Papers by Keyword: Pechini Method

Abstract: Industrial applications of partially stabilized zirconia (PSZ) has increased substantially recently, considering its excellent thermal stability, strength and ionic conductibility. Its main application includes oxygen sensors and fuel cells. In this work zirconia ceramic powder is produced by Pechini process, mixing citric acid and ethylene glycol, adding yttrium and zirconium precursors. All the process was carried out with complete agitation. The obtained powder after this procedure is heat treated at 650°C during two hours. Characterization was performed by infra-red spectroscopy, x-ray diffractometry and quantitative analysis by Rietveld Method. The results show tetragonal and monoclinic phases, with nanometric crystallite.

Abstract: In recent years, scientific research showed an increasing interest in the field of nanotechnology, resulting in several techniques for the production of nanoparticles, such as methods of chemical synthesis. Among the various existing methods, the Pechini method has been used to obtain nanoparticles of titanium dioxide (TiO2). Thus, this work aims to synthesize and characterize nanoparticles of TiO2 obtained by this method. The technique constitutes in the reaction between citric acid with titanium isopropoxide, resulting as the product the titanium citrate. With the addition of the ethylene glycol polymerization occurs, resulting in a polymeric resin. At the end of the process, the resin is calcined to remove organic matter, creating nanoparticles of TiO2. The resulting powders were characterized by thermogravimetric analysis (TGA) and thermal differential analysis (DTA), X-ray diffraction, absorption spectrophotometry in the infrared, method of adsorption nitrogen / helium (BET method) and scanning electron microscopy. The results obtained in the characterization techniques showed that the Pechini method is promising in obtaining nanosized TiO2.

Abstract: Pb(Zr0.95Ti0.05)O3 powders were prepared by one-step pyrolysis process from non-aqueous Pechini method. Porous Pb(Zr0.95Ti0.05)O3 ceramics were obtained by sintering the chemically prepared powders and the grain growth in the porous ceramics was investigated. For the powders calcined at 450 °C for 10 h by one-step pyrolysis process, the grain growth exponent value was observed to be 3.3 while the apparent activation energy was 193 kJ/mol.

Abstract: Diluted magnetic semiconductors (DMS), which have both semiconducting and magnetic properties, are those in which transitions metal ions substitute cations of host semiconductor materials [1]. There is a great interest for DMS for use as the material of spintronics. In this study is reported the structural and morphologic characterization of Zn1.95Co0.05O nanoparticles obtained by Pechini method and combustion reaction. The powders resulting were characterized by X-ray diffraction (XRD) for determination of the phases, crystalline phase and lattice parameter; nitrogen adsorption by BET for determination of the specific superficial area and calculation the particle size from the superficial area and scanning electron microscopy (SEM) for morphologic analysis. The XRD results demonstrated the viability of obtaining crystalline and nanosize powders by the both synthesis routes. For all samples the average crystallite sizes was nanosized, but the powders obtained by reaction combustion is smaller. The SEM micrographs shows that the powders obtained for both syntheses are constituted of soft agglomerates.

Abstract: To adjust the morphology and crystallinity of the chemically prepared Zr-riched` lead zirconate titanate (Pb(Zr0.95Ti0.05)O3) powders, polyethylene glycol (PEG 20000) was used in aqueous solution (modified Pechini method). Thermal analysis of the as-synthesized gel showed two distinct stages, which indicates the volatilization of water and the decomposition of polymers, respectively. When the gel were calcined at 400 oC, the powders consisted mainly of perovskite PZT accompanied with small amounts of secondary phases. The higher the calcination temperature applied, the stronger the intensity of XRD, which means the crystallinity were improved. Scanning electron microscopy of as-prepared powders suggested that the powders were soft agglomerate particles when calcined at 600 to 800 oC. Compared with the normal Pechini method, PEG could help the formation of crystalline phase and soft agglomerate. When the powders compacts were sintered at 975 to 1125 oC, high pure (>99.5%) of tetragonal phase ceramics were got having relative density of 85% to 94%.

