WO2007079806A1

WO2007079806A1 - Mix for a refractory ceramic product and refractory ceramic product produced therefrom

Info

Publication number: WO2007079806A1
Application number: PCT/EP2006/010582
Authority: WO
Inventors: Christian Majcenovic; Dieter Pirkner
Original assignee: Refractory Intellectual Property Gmbh & Co. Kg
Priority date: 2005-12-23
Filing date: 2006-11-04
Publication date: 2007-07-19
Also published as: EP1966106A1

Abstract

The invention relates to a mix for a ceramic product which is refractory when used as intended, for example a shaped body or a casting composition.

Description

Offset for a refractory ceramic product and refractory ceramic product formed therefrom

Description

The invention relates to an offset for a refractory under normal use ceramic product, such as a molding or a casting.

Refractory ceramic products, both masses (such as castables, shotguns, ramming masses, mortar) and molded parts (such as bricks, cuboids, cones, plates) are used for lining metallurgical melting vessels as well as for use as functional parts (such as slide plates, sleeves, Plugs, lances, pipes), in particular in the context of secondary metallurgical processes. -I-

This applies both to intended applications in the ferrous metal industry and to applications in the non-ferrous metal industry.

The refractory material comes into contact not only with the metallurgical melts but also with corresponding slags. In that regard, the refractory material is subject to considerable wear, in particular wear due to a chemical / metallurgical corrosion attack, wherein an infiltration of melt and / or slag into the refractory material may be a cause of wear.

In this context, the use of additives is known, which can lead to a reduction in the wear of the refractory material. These additives, which are said to make the finished refractory material more corrosion resistant and / or which better protect the refractory material from infiltration of contaminants, are hereinafter referred to as "corrosion / infiltration inhibitors." Barium sulfate (BaSO ₄ ) and calcium fluoride (CaF ₂ ) are such substances.

Barium sulfate, however, decomposes at higher temperatures. For example, in contact with bauxite from the offset of the refractory product, BaSO ₄ reacts to Celsian (BaAl ₂ Si ₂ Oe) and the protective effect of the additive is lost. This is especially true in the temperature range> 900 ° C.

For example, by using modern burners, a refractory lining in a melting vessel may become hot during heating between 1100 and 1250 ° C. It is then often hotter than the subsequently treated in the vessel melt. BaSO ₄ then fails completely as wear protection.

Although CaF ₂ is thermally more stable than BaSO ₄ , the infiltration / corrosion inhibiting effect is worse than when using BaSO ₄ . The invention is so far the object of demonstrating a way to improve the infiltration / corrosion behavior of refractory ceramic products, especially in the high-temperature application (> 1,200 ° C).

In experiments it has been found that calcium sulfate in offset drastically reduces the wear of an associated fired finished product without adversely affecting the mechanical performance of the products and without adversely affecting temperature and thermal shock resistance.

The calcium sulfate can be used anhydrous, ie as anhydrite (CaSO ₄ ), or hydrous, for example as hemihydrate (CaSO ₄ • Vi H ₂ O) or dihydrate (CaSO ₄ • 2H ₂ O), as a fine powder or in various coarser particle fractions.

For example, Blaine's specific surface area may be> 2000 cm ² / g. It can be over 4000 cm ² / g and reach values> 7000 cm ² / g. The residue on a sieve according to DIN 4188 is then for example: R 0.02 mm:> 40%, R 0.02 mm> 25% or R 0.02 mm: <20%. Usually Blaine's specific surface area is> 1000 cm ² / g.

The said corrosion-inhibiting substances (additives) are used as an offset component, optionally also added to the finished product, for example by infiltration by means of vacuum treatment. During subsequent heat treatment (during the firing / sintering of the products or during their intended use), the CaSO ₄ decomposes, but forms new compounds with the surrounding refractory material, which are likewise infiltrations / corrosion inhibitors. The reasons / phenomena are not fully understood yet. However, it was found, inter alia, that CaSO ₄ reacts at higher temperatures with alumina from the refractory product to yeelimite (Ca ₄ AloOi ₂ SO ₄ ). Yeelimit is stable up to> 1200 ° C and obviously takes over the protective function of the calcium sulfate additive at higher temperatures.

In its most general embodiment, the invention comprises an offset for a refractory under normal use ceramic product, the

a) 75-99.5% by mass of at least one refractory base component and b) 0.5-25% by mass of at least one additive from the group: calcium sulfate, calcium sulfate hydrate

contains.

Basic refractory components are substances (compounds such as oxides) that are refractory or fire-resistant at higher temperatures (> 900 ° C). They are used according to the invention in grain sizes <6 mm and may contain a fine grain fraction (<250 microns).

