This invention relates to carbon nanotubes and their synthesis, more particularly, to a sing\e step process for the synthesis of single-walled carbon nanotubes, alloy nanowire encapsulated multi-walled carbon nanotubes with hydrogen as a by product, by cataVytic decomposition of a selected hydrocarbon and selected alloy hydride catalysts.
This invention relates to the field of manufacturing caTbon nanotubes for fuel cell applications, such nanotubes being free from CO and C02 and higher hydrocarbons.
Carbon fibers have been identified as materials of interest for a
variety of applications which were produced from metal catalyst
particles in the presence of hydrocarbon containing gas. Mufti-
walled nanotubes having similar morphology of catalytically grown
carbon fibers have been grown in an arc discharge
apparatus using carbon electrodes. The process for making single walled nanotubes over cobalt catalyst from carbon vapour is known. Laser vaporization of graphite rods and a transition metal has been shown to produce single-walled nanotubes. These methods are expensive as they employ solid carbon vaporization via electric arc or laser apparatus. Single-waifed nanotubes have afso been synthesized using supported metal catalysts by chemical vapour deposition.

However, the process proposed herein is simple, low-cost, using ' active metal catalysts that eliminates the need for extensive purification. In addition it is desirable to fabricate encapsulated nanowires in the cavities of long multi-walled nanotubes with uniform diameter for their fundamental importance and potential applications in fuel cell technology.
It is an object of the present invention to propose a single step process
> for the synthesis of single walled carbon nanotubes (SWNTs) by the
pyrolysis of CH4 over ZrCrFeosNio.s alloy hydride catalyst in the temperature range 930 - 970°C,
> for the synthesis of alloy nanowire encapsulated multi walled carbon nanotubes (MWNTs) by the pyrolysis of CH4 over the same alloy hydride catalyst in the temperature range 825 - 860°C and
> for the production of H2 by the pyrolysis of CH4 over the same alloy hydride catalyst in the entire temperature range of 800 - 1000°C.

En
ZrCrFe05Nio,5 alloy hydride powder has been directly used as catalyst for the synthesis of SWNTs, alloy nanowire encapsulated MWNTs and production of hydrogen by the pyrolysis of CH4.
Synthesis of SWNTs and alloy nanowire encapsulated MWNTs along with the production of hydrogen have been carried out by catalytic decomposition of CH4 over ZrCrFe0.sNio,5 aifoy hydride catafyst using a singfe-stage turnace by chemical vapour deposition (CVD) technique.
> A horizontal electrical furnace is, preferably, used.
> A quartz tube of 29 mm inner diameter and 500 mm length is used as the CVD reactor.
> Legris tubes with 6 mm inner diameteT were used as the gas flow lines.
The process according to this invention for the synthesis of single
watted and muVtiwatted nanotubes conmprismg the steps of
heating a furnace to 500°C in argon flow; allowing hydrogen gas
into the furnace for almost 30 min; stopping the hydrogen flow
and raising die temperature of the furnace to die deposition
temperature in the range 825-860 (for production of alloy encapsulated
MWNTs) or 930-970°C (for production of SWNTS); allowing methane
4-

} into the furnace for about 30 min; stopping the methane flow and the furmace cooled to room temperature, the argon flow being maintained throughout the process with the generation of hydrogen as a byproduct; removing the quartz reactor and quartz boat with nanotube deposit from the furnace.
EXAMPLE About 200 mg of ZrCrFeosNio.s alloy hydride catalyst was kept in a quartz boat of 70 mm length inside the CVD reactor placed within the furnace. A quartz tube of 29 mm inner diameter and 500 mm length was used as the CVD reactor. The ends of the quartz reactor were closed with white brick caps.
> Argon with a gas flow rate of 100 standard cubic centimeter (seem) was used as the carrier gas.
> Methane with a flow rate of 100 seem was used as the carbon source.
> Hydrogen gas was allowed at a flow rate of 50 seem before the deposition.

