Embed Size (px)
Citation preview
© 2016 by Zhe Cheng
EMA5001 Lecture 24
Transformation Kinetics for SiC
Formation
EMA 5001 Physical Properties of Materials Zhe Cheng (2016) 24 Transform Kinetics – SiC Formation
Kinetics for the Formation of Nano SiC
via Carbothermal Reduction Reaction
Overall Reaction: SiO2 + 3C = SiC + 2CO
2
Nano-scale SiO2-C Mixture
Cheng, Z., MS Thesis, 2004
EMA 5001 Physical Properties of Materials Zhe Cheng (2016) 24 Transform Kinetics – SiC Formation
Confirmation of SiO &
the Two-Step Reaction
3
EDX
XRD of Vapor Deposits
SiO = Si + SiO2
Cheng, Z., MS Thesis, 2004
EMA 5001 Physical Properties of Materials Zhe Cheng (2016) 24 Transform Kinetics – SiC Formation
Reaction Kinetics from Weight Change
Best fit to Interface-controlled “Grow in”/”Shrinking Core” model
4
Weight Loss Data Fitting to Interface-controlled
“shrinking-core” model
Cheng, Z., MS Thesis, 2004
EMA 5001 Physical Properties of Materials Zhe Cheng (2016) 24 Transform Kinetics – SiC Formation
Comparison with Other Kinetic Models
Good fit also to Nucleation – Growth model
5
Nucleation – Growth Model Diffusion-Controlled “Grow In”
Model – Jander’s Equation
Site saturation, 1D growth
Constant nucleation - no growth Cheng, Z., MS Thesis, 2004
Also good fit, n =1
Very poor fit
EMA 5001 Physical Properties of Materials Zhe Cheng (2016) 24 Transform Kinetics – SiC Formation
Microstructure Changes to Confirm
Reaction Model
6
Essentially very small
growth of SiC
crystallites during
CTR reaction
at intermediate range
Growth of porosity
matching
expectation
Cheng, Z., MS Thesis, 2004
EMA 5001 Physical Properties of Materials Zhe Cheng (2016) 24 Transform Kinetics – SiC Formation
Rate-Limiting Step & Activation Energy
Reaction is limited by sub-step of
SiO + C = SiC + 2CO
For the following reasons
Always have SiO fomartion
Shape of SiC dependent largely
on C size and not SiO2 size
7
Cheng, Z., MS Thesis, 2004
EMA 5001 Physical Properties of Materials Zhe Cheng (2016) 24 Transform Kinetics – SiC Formation
TEM
8
BEFORE Reaction
f = 35%
BEFORE Reaction
f = 63%
Cheng, Z., MS Thesis, 2004 Little grain growth during reaction
EMA 5001 Physical Properties of Materials Zhe Cheng (2016) 24 Transform Kinetics – SiC Formation
SEM
9
BEFORE CTR Reaction AFTER CTR Reaction
f = 0%
Almost fully dense
f = 95%
Highly porous
![Chapter 2 SiC Materials and Processing Technology€¦ · 34 2 SiC Materials and Processing Technology Table 2.1 Key electrical parameters of SiC [1] Property 4H-SiC 6H-SiC 3C-SiC](https://img.dokumen.tips/doc/110x75/5f4fd11797ddad63bf719816/chapter-2-sic-materials-and-processing-technology-34-2-sic-materials-and-processing.jpg)
