Gilmar Patrocínio Thim

Kinetics of phase change

The kinetic model for change of phases developed by M. Avrami at the end of the thirties has been used to describe the temporal behavior of phase changes. Until today this model is studied and adapted to include broader hypotheses. However, the mathematical format presented by M. Avrami is difficult to be understood by beginners. The purpose of this work is to clarify the mathematical treatment of Avramis work, going straightforward to the arguments that led to his main results.

Sol–gel silica film preparation from aqueous solutions for corrosion protection

Abstract SiO2 coatings were deposited on aluminum (98% Al) surfaces by dip-coating in silicic acid aqueous solutions containing urea as dry chemical control agent (DCCA). These films are of special interest for protection of metals against oxidation and acid corrosion at elevated temperature. In this work, we investigate the effect of two different treatments of aluminum surfaces on the adhesivity of the silica films. The optimum urea/silanol ratio in the precursor gel solution and the number of dips were also investigated. The corrosion protection afforded by the silica film was determined by anodic polarization of the coated surfaces in 0.5 mol/l sodium chloride aqueous solution exposed to air at room temperature. The best performance was obtained for surfaces anodized prior to dip coating, and for urea/silanol ratio and number of dips equal to, respectively, 7 and 5.

Adsorption of phosphate from aqueous solution by hydrous zirconium oxide

Synthetic ZrO2·nH2O was used for phosphate removal from aqueous solution. The optimum adsorbent dose obtained for phosphate adsorption on to hydrous zirconium oxide was 0.1 g. The kinetic process was described very well by a pseudo-second-order rate model. The phosphate adsorption tended to increase with the decrease in pH. The adsorption capacity increased from 61 to 66 mg g−1 when the temperature was increased from 298 to 338 K. A phosphate desorption of approximately 74% was obtained using water at pH 12.

Citric acid effect on aqueous sol-gel cordierite synthesis

Cordierite was synthesized by a simple aqueous sol-gel route. Citric acid action as a chelant for the Al 3+ ion, and for controlling phase segregation during the drying and initial thermal treatment of the gel, results in an amorphous precursor that crystallizes to μ-cordierite and spinel. The changes in the ratios of the crystalline phases, formed during dry gel calcination at 1000°C for 12 h were dependent on the ratio (L/M) of citric acid/Al 3+ (mol/mol). For L/M3 and L/M5 samples, the ratio between the amount of μ-cordierite phase and the amount of spinel phase was the same, while, for the sample L/Ml, the amount of μ-cordierite was larger than that found in the other samples.

Experimental and Monte Carlo simulation: the role of urea in mullite synthesis

Abstract Mullite was synthesized by a sol–gel process employing aqueous solution of silicic acid, aluminum nitrate and urea in high concentration (9 mol/l). t-Mullite crystallizes at temperatures around 1050°C, the fraction of the spinel phase formed was small and the apparent activation energy obtained by fitting the XRD results with the JMAK model was (770±4) kJ mol −1 . Monte Carlo simulations were performed to investigate the site-site correlation function for ion (I)–urea (Ou) and ion (I)–water (Ow) interactions, g(r IOu ) and g(r IOw ,), respectively. The integration of these two correlation functions indicated the presence of four water and two urea molecules in the first Al 3+ coordination shell. The 27 Al nuclear magnetic resonance (NMR) results also indicate the presence of species like [Al(H 2 O) 4 (urea) 2 ] 3+ .

Sonocatalytic Degradation of Methylene Blue in the Presence of TiO2 Doped Carbon Nanostructures—Catalytic and Adsorption Comparison by Different Carbon Forms

The main objective of this work was to evaluate nanocomposites formed by TiO2-CNT (carbon nanotube) and TiO2-C (resorcinol/formaldehyde) via a sonocatalytic process. The synthesis of composites was performed by the sol-gel method using titanium isopropoxide (Ti(OPr)4-TTIP), acetic acid and ethylene glycol as dispersing medium. Ultrasound was used as the irradiation source and methylene blue was chosen as a model substance. In addition, the adsorption capacity was studied in an attempt to achieve greater ratio degradation/adsorption. The methylene blue concentration after adsorption and sonocatalysis was investigated by UV–vis spectroscopy. It was found that adsorption was an important factor to achieve high degradation capacity. However, the sonocatalytic activity decreased when adsorption was too intense.

