WO1999008981A1 - Refractory ceramic moulding - Google Patents

Abstract

The invention relates to a refractory ceramic moulding with a finish that at least partially fills the open pore volume. The finish is made of a dispersion comprising at least one silica sol and one additive which suppresses gelation of the silica sol.

Description

 Fireproof ceramic

3 e s c h b u n g

The invention relates to a refractory ceramic molded part with an impregnation that at least partially fills the open pore volume.

The impregnation with petroleum products such as tar or pitch has long been known. It primarily serves to increase the resistance to infiltration or resistance to aggressive slags of the corresponding refractory ceramic products. The volatile constituents of these impregnation agents represent a significant environmental burden.

DE 40 01 180 Cl describes a method for impregnating a refractory ceramic molded part with open porosity is known in which a thixotropic slip is liquefied by means of a mechanical and / or physical excitation unit and introduced into the open pore volume of the molded part. After the open pore volume has been filled, the excitation unit is switched off. The impregnation agent stiffens. The molded body is then tempered. In this way, an almost complete impregnation can be achieved.

In addition to a refractory ceramic component, the slip used contains a carbon-containing component, in particular a resin.

However, in particular when a shallow product comes into contact with oxidizing melts, for example Cu-Cu ₂ O, the impregnating agent is oxidized, as a result of which the impregnating effect is at least partially lost again.

The object of the invention is to provide a refractory ceramic molded part with an impregnation that at least partially fills the open pore volume, which is environmentally friendly and also resistant to oxidizing melts. Particular importance is attached to high resistance to infiltration and corrosion against metallurgical melts and slags.

The invention is based on the finding that this goal can be achieved in two alternative forms with a specially set impregnation agent. An essential component of the impregnating agent provided as a dispersion is a silica sol in both cases. From the group of silica sols, however, only those are suitable which have a maximum viscosity of 50 mPas, preferably a maximum of 25 mAs.

As a further essential component, the dispersion comprises an additive which preferably suppresses the gelation of the silica sol. This is especially true in contact with basic refractory molded parts.

The term gelation is to be understood as meaning that any type of solidification of the dispersion should be reduced by gelation, flocculation or coagulation or addition of solid particles or dispersion to the upper surface of the molded part (filter effect).

In its most general embodiment, the invention then relates to a refractory ceramic molded part with an impregnation which at least partially fills open pore volumes, in which the impregnation is formed from a dispersion and comprises at least the following components:

Alternative 1:

90 to 99.5% by weight of a silica sol with a maximum viscosity of 50 mPa-s,

0.5 to 10.0% by weight of an additive which suppresses the gelation of the silica sol. Alternative 2:

40 to 80% by weight of a silica sol with a maximum viscosity of 50 Pa s,

0.5 to 10.0% by weight of an additive which suppresses the gelation of the silica sol,

10 to 59.5% by weight of one or more refractory components with a partial core size <3 µm.

In preliminary trials, alternative 2 have shown the following limits to be sufficiently negative:

52 to 72% by weight of silica sol,

1 to 3% by weight of additives,

- 25 to 47% by weight of refractory component (s).

As stated, the viscosity of the silica sol is important in order to be able to set the desired solids concentration as high as possible. This applies in particular to the second alternative. It is only in this viscosity range that it is possible to see the dispersion as a further essential constituent in one or more refractory component (s) in the desired amount, which corresponds to the degree of filling of the open porosity sustainably promote and stand in uncritical chemical interaction with the silica sol. The particle size of the refractory components should be limited to values <3 µm.

This effect can be enhanced by additional wetting and dispersing agents (01 - 1.0%, based on the total dispersion).

In this sense, an embodiment of the invention proposes to limit the degree of concentration (SiOr content) of the silica sol to values below 50% by weight, since the viscosity increases rapidly at higher concentrations.

The size of the Si0 ₂ particles of the silica sol should be <200 nm, in one embodiment <50 nm.

The use of an anionic silica sol also promotes the setting of highly concentrated, low-viscosity dispersions.

The additives which suppress gelation of the silica sol comprise a large number of chemical substances. Organic amines have proven to be particularly effective. The additives lead to a stabilization of the dispersion as a whole, which can be determined by increasing the negative surface charge of the dispersion particles. No gelation of the silica sol on contact with refractory, in particular basic, molded parts could be found within the mass proportions of the components mentioned above.

