Aqueous suspension of calcium hydroxide nanoparticles with improved storage stability, preparation and use thereof

Abstract

The present invention relates to aqueous suspensions, their preparation and use as accelerators for mineral binders, comprising: a) 5-65% by weight, relative to the total weight of the aqueous suspension, of calcium hydroxide in the form of suspended nanoparticles, b) optionally at least one organic compound for stabilizing the aqueous suspension against precipitation, c) optionally at least one inorganic compound for stabilizing the aqueous suspension against precipitation, and d) optionally at least one inorganic compound for stabilizing the aqueous suspension against precipitation. And c) at least one alkali metal or alkaline earth metal salt, 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.

Description

Technical Field

[0001] The invention relates to an aqueous suspension of calcium hydroxide nanoparticles, a method for preparing the same and the use of the suspension as an accelerator for a mineral binder composition. Background of the Invention

[0003] Cement is a mineral binder used primarily in concrete and mortar. When cement is mixed with water, it sets and hardens in a chemical process called cement hydration. The cement hydrate thus formed acts as a binder for aggregates (usually sand, gravel and stone) in concrete and mortar to form a solid material. Mortar or concrete has many applications where rapid setting and hardening and therefore rapid development of strength is very important.

[0004] There are various methods to accelerate the setting and / or hardening of cement. An increase in temperature accelerates setting and is used, for example, in the production of precast concrete elements. Heating is particularly difficult or even impossible at outdoor construction sites.

[0005] Another possible way to accelerate cement hydration is to add water-soluble salts, such as calcium chloride, calcium nitrite or sodium nitrite and / or amines, such as hydroxyalkylamines. Water-soluble accelerators of the prior art generally have the disadvantage that the mortar or concrete mixes accelerated with them undergo rapid hardening and therefore rapidly lose workability.

[0006] Another known method of accelerating the setting of cement is to add fine inorganic powders. However, the handling of powders is usually dusty, especially if the powder is very fine. Alkaline calcium hydroxide powder is prone to damage to the eyes, airways and skin of those who use it.

[0007] Therefore, WO2019 / 180191 discloses aqueous suspensions of calcium hydroxide nanoparticles, which are effective as promoters for mineral binder compositions. These aqueous suspensions can solve many problems of other known mineral binder promoters. However, the aqueous suspensions disclosed therein sometimes have limited storage stability and the calcium hydroxide nanoparticles tend to precipitate.

[0008] Therefore, there is a need to further improve the storage stability of aqueous suspensions of calcium hydroxide nanoparticles. SUMMARY OF THE INVENTION

[0010] An object of the present invention is to provide an aqueous suspension of calcium hydroxide nanoparticles which exhibits less precipitation and therefore has, in particular, improved storage stability. Improved storage stability means that they can be stored for an extended period of time without separation, in particular without precipitation of calcium hydroxide. Another object of the present invention is to provide a method for preparing an aqueous suspension of calcium hydroxide nanoparticles having improved storage stability.

[0011] Surprisingly, it has been found that the addition of an alkali metal salt or alkaline earth metal salt to an aqueous suspension of calcium hydroxide improves storage stability. It is believed that the addition of an alkali metal salt or alkaline earth metal salt results in the adjustment of the density of the aqueous suspension of calcium hydroxide, thereby allowing the resulting suspension to be stored for days or months without significant phase separation.

[0012] These and other objects of the invention are therefore solved by the subject-matter of the independent claims.

[0013] Preferred embodiments of the invention are subject matter of the dependent claims.

[0014] Mode for Carrying Out the Invention

[0015] In a first aspect, the present invention relates to an aqueous suspension comprising:

[0016] a) 5-65 w % of calcium hydroxide in the form of suspended nanoparticles, relative to the total weight of the aqueous suspension,

[0017] b) optionally at least one organic compound for stabilizing the aqueous suspension against precipitation, and

[0018] c) at least one salt of an alkali metal or alkaline earth metal, preferably at least one of a hydroxide, nitrate, nitrite, phosphate, phosphite, sulfate, thiocyanate, carbonate, bicarbonate, silicate, aluminate, format, acetate, lactate, citrate, tartrate and / or gluconate of an alkali metal or alkaline earth metal.

[0019] "Aqueous suspension" herein is a suspension of particles in a continuous liquid phase, which contains water or consists essentially of water. Specifically, for example, the continuous liquid phase does not contain other solvents, such as alcohols, glycols or ketones, besides water. The liquid phase may contain a surfactant.

[0020] "Nanoparticles" are particles with a particle size in the nanometer range. These ultrafine particles are distinguished by a very high specific surface area and therefore specific properties. "Nanoparticles" in this context are particles with a particle size of less than 1 μm. The particle size of nanoparticles in suspension can be measured by dynamic light scattering with photon cross-correlation spectroscopy according to standard ISO 22412:2017.

