Modelling the aerosol synthesis of silica nanoparticles from TEOS. - - PowerPoint PPT Presentation

▶
modelling the aerosol synthesis of silica nanoparticles
SMART_READER_LITE
LIVE PREVIEW

Modelling the aerosol synthesis of silica nanoparticles from TEOS. - - PowerPoint PPT Presentation

Feb 10, 2023 134 likes •462 views

Modelling the aerosol synthesis of silica nanoparticles from TEOS. Shraddha Shekar 1 , Ali Abdali 2 , Mustapha Fikri 2,3 , Christof Schulz 2,3 and Markus Kraft 1 July, 2011 1 University of Cambridge, UK 2 IVG, University of Duisburg-Essen, Germany

slide-1
SLIDE 1

Shraddha Shekar1, Ali Abdali2, Mustapha Fikri2,3, Christof Schulz2,3 and Markus Kraft1 July, 2011

1 University of Cambridge, UK 2 IVG, University of Duisburg-Essen, Germany 3 CeNIDE, Center for Nanointegration Duisburg-Essen

Modelling the aerosol synthesis of silica nanoparticles from TEOS.

slide-2
SLIDE 2

Some basic questions

  • What is TEOS?
  • What are silica nanoparticles (SiNP)?
  • Why are they important?
  • Why model this system?
slide-3
SLIDE 3

Tetraethoxysilane

TEOS

  • Central silicon attached to 4-ethoxy

branches

  • Vibrations and rotations within the

molecule

  • Many possible ways of bond

breaking, many possible reactions

  • Preferred precursor because

relatively inexpensive and halide- free.

slide-4
SLIDE 4

Silica nanoparticles

What are SiNP? Network of Si-O bonds such that Si:O = 1:2 Why are they important?

  • Support material for

functional/composite nanoparticles, catalysis

  • Bio-medical applications, drug delivery
  • Optics, optoelectronics,

photoelectronics

  • Fabrics, clothes
slide-5
SLIDE 5

Why model this?

Precursor(TEOS) Aerosol reactor P ≥ 1 atm T ≈ 1200 - 2000 K Silica nanoparticles

  • What are the optimal process conditions?
  • What are the final product properties?
  • What is the final particle size distribution?

Industrial Scale Molecular Scale

  • What happens in the gas-phase?
  • How do gas-phase precursors form the particles?
  • How do these particles grow?
  • How to describe the overall system from first-principles?
slide-6
SLIDE 6

Methods: Ab initio modelling

Quantum Chemistry calculations Statistical Mechanics

H(T) S(T) Cp(T)

Thermochemistry calculation Chemical Kinetics Equilibrium calculation Overall Model Species generation Population Balance Model

Ref: W. Phadungsukanan, S. Shekar, R. Shirley, M. Sander, R. H. West, and M. Kraft. First-principles thermochemistry for silicon species in the decomposition of tetraethoxysilane. J. Phys. Chem. A, 113, 9041–9049, 2009

slide-7
SLIDE 7

Reaction kinetics

  • Equilibrium

– Hints towards the existence of stable intermediates & products. – Intermediates Si(OH)x(OCH3)4-x Si(OH)y(OC2H5)4-y – Main Product Si(OH)4

  • Kinetics

– Reaction set generated to include all intermediates and products from equilbrium. – Reactions obey Arrhenius rate law k = ATβe-Ea/RT – Rate parameters (A, β, Ea) fitted to experimental vaues (a)

(a) J. Herzler, J. A. Manion, and W. Tsang. Single-Pulse Shock Tube Study of the decomposition of tetraethoxysilane and Related

  • Compounds. J. Phys. Chem. A, 101, 5500-5508, 1997
slide-8
SLIDE 8

Reaction Mechanism

  • Heuristic reaction mechanism

C8H20O4SI = C6H16O4SI + C2H4 C6H16O4SI = C4H12O4SI + C2H4 C4H12O4SI = C2H8O4SI + C2H4 C2H8O4SI = H4O4SI + C2H4 C8H20O4SI = C7H17O4SI + CH3 C7H17O4SI = C2H4 + C5H13O4SI C5H13O4SI = C2H4 + C3H9O4SI C3H9O4SI = C2H4 + CH5O4SI CH5O4SI = H4O4SI + CH C7H17O4SI = C7H16O4SI + H C7H16O4SI = C6H13O4SI + CH3 C6H13O4SI = C6H12O4SI + H C6H12O4SI = C4H10O4SI + C2H2 C4H10O4SI = C2H8O4SI + C2H2 C8H20O4SI = C2H4 + C6H16O4SI2 C6H16O4SI2 = C2H4 + C4H12O4SI2 C4H12O4SI2 = C2H4 + C2H8O4SI2 C2H8O4SI2 = C2H4 + H4O4SI C8H20O4SI = C2H5 + C6H15O4SI2 C6H15O4SI2 + H = C6H16O4SI2 C6H16O4SI2 = C2H5 + C4H11O4SI2 C4H11O4SI2 + H = C4H12O4SI2 C4H12O4SI2 = C2H5 + C2H7O4SI2 C2H7O4SI2 + H = C2H8O4SI2 C2H7O4SI2 = H3O4SI + C2H4 H3O4SI = H2O3SI + OH H2O3SI = SIO2 + H2O C6H15O4SI2 = C2H3 + C4H12O4SI2 C4H11O4SI2 = C2H3 + C2H8O4SI2 C2H8O4SI2 = H3O4SI + C2H3

slide-9
SLIDE 9

Flux and Sensitivity Analyses

Main Reaction Pathway

Reaction number

slide-10
SLIDE 10

Rate parameter estimation

The rate parameters have been fitted to shock-tube experimental data provided by Herzler et al(a)

