SK280385B6 - Mixture for refractory purposes - Google Patents

Abstract

A mixture for refractory purposes consists of from 22 to 93.6 percent by weight of ground silicate Portland clinker and/or white cement, relative to the total weight of the mixture, and from 5 to 77 percent by weight of other auxiliaries for the preparation of refractory materials, relative to the total weight of the mixture, selected from the group containing a fine-ground metallurgic slag, granulated blast slag, flue ash, alumosilicates calcination products, puzzuolannas, a refractory opening mate rial and/or fine-ground filler selected from the group containing chamotte, ganister, burnt shale and corundum, and, it further contains from 1 to 10 percent by weight of Al2O3-based materials, relative to the total weight of the mixture. The mixture can be characterised in that said Portland clinker and/or white cement contains no gypsum and the mixture contains reactive materials based on, composed of and hydrated with Al2O3. nH2O, and/or bauxite and/or laterite with a particle size less than 150 um in an amount from 1 to 30 percent by weight of Portland clinker and/or white cement with Al2O3-based reactive material, relative to the total weight of the mixture, and it further contains grinding additives in an amount ranging from 0.001 to 2 percent by weight of Portland clinker and/or white cement with Al2O3-based reactive material.

Description

The invention relates to a composition for refractory purposes based on silicate clinker.

BACKGROUND OF THE INVENTION

Aluminous cement is predominantly used for refractory purposes and the use of silicate (Portland) cement for this purpose is very limited. Factors limiting the use of conventional Portland cement in refractory concrete include the negative influence of gypsum solidification regulator on the gland properties of Portland cement and the possibility of very destructive rehydration of free CaO after firing of the refractory concrete. The properties of conventional Portland cement are improved for use in refractory concrete by replacing gypsum with another solidification regulator and the addition of finely ground SiO ₂ or Cr ₂ O ₃ containing binding CaO during firing, with partial stabilization of Portland cement in refractory concrete already occurring using conventional stones , such as fireclay or fired flakes, which reduce the amount of free CaO after firing.

Gypsum-free Portland cement is known from the literature and achieves relatively high strengths even at higher temperatures, see e.g. article by Škvar F., Pckárck L. Velička: "The Gypsum-free Portland Cement Hydration and Thermal Properties", Proceedings 8 th 1CTA Conf., Bratislava 1985, Vol. 2, p. 591-596. The properties and composition of the composition based on gypsum-free Portland cement are also known from the patent literature. It is known from US 3,689,297 (Brunauer) a composition of free-flowing expanding cement paste, mortar or concrete based on ground cement clinker with a surface area of 600 to 900 m ² / kg containing at least 0.002 parts grinding additive and at least 0.0025 parts alkaline lignosulfonate or an alkaline-earth lignosulfonate, or a sulfonated lignin, and at least 0.0025 parts of an alkali carbonate, the aqueous coefficient being in the range of 0.20 to 0.28. As a grinding additive, a substance with polar and non-polar groups in the molecule is specified.

Further, US 4,168,985 (Kolár, Slag) discloses a cementitious binder composition consisting of a cement having a specific surface area of 250 to 300 m ² / kg containing 5 to 95% of particles smaller than 5 µm, at least 0.0025% by weight. % lignin compound, 0.001 to 8 wt. % alkali metal salt and 0.005 to 80 wt. of mixed water. US 4,551,176 (Slag et al.) Discloses a fast setting cementitious binder composition having a specific surface area of 150 to 300 m ² / kg, containing 5 to 95 wt. % of particles smaller than 5 µm, 0.1 to 5 wt. % water-soluble sulfomethylated condensate with trivalent cation-doped formaldehyde and 0.1 to 10 wt. alkali metal compounds such as alkali hydroxide, carbonate, bicarbonate or silicate. U.S. Pat. No. 5,076,851 (Slag et al.) Discloses a composition of a mixed binder containing 60 to 96.7 wt. % Portland cement clinker ground to a specific surface of 350 to 550 m ² / kg and 3 to 40 wt. latent hydraulic substances, such as granulated blast furnace slag, fly ash, and the like, wherein the two substances are ground in the presence of 0.01 to 0.1 wt. 0 to 20 wt. % amorphous SiO ₂ , 0.1 to 3 wt. % of a sulfonated polyelectrolyte, for example a sulfonated polyphenolate, a lignosulfonate and 0.5 to 6 wt. alkali carbonate, bicarbonate, hydroxide.

U.S. Pat. No. 5,125,979 (Slag et al.) Discloses a method for grinding gypsum-free Portland cement by grinding Portland cement clinker with additives of 0.01 to 0.05% by weight. Synthetic surfactant stable at pH 9-12 and optionally dodecylbenzenesulfonic acid triethanolamide.

