walter kenji yoshito | Instituto de Pesquisas Energéticas e Nucleares (IPEN-CNEN/SP) (original) (raw)

Papers by walter kenji yoshito

Materials Science Forum, Sep 1, 2018

A nanosized magnesium substituted beta-tricalcium phosphate (Mg:β-TCP) was synthesized by an aque... more A nanosized magnesium substituted beta-tricalcium phosphate (Mg:β-TCP) was synthesized by an aqueous precipitation method, at room temperature, in one single step. In the present study, the novel and stable Mg:β-TCP resulted in a crystalline and spherical nanoparticles (diameter of approximately 20 nm) with mesoporous structures and a high specific surface area (about 574 m2/g). These special characteristics make this novel crystalline mesoporous Mg: β-TCP nanoparticles ideal candidates for drug delivery system and a promising non-viral vector for gene therapy.

Dental Materials, 2017

To compare the Cyclic Fatigue Limit (CFL) of a control yttria-stabilized tetragonal zirconia poll... more To compare the Cyclic Fatigue Limit (CFL) of a control yttria-stabilized tetragonal zirconia pollycristal (Y-TZP) with a composite produced by adding multi-walled carbon nanotubes (CNT) into Y-TZP. Materials and methods: CNT were coated with zirconium oxide and yttrium oxide to form a powder (CNT/ZYO) using a hydrothermal co-precipitation method. Powders made of Y-TZP + (CNT/ZYO) were produced using 99 vol% of Y-TZP and 1 vol% of CNT/ZYO. CAD-CAM blocks (42.5 × 16.0 × 16.0 mm) were obtained by uniaxial pressing (67 MPa/30 s) of each powder in a steel matrix. These blocks were partially sintered at argon atmosphere (1100 • C/1 h/5 • C/s) and then sectioned to produce 14 bar-shaped specimens (3.0 × 4.0 × 25.0 mm/edges chamfered according to ISO6872:2008) of each material, which were sintered also in argon atmosphere (1.400 • C/4 h/5 • C/min). Density measured by Archimedes' method was used to calculate the relative density (RD), based on the theoretical values for both materials (6.06 g/cm 3). Flexural strength (FS) was measured in four-point bending with specimens immersed in water at 37 • C (inner and outer supports of 10 and 20 mm). CFL was determined in four-point bending, using the staircase method (10,000 cycles/5 Hz). In each cycle, the stress varied between the maximum stress (MS) and 50% of MS. The applied stress in the first specimen was 50% of FS. After 10,000 cycles, in case the specimen did not fracture, 10 MPa was added to the next specimen. RD and FS were analyzed by Student's t test (alpha = 5%). CFL was calculated according to: CLF = X0 + d(SUMini/SUMni ± 0.5), where X0 is the lowest stress value tested, d is the stress added or subtracted to each cycle and n is the number specimens that survived or failed in each stress level. The lowest stress level was computed as i = 0, and the next one was computed as i = 1, and so on. Fracture surfaces were fractographically analyzed. Results: Specimens containing nanotubes showed significantly lower RD compared to the control (p = 0.009). Nanotube addition also caused a 50% significant decrease in FS (p = 0.003). However, the FS coefficient of variation for the control was higher (17%) compared to that of the composite (10%). CFL calculated for the control was 2.5 times higher than that of the composite. The %CFL (CFL in terms of percentage of the FS) was also higher for the control. Fractography indicated fracture origins associated to surface defects and porous regions related to nanotube agglomerates. Conclusions: The processing method used to produce the composite Y-TZP/nanotubes needs to be improved since nanotube addition to Y-TZP caused a significant reduction of the relative density, strength and fatigue limit.

Materials Science Forum, 2020

In this work it was investigated the influence of CTAB surfactant concentration on the synthesis ... more 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 Fr...

