In:
Applied Optics, Optica Publishing Group, Vol. 59, No. 30 ( 2020-10-20), p. 9510-
Abstract:
The measurement of the hydrogen desorption properties of sodium alanate ( N a A l H 4 ) powder compacts presents a
particular challenge due to various material changes. Therefore, a parallel measurement method for both spectral and gravimetrical data
acquisition has been developed. The optical tracking of such chemical reactions with gaseous exhalation requires a special apparatus, since
hydrogen absorption/desorption alters the granularity and volume of the sample. The technique combines a commercial Fourier transform
infrared spectrometer with a self-developed heatable attenuated total reflection (ATR) cuvette that maintains the indispensable close
contact between the ATR medium and sample. In particular, strongly absorbing or scattering samples can be characterized with respect to
their transmission changes and their mass loss, due to the evanescent field’s penetration depth of a few micrometers into the bulk of the
sample. In this work, the first and second desorption step of 2 mol. % C e C l 3 - and T i C l 3 -doped N a A l H 4 compacts has been investigated. It
was shown that the technique is able to monitor the hydrogen content in an alanate compact by means of the purely optically measured
signal. In addition, a detailed analysis of the individual phase transformations was carried out. While the first reaction from the
tetragonal to the monoclinic phase ( N a A l H 4 = 〉 N a 3 A l H 6 ) showed a conversion nearly linear in
time, the following reaction from the monoclinic to the hydride phase ( N a 3 A l H 6 = 〉 N a H ) showed a nonlinear desorption
process. The phase changes were accompanied by discontinuous intensity changes of certain absorption bands, as well as by nonconstant changes
over time. Therefore, the second-phase conversion could be divided into two regions with different desorption behaviors. The optical and
gravimetric measurements were supported by x-ray diffraction measurements to verify the composition of the materials after hydrogen
desorption. For the technical application of this method, e.g., for use as a level sensor, these special optical features are essential
and must be taken into account.
Type of Medium:
Online Resource
ISSN:
1559-128X
,
2155-3165
Language:
English
Publisher:
Optica Publishing Group
Publication Date:
2020
detail.hit.zdb_id:
207387-0
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