SK16697A3 - A mixture for heat-resisting purposes - Google Patents

Abstract

This mixture for refractory purposes containing 22 to 93.6% by weight of milled silicate Portland clinker and/or white cement according to the weight of the mixture, and 5 to 77% by weight, according to the weight of the mixture and other substances for preparing refractory materials selected from the group consisting of finely ground metallurgical clinker, blast-furnace granulated clinker, ash, products of the calcination of aluminosilicates, pozzolans, refractory grog and/or a finely ground filling selected from the group of substances consisting of burnt clay, Dinas clay, burnt mud rock and corundum, and also 1 to 10% by weight, according to the weight of a mixture of substances based on Al2O3, is based on the fact that Portland clinker and/or white cement is free of plaster stone and the mixture contains 1 to 30% by weight of reactive substances based on Al2O3 consisting of Al2O3, hydrated Al2O3.nH2O and/or bauxite and/or laterite with a particle size below 150 micrometers according to the weight of the mixture of the Portland clinker and/or white cement with reactive substances based on Al2O3, and 0.001 to 2% by weight of milling ingredients according to the weight of the mixture of Portland clinker and/or white cement with reactive substances based on Al2O3. In addition, it may contain 0.1 to 5% by weight, according to the total mixture, of the hydrolysable salt of an alkaline metal selected from the group consisting of carbonates, hydrogen carbonates and silicates of alkaline metals, and 0.1 to 5% by weight, according to the total mixture, of a plasticizing additive based on anionic a tenzide stable in a medium with a pH greater than 7 selected from the group of substances consisting of ligninsulphonates of alkaline metals, sulphonated lignin, sulphonated polyphenolate, naphthalene sulphonate, the sulphonated product of the condensation of melamine with formaldehyde, and/or 0.1 to 20% by weight of SiO2 fly ash from metallurgical production, and/or 0.1 to 5% by weight of the setting regulators of gypsum-free cements selected from the group of substances consisting of organic hydroxyacids, boric acid, organosilicon compounds or phosphates.<IMAGE>

Description

(57) Annotation:

The refractory composition contains 22 to 94.999% by weight. ground Portland silicate clinker and / or white cement, free from gypsum and other substances necessary for the preparation of refractory materials selected from the group consisting of finely ground metallurgical slag, blast furnace granulated slag, ash, aluminosilicate calcining or fine granules, puzzolane a filler selected from the group consisting of fireclay, dinas, fired flake and corundum, further comprising substances based on Al ₂ O ₃ .n H ₂ O, bauxite and laterite having a particle size less than 150 µm, preferably less than 30 µm.

The Al ₂ O ₃ -based substance can be milled alone or with the other ingredients of the mixture. It may further comprise hydrolysable alkali metal salts selected from the group consisting of alkali metal carbonates, bicarbonates and silicates and liquefying additives based on an anionic surfactant stable at pH > , a sulfonated condensation product of melamine with formaldehyde and / or grinding agent in an amount of 0.001 to 2% by weight, and / or up to 20% SiO ₂ fluxes of metallurgical products, and / or solidification regulators of gypsum cements selected from organic hydroxy acids, boric acid , organosilicon compounds or phosphates.

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Txní & for refractory purposes

Technical field

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

BACKGROUND OF THE INVENTION

For refractory purposes, predominantly aluminous cement is used and the use of silicate (Portland) cement for this purpose is very limited. Facts that limit the use of conventional Portland cement in refractory concrete include the negative impact of gypsum solidification regulator on the gland properties of Portland cement, as well as 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 SiOi or Cr ₂ O ₃ containing binding CaO during firing, with partial stabilization of Portland cement in refractory concrete already occurring using conventional stoneware, for example 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, e.g. article by Škvara F., Pekárek L. Velička: "The Gypsum-free Portland Cement Hydration and Thermal Properties", Proceedings 8 th ICTA 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 lignin sulfonate or an alkaline earth lignin sulfonate or 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 µmη, at least 0.0025% by weight of lignin compound. 0.001 to 8% by weight.

% Alkali metal salts and 0.005 to 80 wt. water. US 4,551,176 (Slag et al.) Discloses a composition of a fast setting cementitious binder with a 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.

US 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 sulfonated polyelectrolyte, for example sulfonated polyphenolate, lignosulfonate and 0.5 to 6 wt. alkali carbonate, bicarbonate, hydroxide.

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

From AO no. No. 238,713 (Škvara et al.) Is a known refractory material for linings, in particular monolithic linings of metallurgical vessels, consisting of a slag based on, for example, 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. in water-soluble alkali metal silicate, optionally alkali metal or alkaline earth metal carbonate or acidic carbonate, the remainder of the cement consists of cement clinker, free of gypsum, with a surface area of 220 to 1000 m ² / kg. This refractory composition further comprises an optionally water-soluble sulfonated condensation product of phenols 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 production 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 is used as a binder. 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 grit.

