Dear Mr Pukazhselvan
Since many years I am working on NaAlH4 and the dehydrogenation
products, we also have performed dozens of in situ experiments but I
have never observed a splitting of the NaAlH4 peaks. Since the system is
well understood, it sounds more like you have severe problems with your
experimental setup.
Best regards
Claudia Weidenthaler
pukazh selvan schrieb:
Dear All,
I believe some of you in our rietveld mailing group must be having
experience in the area of hydrogen storage in complex hydrides. Kindly
give your views in the following.
I have catalyzed NaAlH4 by Ti (2 mol %) and dehydrogenated this. The
product was again hydrogenated by exposing the product to pure
hydrogen atm at the required H pressure and temperatuare. The forward
and reverse reaction commence through the given route.
3NaAlH4Û Na3AlH6+2Al+3H2Û3NaH+Al+3/2H2.
The rehydrogenated material (from NaH) is now NaAlH4 with unreacted
reaction products mainly of Al. I have taken XRD of the uncatalyzed,
catalyzed and rehydrogenated samples. To my surprise, there is
splitting and shifting of NaAlH4 peaks, or say peak doubling with 0.7
to 1° gap in the 2q angle.. It appears to be there is two set of d
values for NaAlH4. If I calculate the lattice parameter seperately,
the little right shifted (high angle side) gives a=b= 5.00 A and the
left shifted peaks (low angle side) give amazingly high (ie a=b= 5.10
A) lattice parameter to this tetragonal system. The usual parameter is
5.02 A only. There is no any splitting in the unreacted Al peaks which
usually altogether exists with rehydrogenated samples. Therefore
considerable amount of confusion bother me to consider the
experimental error. There is also suggestion in regard to
supperlattice, vacancy mediated lattice changes etc. Any way if there
is no equipmental error, I want to be clear with the science of this
splitting. Have any of you had such problems? Kindly give your
valuable suggestions.
Also, please suggest me any standard research articles where I can
find information related to my problem.
Looking forward....
Sincerely Yours,
D.Pukazhselvan
Senior Research Fellow,
Hydrogen Energy Centre,
BHU,India.
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Dr. Claudia Weidenthaler
Max-Planck-Institut für Kohlenforschung
Kaiser-Wilhelm-Platz 1
D-45470 Mülheim a.d.Ruhr
Phone +49 (0) 208 306 2181
fax +49 (0) 208 306 2989
