EP4277737A1 - Production de particules d'aérogel monodispersées - Google Patents

Production de particules d'aérogel monodispersées

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Publication number
EP4277737A1
EP4277737A1 EP22701913.0A EP22701913A EP4277737A1 EP 4277737 A1 EP4277737 A1 EP 4277737A1 EP 22701913 A EP22701913 A EP 22701913A EP 4277737 A1 EP4277737 A1 EP 4277737A1
Authority
EP
European Patent Office
Prior art keywords
airgel
precursor solution
airgel particles
viscosity
reaction bath
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22701913.0A
Other languages
German (de)
English (en)
Inventor
Barbara Milow
Seeni Meera KAMAL MOHAMED
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Deutsches Zentrum fuer Luft und Raumfahrt eV
Original Assignee
Deutsches Zentrum fuer Luft und Raumfahrt eV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Deutsches Zentrum fuer Luft und Raumfahrt eV filed Critical Deutsches Zentrum fuer Luft und Raumfahrt eV
Publication of EP4277737A1 publication Critical patent/EP4277737A1/fr
Pending legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/0091—Preparation of aerogels, e.g. xerogels
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2205/00—Foams characterised by their properties
    • C08J2205/02—Foams characterised by their properties the finished foam itself being a gel or a gel being temporarily formed when processing the foamable composition
    • C08J2205/026—Aerogel, i.e. a supercritically dried gel

Definitions

  • the present invention relates to a method for producing airgel particles, in which the viscosity of a precursor solution is adjusted using an organic thickener and the precursor solution is then dropped into a reaction bath and gelled there, and corresponding inorganic, organic or carbon-based airgel particles produced using the method.
  • aerogels Open-pored nanostructured solids that can be produced using a sol-gel process and subsequent drying are generally referred to as aerogels.
  • aerogels can be formed from inorganic metal oxides, biopolymers, phenols, proteins, polyols, carbon allotropes, or any other gellable compound. They can be classified as microporous ( ⁇ 2 nm), mesoporous (2 to 50 nm) or macroporous (> 50 nm) and are classified as xerogels (subcritical drying with large shrinkage), cryogels (freeze drying) or aerogels (supercritical drying or air drying with low shrinkage).
  • Aerogels exhibit some remarkable properties such as low densities (0.02 to 0.2 g/cm 3 ), low thermal conductivity (0.005 to 0.1 W/mK), low sound velocity ( ⁇ 100 m/s), high porosity (up to 99.9%) and a high specific surface area (100 to 3000 m 2 /g), which make aerogels versatile.
  • Commonly used organic aerogels include those formed from a sol-gel process between resorcinol (R) and formaldehyde (F), termed RF aerogels.
  • R resorcinol
  • F formaldehyde
  • Typical inorganic aerogels include silica aerogels.
  • the production and properties of RF aerogels and silica aerogels are widely described in the prior art.
  • Aerogels can be used as additives for sand mixtures in sand casting processes.
  • a metal or other material is poured into a sand mold that is a negative of the desired shape.
  • Typical sand mixes include sand, binder and additives.
  • Aerogels can be used as a binder or as an additive in such processes and have some interesting properties that are particularly useful for casting processes.
  • spherical airgel particles can be incorporated as additives in sand casting mixtures.
  • the sand can be replaced with airgel particles and mixed with a binder before the mold is cured.
  • the size of the airgel particles should be of the same order of magnitude as the size of the sand grains to ensure good miscibility.
  • the high specific surface area of the aerogels leads to improved physisorption of the binder's decomposition gases, thus reducing the formation of defects and air pockets.
  • the gases can react with the airgel and thus lead to chemisorption of the gases.
  • Other advantages of using aerogels also include the reduced thermal conductivity of the mixture, which leads to slower cooling and thus lowers the necessary casting temperatures and wall thicknesses, as well as the increased gas permeability of the casting molds.
  • EP 1 820 582 A discloses a water-soluble core that can be used in the field of lightweight casting and/or precision casting.
