Two-component method for preparing geopolymer foams

Abstract

The present invention belongs to the field of geopolymer materials. It relates to a method for preparing a geopolymer foam, the geopolymer foam thereof and its uses thereof. The geopolymer foam is obtained by mixing a first component being an alkaline foaming composition with a second component being a geopolymer slurry.

Description

[0001] TWO-COMPONENT METHOD FOR PREPARING GEOPOLYMER FOAMS

[0002] TECHNICAL FIELD

[0003] The present invention belongs to the field of geopolymer materials. It relates to a method for preparing a geopolymer foam, the geopolymer foam thereof and its uses thereof.

[0004] TECHNICAL BACKGROUND

[0005] Geopolymers are inorganic, typically aluminosilicate-based networks, which are usually ceramic and non-crystalline (amorphous). They are obtained by a chemical reaction between aluminosilicates and an alkaline or acidic aqueous composition.

[0006] Research on geopolymers started in the 1970s.

[0007] Geopolymers are considered as possible alternative materials to concrete or synthetic materials, considering their potential advantageous properties. Indeed, these mineral-based materials have a reduced toxicity (substantially free of volatile organic compounds), a reduced carbon dioxide footprint (low-carbon materials prepared at ambient temperature), a satisfactory long-term durability, a satisfactory recyclability, satisfactory properties in terms of fire- and heatresistance, satisfactory properties in terms of non-flammability and noncombustibility, satisfactory properties in terms of thermal and acoustic insulation properties, and more.

[0008] Geopolymers may be prepared as a geopolymer foam, for example by carrying out a conventional mechanical and / or chemical process.

[0009] However, a disadvantage of the conventional methods of preparing the geopolymer foams is the difficulty of controlling these methods, and particularly the difficulty of maintaining the stability of the foamed structures until the binder sets properly, which is even more difficult for the foams with a low dry density (lower than 200 kg / m3).

[0010] There is thus a need to provide a method, wherein the drainage and / or the coalescence is reduced or even prevented. There is also a need to provide a method for preparing a geopolymer foam, wherein the stability of the foam is maintained all along the method. There is also the need to provide a method for preparing a geopolymer foam, wherein the stability of the foam is increased before the hardening occurs. SUMMARY OF THE INVENTION

[0011] In a first aspect, the invention relates to a method for preparing a geopolymer foam comprising the following steps:

[0012] - providing a first component being an alkaline foaming composition comprising at least one alkali metal silicate, at least one foaming agent, and water;

[0013] - providing a second component being a geopolymer slurry comprising a aluminosilicate, an alkaline activator composition, and optionally water;

[0014] - mixing the first and the second components for obtaining a geopolymer foam.

[0015] In some embodiments, the first component (the alkaline foaming composition) comprises from about 1 to about 99.2 wt.% of the at least one alkali metal silicate, from about 0.3 to about 4 wt.% of the at least one foaming agent, and from about 0.5 to about 98.7 wt.% of water, based on the total weight of the first component.

[0016] In some embodiments, the first component (the alkaline foaming composition) has a wet density (before foaming) from about 1 ,050 to about 1 ,200 g / L, and / or a wet density (after foaming) from about 30 to about 80 g / L.

[0017] In some embodiments, the second component (the geopolymer slurry) comprises from about 40 to about 60 wt.% of the at least one aluminosilicate, from about 40 to about 60 wt.% of the alkaline activator composition, and optionally water, and wherein the total amount of water in the second component is from about 25 to about 45 wt.%, based on the total weight of the second component.

[0018] In some embodiments, the alkaline activator composition comprises from about 40 to about 75 wt.% of the at least one alkali metal silicate, from about 5 to about 25 wt.% of the at least one alkali metal hydroxide, and water, wherein the total amount of water of the alkaline activator composition is from about 45 wt.% to about 75 wt.%, or from about 55 wt.% to about 70 wt.%, based on the total weight of the alkaline activator composition.

[0019] In some embodiments, the second component further comprises at least one filler; preferably at least one inorganic filler.

[0020] In some embodiments, the filler is selected from the group consisting of wollastonite, andesite, phonolite, silicates (for example mica, talc, feldspar and / or kaolin), silicas, graphite, quartz sand, silica fume, diatomaceous earth, calcium carbonate, and mixtures thereof.

[0021] In some embodiments, the filler has a particle size distribution as follow: a dso from about 0.1 m to about 30 pm, preferably, from about 2 pm to about 12 pm; and / or a doo from about 1 pm to about 80 pm, preferably from about 10 pm to about 40pm.

