Caracterização de 2,2',4,4',6,6'-hexanitroestilbeno via análises instrumentais

2,2',4,4',6,6'-hexanitrostilbene (HNS) is a very important high explosive that is used in a range of military, aerospace and industrial formulations owing to its suitable properties. It is an insensitive and thermaly stable explosive that can be produced from 2,4,6-trinitrotoluene (TNT). This paper shows the characterization of synthesized HNS by different techniques, such as elementary analysis, differential scanning calorimetry (DSC), thermogravimetric analysis (TG), Fourier transform infrared spectroscopy (FT-IR) and through the determination of the heat of combustion in a calorimeter.

Análise térmica aplicada ao estudo de materiais energéticos

This paper shows different aspects related to the application of different thermal analysis techniques in the study of energetic materials. The criteria used to choose the best technique and an exact approach to adjust the experimental data with a proper model are here discussed. The paper shows how to use the different thermal analysis results to help develop new compounds, to study the stability of some energetic materials and their compatibility, and the conditions necessary for a secure storing environment.

Estudo da decomposição térmica de propelente sólido compósito de baixa emissão de fumaça

The thermal decomposition of hydroxyl-terminated polybutadiene (HTPB)/ammonium nitrate (AN) based propellants, so called smokeless formulations, and raw materials were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). The thermoanalytical profile of different components and of propellant were evaluated and the Arrhenius parameters for the thermal decomposition of the propellant sample were determined by the Ozawa method. The kinetic parameters of the thermal decomposition of propellant samples were determined by DSC measurements. The values obtained for activation energy (Ea) and pre-exponential factor were 163 kJ mol-1 and 1.94x10(6) min-1.

Tempo de vida útil de propelentes base-simples

The purpose of this work was to determine the safe shelf life of single-base propellants. The kinetic parameters relative to the consumption of the stabilizer diphenylamine (DPA) added to the propellant were determined as a function of the storage and ageing time. High Performance Liquid Chromatography (HPLC) with spectrophotometric detection was used to determine the DPA percentage before and after the artificial ageing at 60, 70 and 80 ºC. The experimental data were very well adjusted to a pseudo-first order kinetic model and the respective kinetic constants are 8.0-10-3 day-1 (60 ºC); 1.9-10-2 day-1 (70 ºC); 1.2-10-1 day-1 (80 ºC). The activation energy was calculated as 130 kJ mol-1 and the half-time for depletion of the DPA at the hypothetical temperature of 40 ºC of storage was estimated as being 6 years.

Determinação quantitativa de TNT e HNS por TG e FT-IR

2,4,6-trinitrotoluene (TNT) is an energetic material that shows scarce crystalline properties that can be improved by addition of 2,2',4,4',6,6'-hexanitrostilbene (HNS) in the crystallization process. HNS is a very important high explosive used in a variety of military, aerospace and industrial formulations owing to its suitable properties. It is an insensitive and thermal stable explosive that can be produced from 2,4,6-trinitrotoluene (TNT). The purpose of this work is the quantitative determination of HNS and TNT in explosives by thermogravimetric analysis (TG) and Fourier transform infrared spectroscopy (FT-IR).

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.

Modelagem da combustão da dinitramida de amônio por simulação computacional

In this work, the combustion process of ammonium dinitramide, ADN, has been modeled in two different situations: decomposition in open environment, with abundant air and decomposition in a rocket motor internal environmental conditions. The profiles of the two processes were achieved, based on molar fractions of the species that compose the products of ADN combustion. The velocity of formation and quantity of species in the open environment was bigger than the ones in the rocket motor environment, showing the effect of the different atmosphere in the reactions kinetics.

Em busca da sustentabilidade: células solares sensibilizadas por extratos naturais

The present work reports the use of anthocyanins extracted from mulberry (Morus Alba L.), raspberry (Rubus Idaeus L.) and blueberry (Vaccinium myrtillus L.) as sensitizers in dye-sensitized solar cells. The conversion efficiency of these devices is dependent on the extracts employed and can be rationalized in terms of their composition and spectral properties. Solar cells sensitized by the mulberry extract showed the highest efficiency among the fruits investigated. Moreover, a 16 cm² active area solar cell with the mulberry extract has presented fair good efficiency of conversion for natural dye-based solar cells, besides stability over twenty weeks, showing perspectives for developing these low cost devices with a commercial viability.

Síntese de poliuretanos modificados por óleo de mamona empregados em materiais energéticos

The aim of this work was to synthesize a polyurethane polymer matrix using castor oil as a polymer chain modifier, whose characteristics can be adjusted for use as a binder in the manufacture of energetic materials such as propellant and pyrotechnics for aerospace use. We attempted the partial substitution of hydroxyl-terminated polybutadiene (HTPB), a pre-polymer commonly used as a starting polyol in obtaining energetic matrix composites. Thermoanalytical techniques were employed to characterize the material based on castor oil and the unmodified HTPB. The results showed similar behaviors, confirming the possibility of their use as polymer matrix composites through the proposed adaptations.

Acúmulo de cargas elétricas em propelente sólido compósito com matriz de polibutadieno líquido hidroxilado

Composite solid propellants prepared with HTPB prepolymer - Hydroxyl Terminated Polybutadiene, AP - Ammonium Perchlorate as oxidizer and aluminum particles as an additive metal, have characteristics of high electrical resistivity. The loading process of the polymer matrix did not obtain homogeneity, resulting in clusters, mainly of metal particles. The effect of clustering in the composite was studied and observed experimentally, and this effect was one of the factors explaining the phenomenon of electrical charging of the composite. This electrical potential, when discharged abruptly, can generate an electric spark with sufficient energy for sustained ignition of a solid rocket motor.

