Inorganic foam based on calcium aluminate

Abstract

The present invention relates to a process for preparing a particle-stabilized inorganic foam based on calcium aluminate, to a particle-stabilized inorganic foam based on calcium aluminate, to a cellular material obtainable by hardening and optionally drying the particle- stabilized inorganic foam based on calcium aluminate, 5 and to a composition for preparing an inorganic foam formulation for providing a particle-stabilized inorganic foam based on calcium aluminate.

Description

[0001] INORGANIC FOAM BASED ON CALCIUM ALUMINATE

[0002] Technical Field

[0003] The present invention relates to a process for preparing a particle-stabilized inorganic foam based on calcium aluminate, to a particle-stabilized inorganic foam based on calcium aluminate, to a cellular material obtainable by hardening and optionally drying the particle- stabilized inorganic foam based on calcium aluminate, and to a composition for preparing an inorganic foam formulation for providing a particle-stabilized inorganic foam based on calcium aluminate.

[0004] Background of the invention

[0005] Inorganic foams can be used as insulation material, e.g., as a thermal insulator, acoustic insulator or acoustic absorber as well as construction material with a low density. In contrast to foams based on organic polymers, inorganic foams are eco- friendly, robust, and non-flammable. The latter may also open up applications in the field of fire protection. Foams in general can be stabilized by use of surfactants or particles. Inorganic foams stabilized by surfactants typically have an open-cell foam structure. However, of particular interest are closed cell foams, as they have improved thermal insulation properties that go along with improved mechanical stability.

[0006] It has been found that stable inorganic foams with a closed-cell foam structure can be obtained by using inorganic particles as foam stabilizers. Typically, the presence of amphiphilic molecules is required to initiate surface activity of the used particles. For example, WO 2018 / 162381 discloses particle stabilized inorganic foams based on calcium sulfoaluminate.

[0007] It has been found that particle-stabilized closed-cell geopolymer foams have advantageous properties in particular with regard to the dry density, the compressive strength and the air flow resistance in comparison to surfactant-stabilized closed-cell geopolymer foams. At the same time, a comparable thermal conductivity can be provided. However, particle-stabilized closed-cell geopolymer foams require a high pH value of about 14 for the setting, which causes problems in terms of the safety and handling. Furthermore, the raw material costs of geopolymer foams are rather high.

[0008] Summary of the invention

[0009] Accordingly, it is an objective of the present invention to provide inorganic foams which exhibit a satisfying thermal conductivity combined with high compressive strength, in particular at a low dry density. In addition, it is also an objective to increase the air flow resistance of the inorganic foams in comparison to geopolymer foams. Very preferably, inorganic foams of the present invention in particular are closed-cell foams with similar or improved properties in comparison to geopolymer foams. Preferably, the process of preparing the inorganic foams does not require such a high pH value as is needed for the geopolymer foams. Advantageously, inorganic foams of the present invention can be produced with lower raw material costs as compared to geopolymer foams.

[0010] It has surprisingly been found that the above objectives can be achieved by the materials and methods as claimed in the independent claims.

[0011] In particular, it has been discovered that by combining (i) at least one group of inorganic particles, (ii) at least one amphiphilic compound, and (iii) at least one inorganic binder comprising at least one calcium aluminate, and optionally at least one further binder material selected from the group consisting of hydraulic binders, latent hydraulic binders, pozzolanic binders, quicklime, hydrated lime, calcium sulfate, and mixtures thereof, inorganic foams can be obtained. As a result, stable inorganic foams with a fine and homogeneous closed-cell structures can be obtained. Furthermore, the inorganic foams of the invention exhibit a satisfying thermal conductivity combined with high compressive strength at a low dry density as well as a very high air flow resistance. Detailed Ways

[0012] In a first aspect, the present invention relates to a process for preparing an inorganic foam comprising the steps of

[0013] (1 ) mixing

[0014] (1) at least one group of inorganic particles;

[0015] (ii) at least one amphiphilic compound;

[0016] (iii) at least one inorganic binder comprising

[0017] (iiia) at least one calcium aluminate, and optionally

[0018] (iiib) at least one further binder material selected from the group consisting of hydraulic binders, latent hydraulic binders, pozzolanic binders, quicklime, hydrated lime, calcium sulfate, and mixtures thereof;

[0019] (iv) water; and optionally

[0020] (v) at least one additive; and

[0021] (2) foaming the resulting foam formulation by chemical, physical or mechanical foaming.

[0022] In another aspect, the present invention relates to an inorganic foam obtainable by the process of the present invention.

[0023] The present invention thus relates to an inorganic foam comprising

[0024] (i) at least one group of inorganic particles;

[0025] (ii) at least one amphiphilic compound;

[0026] (iii) at least one inorganic binder comprising

[0027] (iiia) at least one calcium aluminate, and optionally

[0028] (iiib) at least one further binder material selected from the group consisting of hydraulic binders, latent hydraulic binders, pozzolanic binders, quicklime, hydrated lime, calcium sulfate, and mixtures thereof,

[0029] (iv) water; and optionally

[0030] (v) at least one additive.

[0031] In yet another aspect, the present invention relates to a cellular material obtainable by hardening and optionally drying an inorganic foam as defined herein. In yet another aspect, the present invention relates to a composition for preparing an inorganic foam formulation said comprising as components:

[0032] (i) at least one group of inorganic particles;

[0033] (ii) at least one amphiphilic compound;

[0034] (iii) at least one inorganic binder comprising

[0035] (iiia) at least one calcium aluminate, and optionally

[0036] (iiib) at least one further binder material selected from the group consisting of hydraulic binders, latent hydraulic binders, pozzolanic binders, quicklime, hydrated lime, calcium sulfate, and mixtures thereof; and optionally

[0037] (iv) at least one additive; wherein the components (i), (ii), (iii), and if present (iv), are present separately in spatially separated containers; or the components (i) and (ii) are present as a mixture in a first container, and component (iii) is present separately in a spatially separate second container, and the component (iv) if present is present in the first and / or the second container; or the components (i), (ii), (iii), and (iv) are present as a mixture in one container.

[0038] The following definitions are relevant in connection with the present invention.

[0039] The term "about" in respect to a measurable unit refers to normal deviations of said measurable unit. Such deviations depend on the precision of the measuring apparatus or they depend on statistical deviations that are known to the skilled person. It is to be understood that the term "about" means a deviation of ± 15 %, preferably ± 10 %, more preferably ± 5 %.

[0040] The term "wt.-%" refers to the ratio of the mass of the respective component in relation to the sum of the mass of all components except water in percent, if not stated otherwise. The term vol.-% refers to the ratio of the volume of the respective component in relation to the sum of the volume of all components in percent.

[0041] The meaning of the term "comprising" is to be interpreted as encompassing all the specifically mentioned features as well optional, additional, unspecified ones, whereas the term "consisting of” only includes those features as specified. It is moreover intended that in each actual case the sum of all of the percentages of the specified and unspecified constituents of the formulation of the invention is always 100 %.

[0042] In the context of the process for preparing an inorganic foam, the inorganic foam, the cellular material obtainable by hardening and optionally drying the inorganic foam, and the composition for preparing an inorganic foam formulation according to the present invention, the following definitions are relevant.