[0022] In some embodiments, the second component has a wet density from 1 ,200 to about 2,000 g / L, or from about 1 ,400 to about 1 ,600 g / L.

[0023] In some embodiments, the first and second components are mixed using a mixing device, into which the first and second components are continuously fed or fed by batch. For example, the mixing device is an in-line mixing device.

[0024] In some embodiments, air is injected into the first component, concomitantly to the introduction of the first component into the mixing device.

[0025] In some embodiments, the obtained geopolymer foam is cured at a temperature from about 20 to about 70 °C, or form about 25 to 45 °C.

[0026] In a second aspect, the invention relates to a geopolymer foam, which is obtained by the method as defined above / below, wherein the geopolymer foam has a wet density from about 150 to about 1000 g / L, for example from about 200 to about 500 g / / L.

[0027] In some embodiments, the geopolymer foam has a waterbinder (W / B) weight ratio from about 0.7 to about 1 .5; and / or a watersolids (W / S) weight ratio from about 0.5 to 1 .

[0028] In some embodiments, the geopolymer foam has an average bubble diameter of less than 1 mm, after a cure of 6 hours at 25°C, preferably between 200 pm and 700 pm, as measured with a Turbiscan Lab.

[0029] In some embodiments, the geopolymer foam has a Turbiscan stability index (TSI) of 5 to 30 after a cure of 2 hours at 25°C, or a TSI of 5 to 15 after a cure of 2 hours at 45°C, as measured with a Turbiscan Lab.

[0030] In a third aspect, the invention relates to the use of the geopolymer foam in insulating applications, lightweight screeds, roof tops, geotechnical applications, fire-proof applications, foundry equipment, bricks, block filling, brick filling, floor and / or wall covering, panels as for example insulation panels, or furniture.

[0031] The present invention makes it possible to overcome the drawbacks of the prior art. The inventors have shown that the method according to the present invention allows controlling the quantity of water all along the method. While the presence of water is important for the stability of the foam, the use of two components prevents the occurrence of drainage caused by an excess of water, thereby preventing the destabilization of the foam during the process. The foam stability is thus increased during the process, before the hardening happens.

[0032] DESCRIPTION OF THE FIGURES

[0033] Figure 1 is a graph showing the Turbiscan stability index (TSI, dimensionless) over time (min) obtained with the tested geopolymer foams.

[0034] Figure 2 is a graph showing the average bubble diameter (pm) over time (min) obtained with the tested geopolymer foams.

[0035] DESCRIPTION OF EMBODIMENTS

[0036] The invention will now be described in more detail without limitation in the following description.

[0037] Throughout the description, all the percentages of the various constituents of the composition / product / material are given by weight (wt.%), except if mentioned otherwise. The concentration ranges have to be considered as including the limits.

[0038] Definitions

[0039] By “substantially free of’ is meant a product comprising about 0.1 wt.% or less, or about 0.01 wt.% or less, or about 0 %, of a compound, per total weight of the composition / product / material.

[0040] By “ambient temperature" is meant for example a temperature from about 18 to 25°C, or 25°C.

[0041] The expressions “first component" and “alkaline foaming composition" are used interchangeably.

[0042] The expressions “second component’ and “geopolymer slurry” are used interchangeably.

[0043] The units “g / L” and “kg / m3” may be used interchangeably.

[0044] Method for preparing a geopolymer foam

[0045] In a first aspect, the invention relates to a two-component method for preparing a geopolymer foam. The method for preparing a geopolymer foam comprises the following steps:

[0046] - providing a first component being an alkaline foaming composition comprising at least one alkali metal silicate, at least one foaming agent, and water;

[0047] - providing a second component being a geopolymer slurry comprising at least one aluminosilicate, an alkaline activator composition, and optionally water; and

[0048] - mixing the first and the second components for obtaining a geopolymer foam.

[0049] Providing a first component (the alkaline foaming composition)

[0050] The method comprises the step of providing a first component. The first component is an alkaline foaming composition. The alkaline foaming composition comprises at least one alkali metal silicate, at least one foaming agent, and water.

[0051] The alkaline foaming composition may comprise from about 1 to about 99.2 wt.%, or from about 50 to about 99 wt.%, or from about 65% to about 90 wt.%, or from about 72 to about 85 wt.%, of the at least one alkali metal silicate, based on the total weight of the alkaline foaming composition.

