Self-passivating (Re,Al)B₂ coatings synthesized by magnetron sputtering

Area of Science:

• Materials Science
• Solid State Chemistry
• Thin Film Deposition

Background:

• Rhenium Diboride (ReB2) is a refractory ceramic with potential applications.
• ReB2 is known to be susceptible to corrosion upon atmospheric exposure.
• Understanding and improving the stability of ReB2 is crucial for its practical use.

Purpose of the Study:

• To investigate the effect of aluminum (Al) additions on the chemical stability of ReB2 thin films.
• To explore the corrosion behavior of Al-doped ReB2 under atmospheric conditions.
• To determine if Al can enhance the protective properties of ReB2 surfaces.

Main Methods:

• Thin films of ReB2 and Al-doped ReB2 ((Re0.67Al0.10)B2 and (Re0.74Al0.11)B2) were synthesized using hybrid RF-DC magnetron sputtering.
• X-ray diffraction (XRD) was employed to confirm the crystal structure of the deposited films.
• X-ray photoelectron spectroscopy (XPS) was used to analyze the surface composition and identify corrosion products after atmospheric exposure.

Main Results:

• All deposited films, including Al-doped variants, exhibited the hexagonal ReB2 crystal structure (P63/mmc).
• Pure ReB2 thin films showed signs of corrosion, forming perrhenic acid (HReO4) within two days of exposure.
• (Re0.74Al0.11)B2 films developed a self-passivating aluminum oxide layer, which effectively prevented corrosion for at least 60 days.

Conclusions:

• Aluminum additions significantly improve the atmospheric corrosion resistance of ReB2 thin films.
• The formation of a stable Al-oxide layer is the primary mechanism for enhanced chemical stability.
• Al-doped ReB2 presents a promising material for applications requiring improved durability in ambient environments.