[0043] In general, it is distinguished between the terms "inorganic foam formulation" and "inorganic foam". The inorganic foam formulation may be obtained from a suitable composition for preparing an inorganic foam formulation as defined herein by adding water and optionally at least one additive. The inorganic foam formulation may then be used to prepare an inorganic foam by mechanical, physical or chemical foaming. The freshly prepared inorganic foam is to be distinguished from the hardened inorganic foam, i.e. the cellular material, which is obtainable from the freshly prepared inorganic foam by hardening and optionally drying. Unless otherwise indicated, the term "inorganic foam" as used herein refers to the freshly prepared inorganic foam, and the term "cellular material" refers to the hardened and optionally dried inorganic foam.

[0044] Inorganic foams are three-phase systems, wherein one phase is gaseous, one phase is liquid, and one phase is solid. Thus, it is to be understood that the inorganic foam comprises a gas. The gaseous phase is present as fine gas bubbles separated by cell walls obtained from the liquid and solid phases. The cell walls meet each other at edges which meet each other at nodes, thereby forming a framework. The content of the gaseous phase in the inorganic foam may vary in a range of from 20 to 99 %, preferably from 50 to 98 % by volume. The liquid phase is preferably an aqueous phase, so that the inorganic foam typically also comprises water. However, the water may be partly removed upon drying. The solid phase of an inorganic foam comprises an inorganic binder. Inorganic foams can be open-cell foams or closedcell foams. In closed-cell foams, the gas is completely surrounded by the cell wall. Typically, at the same density, closed-cell foams are more robust than open-cell foams. Accordingly, closed cell foams are preferred within the present context due to their improved mechanical stability. Cellular materials can be obtained from inorganic foams by hardening and optionally drying the inorganic foam.

[0045] Water as denoted herein, can refer to pure, deionized H2O, or water containing up to 0.1 wt.-% impurities and / or salts, such as normal tap water.

[0046] The gas phase present in the foam can be introduced by mechanical, physical or chemical foaming. Non-limiting examples of gases comprise air, nitrogen, noble gases, carbon dioxide, hydrocarbons, hydrogen, oxygen, and mixtures thereof.

[0047] The gas phase present in the foam can be introduced by mechanical foaming in the presence of the respective gas. Mechanical foaming may be performed for example by using a mixer, or by an oscillating process, or by a stator-rotor process.

[0048] The gas phase can also be introduced into the foam by physical or chemical foaming, wherein the physical or chemical foaming process is suitable to liberate a gas. Preferably, blowing agents are used, which evaporate, decompose or react with water and / or an acid, so as to liberate the gas. Non-limiting examples of blowing agents are peroxides, such as hydrogen peroxide, dibenzoylperoxide, peroxobenzoic acid, peroxoacetic acid, alkali metal peroxides, perchloric acid, peroxomonosulfuric acid, dicumyl peroxide or cumyl hydroperoxide; isocyanates; carbonates and bicarbonates, such as CaCOs, Na2COs, and NaHCOs, which are preferably used in combination with an acid, e.g., a mineral acid or a Lewis acid; metal powders, such as aluminum powder; azides, such as methyl azide; hydrazides, such as p- toluenesulfonylhydrazide; hydrazine.

[0049] Chemical foaming can be facilitated by the use of a catalyst. Suitable catalysts preferably comprise Mn2+, Mn4+, Mn7+or Fe3+cations. Alternatively, the enzyme catalase may be used as catalyst. Non-limiting examples of suitable catalysts are MnO2 and KMnO4 . Such catalysts are preferably used in combination with peroxide blowing agents.

[0050] Further details regarding the components as used in the process for preparing an inorganic foam, the inorganic foam, the cellular material obtainable by hardening and optionally drying the inorganic foam, and the composition for preparing an inorganic foam formulation according to the present invention, are provided hereinafter. The term "inorganic particles" as used herein preferably refers to inorganic particles selected from the group consisting of:

[0051] • Oxides, including pure and mixed metal oxides, in particular aluminum oxide, silicon dioxide, spinels, cerium-gadoliniumoxide, zirconium oxide, magnesium oxide, tin oxide, titanium oxide and cerium oxide;

[0052] • Hydroxides, in particular aluminum hydroxide, calcium hydroxide, magnesium hydroxide, very particularly aluminum hydroxide;

[0053] • Carbides, in particular silicon carbide, boron carbide;

[0054] • Nitrides, in particular silicon nitride, boron nitride;

[0055] • Phosphates, in particular calcium phosphates, such as tri-calciumphosphate, hydroxyapatite;

[0056] • Carbonates, in particular nickel carbonate, calcium carbonate (ground limestone or precipitated calcium carbonate), magnesium carbonate;

[0057] • Silicates, in particular silicon dioxide, silica fume, fly ash, quartz, ground glasses, slag, calcium silicates, mullite, cordierite, clay minerals like kaolin or bentonite, zirconium silicate, zeolites, diatomaceous earth, very particularly silica fume, clay minerals, zirconium silicate; specifically clay minerals.

[0058] It has to be understood that the inorganic particles (i) as exemplified hereinabove are not identical to the inorganic binders iiia and / or iiib.

[0059] Preferably, the inorganic particles are obtained from carbonates and / or oxides. Preferred oxides include pure and mixed metal oxides, selected from the group consisting of aluminum oxides (including Al-Mg spinels), silicon dioxides, zirconium dioxides, and zinc oxides, particularly aluminum oxide, silicon dioxide, and zirconium dioxide. A preferred carbonate is calcium carbonate.

[0060] The term "group of inorganic particles" as used herein is to be understood as a plurality if inorganic particles of one kind. It is also to be understood that at least one, i.e. one or more groups, of inorganic particles may be used according to the invention, which means that also various mixtures of the above defined inorganic particles are possible. Thus, in a preferred embodiment of the invention, the at least one group of inorganic particles is selected from the group consisting of oxides, hydroxides, carbides, nitrides, phosphates, carbonates, silicates, sulfates, and mixtures thereof.

[0061] In a more preferred embodiment, the at least one group of inorganic particles is selected from the group consisting of carbonates and / or oxides, more preferably from aluminum oxides, silicon dioxide, zirconium dioxide, zinc oxide, and / or calcium carbonate.

[0062] The particle size of the at least one group of inorganic particles may vary within a broad range. For powders (primary particles), suitable median particle sizes D50 range from 30 nm to 300 pm, preferably from 100 nm to 250 pm, more preferably from 100 nm to 150 pm, even more preferably from 100 nm to 100 pm. In a further embodiment, suitable particle sizes range from 100 nm to 10 pm, preferably 100 nm to 2 pm. It has been found that the particle size distribution is of less importance. Good foams can be obtained with narrow as well as with broad particle size distributions.

[0063] In a preferred embodiment of the invention, the at least one group of inorganic particles has a median particle size D50 measured by dynamic light scattering in the range of from 30 nm to 300 pm.