  • the inorganic mixture of sand and airgel granules is bound with various binders.
  • a remaining challenge for the use of aerogels in the foundry is the cost-effective and efficient provision of suitable airgel particles or airgel granules.
  • Airgel particles or spherical airgel particles can be produced in different ways.
  • Schwan et al. Journal of Materials Science 2020, 55, 5861-5879 have obtained airgel particles from stiff, ductile and flexible carbon airgel monoliths with sandpaper (lowest energy input), by grinding with a cryo vibratory mill (low energy input) or by grinding with a ball mill (high energy input) manufactured. With these methods, particles with a size of 1 to 40 ⁇ m are obtained.
  • US 5,908,896 describes organic airgel microspheres that can be used in condensers, batteries, thermal insulators, adsorption/filtration media and chromatographic assemblies and have diameters in a range from 1 ⁇ m to 3 mm.
  • the emulsion processes mentioned have the disadvantage that the airgel particles obtained are polydisperse and thus have a broad size distribution. Furthermore, the particles have to be washed out of the lipophilic reaction medium.
  • the present invention is therefore based on the object of providing a method for the production of airgel particles and correspondingly produced airgel particles and airgel granules with which the previously mentioned disadvantages of the prior art can be avoided.
  • a cost-effective and efficient method for producing airgel granules with a monodisperse size distribution is to be provided, with the microstructure of the aerogels being retained.
  • the size of the airgel particles obtained should be adjustable.
  • the object of the invention is achieved by a method for producing airgel particles, comprising the following steps i) preparing a precursor solution containing an airgel precursor in a solvent, in particular water, and optionally a catalyst, using an organic thickener to increase the viscosity of the Precursor solution, ii) dropping the precursor solution into a reaction bath, iii) gelation of the droplets formed in the reaction bath, iv) removing the gel bodies obtained from the reaction bath and v) drying the gel bodies to form airgel particles.
  • the present invention thus relates to a method for producing airgel particles, in which the viscosity of a precursor solution is adjusted using an organic thickener and the (viscous) precursor solution is then dropped into a reaction bath and gelled there, as well as corresponding inorganic, organic or carbon-based materials produced with the method airgel particles.
  • Water is preferably used as the solvent in the precursor solution.
  • organic solvents can also be used, in particular acetonitrile and/or dimethyl sulfoxide.
  • the precursor solution can contain a catalyst.
  • airgel precursor any compound or mixture of compounds that is suitable for forming aerogels via a sol-gel process can be used as the airgel precursor in the precursor solution.
  • Suitable airgel precursors are known in the prior art.
  • inorganic metal oxides, biopolymers such as proteins or polysaccharides, precursors of inorganic polymers such as silicates, precursors of organic polymers such as phenols, polyols, isocyanates, amines, amides, imides or the like, or carbon allotropes can be used.
  • phenol formaldehyde, resorcinol formaldehyde, melamine formaldehyde, tannin formaldehyde, lignin formaldehyde, silica, cellulose are used as airgel precursors.
  • Methylcellulose and alginates are also suitable as airgel precursors.
  • the airgel precursor used determines the nature of the airgel particles obtained. In this way, particles of organic aerogels, carbon aerogels or silica aerogels in particular can be obtained with the method according to the invention.
  • the concentration of airgel precursor depends on the compound used. Suitable concentrations of airgel precursor are known in the prior art for the respective compound. The concentration is preferably in a range from 18 to 30% by weight. If, for example, resorcinol-formaldehyde is used as the precursor and water as the solvent, the weight ratio of resorcinol to water (R/W ratio) is preferably 0.03 to 0.5, in particular 0.2 to 0.4.
  • the weight ratio of resorcinol to formaldehyde (R/F ratio) is, for example, in a range from 1.8 to 3, in particular from 2 to 2.7.
  • the catalyst compounds known in the prior art can be used as the catalyst.
  • acids are used as the catalyst, in particular acetic acid, citric acid, hydrochloric acid and/or nitric acid. Acid catalysts can be used in particular when silica is used as the airgel precursor.