Various developments emerge from the features of the subclaims and the other description documents. The raw material offset shall be adjusted accordingly, provided that the corrosion-inhibiting component (s) are not first introduced by impregnation of the finished fired product. The offset thus contains corresponding additives (additives). The amount of the infiltration-inhibiting component in the offset can be adjusted to <15, <10, <7, <5, to <3% by mass, based on the total offset from the refractory base component and the admixture. Usually their share amounts to>1,> 3 or> 5 M .-%. Accordingly, the proportion of the refractory base component (sum of refractory base components and additives calculated in each case to 100% by mass) increases or decreases.

It is also possible to mix further components with the offset, for example a binder, e.g. based on phosphate or cement, or antioxidants (total of all offset components then added to 100 M .-%).

The invention includes the processing of the offset to ceramic bonded refractory products as well as the processing into chemically bonded products. The refractory ceramic products may be monolithic compositions, mortars, moldings, for example in the form of stones, plates, sleeves or the like.

As far as masses are concerned this also includes hydraulically bound masses.

A suitable base component may at least partially be a non-basic basic component, for example from the group: alumina, corundum, ZrO ₂ , zirconium silicate (ZrO ₂ .SiO ₂ ), mullite, TiO ₂ , SiC, andalusite, chromium oxide, microsilica. However, Cr ₂ O ₃ -free products are preferred. BaSO ₄ and / or CaF ₂ can be dispensed with. A suitable offset can be prepared in a conventional manner, for example by mixing the refractory base component (s) with the additive (s) and a binder, then shaping (for example by pressing) and firing for sintering, especially at temperatures> 1200 ° C ,

The invention is exemplified below with reference to four offsets:

Example 1: Offset for a casting compound

Example 2: Offset for a ramming mass

Example 3: Offset for a stone to be pressed

Example 4: Offset for a spray mass

From the offset according to Example 1 four test specimens of size 25x25x51 mm were prepared. The so-called "fill immersion test" was carried out on these test specimens, as it results from "Aluminum Transactions, Vol. 3, No. 1, 2000, 105-120", to which reference is made. The specimens were placed at a distance from each other on the bottom of a lined with silicon carbide casting compound test vessel, which was filled with 3.5 kg of an aluminum melt of the following specification so that the specimens were completely covered by the melt.

The surface of the molten bath was covered with a salt to prevent oxidation. The specimens, each having at least one surface in contact with the melt exposed by a cutting tool, remained in the melt maintained at 850 ° C for 4 days (96 hours) with the melt composition each readjusted after 24 hours.

Composition of aluminum melt:

At the test pieces prebaked at 1200 ° C, no continuous adhesion of metal was observed. No macroscopically visible infiltration could be detected. Microscopy revealed a thin, about 500 micron thick reaction zone in the surface region of the specimens. Further investigations revealed that calcium sulfate was no longer present as such. In contrast, a proportion of yeelimite (Ca ₄ AloOi ₂ SO ₄ ) was found in the sample. In particular, Yeelimit had formed in the interface area of the previously occupied by calcium sulfate space to the surrounding matrix material.

The unfired or fired products formed from an offset of the type mentioned, the latter containing yeelimite, are also the subject of the invention.

Claims

1. offset for a refractory ceramic product when used as intended, containing: a) 75-99.5% by mass of at least one refractory base component and b) 0.5-25% by mass of at least one additive selected from the group consisting of:

Calcium sulfate, calcium sulfate hydrate.

2. Offset according to claim 1, wherein the proportion of the additive is <10% by mass.

3. Offset according to claim 1, wherein the proportion of the additive is <5% by mass.

4. offset according to claim 1, wherein the proportion of the additive> 1 mass%.

5. Offset according to claim 1, wherein the proportion of the additive is> 5 mass%.

6. An offset according to claim 1, wherein at least one refractory base component is a non-basic base component.

7. An offset according to claim 6, wherein the non-basic base component at least partially from the group: alumina, bauxite, corundum, ZrO ₂ , silicon carbide, andalusite, chromium oxide, microsilica, zirconium silicate, mullite, TiO ₂ originated.

8. An offset according to claim 1, wherein the additive is present as a finely divided powder having a specific surface area of Blaine> 1000 cm ² / g.

9. An offset according to claim 1, which is free from at least one of the following constituents except for possible impurities: BaSO ₄ , CaF ₂ Cr ₂ O ₃ .

10. Unburned ceramic product made from an offset according to claim 1.

1 1. A burned refractory ceramic product made from an offset according to claim 1 having a content of yeelimite (Ca ₄ Al ₆ Oi ₂ SO ₄ ).