[0064] The term "particle size (Dx )" refers to the diameter of a particle distribution, wherein x % of the particles have a smaller diameter. The D50 particle size is thus the median particle size. The Dx particle size can e.g. be measured by laser diffraction or dynamic light scattering (DLS) methods. Within the present context, dynamic light scattering (DLS) according to ISO 22412:2008 is preferably used. Dynamic light scattering (DLS), sometimes referred to as Quasi- Elastic Light Scattering (QELS), is a non-invasive, well-established technique for measuring the size and size distribution of molecules and particles typically in the submicron region. In the present invention the particles were characterized, which have been dispersed in a liquid, preferably water or ethanol. The Brownian motion of particles or molecules in suspension causes laser light to be scattered at different intensities. Analysis of these intensity fluctuations yields the velocity of the Brownian motion and hence the particle size using the Stokes-Einstein relationship. The distribution can be a volume distribution (Dv ), a surface distribution (Ds ), or a number distribution (Dn). In context of this application, the Dx value refers to a number distribution, wherein x(number) % of the particles have a smaller diameter.

[0065] The term "amphiphilic compound" is known in the art and relates to organic compounds having a non-polar part (also identified as tail or group R) and a polar part (also identified as head group). Accordingly, suitable amphiphilic molecules contain at least one tail coupled to a head group, typically by covalent bonds. Such amphiphilic molecules typically contain one tail and one head group but may also contain more than one tail and / or head group.

[0066] The at least one tail can be aliphatic (linear or branched) or cyclic (alicyclic or aromatic) and can carry substituents. Such substituents are e.g. -CnH2n+i with n < 8, secondary -OH, secondary -NH2, etc. Preferred tails are optionally substituted linear hydrocarbon chains of 2 to 8 carbon atoms, more preferably linear hydrocarbon chains of 3 to 8, 4 to 8 or 5 to 8 carbon atoms. Throughout the present specification, "secondary -OH" and "secondary -NH2" shall mean that the resulting substituted tail group constitutes a secondary alcohol or a secondary amine.

[0067] The head groups that are coupled to the tail preferably are ionic groups, ionizable groups and / or polar groups. Examples of possible head groups and corresponding salts are phosphates, phosphonates, sulfates, sulfonates, alcohols, amines, amides, pyrrolidines, gallates, carboxylic acids.

[0068] Preferred head groups are selected from carboxylic acid groups, gallates, amines and sulfonates. Particularly preferred head groups are selected from carboxylic acid groups, gallates and amine groups. A preferred carboxylic acid is enanthic acid (heptanoic acid) or nonanoic acid. A preferred gallate is butyl gallate. A preferred amine is heptylamine. Carboxylic acid groups are most preferred.

[0069] Preferably, the amphiphilic molecules reduce the surface tension of an air-water interface to values lower than or equal to 65 mN / m for concentrations lower than or equal to 0.5 mol / l.

[0070] Preferably, amphiphilic molecules have a critical micelle concentration (CMC) higher than 10 pmol / L and / or they have a solubility higher than 1 pmol / L.

[0071] It is to be understood that at least one, i.e. one or more members of amphiphilic compounds may be used according to the invention, which means that also various mixtures of the above defined amphiphilic compounds are possible. Thus, in a preferred embodiment of the invention, the at least one amphiphilic compound comprises amphiphilic compounds with at least one polar head group and at least one non-polar tail group, wherein the at least one head group is selected from the group consisting of phosphates, phophonates, sulfates, sulfonates, alcohols, amines, amides, pyrrolidines, gallates, and carboxylic acids; and wherein the at least one tail group is selected from an aliphatic or an aromatic or a cyclic group with 2 to 8 carbon atoms, wherein the carbon atoms are optionally substituted with one or more, same or different substituents selected from Ci-Cs-alkyl , secondary -OH, and second -NH2.

[0072] In a more preferred embodiment of the invention, the at least one amphiphilic compound comprises amphiphilic compounds with at least one head group selected from the group consisting of carboxylic acids, gallates and amines, and at least one tail group selected from aliphatic groups with 2 to 8 carbon atoms.

[0073] It is to be understood that upon combining the inorganic particles as defined herein with the amphiphilic compounds as defined herein hydrophobized or partially hydrophbized inorganic particles are formed. The term "hydrophobized inorganic particles" relates to inorganic particles, wherein the particle's surface is modified with amphiphilic molecules, so as to reduce the hydrophilic properties of the inorganic particle. Surface modification in this context means that the amphiphilic compounds are adsorbed on the particle's surface.

[0074] In a preferred embodiment, the amount of amphiphilic compound to inorganic particle surface is from 0.5 to 160 pmol / m2, preferably from 1 to 100 pmol / m2, more preferably from 2 to 50 pmol / m2, and in particular from 5 to 10 pmol / m2. In another preferred embodiment, the inorganic particles are provided in an amount of from 0.1 to 25 wt.-%, preferably 0.5 to 20 wt.-%, more preferably 1 to 15 wt.-%, in particular 10 to 15 wt.-%, with regard to the amount of the at least one inorganic binder.

[0075] The hydrophobized inorganic particles are suitable for stabilizing inorganic foams based on the inorganic binder as defined herein.

[0076] In a preferred embodiment, the weight ratio of water to solids in the foam formulation is from 0.1 to 2.0, preferably from 0.2 to 1 .5. Inorganic binders are inorganic compounds that harden in an aqueous environment (hydraulic) or in the presence of air (non-hydraulic). A latent hydraulic binder refers to a binder that only becomes hydraulic when exposed to an alkaline activator.

[0077] In the context of the present invention an inorganic binder is used, which comprises at least one calcium aluminate, and optionally at least one further binder material selected from the group consisting of hydraulic binders, latent hydraulic binders, pozzolanic binders, quicklime, hydrated lime, calcium sulfate, and mixtures thereof.

[0078] According to embodiments, the at least one inorganic binder comprises at least one calcium aluminate and at least one further binder material in a relative weight ratio of from 1 to 8, preferably 1 .9 to 4, more preferably 2.3 to 3.5

[0079] The at least one inorganic binder according to the present invention comprises at least one calcium aluminate. The term "calcium aluminate" refers to a material which comprises or consists of calcium aluminate phase such as CA, C2A, C3A, C12A7, CA2, CA6, and / or calcium aluminosilicate phases such as C2AS. Whereby C stands for CaO, A stands for AI2O3, and S stands for SiO2. The phase CA therefore has the empricial formula CaAl2O4. The at least one calcium aluminate may comprise or consist of any of CA, C2A, C3A, C12A7, CA2, CA6, and C2AS alone or in combination, very preferably C12A7. Other phases such as perovskite, belite (C2S), tricalciumsilicate (C3S), ternesite, ye’elemite (C4A3$, with $ = SO3), or ferrites may additionally be present. Ye’elemite may in particular be contained in an amount of between 0.5 - 15 wt.-% relative to the total weight of the calcium aluminate.

[0080] For example, a calcium aluminate of the present invention may comprise 32 wt.-% of CA, 11 wt.-% of C12A7, and 26 wt.-% of C2S. For example, a calcium aluminate of the present invention may comprise 80 wt.-% or more of CA2 and C2AS. For example, a calcium aluminate of the present invention may comprise 50 wt.-% or more, preferably 75 wt.-% or more, still more preferably 95 wt.-% or more, in particular 100 wt.-% C12A7. For example, a calcium aluminate of the present invention may comprise 50 - 60 wt.-% of CA2, 26 - 32 wt.-% of C2AS, 2 - 4 wt.-% of CA.

