CZ84396A3 - Mixture for refractory 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

Technical field

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

BACKGROUND OF THE INVENTION

For refractory purposes, mainly aluminous cement is used and the use of silicate (Portland) cement for these purposes is very limited. Factors limiting the use of conventional Portland cement in refractory concrete include the negative influence of gypsum solidification regulator on the heat 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 by the addition of finely ground substances containing S1O2 or 0 ^ 03, which bind the resulting CaO at firing, with partial stabilization of Portland cement in refractory concrete already using conventional aggregates, fireclay or burnt flake, which reduce the amount of free CaO after firing.

Gypsum-free Portland cement is known from the literature, which achieves relatively high strengths even at higher temperatures, see, for example, the article by Škvára F., Pekárek L, Velička: The Gypsum-free Portland Cement Hydration and Thermal Properties, Proceedings 8th ICTA Conf., Bratislava 1985 , Vol. 2, pp. 591-596. The properties and composition of the gypsum-free Portland cement mixtures are also known from the patent literature. It is known from US 3,689,297 (Brunauer) a composition of a free-flowing expanded cement paste, mortar or concrete based on a ground cement clinker having a specific surface area of 600 to 900 m @ 2 / kg containing at least 0.002 parts grinding additive and at least 0.0025 parts alkaline ligninsulfonate or an alkaline earth lignin sulphonate or a sulphonated lignin and at least 0.0025 parts of alkali carbonate, the water coefficient being in the range of 0.20 to 0.28. A substance with polar and non-polar groups in the molecule is specified as a grinding additive.

Further, US 4,168,985 (Kolar, Slag) discloses a cementitious binder composition consisting of cement having a specific surface area of 250 to 300 m ² / kg containing 5 to 95% particles smaller than 5 µm, at least 0.0025% by weight. lignin compound, 0.001 to 8 wt. % alkali metal salt and 0.05 to 80 wt. mixing water. U.S. Pat. No. 4,551,176 (Slag et al.) Discloses a fast setting cementitious binder having a specific surface area of 150 to 300 m ² / kg, containing 5 to 95 wt. 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.

It is known from US 5,076,851 (Slag et al.) That a mixed binder composition containing 60 to 96.7 wt. Portland cement clinker ground to a specific surface area 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. grinding additives, 0 to 20 wt. % amorphous SiO2, 0.1 to 3 wt. % of sulfonated polyelectrolyte, for example sulfonated polyphenolate, lignin sulfonate, 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, which comprises grinding Portland cement clinker with additives of 0.01 to 0.05% by weight. Synthetic surfactants stable at a pH of 9-12, for example dodecylbenzenesulfonic acid triethanolamide.

AO 238,713 (Slag et al.) Discloses a refractory mass for linings, in particular monolithic linings of metallurgical vessels, consisting of a grinding material based on, for example, magnesium chromium in a quantity of 70 to 92% by weight and 8 to 30% by weight. cement-based binders, wherein the binder contains 0.01 to 4.5 wt. % of a water-soluble lignin derivative, for example an alkali metal or alkaline earth metal lignin sulfonate, and 0.005 to 2.25 wt. water-soluble alkali metal silicate or alkali metal or alkaline earth metal carbonate or acid carbonate, the remainder of the cement is gypsum-free cement clinker with a specific surface area of 220 to 1000 m ² / kg. This refractory composition further comprises an optionally water-soluble sulfonated condensation product of phenols with formaldehyde in an amount of 0.005 to 2.25% by weight. cement clinker.

AO 253,500 (Baker et al.) Discloses a refractory composition for the manufacture of porous endings used in blowing inert gases into a metal melt, containing, for example, zirconium sand, chrommagnesite, magnesite, chamotte or the like; with a specific surface area of 60 to 800 m ² / kg in an amount of 10 to 20% by weight, based on the sanding material.

