Tsuneharu Ogasawara

Hydrothermal nucleation of hydroxyapatite on titanium surface

Abstract Titanium plates were submitted to nucleation and growth of hydroxyapatite (HAp) under hydrothermal conditions. A group of these plates were submitted to nucleation without any previous treatment and another group was treated with NaOH 1 M at 130°C inside an autoclave followed by heat-treatment at 600°C. The nucleation were performed by soaking all these titanium pieces, in a simulated body fluid (SBF) solution, containing calcium, phosphate and other ions, in order to promote the nucleation and growth of hydroxyapatite under hydrothermal conditions on the titanium surface. The results show that hydrothermal nucleation and growth of HAp occurs even on the non-treated titanium surface at 150°C. However, a better uniformity of the hydroxyapatite layer was observed on the pre-treated titanium surface, at 80°C, with the renewal of the SBF solution.

Nucleation and growth of hydroxyapatite on titanium pretreated in NaOH solution: experiments and thermodynamic explanation.

Titanium was submitted to chemical attack with sodium hydroxide solution under hydrothermal (SBF) conditions and then kept for 4 weeks in simulated body fluid after heat treatment. The resultant coating titanium samples were characterized regarding nucleation and growth of hydroxyapatite on their surfaces using scanning electron microscopy and energy dispersive spectroscopy, as well as low angle X-ray diffraction. In order to obtain a thermodynamic explanation of same results, Eh-pH diagrams of Na-Ti-H2O and Ca-Ti-H2O systems at 25, 100, 200, and 300 degrees C were built for selected activities of the species in aqueous solutions. Values of pairs corresponding to the predominance limit of the species in solution at equilibrium with 0.21 atm of oxygen pressure were taken from these Eh-pH diagrams for subsequent building of the pNa-pH and pCa-pH diagrams of the same systems at each referred temperature (pi = -log10ai). In addition, the titanate-apatite free energy of formation was estimated and then a pCa-pH diagram of the Ca-P-Ti-H2O system at 25 degrees C was built. Examination of the resultant diagrams could elucidate the thermodynamic viability of the process.

Hydrochloric acid leaching of a pre-reduced Brazilian ilmenite concentrate in an autoclave

Abstract As a part of the Project on Integrated utilization of the Fe–Ti–V ore from Campo Alegre de Lourdes (Bahia), the present work have as its main objective to investigate the hydrochloric acid leaching of a pre-reduced ilmenitic concentrate, with the purpose of obtaining synthetic rutile. Initially, the crude ore was submitted to the following steps: partial reduction, grinding, sizing and magnetic separation at low and high intensity (the last one shown to be of low effectiveness). In order to guide the thermogravimetric analysis of the ilmenite during pyrometallurgical treatments, oxidation–reduction diagrams of the Fe–Ti–H–O system were constructed. Tests of those treatments were conducted in a STANTON thermobalance to determine the best operational conditions. Of fundamental importance were the calculation and construction of Eh–pH diagrams for the system Fe–Ti–Cl–H 2 O at elevated temperatures, in the development of the hydrochloric acid leaching processes studied. It was verified, through these diagrams, that a reaction medium of high acidity and moderately reductive potential is necessary to get iron into solution, in the Fe 2+ form, and titanium as a solid oxide (TiO 2 ). Eh–pH diagrams for the system Fe–Cl–H 2 O, at elevated concentrations were also produced, through which it became possible to explain the results of the processes developed by previous researchers. Tests on hydrochloric acid leaching were carried out in a Parr autoclave, model 4562. It was observed that in the hydrochloric acid leaching on the pretreated ilmenitic concentrate, the effect of the oxidation as a pre-treatment step before reduction is not significant. The best results for iron extraction (about 97.5%) and titanium content in the residue (about 47.5%) were obtained with hydrochloric acid leaching of the reduced ilmenitic concentrate at 100°C with 4 M HCl solution.

TA of non-stoichiometric ceria obtained via hydrothermal synthesis

Doped ceria was studied in the last 20 years as a solid electrolyte capable of replacing stabilized zirconia in fuel cells. Nevertheless, one of the problems concerned with the application of this material is the joint presence of the Ce(III) and Ce(IV) in the ceria sublattice, mainly under low partial pressure of oxygen. TG and DTA measurements were performed in order to verify non-stoichiometric character for cerias hydrothermally treated under reflux and in autoclave. X-ray powder diffraction was used to observe long-range structural evolution varying time and temperature of reaction and the type of hydrothermal synthesis. Finally, scanning electron microscopy (SEM) gave the temperature influence for powder morphology. Those techniques pointed out that: i) reaction temperature is not important for converting Ce3+ to Ce4+; ii) testing the reaction time parameter, it is observed quite complete oxidation for the 2-12 h range; and iii) the type of hydrothermal synthesis parameter influences the crystallinity and non-stoichiometric character of products.

Microwave absorption properties of Co, Cu, Zn: substituted hexaferrite polychloroprene nanocomposites

The magnetic behavior and its relationship with microwave absorbing properties have been investigated for doped Z-type barium hexaferrites (Ba3Co1.3Zn0.3Cu0.4Fe 24O41)/ polychloroprene (CR) nanocomposites. Simultaneous substitutions by Co2+, Cu2+, and Zn2+ ions make possible the use of these materials as RAMs, due to the frequency dependence of µr* (permeability), responsible for the location of the hexaferrite natural resonance. The Cu2+ ions distort the crystalline field due to their electronic configuration, and this behavior results in an increase in the saturation magnetization (Ms), which improve the magnetic permeability. Similarly, the superparamagnetic contribution (associated to the nanometric size) led to the improvement of the microwave absorption.