[0052] The at least one alkali metal silicate may be selected from the group consisting of potassium silicate, sodium silicate, lithium silicate, and mixtures thereof.

[0053] The alkaline foaming composition may comprise from about 0.3 to about 4 wt.%, or from about 0.8 to about 2 wt.%, or from about 1 to about 1 .5 wt.%, of the at least one foaming agent, based on the total weight of the alkaline foaming composition.

[0054] The at least one foaming agent may be selected from the group consisting of alkyl-polyglucosides, proteins, and mixtures thereof.

[0055] The alkyl-polyglycosides (APGs) may be selected from the group consisting of non-ionic alkyl-polyglycosides. Alkyl-polyglycosides may be prepared by combining a sugar (for example glucose) with a fatty alcohol, in the presence of acid catalysts at elevated temperatures. For example, alkyl- polyglycosides are commercially available under the tradename Triton BG 10 from Dow or Disponil APG 215 from BASF. The proteins may be selected from the group consisting of vegetable proteins, animal proteins, and mixtures thereof; preferably from the group consisting of vegetable proteins. For example, proteins are commercially available under the tradename Isocem S / L from Isoltech.

[0056] The alkaline foaming composition may comprise from about 0.5 to about 98.7 wt.%, or from about 0.5 to about 50 wt.%, or from about 5 to about 34 wt.%, or from about 10 to about 25 wt.%, of water, based on the total weight of the alkaline foaming composition.

[0057] The alkaline foaming composition may have a wet density (before foaming) from about 1 ,050 to about 1 ,200 g / L.

[0058] The alkaline foaming composition may also have a wet density (after foaming) from about 30 to about 80 g / L, or from about 40 to about 60 g / L, or from about 45 to about 55 g / L.

[0059] Unless specified otherwise, the wet density (for example, of the alkaline foaming composition, before or after foaming) may be measured as follows:

[0060] - providing a container (for example a dry cylindrical container) having a determined volume (for example 100 mL or 250 mL);

[0061] - preparing the composition (for example, to measure the wet density (before foaming) of the alkaline foaming composition, by using a careful mixing in order to avoid incorporating air into the composition);

[0062] - assessing the weight (grams) of the empty container using a precision balance;

[0063] - pouring a determined volume (for example 100 mL or 250 mL) of the composition into the container (for example using a pipette);

[0064] - assessing at least once (for example three times) the weight (grams) of the container comprising the composition, and calculating the weight (or the average weight) of the composition; and

[0065] - calculating the wet density by dividing the weight (average weight) of the composition by its volume.

[0066] The alkaline foaming composition may be prepared by mixing the at least one alkali metal silicate, the at least one foaming agent, and water at high shear. By high shear, it means a shear high enough so that the composition starts to foam; for example with a Hobart mixer equipped with a whip used at 420 to 600 rpm. The at least one alkali metal silicate, the at least one foaming agent, and water may be mixed using any suitable mixers.

[0067] Providing a second component (geopolymer slurry)

[0068] The method comprises the step of providing a second component. The second component is a geopolymer slurry. The geopolymer slurry comprises at least aluminosilicate, an alkaline activator composition, and optionally water. The geopolymer slurry is thus obtained by mixing at least aluminosilicate, an alkaline activator composition, and optionally water. In an embodiment, the materials are mixed at ambient temperature.

[0069] The geopolymer slurry may comprise from about 40 to about 60 wt.%, or from about 40% to about 50 wt.%, of the aluminosilicate, based on the total weight of the geopolymer slurry.

[0070] The at least one aluminosilicate may be selected from the group consisting of calcined clay, fly ashes, slag, and mixtures thereof; preferably the aluminosilicate is metakaolin.

[0071] The geopolymer slurry may comprise from about 40 to about 60 wt.%, or from about 45% to about 55 wt.%, of the alkaline activator composition, based on the total weight of the geopolymer slurry.

[0072] The geopolymer slurry may comprise water.

[0073] The total amount of water in the geopolymer slurry is from about 25 wt.% to about 45 wt.%, based on the total weight of the geopolymer slurry.

[0074] The alkaline activator composition may comprise from about 40 to about 75 wt.%, or from about 45 to about 55 wt.%, of the at least one alkali metal silicate, based on the total weight of the alkaline activator composition.

[0075] The at least one alkali metal silicate may be selected from the group consisting of potassium silicate, sodium silicate, lithium silicate, and mixtures thereof.