  • bases are used as the catalyst, in particular sodium carbonate, sodium hydroxide or ammonium carbonate.
  • Basic catalysts can be used in particular when phenolic resins are used as airgel precursors.
  • Sodium carbonate or sodium hydroxide can particularly preferably be used as a catalyst, in particular when resorcinol-formaldehyde is used as the airgel precursor.
  • the concentration of the catalyst is preferably 2.7 ⁇ 10 5 to 9.1 ⁇ 10 4 , particularly preferably 9 ⁇ 10 5 to 2.84 ⁇ 10 5 , in particular 3.78 ⁇ 10 ⁇ 5 to 3.03 ⁇ 10 5 .
  • the pH of the precursor solution is preferably adjusted.
  • nitric acid can be used to adjust the pH.
  • the pH of the precursor solution is preferably adjusted to a range of 5.4 to 5.6, more preferably 5.48 to 5.58, especially 5.52 to 5.54.
  • the precursor solution is particularly preferably adjusted to the stated pH values if resorcinol-formaldehyde is used as the airgel precursor.
  • a thickener is a chemical substance that can increase the viscosity of the starting system without changing its chemical and physical nature.
  • Prerequisites for suitable thickeners are a high molecular mass, easy solubility, especially in an aqueous medium, no chemical interaction with the precursors, and high viscosity even at very low concentrations.
  • Low-concentration polysaccharide solutions for example, have a low viscosity and cannot be processed with the JetCutter technology.
  • thickeners can make a decisive contribution to adjusting the viscosity at low dosages.
  • a thickening agent is introduced into the precursor solution to adjust the viscosity.
  • Organic thickeners have proven to be effective here, while inorganic particles have proven to be unusable.
  • any organic thickener can be used.
  • polysaccharides, proteins, synthetic polymers, hydrophilic silicates or mixtures thereof are used in the method according to the invention.
  • Polysaccharides are particularly preferably used as thickeners.
  • Preferred polysaccharides include alginates, methyl cellulose, xanthan, Welan gum, guar gum, tara bean gum, locust bean gum, hydroxypropyl methylcellulose (HPMC) and mixtures thereof.
  • shear stress-shear rate diagrams for various materials. 1) shear-thinning (dilatant) fluids, 2) Newtonian fluids, 3) shear-thinning (pseudoplastic) fluids, 4) Binghamplastic fluids and 5) Casson fluids.
  • a fluid with a higher viscosity will flow slower for a constant force.
  • the viscosity can depend on the temperature, the shearing time, the concentration of the dispersed phase and the particle sizes, shapes and interactions with each other.
  • the viscosity of a liquid can be increased in a number of ways. For example, for most materials it can be done simply via cooling. Another way to increase viscosity is to allow the components of a material to react with each other, as in the polymerization process.
  • a very common method of increasing viscosity without changing other properties of the material is to add thickeners.
  • Thickeners can be inorganic materials such as clays and silica, or organic, typically polysaccharides, proteins, or other synthetic polymers such as polyethylene glycols, polyvinyl alcohol, polyacrylates, and polyurethanes. They are used in the food, cosmetics, pharmaceutical, paint, explosives and petrochemical industries.
  • thickeners used in the food, cosmetics and pharmaceutical industries are particularly preferred. These are primarily biological polysaccharides and a few synthetic organic polymers such as polyvinyl alcohol.
  • rheological properties of commercially available thickeners are reviewed for their application as thickeners for precursor solutions containing resorcinol-formaldehyde as an airgel precursor used in the syringe-drop method of preparing microspheres in accordance with the present invention.
  • Xanthan gum is probably the most widely used of the polysaccharide thickeners.
  • the internal mannose unit is O-acetylated and about half of the external mannose unit forms an acetal with pyruvic acid. It is produced by the bacterium Xanthomonas campestris.
  • Xanthan is dispersible in hot and cold water.
