Methods for kinetic description of induction periods,
based on the single-step kinetics approximation and various expressions of
the temperature functions, are presented. The formulas for evaluation of both
isothermal and non-isothermal lengths of induction periods are derived. Use
of the formulas is demonstrated on the thermooxidative degradation of polyolefines.
The kinetic parameters obtained from isothermal and non-isothermal experiments
are compared and possible reasons of inconsistencies are analyzed. Applications
of the determination of induction periods for thermooxidation of various systems
are reviewed. The theory outlined in this paper can be applied not only for
thermooxidation in condensed phase, but also for other processes exhibiting
the induction period, such as the curing of rubber compounds, recrystallization
of nickel sulfide and crystallization of silicate and metal glasses.
A simple and rapid one-step continuous-flow synthesis route has been developed for the preparation of chromene derivatives from the reaction of aromatic aldehydes, α-cyanomethylene compounds, and naphthols. In this contribution, a one-step continuous-flow protocol in a ThalesNano H-Cube Pro™ has been developed for the preparation of these chromene derivatives. This arises from the multicomponent one-step reaction of aromatic aldehydes, α-cyanomethylene compounds, and naphthols. This flow protocol was optimized in 2-methyltetrahydrofuran, which is a more environmentfriendly solvent. The faster residence times (<2 min) coupled with elevated pressure (∼25 bar) results in an efficient, safer, faster, and modular reaction. Results obtained illustrate that this base-catalyzed reaction affords the respective chromene derivative products in very high yields. The products can then be easily purified by recrystallization, if desired.
The thermal decomposition behavior of acesulfame-K (ACK), aspartame (ASP), sodium cyclamate (SCL), saccharine (SAC), and sodium
saccharine (SSA) were investigated. After re-crystallization of the commercial samples the compounds were characterized by
using elemental analysis, IR spectroscopy and thermoanalytical techniques (TG/DTG, DTA, and DSC). Evidences of hydrate water
loss were observed for SSA and ASP. Melting was detected for SSA and SAC. Each compound decomposed in a characteristics way.
The decomposition of APS and SAC took place completely, while ACK, SCL and SSA resulted in K2SO4, Na2SO4, and Na2SO4, as residues respectively. The Flynn-Wall-Ozawa method for kinetic calculations was applied for the volatilization of saccharine
resulting in Ea = 80 ± 1 kJ mol−1 and log A = 7.36 ± 0.07 min−1.
DA-5018 is a new capsaicin derivative and has analgesic effect. The objective of this work was to investigate the existence
of polymorphs and pseudopolymorphs of DA-5018 and the transformation of crystal forms. Eight crystal forms of DA-5018 have
been isolated by recrystallization and characterized by powder X-ray diffractometry (PXRD), differential scanning calorimetry
(DSC), and thermogravimetric analysis (TG).
The PXRD and DSC patterns of the eight crystal forms were different respectively.
In the dissolution studies in simulated intestinal fluid at 37±0.5°C, the solubility of Form 2 was the highest. And the solubility
in water decreased in rank order: Form 2>Form 3>Form 1>Form 5>Form 7>Form 4>Form 6>Form 8.
Eight crystal forms were shown to have a good physical stability at room temperature for 60 days.
The Little Plain Basin is one of the largest units in the Pannonian Basin System. Its continuation in Slovakia is called the Danube Basin. The Little Plain Basin is one of the most underexplored areas in Hungary. Based on archival geologic and geophysical data the lithostratigraphic composition of the area is controversial. The significance of the area is increased by the known Neogene and the supposed basement (Paleozoic and Mesozoic) hydrocarbon systems in Hungary and in Slovakia.
The purpose of this study is to identify the exact age, facies, geologic formations and possible source rocks of the Triassic section penetrated by the Gyõrszemere-2 well in the Little Plain Basin.
Based on new facies and paleontological results it can be stated that two Triassic sequences are identified in the well, separated by fault breccia. A carbonate sequence was deposited between the Induan and Early Anisian and above that a homogeneous recrystallized dolomite appears, the age of which is unknown.
The following formations were encountered, from base upward:
Arács Marl Fm. (3,249.5–3,030 m), silty marl with ooids, bivalves, gastropods and ostracode shells. Occasionally layers of angular quartz grains in large quantities appear. Postcladella kahlori and Spirobis phlyctaena indicates Induan (Early Triassic) age.
