SE504729C2 - Methods and blends to form a cohesive refractory mass on a surface based on a silicon compound - Google Patents

Abstract

A process is described for forming a coherent refractory mass on a surface based on a silicon compound, wherein there is projected against the surface, simultaneously with oxygen, a mixture comprising refractory particles and combustible particles which react in an exothermic manner with the projected oxygen by releasing sufficient heat to form the refractory mass, under the action of heat of combustion. The mixture comprises combustible silicon particles, refractory particles of one or a plurality of substances which constitute the major portion by weight of the mixture, as well as particles of another substance and/or non-metallic particles whose composition is such that, during the formation of the refractory mass, they generate said other substance in such a way that said other substance causes the incorporation of silica, formed by the combustion of the silicon particles, into a crystalline lattice.

Description

504 729 z reasons for combustible metallic substances. It is generally recommended that the particles be expelled in the presence of a high oxygen content, for example by using commercial grade oxygen as a gas carrier. In this way, a coherent refractory mass is formed, which adheres to the surface to which the particles are pushed. Since the ceramic bonding reaction can reach very high temperatures, it can penetrate slag, which may be present on the surface of the refractory being treated, and can soften or melt the surface in such a way that a good bond is achieved between the treated surface and the newly formed refractory mass.

These known ceramic bonding methods can be used to form a refractory object, for example a block with a special shape, but their most widespread use is for forming coatings and for depositing bricks or walls and they are particularly suitable for depositing or reinforcing - fine refractory constructions, eg for laying walls or coating refractory equipment, such as oven walls in glassmaking or in coke ovens.

This process is generally carried out when the refractory base material is hot. This makes it possible to repair eroded refractory surfaces when the equipment essentially remains at its working temperature and in some cases even when it is in operation.

The second known way of forming a refractory mass on a surface is called "flame spraying method". This includes that a flame is directed towards the place where the refractory mass is to be formed and that refractory powder is sprayed through this flame. The flame is fed with a gaseous fuel or liquid or even carbon powder. It is obvious that the efficient use of this flame spraying technique requires complete combustion of the fuel in order to generate the hottest possible flame and to achieve maximum effect. In general, the temperature of the flame obtained with a flame spraying method is not as high as that which can be obtained with a ceramic bonding technique, which has the consequence that the cohesion of the formed refractory mass is not so good, and because the bonding one between the new refractory mass and the surface of the refractory base material is formed at a lower temperature, this bond does not become so strong. In addition, such a flame is less likely than a ceramic bonding reaction to penetrate slag, which may be present on the refractory surface being treated.

The fusion of the mixture used in a ceramic bonding method is generally selected in such a way as to produce a deposition mass which has a chemical composition similar to or close to that of the refractory base material. This facilitates the compatibility of the new material with and adhesion to the base material on which it is formed.

However, we have observed that problems arise if one wishes to repair certain types of refractory structures and that this occurs even if one forms a refractory mass with a chemical composition similar to that of the refractory base material.

Deposition of refractory surface structures, which have a basic material of silicon carbide, by means of a mixture which primarily contains carbon-silicon particles as well as particles of metallic combustible substances, such as aluminum and silicon particles, gives, for example, a refractory mass which does not always exhibits sufficient adhesion to the refractory base material.

Refractory materials based on silicon carbide are used in certain metallurgical equipment, especially in blast furnaces in the iron industry and in zinc distillation columns. When operating this equipment, certain parts of the refractory structures may have a rather low operating temperature, for example in the order of 700 ° C, and may also be exposed to significant variations in ambient temperature. It has been found that the refractory masses 504 729 present on these refractory structural members, which are produced according to the prior art, do not always show sufficient adhesion to the refractory base material and that the new refractory mass in some cases, especially when the deposition is done on a block or a refractory wall whose temperature is low, completely separated from the refractory base material and detaches when the equipment is in operation.