  • Aqueous xanthan dispersions show shear thinning behavior and the viscosity is proportional to the concentration of xanthan. Only a small amount is required to increase viscosity compared to other thickeners.
  • Low concentrated dispersions have a stable viscosity in the range from pH 1 to 13. In the case of a 1% dispersion only a small change in viscosity is observed from pH 3 to 12, with the viscosity decreasing with lower pH and with higher pH increases.
  • the viscosity of the xanthan dispersion is dependent on the temperature and decreases sharply with increasing temperatures at lower shear rates. The viscosity is rather insensitive to temperature changes at low concentrations (0.1 and 0.2% by weight).
  • the concentration of xanthan in the precursor solution is preferably 0.1 to 1.2% by weight, in particular 0.6 to 1.0% by weight.
  • Welan Gum is a material produced by Alcaligenes bacteria. It consists of a (1,3)-ß-D-glucopyranosyl, (1,4)-ß-D-glucuronopyranosyl, (1,4)-ß-D-glucopyranosyl and (1,4 )-oL-rhamnopyranosyl pentasaccharide repeat unit, and a single monosaccharide side chain at O- 3 of the 4-membered glucopyranosyl.
  • the monosaccharide can be either L- Rhamnopyranosyl or L-mannopyranosyl in an approximately 2:1 ratio and about half or more of the repeating units have acetyl and glyceryl substituents.
  • Welan gum dispersions can be prepared at room temperature. They show shear thinning behavior and the viscosity is proportional to the concentration of welan gum. Only a small amount of Welan Gum is needed to increase viscosity. In addition, welan gum dispersions retain more of their viscosity when the temperature is increased compared to xanthan gum.
  • the concentration of welan gum in the precursor solution is preferably 0.1 to 1.0, more preferably 0.4 to 0.6.
  • Guar, tara bean and locust bean gum have in common that their main components are galactomannans with similar structures. They have a linear backbone of 1-4 linked ⁇ -D-mannopyranose units linked by 1-6 linkage to o-D-galactopyranose.
  • the ratio of mannopyranose to galactopyranose is 2:1 for guar gum, 3:1 for tara gum, and 4:1 for locust bean gum.
  • the cold water dispersibility correlates with the mannose/galactose ratio and is best for guar gum and worst for locust bean gum.
  • Aqueous guar gum dispersions show typical shear thinning behavior and the viscosity is proportional to the concentration of guar gum. Increasing temperatures lead to a decreasing viscosity. The viscosity of dispersions is higher at acidic conditions, followed by neutral conditions and the lowest viscosity at base conditions. If guar gum is used as a thickening agent, the concentration of guar gum in the precursor solution is preferably 0.1 to 1.0%, in particular 0.5 to 1.0%.
  • Tara gum dispersions show shear thinning behavior and the viscosity is proportional to the concentration of tara gum.
  • the dispersions generally show a stable viscosity for pH values in the range of 3 to 11, although slight changes occur.
  • the dispersions also show a decrease in viscosity with increasing temperatures. This effect was stronger for dispersions with lower concentrations.
  • the concentration of tara gum in the precursor solution is preferably 0.1 to 2.0%, in particular 0.5 to 2.0%.
  • Locust bean gum dispersions must be stirred at >80 °C in order to obtain a homogeneous dispersion.
  • Aqueous dispersions show shear thinning behavior and the viscosity is proportional to the concentration of locust bean gum. The viscosity also depends strongly on the temperature. An increase of 10 to 30 °C results in less than half the previous viscosity at rest. The temperature effect is stronger for dispersions that have low shear rates.
  • a pH in the range from 3 to 6 an influence on the viscosity is only observed for dispersions with low shear rates.
  • At high shear rates ( ⁇ 1000 s -1 ) only insignificant changes are observed.
  • locust bean gum is used as a thickening agent
  • concentration in the precursor solution is preferably 0.1 to 1.0%, in particular 0.3 to 0.8%.
