22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Plasma-chemical synthesis of oxygen-free compounds TiC and SiC nanosized
powders
A.V. Samokhin, D.E. Kirpichev, N. Alexeev, M. Synaiskiy and Y. Tsvetkov
Russian Academy of Sciences, A.A. Baikov Institute of Metallurgy and Materials Science (IMET RAS), Russia
Abstract: Thermodynamic calculations revealed the synthesis of nanosized powders of
oxygen-free TiC and SiC compounds via interaction of TiCl 4 and SiCl 4 with hydrogen,
octane (for TiCl 4 ) or hexane (for SiCl 4 ). Experimental data for plasma-chemical synthesis
of SiC nanopowder via interaction of SiCl 4 vapor with hydrogen and hexane in H 2 –N 2 –Ar
DC-arc plasma are presented. The physical and chemical characteristics of the
nanopowders are studied. The influence of the process operational parameters on the
nanosized fraction properties were investigated.
Keywords: DC arc plasma torch, oxygen-free nanopowders, Ti(Si) chloride, Ti(Si) carbide
1. Introduction
Powder materials are claimed of many industry areas.
There are some of them - production of wear- and
corrosion-resistant hard alloys, materials with specified
electro physical properties, deposition of coatings, steel
alloying. Separation of microsized powder and nanosized
powders or just nanosized powders allows substantially
improve final product properties. Plasma chemical
DC-arc processes are allocated with high efficiency; these
processes have potential to regulate produced powders
characteristics in the wide range. Use of liquid raw
materials with relative low boiling temperatures (up to
400 K) allows to eject it into plasma chemical synthesis
reaction area as vapor and do not spend heat of plasma jet
for solid particles vaporization, this is take place when
powder (solid) raw materials eject with transport gas.
Results of parameters thermos-dynamical calculation for
synthesis of nanosized powders of oxygen-free TiC and
SiC compounds via interaction of TiCl 4 and SiCl 4 with
hydrogen, octane (for TiCl 4 ) or hexane (for SiCl 4 ) are
revealed in the paper. Plasma-chemical synthesis of SiC
nanopowder via interaction of SiCl 4 vapor with hydrogen
and hexane in H 2 –N 2 –Ar DC-arc plasma experimental
data are also adduced.
2. Thermo-dynamical analyze
Equilibrium compositions and reaction (1), (2) products
thermo-dynamical characteristics were calculated with
program TERRA for thermos-dynamical equilibrium
modeling.
TiCl 4 + x/8 C 8 H 18 + y H 2 + z Ar,
SiCl 4 + x/6 C 6 H 14 + y H 2 + z Ar.
(1)
(2)
Coefficients x, y and z values are presented in the table 1.
Calculation was in temperature range 400-4000 K (step
50 K) at total system pressure 0.1 MPa.
As a result of calculations of interaction (1) and (2)
temperature dependences of titanium and silicon carbides
P-II-7-11
output and condense carbon presence in it at various
reagent concentration in initial mixture are established,
they are characterized with element atomic ratio
С/Ti=(8·C 8 H 18 )/(TiCl 4 ), C/Si=(6·C 6 H 14 )/(SiCl 4 ) and
H/Cl=(2·H 2 )/(4·SiCl 4 ).
Table 1. Reaction (1), (2) coefficients.
№
3
4
5
6
7
8
9
x
1
1
1
0.95
0.71
0.9
1.05
y
4
10
20
20
4
10
20
z
4
10
20
20
4
10
20
Temperature dependences for titanium and silicon
carbides output have an extreme character (Fig. 1).
Maximal titanium carbide output is in the temperature
range 2000-2400 K and its value increase since 0.64 up to
0.95 with relation H/Cl (hydrogen excess) increase since
2 up to 10 (Fig. 1). For achievement of maximal silicon
carbide output temperature range of 1550-1700 K is
required. Hydrogen excess growth since 2 up to 10
results TiC output increase since 0.72 up to 0.97. Lower
chlorides and metal vapors are presented in the
equilibrium system at the temperatures higher then
temperature of maximal output. For reaching of maximal
titanium and silicon carbides outputs in process set-up, it
is necessary to provide the residence time of react system
at corresponded temperatures while system relaxes to
equilibrium state. Quenching may be need to prevent
reactions of carbides chlorination at its interaction with
HCl, which decreases final product output.