[0021] In this context, the average particle size corresponds in particular to the D50 value (50% of the particles are smaller than a specified value, 50% are correspondingly larger than this value). Thus, the value "D10" indicates the particle size at which 10% of the particles are smaller than this value. The value "D90" indicates the particle size at which 90% of the particles are smaller than this value.

[0022] According to an embodiment, the aqueous suspension of the invention is characterized in that the calcium hydroxide nanoparticles have a particle size below 950 nm, preferably between 10 and 800 nm, more preferably between 20 and 500 nm, most preferably between 30 and 400 nm, still more preferably between 40 and 300 nm, in particular between 50 and 200 nm, and / or have a D90 below 800 nm, preferably below 600 nm, more preferably below 400 nm, in particular below 200 nm, measured by dynamic light scattering with photon cross-correlation spectroscopy according to standard ISO 22412:2017.

[0023] For the purposes of the present invention, the particle size of the calcium hydroxide particles was determined using a Nanophox instrument from Sympatec, Germany. In this case, the particle size was determined by dynamic light scattering with photon cross-correlation spectroscopy.

[0024] The suspension comprising calcium hydroxide particles having a particle size as defined above is particularly storage-stable and very effective in promoting mineral binder compositions, especially cement compositions.

[0025] According to an embodiment, at least 50 w%, preferably at least 66 w%, more preferably at least 90 w%, and especially substantially all of the calcium hydroxide present in the aqueous suspension is in the form of suspended nanoparticles.

[0026] The storage stability of the suspension is preferably determined by centrifugation and measuring the turbidity of the solution, as described in the examples. The more turbid the upper phase after centrifugation, the smaller the number of precipitated particles and the more stable the suspension. The turbidity is advantageously determined with a turbidimeter and reported in NTU. NTU stands for nephelometric turbidity unit. The higher the value, the greater the turbidity of the sample and the more stable the suspension. Advantageously, if its calcium hydroxide content is about 10w%, then after centrifuging 50 mL of the suspension at 8000 rpm for 15 minutes in a 50 mL centrifuge tube and removing the top 40 mL for turbidity measurement, the turbidity of the aqueous suspension is higher than 3000 NTU, preferably higher than 4000 NTU, more preferably higher than 5000 NTU, more particularly higher than 6000 NTU, especially higher than 7000 or higher than 8000 NTU, with Measured by 2100AN turbidity meter.

[0027] The aqueous suspension of the present invention optionally comprises at least one organic compound for stabilizing the suspension against precipitation. It is generally preferred that the aqueous suspension of the present invention comprises at least one organic compound for stabilizing the suspension. The term "stable" herein refers to a lower tendency to precipitate, which in particular results in an increase in storage stability.

[0028] According to an embodiment, the at least one organic compound used to stabilize the suspension against precipitation is an organic polymer comprising carboxylate groups, sulfate groups, sulfonate groups, phosphate groups and / or phosphonate groups.

[0029] The organic polymer preferably also serves as a plasticizer for the mineral binder composition, especially for cementitious compositions. Examples of suitable organic polymers include lignin sulfonates, sulfonated naphthalene-formaldehyde condensates, sulfonated melamine-formaldehyde condensates, sulfonated vinyl copolymers, poly(meth)acrylic acid, copolymers of (meth)acrylic acid with (meth)acrylates or hydroxyalkyl (meth)acrylates, polyalkylene glycols with phosphonate groups, polyalkylene glycols with phosphate groups, comb polymers with anionic groups and polyether side chains, or salts thereof, or mixtures of these polymers.

[0030] The organic polymer is advantageously stable in aqueous suspension. Advantageously, it has no groups, more particularly no side chain bonds, which hydrolyze at high pH, ​​especially at a pH above 12.0.

[0031] The organic polymer is more particularly a comb polymer, which comprises a polymer backbone with polyalkylene oxide side chains and anionic groups bonded to the backbone. The side chains here are bonded to the polycarboxylate backbone in particular via ester, ether, imide and / or amide groups. The comb polymer preferably comprises polyalkylene oxide units, more particularly polyethylene oxide units.

[0032] According to a particularly preferred embodiment, the at least one organic compound used to stabilize the suspension against precipitation is a comb polymer and comprises structural units of the formula I and structural units of the formula II,

[0033]

[0034] in

[0035] R 1 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.

[0036] R 2 in each case independently of one another is H, -CH 2COOM or an alkyl group having 1 to 5 carbon atoms,

[0037] R 3 , R 5 and R 6 in each case independently of one another is H or an alkyl group having 1 to 5 carbon atoms,

[0038] R 4 and R 7 in each case independently of one another is H, -COOM or an alkyl radical having 1 to 5 carbon atoms,

[0039] M represents H independently of each other + , alkali metal ions or alkaline earth metal ions;

[0040] m is 0, 1, or 2,

[0041] p is 0 or 1,

[0042] X is in each case independently of one another -O-, NH- or -NR 8 -,

[0043] R 8 It is -[AO] n -R a The group,

[0044] Where A=C 2 To C 4 Alkylene and R a H or C 1 To C 20 alkyl, cyclohexyl or alkylaryl, and

[0045] n is 1-250.

