Aerogels - Structure, Properties And Applications

Aerogels Structure, properties and applicationsLorenz RatkeInstitut für Materialphysik im Weltraum51147 KölnEmail: lorenz.ratke@dlr.de

What are aerogels?Aerogels arenanostructured, open poroussolids made via sol-gel technologyTypes of aerogels!Oxides (Quarz, Titania, Zirkonia. Mixed oxides)!Polymers (Resorcin-, Melamin-Formaldehyd)!Carbon (pyrolysed Polymere)!!cellulose, starch, alginates,.And almost everything that can be gelled

Synthesis of aerogels!General technique is “sol-gel processing” meaning!Mixing of chemicals (alcoxides, water, alcohol, catalyst)!Gelation (catalyst, temperature, fluid flow)!Drying!Final productDLCA-Simulation von B.Halperin , NWU Evanston

Synthesis of aerogels!General technique is “sol-gel processing” meaning!Mixing of chemicals (alcoxides, water, alcohol, catalyst)!Gelation (catalyst, temperature, fluid flow)!Drying!Final product

Preparation of cellulose aerogelsDissolution of cellulose in e.g. salt-hydrate melts ionGelation on cooling (80 C)and regeneration

The wet gel is ready and now?

Drying – determines everything*!methods: airfreeze dryingDrying under ambient conditionleads to Xerogels!huge shrinkage!Destruction of the nanosizedpore system!Fragmentation of the gel body!Porosity between 5 and 50 %!but:proper drying routine can giveperfectly shaped xerogels!supercriticalcapillary forces!wetting stresseslead to a collapseof the gel networkp ! 1/R2R* not really, but it is the essential step

Drying – determines everything!methods: airfreeze drying Shock or rapid freezing (after solventexchange) to minimize freezingeffects on the solid gel structure Sublimation along thesublimation line by–pressure changes and–temperature increasesupercritical

Drying – determines everything!methods: airfreeze drying Solvent exchange gel liquidagainst CO2 Temperature increase abovecritical point Tc 31.1 C, 73.8 bar. Real process 40 C withpressure of 90 bar Slow depressurizationsupercritical

And the result?

Carbon aerogelSilica aerogelRF polymeric aerogelAnswer: almost always a nanostructureCarbon aerogelCellulose aerogelRF-Aerogel (HCl catalysed)

C-AerogelAppearance of some aerogelsTiO2V2O5(G.Reichenauer)RF-Aerogel

Appearance and structure of Cellulose aerogelsCellulose-Aerogels are generallyopaque and milky with densitiesof around 5 - 60 kg/m3Structure: nanofelt of microfibrilsCai et al, ChemSusChem 2008Aerogels with0,5 % Cellulose1,0 % Cellulose2,0 % Cellulose

Properties

Properties of aerogelsØ Ø Ø Ø Ø Ø Ø Ø Low density - high porosity§ 90 - 99,9 % porosityLarge sound absorption - low sound velocity§ damping 50 dB, vl 100 m/sLow thermal conductivity§ 0.005 - 0.1 W/mKTransparent or opaque or can be coloured§ variable refractive index (1,001 to 2,1)No reaction with metallic melts up to 950 C (Silica andsome other oxide aerogels)Huge internal surface§ 10 - 2000 m2/gSurface can be functionalized§ Hydrophobic by polymeric residues (-CH3)§ CVD deposition of magnetic layersFunctionalisation of the gel body§ Embedding of particles (e.g. dyes, ferroelectrics)§ Interpenetrating hybrid aerogel networksUVInfrared

Mechanical properties of aerogelsafter Gross et al. JNCS 1992Young’s moduluspressureσ E(MPa)LΔL"L!E # !EL0Fracture strength:Silica-Aerogels: 20 kPa bis 2 MPaRF-Aerogels: 100 kPa bis 10 MPa" B # 1.5ρ (g/cm3)E # 3.6

Are there applications?

