Calcination

The loss on the ignition or LAW ( loss one ignition in English) is the loss of mass which results from the heating of a material.

This loss on the ignition is noted when the development of manufactured objects requires a strong heat, for example in Métallurgie. In fact, the finished product does not have any more the same chemical composition but the initial product since matter left (what explains the variation of mass).

The calcination is a technique of preparation of sample used in analytical Chimie which makes it possible to take into account this phenomenon. It consists in typically heating the sample under air with high Température (500 to 1.000 °C) to cause physical and chemical reactions and to thus put the sample in a state of reference.

Indeed, a certain number of properties of materials depend on the temperature and the history on the sample such as for example on the moisture. The calcination makes it possible to abstract it from these effects and thus to have reproducible measurements, to be able to compare various samples. On the other hand, it is necessary to be conscious that the analyzed sample is not the taken sample. The method is similar to the analysis of the dry extracted but uses a higher temperature.

Chemical reactions and physics

During the heating, it occurs various reactions which modify the sample:

  • with 100 °C: the free Eau vaporizes
  • with the top, dependant water releases (for example molecules of water dependant in the Gypse, the Argile)
  • towards 550 °C: the organic matter burns giving Carbonic gas (CO2) or Graphite (C);
  • the Carbone oxidizes slowly to form carbonic gas or Carbon monoxide;
  • the Carbonate S break up, for example
    CaCO3 → Ca O + CO2;
  • the metals oxidize;
  • the volatile salt S vaporize.

Loss on the ignition

So of such reactions take seat, one can have:

  • a loss of Mass because of the departure of the volatile species: it is the loss on the ignition;
  • a saving weight due to the incorporation of atoms of Oxygen (oxidation), one speaks then about “negative loss on the ignition” or sometimes about “ profit to fire ” ( profit one ignition , GOI).

The loss on the ignition is thus simply the difference in mass:

loss on the ignition = (mass before calcination) - (mass after calcination)
sometimes one expresses it in Pourcentage:
loss on the ignition (%) = 100× before calcination) - (mass after calcination)/(mass before calcination)

At the beginning of the 18th century, the German chemist Georg Ernst Stahl allotted this loss on the ignition to a fluid which left the body during combustion, the Phlogistique. This theory did not make it possible to interpret a negative loss on the ignition, and was swept by the discovery of the Oxygène by Lavoisier.

See too

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