This solution was refined by Shauman and others, where gypsum was added to the gypsum-free cement up to 0.5% by weight. The properties of this binder were given in the article by Šauman Z. et al .: Research of a new binder for the production of refractory concrete, Stavivo No. 4, 138-142 (1989).

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

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

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

SU 407 857 describes the preparation of refractory concrete from Portland cement, corundum, α-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 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 with hydrated AI2O3 in such an amount that the Ca (OH) ₂ formed by the reaction of Portland clinker with water is saturated with hydrated AI2O3. The binder may further comprise plasticizers, liquefying agents and calcium sulfate. The binder enables the preparation of refractory concretes.

When using the solution according to UK 2,063,240 (Mathieu), the disadvantage is worse workability of the mixtures, when it is necessary to use a significantly larger water coefficient of 20 to 50%, which is probably one of the reasons of lower strength at temperatures

200-1000 ° C, as can be seen from the exemplary embodiment.

SUMMARY OF THE INVENTION

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

A mixture for refractory purposes containing 22 to 94.999% by weight. ground Portland silicate clinker and / or white cement, based on the weight of the mixture and 5 to 77 wt. other materials for the preparation of refractory materials, based on the weight of the mixture, selected from the group consisting of finely ground metallurgical slag, blast-furnace granulated slag, fly ash, alumosilicate calcination products, pozzolans, refractory sanding and / or finely ground filler selected from the class of and from 1 to 10% by weight, based on the weight of the mixture, of the Al2O3-based substances, is that the Portland clinker and / or white cement is gypsum-free and the mixture contains AI2O3-based reactive substances consisting of Al2O3. , 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 wt.% based on the weight of the Portland cement clinker and / or white cement blend with reactive substances based Al 2 O 3 and grinding ingredients in an amount of 0.001 to 2 wt. based on the weight of the mixture of Portland cenent clinker and / or white cement with Al ₂ O ₃ reactive substances.

It may further comprise 0.1 to 5 wt.%, Based on the total composition, of hydrolyzable salts of an alkali metal selected from the group consisting of alkali metal carbonates, bicarbonates and silicates, and 0.1 to 5 wt.%, Based on the total composition. an anionic surfactant stable at pH> 7 selected from the group consisting of alkali metal ligninsulfonates, sulfonated lignin, sulfonated polyphenolate, naphthalenesulfonate, sulfonated melamine-formaldehyde condensation product, and / or up to 20 wt. SiO ₂ flux from metallurgical production and / or 0.1 to 5 wt. 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 cement mass in a much more dispersed form than is the case with hardened Portland cement and its content is lower than that of Portland cement. Furthermore, it has been found that Ca (OH) ₂ occurs in hardened gypsum cement in partially amorphous form, as mentioned in the article by Ševčík V., Škvára F., Ederová J .: Portland Clinker Refractory Materials, Sb. 12. Mez. Conference on refractory concretes, Prague 1995. The firing of hardened gypsum-free cement produces CaO in a more dispersed form than conventional Portland cement with gypsum solidification regulator. This allows for a higher reactivity of CaO with the active ingredients. This gives the possibility for gypsum-free cements to achieve better parameters for thermally stressed applications.

Further research has found that the 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 size of their particles. When using these substances based on Al ₂ O ₃ with particle size above 150 µm, their effect is negligible. When using particles smaller than 30 μηη, the reaction of Ca (OH) ₂ with Al (OH) ₃ to calcium aluminate during hydration of gypsum cement or the reaction of thermally formed CaO with highly fine Al ₂ O ₃ is fully applied. This phenomenon is also aided by the possible grinding of the Al ₂ O ₃ -based substance with the grinding additive. For example, only the fragmented 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 from the presence of a grinding additive, for example a liquid surfactant.

