Here we report the synthesis of barium sulphate (BaSO4) nanoparticles from Ba(OH)2/BaCl2solutions by a combined method of precipitation and quenching in absence of polymer stabilizers. Transmission electron microscopy (HRTEM), Fourier transforms infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were employed to characterize the particles. The Scherrer formula was applied to estimate the particle size using the width of the diffraction peaks. The obtained results indicate that the synthesized material is mainly composed of nanocrystalline barite, with nearly spherical morphology, and diameters ranging from 4 to 92 nm. The lattice images of nanoparticles were clearly observed by HRTEM, indicating a high degree of crystallinity and phase purity. In addition, agglomerates with diameters between 20 and 300 nm were observed in both lattice images and dynamic light scattering measurements. The latter allowed obtaining the particle size distribution, the evolution of the aggregate size in time of BaSO4in aqueous solutions, and the sedimentation rate of these solutions from turbidimetry measurements. A short discussion on the possible medical applications is presented.

Nickel nanoparticles were synthesized by two different routes and their reactivity was assessed during methane catalytic decomposition (MCD) conducted in situ in a thermogravimetric analyzer at atmospheric pressure from room temperature to 930°C. Commercially available nickel nanoparticles were also evaluated for comparative purposes. Carbon buildup was monitored continuously to provide a qualitative comparison of the rate of the reaction for all the systems, while residues composed of nickel nanoparticles and carbon nanotubes (CNTs) were collected at different stages for further evaluation by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The surface composition of the fresh nickel nanoparticles was clearly sensitive to the preparation method and was presumably responsible for the trends observed during the catalytic evaluation. On one hand, an early onset in the temperature of the catalytic reaction at 400°C is distinguished by Ni nanoparticles prepared in a one-step direct thermal decomposition of nickel acetate tetrahydrate while, under the same conditions, Ni nanoparticles produced by an alternative emulsion-mediated synthesis reacted at T > 480°C. When MCD is finished at 930°C, multiwalled carbon nanotubes (MWCNTs) and bamboo-shaped carbon nanotubes (BSCNTs) structures are collected selectively in the systems catalyzed by particles prepared by one-step and emulsion-mediated synthesis, respectively. Commercial nickel nanoparticles, on the other hand, produced low quality CNTs in a comparatively much slower fashion. Methane catalytic decomposition conducted in a thermogravimetric analyzer provides a complementary tool to compare in situ reactivity of nanoparticles and to isolate them for further ex situ characterization.

Abstract. When oil production by natural flow of reservoirs decreases, it is necessary to increase the production by using improved recovery processes, such as water injection. Injection of incompatible water can cause the formation of saline deposits of calcium and magnesium carbonates. The use of chemical inhibitors to treat incrustations involves the use of chemicals with functional groups such as carboxylic acids (R-COOH) or phosphonates (R-PO32-). A new ecological scale inhibitor, carboxymethyl chitosan (CMC1), has been synthesized and its capacity to modify the CaCO3 crystalline phases obtained in the solid residue was compared with that obtained when using a commercial carboxymethyl chitosan (CMC2) and a commercial poly(acrylic acid). The results show that under the used conditions, the CMC´s produce a slightly larger amount of crystalline phases than the synthetic inhibitor. Using the X-ray powder diffraction technique, calcite, vaterite, and aragonite were identified in the residual solid. The ratio of these phases was modified by increasing the concentration of the inhibitor. Using Scanning Electron Microscopy (SEM), it was observed that increasing the concentration of the CMC's the modifies the crystal´s morphology from plates to spheres.   Resumen. Cuando la producción de petróleo por flujo natural disminuye, es necesario aumentar la producción de petróleo crudo y gas mediante procesos de recuperación mejorados. El agua es el líquido que se inyecta y puede provocar la formación de depósitos salinos de carbonato de calcio y magnesio. El uso de inhibidores químicos para el tratamiento de incrustaciones implica el empleo de productos químicos con grupos funcionales del tipo ácido carboxílico (R-COOH) o grupos fosfonatos (R-PO32-). Se sintetizó un nuevo inhibidor de incrustaciones ambientalmente amigable en base a carboximetilquitosano (CMC1), y se compararon las fases cristalinas de CaCO3 obtenidas en el residuo sólido con las obtenidas al utilizar un carboximetilquitosano comercial (CMC2) y un poli (ácido acrílico) comercial. Los resultados muestran que, en las condiciones utilizadas, las CMC producen una cantidad ligeramente mayor de fases cristalinas en comparación con el inhibidor sintético. Mediante la técnica de difracción de rayos X de polvos, en el sólido residual se identificaron las fases: Calcita, Vaterita y Aragonita. La relación de las fases se modificó aumentando la concentración del inhibidor. Mediante Microscopía Electrónica de Barrido (SEM) de los residuos sólidos, se observó que al aumentar la concentración de las CMC's la morfología de los cristales se modificaba de placas a esferas.

No abstract

No abstract