Similar problems arise if it is desired to deposit refractory structures, which comprise high density silica base materials (so named to distinguish them from traditional refractory silica materials, the density of which is lower), which are used in certain coke ovens; although one can form a refractory material which in its chemical composition resembles the refractory base material, the new mass does not always adhere to a sufficiently high extent and can even be quickly separated from the refractory base material when the furnace is in operation.

A method of depositing, for example, furnace linings is known from international patent application WO 90/03848 (Willmet / Willard), in which an inert carrier gas and particles of refractory oxide and combustible oxidizable material are fed to a flame spraying device, in which oxygen under high pressure sucks and accelerates the mixture of carrier gas and particles. Willard uses this method to deposit refractory blocks / stones in the set of molds for a converter for smelting copper, as well as to repair bottom columns of silicon carbide.

For example, a mixture containing 79% silicon carbide, 16.25% silicon, 4% aluminum and 0.75% magnesium is fired through a double venturi-type air-oxygen system against a silicon carbide bottom column.

However, the use of magnesium metal powder in this manner is disadvantageous, at least insofar as there is a degree of uncertainty as to the composition of the refractory coating formed, since magnesium metal is relatively volatile. An object of the present invention is to solve these problems.

The present invention relates to a method of forming a cohesive refractory mass on a surface which is based on a silicon compound, in which a mixture is pushed out against a surface at the same time as oxygen, which mixture comprises refractory particles and combustible particles which react with the expelled oxygen in an exothermic manner, by releasing sufficient heat to form the refractory mass under the action of combustion heat, characterized in that the mixture comprises: (i) combustible silicon particles; (ii) refractory particles of one or more substances as a major part of the mixture; and (iiia) additive particles of another substance selected from magnesium oxide, calcium oxide or iron (II) oxide, which during the formation of the refractory mass cause silicon dioxide formed during the combustion of the silicon particles to form part of a crystalline lattice, and / or (iiib) additive particles of a non-metallic compound which, during the formation of the refractory mass, produce magnesium oxide, calcium oxide or iron (II) oxide, which causes silica, which is formed during the combustion of the silicon particles to form part of a crystalline lattice.

The present invention also relates to a mixture of particles, intended for a method of forming a coherent refractory mass on a surface which is based on a silicon compound, by the mixture and oxygen being pushed out towards the surface, the mixture comprising refractory particles and combustible particles, which is capable of reacting exothermically with oxygen so that sufficient heat is generated to, under the action of combustion heat, form the refractory mass, characterized in that the mixture comprises: (i) combustible silicon particles; (ii) refractory particles of one or more substances as a major part of the mixture; and (iiia) additive particles of another substance selected from magnesium oxide, calcium oxide or iron (II) oxide, which during the formation of the refractory mass cause silicon dioxide formed during the combustion of the silicon particles to form part of a crystalline lattice, and / or (iiib) additive particles of a non-metallic compound which, during the formation of the refractory mass, produce magnesium oxide, calcium oxide or iron (II) oxide, which cause silica, which is formed during the combustion of the silicon particles to form part of a crystalline lattice.

Such a mixture and such a method are suitable for forming refractory masses of high quality and for depositing surfaces based on a silicon compound, such as, for example, refractory furnace constructions as well as for joining pieces. It is possible to provide a refractory mass which exhibits excellent adhesion to the refractory base material when the deposited surface undergoes repeated variations of thermal conditions during operation of the equipment and / or when the deposition is carried out on a surface whose temperature is relatively low, such as 600 1000 ° C (eg 700 ° C), although the invention is applicable to surfaces having a temperature outside this range.

The refractory masses prepared according to the invention have thermal expansion properties at the interface between the surface and the formed refractory mass, which differ from those which would be obtained if the starting mixture did not contain any substance which causes the silica formed during the combustion of silicon to be included in a crystalline lattice. We believe that the advantages obtained by the invention are at least partly due to this difference at the interface and that the refractory masses obtained at the interface exhibit thermal expansion properties, which are well adapted to those which apply to the refractory structures in question.

