Aqueous suspensions of calcium hydroxide nanoparticles with improved storage stability, their preparation and use

Abstract

The present invention relates to an aqueous suspension, its preparation and use as an accelerator for mineral binders, comprising: a) 5 to 65% by weight of calcium hydroxide in the form of suspended nanoparticles, relative to the total weight of the aqueous suspension; b) optionally at least one organic compound for stabilizing the aqueous suspension against settling; and c) at least one salt of an alkali metal or alkaline earth metal, preferably at least one of the hydroxides, nitrates, nitrites, phosphates, phosphites, sulfates, thiocyanates, carbonates, bicarbonates, silicates, aluminates, formates, acetates, lactates, citrates, tartrates and / or gluconates of alkali metals or alkaline earth metals.

Description

[Technical Field]

[0001] The present invention relates to an aqueous suspension of calcium hydroxide nanoparticles, a method for producing same, and the use of the suspension as a promoter for mineral binder compositions. [Background technology]

[0002] Cement is a mineral binder, primarily used in concrete and mortar. When cement is mixed with water, it sets and hardens in a chemical process called cement hydration. The cement hydrate thereby formed acts as a binder for the aggregates, typically sand, gravel, and stone, in concrete and mortar to form a solid material. There are many uses for mortar or concrete where rapid setting and hardening, and therefore rapid development of strength, is very important.

[0003] There are various methods to accelerate the setting and / or hardening of cement. Setting is accelerated by increasing the temperature, which is used, for example, to produce precast concrete components. Heating can be particularly difficult or even impossible on-site.

[0004] Another possible way to accelerate cement hydration is to add water-soluble salts such as calcium chloride, calcium nitrate or sodium nitrite, and / or amines, e.g., hydroxyalkylamines. Prior art water-soluble accelerators usually have the disadvantage that mortar or concrete mixtures accelerated with them harden quickly and therefore lose workability quickly.

[0005] Yet another known method of accelerating the setting of cement is to add fine inorganic powders. However, handling the powders generally involves dusting, especially if the powders are very fine. Alkaline calcium hydroxide powder can easily cause damage to the eyes, respiratory tract, and skin of individuals working with it.

[0006] Thus, WO 2019 / 180191 discloses aqueous suspensions of calcium hydroxide nanoparticles that are effective as accelerators for mineral binder compositions. These aqueous suspensions can solve many of the problems of other known accelerators for mineral binders. However, the aqueous suspensions disclosed therein sometimes have limited storage stability and the calcium hydroxide nanoparticles tend to settle out.

[0007] As a result, there is a need to further improve the storage stability of aqueous suspensions of calcium hydroxide nanoparticles. Summary of the Invention [Means for solving the problem]

[0008] It is an object of the present invention to provide an aqueous suspension of calcium hydroxide nanoparticles which has reduced settling and therefore in particular an improved storage stability. Improved storage stability means that it can be stored for long periods of time without separation, in particular without settling of the calcium hydroxide. It is also an object of the present invention to provide a method for producing an aqueous suspension of calcium hydroxide nanoparticles with improved storage stability.

[0009] It has been surprisingly found that the addition of an alkali metal or alkaline earth metal salt to an aqueous suspension of calcium hydroxide improves storage stability. It is believed that the addition of the alkali metal or alkaline earth metal salt results in adjustment of the density of the aqueous suspension of calcium hydroxide, thereby allowing the resulting suspension to be stored for many days or months without significant phase separation.

[0010] Therefore, these and other objects of the present invention are solved by the subject matter of the independent claims.

[0011] Preferred embodiments of the invention are the subject matter of the dependent claims. DETAILED DESCRIPTION OF THE INVENTION

[0012] Methods of carrying out the present invention In a first aspect, the present invention provides a method for producing a medicament for the treatment of a pulmonary arthritis, comprising: a) 5 to 65% by weight of calcium hydroxide, relative to the total weight of the aqueous suspension, in the form of suspended nanoparticles; b) optionally at least one organic compound for stabilizing the aqueous suspension against settling; c) at least one salt of an alkali metal or alkaline earth metal, preferably at least one of the hydroxides, nitrates, nitrites, phosphates, phosphites, sulfates, thiocyanates, carbonates, bicarbonates, silicates, aluminates, formates, acetates, citrates, tartrates, and / or gluconates of alkali metals or alkaline earth metals; The present invention relates to an aqueous suspension comprising:

[0013] In the context of the present invention, an "aqueous suspension" is a suspension of particles in a continuous liquid phase that comprises or consists essentially of water. In particular, the continuous liquid phase other than water does not contain other solvents, such as alcohols, glycols or ketones. The liquid phase may contain a surfactant.

[0014] "Nanoparticles" are particles with a particle size in the nanometer range. These ultrafine particles are notable for their very high specific surface area and therefore for their specific properties. In the present document, "nanoparticles" refers to particles with a particle size of less than 1 μm. The particle size of nanoparticles in suspension can be measured by dynamic light scattering using photon cross-correlation spectroscopy in accordance with the ISO 22412:2017 standard.

[0015] Within the context of the present invention, the average particle size corresponds in particular to the D50 value (50% of the particles are smaller than the specified value and correspondingly 50% are larger). Thus, the value "D10" indicates the particle size below which 10% of the particles are smaller. The value "D90" indicates the particle size below which 90% of the particles are smaller.