Industrial areas of application!!!!!!!!!!thermal insulation§ home building, vehicles, pipelines, packagingelectronic components§ capacitors, humidity sensors, batteries, fuel cell,soft magnets, Geiger counter, IR detectorfoundry technology§ aerogelic binders, aerogel granules for foundry sandsarchitecture§ illumination, superlight concrete, wall isolationsuperlight compositesnon-linear optics (SHG)CosmeticsPharmacy (drug delivery)Apparel & sportsware§ Tennis rackets§ Security shoes§ Sport shoesSpace§ Space suits§ Anti-sloshing in tanks§ Cryogenic tank insulation

Industrial areas of application!!!!!!!!!!thermal insulation§ home building, vehicles, pipelines, packagingelectronic components§ capacitors, humidity sensors, batteries, fuel cell,soft magnets, Geiger counter, IR detectorfoundry technology§ aerogelic binders, aerogel granules for foundry sandsarchitecture§ illumination, superlight concrete, wall isolationsuperlight compositesnon-linear optics (SHG)CosmeticsCryogenic tankPharmacy (drug delivery)insulationApparel & sportsware§ Tennis rackets§ Security shoes§ Sport shoesSpace§ Space suits§ Anti-sloshing in tanks§ Cryogenic tank insulation

Suppliers? Vendors?Who delivers what?

Aerogel granulatesCompany: Cabot (Frankfurt)!Material: water glass!Shape: polyhedric 0.5 - 4 mm!transparent!super hydrophobic!price 2000 /cbm!dried at ambient conditionsCompany: Dow Corning!material: pure quartz!super hydrophobic!Application in cosmetic productsTL - TranslucentdensityParticle sizeSurface areaporosity40 - 100 kg/cbm5 - 15 µm600 - 800 m2/g 90%

Aerogel tilescompany: Airglass (Schweden)!material: Silica (precursor TMOS:Methanol)!Hydrophilic!Drying is made supercritically (methanol)Airglass ABBOX 150245 22 StaffanstorpSWEDENprice: tiles 10 x 10 x 1 inch 500 granulate 1 L 150 www.airglass.seTEL: 46 46 255200FAX: 46 46 25692

Aerogel pieces & paperscompany: MarkeTech (USA)!material:!Silica (TEOS:Methanol)!RF aerogel pieces and paper!Carbon aerogel (pieces and paper!hydrophilic!shape: small tiles and pieces!price:!Random pieces: 100 g 880 US !Tiles (4x8x0,5“) 1228 US Marketech International Inc.107B Louisa StreetPort Townsend, WA 98368Tel: 360-379-6707Toll Free: 877-452-4910Fax: om/index.shtml

Aerogel blanketscompany: Aspensystems (USA)!material: fibre composite!Silica-Aerogel on polymeric fiber felt!Silica-Aerogel on glass fibers!superhydrophobicASPEN AEROGELS, INC.30 Forbes Road, Building BNorthborough, MA 01532USATel: 1.508.691.1111Fax: 1.508.691.1200http://www.aerogel.com/

Aerogel blanketsComposite of mineral wool and silica aerogelKoebel 2007Brand name: Aerowoλλe Thermal conductivity 0.019 W/mK

And some other companies!!Aerogel Composite!Product: Polymeric (RF) and Carbon aerogels, crushedand compressed into arbitrary shapes!http://www.aerogelcomposite.comAmerican Aerogel!!!Product: VIPshttp://www.americanaerogel.comNano High-tech Co, China!Products: everything all others fabricateGranular materials, tiles, blankets, hydrophobic, fibrereinforced.

Examples of industrial applications

Illuminating systems - diffusersBasic idea: transparent to translucent aerogel granules scatter light into all directionsTechnology: fill hollows plates with aerogel grains.Company: Cabot (brand name: Nanogel) in co-operation with window companiesEffects:a) Diffusive illumination of roomsb) Thermal insulationbeforeafter

Isolation of subsea pipelinesBasic idea:Utilize low thermal conductivity of aerogelsChallenges:-Huge mechanical loads in subsea double walledpipelines (dynamic and static)-High temperature of the raw oil - cooling leads toclogging-High service life

Insulation of Pipelines - solutionsVendors:!Cabot!Aspenssystemssource: Cabot.comDifferent technical solutionsCabot: Compression/Expansion-PackAspen: aerogel blankets

Electronic components - capacitorsBasic idea: use the large internal surface of aerogelscapacity is proportional to area!Material: Carbon aerogels as thin filmsSpecific values100 - 300 F/gFibre reinforced and CNTadditions of aerogels leadto 750 F/g