[0081] The molar ratio C / A in the calcium aluminate preferably is in the range from 0.5 to 3.0, more preferably from 1 .0 to 2.7, still more preferably from 1 .5 to 1 .8. It is further preferred that the total weight of calcium aluminate phases, preferably any of CA, C2A, C3A, C12A7, CA2, CA6, and C2AS alone or in combination, is at least 30 wt.-%, preferably at least 80 wt.-%, relative to the total weight of the calcium aluminate.

[0082] It can be preferred that the calcium aluminate comprises from 20 to 60 wt.-%, preferably 30 to 55 wt.-% of C, from 19 to 80 wt.-%, preferably from 20 to 40 wt.-% of A, from 0 to 20 wt.-%, optionally from 5 to 30 wt.-% of S, from 0 to 15 wt.-% of iron oxides, and from 0 to 5 wt.-% of titanium oxides.

[0083] Preferably, the amount of amorphous phases in the calcium aluminate is not more than 60 wt.-%, preferably not more than 20 wt.-%, relative to the total weight of the calcium aluminate.

[0084] The at least one inorganic binder according to the present invention may optionally additionally comprise at least one further binder material selected from the group consisting of hydraulic binders, latent hydraulic binders, pozzolanic binders, quicklime, hydrated lime, calcium sulfate, and mixtures thereof. It is to be noted that the further binder materials are not calcium aluminates as defined above. In particular, further binder materials are based on silicate and / or aluminosilicate phases

[0085] Non-limiting examples of “latent hydraulic binder" and "pozzolanic binder” are microsilica, metakaolin, natural aluminosilicates, fly ash, activated clay, or mixtures thereof. Pozzolans are siliceous or siliceous and aluminous containing compounds.

[0086] For the purposes of the present invention, a "latent hydraulic binder" is preferably a binder in which the molar ratio (CaO + MgO) : SiO2 is from 0.8 to 2.5 and particularly from 1.0 to 2.0. In general terms, the above-mentioned latent hydraulic binders can be selected from industrial and / or synthetic slag, in particular from blast furnace slag, electrothermal phosphorous slag, steel slag and mixtures thereof, and the "pozzolanic binders" can generally be selected from amorphous silica, preferably precipitated silica, fumed silica and microsilica, ground glass, metakaolin, aluminosilicates, fly ash, preferably brown-coal fly ash and hard-coal fly ash, natural pozzolans such as tuff, trass and volcanic ash, natural and synthetic zeolites and mixtures thereof. As used herein, the term "slag" refers to the by-product of a smelting process, or synthetic slag. The main use of a smelting process is to convert an ore, scrap or a material mixture containing different metals into a form from which the desired metals can be skimmed as a metal layer and the undesired metal oxides, e.g. silicates, alumina, etc., remain as the slag.

[0087] Blast furnace slag (BFS) is formed as a by-product during the smelting of iron ore in the blastfurnace. Other materials are granulated blast furnace slag (GBFS) and ground granulated blast furnace slag (GGBFS), which is granulated blast furnace slag that has been finely pulverized. Ground granulated blast furnace slag varies in terms of grinding fineness and grain size distribution, which depend on origin and treatment method, and grinding fineness influences reactivity here. The Blaine value is used as parameter for grinding fineness, and typically has an order of magnitude of from 200 to 1000 m2 / kg , preferably from 300 to 500 m2 / kg. Finer milling gives higher reactivity. For the purposes of the present invention, the expression "blast furnace slag" is however intended to comprise materials resulting from all of the levels of treatment, milling, and quality mentioned (i.e. BFS, GBFS and GGBFS).

[0088] Blast furnace slag generally comprises from 30 to 45 % by weight of CaO, about 4 to 17 % by weight of MgO, about 30 to 45% by weight of SiO2 and about 5 to 15 % by weight of AI2O3, typically about 40% by weight of CaO, about 10 % by weight of MgO, about 35 % by weight of SiO2 and about 12% by weight of AI2O3.

[0089] Amorphous silica is preferably an X-ray-amorphous silica, i.e. a silica for which the powder diffraction method reveals no crystallinity. The content of SiO2 in the amorphous silica of the invention is advantageously at least 80% by weight, preferably at least 90% by weight.

[0090] Precipitated silica is obtained on an industrial scale by way of precipitating processes starting from water glass. Precipitated silica from some production processes is also called silica gel. Microsilica is a fine powder, mainly comprising amorphous SiO2 powder and is a by-product of silicon or ferrosilicon production. The particles have a diameter of about 100 nm and a specific surface area of from about 15 to about 30 m2 / g .

[0091] Fumed silica is produced via reaction of chlorosilanes, for example silicon tetrachloride, in a hydrogen / oxygen flame. Fumed silica is an amorphous SiO2 powder of particle diameter from 5 to 50 nm with specific surface area of from 50 to 600 m2 / g.

[0092] Metakaolin is produced when kaolin is dehydrated. Whereas at from 100 to 200°C kaolin releases physically bound water, at from 500 to 800 °C a dehydroxylation takes place, with collapse of the lattice structure and formation of metakaolin .

[0093] Accordingly, pure metakaolin comprises about 54 % by weight of SiO2 and about 46 % by weight of AI2O3.

[0094] Natural aluminosilicates are minerals comprising aluminum, silicon, and oxygen, which may be expressed by referring to the SiO2 and AI2O3 content. They are a major component of kaolin and other clay minerals. Andalusite, kyanite, and sillimanite are naturally occurring aluminosilicate minerals that have the composition A SiOs.

[0095] Fly ash is produced inter alia during the combustion of coal in power stations, and comprises fine particles of varying composition. The main ingredients of fly ash are silicon oxide, aluminum oxide, and calcium oxide. Class C fly ash (brown-coal fly ash) comprises according to

[0096] Burnt shale, especially burnt oil shale is obtained at temperatures of about 800 °C by burning of natural shale and subsequent milling.

[0097] In a preferred embodiment, the at least one further binder material is selected from the group consisting of Portland cement, blast furnace slag, microsilica, metakaolin, aluminosilicates, fly ash, quicklime, hydrated lime, calcium sulfate, and mixtures thereof. In a particularly preferred embodiment, the at least one further binder material is selected from the group consisting of metakaolin, fly ash, quicklime, hydrated lime, calcium sulfate, and mixtures thereof.

[0098] Hydrated lime, also called slaked lime or caustic lime essentially consists of Ca(OH)2. For example, hydrated lime can be according to standard ASTM C207-18.

[0099] It is preferred that the composition, the inorganic foam formulation, the inorganic foam, and the cellular material according to the present invention do not comprise an additional alkaline activator. If an alkaline activator is nevertheless added as an additive, it is preferable to select an alkaline activator from alkali metal hydroxides of the formula MOH and alkali metal silicates of the formula m SiO2 x n M2O, where M is the alkali metal, preferably Li, Na or K or a mixture thereof, and the molar ratio m:n is < 4.0, preferably < 3.0, with further preference to < 2.0, and in particular < 1 .70.

