Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/113—Silicon oxides; Hydrates thereof
  • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/16—Preparation of silica xerogels
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/113—Silicon oxides; Hydrates thereof
  • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
  • C01B33/152—Preparation of hydrogels
  • C01B33/154—Preparation of hydrogels by acidic treatment of aqueous silicate solutions
  • C01B33/1546—Preparation of hydrogels by acidic treatment of aqueous silicate solutions the first formed hydrosol being converted to a hydrogel by introduction into an organic medium immiscible or only partly miscible with water
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
  • Y10T428/2991—Coated
  • Y10T428/2993—Silicic or refractory material containing [e.g., tungsten oxide, glass, cement, etc.]
  • Y10T428/2995—Silane, siloxane or silicone coating

Definitions

• organic aerogels have been known In the literature, we find for example organic aerogels based on resorcin/formaldehyde, melamine/formaldehyde or resorcin/furfural (R W Pekala, J Mater Sci 1989, 24, 3221, US-A-5 508 341, RD 388047, WO 94/22943 and US-A-5 556 892) Furthermore, organic aerogels produced from polyisocyanate are also known (WO 95/03358) and from polyurethanes (US- A-5 484 818) As described for example in US-A-5 508 341, the starting materials are such as formaldehyde and melamine dissolved in water, which are brought together and caused to react by suitable catalysts, the water in the pores of the gel formed is exchanged for a suitable organic solvent and super-critical drying follows
• lyogels is understood to mean any gels in the gel pores of which there is at least one solvent.
• hydrogels have more than 50% by volume of water in relation to the solvent phase in the pores.
• a lyosol in order to produce a lyogel, a lyosol must be brought to gelatinisation in order to build up the lyogel network.
• the shaping stage Since the shaping stage must take place in this time in order to guarantee the above-described clearly defined macroscopic form, it must be attuned to the respective gelatinisation time. Since the properties of the lyogel are vitally dependent upon the gelatinisation time, the shaping process is very important to the subsequent properties.
• the literature describes methods of shaping lyogels. In this respect, a distinction is made between methods in which the lyosol is brought either into a vapour and/or gas atmosphere or into a water soluble fluid.
• DE-C-21 03 243 Described in DE-C-21 03 243 is a method in which, by means of a special mixing nozzle, a hydrosol is formed from a acid solution and a raw material containing silicic acid and, for drop forming, it is sprayed into a gaseous medium, e.g. air.
• a gaseous medium e.g. air
• DD-C-253242 and DD-C-253243 Described in DD-C-253242 and DD-C-253243 is a method in which the residues on the gel particles are eliminated by an appropriately expensive process.
• the hydrosol is sprayed into an oil column in which water forms an under layer.
• the gel particles formed in the oil column are freed from any attached oil residues in a CC14 phase and/or water phase. Certainly, then, these cleaning phases must be recycled again by distillation.
• the object of the present invention was to provide a method of producing substantially spherical lyogels in which no residues of the shaping medium have to be removed from the gel particles before they are subjected to silylation and/or subsequent drying.
• step b) both in step b) and also in step c), only one silylating agent is used It is particularly preferred to carry out the shaping in step b) and the gelation in one stage and therefore also in only one silylating agent.
• the various components do not necessarily have to be homogeneously distributed and/or form a continuous network. It is also possible for individual components to be present wholly or partly in the form of inclusions, individual nuclei and/or deposits in the network.
• a silicatic lyosol is produced in that an aqueous water glass solution is transferred by means of an acid ion exchanger resin to a silica Sol having a pH value ⁇ 3.
• the lyosol produced preferably from the above-described silicatic starting compounds may additionally contain zirconium, aluminium, tin and/or titanium compounds which are capable of producing condensation.
• opacifiers can be added as additives, particularly infra-red opacifiers to produce the contribution of radiation to the heat conductivity such as for example carbon black, titanium oxides, ion oxides and/or zirconium oxides.
• a 6 to 25% by weight (in relation to the SiO 2 content) sodium and/or potassium water glass solution is the water glass solution used.
• a 10 to 25% by weight water glass solution and in particular a 10 to 18% by weight water glass solution is used.
• the water glass solution may also contain up to 90% by weight (in relation to SiO 2 ) of zirconium, aluminium, tin and/or titanium compounds capable of producing condensation.
• the pH value of the lyosol ought to be between 2 and 8, preferably between 4 and 5. If necessary, the pH value can also be increased by means of a base in order to achieve a more rapid gel formation in step c).
• the base used is generally NH 4 O 8 , NaOH, KOH, Al(OH) 3 and/or colloidal silicic acid.
• both solutions preferably independently of each other, ought to be at a temperature of between 0 and 30°C, particularly preferably between 5 and 25°C and in particular between 10 and 20°C.
• fibres may be added to the water glass, the acid and/or the Sol in order to increase mechanical stability.
• inorganic fibres such as for example glass fibres or mineral fibres, organic fibres such as for example polyester fibres, aramide fibres, nylon fibres or fibres of vegetable origin as well as mixtures thereof may be used.
• the fibres can also be coated, e.g. polyester fibres metallised with a metal such as for example aluminium.
• step b) the lyosol obtained n step a) is transferred to at least one water insoluble silylating agent.
• the silylating agent is present as a fluid.
• Disiloxanes to formula (I) are used as silylating agents in steps b) and c),
• the radical s R independently of one another, are the same or different, each representing a hydrogen atom or a non-reactive, organic, linear, branched, cyclic, saturated or unsaturated aromatic or heteroaromatic radical, preferably C r C ]8 -alkyl or C 6 -C 14 -aryl and particularly preferably - -alkyl, cyclohexyl or phenyl and in particular methyl or ethyl.
• any silylating agents known to the man skilled in the art may be used which are not miscible with water.
• the temperature of the silylating agent in step b) can be between 0°C and the boiling point of the liquid phase in the lyosol. Preferred temperatures are between 20°C and 120°C, particularly preferably between 40°C and 120°C and quite particularly preferably between 40°C and 100°C. It is also possible to work under pressure at higher temperatures.
• the lyosol can thereby be incorporated into the silylating agent by any methods known to a man skilled in the art, such as for example by using mixing jets or dispensing means.
• the silylating agent forms thereby a phase in which the lyosol forms substantially spherical droplets by virtue of the interphase tension.
• the droplet size can thereby be adjusted for instance according to the manner of introduction, the mass flows and the distance from the surface of the liquid.
• step c) the spherical lyosol formed in step b) becomes gelated in the silylating agent to produce the lyogel.
• the water-insoluble silylating agent can thereby be present in any kind of container, a column arrangement being however preferred.
• the lyosol is preferably transferred from above (if the density of the silylating agent(s) is less than the density of the lyosol) or from below onto or into the silylating agent(s).
• the above-described method known to a man skilled in the art may be used.
• the dwell time of the lyosol droplets or lyogel particles can be adjusted by the height of the column filled with silylating agent.
• the gelating rate can also be adjusted by this means.
• the silylating agent can basically be present in stationary or moving form, and preferably however it is still.
• an aqueous phase may be present under the silylating agent. If the lyosol droplets are gelated during the dwell time in the silylating agent, then the gel particles formed fall through the phase limit of the two fluids and the silylating agent is eliminated from the gel particles virtually without residue.
• a longer dwell time in the silylating agent can produce silylation of the outer surface.
• the particles can be better suspended in an organic solvent for subsequent further treatment.
• the gel particles obtained in this way can be further processed by known methods to produce aerogels.
• lastingly hydrophobic aerogels which are modified by silylating agents are preferred.
• a further advantage of the present invention is that upon further processing of the lyogels produced in order to obtain permanently hydrophobic aerogels by silylation and subsequent preferably sub-critical drying, no expensive washing stages have to be carried out.
• the Sol from the ion exchanger is adjusted to a pH value of 4.6 to 4.9 by NaOH (0.5 to 1 molar) in a mixer. It is then cooled (7 °C) and by means of a pump it is passed through a hose (inside diameter 4 mm; distance from the surface of the HMDSO about 5 to 10 cm) and onto the heated HMDSO surface.
• the resulting hydrosol droplets fall slowly downwards in the HMDSO fluid and can be removed as hydrogel balls either directly from the hot HMDSO or, by means of a second water phase (below the HMDSO phase in the column) suspended in the water and removed from the column.
• the gel particles have a mean diameter of 2 mm.