The combustible silicon particles (i) can be used as the sole combustible material or mixed with particles of an additional combustible material, such as aluminum. Thus, the mixture preferably further comprises combustible aluminum particles. Aluminum particles can be oxidized rapidly with significant heat release to form refractory oxides themselves. Use of this property thus favors the formation of high quality refractory masses. The mixture according to the invention preferably comprises not more than 15% by weight of silicon. This is important to limit the amount of unreacted silicon that may remain in the refractory mass formed. We have found that the presence of unreacted silicon in the formed refractory mass can lower its quality.

The refractory particles (ii) may be present in an amount of at least 70% by weight, preferably at least 75% by weight, to obtain a homogeneous mass.

The additive particles (iiia) and / or (iiib) preferably constitute the remainder of the mixture and may comprise up to% by weight of the mixture, preferably 5-15% by weight.

The combustible particles (i) used in the mixture preferably have an average particle size of less than 50 μm.

The refractory particles (ii) preferably comprise substantially no particles with a size larger than 4 mm, preferably not larger than 2.5 mm, in order to facilitate the formation of a uniform powder jet.

The additive particles (iiia) and / or (iiib) used in the mixture preferably have a particle size of 5,500 μm.

If you use particles that are too large, there is a risk that they do not play an effective role. These particles preferably have a size of at least 10 μm. If particles that are too small are used, there is a risk that they will volatilize during the reaction.

There are several different suitable substances for, during the formation of the refractory mass, causing silica, which is formed during the combustion of silicon, to form part of a crystalline lattice.

The aforementioned additive (iiia), which causes silica formed during the combustion of silicon to be included in a crystalline lattice, can be introduced into the mixture in the form of magnesium oxide particles. The presence of this compound in the mixture which is ejected onto the refractory surface to be deposited helps to ensure the correct heat resistance properties of the refractory mass formed.

The introduction of magnesium oxide into the mixture also enables the formation of a refractory mass in which at least a part of the silica formed during the combustion of silicon is included in a crystalline lattice of forsterite type. This also helps to ensure the correct heat resistance properties of the formed refractory mass.

If the mixture contains both aluminum and magnesium oxide, a refractory mass can be formed in which at least a part of the silica formed during the combustion of silicon is contained in a crystalline lattice of forsterite structure and / or in a crystalline lattice of spinel structure and / or in a crystalline lattice of cordierite structure.

The presence of a crystalline lattice of cordierite structure in the formed refractory mass helps to ensure excellent heat shock resistance for this mass. On the other hand, the presence of a crystalline lattice of forsterite structure and / or spinel structure has a favorable influence on the heat resistance of the formed refractory mass.

Other oxides such as calcium oxide or iron (II) oxide can also be used as the additive (iiia), which causes silica formed during the combustion of silicon to be included in a crystalline lattice.

A mixture of particles may be used, which additionally or alternatively comprises an additive substance or substances (iiib), the composition of which is such that when the refractory mass is formed, it (they) produces a substance which causes silica, which is formed at combustion of silicon is included in a crystalline lattice. For example, peroxides such as calcium peroxide, nitrides or carbides can be used. 9 504 729 An oxide, eg calcium oxide, can be introduced in the form of a compound, in the case of calcium oxide, for example in the form of wollastonite (cao.sio2).

The present invention is particularly suitable for the deposition of refractory materials, the base material of which is silicon carbide or refractory materials, the base material of which is high density silica. Thus, it is preferred to carry out ceramic bonding by means of a mixture, the main part of which comprises silicon carbide resp. silica.

Of course, the invention may also be suitable for depositing other types of refractory materials based on a silicon compound than those mentioned above, such as ordinary silica brick and silica-alumina brick.

The substance or substances which constitute the major part of the mixture may correspond to the composition of the refractory material which it is desired to prepare or be of another substance.

