In this work the influence of Cu admixtures on the crystallization process of amorphous Fe-Si-B alloys is studied, based on
measurements of differential thermal calorimetry of the series Fe75-xCuxSi9B16 (x=0, 1, 2, 2.8 and 3.5) during their heating with different heating rates. The first crystallization stage can not be traced
for any of the amounts of Cu content examined, while the second stage is observed only when the Cu content is 1 at%. The activation
energy as estimated with Kissinger's method for the third crystallization stage has a mean value of 326 kJ mol-1 and with the isoconversional Flynn, Wall and Ozawa method is almost constant when 0.05<a<0.6 and exhibits a small monotical
decrease when a>0.6. The main crystallization peak can not be described by means of a single JMA-type function.
Different samples of limestones, with small differences in their stoichiometry, have been studied comparatively. The carbonation
reaction has been studied for a large area of isothermal temperatures. The conditions for the multicyclic experiments of calcination/carbonation
were: isothermal temperature 670°C, heating time 60 min and carrier gas CO2. The final carbonation conversion depends mainly on the isothermal temperature of the carbonation reaction and the heating
time. The final temperature of the calcination reaction depends on the percentage of CaO that it has not been conversed to
CaCO3 in the repeated carbonation experiments. The quantity of CaO that has not been carbonated, in the same sample, affects the
values of the coefficients of the kinetic model that fit the calcination reaction. In the multicyclic experiments the carbonation
conversion for two of the four studied samples, was high enough in comparison to other samples of calcite. At sample A the
reduction of the carbonation conversion during the first five cycles is less than it is at other samples from the literature.
Under the above experimental conditions — isothermal temperature and heating time — specific samples consisted mainly of calcite
can absorb larger quantities of CO2 than samples consisted mainly of dolomite.
The thermal degradation of polymers has been studied quite extensively using thermogravimetric measurements. For the kinetic
description, most of the times single rate heating data and model-fitting methods have been used. Since the thermal degradation
of the polymers is a very complex reaction, the choice of a reliable model or a combination of kinetic models is very important.
The advantages or the disadvantages of using a single heating rate or multiple heating rates data for the determination of
the kinetic triplet have been investigated. Also, the activation energy has been calculated with the isoconversional and model-fitting
methods. The reaction model was determined with the model-fitting method. The limits of all these procedures were investigated
with experimental data of the thermal degradation of the poly(ethylene adipate) (PEAd).
Summary The effect of sintering on the maximum capture efficiency of CO2 is studied, using a carbonation/calcination cycle for a series of samples with different stoichiometries of dolomite and calcite. For the materials that belong to the categories of limestone and dolomitic limestone, sintering decreases the extent of carbonation significantly at the two different highest temperatures studied. The extent of carbonation for the same maximum heating temperature depends mainly on the percentage of dolomite. Sintering is negligible in the dolomitic rocks, especially at the maximum heating temperature of 1005°C. The composition of the carrier gas does not seem to play a significant role. The reduction of the extent of carbonation at the second heating /cooling cycle in limestone, and the durability after enough successive cycles of calcination/carbonation in the dolomitic rocks, does not seem to be affected by the maximum temperatures of calcination that were used at the experiments.
Authors:K. Chrissafis, K. Paraskevopoulos, and C. Manolikas
thermal effect accompanying the transition of Cu2–xSe
into a superionic conduction state was studied by non-isothermal measurements,
at different heating and cooling rates (β=1, 2.5, 5, 10 and 20C
min–1). During heating the peak temperature
(Tp) remains almost
stable for all values of β, (136.80.4C for Cu2Se
and 133.00.3C for Cu1.99Se). A gradual
shift of the initiation of the transformation towards lower temperatures is
observed, as the heating rate increases. During cooling there is a significant
shift in the position of the peak maximum (Tp)
towards lower temperatures with the increase of the cooling rate. A small
hysteresis is observed, which increases with the increase of the cooling rate, β.
The mean value of transformation enthalpy was found to be 30.30.8
J g–1 for Cu2Se and
28.90.9 J g–1 for Cu1.99Se.
The transformation can be described kinetically by the model f(ǯ)=(1–ǯ)n(1+kcatX), with activation energy E=175 kJ mol–1,
exponent value n equal to 0.2, logA=20 and log(kcat)=
Authors:K. Chrissafis, M. Lalia-Kantouri, and P. Aslanidis
Two series of copper (I) halide complexes formulated as [(L)CuX(μ2-L)2CuX(L)] and [(L)2Cu(μ2-L)2Cu(L)2]2+ 2χ−, respectively (X = Cl, Br and L = 4,6-dimethylpyrimidine-2-thione (dmpymtH)) were prepared. From the thermogravimetric curves it was found that among the four studied materials, [Cu2(dmpymtH)6]2+2Cl− presents a lower thermal stability. For the determination of the activation energy (E) two different methods have been used comparatively, since every method has its own error. These methods were the isoconversional methods of Ozawa, Flynn and Wall (OFW), and Friedman. The dependence of the E on the value of the mass conversion α, as calculated with OFW and Friedman’s methods, can be separated in three distinct regions. The decomposition mechanism is very complex and can be described using at least three different mechanisms with different activation energies. The best fitting of experimental data with theoretical models gave nth-order for all the three mechanisms (Fn–Fn–Fn).
