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Synthesis of Cr3C2 by SHS process
Scripta Materielie, Vol. 31, No. 6, pp. 889495, 1997 Elsevier Science Ltd Copyright 0 1997 Acte Metallurgica Inc. Printed in the USA. All rights resewed 1359~6462/97 $17.00 + .OO
Pergamon
PI1 S1359-6462(97)00181-4
SYNTHESIS OF Cr&
BY SHS PROCESS
Seog-Kwon Ko, Chang-Whan Won, and In-Jin Shon’ Rapidly Solidified Materials Research Center Chungnam National University, Daejon 302-764, Republic of Korea ‘Dept. of Materials Engineering, Chonbuk University, Chonju 560-756, Republic of Korea (Received January 13,1997) (Accepted April 14, 1997) Introduction Self-propagating high-temperature synthesis has been recently centered on considerable attention as an attractive process for synthesis of high temperature materials. Its method offers several advantages including the use: of elemental powders, short processing times, and energy saving [l-3]. CrG compound has been the focus of considerable attention as an attractive coating material for roll and valve. Its properties provide a desirable combination of high hardness, excellent wear resistance, low density and chemical stability [4,5]. It has been empirically concluded that materials with adiabatic temperature (Ta) < 1800K cannot be prepared by SHS [6]. CrG cannot be synthesized directly from 3Cr + 2C by this method because the adiabatic temperature (1070K) calculated from thermochemical data. [7] is lower than the limited temperature. Adiabatic temperature (3040K) of 3CrzOJ + 9Mg + 4C reaction calculated from thermochemical data [7] is extremely higher than the limit of existence of SH!3. Therefore, the C&2 compound can be synthesized from the 3CrZ03+ 9Mg + 4C reaction by SHS process. In this study, (combustion temperature, combustion wave velocity, particle size of CrG with diluents and activation energy of CrG formation from 3CrZOs+ 9Mg + 4C reaction were investigated. Experimental Procedure The materials used in this work were 99% pure CrZOspowder with an average particle size of 1km (Yakri co.), 99.9% pure carbon black with an average particle size of OSpm, and 99.8% pure Mg powder with an average particle size of 1Opm as obtained from a Mg ingot by crushing. Cylindricalshaped pellets with dimension of 25mm diameter and 20mm height were made in a two-plunger steel die by uniaxial FIressing. Typical pelletizing pressure and the relative green density of the pellet were about lOOMpa and 65%, respectively. The pellets were combusted inside a stainless steel combustion chamber under 1 atm pressure of Ar gas. Combustion temperatures were determined from the output of a W-5%Re/W-26%Re thermocouple inside a small hole drilled in the side of the specimen. Wave velocities were calculated from the time interval between heating profile peaks obtained from the W-Re thermocouple tips at two different locations in the pellet (Fig. 1).
890
SYNTHESIS OF Cr,C2 BY SHS PROCESS
Vol. 37, No. 6
d 2
4 1
2)h gar
UV~umpumP
4) Cooling
system
3) Gauge
6) Power supply 8) ThermocoupIe 9) Dataaquisition 1 I) Heat-resistingglass 5) Grcal pdkt
7) Tuttgsten filament 10) computer
12) van Figure 1. Schematic of experimental apparatus used for synthesis of C&.
The combustion-synthesized product was leached by acid (25%HCl) for 30min at 70% to remove the MgO. Analysis of the product was made through X-ray diffraction and microstructures were made by scanning electron microscopy with EDAX. The chemical analysis also was investigated by inductively-coupled plasma and atomic absorption techniques Results and Discussion In the formation of CrE2 from 3CrzOj + 9Mg + 4C, the first step is believed to be the reaction of Mg with the Crz03 because the interaction energy of Mg with Cr203 is higher than that of C with
2200 2000 1800
E- 1400 5 I200 E g1000 g
800 600
0
20
40
60
80
100 120 140 160 180 200
Time (set) Figure 2. Temperature profile during the combustion synthesis of CrG from 3Crz0, + 9Mg + 4C
reaction.
Vol. 37, No. 6
20.
300
SYNTHESIS OF Cr3Cz BY SHS PROCESS
40.
60.
60.
891
70.
Diffraction Angle, 20 Figure 3. X-ray difiaction pattern of combustion-synthesized C&.
Figure 4. TEM photograph of Cr& product.
