Study on the influence of PTFE particle size on the polymer thermal behavior: I. Melting

The influence of the size of poly(tetrafluoroethylene) (PTFE) particles, obtained from the formed polymer (bar) by cutting on the fusion was studied in order to get information on the polymer breaking consequence.Three fractions of particle diameters between 1.62–0.42 mm were submitted to DSC in nitrogen, DTA in air and DRX analyses and the results compared to those obtained with the non-processed formed polymer and PTFE mentioned in literature.The study on the heating rate influence on the melting temperature range (T) and the specific heat of fusion (Q/J g^–1) carried out with the fraction of 0.82 mm diameter afforded a method for estimating the polymer specific caloric capacity by means of DSC data.This revised version was published online in November 2005 with corrections to the Cover Date.     

The Effect of Side Chain Association on Thermal and Viscoelastic Properties: Cellulose acetate based polycaprolactones

Cellulose acetate-based polycaprolactones (CAPCL's) were synthesized by the polymerization of -caprolactone which was initiated by non-substituted OH group in cellulose acetate. The CL/OH (mol mol^–1) ratios of the CAPCL's were changed from 2 to 20. Thermal and viscoelastic properties of the CAPCL sheets were studied by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Glass transition, cold crystallization and melting were determined by DSC. Dynamic modules (E'), dynamic loss modules (E') and tan were measured in a temperature range from –150 to 50°C by DMA. Apparent activation energy of a dispersion was calculated from the frequency dependency of E' peak temperature. It was found that the main chain motion of both CA and PCL is observed in a CL/OH ratio from 0 to 10 mol mol^–1. However, when CL/OH ratio exceeds 10 mol mol^–1, the crystalline region which is rearranged by the PCL chain association is observed and only the main chain motion of PCL can be detected.This revised version was published online in November 2005 with corrections to the Cover Date.     

Study of a hollow cathode arc discharge in the presence of chromium oxide

A hollow cathode arc discharge in hydrogen has been used for the purpose of chromium oxide reduction, the solid oxide being placed inside the anode. Mass transport from the oxide to the gas phase and excitation conditions in the plasma have been investigated. The results show that a substantial amount of oxide is transferred to the gas phase with subsequent reduction and deposition inside the cathode cavity, in the form of a pure metal. The residual part condenses on the discharge chamber wall as an amorphous substance, containing 50–60% of Cr metal, and on the anode surface under the form of a mixture of chromium oxide and metal crystals (10%). From spectroscopic investigations it follows that, inside the anode zone, total Cr concentration in the gas phase is of the order of 10¹⁴ cm^–3, the excitation temperature of the atoms and ions being 4500 and 5500 K, respectively, and the ionization temperature being about 6000 K.Notation I absolute spectral line intensity (W cm^–2 sr^–1) - emission coefficient (W cm^–3 sr^–1) - A relative absorption - absorption coefficient (cm^–1) - L plasma diameter (mm) - f _tk oscillator strength - _D full Doppler width (cm^–1) - S( ₀ L) Ladenburg-Levy function - wave number (cm^–1) - k _pl mass transport rate (mol cm^–2 s^–1) - k _th thermal reduction rate (mol cm^–2 s^–1) - u ion mobility (mm V^–1 s^–1 ) - E electric field strength (V mm^–1) - drift velocity (cm s^–1)     

Determination of freezable water content of beef semimembranous muscle DSC study

The freezable water contents of samples obtained from previously chilled semimembranous muscle of middle-aged beef carcasses after a 24 h cooling period a room at in 5±1C were determined by differential scanning calorimetry (DSC) at –5, –10, –15, –20, –30, –40, –50 and –65C. This was accomplished by freezing the samples at the above-mentioned temperatures, followed by thawing to 35C, and measuring the melting peaks of freezable water. The areas of these peaks were determined by using the peak integration method programs through a computer linked to the DSC, and they were then used to determine the latent heat of melting (H _m) in kJ kg^–1 at each freezing temperature. The resultant latent heat of melting per sample was divided by the latent heat for pure water to determine the amount of freezable water present in these samples. This amount of freezable water was divided by the total water content of the meat sample to determine the percentage of freezable water in the sample. The percentage of freezable water was subtracted from 100 to determine the percentage of bound water present in the sample.     