The aluminum oxide composes the modern TL and OSL radiation dosimeters. TL and OSL phenomena are ... more The aluminum oxide composes the modern TL and OSL radiation dosimeters. TL and OSL phenomena are related to chemical elements in the crystalline structure of α-Al 2O3. The aim of this work was to develop materials based on aluminum oxide for use in TL and OSL dosimetry. The studies included the dosimetric properties of alumina samples obtained by electrofusion, adsorption and coprecipitation. Electrofused alumina commercially available as abrasive particles was used to produce the pellets by glass sintering. Adsorption and coprecipitation were the methods used to insert metal ions to alumina. The best results were achieved with electrofused alumina and Tm 3+ doped Al 2O3 pellets. The electrofused alumina-glass (EAG) pellets show TL and OSL signals and the TL curve has two peaks. Its minimum detectable radiation dose is 7.2 mGy and the linearity of TL response as function of dose is up to about 800 mGy. The α-Al 2O3:Tm pellets produced by sintering at 1550 o C presented a meaningful ...

EPL (Europhysics Letters), 2018

Mn-Zn ferrite nanoparticles were synthesized by chemical co-precipitation method and analysed usi... more Mn-Zn ferrite nanoparticles were synthesized by chemical co-precipitation method and analysed using X-ray synchrotron diffraction data. Pair distribution function (PDF) analysis was used to probe the local structure and revealed that the first-neighbour distances of Fe-Fe and Mn-Zn in the 3.0 up to 3.5 A range are different from the ones usually reported in the literature. For the sample with the best magnetic behaviour, resonant X-ray scattering (RXS) using three energies close to the absorption edges of Mn, Zn and Fe was applied to determine the cation distribution which explained the previous result from PDF analysis.

International Journal of Adhesion and Adhesives, 2017

This study aimed to evaluate the effect of various zirconia surface pretreatments on the adhesion... more This study aimed to evaluate the effect of various zirconia surface pretreatments on the adhesion between full contour 3Y-TZP zirconia and glaze, and the shear bond strength (SBS) between glazed/3Y-TZP and resin cement. Specimens were allocated into groups: GL-glaze; AL+GL-sandblasting with Al 2 O 3 +GL; CJ+GL-tribochemical silica coating (Cojet ® /CJ)+GL; PS+GL-piranha solution+GL; and CJ. Adhesion between 3Y-TZP and GL was evaluated using the scratch test. Surface topography and glaze thickness were evaluated by using a scanning electron microscope (SEM). For SBS, glazed/3Y-TZP surface was etched with hydrofluoric acid and a silane was applied. For CJ only the silane was applied. Samples were tested after 24 h (24 h wet) or after 15,000 thermal cycles and 90 days storage (thermocycled). After SBS, the type of failure was classified as: adhesive, mixed or cohesive. The data were analyzed using two-way ANOVA and Tukey's test. SEM analysis after scratch test revealed circular cracks in the GL group and conformal cracks in the others groups. SEM micrographs suggested that zirconia specimens submitted to airborne-particle abrasion presents rougher and porous surface when compared to surfaces treated with GL and PS. The glaze layer was approximately 1.86 µm thick in all groups. After 24 h, SBS test showed highest values for AL+GL and CJ+GL and were significantly higher when compared to the GL group. Differences were not significant between PS+GL and the other groups. After aging (thermo-cycling+storage), groups GL and CJ presented no statistically significant difference compared to 24 h and aged AL+GL, CJ+GL and PS+GL groups. The predominant type of failure was mixed. 3Y-TZP surface treatment with glaze application could be considered as an alternative treatment, since it yielded a similar resin bond strength without the need for airborne-particle abrasion.

