Particle growth during calcination of polycation oxides synthesized by the polymeric precursors method

The particle-growth kinetics of sodium niobate and zirconium titanate powders that were processed by the polymeric precursors method were studied. The growth kinetics that were studied for the particle, in the final stage of crystallization, showed that the growth process occurs in two different stages. For temperatures <800°C, the particle-growth mechanism is associated with surface diffusion, with an activation energy in the range of 40-80 KJ/mol. For temprratures >800°C, particle growth is controlled by densification of the nanometric particle cluster and by a neck-size-controlled particle-growth mechanism. The results suggest that this behavior was typical of the synthesis method, because two different polycation oxides presented the same behavior.

LiNbO3 thin films prepared from a polymeric precursor method

LiNbO3 thin films were prepared from polymeric precursor method by dip coating. The precursor films, deposited on Si(111) substrates, were heat-treated from 400°C to 900°C in order to study the heat treatment influence on the crystallinity and microstructure of the final film. The X-ray diffraction patterns showed, in particular, that these films crystallize at low temperature (450°C) and present no preferential orientation. The scanning electron microscopy studies showed that the film microstructure is strongly influenced by the annealing temperature. © 1997 Trans Tech Publications.

Influence of heat treatment on LiNbO3 thin films prepared on Si(111) by the polymeric precursor method

The effects of heat-treatment temperature on LiNbO3 thin films prepared by the polymeric precursor method were investigated. The precursor solution was deposited on Si(111) substrates by dip coating. X-ray diffraction and thermal analyses revealed that the crystallization process occurred at a low temperature (420 °C) and led to films with no preferential orientation. High-temperature treatments promoted formation of the LiNb3O8 phase. Scanning electron microscopy, coupled with energy dispersive spectroscopy analyses, showed that the treatment temperature also affected the film microstructure. The surface texture - homogeneous, smooth, and pore-free at low temperature - turned into an `islandlike' microstructure for high-temperature treatments.

Effect of thermal treatment on the morphology of PLZT thin films prepared from polymeric precursor method

Lead lanthanum zirconate titanate (PLZT) thin films with (9/65/35) stoichiometry were prepared by dip coating from polymeric precursor method. The films deposited on silicon (100) substrates, were thermally treated from 450° to 700°C for 6 hours in order to study the influence of thermal treatment on the crystallinity, microstructure, grain size and roughness of the final film. X-ray diffraction results showed that PLZT phase crystallizes at low temperature (500°C) and present preferential orientation. It was observed by scanning electron microscopy (SEM) that it is possible to obtain dense thin films at temperatures around 650°C. The atomic force microscopy (AFM) studies showed that the grain size and roughness are strongly influenced by the annealing temperature.

Structure and properties of donor doped barium titanate prepared by citrate process

Niobium doped barium titanate was prepared using two procedures. First, doped barium titanate was prepared starting from citrate solutions of all components and second, pure barium titanate powder was obtained from the citrate solutions and after that doped. Besides niobium, a small amount of manganese, as acceptor dopant was added. Phase composition, crystal structure, microstructure and dielectric properties were reported. The influence of powder processing on the properties of niobium doped barium titanate was analysed. The grain growth and the concentration of dopants on the dielectric properties were considered. © 2002 Taylor & Francis.

Influence of oxygen flow on crystallization and morphology of LiNbO 3 thin films

Polymeric precursor solution (Pechini method) was used to deposit LiNbO 3 thin films by spin-coating on (100) silicon substrates. X-ray diffraction data of thin films showed that the increase of oxygen flow promotes a preferred orientation of (001) LiNbO 3 planes parallel to the substrate surface. Surface roughness and grain size, observed by atomic force microscopy, change also with oxygen flow. © 2002 Taylor & Francis.

