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- Author or Editor: E. Reguera x
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Abstract
Mössbauer spectra of low-spin ferric and high-spin ferrous compounds may be sensitive to the local humidity during the measuring process or to other parameters associated with the hydration degree of the sample. This effect is related to the location of water molecules around the t2g orbitals (dxy, dxz, dyz). The results indicate that for comparative studies all Mössbauer measurements must be carried out in well standardized conditions.
Abstract
The Mössbauer spectra of 29 nitroprussides have been measured and the parameters 
and 
correlated with the polarizing power Z/r2 of the outer cations. There is no overall correlation but there are limited groups in which a trend can be ascertained. In isoelectronic sequences such as Li+, Be2+; Mn2+, Fe3+, where the outer electronic shell remains fixed, while Z/r2 increases, a definite trend of decreasing and with increasing Z/r2 is observed.
Abstract
Divalent transition metal nitroprussides form a family of microporous materials which lose their crystallization water (coordinated and zeolitic) below 100°C and then remain stable up to above 150°C. The dehydration process of representative samples in their stable phases was studied by thermo-gravimetry (TG) and differential scanning calorimetry (DSC). The copper complex dehydrates in a single step through a practically irreversible process. For cadmium and cobalt complexes the water evolution on heating takes place in two stages. The first one, where only zeolitic waters are removed, is dominated by a diffusion mechanism while, during the loss of the strongly bonded waters (second stage) the material framework effect is added. The involved activation energy and its dependence on the conversion degree were estimated evaluating the thermo-gravimetric data according to an isoconversion model.
Abstract
Rancy type catalysts were prepared by means of a two step procedure: (1) Mechanical alloying of the metals and, (2) alkaline aluminum leaching. Mechanical alloying is a novel atlernative related to the synthesis of skeletal Ni catalysts. X-ray diffraction, and Mössbauer spectroscopies were performed for catalysts characterization. Binary Al-Ni and ternary Al-Ni-Fe alloys were produced by mechanical alloying from pure metallic powders; in particular, the intermetallic 
-(AlNi) phase was formed with a fine microstructure as a non-equilibrium phase; then, aluminum was selectively removed. After aluminum leaching the -(AlNi) phase was transformed into the more stable nickel fee structure.