[0076] The alkaline activator composition may comprise from about 5 to about

[0077] 25 wt.%, or from about 10 to about 22 wt.%, or from about 15 to about 21 wt.%, of the at least one alkali metal hydroxide, based on the total weight of the alkaline activator composition.

[0078] The at least one alkali metal hydroxide may be selected from the group consisting of potassium hydroxide, sodium hydroxide, lithium hydroxide, and mixtures thereof.

[0079] The alkaline activator composition may comprise water.

[0080] The total amount of water of the alkaline activator composition may be from about 45 wt.% to about 75 wt.%, or from about 55 wt.% to about 70 wt.%, based on the total weight of alkaline activator composition.

[0081] The alkaline activator composition may comprise from about 25 to about 45 wt.%, or from about 30 to about 40 wt.%, or from about 32 to about 38 wt.%, of water, based on the total weight of the geopolymer slurry.

[0082] The geopolymer slurry may further comprise at least one filler.

[0083] The at least one filler may be at least one inorganic filler; or at least one filler being selected from the group consisting of wollastonite, andesite, phonolite, silicates (for example mica, talc, feldspar and / or kaolin), silicas, graphite, quartz sand, silica fume, diatomaceous earth, calcium carbonate, and mixtures thereof.

[0084] The at least one filler may be uncoated. Alternatively, the at least one filler may be hydrophobically coated (also called a hydrophobized inorganic filler or hydrophobically-coated inorganic filler). The at least one hydrophobically-coated inorganic filler may be coated with at least one hydrophobic compound. The hydrophobically-coated inorganic filler may be obtained by providing an uncoated inorganic filler, and by applying at least one hydrophobic compound on the at least one hydrophobized inorganic filler in order to form a hydrophobic coating on it. The hydrophobic compound may be a hydrophobic organic compound. For example, the hydrophobic organic compound may be selected from the group consisting of stearic acid, silane, and mixtures thereof; preferably from the group consisting of stearic acid, an aminosilane, an alkoxysilane, a vinyl silane, a poly(vinyl)silane, and mixtures thereof. For example, the alkoxysilane may be phenyltrimethoxysilane and / or hexadecyltrimethoxysilane), vinylsilane, poly(vinyl) silane, and mixtures thereof. The at least one filler may have a dso from about 0.1 m to about 30 pm, for example, from about 2 pm to about 12 pm.

[0085] The at least one filler may have a doo from about 1 pm to about 80 pm, for example, from about 10 pm to about 40pm.

[0086] Particle size distributions are measured by wet Malvern laser scattering (standard ISO 13320-1 :2020). In this technique, the size of particles in powders, suspensions and emulsions may be measured using the diffraction of a laser beam, based on the application of Fraunhofer theory. Such a machine, for example a Laser Master Sizer 3000 (as supplied by Malvern instruments), provides measurements and a plot of the cumulative percentage by volume of particles having a size, referred to in the art as the “equivalent spherical diameter” (e.s.d), less than given e.s.d values. The mean particle size dso is the value determined in this way of the particle e.s.d. at which there are 50% by volume of the particles which have an equivalent spherical diameter less than that dso value. The dgg, dgs, dgo, d?s, d25 and the dio are the values determined in this way of the particle e.s.d. at which there are 99%, 95%, 90%, 75%, 25% and 10% respectively by volume of the particles which have an equivalent spherical diameter less than that dgg, dgs, dgo, d?s, d25 or dio value. For the avoidance of doubt, the measurement of particle size using laser light scattering is not an equivalent method to a sedimentation measurement method.

[0087] The geopolymer slurry may comprise from about 4 to about 20 wt.%, or from about 6 to about 15 wt.%, of the at least one filler, based on the total weight of the geopolymer slurry.

[0088] The geopolymer slurry may further comprise at least one free hydrophobic organic compound. By “free hydrophobic organic compound” is meant a hydrophobic organic compound, which is not part of a coating, for example of the coating of a hydrophobically-coated inorganic filler. The at least one free hydrophobic organic compound may be selected from the group consisting of stearate (metallic) salts, polydimethylsiloxane, and mixtures thereof; preferably from the group consisting of stearate magnesium, stearate zinc, stearate sodium, stearate barium, stearate strontium, polydimethylsiloxane, and mixtures thereof. The geopolymer slurry may have the following molar ratios:

[0089] - a molar ratio SiO2:Al2SO3 from about 2.5 to about 4.5, or from about 3 to about 4, or from about 3.25 to about 3.75;

[0090] - a molar ratio (Na2O + K2O): AI2SO3 from about 0.7 to about 1 .6, or from about 0.8 to about 1 .2,

[0091] - a molar ratio (Na2O+ K2O): SiC from about 0.2 to about 0.5.

