Firing transformations and hue changes

of a dolomitic raw clay

M. Echajia1, M. Hajjaji1*, S. Kacim1, A. Outzourhit2

1 Laboratoire de Chimie-Physique, Faculté des Sciences Semlalia,

Université Cadi Ayyad, Bd. Prince My Abdellah, B.P. 2390, Marrakech, Maroc.

2 Laboratoire de Physique des Solides et des Couches Minces, Faculté des Sciences Semlalia,

Université Cadi Ayyad, Bd. Prince My Abdellah, B.P. 2390, Marrakech, Maroc,

* Corresponding author. Email: hajjaji@ucam.ac.ma

Received: 07 July 2004; revised version accepted: 14 May 2005

Abstract

Firing transformations and hue changes of a carbonatic raw clay were investigated, in the range of temperature 850-1125 °C, by using x-ray diffraction and spectrocolorimetry. It is observed that the nature of crystalline phases and hue of shards evolved with increasing firing temperature. The main changes of colour were related to the transformation of iron oxyhydroxide into hematite, the dissolution of hematite and to the incorporation of Fe3+ ions into the network of pyroxenes, which were developed from the breakdowns of dolomite and fibrous minerals.

Keywords: Spectrocolorimetry; Clays; Firing transformations.

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