Chloride substitution induced by mechano-chemical reactions between NaBH4 and transition metal chlorides

• Published in: Journal of alloys and compounds 2012-07, Vol.530, p.186-192
• Main Authors: Llamas-Jansa, Isabel, Aliouane, Nadir, Deledda, Stefano, Fonneløp, Jon Erling, Frommen, Christoph, Humphries, Terry, Lieutenant, Klaus, Sartori, Sabrina, Sørby, Magnus H., Hauback, Bjørn C.
• Format: Article
• Language: English
• Subjects: Alloys; Cadmium; Chlorides; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Gaussian; Infrared spectroscopy; Materials science; Materials synthesis; materials processing; Mechano-chemical processes; Metal hydrides; Neutron diffraction; Physics; SEM; Thermal analysis; Transition metals; Vibrational spectroscopy; X-ray diffraction; Zinc
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2012.02.167

▸ The metathesis reaction between NaBH4 and TM-chlorides does not proceed under all experimental conditions. ▸ Cl− to BH4− ion substitution is systematically induced by ball milling in NaBH4 samples when using a variety of transition metal (TM) chlorides. ▸ This leads to Na(BH4)1−xClx borohydrides, with x ranging from x=0.69 to 0.92 depending on the TM. ▸ Our experimental work evidences the difficulties encountered for the successful synthesis of mixed metal borohydrides by mechano-chemical methods, which remain a challenge. Cl− to BH4− ion substitution was induced in NaBH4 through mechano-chemical reactions with all the first period transition metal chlorides and CdCl2. The products were identified by Rietveld refinement of powder X-ray and neutron diffraction data to be mainly Na(BH4)1−xClx. These possess cubic NaCl-type structures, with unit cell parameters between 5.7801(3) and 5.6576(2)Å, and compositions ranging from x=0.69 (with Cu) to 0.92 (with Zn). Infrared spectroscopy of selected samples confirms the substitution through a shift of the vibrational modes of the BH4− group towards higher wavenumbers. An observed shape change of the vibrational features from Lorentzian to Gaussian is related to the presence of the transition metal. There is no correlation between x and the thermal behavior of the samples. The lowest decomposition temperature is found for the Zn containing sample (103°C), while Cd leads to the highest value (521°C). Their behavior is related to the presence of NaZn(BH4)3 and metallic Cd in the samples, respectively.