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According to Watson′s DSC principle, a new design of electric circuit of DSC was proposed, Referring to the instrument constraction of DSC of Perkin-Elmer corporation, a new instrument construction of DSC was designed.This new electric circuit and this new instrument construction can overcome the shortcomings in de- sign of DSC of Perkin-Elmer corporation, Figure 1 is a schematic diagram of the new electric circuit. The temperatures and enthalpies of phase transitions of stan- dard materials were measured by using the new DSC. The experimental results are shown in table 1. 相似文献
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DSC measurements in open pans are often disturbed by mass losses such as sublimation during melting or release of water during
chemical reactions. By simultaneous DSC and TG measurements the DSC signal can be corrected. For this purpose, a temperature
dependent calibration function has to be determined by which the SDTA signal from the TGA/SDTA851e measuring cell can be converted into a heat flow curve (DSC).
By this procedure, accurate heat of melting can be determined despite ongoing sublimation in open pans. This method is illustrated
with reference of the melting of anthracene.
Additionally, condensation reactions were investigated and analyzed by DSC/TG even under ambient pressure, knowing the heat
of evaporation. Using phenol formaldehyde resins the influence of the presence or the release of volatile reaction products
on the reaction rate and kinetic parameters were studied.
In general, the method can be used to correct DSC curves for thermal effects related to mass change.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Y Birol 《Journal of Thermal Analysis and Calorimetry》2006,83(1):219-222
The deformation introduced
during the sample preparation had a high impact on the response of the alloy
AA6082 to heating in the DSC cell. The DSC curve was strikingly different
when DSC samples of this alloy were punched after the solution treatment.
Dislocations introduced by punching have annihilated the quenched-in vacancies
and have suppressed clustering initially. Dislocations have also provided
heterogeneous nucleation sites for the GP-1 zones that readily grew to become
stable nuclei for the β" phase owing to the enhanced atomic transport.
β" as well as the β' precipitation kinetics were thus accelerated
leading to a substantial change in the DSC peak arrangement. Deformation introduced
during sample preparation by gentle grinding alone, on the other hand, did
not suffice to alter the precipitation sequence, producing a DSC curve very
similar to that obtained with samples punched before the solution treatment. 相似文献
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TG and DSC were carried out on PMAA-net-POTM in order to elucidate the relation between the heterogeneity and the thermal changes; moreover, TG and DSC were carried out on PPOTMDM and PMAA to compare the results. The onset temperature in the last stage in the TG curve of PMAA-net-POTM increases as the concentrations of DMF and POTMDM in the polymerization decrease. This is explained in terms of plasticizers effects. A single peak due to fusion of POTM chains appears in the DSC curves of most copolymers. However, it is not seen in the DSC curves of copolymers with high heterogeneity. This is explained in terms of the freezing of POTM chains by frozen heterogeneous moieties. 相似文献
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C. J. G. Plummer J.-E. Zanetto P.-E. Bourban J.-A. E. Månson 《Colloid and polymer science》2001,279(4):312-322
The crystallization kinetics of polyamide-12 has been investigated using a combination of differential scanning calorimetry
(DSC) and hot-stage optical microscopy. The DSC data for isothermal crystallization were consistent with a simple two-parameter
Avrami model for isothermal crystallization and optical measurements of the spherulite growth rates and nucleation density.
On the basis of semiempirical expressions for these quantities, it is shown that with small adjustments the model can also
account for DSC data for nonisothermal crystallization, provided that corrections are made for the dynamic heat balance between
the sample and the DSC oven.
Received: 9 March 2000 Accepted: 28 September 2000 相似文献
8.
