RODRIGO UCHIDA ICHIKAWA

RODRIGO UCHIDA ICHIKAWA

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Thickness estimation of TiO2-based nanotubes using X-ray diffraction techniques
2020 - FARIA, MARCELA E.M.; LEITE, MARINA M.; ICHIKAWA, RODRIGO U.; VICHI, FLAVIO M.; TURRILLAS, X.; MARTINEZ, L.G.
TiO2-based nanotubes are a very promising material with many applications in solar cells, biomedical devices, gas sensors, hydrogen generation, supercapacitors, and lithium batteries, among others. Nanotube thickness is a very important property since it is related to electronic and surface mechanics. In this sense, transmission electron microscopy (TEM) can be used. However, it can be difficult to acquire a good TEM image because the transversal section of the nanotubes needs to be visible. In this work, TiO2-based nanotubes obtained via hydrothermal synthesis were studied using X-ray line profile analysis. Scherrer and Single-Line methods provided consistent results for the thickness of the nanotubes (≃ 5 nm) when compared with TEM. Additionally, Single-Line method was also applied to estimate the microstrain. The advantage of using XRD is given by the fact that it is a quick and statistically significant analysis when compared with TEM. The results show that XRD can be used as a rapid and reliable alternative for the thickness estimation of nanotubes.
Characterization of nanostructured Mn-Zn ferrites synthesized by coprecipitation method using CTAB
2020 - MARANHAO, W.C.A.; ICHIKAWA, R.U.; TURRILLAS, X.; YOSHITO, W.K.; SAEKI, M.J.; ORLANDO, M.T.D.; MARTINEZ, L.G.
In this work it was investigated the influence of CTAB surfactant concentration on the synthesis of the compound Mn0.75Zn0.25Fe2O4 by the coprecipitation method. It was also compared the influence of hydrothermal treatment on the synthesized materials. The magnetic properties were characterized by AC susceptometry for the determination of the magnetic susceptibility and magnetic density energy. The phases, crystal structure and morphology of the nanoferrites were determined by Rietveld analysis of X-ray diffraction data. It was found the presence of two phases: Franklinite and Akaganeite and it was shown that the samples synthesized only by coprecipitation presented the tendency to increasing the crystallite sizes of the akaganeite phase and decreasing of crystallite sizes of the Franklinite phase as a function of CTAB concentration. The samples submitted to subsequent hydrothermal treatment presented a tendency to decreasing the crystallite sizes of both phases and increasing in Franklinite phase fraction, compared to the samples synthesized only by coprecipitation, suggesting that the hydrothermal treatment was effective in obtaining nanostructured materials of smaller particles.
Study on the microstructure of UNS S32304 duplex steel submitted to heat-treatments
2017 - GOULART, F.; ICHIKAWA, R.U.; TURRILLAS, X.; MARTINEZ, L.G.
Duplex stainless steels are characterized by a good combination of mechanical properties and corrosion resistance. Due to the metastable equilibrium between the ferritic (α) and austenitic (γ) phases, significant changes in the microstructure of these steels may occur when subjected to temperatures higher than the ambient, degrading their properties. In this work, it was investigated the influence of heat treatments on the microstructure and mechanical properties of a duplex stainless steel UNS-S32304. The heat-treatments were performed at four temperatures (300°C, 600°C, 900°C and 1000°C) with two treatment times (1 h and 6 h) and two processes of cooling down (in air and water). The samples were studied by X-ray diffraction using Pawley method to determine the lattice parameters, mean crystallite sizes and microstrain for the two phases and compared to Vickers microhardness results.
The influence of iron content and alkaline concentration on Mn0.75Zn0.25FeyO4 structure, surface charge and acb response
2017 - MOURA, TIAGO F.A.; NAVARRO, RAPHAELLA; SHIOTSUKI, AUGUSTO K.; UTIYAMA, ANA P.M.S.; ICHIKAWA, RODRIGO U.; MATOS, RONALDO V.R.; CASTRO, GUSTAVO R.; YOSHITO, WALTER K.; MARTINEZ, L.G.; MIRANDA, JOSE R.A.; SAEKI, MARGARIDA J.
