P.J. van Ekeren

Slow desorption of PCBs and chlorobenzenes from soils and sediments: relations with sorbent and sorbate characteristics.

The kinetics of slow desorption were studied for four soils and four sediments with widely varying characteristics [organic carbon (OC) content 0.5-50%, organic matter (OM) aromatic content (7-37%)] for three chlorobenzenes and five polychlorinated biphenyls (PCBs). Slowly and very slowly desorbing fractions ranged from 1 to 50% (slow) and 3 to 40% (very slow) of the total amount sorbed, and were observed for all compounds and all soils and sediments. In spite of the wide variations in sorbate K(OW) (factor 1000) and sorbent characteristics, the rate constants of slow (k(slow), around 10(-3) h(-1)) and very slow (k(very slow), 10(-5)-10(-4) h(-1)) desorption appeared to be rather constant among the sorbates and sorbents (both within a factor of 5). There was a good correlation (r(2) above 0.9) between the distribution over the slow, very slow and rapid sediment fractions and log K(OC), indicating that sorbate hydrophobicity may be important for this distribution. No correlation could be found between sorbent characteristics [OC, N, and O in the organic matter, polarity index C/(N+O), OC aromaticity as determined by CP-MAS (13)C-NMR] and slow desorption parameters (slowly/very slowly desorbing fractions+corresponding rate constants). The absence of (1) a correlation between k(slow) and k(very slow), respectively, and OC content, and (2) the narrow range of k(slow) and k(very slow) values, indicates that intra-OM diffusion is not the mechanism of slow or very slow desorption, because on the basis of this mechanism it would be expected that increasing OC content would lead to longer diffusion pathlengths and, consequently, to smaller rate constants. In addition, it was tested whether differential scanning calorimetry would reveal a glass transition in the soils/sediments. In spite of the sensitivity of the equipment used (changes in heat flow in the micro-Watt range were measurable), a glass transition was not observed. This means that activation enthalpies of slow desorption can be calculated from desorption measurements at various temperatures. In the present study these values ranged from 60 to 100 kJ/mol among the various soils and sediments studied.

The vapour pressure and enthalpy of sublimation of ferrocene

The vapour pressure of ferrocene was measured in the temperature range 277 to 360 K. A static method (diaphragm manometer) and dynamic methods (torsion and mass-loss effusion) were used. The results are represented by the equation: {R/(·K−1·mol−1}1n(p/p°) =-(4817±26)(K/θ)+(74.29±0.14)x103(K/θ-K/T)-(71±){(θ/T)-1+1n(T/θ)} , where R is the gas constant, po is a standard pressure of 1 Pa, and θ = 317.20 K (mean experimental temperature). The numerical values with their root-mean-square-error ranges represent the thermodynamic function changes on sublimation: ΔsgGmo, ΔsgHmo, and ΔsgCp, mo respectively at 317.20 K.

Vapour-pressure measurements on trans-diphenylethene and naphthalene using a spinning-rotor friction gauge

Abstract Vapour pressures of trans-diphenylethene and naphthalene were measured in the temperature ranges 297.5 to 316.5 K and 244 to 256 K respectively with a spinning-rotor friction gauge. Together with results obtained with a diaphragm manometer (and for trans-diphenylethene, also torsion mass-loss effusion results) these results were fitted to a vapour-pressure equation derived by Clarke and Glew. For the mean temperatures and reference pressure of 1 Pa the following thermodynamic function changes were evaluated: for trans-diphenylethene: ΔsgGmo(331.64 K) = (2065.1 ± 1.2) J · mol−1; ΔsgHmo(331.64 K) = (100.17 ± 0.11) kJ · mol−1; ΔsgCp,mo(331.64 K) = −(63 ± 13) J · K−1 · mol−1, and for naphthalene: ΔsgGmo(306.74 K) = −(8243.1 ± 3.8) J · mol−1; ΔsgHmo(306.74 K) = (72.146 ± 0.049) kJ · mol−1; ΔsgCp,mo(306.74 K) = −(57.3 ± 2.1) J · K−1 · mol−1; ( ∂Δ s g C p, m o ∂T ) p (306.74 K ) = −(1.17 ± 0.15) J · K −2 · mol −1 . From an intercomparison of the results obtained by the different techniques we conclude that the coefficient of tangential momentum exchange is unity within experimental error.

A comparative test of differential scanning calorimeters

The Dutch Society for Thermal Analysis has developed tests to measure the resolution and the sensitivity of Differential Scanning Calorimeters. For this test the substance 4,4′-azoxyanisole is used. This substance shows two transitions: a solid to liquid crystal transition at about 117°C (ΔH≈120 J g−1) and a liquid crystal to isotropic liquid transition at about 134°C (ΔH≈2 J g−1). The resolution test is performed using an amount of 5 mg substance and a high heating rate of 20°C min−1. The resolution is evaluated by measuring how well the two peaks are separated. An amount of 0.25 mg substance and a low heating rate of 0.1 °C min−1 is used for the sensitivity test. The sensitivity is evaluated as the ratio of the peak height of the LC-transition and the top-top noise level.Members of the TAWN were asked to participate in the test. Each participant was provided with an amount of sample and a test procedure. 47 Contributions were received and these results are presented.

