Chlorination of lanthanum oxide.

Area of Science:

• Solid-state chemistry
• High-temperature reactions
• Chemical kinetics

Background:

• Understanding the reactivity of lanthanum(III) oxide (La2O3) with chlorine gas is crucial for materials processing and chemical synthesis.
• Previous studies have not fully elucidated the reaction mechanism and kinetics across a wide temperature range.

Purpose of the Study:

• To investigate the reaction system between lanthanum(III) oxide (La2O3) and chlorine gas (Cl2) from 260-950 °C.
• To determine the reaction products, mechanisms, and kinetics, including the influence of various parameters.

Main Methods:

• Thermogravimetry (TG) to monitor reaction progress.
• X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) for solid-state characterization.
• Kinetic analysis using Johnson-Mehl-Avrami (JMA) model and variation of chlorine partial pressure.

Main Results:

• Formation of lanthanum oxychloride (LaOCl) as a primary product.
• Above 850 °C, LaOCl further reacts to form liquid lanthanum trichloride (LaCl3).
• The formation of LaOCl follows a nucleation and growth mechanism, with chemical control below 325 °C.

Conclusions:

• The reaction kinetics are dependent on temperature, chlorine partial pressure, and reaction degree.
• Diffusive processes, including gas flow rate and boundary layer diffusion, influence LaOCl formation kinetics.
• A comprehensive rate equation was derived, describing the reaction under varied conditions.