Hydrogen Utilization in Chemical Processes - Hydrogen Generation, Storage, and Utilization - page 181

FIGURE 10.8 SEM images show different morphologies of Mo metals obtained from hydrogen reduc-
tion under (left) low and (right) high moisture content. Source : Reproduced with permission from Schul-
meyer [17].

As another example, molybdenum metal powder is produced industrially
by reducing high purity molybdenum compounds such as molybdenum tri-
oxide (MoO 3 , grey-green powder), ammonium hexamolybdate ((NH 4 ) 2 Mo 6 O 19 ,
yellow powder) and ammonium dimolybdate ((NH 4 ) 2 Mo 2 O 7 , white powder),
with hydrogen gas [15]. The mechanism of reduction consists of two stages
[17]. The first stage involves a reaction from MoO 3 to MoO 2 via chemical
vapor transport process. In the second stage, MoO 2 is further reduced to
metal Mo:

MoO + 2 H → + Mo 2 H O .

(10.9)

2 2 2

Different grain sizes and shapes of metal molybdenum can be obtained
by adjusting moisture content of H 2 at entry (Fig. 10.8).

10.5 HYDROGEN UTILIZATION IN MANUFACTURING PROCESSES

10.5.1 Welding Gas: Oxy-Hydrogen Welding

Hydrogen has been used for welding as early as the beginning of the last
century [18]. Hydrogen reacts with oxygen in a flame to form water, and
simultaneously produces enormous energy for the welding process:

− 1

2 H + → O 2 H O H ; ∆ =− 572 kJ mol ⋅ .

(10.10)

2 2 2