(a) J. Herzler, J. A. Manion, and W. Tsang. Single-Pulse Shock Tube Study of the decomposition of tetraethoxysilane and Related

  • Compounds. J. Phys. Chem. A, 101, 5500-5508, 1997

Step 2: Sensitivity Analysis To identify the 4 most sensitive parameters Step 1: Low discrepancy series To perform a pre-scan of parameters for 18 Si reactions. Step 3: Response Surface Methodology To estimate model uncertainties

Uncertainties in model parameters for reactions R1 and R15

slide-11
SLIDE 11

Optimisation Theory

  • Experimental data
  • Model response with paramaters x
  • and

( )

x B A x + = η

For a simple linear model, K=1

( ) ( )

ξ ξ η c x B A c x + + = , ,

( ) ( ) [ ]

x B A c x E x + = = ξ η µ , ,

( ) ( ) ( )

2 2

c B c x c = = ξ η σ , , Var

exp exp exp

σ η η ± = ξ c x x + =

( )

x η η =

( )

K

x x ,...,

1

= x with

with uncertainty factor c and standard normally distributed ξ

  • A. Braumann, P. L. W. Man, and M. Kraft. Statistical approximation
  • f the inverse problem in multivariate population balance modelling.
  • Ind. Eng. Chem. Res., 49: 428–438, 2010. doi:10.1021/ie901230u
slide-12
SLIDE 12

Experimental validation

(a) J. Herzler, J. A. Manion, and W. Tsang. Single-Pulse Shock Tube Study of the decomposition of tetraethoxysilane and Related

  • Compounds. J. Phys. Chem. A, 101, 5500-5508, 1997
slide-13
SLIDE 13

Gas-phase mechanism

slide-14
SLIDE 14

Reactor Plot

Conclusion from kinetic model: Si(OH)4 is the predominant gas-phase precursor

slide-15
SLIDE 15

Particle Model

Si(OH)4 molecules undergo dehydration to form particles. These particles change in size and shape through their lifetime.

Particles Particle processes

Move in type spce

slide-16
SLIDE 16

Type Space

( )

slide-17
SLIDE 17
  • 1. Inception

Inception increases the number of particles in the system.

slide-18
SLIDE 18
  • 2. Surface Reaction

Si(OH)4 from gas-phase reacts on a particle surface.

slide-19
SLIDE 19
  • 2. Rounding due to surface reaction

Surface reaction alters the common surface between different primaries of a particle:

slide-20
SLIDE 20
  • 3. Coagulation

Particles collide and stick to each other.

slide-21
SLIDE 21
  • 4. Intra-particle reaction

Adjacent OH sites react with each other to form Si- O-Si bonds.

slide-22
SLIDE 22
  • 5. Sintering

Sintering calculated on a primary particle-level & alters composition.

slide-23
SLIDE 23

Particle model parameter estimation

Parameter estimation method: Sobol sequences followed by simultaneous perturbation stochastic approximation

Unknown parameters

Parameter space: Objective function:

Ref (a): T. Seto, A. Hirota, T. Fujimoto, M. Shimada, and K.

  • Okuyama. Sintering of Polydisperse Nanometer-Sized

Agglomerates, Aerosol Sci. Tech., 27, 422-438, 1997

slide-24
SLIDE 24

Particle model parameter estimation

Ref (a): T. Seto, A. Hirota, T. Fujimoto, M. Shimada, and K.

  • Okuyama. Sintering of Polydisperse Nanometer-Sized

Agglomerates, Aerosol Sci. Tech., 27, 422-438, 1997

slide-25
SLIDE 25

Particle model validation

T = 900 oC T = 1750 oC T = 1500 oC

slide-26
SLIDE 26

Precursor + Fuel +Air

Isothermal Batch Reactor (T = 1500 K, P = 1 atm)

TEOS decomposition Formation of Si(OH)4 Particle formation

Simulation for industrial conditions

Sensitive applications of SiNP require highly specific properties

slide-27
SLIDE 27

Simulation results

Low Standard deviation dc Mean Diameter 20-40nm

slide-28
SLIDE 28

Simulation results

TEOS decomposition rate High surface activity

slide-29
SLIDE 29

Desirable process zones

  • Catalysis / functional materials / fillers
slide-30
SLIDE 30

Desirable process zones

  • Drug delivery / bio-medical applications
slide-31
SLIDE 31

Thank you!

slide-32
SLIDE 32

Particle size distribution evolution

T = 1500 K