Firing transformations of an argentinean calcareous commercial clay

Abstract

Mineralogical transformations caused by firing are usually studied by XRD methods only semi-quantitatively. In this work the original mineral disappearance and the neo-mineralization were evaluated quantitatively. Furthermore an indirect non crystalline phase quantification was performed under 1100 ºC was also carried out using the quartz content as internal standard. This study specifically discusses the behavior of an Argentinean white calcareous earthenware commercial when subjected to traditional ceramic firing, besides the technological importance of this particular material, it acts as a model for other clay based ceramic materials. Materials were subjected to thermal treatments between 700 ºC and 1100 ºC. A preliminary sintering characterization was carried out by contraction and porosity evolution. Simultaneous thermogravimetric and differential thermal analysis (TG-DTA) was carried out to elucidate the actual temperature at which the chemical changes occur. Finally, a quantitative analysis based on the Rietveld refinement of the X-ray diffraction patterns was performed to characterize the crystalline phases present in both the clay and in the materials obtained after different thermal treatments. The actual chemical reactions are proposed. The phases identified after firing at traditional working temperature (1040 ºC) are quartz, plagioclase, and the Spinel type alumino-silicate, accompanied by the non-diffracting un-reacted metakaolin and some amount of amorphous glassy phase. At intermediate temperatures (900 ºC) the presence of gehlenite was also detected. The carbonates (calcite and dolomite) presence and decomposition were also evaluated and demonstrated to determine the sintering characteristics of this material. Keywords: silicate ceramic processing, structure, X-ray diffraction. Resumo Transformações mineralógicas causadas por queima são estudadas pelo método semiquantitativo de difração de raios X. O desaparecimento do mineral original e o neomineral foram avaliados quantitativamente. Além disso, a quantificação de fase não

Thermal behavior (TG-DTA-TMA), sintering and properties of a kaolinitic clay from Buenos Aires Province, Argentina

“…The results of the Rietveld refinement quantification including Rwp Rietveld residuals and PDF files for each phase are shown and compared in Table III. The Rwp values were adequate and similar to the ones achieved in similar materials [48][49][50][51][52][53]. The results were concordant with the thermal analyses (TG, DTA) [20].…”

Characterization of raw and thermally treated Nigerian kaolinite-containing clays using instrumental techniques

“…The endothermic reaction of IJ at 390-650 °C may be attributed to dehydroxylation of small amounts of kaolinite and other clay minerals contained in the clay overlapping with transition of α-quartz (SiO 2 ) to β-quartz (SiO 2 ). As already documented [32,33], the endothermic reaction of quartz at around 573 °C corresponds to structural transition of trigonal (alpha) to hexagonal (beta). Based on this fact, if IJ contained only quartz, mass change was not expected to occur at these temperatures for IJ.…”

Acid gas emissions from structural clay products containing secondary resources: foundry sand dust and Waelz slag

“…Finally, the endothermic peaks at temperatures between 750 and 850 ºC are due to carbonate decomposition (dolomite and calcite) (Serra et al, 2013). The decomposition of calcite is associated with a sharp peak at 827 ºC for C1 and a weak peak at 850 ºC for the non-calcareous clays (C2 and C3).…”