Sabine Danthine Nathalie De Clercq Koen Dewettinck Véronique Gibon 《Journal of Thermal Analysis and Calorimetry》2014,115(3):2219-2229
The melting profiles of palm oil, palm olein, and soft palm mid fraction were investigated by differential scanning calorimetry (DSC) before, during and after enzymatic interesterification. The DSC melting profiles of the three palm fats changed drastically due to the random redistribution of the fatty acids on the glycerol occurring upon interesterification. A high melting peak (already present for native palm oil) was observed for the three interesterified products and attributed to the increase in trisaturated triacylglycerols; modifications of the shape of the medium-melting peak (observed in the three products) were attributed to modifications within the mono-unsaturated triacylglycerols. In view of the drastic changes observed, the applicability of DSC to monitor enzymatic interesterification reactions was considered. While the degree of interesterification was supposed to be completed after 8 h according to the HPLC data, significant modifications were still observed within the DSC melting profiles. Minor changes within the structure of the medium-melting peak were selected as indicator of the reaction progress, and it was shown that intensities of DSC melting endotherms can be used to monitor the enzymatic interesterification reaction of these palm products. 相似文献
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Differential scanning calorimetry (DSC) and thermal optical analysis (TOA) were applied as part of a series of characterization methods to solid chemically crosslinked polyethylene insulation. The DSC was used to study the melting and recrystallization. The ΔH of fusion has a lower value than expected. The TOA shows premelting behavior and is more sensitive to crystalline charges, on cooling, than DSC. 相似文献
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This paper describes the DSC study of 4-trifluorocoumarin derivatives, C_(481), C_(485), C_(500) and C_(480), providing their DSC thermograms and thermodynamic parameters during the phase transitions of these compounds. Singlemelting peaks were observed on DSC thermogram respectively.Experimental results show the existence of certain correlations between the melting point, heat of fusion and molecular structure for this series of compounds. 相似文献
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A DSC compositional analysis of 3 model binary systems of pharmaceutical significance has been conducted. Mixtures of known selected composition for each of the systems 3,5-dinitrobenzoic acid/benzoic acid, paracetamol/4-aminobenzoic acid and acetylsalicylic/salicylic acid were prepared and analyzed by DSC. The respective compositions derived from applications of the van't Hoff equation were correlated with the corresponding theoretical values and with the corresponding fusion temperatures and fusion enthalpies, obtained from the relevant DSC profiles. Linear correlations were found to exist between the theoretical compositions, fusion temperatures and fusion enthalpies for each of these systems and it is apparent that with suitable calibration procedures, the DSC compositional analysis method can be applied to determine the purity at the 90–95 mole% level. This level is of considerable interest in drug stability studies and has real significance in purity assays of commercial pharmaceutical preparations. 相似文献
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Tamíris A. Júlio Igor F. Zâmara Jerusa S. Garcia Marcello G. Trevisan 《Journal of Thermal Analysis and Calorimetry》2013,111(3):2037-2044
The evaluation of sildenafil citrate (SC), the best-selling drug for treatment of impotence, for compatibility with various excipients was investigated using thermal and isothermal stress testing. Differential scanning calorimetry (DSC), hot-stage microscopy (HSM) and liquid chromatography (LC) with ultraviolet detection were successfully employed to investigate the compatibility between SC and various excipients commonly used in solid form in the pharmaceutical industry. The studies were performed using 1:1 (m/m) drug/excipient physical mixtures and samples were stored under accelerated stability conditions (40 °C at 75% relative humidity). All excipients tested (such as colloidal silicon dioxide, croscarmellose sodium, lactose, mannitol and sucrose) showed potential incompatibilities by DSC and LC analysis after accelerated stability testing. However, some incompatibilities were not detected by the DSC method and were observed only when LC analysis was performed. HSM was able to differentiate active pharmaceutical ingredient degradation from solubilisation, supporting the interpretation of DSC in excipients where thermal events either overlapped or disappeared. The combination of both the analytical techniques (DSC and LC) and use of a stability chamber is extremely helpful in detecting incompatibilities and providing more robust and accurate approaches for pre-formulation studies. 相似文献
