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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