Acrylonitrile-butadiene-styrene toughened nylon 6: The influences of compatibilizer on morphology and impact properties

Polymer alloys have been used as an alternative to obtain polymeric materials with unique physical properties. Generally, the polymer mixture is incompatible, which makes it necessary to use a compatibilizer to improve the interracial adhesion. Nylon 6 (PA6) is an attractive polymer to use in engineering applications, but it has processing instability and relatively low notched impact strength. In this study, the acrylonitrile-butadiene-styrene (ABS) triblock copolymer was used as an impact modifier for PA6. Poly(methyl methacrylate-co-maleic anyhydride) (MMA-MA) and poly(methyl methacrylate-co-maleic methacrylate) (MMA-GMA) were used as compatibilizers for this blend. The morphology and impact strength of the blends were evaluated as a function of blend composition and the presence of compatibilizers. The blends compatibilized with maleated copolymer exhibited an impact strength up to 800 J/m and a morphology with ABS domains more efi8ciently dispersed. Moderate amounts of MA functionality in the compatibilizer (∼5%) and small amounts of compatibilizer in the blend (∼5%) appear sufficient to improve the impact properties and ABS dispersion. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87.

Effect of magnesium on the properties of LiNbO 3 thin films prepared from polymeric precursors

The effect of magnesium addition on the phase formation, microstructure and electric and ferroelectric properties of LiNbO 3 thin films prepared through polymeric precursors was analyzed. By X ray diffraction no secondary phase was observed with the increase of magnesium concentration. Comparing to pure LiNbO 3, the addition of 0.5 and 1.0 mol% of Mg +2 increased of the dielectric constant, while 2.0 mol% decreased it. It was noticed that the increase in additive concentration decreases the ferroelectric remanent polarization and increases the coercive field. © 2002 Taylor & Francis.

Microstructure of doped barium titanate prepared from polymeric precursors

Barium titanate is used extensively as a dielectric in ceramic capacitors, particularly due to its high dielectric constant and low dielectric loss characteristics. It can be made semiconducting by addition of certain dopants and by proper modification of grains and grain boundary properties obtaining very interesting characteristics for various applications. The synthesis method and sintering regime have a strong influence on properties of obtained barium titanate ceramics. Doped barium titanate was prepared with Nb+5 and Y+3 ions as donor dopants, and with Mn+2 ions as acceptor dopant by polymeric precursors method. By this procedure nanosized powders were obtained after calcination. Sintering was performed in the temperature range of 1290°C to 1380°C The microstructure of doped BaTiO3 was performed using scanning electron microscopy. The influence of dopants and sintering temperature on grain size was analysed.

Production and preservation of fresh-cut 'Tommy Atkins' mango chunks

During the 1999/00 and 2000/01 seasons, sliced 'Tommy Atkins' mangoes were packaged with three different types of polymeric films; polypropylene (PP) cups, low-density polyethylene (LPDE) bags or polyethylene terephthalate (PET) clamshell trays, and stored at 3°C for 2 weeks. The mango chunks were evaluated for flavor, appearance, colour, total soluble solids (TSS), total titratable acidity (TTA), ascorbic acid (AA) contents, O2 and CO 2 concentration in the packages, as well as respiration. Shelf life based on visual appearance was 14 days, with the products showing good appearance and agreeable aroma. The TTA content in chunks packaged in PP cups or PET trays were reduced during the storage, and with the color changing from light yellow to dark yellow. The chunks respiration in PP cups or LPDE bags were 64.6 and 87.9 mL CO2.kg-1.h-1, and in PP cups or PET trays were 45.86 and 43.92 mL CO2.kg-1.h -1, respectively for 1999/00 and 2000/01 seasons. The percentages of O2 and CO2 in the packages were stabilized after 2-4 hours, and the atmosphere had 11-17% and 1-10% of them. The microbiological content was lower than the allowed. No differences were observed between the seasons, and the best packages were the cups.