In the latter case, a refractory mass is formed, the properties of which may differ from, and ideally exceed, those of the refractory material being deposited, for example having improved abrasion resistance or improved refractory.

The present invention will now be described in more detail by means of the following examples: EK§M2EL_1 A refractory mass is formed on a wall of a zinc distillation column. This wall comprises bricks, which have a matrix of silicon carbide. A mixture of refractory particles, particles of a combustible substance which is exothermically oxidizable by formation of a refractory oxide and magnesium oxide particles are ejected onto these bricks. The wall temperature is 800 ° C.

The mixture is expelled at a mass flow of 60 kg / h in a stream of pure oxygen. The mixture has the following composition: 504 729 SiC 79 wt% Si 8 wt% Al 5 wt% Mg0 8 wt% The silicon particles have a size below 45 μm and a specific area of 2,500-8,000 cm2 / g. The aluminum particles have a size below 45 μm and a specific area of 3,500-6,000 cmz / g.

The size of the silicon carbide particles is less than 1.47 mm, 60% by weight being 1-1.47 mm, 20% being 0.5-1 mm and 20% being less than 0.125 mm. The MgO particles have an average size of about 300 μm.

By "average size" is meant a size such that 50% by weight of the particles have a smaller size than this average.

The wall that has been deposited in this way is subjected to significant variations in the ambient temperature and it is observed that the new refractory mass adheres to the substrate in a durable manner.

The structure of the formed mass is examined under a microscope. Excellent continuity is observed between the new refractory mass and the refractory base material. It is also observed that the silica, which is formed during the combustion of silicon, is contained in crystalline lattices of forsterite, cordierite and aluminum-containing spinel.

For comparison, a mixture containing no magnesium oxide is expelled under the same conditions. The composition of the mixture is as follows: SiC 87% by weight Si 12% by weight Al 1% by weight It is observed that the refractory mass formed rapidly separates from the wall and releases in solid pieces if the zinc distillation column continues to be in operation. In a modification of this example, the mixture was used to prepare the bottom of a coke oven made of ordinary silica brick and silica-alumina brick. A deposition mass is obtained which has good abrasion resistance and which has good adhesion to the wall, even when it is exposed to significant thermal variations.

As a variation of Example 1, a mixture having the following composition was used: SiC 82% by weight Si '8% by weight Al 5% by weight Mgo s weight-t The wall to be repaired comprises bricks with a basic material of silicon carbide and has a temperature of 700 ° C.

The resulting refractory mass also adheres permanently to the wall.

EXAMPLE 3 The object is to form a refractory mass on a wall of a coke oven, which comprises high density silica gel. The bulk density for high density bricks is about 1.89, while the bulk density for traditional silica bricks is in the order of 1.80. Such bricks have recently entered the market for refractories and exhibited advantageous properties over traditional silica bricks, in particular with respect to their gas permeability and thermal conductivity properties.

The deposition is carried out on a wall, the temperature of which is about 750 ° C, by means of the following mixture: 504 729 12 S102 80.5% by weight Si 11.1% by weight A1 1% by weight Mg0 7.4% by weight SiO2 the size of the particles is less than 2 mm, with a maximum weight% of 1-2 mm and less than 15% by weight below 100 μm.

The formed mass adheres to the wall in a durable way.

As a contrast, a similar mixture was fired under the same operating conditions, but which did not contain magnesium oxide, a refractory mass which easily differed from the wall if the latter was subjected to different thermal conditions which occur in the furnace when it is in operation.

Eħ! 2EL_i The purpose is to form a refractory mass on a wall in a coke oven made of a refractory material, which is based on a silicon compound, which is exposed to significant variations in the ambient temperature and whose temperature does not exceed 900 ° C. The deposition is carried out on a wall, the temperature of which is about 750 ° C, by means of the following mixture: S102 80% by weight CaO.SiO2 (wollastonite) 8% by weight Si 8% by weight Al 4% by weight The average size of wollastonite particles is about 300 um. The size of the metal particles is the same as in Example 1 and the size of the silicon particles is the same as in Example 3.

