Advanced Materials Research Vol. 976

Abstract: A comparative study of the synthesis of cadmium selenide (CdSe) nanoparticles (NPs) using different cadmium precursors such as, cadmium nitrate (Cd (NO₃)₂·4H₂O), cadmium acetate ((CH₃COO)₂Cd·2H₂O) and cadmium chloride (CdCl₂·2.5H₂O) is presented in this work. The method used to obtain the CdSe NPs was the colloidal synthesis at low temperature and atmospheric pressure. The Cd²⁺ ions were obtained in aqueous solution at room temperature, the surfactant used in the process was an aqueous solution of sodium hydroxide (NaOH), penta-sodium tripolyphosphate and H₂O named commonly extran, which not only helps to stabilize the NPs, but also allows adjusting the pH of the solution. Se^2- ions were obtained with sodium borohydride (NaBH₄) as reductant at 75 oC. The by-products from the reaction were eliminated through a cleaning process with hydrochloric acid (HCl). Molar concentration of Cd:Se was varied from 3:1 to 1:3 and the pH value was varied between 8 and 11. The obtained samples were characterized by X-ray diffraction (XRD), it was seen that the obtained NPs present cubic centered face structure. The crystallite size from the powder was calculated using the Debye-Scherrer equation and was found between 3.3 nm and 5.6 nm, the variation in size depends on the molar concentration of cadmium and selenium. Morphological study was done using scanning electron microscopy (SEM) and compositional analysis was done by energy dispersive x-ray analysis (EDAX).

Abstract: Two bifunctional monomers, bis (acryloxyethyl) terephthalate (BAOET) and bis (allyloxycarboniloxyethyl) terephthalate (BAOCOET), derived from PET waste were tested as crosslinking agents for acrylic and methacrylic acids (AA and MA, respectively). BAOET and BAOCOET were obtained from the reactions of acryloyl chloride and allyl chloroformate, respectively, with bis (hydroxyethyl) terephthalate (BHET). This was obtained from the glycolysis of postindustrial PET with ethyleneglycol (EG). Both bifunctional monomers were characterized by NMR ¹H. Polymerizations of BAOET and BAOCOET with the acrylic monomers were performed using bifunctional monomer to acrylic monomer weight ratios of 1:10, 1:2 and 1:1, for each of the four combinations, using 2 wt % of benzoyl peroxide (BPO) as thermal initiator. The obtained gel proportions of the crosslinked polymers were above 90% for most of the cases, requiring times from 10 to 60 min. For all of the experiments, complete double bond conversion was observed by FT-IR. Polymers showed thermal stabilities higher than 200°C.

Abstract: In this work, we report the conventional and mechanochemical synthesis of the a-diimine derivate of 2, 3-butanedione and the primary amine 2-aminoethanethiol designated DD-DC and DD-DC/MS respectively. The products were characterized by ¹H and ¹³C-NMR, FT-IR, MS-EI and elemental analysis. The products were also electrochemically evaluated by potentiodynamic polarization technique in order to measure their corrosion inhibition efficiency on AISI 1018 steel, immersed in a corrosive solution type NACE TM 0177. The results indicate that the compound obtained under mechanosyntesis conditions, DD-DC/MS, presents better inhibitory properties with 53% efficiency at 10 ppm concentration. On the other hand, the compound obtained by conventional synthesis (DD-DC) presented efficiency of 29% at 10 ppm concentration. Also, the DFT results show that a-diimine derivatives possesses corrosion inhibition properties, consisting of the transfer of high-charge density which in the delocalization region (N=C–C=N) is formed by p (C=N) and SH, these moiety play an important role, because their electron lone pairs help to form a protective coating to form an adsorption layer. The results showed that cysteamine compound turns out to be a good corrosion inhibitor for the steel iron surface in an acid medium forming an adsorption film over metallic surface.

Abstract: Several methods for processing tubular anodes for solid oxide fuel cells have been developed, but many of them are expensive and sophisticated, therefore, there is a great interest in researching the use of a simple process to produce them. In this paper, the results of using slip casting for processing minitubes of NiO-8YSZ with the dimensions of 100x5x1 mm are presented. This is a versatile method for obtaining complex geometries with a suitable surface finish and dimensional precision at low cost compared with ceramic processing which uses high energy consumption and/or has high startup costs. In order to carry out this study, an aqueous slurry of an oxide mixture of NiO-8YSZ with poly-etilenglycol as a dispersant agent was used. The modification of the ratio of water:ceramic powders, the composition NiO:x8YSZ (30, 50 and 70 in wt.) and the casting time (3 to 30 min) were also applied. The minitubes obtained were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectroscopy of dispersive energy (EDS). The results show that slip casting is an appropriate method to obtain NiO-8YSZ minitubes. Minitubes of varying composition (30, 50 and 70% in wt. of NiO) with dimensions of 100x5x1 mm were obtained showing an excellent porosity (higher than 96% in v/v) and a homogeneous distribution of NiO and 8YSZ particles. XRD analysis confirms the presence of starting oxides before and after the casting process.