[0092] The geopolymer slurry may have a wet density from about 1 ,200 to about 2,000 g / L, or from about 1 ,400 to about 1 ,600 g / L. The wet density of the geopolymer slurry may be measured as detailed above.

[0093] The geopolymer slurry may be prepared by mixing the at least one aluminosilicate, the alkaline activator composition, and optionally water, preferably at low shear. The at least one aluminosilicate, the alkaline activator composition, and optionally water may be mixed using a colloidal mixer, standard concrete mixer or any alternative suitable mixer.

[0094] The second component may be stored before being mixed with the first component, or alternatively may be prepared just before being mixed with the first component (extemporaneous preparation). When stored prior mixing with the first component, the second component may be hold in a tank.

[0095] Mixing the first and second components

[0096] The step of mixing the first component (the alkaline foaming composition) and the second component (the geopolymer slurry) allows obtaining a geopolymer foam.

[0097] The first component and the second component are mixed in a weight ratio from 30:70 to 5:95, or from 22:78 to 11 :89, from 20:80 to 25:85. The density of the geopolymer foam (final product) depends on the proportions (by weight) of each component, as defined above.

[0098] The step of mixing the first and second components may be carried out using a mixing device, into which the first and second components are continuously fed or fed by batch. For example, the mixing device is an in-line mixing device, as for example, an in-line mixing device from Gertec. Air may be injected into the first component, concomitantly to the introduction of the first component into the mixing device.

[0099] For obtaining a flow rate of geopolymer foam from about 10 to about 15 L / min, the first component may be introduced into the mixing device at a flow rate from about 0.32 to about 0.5 L / min, and the second component may be introduced into the mixing device at a flow rate from about 1 to about 2 L / min. The flow rate may be assessed using a flowmeter. The introduction of the first and second components at these ranges of flow rates for the first and second components are particularly suitable for obtaining satisfactory wet densities.

[0100] Upon introduction into the mixing device, the first component may have a wet density from about 30 to about 80 g / L, or from about 40 to about 60 g / L, or from about 45 to about 55 g / L.

[0101] Upon introduction into the mixing device, the second component may have a wet density from about 1 ,200 to about 2,000 g / L, or from about 1 ,400 to about 1 ,600 g / L. These ranges of wet density for the first and the second components are particularly suitable for preparing a geopolymer foam.

[0102] In an embodiment, air may be injected into the first component, concomitantly to the introduction of the latter into the mixing device. Air injection allows controlling the density of the first component and keeping it within this expected range.

[0103] The step of mixing the first and second components may be controlled by the volume of mixing device chamber. The mixing speed may be from about 500 rpm to 900 rpm.

[0104] Curing

[0105] The obtained geopolymer foam may be cured at a temperature from about 20 to about 80 °C, or from about 25 to 45 °C.

[0106] The obtained geopolymer foam may be cured in an oven, for example an oven from Binder.

[0107] The obtained geopolymer foam may be cured endogeneously (i.e. with no water evaporation).

[0108] Geopolymer foams In a second aspect, the invention relates to a geopolymer foam, which is obtained by the method described above, wherein the geopolymer foam has a wet density from about 200 to about 700 L / min, or from about 200 to about 500L / min.

[0109] In an embodiment, the geopolymer foam has the following molar ratios:

[0110] - a molar ratio SiO2:Al2SO3 from about 3.25 to about 4.25 or from about 3.5 to about 4;

[0111] - a molar ratio (Na2O+K2O):Al2SO3 from about 0.8 to about 1 .2, or from about 0.9 to about 1 ; and / or

[0112] - a molar ratio (Na2O+K2O): SiC from about 0.2 to about 0.48.

[0113] The geopolymer foam may have a water: binder (W / B) weight ratio from about 0.7 to about 1 .5.

[0114] The geopolymer may have a water: solids (W / S) weight ratio from about 0.5 to 1.

[0115] The factor “water"’, as used on the W:B and W:S weight ratios, corresponds to the total water originating from the first component (the alkaline foaming solution) and the second component (the geopolymer slurry).