Nucleation of Hydroxyapatite on Silica-Gel: Experiments and Thermodynamic Explanation

Silica-gels prepared from ethanol, TEOS and water, using a hydrochloric acid as catalyst, were slowly dried and heated in air up to 900°C. Plate-like pieces of heat treated silica-gel were used for hydroxyapatite nucleation experiments in a simulated body fluid (SBF) medium since sol-gel processing gives the silica an active surface. The SBF was changed every 3 days.After 9 days in the SBF, hydroxyapatite was observed by SEM on the surface of the silica-gel samples. The presence of hydroxyapatite was confirmed by FTIR. Subsequent growth of hydroxyapatite was evaluated after 12 and 21 days total soaking time in SBF. A thermodynamic analysis was made in order to explain the nucleation and growth of the hydroxyapatite on the silica-gel.

Microstructure and Hysteresis Curves of Samarium-Holmium-Iron Garnet Synthesized by Coprecipitation

An investigation was made into the synthesis and magnetic properties of Sm(3-x)HoxFe5O12 (samarium-holmium-iron) garnet ferrite, as yet absent from the literature. The material in question was synthesized by co-precipitation, starting from hydrated chlorides of rare-earth elements and ferrous sulfate, and the mixed hydroxide co-precipitate was calcined at 1000 °C. Using PVA as a binder, rectangular cross section-shaped compacts were produced by means of steel-die pressing, drying and sintering from 1200 to 1450 °C. The main conclusions of this study were that the coercive force decreases as the sintering temperature increases, and that the effect of substituting holmium for samarium in SmIG is entirely different from that provided by replacing yttrium by gadolinium in YIG, which is the most important result of this work. An in-depth investigation will be necessary to determine the correlation between microstructure/magnetic properties and ceramic processing variables.

Detailed crystallization study of co-precipitated Y1.47Gd1.53Fe5O12 and relevant magnetic properties

The crystallization process of co-precipitated Y1.5Gd1.5Fe5O12 powder heated up to 1000 oC at rate of 5 °C min-1 was investigated. Above 810 oC crystalline Y1.47Gd1.53Fe5O12 was obtained with a lattice parameter of 12.41 A and a theoretical density of 5.84 g cm-3. Dry pressed rings were sintered at 1270 and 1320 oC, increasing the grain-size from 3.1 to 6.5 µm, the theoretical density by 87.6 to 95.3% and decreasing Hc from 2.9725 to 1.4005 Oe. Additionally, Hc increased when the frequency of the hysteresis graph varied from 60 Hz to 10 kHz, the curie temperature was 282.4 oC and Ms equalled 9.25 emu g-1 (0.17 kG) agreeing well with the Bs-value of the hysteresis graph and literature values.

Co2Z hexaferrite obtained by the citrate precursor method in an inert atmosphere

Nanoparticles of Co2Z hexaferrite were synthesized by the citrate sol-gel process under an inert atmosphere, then thermally analyzed by Thermogravimetric and Differential Thermal Analysis and characterized by X-ray Diffraction, Scanning Electron Microscopy, Atomic Force Microscopy, X-ray Fluorescence and Vibration Sample Magnetometry. Z-type barium hexaferrite is a promising material for application in high frequency electronic devices involving up to 100 MHz, such as multi-layer chip inductors (MLCI), which require magnetic materials with high initial permeability, high resistivity, low magnetic and dielectric loss, and good thermal stability.

Compósitos de ferrita de Ni-Zn com policloropreno para utilização como materiais absorvedores de radar para a banda S

Abstract The aim of this work was to obtain Radar Absorbing Materials (RAMs) for the frequency range from 2.6 to 4.0 GHz (S-band). The80 wt.% magnetic filler addition to a polychloroprene matrix was a Ni-Zn ferrite. The composite with 6 mm thickness showed agood RAM performance for the whole range of frequency analyzed, with a microwave absorption greater than 96.9% (-15 dB),emphasizing the greatest absorption of 99.5% (- 25 dB) at 3.2 GHz, allowing its use as an external coating for naval applicatio ns,in accordance with the salt spray testing. Keywords : Ni-Zn ferrite, S-band, RAM, salt spray testing. durabilidade, baixa densidade, baixo custo, a abrangencia deuma ampla faixa de frequencia e ser de facil aplicacao [3].Dentre as matrizes polimericas empregadas para aconfeccao dos RAMs, os elastomeros apresentam comovantagens a elevada flexibilidade e resistencia a intemperies.O policloropreno (CR) e um elastomero que por apresentarelevada resistencia a atmosfera salina, torna-se ade quado parainumeras aplicacoes navais [3].As ferritas sao materiais cerâmicos com propriedadesmagneticas, que devido as possiveis combinacoes decomposicoes quimicas e estruturais, podem ser utilizadas emvarias aplicacoes especificas, tais como RAMs. Para cada tipode estrutura cristalina (espinelio, granada e hexagonal) o ajustedas propriedades magneticas possibilita a absorcao demicroondas em diferentes frequencias [5-11].