Mechanism of the formation and properties of antimony polyphosphate

Formation of antimony polyphosphate using Sb2O3 and/or (NH4)2HPO4 and NH4H 2PO4 as starting materials has been simulated by thermal analysis technique. The elimination of water and ammonia molecules induced by heating leads to the formation of intermediate ammonium polyphosphate, which subsequently reacts with Sb2O3. Morphologically, vitreous Sb(PO3)3 is composed of plaques having irregular shapes. Infrared spectra and NMR study is consistent with tetrametaphosphate anion arrangement. The compound is thermally unstable and may be recommended as a donor of -O-P-O- linkers in the preparation of special phosphate glasses. © 2005 Akadémiai Kiadó, Budapest.

Uso de métodos químicos para obtener polvos cerámicos del sistema (Sn, Ti)O2

The (Sn,Ti)O2, system has a great interest due to its technological applications such as gas sensor and varistor. Although the thermodynamic properties and the kinetics of spinoidal decomposition in this system have been extensively studied, the general properties and applications of SnO2 - TiO2 binary compositions have been not investigated yet in depth. On the other hand, little work has been done to optimize the synthesis methods to obtain (Sn,Ti)O2 cerallmic powders, with pre - determinate physical and chemical characteristics. In this work the ceramic powders has been obtained by coprecipitation and polymeric precursor (Pechini) methods. The different physical chemistry phenomena that occurred during the synthesis were discussed. The (Sn,Ti)O2, ceramic powders were characterized with X- ray diffraction (XRD), thermal analysis (DTA/TG) and scanning electron microscopy (SEM). The knowledge about of steps and variables of synthesis process acquired with development of this work, we permited to obtain (Sn, Ti)O2, nanometers particles to low temperatures: to 450°C for coprecipitation method and to 600°C for Pechini method. The spinodal decomposition that ocurr to 900°C was discussed also.

Study of the thermo-mechanical and electrical properties of conducting composites containing natural rubber and carbon black

This work shows the preparation and characterization of composites obtained by mixing natural rubber (NR) and carbon black (CB) in different percentages aiming suitable mechanical properties, processability and electrical conductivity for future applications as transducers in pressure sensors. The composites NR/CB are characterized through dc conductivity, thermal analysis using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMA), thermogravimetry (TGA) and stress-strain test. The electrical conductivity changed from 10-9 to 10 Sm-1 depending on the percentage of CB in the composite. Besides, it was found a linear (and reversible) dependence of the conductivity on the applied pressure in the range from 0 to 1.6 MPa for the sample 80/20 (NR/CB wt%).

Análise térmica de esparfloxacino

Sparfloxacin, a third-generation fluoroquinolone, is a potent antibacterial agent against a wide range of Gram-positive and Gram-negative organisms, for example Streptococcus pneumonias, Staphylococcus aureus (including methicillin-resistant strains), Legionella spp., Mycoplasma spp., Chlamydia spp. and Mycobacterium spp. This compound has been submitted to thermal analysis and the results are presented here. The DSC curve of sparfloxacin has an endothermic peak that indicates a melting point at 276.5 °C. The DTA curve of the sample in synthetic air shows two exothermic peaks, at 341.6 and 579.2 °C, attributed to compound decomposition. In the TG curve, the loss of mass can be seen to occur in two steps between 285.5 and 645.3 °C. The DTA curve obtained in a nitrogen atmosphere shows an exothermic peak, with decomposition of sparfloxacin at 340.0 °C; from the corresponding TG plot, the loss of mass starts at 254.4 °C.

Thermoanalytical study of praziquantel-loaded PLGA nanoparticles

Polymeric nanoparticles have received great attention as potential controlled drug delivery systems. Biodegradable polymers has been extensively used in the development of these drug carriers, and the polyesters such as polylactic acid, polyglycolic acid and their copolymers as poly-lactide-co- glycolide are the most used, considering its biocompatibility and biodegradability. Thermal analysis techniques have been used for pharmaceutical substances for more than 30 years and are routine methods for screening drug-excipient interactions. The aim of this work is to use thermal analysis to characterize PLGA nanoparticles containing a hydrophobic drug, praziquantel. The results show that the drug is in an amorphous state or in disordered crystalline phase of molecular dispersion in the PLGA polymeric matrix and that the microencapsulation process did not interfere with the chemical structure of the polymer, mantaining the structural drug integrity.

