Effect of hydrolysis on structures and surfaces of La2O3, Nd2O3 and Sm2O3

M. Ghelamallah*, H. Heireche, S. Kacimi,

Materials and Catalysis Laboratory, Department of Chemistry, Faculty of Sciences,

Djillali Liabes University, P.O. Box 89 Larbi Ben Mhidi City, 22000 Sidi Bel-Abbes, Algeria.

* Corresponding author. E-mail:gh_madani@hotmail.com

Received: 23 December 2006; revised version accepted: 12 April 2007

Abstract

The rare earths oxides (REO), Ln2O3 (Ln = La, Nd and Sm) are hydrolysed then calcined under air at 723 and 1423K. After 723K, the XRD, programmed thermoreduction (TPRH2) and XPS measurements show La(OH)3, Nd2O3, NdO(OH), Nd(OH)3, Sm2O3, SmO(OH), carbonates and water. Pretreatement increases the surface area of lanthanum and neodymium oxides by factors of 2 and 3 respectively. The surface of samarium oxide is not affected. The procedure results in complete conversion of La2O3 to trihydroxide, La(OH)3 and yields a product having a considerably larger surface area, whereas Nd2O3 and Sm2O3 are only partly converted.

After calcinations at 1423K, oxides are in Ln2O3 form, the effect of sintering is important particularly for lanthanum and samarium: the surfaces decrease by 20% for La2O3, 48% for Sm2O3 and 2% for Nd2O3 in comparison with surfaces of oxides before hydrolysis.

Keywords: REO; Hydrolysis; Calcination; Surface; Structure.

2015