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.
Thermogravimetric (TG) and differential thermal analysis (DTA) curves of methyltributylammonium smectite (MTBAS), methyltrioctylammonium
smectite (MTOAS), and di(hydrogenatedtallow)dimethylammonium smectite (DHTDMAS), and also corresponding sodium smectite (NaS)
and tetraalkylammonium chlorides (TAAC) were determined. The TAACs was decomposed exactly by heating up to 500°C. The adsorbed
water content of 8.0% in the pure NaS was decreased down to 0.2% depending on the size of the non-polar alkyl groups in the
tetraalkylammonium cations (TAA+). The thermal degradation of the organic partition nanophase formed between 2:1 layers of smectite occurs between 250–500°C.
Activation energies (E) of the thermal degradations in the MTBAS, MTOAS and DHTDMAS are 13.4, 21.9, and 43.5 kJ mol−1, respectively. The E value increases by increasing of the interlayer spacing along a curve depending on the size of the alkyl groups in the TAA+.
The thermal degradation of poly(vinyl acetate) (PVA), poly(vinyl alcohol) (PVAL), vinyl acetate-vinyl alcohol (VAVAL), vinyl
acetate-vinyl-3,5-dinitrobenzoate (VAVDNB) and vinyl alcohol-3,5-dinitrobenzoate (VALVDNB) copolymers have been studied using
differential thermal analysis (DTA) and thermogravimetry (TG) under isothermal and dynamic conditions in nitrogen. Thermal
analysis indicates that PVA and PVAL are thermally more stable than VAVAL copolymers, being PVAL the most stable polymer.
The presence of small amounts of vinyl-3,5-dinitrobenzoate (VDNB) in PVA or PVAL produces a marked decrease in the thermal
stability of both homopolymers, being VALVDNB copolymers the less stable materials. The apparent activation energy of the
degradative process was determined by the Kissinger and Flynn-Wall methods which agree well.
The equation for calculation of the activation energy of the diffusion of the evolved products through the matrix (E) from a single TG curve were proposed by solving Fick's laws. The solution is based on the similarly theory by utilizing
a Fourier number.
The proposed method was examined by using mass loss data for the dehydroxylation of some micas with and without FeO (muscovite
and its varieties and lepidolite) as determined from their TG curves. TheE values for the first stage of the dehydroxylation of these micas areE1,=85±10 kJ mol−1; for the final stageE2=380±40 kJ mol−1 and for the mass loss connected with fluorineEF=85±10 kJ mol−1.
presents the model-free kinetic approach in the context of the traditional
kinetic description based on the kinetic triplet, A, E, and f(α)
or g(α). A physical meaning and interpretability
of the triplet are considered. It is argued that the experimental values of f(α) or g(α)
and A are unlikely to be interpretable in the respective terms of the reaction
mechanism and of the vibrational frequency of the activated complex. The traditional
kinetic description needs these values for making kinetic predictions. Interpretations
are most readily accomplished for the experimental value of E
that generally is a function of the activation energies of the individual
steps of a condensed phase process. Model-free kinetic analysis produces a
dependence of E on α that is sufficient
for accomplishing theoretical interpretations and kinetic predictions. Although
model-free description does not need the values of A
and f(α) or g(α),
the methods of their estimating are discussed.
Authors:M. Kök, G. Pokol, C. Keskin, J. Madarász, and S. Bagci
In this research thermal analysis and kinetics of ten lignite's and two oil shale samples of different origin were performed
using a TA 2960 thermal analysis system with thermogravimetry (TG/DTG) and differential al analysis (DTA) modules. Experiments
were performed with a sample size of ~10 mg, heating rate of 10C min-1. Flow rate was kept constant (10 L h-1) in the temperature range of 20-900C. Mainly three different reaction regions were observed in most of the samples studied.
The first region was due to the evaporation of moisture in the sample. The second region was due to the release of volatile
matter and burning of carbon and called as primary reaction region. Third region was due to the decomposition of mineral matter
in samples studied. In kinetic calculations, oxidation of lignite and oil shale is described by first-order kinetics. Depending
on the characteristics of the samples, the activation energy values are varied and the results are discussed.
A cracking catalyst designatedSRNY was manufactured from a commercialSRNY molecular sieve (M.S.). The support consisted of kaolin, clay and SiO2. The coking behaviour of theSRNY M.S., the support and the catalyst were examined with light diesel oil (LDO) as feedstock in a microreactor. The physico-chemical properties of both fresh and aged samples, subjected to or not subjected
to the cracking reaction ofLDO, were sequentially characterized by means of pore structure determination and thermal analysis. The pore structure included
the specific surface area and the pore volume or porosity. Thermal analysis methods used included TG and DSC.
The results indicated that all coked samples exhibited obvious changes in surface pore structure and acidity in comparison
with non-coked samples. Their specific surface area and acid amount decreased with increase in the coke content of the samples.
The apparent activation energy data obtained from decoking samples in an air flow, using the temperature-programmed oxidation
(TPO) method, showed that the kinetic parameters of theSRNY M.S. differed from those of theSRNY catalyst and its support.
The TG(DTG) and DTA of poly(p-xylylene) and poly(α,α,α′,α′-tetrafluoro-p-xylylene) are reported. The degradation was performed from ambient temperature to 900°C in both air and nitrogen. Both polymer
degrade faster in air than under nitrogen but the fluorinated polymer eventually decomposed at higher temperature in air than
in nitrogen atmosphere. The activation energies of the degradation processes is given.