Papers by Keyword: Pechini Method

Abstract: The objectives of this study were to produce ZrO₂-based nanoparticles doped with silver, using the polymeric precursor method (Pechini), and to verify their bactericidal activity against Escherichia coli and Staphylococcus aureus. Zirconium and silver oxides were chosen due to their bactericidal activity. The oxides were characterized by X-ray diffraction and field emission gun-scanning electron microscopy. The support for the oxides was a porous surface used in gravity filters. The method was not effective against the bacterium Escherichia coli in the sample subjected to UV light for 45 min, since it did not eliminate the bacterium, and did not inhibit colony growth and formation. However, the bactericidal activity test proved effective against Staphylococcus aureus, eliminating the bacterium when the sample was subjected to UV light for 45 min, thus preventing colony growth and formation.

Abstract: Calcium silicate (CS) is a main component of Portland cement and is responsible for the strength development. Recent research has shown that dicalcium silicate cement (CSC) is bioactive and is a potential candidate for bone replacement. Traditionally, dicalcium silicate powder is synthesized by a solid state reaction or a sol-gel method. The solid-state reaction, however, usually needs a higher temperature and a longer calcination time. Furthermore, the dicalcium silicate powder made by the sol-gel method is not pure, and contains a significant quantity of CaO which is harmful to the strength and biological properties of the CSC. The Pechini technique is an alternative, low temperature polymeric precursor route for synthesis of high purity powders. In this study, purer CS powder was synthesized via the Pechini method by calcination at 800°C for 3h. DSC-TGA, XRD, SEM were used for characterization of CS powder and the hydrated cement. The DSC-TGA curves showed that the main exothermic peak was at 479°C and the total mass loss was 79.2%. The XRD patterns of CSC after hydration for 7, 14, and 35 days illustrated that dicalcium silicate hydrate (Ca_1.5SiO_3.5·xH₂O, C-S-H) was formed in the hardened CS paste. The XRD peaks on the diffraction pattern of the C-S-H of the day 35 sample were of greater intensity than those at day 7 and day 14. This demonstrates that the hydration speed was slow and complete hydration could take more than one month. Flake-like crystals were observed on scanning electron micrographs following hardening. The degradation study result showed that there was no mass loss of CSC after the samples were soaked into phosphate buffered saline (PBS) for 40 days. The silicon assay revealed that orthosilicic acid could be released from CSC after the samples were soaked in simulated body fluid (SBF). Silicon is known to be critical to skeletal mineralization. The existence of silicon may stimulate the proliferation of bone and activate cells to produce bone. Investigation of cell attachment confirmed that the MC-3T3 cells attached well to the surfaces of CSC after seeding.

Abstract: In this study, modification of the anodizing titanium substrate surface will be used to prepare titanium oxide films that have a porous structure. A Ru-Ir-Ti/Ti anode oxide coating was prepared by the Pechini method. The microstructure of the coating is observed by scanning electronic microscope (SEM). The phase of the coating is analyzed by X-ray diffraction. The electrochemical properties of the coating are studied by Energy Dispersive X-ray (EDX) and the tests of polarization curves, cyclic voltammetry and strengthen electrolysis life. The results show that titanium oxide film prepared by anodic oxidation owns porous morphology and the chlorine release of the anode coating is less active, while the electro-catalytic activity of this coating is slightly better than non-anodized anodic coating. Its strengthening electrolysis life is also poor.

Abstract: TiN intermediate layer was prepared by heating treatment of titanium plates under N₂ flow at 800°C, and the Ru-Ir-Ti/Ti oxide coating anodes were prepared by pechini method based on the as-prepared Ti/TiN substrate. The properties of the Ru-Ir-Ti/Ti coating anodes with and without TiN intermediate layer, such as microstructure, chlorine evolution, cyclic voltammetry and accelerated life test were investigated. The results show that the method of surface nitriding on titanium-based has not a significant impact on the chlorine evolution and catalytic activity, but has a certain role in the improvement of the anodic accelerated life.

Abstract: Because of the unique properties that the system TiO2-ZrO2 has, this system has attracted great interest in catalytic circles. In general, the TiO2-ZrO2 oxides composites have a greater surface area and a stronger acidity when compared to the single oxide and they are used as catalysts supports for many catalytic reactions. This work is to evaluate the effect of calcined temperature in structural and morphological characteristics of Ti_1-xZr_xO₂ nanopowders obtained by Pechini method. For this study, the doping value was 0.25 moles of Zr. The powders were calcined at temperature of 500 to 900°C for one hour. The powders were characterized by XRD, SEM and BET. The X-ray diffraction showed that the powders present a TiO₂ anatase phase and another of ZrO₂ tetragonal. The crystallite size ranged from 4.8 to 14.6 nm for the temperature of 500 to 900°C, respectively. The analysis of scanning electron microscopy showed soft homogeneous agglomerates with particles around 100 nm. The main particles sizes by BET were ranged from 10 to 20 nm, showing that the synthesis is effective to obtain nanometric powders.