Nanotechnology applied on magnetic material provide a good opportunity to develop biomaterials as tracers for Alternating Current Biosuceptometry (ACB)and Magnetic Resonance Imaging (MRI) to diagnose certain diseases as cancer. The magnetic nanoparticles can still constitute drug carrier systems and hyperthermia agent for cancer treatment. Neverthless, the efficiency for therapy and diagnosis depends on the magnetic susceptibility. In this work, the ferrite nanoparticles with nominal composition Mn0.75Zn0.25FeyO4, where 1.5 ≤ y ≤ 2.8, were synthesized by the co-precipitation method and, the influence of iron content and concentration of precipitating agent on the structure, ACB response and surface charge was analyzed. It was noted that the synthesis using alkaline metal hydroxide between 0.1, 0.15 and 0.2 mol/L provides single-phase materials [ICSD 28515 (PDF - 742 402), space group Fd3m]. The higher concentration (0.25 mol/L) leads to materials with higher crystallinity and similar ACB response to those precipitated by lower concentration base, despite the secondary phase. A surface charge of 30 mV in module was achieved, which decreased as the concentration of the precipitating agent increased.
X-ray diffraction analysis of KY3F10 nanoparticles doped with Nd and preliminary studies for its use in high-dose radiation dosimetry
2019 - ICHIKAWA, R.U.; LINHARES, H.M.S.M.D.; SILVA, A.S.B. da; TEIXEIRA, M.I.; RANIERI, I.M.; TURRILLAS, X.; MARTINEZ, L.G.
In this work, the structure and microstructure of Nd:KY3F10 nanoparticles was probed using X-ray synchrotron diffraction analysis. Rietveld refinement was applied to obtain cell parameters, atomic positions and atomic dis-placement factors to be compared with the ones found in literature. X-ray line profile methods were applied to determine mean crystallite size and crystallite size distribution. Thermoluminescent (TL) emission curves were measured for different radiation doses, from 0.10 kGy up to 10.0 kGy. Dose-response curves were obtained by area integration beneath the peaks from TL. The reproducibility of the results in this work has shown that this material can be considered a good dosimetric material.
Estimativa da espessura de nanotubos através de dados de difração de raios X
2018 - FARIA, MARCELA E.M.; LEITE, MARINA M.; ICHIKAWA, RODRIGO U.; VICHI, FLAVIO M.; MARTINEZ, LUIS G.; TURRILLAS, XAVIER
Size-strain analysis of iron-excess Mn–Zn ferrite nanoparticles using synchrotron diffraction and its correlation with magnetic saturation and isoelectric pH
2018 - ICHIKAWA, RODRIGO U.; PARRA, JOAO P.R.L.L.; MARTINS, MURILLO L.; YOSHITO, WALTER K.; SAEKI, MARGARIDA J.; TURRILLAS, XAVIER; MARTINEZ, LUIS G.
Iron-excess Mn–Zn ferrite nanoparticles were prepared by coprecipitation with sodium hydroxide (NaOH) at different concentrations (0.1, 0.2, 0.5 and 1.0 mol/L). The results of X-ray diffraction (XRD) analysis using Whole Powder Pattern Modeling (WPPM) showed that higher concentrations of NaOH promote crystallite growth and broader dispersion in crystallite sizes. Energy dispersive X-ray spectroscopy indicates that zinc loss is noticeable when [NaOH] ≥ 0.2 mol/L. XRD revealed also a significant less-crystalline phase contribution alongside the main peaks of the nanocrystalline cubic spinel ferrite phase. The less-crystalline fraction is lower for the ferrite obtained with 0.2 mol/L of NaOH, being about 50% and more than 70% for the other samples. Despite of the less-crystalline fraction and the excess of iron, no secondary phases were detected. The Warren curves showed that the concentration of NaOH significantly influences the microstrain in the crystallites, being smaller for the sample obtained with NaOH at 0.2 mol/L. The sample prepared with this condition presented the better properties to be used as magnetic tracer in clinical diagnoses combining small mean crystallite size, low microstrain, which resulted in materials with higher magnetic saturation and high surface charge under blood pH.
