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  Section: Practical Skills in Chemistry » Instrumental techniques
 
 
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Thermal analysis

 
     
 
Content
Instrumental techniques
  Basic spectroscopy
    Introduction to spectroscopy
    UV Ivisible spectrophotometry
    Fluorescence
    Fluorescence spectrophotometry
    Phosphorescence and luminescence
    Atomic spectroscopy
  Atomic spectroscopy
    Atomic Absorption Spectroscopy
    Atomic Emission Spectroscopy
    Inductively coupled plasma
    Decomposition techniques for solid inorganic samples
  Infrared spectroscopy
  Nuclear magnetic resonance spectrometry
    1H-NMR spectra
    13C-NMR spectra
  Mass spectrometry
    Interfacing mass spectrometry
  Chromatography ~ introduction
    The chromatogram
    Resolution
    Detectors
  Gas and liquid chromatography
    Gas chromatography
    Liquid chromatography
    High-performance liquid chromatography
    Interpreting chromatograms
    Optimizing chromatographic separations
    Quantitative analysis
  Electrophoresis
    The supporting medium
    Capillary electrophoresis
    Capillary zone electrophoresis (CZE)
    Micellar electrokinetic chromatography (MEKC)
  Electroanalytical techniques
    Potentiometry and ion-selective electrodes
    Voltammetric methods
    Oxygen electrodes
    Coulometric methods
    Cyclic voltammetry
  Radioactive isotopes and their uses
    Radioactive decay
    Measuring radioactivity
    Chemical applications for radioactive isotopes
    Working practices when using radioactive isotopes
  Thermal analysis
    Thermogravimetry
    Applications

Thermal methods are techniques in which changes in physical and/or chemical properties of a substance are measured as a function of temperature. Several methods of analysis are used:
  • Thermogravimetry (TG) is a technique in which a change in the weight of the substance under investigation is monitored with respect to temperature or time.
  • Differential thermal analysis (DTA) is a technique for measuring the difference in temperature between the substance under investigation and an inert reference material with respect to temperature or time.
  • Differential scanning colorimetry (DSC) is a technique in which the energy necessary to establish a zero temperature difference between the substance under investigation and a reference material is monitored with respect to temperature or time.
When carrying out a thermal analysis procedure it is important to consider and record the following details:
  • Sample: a chemical description of the sample, plus its source and any pretreatment. Also, the purity, chemical composition and formula, if known. Other important items to note are: the particle size, whether the sample has been mixed with a 'binder' (and, if so, what it has been mixed with and in what ratio) and the 'history' of the sample.
  • Crucible: the material and design of the sample holder is important. Obviously it is important that the crucible does not react with the sample during heating. In addition, the geometry of the crucible can influence the gas flow.
  • Rate of heating: this is very important if you intend to repeat the experiment on a subsequent occasion. Obviously the rate of heating of the sample in the crucible is not instantaneous but depends upon conduction, convection and radiation within the system. Thermal lag is therefore likely to be observed.
  • Atmosphere: The nature of the atmosphere surrounding the sample is important in relation to the transfer of heat and the chemistry of the sample reaction. Common sample atmospheres are shown in Table 36.1. In addition, the flow rate of the gas is important: a static system will not remove reaction products from the sample.
  • Mass of sample: obviously the amount of sample will have an effect on the heating rate. Also, sample homogeneity may be an issue with very small samples.

    Common sample atmospheres
    Table 36.1 Common sample atmospheres


 
     
 
 
     



     
 
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