New compositions of fluoroindate glasses with higher chemical resistance

In this paper, glasses in the systems In-Ba-Mg and In-Ba-Zn-Sr-Mg were water leachead at 80ºC showing surface degradation after 72 hours of leaching. The extent of such degradation is determined by the solubility and the concentration of the elemental fluorides that constitute the glasses. The formation of a layer of crystallized phases on the surface of the samples was observed. Small weight losses were registered and the absence of water on the glass matrix after the attack suggested that the use of MgF2 in the systems studied can lead to better results against moisture corrosion when compared to other fluoride glasses such as the fluorozirconates.

Espectroscopia óptica de vidros fluoroindatos dopados com íons Er3+ e Yb3+

Optical spectroscopy in the 400-1700nm wavelength range was performed on rare earth doped heavy metal fluoride (HMF) glasses. In the present work In-based fluoride glasses with a fixed 2 mol % YbF3 concentration and an ErF3 content ranging from 0 to 8 mol % were investigated. According to the experimental spectroscopic data a dependence in the absorption coefficient, the photoluminescence intensity and in the radiative lifetime could be verified as a function of the ErF3 content. In addition, at liquid nitrogen temperature, light emission corresponding to indirect transitions in the infrared energy range could be easily observed as a consequence of the low phonon frequency characteristic of this class of fluoride glasses. For all the studied compositions, strong upconversion to the green and red light was observed by pumping these Er3+- and Yb3+-doped HMF glasses with 790 and 980nm photon sources.

Isolamento e caracterização de acil-tiossemicarbazidas como intermediários na síntese de compostos mesoiônicos

1,3,4-thiadiazolium-2-aminides and their isomers 1,3,4-triazolium-2-thiolates have been synthesized via anhydroacylation reactions. This work presents a study by infrared monitoring of the reaction between substituted aroyl acid chlorides and 1,4-diphenylthiosemcarbazide. The intermediates and products were isolated, purified and charaterized by IR and 13C NMR spectroscopy. The increasing or decreasing in intensity of characteristic stretching bands indicated the rate dependence on the electronic nature of substituents. The results also demonstrate that 1,3,4-triazolium-2-thiolates are obtained in anhydrous conditions whereas presence of water leads to a mixture of the isomers.

Preparation and thermal decomposition of copper(II), zinc(II) and cadmium(II) chelates with 8-hydroxyquinoline

When the compounds are heated in an inert atmosphere it can be verified the consecutive partial sublimation, fusion, partial volatilization and partial thermal decomposition of the anhydrous complexes. When in an oxidating atmosphere the above process is only verified to Cu(II) chelates. Anhydrous copper(II) complexes present a monoclinic structure in the b form and the volatilized compound in a a form. Zinc(II) and cadmium(II) hydrated complexes are isomorphous and they present different cell dimensions from those reported previously.

Propagação da poluição atmosférica por flúor nas águas subterrâneas e solos de regiões próximas às indústrias de fertilizantes (Rio Grande, RS)

Fluoride concentration was determined in rainwater, ground water and soil in the zone of fertilizer industry in the city of Rio Grande. In contaminated rainwater fluorine concentration was registered up to the value of 4,4 mg.L-1. Fluorine concentration in the shallow ground water in general reflects its distribution in the atmosphere, but cannot be used as marker of atmosphere contamination in the urban area due to dissolving influence of residential effluents. The 0,01% HCl extracts from the set of surface soil samples demonstrates fluoride distribution in the zone of influence of industrial emissions, which coincides to the numerical simulation of fluorides dispersion in the air.

Dinámica de reacciones unimoleculares en fase gas: Desviaciones del comportamiento estadístico

The present review summarizes the most relevant results of our research group obtained recently in the field of unimolecular reaction dynamics. The following processes are specifically analyzed: the isomerization, dissociation and elimination in methyl nitrite, the fragmentation reactions of the mercaptomethyl cation, the C-CO dissociation in the acetyl and propionyl radicals, and the decomposition of vinyl fluoride. In all the cases, only state- or energy-selected systems are considered. Special emphasis is paid to the possibility of systems exhibiting non-statistical behavior.

Recuperação de metais de catalisadores mássicos e monometálicos

This work presents a study on the dissolution of some commercial monometallic and non-supported deactivated catalysts in HF + H2O2 mixtures (and, eventually, other media) under mild experimental conditions, after a previous oxidation step. The samples were neither crushed nor grinded. The best experimental conditions were dependent on the nature of the support and of the active phase. For example, the Pt/Al2O3 catalyst was dissolved in about 10 minutes, without agitation and heating; however, dissolution of the Pd/Al2O3, Ni/Al2O3, Ni/SiO2, Cu/Al2O3 and V2O5 samples required a temperature of 60 ºC and an agitation of 400 rpm. A careful addition of a NaOH solution allowed a quantitative precipitation of aluminium as criolite (Na3AlF6) or precipitation of Si as Na2SiF6; NaF was obtained as a by-product. As expected, processing of Pd/C, V2O5 and CuO.Cr2O3 samples was relatively simple. Metals recovery from catalysts reached a quantitative level in all samples studied; it is particularly interesting that platinum and palladium could be easily recovered in a single step process, thus separing them from aluminium.