Thermochemistry of Alcohols: Experimental Standard Molar Enthalpies of Formation and Strain of Some Alkyl and Phenyl Congested Alcohols

The standard molar enthalpies of formation _f H _m ^° (cr) at the temperature T = 298.15 K were determined using combustion calorimetry for di-tert-butyl-methanol (A), di-tert-butyl-iso-propyl-methanol (B), and di-phenyl-methyl-methanol (C). The standard molar enthalpies of sublimation _cr ⁸ H _m ^° of these compounds and of di-phenyl-methanol (D) were obtained from the temperature variation of the vapor pressure measured in a flow system. Molar enthalpies of fusion _cr ¹ H _m ^° of the compounds A–D and of tri-phenyl-methanol (E) were measured by differential scanning calorimeter (DSC). From these data and data available from the literature, the following standard molar enthalpies of formation in gaseous phase _f H _m ^° (g) for A, (–397.0 ± 1.2); B, (–418.1 ± 2.3); C, (–34.2 ± 1.3); and D, (0.9 ± 2.1) kJ · mol^–1 were derived, which correspond to strain enthalpies (H _S) of 46.1, 114.7, 8.1, and 5.0 kJ · mol^–1, respectively.     

New books

Summary Micromolar analyses of the nitrogen species NH₃, NO ₂ ^– , and NO ₃ ^– in soil and other samples are usually accomplished by extracting several samples and testing each for a different species. This procedure is not viable when the quantity of the initial sample is limited. An improved method of separating and analysing for ammonia NH₃(aq), nitrite NO ₂ ^– (aq), and nitrate NO ₃ ^– (aq) from a single small sample with concentrations of 0–50 mol/l is reported. No interferences or carryovers among the three nitrogen containing species were found. Uncertainties were ±2–5 mol/l and accuracies with respect to standards were ±3 mol/l.     

Association-Assisted Kinetics of Pentanol-1 and Heptanol-1 Oxyethylation: Kinetic Parameters of Reactions and Association Parameters of Alcohols in the Series Butanol-1–Heptanol-1

The kinetics of pentanol-1 and heptanol-1 oxyethylation in the absence and in the presence of solvents (dodecane, p-xylene, and 1,4-dioxane) is studied under the conditions of base catalysis at 80–150°C and the concentrations of the catalyst (the corresponding sodium alkoxide) and ethylene oxide in the starting mixture of 1 and 10^–3–10^–1 mol/l, respectively. The experimental results are adequately described by the rate law that takes into account the association of alcohol molecules via hydrogen bonds. A hypothesis is advanced that an associate consisting of n alcohol molecules acts as a kinetically independent species in this reaction. The kinetic and association parameters for alcohols in the C₄–C₇ series are compared with the published data.     

Untersuchung der Ionengleichgewichte in Tetrahydrofuranlösungen des 2-Naphthonitril-Natriums

With the aid of conductometric measurements the ion equilibria inTHF solutions of 2-naphthonitrile sodium were studied. It was established that in the concentration interval of 10^–4–10^–5 mol/l the equilibrium ion pairs—free ions is predominant . The ion pairs are contact (average interion distance about 4.1 Å). In the temperature interval of 25 to 40° the heat of dissociation –H=3.1 kcal/mol, whereas between –40 and –70°–H is 1.26 kcal/mol. At higher concentrations (10^–2–10^–3 mol/l) triple ion formation is observed.     

Tris(2-ethylhexyl)phosphate as an extractant for quadrivalent tin,with subsequent determination with pyrocatechol violet in alloy samples

The solvent extraction of tin(IV) from chloride media withtris(2-ethylhexyl)phosphate is presented. Tin(IV) is extracted quantitatively from 2.75–3.20 mol dm^–3 hydrochloric acid using 6.38–6.91 mol dm^–3 tris(2-ethyl-hexyl)phosphate dissolved in toluene as an extractant. After back-extraction of tin(IV) with water from thetris(2-ethylhexyl)phosphate phase, it is estimated spectrophotometrically following complexation with pyrocatechol violet. The recommended range for determination of tin(IV) is 10–100 g. The probable extracted species is SnCl₄·2TEHP. The method is applicable to the analysis of alloy samples with a detection limit of 0.4 g/ml (for 10 g of tin) and a relative standard deviation between 0.21–0.32%.     