[0016] According to an embodiment, the aqueous suspension of the invention is characterized in that the calcium hydroxide nanoparticles have a particle size of less than 950 nm, preferably between 10 and 800 nm, more preferably between 20 and 500 nm, most preferably between 30 and 400 nm, even more preferably between 40 and 300 nm, in particular between 50 and 200 nm, and / or a D90 of less than 800 nm, preferably less than 600 nm, more preferably less than 400 nm, in particular less than 200 nm, measured by dynamic light scattering using photon spectroscopy according to the ISO 22412:2017 standard.

[0017] For the purposes of the present invention, the particle size of calcium hydroxide particles has been determined using a Nanophox instrument from Sympatec (Germany), where the particle size is determined by dynamic light scattering using photon cross-correlation spectroscopy.

[0018] Suspensions comprising calcium hydroxide particles having the particle size defined above are particularly storage stable and highly effective in promoting mineral binder compositions, especially cementitious compositions.

[0019] According to an embodiment, at least 50% by weight, preferably at least 66% by weight, more preferably at least 90% by weight, in particular essentially all, of the calcium hydroxide present in the aqueous suspension is in the form of suspended nanoparticles.

[0020] The storage stability of a suspension is preferably determined by centrifuging the solution and measuring the turbidity of the solution, as described in the Examples. After centrifugation, the higher the phase, the higher the turbidity, and the fewer the number of sedimented particles, the more stable the suspension. The turbidity is advantageously determined with a turbidimeter and reported in NTU. NTU stands for nephelometric turbidity units. The higher this value, the more turbid the sample and the more stable the suspension. Advantageously, when an aqueous suspension has a calcium hydroxide content of about 10% by weight, after centrifuging 50 ml of this suspension in a 50 ml centrifuge tube at 8000 rpm for 15 minutes and removing the top 40 ml for turbidity measurement, the turbidity measured with a HACH® 2100AN turbidimeter is greater than 3000 NTU, preferably greater than 4000 NTU, more preferably greater than 5000 NTU, even more particularly greater than 6000 NTU, particularly greater than 7000 or 8000 NTU.

[0021] The aqueous suspension of the present invention optionally comprises at least one organic compound for stabilizing the suspension against settling. It is generally preferred that the aqueous suspension of the present invention comprises at least one organic compound that stabilizes the suspension. In this context, the term "stabilize" means a low tendency to settling. This leads, in particular, to improved storage stability.

[0022] According to an embodiment, the at least one organic compound that stabilizes the suspension against settling is an organic polymer containing carboxylic, sulfate, sulfonic, phosphate and / or phosphonic acid groups.

[0023] The organic polymer preferably also acts as a plasticizer for the mineral binder composition, especially the cementitious composition. Examples of suitable organic polymers include lignosulfonates, sulfonated naphthalene-formaldehyde condensates, sulfonated melamine-formaldehyde condensates, sulfonated vinyl copolymers, poly(meth)acrylic acid, copolymers of (meth)acrylic acid with (meth)acrylic acid esters or hydroxyalkyl (meth)acrylates, polyalkylene glycols with phosphonic acid groups, polyalkylene glycols with phosphoric acid groups, comb polymers with anionic groups and polyether side chains, or salts thereof, or mixtures of these polymers.

[0024] The organic polymer is advantageously stable in aqueous suspension. Advantageously, it has no groups, and more particularly no side chain bonds, that are subject to hydrolysis at high pH, ​​especially above 12.0.

[0025] The organic polymer is more particularly a comb polymer comprising a polymer backbone having polyalkylene oxide side chains and anionic groups attached to the backbone, wherein the side chains are attached to the polycarboxylate backbone, particularly by ester, ether, imide and / or amide groups. The comb polymer preferably comprises polyalkylene oxide units, more particularly polyethylene oxide units.

[0026] According to a particularly preferred embodiment, the at least one organic compound that stabilizes the suspension against settling is a comb polymer and comprises structural units of formula I and structural units of formula II: [ka] Including, In the above formula, R 1 are in each case independently of one another -COOM, -SO2-OM, -O-PO(OM)2, -PO(OM)2, -(CO)-NH-C(CH3)2-CH2-SO3M, -CH2-SO3M, [ka] and R 2 are, in each occurrence independently of one another, H, —CHCOOM or an alkyl group having 1 to 5 carbon atoms, R 3 , R 5 and R 6 are, in each occurrence independently of one another, H or an alkyl group having 1 to 5 carbon atoms, R 4 and R 7 are, in each occurrence independently of one another, H, —COOM or an alkyl group having 1 to 5 carbon atoms, M are independently H + , an alkali metal ion or an alkaline earth metal ion; m is 0, 1 or 2; p is 0 or 1; X, in each occurrence, independently of one another, is —O—, NH— or —NR 8 - and R 8 is the formula -[AO] n -R a is the basis of In the above formula, A=C2-C4 alkylene, and R a is H or C1~C 20 It is an alkyl, cyclohexyl or alkylaryl group, and n is 1-250.

[0027] Particularly preferred are comb polymers comprising structural units (I) and (II), In the above formula, R 1 is -COOM, R 2 and R 5 are, in each occurrence independently of one another, H or CH3, R 3 , R 6 and R 7 is H, R 4 are, in each occurrence independently of one another, H or -COOM, M is, in each case independently of one another, H + , an alkali metal ion or an alkaline earth metal ion; m is 0, 1 or 2; p is 0 or 1; X, in each occurrence independently, is —O— or —NH—, R 8 is the formula -[AO] n -R a is the basis of In the above formula, A is C2 to C3 alkylene, preferably C2 alkylene, and R a is H or a C1-C4 alkyl group, n is 10 to 200, preferably 22 to 150, and more specifically 50 to 120.