Cr203 [7]. And; then 3Cr reacts with 2C to produce CtG. A temperature profile for a diluent-free 3CrzO3 + 9Mg + 4C reaction is shown in Fig. 2. The adiabatic temperature is about 195OT. X-ray diffraction pattern and TEM photograph of the product synthesized from 3CrzO3+ 9Mg + 4C reaction after acid 1each:ingare shown in Fig. 3 and Fig. 4, respectively. Fig. 3 shows that the diffiction peaks all correspond to Cr& with orthorhombic structure from the analysis of the X-ray diffraction peaks. It is confumed that C&2 compound was successfully synthesized. The average particle size of Cr& is about 2pm as seen in Fig. 4. A comparison of the level of impurities between reactants and product is shown in Fig. 5. The level of impurities in the product is lower than that of the reactants because of the volatilization ofimpurities during the synthesis due to the high combustion temperature.
Al
Ca
Fe
Na
Cd
Si
Mn
K
Ti
Figure 5. Comparison of impurities between reactants and product.
892
SYNTHESIS OF C&z BY SHS PROCESS
Vol. 37, No. 6
1700 * 1660 -
1526~""'. 5
16
'*I 20
1s
* 26
' 30
*
' 3s
Diluent Content(%) Figure 6. Effect of diluent content on combustion temperature
To investigate the activation energy of CrG formation, Cr3Cz diluent is added to 3Cr203 + 9Mg + 4C. The combustion temperature and the combustion wave velocity of 3Crz03 + 9Mg + 4C reaction with diluent are shown in Fig. 6 and Fig. 7, respectively. As expected, the combustion temperature and combustion wave velocity decrease with increasing CrG diluent content. X-ray diffraction patterns of the product with an added 5, 10, 20, and 35wW0 Cr3C2diluent are identical with that without addition of diluents.
3.2"""
5
10
15
n
" 20
'. 25
’
30
”
Diluent Content(wt%) Figure 7. Effect of diluent content on combustion rate.
35
Vol. 37, No. 6
SYNTHESIS
OF Cr3C2 BY SHS PROCESS
Figure 8. SEM photomicrographs of combustion-synthesized Cr& (d) 35wt%.
893
with diluent content. (a) 5wt% (b) lOwt% (c) 20wt%
A : Diluent(%%) f3 : Diluent(lbt%) C : Diluent(2Owt%) D : Diluent(Swt%)
0 C f3 A
I
I
I
I
I
0
25
50
75
100
Time(sec) Figure 9. Temperature profiles during synthesis of Cr3C2with diluent content.
894
SYNTHESIS OF Cr3C2BY SHS PROCESS
Vol. 37, No. 6
Figure 10. The temperature dependence of the wave velocity in the synthesis of C&.
Fig. 8 shows SEM images of combustion-synthesized Cr3C2with Swt%CrG (A), lOwt% CrG (B), 2Owt% CrG (C), and 35wt% Cr3C2 (D) diluent. In the figure, fine particles and relatively coarse particles are present. It is believed that the fme particles are CrG added as a diluent and the coarse particles are Cr3C2 synthesized from 3CrZOJ+ 9Mg + 4C. The particle size of the synthesized CrG noticeably increases with an increase in the CrG diluent. Temperature profiles during the Cr& formation with diluent were determined as shown in Fig. 9. The figure shows that the cooling rate decreases with the addition of the diluent. It is believed that the difference in the particle size among the different diluent contents is the result of slower cooling rates in the sample with the higher diluent. Arrehenius plot of Cr3C2 with diluent content is shown in Fig. 10. The activation energy calculated from the present investigation is about 125KJ/mole. Conclusions Self-propagating high temperature synthesis of Cr3C2 was investigated. CrG compound could be obtained from the 3Cr203 + 9Mg + 4C reaction by SHS using Mg reduction method. Combustion temperature and combustion wave velocity decreased with increasing addition of diluent. Average particle size of Cr3C2prQduct increased with increasing addition of diluent. High purity Cr& (99.9%) was obtained by SHS and acid leaching. The activation energy of Cr& formation was calculated as 125KJ/mole.
Vol. 37, No. 6
SYNTHESIS OF CrF2 BY SHS PROCESS
895
References 1. 2. 3. 4. 5. 6. 7.
Z.A. Munir, W. Lai and K. Ewald, US Patent, No. $380,409, January 10,199s. V.A. Knyazik, A.G. Merzhanov, V.B. Solomov and A.S. Shteinberg, Combust. Explos. Shock Wave, 21,333 (1985). I.J. Shon and Z.A. Munir, Mater. Sci. Eng., A 202,256 (1995). N.P. Bansal, Advances in Ceramic-Matrix Composites, p.435, The American Ceramic Society, Westerville, Ohio (1993). J. Hinnuber and 0. Rudiger, Arch. Eisenhuttenwes., 24,267 (1953). Z.A. Munir and U. Anselmi-Tamburini, Mater. Sci. Rep., 3,277 (1989). 0. Knacke, 0. Kubaschewski and K. Hesselmann, Thermochemical Properties of Inorganic Substances, p.309, ~521, p.532,p.l136, Springer-Verlag, Berlin, Heidelberg, New York (1991).