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Dispersion Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Silicon Compounds (AREA)
• Colloid Chemistry (AREA)
• Medicinal Preparation (AREA)
• Silicates, Zeolites, And Molecular Sieves (AREA)

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• 1998
  • 1998-01-14 DE DE19801004A patent/DE19801004A1/de not_active Withdrawn
• 1999
  • 1999-01-12 CA CA002313182A patent/CA2313182A1/en not_active Abandoned
  • 1999-01-12 DE DE69904142T patent/DE69904142T2/de not_active Expired - Lifetime
  • 1999-01-12 KR KR1020007007276A patent/KR20010033752A/ko not_active Withdrawn
  • 1999-01-12 WO PCT/EP1999/000334 patent/WO1999036354A2/en not_active Ceased
  • 1999-01-12 JP JP2000540075A patent/JP4331894B2/ja not_active Expired - Fee Related
  • 1999-01-12 AU AU28285/99A patent/AU2828599A/en not_active Abandoned
  • 1999-01-12 BR BR9906928-8A patent/BR9906928A/pt not_active IP Right Cessation
  • 1999-01-12 ES ES99908803T patent/ES2187145T3/es not_active Expired - Lifetime
  • 1999-01-12 EP EP99908803A patent/EP1047633B1/en not_active Expired - Lifetime
  • 1999-01-12 CN CN99802075A patent/CN1126715C/zh not_active Expired - Fee Related
• 2003
  • 2003-05-02 US US10/428,271 patent/US7297718B2/en not_active Expired - Fee Related

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