Home building & insulation - Challenges!!!!!!!Energy savings by thermal isolationmeasuresRegulation of indoor climateLight weight material (1-personstructural panel)High fire protection class ( F120)Utilization of natural constructionmaterialsNo colonization by fungiLow cost materialA solutionaerogel concrete

Aerogel concrete is a!composite made from§ hydrophobic Aerogel granulateand§ !!inorganic Binder/Matrixbinder / matrix materials§ gypsum or plaster§ cement or renderingAerogel granules Goldband TMtechnical challenges§ Extreme density differenceaerogel / matrix§ Bonding strength aerogelmatrix interfaceAerogel granules cement

DensityLowest density with hydrophobic Aerogelgranules:Values between 600 and 1100 kg/m3Lowest density material made by us:Pure building plaster with 80% aerogelgranules at 250 kg/m3

Fire protectionrequirement: better than fire class F90!Laboratory tests close to DIN-Norm1000950900850800750700650600Temperatur [ 100500010203040506070Zeit [min]8090100110120130

Thermal conductivity and U-valueAerogel content[vol%]Heatconduction[W/mK]U-value(25 cm wallthickness)65% ( 10% Sand)0,160,6470% ( 10% Sand)0,110,4470% (without Sand)0,130,52construction materialwall thicknessU-value [W/m2K]massive concrete25 cm3,3common brick24 cm1,5common brick (17,5 cm) plus PURdamping30 cm0,32honeycomb brick25 cm0,34 - 0,4620,5 cm0,525 cm0,15 - 0,2massive woodtimber frame construction

The future of aerogel concrete in theNetherlands?Built by students of theUniversity Duisburg-EssenCanoe made form high strengthconcrete and aerogel to saveweight.

Other solutions!!Structural panels: Composite of PU-foams orstyrofoams plates withaerogel-infiltarted feltsU-value 0.34Aerogel wrap for storefrontStadur-Süd

Foundry applicationsCasting of metals in a mould needs a mould materialMould materials: sands sand castingmetals permanent mould castingceramics investment castingSand grains must be bonded!Binders used:oils, polymers (phenol based, polyurethane, epoxy resins,.)water glass,.new: binder RF Aerogel AeroSandTechnology:Preparation of RF-sol, mixing with sand, core shooting,ambient drying, ready!CerabeadsAl2O3Brück-Ratke Giessereiforschung 56 (2004) 55 - 65Voss-Ratke Giessereiforschung 57 (2005) 18-25Reuß-Ratke Giessereiforschung 61 (2009) 24 - 33

AeroSands - real structureRF-Aerogel with corundum sandCarbon aerogel withCorundum sand

AeroSands - properties!!!!!!!Easy core removalThermal conductivity 0,3 - 2 W/KmHigh strength 100 to 600 N/cm2Smooth surfacesNo shrinkageNo gas release during castingInsensitive to humidity

Aerogel based additivesidea:Mix aerogel granules with foundry sands to improve the cast piece and workwithout a facingutilizing: Large surface area High adsorption capability Non-wetting with metals!Granulate from!Silica-Aerogel (sc and ambientdried)!RF Aerogel!Carbon aerogel!Particle size:!Fits to sand grain size!Volume fraction: 5 Vol.%!Binder:!Whatever is used in a foundryshop!RF-aerogel binder

Aero-Additiveswith 1.5 vol.-% RF-AerogelUse of Aero-Additive in a brass cast shopaluminiumbrassw/o Nano-AdditivesEffects of aerogels in brass, aluminiumand bronze castings

SummaryOxide aerogels, polymeric aerogels, mixed aerogels, hybrids,composites with fibers and felts offer a wide variety of applicationsgoing far beyond what is explored today and is on the market.„The global market for aerogels is expected to grow up from 62 Million in 2006 (700t) to 951 Million in 2011 (12,679t).“JOM 58 (August 2006) 10-11

Appearance and structure of Cellulose aerogels Cellulose-Aerogels are generally opaque and milky with densities of around 5 - 60 kg/m3 Structure: nanofelt of microfibrils Aerogels with 0,5 % Cellulose 1,0 % Cellulose 2,0 % Cellulose Cai et al, ChemSusChem 2008