Search results for "Isothermal microcalorimetry"
showing 10 items of 19 documents
Natural fluorapatite as a raw material for Portland clinker
2018
Abstract The present work focuses on the mineralogy and the reactivity of clinkers made from the integration of natural fluorapatite in the raw meals with percentages ranging from 0 up to15%. The samples were characterized by infrared spectrometry, X-ray diffraction and microscopy techniques. The distribution of phosphorous and fluorine into clinkers minerals was determined by MEB/EDS mapping. The mineralogical composition was determined by XRD/Rietveld and the samples reactivity followed by isothermal microcalorimetry. It has been found that fluorine stabilizes C3S and β-C2S which still are found with high levels of P2O5. Cements obtained from up to 8% natural fluorapatite incorporation st…
Determination of Kinetic and Thermochemical Parameters of a Substitution Reaction at a Square-Planar Palladium(II) Complex in Water/AOT/n-Heptane Mic…
1995
Abstract The substitution reaction [Pd(bipy)(en)] 2+ + en → [Pd(en) 2 ] 2+ + bipy (where bipy = 2,2′-bipyridine and en = ethylenediamine) has been studied in water and water/AOT/ n -heptane microemulsions at various values of the molar ratio R ( R = [water]/[AOT]) by flow microcalorimetry. From calorimetric data, molar enthalpies of reaction and rate constants were obtained. These quantities indicate that, by increasing R , the reaction becomes less exothermic and its rate constant decreases, trending to the value observed in water. These features can be reasonably rationalized in terms of the peculiar solvation state of reactants inside the AOT reversed micelles and/or the peculiar physico…
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…