The quality of measurement of heat capacity by differential scanning calorimetry (DSC) is based on strict symmetry of the
twin calorimeter. This symmetry is of particular importance for temperature-modulated DSC (TMDSC) since positive and negative
deviations from symmetry cannot be distinguished in the most popular analysis methods. The heat capacities for sapphire-filled
and empty aluminum calorimeters (pans) under designed cell imbalance caused by different pan-masses were measured. In addition,
the positive and negative signs of asymmetry have been explored by analyzing the phase-shift between temperature and heat
flow for sapphire and empty runs. The phase shifts change by more than 180° depending on the sign of the asymmetry. Once the
sign of asymmetry is determined, the asymmetry correction for temperature-modulated DSC can be made.
Authors:Elena Boldyreva, V. Drebushchak, I. Paukov, Yulia Kovalevskaya, and Tatiana Drebushchak
Monoclinic (I) and orthorhombic (II) polymorphs of paracetamol were studied by DSC and adiabatic calorimetry in the temperature
range 5 - 450 K. At all the stages of the study, the samples (single crystals and powders) were characterized using X-ray
diffraction. A single crystal → polycrystal II→ I transformation was observed on heating polymorph II, after which polymorph
I melted at 442 K. The previously reported fact that the two polymorphs melt at different temperatures could not be confirmed.
The temperature of the II→I transformation varied from crystal to crystal. On cooling the crystals of paracetamol II from
ambient temperature to 5 K, a II→ I transformation was also observed, if the 'cooling-heating' cycles were repeated several
times. Inclusions of solvent (water) into the starting crystals were shown to be important for this transformation. The values
of the low-temperature heat-capacity of the I and II polymorphs of paracetamol were compared, and the thermodynamic functions
calculated for the two polymorphs.
This study examines the polymerization of dental monomers catalyzed by synthesized acylphosphine oxides in a differential
scanning calorimetry (DSC) cell. This research focuses on establishing a relationship between radicals generated by the acylphosphine
oxide photoinitiators and the kinetic reaction rates of methyl methacrylate (MMA) and acrylamide (ACM), a model monomer. The
thermal stability of mono- and di-acylphosphine oxides was examined by DSC. Endothermic melting and exothermic polymerization
reactions initiated with the two initiators were recorded. The acrylamide model system laid the ground work for the critical
evaluation of the synthesized new initiators of mono (2,4,6-trimethylbenzoyl) diphenylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)
phenylphosphine oxide. The bis(acyl) phosphine oxide photoinitiator was more reactive than the mono-(acyl) phosphine oxide
with methyl methacrylates under laboratory conditions. In exothermic reactions, temperatures rose higher and more rapidly
for bis(acyl) phosphine oxide initiated reactions than mono-(acyl) phosphine oxide initiated reactions.
Heat divided by ligand concentration vs. heat, similar to the Scatchard plot, was introduced to obtain the equilibrium constant
(K) and the enthalpy of binding (DH) using isothermal titration calorimetry data. Values of K and DH obtained by this linear
pseudo-Scatchard plot for a system with a set of independent binding sites (such as binding fluoride ions on urease and monosaccharide
methyl a-D-mannopyranoside on concavalin A) were remarkably like that obtained from a normal fitting Wiseman method and other
our technical methods. On applying this graphical method to study the binding of copper ion on myelin basic protein (MBP),
a concave downward curve obtained was consistent with the positive cooperativity in the binding. A graphical fitting by simple
method for determination of thermodynamic parameters was also introduced. This method is general, without any assumption and
restriction made in previous method. This general method was applied to the product inhibition study of adenosine deaminase.
of polyurethane formation between several polyols and isocyanates with dibutyltin
dilaurate (DBTDL) as the curing catalyst, were studied in the bulk state by
differential scanning calorimetry (DSC) using an improved method of interpretation.
The molar enthalpy of urethane formation from secondary hydroxyl groups and
aliphatic isocyanates is 723 kJ mol-1
and for aromatic isocyanates it is 552 kJ mol-1
. In the case of a single second order reaction for aliphatic isocyanates
reaction, activation energy is 705 kJ mol-1
with oxypropylated polyols and 503 kJ mol-1
with Castor oil. For aromatic isocyanates and oxypropylated polyols the activation
energy is higher around 77 kJ mol-1 .
