Search Results
Heat transfer in a disc-type DSC apparatus
Part 5. Theoretical equation of melting with a heat flux coupled cells DSC
Abstract
The literature describes models of DSC apparatuses. However, the use of these models require a precise determination of the values of the resistors and the capacitors of the apparatus. Theoretical equations of a first order transition in a coupled cells heat flux DSC at a constant heating rate are given. It is shown that the value of the resistors and capacitors may be obtained. The influence of resistors product — crucible or crucible — detectors is established.
Abstract
The processes of production of drugs and dosage forms in the solid state often cause unwanted transformation of portions of the substances into amorphous state, with significant changes of properties such as stability and bio-availability. When this amorphous fraction is of the order of a few percent, it usually goes unnoticed, but it should be accurately determined within a quality control system. In this work, we consider a model drug, perphenazine, where partial amorphisation may be induced by standard mechanical treatments. We show that Differential Scanning Calorimetry (DSC) leads to consistent estimations of the amorphous fractions induced by the treatment. Furthermore, DSC also yields the expected amounts of amorphous perphenazine when analysing known mixtures of perfectly crystalline samples (untreated) and partially amorphous samples (treated). We show that even amorphous fractions of the order of 1% are accurately estimated by our method.
Abstract
Glutelin, the major protein fraction from guava seed, was obtained by fractioning as described by Osborne. The total proteins were extracted and the isolates obtained by isoelectric precipitation presented similar DSC curves, concordant with the results obtained by gel filtration chromatography and electrophoresis in polyacrylamide gel (PAGE-SDS). However, the DSC curves showed a higher enthalpy with regard to the denaturing protein isolate (PI) extracted at pH 10.0 when compared to a PI at pH 11.5. Such results are in accordance with those obtained for PI extracted at pH 10.0 using chromatography, this one being present in the form of molecular aggregates of greater molecular mass. The glutelin fraction, however, did not present a denaturation peak in the DSC curve, showing that the process for obtaining the same significantly altered its conformation.
Abstract
The unusual mechanical properties (i.e. shape memory effect and superelasticity) of shape memory alloys (SMA) rely on the thermoelastic martensitic transformation (TMT) which is a first-order solid-solid, non-diffusive phase transition, athermal in character. Differential scanning calorimetry (DSC) is often used as a convenient method of investigating the thermal properties ofSMAs. The common practice of standard temperature calibration, required for a correct instrument performance, is here critically discussed in relation to the study of both the direct exothermic transformation on cooling, and the reverse endothermic transformation on heating in a NiTiSMA. The DSC results show that, with the standard temperature calibration, the instrument is calibrated on heating but un-calibrated on cooling. A general method is advanced to overcome this problem, intrinsically related to the dynamic character of DSC.
phase structure, thermal properties of polymer blends [ 1 – 3 ]. In the present work, two thermal analysis techniques, thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) [ 4 – 16 ], were used for characterization of modified
Abstract
In order to identify the kinetic process of self-heating in DSC experiment for Ti+3Al→TiAl3 reaction, two approaches, linear-fitting approach developed from Semenov"s theory of spontaneous ignition and variation of Friedman method, were carried out with cylindrical Ti-75 at% Al samples. Following these approaches, two identical activation energies are obtained as 16915 kJ mol-1 and 1705 kJ mol-1, respectively. Compared with the activation energies of reactions and interdiffusions between Ti and Al, the possible rate-controlling process of self-heating in DSC experiment for Ti+3Al→TiAl3 reaction is the interdiffusion between Ti and Al through TiAl3-layer.
Abstract
The recovery of metals is the process of softening without crystallization in the mechanical stressed pieces and is well characterized by DSC measurements at temperatures < 600C. The present investigation was undertaken to detect similar effects also in traditional ceramics. Several ceramic samples, coming from different productions, were thermally analyzed by DSC and the presence, in the most stressed samples, of an exothermic peak at about 350C, was detected, confirming the presence of recovery in the ceramics too. However, owing to the complex structures of these materials, at present no mathematical model could be introduced.
Abstract
One of the benefits of temperature-modulated DSC (TMDSC) is its ability to measure thermal conductivity and thermal diffusivity without DSC cell modifications or additional accessories. Thermal conductivity of solid materials from 0.1 to about 1 W m-1 K-1 measured. Applications of this approach have been discussed in the literature but no description is yet available concerning the derivation of the working equations. This presentation provides a detailed derivation of the working equations used to obtain thermal conductivity and thermal diffusivity from TMDSC data.
Abstract
A DSC instrument modified to incorporate a chemiluminescence (CL) detector has been used to make simultaneous measurements of heat flow and light emission for oxidising polymer samples. Comparison of heat flow and light emission from unstabilised polypropylene shows a linear relation between heat flow and square root of intensity, giving indirect confirmation of the Russell mechanism for CL emission. Measurements of oxidation induction times (OIT) for stabilised samples show excellent correlation of the two techniques. The advantage of the CL method in being insensitive to thermal transitions in the sample is illustrated by a study of poly(ethylene terephthalate), whilst the very high sensitivity of CL detection is illustrated by its ability to detect peroxides at levels which are not detected by DSC. Finally, the limitations of the OIT approach in lifetime prediction by Arrhenius extrapolation are emphasised.
Abstract
The photopolymerization of a commercial sheet material as used in the dental laboratory was investigated by using the photocalorimeter DSC7/DPA7 (Perkin-Elmer). Using normal reaction conditions (light wavelength 
400 nm, light intensity 
1 mW cm–2 and sample thickness 2.5 mm), the curing was completed within few min. The reaction rate was nearly independent on the light wavelength in the range between 
=300 and 380 nm, but decreased distinctively at longer wavelengths. After desmearing the DSC curves, the dependence of the reaction rate on light intensity and sample thickness could be described in very good approximation by an equation derived by Tryson [1]. Comparable with pure acrylates or methacrylates, a pronounced dark reaction was found after interruption of the illumination.