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In this study, polyimide fibers at different stages of imidization were characterized by TGA, DSC, and FTIR. The imidization degree(ID) calculated by TGA was based on the weight loss of each sample, which was caused by the imidization of residual amic acid groups. The results of TGA showed good regularity with the thermal treatment temperature of the PI fibers. For DSC, the ID was calculated based on the area of endothermal peak of each sample. Compared with TGA, DSC showed a relatively higher value because the endothermal peak was reduced by the exothermic re-formation of polyamic acid which may be partially degraded during thermal treatment. The IDs obtained by the FTIR spectra generally showed poorer regularities than those obtained by both TGA and DSC, especially for the results calculated using the 730 cm-1 band. Based on the 1350 cm-1 band, the obtained IDs showed better agreement with the TGA or DSC results. The results obtained by these three methods were compared and analyzed. The ID obtained by TGA showed much more reliability among these three methods. 相似文献
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Yimin Jin J. Bonilla Ye-Gang Lin J. Morgan Linda McCracken J. Carnahan 《Journal of Thermal Analysis and Calorimetry》1996,46(3-4):1047-1059
Two poly(butylene terephthalate)/polycarbonate (PBT/PC) blends with different formulations were analyzed by modulated DSC (MDSC) and conventional DSC to determine differences in crystallization behavior. A significant difference (30°C in cold crystallization temperature) between the two samples was detectable by MDSC while no significant difference was seen by conventional DSC. That indicatesthe total heat flow from MDSC is not always equivalent to the heat flow from conventional DSC as we have assumed or seen before. The reason has not been fully understood, but may be related to unusual nucleation and crystallization induced by modulation. Alternative conventional DSC methods were developed and compared to the MDSC results.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThe authors like to thank Drs. Bernhard Wunderlich and Robert Gallucci for helpful discussion, David Shaker and Mary Parsonage for some DSC experiments. Technical support from TA Instruments is also greatly appreciated. 相似文献
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S.H. Goh 《Thermochimica Acta》1984,75(3):323-328
The oxidation induction times of natural rubber stabilized by various antioxidants were measured by differential scanning calorimetry (DSC). Various Arrhenius plots could be superimposed to form a single plot by using a shift factor dependent on the oxidation peak temperature obtained from a dynamic DSC test. The superimposed plot provides a simple means to predict the induction time from a dynamic DSC test result. 相似文献
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Mingbi Qi Fengying Yao Jun Zheng Renyuan Qian 《Journal of Thermal Analysis and Calorimetry》1993,40(2):783-789
In this paper two LLDPE samples with their own structural parameters were studied by means of DSC. Experimental results show
that DSC was good for revealing slight structural difference between these two samples. Furthermore, the effect of thermal
history on crystallization and melting behaviour of LLDPE was observed clearly through varying conditions of thermal treatment.
Zusammenfassung Mittels DSC werden zwei LLDPE-Proben mit ihren eigenen Strukturparametern untersucht. Die Versuchsergebnisse zeigen, da\ sich DSC gut eignet, um gering fügige Unterschiede dieser zwei Proben nachzuweisen. Weiterhin wurde unter verschiedenen Bedingungen der Einflu\ der thermischen Vorgeschichte auf das Kristallisations-und Schmelzverhalten von LLDPE untersucht.相似文献
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Antonilêni F. D. Medeiros Ana Flávia O. Santos F. S. de Souza I. D. B. Júnior J. Valdilânio J. V. V. Procópio D. P. de Santana R. O. Macêdo 《Journal of Thermal Analysis and Calorimetry》2007,89(3):775-781
Compatibility studies between active drugs and excipients are substantial in the pharmaceutical technology. The objective
of the present work was to develop pre-formulated mixtures of metronidazole (MT) obtained by spray drying (SPDR) and their
thermoanalytical characterization. Dynamic and isothermal TG, conventional DSC and DSC coupled to a photovisual system were
used. DSC experiments with both techniques confirmed the homogeneity of the conventional and pre-formulated mixtures. The
TG data made possible the comparison the thermal stability of the different mixtures. Similar thermal stabilities were found
of the conventional and pre-formulated mixtures, with slower particles sizes of MT. 相似文献
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A. Swiderski A. Wojtal P. Muras A. Mikulko S. Wrobel H. Koloczek 《Journal of Thermal Analysis and Calorimetry》2006,83(3):631-636
The DSC
method was used to study phase transitions in Rhododendron
L. leaf tissues caused by temperatures below the freezing point of water.
The curves show several stages of water crystallisation, demonstrating that
these processes do not occur simultaneously in various types of cell organelles.
Temperatures and enthalpies of the phase transitions were determined and significant
changes were found in the DSC curves when the sample was repeatedly subjected
to sub-zero temperature cooling and heating. Also, frost resistance of the
same rhododendron taxons was studied by conductometric analysis and the DSC
results were compared with the data from other laboratory studies. 相似文献