Köveskál Dolomite Fm. (3,030–2,790 m), rich in ooids and also containing anhydrite. The Glomospira and Glomospirella dominance indicates an age interval between Olenekian and earliest Anisian age.
Fault breccia (2,790–2,690 m) separating the Köveskál and overlying dolomites.
Upper dolomite (2,690–2,200 m): homogeneous, saccharoidal, and totally recrystallized. The age is unknown.
The low TOC values of the supposed source rock interval (marl between 3,249.5 and 3,030 m) indicate poor hydrocarbon potential.
A new method is presented to analyze the irreversible melting kinetics of polymer crystals with a temperature modulated differential
scanning calorimetry (TMDSC). The method is based on an expression of the apparent heat capacity,
. The present paper experimentally examines the irreversible melting of nylon 6 crystals on heating. The real and imaginary
parts of the apparent heat capacity showed a strong dependence on frequency and heating rate during the melting process. The
dependence and the Cole-Cole plot could be fitted by the frequency response function of Debye's type with a characteristic
time depending on heating rate. The characteristic time represents the time required for the melting of small crystallites
which form the aggregates of polymer crystals. The heating rate dependence of the characteristic time differentiates the superheating
dependence of the melting rate. Taking account of the relatively insensitive nature of crystallization to temperature modulation,
it is argued that the ‘reversing’ heat flow extrapolated to ω → 0 is related to the endothermic heat flow of melting and the
corresponding ‘non-reversing’ heat flow represents the exothermic heat flow of re-crystallization and re-organization. The
extrapolated ‘reversing’ and ‘non-reversing’ heat flow indicates the melting and re-crystallization and/or re-organization
of nylon 6 crystals at much lower temperature than the melting peak seen in the total heat flow.
four types of thermal behavior for the series A and B:
• Behavior I Compounds that do not alter the thermal behavior after an initial fusion–recrystallization cycle ( Fig. 1 ). Under these conditions there is no evidence of polymorphic behavior. The
The kinetics of bulk crystallization of Se61.5Ge15 4Sb23.1 glasses was investigated from their thermal behaviour. In the thermal characterization of a glass the recrystallization temperature is highly dependent on both the rate of heating and the thermal history of the glass. Vitreous samples were prepared by quenching. From ratedependent curves it was found that the recrystallization process obeys first-order kinetics with an apparent activation enthalpy of 48±5 kcal/mole. Further analysis allows determination of both the activation enthalpy,H=90±4 kcal/mole, and the kinetic exponent of the Avrami equation,n=1.9±0.3.
The heterogeneous isotopic exchange reactions in strontium polymolybdates of Sr2+ and MoO42- ions in the strontium nitrate and sodium molybdate solutions have been studied using 90Sr and 99Mo as tracers. Electrometric methods have been used to study the compositions of strontium molybdates obtained by adding strontium chloride to a progressively acidified solution of sodium molybdate. It has been found that the exchange fraction increases with increasing chain length of strontium polymolybdate. The exchange equilibrium constant (Kex) has been calculated between 298 and 348 K as well as DG°, DH° and DS°. The results indicate that Sr2+ cations have a much higher affinity for exchangers than MoO42- anions. By fitting the data to the Dubinin-Radushkevich (D-R) isotherm it has been shown that the exchange capacity (Xm) for both ions is affected by the ion adsorption process at low temperatures and by the ion exchange process at high temperatures. At high concentrations, the recrystallization process contributes to on the cation exchange but is ineffective on the anion exchange mechanism.
The kinetics of solute segregation to partial dislocations in a Cu–3.4 At.% Sb alloy was studied by using a phenomenological approach with differential scanning calorimetry and isothermal calorimetry. The material, severely deformed by repeated bending, presented an excess of dissociated edge dislocations with a dislocation density amounting to about 8.5·1014 m–2, calculated using a prior model of the authors, together with calorimetric recrystallization trace analysis. The kinetics was found to be ruled by two overlapping mechanisms: diffusion of solute atoms mostly through dislocation pipes in the initial and middle stages of the reaction process, acting together with bulk solute diffusion in these stages and later. Bulk solute diffusion increases as the reaction proceeds, as shown by the increasing values of apparent activation energy in the reaction. The exponent of the Mehl-Johnson-Avrami equation used in the phenomenological description was successfully fitted to a time—temperature-dependent function, increasing in agreement with the apparent activation energy behaviour, as may be expected.