In situ hydration of sulfoaluminate cement mixtures monitored by synchrotron X-Ray diffraction
2018 - ROSSETTO, CLEUSA M.; ICHIKAWA, RODRIGO U.; MARTINEZ, LUIS G.; CAREZZATO, GERALDO L.; CARVALHO, ALEXANDRE M.G.; TURRILLAS, XAVIER
Mixtures of calcium sulfoaluminate and Portland clinkers with gypsum were hydrated with deionized water. The pastes were introduced in 0.7 mm borosilicate capillary tubes and kept at 40 ºC while diffraction patterns were collected every 35 s for approximately 3 hours with a monochromatic radiation of 12 keV at the XRD1 beamline of the Laboratório Nacional de Luz Síncrotron (LNLS) in Campinas, SP - Brazil. The main crystalline phases (C2S, C3S, ettringite, ye’elemite and gypsum) involved in the hydration were quantified by Rietveld analysis. The most noticeable fact was the absence of portlandite as a crystalline precipitate, most likely due to the capture of calcium ions to form ettringite.
Evidence for a core–shell configuration in Tb-doped KY3F10 nanoparticles using synchrotron x-ray line profile and pair distribution function analyses
2018 - ICHIKAWA, R.U.; LINHARES, H.S.M.D.; PERAL, I.; BALDOCHI, S.L.; RANIERI, I.M.; TURRILLAS, X.; MARTINEZ, L.G.
The microstructure of Tb-doped KY3F10 nanoparticles synthesized by coprecipitation was analysed using x-ray synchrotron diffraction data. Size-strain analysis was performed by means of x-ray line profile (XLPA) methods such as Warren–Averbach and whole powder pattern modelling. Additionally, the structural coherence of the sample was accessed using pair distribution function analysis, supporting the XLPA results. The combination of all methods revealed that the nanoparticles exhibit a more ordered core and a less ordered surface comprising a core–shell configuration.
An alternative route to produce easily activated nanocrystalline TiFe powder
2018 - FALCAO, R.B.; DAMMANN, EDGAR D.C.C.; ROCHA, C.J.; DURAZZO, M.; ICHIKAWA, R.U.; MARTINEZ, L.G.; BOTTA, W.J.; LEAL NETO, R.M.
In this paper, an alternative process route to produce active nanocrystalline TiFe compound was investigated. First, TiH2 and Fe powders were dry co-milled in a planetary ball mill for 5e40 h. TiH2 was selected as precursor powder, instead of Ti powder, due its fragility, which has proved to be beneficial to decrease powders adherence on milling tools. In terms of loose powder mass, milling yields ranged from 90 to 95 wt.%. Next, milled powders were post-heated at 873 K under dynamic high-vacuum for TiFe synthesis reaction. First hydrogen absorption was verified in situ during the cooling process of samples (until the room temperature), being the amount of hydrogen absorbed and desorbed by this samples measured by automated Sievert's apparatus, under constant hydrogen flow rate of 9 cm3. min-1 (dynamic measurements). Besides to allowing the first absorption in situ, the investigated process route also allowed the production of the non-stoichiometric TiFe compound (rich in Ti) in samples milled for shorter times (5 and 10 h), both characteristics associated with maintaining the mechanical compound activity. Each sample absorbed hydrogen at 2 MPa during the cooling process, requiring no additional thermal activation cycles, since the samples milled for shorter times (mainly for 10 h) could absorb hydrogen for the first time more easily. However, the samples milled for longer times (25 and 40 h) shown better results in terms of reversible and storage capacities (0.73 and 0.94 wt.%, respectively).