High intensity laser light act as energy source to excite carbon atoms
in laser ablation technique. Laser beam like YAG or CO2 vaporizes a
graphite target under high temperature in an inert atmosphere. Carbon
species are produced by the laser. These species are swept from a high
temperature zone to a water cooled copper collector by
the flowing inert gases. The reaction temperature determines the quality
& yield. Small amounts of transition metal such as Ni, Fe or Co when
added to the carbon target, SWCNTs are produced. Various parameters like
catalyst composition, growth temperature, nature of gases & gas
pressure, average nanotube diameter and size distribution can be varied
by varying the laser used. Carbon atoms and molecules condense from
these vaporized species to form large carbon clusters. Catalysts which
also start to condense, but rather slowly, attaches to these carbon
clusters. The tubular structured carbon molecules from this form SWCNTs.
This process of CNT growth continues until conditions have cooled
sufficiently so that carbon atoms can no longer diffuse through or over
catalyst surface particle. This growth also gets hindered as the size of
catalyst particles become too large.
Selective Laser Melting (SLM) is another technique used for fabricating
CNT reinforced Al nanocomposites[Dongdong et al, 2019]. This
material is used to prepare Aluminium metal matrix which are used in
combination with phase changing materials for energy storage. This
process uses laser based additive manufacturing technique. Both arc
discharge & laser ablation techniques are very expensive due to the
high power equipment so they are mainly used for SWCNTs production.
These methods also produce small quantities of CNTs with a lot of
impurities.