[0046] Particularly preferred are comb polymers comprising structural units (I) and structural units (II), wherein

[0047] R 1 For-COOM,

[0048] R 2 and R 5 in each case independently of one another is H or CH 3 ,

[0049] R 3 , R 6 and R 7 It is H.

[0050] R 4 in each case independently of one another is H or -COOM,

[0051] M represents H in each case independently of each other+ , alkali metal ions or alkaline earth metal ions;

[0052] m is 0, 1, or 2,

[0053] p is 0 or 1,

[0054] X is in each case independently of one another -O- or -NH-,

[0055] R 8 It is -[AO] n -R a The group,

[0056] Where A=C 2 To C 3 Alkylene, preferably C 2 Alkylene, and R a Is H or C 1 To C 4 Alkyl, and

[0057] n is 10-200, preferably 22-150, more particularly 50-120.

[0058] Advantageously, the comb polymer consists only of structural units (I) and (II). The molar ratio of structural unit (I) to structural unit (II) is preferably 1:1 to 25:1, more preferably 1.5:1 to 23:1, still more preferably 2:1 to 20:1, more particularly 2.3:1 to 18:1.

[0059] However, it is also advantageous if the comb polymer comprises further structural units (III) and the structural units (III) are different from the structural units (I) and (II). The further structural units are preferably selected from alkyl (meth)acrylates, hydroxyalkyl (meth)acrylates, N-vinylpyrrolidone, vinyl esters, styrene, monoamides of maleic acid with p-aminobenzenesulfonic acid or with alkylamines, in particular hydroxyethyl acrylate and hydroxypropyl acrylate.

[0060] The structural unit (III) is advantageously present in the comb polymer in an amount of 0 to 70% by weight, preferably 0.1 to 50% by weight and more particularly 0.5 to 40% by weight.

[0061] In particular, the aqueous suspension of the present invention has lower phase separation, especially less precipitation of calcium hydroxide, without adding a large amount of organic compounds for stabilization. According to an embodiment, based on 100 parts by weight of calcium hydroxide, at least one organic compound for stabilizing the suspension to prevent precipitation is present in 5-40 parts by weight, preferably 8-35 parts by weight, more preferably 10-32 parts by weight, more preferably 11-30 parts by weight.

[0062] According to an embodiment, the at least one alkali metal salt or alkaline earth metal salt is added in an amount which is completely soluble in the aqueous suspension at 23°C and atmospheric pressure or in water at a pH of 12-13 at 23°C and atmospheric pressure.

[0063] The at least one alkali metal or alkaline earth metal salt is preferably at least one of an alkali metal or alkaline earth metal hydroxide, nitrate, nitrite, phosphate, phosphite, sulfate, thiocyanate, carbonate, bicarbonate, silicate, aluminate, formates, acetates, lactates, citrates, tartrates and / or gluconates. Preferably, the at least one alkali metal or alkaline earth metal salt 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 hydrated calcium silicate.

[0064] 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.

[0065] According to an embodiment, the at least one alkali metal or alkaline earth metal salt is preferably at least one of an alkali metal or alkaline earth metal hydroxide, nitrate, nitrite, phosphate, phosphite, sulfate, thiocyanate, carbonate, bicarbonate, silicate, aluminate, format, acetate, lactate, citrate, tartrate and / or gluconate, 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 20-33w%, preferably 21-27w%, relative to the total weight of the aqueous suspension.

[0066] Surprisingly, it has been found that the aqueous suspension according to the invention is particularly stable if it has a calcium hydroxide content in the form of suspended nanoparticles of 8 to 12 w-% and if its density measured in accordance with standard DIN EN ISO 15212-1 is 1.2500 to 1.3200, preferably 1.2521 to 1.2778, more preferably 1.2582 to 1.2684.

[0067] It has likewise surprisingly been found that an aqueous suspension according to the invention is particularly stable if it has a calcium hydroxide content in the form of suspended nanoparticles of 13-20 w % and if it has a density of 1.3201-1.4500 measured in accordance with standard DIN EN ISO 15212-1.

[0068] It has likewise surprisingly been found that an aqueous suspension according to the invention is particularly stable if it has a calcium hydroxide content of 21-30 w-% in the form of suspended nanoparticles and a density of 1.4501-1.5500 measured in accordance with standard DIN EN ISO 15212-1.

[0069] It has likewise surprisingly been found that an aqueous suspension according to the invention is particularly stable if it has a calcium hydroxide content of 31-40 w % in the form of suspended nanoparticles and a density of 1.5501-1.7500 measured in accordance with standard DIN EN ISO 15212-1.