[0100] The alkali metal silicate is preferably water glass, particularly preferably an aqueous water glass and in particular a sodium water glass or potassium water glass.

[0101] However, it is also possible to use lithium water glass or ammonium water glass or a mixture of the water glasses mentioned. The m:n ratio stated above (also termed "modulus") should preferably not be exceeded, since otherwise reaction of the components is likely to be incomplete. It is also possible to use very much smaller moduli, for example about 0.2. Water glasses with higher moduli should be adjusted before use to moduli in the range of the invention by using a suitable aqueous alkali metal hydroxide.

[0102] If an alkaline activator is used, the preferred quantity of the alkaline activator is from 1 to 55 wt.-% and in particular from 5 to 25 wt.-%.

[0103] In a preferred embodiment, the at least one inorganic binder additionally comprises at least one Portland cement selected from CEM I, CEM II, CEM III, CEM IV, CEM V cements, according to DIN EN 197-1 (11 / 2011), preferably CEM I cement.

[0104] Furthermore, various additives may be used according to the present invention. In a preferred embodiment, the at least one additive is selected from the group consisting of pH modifiers, fillers, accelerators, retarders, rheology modifiers, superplasticizers, surfactants, fibers, water-glass, further hydrophobization agents, catalysts, and mixtures thereof.

[0105] Rheology modifiers adjust the viscosity and thus the flow behavior and ensure a good balance between consistency, durability and application properties. These modifiers can be based on synthetic polymers (e.g. acrylic polymers), cellulose, silica, starches or clays.

[0106] Superplasticizers are polymers that function as dispersant to avoid particle segregation and improve the rheology and thus workability of suspensions. Superplasticizers generally can be divided into four categories: lignosulfonates, melamine sulfonates, naphthalene sulfonates, and comb polymers (e.g. polycarboxylate ethers, polyaromatic ethers, cationic copolymers, and mixtures thereof). The setting time of the inorganic foam can be prolonged I shortened by the addition of certain compounds called retarders I accelerators. Retarders can be divided into the groups of lignosulfonates, cellulose derivatives, hydroxyl carboxylic acids, organophosphates, synthetic retarders, and inorganic compounds. Non-limiting examples of retarders are hydroxyethyl cellulose, carboxymethyl hydroxyethyl cellulose, citric acid, tartaric acid, gluconic acid, glucoheptonate, maleic anhydride, 2-Acrylamido-2-methylpropanesulfonic acid (AMPS) copolymers, borax, boric acid, and ZnO. Non-limiting examples of accelerators are CaCl2, KCI, Na2SiOs, NaOH, Ca(OH)2, and CaO x A^Os, lithium silicate, potassium silicate, and aluminum salts, such as aluminum sulfate.

[0107] Fibers (or stabilizing fibers) can be added during the foaming process to further increase the stability of the foam. Such fiber can be made of a variety of materials, such as rock (e.g. basalt), glass, carbon, organic polymers (e.g. polyethylene, polypropylene, polyacrylonitrile, polyamides, and polyvinyl alcohols), cellulose, lignocellulose, metals (e.g. iron or steel), and mixtures thereof. Organic fibers are preferred. The amount of the fibers can be up to 3 wt.-%, preferably from 0.1 to 2 wt.-%, more preferably 0.1 to 1.5 wt.-% and in particular 0.2 to 1 wt.-%, based on the at least one inorganic binder. The fibers preferably have a length of up to 200 mm or up to 120 mm, preferably up to 100 mm, more preferably up to 50 mm, most preferably up to 25 mm and in particular up to 20 mm, and a diameter of up to 100 pm.

[0108] The term "filler" refers primarily to materials that can be added to increase the volume without impairing the properties of the foam. The fillers mentioned can be selected from the group consisting of quartz sand or powdered quartz, calcium carbonate, rock flour, low-density fillers (for example vermiculite, perlite, diatomaceous earth, mica, talc powder, magnesium oxide, foamed glass, hollow spheres, foam sand, clay, polymer particles), pigments (e.g. titanium dioxide), high density fillers (e.g. barium sulphate), metal salts (e.g. zinc salts, calcium salts, etc.), and mixtures thereof. Grain sizes suitable here are in particular up to 500 pm. It is particularly preferable that the average grain size is up to 300 pm, preferably up to 150 pm.

[0109] Surfactants, which may be used in addition to the amphiphilic compounds as defined herein, include non-ionic surfactants, anionic surfactants, cationic surfactants, zwitterionic surfactants and proteins or synthetic polymers. However, surfactants are not preferred as they tend to yield open-cell foams.

[0110] Non-ionic surfactants include fatty alcohols, cetyl alcohol, stearyl alcohol, and cetostearyl alcohol (comprising predominantly cetyl and stearyl alcohols), and oleyl alcohol. Further examples include polyethylene glycol alkyl ethers (Brij) CHS-(CH2)IO- i6-(O-C2H4)i-25-OH such as octaethylene glycol monododecyl ether or pentaethylene glycol monododecyl ether; polypropylene glycol alkyl ethers CH3-(CH2) -i6-(O- CSH6)I-25-OH; glucoside alkyl ethers CH3-(CH2)io-i6-(0-Glucoside)i-3-OH such as decyl glucoside, lauryl glucoside, octyl glucoside; polyethylene glycol octylphenyl ethers CsHi7-(C6H4)-(O-C2H4)i-25-OH such as Triton X-100; polyethylene glycol alkylphenyl ethers C9Hi9-(CeH4)-(O-C2H4)i-25-OH such as nonoxynol-9; glycerol alkyl esters such as glyceryl laurate; polyoxyethylene glycol sorbitan alkyl esters such as polysorbate; sorbitan alkyl esters such as spans; cocamide MEA, cocamide DEA; dodecyldimethylamine oxide; block copolymers of polyethylene glycol and polypropylene glycol such as poloxamers; polyethoxylated tallow amine (POEA). Preferred non-ionic surfactants also include alkyl polyglucosides. Alkyl polyglucosides generally have the formula H-(C6HioOs)m-0-R1 , where (CeH Os) is a glucose unit and R1 is a C6-C22-alkyl group, preferably a C8-C16-alkyl group and in particular a C8-C12-alkyl group, and m = from 1 to 5.

[0111] Anionic surfactants contain anionic functional groups at their head, such as sulfate, sulfonate, phosphate, and carboxylates. Prominent alkyl sulfates include ammonium lauryl sulfate, sodium lauryl sulfate (sodium dodecyl sulfate, SLS, or SDS), and the related alkyl-ether sulfates sodium laureth sulfate (sodium lauryl ether sulfate or SLES), and sodium myreth sulfate. Others include docusate (dioctyl sodium sulfosuccinate), perfluorooctanesulfonate (PFOS), perfluorobutanesulfonate, alkylaryl ether phosphates, alkyl ether phosphates. Preferred carboxylates include the alkyl carboxylates, such as sodium stearate. More specialized species include sodium lauroyl sarcosinate and carboxylate-based fluorosurfactants such as perfluorononanoate, perfluorooctanoate (PFOA or PFO).