At the element relation Me/C=1 it may be high quantity
of free carbon, which increase with decreasing of element
relation H/Cl (Fig. 1). Carbon excess influences to free
carbon concentrations in products (Fig. 2). Its decreasing
1
12
0,7
3
10
0,6
0,5
8
3
0,4
6
0,3
4
0,2
4
5
0,1
2
0,0
500
1000
1500
2000
2500
3000
0
3500
Temperature, К
0,9
0,8
SiC output
20
5
4
b)
3
0,7
0,6
18
16
14
12
3
0,5
10
0,4
8
0,3
6
0,2
4
4
0,1
2
5
0,0
500
1000
Free carbon content, mass %
1,0
1500
2000
2500
Temperature, К
3000
0
3500
Fig. 1. Temperature dependences of TiC (a) and SiC (b)
output (solid line) and carbon impurities concentration in
it (dot line) at various ratio H/Cl (C/Me=1). 3 – MeCl 4 +
x/n C n H m + 4 H 2 + 4 Ar; 4 – MeCl 4 + x/n C n H m + 10 H 2
+ 10 Ar; 5 – MeCl 4 + x/n C n H m + 20 H 2 + 20 Ar.
leads to decrease of carbon impurities and allows
excluding its presence at the element relation H/Cl near 4
and upper, besides the relation increase leads to widening
of temperature range, where these impurities are absent.
Energy consumption, needed to produce equilibrium
composition at this temperature and related to initial gas
mixture Ar – H 2 quantity, determines required gas flow
enthalpy, which injected with initial tetrachloride and
hydrocarbon. Temperature relation of required gas
mixture Ar – H 2 enthalpy for different element ratio H/Cl
values is on the Fig. 3. Fig. 3 relations may be used for
determine theoretical temperature of reaction with
injection of MeCl 4 and C n H m vapors into Ar – H 2 flow
with specified enthalpy value.
4
1,0
9
0,8
3
0,6
2
0,4
3
1
4
0,2
9
0
500
1000
1500
2000
2500
Temperature, К
3000
5
0,8
9
6
a)
12
10
0,6
8
0,5
0,4
6
0,3
4
0,2
9
0,1
6
2
5
0,0
500
1,0
1000
1500
2000
2500
Temperature, К
3000
b)
6
0,8
14
12
0,7
10
0,6
0,5
8
0,4
6
0,3
9
0,1
5
1000
1500
2000
2500
Temperature, К
3000
0
3500
Fig. 2. Temperature dependence of TiC (a) and SiC (b)
output (solid line) and carbon impurities concentration in
it (dot line) at alter ratio C/Me (H/Cl=10). 5 – MeCl 4 +
1/n C n H m + 20 H 2 + 20 Ar; 6 – MeCl 4 + 0.95/n C n H m +
20 H 2 + 20 Ar; 9 – MeCl 4 + 1.05/n C n H m + 20 H 2 + 20
Ar.
2
0,6
2
0,4
1
3
0,2
4
5
1000
1500
2000
Temperature, К
2500
0,0
3000
Fig. 3. Dependences of Ar – H 2 gas flow enthalpy
required at injection of TiCl 4 + C 8 H 18 (a) and SiCl 4 +
C 6 H 14 (b) vapors (solid line) and TiC (a) and SiC (b)
output (dot line) from synthesis temperature with different
ratio H/Cl (C/Me = 1). 3 - MeCl 4 + 1/n C n H m + 4 H 2 + 4
Ar; 4 - MeCl 4 + 1/n C n H m + 10 H 2 + 10 Ar; 5 - MeCl 4 +
1/n C n H m + 20 H 2 + 20 Ar.
2
6
0,0
500
0,8
3
500
4
0,2
0,0
3500
1,0
0
16
5; 9
0,9
0
3500
Free carbon content, mass %
TiC output
0,7
SiC output
14
Free carbon content, mass %
0,9
Requirement plasma jet enthalpy, kW·h/m3
4
16
1,0
TiC output
TiC output
0,8
14
SiC output
a)
4
Requirement plasma jet enthalpy, kW·h/m3
16
5
0,9
Free carbon content, mass %
1,0
3. Experimental setup, synthesis conditions and
product characterization methods
Opportunity of TiC and SiC powders produce
confirmation by the example of the interaction SiCl 4 and
hexane in H 2 plasma process and product properties
control on application of plasmachemical process
parameters are experimental investigations aims. For
investigations of SiC nanopowders production in the
thermal hydrogenous plasma flow experimental plasma
P-II-7-11
setup on the base of electro-arc thermal plasma generator
with power rating 25 kW were used. Process scheme is
present in the Fig. 4.
DC power
supply
Plasma
torch
N?, H?, Ar
N?, H?, Ar
vaporizer
piston
distemper
reactor
filter
scrubber
Fig. 4. Scheme of the silicon carbide nanopowder
production process.
The hydrocarbon and chloride mixture feeded with
piston dispenser to vaporizer. Resulting vapor feeded
with transport gas to plasma jet through mixing chamber.