From AO no. 238 713 (Slag et al.) Is known a refractory material for linings, in particular monolithic linings of metallurgical vessels, consisting of an agglomerate based on e.g. magnesite chromium in an amount of 70 to 92% by weight. and from 8 to 30 wt. cement-based binder, wherein the binder contains 0.01 to 4.5 wt. % water soluble lignin derivative, for example an alkali metal or alkaline earth metal lignosulfonate, and 0.005 to 2.25 wt. water-soluble alkali metal silicate, optionally alkali metal or alkaline earth metal carbonate or acid carbonate, the remainder of the cement is cement-free clinker with a surface area of 220 to 1000 m ² / kg. This refractory composition further comprises an optionally water-soluble sulfonated phenol condensation product with farmaldehyde in an amount of 0.005 to 2.25% by weight. cement clinker. From AO no. 253 500 (Pekarek et al.) Is a known refractory composition for the manufacture of porous endings used in blowing internal gases into a metal melt, containing, for example, zircon sand, chromium-magnesite, magnesite, chamotte or the like, where gypsum-free silicate and high-strength cement with a specific surface area of 60 to 800 m ² / kg in an amount of 10 to 20% by weight, based on the seed.

Sauman et al., Where gypsum was added to the gypsum cement in an amount of up to 0.5 wt. The properties of this binder were presented in the article by Šauman Z. et al. 4,138-142 (1989).

A common disadvantage of these solutions is the inferior heat properties that allow the preparation of refractory castings for temperatures in the range of 800 to 1000 ° C.

The disadvantages of some solutions include the insufficient stabilization of Portland cement when binding CaO solely with aggregates.

Budnikov in the book Ceramics and Refractory Technology discusses the possibility of using Portland cement mixtures with fine fillers and notes that between the cement hydration products and the fine fillers at 600 ° C in solid phase and in liquid paint at sufficiently high temperatures, reaction and formation occur of anhydrous silicates and calcium aluminates, which substantially strengthen the structure of the concrete.

SO 407 857 describes the preparation of refractory concrete from Portland cement, corundum, alumina and titanium dioxide. In this case, too, it is essentially the binding of free calcium oxide only when fired with alumina.

This substantial disadvantage was solved in GB 2,063,240 (Mathieu).

GB 2,063,240 (Mathieu) discloses a hydraulic binder in which Portland cement clinker with hydrated Al ₂ O ₃ is mixed or ground in such an amount that the resulting CA (OH) 2 reaction of Portland clinker with water is saturated with Al ₂ O ₃ . The binder may further comprise plasticizers, flowing agents and calcium sulfate. The binder allows the preparation of refractory concrete.

When using the solution according to GB 2,063,240 (Mathieu), a further disadvantage is the worse workability of the mixtures, where a significantly larger water coefficient of 20 to 50% has to be used, which is probably one of the reasons for lower strength at 200 to 1000 ° C. as can be seen from the examples.

Further, Czech published application 97-91 is known which relates to geopolymic gypsum-free Portland cement containing 0.5 to 25 wt. a thermally activated ceramic material comprising alumina and silica. Aluminum oxide is dehydrated after thermal activation and serves only to increase the initial strength at temperatures up to 50 ° C. There is no binding of calcium hydroxide in the mass of the hydrated mortar, and high firing is not achieved after firing. Here, alumina serves as a filler.

SUMMARY OF THE INVENTION

Based on systematic experimental work, a solution has been found which allows to increase the refractoriness of the binder based on silicate clinker and eliminates the disadvantages of known solutions.

% A mixture for refractory purposes containing 22 to 93.6 wt. % Portland Portland clinker and / or white cement, based on the weight of the total mixture, and 5-77 wt. other substances for the preparation of refractory materials, based on the total weight of the mixture, selected from the group consisting of finely ground metallurgical slag, blast furnace slag, ash, ash calcination products, pozzolans, refractory sanding and / or finely ground filler groups, , fired flake and corundum, and further from 1 to 10% by weight, based on the total weight of the mixture, of Al ₂ O ₃ -based substances, is that the Portland clinker and / or white cement does not contain gypsum and the mixture contains reactive substances Al ₂ O ₃ , consisting of Al ₂ O ₃ , hydrated Al ₂ O ₃ . % nH ₂ O, and / or bauxite and / or laterite having a particle size of less than 150 µm in an amount of 1 to 30 wt. % based on the weight of the whole mixture of Portland clinker and / or white cement with reactive substances based on Al ₂ O ₃ and grinding additives in an amount of 0.001 to 2 wt. based on the weight of the mixture of Portland clinker and / or white cement with reactive substances based on Al ₂ O ₃ .

