Estudo cinético da decomposição térmica do pentaeretritol-tetranitrado (PETN)

The pentaerythritol-tetranitrate (PETN) is a nitroether used in explosives and propellant formulations. Due to its suitable properties, PETN is used in booster manufacture. Knowing the thermal decomposition behavior of an energetic material is very important for storage and manipulation, and the purpose of this work is to study the kinetic parameters of the decomposition of PETN, compare the results with literature data and to study the decomposition activation energy differences between two crystalline forms of PETN (tetragonal and needle) by means of differential scanning calorimetry (DSC). Fourier transform infrared spectroscopy (FT-IR) is used to study the two crystalline forms.

Uso da cinza da casca do arroz (CCA) obtida da geração de energia térmica como adsorvente de Zn(II) em soluções aquosas

The removal study was conducted using 1.00 g of the rice husk ash (RHA) and 20.0 mL solution with concentrations in the range of 10-1000 mg/L of Zn(II). The influence of contact time, initial metal concentration, agitation and pH of the removal process was investigated. Superior removals to 95% were obtained at the end of 24 h of contact. The agitation increased in 20% the removal of Zn(II), being needed only 5 min to reach the equilibrium. The adsorption process was studied by the models of isotherms of Langmuir, Freundlich and BET, obtaining results of R L and 1/n for a process favorable of adsorption. BET isotherm best represents the equilibrium adsorption. The results showed that the RHA has the largest capacity and affinity for the removal of Zn(II).

Argilas como catalisadores verdes na esterificação do colesterol: caracterização espectroscópica e identificação de polimorfos por métodos de análise térmica. Uma proposta laboratorial interdisciplinar para o 1º ciclo universitário

A laboratory experiment that enables the professor to introduce the problematic of sustainable development in pharmaceutical chemistry to undergraduate students is proposed, using a simple synthetic procedure. Cholesteryl acetate is prepared by the esterification of cholesterol using Montmorillonite K10 as heterogeneous catalyst. Cholesterol and cholesteryl acetate are characterized by spectroscopic (¹H RMN, 13C RMN, FTIR) and thermal analysis techniques. The thermal methods are used to introduce the concepts of polymorphism and the nature of mesophases.

Análise térmica aplicada à caracterização da sinvastatina em formulações farmacêuticas

Thermogravimetry (TG) and differential scanning calorimetry (DSC) are used in pharmaceutical studies for drugs characterization, purity, formulations compatibility, polymorphism identification, stability evaluation, and thermal decomposition of drugs and pharmaceutical formulations. Simvastatin showed fusion at 138.5 ºC and thermal stability up to 248 ºC. Simvastatin was incompatible with preservative excipient butylhydroxyanisole (BHA) performing a process of crystal amorphization. The drug showed morphological polymorphism, where it has the same unit cell but with different crystal habits according to the recrystallization solvent.

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.

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.

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.

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.

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.

Parâmetros cinéticos da degradação térmica de complexos entre percloratos de terras raras com lactama

Complexos de percloratos à base de terras raras com a 2-azaciclononanona (AZA) foram obtidos a partir da reação entre os respectivos sais hidratados com a AZA (proporção molar 1:8) pelo método de difusão de vapor e caracterizados por titulação complexiométrica com EDTA, microanálise (CHN), espectroscopia vibracional na região do IV, termogravimetria em atmosfera de ar e N2 e calorimetria exploratória diferencial (DSC) em atmosfera de N2. O estudo cinético desse trabalho foi realizado utilizando um software em QBASIC que faz a simulação dos dados termogravimétricos a partir de um conjunto dado de parâmetros cinéticos.

Estudo da estabilidade térmica de óleos e gorduras vegetais por TG/DTG e DTA

Óleos e gorduras vegetais são muito ultilizados pela indústria alimentícia e farmacêutica, tem exigido de pesquisadores e técnicos métodos analíticos capazes de avaliar as condições de processamento e estocagem. A estabilidade térmica de óleos vegetais é um fator determinante na sua qualidade. Neste trabalho avaliou-se a estabilidade térmica de óleos e gorduras vegetais extraídos de semente de plantas do cerrado ( araticum, babaçu, buriti, guariroba e murici) usando os resultados de TG, DTG e DTA, numa faixa de temperatura entre 30 e 650ºC, em atmosfera de nitrogênio, com razão de aquecimento de 10ºC min-1. As técnicas termoanalíticas utilizadas mostraram-se eficientes e rápidas na determinação da estabilidade térmica dos óleos e gorduras estudados.