Mixtures of d- and l-carvone: I. Differential scanning calorimetry and solid-liquid phase diagram

Abstract Pure l -carvone and mixtures of d - and l -carvone have been studied by differential scanning calorimetry. The obtained curves of heat flow against temperature show the glass transition of the samples, followed by two crystallisation events and, finally, the melting of the carvone mixtures. The measured temperature of melting of pure l -carvone is (247.7 ± 0.5) K and the heat of fusion (11.55 ± 0.05) kJ mol −1 . Five precrystallised samples with compositions ranging from equal amounts of d - and l -carvone up to pure l -carvone have been studied. The carvone system shows mixed crystals at all compositions corresponding to a phase diagram with a minimum at equimolar composition. The data obtained by computer calculations agree with the experimental values, thus showing the thermodynamic consistency of the obtained phase diagram.

Binary common-ion alkali halide mixtures; a uniform description of the liquid and solid state

Abstract Empirical relations for the thermodynamic excess behaviour of binary common-ion alkali halide mixtures were derived. For the liquid state this gave rise to G E(1) ( x , T g ) = 0.68 H E(1) ( x , T g ) and S E(1) ( x , T g )=0.32 H E(1) ( x , T g )/ T g , and for the solid state G E(1) ( x , T )= A (1− T / (2565 K)) x (1− x )(1+ B (1−2 x )), in which the A parameter can be calculated from relative differences in unit cell volumes of the pure solid components A calc (kJ mol −1 ) = 11.53(Δ V / V s )+ 89.40(Δ V / V s ) 2 and the B parameter which is a measure for the asymmetry can be calculated from the A parameter using B = 1.04 × 10 −2 ( A calc /kJ mol −1 ). The phase diagrams were calculated and compared with experimental phase diagram data for twenty binary common-ion alkali halide systems that show complete sub-solidus miscibility.

DSC Calibration During Cooling. A survey of possible compounds

A number of compounds is investigated for DSC calibration during cooling. Adamantane and Zn show fast reversible transitions and can be applied both for temperature and for heat calibrations. A third compound, namely 4,4’-azoxyanisole, has a liquid crystal to isotropic liquid transition at 409K. This compound can be used for temperature calibration. Heat calibration with this compound is more problematic because of the small heat effect and the construction of the baseline. Other compounds like NaNO3, In, Hg and Pb, show a slight supercooling. Nevertheless they can be used for heat calibration. The use of large samples of NaNO3 and In gives the possibility to construct the equilibrium onset temperatures of the cooling peaks, so these two compounds are also appropriate for temperature calibration on cooling.

Measurement of the evaporation coefficient and saturated vapour pressure of trans-diphenylethene using a temperature-controlled vacuum quartz-crystal microbalance

Abstract At a temperature of 307.80 K the net evaporation coefficient αψ of trans -diphenylethene is measured in vacuum and at 0 to 4 per cent relative undersaturation using a temperature-controlled vacuum quartz-crystal microbalance. The net evaporation coefficient appears to be pressure independent and is found to be (0.99 ± 0.07). The saturated vapour pressure is p sat = (0.0274 ± 0.0012) Pa.

The binary system (Li, Na)Br: measurement of the excess enthalpy of solid mixtures; measurement and analysis of the solid-liquid phase diagram

Abstract Excess enthalpies of solid mixtures of (1- X ) LiBr+ X NaBr were evaluated from measured enthalpies of solution. The result is represented by H E ( X , T = 29%K) = X (1- X )12.33+2.3(1-2 X )]kJmol −1 DTA was used to redetermine the position of the liquidus curve, from which the solidus was calculated by LIQFIT, together with the excess Gibbs energy difference function Δ G E X , T = 860 K) = G E liq ( X , T = 860 K) - G E sol ( X , T = 860 K) = X (1- X ){−9.63-1.13(1 -2 X )}kj mol −1 The thermochemical and phase-diagram data give rise to the following excess Gibbs energy function for the solid phase 4 G E sol = (12.1−5.8× 10 −3 T / K )kj mol −1

Specific heat capacities and thermal properties of a homogeneous ethylene-1-butene copolymer by adiabatic calorimetry

Specific heat capacities of a homogeneous ethylene-1-octene copolymer were measured by adiabatic calorimetry in the temperature range from 5 to 400 K (stepwise heating at averaged rates of approximately 1 to 34 K h–1, after cooling at rates in the range from 8 K h–1 to 4 K min–1). The glass transition takes place from roughly 205 to225 K and is centred around approximately 215 K. At the latter temperature, also the temperature drifts during the stabilisation periods are at maximum. Clearly, with devitrification above 215 K also melting sets in. Using two sets of reference data (one for branched and linear polyethylenes, BPE, and the other for strictly linear polyethylene, LPE)for completely crystalline and for completely amorphous material, the crystallinity of the polymer was calculated as a function of temperature, within the two-phase model. In heating, the crystallinity decreased from 0.254 to zero in the temperature range from 220 to 360 K, confirming earlier DSC heat capacity measurements. During the stabilisation periods, below325 K, negative drifts were observed, related to endothermic effects caused by melting. However, in the temperature range from 325 K up to the end melting temperature, 360 K, positive drifts were measured, reflecting exothermic effects. These are attributed to recrystallisation phenomena. The occurrence and amount of recrystallisation depend on the thermal history of the sample: slower cooling and a longer time spent at a temperature of annealing clearly diminish recrystallisation.