  • Hypromellose or hydroxypropylmethylcellulose (HPMC) is a partially O-methylated (21-35% substitution) and O-hydroxypropylated (14-35% substitution) cellulose ether. It is available as a solid off-white to beige powder and also as granules, and is soluble in water to form colloids. They are used as a food additive, as well as an emulsifier, thickening and suspending agent and as an alternative to animal-based gelatin.
  • HPMC has a viscosity of about 50 mPa.s at 2% by weight aqueous solution up to a maximum concentration of 5% by weight for use as a thickener.
  • HPMC is available in different viscosity grades from 4000-100,000 mPa.s. It has a cloud point of 65°C and requires hot water (> 65°C) with vigorous agitation, followed by the addition of cold water.
  • HPMC shows thermal dilution behavior with increasing temperature from 30 to 80°C and acts as a viscosifier (increased viscosity) above its gelation temperature of 90°C and is then stable at even higher temperatures (G. Abbas, S. Irawan, KR Memon, p .Kumar, AAI Elrayah, /International Journal of Automotive and Mechanical Engineering, 2013, 8, 1218-1225).
  • Alginates are produced by various Laminaria brown algae. They are salts of alginic acid, which is a polysaccharide composed of 1,4-linked ß-D-mannuronic acid (M) and its C-5 epimer o-L-guluronic acid (G). The polymer is composed of pure M, pure G and mixed MG blocks. Alginates used with preference include, in particular, sodium alginate from brown algae.
  • the viscosity of the precursor solution is set in a range from 0.05 to 5000 Pa.s.
  • the viscosity is particularly preferably adjusted to a range from 0.09 to 3000 Pa.s, in particular from 0.1 to 1000 Pa.s.
  • the prepared precursor solution can first be stored (particularly pre-gelled) or dropped directly into a reaction bath for gelation. If the precursor solution is stored, it must be ensured that the gelation has not already progressed too far in order to ensure a sufficient pot life for the continuation of the method according to the invention.
  • the precursor solution can be stored at a low temperature.
  • a precursor solution containing resorcinol formaldehyde can be stored at a temperature below 4°C for up to three weeks.
  • the temperature and pre-gelation time depends on the airgel precursor compound used.
  • the temperature is preferably in a range from 40°C to 80°C, particularly preferably 50 to 70°C, in particular 55 to 65°C.
  • the pre-gelation time is preferably 80 to 260 minutes, particularly preferably 100 to 200 minutes, in particular 120 to 180 minutes.
  • the pre-gelation can be dispensed with.
  • the precursor solution is dropped into a reaction bath.
  • drops are formed from the precursor solution, which are immersed in the reaction bath. Any means of forming beads known in the art can be used.
  • the droplets are formed by the precursor solution being replaced by a drop into the reaction bath through the outlet opening of a syringe with a cannula, a pipette, a burette, a nozzle or a jet tube cutter.
  • the outlet opening preferably has a round or oval shape.
  • the diameter of the outlet opening is preferably 0.5 to 4 mm, in particular 0.8 to 2.0 mm.
  • a device which has an outlet opening of variable size is particularly preferably used for the dripping, with the size being adjusted depending on the desired droplet size.
  • the droplets formed preferably have a diameter in a range from 0.6 to 6 mm, particularly preferably 0.8 to 4 mm, in particular 1.0 to 2.0 mm.
  • the formation of droplets can occur due to the gravity of the precursor solution by placing the solution above the orifice of a syringe, nozzle or the like and flowing through the orifice under its own gravity.
  • the shape and size of the droplets formed depend in particular on the surface tension, density and apparent viscosity of the precursor solution and the shape of the outlet opening and its distance from the reaction bath.
  • Such conventional dropping methods which only make use of gravity, can produce drops with a size of a few millimeters in particular.
  • the formation of droplets can also be assisted by, for example, vibration, ultrasound, or electrostatic forces. Vibrations can be used to destabilize the stability of a liquid jet of precursor solution. To do this, the precursor solution can be forced through a nozzle to create a jet.
