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Thermal expansion of niobium carbide, hafnium carbide and tantalum carbide at high temperatures
323
JOURNAL OF THE LESS-COMMON METALS Elsevier Sequoia S.A., Lausanne .- Printed in The Netherlands
SHORT CO~~ICA~ON
Thermal expansion of niobium carbide, hafnium carbide and tantalum carbide at high temperatures
C. K. JUN
AND
P. T. B. SHAFFER
Research and Developmenf Division, The Carborundum Company, Niagara Falls, N. Y. 14302 (U.S.A.)
(Received December 19th, 1970)
There has been considerable interest in the refractory carbides of the Group IV and Group V transition metals for high-temperature applications. This has inspired many investigators to explore the thermal properties of these carbides. The thermal expansion data for NbC _ 1, TaC y 1 and HfC, *, including those previously reported, are given in Figs. 1-3. In the present investigation the thermal expansion was measured by a method which permits the determination of the expansion without resorting to reference standards. Experimental
The specimens, $ in. by Qin. by 2.8 in,, were cut from the center part of cylindrical slugs, 3 in. diam. by 3 in. high, which were hot pressed at 3100”-315OOC. The chemical analyses are given in Table I. The apparatus, similar to that described by Rasor and McClelland’ and by 2.5-
..
2.0 -
PRESENT
A
ToCi,.sT
B
10Cg.~~
C
T&G
INVESTIGATION
fToC,,,g~)
(X-RAY 1’ (X-RAY t ’ tX-RAYI
0
T(IC~,~~ (0 (DILATOMETER)
E
ToCogG 3 (DILATOMETER)
F
W&G4
(X-RAY 14
1.5
(5 tj
z2
l.O-
c 0.5 -
I-+--
500
1000
I500
i
2000
TEMPERATURE Fig.
2500
3000
OC
1. Thermal expansion of tantalum carbide. 1. Less-Common Metals, t4 (1971) 323-327
324
SHORT
2.5 l
2.0
l
PRESENT
INVESTIGATION
A
NbC ,,. 3 (DILATOMETER)
B
NbCG,ggg ” (DILATOMETER)
C
NbCG,ggG
(X-RAYIs
D
NbCG.gg.,
(X-RAYI
E
NbCG,g24
O(-RAYlg
F
NbCG.702
(X-RAY)*
500
1000
(NbCo.gs)
1500
TEMPERATURE
Fig. 2. Thermal 2.5-
. .
2.0-
expansion
PRESENT
of niobium
HfC g
(DILATOMETER)
G
HfCO,=
IX-RAY)
~fc~.gg
O~-RAY) 6
c
2000 “C
carbide.
INVESTIGATION
A
COMMUNICATIONS
(Hft&g)
5 C .* 5 “0/
g z a b liJ ae
1.5-
I.O-
0.5
-
I
I
500
IO00
1500
expansion
of hafnium
TEMPERATURE
Fig. 3. Thermal
I
2000
1
2500
I
3000
“C
carbide.