[0028] Advantageously, the comb polymer is composed exclusively of structural units (I) and (II), the molar ratio of structural units (I) to structural units (II) being preferably from 1:1 to 25:1, more preferably from 1.5:1 to 23:1, more preferably from 2:1 to 20:1, and even more preferably from 2.3:1 to 18:1.

[0029] However, it can also be advantageous if the comb polymer comprises further structural units (III), which are different from the structural units (I) and (II). The further structural units are preferably selected from (meth)acrylic acid alkyl esters, hydroxyalkyl (meth)acrylates, N-vinylpyrrolidone, vinyl esters, styrene, sulfanilic acid or monoamides of alkylamines with maleic acid, in particular hydroxyethyl acrylate, and hydroxypropyl acrylate.

[0030] The structural unit (III) is advantageously present in the comb polymer in an amount of from 0 to 70% by weight, preferably from 0.1 to 50% by weight, and more particularly from 0.5 to 40% by weight.

[0031] In particular, the aqueous suspensions of the present invention exhibit reduced phase separation, and in particular reduced settling of calcium hydroxide, without the addition of large amounts of stabilizing organic compounds. According to an embodiment, the at least one organic compound for stabilizing the suspension against settling is present in an amount of 5 to 40 parts by weight, preferably 8 to 35 parts by weight, more preferably 10 to 32 parts by weight, and even more particularly 11 to 30 parts by weight, per 100 parts by weight of calcium hydroxide.

[0032] According to an embodiment, at least one salt of an alkali metal or alkaline earth metal is added in an amount that is completely soluble in aqueous suspension at 23° C. and atmospheric pressure, or completely soluble in water at a pH of 12-13 at 23° C. and atmospheric pressure.

[0033] The at least one salt of an alkali metal or alkaline earth metal is preferably at least one of an alkali metal or alkaline earth metal hydroxide, nitrate, nitrite, phosphate, phosphite, sulfate, thiocyanate, carbonate, bicarbonate, silicate, aluminate, formate, acetate, lactate, citrate, tartrate, and / or gluconate. Preferably, the at least one salt of an alkali metal or alkaline earth metal is selected from sodium nitrate, sodium nitrite, sodium thiocyanate, lithium carbonate, sodium carbonate, sodium bicarbonate, sodium silicate, potassium silicate, sodium formate, sodium acetate, sodium lactate, sodium citrate, sodium tartrate, sodium gluconate, and / or calcium silicate hydrate.

[0034] According to an embodiment, the at least one salt of an alkali metal or alkaline earth metal is not calcium hydroxide, calcium nitrate, sodium hydroxide, and / or sodium nitrate.

[0035] According to an embodiment, the at least one salt of an alkali metal or alkaline earth metal is preferably at least one of alkali metal or alkaline earth metal hydroxides, nitrates, nitrites, phosphates, phosphites, sulfates, thiocyanates, carbonates, bicarbonates, silicates, aluminates, formates, acetates, lactates, citrates, tartrates, and / or gluconates, in particular selected from sodium nitrate, sodium nitrite, sodium thiocyanate, lithium carbonate, sodium carbonate, sodium bicarbonate, sodium silicate, potassium silicate, sodium formate, sodium acetate, sodium lactate, sodium citrate, sodium tartrate, sodium gluconate, and / or calcium silicate hydrate, and is present in an amount of 20 to 33% by weight, preferably 21 to 27% by weight, relative to the total weight of the aqueous suspension.

[0036] Surprisingly, it has been found that the aqueous suspension of the invention is particularly stable if it has a calcium hydroxide content of 8 to 12% by weight in the form of suspended nanoparticles and if it has a density, measured according to the DIN EN ISO 15212-1 standard, of 1.2500 to 1.3200, preferably 1.2521 to 1.2778, more preferably 1.2582 to 1.2684.

[0037] It has also surprisingly been found that the aqueous suspension of the invention is particularly stable if it has a calcium hydroxide content of 13 to 20% by weight in the form of suspended nanoparticles and if it has a density of 1.3201 to 1.4500, measured according to the DIN EN ISO 15212-1 standard.

[0038] It has also surprisingly been found that the aqueous suspension of the invention is particularly stable if it has a calcium hydroxide content of 21-30% by weight in the form of suspended nanoparticles and if it has a density of 1.4501-1.5500, measured according to the DIN EN ISO 15212-1 standard.

[0039] It has also surprisingly been found that the aqueous suspension of the invention is particularly stable if it has a calcium hydroxide content of 31-40% by weight in the form of suspended nanoparticles and if it has a density of 1.5501-1.7500, measured according to the DIN EN ISO 15212-1 standard.

[0040] It has also surprisingly been found that the aqueous suspension of the invention is particularly stable if it has a calcium hydroxide content of 41 to 65% by weight in the form of suspended nanoparticles and if it has a density of 1.7501 to 2.0000, measured according to the DIN EN ISO 15212-1 standard.

[0041] According to an embodiment, the at least one salt of an alkali metal or alkaline earth metal is present in a molar ratio of 1 to 3, preferably 1.8 to 2.1, relative to the calcium hydroxide.

