Study of Onion-Like Carbon (OLC) Formation from Ultra Disperse Diamond (UDD)
- PDF / 2,695,680 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 58 Downloads / 165 Views
inductive heating method
(see the references
in [3,41).
However, Ugarte [5,6] discovered the curling and closure of graphitic networks of the soot taken from arc-eveporation experiment under the electron-beam irradiation into the multiple-shell spheres in condensed phase. Later it was shown [7] that a conventional microporous carbon could so be converted into onions by electron irradiation. Recently a new material containing the hollow nanometric carbon onions with from 2 to about 8 graphitic shells was produced by the heart treatment of pure carbon soot at 2250-24000C [8]. We have found quasi-spherical particles with closed concentric graphite shells (OLC) among the high explosives detonation products UDD of the size 3.0-7.0 nm, graphite ribbons and amorphous carbon) [9]. This made us investigate the UDD annealing. We have shown that UDD annealing at the temperature higher than 1100 0C leads to the formation of OLC [10,11]. Here we discuss the peculiarities of OLC formation from UDD. EXPERIMENT UDD (with average particle diameter, d=4.5 nm) has been isolated from the detonation soot (prepared by 50/50 trotyl/cyclotrimethylene-trinitraminine charges 105
Mat. Res. Soc. Symp. Proc. Vol. 359 01995 Materials Research Society
fired in the hermetical tank [91) by the oxidative removal of nondiamond carbon with HC10 4. Synthetic diamond ASM 1/0 (average particle diameter d-1000nm) was provided by the Institute of Superhard Materials (Kiev). UDD properties were described elsewhere 112]. UDD annealing was performed in a vacuum furnace (max T - 2400 K) equipped with a narrow beam gamma quanta 137Cs source and scintillation detector for registration of changes of bulk density. Experimental equipment and procedures have been described in details elsewhere [13,141. Temperatures were measured with a tungsten-rhenium thermocouple. The micrographs of UDD and annealing products (AP) were obtained with transmission electron microscope (TEM) JEM4000 EX. The surface area of samples (Sa) was estimated from argon adsorption and desorption. Sa values were calculated from unit area of argon molecule adsorption over graphite. The true density of UDD and AP (PHe) was measured using Micrometrics Auto Picnometer-1320. Prior to density measurements, the samples were heated under vacuum at 3000C. RESULTS AND DISCUSSION Variation of bulk density with temperature for UDD, ASM and corresponding AP is presented in Fig.1 (heating rate was 10 O/min). Arrows indicate the temperatures p kg/m3
p kg/m
2
14 m /g
3
-
1300 .
-
-
-
A
14 m2/g - sa 580 -
A
A
A
A
£
a
3.49 kg/m 3 - PH, 1200
._• 560 • ao• .
•~
540-
1 1100
t 1123
520-
1413 500-
T
•.
319
1603
2.9
368
2.53
480-
43 2.08 - 1000
•
214 9
1802 434 2.14 430
212153 2.03
900
i
0
600
1
1400
000
1800
Fig.1. Density change on diamond annealing, a) UDD; b) ASM.
106
2200 T, K
of UDD vacuum treatment in separate experiments for the sample preparation for TEM study, surface area and true density measurements (see the numbers in Fig. 1). It should be noted th
Data Loading...