Engberg and Zehm?, was described by Miccioli and Shaffer3. Each specimen length was measured directly by sighting on the ends through the front port with 8 in. focal length Gaertner optical micrometers. The limit of resolution under experimental conditions was found to be within + 0.0005 in. This gives an accuracy of kO.02 % with specimens averaging 2.8 in. length. An argon atmosphere was maintained in the apparatus following at least three evacuations and purgings. J. Less-Common
Metals, 24 (1971) 323-327
325
SHORT COMMUNICATIONS TABLE CHEMICAL
I ANALYSES
EltWlent Hf Ta Nb C (combined) C (free) N 0 Ti Zr Fe w Cr
OF RAW
MATERIALS
NbC
0.28 % 88.2 % 10.9 % 0.34 % 200 ppm 300 ppm 75 pp* 10 ppm 160 ppm 600 ppm 10 ppm
USED IN HOT-PRESSED
HfC 91.8% 0.02 % 0.02 % 5.93 “/, 0.31% 30 ppm 320 ppm 300 ppm 1.6% 54 ppm 20 ppm 25 ppm
CARBIDES
TaC
93.5 ;< 0.08 “/, 6.16% 0.06 :i 100 ppm 300 ppm 100 ppm 150 ppm 800 ppm 200 ppm
Results and discussion
The thermal expansion results are summarized in Table II and are shown in comparison with others in Figs. l-3. Fries and Wahman’ measured the lattice thermal expansion of TaC0,997, TaC,,.,,, and TaC,,,,, at temperatures to 1000°C and reported that the linear expansion coefficient, CI,increases with increasing carbon content. Kempter and Storms’ measured the lattice thermal expansion of NbC,,924, NbC 0.825, NbC0.766 at temperatures up to 620°C and likewise conand NbC0.702 cluded that c1increases with increasing carbon content. Grisaffe’ measured the dilatometric thermal expansion of hot-pressed HfC, and concluded that density variation in the high-density.range appears to have no effect on thermal expansion. Miccioli and Shaffer3 measured the dilatometric thermal expansion of hot-pressed NbC,,, and TaC,,,, in their extensive thermal expansion study and reported the anomalous inversion in their ascending data at temperatures of about 2000°C. Kempter and Nadler” measured the dilatometric thermal expansion of hot-pressed Taco,,,. Their final run was carried out in argon atmosphere from 1186°C to 3020°C and only the descending data points were used in their plot, because they found a noticeable specimen densification in the ascending data. Brenton, Saunders and Kempter” measured the dilatometric thermal expansion of NbC0,969, which was hot pressed at 3050°C. No specimen densitication was detected in their data. In the present investigation, all thermal expansion measurements of carbides, which were hot pressed at 3100-3150°C were taken during the heating and cooling cycle. Neither specimen densilication nor significant deviations between the ascending data and descending data were detected. This seems to indicate that the previously reported, anomalous inversions, in the vicinity of 2OOO”C,were due to the specimen densification in the vicinity of the hot-pressing temperature of those specimens. The refractory carbides of the Group IV and Group V transition metals exhibit a wide homogeneity rangei having a carbon-deficient, NaCl-type structure, and their lattice constants increase with increasing carbon/metal ratios in the homogeneity ranges. Also these carbides exhibit the non-congruent vaporization at high temperature. The carbon preferential J. Less-Common
Metals, 24 (1971) 323-327
326 TABLE
SHORT COMMUNICATIONS II
AVERAGE THERMAL
Materials
EXPANSION
COEFFICIENTS
cc(10-6xe-1)
Temperature range e C)
NbCcm
6.55 7.34 7.86 8.37 8.72
R.T.-1000 1500 2000 2400 2600
HG.,,
6.19 6.59 7.10 7.34 7.54
R.T.-1000 1500 2000 2400 2600
6.61 6.67 7.31 7.62 7.80
R.T.-1000 1500 2000 2400 2600