[0042] Particularly suitable aqueous suspensions comprise (in each case based on the total weight of the aqueous composition): a) 8-15% by weight of calcium hydroxide in the form of suspended nanoparticles; b) 0.8 to 5 wt. % of at least one organic polymer as described above, preferably a comb polymer; c) 20 to 33% by weight of at least one salt of an alkali metal or alkaline earth metal, preferably at least one of hydroxide, nitrate, nitrite, phosphate, phosphite, sulfate, thiocyanate, carbonate, bicarbonate, silicate, aluminate, formate, acetate, lactate, citrate, tartrate, and / or gluconate of an alkali metal or alkaline earth metal; and d) The remaining amount of water It consists of:

[0043] Preferably, the aqueous suspension of the invention contains less than 0.1% by weight, preferably less than 0.01% by weight, of methanol, ethanol, n-propanol, isopropanol, n-butanol, glycols such as ethylene glycol, glycerol, ketones, and / or sugar alcohols such as xylitol, sorbitol, and erythritol, relative to the total weight of the suspension. Such alcohols have a retarding effect on the setting of mineral binder compositions, in particular cementitious compositions, and are therefore less desirable in set accelerators.

[0044] Therefore, the present invention also provides a method for producing a method for manufacturing a semiconductor device comprising: a) 5 to 65% by weight of calcium hydroxide in the form of suspended nanoparticles, relative to the total weight of the aqueous suspension; b) optionally at least one organic compound for stabilizing the aqueous suspension against settling; This refers to the use of at least one salt of an alkali metal or alkaline earth metal to increase the density of an aqueous suspension, including

[0045] The at least one salt of an alkali metal or alkaline earth metal is preferably as described above.

[0046] A further aspect of the present invention is a method for producing the aqueous suspension described above.

[0047] The aqueous suspension is preferably produced by reacting an alkali metal hydroxide with a water-soluble calcium salt. More particularly, the water-soluble calcium salt is selected from the group consisting of calcium nitrate, calcium chloride, calcium acetate, calcium formate, calcium thiocyanate, and mixtures thereof. For certain applications, it is advantageous if the water-soluble calcium salt is not a chloride salt. Chlorides promote corrosion of, for example, reinforcing steel in concrete. The alkali metal hydroxide is preferably sodium hydroxide or potassium hydroxide.

[0048] According to an embodiment, during the reaction, the molar ratio of calcium salt to alkali metal hydroxide is 0.41-0.55, preferably 0.50-0.53.

[0049] According to an embodiment, the at least one organic compound for stabilizing the aqueous suspension against settling is present during the reaction or added after the reaction, in particular during the reaction.

[0050] Preferably, the reaction is carried out in water or in a mixture of water and a water-miscible solvent such as an alcohol, most preferably in pure water. Alcohols, especially methanol, ethanol, or 2-propanol, are flammable liquids, and therefore require explosion-proof equipment when producing the suspension, which increases costs. Organic solvents, especially alcohols, glycols, or ketones, can slow down or even prevent the setting of the cementitious binder, and are therefore less preferred. Particularly preferably, the aqueous suspension does not contain organic solvents, especially alcohols, glycols, more particularly ethylene glycol or propylene glycol, or ketones.

[0051] Preferably, a water-soluble calcium salt is reacted with an alkali metal hydroxide in water containing dissolved CO2.

[0052] In some embodiments, the reaction is carried out under an inert gas or in a CO2-depleted atmosphere, which reduces the formation of calcium carbonate.

[0053] In one aspect, the present invention relates to a method of producing an aqueous suspension, said method comprising the steps of: a) providing an aqueous solution A comprising a water-soluble calcium salt, preferably calcium nitrate, calcium chloride, calcium acetate, calcium formate, calcium thiocyanate or mixtures thereof; b) providing an aqueous solution B comprising an alkali metal hydroxide, preferably sodium hydroxide, potassium hydroxide, or a mixture thereof; c) rapidly and vigorously mixing solution A and solution B to obtain an aqueous suspension; Including, Further steps: d) dissolving at least one salt of an alkali metal or alkaline earth metal in the aqueous solution A, the aqueous solution B, and / or the aqueous suspension obtained in step c).

[0054] In particular, the aqueous suspension obtained in step c) has a density D1, into which at least one salt of an alkali metal or alkaline earth metal is dissolved in step d) in an amount effective to increase the density of the aqueous suspension to a density D2 (D2>D1).

[0055] The method of producing the aqueous suspension of the present invention comprises the steps of: a) providing an aqueous solution A comprising a water-soluble calcium salt, preferably calcium nitrate, calcium chloride, calcium acetate, calcium formate, calcium thiocyanate or mixtures thereof; b) providing an aqueous solution B comprising an alkali metal hydroxide, preferably sodium hydroxide, potassium hydroxide, or a mixture thereof; c) rapidly and vigorously mixing solution A and solution B to obtain an aqueous suspension of density D1; Including, The method further comprises the steps of: d) dissolving at least one salt of an alkali metal or alkaline earth metal in the aqueous suspension obtained in step c) in an amount effective to increase the density of the aqueous suspension to a density D2 higher than density D1; Particularly preferably, the at least one salt of an alkali metal or alkaline earth metal is selected from the group consisting of alkali metal or alkaline earth metal hydroxides, nitrates, nitrites, thiocyanates, carbonates, bicarbonates, silicates, aluminates, formates, citrates, tartrates and / or gluconates, in particular sodium nitrate, sodium nitrite, sodium thiocyanate, sodium carbonate, lithium carbonate, sodium bicarbonate, sodium silicate, sodium formate and / or calcium silicate hydrate.