The Al ₂ O ₃ -based substance may be milled separately and then homogenized with the other ingredients, or it may be milled together with the other ingredients.

Further, it may contain from 0.1 to 5% by weight of the total composition of a hydrolyzable alkali metal salt selected from the group consisting of alkali metal carbonates, bicarbonates and silicates, and from 0.1 to 3% by weight of the total composition. , liquefying additives based on an anionic surfactant stable in a pH> 7 environment selected from the group consisting of alkali metal lignosulfonates, sulfonated lignin, sulfonated polyphenolate, naphthalenesulfonate, sulfonated melamine-formaldehyde condensation product and / or up to 20% of SiO ₂ production and / or 0.01 to 5% solidification regulators of gypsum-free cements selected from the group consisting of organic hydroxides, boric acid, organosilicon compounds or phosphates.

It has been found that Ca (OH) 2 (portlandite) exists in the hardened gypsum-free cement in a much more dispersed form than in hardened gypsum-free cement and its content is lower than that of Portland cement. Furthermore, it has been found that Ca / OH 3 is present in partially hardened gypsum cement in a partially amorphous form, as described in Ševčík V., Škvara F., Ederová J .: "Portland Clinker Refractory Materials", Sb. 12 Int. Refractory concrete conference, Prague 1995. CaO in firing hardened gypsum cement results in more dispersed form than in conventional Portland cement with gypsum solidification regulator. This fact enables higher reactivity of CaO with active ingredients. This gives the possibility to achieve better parameters for thermally stressed applications in gypsum-free cements.

Further research has found that a decisive factor in the reaction of Al ₂ O ₃ -based substances, such as fine Al ₂ O ₃ , hydrated Al ₂ O ₃ . nH ₂ O, bauxite, laterite with Ca (OH) ₂ or CaO produced during firing, is the particle size of the particles. When using these substances based on Al ₂ O ₃ with particle sizes above 150 µm, their effect is negligible. When using particles smaller than 30 µm, the reaction of Ca (OH) ₂ with Al (OH) ₃ to calcium aluminate during hydration of the gypsum-free cement, or the reaction of thermally formed CaO with high-fine Al ₂ O _3, is then fully applied. This is also aided by the possible grinding of the Al ₂ O ₃ -based substance with the grinding additive. For example, only crushed natural bauxite in the composition according to the invention has virtually no improvement in properties compared to the use of finely ground bauxite, optionally ground in the presence of a grinding additive, for example a liquid surfactant.

Of great importance for the strength of the composition according to the invention at temperatures of 200 to 1200 ° C is the value of the water coefficient, i.e. the amount of mixed water necessary to achieve acceptable processability. The corundum cement mortars mentioned in the examples of the invention were well workable even at an aqueous coefficient of 0.31.

Another reason why higher strengths are achieved in the present invention is the presence of a hydrolyzable alkaline compound which acts on Al (OH) ₃ and first forms with it alkali phthalts that react with Ca (OH) ₂ to calcium aluminates. In the presence of an alkaline hydrolyzable compound, aluminates appear to be easier to form. Ca (OH) ₂ binding occurs in the solution according to the invention, ie two types of reactions:

1. Reaction of Ca (OH) 2 with Al 3 OH 3 directly to hydrated calcium aluminates, most preferably to 3 CaO. Ä1 ₂ O ₃ .6H ₂ O.

2. Reaction of Al (OH) ₃ with NaOH to sodium aluminate, which reacts with Ca (OH) ₂ to calcium aluminate, apparently again to 3CaO. Al ₂ O ₃ .6 H ₂ O. In this case, alkaline activation of Al (OH) ₃ applies.

Thus, the alkaline activation of the components of the mixture according to the invention manifests itself not only in the alkaline activation of silicate clinker, but also in the alkaline activation of the other components of the mixture, in particular Al (OH) ₃ . This results in increased firing strengths and improved refractory properties of the materials prepared according to the invention.

SO ₄ ' ² ions derived from CaSO ₄ . The 2 H ₂ O, which is part of conventional Portland cement, results in a reduction in the viscosity and surface tension of the silica-aluminum melt that is produced in Portland cement when heated to temperatures above 1100 to 1200 ° C. The properties of this melt then inherently negatively translate into the glow properties of the Portland clinker-based materials without replacing the gypsum solidification regulator. Presence of gypsum CaSO ₄ . 2 H ₂ O in the composition according to the invention is therefore not desirable and is at the same time fully replaced by the action of the other components of the composition.

