Production of calcium hydroxide nanoparticles and their use as accelerators in mineral binder compositions

Abstract

An aqueous suspension including 5 to 65 wt. % of calcium hydroxide, wherein at least 50 wt. % of the calcium hydroxide is present in the form of nanoparticles, and at least one compound for stabilizing the suspension. The aqueous suspension accelerates the setting of mineral binder compositions without adversely affecting the processing properties of the composition.

Claims

1. A method for producing an aqueous suspension, comprising: (a) providing an aqueous solution A comprising at least 5 weight % of a water-soluble calcium salt, (b) providing an aqueous solution B comprising at least 5 weight % of an alkali metal hydroxide, (c) metering solution A and solution B simultaneously into a continuous reactor and contacting solution A and solution B such that solution A and solution B are mixed rapidly and intensely to form a suspension, wherein the rapid and intense mixing of the solution A and the solution B takes place continuously and a mixing time is below 1 minute, wherein the solution A and solution B are metered under pressure of at least 5 bar into the continuous reactor by means of pumps, wherein the pressure and a resulting velocity of the solution A and the solution B on introduction into the continuous reactor produces the rapid and intense mixing, and (d) discharging the suspension from the continuous reactor, where a compound for stabilizing the suspension is added to the solution A, to the solution B or to both solutions, or to the suspension produced, wherein the suspension includes calcium hydroxide in the form of nanoparticles having a particle size D90 of below 800 nm, measured by dynamic light scattering with photon cross-correlation spectroscopy, and wherein the suspension is free from calcium silicate hydrate.

2. The method as claimed in claim 1, wherein the compound for stabilizing the suspension is a comb polymer and comprises structural units of formula I and structural units of formula II, ##STR00003## where: R.sup.1, in each case independently of one another, is —COOM, —SO.sub.2—OM, —O—PO(OM).sub.2, —PO(OM).sub.2, —(CO)—NH—C(CH.sub.3).sub.2—CH.sub.2—SO.sub.3M, —CH.sub.2—SO.sub.3M, = ##STR00004## R.sup.2, in each case independently of one another, is H, —CH.sub.2COOM or an alkyl group having 1 to 5 carbon atoms, R.sup.3, R.sup.5 and R.sup.6, in each case independently of one another, are H or an alkyl group having 1 to 5 carbon atoms, R.sup.4 and R.sup.7, in each case independently of one another, are H, —COOM or an alkyl group having 1 to 5 carbon atoms, M, independently of one another, represents H.sup.+, an alkali metal ion or an alkaline earth metal ion; m is 0, 1 or 2, p is 0 or 1, X, in each case independently of one another, is —O—, NH— or —NR.sup.8—, and R.sup.8 is a group of the formula -[AO].sub.n—R.sup.a, where A is a C.sub.2 to C.sub.4 alkylene, R.sup.a is H or a C.sub.1 to C.sub.20 alkyl, cyclohexyl or alkylaryl group, and n is 1 to 250.

3. The method as claimed in claim 1, wherein the suspension comprises 0.01 to 2.5 mol of an alkali metal salt based on 1 mol of calcium hydroxide.

4. The method as claimed in claim 1, wherein the water-soluble calcium salt is selected from the group consisting of calcium nitrate, calcium chloride, calcium acetate, calcium formate, calcium thiocyanate, or a mixture thereof.

5. The method as claimed in claim 1, wherein the water-soluble calcium salt is calcium nitrate.

6. The method as claimed in claim 1, wherein the aqueous solution A contains the calcium salt in an amount within a range of 10 to 87 weight %.

7. The method as claimed in claim 1, wherein the aqueous solution A contains the calcium salt in an amount within a range of 20 to 80 weight %.

8. The method as claimed in claim 1, wherein the aqueous solution B comprises the alkali metal hydroxide in an amount in a range of 20 to 40 weight %.

9. The method as claimed in claim 1, wherein the alkali metal hydroxide is sodium hydroxide.

10. The method as claimed in claim 1, wherein the aqueous solution A and the aqueous solution B are metered into the continuous reactor such that a molar ratio of calcium salt to alkali metal hydroxide is in a range of 1:2.0 to 2.4:1.

11. The method as claimed in claim 1, wherein the mixing time is below 30 seconds.

12. The method as claimed in claim 1, wherein the mixing time is below 1 second.

13. The method as claimed in claim 1, further comprising concentrating the suspension to increase a solids content by removal of water.

14. The method as claimed in claim 1, further comprising cleaning the suspension to remove auxiliaries or byproducts by means of ion exchange, filtration, or ultrafiltration.