[0056] According to an embodiment, the water-soluble calcium salt and alkali metal hydroxide are present in step c) in a molar ratio of water-soluble calcium salt to alkali metal hydroxide of 0.41 to 0.55, preferably 0.50 to 0.53.

[0057] According to an embodiment, solution A has a content of calcium salts of at least 5% by weight, preferably at least 15% by weight, more preferably at least 20% by weight, and solution B has a content of alkali metal hydroxides of at least 5% by weight, preferably at least 10% by weight, more preferably at least 18% by weight.

[0058] The calcium salt present in solution A is preferably calcium nitrate, more particularly calcium nitrate tetrahydrate, which has particularly high water solubility and is advantageous for the reaction.

[0059] Solution B preferably contains sodium hydroxide.

[0060] In the method of the present invention, it is particularly preferred that at least one salt of an alkali metal or alkaline earth metal is dissolved in the aqueous suspension in an amount effective to adjust the density of the aqueous suspension to a value between 1.2500 and 1.3200, preferably between 1.2521 and 1.2778, and more preferably between 1.2582 and 1.2684, as measured according to the DIN EN ISO 15212-1 standard. Thus, in particular, the density D2 of the aqueous suspension is between 1.2500 and 1.3200, preferably between 1.2521 and 1.2778, and more preferably between 1.2582 and 1.2684, as measured according to the DIN EN ISO 15212-1 standard. Density D1 is lower than density D2. For example, the difference between D2 and D1 can be as little as 0.0001. However, the difference between D2 and D1 can also be greater than 0.0001, provided that it is always a positive value.

[0061] According to an embodiment, in the process of the invention, the at least one salt of an alkali metal or alkaline earth metal is present in a molar ratio relative to calcium hydroxide of between 0.01 and 2.5, preferably between 0.1 and 2.2.

[0062] Preferably, solution A and solution B are metered very rapidly, advantageously under pressure, preferably by means of a pump, into the continuous reactor. Upon introduction into the reactor, the high pressure and the high viscosity of the resulting solutions cause a vigorous swirling of the two solutions, thus resulting in rapid and intensive mixing.

[0063] "Pressure" within the context of the present invention means the pressure difference relative to the surrounding external air pressure. Thus, positive pressure represents an increase in pressure relative to the ambient air pressure.

[0064] According to an embodiment, in step c) of the process of the present invention, the two aqueous solutions A and B are metered separately into a continuous reactor under pressure, preferably under a pressure of at least 5 bar, the pressure in said continuous reactor being less than 90%, preferably less than 50%, more preferably less than 10%, in particular less than 1% of the pressure of the aqueous solutions A and B during metering, and the residence time of the materials in the continuous reactor being less than 1 minute, preferably less than 30 seconds, more preferably less than 10 seconds, in particular less than 1 second.

[0065] The continuous reactor is preferably not itself under pressure or has a pressure of 0.5 bar or less in the reaction compartment.

[0066] In a preferred embodiment, in the process of the invention, solution A and solution B are metered simultaneously into a reaction vessel or a continuous reactor. The manner in which the solutions are metered is preferably such that the molar ratio of calcium salt to alkali metal hydroxide is between 0.41 and 0.55, preferably between 0.50 and 0.53, throughout the metering period.

[0067] In particular, the mixing energy with which solution A and solution B are mixed is less than or equal to 200 kJ, preferably less than or equal to 150 kJ, in particular less than or equal to 100 kJ, in particular less than 70 kJ per kilogram of calcium hydroxide suspension produced.

[0068] The continuous reactor is preferably a tubular reactor, in which static and / or dynamic mixing elements may also be present.

[0069] The method of the present invention is simple and rapid, and results in calcium hydroxide nanoparticles with a narrow particle size distribution.

[0070] If present, the at least one organic compound which stabilizes the suspension against settling is preferably present in solution A and / or solution B, particularly preferably completely in solution A. Preferred organic compounds for stabilizing the suspension against settling are as described above.

[0071] According to an embodiment, the method of the present invention may further comprise a step of increasing the solids content of the aqueous suspension, in particular a step of removing water, for example by evaporation.

[0072] According to an embodiment, the method of the present invention may further comprise the step of removing auxiliary agents or by-products from the aqueous suspension, which may be carried out in particular by ion exchange, filtration or ultrafiltration.

[0073] The method of the present invention may further comprise the step of ejecting the resulting aqueous suspension.

[0074] In another aspect, the present invention relates to the use of an aqueous suspension as described above, or an aqueous suspension produced by a method as described above, as an accelerator for mineral binder compositions, in particular for mortar or concrete.

[0075] In particular, the present invention provides a) 5 to 65% by weight of calcium hydroxide in the form of suspended nanoparticles, relative to the total weight of the aqueous suspension; b) optionally at least one organic compound for stabilizing the aqueous suspension; 1. The method of claim 1, further comprising the step of: increasing the density of an aqueous suspension comprising at least one salt of an alkali metal or alkaline earth metal, preferably selected from the group consisting of hydroxides, nitrates, nitrites, thiocyanates, carbonates, bicarbonates, silicates, aluminates, formates, citrates, gluconates, and / or tartrates of alkali metals or alkaline earth metals, in particular selected from sodium nitrate, sodium nitrite, sodium thiocyanate, sodium carbonate, lithium carbonate, sodium bicarbonate, sodium silicate, sodium formate, and / or calcium silicate hydrate, for increasing the density of an aqueous suspension comprising

[0076] All the embodiments and preferred features described above also apply to this aspect.