Abstract: The modified polymeric precursor method (Pechini method) was successfully used for the preparation of epitaxial and polycrystalline ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) thin films. Films were deposited on LaNiO3 (LNO) – coated silicium (1 0 0) and platinum substrates (Pt (1 1 1)/Ti/SiO2/Si) by spin coating technique. LNO electrodes were also prepared by the Pechini method and treated under different thermal treatment conditions to obtain films with different structural and microstructural properties. Investigation of PZT microstructure was performed as a function of orientation and morphology of the bottom electrode, as well as of thermal treatment conditions. Grain size and morphology were analyzed by AFM, while the quality and orientation of PZT films were determined by GIXRD analysis. It has been found that the proposed thermal treatment on a hot plate, with slow heating rate and long annealing time, can result in the formation of epitaxial PZT films on Si and LNO-coated Si substrates.

Abstract: In this work pure and doped LMO were prepared using modified Pechini method from lanthanum and manganese citrates. Lanthanum citrate was prepared starting from La2O3, while manganese citrate was prepared from Mn(NO3)2. Valence state of the manganese was controlled by adjusting pH value of the solution and confirmed by EPR and UV/VIS analysis. Thermal treatment conditions for preparation of LMO powders were determined from TG/DTA of dried precursors. XRD results confirmed that pure perovskite phase was successfully prepared in single LMO and Cadoped LMO. SEM and measurements of specific surface area of the powders showed the existence of large agglomerates consisting of submicronic primary particles.

Abstract: The characteristics of La0.8Sr0.05Ca0.15CrO3 interconnect material synthesized by modified pechini method, USP, and GNP was investigated. The powder synthesized by Pechini method exhibited somewhat aggregated shape. The precursor synthesized by USP had spherical shape and their particle size decreased somewhat after calcining procedure at 1000oC. In the case of GNP, the precursor formed agglomerated particles. The average particle size of powders synthesized by Pechini method, USP, and GNP were 0.4+m, 0.6+m, and below 10nm, respectively. The La0.8Sr0.05Ca0.15CrO3 powder had a single perovskite phase and orthorhombic structure. After sintering at 1400oC and 1500oC, the relative density of samples synthesized by pechini method was approximately 95% and that of samples synthesized by USP was slightly small. However, that of the samples synthesized by GNP was approximately 92%.

Abstract: Lithium niobate thin films have been deposited on Pt/Ti/SiO2/Si substrates by the Pechini method from metal carboxylate gels and heat-treated at temperatures ranging from 400 to 600°C. The thermal decomposition of the metal carboxylate precursor gels has been studied by differential thermal analysis and thermogravimetry. The products derived from calcination of the gels at different temperatures have been characterized by Fourier transform infrared, Roman spectrum and X-ray diffraction. Scanning electron microscopy analysis shows the surface of the films to be smooth, dense and crack-free. Electric properties measurement indicates that the LiNbO3 films demonstrate a ferroelectric hysteresis loop. The remanent polarization (Pr) and coercive field (Ec) are 17.89 μC/cm2 and 35.23 kV/cm, respectively.

Abstract: Conventional methods to obtain ceramic powders are inadequate for many technological applications because these powders react but slightly to sinterization, displaying weak reproducibility, nonhomogeneity and imprecise stoichiometric control of cations. Better results can be obtained by chemical synthesis because the powder retains its homogeneity on the atomic scale and may be calcined at low temperatures, yielding fine particulate oxides whose chemistry can be precisely controlled. Therefore, the objective of this work was to obtain the NiAl2O4 phase by the Pechini and combustion reaction methods, and comparatively analyze how these two synthesization methods affect the characteristics of the resulting powder, which was characterized by DRX, MEV and BET. The results revealed that both methods yield nanometric and crystalline NiAl2O4 powder having homogenous particle sizes and shapes. The powder obtained by the Pechini method exhibited agglomerate sizes 60% smaller than those obtained by combustion reaction.