Rotas de síntese e a homogeneidade dos precursores de mulita e cordierita

Multicomponent ceramics are mainly synthesized by conventional solid-state reaction route and sol-gel routes. In the sol-gel route, colloidal or polymeric gel are envolved. In this work, some principles of the chemistry of theses routes are discused and it is ilustrated a variety of strategies for obtaining a homogeneous multicomponent precursors.

Influence of carbon nanotube concentration and sonication temperature on mechanical properties of HDPE/CNT nanocomposites

ABSTRACT Carbon nanotube (CNT) reinforced high-density polyethylene (HDPE) composites were prepared by a melt mixing procedure. The mechanical properties were analyzed using a central composite design where key factors were CNT concentration and sonication temperature during the sample preparation process. The results indicated that the optimum values were 0.8 wt% for the concentration of CNT and 55°C for the sonication temperature. The samples obtained at optimal conditions were systematically studied. Nanoindentation analysis showed an increase of 43% in Vickers hardness of the nanocomposite when compared to pure polymer. The improvement on the mechanical property is related to changes in the thermo-physical and viscoelastic properties of the nanocomposite.

Organic acids effect on crystallization kinetics of cordierite obtained by diphasic gel

Abstract α-Cordierite (Mg2Al4Si5O18) was obtained, by a sol–gel aqueous route, from aqueous solutions containing Si:Al:Mg in a molar ratio equal to 5:2.15:2.25 and citric ( l cit samples), or oxalic ( l ox samples), or tartaric acid ( l tart samples), in such amount that the molar ratio organic acid/aluminum ion was equal to 1. The effect of each organic chelating upon the quantity of crystallized α-cordierite was investigated. The influence of a heating treatment time, to eliminate the organic material from the xerogels containing citric acid, on the quantity of α-cordierite formed was also investigated. Thermal gravimetric analysis was used to investigate the thermal decomposition process of each sample. Based on thermal gravimetric results we suggest that the thermal decomposition of the l cit, l ox and l tart xerogels takes place in three major steps and little difference was observed for each case. X-ray diffraction (XRD) measurements were carried out to determine the crystalline phases present after heat treatment of each sample at 1000 °C. X-ray diffraction results showed that the sequence for the quantity of crystallized α-cordierite from each sample is: l cit > l ox > l tart. XRD results also indicate that the quantity of crystallized α-cordierite from samples containing citric acid ( l cit) increased with the time of the heating treatment used to eliminate the organic material.

Functionalization of Carbon Nanotube and Applications

Carbon nanotubes (CNTs) have unique structures, comprising diameters of few nanometers and length of several hundred nanometers, which provides outstanding mechanical, electrical, and thermal properties. Since their discovery in 1991, CNTs have received much attention and are a worldwide research subject due to their wide range of applications as biosensors, drug delivery, electrochemistry, nanoelectronics, superconductors, nanowires, graphene nanoribbons, nanocomposite materials, and so on. The functionalization treatments can enhance the usual CNT poor dispersion in solvents and improve their interactions with other materials, improving their technological application. Then, carbon nanotube is an extremely hot topic, and every day new research papers are published on this subject. This book contains complete and current reviews on CNT topics, such as synthesis, characterization, and application of functionalized CNTs. The characterization of functionalized CNTs is extremely important for determining the real physicochemical properties of the material obtained after functionalization treatments. However, this characterization is rarely addressed in books or review articles. Generally, the functionalization reviews are too wide-ranging, discussing the functionalization of various materials (e.g., nanomaterials), or too specific, analyzing only one functionalization agent (with some specific chemical group, e.g.). This book, however, proposes to discuss the functionalization of one of the most widely used nanomaterials in recent years: carbon nanotube. Thus, the reader will find information on CNT functionalization, using several functionalization agents, in the same book.