Claims (16)

10 15 20 25 504 729 13 Patent claims A method of forming a coherent refractory mass on a surface which is based on a silicon compound, in which at the same time with oxygen a mixture is ejected against a surface, which mixture comprises refractory particles and combustible particles which react with the expelled oxygen in an exothermic manner, by releasing sufficient heat to form the refractory mass under the action of combustion heat, characterized in that the mixture comprises: (i) combustible silicon particles; (ii) refractory particles of one or more substances as a major part of the mixture; and (iiia) additive particles of another substance selected from magnesium oxide, calcium oxide or iron (II) oxide, which during the formation of the refractory mass cause silica formed during the combustion of the silicon particles to be contained in a crystalline lattice; and / or (iiib) additive particles of a non-metallic compound which, during the formation of the refractory mass, produce magnesium oxide calcium oxide or iron (II) oxide, which causes silica, which is formed during the combustion of the silicon particles to form part of a crystalline lattice. 2. A method of forming a refractory mass according to claim 1, characterized in that the substance (iiia) which causes the silica formed during combustion of the silicon particles is contained in a crystalline lattice, is introduced in the form of magnesium oxide particles. 3. A method of forming a refractory mass according to any one of claims 1-2, characterized in that the combustible particles (i) further comprise aluminum particles. A method of forming a refractory mass according to any one of the preceding claims, characterized in that the non-metallic compound (iiib) is introduced into the mixture in the form of particles of a peroxide or a silicate. 5. A method of forming a refractory mass according to any one of claims 1-4, characterized in that the refractory particles (ii), which constitute the major part of the mixture, are silicon carbide particles. A method of forming a refractory mass according to any one of claims 1-4, characterized in that the refractory particles (ii), which constitute the main weight part of the mixture, are silica particles. 7. A method according to any one of the preceding claims, characterized in that the surface temperature is lower than 1000 ° C. A mixture of particles, intended for a method of forming a cohesive refractory mass on a surface which is based on a silicon compound, by pushing the mixture and oxygen towards the surface, the mixture comprising refractory particles and combustible particles which are capable of react exothermically with oxygen so that sufficient heat is given off to form, under the action of combustion heat, the refractory mass, characterized in that the mixture comprises: (i) combustible silicon particles; (ii) refractory particles of one or more substances as a major part of the mixture; and (iiia) additive particles of another substance selected from magnesium oxide, calcium oxide or iron (II) oxide, which during the formation of the refractory mass cause silica formed during the combustion of the silicon particles to be contained in a crystalline lattice; and / or (iiib) additive particles of a non-metallic compound which, during the formation of the refractory mass, produce magnesium oxide, potassium oxide or iron (II) oxide, which causes silica, which is formed during the combustion of the silicon particles to form part of a crystalline lattice. Mixture according to claim 8, characterized in that the mixture contains particles of magnesium oxide such as particles of the second substance (iiia). Mixture according to claim 8 or 9, characterized in that the mixture contains particles of a peroxide or a silicate such as of the non-metallic compound (iiib). 11. ll. Mixture according to any one of claims 8-10, characterized in that the combustible particles (i) further comprise aluminum particles. lO 15 20 504 729 16 Mixture according to one of Claims 8 to 11, characterized in that the refractory particles (ii), which form the major part of the mixture, are silicon carbide particles. Mixture according to one of Claims 8 to 11, characterized in that the refractory particles (ii), which form the major part of the mixture, are silica particles. Mixture according to one of Claims 8 to 13, characterized in that the additive particles (iiia) or (iiib) have a particle size of S 500 μm. Mixture according to one of Claims 8 to 14, characterized in that the additive particles (iiia) or (iiib) have a particle size of at least 10 μm. Mixture according to one of Claims 8 to 15, characterized in that the silicon content therein does not exceed 15% by weight.