Abstract—In the attempt to develop a clean process, study
has been conducted to determine the effect of absorbed CO
2 gas
as source of carbon to the case hardening of treated mild steels
in the recently developed process of electro-carburisation in
non-toxic molten carbonate salts. The concentration of CO
2 in
the process was varied by purging a CO
2 and N
2 mixture at flow
rate ratios of CO
2:N
2 of 200:0, 150:50, 100:100, 50:150 and
0:200 mL.min-1. Electro-carburisation was performed in two
types of molten salt electrolyte i.e. a mixed anion Na
2CO
3-NaCl
(mole ratio 4:1) and a pure carbonate Li
2CO
3-K
2CO
3 (1:1 mole
ratio). A voltage of 2.5V was applied between mild steel cathode
and an inert SnO
2 anode at a carburisation temperature of
800oC for 60 minutes. The results show that greater CO
2
concentration produced samples with greater surface hardness
and thicker case-hardening, attributed to the increased
availability of the electro-active carbon source which was
generated by absorption of CO
2. Electro-carburisation in
Li
2CO
3-K
2CO
3 and Na2CO
3-NaCl gave surface hardness of
1075 ± 25 HV, however Li
2CO
3-K
2CO
3 (540 thickness) gave
thicker case depth compared to Na
2CO
3-NaCl (500 thickness).
This is thought to be due to the amount of carbon deposited in
each salt; 12.70 wt.% C in Li2CO3-K
2CO
3 and 11.10 wt.% C in
Na
2CO
3-NaCl.
Index Terms—Molten salt, carburisation, carbonate salt,
surface hardness, case depth.
Nancy Julius Siambun is with the Universiti Malaysia Sabah, Engineering
Faculty, 88999 Kota Kinabalu, Sabah, Malaysia (e-mail:
nancyjs@ums.edu.my).
Daniel A. Jewell and George Z. Chen are with the University of
Nottingham, Department of Chemical and Environmental Engineering, and
Energy and Sustainability Research Division, Faculty of Engineering,
Nottingham, NG7 2RD, UK (e-mail: daniel.jewell@coogeeenergy.com.au,
george.chen@nottingham.ac.uk).
[PDF]
Cite: Nancy Julius Siambun, Daniel A. Jewell, and George Z. Chen, "Influence of CO2 Gas in the Electro-Carburisation Process of Mild Steel," International Journal of Chemical Engineering and Applications vol. 6, no. 5, pp. 341-345, 2015.
