Synthesis,Thermal Properties and Electrical Conductivity of Na-Sialate Geopolymer

This work aims to study the thermal behavior of basic-geopolymers derived from metakaolin (clay). The geopolymers were characterized by different techniques: thermal analysis (DTA, TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and impedance spectroscopy. Some physicochemical properties of the products were also determined: the phases obtained after geopolymer heat treatment and their electrical properties. The results obtained after drying and heat treatment showed that the products kept their initial shapes, but revealed variable colors depending on the temperatures at which they were treated. The products obtained are amorphous between 300 up to 600 °C with peaks relating to the presence of nanocrystallites of muscovites and zeolite, thus at 900 °C it is quite amorphous but only contains nanocrystallites of muscovites. From the temperature of 950 °C, we notice that the geopolymer has been transformed into a crystalline compound predominated by the Nepheline (NaAlSiO₄) with the presence of a crystalline phase by minor peaks of Muscovite, this crystalline character has been increased at 1100 °C to obtain a whole phase crystalline of a Nepheline. The treatment of this geopolymer for one hour at 1200 °C shows an amorphous phase again corresponding to corundum (α-Al₂O₃). This indicates that the dissolution of the grains by the liquid phase induces the conversion of the material structure from sialate [–Si–O–Al–O] to sialate siloxo [–Si–O–Al–O–Si–O–] and the formation of a new crystalline phase (α-Al₂O₃). This development of sialate to sialate-siloxo was confirmed by IR spectroscopy. As mentioned above, from 300 to 900 °C, Na-sialate geopolymer exhibits the same disorder structure of nepheline. The crystal structure of nepheline is characterized by layers of six-membered tetrahedral rings of exclusively oval conformation. The rings are built by Regularly alternating tetrahedral AlO₄ and SiO₄. Stacking the layer’s parallel to the c axis gives a three-dimensional network containing channels occupied by Na cations. This topology favors easy movement of Na⁺ ions throughout the structure. For this reason, ionic migration in nepheline is widely reported. The refinement of Na-Sialate geopolymer at room temperature gives bulk high ionic conductivity of about 5 × 10^?5 S cm^?1 and this is due to the probable joint contribution of H⁺ and Na⁺ ions. Above 200 °C, Na⁺ seems to remain the only charge carrier with a low activation energy of about Ea?=?0.26 eV. At higher temperatures, the characteristic frequencies become so close that it is impossible to distinguish the contributions. A total resistance comprising both grain and grain boundaries contribution is then determined.

     

Olfactory Responses of Parasitoid Apoanagyrus lopezi to Odor of Plants, Mealybugs, and Plant–Mealybug Complexes

Apoanagyrus (Epidinocarsis) lopezi De Santis is an endoparasitoid used in the biological control of the cassava mealybug Phenacoccus manihoti Matile-Ferrero in Africa. The response of naive and mated females of A. lopezi to odors from cassava plant (var. Zanaga), parasitized or unparasitized mealybugs, and plant–mealybug host complexes with or without feeding hosts was investigated in a Y-tube olfactometer. Dual-choice tests revealed that mealybug-infested plants and mealybug-damaged plants were the major sources of volatiles that attract female parasitoids to the microhabitat of its hosts. The emission of volatile chemicals appears not to be limited to the infested plant part but to occur systemically throughout the plant. On their own, unparasitized mealybugs were more attractive than uninfested plants or parasitized mealybugs alone. Parasitization of P. manihoti by A. lopezi decreased the response of parasitoids to mealybugs or mealybug–plant complexes. Plants infested with unparasitized hosts attracted more female parasitoids than plants infested with parasitized mealybugs. These results indicate that, in the long-range host-searching process, females of A. lopezi respond mainly to mealybug-induced synomones, and specific host-derived cues play a minor role.     