This solution was refined by Sauman et al., Where gypsum in a quantity of up to 0.5% by weight was added to the gypsum-free cement. The properties of this binder were presented in the article by Šauman Z. et al. Building no. 4, 138142 (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 in CaO binding exclusively by aggregates. This substantial disadvantage has been eliminated in the UK 2,063,240 (Mathieu).

From UK 2,063,240 (Mathieu) a hydraulic binder is known where Portland cement clinker is mixed or ground with hydrated Al ₂ O ₃ . in such an amount that the CA (OH) ₂ formed by the 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 UK 2,063,240 (Mathieu), another disadvantage is the worse workability of the mixture, where it is necessary to use a significantly larger water coefficient of 20 to 50%. In UK Patent 2,063,240, a gypsum regulator replacement is not equally reliably solved, which would reliably prevent premature solidification of the cement when applied according to most conventional technologies.

The essence 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 94.999% by weight. ground gypsum silicate clinker and / or white cement free of gypsum and other substances necessary for the preparation of refractory materials, selected from the group consisting of finely ground metallurgical slag, blast-furnace granulated slag, ash, aluminosilicate calcination products, puzzolane selected from the group consisting of fireclay, dinas, burnt lupine and corundum according to the invention consists in containing substances based on Al ₂ O ₃ selected from the group consisting of Al ₂ O ₃ , hydrated with Al ₂ O ₃ . nH ₂ O, bauxite and laterite with smaller particle size

At about 150 gm, preferably less than 30 gm. The Al ₂ O ₃ -based substance can be milled alone or with the other ingredients of the mixture.

It may further comprise hydrolyzable alkali metal salts selected from the group consisting of alkali metal carbonates, bicarbonates and silicates and flowable additives based on an anionic surfactant stable at pH > % sulfonated condensation product of melamine with formaldehydes and / or grinding additive in an amount of 0.001 to 2 wt. and / or up to 20% SiO ₂ flux from metallurgical products and / or solidification regulators of gypsum-free cements selected from the group consisting of organic hydroxides, boric acid, oiganosilicon 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> 2 vs in hardened gypsum-free cement occurs in partially amorphous form as described in the article by Ševčík V., Škvara F., Ederová J .: "Portland Clinker Refractory Materials", Sb. 12 International Conference on Refractory Concrete, Prague 1995. The firing of hardened gypsum-free cement generates CaO in a more dispersed form than conventional Portland cement with gypsum solidification regulator, which allows for a higher reactivity of CaO with active ingredients. better parameters for thermally stressed applications.

Further research has found that a critical 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 CaOHOH or CaO formed in the firing process is their particle size. When using these substances based on Al ₂ O ₃ with a particle size above 150 gm, their penetration is negligible. When using particles smaller than 30 gm, the reaction of Ca (OH) with Al (OH) 3 to calcium aluminate in 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 shows practically 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 of the invention at temperatures of 200 to 1200 ° C is the value of the water coefficient, i.e. the amount of mixing 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 aluminates which react with Ca (OH> 2 to calcium aluminates). Ca (OH) 2 binding occurs in two solutions according to the invention:

1. Reaction of Ca (OH) 2 with Al (OH> 3) directly to hydrated calcium aluminates, probably mainly to 3 Ca.Al ₂ O ₃ .6 H 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 AKOH 4 is applied.

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

SO / ² ions derived from CaSO 2. The 2 H ₂ O, which is part of a conventional Portland cemnet, results in a reduction in the viscosity and surface tension of the silica-aluminum melt that is formed in Portland cement when heated to temperatures above 1100 to 1200 ° C. The properties of this melt then inevitably translate into the heat grease of 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.

in

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

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

-6Examples of embodiments of the invention

Example 1

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 2

The ground clinker (raw material A according to Example 1) was mixed with 30 wt. bauxite, which has been ground to particles with an average size of 10 μτη. This mixture was treated with the addition of 1% Na ₂ CO ₃ and 0.8% sodium lignosulfonate to a well processable slurry 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 3

From raw material A with additions of 1% Na ₂ CO ₃ , 0.8% sodium lignosulfonate and 10 to 30% finely ground bauxite (average particle size less than 5 µτη), slurries were made with sw / c = 0.26 to 0.32 s very good workability and start, solidification in the range of 30 to 45 minutes (product 2) and hydration strength of 51 MPa.

