Environmental Engineering Reference
In-Depth Information
10.6 HYDROGEN UTILIZATION IN PHYSICS
10.6.1 Lifting Gas
Hydrogen was once used as lifting gas for balloons and airships in the early
1900s. A famous airship filled with hydrogen was the Hindenburg airship,
made in Germany in 1936. It was the longest class of flying machine and
the largest airship by envelope volume. However, in 1937, the Hindenburg
suddenly caught on fire and collapsed at Lakehurst Naval Air Station,
New Jersey, while completing a single round trip passage to Rio de
Janeiro. Although the exact cause of the Hindenburg disaster has not been
determined yet, the drawback of using flammable hydrogen is clear. There-
after, hydrogen was no longer used as filling gas for airships and it was
replaced by helium gas.
10.6.2 Superconductor Industry
It is well known that superconductivity can be observed only at the tempera-
ture below a certain characteristic temperature, called critical temperature
(
T
c
). Since most high temperature superconductors have
T
c
below 200 K [23],
it is necessary to find a refrigerant to cool the superconductors. Liquid hydro-
gen has a boiling temperature of 20 K [24], which is even lower than that of
liquid nitrogen (77 K) [25]. This makes liquid hydrogen a suitable candidate
as a refrigerant for those superconductors with a T
c
lower than the boiling
point of liquid nitrogen, such as the magnesium diboride with a T
c
of 39 K
[24]. In addition, the current density of superconductors, for example, Ba-
La-Cu-O (
T
(T = 30 K) [26] and Ag-sheathed Bi-2223 (
T
= 20 K) [27] super-
conductors, at liquid hydrogen temperature are higher than that at liquid
nitrogen temperature.
10.6.3 Semiconductor Industry
Hydrogen can be easily introduced into semiconductors by occupying dif-
ferent sites in different charge states, forming complexes with impurities and
defects [28, 29]. Hydrogen as an impurity can substantially affect the elec-
tronic properties of semiconductor materials. Significantly, hydrogen exhib-
its different behavior depending on the host crystal structure. As an isolated
interstitial impurity, hydrogen can occupy a number of different lattice sites
and modify the host structure, to the point of breaking host-atom bonds. It
can act as either a donor (H
+
) or an acceptor (H
−
) [28]. Density-function
Search WWH ::
Custom Search