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Abstract : Determination of Ion-Pair Formation Constants for MA+ Ions (M = Ca, Sr, Ba, Cu, Cd) with A- = Picrate Ion in Water by Picric Acid Extraction into Benzene
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Abstract: Ion-pair formation constants (KMA0) for MA+ = MPic+ and MCl+ in water were determined at 298 K and ionic strength → 0 by extraction experiments of picric acid (HPic) in the presence of M(II) in the water phase into benzene (Bz) and by potentiometry with a commercial Cl--selective electrode, respectively. Here, M denotes Ca(II), Sr(II), Ba(II), Cu(II), and Cd(II). In adding Pb(II) data, a relation between KMA0 values was KMCl0<KMPic0 for a given M(II).For CdPic+, the KMA0 value (= 136mol-1 dm3) determined by the HPic extraction was somewhat larger than that (= 108) potentiometrically-determined before with a Cd2+-selective electrode, while for CaPic+ the former value (= 89) equaled the latter one (= 88) determined before with a Ca2+-selective electrode. Keywords: Ion-pair formation constants, extraction, potentiometry, divalent metal ions, picrates, chlorides.Download Full Article |
Abstract : The Ternary System H3PO4– Ca(OH)2–H2O Isotherms at 15 and 45 °C
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Abstract: The solid–liquid phase equilibria of the system H3PO4– Ca(OH)2–H2O were studied under air pressure using a synthetic method based on conductivity measurements. Two isotherms at 15 and 45 °C were completely defined. The stable solid phases which appear in this range of temperature are hydroxyapatite (Ca10(PO4)6(OH)2), calcium hydrogen phosphate dihydrate (CaHPO4.2H2O), calcium hydrogen phosphate anhydrous (CaHPO4) and calcium dihydrogen phosphate monohydrate (Ca(H2PO4)2.H2O). These solid phases were characterized using X ray diffraction. Keywords: Solid-liquid phase equilibria, ternary system H3PO4– Ca(OH)2–H2O, calcium phosphate, isotherm.Download Full Article |
Abstract : Sol–Gel Synthesis and Crystal Nucleation of Photosensitive Au/Ag-Containing Glasses of Lithium Silicate System
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Abstract: A sol–gel method has been proposed for obtaining the sintering mixture used in the preparing of a photosensitive Au/Ag-containing glasses of the Li2O - SiO2 system. It has been established that the use of sol–gel method for the production of the batch for synthesizing photosensitive Au/Ag-containing glasses gives more homogeneous distribution of Au/Ag metals in the bulk of the glass. Crystal-nucleation main characteristics have been defined in a large area of compounds of photo-structured compositions of a lithium–silicate system (23.4–46.0 Li2O mol % by analysis) both for spontaneous and catalyzed nucleations. The spontaneous (homogeneous) nucleation happened in the samples without any photosensitive metals and with photosensitive gold–silver additives (0.05 wt % above 100%) without irradiation; the catalyzed (heterogeneous) nucleation happened in the samples with photosensitive silver ore gold additives under x-ray CuKα irradiation. The ranges of the compositions of the glasses in which the effect of catalyzing irradiation is reversed (suppressing nucleation in accordance with the autocatalytic mechanism) under certain conditions. The spontaneous and catalyzed nucleation of crystals in the glasses of Li2O – SiO2 system caused by the addition of photosensitive impurities and X-ray irradiation was analyzed in glasses with a very wide range of compositions in Li2O – SiO2 system. Composition ranges with positive (+) and negative (-) differences in the rates of catalyzed and spontaneous steady-state nucleation were established. This finding point is favorable for obtaining photostructured (photosensitive) materials. The concentration limit was determined to be 37.98 mol % Li2O. About this value, we observe a modification of the mechanism of nucleation of crystals. The behavior of crystal nucleation in photostructured glasses under X-ray irradiation changes to the reverse: autocatalytic nucleation is suppressed rather than induced by x-ray CuKα irradiation. These peculiarities of crystallization mechanism in glasses under study give one the possibility to choose the correct composition range depending on the problems facing researchers. Keywords: Photosensitive glasses, stages of preparation of crystallized photosensitive glass, sol–gel method for producing the batch, parameters of crystal nucleation in photosensitive glass, catalyzed nucleation on photosensitive Ag and Au impurities, effect of X-rays CuKα on crystal nucleation.Download Full Article |
Abstract : Effect of Composting on the Behavior of Polyolefin Films – A True-to-Life Experiment
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Abstract: Commercial polypropylene (PP), high-, medium- and low density polyethylene (HDPE, MDPE, LDPE) films, as well as MDPE films containing pro-oxidative additives and thermoplastic starch (TPS) were composted for six weeks together with biologically degradable films, such as poly (lactic acid) (PLA), Ecovio (BASF), Mater Bi(Novamont) and cellophane. Visual appearance of the polyolefin-based films did not change significantly, while the biologically degradable films fell apart. Thickness and mechanical properties of the polyolefin-based films also did not vary significantly after composting. The thickness of the degradable films however increased due to biofilm formation and finally decreased due to biodegradation, and their mechanical properties drastically dropped. FTIR proved the formation of carbonyl absorption of commercial and of the additive-containing films respectively) after composting due to oxidation. The FTIR-spectrum of the biodegradable films showed drastic change after composting. Formation of free radicals was detectable by ESR-spectroscopy, if pro-oxidative additive containing MDPE film was exposed for one week to sunlight, and the intensity of free radical formation increased after composting. The number-average molecular mass of MDPE films containing pro-oxidative additives decreased, low molecular mass fractions appeared and polydispersity increased after composting. Commercial polyolefin films were covered by microorganisms much more densly than films containing pro-oxidative additives detected by SEM. Even TPS did not increase the quantity of microorganisms. Biodegradable films were densly covered by microorganisms of different types and they became porous and holes were observable on their surface. It can be concluded that composting had no significant effect on the behaviour of the commercial PP and PE films. Signs of initial degradation were observable on MDPE films with pro-oxidative additives and TPS after 6 weeks composting, although it cannot be considered as biological degradation. Non of the tested polyolefin films suffered such degree of degradation in compost, as the biologically degradable films. It may be concluded that polyolefin films neither degrade in compost nor they undergo biodegradation. Keywords: Polyolefin films, degradation in compost, material testing.Download Full Article |
