Authors:P. Jablonski, A. Müller-Blecking, and W. Borchard
A method has been developed that utilizes a special custom-made mixing device and HPLC micro liter syringe to perform mixing
experiments of liquid systems directly in open measuring cells of differential scanning calorimeters. The present paper describes
how to determine mixing enthalpies from time scans of the isothermal heat flux during an exothermal or endothermal process.
Using ethylene glycol and the slightly volatile component water to calibrate the mixing calorimeter, the mixing enthalpy of
the binary system poly(ethylene glycol) 400/water could be determined with sufficient precision compared to the results of
measurements with a conventional flow calorimeter.
Authors:E. Aragon, D. Vincent, A. Zahra, and A. Sebaoun
A systematic study of Al-Zn-Sn ternary alloys by using a Tian-Calvet calorimeter with slow heating and cooling rate was carried
out and supplemented by scanning electron microscopic observations.
The results have shown that crystallization coupled with dissolution of tin into the αss′ ternary solid solution on heating is an endothermic process, while melting coupled with tin expulsion on cooling is an exothermic
one. It seems that the thermal effects of phase transition are outweighed by much stronger ones due to a large composition
change of the αss′ ternary phase.
Authors:A. Książczak, M. Ostrowski, and W. Tomaszewski
The melting and mixing enthalpy of the binary system nitrocellulose and N-nitrodiethanolamine dinitrate (DINA) was determined
by DSC. The mixing enthalpy HmaxM = 1.95 kJ mol−1 had maximum at mass fraction xwDINA=0.46. The influence of samples storing on glass and endothermic transitions were studied. The temperature range of glass
transition broadened with xwDINA what proved the increase of samples heterogeneity. For xwDINA≤0.750 no influence of samples storing on the phase changes was observed. The heat capacity change decreased and temperature
range of glass transition increased for xwDINA≤0.500 what indicated the reduction of glass phase fraction in studied samples.
The results of calorimetric investigations in the section Pb-Bix-Mgy-Sbz (mole ratio Bi:Mg:Sb=8:1:1) of the system Pb-Bi-Mg-Sb with Oelsen's method are presented. The constructed space diagram and
enthalpy isotherm diagram were used to determine integral mixing enthalpies for the investigated section in the temperature
interval 450–1100 K.
Authors:A. Książczak, Teresa Książczak, and M. Ostrowski
Values of the Flory-Huggins interaction parameters c were predicted on the base of mixing enthalpy HM for nitrocellulose-s-diethyldiphenylurea system. The phase diagram of the system and the glass transition temperature of
mixtures Tg12 were estimated using calculated c parameters. The predicted glass transition temperatures were in accordance with values
Authors:C. Cardelli, G. Conti, P. Gianni, and R. Porta
The mixing enthalpies of blends of polymethylmethacrylate (PMMA) with poly(styrene-co-acrylonitrile) (SAN) were investigated
by analogue calorimetry through the determination of the excess enthalpies of pseudobinary model mixtures corresponding to
the addition of methyl-i-butyrate to a binary mixture of acetonitrile or propionitrile plus toluene or ethylbenzene.
A group contribution procedure, based on UNIQUAC equation, was also devised and the polymeric mixing enthalpies were calculated
from properly defined group contributions. Enthalpies for polymeric interactions were introduced into the Flory-Huggins equation
and the miscibility window of PMMA-SAN mixtures was calculated.
The results show a qualitative agreement with the experimental miscibility data and indicate that both the analogue calorimetry
and the group contribution procedures yield correct results when acetonitrile, and not propionitrile, is chosen as the model
for the polyacrylonitrile repeat unit of the copolymer.
Authors:T. Wolszakiewicz, A. Książczak, and T. Książczak
Melting enthalpy and mixing enthalpy of binary system 2,4-dinitrotoluene and nitrocellulose were determined by DSC method.
The maximum value of mixing enthalpy was HmaxM=1.38 kJ mol−1 for molar fraction xw24DNT = 0.501. The Flory-Huggins parameter (c) was estimated. The solubility curves and glass transition temperatures were predicted
and compared with the experimental results.
The measurements were performed for the samples with different times of storage at room temperature. The analysis of melting
peaks for the mixture leads to the conclusion that for the long periods of storage the melting of 2,4-dinitrotoluene takes
place in the confined spaces (pores) and unconfined space (bulk). The crystallization and melting is observed during the short
time of storage in mixtures with low nitrocellulose content and in the case of mixtures with a large amount of NC the glass
transition is additionally observed.
The mixing and melting enthalpy of the binary system nitrocellulose+2,6-dinitrotoluene was determined using the DSC method.
The mixing enthalpy of the components was calculated. At the melting temperature the maximum value of the mixing enthalpy
for the mole fractionxw26DNT=0.607 is equal HMmax= −3.41 kJ mol−1. Measurements of the melting process (second measurement) were conducted after a storage period of several days at room temperature.
Analysis of the melting peaks shows that the melting process of 26DNT takes place in pores of the micro-fiber and bulk outside
the fibers. In the case of a mass fraction of xw26DNT>0.9 the melting process takes place in the bulk, which suggests that in the case of such concentrations separation of the
Authors:K. Ardhaoui, J. Rogez, A. Ben Chérifa, M. Jemal, and P. Satre
Lanthanum-bearing silicate-oxyapatites or britholites, Ca10–xLax(PO4)6–x(SiO4)xO with 1≤x≤6, have been synthesized by solid state reaction
at high temperature. They were characterized by X-ray diffraction and IR spectroscopy.
Using two microcalorimeters, the heat of solution of these compounds have
been measured at 298 K in a solution of nitric and hydrofluoric acid. A strained
least squares method was applied to the experimental results to obtain the
solution enthalpies at infinite dilution, and the mixing enthalpy in two steps.
In the first step the mixing enthalpy obtained is referenced to the britholite
monosubstituted and to the oxysilicate. The mixing enthalpy referenced to
the oxyapatite and to the oxysilicate is then extrapolated. In order to determine
the enthalpies of formation of all the terms of the solution, thermochemical
cycles were proposed and complementary experiments were performed. The results
obtained show a decrease of the enthalpy of formation with the amount of Si
and La introduced in the lattice. This was explained by the difference in
the bond energies of (Ca–O, P–O) and (La–O, Si–O).
Excess molar enthalpies were measured at 298.15 K with a flow calorimeter built in our laboratory for the two ternary systems
(acetonitrile+methyl isobutyrate+toluene) and (propionitrile+methylisobutyrate+ethylbenzene). Experimental data were nicely
predicted by some empirical andsemi empirical procedures, exception made for UNIFAC group contribution method. The latter
equation proved unsatisfactory for all mixtures containing methyl isobutyrate. The first ternary set proved a good model system
to simulate mixing enthalpies reported in the literature for mixtures of poly(styrene-co-acrylonitrile) with polymethylmethacrylate.