to 25% by weight of the blend. 2. A mixture according to claim The method of claim 1, wherein the additional particles have dimensions less than or equal to 500 gm. 3. A mixture according to claim The method of claim 2, wherein the additional particles have a size of at least 10 gm. 4. A mixture according to claim The composition of claim 1, comprising 79 to 82 wt.% SiC, 8 wt.% Si, 5 wt.% Al and 5 to 8 wt.% MgO. 5. A mixture according to claim The composition of claim 1, comprising 80.5 wt.% SiO ₂ , 11.1 wt.% Si, 1 wt.% Al and 7.4 wt.% MgO. 6. A mixture according to claim The composition of claim 1, characterized in that it contains 80% by weight of SiO ₂ , 8% by weight of CaO · SiO ₂ , 8% by weight of Si and 4% by weight of Al.