[0070] It has likewise surprisingly been found that an aqueous suspension according to the invention is particularly stable if it has a calcium hydroxide content of 41-65 w-% in the form of suspended nanoparticles and has a density of 1.7501-2.0000 measured in accordance with standard DIN EN ISO 15212-1.

[0071] According to an embodiment, the at least one alkali metal salt or alkaline earth metal salt is present in a molar ratio of 1 to 3, preferably 1.8 to 2.1, relative to the calcium hydroxide.

[0072] Particularly suitable aqueous suspensions consist of (in each case relative to the total weight of the aqueous composition):

[0073] a) 8 to 15 w% of calcium hydroxide in the form of suspended nanoparticles,

[0074] b) 0.8 to 5 wt. % of at least one organic polymer, preferably a comb polymer as described above,

[0075] c) 20 to 33 wt% of at least one alkali metal or alkaline earth metal salt, preferably at least one of an alkali metal or alkaline earth metal hydroxide, nitrate, nitrite, phosphate, phosphite, sulfate, thiocyanate, carbonate, bicarbonate, silicate, aluminate, format, acetate, lactate, citrate, tartrate and / or gluconate, and

[0076] d) Remaining water.

[0077] Preferably, the aqueous suspension of the present invention contains less than 0.1 w%, preferably less than 0.01 w%, of methanol, ethanol, n-propanol, isopropanol, n-butanol, glycols (e.g. ethylene glycol), glycerol, ketones and / or sugar alcohols (e.g. xylitol, sorbitol and erythritol), based on the total weight of the suspension. These alcohols have a retarding effect on the setting of mineral binder compositions, especially cementitious compositions, and are therefore less desirable in accelerators.

[0078] The present invention therefore also relates to the use of at least one alkali metal or alkaline earth metal salt for increasing the density of an aqueous suspension comprising:

[0079] a) 5-65 w % of calcium hydroxide in the form of suspended nanoparticles, relative to the total weight of the aqueous suspension, and

[0080] b) optionally at least one organic compound for stabilizing the aqueous suspension against precipitation.

[0081] The at least one alkali metal or alkaline earth metal salt is preferably as described above.

[0082] Another aspect of the invention is a process for producing an aqueous suspension as described above.

[0083] The aqueous suspension is preferably prepared by reacting a water-soluble calcium salt with an alkali metal hydroxide. More particularly, the water-soluble calcium salt is selected from 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. Chlorides promote corrosion of steel reinforcement in, for example, concrete. The alkali metal hydroxide is preferably sodium hydroxide or potassium hydroxide.

[0084] According to an embodiment, during the reaction, the molar ratio of calcium salt to alkali metal hydroxide is from 0.41 to 0.55, preferably from 0.50 to 0.53.

[0085] According to an embodiment, at least one organic compound for stabilizing the aqueous suspension against precipitation is present during the reaction or is added after the reaction, in particular during the reaction.

[0086] 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 explosion-proof devices are required when preparing the suspension, thus increasing costs. Organic solvents, especially alcohols, glycols or ketones, may also delay or even prevent the setting of cementitious adhesives, and are therefore less preferred. Especially preferably, the aqueous suspension does not contain an organic solvent, especially alcohols, glycols, more particularly ethylene glycol or propylene glycol, or ketones.

[0087] It is preferred to make the water-soluble calcium salt and the alkali metal hydroxide in a solution of CO 2 Reaction in water content.

[0088] In some embodiments, the reaction is carried out under an inert gas or in the absence of CO 2 This reduces the formation of calcium carbonate.

[0089] In one aspect, the present invention relates to a method for producing an aqueous suspension, the method comprising the steps of:

[0090] a) providing an aqueous solution A comprising a water-soluble calcium salt, wherein the water-soluble calcium salt is preferably calcium nitrate, calcium chloride, calcium acetate, calcium formate, calcium thiocyanate or a mixture thereof,

[0091] b) providing an aqueous solution B comprising an alkali metal hydroxide, preferably sodium hydroxide, potassium hydroxide or a mixture thereof,

[0092] c) rapidly and vigorously mixing solution A and solution B to obtain an aqueous suspension,

[0093] Characterized in that the method further comprises the following steps:

[0094] d) dissolving at least one alkali metal or alkaline earth metal salt in aqueous solution A, aqueous solution B and / or the aqueous suspension obtained in step c).

[0095] In particular, the aqueous suspension obtained in step c) has a density D1 and the at least one alkali metal or alkaline earth metal salt is dissolved in step d) in an amount effective to increase the density of the aqueous suspension to a density D2, wherein D2>D1.

