Eder Julio Kinast

Surface modification of titanium by plasma nitriding

A systematic investigation was undertaken on commercially pure titanium submitted to plasma nitriding. Thirteen different sets of operational parameters (nitriding time, sample temperature and plasma atmosphere) were used. Surface analyses were performed using X-ray diffraction, nuclear reaction and scanning electron microscopy. Wear tests were done with stainless steel Gracey scaler, sonic apparatus and pin-on-disc machine. The obtained results indicate that the tribological performance can be improved for samples treated with the following conditions: nitriding time of 3 h; plasma atmosphere consisting of 80%N2+20%H2 or 20%N2+80%H2; sample temperature during nitriding of 600 or 800 °C.

Structural, Magnetic, and Dielectric Investigations of the FeAlO3 Multiferroic Ceramics

The FeAlO3 phase presents an orthorhombic symmetry (Pna21 space group) with a double combination of hexagonal and cubic closed packing of oxygen ions. In this phase, there are four distorted different cationic sites, promoting piezoelectricity, ferrimagnetism and magnetoelectric effects at low temperatures. In this work, high-energy ball milling was employed to produce the FeAlO3 multiferroic compound. Its structural (Rietveld refinement), dielectric and magnetic properties were carefully investigated.

New investigation of the magnetic structure of CoNb2O6 columbite

The structural and magnetic properties of the CoNb2O6 compound have been investigated with a particular interest in their low-dimensional magnetic behavior which is characterized by the presence of weakly interacting ferromagnetic chains. We investigate this cobalt niobate by combining magnetic measurements; x-ray and neutron diffraction (ND). The ND was carried out on powder samples at different temperatures above (20 K) and below the ordering temperature (2.4, 1.8, and 1.4 K). The compound exhibits an orthorhombic crystal structure of Pbcn symmetry, typical of a columbite structure. Magnetic ordering at 2.5 K is found with the propagation vector (0, 0.4, 0), in agreement with earlier studies. However, at lower temperatures the present investigation shows the coexistence of two different magnetic phases: the propagation vector (0.5, 0.5, 0) is found to be necessary to refine the ND measurements at both 1.8 and 1.4 K, in addition to (0, 0.5, 0) which was the only one reported in earlier works.

Near-surface composition and tribological behaviour of plasma nitrided titanium

Near-surface composition and tribological behaviour of plasma nitrided commercially pure (CP) Ti have been investigated using x-ray diffraction, nuclear reaction analysis, scanning electron microscopy, wear assays with stainless steel Gracey scaler and sonic apparatus, and friction coefficient measurements. The total wear behaviour can be divided into two steps. The first step is the growth of an oxynitride layer. The second step is the breakdown of the oxynitride layer during which debris is produced, increasing the friction coefficient. Each sample exhibits features that correlate with the near-surface composition. For instance, the presence of thin layers of e-Ti2N and δ-TiN precipitating on the near-surface region control the transition from the first to the second step.

Structure refinement of mixed oxides FexCo1−xTa2O6

Abstract We report X-ray powder diffraction measurements performed on synthetic samples of the tapiolite-like Fe x Co 1− x Ta 2 O 6 solid solution. The crystal structure has been refined by the Rietveld method, by using the program fullprof . All the samples are tetragonal and were indexed to the space group P 4 2 / mnm . The end-members (FeTa 2 O 6 and CoTa 2 O 6 ) have unit-cell parameters quite similar to those previously published. The unit-cell parameters a and c for the mixed samples vary linearly with the cation substitution (Co→Fe) according to the Vegards law in all the range of substitution.

Crystal chemistry and structure of the orthorhombic (Fe,Mn)(Ta,Nb)2O6 family of compounds

In this paper we review the crystal chemistry and structure data from the literature and our results reported in the last decade for natural and synthetic samples of the tantalite-columbite series. Order-disorder transitions and oxidation reactions on the ixiolite-columbite-wodginite system are reported for one Brazilian sample. It is shown that reports on these subjects are sometimes dubious and incomplete. In addition to the reaction atmosphere (air or vacuum), order-disorder and oxidation are strongly dependent on the physical state of the samples (powdered or crystal). Structure and chemical composition have been investigated in our laboratory using X-ray diffraction (XRD), electron probe microanalysis (EPMA) and Mossbauer spectroscopy (MS).

