Vitreous solder glasses, such as Mansol #40 and FEG-2002, are commercialized solder glasses, which are compression sealing
glasses that can be used to solder materials with expansions between 55-68⊙10-7C-1, such as Al2O3.
In order to understand and tailor the thermal behaviour of solder glasses, cylindrical-like glasses were first carefully ground
with a stainless steel mortar and pestle. Initially, no exothermic or endothermic data were obtained from the DTA/DSC curves
except those relating to melting. However, exothermic peaks appeared after the glass samples were re-melted. In this work,
kinetic parameters such as the activation energy, and the morphology of the devitrification mechanisms for two kinds of solder
glasses were also investigated, using non-isothermal DTA techniques. The activation energies ranged from 220 to 235 kJ mol-1 and the devitrification mechanism parameters were close to 1. This indicates that the devitrification mechanisms of the two
kinds of solder glasses involve surface nuclei.
Authors:F. Fraga, T. Salgado, J. Rodríguez Añon, and L. Nuñez Regueira
Mechanical behaviour play an important role in the election of an epoxidic formulation of well determined properties as it
has a marked influence on both structural and external factors.
Temperature and time strongly act on polymers properties owing to their viscoelastic nature.
Knowledge of the dynamic moduli and properties of polymeric materials is indispensable for the design of this materials. At
the same time, the influence of the temperature on polymers behaviour may be studied once the activation energy is known.
In this paper the different dynamic moduli and activation energy are measured using a Perkin Elmer DMA 7.
The relationships between the dynamic mechanical properties and the molecular weight of the polymers make possible the calculation
of the molecular weight.
Results reasonably agree with literature values.
Strontium(II) bis (oxalato) strontium(II) trihydrate, Sr[Sr(C2O4)2]·3H2O and mercury(II) bis (oxalato) mercurate(II) hexahydrate, Hg[Hg(C2O4)2]·6H2O have been synthesized and characterized by elemental analysis, reflectance and IR spectral studies. Thermal decomposition
studies (TG, DTG and DTA) in air showed SrCO3 was formed at ca. 500°C through the formation of transient intermediate of a mixture of SrCO3 and SrC2O4 around 455°C. Sharp phase transition from γ-SrCO3 to β-SrCO3 indicated by a distinct endothermic peak at 900°C in DTA. Mercury(II) bis (oxalato) mercurate(II) hexahydrate showed an inclined
slope followed by surprisingly steep slope in TG at 178°C and finally 98.66% of weight loss at 300°C. The activation energies
(E*) of the dehydration and decomposition steps have been calculated by Freeman and Carroll and Flynn and Wall's method and compared
with the values found by DSC in nitrogen. A tentative reaction mechanism for the thermal decomposition of Sr[Sr(C2O4)2]·3H2O has been proposed.
In this research, non-isothermal kinetics and feasibility study of medium grade crude oil is studied in the presence of a
limestone matrix. Experiments were performed at a heating rate of 10°C min−1, whereas the air flow rate was kept constant at 50 mL min−1 in the temperature range of 20 to 600°C (DSC) and 20 to 900°C (TG). In combustion with air, three distinct reaction regions
were identified in all crude oil/limestone mixtures, known as low temperature oxidation (LTO), fuel deposition (FD) and high
temperature oxidation (HTO). The activation energy values were in the order of 5–9 kJ mol−1 in LTO region and 189–229 kJ mol−1 in HTO region. It was concluded that the medium grade crude oil field was not feasible for a self-sustained combustion process.
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 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.
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.
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.
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.