長岡工業高等専門学校研究紀要

論第45巻第２号（2009）

文― 69 ―

observing the microstructure of the baked carbonmaterial.
Shinsuke HOSHII, Akira KOJIMA, Masahiro GOTO

31.8o

HTT1800 C

1.7
1.6o

HTT1600 C

1.5
1.4
1020

30

40

50

60

70

Pressure (MPa)Fig.1 Bulk density of the baked carbon materials.
.
60
Shore hardness

Table 1 Characteristics of the raw coke powder.
We used high-purity coke powder manufactured
10~15�mby Tokai Average
CarbondiameterCo.,Ltd as the startingmaterial.
�Table 1 shows
Absolutethe
specificgravitycharacteristics
of 2.00
the raw cokedisk-shaped
bakedcarbonusedmaterial
sample
20 mm inpowder. The
SPS systemin theexperiment
Purity99.8%
or higher wasdiameterand
5mm
thick
wasremoved.
SPS
DR.SINTER, SPS-1050, manufactured by Izumi
treatment
conductedBakedat heatTechnology wascompany,Ltd.
carbontreatment
material
Impurities containedo (ppm)oand 1800
C, forat
temperatures
1600 C way.
was fabricated(HTT)in theoffollowing
A moldNa600
pressuresof 20,30, with40, 503 andMPa,
andthe baked
graphite wasfilled
g of60
rawcokepowderandcarbonwassystem.
fabricated.
Si550
placed material
in the SPS
Under vacuum,
the cokeWe
measured
thebulk
density,hardness(shorepowder was heated
Al up to the prescribed
350 temperatureohardness),shearing
strengthandcompressiveat a rate of 120 C /min and with the application ofFe
330obtained. For
strength
thethenbakedmaterialpressure,ofandkeptcarbon
at the prescribedtemperature
thecarbon
material
underZn cooling250
for 3bakedmin. Afterfor fabricatedapproximately
2 h,theaoC-60
MPa,
wemeasured
conditions of HTT
1800
Mg
34
specific resistance using the four-terminal method
K26and measured thecoefficient of thermal
expansion
Pand thermal conductivity.
For the10baked carbon
material fabricated under the conditions of HTT 1600oC-60 MPa and HTT 1800 oC-60 MPa, the samples
were ground and subjected to X-ray diffraction
analysis, and we observed the cross section using
scanning electron microscopy (SEM).

Bulk density (g/cm )2. EXPERIMENTAL METHODSo

HTT1800 C50o

HTT1600 C

4030102030

40506070

Pressure (MPa)

3. RESULTS AND DISCUSSION

Fig.2 Shore hardness of the baked carbonmaterials.

By SPS, baked carbon material made of cokepowder was obtained at a sintering time of less than
1218 min in an entire fabrication time including cooling
10oof less than 2 h, without adding binders or additives.
HTT1800 C
8Using SPS, the simplification of the fabrication of
6
baked carbon material with a short sintering time wasmade possible. The baked carbon material thus
4oHTT1600 C
obtained was solid and did not degrade or collapse.
2The bulk density and shore hardness of the baked0carbon material increased as HTT and pressure were10203040506070
increased, and showed the highest values when thePressure (MPa)baked carbon material was fabricated underoconditions of HTT 1800 C-60 MPa. Fig. 1 shows theFig.3 Shear strength of the baked carbonchange in the bulk density of the baked carbon
materials.
material fabricated under different HTTs andpressures, and Fig. 2 shows the change in shore
hardness. The bulk density and shore hardness of thewere 11.5 MPa and 11.3 MPa, respectively. The
baked carbon material fabricated under thebending strength of extruded artificial graphite usedconditions of HTT 1800 oC-60 MPa were 1.77 g/cm3in general processing was 24.5 MPa11), although theand 59, respectively. These values are higher than themechanical properties of the baked carbon materialbulk density and shore hardness of extruded artificial
could not be directly compared with those of artificial
graphite used in general processing, which are 1.72
3graphite because the test piece of the baked carbon
g/cm and 44, respectively. Similarly to bulk density
material used to measure mechanical properties wasand shore hardness, mechanical properties of thenot in the size prescribed by Japanese Industrial
obtained baked carbon material were improved asStandards (JIS)12). The mechanical properties of theHTT and pressure increased. Fig. 3 shows the change
baked carbon material were improved as the bulk
in the shear strength of the baked carbon material
density, accordingly the structural density, of thefabricated at various HTTs and pressures. The best
baked carbon material increased with HTT andmechanical properties were obtained when the bakedpressure. This tendency is also indicated in thecarbon material was fabricated under the conditions
observations by SEM. Due to the capabilities of theof HTT 1800 oC-60 MPa, at which the shearing― 70 ―SPS system used, HTT cannot be increased beyond
strength and compressive strength of the material
Shear strength (MPa)hite powder
oordinatingn a mold forated among
rect-pulsed
hod are thatin a shortered at aot pressinge, SPS has
ramics andnd overallted7),8). SPS
fabrication
few studiesrted9),10).
rless baked
urity cokeamined thes on the�

