Estudo das condições de estocagem do bagaço de cana-de-açúcar por análise térmica

An evaluation was made of the properties of sugarcane bagasse during the storage process for subsequent burning in a boiler. Samples of bagasse were collected over a period of 150 days from the Caeté sugar mill (MG) at various points of the stockpile soon after the sugarcane was pressed to extract its juice, as well as from natural bagasse, dry and damp. Thermal analyses of the samples were carried out and the results indicated that, during the storage of bagasse, dry or damp, the biomass loses up to 32% of its calorific power, due to decomposition of the hemicellulose.

Análise térmica aplicada a fármacos e formulações farmacêuticas na indústria farmacêutica

Several matters of the pharmaceutical demonstrate the great importance of thermal analysis application, especially TG and DSC for the pharmaceutical industry future, namely: characterization of the drugs with the thermal events definition, in studies of drug purity, in the polymorphs identification, in compatibility studies of solid dosage pharmaceutical formulations, in drugs and pharmaceutical formulations thermal stability, and in determination of shelf life for isothermal degradation kinetics by extrapolation using the Arrhenius equation. Thus, the test results obtained from thermal analysis are directly related to the quality of a pharmaceutical product, whether the stability or bioavailability of the pharmaceutical product.

Avaliação dos efeitos do ultrassom terapêutico sobre a cafeína e verificação da liberação em sistema de difusão vertical

Currently, the physiotherapists use the phonoforesis, which consists in the therapeutical ultrasound (US) used to increase the drug molecules migration through the skin, however, the US can shows oxidative effects, and is used, for example, in chemical reactions acceleration. The present study aimed to perform the electrochemical evaluation and the diffusion investigation of gel/caffeine 5% solutions submitted to therapeutical US (continuous mode, 1.0 W cm-2 and 1 MHz). It this study, it has been verified diffusion increase and a possible oxidation of the caffeine molecules, when subjected to therapeutical US.

Efeitos da história térmica nas propriedades do polímero pet: um experimento para ensino de análise térmica

Polyethilenetherephtalate (PET) is commonly used in manufacturing of beverage bottles representing a didactic appeal in thermal analysis education due to its presence in the student's day life. Additionally such polymer presents well defined thermal analytical curves and a well known thermal behavior. TGA curve is used to present the thermal stability. The thermal history effects in the thermal properties of a PET sample from a soft drink bottle are used to demonstrate the effect of different heating/cooling conditions on glass transition, melting, crystallization and crystalline degree using DSC curves.

O efeito da desativação térmica nas propriedades oxirredutoras e na atividade catalítica de catalisadores CZ e Pd-CZ

Automotive catalyst, using in Brazil since 1992, is a essential technology for vehicular emissions control. Noble metals are the active phase of these catalysts, and cerium zirconium mixed oxides (CZ), responsibles for the oxygen storage capacity (OSC), one of the most important aspect for the operational performance of the catalyst. In this context, the oxireduction properties analysis of CZ and Pd/CZ (palladium supported in CZ) system are the objective of this study, as well as, the impact of the thermal aging in the OSC. Aging consisted of treatments at 900 or 1200 °C, for 12 or 36 h, in oxidizing condition.

Coeficientes de difusão de metais em materiais não convencionais (agarose e acetato de celulose) usados na técnica de difusão em filmes finos por gradientes de concentração

The DGT technique allows one to measure quantitatively free and labile metal species in aquatic systems. Nevertheless, for this approach, knowledge is required of the diffusion coefficients of the analytes in a diffusive layer. In this study, the diffusion coefficients of Hg(II), As(III), Mn(II), Mg(II), Cu(II), Cd(II) were determined in agarose gel and those of Ba(II), Cd(II), Cu(II), Mg(II), Mn(II) e Zn(II) in cellulose acetate membranes. These materials presented good performance and the reported results can be used as a data base for further DGT studies.