Control mixtures omitting sodium carbonate were also made from the mixture of product A with bauxite. The omission of the carbonate resulted in a worse workability of the mixture w / c = 0.35 and in particular an unfavorable reduction in the workability time to less than 5 minutes. Also after 7 days of hydration, the strengths were lower by more than 30% (34 MPa).

Example 4

From feedstock A (according to Example 1), 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 of the bauxite ground in a ball mill

-7bola 10 μχη. 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.

Cold compressive strength after firing (MP ") bauxite ° C

% 20 550 800 1000 1 100 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 the} sample has partially disintegrated after firing “the increase in firing strength is caused by unwanted melt formation at the given 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 = 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 5

Practically the same results as in Example 4 were obtained when the mixture was dry prepared and only the mixed water was added to the dry mixture.

Example 6

Following the procedure of Example 4, mortars were prepared except that pure Al (OH) a was used instead of bauxite. A1 (OH > 3) was ground on a vibratory mill. Unground A1 (OH) ₃ had a mean particle size d &gt; = 100 pm, while Al (OH) ₃ ground on a vibratory mill had d &gt; = 7.5 pm. in the following table:

-8Pevnosti cold crushing after firing (MP _a)

Al (OH) ₃ ° C % 20 550 800 1000 1 100 1 200 0 60 45 20 ^x * 10 5 * 25 " 15 52 45 20 12 - - unmilled 15 50 60 40 25 - 20

vibr. mill * sample partially disintegrated ”increase in firing strength is caused by unwanted melt formation at firing to specified temperature

Example 7

In further experiments, gypsum-free Portland cement from the Prachovice cement plant (Portland clinker ground to a specific surface of 450 m ² / kg in the presence of a liquid grinding additive - raw material A) was used.

From this cement, corundum fillers with a cement: filler ratio of 1: 2.5 were prepared. Additives were dissolved in the mixing water: 1.1 wt. % sodium lignosulfonate + 2.25 wt. Na ₂ CO ₃ . The water mortar coefficient was 0.31. In some cases, 12 wt. % SiO ₂ (sample A), or 15 wt. Al (OH) j according to the invention (sample B).

For comparison, a mortar with the same filler content and the same consistency at w = 0.42 of Lafarge Fund alumina cement (sample C) was prepared which contained 41% Al ₂ O ₃ , 38% CaO, 4.3% SiO ₂ and 13, 8% FeO + Fe ₂ O ₃ .

From the above mortars A, B, C, bodies with a height of 50 mm with an axial bore of 12 mm diameter were prepared. The bodies were hydrated in saturated water vapor at 20 ° C for 7 days. They were then dried at 105 ° C and baked to 1200 ° C (classification temperature). The radiant resistance of these elements was determined by the procedure according to ČSN ISO 1893.

The results are shown in the following table.

-9to, p (° C)

Sample A (BS cement + SiO drift) 1189

Sample B (Aluminous Cement) 1193

Sample C (Solution of the Invention) 1238 t0.5 is the temperature at which 0.5% deformation occurs under standard load.

Industrial usability

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

* ♦

-10PV / a- £

Claims (6)

A mixture for refractory purposes comprising 22 to 94.999% by weight. ground pordandic and / or white cement, gypsum-free and other substances necessary for the preparation of refractory materials selected from the group consisting of finely ground metallurgical slag, blast-furnace granulated slag, ash, aluminosilicate calcination products, or puzzolari, selected from the group consisting of fireclay, dinas, burnt lupine and corundum, further comprising substances based on Al ₂ O ₃ selected from the group consisting of Al ₂ O ₃ , hydrated Al ₂ O ₃ .n H ₂ O, bauxite and laterite having a particle size of less than 150 µm. A composition according to claim 1, characterized in that the Al ₂ O ₃ -based substances have a particle size of less than 30 µm. 3. A composition according to claim 1, comprising a hydrolyzable alkali metal salt selected from the group consisting of alkali metal carbonates, bicarbonates and silicates, and a flowable anionic surfactant additive based on pH> 7 selected from the group consisting of alkali metal lignosulfonates. metals, sulfonated lignin, sulfonated polyphenolate, naphthalenesulfonate, sulfonated product of melamm-formaldehyde condensation. A composition according to claim 1 to 3, characterized in that the Al ₂ O ₃ -based substance is ground separately or with the other ingredients of the composition. 5. A composition according to claim 1 comprising grinding ingredients in an amount of 0.001 to 2% by weight. 6. The composition according to claim 1 to 5, you characterized thereby that it comprises up to 20% SiO ₂ dusts from metallurgical production. 7. A composition according to any one of claims 1 to 6 comprising solidification regulators of gypsum-free cements selected from the group consisting of organic matter.