Synthesis and characterization of Fe and P substituted 3:2 mullite

The incorporation in mullite structure of foreign elements has been studied since 1924. In this paper the isovalent 12P plus 12Al for Si substitution has been investigated employing wet chemistry preparative route with a final firing temperature of 1300°C. The extent of solid solution and the crystallographic features of the end term with composition Al6.22Si1.56P0.22O13 are described on the basis of XRPD profile fitting. This substitution has also been examined in the presence of the contemporary Fe for Al substitution; the end term of this coupled isovalent compositional series Al5.90Fe0.20Si1.80P0.10O13 has been characterized too. In this latter case, the crystallographic results are confirmed by Mِssbauer spectroscopy. The simple Fe for Al substitution at 1300°C has also been re-examined in the same preparative conditions. The composition and the structure of the end term (Al5.60Fe0.40Si2O13 ) are in agreement with previous studies. The incorporation degree of Fe and P in the coupled substitution results in being approximately halved in respect to simple substitutions of the two elements.