Iron oxidation and order-disorder in the (Fe2+, Mn)(Ta, Nb)2O6(Fe2+, Mn)Fe3+(Ta, Nb)2O8 transition

Heat treatments in air and in vacuum have been performed on crystal and powder of the natural tantalite (Mn2+0.88Fe2+0.09)(Ta5+0.86Nb5+0.14)2O2-6, as well as on powder of synthetic Fe2+(Nb5+0.6Ta5+0.4)2O6. Crystal parameters and hyperfine interactions were obtained by use of x-ray diffraction and Mossbauer spectroscopy. It is shown that the partially ordered natural sample is completely ordered after heat treatment in vacuum. Conversely, heat treatment in air induced the tantalite [(Mn2+0.88Fe2+0.09)(Ta5+0.86Nb5+0.14)2O2-6]wodginite [(Mn2+,Fe2+)Fe3+(Ta,Nb)2O8] transformation on the powdered sample. When applied to the crystal sample, the heat treatment in air produced a mixture of two phases: the one in large amount is the ordered (Mn2+0.88Fe2+0.09)(Ta5+0.86Nb0.145+)2O62-, the other, in minor amount, is (Mn2+0.88,Fe2+0.09)Fe3+(Ta,Nb)2O8. The former arrives from cation ordering in the bulk portion of the sample, while the latter results from the near-surface oxidation. The Mn content as well as the oxidant atmosphere appears to play an important role in the transition mechanism. The same heat treatment applied to the synthetic columbite induces a different reaction: ferrocolumbite is transformed into the ixiolite Fe3+(Nb0.6Ta0.4)O4 with a minor amount of (Nb,Ta)2O5.

X-ray diffraction and magnetic susceptibility measurements for FexNi1−xTa2O6

The trirutile family of the tapiolite-like compound FexNi1−xTa2O6 was investigated by means of x-ray powder diffraction (XRD) and magnetic susceptibility measurements. From Rietveld refinement it is demonstrated that the family is a homogeneous solid solution obeying Vegards law. Magnetic susceptibility curves exhibit typical signatures of low-dimensional systems, with broadened maxima due to short range correlations immediately above the antiferromagnetic transition temperature TN. The T versus x phase diagram presents a minimum that suggests bicritical behaviour.

Magnetic phases of the quasi-two-dimensional compounds FexCo1 − xTa2O6

We report new results on the magnetic properties of the FexCo1 - xTa2O6 series of compounds. Essentially using neutron-diffraction and magnetic measurements we study, in more detail, the low-x limit of the temperature versus x phase diagram, where a new bicritical point is observed. The complete phase diagram shows three different magnetic phases at low temperature, for a high, intermediate and very low iron content. These phases consist of distinct antiferromagnetic orderings, characterized by different pairs of propagation vectors. We obtain information about the intraplane exchange interactions by fitting a high-temperature series of the magnetic susceptibility. Here we improve on a previously employed model, showing that two non-equivalent next-nearest-neighbor interactions must be taken into account in order to allow for in-plane magnetic orderings that are consistent with the neutron-diffraction results.

Structure and magnetic properties of layered (FexCo1 -x)Ta2O6 compounds

Abstract Samples of (FexCo1 − x)Ta2O6 were prepared from pure FeTa2O6 and CoTa2O6. From X-ray diffraction (XRD) measurements followed by Rietveld refinement, it is demonstrated that the solid solution obeys the Vegards law. Mossbauer spectroscopy (MS) measurements at 4.2 and 300 K show that for x ⩾ 0.8 the Fe → Co substitution has no apparent effect on the hyperfine parameters.