[0096] The method for preparing the aqueous suspension of the present invention may comprise the following steps:

[0097] a) providing an aqueous solution A comprising a water-soluble calcium salt, wherein the water-soluble calcium salt is preferably calcium nitrate, calcium chloride, calcium acetate, calcium formate, calcium thiocyanate or a mixture thereof,

[0098] b) providing an aqueous solution B comprising an alkali metal hydroxide, preferably sodium hydroxide, potassium hydroxide or a mixture thereof,

[0099] c) rapidly and vigorously mixing solution A and solution B to obtain an aqueous suspension with a density of D1,

[0100] Characterized in that the method further comprises the following steps:

[0101] d) dissolving at least one alkali metal or alkaline earth metal salt in the aqueous suspension obtained in step c) in an amount effective to increase the density of the aqueous suspension to a density D2 which is higher than the density D1. Particularly preferably, the at least one alkali metal or alkaline earth metal salt is selected from hydroxides, nitrates, nitrites, thiocyanates, carbonates, bicarbonates, silicates, aluminates, formates, citrates, tartrates and / or gluconates of alkali metals or alkaline earth metals, in particular from sodium nitrate, sodium nitrite, sodium thiocyanate, sodium carbonate, lithium carbonate, sodium bicarbonate, sodium silicate, sodium formate and / or calcium silicate hydrate.

[0102] According to an embodiment, the water-soluble calcium salt and the alkali metal hydroxide are present in step c) in a molar ratio of water-soluble calcium salt to alkali metal hydroxide of from 0.41 to 0.55, preferably from 0.50 to 0.53.

[0103] According to an embodiment, solution A has a calcium salt content of at least 5% by weight, preferably at least 15% by weight, more preferably at least 20% by weight, and solution B has an alkali metal hydroxide content of at least 5% by weight, preferably at least 10% by weight, more preferably at least 18% by weight.

[0104] The calcium salt present in solution A is preferably calcium nitrate, more particularly calcium nitrate tetrahydrate. Calcium nitrate tetrahydrate has particularly high water solubility, which is advantageous for the reaction.

[0105] Solution B preferably contains sodium hydroxide.

[0106] Particularly preferably, in the process according to the invention, at least one alkali metal or alkaline earth metal salt 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, more preferably between 1.2582 and 1.2684, measured according to standard DIN EN ISO 15212-1. Thus, in particular, the density D2 of the aqueous suspension, measured according to standard DIN EN ISO 15212-1, is between 1.2500 and 1.3200, preferably between 1.2521 and 1.2778, more preferably between 1.2582 and 1.2684. The density D1 is lower than the density D2. For example, the difference D2 - D1 can be as low as 0.0001. However, the difference D2 - D1 can also be higher than 0.0001, provided that it is always positive.

[0107] According to an embodiment, in the process according to the invention, at least one salt of the alkali metal or alkaline earth metal is present in a molar ratio of from 0.01 to 2.5, preferably from 0.1 to 2.2, relative to the calcium hydroxide.

[0108] Preferably, solution A and solution B are advantageously metered very rapidly into the continuous reactor under pressure, preferably by means of a pump. The high pressure of the solutions and the resulting high speed on introduction into the reactor produce strong vortices of the two solutions and thus rapid and intense mixing.

[0109] The "pressure" herein refers to the pressure difference relative to the ambient external air pressure. Thus, a positive pressure represents a pressure increased relative to the ambient air pressure.

[0110] According to an embodiment, in the process of the present invention, in step c), two aqueous solutions A and B are separately metered into a continuous reactor under pressure, preferably at a pressure of at least 5 bar, wherein the pressure in the continuous reactor is less than 90%, preferably less than 50%, more preferably less than 10%, and especially less than 1% of the pressure of the aqueous solutions A and B during metering, and wherein the residence time of the material in the continuous reactor is less than 1 minute, preferably less than 30 seconds, more preferably less than 10 seconds, and especially less than 1 second.

[0111] The continuous reactor is preferably not itself under pressure or has a pressure in the reaction chamber of not more than 0.5 bar.

[0112] 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 solutions are metered in such a way that the molar ratio of calcium salt to alkali metal hydroxide is preferably 0.41-0.55, preferably 0.50-0.53 during the entire metering period.

[0113] In particular, the mixing energy of solution A and solution B does not exceed 200 kJ, preferably 150 kJ, especially 100 kJ, and in particular less than 70 kJ per kilogram of calcium hydroxide suspension produced.

[0114] The continuous reactor is preferably a tubular reactor. Static and / or dynamic mixing elements may also be present in the reactor.

[0115] The process of the present invention is simple and rapid, and thereby calcium hydroxide nanoparticles having a narrow particle size distribution are obtained.

[0116] The at least one organic compound for stabilizing the suspension against precipitation, if present, is preferably present in solution A and / or solution B, particularly preferably completely in solution A. Preferred organic compounds for stabilizing the suspension against precipitation are as described above.

[0117] According to an embodiment, the method of the 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.