The refractory compositions according to the invention can be prepared as a dry mixture, for which only mixed water is required. Gypsum-replacing additives (e.g. Na ₂ CO ₃ + lignin sulfonate) can also be dissolved in mixed water.

The invention is illustrated by the following non-limiting examples. The weight percentages of the ingredients in the examples are based on the weight of the milled clinker (raw material A).

DETAILED DESCRIPTION OF THE INVENTION

Preparation of raw material A,

Cement clinker from conventional Portland cement dry production was ground to a surface area of 550 m ² / kg in the presence of 0.05 wt. dodecylbenzenesulfonic acid derivative. This procedure yielded raw material A, which constitutes the basic component of the mixture in the other examples given.

Example 1

The ground clinker - raw material A was mixed with 30 wt. bauxite, which was ground to fineness, where the average particle size was 10 µm. This mixture was treated with the addition of 1% Na ₂ CO ₃ and 0.8% sodium lignosulfonate to a well processable slurry with sw / c = 0.28 (product 1). In the same way, a slurry was prepared from raw material A except bauxite. From these slurries were prepared "glow lamps". Refractoriness was determined by the procedure according to ČSN ISO 528 and ČSN ISO 1146. The sample treated without bauxite had a final heat resistance of 1020 ° C and the sample of the invention then reached a final heat resistance of 1520 ° C.

Example 2

From raw material A with the addition of 1% Na ₂ CO ₃ , 0.8% sodium lignin sulphonate and 10 to 30 wt. fine ground bauxite (average particle size less than 5 µm) were prepared with slurries sw / c = 0.26-0.32 with very good workability and solidification of 30-45 minutes (product 2) and hydration strength 51 MPa.

Furthermore, a control experiment according to GB 2,063,240 (Mathieu), i.e., a control experiment, was carried out. j. from a mixture of ground clinker without grinding additive with bauxite and omitting sodium carbonate and plasticizer. The omission of carbonate and plasticizer led to a worse workability of the mixture w / c = 0.35 and in particular to an unfavorable reduction of the workability time to less than 5 minutes. Also after 7 days of hydration, the strengths were lower by more than 30% (34 MPa). In another control experiment GB 2,063,240 (Mathieu), a plasticizer (sodium lignosulfonate) was added at a concentration of 0.2% by weight, which improved the processability of the mixture so that the slurries could be processed at w / c = 0.35. However, these slurries had a very short start to solidify.

Example 3

From feedstock A, 1.2 wt. % Na ₂ CO ₃ , 1 wt. % sodium lignosulfonate and 0 to 30 wt. finely ground bauxite prepared mortar with a ratio of binder: grit = 1: 2.5, where the grit was 2 fractions of corundum. The water coefficient of these mortars was 0.31 to 0.32 and the mean particle size d _{50 of the} bauxite ground in a ball mill was 10 µm. This mortar was stored for 7 days in a humid environment. The test specimens thus prepared were dried at 105 ° C after hydration. The dried bodies were then fired at 800 to 1000 ° C for 2 hours. The results are shown in the following table.

Compressive strength for cold after firing (MP _a)

bauxite ° C % 20 550 800 1000 1100 1200 0 60 45 20 ^x 10 ^x 5 ^X 25 5 57 55 20 12 - 15 15 52 57 25 30 - 18 30 50 80 50 35 - 17

^x Sample partially disintegrated after firing ™ Increased firing strength is caused by unwanted melt formation at the specified temperature

Control experiments of GB 2, 063, 240 (a mixture of clinker and the hydroxide with the addition of 2 wt.% CaSO _2. H ₂ O) had a strength of the same conditions significantly lower by an average of 30 to 50% lower after the firing at the temperature.

In other experiments the same procedure was used, but the bauxite was not ground, it was only mechanically crushed. The mean particle size of this bauxite was d ₅₀ = 155 µm. Mortars were prepared under the same conditions and fired in the same way. The firing strengths of these mortars after firing at temperatures of 800 to 1200 ° C were 30 to 50% lower.

Example 4

Practically the same results as in Example 3 were obtained when the mixture was prepared dry and only mixed water was added to the dry mixture.

Example 5

The mortar prepared according to Example 4 was used except that pure A1 (OH) ₃ was used instead of bauxite. Al (OH) ₃ was ground on a vibratory mill. Unground Al (OH) ₃ had a mean particle size d _{50 of} = 100 µm, while Al (OH) ₃ ground on a vibratory mill had a d ₅₀ = 7.5 µm.