[0077] Preferably, the at least one salt of an alkali metal or alkaline earth metal is used in a molar ratio of 1 to 3, preferably 1.8 to 2.1, relative to the calcium hydroxide nanoparticles.

[0078] Preferably, the at least one organic compound for stabilizing the suspension is a comb polymer and comprises a structural unit of formula I and a structural unit of formula II: [ka] Including, In the above formula, R 1 are in each case independently of one another -COOM, -SO2-OM, -O-PO(OM)2, -PO(OM)2, -(CO)-NH-C(CH3)2-CH2-SO3M, -CH2-SO3M, [ka] and R 2 are, in each occurrence independently of one another, H, —CHCOOM or an alkyl group having 1 to 5 carbon atoms, R 3 , R 5 and R6 are, in each occurrence independently of one another, H or an alkyl group having 1 to 5 carbon atoms, R 4 and R 7 are, in each occurrence independently of one another, H, —COOM or an alkyl group having 1 to 5 carbon atoms, M are independently H + , an alkali metal ion or an alkaline earth metal ion; m is 0, 1 or 2; p is 0 or 1; X, in each occurrence, independently of one another, is —O—, NH— or —NR 8 - and R 8 is the formula -[AO] n -R a is the basis of In the above formula, A=C2-C4 alkylene, and R a is H or C1~C 20 is an alkyl, cyclohexyl, or alkylaryl group; n is 1 to 250.

[0079] Preferably, the at least one organic compound for stabilizing the suspension is present in an amount of 5 to 40 parts by weight, preferably 8 to 35 parts by weight, more preferably 10 to 32 parts by weight, and even more particularly 11 to 30 parts by weight, per 100 parts by weight of calcium hydroxide.

[0080] Preferably, the calcium hydroxide nanoparticles have a particle size of less than 950 nm, preferably between 10 and 800 nm, more preferably between 20 and 500 nm, most preferably between 30 and 400 nm, also more preferably between 40 and 300 nm, and especially between 50 and 200 nm, and / or a D90 of less than 800 nm, preferably less than 600 nm, more preferably less than 400 nm, and especially less than 200 nm, measured by dynamic light scattering using photon cross-correlation spectroscopy according to the ISO 22412:2017 standard.

[0081] The aqueous suspension is preferably used to accelerate the setting of the mineral binder composition, in particular the cementitious composition. The mineral binder composition may further comprise aggregate.

[0082] The mineral binder composition is preferably a mortar or concrete.

[0083] The aqueous suspensions of the present invention are eminently suitable for accelerating the setting of mineral binders, especially cement, so that the highly desired high strengths are rapidly achieved.

[0084] The aqueous suspension of the present invention is a suitable accelerator for all common cements, in particular the following cements classified under DIN EN 197-1: Portland cement (CEM I), Portland composite cement (CEM I), blast furnace slag cement (CEM III), pozzolanic cement (CEM IV) and composite cement (CEM V), as well as for special cements such as calcium aluminate cement or calcium sulfoaluminate cement. The aqueous suspension of the present invention is of course also a suitable accelerator for cements produced according to alternative standards, such as ASTM or JIS standards.

[0085] According to an embodiment, the aqueous suspension of the invention is metered to the mineral binder composition in an amount such that the content of calcium hydroxide particles is between 0.05 and 6% by weight, preferably between 0.1 and 5% by weight, more preferably between 0.2 and 4% by weight, relative to the weight of the mineral binder.

[0086] The aqueous suspensions of the present invention shorten the curing period and also accelerate the hydration reaction itself. The curing period is the time between mixing water and cement and the onset of the exothermic hydration reaction, also known as setting. This is particularly important for applications at relatively low temperatures, especially below 20°C or below 15°C, since at low temperatures the curing period is prolonged and the hydration reaction of the cement is significantly slower.

[0087] As a result of this acceleration, surprisingly, the good workability of the cementitious composition is not affected, nor is the slump life reduced. This means that a mortar or concrete mixture containing the aqueous suspension of the present invention has a slump equivalent both immediately and after 60 or 90 minutes to a concrete or mortar mixture without the aqueous suspension and having the same w / c, where w / c denotes the weight ratio of water to cement.

[0088] The cementitious composition preferably further comprises at least one additive, for example as a concrete and / or mortar admixture, the at least one additive preferably being selected from an antifoaming agent, a wetting agent, a dye, a preservative, a plasticizer, a set retarder, another accelerator, a polymer, an air entraining agent, a rheology aid, a viscosity modifier, a pumping aid, a shrinkage reducing agent, a corrosion inhibitor or a fiber, or a combination thereof.

[0089] Such admixtures are known to those skilled in the art.

[0090] The aqueous suspension of the present invention is preferably added to a mineral binder composition, in particular a cementitious composition, together with or after the mixing water.

[0091] The suspension is preferably thoroughly mixed with the composition in a suitable mixing vessel equipped with a mechanical mixer for at least 20 seconds.

[0092] This ensures a uniform distribution of the calcium hydroxide particles in the mixture and a good, uniform action as an accelerator.

[0093] A further subject of the present invention is a mineral binder composition, in particular a cementitious binder composition, comprising the aqueous suspension of the present invention.

[0094] A further subject of the invention relates to shaped articles obtainable by hardening a mineral binder composition, in particular a cementitious binder composition as described above.

[0095] The moulded article is preferably an edifice or part of an edifice, which may be, for example, a bridge, a building, a tunnel, a roadway or a runway.

