Progressive Assessment on the Decomposition Reaction of Na Superionic Conducting Ceramics

Area of Science:

• Materials Science
• Ceramic Engineering
• Electrochemistry

Background:

• Hong-type sodium superionic conductor (NASICON) ceramics are crucial for solid-state electrolytes.
• Understanding their stability in aqueous environments is vital for practical applications.
• Microstructural characterization is key to predicting material performance.

Purpose of the Study:

• To investigate the microstructural evolution and chemical stability of NASICON ceramics in seawater.
• To elucidate the ion exchange mechanisms and structural decomposition pathways.
• To assess the impact of seawater immersion on NASICON ceramic integrity.

Main Methods:

• In situ analysis of microstructural evolution.
• X-ray diffraction (XRD) for structural decomposition analysis.
• Time-of-flight secondary-ion mass spectrometry (ToF-SIMS) for elemental distribution.

Main Results:

• NASICON ceramics exhibit heterogeneous microstructures including NASICON grains, ZrO2, amorphous phases, and pores.
• Seawater immersion at 80°C induced dramatic microstructural changes, transforming NASICON grains into comminuted particles.
• XRD revealed shear stress-induced decomposition, with H3O+ ions replacing Na+ ions.
• ToF-SIMS confirmed Cl- and Na+ ion accumulation, leading to a densified 20 μm surface layer.

Conclusions:

• NASICON ceramics undergo significant structural and microstructural degradation when exposed to seawater at elevated temperatures.
• Ion exchange and structural decomposition are primary mechanisms of degradation.
• The observed surface densification indicates potential changes in interfacial properties.