  • the size of the droplets generated by vibration is typically in the range of twice the size of the nozzle opening, in particular it can twice the size of the nozzle opening.
  • the size of the droplets can also be controlled by the flow rate of the precursor solution. The flow rate is preferably in a range from 4 to 5.6 g/s.
  • Another possibility is to force a low-viscosity precursor solution through an electrically charged nozzle.
  • the electric field thus formed pushes the droplets formed away from the nozzle in addition to gravity.
  • An induced surface charge prevents the droplets from coalescing as they fall towards the reaction bath.
  • the comminution of the droplets and their size depend in particular on the viscosity of the precursor solution, the diameter of the nozzle, the distance between the nozzle and the reaction bath, and the voltage applied.
  • a particular advantage of dripping methods that use the gravity of the solution, vibrations and/or an applied voltage is that the methods can be carried out very easily and, in particular, no further additives are required.
  • very small droplets can be obtained with the dropping method, in particular droplets smaller than 200 ⁇ m.
  • the droplets can also be formed with an automated device such as a jet tube cutter.
  • an automated device such as a jet tube cutter.
  • a continuous liquid jet of the precursor solution is cut into cylinders with a rotating cutting disk, which fall into the reaction bath, the cylinders forming spherical droplets of the precursor solution as they fall due to their surface tension. Some of the precursor solution is lost in the process.
  • the size the drop can be set in a range from a few hundred micrometers to a few millimeters, in particular by varying the nozzle size, the flow rate of the liquid jet and the cutting frequency.
  • the advantages of using a jet tube cutter or similar devices is that large quantities of droplets can be produced in a short time (several kg/h), no additives have to be used and monodisperse droplets with a homogeneous size distribution are also obtained.
  • the drops of the precursor solution reach a reaction bath in which the gelation takes place or is continued.
  • Any liquid which induces the gelation of the precursor solution without destroying the shape of the droplets or inducing their agglomeration or coalescence is suitable as the reaction bath.
  • liquids known from the prior art for gelation can be used here.
  • the reaction bath can be adapted to the respective precursor solution or the airgel precursor used therein.
  • the gelation of polysaccharides is based in particular on the precipitation of dissolved polymers and is induced by temperature, cross-linking agents such as ions or pH.
  • the gelation takes place as a result of the polymerization itself, so that the polymerization reaction in the reaction bath must be started quickly.
  • the precursor solution may contain one component while the reaction bath contains the other component such that polymerization proceeds immediately after the precursor solution drops into the reaction bath.
  • reaction rate of the gelation by chemical or to accelerate physical means so that the droplets of precursor solution are rapidly solidified after being immersed in the reaction bath.
  • high concentrations of the reactants, high temperatures or acidic reaction baths can be used for this purpose.
  • a suitable reaction bath When selecting a suitable reaction bath, the approach can also be followed, for example, to physically stabilize the droplets of the precursor solution in the reaction bath in order to prevent the agglomeration and coalescence of the droplets and thus enable slow gelation.
  • a reaction bath can be used which is not miscible with the precursor solution, the reaction bath containing in particular a surfactant and the drops of the precursor solution being stirred in the reaction bath.
  • An acidic aqueous solution for example, can be used as the reaction bath. Any organic or inorganic acid that does not lead to any undesired reactions with the precursor solution is suitable as the acid. Nitric acid, hydrochloric acid, formic acid, acetic acid, citric acid or mixtures thereof are preferably used. Apart from the acid, the aqueous reaction bath preferably contains no other ingredients.
  • the pH of the aqueous reaction bath before dropping the precursor solution is preferably in a range of -0.5 to 1.0, more preferably -0.3 to 0.8, especially -0.12 to 0.6.
  • a 0.5 to 2 molar solution of nitric acid, hydrochloric acid or formic acid in water can be used as the reaction bath.
  • An acidic aqueous reaction bath is particularly suitable for aerogels based on synthetic organic polymers.