[0116] The factor “binder"’, as used on the W:B weight ratio, corresponds to the oxide components present in the geopolymer foam, and originating from the alkali metal silicate(s) (present in both the first and second components), the alkali metal hydroxides (present in the second component), and the reactive part of the aluminosilicate (that correspond to the amorphous part of the second component). The oxides present may be, for example, SiC>2, Na2O, K2O, U2O and / or AI2O3.

[0117] The factor “so / ic / s” correspond to the sum of the crystalline part of aluminosilicate and the fillers.

[0118] Applications

[0119] The geopolymer foam obtained by the method described above may be used in insulating applications, lightweight screeds, roof tops, geotechnical applications, fire-proof applications, foundry equipment, bricks, block filling, brick filling, floor and / or wall covering, panels as for example insulation panels, or furniture.

[0120] EXAMPLES

[0121] Example 1 Materials

[0122] Alkali metal silicate: sodium silicate

[0123] Alkali metal hydroxides: sodium hydroxide, potassium hydroxide Aluminosilicate:

[0124] - mineral: metakaolin;

[0125] - amorphous rate: 62.80 % amorphous phase and 37.20 % crystalline phase;

[0126] - chemical composition of the amorphous phase (total 100 wt.%): 52.60 % SiO2, 41.07 % AI2O3, 0.31 % K2O, 0.07 % Na2O, 5.95 % others;

[0127] - the crystalline phase and the “others" of the amorphous phase are considered as non-reactive “fillers" below.

[0128] Fillers: wollastonite, ground calcium carbonate coated with 1 wt.% stearic acid

[0129] Foaming agent: Triton BG-10 (glucose alkyl ether, glucoside)

[0130] Method (foam stability)

[0131] The stability of the foam is assessed using a Turbiscan comprising a scanning head composed of a near infra-red-light source (880 nm) with two detectors (one in transmission and one in backscatter). The readhead scans a sample by moving vertically along the analysis cell and acquiring data every 40 pm. By making these measurements over time, changes in backscatter and transmission levels due to sample instability are recorded. These changes indicate water drainage in the sample as well as a change of bubble size due to coalescence or fill rupture, and allow to define a stability index and to measure bubble diameter.

[0132] Components

[0133] First component (alkaline foaming composition):

[0134] - formulation (total 100 wt.%): 75 wt.% sodium silicate, 1.3 wt.% surfactant (Triton BG-10: glucose alkyl ether, glucoside), q.s. water;

[0135] - chemical composition (total 100 wt.%): 18.53 wt.% SiO2,

[0136] 5.17 wt.% Na2O, 1.3 wt.% surfactant, q.s. water;

[0137] - wet density (before foaming): 1 , 150 g / L;

[0138] - wet density (after foaming): 45 g / L.

[0139] Second component (geopolymer slurry): - formulation (alkaline activator composition) (total 100 wt.%): 49 wt.% sodium silicate, 13.5 wt.% potassium hydroxide, 5 wt.% sodium hydroxide, q.s. water;

[0140] - chemical composition (alkaline activator composition) (total 100 wt.%): 12.10 wt.% SiC>2, 9.75 wt.% K2O, 7.25 wt.% Na2O, q.s. water;

[0141] - formulation (geopolymer slurry) (total 100 wt.%): 53.60 wt.% alkaline activator composition, 40.40 wt.% metakaolin, 3.00 wt.% wollastonite, and 3.00 wt.% ground calcium carbonate / 1 wt.% stearic acid;

[0142] - chemical composition (geopolymer slurry) (total 100 wt.%): 19.84 wt.% SiO2, 10.43 wt.% AI2O3, 5.30 wt.% K2O, 3.91 wt.% Na2O,

[0143] 22.55 wt.% filler, q.s. water;

[0144] - molar ratios (geopolymer slurry): SiO2:Al2SO3 = 3.23, H2O:M2O = 17.86, M2O:SiO2 = 0.36, M2O:Al2SO3 = 1.16, wherein M corresponds to Na and K; and

[0145] - wet density (geopolymer slurry): 1 ,450 g / L.

[0146] The geopolymer slurry thus comprises 40.97 wt.% of a binder (7.e. , SiO2 Na2O and K2O coming from the alkaline activator composition and the reactive SiO2 and AI2O3 from metakaolin), and 21.03 wt.% of fillers (i.e., “unreactive" minerals meaning filler + crystalline part of metakaolin) and 38 wt.% weight of water.

[0147] Mixing conditions (lab scale)

[0148] - proportion of the first component: 18 wt.%;

[0149] - proportion of the second component: 82 wt.%.