Of great importance for the strengths 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 mixing water necessary to achieve acceptable processability. The corundum-cement cement mortars mentioned in the examples of the invention were well workable even at a water 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 to form with it first alkali aluminates which 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 in the solution according to the invention thus occurs by two types of reaction reactions:

1. Reaction of Ca (OH) ₂ with Al (OH) 3 directly to hydrated calcium aluminates, probably primarily to 3CaO.Al2O3.6H2O,

2. Reaction of Al (OH) ₃ with NaOH to sodium aluminate, which reacts with Ca (OH) 2 to calcium aluminate, apparently again to 3CaO.Al2O3.6H2O. 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 the 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.

SO4 ² 'ions originating from CaSO ₄ .2H ₂ O that are part of conventional Portland cement result 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 inherently negatively translate into the heat properties of Portland clinker-based materials without replacing the gypsum solidification regulator. The presence of gypsum CaSO4.2H ₂ O in the composition of the invention is therefore undesirable and it is completely replaced by the effect of other components.

The refractory compositions according to the invention can be prepared as a dry mixture, for which only mixing water is required. Replacing gypsum additive effect (e.g., Na 2 CO ₃ + lignin) can also be dissolved in the mixing 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 ground clinker (raw material A).

Examples

Example 1.

Cement clinker from conventional Portland cement dry production was ground to a specific surface area of 550 m ² / kg in the presence of 0.05 wt%. dodecylbenzenesulfonic acid derivative. By this procedure, raw material A, which constitutes an essential component of the mixtures in the other examples given, was obtained.

Example 2.

The ground clinker (raw material A according to Example 1) was mixed with 30 wt. bauxite, which was ground to fineness when the average particle size was 10 μίτι. This mixture was treated with 1% wt. Na 2 CO ₃ and 0.8 wt%. sodium lignin sulphonate to a well processable slurry sw / c = 0.28 (product 1). A slurry of raw material A except bauxite was prepared in the same manner. Fluorescent tubes were prepared from these slurries. In accordance with ČSN ISO 528 and ČSN ISO 1146, the refractories were determined. 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 additives 1 wt. Na 2 CO _3, 0.8% wt. % sodium ligninsulfonate and 10 and 30 wt. finely ground bauxite (average particle size less than 5µΐτι) were prepared with slurries sw / c = 0.26-0.32 with very good workability and a setting time of 30 to 45 minutes (product 2) and a hydration strength of 51 MPa.

Furthermore, a control experiment according to UK 2,063,240 (Mathieu) was carried out with 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 = 0.43 and above all to an unfavorable reduction of the workability time to less than 5 minutes. Also, the strengths after 7 days of hydration were lower by more than 30% (34 MPa). In another control experiment according to UK 2,063,240 (Mathieu), a plasticizer (sodium lignin sulfonate) was added at a concentration of 0.2 wt%, which improved the processability of the compositions so that the slurries could be processed at w / c = 0.35. However, these slurries had a very short onset of solidification.

Example 4.

Of the raw material A (according to Example 1), 1.2 wt. Na 2 CO ₃ 1% wt.

% sodium ligninsulfonate 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 ₅ of the bauxite ground in a ball mill was 10 μιτι. This mortar was stored for 7 days in a humid environment. The specimens thus prepared were dried at 105 ° C after the hydration was completed. The dried bodies were then fired at 800 and 1000 ° C for 2 hours. The results are shown in the following table.

Cold compressive strength after firing (MPa) Noc: 18 ° C 550 ° C 800 [deg.] C 1000 ° C 1100 ° C 1200 ° C bauxite 0% 60 45 20 ^x 1 5 ^X 25 xx 5% 57 55 20 May 12 - 15 Dec 15% 52 57 25 30 - 18 30% 50 80 50 35 - 17 ^{x the} sample partially disintegrated after firing

^xx increase in firing strength is caused by undesired melt formation at firing to said temperature.

Control experiments according to UK 2,063,240 / a mixture of clinker and aluminum hydroxide with 2% wt. CaSO ₂ .H ₂ 0 / showed strengths under the same conditions significantly lower and on average 30% to 50% lower after firing at the stated temperatures.