  • An acidic aqueous reaction bath is particularly suitable for aerogels based on resorcinol-formaldehyde or other phenolic resins that are known in the prior art, such as melamine, tannin or lignin-formaldehyde. Under the acidic conditions, the polymerization and thus the gelation is accelerated and the droplets are thus stabilized.
  • a basic aqueous solution can also be used as the reaction bath.
  • Any organic or inorganic base that does not lead to any undesired reactions with the precursor solution is suitable as the base.
  • Ammonia, sodium hydroxide, sodium carbonate, ammonium fluoride or mixtures thereof are preferably used.
  • the aqueous reaction bath preferably contains no other ingredients.
  • the pH of the aqueous reaction bath before dropping the precursor solution is preferably in a range of 8 to 10.
  • a 1 molar ammonia solution or 1 molar to 2 molar sodium hydroxide solution can be used as the basic reaction bath.
  • a basic aqueous reaction bath is particularly suitable for aerogels based on silica, aluminum oxide, zirconium oxide, titanium oxide, iron oxide and mixtures thereof
  • an organic solution that is immiscible with an aqueous precursor solution can be used as the reaction bath, which makes it difficult or impossible to dissolve or dilute the droplets.
  • 3-aminopropanol or rapeseed oil can be used as the organic solution.
  • the surface tension of the reaction bath must not be too high, otherwise there is a risk that the droplets will be destroyed when they hit the reaction bath.
  • the surface tension of the reaction bath is preferably in a range from 45 to 75 mN/m.
  • the temperature and gelation time depend on the composition of the reaction bath solution used.
  • the temperature is preferably in a range from 10°C to 40°C, particularly preferably 15 to 30°C, in particular 20 to 25°C.
  • the gelation time is preferably 3 to 30 minutes, particularly preferably 5 to 20 minutes, in particular 10 to 15 minutes.
  • the formed gel bodies are removed from the reaction bath and dried to form airgel particles.
  • the gel bodies Before drying, the gel bodies can first be washed. For washing, in particular water can be used for neutralization.
  • the gel bodies are preferably washed several times.
  • the gel bodies can be washed in particular if an organic-based reaction bath was used. Washing in particular removes residues such as salts, unreacted monomers, dimers and oligomers.
  • the gel bodies are preferably dried to form airgel particles at a temperature in a range from 20 to 80.degree. C., particularly preferably 40 to 70.degree. C., in particular 50 to 60.degree.
  • the drying can take place in air, for example.
  • the gel bodies are preferably dried for a period of 24 to 72 hours, particularly preferably 36 to 60 hours, in particular 48 to 54 hours.
  • the airgel particles formed are organic airgel particles, they can be converted into carbon airgel particles by pyrolysis after drying.
  • the pyrolysis can be carried out according to methods known from the prior art, for example at a temperature of 1000° C. with the exclusion of air.
  • the object according to the invention is achieved by airgel particles which can be obtained using the method according to the invention described above.
  • the airgel particles according to the invention are preferably approximately spherical.
  • the shape of the airgel particles results from the shape of the droplets that are gelled in the reaction bath. Spherical droplets are preferably formed which deform as little as possible during gelation.
  • the spherical airgel particles according to the invention preferably have a diameter in a range from 0.5 to 6 mm, particularly preferably 0.8 to 5 mm, in particular 1 to 4 mm.
  • the diameter of the spherical airgel particles according to the invention can be adjusted in particular using the method according to the invention, with the adjustment taking place according to the invention by varying the viscosity of the precursor solution with the aid of organic thickeners.
  • the airgel particles according to the invention preferably have a density in a range from 0.12 to 0.26 g/cm 3 , particularly preferably 0.15 to 0.22 g/cm 3 , in particular 0.18 to 0.20 g/cm 3 .
  • the porosity of the airgel particles is preferably in a range from 75 to 88%, particularly preferably 77 to 85%, in particular 78 to 82%.
  • the specific surface area (BET surface area) of the airgel particles is preferably in a range from 5 to 40 m 2 /g, particularly preferably 7 to 30 m 2 /g, in particular 10 to 20 m 2 /g.
