Nano Materials Synthesis, Characterisation and Properties

Transcription

1 Nano Materials Synthesis, Characterisation and Properties Prof. Dr. Cordt Zollfrank Wissenschaftszentrum Weihenstephan Wissenschaftszentrum Straubing Prof. Dr. Johann Plank/ Department Chemie Technische Universität München

2 Synthetic Methods For Colloids and Nano Particles Two principle approaches: Bulk Material Break down method (Top down process) Colloid, Nanoparticle Solution Bottom up method

3 Synthesis via Bottom up Principle Methods Synthesis of colloids/nanos from solution Precipitation from solution by addition of a nonsolvent - precipitation of colloidal S from ethanol by addition of water - Colloidal carotenoid (food colorant) by addition of water to a solution of carotenoid in acetone Ionic precipitation reactions - exceeding the solubility product - surface energy of particle increases with decreasing particle size Hydrolysis of organometal compounds - preparation of silica sol from Stöber process - preparation of TiO 2 sol Reduction of ions to the element followed by agglomeration - Preparation of gold ruby Polymerisation and polycondensation of monomers into polymers

4 Bottom Up Methods: Seed Crystallisation Change of free energy of a seed crystal with size; n= number of building units A) Minor oversaturation B) High oversaturation n c = critical size from which seeds start to grow Conditions necessary to achieve monodisperse particles: A) Solution of particles B) Concentration where seeds form C) Maximum oversaturation I) No seed formation II) Range where seeds form III) Growth regime for particles, seeds are no (La Mer diagram) longer formed Opposite precipitatates (no seeds)

5 Nucleation - crystal growth - I Borchardt-Ott, S 33ff

6 Bottom Up Methods: Nano Crystals by Seeding - Principle: small particles possess higher solubility than large ones - large particles grow at the expense of small particles (Ostwald ripening) - Method to achieve nano sized crystals: a) initially high oversaturation spontaneous formation of many seed crystals b) then lower concentration no more seeds are being formed c) maintain low concentration particles continue to grow

7 Homogeneous - heterogenous nucleation surface volume

8 Bottom Up Methods Synthesis of colloidal sulfur sol: colloidal S particles are used as insecticides and fungicides a) Dilution of solution of S in ethanol with water: Colloidal S precipitates b) Comproportioning of S in water or air SO H 2 S 3 S + 2 H 2 O c) Acid degradation of sodium thiosulfate in water Na 2 S 2 O 3 1/8 S 8 + Na 2 SO 3

9 Application of colloidal sulfur

10 Application of colloidal sulfur

11 Biomimetic tooth paste

12 5Ca(OH) 2 3 H 3 PO 4 Ca 5 [OH(PO 4 ) 3 ] + 9H 2 O

13 Synthesis of Nano Particles Carbon Black Industrial manufacture of carbon black: Incomplete combustion of aromatic compounds Global production: approx. 6-7 mio. to/year Air inlet Complete combustion Incomplete combustion Water cooling

14 Carbon Black Worker at a Texas carbon black plant (photo by John Vachon, 1942)

15 Industrial Carbon Black Primary particles : diameter ~ nm, 30 nm often aggregated to chains and intergrown Chemical structure: layered, like graphite C 6 rings, but irregular arrangement Extremely high surface area, ca m 2 /g Ideal pigment: insoluble in all common solvents, resistent against most chemicals, UV stable, very intensive color As filler for strength enhancement of elastomers

16 Carbon Black Examples for industrial use of carbon black > 90 % as filler for elastomers, thereof 2/3 for tire industry, remainder for rubber Printing inks for newspapers (only 0,015 g of carbon black are needed for one page!) Coatings and paints a point (.) on a newspaper page contains carbon black nano particles!!!

17 Synthesis of (Pyrogenic) Fumed Silica Industrial manufacture by flame pyrolysis: 2 H 2 + O 2 2 H 2 O SiCl H 2 O SiO HCl Combustion in O 2 /H 2 flame

18 Manufacture of Fumed Silica

19 Fumed Silica Pyrogene Kieselsäure Fumed silica has a very strong thickening effect. Primary particle size is 5 50 nm. The particles are non-porous and have a surface area of m 2 /g. Density kg/m 3.