Pergamon
PI1 S1359-6462(97)00181-4
SYNTHESIS OF Cr&
BY SHS PROCESS
Seog-Kwon Ko, Chang-Whan Won, and In-Jin Shon’ Rapidly Solidified Materials Research Center Chungnam National University, Daejon 302-764, Republic of Korea ‘Dept. of Materials Engineering, Chonbuk University, Chonju 560-756, Republic of Korea (Received January 13,1997) (Accepted April 14, 1997) Introduction Self-propagating high-temperature synthesis has been recently centered on considerable attention as an attractive process for synthesis of high temperature materials. Its method offers several advantages including the use: of elemental powders, short processing times, and energy saving [l-3]. CrG compound has been the focus of considerable attention as an attractive coating material for roll and valve. Its properties provide a desirable combination of high hardness, excellent wear resistance, low density and chemical stability [4,5]. It has been empirically concluded that materials with adiabatic temperature (Ta) < 1800K cannot be prepared by SHS [6]. CrG cannot be synthesized directly from 3Cr + 2C by this method because the adiabatic temperature (1070K) calculated from thermochemical data. [7] is lower than the limited temperature. Adiabatic temperature (3040K) of 3CrzOJ + 9Mg + 4C reaction calculated from thermochemical data [7] is extremely higher than the limit of existence of SH!3. Therefore, the C&2 compound can be synthesized from the 3CrZ03+ 9Mg + 4C reaction by SHS process. In this study, (combustion temperature, combustion wave velocity, particle size of CrG with diluents and activation energy of CrG formation from 3CrZOs+ 9Mg + 4C reaction were investigated. Experimental Procedure The materials used in this work were 99% pure CrZOspowder with an average particle size of 1km (Yakri co.), 99.9% pure carbon black with an average particle size of OSpm, and 99.8% pure Mg powder with an average particle size of 1Opm as obtained from a Mg ingot by crushing. Cylindricalshaped pellets with dimension of 25mm diameter and 20mm height were made in a two-plunger steel die by uniaxial FIressing. Typical pelletizing pressure and the relative green density of the pellet were about lOOMpa and 65%, respectively. The pellets were combusted inside a stainless steel combustion chamber under 1 atm pressure of Ar gas. Combustion temperatures were determined from the output of a W-5%Re/W-26%Re thermocouple inside a small hole drilled in the side of the specimen. Wave velocities were calculated from the time interval between heating profile peaks obtained from the W-Re thermocouple tips at two different locations in the pellet (Fig. 1).
890
SYNTHESIS OF Cr,C2 BY SHS PROCESS
Vol. 37, No. 6
d 2
4 1
2)h gar
UV~umpumP
4) Cooling
system
3) Gauge
6) Power supply 8) ThermocoupIe 9) Dataaquisition 1 I) Heat-resistingglass 5) Grcal pdkt
7) Tuttgsten filament 10) computer
12) van Figure 1. Schematic of experimental apparatus used for synthesis of C&.
The combustion-synthesized product was leached by acid (25%HCl) for 30min at 70% to remove the MgO. Analysis of the product was made through X-ray diffraction and microstructures were made by scanning electron microscopy with EDAX. The chemical analysis also was investigated by inductively-coupled plasma and atomic absorption techniques Results and Discussion In the formation of CrE2 from 3CrzOj + 9Mg + 4C, the first step is believed to be the reaction of Mg with the Crz03 because the interaction energy of Mg with Cr203 is higher than that of C with
2200 2000 1800
E- 1400 5 I200 E g1000 g
800 600
0
20
40
60
80
100 120 140 160 180 200
Time (set) Figure 2. Temperature profile during the combustion synthesis of CrG from 3Crz0, + 9Mg + 4C
reaction.
Vol. 37, No. 6
20.
300
SYNTHESIS OF Cr3Cz BY SHS PROCESS
40.
60.
60.
891
70.
Diffraction Angle, 20 Figure 3. X-ray difiaction pattern of combustion-synthesized C&.
Figure 4. TEM photograph of Cr& product.
Cr203 [7]. And; then 3Cr reacts with 2C to produce CtG. A temperature profile for a diluent-free 3CrzO3 + 9Mg + 4C reaction is shown in Fig. 2. The adiabatic temperature is about 195OT. X-ray diffraction pattern and TEM photograph of the product synthesized from 3CrzO3+ 9Mg + 4C reaction after acid 1each:ingare shown in Fig. 3 and Fig. 4, respectively. Fig. 3 shows that the diffiction peaks all correspond to Cr& with orthorhombic structure from the analysis of the X-ray diffraction peaks. It is confumed that C&2 compound was successfully synthesized. The average particle size of Cr& is about 2pm as seen in Fig. 4. A comparison of the level of impurities between reactants and product is shown in Fig. 5. The level of impurities in the product is lower than that of the reactants because of the volatilization ofimpurities during the synthesis due to the high combustion temperature.