Authors:P. Aslanidis, K. Chrissafis, and M. Lalia-Kantouri
Copper (I) halide complexes formulated as [(L)2Cu(μ2-L)2Cu(L)2]2+ 2χ−, (X = Cl, Br and L = pyridine-2-thione (py2SH) or 4,6-dimethylpyrimidine-2-thione (dmpymtH)) were prepared, and their photoluminescence and thermal properties were investigated. The complexes are strongly emissive in the solid state, with the emissions being dominated by large Stokes shifts (>200 nm), which are depending on both the heterocyclic thione and the nature of the halogen. These emissions can be assigned to MLCT with some mixing of the halide-to-ligand (XL) CT characters. Simultaneous TG/DTG–DTA technique was used for two complexes with the dmpymtH ligand to determine their thermal degradation, which was found to be very complicated. In inert atmosphere the residues at 1,000 °C (verified with PXRD) were mainly Cu2S, while at 1,300 °C a mixture of Cu2S and Cu. In oxygen atmosphere the residues were CuO.
Authors:A. Vassiliou, K. Chrissafis, and D. Bikiaris
A series of PET/acid-treated multi-walled carbon nanotubes (MWCNTs) nanocomposites of varying nanoparticles’ concentration
were prepared, using the in situ polymerization technique. TEM micrographs verified that the dispersion of the MWCNTs into
the PET matrix was homogeneous, while some relatively small aggregates co-existed at higher filler contents. Intrinsic viscosity
of the prepared nanocomposites was increased at low MWCNTs contents (up to 0.25 wt%), while at higher contents a gradual reduction
was observed. The surface carboxylic groups of acid-treated MWCNTs probably reacted with the hydroxyl end groups of PET, acting
as chain extenders at smaller concentrations, while at higher concentrations, on the other hand, led to the formation of branched
and cross-linked macromolecules, with reduced apparent molecular weights. From the thermogravimetric curves, it was concluded
that the prepared samples exhibited good thermostability, since no remarkable mass loss occurred up to 320 °C (<0.5%). The
activation energy (E) of degradation of the studied materials was estimated using the Ozawa, Flynn, and Wall (OFW), Friedman and Kissinger’s methods.
Pure PET had an E = 223.5 kJ/mol, while in the PET/MWCNTs nanocomposites containing up to 1 wt% the E gradually increased, indicating that MWCNTs had a stabilizing effect upon the decomposition of the matrix. Only the sample
containing 2 wt% of MWCNTs exhibited a lower E due to the existence of the aforementioned cross-linked macromolecules. The form of the conversion function for all the studied
samples obtained by fitting was the mechanism of nth-order auto-catalysis.
Authors:M. Daviti, K. Chrissafis, K. Paraskevopoulos, E. Polychroniadis, and T. Spassov
The kinetics of the α-β phase transition of HgI2 were investigated by isothermal and non-isothermal differential scanning calorimetry. The effective activation energy of
the transition, 41540 kJ mol-1, was determined applying the methods of Kissinger and Ozawa. The transition kinetics were described by the Johnson-Mehl-Avrami
model and the value of the Avrami exponent n was found to range from high values (n>3) at the early stages to lower values at later stages of the transformation, with an average value of 2.
Authors:K. Chrissafis, K. Efthimiadis, E. Polychroniadis, and S. Chadjivasiliou
In this work we study the influence of Mo admixtures on the crystallization process of amorphous Fe78-xMoxSi9B13 (x=1, 2, 3 and 4) alloys by measurements of differential scanning calorimetry and on the soft ferromagnetic properties of the
alloys by magnetic measurements. The addition of Mo by replacing Fe, results in magnetic hardening of materials. In DSC curves
two peaks appear which are distinct when the concentration of Mo is 1 at.% and partly overlap when the Mo content is 2 at.%.
Further increase in the Mo content leads to the appearance of just one peak. The activation energy was calculated both with
Kissinger's and isoconversional Flynn, Wall and Ozawa methods.