20 Umsetzung in der Gasphase Verwendung pyrogener Kieselsäure In Siliconkautschuk als Verstärkerfüllstoff, aber auch in vielen anderen Anwendungen zur Kontrolle der Rheologie (z.b. Ketchup). Zur Verdickung und Thixotropierung in Lacken und Farben, Druckfarben und ungesättigten Polyesterharzen sowie Epoxidharzen. Als Zusatzstoff und Verarbeitungshilfsmittel in der Kosmetik und der pharmazeutischen Industrie sowie als Rieselhilfsmittel bei Lebensmitteln, Futtermitteln und in der chemischen Industrie eingesetzt.

21 Chemical Vapour Deposition - CVD Chemical vapor deposition (CVD) is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer (substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber.

22 Chemical Vapour Deposition - CVD CVD-Variante APCVD (atmospheric) LPCVD (low pressure) HFCVD (hot filament) PECVD (plasma enhanced) typ. Arbeitstempe ratur C 1 bar thermisch typ. Arbeitsdruck C 0,01 10 mbar C 0, mbar C 1 mbar Aktivierungs energie aktiviert thermisch aktivierter Prozess thermisch aktivierter Prozess plasma + thermisch Verwendungszwecke Poly-Si abscheiden für Leiterbahnen, Gateoxid, Epitaxie von Si-Wafern Leiterbahnen, Siliciumdioxid, Siliciumnitrid, poly- Silicium Kohlenstoffbasierte Abscheidung (Diamant, amorpher Kohlenstoff, Kohlenstoffnanoröhren), silicium-basierte Schichten (amorphes/kristallines Si, Si 3 N 4, ) SiO 2 abscheiden Dielektrikum Si 3 N 4 Passivierung

23 Chemical Vapor Deposition (CVD) Processes in use

24 Chemical Vapor Deposition (CVD) Principle of chemical vapor deposition : Deposition from gas phase

25 Chemical Vapor Deposition (CVD) Preparation of a Cu nano film on a substrate Schematic hot-wall-reactor Schematic cold-wall-reactor

26 CVD Copper precursors

27 Chemical vapor deposition (CVD) Deposition of Al layers from Al i Bu 3 At low T homogeneous Al surface At high T Al layer contaminated with impurities of C CVD von Al-Schichten aus Me 3 N-AlH 3

28 Chemical vapor deposition (CVD) Manufacture of diamond films for dental instruments etc.

29 Chemical vapor deposition (CVD) Manufacture of diamond films Different morphologies achieved by different gas pressures during synthesis Different morphologies achieved through different temperatures during synthesis

30 Bottom Up Synthesis: Organic Colloids and Nano Particles Polymer latex dispersions Global production of synthetic polymers 2000: ca. 190 Mio. t ca. 200 Bio. sales Global production of synthetic polymers, broken down by categories Polymer latex dispersions by product categories

31 Latex Dispersions

32 Latex Dispersions CH 2 CH CH 2 CH C O m O C 4 H 9 n CH 2 CH 2 m CH 2 CH O 2 2 C O CH 3 n

33 Synthesis of Latex Dispersions via Emulsion Polymerisation

34 Morphology of Latex Particles

35 Morphology of Latex Particles

36 Morphology of Latex Particles

37 Film Forming of Latex Particles (Coalescence)

38 Film Forming of Latex Particles (Coalescence) Film formation Minimum film-forming temperature MFFT Latex dispersion Above MFFT temperature, a homogeneous polymer film is formed elimination of water close sphere packing Depends on: Polymer composition particle deformation Surfactant (emulsifier) Particle size Particle morphology Coalescence into a Film

39 Film Formation (Coalescence)

40 Particle Coalescence (Film Forming Process) Latex particles at beginning of coalescence Starting coalescence (film formation) of anionic dispersion A2

41 Film Forming Process of Latex Polymers

42 Redispersible Powders in Tile Adhesives Only redispersible powders provide: - adhesion of tiles with sintered surface (low water uptake, E 0.5 %) - adhesion after 70 C storage Adhesion between sintered tile and mortar

43 Adhesion Tile Cement Mortar Achieved with Latex Dispersion

44 Industrial Applications of Latex Dispersions Paints and Coatings (Latex paint) provides adhesion, elastic (no cracks), low dirt Protection of buildings against corrosion and ageing water repellent, prevents attack by aggressive gases Building materials (tile adhesives, flooring compounds etc.) adhesion, flexibility Paper manufacturing Binder, surface coating Leather industry softness, strength, water repellent Textil and carpet coating strength enhancement Latex foams Adhesives etc.