[0112] Cationic surfactants include, dependent on the pH, primary, secondary, or tertiary amines: Primary and secondary amines become positively charged at pH < 10. An example is octenidine dihydrochloride. Furthermore, cationic surfactants include permanently charged quaternary ammonium salts, such as cetrimonium bromide (CTAB), cetylpyridinium chloride (CPC), benzalkonium chloride (BAC), benzethonium chloride (BZT), dimethyldioctadecylammonium chloride, dioctadecyldimethylammonium bromide (DODAB).

[0113] Zwitterionic (amphoteric) surfactants have both cationic and anionic centers attached to the same molecule. The cationic part is based on primary, secondary, or tertiary amines or quaternary ammonium cations. The anionic part can be more variable and include sulfonates, as in the sultaines CHAPS (3-[(3-Cholamidopropyl)dimethylammonio]-1 -propanesulfonate) and cocamidopropyl hydroxysultaine. Betaines such as cocamidopropyl betaine have a carboxylate with the ammonium. The most common biological zwitterionic surfactants have a phosphate anion with an amine or ammonium, such as the phospholipids phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, and sphingomyelins. Non-limiting examples of proteins are bovine serum albumin, egg ovalbumin, milk caseins or beta-lactoglobulin.

[0114] The proportion of the surfactant can vary over a broad range. The surfactant may be present in an amount of up to 2.5 wt.-%, preferably up to 1 .5 wt.-%.

[0115] Waterglass may function as alkaline activator as explained above. The term "waterglass" has also been defined above.

[0116] Catalysts that may be used as additives are catalysts that may be used in combination with a blowing agent for foaming. Suitable catalysts are mentioned above and below in the context of blowing agents.

[0117] Geopolymers are described by way of example in US 4,349,386, WO 85 / 03699 and US 4,472,199. Geopolymers are binders that are primarily based on SiO2 and / or AI2O3, such as poly(sialate), poly(siloxo), poly(sialate-siloxo), or poly(sialate-disiloxo), which harden in alkaline aqueous environment. Sialate is an abbreviation for silicon- oxo-aluminum. Geopolymer binders do not contain calcium aluminates as defined above in significant amounts. Geopolymers material is similar to zeolite, however, the microstructure is amorphous and not crystalline. These binders may also contain compounds based on Fe20s, TiO2, CaO, MgO, NaO, or K2O. Pure geopolymers generally have a low calcium content. Further details regarding the amounts of the components as used according to the present invention are defined hereinafter.

[0118] In particular, the amount of amphiphilic compound to inorganic particle surface is from 0.5 to 160 pmol / m2; and / or the inorganic particles are provided in an amount of from 0.1 to 25 wt.-% with regard to the amount of the at least one inorganic binder; and / or the weight ratio of water to solids is from 0.1 to 2.0.

[0119] In one exemplary embodiment, the amount of amphiphilic compound to inorganic particle surface is from 10 to 140 pmol / m2, preferably from 20 to 120 pmol / m2; and / or the inorganic particles are provided in an amount of from 0.25 to 15 wt.-%, with regard to the amount of the at least one inorganic binder; and / or the weight ratio of water to the inorganic binder is from 0.2 to 1 .5.

[0120] As explained above, it is to be understood that at least one group, i.e. one or more groups, of inorganic particles and at least one member, i.e. one or more members, of amphiphilic compounds may be used. The above amounts refer to the overall amount of amphiphilic compounds and inorganic particles, respectively, being used in the process of the invention or being present in the composition, the inorganic foam or the cellular material of the invention. Furthermore, the above amount in relation to the inorganic binder refers to the overall amount of inorganic binders being used in the process of the invention or being present in the composition, the inorganic foam or the cellular material of the invention.

[0121] If the at least one inorganic binder comprises (iiia) at least one calcium aluminate, and (iiib) at least one further binder material selected from the group consisting of hydraulic binders, latent hydraulic binders, pozzolanic binders, quicklime, hydrated lime, calcium sulfate, and mixtures thereof, the components (iiib) and (iiia) may be present in a relative weight ratio of from 0.1 to 3.4, preferably 0.1 to 2.0, more preferably 0.3 to 1 .5.

[0122] Suitable amounts of the additives may vary over a broad range and also depend on the type of additive. Typically, the at least one additive is provided in weight ratio of from 0.0003 to 30 wt.-%, or of from 0.03 to 25 wt.-%, based on the amount of the at least one inorganic binder. However, fillers may also be used in higher amounts. In particular, the filler may be present in similar amounts as the inorganic binder. Preferably, the weight ratio of filler to at least one inorganic binder may be from 2:1 to 1 OO, preferably from 1 :1 to 1 :10.

[0123] Further details regarding the process of the invention are provided hereinafter.

[0124] In a preferred embodiment of the process of the invention, step (1 ) comprises the steps of

[0125] (la) functionalizing the at least one group of inorganic particles with the at least one amphiphilic compound; and

[0126] (l b) mixing the functionalized particles with the at least one inorganic binder, water, and optionally additives

[0127] The functionalization in step (1a) is not particularly limited.

[0128] For example, the at least one group of inorganic particles can be mixed with the at least one amphiphilic compound in dry state. It is likewise possible to spray the at least one amphiphilic molecule on the surface of the inorganic particles. It is possible to functionalize at 25 °C and 1013 mbar. It is, however, also possible to functionalize and elevated temperature such as 35 °C, 50 °C, or 100 °C and / or at reduced pressure such as 500 mbar, 100 mbar or 10 mbar. Functionalization at reduced pressure can be preferred in case where volatile side products should be removed.

[0129] It is also possible to functionalize the at least one group of inorganic particles with the at least one amphiphilic compound in aqueous dispersion. Therefore, the at least one group of inorganic particles is first dispersed in water, then the at least one amphiphilic compound is added. The water can subsequently be removed or the aqueous dispersion of functionalized inorganic particles can be used for step (1 b).

[0130] Preferably, in step (1 b) the functionalized particles are first dispersed in water, followed by addition of the at least one inorganic binder and optionally additives.

[0131] In a preferred embodiment, in step (1) of the process of the invention the pH-value is below 12. This is mainly due to the low amount or absence of any strongly alkaline materials. This in turn is in contrast to processes of geopolymer manufacture where strongly alkaline activators such as NaOH or silicates are used. If the pH in step (1) is above 12, strongly alkaline materials such as further hydraulic binder, if present, can be reduced. It is also possible to add neutralizing agents to reduce the pH to below 12. Neutralizing agents can be acids, in particular Brdnsted acids. Examples of useful acids are carboxylic acids, carbonic acid, or phosphoric acid.

[0132] It is preferred that the foam formulation resulting from step (1) has a pH of below 12.

[0133] In a preferred embodiment of the process of the invention, step (2) comprises foaming the resulting foam formulation by chemical foaming. In another preferred embodiment of the process of the invention, step (2) comprises foaming the resulting foam formulation by physical foaming. In yet another preferred embodiment of the process of the invention, step (2) comprises foaming the resulting foam formulation by mechanical foaming.