Al
Ca
Fe
Na
Cd
Si
Mn
K
Ti
Figure 5. Comparison of impurities between reactants and product.
892
SYNTHESIS OF C&z BY SHS PROCESS
Vol. 37, No. 6
1700 * 1660 -
1526~""'. 5
16
'*I 20
1s
* 26
' 30
*
' 3s
Diluent Content(%) Figure 6. Effect of diluent content on combustion temperature
To investigate the activation energy of CrG formation, Cr3Cz diluent is added to 3Cr203 + 9Mg + 4C. The combustion temperature and the combustion wave velocity of 3Crz03 + 9Mg + 4C reaction with diluent are shown in Fig. 6 and Fig. 7, respectively. As expected, the combustion temperature and combustion wave velocity decrease with increasing CrG diluent content. X-ray diffraction patterns of the product with an added 5, 10, 20, and 35wW0 Cr3C2diluent are identical with that without addition of diluents.
3.2"""
5
10
15
n
" 20
'. 25
’
30
”
Diluent Content(wt%) Figure 7. Effect of diluent content on combustion rate.
35
Vol. 37, No. 6
SYNTHESIS
OF Cr3C2 BY SHS PROCESS
Figure 8. SEM photomicrographs of combustion-synthesized Cr& (d) 35wt%.
893
with diluent content. (a) 5wt% (b) lOwt% (c) 20wt%
A : Diluent(%%) f3 : Diluent(lbt%) C : Diluent(2Owt%) D : Diluent(Swt%)
0 C f3 A
I
I
I
I
I
0
25
50
75
100
Time(sec) Figure 9. Temperature profiles during synthesis of Cr3C2with diluent content.
894
SYNTHESIS OF Cr3C2BY SHS PROCESS
Vol. 37, No. 6
Figure 10. The temperature dependence of the wave velocity in the synthesis of C&.
Fig. 8 shows SEM images of combustion-synthesized Cr3C2with Swt%CrG (A), lOwt% CrG (B), 2Owt% CrG (C), and 35wt% Cr3C2 (D) diluent. In the figure, fine particles and relatively coarse particles are present. It is believed that the fme particles are CrG added as a diluent and the coarse particles are Cr3C2 synthesized from 3CrZOJ+ 9Mg + 4C. The particle size of the synthesized CrG noticeably increases with an increase in the CrG diluent. Temperature profiles during the Cr& formation with diluent were determined as shown in Fig. 9. The figure shows that the cooling rate decreases with the addition of the diluent. It is believed that the difference in the particle size among the different diluent contents is the result of slower cooling rates in the sample with the higher diluent. Arrehenius plot of Cr3C2 with diluent content is shown in Fig. 10. The activation energy calculated from the present investigation is about 125KJ/mole. Conclusions Self-propagating high temperature synthesis of Cr3C2 was investigated. CrG compound could be obtained from the 3Cr203 + 9Mg + 4C reaction by SHS using Mg reduction method. Combustion temperature and combustion wave velocity decreased with increasing addition of diluent. Average particle size of Cr3C2prQduct increased with increasing addition of diluent. High purity Cr& (99.9%) was obtained by SHS and acid leaching. The activation energy of Cr& formation was calculated as 125KJ/mole.
Vol. 37, No. 6
SYNTHESIS OF CrF2 BY SHS PROCESS
895
References 1. 2. 3. 4. 5. 6. 7.
Z.A. Munir, W. Lai and K. Ewald, US Patent, No. $380,409, January 10,199s. V.A. Knyazik, A.G. Merzhanov, V.B. Solomov and A.S. Shteinberg, Combust. Explos. Shock Wave, 21,333 (1985). I.J. Shon and Z.A. Munir, Mater. Sci. Eng., A 202,256 (1995). N.P. Bansal, Advances in Ceramic-Matrix Composites, p.435, The American Ceramic Society, Westerville, Ohio (1993). J. Hinnuber and 0. Rudiger, Arch. Eisenhuttenwes., 24,267 (1953). Z.A. Munir and U. Anselmi-Tamburini, Mater. Sci. Rep., 3,277 (1989). 0. Knacke, 0. Kubaschewski and K. Hesselmann, Thermochemical Properties of Inorganic Substances, p.309, ~521, p.532,p.l136, Springer-Verlag, Berlin, Heidelberg, New York (1991).