[0150] It corresponds for a production of 10L / min of geopolymer foam to:

[0151] - flow rate of the first component: 0.33 L / min;

[0152] - flow rate of the second component: 1.21 L / min.

[0153] Curing

[0154] The foam composition was then cured in an oven at 35°C. The curing is endogeneous (to prevent water evaporation).

[0155] Geopolymer foam

[0156] - chemical composition (total 100 wt.%): 19.60 wt.% SiC>2,

[0157] 8.55 wt.% AI2O3, 4.35 wt.% K2O, 4.13 wt.% Na2O, 17.24 wt.% filler, 0.23 wt.% surfactant, q.s. water; and - molar ratios (geopolymer slurry): SiO2:Al2SO3 = 3.89, H2O:M2O = 21 .99, M2O:SiO2 = 0.35, M2O:Al2SO3 = 1.17, wherein M corresponds to Na and K;

[0158] - water: binder weight ratio: 1.18; and

[0159] - watersolids weight ratio: 0.81 .

[0160] Results

[0161] The Turbiscan stability index (TSI, dimensionless) over time (min) obtained with the geopolymer foam according to example 1 is shown in figure 1 (graph).

[0162] The bubble diameter (pm) over time (min) obtained with the geopolymer foam according to example 1 is shown in figure 2 (graph).

[0163] Example 2

[0164] Materials

[0165] See example 1 .

[0166] Components

[0167] First component (alkaline foaming composition):

[0168] - Formulation (total 100 wt.%): 78 wt.% sodium silicate, 1.3 wt.% surfactant (Triton BG-10: glucose alkyl ether, glucoside), q.s. water

[0169] - chemical composition (total 100 wt.%): 19.27 wt.% SiC>2,

[0170] 5.38 wt.% Na2O, 1.3 wt.% surfactant, q.s. H2O ;

[0171] - wet density (before foaming): 1 , 155 g / L;

[0172] - wet density (after foaming): 46 g / L.

[0173] Second component (geopolymer slurry):

[0174] - formulation (alkaline activator composition) (total 100 wt.%): 55 wt.% sodium silicate, 15 wt.% potassium hydroxide, 6 wt.% sodium hydroxide, q.s. water;

[0175] - chemical composition (alkaline activator composition) (total 100 wt.%):

[0176] 13.59 wt.% SiC>2, 10.83 wt.% K2O, 8.45 wt.% Na2O, q.s. water;

[0177] - formulation (geopolymer slurry) (total 100 wt.%): 44.2 wt.% alkaline activator composition, 47.8 wt.% metakaolin, 4 wt.% wollastonite, and 4 wt.% ground calcium carbonate / 1 wt.% stearic acid;

[0178] - chemical composition (geopolymer slurry) (total 100 wt.%): 21.80 wt.% SiO2, 12.34 wt.% AI2O3, 4.88 wt.% K2O, 3.75 wt.% Na2O,

[0179] 27.59 wt.% filler, q.s. water; - molar ratios (geopolymer slurry): SiO2:Al2SO3 = 3, H2O: M2O = 14.85, M2O:SiO2 = 0.31 , M2O:Al2SO3 = 0.92, wherein M corresponds to Na and K; and

[0180] - wet density (geopolymer slurry): 1 ,450 g / L.

[0181] The geopolymer slurry thus comprises 92 wt.% of a binder ( / .e., the alkaline activator composition and the metakaolin), and 8 wt.% of fillers (i.e., “unreactive" minerals).

[0182] Mixing conditions (lab scale)

[0183] - proportion of the first component: 18 wt.%

[0184] - proportion of the second component: 82 wt.%

[0185] It corresponds for a production of 10L / min of geopolymer foam to:

[0186] - flow rate of the first component: 0.33 L / min;

[0187] - flow rate of the second component: 1.21 L / min.

[0188] Geopolymer foam

[0189] - chemical composition (total 100 wt.%): 21.35 wt.% SiC>2,

[0190] 10.12 wt.% AI2O3, 4.00 wt.% K2O, 4.04 wt.% Na2O, 22.62 wt.% filler, 0.23 wt.% surfactant, q.s. H2O;

[0191] - molar ratios (geopolymer slurry): SiO2:Al2SO3 = 3.58, H2O:M2O = 19.42, M2O:SiO2 = 0.3, M2O:Al2SO3 = 0.92, wherein M corresponds to Na and K;

[0192] - wet density (geopolymer slurry): 270 g / L.