The refractory components mentioned within the dispersion consist, for example, of Al ^ Oa, Cr ₂ 0 ₃ , Ti0 ₂ , ZrOr, clay or SiC.

The impregnation is optimized by reducing the particle size of the refractory components. Particle sizes between 0.5 and 1 .mu.m give very good results, agglomeration should, if appropriate, be suppressed by the wetting and dispersing agents mentioned.

Using those described above

Impregnation dispersion can reduce the gas permeability of a refractory ceramic molded part from, for example, 20 nPm to values <2, in some cases <0.5 nPm.

Due to the small particle size and low viscosity of the impregnation dispersion, even ceramic molded parts with a gas permeability that is already low due to production can be further “compressed” and thus improved with regard to their tendency to infiltration and their corrosion protection.

This also applies in particular to the resistance of basic refractory bricks to infiltration of oxidized copper melts. In such dispersions with SiC as the refractory dispersion component, a reduction of copper oxides (metallic copper wets basic stones slightly) was observed. The effect of SiC can be attributed in parallel to the reduction in the solids content of the impregnation medium due to the oxidation (SiC + 20 ₂ = SιO _: - ¹ - C0 ₂ ).

A similar effect can also be achieved by easily oxidizable

Achieve metals or metal compounds that can or can partially replace α or refractory component or dispersion.

The impregnation can be done with conventional systems (soaking under vacuum and / or pressure).

The invention is described in more detail below using an exemplary embodiment:

The following dispersion was used:

57% silica sol with a viscosity of 15 m? As, a particle size (d ₅₀ ) of 30 nm and a solids concentration of 45% by weight.

3% by weight of a wet nurse.

10% by weight SiC with a particle size <3 μm.

30 wt .-% A1 ₂ 0 ₃ with a particle size <2 microns. Magnesia chromite stones with a gas permeability of 17 nPm were drunk.

After impregnation by impregnation, the gas permeability was determined to be 1.3 nPm.

The stones show an excellent corrosion resistance and infiltration resistance even against difficult non-ferrous metal blocks.

Claims

Refractory ceramic molded parts ennsruche 1. Refractory ceramic molded part with an impregnation which at least partially fills the open pore volume, in which the impregnation is formed from a dispersion which comprises at least the following components: a) 90 to 99.5% by weight of a silica sol with a maximum viscosity of 50 mPa's, b) 0.5 to 10.0% by weight of an additive which suppresses the gelation of the silica sol. Refractory ceramic molded part with an impregnation which at least partially fills the open pore volume, in which the impregnation is formed from a dispersion which comprises at least the following components: a) 40 to 80% by weight of a silica sol with a maximum viscosity of 50 m? a «s, b) 0.5 to 10.0% by weight of an additive which suppresses the gelation of the silica sol, c) 10 to 59.5% by weight of one or more refractory components with a particle size <3 μm. Molding according to claim 2, in which the impregnation is formed from a dispersion which comprises the following components: a) 52 to 72% by weight of the silica sol, b) 1 to 3% by weight of the additive, c) 25 to 47% by weight of the refractory component (s). Molding according to claim 1 or 2, wherein the silica sol has a maximum Si0 ₂ content of 50 wt .-% within the dispersion. 5. Molding according to claim 1 or 2, wherein the size of the Si0 ₂ particles of the silica sol within the dispersion Is <200 nm. 6. Molding according to claim 5, in which the size of the Si0 ₂ particles of the silica sol within the dispersion is <50 nm. 7. Molding according to claim 1 or 2, wherein the silica sol is an anionic silica sol. 8. Molding according to claim 1 or 2, in which the additive is an organic amine. 9. Molding according to claim 2, wherein the refractory component is A1 ₂ 0 _{3 /} Cr _: 0 ₃ , TiC ₂ , Zr0 ₂ , clay or SiC. 10. Molding according to claim 2, wherein the refractory component has a maximum particle size of 2 microns. 11. Molding according to claim 1 or 2, wherein the viscosity of the silica sol in the dispersion is a maximum of 25 mPa. s is. 12. The molded part as claimed in claim 1, in which the impregnation is formed from a dispersion which comprises the following components: a) 95-99.5% by weight of silica sol, b) 0.5 to 5% by weight of additive.