Desenvolvimento de tecnologia de pré-polímeros na síntese de poliuretanos empregados em combustíveis sólidos

The aim of this work was to synthesize a polyurethane polymer matrix using polyols as a raw material to obtain a binder such as the hydroxyl terminated polybutadiene (HTPB) pre-polymer in energetic material formulation. The soybean-based polyol was the best starting raw material for producing a binder for solid fuel formulation in rocket motor applications. Characterization of the obtained soybean-based polyurethane binder was carried out by employing FT-IR analysis and thermo analytical techniques that showed similar HTPB binder thermo decomposition behaviors, confirming their potential for use as polymer matrix composites.

Amphoteric behavior of di-2-pyridyl ketone benzoylhydrazone in ethanol-water mixtures

The ligand di-2-pyridyl ketone benzoylhydrazone (DPKBH) is widely used for the determination of transition metal ions in environmental samples. Due to its low solubility in water it is used in aqueous-ethanol (1:1) solvent and for higher sensitivity the pH must be properly adjusted. The properties of DPKBH solutions must be known at different ethanol-water percentages in order to achieve higher sensitivity and/or selectivity for metal analysis. The acid-base behavior of this reagent in aqueous-ethanol solvent and the dissociation/ionization constants (pK1 and pK2) of DPKBH have been determined in different aqueous-ethanol solvent mixtures (10, 20, 30 and 50 % V/V of ethanol) from potentiometric titrations at 25.0 ± 0.1° C. As the amount of ethanol increases from 10 to 30% the pK1 and pK2 values increased, but they decreased in 50% of the organic solvent. The results are correlated with the medium composition and its effects.

Determinação dos parâmetros cinéticos de decomposição térmica para propelentes BS e BD

O propósito deste trabalho foi determinar os parâmetros cinéticos de decomposição térmica para uma amostra de propelente base simples e base dupla. Os dados obtidos pela calorimetria exploratória diferencial foram ajustados para o modelo cinético de pseudo-primeira ordem de Flynn, Wall e Ozawa. Os respectivos parâmetros obtidos foram: BS REX 1200 (Ea) (2,3 ± 0,2) 10² kJ mol-1 e (A) 1,34 10(25) min-1; BD-111 (Ea) (1,6 ± 0,1) 10² kJ mol-1 e (A) 3,31 10(17) min-1. O espectro de infravermelho da amostra de propelente base dupla indicou a presença de salicilato, justificando o comportamento de decomposição observado na respectiva curva térmica.

Estudo da cinética de consumo do estabilizante 2NDPA no propelente base dupla

Este trabalho tem como propósito avaliar a cinética de consumo do estabilizante 2NDPA presente em uma amostra de propelente tipo base-dupla (BD). Tópicos relativos ao método analítico empregado e, a interferências na cinética de consumo do estabilizante pela nitroglicerina e o salicilato de chumbo presente no propelente, também são abordados. Foram obtidos, ainda, os parâmetros cinéticos de consumo do 2NDPA. Para isto, foi empregada a técnica da Cromatografia Líquida de Alta Eficiência (CLAE). Os dados experimentais foram bem ajustados para uma cinética de pseudoprimeira ordem. A energia de ativação (Ea) e o fator pré-exponencial (A) determinados foram, respectivamente, (1,22 ± 0,42) 10² kJ mol-1 e (10(16) ±10(6)) dia-1.

Occurrence of virulence-related sequences and phylogenetic analysis of commensal and pathogenic avian Escherichia coli strains (APEC)

The presence of iron uptake (irp-2, fyuA, sitA, fepC, iucA), adhesion (iha, lpfA O157/O141, lpfA O157/O154, efa, toxB) and invasion (inv, ial-related DNA sequences and assignment to the four main Escherichia coli phylogenetic groups (A, B1, B2 e D) were determined in 30 commensal E. coli strains isolated from healthy chickens and in 49 APEC strains isolated from chickens presenting clinical signs of septicemia (n=24) swollen head syndrome (n=14) and omphalitis (n=11) by PCR. None of the strains presented DNA sequences related to the inv, ial, efa, and toxB genes. DNA sequences related to lpfA O157/O154, iucA, fepC, and irp-2 genes were significantly found among pathogenic strains, where iucA gene was associated with septicemia and swollen head syndrome and fepC and irp-2 genes were associated with swollen head syndrome strains. Phylogenetic typing showed that commensal and omphalitis strains belonged mainly to phylogenetic Group A and swollen head syndrome to phylogenetic Group D. Septicemic strains were assigned in phylogenetic Groups A and D. These data could suggest that clonal lineage of septicemic APEC strains have a multiple ancestor origin; one from a pathogenic bacteria ancestor and other from a non-pathogenic ancestor that evolved by the acquisition of virulence related sequences through horizontal gene transfer. Swollen head syndrome may constitute a pathogenic clonal group. By the other side, omphalitis strains probably constitute a non-pathogenic clonal group, and could cause omphalitis as an opportunistic infection. The sharing of virulence related sequences by human pathogenic E. coli and APEC strains could indicate that APEC strains could be a source of virulence genes to human strains and could represent a zoonotic risk.