Page 72 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon
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between the extended thermal contact of the furnace and the simplicity of the filament (or rod) has been
reported.
3.2 Heated Graphite Atomizers
Tubes are typically 20-30 mm long and 5-10 mm in diameter after the design of Massman. In the past,
the tube may have been turned down at the centre to increase the temperature at that point, or the whole
tube may have tapered towards the centre ('profiling') to shape the tube to the optical beam and increase
the free atom density at the centre. Modern tubes tend not to have either of these modifications made to
them. The graphite tube is held in place between two electrodes, axially in line with the light source, as
shown in Fig. 3.4.
The two major disadvantages of graphite are its porosity and tendency for carbide formation. These
may be partially overcome by coating the tube with pyrolytic graphite (e.g. by heating the tubes in a
methane atmosphere), which is far less porous. Some manufacturers also produce total pyrolytic
carbon (TPC) tubes. Other more exotic materials such as glassy carbon have also been used in the
manufacture of the tubes but are not common. Some workers have also inserted other linings (e.g.
tungsten and tantalum) into
Figure 3.4
Modern design for a graphite furnace.