vaporization in TaC, was investigated by Hoch et ~1.‘~ and Kempter and Nadler14. The carbon preferential vaporization in NbC, was investigated by Kempter and Nadler14 and Fries”. In the lattice thermal expansion measurements of NbC, and TaC,, the lattice constants of NbC, and TaC, decrease with the decreasing carbon/metal ratio, which decreases with increasing heating temperature and heating period because of the carbon preferential vaporization. Then it is apparent that the divergences between the bulk thermal expansion and the lattice thermal expansion at high temperature in NbC, and TaC, plots are largely due to the effect of nonstoichiometry due to the preferential vaporization of carbon at high temperatures. This divergence was not observed in HfC, plot, since HfC, does not show the preferential vaporization of carbon as do NbC, and TaC,. Hoch” concluded that the constant boiling composition of HfC, extends between x = 0.97 and x = 0.9. According to Lyon”, hafnium carbide has a congruently vaporizing composition at a carbon concentration slightly less than stoichiometric. Research reported in this publication was performed under Naval Ordnance Systems Command, Contract No 0017-70-C-4402. REFERENCES 1 N. S. RA~GRANDJ. D. MCCLELLAND, WADC-TR-56400, Part 1, March 1957. 2 G. J. ENGBERGAND E. H. ZEHMS,J. Am. Ceram. Sot., 42 (6) (1959) 300. 3 B. R. MICCIOLIANDP. T. B. SHAFFER,J. Am. Ceram. Sot., 47 (1964) 351. 4 R. 0. ELLIOTTANDC. P. KEMPTER,J. Phys. Chem., 62 (1958) 630. 5 C. R. HOUSKA,J. Am. Ceram. Sot., 47 (1964) 310. 6 J. H. RICHARDSON, J. Am. Ceram. Sot., 48 (1965) 497. J. Less-Common Metals, 24 (1971) 323-327
327
SHORT COMMUNICATIONS 7 8 9 10 11 12 13 14 15 16
R. J. FRIP~ ANDL. A. WAHMAN,J. Am. Ceram. SOL, 50 (1967) 475. C. P. KEMPTERANDE. K. STORMS,J. Less-Common Metals, I3 (1967) 443. S. J. GRISAFFE,J. Am. Ceram. Sot., 43 (1960) 494. C. P. KEMPTFXAND M. R. NADLER, J. Chem. Phys., 43 (1965) 1739. B. F. BRENTON,C. R. SAUNDERSANDC. P. KEMPTER,J. Less-Common Metals, 19 (1969) 273. EDMUNDK. STORMS,The Refractory Carbides, Academic Press, New York, London, 1967. M. HOCH, P. E. BLACKBURN,D. P. DINGLEDYAND H. L. JOHNSON,J. Phys. Chem., 59 (1955) 97. C. P. KEMPTERAND M. R. NADLER, J. Chem. Phys., 32 (1960) 1477. R. J. FRIES, J. Chem. Phys., 37 (1962) 320. M. HOCH, in P. S. RUDMAN,J. STRINGERANDR. I. JAFFEE (eds.), Phase Stability in Metals and Alloys, McGraw-Hill, New York, 1967. 17 T. F. LYON, in E. RUTNER, P. GOLDFINGERANDJ. P. HIRTH (eds.), Condensation and Euaporization of Solids,Gordon and Breach, New York, 1964.
J. Less-Common
Metals, 24 (1971) 323-327
JOURNAL OF THE LESS-COMMON METALS Elsevier Sequoia S.A., Lausanne .- Printed in The Netherlands
SHORT CO~~ICA~ON
Thermal expansion of niobium carbide, hafnium carbide and tantalum carbide at high temperatures
C. K. JUN
AND
P. T. B. SHAFFER
Research and Developmenf Division, The Carborundum Company, Niagara Falls, N. Y. 14302 (U.S.A.)
(Received December 19th, 1970)
There has been considerable interest in the refractory carbides of the Group IV and Group V transition metals for high-temperature applications. This has inspired many investigators to explore the thermal properties of these carbides. The thermal expansion data for NbC _ 1, TaC y 1 and HfC, *, including those previously reported, are given in Figs. 1-3. In the present investigation the thermal expansion was measured by a method which permits the determination of the expansion without resorting to reference standards. Experimental
The specimens, $ in. by Qin. by 2.8 in,, were cut from the center part of cylindrical slugs, 3 in. diam. by 3 in. high, which were hot pressed at 3100”-315OOC. The chemical analyses are given in Table I. The apparatus, similar to that described by Rasor and McClelland’ and by 2.5-
..
2.0 -
PRESENT
A
ToCi,.sT
B
10Cg.~~
C
T&G
INVESTIGATION
fToC,,,g~)
(X-RAY 1’ (X-RAY t ’ tX-RAYI
0
T(IC~,~~ (0 (DILATOMETER)
E
ToCogG 3 (DILATOMETER)
F
W&G4
(X-RAY 14
1.5
(5 tj
z2
l.O-
c 0.5 -
I-+--
500
1000
I500
i
2000
TEMPERATURE Fig.