Métodos químicos para obtener varistores basados en SnO2

Synthesis of SnO2 ceramic powders was made by coprecipitation method and polymeric precursor method (Pechini) to obtain Sn-Co-Nb-Ti-Al varistor systems. The particles of the obtained ceramic powder presented nanometric size and SnO2 was the principal crystalline phase in them according to X-ray diffraction results. To determine the behavior of the synthesized samples in front of the thermal treatments, thermal analysis (DTA/TG) were made. Dilatometric studies on previously pressed samples were carried out. The optimal conditions of sintering of this raw material were determined. Microstructures and electric properties of sintered samples were studied using scanning electron microscopy (SEM) and I-V characteristics curves. The samples presented varistor behavior independent of the synthesis method used, with high nonlinearity values as 32. The presence of Al3+ favored the concentration of oxygen vacancies, and the grain growth.

Martensite aging kinetics in the Cu-10 wt.%Al and Cu-10 wt.%Al-10 wt.%Ag alloys

The martensite aging kinetics in the Cu-10 wt.%Al and Cu-10 wt.%Al-10 wt.%Ag alloys was studied using microhardness measurements, classical differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and in-situ high-temperature X-ray diffractometry (XRD). The results for the Cu-10%Al alloy indicated a process dominated by the martensite ordering assisted by migration of quenched-in vacancies and followed by the consumption of the α phase. For the Cu-10%Al-10%Ag alloy the dominant process is the consumption of the α phase associated with a decrease in the ordering degree of the martensitic phase. © 2007 Springer Science+Business Media, LLC.

Application of non-isothermal cure kinetics on the interaction of poly(ethylene terephthalate) - Alkyd resin paints

Samples of paint (P), reused PET (PET-R) and paint/PET-R mixtures (PPET-R) were evaluated using DSC to verify their physical-chemical properties and thermal behavior. Films from paints and PPET-R are visually similar. It was possible to establish that the maximum amount of PET-R that can be added to paint without significantly altering its filming properties is 2%. The cure process (80-203°C) was identified through DSC curves. The kinetic parameters, activation energy (E a) and Arrhenius parameters (A) for the samples containing 0.5 to 1% of PET-R, were calculated using the Flynn-Wall-Ozawa isoconversional method. It was observed that for greater amounts of PET-R added, there is a decrease in the E a values for the cure process. A Kinetic compensation effect (KCE), represented by the equation InA=-2.70+0.31E a was observed for all the samples. The most suitable kinetic model to describe this cure process is the autocatalytic Šesták-Berggreen, model applied to heterogeneous systems. © 2007 Springer Science+Business Media, LLC.

Protocolo para ensaios físico-químicos de estabilidade de fitocosméticos

The growing demand for stable, safe and effective cosmetics has required increasingly complex studies by the scientific community and the use of more efficient techniques to determine the stability of these products. The use of active principles from the Brazilian flora has led to the development of numerous products, in the most varied pharmaceutical forms, making it, even more difficult to standardize experimental protocols to certify the stability of cosmetic preparations. While in Brazil there is no one protocol that standardizes the tests that should be carried out to determine product stability, several studies have been conducted in academic laboratories to determine the stability of specific raw materials. The rheological properties of topical use products have to be taken into account in their manufacture, storage and application. The determination of the rheological behavior of a formulation helps in evaluating the physicochemical nature of the vehicle, allowing early signs of physical instability to be detected and thus enabling quality control of the constituents, test formulations and final products. Thermal analysis has also been used to assist in the study of cosmetic stability and differential scanning calorimetry to guide the development of new products. Other tools, such as fluorimetry and laser granulometry can be used to help the study and development of both emulsified and non-emulsified systems. The aim of the present study is to develop a protocol for the investigation of the physical and chemical stability of phytocosmetics - systems containing active compounds extracted from the Brazilian biodiversity.

Estudo de metodologia analítica para a determinação do cetoconazol em formulações farmacêuticas

Ketoconazole is a synthetic broad-spectrum oral and topical antifungal drug derived from imidazole, effective in the treatment of superficial mycoses and systemic infections. In this study we have tested several methods to analyze ketoconazole in various pharmaceutical products containing this drug, employing techniques such as UV and IR spectrophotometry and thermal analysis. The results showed that UV spectrophotometry is a fast, practical and economical method and indicated that other methods, such as IR spectrophotometry and thermal analysis, could be good alternative methods for ketoconazole analysis in certain pharmaceutical forms.