Abstract: Liquid crystals (LCs) are compounds that have properties between isotropic liquids and solid crystal materials. Although there is not a parameter to predict this behavior, the liquid crystals reported until now have common characteristics, for example rigid groups such as columns or rods within its structures, and long hydrocarbon chains that give flexibility. In this work we report the synthesis and characterization of LC N,N'-(1,4-phenylene bis (methanylylidene)) bis (4-(hexyloxy) aniline). The compound was characterized by infrared (IR), raman and ¹H-nuclear magnetic resonance (¹H-NMR) spectroscopies. The mesomorphic properties were determined by Differential Scanning Calorimetry (DSC) and Polarized Optical Microscopy (POM). The compound N,N'-(1,4-phenylene bis (methanylylidene)) bis (4-(hexyloxy) aniline) was obtained with a yield of 87 % and purity of 99.9 % determined by elementary analysis. The POM study revealed that this compound have a typical low molecular weight liquid crystal behavior. At temperatures of 157 and 174 °C typical mesophases of liquid crystals were observed; the phase transitions were analyzed by DSC. The POM images reveal the typical birefringence of liquid crystal behavior and different anisotropic textures of smectic and nematic mesophases, these textures are characteristic of the benzylideneanilines or Schiff bases.

Abstract: 2,2'–(2,5-bisoctyloxy-1,4-phenylenvinylidene)bis-8-acetoxyquinoline (TrimQ1), 2,2’-(2,5-bisoctyloxy-1,4-phenylendivinylene)bis-6-bromoquinoline (TrimQ2) 2,2'–(2,5-bisoctyloxy-1,4-phenylendivinylene)bis(8-acetoxy-5,7-dichloro)quinoline (TrimQ3), were synthesized and characterized by different spectroscopic methods. The fluorescent properties of these bisphenylenvinylenquinoline oligomers were analyzed by fluorescence spectroscopy and then the quantum yields were calculated. The order of light emitting properties: (TrimQ3) (quantum yield, 75%) > (TrimQ2) (quantum yield, 21% ) > (TrimQ1) (quantum yield, 5%), showing that TrimQ3 is more suitable for OLED construction than other compounds. Thin films were prepared by spin coating from concentrated solutions of the compounds using a polystyrene (PS) matrix on glass. Prototypes of diodes were fabricated using ITO/organic film/In-Ga a configuration. For all the devices, electroluminescence properties also were analyzed through applying a voltage larger than 8 V and a current of 4 mA.

Abstract: A thermodynamic study (Pourbaix type diagrams, using the software Hydra/Medusa) of acid leaching solutions to obtain the electrochemical recovery of Ni, Cu and Zn present in printed circuit boards is reported. Solutions were characterized by atomic absorption spectroscopy at room temperature. The metals were leached in a 0.9237 M H₂SO₄ solution (pH = 1.56) at temperatures of 313, 323, 333 and 343 K. From this data, the reduction potentials were determined for each metal, finding the values of -0.0024, -1.1274 and-0.5892 V vs calomel for Cu, Ni and Zn, respectively. Displacement in the reduction potential with the increase of the metal concentration in the leaching solution was observed.

Abstract: HfN is a transition metal nitride that shows interesting mechanical and chemical properties for using electronic, mechanical, corrosion, wear areas. In this work HfN thin films were fabricated by D.C. sputtering varying nitrogen flux. The Ar/N₂ ratio used inside in the deposition chamber was 10, 6.66, 5, 4 and 3.33. The obtained films were analyzed by X-ray diffraction, Vickers microhardness, high resistivity measurement package and tested by D.C. electrochemical techniques in order to know their crystalline structure, hardness, resistivity and corrosion resistance. We found that a straight relationship of resistivity and crystalline structure with Ar/N₂ flux ratio, because of decreasing that ratio resistivity increases meanwhile hardness decreased, this behavior due to amorphous phase of HfN. Electrochemical tests showed that sample at Ar/N₂ ratio = 5 showed the maximum polarization resistance while the sample at Ar/N₂ ratio = 4 showed less polarization resistance value. All results establish that HfN is a good material in corrosion and electronic areas.

Abstract: Ribbons of Co-base alloy were tested as biocompatible material at in vitro process to develop in the future an implant dental device. Regarding research on the effect of rapid solidification on Co-alloys, few or absent studies to date have been assessed for the evaluation of surfaces properties when the alloys are placed in contact with human mesenchyme stem cells (hMSC). The Co-based ribbons were prepared by rapid solidification process and its surface attached with human adipose-derived mesenchymal stem cells to determine it toxicity, cells viability, adhesive and proliferation of the cells. Experimental results showed that Co-based ribbons are non-toxic material with 80% of increased cellular adhesion and exhibited excellent biocompatibility.

Abstract: ZnS is a promising material to substitute the CdS layer into the thin film solar cells, given its high reflectance and its wide wavelength to catch the solar radiation. ZnS films prepared by chemical bath technique present a low cost and a simple method to produce controlled films. However, the films quality depends on the chemical reagents and their concentration used. In this work, different chemical conditions are proposed for preparing ZnS films by the chemical bath deposition (CBD) technique. ZnS thin films were deposited at 80 °C by CBD by changing the concentrations of the chemical reagents NH₄NO₃, KOH, and maintaining the concentrations of ZnCl₂ and thiourea (SC(NH₂)₂) in the chemical bath. The best conditions of the chemical reagents under the different deposition times (60 to 140 min) were obtained as a result of the experimentation done in order to produce ZnS thin films with good optical quality. The mean optical band gap energy measured on the prepared ZnS films was 3.77 eV, with a film thickness between 40 and 63 nm. The crystalline structure of films was amorphous as obtained by x-ray diffraction analysis. The surface roughness measured on the ZnS films was between 5 to 13 nm as obtained from atomic force microscopy images. Energy Dispersive Spectroscopy analysis show a Zn/S atomic ratio between 0.05 to 0.64.