2500
3000
OC
1. Thermal expansion of tantalum carbide. 1. Less-Common Metals, t4 (1971) 323-327
324
SHORT
2.5 l
2.0
l
PRESENT
INVESTIGATION
A
NbC ,,. 3 (DILATOMETER)
B
NbCG,ggg ” (DILATOMETER)
C
NbCG,ggG
(X-RAYIs
D
NbCG.gg.,
(X-RAYI
E
NbCG,g24
O(-RAYlg
F
NbCG.702
(X-RAY)*
500
1000
(NbCo.gs)
1500
TEMPERATURE
Fig. 2. Thermal 2.5-
. .
2.0-
expansion
PRESENT
of niobium
HfC g
(DILATOMETER)
G
HfCO,=
IX-RAY)
~fc~.gg
O~-RAY) 6
c
2000 “C
carbide.
INVESTIGATION
A
COMMUNICATIONS
(Hft&g)
5 C .* 5 “0/
g z a b liJ ae
1.5-
I.O-
0.5
-
I
I
500
IO00
1500
expansion
of hafnium
TEMPERATURE
Fig. 3. Thermal
I
2000
1
2500
I
3000
“C
carbide.
Engberg and Zehm?, was described by Miccioli and Shaffer3. Each specimen length was measured directly by sighting on the ends through the front port with 8 in. focal length Gaertner optical micrometers. The limit of resolution under experimental conditions was found to be within + 0.0005 in. This gives an accuracy of kO.02 % with specimens averaging 2.8 in. length. An argon atmosphere was maintained in the apparatus following at least three evacuations and purgings. J. Less-Common
Metals, 24 (1971) 323-327
325
SHORT COMMUNICATIONS TABLE CHEMICAL
I ANALYSES
EltWlent Hf Ta Nb C (combined) C (free) N 0 Ti Zr Fe w Cr
OF RAW
MATERIALS
NbC
0.28 % 88.2 % 10.9 % 0.34 % 200 ppm 300 ppm 75 pp* 10 ppm 160 ppm 600 ppm 10 ppm
USED IN HOT-PRESSED
HfC 91.8% 0.02 % 0.02 % 5.93 “/, 0.31% 30 ppm 320 ppm 300 ppm 1.6% 54 ppm 20 ppm 25 ppm
CARBIDES
TaC
93.5 ;< 0.08 “/, 6.16% 0.06 :i 100 ppm 300 ppm 100 ppm 150 ppm 800 ppm 200 ppm
Results and discussion
The thermal expansion results are summarized in Table II and are shown in comparison with others in Figs. l-3. Fries and Wahman’ measured the lattice thermal expansion of TaC0,997, TaC,,.,,, and TaC,,,,, at temperatures to 1000°C and reported that the linear expansion coefficient, CI,increases with increasing carbon content. Kempter and Storms’ measured the lattice thermal expansion of NbC,,924, NbC 0.825, NbC0.766 at temperatures up to 620°C and likewise conand NbC0.702 cluded that c1increases with increasing carbon content. Grisaffe’ measured the dilatometric thermal expansion of hot-pressed HfC, and concluded that density variation in the high-density.range appears to have no effect on thermal expansion. Miccioli and Shaffer3 measured the dilatometric thermal expansion of hot-pressed NbC,,, and TaC,,,, in their extensive thermal expansion study and reported the anomalous inversion in their ascending data at temperatures of about 2000°C. Kempter and Nadler” measured the dilatometric thermal expansion of hot-pressed Taco,,,. Their final run was carried out in argon atmosphere from 1186°C to 3020°C and only the descending data points were used in their plot, because they found a noticeable specimen densification in the ascending data. Brenton, Saunders and Kempter” measured the dilatometric thermal expansion of NbC0,969, which was hot pressed at 3050°C. No specimen densitication was detected in their data. In the present investigation, all thermal expansion measurements of carbides, which were hot pressed at 3100-3150°C were taken during the heating and cooling cycle. Neither specimen densilication nor significant deviations between the ascending data and descending data were detected. This seems to indicate that the previously reported, anomalous inversions, in the vicinity of 2OOO”C,were due to the specimen densification in the vicinity of the hot-pressing temperature of those specimens. The refractory carbides of the Group IV and Group V transition metals exhibit a wide homogeneity rangei having a carbon-deficient, NaCl-type structure, and their lattice constants increase with increasing carbon/metal ratios in the homogeneity ranges. Also these carbides exhibit the non-congruent vaporization at high temperature. The carbon preferential J. Less-Common