[0096] Further advantageous embodiments of the invention are evident from the following working examples. [Example]

[0097] Nanophox particle size The particle size of calcium hydroxide nanoparticles in aqueous suspension was determined by dynamic light scattering using photon cross-correlation spectroscopy. The instrument used for the measurements was a Nanophox commercially available from Sympatec GmbH (Germany). The aqueous suspensions were analyzed without further dilution. Before the measurements, the samples were homogenized with an ultrasonic probe for 1 min.

[0098] Turbidity 50 ml each of the fresh and thoroughly stirred suspensions was introduced into Falcon® centrifuge tubes (50 ml) with screw caps and centrifuged at 8000 rpm and 23°C for 15 minutes in a centrifuge (Heraeus® Biofuge Primo®, available from Thermo Scientific®) with a rotor at a fixed 45° angle. The top 40 ml was then removed from the centrifuge tubes. The turbidity of these 40 ml was determined nephelometrically in accordance with US EPA 180.1. The equipment used for these purposes was a HACH® 2100AN turbidimeter, available from HACHR® (Germany), with a tungsten light source and NTU units (nephelometric turbidity units).

[0099] Storage stability Storage stability was determined visually. Therefore, 50 ml samples of the aqueous suspension were stored at 23°C in sealed transparent sample tubes with volumetric gradation. After a predefined time from production, the sediment volume was determined. Less sediment is a sign of improved storage stability.

[0100] density The density was determined according to DIN EN ISO 15212-1.

[0101] Preparation of an aqueous suspension of calcium hydroxide A first solution was prepared by dissolving 174.4 g of Ca(NO3)2·4H2O (0.739 mol) and 10 g of comb polymer (copolymer of acrylic acid and polyethylene glycol methacrylate; polyethylene glycol Mw: 5000 g / mol) in 82 g of water. A second solution was prepared by dissolving 59.1 g of NaOH (1.478 mol) in 220 g of water. The first solution was placed in a 1-liter round-bottom flask. Under vigorous stirring using a propeller stirrer, the second solution was added via a dropping funnel over a period of 5 minutes. The resulting suspension was stirred for an additional 60 minutes. The resulting suspension S1 had a Ca(OH)2 content of 10 wt.% in the form of nanoparticles. The turbidity, measured as described above, was 227 NTU. The particle size D50, measured as described above, was 163 nm. The density, measured as described above, was 1.2521.

[0102] Suspension S1 was purified by ultrafiltration using a polyethersulfone membrane with a size exclusion limit of 30 kDa. In this procedure, NaNO was removed and the suspension was concentrated. The suspension was then diluted with purified water to a Ca(OH) content of 10 wt. % in the form of nanoparticles, resulting in suspension S2.

[0103] The types and amounts of alkali metal salts shown in Table 1 below were added to suspension S2. Table 2 below shows the storage stability of the aqueous suspensions thus obtained.

[0104] [Table 1]

[0105] [Table 2]

[0106] It can be seen from the above results that the storage stability of the aqueous suspension increases within a specific molar ratio of the alkali metal salt to calcium hydroxide in the aqueous suspension and / or within a specific density range of the resulting aqueous suspension. If the molar ratio of the alkali metal salt to calcium hydroxide in the aqueous suspension is too low or too high, and / or if the density range of the resulting aqueous suspension is too low or too high, the storage stability decreases.

Claims

1. An aqueous suspension comprising: a) 5 to 65% by weight of calcium hydroxide in the form of suspended nanoparticles, relative to the total weight of the aqueous suspension; b) optionally at least one organic compound for stabilizing the aqueous suspension against settling, and c) an aqueous suspension comprising at least one salt of an alkali metal or alkaline earth metal, preferably at least one of alkali metal or alkaline earth metal hydroxides, nitrates, nitrites, phosphates, phosphites, sulfates, thiocyanates, carbonates, bicarbonates, silicates, aluminates, formates, acetates, lactates, citrates, tartrates, and / or gluconates, in particular at least one salt selected from sodium nitrate, sodium nitrite, sodium thiocyanate, lithium carbonate, sodium carbonate, sodium bicarbonate, sodium silicate, potassium silicate, sodium formate, sodium acetate, sodium lactate, sodium citrate, sodium tartrate, sodium gluconate, and / or calcium silicate hydrate.

2. 2. Aqueous composition according to claim 1, characterized in that it has a calcium hydroxide content of 8 to 12% by weight in the form of suspended nanoparticles and a density measured according to the DIN EN ISO 15212-1 standard of 1.2500 to 1.3200, preferably 1.2521 to 1.2778, more preferably 1.2582 to 1.2684.

3. 2. Aqueous composition according to claim 1, characterized in that it has a calcium hydroxide content of 13 to 20% by weight in the form of suspended nanoparticles and a density measured according to the DIN EN ISO 15212-1 standard of 1.3201 to 1.4500.

4. 2. Aqueous composition according to claim 1, characterized in that it has a calcium hydroxide content of 21 to 30% by weight in the form of suspended nanoparticles and a density of 1.4501 to 1.5500, measured according to the DIN EN ISO 15212-1 standard.

5. 2. Aqueous composition according to claim 1, characterized in that it has a calcium hydroxide content of 31 to 40% by weight in the form of suspended nanoparticles and a density of 1.5501 to 1.7500, measured according to the DIN EN ISO 15212-1 standard.