Temperature and stoichiometry effect on microstructural and ferroelectric properties of Pb(Zr1-xTix)O3 thin films prepared by chemical soulution deposition

Lead zirconate titanate (PZT) solutions were prepared using a polymeric precursor method, Zr n-propoxide and Ti i-propoxide were used as starting materials with ethylene glycol and water as solvents. The PZT solution was spin-coated on Pt/Ti/SiO2/Si substrates, baked on a hot plate, and finally heat-treated in a tube furnace between 400 and 800°C. The surface morphology and grain size of the films were characterized by atomic force microscopy (AFM), using a tapping mode with amplitude modulation. The films, thermal annealed at temperatures higher than 500°C, exhibited a dense microstructure, without noticeable cracks or voids. Electrical properties were investigated as a function of composition and annealing temperature.

Dielectric and ferroelectric properties of PZT and PT thin films for saw sensors applications

It is very important for the building of the SAW devices to study dielectric and ferroelectrics properties because every SAW device is based in piezoelectric effect that it is made up to transform an electric sign in the mechanical or acoustic sign and a mechanical or acoustic sign in an electric sign. Thus, the purpose of the present work is to prepare PbZr 0,53Ti0.47O3 (PZT) and PbTiO3 (PT) thin films on the Si (100) substrates across spin-coating using a chemical method based in polymeric precursors. After conventional treatment in the furnace, the films were characterized by impedance spectroscopy and hysteresis loops to know its dielectric and ferroelectric properties.

Morphological, mechanical and thermal properties of nylon 6/ABS blends using glycidyl methacrylate-methyl methacrylate copolymers

Nylon6 is an attractive polymer for engineering applications because it has reactive functionality through amine and carboxyl end groups that are capable of reacting. For this reason, it has been used a lot in polymeric blends. Blends of nylon6/ABS (acrylonitrile-butadiene-styrene) were produced using glycidyl methacrylate-methyl methacrylate (GMA-MMA) copolymers as compatibilizer. The binary blends were immiscible and exhibited poor mechanical properties that stemmed from the unfavorable interactions among their molecular segments. This produced an unstable coarse phase morphology and weak interfaces between the phases in the solid state. The presence of the copolymer in the blends clearly led to a more efficient dispersion of the ABS phase and consequently optimized Izod impact properties. However, the compatibilized blend showed poor toughness at room temperature and failed in a brittle manner at subambient temperatures. © 2005 Springer Science + Business Media, Inc.

Preparation of lanthanum doped Bi4Ti3O12 ceramics by the polymeric precursor method

Lanthanum-modified bismuth titanate, Bi4 - xLaxTi3O12 (BLT) ceramics, with x ranging from 0 to 0.75 were prepared by the polymeric precursor method. Orthorhombicity of the system is decreased with the increase of lanthanum content in the bismuth titanate (BIT) crystal lattice. No secondary phases were evident after lanthanum addition. Increasing lanthanum content causes a structural distortion in the bismuth titanate lattice. The shape of the grains is strongly influenced by the lanthanum added to the system. © 2005 Elsevier B.V. All rights reserved.

Electrical devices obtained from polymeric precursors process

Nowadays, many investments have been made in the area of superconductor materials, with the aim to improve their potential technological applications. Applications on the energy transport using cables, to get high resolution images in the medicine use high magnetic fields, high speed signals use superconductor devices all of them are in crescent evidence and they are showing that the future is coming and next for this new kind of materials. Obviously that everything of this is possible due to the increasing of research with new materials, where the synthesis, characterization and applications are of the mainly objective of these researches. The production of cable for the energy transport has been in advanced stage as the bulks production is too. However, the film production that to aim at the electronic devices area is not as developed or it still need expensive investments. Thinking about that, we are developing a research where we may increase the relation of cost/benefits. Thereby, we are applying the polymeric precursors method to obtain films that will be used in the built of electronic devices. Thin films (mono and multilayers, on crystalline or metallic substrates, controlled thickness) of the BSCCO system have been obtained from dip coating deposition process with excellent results in terms of preferential orientation, controlled thickness, a large area, which may indicate future applications. Based on these results, we present an electrical circuit and their principal characteristics as superconductor transition (85K), transport current density and structure. DC four probes method, scanning electron microscopy, digital optical microscopy and X-ray diffractometry were some techniques used for the characterization of this superconductor electric device. © 2006 Materials Research Society.