Journal of Luminescence, 2017

A novel class of upconversion luminescent nanocrystals of Yb/Tm:calcium deficient hydroxyapatite ... more A novel class of upconversion luminescent nanocrystals of Yb/Tm:calcium deficient hydroxyapatite were synthesized by co-precipitation method in aqueous solution (pH adjusted to 6) and specially heat-treated with microwave radiation at different temperatures (from 900°C to 1000°C) and times (2-10 min) to produce small nanocrystals of Yb/Tm:β-tricalcium phosphate (β-TCP). As a result, we report for the first time, a single-phase Yb/Tm-doped β-TCP nanocrystals with a mean crystallite size of 55.3 nm. This material has an efficient visible luminescence from the 1 G 4 (blue emission) and 3 F 2 (red emission) and near infrared emission from the 3 H 4 excited states of Tm 3 þ induced by the Yb 3 þ-Tm 3 þ energy transfer under laser excitation (Yb 3 þ) at 972 nm. This β-TCP activated by Yb 3 þ and Tm 3 þ ions constitutes a new nano-fluoroprobe that can be used as optical contrast agents, affording high resolution and sensitivity for visible-near infrared applications.

Journal of Thermal Analysis and Calorimetry, 2009

A porous nickel–8 mol% yttria stabilized zirconia (Ni–8YSZ) composite, used as anode for solid ox... more A porous nickel–8 mol% yttria stabilized zirconia (Ni–8YSZ) composite, used as anode for solid oxide fuel cell, was obtained by reduction of NiO–8YSZ cermet. The first goal was the evaluation of the temperature effect of powder processing by thermogravimetry. In addition, the influence of porosity in the reduction kinetic of the sample sintered at 1450 °C was evaluated. The final porosity produced

Este estudo visa a definição de condições de síntese e processamento cerâmico que possibilitem a ... more Este estudo visa a definição de condições de síntese e processamento cerâmico que possibilitem a obtenção do componente anódico com características adequadas para a operação de uma SOFC (Solid Oxide Fuel Cell), ou seja, boa distribuição microestrutural do NiO na matriz de YSZ e porosidade cerca de 30% após redução de NiO. As rotas de síntese selecionadas englobaram a coprecipitação em meio amoniacal, mistura mecânica dos pós e combustão a partir de sais de nitrato. As técnicas de caracterização de pós empregadas incluíram a difração de raios X, microscopia eletrônica de varredura, microscopia eletrônica de transmissão, difração a laser, adsorção gasosa (BET) e picnometria de hélio. Os resultados obtidos indicaram que empregando-se a técnica de coprecipitação, a perda de Ni2+, na forma de complexo [Ni(NH3)n]2+, pode ser minimizada pelo controle do pH em 9,3, mantendo-se a concentração de Ni2+ na solução inicial em 0,1M. No método de mistura mecânica a melhor condição de dispersão dos...

Materials Science …, 2008

Zirconia stabilized with 8 mol% yttria (YSZ) is the most effective material for use as electrolyt... more Zirconia stabilized with 8 mol% yttria (YSZ) is the most effective material for use as electrolytes in solid oxide fuel cell. Ceramic powders of YSZ were synthesized in IPEN by coprecipitation route and are composed by fine particles (less than 01µm) with large surface area (~60m 2 .g-1). These powders have a strong tendency to agglomerate. and it make difficult the compaction process and to achieve a good density. To exert control over the compaction process. the powders were spray dried to obtain spherical granules. Thus the stability of slurries of these powders was studied by adding ammonium polyacrylate (Duramax D3005) as dispersant and the suspension stability was measured by electrophoretic mobilities. Slurries prepared with the better conditions were dried in a laboratory scale spray dryer. The prepared granules were characterized by morphology observation (SEM). surface area (BET). Vickers hardness and sintered ceramics bodies density were measured.