Eletrodo íon-seletivo para determinação potenciométrica de alumínio(III) em meio de fluoreto

The construction and analytical evaluation of a coated graphite Al(III) ion-selective electrode, based on the ionic pair formed between the Al(F)n3-n anion and tricaprylylmethylammonium cation (Aliquat 336S) incorporated on a poly(vinylchloride) (PVC) matrix membrane are described. A thin membrane film of this ionic pair and dibutylphthalate (DBPh) in PVC was deposited directly on a cylindric graphite rod (2 cm length x 0.5 cm diameter) attached to the end of a glass tube using epoxy resin. The membrane solution was prepared by dissolving 40% (m/m) of PVC in 10 mL of tetrahydrofuran following addition of 45% (m/m) of DBPh and 15% (m/m) of the ionic pair. The effect of membrane composition, fluoride concentration, and several concomitants as potential interferences on the electrode response were investigated. The aluminium(III) ion-selective electrode showed a linear response ranging from 1.4 x 10-4 to 1.0 x 10-2 mol L-1, a detection limit of 4.0 x 10-5 mol L-1, aslope of -54.3±0.2mV dec-1 and a lifetime of more than 1 year (over 3000 determinations for each membrane). The slope indicates that the ion-selective electrode responds preferentially to the Al(F)4- species. Application of this electrode for the aluminium(III) determination in stomach anti-acid samples is reported.

Biodiesel de soja: taxa de conversão em ésteres etílicos, caracterização físico-química e consumo em gerador de energia

Biodiesel was produced by the transesterification of neutral soybean oil and anhydrous ethanol using NaOH as catalyst. Combinations of biodiesel and diesel in the proportions of 0, 5, 10, 20, 40, 60, 80 and 100% were tested, respectively, as fuel in an energy generator. The average consumption and mixture performance were analysed. The tests showed a reduction in Diesel oil consumption when mixed with up to 20% of biodiesel. The quality characteristics of these fuels were analyzed.

O impacto industrial na composição química das águas subterrâneas com enfoque de consumo humano (Rio Grande, RS)

The alteration in the quality of groundwater in the industrial zone of Brazil's southernmost state was assessed by a hydrogeochemical study. In 70-85% of the studied area, fluoride, nitrate and phosphate in groundwater surpass the maximum limits for human consumption according to Brazilian environmental legislation. The chemical spectrum of contaminants and their spatial distribution show that fertilizer production processes are responsible for groundwater pollution. The natural conditions of the region are not favorable for minimal protection against infiltration of pollutants into the aquifer.

Biodiesel de babaçu (Orbignya sp.) obtido por via etanólica

Biodiesel was obtained by transesterification of babassu oil in anhydrous ethanol and methanol, employing NaOH as catalyst. The products obtained were characterized by physico-chemical and thermogravimetric analysis. It could be concluded that the properties of the two types of biodiesel (ethanolic and methanolic) are very similar when compared with diesel oil.

Processamento de pilhas Li/MnO2 usadas

This work presents two recycling processes for spent Li/MnO2 batteries. After removal of the solvent under vacuum the cathode + anode + electrolyte was submitted to one of the following procedures: (a) it was calcined (500 ºC, 5 h) and the calcined solid was submitted to solvent extraction with water in order to recover lithium salts. The residual solid was treated with sulfuric acid containing hydrogen peroxide. Manganese was recovered as sulfate; (b) the solid was treated with potassium hydrogeno sulfate (500 ºC, 5 h). The solid was dissolved in water and the resulting solution was added dropwise to sodium hydroxide. Manganese was recovered as dioxide. The residual solution was treated with potassium fluoride in order to precipitate lithium fluoride.

Recuperação de cobalto e de lítio de baterias íon-lítio usadas

The "active mass" (cathode + anode + electrolyte) of spent Li-ion batteries was submitted to one of the following procedures: (a) it was calcined (500 ºC) and submitted to extraction with water to recover lithium salts. The residual solid was treated with sulfuric acid containing hydrogen peroxide. Cobalt was recovered as sulfate; (b) the "active mass" was treated with potassium hydrogen sulfate (500 ºC) and dissolved in water. Cobalt was precipitated together with copper after addition of sodium hydroxide. Lithium was partially recovered as lithium fluoride. Co-processing of other battery components (aluminum and copper foils) affected negatively the behavior of the recovery procedures. Previous segregation of battery components is essential for an efficient and economical processing of the "active mass".

Teor de fluoretos em infusões de chá verde (Camellia sinensis)

The aim of this work was to study the influence of green tea consumption on fluoride ingestion. The extraction conditions of fluorides from green tea infusions were defined and nine brands of green tea available in Portugal were analyzed. The quantification of fluorides in the green tea was preceded by the implementation and validation of the potentiometric method (commercial fluoride selective electrode). The concentration of fluorides in the samples ranged from 0. 8 to 2. 0 mg L-1.

O ressurgimento da química de benzino com sililaril triflatos no contexto das reações de inserção em ligações sigma

In this paper we gathered articles concerning insertion reactions of arynes, exclusively generated from 2-(trimethylsilyl)aryl triflates in the presence of fluoride ions, in substrates bearing nucleophilic and electrophilic portions separated by sigma bonds. Accordingly, we stand out the great importance and versatility of such transformations in the preparation of highly functionalized aromatic systems, which are hardly synthesized in just one step for other methods.