Diffusion Flames and Scale-up

Transcription

1 Verbrennung und chemisch reaktive Prozesse in der Energie- und Materialtechnik Diffusion Flames and Scale-up Dr. Frank Ernst phone: Office hour: Thursdays after the lecture 200 nm Department of Mechanical and Process Engineering ETH Zurich,

2 Lecture outline Particle morphology Product control by nozzle quenching Sate-of-the-art nanoparticle production 2

3 Degree of Agglomeration matters... Agglomerated: fillers catalysts lightguide performs particles for chemical mechanical polishing (CMP) catalysts Non-Agglomerated: pigments composites (e.g. for dental applications) electronics 3

4 Morphology control: Agglomerated Particles Non-Agglomerated Particles t Coagulation and Sintering 100nm Primary Particles Nucleation Molecules Gaseous Precursor 4

5 Fractal Aggregates Fractal dimension d c x i d d c p D f d p D f = 1 D f = 3 Measurable by small angle x-ray scattering (SAXS) 5

6 Morphology / Fractal Dimension Non-Fractal 17 g/h 2.5 l/min 4.7 l/min Non-Fractal d BET = 44 nm d BET = 78 nm Non-Fractal d BET = 55 nm 8.5 l/min 13.3 l/min D f = 1.6 d BET = 41 nm D f = 1.9 d BET = 23 nm 24 l/min Degussa OX-50 D f = d BET = 55 nm Mueller R., Kammler H.K., Pratsinis S.E., Vital A., Beaucage G., Burtscher P., Powder Technol., 140, (2004). 6

7 Morphology / Fractal Dimension 9 g/h 1.3 l/min 4.7 l/min NF NF 11.4 l/min 24 l/min NF NF Mueller R., Kammler H.K., Pratsinis S.E., Vital A., Beaucage G., Burtscher P., Powder Technol., 140, (2004). 7

8 SiO 2 Nanocomposites in a Dimethylacrylate matrix (50:50) Degussa (OX-50) ETH (non-aggl. SiO 2 at 4.7 l/min O 2 ) Elastic Modulus Mueller R., Kammler H.K., Pratsinis S.E., Vital A., Beaucage G., Burtscher P., Powder Technol., 140, (2004). 8

9 Nozzle-Quenching for TiO 2 Precision Synthesis Prevention of Agglomeration Precision Control of Particle Size Objective: Stop particle growth process at early stages before agglomeration sets in. Method: Control of flame length (particle residence time) by rapid quenching. 9

10 TiO 2 Particle Size Control by O 2 Flow 10

11 Nozzle Quenching Controls Flame Length Wegner K., Stark W.J., Pratsinis S.E., Mater. Lett. 55, 318 (2002). 11

12 Sudden temperature drop across nozzle Centerline Flame Temperature, C Without nozzle Critical temperature for rapid coalescence of TiO 2 nanoparticles: 800 C 0.8 cm behind nozzle (4 L/min O 2 ) 4 L/min Distance from Burner, cm 12

13 TiO 2 Particle Size Control by Nozzle Quenching BET-equivalent Particle Diameter, nm 30 2 L/min O Burner - Nozzle Distance, cm Filter No Nozzle 13

14 Particle Morphology by Thermophoretic Sampling (TS) Rapid insertion and withdrawal of a TEM grid into the flame for particle collection (Dobbins & Megaridis, 1987). 14

15 Size Control of Non-agglomerate TiO 2 Particles by BND (2 L/min O 2 ) TS in flame Nozzle Product 3 cm d BET = 18 nm 5 cm d BET = 27 nm Product powder No nozzle d BET = 55 nm 15

16 Reduction of Agglomeration 6 L/min O 2 flow rate TS in front of nozzle (BND = 1.5 cm) No nozzle Product powder Nozzle BND = 1.5 cm 16

17 Effect of Quenching Distance (BND) on Particle Crystallinity X-ray diffraction pattern 2 L/min O 2 2 phases obtained: Anatase Rutile Intensity No Nozzle R R R 5 cm 3 cm 1 cm

18 Control of Phase Composition by TTIP Concentration BET-equivalent Particle Diameter, nm Koch & Friedlander, 1991 Anatase wt-% d BET Anatase wt-% 2 L/min O 2 BND: 5 cm TTIP Flow Rate, g/h 18