[0118] According to an embodiment, the method of the invention may further comprise a step of removing auxiliaries or by-products from the aqueous suspension. This may be carried out in particular by ion exchange, filtration or ultrafiltration.

[0119] The process of the invention may further comprise the step of draining off the obtained aqueous suspension.

[0120] In another aspect, the present invention relates to the use of an aqueous suspension as described above or an aqueous suspension prepared by a process as described above as an accelerator for a mineral binder composition, in particular a mortar or concrete.

[0121] In particular, the present invention relates to the use of at least one alkali metal or alkaline earth metal salt, 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 the group consisting of sodium nitrate, sodium nitrite, sodium thiocyanate, sodium carbonate, lithium carbonate, sodium bicarbonate, sodium silicate, sodium formate and / or calcium silicate hydrates, for increasing the density of an aqueous suspension comprising:

[0122] a) 5-65 w % of calcium hydroxide in the form of suspended nanoparticles, relative to the total weight of the aqueous suspension, and

[0123] b) optionally at least one organic compound for stabilizing the aqueous suspension.

[0124] All embodiments and preferred features described above also apply to this aspect.

[0125] Preferably, the at least one alkali metal or alkaline earth metal salt is used in a molar ratio of 1 to 3, preferably 1.8 to 2.1, relative to the calcium hydroxide nanoparticles.

[0126] Preferably, the at least one organic compound used to stabilize the suspension is a comb polymer and comprises structural units of the formula I and structural units of the formula II,

[0127]

[0128] in

[0129] R 1 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.

[0130] R 2 in each case independently of one another is H, -CH 2 COOM or an alkyl group having 1 to 5 carbon atoms,

[0131] R 3 , R 5 and R 6in each case independently of one another is H or an alkyl group having 1 to 5 carbon atoms,

[0132] R 4 and R 7 in each case independently of one another is H, -COOM or an alkyl radical having 1 to 5 carbon atoms,

[0133] M represents H independently of each other + , alkali metal ions or alkaline earth metal ions;

[0134] m is 0, 1, or 2,

[0135] p is 0 or 1,

[0136] X is in each case independently of one another -O-, NH- or -NR 8 -,

[0137] R 8 It is -[AO] n -R a The group,

[0138] Where A=C 2 To C 4 Alkylene and R a H or C 1 To C 20 alkyl, cyclohexyl or alkylaryl, and

[0139] n is 1 to 250.

[0140] Preferably, the at least one organic compound for stabilizing the suspension is present in 5 to 40 parts by weight, preferably 8 to 35 parts by weight, more preferably 10 to 32 parts by weight, more particularly 11 to 30 parts by weight, based on 100 parts by weight of calcium hydroxide.

[0141] Preferably, the calcium hydroxide nanoparticles have a particle size of less than 950 nm, preferably from 10 to 800 nm, more preferably from 20 to 500 nm, most preferably from 30 to 400 nm, still more preferably from 40 to 300 nm, especially from 50 to 200 nm, and / or have 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 with photon cross-correlation spectroscopy according to standard ISO 22412:2017.

[0142] The aqueous suspension is preferably used to accelerate the setting of a mineral binder composition, especially a cement composition.The mineral binder composition may also comprise aggregates.

[0143] The mineral binder composition is preferably mortar or concrete.

[0144] The aqueous suspensions of the invention are particularly suitable for accelerating the setting of mineral binders, especially cement, so that high strength is achieved quickly, which is highly desirable.

[0145] The aqueous suspension of the invention is a suitable accelerator for all common cements, in particular the following cements classified according to DIN EN 1971: Portland cement (CEM I), Portland composite cement (CEM I I), blast furnace slag cement (CEM III), pozzolanic cement (CEM IV) and composite cement (CEM V), as well as special cements such as calcium aluminate cement or calcium sulfoaluminate cement. The aqueous suspension of the invention is of course also a suitable accelerator for cements produced according to alternative standards, such as ASTM standards or JIS standards.

[0146] According to an embodiment, the aqueous suspension of the invention is metered into the mineral binder composition in an amount such that the content of calcium hydroxide particles is 0.05 to 6 w %, preferably 0.1 to 5 w %, more preferably 0.2 to 4 w %, based on the weight of the mineral binder.

[0147] The aqueous suspension of the invention shortens the dormant period and also accelerates the hydration reaction itself. The dormant period is the time between mixing cement with water and the start of the exothermic hydration reaction (also called the start of setting). This is particularly important for applications at relatively low temperatures, especially below 20°C or below 15°C, because at low temperatures the dormant period is prolonged and the hydration reaction of the cement is severely slowed down.

[0148] As a result of this acceleration, surprisingly, the good workability of the cementitious composition is not affected and the slump life is not reduced. This means that the mortar or concrete mix comprising the aqueous suspension according to the invention has a comparable slump both immediately and after 60 or 90 minutes as a concrete or mortar mix without the aqueous suspension and with the same w / c. w / c here denotes the weight ratio of water to cement.