CHARACTERISTICS OF BAKED CARBON MATERIAL PREPARED BY SPARK PLASMA SINTERING

Table 2 Characteristics of the baked carbonmaterial.
(HTT1800)oC -60MPa)(�Bulk density (g/cm3)
1.77
o1800 C; however, pressure can be increased. By
applying higher pressure during SPS treatment,
Shore hardness
59
further improvement in the mechanical properties ofbaked carbon material is expected.
Shear strength (MPa)11.5
Table 2 shows the characteristics of the bakedcarbon material fabricated under the conditions ofCompressive strength (MPa)11.3
HTT 1800 oC-60 MPa, under which bulk density,shore hardness and mechanical properties were theSpecific resistance (��m)
56.1highest. For the baked carbon material fabricatedounder the conditions of HTT 1800 C-60 MPa,
Coefficient of thermal expansion
3.8
specific resistance was 56.1 ��m, the coefficient of(10-6/K, 200�400oC)
thermal expansion was 3.8�10-6/K, and thermal
Thermal conductivity (W/m�K)
20conductivity was 20 W/mK. For an extruded
artificial graphite used in general processing, thespecific resistance was 7.5 ��m, the coefficient ofthermal expansion in the extrusion direction was3.6�10-6/K, that vertical to the extrusion direction
was 4.1�10-6/K, and the thermal conductivity was
162 W/mK. Compared with artificial graphite, theHTT1800 oC-60MPa
specific resistance of the baked carbon material was
HTT1600oC-60MPa
high and its thermal conductivity was small. InRaw coke powder
general, it is known that the crystallinity of carbon
materials affects these characteristics; therefore, we2030
40
50
60
7080
examined the graphitic crystallinity of baked carbon 102� / deg [Cu K�]material.
We carried out X-ray diffraction analysis on raw
Fig.4 XRD patterns of the raw coke powder andcoke powder and baked carbon materials fabricatedthe baked carbon materials.
under the SPS conditions of HTT 1600 oC-60 MPaand HTT 1800 oC-60 MPa (Fig. 4). In the raw cokethat the specific resistance of the bakedpowder, a broad diffraction pattern of carbon in the― 71 determined―
carbonmaterial
was large and the thermalovicinity of 2�=26 was observed. After SPS
conductivity
wassmall because the graphitic
treatment, the diffraction pattern intensity in thecrystallinityofthebakedcarbon material was lowovicinity of 26 increased, and the diffraction patterncompared with that of artificial graphite.
intensity increased with HTT. When natural graphite

Shinsuke HOSHII, Akira KOJIMA, Masahiro GOTO

― 72 ―

CHARACTERISTICS OF BAKED CARBON MATERIAL PREPARED BY SPARK PLASMA SINTERING― 73 ―