March 2009
Plasma Synthesis of Tungsten Carbide Nanopowder
659
Table I. Summary of Experimental Results
Test parameter
Range
Effect
Other fixed conditions
Methane
concentration
C/W ratio:
3.7–5.7
Increased W C phase with decreasing C/W APT feeding rate5 3.1 g/min
2
ratio
Grain size of WC1 , 1171 nm, not
Plasma torch power5 16 kW
Plasma gas flow rate5 38 L/min
(251C, 86.1 kPa)
ꢀx
affected by the methane concentration
%
excess carbon, 130% at C/W ratio of 5.7 Flow rate of carrier gas (Ar–CH –H ) 5 4
4 2
decreased to 29% at C/W ratio of 3.7
The product composition, not affected
L/min (251C, 86.1 kPa)
APT feeding rate5 3.1 g/min
C/W ratio 5 5.7
Plasma gas flow rate5 38 L/min
(251C, 86.1 kPa)
Plasma torch
power
7–29 kW
Grain size of WC1 , 571 nm at 7 kW
ꢀx
increased to 1371 nm at an increased
plasma torch power of 29 kW
Flow rate of carrier gas (CH –H ) 5 4
2
4
L/min (251C, 86.1 kPa)
APT feeding rate5 3.1 g/min
C/W ratio 5 5.7
Plasma torch power5 16 kW
Plasma gas (Ar)
flow rate
29–66 L/min
(251C, 86.1 kPa) product with increasing flow rate
Slightly increased W C phase in the
2
Grain size of WC1 , 1171 nm, not
ꢀx
affected by the flow rate
Flow rate of carrier gas (CH –H ) 5 4
4 2
L/min (251C, 86.1 kPa)
APT feeding rate5 3.1 g/min
C/W ratio 5 5.7
Plasma gas flow rate5 38 L/min
(251C, 86.1 kPa)
Addition of
secondary
plasma gas (H2)
0.05–1.89 L/min
(251C, 86.1 kPa) product with the addition of secondary
plasma gas (H2)
Slightly increased W C phase in the
2
% excess carbon, 130% without the
addition, decreased to 13% with the
Flow rate of carrier gas (CH –H ) 5 4
4 2
addition of secondary plasma gas (H ) of
2
L/min (251C, 86.1 kPa)
1.89 L/min (251C, 86.1 kPa)
Grain size of WC1 , 1171 nm with no
ꢀx
secondary plasma gas (H ) increased to
2
1471 nm when the secondary plasma gas
(
H ) was added at 1.89 L/min (251C, 86.1
2
kPa)
APT, ammonium paratungstate.
also go to Mr. Robert W. Byrnes of the University of Utah for his competent work
with the design and repair of the experimental facilities.
product composition, which mainly consisted of WC1ꢀx, was
not affected by plasma torch power. The amount of W C phase
2
in the product, although small in all cases tested, increased with
decreasing methane concentration in the feed stream, increasing
the flow rate of plasma gas, and the addition of secondary
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Acknowledgments
(
14
The authors extend special thanks to Messrs. Rick Riley and Tim Webb of
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Smith International for his helpful suggestions. The authors wish to express their
gratitude to Prof. Patrick R. Taylor of Colorado School of Mines and Dr. Gilsoo
Han of Yanbian University of Science and Technology, China for their help with
the selection, design, and initial operation of the plasma reactor system. Thanks
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