Voltammetric behaviour of an archeaological bronze alloy in aqueous chloride media

The interface archaeological bronze alloy‐chloride media was characterized by using linear sweep rate cyclic voltammetry. The electrochemical behaviour of the Cu‐Sn alloy being different from pure copper and pure tin. In fact, the voltammograms show an anodic peak and two cathodic peaks. Surface examination revealed a compact layer which spread over the ancient material. The influence of different parameters such as scan rate, chloride concentration and repetitive cycling on the voltammetric response of the archaeological bronze was also studied. The results indicate that patina layer formation is a spreading process over the electrode surface leaving only small pores. Diffusion of the halide controls the growing rate of this layer. Two other anodic peaks are evidences when potential cycling increases. The oxidation became more difficult as a result of a constant layer thickness.     

Identification of In Vitro Metabolites of Synthetic Phenolic Antioxidants BHT,BHA, and TBHQ by LC-HRMS/MS

Butylated hydroxytoluene (BHT) and its analogs, butylated hydroxyanisole (BHA) and tert-butyl-hydroquinone (TBHQ), are widely used synthetic preservatives to inhibit lipid oxidation in the food, cosmetic and pharmaceutical industries. Despite their widespread use, little is known about their human exposure and related biotransformation products. The metabolism of these compounds was investigated using in vitro incubations with human and rat liver fractions. Liquid chromatography coupled to high-resolution tandem mass spectrometry was employed to detect and characterize stable and reactive species formed via oxidative metabolism, as well as phase II conjugates. Several oxidative metabolites have been detected, as well as glutathione, glucuronide, and sulfate conjugates, many of which were not previously reported. A combination of accurate mass measurements, MS/MS fragmentation behavior, and isotope-labeling studies were used to elucidate metabolite structures.     

Physical investigations on Ni doping ZnO thin films along with ethanol response

Journal of Materials Science: Materials in Electronics - Undoped and Ni-doped ZnO thin films were grown on glass substrates at 460 °C using the spray pyrolysis method. All samples...     

A diversity combining DS/CDMA system with convolutional encodingand Viterbi decoding

Averaged diversity combining is applied to an asynchronous DS/CDMA system using convolutional encoding and Viterbi decoding. A cyclic redundancy check (CRC) code is included in the scheme to trigger retransmission requests. Multiple received packets are combined on a bit by bit basis to form a single, more reliable packet. The error correcting decoder operates on the combined packet, as opposed to the most recently received individual packet (e.g., as in a type-I hybrid ARQ protocol), substantially increasing the probability of acceptance with each additional transmission. We show that the proposed technique allows a significant increase in the CDMA system capacity, throughput, and reliability     

Effect of (R+, X–) salts addition on nickel corrosion in 1M sulfuric acid medium

We used the electrochemical techniques to study the effect of the addition of four salts, K⁺,Cl^?, K⁺,Br^?, K⁺,I^? and C₈H₁₇Ph₃P⁺,I^?, on the corrosion behaviour of nickel when submitted to 1M sulphuric acid medium. After one hour of immersion time, we noted an acceleration of nickel corrosion process after the addition of K⁺,Cl^? and K⁺,Br^? in the 1M H₂SO₄ electrolyte. K⁺,I^? exhibited an inhibition of the anodic Ni corrosion process whereas the phosphonium iodine (R⁺,I^?) acts simultaneously on both processes: it is a mixed inhibitor. Such result is due to the adsorption of the alkyl group C₈H₁₇ which limited oxygen diffusion. EIS characterization of Ni exhibited surfaces after iodine salts addition allowed us simulating the resulting interfaces by electrical equivalent circuits. We concluded that (K⁺,I^?) addition decreased the material corrosion rate without changing the alteration mechanism. That result is due to the formation of NiI at the electrode surface. On the other hand, phosphonium iodine addition modifies the interface behaviour. In fact, the alkyl part of the organic iodine adsorbs at the surface preserving it against the corrosive action of the sulfuric acid.