19 Operation Diagram for TiO 2 Production with the Flame-Nozzle Process 100 Increasing BND Anatase wt-% g/h 16.3 g/h 3 cm BND 5 cm BND BET-equiv. Particle Diameter, nm Increasing TTIP Wegner K., Pratsinis S.E., AIChE J. 49, (2003). 19

20 Rutile Formation by Oxygen Defects Anatase wt-% O 2 /Ti molar ratio Oxygen defects promote rutile formation. Blue color indicates suboxide-formation by quenching. 20

21 Nanoparticles nm (at least into two dimensions) The thickness (diameter) of a human hair is 50, ,000 nm! 21

22 22

23 Melting Point, K The Melting Point Decreases with Decreasing Nanoparticle Size Au Particle diameter, Å Buffat and Borel, Phys. Rev. A 13, 2287 (1976) 23

24 Applications of Nanoparticles Large surface area per gram (adsorbents, membranes) Stepped surface at the atomic level (catalysts) Easily mix in gases and liquids (reinforcers) Superfine particle chains (recording media) Easily carried in an organism (new medicines) Cosmetics that last way into the night mm 10 nm SSA = 200 m 2 /g Some people believe that nanoparticles are a new state of matter! SSA = 0.2 m 2 /g 24

25 How are they made? Many processes & synthesis conditions Plasma-arc Laser ablation Chemical Vapor Deposition Wet-phase chemistry etc. Need synthesis technique that is: Rapid, continuous & scaleable Flame synthesis carbon black TiO 2 SiO t/year Scale-up limitations C 60 /C t/year 25

26 Particle formation & growth flames Aggregation HCl TiO 2 TiO 2 TiO 2 H 2 O TiO 2 H 2 O H 2 O HCl Coagulation T (K) O 2 TiCl 4 H 2 TiCl 4 TiCl 4 O 2 H 2 H 2 O 2 Nucleation Chemical reaction 26

27 Vapor flames Can make many interesting materials: Fillers for composites, catalysts etc. However, limited compositions H C, TiO 2, SiO 2, Al 2 O 3 He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fw Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 27

28 Vapor flames Aggregation HCl TiO 2 TiO 2 TiO 2 H 2 O TiO 2 H 2 O H 2 O HCl Coagulation T (K) O 2 TiCl 4 H 2 TiCl 4 TiCl 4 O 2 H 2 H 2 O 2 Nucleation Chemical reaction Reactants in vapor phase 28

29 Spray flames Keep aerosol processes Dispersed Product- Molecules & Cluster Droplets contain: - Organic solvent (comb. energy) - Reactant precursor compound Reactants in LIQUID phase 29

30 Spray flames 30

31 30 mm Flame synthesis 300 nm 200 nm Dispersed Product- Molecules & Cluster Vapor Flame Spray Flame Mädler, L., Kammler, H.K., Mueller, R., and Pratsinis, S.E., J. Aerosol Sci. 33 (2) (2002). 31

32 Spray flames Spray Flame Pyrolysis (FSP) Liquid enables composition flexibility Opens up many possibilities H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fw Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 32

33 Devices Immobilization, films & 2D coatings Formulations Surface functionalization Embedded, surface clusters & shells Mixed-phase & composition Single-phase particles & aggregates 33

34 Tailor-made particle structures (size, morphology, crystallinity etc.) with a large variety chemical compositions 34

35 Flame Spray Pyrolysis 35

36 In-situ deposition of noble metals 15 nm For applications in catalysts sensors optical devices, etc. Au on TiO 2 Mädler, L., Stark, W.J., Pratsinis. S.E., J. Mater. Res., 18 (1), (2003). 36

37 Concentration vs. crystallite size Doubling gold concentration 20 Au / TiO 2 (~ 100 m 2 /g) doubles Au crystallite size leaves support unchanged Average crystal size, nm Au wt% 4.0 Mädler, L., Stark, W.J., Pratsinis. S.E., J. Mater. Res., 18 (1), (2003). 37

38 Concentration vs. crystallite size Doubling gold concentration doubles Au crystallite size leaves support unchanged Gold particle size is independent of ceramic supporting surface area Average crystal size, nm Au / TiO 2 (~ 100 m 2 /g) Au / SiO 2 (~ 320 m 2 /g) Au wt% 4.0 Mädler, L., Stark, W.J., Pratsinis. S.E., J. Mater. Res., 18 (1), (2003). 38

