Structural Change of Fired Halloysite of the Democratic and People's Republic of Algeria

Abstract

Halloysite transformed into intermediate compound with two dimensional structure at 1223 K before fully converting to the spinel compound above 1473 K. This reaction was studied by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffractometry (XRD) and thermogravimetric and differential thermal analysis (TG-DTA). Heat treatment at 1223 K provided the oriented intermediate phase with two dimensional structure which was characterized by the selected area diffraction (SAD) with tilting the specimen in TEM. A small amount of fine spinel crystal in nanometric size was also confirmed with the two dimensional intermediate phase by TEM and XRD. Most of the spinel compound formed at the temperature higher than 1473 K decomposed and subsequently formed both of mullite and silica at 1673 K.