Kinetics and mechanism of complex formation between beryllium(II) and the 3-nitrosalicylatopentaamminecobalt(III) ion

Summary The kinetics of formation and dissociation of the binuclear complex of Be²⁺ with 3-nitrosalicylatopentaamminecobalt(III) have been investigated in the 20–40 and 25–40 °C ranges (I = 0.3 mol dm ^–3), respectively. At 25 °C the rate and activation parameters for the formation of the binuclear species are: k _f = 26.9 × 10² dm³mol^–1s^–1, H = 104 ± 7kJ mol^–1 S = 91 ± 22JK^–1mor^–1.The rate constant, activation enthalpy and activation entropy for the acid-catalysed dissociation of the binuclear species are: 1.25 ± 0.08dm³mol ^–1 at 25 °C, 53 ± 3kJ mol^–1 and - 67 ± 9 J K ^–1 mol^–1, respectively. The formation of the binuclear species is chelation controlled while the dechelation is acid catalysed.     

The aggregation in dodecyltrimethylammonium hydroxide aqueous solutions

The aggregation of dodecyltrimethylammonium hydroxide (DTAOH) aqueous solutions has been studied by several methods. It is stepwise and four critical points were found. AtC _T=(2.51±0.10)×10^–4 mol · dm^–3 the surface excess becomes zero, atC _T=(1.300±0.041)×10^–3 mol · dm^–3 small aggregates from, which grow with concentration. AtC _T=(1.108±0.010)×10^–2 mol · dm^–3 true micelles form (CMC) and at (3.02±0.28)×10^–2 mol · dm^–3 the structure of micelles probably changes affecting their properties. The DTAOH micelles are highly ionized (=0.8) at the CMC, and decreases to reach very small values when the total concentration increases.     

The reductions of chloro-, bromo- and iodopentacyanocobaltate(III) anions by titanium(III) in aqueous acidic solution

Summary The reduction of chloro-, bromo- and iodopentacyanocobaltate(III) anions by aquatitanium(III) has been studied in aqueous solution with ionic strength, I = 1.0 mol dm^-3 (LiCl, KBr or KI) at T = 25 °C. The dependence of the observed second-order rate constant, k _obs, on [H⁺] has been investigated over the acid range 0.005–0.100 mol dm ^–3 and is of the general limiting form: k _obs k ₀ + k[H ⁺] ^–1, where k ₀ is appreciable in all cases and k is a composite rate constant. Using values of K _a (associated with the Ti^III hydrolytic equilibrium constant), obtained from the kinetic data for the Ti^III/Co^III redox reactions, and comparison of the rate constants obtained with those for the corresponding V^II reductions of the same Co^III complexes, it is concluded that the Ti^III reductions of these halopentacyanocobaltate(III) complexes proceed via an outer-sphere mechanism.Author to whom all correspondence should be directed, who is presently on leave of absence from Obafemi Awolowo University.     

Hygrometric Determination of the Water Activities of the Aqueous Solutions of the Mixed Electrolyte NaCl–CaCl2–H2O at 25°C

The mixture {yNaCl + (1 – y)CaCl₂}(aq) has been studied with the hygrometric method at the temperature 25°C. The water activities were measured at total molalities from 0.25 mol-kg^–1 to near saturation for different ionic-strength fractions y of NaCl with y = 0.33, 0.50, and 0.67. The obtained data allow the calculation of osmotic coefficients. The experimental results are compared with the predictions of the Zdanovskii–Stokes–Robinson (ZSR), Kusik and Meissner (KM), Robinson and Stokes (RS), Lietzke and Stoughton (LS II), Reilly–Wood–Robinson (RWR), and Pitzer models. From the measured osmotic coefficients, the Pitzer ionic mixing parameters _{Na Ca} and _{Na Ca} Cl are determined and are used to predict the solute activity coefficients in the mixtures. The excess Gibbs energy is also determined. These results are compared with those given in the literature.     