Condensed reaction product deposited on the reactor
water cooled walls and filter. Contained in exhaust gas
chlorine was trapped with alkaline solution scrubber.
Experimental
investigations
of silicon
carbide
nanopowder production in thermal plasma flow was made
in parameters ranges which shown in the Table 2.
4. Results and discussion
Silicon carbide nano powders samples received are
nanosize. SEM and TEM analyses shown that powders
are strong aggregated and consisted of primary 10-30 nm
size particles (Fig. 5). Primary particles had not regulated
shape. Direct shape particles (nano fibers, nano tubes
etc.) presence was not marked. Powders produced
specific surface changed in the range 20-77 m2/g (Fig. 6),
besides powders produced prevail number had specific
surface equal 55-65 m2/g. prevail phase in the samples
was β-SiC with α-SiC presence (Fig. 7). Total carbon
concentration in the powders produced is in the range
24.7-31.1 mass% and determined with initial element
relation C/Si. Chlorine concentration in the powder
produced was in range 1-11 mass % and it had a
minimum (Fig. 8). It is caused with use degree of SiCl 4 .
Concentration of nitrogen changed in the range
1-6 mass %. Oxygen presence in the powders up to
6 mass % was marked. It was appear in the contact with
air when powders was discharged from reactor.
Table 2. Plasma process parameters ranges.
Fig. 5. SEM and TEM results of produced powders.
Parameter
Plasmatron useful power
Plasma forming gas
Total plasma forming gases consumption
Plasma jet useful enthalpy
SiCl 4 consumption
C 6 H 4 consumption
Transport gas
Transport gas consumption
Element relation H/Cl
Element relation C/Si
Range
4.8 – 9.3 kW
H 2 + Ar + N 2
1.4 – 2.5 n.m3/h
1. 6 – 5.9 kWh/n.m3
0.17 – 0.2 kg/h
0.02 – 0.09 kg/h
N2 , N2 + H2
0.57 – 1.0 n.m3/h
11.5 – 19.2
1.0 – 5.1
The produced powders were analysed by the following
methods: X-ray diffraction (XRD) analysis was done
using difractometer RIGAKU Ultima – 4 with
monochromatic CuK radiation and high-speed detector
D/teX, PDXL software and PDF-2 database; Specific
Surface Area (SSA) measurements were done using
Micromeritics TriStar 3000 porosity analyser; particle
size distribution (both raw powder and synthesized
powder) were measured using laser difractometer
Mastersizer 2000; particle morphology was studied using
Helios 650 NanoLab (SEM + EDX) with Apollo X SDD
analyzer; final carbon content in the produced powder
was measured by LECO RC-412 analyser; final nitrogen
content in the produced powder was measured by LECO
ТС-600 analyzer.
P-II-7-11
80
75
Specific surface, m2/g
№
1
2
3
4
5
6
7
8
9
10
70
65
60
55
50
1
2
3
4
5
6
7
Plasma jet enthalpy, kWh/n.m3
Fig. 6. Experimental dependences specific surface area
from plasma jet enthalpy.
SiC nano powder output was in the range 43-74 %
(Fig. 9). Increase of reactor walls temperature allows to
increase output from 65 to 74 %. The experimental SiC
output dependence from plasma jet enthalpy quality
corresponds to calculate for equilibrium SiC output
dependence from temperature - the both dependences had
a maximum. Experimental value reached was lower than
calculated equilibrium SiC output. This is related with
3
near 1500 K, where end product output is maximal, and
unsufficient system quench rate. Product output may be
reached by the reactor construction change with high
temperature zone increased.
5. Acknowledgements
This research was conducted with support of the
Russian Ministry of Education and Science (Federal
Target Program «Research and development on priority
directions of scientific-technological complex of Russia
for 2014 - 2020 years», project «Development of bases of
plasma-chemical technologies for production of
nanosized powders of titanium anoxic compounds nitride, carbide and carbo-nitride for developing of new
structural and functional materials», agreement №
14.607.21.0103, unique code RFMEFI60714X0103).
unsufficient duration of reagents stay in temperature zone
Fig. 7. SiC nano powders X-ray diffractogram.
30
O
N
C total
Concentration, mass%
25
Cl
20
15
10
5
0
0
1
2
3
4
5
6
7
Plasma jet enthalpy, kWh/m3
Fig. 8.
Experimental dependences of impurities
concentration in produced SiC powders from plasma jet
enthalpy.
0,6
0,6
SiC output
0,5
0,5
0,4
0,4
0,3
0
1
2
3
4
5
6
7
Plasma jet enthalpy, kWh/m3
Fig. 9. Experimental dependences of SiC output from
plasma jet enthalpy.
4
P-II-7-11