Metals, 24 (1971) 323-327
326 TABLE
SHORT COMMUNICATIONS II
AVERAGE THERMAL
Materials
EXPANSION
COEFFICIENTS
cc(10-6xe-1)
Temperature range e C)
NbCcm
6.55 7.34 7.86 8.37 8.72
R.T.-1000 1500 2000 2400 2600
HG.,,
6.19 6.59 7.10 7.34 7.54
R.T.-1000 1500 2000 2400 2600
6.61 6.67 7.31 7.62 7.80
R.T.-1000 1500 2000 2400 2600
vaporization in TaC, was investigated by Hoch et ~1.‘~ and Kempter and Nadler14. The carbon preferential vaporization in NbC, was investigated by Kempter and Nadler14 and Fries”. In the lattice thermal expansion measurements of NbC, and TaC,, the lattice constants of NbC, and TaC, decrease with the decreasing carbon/metal ratio, which decreases with increasing heating temperature and heating period because of the carbon preferential vaporization. Then it is apparent that the divergences between the bulk thermal expansion and the lattice thermal expansion at high temperature in NbC, and TaC, plots are largely due to the effect of nonstoichiometry due to the preferential vaporization of carbon at high temperatures. This divergence was not observed in HfC, plot, since HfC, does not show the preferential vaporization of carbon as do NbC, and TaC,. Hoch” concluded that the constant boiling composition of HfC, extends between x = 0.97 and x = 0.9. According to Lyon”, hafnium carbide has a congruently vaporizing composition at a carbon concentration slightly less than stoichiometric. Research reported in this publication was performed under Naval Ordnance Systems Command, Contract No 0017-70-C-4402. REFERENCES 1 N. S. RA~GRANDJ. D. MCCLELLAND, WADC-TR-56400, Part 1, March 1957. 2 G. J. ENGBERGAND E. H. ZEHMS,J. Am. Ceram. Sot., 42 (6) (1959) 300. 3 B. R. MICCIOLIANDP. T. B. SHAFFER,J. Am. Ceram. Sot., 47 (1964) 351. 4 R. 0. ELLIOTTANDC. P. KEMPTER,J. Phys. Chem., 62 (1958) 630. 5 C. R. HOUSKA,J. Am. Ceram. Sot., 47 (1964) 310. 6 J. H. RICHARDSON, J. Am. Ceram. Sot., 48 (1965) 497. J. Less-Common Metals, 24 (1971) 323-327
327
SHORT COMMUNICATIONS 7 8 9 10 11 12 13 14 15 16
R. J. FRIP~ ANDL. A. WAHMAN,J. Am. Ceram. SOL, 50 (1967) 475. C. P. KEMPTERANDE. K. STORMS,J. Less-Common Metals, I3 (1967) 443. S. J. GRISAFFE,J. Am. Ceram. Sot., 43 (1960) 494. C. P. KEMPTFXAND M. R. NADLER, J. Chem. Phys., 43 (1965) 1739. B. F. BRENTON,C. R. SAUNDERSANDC. P. KEMPTER,J. Less-Common Metals, 19 (1969) 273. EDMUNDK. STORMS,The Refractory Carbides, Academic Press, New York, London, 1967. M. HOCH, P. E. BLACKBURN,D. P. DINGLEDYAND H. L. JOHNSON,J. Phys. Chem., 59 (1955) 97. C. P. KEMPTERAND M. R. NADLER, J. Chem. Phys., 32 (1960) 1477. R. J. FRIES, J. Chem. Phys., 37 (1962) 320. M. HOCH, in P. S. RUDMAN,J. STRINGERANDR. I. JAFFEE (eds.), Phase Stability in Metals and Alloys, McGraw-Hill, New York, 1967. 17 T. F. LYON, in E. RUTNER, P. GOLDFINGERANDJ. P. HIRTH (eds.), Condensation and Euaporization of Solids,Gordon and Breach, New York, 1964.
J. Less-Common
Metals, 24 (1971) 323-327