Volumes and heat capacities of anionic-nonionic surfactant mixtures

Density, heat capacity and surface tension measurements of sodium decylsulfate (NaDeS)-dodecyldimethylamine oxide (DDAO)-water mixtures were carried out as functions of the surfactants total molality m_t at fixed stoichiometric mixture compositions X_NaDeS. From the surface tension data, the critical micelle concentration of NaDeS-DDAO mixtures as a function of X_NaDeS were obtained. From density and heat capacity data, the apparent molar volume V_,2 and heat capacity C_,2 of NaDeS-DDAO mixtures in water were calculated, respectively. At a given mole fraction, V_,2 and C_,2 monotonically increases and decreases, respectively, with increasing mt. However, anomalies were observed at X_NaDeS=0.1 and 0.3 for both V_,2 and C_,2 vs. mt curves. The nonideal contributions to the thermodynamic properties for the formation of surfactant-surfactant mixed micelles in water by mixing aqueous solutions of pure NaDeS and DDAO micelles were calculated at 0.3 mol-kg^–1 for the micellized surfactants mixture. The excess volume V^exc and heat capacity as functions of X_NaDeS are concave and S-shaped curves, respectively. All the properties are compared to those for sodium dodecylsulfate-DDAO mixture. In addition, to clarify the effect of the change in the hydrophobicity of the surfactants mixtures V^exc for the dodecyltrimethylammonium bromide-decyltrimethylammonium bromide mixture were calculated from literature data.     

Substitution of [Pt(terpy)H2O]2+ and [Pt(bpma)H2O]2+ with thiols in acidic aqueous solution. terpy = 2,2′:6′2″-terpyridine; bpma = bis(2-pyridylmethyl)amine

The substitution behaviour of [Pt(terpy)H₂O]²⁺ and [Pt(bpma)H₂O]²⁺, where terpy is 2,2:62-terpyridine and bpma is bis(2-pyridylmethyl)amine, was studied as a function of entering thiol concentration and temperature. The reactions between the Pt-complexes and DL-penicillamine, L-cysteine and glutathione were carried out in a 0.10 mol dm^–3 aqueous HClO₄ medium using stopped-flow and conventional u.v.–vis spectrophotometry. The observed pseudo-first-order rate constants for the substitutions are given by k _obs = k ₂[thiol] + k _–2. The k _–2 term represents the reverse solvolysis. This was found to be zero for Pt^II(terpy) which was the most reactive complex. The second-order rate constants, k ₂, for the three thiols varied between 0.107 ± 0.001 and 0.517 ± 0.025 M^–1 s^–1 for Pt^II(bpma) and 10.7 ± 0.7–711.9 ± 18.3 M^–1 S^–1 for Pt^II(terpy), whereas glutathione was found to be the strongest nucleophile. An analysis of the activation parameters, H and S , clearly shows that the substitution process is associative in nature.     

Solubility of pentane, 2-methylbutane,and cyclopentane in liquid nitrogen at 77.4 K

The solubilities of pentane, 2-methylbutane (isopentane) and cyclopentane were measured in liquid nitrogen at 77.4 K by the filtration method. The solubilities of the C₅ hydrocarbons in liquid nitrogen at 77.4 K vary from 1.8×10^–8 mole fraction for cyclopentane, to 3.0×10^–8 mole fraction for pentane and 3.2×10^–7 mole fraction for 2-metylbutane. Correlations between the solubilities of alkanes, alkenes and cyclic hydrocarbons in liquid nitrogen, and some properties of solutes [normal boiling point T _b , enthalpy of vaporization at normal boiling point H _b and the mean of the enthalpy of vaporization and the enthalpy of melting [(H _b +H _m )/2] are presented.     