Novel cellulose/NbOPO 4.nH 2O hybrid material from sugarcane bagasse

In recent years studies concerning the applications of lignocellulosic/ inorganic couples have resulted in the development of an interesting class of functional materials. In this work a cellulose/NbOPO 4.nH 2O hybrid using cellulose from surgacane bagasse was prepared and characterized in order to test for adsorption applications. The preparation process was conducted by carrying out metallic niobium dilution in hydrofluoric acid in the presence of nitric acid, then adding boric acid to form the complex and, finally, the cellulose sugar cane bagasse was added. Concentrated phosphoric acid was also inserted to precipitate hydrous niobium phosphate particles in the cellulose fiber. This material was characterized by X-ray diffractometry (XRD), thermogravimetry (TG/DTG), and scanning electronic microscopy (SEM) connected to an energy dispersive spectrophotometer (EDS). Results by SEM/EDS show that NbOPO 4.nH 2O was present in structure of the cellulose. During the preparation of the material, using boric acid it was observed that the formation of precipitate occurred in a shorter time than the material prepared without boric acid.

Methodology for DSC calibration in high heating rates

Despite the large use of differential scanning calorimetry (DSC) technique in advanced polymer materials characterization, the new methodology called DSC in high heating rates was developed. The heating rate during conventional DSC experiments varying from 10 to 20°C.min-1, sample mass from 10 to 15mg and standard aluminum sample pan weighting, approximately, 27mg. In order to contribute to a better comprehension of DSC behavior in different heating rates, this work correlates as high heating rate influences to the thermal events in DSC experiments. Samples of metallic standard (In, Pb, Sn and Zn) with masses varying from 0.570mg to 20.9mg were analyzed in multiples sample heating rate from 4 to 324°C. min-1. In order to make properly all those experiments, a precise and careful temperature and enthalpy calibrations were performed and deeply discussed. Thus, this work shows a DSC methodology able to generate good and reliable results on experiments under any researcher choice heating rates to characterize the advanced materials used, for example, for aerospace industry. Also it helps the DSC users to find in their available instruments, already installed, a better and more accurate DSC test results, improving in just one shot the analysis sensitivity and resolution. Polypropylene melting and enthalpy thermal events are also studied using both the conventional DSC method and high heating rate method.

Glass-ceramic material from the SiO 2-Al 2O 3-CaO system using sugar-cane bagasse ash (SCBA)

Brazil is the world's largest producer of alcohol and sugar from sugarcane. Currently, sugarcane bagasse is burned in boilers to produce steam and electrical energy, producing a huge volume of ash. The major component of the ash is SiO 2, and among the minor components there are some mineralizing agents or fluxing. Published works have shown the potential of transforming silicate-based residues into glass-ceramic products of great utility. This work reports the research results of SCBA use to produce glass-ceramics with wollastonite, rankinite and gehlenite as the major phases. These silicates have important applications as building industry materials, principally wollastonite, due to their special properties: high resistance to weathering, zero water absorption, and hardness among others. The glasses (frits) were prepared mixing ash, calcium carbonate and sodium or potassium carbonates as flux agents, in different concentrations. X-ray fluorescence was used to determine the chemical composition of the glasses and their crystallization was assessed by using thermal analysis (DTA/DSC/TGA) and X-ray diffraction. The crystallization kinetics was evaluated using the Kissinger method, giving activation energies ranging from 200 to 600 kJ/mol. © 2011 Ceramic Society of Japan.

Blends of cross-linked high amylose starch/pectin loaded with diclofenac

Polymers blends represent an important approach to obtain materials with modulated properties to reach different and desired properties in designing drug delivery systems in order to fulfill therapeutic needs. The aim of this work was to evaluate the influence of drug loading and polymer ratio on the physicochemical properties of microparticles of cross-linked high amylose starch-pectin blends loaded with diclofenac for further application in controlled drug delivery systems. Thermal analysis and X-ray diffractograms evidenced the occurrence of drug-polymer interactions and the former pointed also to an increase in thermal stability due to drug loading. The rheological properties demonstrated that drug loading resulted in formation of weaker gels while the increase of pectin ratio contributes to origin stronger structures. © 2012 Elsevier Ltd.

High-density nanoparticle ceramic bodies: A study of heating rates in the sinterization of Gadolinium-doped Ceria

An investigation on the sinterization of Gd:CeO2 (Ce 0.85Gd0.15O1.9-δ ceramic system) 3-10 nm nanoparticles in pressed bodies was done. The heating rate was taken as a key parameter and two competing sinterization processes were identified, associated with different diffusional mechanisms. Using heating rates of 113 C min -1, a high-final density (98 % of the theoretical) was obtained by superposing the two aforementioned mechanisms, resulting in a homogeneous microstructure at lower temperatures. © 2012 Akadémiai Kiadó, Budapest, Hungary.