[0149] The cementitious composition preferably further comprises at least one additive, such as a concrete admixture and / or a mortar admixture. The at least one additive is preferably selected from a defoamer, a wetting agent, a dye, a preservative, a plasticizer, a retarder, another accelerator, a polymer, an air entraining agent, a rheological additive, a viscosity modifier, a pumping aid, a shrinkage reducing agent, a corrosion inhibitor or a fiber, or a combination thereof.

[0150] Such admixtures are known to those skilled in the art.

[0151] The aqueous suspension according to the invention is preferably added to a mineral binder composition, in particular a cementitious composition, together with or after mixing the water.

[0152] Preferably the suspension is thoroughly mixed with the composition in a suitable mixing container with a mechanical mixer for at least 20 seconds.

[0153] This ensures an even distribution of the calcium hydroxide particles in the mix and a good, uniform effect as an accelerator.

[0154] Another subject of the present invention is a mineral binder composition, in particular a cement binder composition, comprising the aqueous suspension according to the invention.

[0155] Another subject of the present invention relates to shaped articles obtainable by curing a mineral binder composition, in particular a cementitious binder composition, as described above.

[0156] The shaped article is preferably an edifice or part of an edifice, wherein the edifice may be, for example, a bridge, a building, a tunnel, a traffic passage or a runway.

[0157] Further advantageous embodiments of the invention are apparent from the following working examples. Example

[0158] Particle size measured by Nanophox

[0159] The particle size of calcium hydroxide nanoparticles in aqueous suspensions was determined by dynamic light scattering with photon cross-correlation spectroscopy. The instrument used for the measurement was a Nanophox from Sympatec GmbH (Germany). The aqueous suspensions were analyzed without further dilution. Prior to the measurement, the samples were homogenized for 1 minute with an ultrasonic probe.

[0160] Turbidity

[0161] The centrifuge was equipped with a 45° fixed-angle rotor (from Thermo Scientific). TM Heraeus TM In a Biofuge Primo R), 50 ml of each fresh and well-stirred suspension was introduced into a screw-capped The 50 ml was centrifuged at 8000 rpm for 15 minutes at 23°C. The top 40 ml was then taken from the centrifuge tube. The turbidity of these 40 ml was determined by nephelometry according to US EPA 180.1. The instrument used for this purpose was (Germany) 2100AN turbidimeter with tungsten light source and units NTU (nephelometric turbidity units).

[0162] Storage stability

[0163] The storage stability is measured visually. Therefore, 50 ml samples of the aqueous suspension are stored at 23° C. in tightly closed transparent sample tubes with volume grading. The volume of the precipitate is determined after a predetermined time from production. Less precipitate is a sign of improved storage stability.

[0164] density

[0165] The density is measured according to DIN EN ISO 15212-1.

[0166] Preparation of Calcium Hydroxide Aqueous Suspension

[0167] By adding 174.4 g Ca(NO 3 ) 2 ·4H 2 A first solution was prepared by dissolving 10 g of O (0.739 mol) and 10 g of a comb polymer (copolymer of acrylic acid and polyethylene glycol methacrylate; Mw of polyethylene glycol: 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 added to a 1 L round-bottom flask. Under vigorous stirring using a propeller stirrer, the second solution was added via a dropping funnel within 5 minutes. The resulting suspension was stirred for a further 60 minutes. The resulting suspension S1 had 10 wt. % of Ca(OH) in the form of nanoparticles. 2 The turbidity measured as above was 227 NTU. The particle size D50 measured as above was 163 nm. The density measured as above was 1.2521.

[0168] Suspension S1 was purified by ultrafiltration using a polyethersulfone membrane with a size exclusion limit of 30 kDa. In this procedure, NaNO 3 The suspension was then diluted with purified water to a concentration of Ca(OH) 2 The content was 10w%, and suspension S2 was obtained.

[0169] Alkali metal salts of the type and in the amount indicated in the following Table 1 were added to the suspension S2. The following Table 2 shows the storage stability of the aqueous suspensions thus obtained.