In other experiments the same procedure was used, but the bauxite was not milled, it was only mechanically separated. 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 at 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 prepared dry, and only the mixing water was added to the dry mixture.

Example 6.

Using the procedure of Example 4, mortars were prepared except that pure Al (OH) ₃ was used instead of bauxite. Al (OH) ₃ was milled 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 Noc: 18 ° C 550 ° C 800 [deg.] C 1000 ° C 1100 ° C 1200 ° C 0% 60 45 20 ^x 10 ^x 5 ^X 25 ^xx 15% unground 52 45 20 May 12 - 15% 50 60 40 25 20 May

vibration mill ^x sample partially disintegrated ^xx increase in firing strength is caused by unwanted melt formation at firing to specified temperature

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

Example 7.

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

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 30 μ and 3 parts of 3 corundum fractions. additives: 1 wt% Na ₂ CO ₃ , 0.1 wt% Na, Ka tartrate 1 wt% Umaform SM (urea-formaldehyde condensate) The water coefficient of the mortar with good workability was 0.28.

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

After firing (at hydration for 7 days at 20 ° C) the compressive strength was measured to 50 MPa, after firing to 550 ° C the compressive strength was 45 MPa, after firing to 800 ° C the compressive strength was 20 MPa and after firing to 1000 ° C compressive strength 10 MPa.

Example 8

The ground clinker of Example 1 was dried with ground aluminum hydroxide with an average particle size of 5 µητι. This mixture was sprayed with the addition of water into molds 4 x 4 x 16 cm using a sprinkler. The sample was stored in moisture, then dried at 105 ° C. It was fired at 800 ° C for two hours. The firing strength was 15 MPa.

The use of aluminum hydroxide with a particle size greater than 30 gm or using split bauxite resulted in a firing strength of 5% lower.

Industrial applicability

The invention is applicable in the construction industry in particular for the production of refractory mixtures

Claims (6)

Patent claims I.Mixture for refractory purposes containing 22 to 94.999% by weight ground Portland silicate clinker and / or white cement, based on the total weight of the mixture and 5 to 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 granulated slag, fly ash, calcareous alumosilicates, pozzolans, refractory sanding and / or finely ground filler , burnt flake and corundum, and 1 to 10 wt.%, based on the total weight of the mixture, of Al ₂ O ₃ -based materials, characterized in that the Portland clinker and / or white cement is gypsum-free and the mixture contains reactive substances to Al ₂ O ₃ base, 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 wt.%, based on weight mixtures of Portland cement clinker and / or white cement with Al ₂ O ₃ -based reactive substances and further contains grinding additives in an amount of 0.001 to 2 wt. Portland cenentine clinker and / or white cement with Al ₂ O ₃ reactive substances. Mixture according to claim 1, characterized in that the reactive substances based on Al ₂ O ₃ have a particle size of less than 30 μηη. 3. A composition according to claim 1 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 wt.%, Based on the weight of the total mixture, of an anionic surfactant stable at pH> 7, selected from the group consisting of alkali metal ligninsulfonates, sulfonated lignin, sulfonated polyphenolate, naphthalenesulfonate, sulfonated melamine condensation product with melamine formaldehyde. A composition according to claims 1 to 3, characterized in that the Al ₂ O ₃ -based substance is ground separately or with the other ingredients of the composition. The composition according to claims 1 to 4, characterized in that it contains up to 20% by weight, based on the weight of the whole composition, of SiO ₂ flux from metallurgical products. Mixture according to one of Claims 1 to 5, characterized in that it contains from 0.01 to 5% by weight, based on the weight of the mixture of Portland cenetic clinker and / or white cement with Al ₂ O ₃ reactive substances, solidification regulators of gypsum-free cements selected from the group consisting of organic hydroxides, boric acid, organosilicon compounds or phosphates.