Application Of Mössbauer Spectroscopy To The Study Of Corrosion Resistance In Nacl Solution Of Plasma Nitrided Aisi 316l Stainless Steel

Corrosion research in steels is one of the areas in which Mössbauer spectroscopy has become a required analytical technique, since it is a powerful tool for both identifying and quantifying distinctive phases (which contain Fe) with accuracy. In this manuscript, this technique was used to the study of corrosion resistance of plasma nitrided AISI 316L samples in the presence of chloride anions. Plasma nitriding has been carried out using dc glow-discharge nitriding treatments, in medium of 80 vol.% H 2 and 20 vol.% N 2, at 673 K, and at different time intervals: 2, 4, and 7 h. Treated samples were characterized by means of phase composition and morphological analysis, and electrochemical tests in NaCl aerated solution in order to investigate the influence of treatment time on the microstructure and the corrosion resistance, proved by conversion electron Mössbauer spectroscopy (CEMS), glancing angle X-ray diffraction (GAXRD), scanning electron microscopy (SEM) and potentiodynamic polarization. A modified layer of about 8 μm was observed for all the nitrided samples, independently of the nitriding time. A metastable phase, S phase or γ N, was produced. It seems to be correlated with γ′-Fe 4 N phase. If the γ N fraction decreases, the γ′ fraction increases. The γ N magnetic nature was analyzed. When the nitriding time increases, the results indicate that there is a significant reduction in the relative fraction of the magnetic γ N (m) phase. In contrast, the paramagnetic γ N (p) phase increases. 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Nitriding of H-12 tool steel by direct-current and pulsed

Abstract Direct-current (DC ) and pulsed plasmas were used to nitride samples of AISI H-12 tool steel with treatment time varying from 1 h to 6 h. X-ray diffraction (glancing-angle and h-2h geometry), conversion electron Mö ssbauer spectroscopy, conversion X-ray Mö ssbauer spectroscopy and Vickers microhardness were used as analytical techniques. The near-surface compound layer consists of a mixture of c∞-Fe 4 N and e-Fe x (N,C ), while the near-diffusion zone compound layer consists of a mixture of c∞-Fe 4 N, e-Fe x (N,C ), a◊-Fe 16 N 2 and c-austenite. For a DC plasma the dependence of compound layer thickness on nitriding time obeys a parabolic law, but for a pulsed plasma this dependence does not follow a parabolic law

Ferroic investigations in LuFe2O4 multiferroic ceramics

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)In this paper, the ferroic properties of polycrystalline LuFe2O4 samples were carefully investigated, and a dissimilar charge ordered state was identified. Strong dielectric dispersion, between 350 K and 225 K; the formation of cluster glass magnetic phases in the same temperature range; and the existence of a ferrimagnetic transition at 230 K indicate the coupling between the ferroelectric and the magnetic orders. Mossbauer spectroscopic investigations, at room temperature, revealed unbalanced contributions of the ferric and ferrous iron ions to the charge ordered state. (C) 2011 American Institute of Physics. [doi:10.1063/1.3622147]1103Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundacao Araucaria de Apoio ao Desenvolvimento Cientifico do Parana Brazilian agency [10779, 15727]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)CNPq [476964/2009-1, 552900/2009-5]Fundacao Araucaria de Apoio ao Desenvolvimento Cientifico do Parana Brazilian agency [10779, 15727]FAPESP [2008/04025-0]CAPES [PROCAD 082/2007

Magnetic states and valence fluctuations in charge frustrated polycrystalline lutetium ferrite samples

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)LuFe2O4 polycrystalline materials were processed by an innovative protocol using high-energy ball milling and thermal treatments in an argon flux. The results of room-temperature Mossbauer spectroscopy showed different concentrations of Fe2+ and Fe3+ in samples treated for different time periods. Magnetic studies revealed multiple magnetic transitions and showed that valence fluctuations resulted in samples with distinguishable magnetic behaviors. In fact, an additional anomaly in the M x T curve was observed for the LuFe2O4 sample thermally treated for 1 h at 1473 K. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.699670673Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundacao Araucaria de Apoio ao Desenvolvimento Cientifico e Tecnologico do Parana [22825, 22870]Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CNPq [proc. 305129/2010-4]Fundacao Araucaria de Apoio ao Desenvolvimento Cientifico e Tecnologico do Parana [22825, 22870]CAPES [Procad 082/2007]FAPESP [proc. 2008/04025-0

Ferroic states and phase coexistence in BiFeO3-BaTiO3 solid solutions

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)In this paper structural, electric, magnetic, and Mossbauer spectroscopy studies were conducted in (x) BiFeO3-(1-x) BaTiO3, 0.9 >= x >= 0.3, solid solutions. X-ray diffraction and Rietveld refinement studies indicated the formation of single-phased materials crystallized in a distorted perovskite structure with the coexistence of rhombohedral and monoclinic symmetries. Room temperature ferroelectric hysteresis loops showed that the electric polarization increases with the increase of the BaTiO3 content due to the singular structural evolution of the studied solid solutions. All samples presented weak ferromagnetic ordering, which indicates that the BaTiO3 substitution in the BiFeO3 matrix released the latent magnetization. Mossbauer studies revealed a magnetic spectral signature corresponding to ordered Fe3+ ions, and a decrease of the magnetic hyperfine magnetic fields with the increase of the BaTiO3 content. The composition 0.3BiFeO(3)-0.7BaTiO(3) presented a spectral signature corresponding to a paramagnetic behavior, which strongly suggests that the observed magnetization in this sample is due to the Ti3+ ions. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4766450]11210Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundacao Araucaria de Apoio ao Desenvolvimento Cientifico e Tecnologico do Parana [Prots. 22825, 22870]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CNPq [proc. 305129/2010-4]Fundacao Araucaria de Apoio ao Desenvolvimento Cientifico e Tecnologico do Parana [Prots. 22825, 22870]FAPESP [proc. 2008/04025-0