15. The method as claimed in claim 1, wherein a mixing energy with which the solution A and the solution B are rapidly and intensely mixed is not more than 200 kJ per kilogram of calcium hydroxide suspension produced.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is used to illustrate the working examples.

(2) FIG. 1 shows: graph of the development over time of the heat of hydration.

(3) FIG. 1 depicts the graph of the development over time of the heat of hydration of a cement paste, measured by isothermal heat flow calorimetry. The arrow marks the start of setting, and the interrupted line marks the rise in the curve, with a rise angle drawn in.

EXAMPLES

(4) Set out below are working examples which are intended to illustrate the invention described in more detail. The invention is of course not confined to these working examples described.

(5) “Ex.” stands for “Example”

(6) “Ref.” stands for “Reference example”

(7) 1. Description of the Measurement Methods

(8) Particle size by HELOS: The particle size of the calcium hydroxide suspensions was determined by laser diffraction. The instrument used for the measurement was the HELOS, equipped with the Quixel dispersing unit, both from Sympatec, Germany. The instrument captures particle sizes from 0.10 to 8750 μm. For the measurements, the suspensions were diluted with saturated calcium hydroxide solution.

(9) Particle size by Nanophox: The particle size of the calcium hydroxide nanoparticles was determined by dynamic light scattering with photon cross-correlation spectroscopy. The instrument used for the measurement was the Nanophox from Sympatec GmbH, Germany. The instrument captures particle sizes from 0.5 to 10 000 nm. There is no need for the sample to be diluted. Prior to the measurement, the sample was homogenized with an ultrasound probe for one minute.

(10) The storage stability of the suspensions was determined as follows:

(11) In a centrifuge (Heraeus™ Biofuge Primo R from Thermo Scientific™), fitted with a rotor with fixed angles of 45°, 50 ml of each of the fresh and thoroughly stirred suspensions were introduced into Falcon® centrifuge tubes (50 ml) with screw closure and centrifuged at 8000 revolutions per minute for 15 minutes at 23° C. The top 40 ml were then removed from the centrifuge tube, and their turbidity was ascertained.

(12) The turbidity was determined nephelometrically (90°) in accordance with US EPA 180.1. The instrument used for this purpose was a HACH® 2100AN turbidimeter from HACH®, Germany, with a tungsten light source and the unit NTU (Nephelometric Turbidity Unit).

(13) The hydration behavior of the cement pastes was measured using isothermal heat flow calorimetry. The instrument used for this purpose was the TAM Air from TA Instruments, USA. The development of the heat of hydration over time in comparison to a cured cement reference sample was measured. The timespan between the mixing of the cement with water until the first increase in the heat flow after attainment of the first minimum is rated as the time to the start of setting.

(14) To determine the angle of rise of the heat flow curve, a tangent was placed at the turning point of the curve section located between the start of setting and the next maximum. The angle formed by the tangent with the horizontal axis is rated as the angle of rise of the heat flow curve. The angle of rise is a measure of the rate of the hydration reaction. The faster the reaction, the steeper the rise and the larger the angle.

(15) A typical heat flow curve and its evaluation are represented in FIG. 1.

(16) The slump of the mortar mixtures was determined in accordance with EN 1015-3.

(17) Start of setting and end of setting of the mortar mixtures were ascertained by measuring the temperature in the course of the time after mixing with water. The temperature measurement took place with a thermocouple as temperature sensor on a mortar sample which was stored in an isolated vessel in a room conditioned at 20° C.

(18) For these examples, the start of setting is the time elapsed between the mixing with water to the time of the rise in the temperature curve after the induction phase (i.e., rest phase).

(19) The end of setting for these examples is the time elapsed between the mixing with water to the attainment of the temperature maximum occurring after the induction phase.

(20) The compressive strength of the cured mortars was determined on mortar prisms of 4×4×16 cm. For this purpose, the fresh mortar was introduced into corresponding molds and stored at 20° C. After 8 and 24 hours, a determination was made of the compressive strength of the mortar prisms in according with EN 196-1.

(21) 2. Materials Used

(22) Polymer P1 is an aqueous solution of a comb polymer which consists of acrylic acid units and polyethylene glycol methacrylate units (Mw of the polyethylene glycol: 5000 g/mol) in a molar ratio of 15:1 and has a solid content of 32 weight %. Sika® ViscoCrete®-20 HE (VC 20 HE) is an aqueous solution of a superplasticizer based on a modified polycarboxylate, available from Sika Schweiz AG, Switzerland.

