José Atílio Fritz Fidel Rocco

Synthesis, characterization, and computational study of a new dimethoxy-chalcone.

Chalcones are an important class of medicinal compounds and are known for taking part in various biological activities as in anti-inflammatory, anti-leishmania, antimitotic, and antiviral. Chemically, chalcones consist of open-chain flavonoids in which the two aromatic rings are joined by a three-carbon α,β-unsaturated carbonyl system. The wide action spectrum has attracted our attention to synthesize, crystallize, and characterize the dimethoxy-chalcone C18H18O3. Aiming to understand the process of crystal lattice stabilization, a combination of technique has been used including X-ray diffraction, infrared spectroscopy and computational molecular modeling. The theoretical calculations were carried out by the density functional method (DFT) with the M06-2X functional, with the 6-311+G(d,p) basis set. The vibrational wavenumbers were calculated and the scaled values were compared with experimental FT-IR spectrum. The intermolecular interactions were quantified and intercontacts in the crystal structure were analyzed using Hirshfeld surfaces. Bond distances and angles described by the X-ray diffraction and theoretical calculation are very similar. The C-H….O contacts contributing to assemble the supramolecular architecture are also responsible for the molecular structure assembly.

Hydrogen Abstraction from the Hydrazine Molecule by an Oxygen Atom

Thermochemical and kinetics properties of the hydrogen abstraction from the hydrazine molecule (N2H4) by an oxygen atom were computed using high-level ab initio methods and the M06-2X DFT functional with aug-cc-pVXZ (X = T, Q) and maug-cc-pVTZ basis sets, respectively. The properties along the reaction path were obtained using the dual-level methodology to build the minimum energy path with the potential energy surface obtained with the M06-2X method and thermochemical properties corrected with the CCSD(T)/CBS//M06-2X/maug-cc-pVTZ results. The thermal rate constants were calculated in the framework of variational transition-state theory. Wells on both sides of the reaction (reactants and products) were found and considered in the chemical kinetics calculations. Additionally, the product yields were investigated by means of a study of the triplet and singlet surfaces of the N2H4 + O → N2H2 + H2O reaction.

Gaseous Oxygen Injection Effects in Hybrid Labscale Rocket Motor Operations

4Hybrid rocket motor features such as operational safety, thrust tailoring, low investment cost and constructive simplicity are currently widespread. Nevertheless, inefficient combustion reduced mass fraction and mostly low regression rates still play a role in the major disadvantages. Swirling oxidizer flow is known to affect the mixing between oxidizer and fuel, intensifying heat exchange thus increasing regression rate. A laboratory scale hybrid engine was developed, and tests were conducted with gaseous oxygen (GOX) supply, ultra high molecular weight (UHMW) polyethylene, one axial and two swirl injector types. Oxygen mass flow, grain length and diameter and test time were maintained constant in order to evaluate the GOX injection influence on the motor performance and combustion characteristics. Series of six tests for each injector were performed with one unique set of machined throat diameters, to acquire a range of oxidizer mass flux for comparison. The data of oxidizer mass and fuel consumption were collected, and average regression rate values were calculated. Empirical correlations for the regression rate coefficients were obtained for each injection method. The burn grain profiles were analyzed and compared, sustaining that the income oxidizer flow pattern strongly affects the regression rates.

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.

Design and Testing of a Hybrid Rocket Motor

This research aims to provide a methodology for the project of labscale hybrid motors. This development begun with the thermal analysis of the fuel grain using the Flynn, Wall and Ozawa method; this provided the simulation entry data to maximize the motor performance. The computer simulation was performed with the Chemical Equilibrium Specific Impulse Code of the U.S. Air Force, also known as ISP Code. Based on the optimum oxidizer to fuel ratio, the literature was used to supply the mathematical background for the calculation of the motor geometrical parameters whose operating conditions were determined throughout the simulation. Finally, firing tests were conducted to verify the reliability of the project methodology. The firing tests were performed with three injectors: 2 swirling and one axial. The tests showed that the higher the operation pressure the more suitable is the project, meaning the methodology developed works best in hybrid rocket motors with high operating pressures.

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 1.94x106 min-1.

Hydrazine decomposition on a small platinum cluster: the role of N2H5 intermediate

This work presents a comprehensive DFT study on the interaction between hydrazine derivatives with a platinum catalyst surface, which is represented by a tetrahedral Pt4 cluster model. Three separate reaction pathways were investigated; two of which are related to possible pathways of NH3 formation. The first pathway describes the intramolecular transfer of one hydrogen atom in the hydrazine molecule forming the NHNH3 intermediate, then dissociating into NH and NH3. The second describes the addition of one external hydrogen atom to hydrazine forming N2H5, followed by its dissociation to NH2 and NH3. The third reaction pathway involves the formation of N2H3 by means of hydrogen abstraction by an external hydrogen. The reactions were studied in both the absence and the presence of a Pt4 cluster. We find that the assistance of the Pt4 cluster lacks a systematic effect on the reactions barrier heights. It is also shown that the ammonia formation can possibly proceed through the formation of the N2H5 intermediate, leading to more exothermic intermediate steps in the presence of the Pt4 cluster.

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.

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.

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

The purpose of this work was to determine the kinetics parameters of the thermal decomposition of a sample single-base (BS) and double-base (BD) propellants. The experimental data obtained by differential scanning calorimetry (DSC) were adjusted to the pseudo-first order kinetic model of Flynn, Wall and Ozawa. The respective parameters obtained are: BS REX 1200 (Ea) (2.3 ± 0.2) 102 kJ mol-1 and (A) 1.34 1025 min-1; BD-111 (Ea) (1.6 ± 0.1) 102 kJ mol-1 and (A) 3.31 1017 min-1. IR spectrum has confirmed the presence of salicilate in the double-base (BD) propellant and some correlations corroborate the conclusions about the decomposition mechanism.