Search Results

You are looking at 71 - 80 of 2,413 items for :

  • "calorimetry" x
  • Chemistry and Chemical Engineering x
  • Refine by Access: All Content x
Clear All

to its complexity. As the oxidation proceeds, several reactions occur simultaneously at different rates. These reactions release heat that can be measured using differential scanning calorimetry (DSC). Recording the heat released from a particular

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
Christelle Herman
,
Tom Leyssens
,
Valérie Vermylen
,
Véronique Halloin
, and
Benoît Haut

with metastable forms [ 2 ]. Differential Scanning Calorimetry (DSC) is commonly used to evaluate most of the thermal properties of solid states, such as melting temperatures and enthalpies or specific heat capacities [ 3 ]. Whilst recent

Restricted access

Abstract  

This personal review focuses on two aspects. First, glass transition dynamics and hence also calorimetry is connected to dynamic heterogeneity. This results in an interplay of the corresponding dynamic length scales and length scales from structural heterogeneities in polymeric samples. Second, the complexity of the dynamic glass transition itself results in different effects of this interplay for different experimental observables. Hence the comparison of results from calorimetry with other relaxation methods gives important clues to an understanding of the complex glass transition phenomenon.

Restricted access

Abstract  

October 2–5, 2005 Congress Center ACADEMIA Star Lesn, Slovak Republic Guest Editor: Peter Šimon Organizers — Slovak Group of Thermal Analysis and Calorimetry Slovak Society of Chemistry Faculty of Technology and Food Technology, Slovak University of Technology Slovak Silicate Society Selected Papers

Restricted access

Abstract  

The mathematical-physical equation concerning the process of calorimetry of electrode reactions was deduced, and the corresponding solutions were obtained respectively for the period of the electrochemical polarization and that of the natural cooling. The calorimetry of the anodic oxidation of ferrocyanide to ferricyanide under linear sweep-current polarization was carried out, the obtained apparent enthalpy change of the electrode reaction agreed well with that obtained by the calorimetry with constant currents. The developed calorimetry with linear sweep-current and the data processing method are applicable for quick determination of apparent enthalpy changes of electrode reactions.

Restricted access

Abstract  

Reading and co-workers introduced a new technique a few years ago called Modulated Differential Scanning Calorimetry or MDSC. Here the first part of a theoretical analysis for this technique is given. A simple mathematical model for modulated differential scanning calorimetry in the form of an ordinary differential equation is derived. The model is analysed to find the effect of a kinetic event in the form of a chemical reaction. Some possible sources of error are discussed. A more sophisticated version of the model allowing for spatial variation in a calorimeter is developed and it is seen how it can be reduced to the earlier model. Some preliminary work on a phase change is also presented.

Restricted access

Abstract  

This article is a review of some of the results we have obtained by studying various kinds of emulsions using techniques from the simplest one, a home-made differential thermal analysis to elaborated ones such as differential scanning calorimetry commercial devices. These techniques were used not only to determine energetic values but also essentially to show and quantify physical chemical phenomena such as undercooling, freezing, melting, mass transfer between droplets and solid formation involved in hydrate formation.

Restricted access

Abstract  

The physico-chemical properties of poly(ethylene) glycol solutions in water have been studied with use of pressure perturbation calorimetry. The three PEGs of average molecular mass (M r) 6000, 10000, 20000 were used. The concentration of polymers was changed in the range 0–30% mass per volume (w/v%). On the basic of VP-DSC measurements with use of PPC technique the dependencies of thermal expansion coefficient (α) and excess specific heat capacity (C p,exc) on temperature were determinated for PEG–water solutions.

Restricted access

Abstract  

Semi-batch reactors are widely spread in the fine chemicals and specialties industry. The reason is that, compared to the pure batch operation, the feed of at least one of the reactants provides an additional way of controlling the reaction course, which represents a safety factor and increases the constancy of the product quality. Process temperature and feed rate can be optimized to satisfy safety constraints, i.e. cooling capacity and allowable accumulation. An economically better way of operating a semi-batch reactor is to adapt the feed rate to the allowed accumulation of reactants. An experimental method based on calorimetry will be presented and illustrated by an example.

Restricted access

Abstract  

The melting and crystallization of a sharply melting standard has been explored for the calibration of temperature-modulated differential scanning calorimetry, TMDSC. Modulated temperature and heat flow have been followed during melting and crystallization of indium. It is observed that indium does not supercool as long as crystal nuclei remain in the sample when analyzing quasi-isothermally with a small modulation amplitude. For standard differential scanning calorimetry, DSC, the melting and crystallization temperatures of indium are sufficiently different not to permit its use for calibration on cooling, unless special analysis modes are applied. For TMDSC with an underlying heating rate of 0.2 K min−1 and a modulation amplitude of 0.5–1.5 K at periods of 30–90 s, the extrapolated onsets of melting and freezing were within 0.1 K of the known melting temperature of indium. Further work is needed to separate the effects originating from loss of steady state between sample and sensor on the one hand and from supercooling on the other.

Restricted access