Hydrogen Utilization in Chemical Processes - Hydrogen Generation, Storage, and Utilization - page 182

FIGURE 10.9 Schematic diagram illustrating the device for arc-atom welding. Source : Reproduced
with permission from Suban et al. [18].

Before the introduction of acetylene, hydrogen was the basic combustible
component in this kind of welding. Moreover, hydrogen gas has also been
used for arc-atom welding (Fig. 10.9) [18].
As shown in Figure 10.9, an alternating arc is maintained between two
tungsten electrodes, with hydrogen fed into the arc. When hydrogen is passed
through the electric arc, the temperature in the arc core is sufficiently high
to initiate dissociation of hydrogen gas to form atomic hydrogen:

− 1

H ← → + H H H ; ∆ =− 422 kJ mol ⋅ .

(10.11)

2

→

The energy required to break down the H-H covalent bond is provided
by the arc. When the hydrogen atoms are recombined, they give the energy
back and the flame at this point can reach as high as 3700°C and can thereby
be used for welding. This process has been widely used for manual and
automatic welding of metal sheets.
Recently, Tusek et al. has found that the static characteristic of the welding
arc can be changed by adding different amounts of hydrogen in argon gas.
The energy of the arc and the thermal and melting efficiency can be enhanced
as a result of mixing hydrogen and other gases with different physical and
chemical properties (e.g., thermoconductivity, enthalpy, and electric conduc-
tivity) [19].

10.5.2 Coolant

The thermal conductivity of hydrogen is substantially higher than that of
other gases (Fig. 10.10). Moreover, it has high specific heat capacity, low