  • the airgel particles according to the invention are distinguished in particular by a high degree of monodispersity in their size distribution. Accordingly, the airgel particles have a narrow size distribution.
  • the diameters of the spherical airgel particles have a standard deviation in a range from 0.04 to 0.20 mm.
  • the standard deviation is particularly preferably in a range from 0.06 to 0.15 mm, in particular 0.06 to 0.125.
  • Airgel particles according to the invention can be used as an additive in foundry cores for lightweight casting and/or precision casting of metals and other materials, in particular because of their monodisperse size distribution and their size, which can be adjusted via the viscosity of the precursor solution.
  • Other possible areas of application include filtering (chemical pollutants, biological hazardous substances), battery materials (electrodes, solid electrolyte), in particular as carbon airgel particles after pyrolysis, absorption, adsorption, acoustic and thermal insulation materials, dyes and other electrochemical applications and other applications.
  • resorcinol and formaldehyde were first dissolved in deionized water. 0.1 percent by weight of xanthan gum was then added as thickener (T) (viscosity approximately 0.05 to 1 Pa ⁇ s) and the solution was stirred for 30 minutes. This was followed by the addition of NazCCh as a catalyst.
  • the mixture is then pre-gelled to 60°C in an oven and this solution is stored at 4°C until use to achieve the necessary pot life.
  • the solution was dripped into an acidic reaction bath via a syringe with a cannula, diameter 0.8 mm.
  • 2M nitric acid (Example 1)
  • 2M hydrochloric acid (Example 2)
  • 2M formic acid (Example 3) were used as the reaction bath.
  • the resulting spherical gel bodies were removed from the bath after a maximum of 5 minutes, washed acid-free with water and dried in air at 60° C. for 2 days.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Dispersion Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Colloid Chemistry (AREA)

Abstract

La présente invention concerne un procédé de production de particules d'aérogel, selon lequel la viscosité d'une solution de précurseur est ajustée au moyen d'un épaississant organique et la solution de précurseur est ensuite ajoutée goutte à goutte dans un bain de réaction et sa gélification y est permise. L'invention concerne également des particules d'aérogel inorganiques, organiques ou carbonées correspondantes produites selon ce procédé.
EP22701913.0A 2021-01-18 2022-01-14 Production de particules d'aérogel monodispersées Pending EP4277737A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102021100898.0A DE102021100898A1 (de) 2021-01-18 2021-01-18 Herstellung von monodispersen Aerogelpartikeln
PCT/EP2022/050747 WO2022152846A1 (fr) 2021-01-18 2022-01-14 Production de particules d'aérogel monodispersées

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EP4277737A1 true EP4277737A1 (fr) 2023-11-22

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WO (1) WO2022152846A1 (fr)

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CN117736666B (zh) * 2023-11-30 2024-07-16 南通科顺建筑新材料有限公司 生物质阻燃、隔热自粘防水卷材及其制备方法

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Publication number Priority date Publication date Assignee Title
FR2668081B1 (fr) 1990-10-19 1994-11-18 Lvmh Rech Procede et appareil de fabrication de particules solides a partir d'un materiau solidifiable en presence d'un agent de solidification en de bons rendements.
DE4125133C2 (de) 1991-07-30 1993-09-30 Nukem Gmbh Verfahren und Vorrichtung zur Herstellung von Alginatkugeln
US5508341A (en) 1993-07-08 1996-04-16 Regents Of The University Of California Organic aerogel microspheres and fabrication method therefor
DE10058221A1 (de) 1999-12-03 2001-07-26 Maik Nicklisch Verfahren und Vorrichtung zur Herstellung von Alginatkugeln mit großer Festigkeit
DE102006003198A1 (de) 2006-01-24 2007-07-26 Deutsches Zentrum für Luft- und Raumfahrt e.V. Kerne für den Leichtmetall- und/oder den Feinguss

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WO2022152846A1 (fr) 2022-07-21

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