[0170] Table 1: Examples 1-9: Composition

[0171] Example Alkali metal salts dose* Molar Ratio** Density [g / ml] 1 Sodium formate 24 2.51 1.2582 2 Sodium formate 25 2.72 1.2634 3 Sodium formate 33 3.59 1.3055 4 Sodium nitrate 23 2.00 1.2521 5 Sodium nitrate 24 2.09 1.2606 6 Sodium nitrate 25 2.18 1.2661 7 Sodium nitrate 27 2.35 1.2778 8 Sodium nitrate 28 2.44 1.2851 9 Sodium nitrate 33 2.88 1.3149

[0172] *w% alkali metal salt / suspension weight

[0173] **Alkali metal salts than calcium hydroxide

[0174] ***Visual phase separation time

[0175] Table 2: Examples 1-9: Storage stability

[0176]

[0177]

[0178] From the above results, it can be seen that within a certain molar ratio of alkali metal salt to calcium hydroxide in the aqueous suspension and / or within a certain density range of the resulting aqueous suspension, the storage stability of the aqueous suspension increases. If the molar ratio of 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) 5-65 w % 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 precipitation, and c) at least one salt of an alkali metal or alkaline earth metal, preferably at least one of an alkali metal or alkaline earth metal hydroxide, nitrate, nitrite, phosphate, phosphite, sulfate, thiocyanate, carbonate, bicarbonate, silicate, aluminate, format, acetate, lactate, citrate, tartrate and / or gluconate, 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 hydrated calcium silicate.

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

3. The aqueous composition according to claim 1, It is characterized in that The aqueous composition has a calcium hydroxide content in the form of suspended nanoparticles of 13-20 w %, and the aqueous composition has a density between 1.3201 and 1.4500 measured according to standard DIN EN ISO 15212-1.

4. The aqueous composition according to claim 1, It is characterized in that The aqueous composition has a calcium hydroxide content in the form of suspended nanoparticles of 21-30 w %, and the aqueous composition has a density measured according to standard DIN EN ISO 15212-1 between 1.4501 and 1.5500.

5. The aqueous composition according to claim 1, It is characterized in that The aqueous composition has a calcium hydroxide content in the form of suspended nanoparticles of 31-40 w %, and the aqueous composition has a density measured according to standard DIN EN ISO 15212-1 between 1.5501 and 1.7500.

6. Aqueous suspension according to at least one of the preceding claims, It is characterized in that The calcium hydroxide nanoparticles have a particle size below 950 nm, preferably from 10 to 800 nm, more preferably from 20 to 500 nm, most preferably from 30 to 400 nm, still more preferably from 40 to 300 nm, especially from 50 to 200 nm, and / or have a D90 below 800 nm, preferably below 600 nm, more preferably below 400 nm, especially below 200 nm, the D90 being measured by dynamic light scattering with photon cross-correlation spectroscopy according to standard ISO 22412:2017.

7. An aqueous suspension according to at least one of the preceding claims, Features The at least one alkali metal salt or alkaline earth metal salt is present in a molar ratio relative to the calcium hydroxide of between 1 and 3, preferably between 1.8 and 2.

1.

8. Aqueous suspension according to at least one of the preceding claims, It is characterized in that The at least one organic compound for stabilizing the suspension against precipitation is a comb polymer and comprises structural units of the formula I and structural units of the formula II, in R 1 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, R 2 in each case independently of one another is H, -CH 2 COOM or an alkyl group having 1 to 5 carbon atoms, R 3 , R 5 and R 6 in each case independently of one another is H or an alkyl group having 1 to 5 carbon atoms, R 4 and R 7 in each case independently of one another is H, -COOM or an alkyl radical having 1 to 5 carbon atoms, M represents H independently of each other + , alkali metal ions or alkaline earth metal ions; m is 0, 1, or 2, p is 0 or 1, X is in each case independently of one another -O-, NH- or -NR 8 -, R 8 It is -[AO] n -R a The group, Where A=C 2 To C 4 Alkylene and R a H or C 1 To C 20 alkyl, cyclohexyl or alkylaryl, and n is 1 to 250.

9. A method for preparing an aqueous suspension, the method comprising the following steps: a) providing an aqueous solution A comprising a water-soluble calcium salt, wherein the water-soluble calcium salt is preferably calcium nitrate, calcium chloride, calcium acetate, calcium formate, calcium thiocyanate or a mixture 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, It is characterized in that The method further comprises the following steps: d) dissolving at least one alkali metal or alkaline earth metal salt in aqueous solution A, aqueous solution B and / or the aqueous suspension obtained in step c).

10. The method according to claim 9, It is characterized in that The at least one alkali metal or alkaline earth metal salt 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, more preferably between 1.2582 and 1.2684, measured according to standard DIN EN ISO 15212-1.

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

53.

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

13. The method according to at least one of claims 9 to 12, It is characterized in that The alkali metal or alkaline earth metal salt 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 hydrated calcium silicate.

14. Use of an aqueous suspension according to at least one of claims 1 to 8 or an aqueous suspension prepared by a process according to at least one of claims 9 to 13 as an accelerator for mineral binder compositions, in particular mortar or concrete.

15. Use of at least one alkali metal or alkaline earth metal salt, preferably selected from 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 hydrated calcium silicate, for increasing the density of an aqueous suspension comprising: a) 5-65 w % of calcium hydroxide in the form of suspended nanoparticles, relative to the total weight of the aqueous suspension, and b) optionally, at least one organic compound for stabilizing the aqueous suspension against precipitation.

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