In the case of two
parallel reactions (situation for IPDI and TDI 2-4) best fits are observed
considering two different activation energies.
Isothermal titration calorimetry (ITC) has been used to develop a method to construct the solid-liquid equilibrium line in
ternary systems containing the solute to precipitate and an aqueous mixed solvent. The method consists in measuring the heat
of dissolution of a solid component (the solute) during successive additions of the liquid solvent. The cumulated heat, resulting
from the successive heat peaks obtained for the different injections of known volumes of solvent, plotted vs. the ratio of the numbers of moles nsolvent/nsolute is represented by two nearly straight lines. The intercept of the two lines gives the solubility limit and the corresponding
enthalpy of dissolution of the solute in the solvent.
Solubility diagrams have been established at 303.15 K in binary mixed solvents ethanol-water over the whole concentration
range for seven compounds of pharmaceutical interest, namely: urea, phenylurea, l-valine, dl-valine, l-valine ethyl ester hydrochloride, tris(hydroxymethyl)amino methane.
The thermal polymerization of inhibited styrene monomer is investigated by Accelerating Rate Calorimetry (ARC). The time-temperature-pressure data generated by this technique are utilized in evaluating the thermal hazards associated with the industrial processing of styrene monomer. Several examples are given on the interpretation and application of ARC data to environments ranging from lab to plant-scale conditions including discussions concerning the similarities and dissimilarities between the ARC and large-scale equipment. The polymerization of styrene monomer is also used to evaluate the performance of the ARC over a broad temperature range, 80–300°C. The data indicate that removal of the radiant heater assembly yields better agreement between the heat of polymerization of styrene as measured by the ARC and corresponding values from the literature. This effect is believed to be observable only under conditions of low reaction rates for long periods of time such as in the case of styrene monomer.
Authors:D. Živković, Ž. Živković, L. Yonghua, and K. Chou
Results of the comparative thermodynamic analysis of the Pb-BixMgySbz section (x:y:z=8:1:1, in mole ratio) in the Pb-Bi-Mg-Sb system, obtained experimentally by Oelsen calorimetry and predicted by general solution
model in the temperature range 600–1100 K, are given in this paper.
Authors:T. J. Snee, C. Barcons, H. Hernández, and J. M. Zaldívar
A simple esterification reaction is used to demonstrate standard procedures for determining the thermokinetic parameters of an exothermic reaction from adiabatic calorimetric data. The influence of variations in the heat capacity of the sample due to changes in temperature and concentration is explored. Shortcomings in the simple interpretation of adiabatic data are identified and isothermal heatflow calorimetry is used to reveal autocatalytic effects which were not apparent from the adiabatic experiments. A more rigourous interpretation of the adiabatic and isothermal data is outlined and used to predict the conditions which can lead to exothermic runaway in a batch reactor. Mathematical simulation of the conditions in a jacketed reactor is used to demonstrate the importance of developing reliable kinetic expressions before assessing the safety of a batch process.
Temperature-modulated calorimetry (TMC) allows the experimental evaluation of the kinetic parameters of the glass transition
from quasi-isothermal experiments. In this paper, model calculations based on experimental data are presented for the total
and reversing apparent heat capacities on heating and cooling through the glass transition region as a function of heating
rate and modulation frequency for the modulated differential scanning calorimeter (MDSC). Amorphous poly(ethylene terephthalate)
(PET) is used as the example polymer and a simple first-order kinetics is fitted to the data. The total heat flow carries
the hysteresis information (enthalpy relaxation, thermal history) and indications of changes in modulation frequency due to
the glass transition. The reversing heat flow permits the assessment of the first and higher harmonics of the apparent heat
capacities. The computations are carried out by numerical integrations with up to 5000 steps. Comparisons of the calculations
with experiments are possible. As one moves further from equilibrium, i.e. the liquid state, cooperative kinetics must be
used to match model and experiment.