7.3
Synthesis of Diamond, Carbon Nanotubes and Carbides
Diamonds were first synthesized through a high-temperature and high-pressure
process [50]. Using diamond seeds, micrometer-sized diamonds have been grown
in a hydrothermal process at 800
C and 1.4 kbar [51]. Chemical vapor deposition
(CVD) is a low-pressure technique for the preparation of polycrystalline diamonds
films using CH 4 or C 2 H 2 as a carbon source [52].
In traditional organic synthesis, the Wurtz reaction:
R
1 X þ R
2 X þ 2Na ! R
1 -R
2 þ NaX
ð14Þ
can be used to link two alkyl groups by forming a CaC single bond. Employing a
Wurtz-type reaction coupling alkyl halides with excess metal sodium as both reductant and flux, fine carbon powders containing a trace amount of diamond
(yield @ 2%) (Figure 7.14(c)) were synthesized via a reduction–pyrolysis–catalysis
route by reacting CCl 4 with metallic sodium at 700
C [53]. This temperature is
Fig. 7.13. XRD patterns of GaP and InP nanowires (A), TEM
(B), ED (insert C) and HRTEM (D) images of InP nanowires
prepared by an Ullmann-like reaction.
7.3 Synthesis of Diamond, Carbon Nanotubes and Carbides 181