Desenvolvimento e uso do compósito de Nb2O5|Cu como revestimento aplicado por aspersão térmica sobre o aço AISI 1020 para proteção contra a corrosão pelo solo em estruturas enterradas

An Nb2O|Cu corrosion-resistant coating was developed and applied onto AISI 1020 steel substrate by Powder Flame Spray. A galvanostatic electrochemical technique was employed, with and without ohmic drop, in four different soils (two corrosively aggressive and two less aggressive). Behavior of coatings in different soils was compared using a cathodic hydrogen reduction reaction (equilibrium potential, overvoltage and exchange current density) focusing on the effect of ohmic drop. Results allow recommendation of Nb2O5|Cu composite for use in buried structure protection.

Desenvolvimento e avaliação de eletrodos de difusão gasosa (EDG) para geração de H2O2 in situ e sua aplicação na degradação do corante reativo azul 19

This work reports the development of GDE for electrogeneration of H2O2 and their application in the degradation process of Reactive Blue 19 dye. GDE produced by carbon black with 20% polytetrafluoroethylene generated up to 500 mg L-1 of H2O2 through the electrolysis of acidic medium at -0.8 V vs Ag/AgCl. Reactive Blue 19 dye was degraded most efficiently with H2O2 electrogenerated in the presence of Fe(II) ions, leading to removal of 95% of the original color and 39% of TOC at -0.8 V vs Ag/AgCl.

Estudo comparativo entre as metodologias eschka, infravermelho, condutividade térmica (TCD) e ultravioleta para a determinação de enxofre total em combustíveis sólidos

The oxidation of sulphur compounds upon burning emits large quantities of SOx into the atmosphere. Therefore, there is growing interest in fast and accurate methods for analyzing sulphur content in fuels. The objective of this work was to compare four different methods of total sulphur determination in solid fuels. The methods used in this work were Eschka, Infrared, Thermal Conductivity Detection (TCD) and Ultraviolet Fluorescence Detection (UV). The preliminary results showed that TCD and UV methods (nonstandard methods for solid fuels) have similar precision to the infrared method (standard method) for high-sulphur coal samples.

Comportamento eletroquímico e avaliação da difusão in vitro do α-tocoferol associado à iontoforese

Iontophoresis is a method of administering substances through the skin, which uses electrical current or potential to promote transdermal delivery. We focused on α-tocopherol (vitamin E), a natural antioxidant able to reduce or block the oxidation reactions induced by free radicals in biological membranes. The aim of this study was to perform electrochemical evaluation and analysis of vertical diffusion of gel + α-tocopherol undergoing iontophoresis. The results showed a reduction in peak current at 0.78 V of α-tocopherol molecules when subjected to iontophoresis, increasing the diffusion and degradation of the system.

COMPREENSÃO MATEMÁTICA DA DIFUSÃO NO CONTEXTO ELETROQUÍMICO

The aim of this study was to explain in detail the mathematical methods used to deal with diffusion equations, mainly for students and researchers interested in electrochemistry and related areas. Emphasis was placed on the deduction and resolution of diffusion equations, as well as addressing cartesian, spherical and cylindrical coordinates. Different aspects of mass transfer processes were discussed including the importance of the resolution of Fick's laws equations to understand and derive parameters of the electroactive species (e.g., diffusion coefficients, formal electrode potentials) from the electrochemical techniques. As an example, the resolution of diffusion equations for a reversible reduction process of soluble oxidized species was presented for the chronopotentiometry technique. This study is envisaged to broaden the understanding of these frequently used methods, in which mathematical deductions are not always completely understood.

Aplicação da calorimetria exploratória diferencial (dsc) na caracterização térmica do acetato de dexametazona, excipientes e do creme de dexametazona

A calorimetria exploratória diferencial (DSC) foi utilizada na caracterização do acetato de dexametazona (princípio ativo), álcool cetílico, emulgin, polawax, nipagim-M (excipientes). O princípio ativo também foi investigado utilizando-se a termogravimetria (TG) e espectroscopia de absorção na região do ultravioleta e visível (UV-VIS). Os resultados obtidos permitiram verificar a estabilidade térmica e o ponto de fusão do princípio ativo, bem como o ponto de fusão dos excipientes utilizados na fabricação do creme de dexametazona.