39 Flame Spray Pyrolysis 39

40 Glucose sensor Proton Exchange Membrane Fuel Cell detection of hydrogen peroxide biomolecules (glucose, choline,...) Ernst et al., J. Mat.Chem., 20 (6), (2008). hydrogenation oxidation reforming electrodes for fuel cells 40

41 Hydrogenation of cyclohexene Cyclohexene conversion (%) supported (12 wt% Pt) reference (5 wt% Pt) supported (10 wt% Pt) embedded (2.6 wt-%) time (min) Ernst et al., J. Mat.Chem., 20 (6), (2008). 41

42 Devices Immobilization, films & 2D coatings Formulations Surface functionalization Embedded, surface clusters & shells Mixed-phase & composition Single-phase particles & aggregates 42

43 Direct deposition on sensor substrate Filter housing Water out Spray flame Support flame Shield gas Exhaust vent Water in Deposition substrate 120 C Precursor liquid Syringe pump PI MFCs Oxygen Methane Oxygen Oxygen 500 C sensing area: 7 x 3.5 mm 2 Mädler et al., European patent, Dec. 9th

44 Layer morphology top view SnO mm Deposition time: 180 s 44

45 Layer morphology top view SnO 2 5 mm 500 mm Deposition time: 180 s 45

46 Layer morphology cross section SnO 2 Al 2 O 3 5 mm Deposition time: 180 s 46

47 Devices Immobilization, films & 2D coatings Formulations Surface functionalization Embedded, surface clusters & shells Mixed-phase & composition Single-phase particles & aggregates 47

48 Examples for FSP materials Metal oxides SiO 2, TiO 2, Al 2 O 3, Bi 2 O 3, CeO 2, ZnO Mixed metal oxides SiO 2 /TiO 2,V 2 O 5 /TiO 2, ZnO/SiO 2, Zn 2 SiO 4, BaTiO 3, Ce x Zr (1-x) O y Noble metals on oxides Au, Pt, Pd on TiO 2, SiO 2, Al 2 O 3 TiO 2 Ce x Zr (1-x) O y Pt on Al 2 O 2 Bi 2 O 3 hollow ZnO/SiO 2 50 nm 200 nm 5 nm Versatile Process Mädler, et al., J. Appl. Phys (2002). Stark, W. J. et al., A., Chem. Commun. (2003). Strobel, R. et al., J. Catal. (2003). 48

49 Lecture summary Flame nozzle quenching agglomerated vs. non-agglomerated particles controlled synthesis: operation diagram Nanoparticles for Materials Flame Spray Pyrolysis & metal-oxide materials Vapor Spray flame: extend range of accessible compositions Flame Spry Pyrolysis (FSP) Metal-oxide nanomaterials for many applications Metal on metal-oxides Sensors and emerging areas Nanoparticle Technology is a frontier for scientific advances and business opportunities 49

50 Further reading Chung S.-L., Katz J.L., The Counterflow Diffusion Flame Burner: A New Tool for the Study of the Nucleation of Refractory Compounds. Combustion and Flame 61, (1985). Xing Y., Kole T.P., Katz J.L., Shape-controlled synthesis of iron oxide nanoparticles. J. Materials Science Letters 22, (2003). Santoro R.J., Miller J.H., Soot Particle Formation in Laminar Diffusion Flames. Langmuir 3 (2), (1987). Pratsinis S.E., Zhu W., Vemury S., Teh role of gas mixing in flame synthesis of titania powder. Powder Technol. 86, (1996). Mueller R., Kammler H.K., Pratsinis S.E., Vital A., Beaucage G., Burtscher P., Non-agglomerated dry silica nanoparticles. Powder Technol. 140, (2004). Wegner K., Pratsinis S.E., Scale-up of nanoparticle synthesis in diffusion flame reactors. Chem. Eng. Sci. 58, (2003). Pratsinis S.E., Zhu W., Vemury S. The role of gas mixing in flame synthesis of titania powders. Powder Technology 86, (1996). Johannessen T., Pratsinis S.E., Livbjerg H. Computational analysis of coagulation and coalescence in the flame synthesis of titania particles. Powder Technology 118, (2001). Wegner K., Stark W.J., Pratsinis S.E., Flame-nozzle synthesis of nanoparticles with closely controlled size, morphology and crystallinity. Materials Letters 55, 318 (2002). Wegner K., Pratsinis S.E., Nozzle-quenching process for controlled flame synthesis of titania nanoparticles. AIChE J. 49, (2003). 50