Abstract: In this paper we propose the stabilization of zirconium oxide with controlled additions of a rare earth elements concentrate, in the system ZrO2: ƞ wt% Re2O3 (with ƞ=5.36, 10.47, 13.74, 16.91 e 20) where Re₂O₃ is a rare earth elements concentrate composed mainly of 76.88% of yttrium oxide, 12.1% of Dysprosium oxide, 4.04% of Erbium oxide and 1.94% of Holmium oxide. The synthesis method used was the Pechini method. The results show that additions of 5.36 and 20 wt% of the concentrate are enough to stabilize the tetragonal and cubic zirconia phases respectively, and that zirconium oxide polymorphs can coexist with additions within these limit. In the characterization of the obtained powders are presented and discussed the following results: differential scanning calorimetry, transmission electron microscopy and X-ray diffraction. Also, it was necessary to make analysis by Rietveld refinement because they had severe overlap in the diffraction peaks. One of the most relevant results is obtaining a raw material, cheap to be used in many technological applications.

Abstract: This aim of this work is to evaluate the influence of citric acid/metallic cation ratio of 3:1, 4:1 and 5:1 used in the TiO₂ synthesis by Pechini method in the structure, morphology and photocatalytic activity of methyl red dye. The prepared samples were characterized by X-ray Diffraction (XRD) using Rietveld refinement method, textural analyses, and photocatalytic activity. The results obtained by XRD technique confirm the efficiency of the Pechini method in the preparation of TiO₂ samples with nanosize particle. All samples present anatase phase and presence of rutile as secondary phase with content of 15.6, 10.5 and 18.3%. The isothermal adsorption showed that samples have mesopores characteristics and morphology with irregular shape agglomerates. The sample 4:1 presented better photocatalytic performance discoloring 70% of dye in 24h, indicating that the presence of 10.5% of rutile phase jointly with anatase phase improve the photocatalytic activity.

Abstract: The microstructures of solid electrolytes play an important role in the level of ionic conductivity of these materials. Thus join the mechanical properties of partially stabilized tetragonal phase and the ionic conductivity displayed by the large area of the grain boundaries of polycrystalline zirconia nanometric is an advantage. The objective of this work is to study the densification of ultrafine particles of yttria stabilized zirconia in the tetragonal phase (Y-TSZ) obtained by chemical routes using the unconventional method of sintering the Two Steps Sintering (TSS). The nanocrystalline powders Y-TSZ (4.5 mol%) were prepared by Pechini method and were characterized by X-ray diffraction and scanning electronic microscopy (SEM). The powders were pressed and sintered per TSS. The density of sintered samples was measured by Archimedes method, the crystalline structure was determinate by X-ray diffraction and the grain size and microstructure were observed by SEM. The TSS prevented the grain growth keeping your submicrometer grain size.

Abstract: The anodes of RuO₂-IrO₂-TiO₂/Ti were prepared by Pechini method. The surface morphology and electrocatalytic capability of anodes were studied by SEM, EDX, XRD, polarization curve, cyclic voltammetry curve and accelerated life test. It has been shown that the anodes have uniform surface composition, and the surface density of the anodes were increased as the sintering temperature increased, some active elements were crystallization grains at the surface of the anode when sintering temperature ≥500°C. The chlorine evolution capability of anode had a tendency to increase firstly then fall down afterwards as the sintering temperature increased. But the electrocatalytic capability of anodes showed an opposite tendency. The RuO₂-IrO₂-TiO₂/Ti anode prepared at 500°C presents the longest service life.

Abstract: Titanium substrate was etched by oxalic acid and hydrochloric acid respectively. Then the anodes of RuO₂-IrO₂-TiO₂/Ti were prepared by Pechini method. The surface morphology of anodes was studied with SEM, EDX and XRD. The electrocatalytic capability of anodes was studied by polarization curve and cyclic voltammetry curve. The effect of Acid etching process on anode life was studied by accelerated life test. The results show that there was an obvious effect of acid etching on surface morphology of the anodes. The result indicates that the anode with hydrochloric acid etching have the better electrocatalytic capability and accelerated life.