I For the synthesis of SWNTs, the furnace was heated to 500°C in argon flow of 100 seem. At this temperature, hydrogen gas was allowed into the furnace for almost 30 min at a flow rate of 50 seem. Hydrogen flow was stopped and the temperature of the furnace was raised to the deposition temperature in the range 930-970°C. Once this temperature is reached, methane was allowed at a flow rate of 100 seem for about 30 min. After the experiment, the methane flow was stopped and the furnace was cooled to room temperature. The argon flow was maintained through out the experiment. Once the temperature of the furnace reaches ambient, the quartz reactor is taken out of the furnace and the quartz boat with carbon deposit is removed and the yield of the carbon deposit (SWNTs) is measured.
SWNTs was obtained using a single step process by catalytic decomposition of methane over ZrCrFeo.sNio.s catalyst at a deposition temperature of 930 -970°C. The as-grown carbon deposit has been characterized using XRD, TGA, SEM and TEM and Raman spectroscopy. The yield of carbon deposit has been calculated. A maximum yield of SWNTs was obtained at a temperature of 950°C.

Alloy nanowire encapsulated MWNTs
For the synthesis of alloy nanowire encapsulated MWNTs, the furnace was heated to 500°C in argon flow of 100 seem. At this temperature, hydrogen gas was allowed for almost 30 min at a flow rate of 50 seem. Hydrogen flow was stopped and the temperature of the furnace was raised to the deposition temperature in the range 825 - 860°C. Once this temperature is reached, methane was allowed at a flow rate of 100 seem for about 30 min. After the experiment, the methane flow was stopped and the furnace was cooled to room temperature. The argon flow was maintained through out the experiment. Once the temperature of the furnace reaches ambient, the quartz reactor is taken out of the furnace and the quartz boat with carbon deposit (MWNTs with encapsulated alloy n#nowires) is removed and the yield of the carbon deposit is measured.
Alloy nanowire encapsulated MWNTs were obtained using a single step process by catalytic decomposition of methane over ZrCrFeo.sNio.5 alloy hydride catalyst at a deposition temperature of 825 - 860°C. The as-grown carbon deposit has been characterized using XRD, TGA, SEM, EDAX and TEM and Raman spectroscopy. TEM image shows the presence of alloy

nanowire encapsulated MWNTs and the EDX analysis clearly reveals the composition of ZrCrFe0,5Ni0^ A maximum yield of the carbon deposit containing alloy nanowire encapsulated MWNTs was obtained at a temperature of 850°C.
For the production of hydrogen, as a byproduct, the furnace was heated to 500°C in argon flow of 100 seem. At this temperature, hydrogen gas was allowed for almost 30 min at a flow rate of 50 seem in order to remove the oxide layer, if any, from the surface of the alloy hydride catalyst. Hydrogen flow was stopped and the temperature of the furnace was raised to the deposition temperature in the range 800 - 1000°C. Once this temperature is reached, methane was allowed at a flow rate of 100 seem for about 30 min. The outlet gas was collected in a round bottom (RB) flask for 3 min after 5 min from the start of the experiment. The gas collected at different deposition temperatures under the same experimental conditions has been analyzed using mass spectroscopy. The generation of hydrogen free from CO/C02 in the temperature range 800 - 1000°C was confirmed from the analysis using mass spectrometer. Hydrogen with maximum purity was obtained at a decomposition temperature of 930 - 970°C, corresponding to the deposition of SWNTs.

ZrCrFeo.5Ni0.5 alloy is of low cost and hence the present technique is cost effective and produces SWNTs, alloy nanowire encapsulated MWNTs and generate hydrogen using a single step process, by varying the deposition temperatures. The produced hydrogen is free from

1. A> process for the synthesis of single walled and multiwalled nanotubes
comprising the steps of heating a furnace to 500°C in argon flow, allowing
hydrogen gas into the furnace for almost 30 min; stopping the hydrogen
flow and raising the temperature of the furnace to the deposition temperature
in the range 825-860 (for production of alloy encapsulated MWNTs) or
930-970°C (for production of SWNTS); allowing methane into the furnace
for about 30 mirv; stopping the methane flow and the turmace cooled to room
temperature, the argon flow being maintained throughout the process with
the generation of hydrogen as a byproduct; removing the quartz reactor and
quartz boat with nanotuhe deposit from the furnace
2. A process as ckimed in Claim 1 wherein the argon flow is of I 00 seem.
3. A process as ckimed in Claim I or Claim 2 wherein the hydrogen gas is allowed into the furnace at a flow rate of 50 seem,
4. A process as chimed in any one of the preceding Claims wherein methane is allowed into thQ furnace at a flow rate of 100 seem

5. A process for the synthesis of single walled and multiwalled nanotubes substantially as herein described and illustrated with reference to the example.
6. Single watted and mufti watted (with encapsulated nanowire) nanotubes when manufactured by a process as claimed in any one of the preceding Claims.