Search results for "Calorimetry"
showing 10 items of 504 documents
A microcalorimetric study of the different states of argon and nitrogen adsorbed AT 77 K on silicalite-I and ZSM-5
1992
The adsorption of argon and nitrogen on a series of MFI-type zeolites (silicalite-I (Si/Al>1000) and HZSM-5 (16<Si/Al<120)) was studied by isothermal microcalorimetry, volumetry and neutron diffraction.
Confinement in micropores and enthalpies of physisorption
1994
Abstract The use of quasi-equilibrium volumetry associated with isothermal microcalorimetry at 77 K allows direct measurement of the interactions on adsorption of simple probe molecules within well crystallised aluminophosphate and zeolite molecular sieves. Four particular cases are presented which show: the effect of varying micropore diameter, the effect of adsorbing molecules with a favourable geometric compatibility with a given micropore system, the effect of varying the field potential within a given micropore system and finally, the effect of variable selective blocking of the micropore system.
A microcalorimetric comparison of the effect ofn-alkane preadsorption on the adsorption of argon and nitrogen on Silicalite-I
1994
Then-alkanes of different lengths were preadsorbed to selectively block part of the micropores of a MFI-type zeolite, Silicalite-I. The porosity available to argon and nitrogen was then studied by quasi-equilibrium adsorption microcalorimetry and volumetry at 77K and compared to what was found for the bare zeolite. Indeed, although partial adsorption ofn-alkanes does not alter the value of the differential enthalpies of adsorption for both argon and nitrogen, then-butane preadsorption diminishes the adsorption capacity by inducing inaccessible volumes in the micropore network. Moreover, the microcalorimetric experiments clearly show thatn-butane is not evenly distributed in the zeolite chan…
Thermodynamics of transfer of polar additives from the aqueous to the dodecylsurfactant micellar phases
1990
The enthalpies of transfer from water to aqueous surfactant solutions, ΔH(W→W+S), of polar additives have been determined as a function of the surfactant concentration at fixed additive concentration. The surfactants used are sodium dodecylsulfate (NaDS), dodecyltrimethylammonium bromide and dodecyldimethylamine oxide (DDAO). The additives used are iso-butanol t-butanol, butoxyethanol, phenol, benzene, tributylphosphine oxide (TBPO), octyldimethylphosphine oxide (ODPO), octydimethylamine oxide (ODAO), DDAO and NaDS. A maximum was observed in the plots of ΔH(W→W+S) vs. fsms curves for ODPO and ODAO in NaDS while a small minimum was observed for TBPO. The experimental data are rationalized on…
Effect of Nitrogen Methylation on Cation and Anion Coordination by Hexa- and Heptaazamacrocycles. Catalytic Properties of These Ligands in ATP Dephos…
1996
The stability constants of the complexes formed by 1,10-dimethyl-1,4,7,10,13,16-hexaazacyclooctadecane (L) and 1,4,7-trimethyl-1,4,7,10,13,16,19-heptaazacyclohenicosane (L1) with Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Pb(2+), as well as that for the formation of PbL2(2+) (L2 = 1,4,7,13-tetramethyl-1,4,7,10,13,16-hexaazacyclooctadecane), were determined by means of potentiometric (pH-metric) titrations in 0.15 mol dm(-)(3) NaClO(4) at 298.1 +/- 0.1 K. The enthalpy changes for the formation of Cu(2+) complexes with L and L1 were measured by means of microcalorimetry. These thermodynamic data were compared with those previously reported for L2, 1,4,7,10,13,16-hexaazacyclooctadecane (L3), and 1,4,…
Interactions of lysozyme with hydrophilic and hydrophobic polymethacrylate stationary phases in reversed phase chromatography (RPC)
1994
Two silicas, one with a mean pore diameter of 30 nm and the other non-porous, were coated with polymethacrylates of increasing hydrophobicity in the sequence: poly-2-hydroxyethylmethacrylate (P2HEMA)1 polyethylmethacrylate (PEMA) and poly-n-octylmethacrylate (POMA). Association constants, Kass, between lysozyme and the coated silicas were determined by means of frontal analysis, and the apparent heats of adsorption, delta Happ, by means of microcalorimetry. Using Kass and delta Happ the changes in the apparent free energy, delta Gapp, and in the apparent entropy, delta Sapp, were calculated at a concentration of lysozyme < 10 mumol/l. The association between the lysozyme and the coated sili…
Mechanisms and parameters controlling the tricalcium aluminate reactivity in the presence of gypsum.
2007
International audience; To understand the mechanisms and the parameters controlling the reactivity of tricalcium aluminate in the presence of gypsum at an early age, a study of the hydration of the “C3A–sulphate” system by isothermal microcalorimetry, conductimetry and a monitoring of the ionic concentrations of diluted system suspensions have been carried out with various gypsum quantities. The role of C3A source and its fineness were also studied. This work shows the fast initial formation of AFm phase followed by ettringite formation during the period when the sulphate is consumed. It has been highlighted that the time necessary to consume all the gypsum varies with the type of C3A and i…
Early C3A hydration in the presence of different kinds of calcium sulfate.
2009
International audience; Hydration reactions of C3A with various amounts of calcium sulfate hemihydrate, gypsum or a mixture of two, were investigated by isothermal microcalorimetry, and a monitoring of the ionic concentrations of diluted suspensions. This study shows that sulfate type used modifies the early C3A-CaSO4 hydration products and the rate of this hydration. The fast initial AFm formation observed before ettringite precipitation in the C3A-gypsum system is avoided as soon as hemihydrate is present in the suspension. This was attributed to.higher super saturation degrees and then higher nucleation frequency with regard to the ettringite obtained in the presence of hemihydrate. More…
Switching of easy-axis to easy-plane anisotropy in cobalt(ii) complexes
2021
A tetranuclear cubane-type complex [Co4(ntfa)4(CH3O)4(CH3OH)4] (1) with a {Co4O4} core, and a mononuclear complex [Co(ntfa)2(CH3OH)2] (2) have been rationally obtained by adjusting the ratio of the β-diketonate and Co(II) ions, with the synthetic processes being monitored by in situ microcalorimetry. Then, following synthetic conditions to obtain 2, but using three distinct N-donor coligands - 2,2'-bipyridyl (bpy), 6,6'-dimethyl-2,2'-bipyridyl (6,6-(CH3)2-bpy) and 5,5'-dimethyl-2,2'-bipyridyl (5,5-(CH3)2-bpy) - three novel mononuclear complexes have been obtained, [Co(ntfa)2(bpy)2] (3), [Co(ntfa)2(6,6-(CH3)2- bpy)2] (4) and [Co(ntfa)2(5,5-(CH3)2-bpy)2] (5). The introduction of different cap…
Microemulsions: Phase transitions and their dynamics
2007
By differential scanning microcalorimetry we investigate temperature-induced phase transitions and their dynamics in mixtures of water, oil and a non-ionic surfactant. Special emphasis is on an investigation of the transition from a lamellar to a microemulsion phase and on the emulsification failure. The first-order phase transition from a lamellar to a microemulsion phase leads to heat changes up to 1k BT per surfactant molecule. These large values for the latent heat are quantitatively described by an interfacial model which takes into account the temperature dependence of the spontaneous curvature.