Isocratic high-performance liquid chromatographic determination of plasma adenosine

Summary Due to manifold physiological and cardioprotective actions of adenosine, the demand for a simple but accurate method to determine its concentration in plasma is increasing. The aim of this study was firstly to develop a simple isocratic method instead of the gradient elution or peak-shifting techniques used earlier and secondly to check conflicting data on the composition of stop-solution, added to the sample in order to prevent changes in adenosine concentration. Isocratic elution improved signal to noise ratio and concentrations of 100 mol L^–1 dipyridamole and 2.5 mol L^–1 erythro-9(2-hydroxy-3-nonyl)adenine in the blood sample effectively prevented both adenosine formation and degradation, even without the use of a 5-ecto-nucleotidase inhibitor. Lowering the concentration of dipyridamole to 25 mol L^–1 caused more than a tenfold increase of adenosine concentration in two out of five cases and even 100 mol L^–1 dipyridamole alone is not sufficient to inhibit adenosine deaminase in blood samples.     

Determination of traces of vanadium with the catalytic maximum wave in differential pulse polarography

Summary A differential pulse-polarographic method has been studied for the determination of vanadium employing the catalytic maximum wave. A well-defined differential pulse polarographic peak is observed in the potential range from –0.2 to –0.7 V vs. SCE for vanadium(V) in 10 mmol 1^–1 NaCl containing 10 mmol 1^–1 acetic acid, 40 mmol 1^–1 pyrocatechol, and 2.5 mmol 1^–1 KBrO₃. The peak current is very large and proportional to the concentration of vanadium(V) between 1×10^–7 and 1×10^–6 mol 1^–1. The relative standard deviation at 0.5 mol l^–1 vanadium(V) was 2.06% (n=7). This method has been successfully applied to the determination of vanadium in standard materials such as pond sediment.

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Spurenbestimmung von Vanadium mit Hilfe der katalytischen Maximumsstufe in der Differential-Puls-Polarographie

Zusammenfassung Ein gut definierter differentialpuls-polarographischer Peak wurde für Vanadium(V) in 10 mmol/l NaCl-Lösung, die 10 mmol/l Essigsäure, 40 mmol/l Brenzcatechin und 2,5 mmol/l KBrO₃ enthielt, beobachtet (Potentialbereich –0,2 bis –0,7 V gegen SCE). Der Peakstrom ist sehr groß und die Vanadiumkonzentration im Bereich von 1×10^–7 bis 1×10^–6 mol/l proportional. Die relative Standardabweichung betrug 2,06% (n=7) bei 0,5 mol/l Vanadium(V). Das Verfahren wurde mit gutem Erfolg zur Vanadiumbestimmung in Standardproben (z.B. Teichsediment) eingesetzt.

     

Measurements of Heat of Zeolite Dehydration by Scanning Heating

A procedure for measurement of the heat of zeolite dehydration by scanning heating has been designed. Simultaneous data on heat flow (DSC) and mass loss (TG) are required for evaluation. The heating rate depends on the experimental conditions (point-spread function, sample mass, crucible design, and calorimetric reproducibility). Dehydration measurements have three advantages as compared with the sorption procedure: i) one can investigate samples with irreversible dehydration; ii) no approximation model is needed for calculation of the partial molar heat of dehydration; and iii) the procedure is not labor-consuming.The procedure was tested on the natural zeolites heulandite, chabazite and mordenite. The results are close to those measured by the sorption procedure. The partial molar heat of dehydration was found to depend on the water content. It increases from 50 to 87 J mol^–1 K^–1 for heulandite, from 53 to 81 J mol^–1 K^–1 for chabazite, and from 51 to 71 J mol^–1 K^–1 for mordenite.The approximation of the heat of sorption by linear regression was found to be wrong. Detection of a phase transitioN after this approximation has no meaning.This revised version was published online in November 2005 with corrections to the Cover Date.     

Mechanism of reaction of n-butane with but-2-enes in the presence of LaCaX faujasites

The reactions of n-butane and an n-butane (80 mol.%)—isobutane (20 mol.%) mixture with but-2-enes in the presence of polycationic PdLaCaX faujasites were studied. Quantum-chemical calculation of the enthalpies of formation of alkanes C₄—C₈ and their cations showed that the reaction [Bnⁿ]⁺ [Buⁱ]⁺ is of crucial importance for the isomeric composition of the products of alkane alkylation. The general scheme of transformations of the hydrocarbons in the alkylation of n- and iso-paraffins was proposed based on the experimental data on the distribution of the C₈ isomers in the catalyzate at different temperatures and duration of the reaction.