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Table of Contents:
TA Tip
- The glass transition temperature measured by different TA techniques; Part 2: Determination of glass transition temperatures
New in our sales program
- New server-compatible V8.10 STARe software
- Small tension sample holder for the DMA instrument
- New HSS7 DSC sensor
Applications
- Determination of binary phase diagrams of aqueous systems that are of importance for processes in the stratosphere
- Kinetic studies of complex reactions. Part 1: model free kinetics
- Thermal analysis of high melting ceramics
Determination of binary phase diagrams of aqueous systems that are of importance for processes in the stratosphere
Introduction
Depletion of ozone in the earth’s stratosphere, especially over the North and South Poles, has been recognized as a serious problem for the past twenty-five years or more. This phenomena is linked to the release of chlorofluorocarbons at the earth’s surface that are transferred by convection to the mid or upper stratosphere over time (about five years) [1]. Here the action of short wavelength UV radiation causes them to undergo photolytic dissociation with the release of free chlorine radicals. For example:
CF2Cl2 + hv → CF2Cl + Cl (1)
The free chlorine radicals then react with methane to form HCl, or with ozone and then NO2 to form chlorine nitrate:
CH4 + Cl → CH3 + HCl (2)
Cl + O3 → ClO + O2 (3)
ClO + NO2 → ClONO2 (4)
[…]
Literature
[1] Molina, M. J.; Rowland, F. S. Nature, 1974 , 249, 810.
Kinetic studies of complex reactions. Part 1: model free kinetics
Introduction
Model Free Kinetics (MFK) has proven to be an excellent method for describing chemical reactions [1-4]. To apply MFK to dynamic DSC measurements, the reaction has to be measured at three or more different heating rates. MFK assumes that the reaction mechanism does not change with heating rate. In most practical cases, this condition is met. An exception can be the cross-linking reaction of a “hot curing” system. The material may vitrify during the reaction, i.e. pass from the liquid to the glassy state. The reaction kinetics changes from being chemically controlled (in the liquid state) to diffusion controlled (in the glassy state). This article shows how MFK can be used to identify and describe such a reaction. The experiments were performed using a two-component epoxy resin con- sisting of the diglycidylether of bisphenol A (DGEBA) and diaminodiphenylmethane (DDM) as hardener or curing agent. This article is the first part of a two-part study.
This first part discusses the experimental approach for the investigation of complex curing reactions and for the evaluation with MFK.
The second part [5] presents an extension of MFK that describes the influence of vitri- fication on the reaction kinetics.
[…]
Literature
[1] J. de Buhr, UserCom 2 (1995) 7.
[2] METTLER TOLEDO, UserCom 5 (1997) 9.
[3] METTLER TOLEDO, UserCom 8 (1999) 1.
[4] S. Vyazovkin, UserCom 10 (1999) 9.
[5] J. Schawe, UserCom 19 (2004).
Thermal analysis of high melting ceramics
Introduction
High melting ceramics are nowadays employed for very many different purposes. T raditionally, they are used for the construction of melting and sintering furnaces. The production of ceramic materials requires careful control of the starting materials. This article shows how thermal analysis can be used to characterize a typical starting material for the production of the fire-resistant lining of a furnace. The main constituent of the sample is MgO. Besides this it contains organically bound carbon (1.5%), graphite (10%), SiO2 (1.5%), CaO (1.5%), Fe2O3 (1.1%) as well as metallic aluminum (2.1%). The measurements were performed with a TGA/SDTA851e coupled to an Inficon Thermostar QMS mass spectrometer (mass range 1-300) and also with a DSC822e .
[…]