[0193] - water: binder weight ratio: 0.95; and

[0194] - watersolids weight ratio: 0.61 .

[0195] Results

[0196] The Turbiscan stability index (TSI, dimensionless) over time (min) obtained with the geopolymer foam according to example 1 is shown in figure 2 (graph).

[0197] The average bubble diameter (pm) over time (min) obtained with the geopolymer foam according to example 1 is shown in figure 2 (graph).

Claims

CLAIMS1. A method for preparing a geopolymer foam, wherein the method comprises the following steps: o providing a first component being an alkaline foaming composition comprising at least one alkali metal silicate, at least one foaming agent, and water; o providing a second component being a geopolymer slurry comprising aluminosilicate, an alkaline activator composition, and optionally water; and o mixing the first and the second components for obtaining a geopolymer foam.

2. The method, according to claim 1 , wherein the first component comprises, based on the total weight of the first component: o from about 1 to about 99.2 wt.% of the at least one alkali metal silicate; o from about 0.3 to about 4 wt.% of the at least one foaming agent; optionally the foaming agent is an alkyl-polyglucoside, a protein, or a mixture thereof; and o from about 0.5 to about 98.7 wt.% of water.

3. The method, according to any preceding claims, wherein the first component has a wet density (before foaming) from about 1 ,050 to about 1 ,200 g / L, and / or a wet density (after foaming) from about 30 to about 80 g / L.

4. The method, according to any preceding claims, wherein the second component comprises, based on the total weight of the second component: o from about 40 to about 60 wt.% of the at least one aluminosilicate; and o from about 40 to about 60 wt.% of the alkaline activator composition, and o optionally water; wherein the total amount of water in the second component is from about 25 to about 45 wt.%, based on the total weight of the second component.

5. The method, according to any preceding claims, wherein the alkaline activator composition comprises, based on the total weight of the alkaline activator composition: o from about 40 to about 75 wt.% of the at least one alkali metal silicate; o from about 5 to about 25 wt.% of the at least one alkali metal hydroxide; and o water; wherein the total amount of water of the alkaline activator composition is from about 45 wt.% to about 75 wt.%, or from about 55 wt.% to about 70 wt.%, based on the total weight of alkaline activator composition.

6. The method, according to any preceding claims, wherein the second component comprises at least one filler; preferably the filler is selected from the group consisting of wollastonite, andesite, phonolite, silicates (for example mica, talc, feldspar and / or kaolin), silicas, graphite, quartz sand, silica fume, diatomaceous earth, calcium carbonate, and mixtures thereof.

7. The method, according to claim 6, wherein the filler has a particle size distribution as follow: a dso from about 0.1 pm to about 30 pm, preferably, from about 2 pm to about 12 pm; and / or a doo from about 1 pm to about 80 pm, preferably from about 10 pm to about 40pm.

8. The method, according to any preceding claims, wherein the second component has a wet density from about 1 ,200 to about 2,000 g / L, or from about 1 ,400 to about 1 ,600 g / L.

9. The method, according to any preceding claims, wherein the first and second components are mixed using a mixing device, into which the first and second components are continuously fed or fed by batch.

10. The method, according to any preceding claims, wherein air is injected into the first component, concomitantly to the introduction of the first component into the mixing device.

11. The method, according to any preceding claim, wherein the method further comprises curing the obtained geopolymer foam, for example at a temperature from about 20°C to about 80°C and / or under an endogeneous condition.

12. A geopolymer foam, which is obtained by the method according to any preceding claims, wherein the geopolymer foam has a wet density from about 150 to about 1000 g / L, or from about 200 to about 500g / L.

13. A geopolymer foam, according to claim 12, wherein the geopolymer foam has a water binder (W / B) weight ratio from about 0.7 to about 1.5, and / or the geopolymer foam has a watersolids (W / S) weight ratio from about 0.5 to 1.

14. A geopolymer foam, according to claim 12 or 13, wherein the geopolymer foam has an average bubble diameter of less than 1 mm, after a cure of 6 hours at 25°C, preferably between 200 pm and 700 pm, as measured with a Turbiscan Lab.

15. Use of a geopolymer foam according to any claim 12 to 14, in insulating applications, lightweight screeds, roof tops, geotechnical applications, fire-proof applications, foundry equipment, bricks, block filling, brick filling, floor and / or wall covering, panels as for example insulation panels, or furniture.

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