[0134] In a preferred embodiment, step (2) of the process for preparing an inorganic foam comprises foaming the resulting foam formulation with a blowing agent, preferably by mixing the foam formulation obtained in step (1) with carbonates or bicarbonates, such as CaCOs, Na2COs, and NaHCOs, aluminium powder, p-toluenesulfonylhydrazide, hydrogen peroxide, dibenzylperoxide, perchloric acid, peroxomonosulfuric acid, dicumyl peroxide, cumyl hydroperoxide or mixtures thereof, more preferably hydrogen peroxide. In a more preferred embodiment, foaming of the foam formulation in step (2) is performed with a blowing agent, preferably by mixing the foam formulation obtained in step (1) with aluminum powder or with a carbonate in the presence of an acid or with an aqueous solution of hydrogen peroxide, optionally in the presence of a catalyst.

[0135] In a more preferred embodiment, step (2) of the process for preparing an inorganic foam comprises foaming the resulting foam formulation with a blowing agent, preferably a blowing agent as defined above, wherein the blowing agent is added in an amount of from 0.1 to 10 wt- %, based on the total amount of the foam formulation.

[0136] It is possible to accelerate the foaming process, in particular foaming with a peroxide as blowing agent, by the addition of a suitable catalyst. In a preferred embodiment, step (2) of the process for preparing an inorganic foam therefore comprises foaming the resulting foam formulation with a chemical blowing agent in the presence of a catalyst, wherein preferably the catalyst comprises Mn2+, Mn4+, Mn7+or Fe3+cations, or the catalyst is the enzyme catalase. More preferably, the catalyst is selected from the group consisting of MnSO4 , MnO2, KMnO4 , and mixtures thereof. The catalyst may be used in an amount of from 0.01 to 5 wt.-%, preferably from 0.01 to 2 wt.-%, more preferably from 0.05 to 1 .0 wt.-% and in particular from 0.1 to 0.6 wt.-%, based on to total amount of foam formulation.

[0137] In a preferred embodiment, the chemical blowing agent is hydrogen peroxide provided as an aqueous hydrogen peroxide solution comprising from 10 to 60 wt.-%, preferably from 20 to 60 wt.-% and in particular from 40 to 60 wt.-% hydrogen peroxide, wherein the aqueous hydrogen peroxide solution is added in an amount of from 0.1 to 6 wt.-%, preferably from 0.5 to 5.0 wt.-% and in particular from 1 to 4 wt.- % based on the total weight of the foam formulation, assuming an about 50 wt.-% hydrogen peroxide solution.

[0138] In another preferred embodiment, mechanical foaming is performed, preferably by using a mixer, or by an oscillating process, or by a stator-rotor process.

[0139] After the foaming step (2), the inorganic foam according to the invention is obtained.

[0140] In a preferred embodiment, the freshly prepared inorganic foam is allowed to harden in a sealed container after step (2). In a more preferred embodiment, the freshly prepared inorganic foam is allowed to harden for at least 12 h in a sealed container after step (2). Hardening can be performed at a temperature in the range of from 0 °C to 100 °C, preferably 20 °C to 80 °C.

[0141] A cellular material is obtained by hardening, and optionally drying the above mentioned inorganic foam. The cellular material according to the present invention may be used as a construction material, in particular a heat insulation element, an acoustic absorption element or a fire protection element, wherein the element may in each case, e.g., be a sheet or board.

[0142] An inorganic foam of the present invention may also be used to fill cavities, for example the cavities of bricks or concrete blocks. Thereby, in particular, the thermal insulation and / or acoustic insulation properties of materials can be improved.

[0143] The inorganic foams and cellular materials according to the invention have a mostly closed-cell structure and the following advantageous features.

[0144] The dry density is typically below 300 kg / m3, suitably below 200 kg / m3, preferably below 150 kg / m3and more preferably below 100 kg / m3. In particular, the dry density can be even further reduced to below 100 kg / m3, preferably below 90 kg / m3, if the at least one inorganic binder not only comprises the at least one calcium aluminate, but also the at least one further binder material selected from the group consisting of hydraulic binders, latent hydraulic binders, pozzolanic binders, quicklime, hydrated lime, calcium sulfate, and mixtures thereof.

[0145] The thermal conductivity (measured according to standard DIN EN 12667) is preferably below 50 mW / m*K, more preferably below 45 mW / m*K and in particular below 40 mW / m*K.

[0146] The compressive strength (measured according to standard DIN EN 826) is preferably at least 30 kPa. As a matter of fact, due to the lower dry density, the ratio of compressive strength to dry density is improved. For certain applications, such as for example cavity filling, the compressive strength can also be lower than 30 kPa.

[0147] The air flow resistance (measured according to standard DIN EN 29 053) is preferably at least 1000 kPa*s / m2, more preferably at least 1500 kPa*s / m2, most preferably at least 1800 kPa*s / m2. In particular, the airflow resistance can be even further increased to at least 2000 kPa*s / m2, if the at least one inorganic binder not only comprises the at least one calcium aluminate, but also the at least one further binder material selected from the group consisting of hydraulic binders, latent hydraulic binders, pozzolanic binders, quicklime, hydrated lime, calcium sulfate, and mixtures thereof.

[0148] According to preferred embodiments, a composition for preparing an inorganic foam formulation, said composition comprising, relative to the total dry weight of the composition unless where otherwise stated,

[0149] (i) 9 - 20 wt.-% of at least one group of inorganic particles, in particular of carbonates;

[0150] (ii) 0.1 - 1 wt.-% of at least one amphiphilic compound;

[0151] (iii) 60 - 90 wt.-% of at least one inorganic binder comprising

[0152] (iiia) 10 - 40, wt.-% preferably 20 - 40 wt.-%, relative to the inorganic binder, of at least one calcium aluminate,

[0153] (iiib) 60 - 90 wt.-%, preferably 60 - 80 wt.-%, relative to the inorganic binder, of at least one further inorganic binder selected from the group consisting of latent hydraulic binders, pozzolanic binders, quicklime, hydrated lime, calcium sulfate, and mixtures thereof. According to preferred embodiments, a composition for preparing an inorganic foam formulation, said composition comprising, relative to the total dry weight of the composition unless where otherwise stated,

[0154] (i) 9 - 20 wt.-% of at least one group of inorganic particles, in particular of carbonates;

[0155] (ii) 0.1 - 1 wt.-% of at least one amphiphilic compound;

[0156] (iii) 35 - 55 wt.-% of at least one inorganic binder comprising

[0157] (iiia) 10 - 40, wt.-% preferably 20 - 40 wt.-%, relative to the inorganic binder, of at least one calcium aluminate,

[0158] (iiib) 60 - 90 wt.-%, preferably 60 - 80 wt.-%, relative to the inorganic binder, of at least one further inorganic binder selected from the group consisting of latent hydraulic binders, pozzolanic binders, quicklime, hydrated lime, calcium sulfate, and mixtures thereof;

[0159] (iv) 35 - 55 wt.-% of additives, especially limestone powder.

[0160] Examples

[0161] The present invention is further illustrated by the following examples.

