A. Vasquez

Structure and electrochemical property of the cobalt(II) hexacyanoferrate complex immobilized on Sn(IV) oxide coated on silica gel surface

Abstract The complex cobalt hexacyanoferrate was immobilized onto a silica gel surface, chemically modified with tin(IV) oxide. The formal potential of the attached electroactive species was dependent on the supporting electrolyte used: NaNO 3 = 0.39 V, KNO 3 = 0.50 V and NH 4 NO 3 = 0.53 V. A Nernstian behavior was observed for KNO 3 and NH 4 NO 3 and a quasi-Nernstian one for NaNO 3 when they were used as the supporting electrolyte. The LiNO 3 did not generate a reversible current peak since the hydrated ionic radius is larger than the zeolite-type cavity of the surface mixed valence complex.

PREPARATION, CHARACTERIZATION AND ELECTROCHEMICAL STUDIES OF 1,1'-BIS( DIPHENYLPHOSPHINO)FERROCENE (DPPF) DERIVATIVES. CRYSTAL STRUCTURE OF DPPFCO(NO) 2 SBF6

Abstract The neutral dppfFe(NO)2 (1), the novel cationic [dppfCo(NO)2][SbF6] (2), as well as the dppfFe(CO)3 (3) dppf = 1,1′-bis-(diphenylphosphino)ferrocene) complexes were prepared and characterized. The interaction between the two metallic centers through the dppf ligand was studied in the solid state by 57Fe Mossbauer spectroscopy and in solution by cyclic voltammetry. The Mossbauer parameters are compared with those of other dppfMLn, complexes. Electrochemical studies performed on these complexes show the great influence of the MLn moiety on the redox processes of the dppf iron center. The crystal structure of complex 2 was determined (C34H28CoF6FeN2O2P2Sb). The compound crystallizes in the triclinic, space group P 1 , a = 10.441(2), b = 10.755(2), c = 17.320(5) A , α = 104.10(2), β = 0.504(10), γ = 111.504(10)°, U = 1744.7(7) A 3 , Z = 2, R = 0.0765, wR2 = 0.1878 . In this complex, the cobalt atom is coordinated to two nitrosyl ligands and to phosphorus atoms of the dppf ligand, providing a distorted tetrahedral geometry.

Dissolution and reprecipitation of carbonitride precipitates in a low carbon steel by Ar irradiation

Abstract The effects of Ar bombrdment on carbonitrides produced by N implantation in a low carbon steel are studied by Conversion Electron Mossbauer Spectroscopy. The results show two main features: dissolution and reprecipitation of the produced carbonitrides and modification of the thermal behaviour of the precipitates. Recently we have performed similar experiments bombarding samples of the same steel with He. The comparison of both experiments shows that the Ar post-bombardment is not only more effective in the dissolution and reprecipitation process, but also is more efficient in the carbonitride retention at 450°C.

Characterization of europium implanted LiNbO3

LiNbO 3 single crystals were implanted at room temperature with Eu + ions at 70 keV with fluence ranging from 0.5 to 5 × 10 16 ions · cm −2 . The damage in the implanted layer has been investigated by Channeling Rutherford Backscattering (RBS-C), and the oxidation states of the cations have been determined by x-ray photoelectron spectroscopy (XPS). Following implantation, a fully amorphized layer of 60 nm is generated, even for the lowest fluence employed. Subsequent annealing in air, in the range 800–1250 K, was applied to restore tentatively the crystallinity and promote the substitutional incorporation of Eu in the crystal. Only a partial recrystallization of the damaged layer was observed. For as-implanted samples, XPS spectra clearly reveal europium in Eu 2+ and Eu 3+ states, and the Nb 5+ ions are driven to lower charge states.

X-Ray photoelectron spectroscopy and mössbauer spectroscopy study of iron(III) and antimony(V) oxides grafted onto a silica gel surface

Pronounced antimony surface enrichment on a silica gel surface grafted with Sb2O5 is evident after adsorption of Fe3–, and the surface new phase, presumably FeSbO4, is thermally very stable.

The effects of α-particle irradiation on carbonitrides produced in a nitrogen-implanted low-carbon steel☆

The effects of α bombardment on carbonitrides produced by nitrogen implantation in a low carbon steel are studied through the conversion electron Mossbauer spectroscopy technique. The results show that the thermal behaviour of the carbonitrides is strongly affected by the presence of helium particles in the nitrogen-implanted region. In addition, low-dose helium implantation (1014 α cm−2) already produces dissolution and reprecipitation of ϵ-Fe3.2(C, N) into Fe2+x(C, N) (x < 1) precipitates.

Mössbauer study of the planar antiferromagnet FeTa2O6

Abstract We report on Mossbauer spectroscopy study of magnetic ordering in FeTa 2 O 6 . At temperatures above 10 K, the compound is paramagnetic; the spectrum obtained at 10 K shows a very asymmetric doublet, suggesting the onset of the magnetic ordering; between 9.75 K and 4.2 K the spectra consist of magnetic components. The temperature dependence of the sublattice magnetization, as determined from Mossbauer measurements, qualitatively resembles that calculated for the two-dimensional Ising model.

He and Ar post-bombardment effects on carbonitrides formed in a Cr-rich steel

The effects of He and Ar bombardment on carbon produced in a N-implanted Cr-rich steel are studied by means of conversion electron Mössbauer spectroscopy, glancing X-ray and nuclear reaction analysis techniques. The results show two main features: dissolution and reprecipitation of the produced carbonitrides and modification of the thermal behavior of the precipitates. Comparison with similar experiments performed on Fe and on low-carbon steel show that the matrix composition plays an important role in the above processes.

Structural and magnetic properties of iron-tin thin films

Abstract This paper reports a study of FeSn thin films produced by co-sputtering. Rutherford backscattering, Auger electron spectroscopy, X-ray diffraction and conversion electron Mossbauer spectroscopy indicate the formation of a homogeneous solid solution of tin in iron, with a tin concentration well above the limit of the equilibrium solid solubility. No evidence of tin or FeSn compound precipitates is found. Magnetic measurements with a vibrating sample magnetometer show that the films present a saturation magnetization and remanence similar to those of pure iron films, but with a much smaller coercivity.

Site and probe dependence of hyperfine magnetic field in L21 Heusler alloys X2MnZ (X=Ni, Cu, Rh, Pd and Z=Ga, Ge, In, Sn, Pb)

Results of TDPAC and Mössbauer measurements of hyperfine magnetic fields in L21 Heusler alloys X2MnZ are given. TDPAC utilized Cd-111 from In-111 at the Z site and Ag-111 at the X site, and Ru-99 from Rh-99 at the X site. Mössbauer studies utilized Sn-119 at the Z site or at the Mn site. A compilation of hmf values is presented, and estimates of the polarized electron density are given for 1 nn, 2 nn, and 3 nn of the Mn ions in these alloys.