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B. Tiţa Eleonora Marian D. Tiţa Gabriela Vlase N. Doca T. Vlase 《Journal of Thermal Analysis and Calorimetry》2008,94(2):447-452
Thermal analysis is one of the most widely used methods for studying the solid state of pharmaceutical substances.
TG/DTG and DSC curves provide important information regarding the physical properties of the pharmaceutical compounds (stability,
compatibility, polymorphism, kinetic analysis, phase transitions etc.).
The purpose of a kinetic investigation is to calculate the kinetic parameters and the kinetic model for the studied process.
The results are further used to predict the system’s behaviour in various circumstances.
A kinetic study regarding the diazepam, nitrazepam and oxazepam thermal decomposition was performed, under non-isothermal
and isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 483, 498, 523, 538 and 553 K. The TG/DTG
data were processed by three methods: isothermal model-fitting, Friedman’s isothermal-isoconversional and Nomen-Sempere non-parametric
kinetics.
In the model-fitting methods the kinetic triplets (f(α), A and E
a) that defines a single reaction step resulted in being at variance with the multi-step nature of diazepines decomposition.
The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation
energies on the extent of conversion.
It is very difficult to obtain an accord with the similar data which resulted under non-isothermal conditions from a previous
work.
The careful treatment of the kinetic parameters obtained in different thermal conditions was confirmed to be necessary, as
well as a different strategy of experimental data processing. 相似文献
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C. P?curariu R. I. Laz?u I. Laz?u R. Iano? T. Vlase 《Journal of Thermal Analysis and Calorimetry》2009,97(2):409-414
The influence of the specific surface area on the crystallization processes of two silica gels with different specific surface
areas has been investigated in non-isothermal conditions using DTA technique. The activation energies of the crystallization
processes were calculated using four isoconversional methods: Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose, Starink and Tang.
It has been established that, the decrease of the surface area from S=252.62 m2 g−1, in the case of sample GS2, to S=2.52 m2 g−1, in the case of sample GS1, has determined a slight increase of the activation energy of the crystallization process of the
gels. Regardless of the isoconversional method used, the activation energy (E
α) decreases monotonously with the crystallized fraction (α), which confirms the complex mechanism of gels crystallization.
It has been proved that the Johnson-Mehl-Avrami model cannot be applied for the crystallization processes of the studied silica
gels. 相似文献
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Ionut Ledeti Gabriela Vlase Titus Vlase Nicolae Doca Vasile Bercean Adriana Fulias 《Journal of Thermal Analysis and Calorimetry》2014,115(2):1057-1063
The thermo-physical properties for four rock types (granite, granodiorite, gabbro, and garnet amphibolite) from room temperature to 1,173 K were investigated. Thermal diffusivity and specific heat capacity were measured using the laser-flash technique and heat flux differential scanning calorimetry, respectively. Combined with the density data, rock thermal conductivities were calculated. Rock thermal diffusivity and conductivity decrease as the temperature increases and approach a constant value at high temperatures. At room temperature, the measured thermal conductivity is consistently near or lower than the calculated conductivity using the mineral series model, which suggests that real thermal conduction is more complicated than is depicted in the model. Therefore, in situ measurement remains the best method for accurately obtaining thermal conductivity for rocks. 相似文献
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Dorina?Modra Gabriela?Vlase Paul?Albu Constantin?Bolcu Titus?VlaseEmail author 《Journal of Thermal Analysis and Calorimetry》2015,121(3):1021-1030
This study presents the synthesis of polyesters obtained from phthalic anhydride as acidic components and one mixture of monoethylene glycol and monohydric alcohol (in ratio 1.1:0.15). Molar ratio of the acid component and alcohol component was 1:1.25. n-Propanol, n-butanol, n-octanol and isoamyl alcohol were used as monohydric alcohol. Physicochemical characterization was performed by elemental analysis, FTIR/UATR spectroscopy of polyesters and char, EGA (evolved gas analysis), thermal analysis in synthetic air and in nitrogen atmosphere. 相似文献
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Corina Duda-Seiman T. Vlase Gabriela Vlase Rodica Cinca Mariana Anghel N. Doca 《Journal of Thermal Analysis and Calorimetry》2011,105(3):851-858
Verapamil is a phenyl-alchil-amine type pharmaceutical largely used as a specific calcium antagonist. Knowledge of drug-excipient
compatibility represents an important phase in development of different dosage forms. Hyphenated techniques are versatile
for obtaining such necessary information’s. The TG/DTG/DTA curves were obtained in air at different heating rates and in nitrogen.
The IR spectra of pure compound and its char at 400 °C (by U-ATR technique) and the IR identification of Evolved Gasses allowed
some discussions on the thermally induced events. In the solid dosage forms verapamil was mixed with talc, magnesium stearate,
starch, and cellulose, and the corresponding thermoanalytical curves were compared with that one of pure I. No physical or
chemical interactions were observed till 250 °C. A kinetic analysis was performed for TG step of verapamil between 250 and
350 °C. The data at four heating rates (7, 10, 12, 15 °C min−1) were processed on a strategy using at last three different kinetic methods. For these, the NPK method seems to be less speculative,
allowing an objective determination of the kinetic parameters. 相似文献
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Sbârcea Laura Ledeţi Adriana Udrescu Lucreţia Văruţ Renata-Maria Barvinschi Paul Vlase Gabriela Ledeţi Ionuţ 《Journal of Thermal Analysis and Calorimetry》2019,138(4):2787-2797
Journal of Thermal Analysis and Calorimetry - Betulonic acid (BA) is a pentacyclic lupane-type triterpenoid possessing valuable pharmacological activities, exhibiting very low water solubility.... 相似文献
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