Kinetic schemes of chemical transformations and particle morphology upon interaction between Ln2(SO4)3 (Ln = La, Pr, Nd, Sm) and hydrogen

Abstract

The phase compositions of samples obtained during the treatment of anhydrous sulfates Ln₂(SO₄)₃ (Ln = La, Pr, Nd, Sm) in a stream with an excess of hydrogen in the temperature range of 400 to 1100°C at exposures of up to 420 min are determined. Kinetic schemes are compiled for the chemical transformations and changes of phase composition of the mixtures in coordinates of temperature and time that have six fields of the phase combinations: Ln₂(SO₄)₃, Ln₂(SO₄)₃ + Ln₂O₂SO₄, Ln₂O₂SO₄, Ln₂O₂SO₄ + Ln₂O₂S, Ln₂O₂S, and Ln₂O₂S + Ln₂O₃. Single-phase samples of Ln₂O₂SO₄ compounds are obtained at temperatures (°C) of 540–560 (La), 460–520 (Pr), 470–520 (Nd), and 480–520 (Sm). The temperatures (°C) of Ln₂O₂S compounds are 580–920 (La), 600–900 (Pr), 600–900 (Nd), and 600–800 (Sm). It is shown via electron microscopy that particles of La₂(SO₄)₃ in the shape of cylinders are converted into flakes of Ln₂O₂SO₄, predominantly flat Ln₂O₂S crystallites.