6. 6. Aqueous suspension according to any one of claims 1 to 5, characterized in that the calcium hydroxide nanoparticles have a particle size of less than 950 nm, preferably between 10 and 800 nm, more preferably between 20 and 500 nm, most preferably between 30 and 400 nm, also more preferably between 40 and 300 nm, in particular between 50 and 200 nm, and / or a D90 of less than 800 nm, preferably less than 600 nm, more preferably less than 400 nm, in particular less than 200 nm, measured by dynamic light scattering using photon cross-correlation spectroscopy according to the ISO 22412:2017 standard.

7. 7. Aqueous suspension according to any one of claims 1 to 6, characterized in that the at least one salt of an alkali metal or alkaline earth metal is present in a molar ratio relative to the calcium hydroxide of from 1 to 3, preferably from 1.8 to 2.

1.

8. The at least one organic compound for stabilizing the suspension against settling is a comb polymer and comprises structural units of formula I and structural units of formula II: 【Chemistry 1】 Including, In the above formula, R １ are, in each case independently of one another, -COOM, -SO ２ -OM, -O-PO(OM) ２ , -PO(OM) ２ , -(CO)-NH-C(CH ３ ) ２ -CH ２ -SO ３ M, -CH ２ -SO ３ M. 【Chemistry 2】 and R ２ are, in each case independently of one another, H, —CH ２ COOM or an alkyl group having 1 to 5 carbon atoms, R ３ , R ５ and R ６ are, in each occurrence independently of one another, H or an alkyl group having 1 to 5 carbon atoms, R ４ and R ７ are, in each occurrence independently of one another, H, —COOM or an alkyl group having 1 to 5 carbon atoms, M are, independently of each other, H ＋ , an alkali metal ion or an alkaline earth metal ion; m is 0, 1 or 2; p is 0 or 1; X, in each occurrence, independently of one another, is —O—, NH— or —NR ８ - and R ８ is represented by the formula -[AO] ｎ -R ａ is the basis of In the above formula, A = C ２ ~C ４ alkylene, and R ａ is H or C １ ~C ２０ is an alkyl, cyclohexyl, or alkylaryl group; 8. Aqueous suspension according to any one of claims 1 to 7, characterized in that n is between 1 and 250.

9. 1. A method for producing an aqueous suspension, comprising the steps of: a) providing an aqueous solution A comprising a water-soluble calcium salt, preferably calcium nitrate, calcium chloride, calcium acetate, calcium formate, calcium thiocyanate or mixtures thereof; b) providing an aqueous solution B comprising an alkali metal hydroxide, preferably sodium hydroxide, potassium hydroxide, or a mixture thereof; c) rapidly and vigorously mixing solution A and solution B to obtain an aqueous suspension; Including, Further steps of: d) dissolving at least one salt of an alkali metal or alkaline earth metal in said aqueous solution A, said aqueous solution B, and / or said aqueous suspension obtained in step c).

10. 10. The method according to claim 9, characterized in that the at least one salt of an alkali metal or alkaline earth metal is dissolved in the aqueous suspension in an amount effective to adjust the density of the aqueous suspension to a value of 1.2500 to 1.3200, preferably 1.2521 to 1.2778, more preferably 1.2582 to 1.2684, measured according to the DIN EN ISO 15212-1 standard.

11. 11. The method according to claim 9 or 10, characterized in that the water-soluble calcium salt and the alkali metal hydroxide are present in step c) in a molar ratio of alkali metal hydroxide to water-soluble calcium salt of 0.41 to 0.55, preferably 0.50 to 0.

53.

12. 12. The method according to any one of claims 9 to 11, characterized in that in step c) the two aqueous solutions A and B are metered separately into a continuous reactor under pressure, preferably under a pressure of at least 5 bar, and the pressure in the continuous reactor is less than 90%, preferably less than 50%, more preferably less than 10%, in particular less than 1% of the pressure of the aqueous solutions A and B during metering, and the residence time of the materials in the continuous reactor is less than 1 minute, preferably less than 30 seconds, more preferably less than 10 seconds, in particular less than 1 second.

13. 13. The method according to any one of claims 9 to 12, characterized in that the salt of an alkali metal or alkaline earth metal is selected from the group consisting of alkali metal or alkaline earth metal hydroxides, nitrates, nitrites, thiocyanates, carbonates, bicarbonates, silicates, aluminates, formates, citrates, tartrates and / or gluconates, in particular selected from sodium nitrate, sodium nitrite, sodium thiocyanate, sodium carbonate, lithium carbonate, sodium bicarbonate, sodium silicate, sodium formate and / or calcium silicate hydrate.

14. Use of an aqueous suspension according to any one of claims 1 to 8 or an aqueous suspension produced by the method according to any one of claims 9 to 13 as an accelerator for a mineral binder composition, in particular for mortar or concrete.

15. An aqueous suspension comprising: a) 5 to 65% by weight of calcium hydroxide in the form of suspended nanoparticles, relative to the total weight of the aqueous suspension; b) optionally at least one organic compound for stabilizing said aqueous suspension against settling; 1. Use of at least one salt of an alkali metal or alkaline earth metal, preferably selected from the group consisting of alkali metal or alkaline earth metal hydroxides, nitrates, nitrites, thiocyanates, carbonates, bicarbonates, silicates, aluminates, formates, citrates, gluconates, and / or tartrates, in particular selected from sodium nitrate, sodium nitrite, sodium thiocyanate, sodium carbonate, lithium carbonate, sodium bicarbonate, sodium silicate, sodium formate, and / or calcium silicate hydrate, for increasing the density of an aqueous suspension comprising

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