(23) SikaRapid®-1 is a hardening accelerator, available from Sika Schweiz AG, Switzerland.

(24) SikaRapid® C-100 is a hardening accelerator, available from Sika Schweiz AG, Switzerland.

(25) Emsure® ACS is a calcium hydroxide powder, available from Merck KGaA, Germany.

(26) Verit Natur is a white lime hydrate with at least 93 weight % of the particles <90 μm and a Blaine value of 20 000 m.sup.2/g (information from the product datasheet), available from Schretter and Cie GmbH & Co KG, Austria.

(27) Zement CEM I 42.5 N is a Portland cement, available from Jura-Cement-Fabriken AG, Switzerland.

(28) Zement CEM I 52.5 R is a Portland cement, available from Holcim Schweiz under the trade name Normo 5R.

(29) 3. Aqueous Calcium Hydroxide Suspensions

(30) Production of Suspensions S1 and S2

(31) In a beaker, 30.0 g of polymer P1 were dissolved in 335.2 g of water, after which, with vigorous stirring using a propeller stirrer, 54.7 g of calcium hydroxide powder were scattered in, and then the sodium nitrate was dissolved in the suspension. As soon as the stirrer was shut off, part of the calcium hydroxide settled on the bottom of the stirring vessel.

(32) The suspensions S1 and S2 had the compositions and properties reported in table 1.

(33) Production of Suspension S3

(34) Suspension S3 was produced like suspension S2, but the sodium nitrate added was replaced by the same amount by weight of water. As soon as the stirrer was shut off, part of the calcium hydroxide settled on the bottom of the stirring vessel. The suspension S3 had the composition and properties reported in table 1.

(35) Production of Suspension S4

(36) Calcium nitrate solution: 174.4 g of Ca(NO.sub.3).sub.2*4H.sub.2O (0.739 mol) were dissolved in 62 g of hot water (45° C.) and then 30 g of polymer P1 were dissolved in the solution.

(37) Sodium hydroxide solution: 59.1 g of NaOH (1.478 mol) were dissolved with cooling in 220 g of water.

(38) The calcium nitrate solution was charged to a 1 liter round-bottom flask. With stirring using a propeller stirrer, the sodium hydroxide solution was added via a dropping funnel over the course of 5 minutes. The resulting suspension was stirred for a further 60 minutes.

(39) The suspension S4 had the composition and properties reported in table 1.

(40) Production of Suspension S5

(41) The solutions used were the same as those described for suspension S4. In this example, however, both solutions were metered simultaneously into a continuous reactor, and mixing took place with high mixing intensity in a short mixing time. The resulting suspension was discharged continuous from the reactor.

(42) The suspension S5 had the composition and properties reported in table 1.

(43) Production of Suspension S5-UF

(44) Suspension S5 was purified by ultrafiltration using a polyethersulfone membrane having a 30 KDa size exclusion limit. In this procedure, the NaNO.sub.3 was removed and the suspension was concentrated. Thereafter the suspension was diluted with saturated calcium hydroxide solution so as to give 10 g of calcium hydroxide in 100 g of the suspension.

(45) Production of Suspension S5-2

(46) The production of suspension S5-UF was repeated, but at the dilution stage NaNO.sub.3 was also added, in a quantity such that there were 10 g of calcium hydroxide and 23 g of NaNO.sub.3 in 100 g of the suspension.

(47) The compositions in weight % and also the properties of suspensions S1 to S5 are reported in table 1.

(48) TABLE-US-00001 TABLE 1 Ref. 1 Ref. 2 Ref. 3 Ref. 4 Ex. 1 S1 S2 S3 S4 S5 Calcium Emsure ® Verit Verit From From hydroxide ACS Natur Natur precipitation precipitation type reaction reaction Composition in weight % Water 65.2 65.2 88.2 65.2 65.2 Calcium 10.0 10.0 10.0 10.0 10.0 hydroxide NaNO.sub.3 23.0 23.0 0 23.0 23.0 Polymer 1.8 1.8 1.8 1.8 1.8 P1** Turbidity of the upper phase after centrifuging Turbidity 256 291 n.m.* 227 9614 (NTU) Particle size with HELOS (μm) D10 0.78 0.8 n.m.* 0.41 0.17 D50 2.42 3.0 2.9 0.50 Particle size with Nanophox (nm) D10 n.m.* n.m.* n.m.* n.m.* 140 D50 163 D90 192 *not measured **calculated without water, pure solid

(49) 4. Utility Tests

(50) 4.1 Test in Cement Paste

(51) 32.4 g of water and 4 g of the aqueous suspension as per table 2 and 3 were added to 100 g of CEM I 42.5 N cement and mixing was carried out for 2 minutes using a mechanical stirrer. The development of the heat of hydration was then measured.