[0162] Inorganic foams were prepared with the composition as shown in the following tables 1 and 2. Therein, CA is calcium aluminate as described above with a main phase of C12A7. MK is a metakaolin (Argical M1000). FA is fly ash (Microsit 10). Pozzolane used is a natural pozzolane (Micrasil). CaSO4 used is a calcium sulfate anhydrite. CaO used is Precal 643. Fiber is PAN fibers (6mm, 6.7dtex). Foaming powder (F.P.) is a dry pre-mix of 99 wt.-% of CaCOs (Schafer Precarb 100) and 1 wt.-% of nonanoic acid. Hydrogen peroxide was used as a 30% solution in water, w / s is the water to solids weight ratio and includes water from the hydrogen peroxide. PCE is a polycarboxylate ether superplasticizer.

[0163] For the preparation of foams, the foaming powder was first dispersed in water. Then, the calcium aluminate, the metakaolin, the fly ash, the calcium oxide, the MnO2, calcium sulfate, pozzolane, PCE, and citric acid where present, and the fibers were added to prepare an aqueous suspension. After 5 min of stirring, the foaming of the suspension was initiated by adding the hydrogen peroxide. The so obtained slurry was poured to a mold where the foam expansion evolved until the decomposition of the hydrogen peroxide was completed. The prepared wet foam was stored in humid atmosphere over night to allow proper setting. Thereafter, it was demolded and dried at 23 °C / 50% r.h. until constant mass.

[0164] Table 1: Foam formulations (values in [g] unless otherwise indicated)

[0165] ’ Wt.-% relative to solids

[0166] Table 2: Foam formulations (values in [g] unless otherwise indicated)

[0167] ’ Wt.-% relative to solids

[0168] The following table 3 shows the results. The thermal conductivity (T.C.) was measured according to standard DIN EN 12667. The compressive strength (C.S.) was measured according to standard DIN EN 826.

[0169] Table 3: Measured results

[0170] *1 : The aqueous suspension prepared was compact and very poor foaming was observed. The dried foam was soft and not properly cured.

[0171] *2: The aqueous suspension prepared was compact. Foaming was very fast and hydrogen peroxide as not properly homogenized. The dried foam was cured but inhomogeneous with cracks and voids.

[0172] Table 3 (continued)

Claims

Claims1. A process for preparing an inorganic foam comprising the steps of(1) mixing(i) at least one group of inorganic particles;(ii) at least one amphiphilic compound;(iii) at least one inorganic binder comprising(iiia) at least one calcium aluminate, and optionally(iiib) at least one further binder material selected from the group consisting of hydraulic binders, latent hydraulic binders, pozzolanic binders, quicklime, hydrated lime, calcium sulfate, and mixtures thereof;(iv) water; and optionally(v) at least one additive; and(2) foaming the resulting foam formulation by chemical, physical or mechanical foaming.

2. The process according to claim 1 , characterized in that the at least one group of inorganic particles is selected from oxides, hydroxides, carbides, nitrides, phosphates, carbonates, silicates, and / or sulfates, preferably from carbonates and / or oxides, more preferably from aluminum oxides, silicon dioxide, zirconium dioxide, zinc oxide, and / or calcium carbonate.

3. The process according to at least one of the preceding claims, characterized in that the at least one group of inorganic particles has a median particle size D50 measured by dynamic light scattering in the range of from 30 nm to 300 pm.

4. The process according to at least one of the preceding claims, characterized in that the at least one amphiphilic compound is selected from amphiphilic compounds with at least one polar head group and at least one non-polar tail group, wherein the at least one head group is selected from the group consisting of phosphates, phophonates, sulfates, sulfonates, alcohols, amines, amides, pyrrolidines, gallates, and carboxylic acids; and wherein the at least one tail group is selected from an aliphatic or an aromatic or a cyclic group with 2 to 8 carbonatoms, wherein the carbon atoms are optionally substituted with one or more, same or different substituents selected from Ci-Cs-alkyl , secondary -OH, and second -NH2.

5. The process according to at least one of the preceding claims, characterized in that the molar ratio C / A in the calcium aluminate is in the range from 0.5 to 3.0, preferably from 1 .0 to 2.7, more preferably from 1 .5 to 1 .8.

6. The process according to at least one of the preceding claims, characterized in that the at least one calcium aluminate comprises calcium aluminate phases, preferably comprises any of CA, C2A, C3A, C12A7, CA2, CA6, and C2AS alone or in combination, with at least 30 wt.-%, preferably at least 80 wt.-%, relative to the total weight of the calcium aluminate.

7. The process according to at least one of the preceding claims, characterized in that the amount of amphiphilic compound to inorganic particle surface is from 0.5 to 160 pmol / m2, preferably from 1 to 100 pmol / m2, more preferably from 2 to 50 pmol / m2, and in particular from 5 to 10 pmol / m2.

8. The process according to at least one of the preceding claims, characterized in that the inorganic particles are provided in an amount of from 0.1 to 25 wt.-%, preferably 0.5 to 20 wt.-%, more preferably 1 to 15 wt.-%, in particular 10 to 15 wt.-%, with regard to the amount of the at least one inorganic binder.

9. The process according to at least one of the preceding claims, characterized in that the at least one inorganic binder comprises at least one calcium aluminate and at least one further binder material in a relative weight ratio of from 1 to 8, preferably 1 .9 to 4, more preferably 2.3 to 3.5.

10. The process according to at least one of the preceding claims, characterized in that step (1) comprises the steps of(1a) functionalizing the at least one group of inorganic particles with the at leastone amphiphilic compound; and(1 b) mixing the functionalized particles with the at least one inorganic binder, water, and optionally additives.11 . The process according to at least one of the preceding claims, characterized in that the pH-value is below 12 in step (1).

12. An inorganic foam obtainable by a process as claimed in any of claims 1 - 11.

13. A cellular material obtainable by hardening and optionally drying the inorganic foam as claimed in claim 12.

14. The cellular material as claimed in claim 13, characterized in that it has a dry density below 300 kg / m3, preferably below 200 kg / m3, more preferably below 150 kg / m3, still more preferably below 100 kg / m3; and / or in that it has an air flow resistance, measured according to standard DIN EN 29 053, of at least 1000 kPa*s / m2, preferably at least 1500 kPa*s / m2, most preferably at least 1800 kPa*s / m2; and / or in that it has a thermal conductivity, measured according to standard DIN EN 12667, of below 50 mW / m*K, preferably below 45 mW / m*K, and in particular below 40 mW / m*K.

15. Use of an inorganic foam as claimed in claim 12 or of a cellular material as claimed in any of claims 13 - 14 as a construction material, in particular as a heat insulation element, an acoustic absorption element, or a fire protection element, or for the filling of cavities.

16. A composition for preparing an inorganic foam formulation, said composition comprising as components:(i) at least one group of inorganic particles;(ii) at least one amphiphilic compound;(iii) at least one inorganic binder comprising(iiia) at least one calcium aluminate, and optionally(iiib) at least one further binder material selected from the group consisting of hydraulic binders, latent hydraulic binders, pozzolanic binders, quicklime, hydrated lime, calcium sulfate, and mixtures thereof, and optionally (iv) at least one additive; wherein the components (i), (ii), (iii), and if present (iv), are present separately in spatially separated containers; or the components (i) and (ii) are present as a mixture in a first container, and component (iii) is present separately in a spatially separate second container, and the component (iv) if present is present in the first and / or the second container; or the components (i), (ii), (iii), and (iv) are present as a mixture in one container.

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