The strength results are shown in the following table:

Cold compressive strength after firing (MPa)

Al (OH) ₃ ° C % 20 550 800 1000 1100 1200 0 60 45 20 ^x 10 ^x 5 ^X 25 " 15 52 45 20 12 - - unmilled 15 50 60 40 25 - 20 vibr. mill

^x sample partially disintegrated ™ increase in firing strength is caused by unwanted melt formation at the specified temperature

The control trials of GB 2,063,240 had significantly lower strengths under the same conditions, an average of 30 to 50% lower after firing at the indicated temperatures.

Example 6

The white cement clinker from the Rohožník cement plant (SR) was ground with the addition of 0.01 wt. Abeson TEA on a specific surface of 520 m ² .kg- ¹ in the absence of gypsum.

A mortar of 1 part ground clinker was prepared from this product (10% by weight ground clinker was replaced by ground bauxite containing more than 80% by weight of particles smaller than 30µ and 3 parts of 3 corundum fractions. additives: 1 wt% Na ₂ CO _3> 0.1 wt% sodium, potassium tartrate and 1 wt% Umaform SM (urea-formaldehyde condensate) The aqueous mortar coefficient with good workability was 0.28.

Bodies of 4x4x16 cm size were prepared from mortar and left for 7 days in saturated water vapor at + 20 ° C. After 7 days, the bodies were dried at 105 ° C. The bodies were then fired for 2 hours at 550 to 1000 ° C. After firing, the cold strength at + 20 ° C was determined.

Without firing (hydration for 7 days at 20 ° C) the measured compressive strength was 50 MPa, after firing at 550 ° C the compressive strength was 45 MPa, after firing at 800 ° C the compressive strength was 20 MPa and after firing at 1000 ° C compressive strength 10 MPa.

SK 280385-6

Example 7

The ground clinker - raw material A was dried with ground aluminum hydroxide with an average particle size of 5 µm. This mixture was sprayed while adding water to the 4x4x16 cm molds using a flow-through device. The sample was stored in a humid environment and then dried at 105 ° C. It was then baked for 2 hours at 800 ° C. The firing strength was 15 MPa.

When using aluminum hydroxide with a particle size greater than 30 µm, or using crushed bauxite, the firing strengths were 5% lower.

Industrial usability

The invention can be used in the construction industry, in particular in the manufacture of mixtures for refractory purposes.

Claims (5)

PATENT CLAIMS 1. A mixture for refractory purposes comprising 22 to 20 93.6 wt. % Portland Portland clinker and / or white cement, based on the weight of the total mixture, and 5-77 wt. other refractory materials, based on the total weight of the mixture, selected from the group consisting of finely ground metallurgical slag, blast furnace slag, fly ash, alumosilicate calcination products, pozzolans, refractory grit and / or finely ground filler , fired flake and corundum, and further from 1 to 10% by weight, based on the total weight of the mixture, of Al ₂ O ₃ -based substances, characterized in that the Portland clinker and / or white cement does not contain gypsum and the mixture contains reactive substances Al ₂ O ₃ , consisting of Al ₂ O ₃ , hydrated Al ₂ O ₃ . nH ₂ O, and / or bauxite and / or laterite with a particle size of less than 150 µm in an amount of 1 to 30% by weight, based on the weight of the whole mixture, Portland clinker and / or white cement with reactive substances based on Al ₂ O ₃ and further comprises grinding ingredients in an amount of 0.001 to 2% by weight, based on the weight of the mixture of Portland clinker and / or white cement with Al ₂ O ₃ reactive substances 2. The composition according to claim 1, characterized in that the reactive species on the basis of A1 ₂ O ₃ have a particle size below 30 pm. The composition of claim 1, further comprising from 0.1 to 5% by weight of the total composition of a hydrolyzable alkali metal salt selected from the group consisting of alkali metal carbonates, bicarbonates and silicates, and 1 to 3% by weight, based on the total weight of the mixture, of an anionic surfactant stable in pH> 7, selected from the group consisting of alkali metal ligninsulfonates, sulfonated lignin, sulfonated polyphenolate, naphthalenesulfonate, sulfonated melamine condensation product formaldehyde. The composition according to claims 1 to 3, further comprising 0.1 to 20% by weight, based on the total weight of the mixture, of SiO ₂ drift from metallurgical products. 5. The composition according to claim laž4, characterized in that it further comprises 0.01 to 5 wt.%, Based on the weight of the total composition, Portland cement clinker and / or white cement with reactive species on the basis of A1 ₂ O _3, the setting regulators bezsadrovcových cements selected from the group consisting of organic hydroxides, boric acid, organosilicon compounds or phosphates.