Journal of Materials Science

, Volume 48, Issue 12, pp 4396–4407 | Cite as

Diffusional effects for the oxidation of SiC powders in thermogravimetric analysis experiments

Article

Abstract

The oxidation behavior of SiC powders was studied using a thermogravimetric analysis (TGA). The effects of temperature (910–1010 °C), particle size (120 nm, 1.5 μm), and the initial reactant mass on the oxidation behavior of SiC were investigated. Kinetics analysis showed that intra-particle diffusion and chemical reaction controls the oxidation rate. Moreover, a new kinetics model was proposed to describe the oxidation rate of where all diffusion steps (bulk, inter- and intra-diffusion) and the chemical reaction may affect the overall reaction rate. The model was validated through a comparison with the experimental results obtained from the oxidation of SiC powders in TGA experiments. It was found that during the experiments, inter diffusion must also be taken account to describe adequately the oxidation rate. Numerical analysis indicated that inter-particle diffusion has a significant effect on the oxidation rate, especially for larger system.

List of symbols

A

Gas reactant

Ab

Bed surface area

b

Stoichiometric coefficient

CA

Concentration of gas reactant

CAs

Concentration of gas reactant at the surface of the bed

ρSiC

Molar density of SiC

Ct

Total molar density of gas

D0

Pre-exponential factor in Arrhenius equation in Eq. 24

\( D_{{{\text{air}} - {\text{CO}}_{ 2} }}^{{}} \)

Diffusion coefficient of the reactant in gas in the bulk system

\( D_{\text{e}}^{\text{s}} \)

Effective diffusivity of the reactant gaseous in solid

k0

Pre-exponential factor in Arrhenius equation in Eq. 25

L

Bed height

L0

Crucible height

m0

Initial sample weight

\( N_{\text{A}}^{\prime } \)

Molar flux of gaseous reactant inside the powder

NA

Molar balance of the gaseous reactant in the crucible

R0

Radius of the crucible

rc

Radius of unreacted shell of powder

r0

Initial powder radius

Sv

Total surface area of the powder per unit volume

t

Time

T

Temperature

\( \tau_{\text{S}} \)

Time for a complete reaction of the particles as defined in Eq. 4

\( \tau_{\text{r}} \)

Time to complete oxidation of the particles as defined in Eq. 4

τb

Time to complete oxidation of the particles as defined in Eq. 10

τc

Time to complete oxidation of the particles as defined in Eq. 27

X

Fractional conversion as defined in Eq. 5

x0

Thickness of the oxide layer

xA

Mole fraction of gas A in crucible

xAb

Mole fraction of gas A at bulk

xAs(t)

Mole fraction of gas A at the surface of the bed

\( X_{\text{A,Loc}}^{\prime } \)

Local fractional conversion defined by Eq. 22

Z

Dimensionless of bed height in the crucible (z/L)

Z*

Dimensionless of moving boundary in the bed

\( \Upomega \)

Function defined by Eq. 19

η

Function defined by Eq. 18

θ

Function defined by Eq. 27

\( \Upphi \)

Function defined by Eq. B1

ε

Porosity

τ

Tortuosity

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Copyright information

© Springer Science+Business Media New York 2013

Authors and Affiliations

  • Omid Ebrahimpour
    • 1
  • Jamal Chaouki
    • 1
  • Charles Dubois
    • 1
  1. 1.Department of Chemical EngineeringÉcole Polytechnique de MontréalMontréalCanada

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