International Journal of Adhesion and Adhesives

This study evaluated the effect of distinct bonding strategies on the retention of full-contour z... more This study evaluated the effect of distinct bonding strategies on the retention of full-contour zirconia ceramic (Y-TZP, FCZ) crowns, and it characterized some physicochemical and mechanical properties of FCZ ceramic and its corresponding glazing system. To evaluate retention strength, dies were made with a dentin-analogue material to simulate a prepared tooth. FCZ crowns were manufactured using CAD-CAM technology and allocated into groups according to the bonding strategy: no ceramic treatment (PF -Panavia F cementation), glaze (GL), tribochemical silica coating (CJ), CJ + GL, and piranha solution followed by glaze (PS + GL). The specimens were subjected to thermocycling and storage in distilled water for 100 days before the retention tests. FCZ presented a porosity volume fraction of 0.2%, an apparent density of 6.06 g/cm 3 , Vickers hardness of 12.4 ± 0.07 GPa, and fracture toughness of 5.54 ± 0.24 MPa m 1/2 . SEM revealed a homogeneous microstructure composed of submicron-sized grains. XRD identified mainly zirconia's tetragonal phase. Glaze powder morphology was observed to be irregular, with a nanometric particle size, and a diffraction pattern characteristic of an amorphous material with several peaks of leucite. The PF and GL groups had higher retention values. The majority of the groups presented pre-test bonding failures, and two catastrophic failures of the FCZ-crown (GL and PF groups) were noted. The use of an MDP-containing resin cement or glaze application might improve retention of the FCZ crowns.

$Research paper thumbnail of Size-Strain Analysis of Iron-Excess Mn-Zn Ferrite Nanoparticles Using Synchrotron Diffraction and Its Correlation with Magnetic Saturation and Isoelectric pH$

Journal of nanoscience and nanotechnology, 2018

Iron-excess Mn-Zn ferrite nanoparticles were prepared by coprecipitation with sodium hydroxide (N... more 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 s...

2011 i A meu pai (In Memorian), minha mãe A meu pai (In Memorian), minha mãe A meu pai (In Memori... more 2011 i A meu pai (In Memorian), minha mãe A meu pai (In Memorian), minha mãe A meu pai (In Memorian), minha mãe A meu pai (In Memorian), minha mãe e irmãos, que sempre deram apoio e irmãos, que sempre deram apoio e irmãos, que sempre deram apoio e irmãos, que sempre deram apoio ii AGRADECIMENTOS Ao Instituto de Pesquisa Energéticas e Nucleares, pela oportunidade de realizar este trabalho. Ao Dr. José Octavio Armani Paschoal, pela orientação, confiança, apoio, incentivo e amizade. À Dra. Dolores Ribeiro Ricci Lazar, pela orientação, apoio, incentivos, e constantes contribuições no desenvolvimento do trabalho. Rodrigo Arakaki pela amizade e apoio nas execuções das atividades. Ao amigo Dr. Hidetoshi Takiishi pela amizade, apoio e por tornar o ambiente de trabalho mais agradável. A Dra. Emília Satoshi Miyamaru Seo pela amizade e por participar na etapa inicial deste trabalho.

Materials Science Forum, 2008

a wyoshito@ipen.br, b mascapin@ipen.br, c vussui@ipen.br, d drlazar@ipen.br, e paschoal@ipen.br A... more a wyoshito@ipen.br, b mascapin@ipen.br, c vussui@ipen.br, d drlazar@ipen.br, e paschoal@ipen.br Abstract. Nickel oxide-yttria stabilized zirconia (NiO-YSZ) anode materials were synthesized by combustion process involving metal nitrate-urea decomposition. The precursor was heated to evaporate water undergoing dehydration, and then the mixtures froth and swell. Further heating produces large amounts of gases that ignite at ambient atmosphere. Different nitrate/urea initial molar ratios were employed in order to investigate the influence of the reaction temperature in the physical characteristics of the powder composite. The flame temperature was measured by infrared optical pyrometer. The combustion was rapid and self-sustaining, with flame temperatures ranging from 870 to 1330°C. The as-synthesized powders were uniaxially pressed and sintered in air. Powders were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), helium picnometry for density measurements and gas adsorption technique (BET). The ceramic samples were evaluated by SEM and Archimedes density measurements.

Materials Science Forum, Nov 18, 2010