(52) For the comparison without admixtures (Ref. 5 and Ref. 11), 100 g of cement were mixed with 35 g of water in the same way.

(53) For the comparison with NaNO.sub.3 as sole admixture (Ref. 6), 0.92 g of NaNO.sub.3 was dissolved in 35 g of water and mixed with the cement as described above.

(54) The evaluations of the measurements of the heat of hydration are reported in table 2 and 3.

(55) TABLE-US-00002 TABLE 2 Ref. 5 Ref. 6 Ref. 7 Ref. 8 Ref. 9 Ref. 10 Ex. 2 Admixture none NaNO.sub.3 S1 S2 S3 S4 S5 Start of setting 1:40 1:30 1:43 1:36 1:35 1:44 1:25 (h:min) Angle of rise 40 45 48 48 45 48 53 of the heat flow curve (°)

(56) TABLE-US-00003 TABLE 3 Ref. 11 Ex. 3 Ex. 4 Ex. 5 Admixture none S5 S5-UF S5-2 Start of setting 1:30 1:21 1:25 1:21 (h:min) Angle of rise of the 34 48 45 48 heat flow curve (°)

(57) When comparing the results from table 2 and table 3, especially Ref. 5 and Ref. 11 and also Ex. 2 and Ex. 3, it should be borne in mind that the experiments described in table 2 and in table 3 were carried out at different points in time and with different cement supplies. Cements with different ages and from different batches are subject to fluctuations which may influence the measurement values. Within each measurement series (measurement series in table 2 and measurement series in table 3, respectively), however, the cement used was the same.

(58) 4.2 Test in Mortar Mixtures

(59) Mortar Series 1

(60) In a forced mixer from Hobart, 750 g of CEM I 52.5 R cement, 141 g of limestone filler, 738 g of 0-1 mm sand, 1107 g of 1-4 mm sand and 1154 g of 4-8 mm sand were mixed dry for 1 minute. Then 292.5 g of a mixture of water and the admixtures reported in table 4 were added to the dry mortar mixture in the mixer over the course of 30 seconds, with stirring, and the mortar was mixed for a further 2.5 minutes. The total wet mixing time lasted 3 minutes in each case. The level of metered addition of the admixtures, the slump, and also the setting time of the mortar mixtures are reported in table 4.

(61) TABLE-US-00004 TABLE 4 Slump (in mm) Setting 0 30 60 90 time (h:min) Admixture Met..sup.1) min. min. min. min. start end Ref. VC 20 HE.sup.2) 1 257 257 247 171 3:40 12:30 12 Ref. VC 20 HE 1 233 226 184 135 3:15  9:50 13 SikaRapid ®-1 1 Ref. VC 20 HE 1 270 248 194 128 3:00  9:50 14 SikaRapid ® 1 C-100 Ex. VC 20 HE 1 268 262 241 174 2:40  9:50 6 S5 2 .sup.1)level of metered addition in weight % of solution or suspension to cement .sup.2)Sika ® ViscoCrete ®-20 HE .sup.3) not measured, mixture too stiff

(62) Mortar Series 2

(63) Mortar mixtures as described in mortar series 1 were produced. In this series, however, 300 g of a mixture of water and the admixtures as per table 5 were used. The level of metered addition of the admixtures, the slump, and also the compressive strength of the mortar mixtures are reported in table 5.

(64) TABLE-US-00005 TABLE 5 Compressive strength Slump (in mm) (N/mm.sup.2) 0 30 60 90 8 24 Admixture Met. .sup.1) min. min. min. min. hours hours Ref. VC 20 HE.sup.2) 1 240 220 171 114 5.4 48.7 15 Ex. VC 20 HE 1 249 218 165 116 7.9 53.8 7 S5 2 .sup.1) level of metered addition in weight % of solution or suspension to cement .sup.2)Sika ® ViscoCrete ®-20 HE

(65) In a comparison of the results in table 4 and table 5, especially of Ref. 12 and Ref. 15, it should be borne in mind that the mortar tests were carried out in different measurement series and on different dates. Cements of different ages and sands from different batches are subject to fluctuations which may influence the measurement values. Within each measurement series (measurement series in table 4 and measurement series in table 5, respectively), however, the cement and the sands used were always the same.