Corrosion Resistance of Nanosized Silicon Carbide-Rich Composite Coatings Produced by Noble Gas Ion Mixing

Effect of Long-Term Sodium Hypochlorite Cleaning on Silicon Carbide Ultrafiltration Membranes Prepared via Low-Pressure Chemical Vapor Deposition

Sodium hypochlorite (NaClO) is widely used for the chemical cleaning of fouled ultrafiltration (UF) membranes. Various studies performed on polymeric membranes demonstrate that long-term (>100 h) exposure to NaClO deteriorates the physicochemical properties of the membranes, leading to reduced performance and service life. However, the effect of NaClO cleaning on ceramic membranes, particularly the number of cleaning cycles they can undergo to alleviate irreversible fouling, remains poorly understood. Silicon carbide (SiC) membranes have garnered widespread attention for water and wastewater treatment, but their chemical stability in NaClO has not been studied. Low-pressure chemical vapor deposition (LP-CVD) provides a simple and economical route to prepare/modify ceramic membranes. As such, LP-CVD facilitates the preparation of SiC membranes: (a) in a single step; and (b) at much lower temperatures (700-900 °C) in comparison with sol-gel methods (ca. 2000 °C). In this work, SiC ultrafiltration (UF) membranes were prepared via LP-CVD at two different deposition temperatures and pressures. Subsequently, their chemical stability in NaClO was investigated over 200 h of aging. Afterward, the properties and performance of as-prepared SiC UF membranes were evaluated before and after aging to determine the optimal deposition conditions. Our results indicate that the SiC UF membrane prepared via LP-CVD at 860 °C and 100 mTorr exhibited excellent resistance to NaClO aging, while the membrane prepared at 750 °C and 600 mTorr significantly deteriorated. These findings not only highlight a novel preparation route for SiC membranes in a single step via LP-CVD, but also provide new insights about the careful selection of LP-CVD conditions for SiC membranes to ensure their long-term performance and robustness under harsh chemical cleaning conditions.

Tungsten Carbide Nanolayer Formation by Ion Beam Mixing with Argon and Xenon Ions for Applications as Protective Coatings

A novel nanolayer is formed by means of ion irradiation applicable as protective coating. Tungsten carbide (WC)-rich nanolayers were produced at room temperature by applying ion beam mixing of various carbon/tungsten (C/W) multilayer structures using argon and xenon ions with energy in the range of 40-120 keV and fluences between 0.25 and 3 × 10¹⁶ ions/cm². The hardness of the nanolayers was estimated by means of standard scratch test applying an atomic force microscope equipped with a diamond-coated tip (radius < 10 nm); the applied load was 2 μN. The irradiation-induced hardness of the nanolayers correlated with the areal density of the WC; with the increasing amount of WC, the hardness of the nanolayer increased. The produced layers had an order of magnitude better corrosion resistance than a commercially available WC cermet circular saw. If the WC amount was high enough, the hardness of the layer became higher than that of the investigated WC cermet. These findings allow us to tune and design the mechanical and chemical properties of the WC protective coatings.

Design of Corrosion Resistive SiC Nanolayers

Recently, we have shown that the protecting layer of nanosize can be produced by means of ion beam mixing (IBM) of a Si/C multilayer system. The corrosion resistance of the layer correlated with the SiC amount and distribution, determined by Auger electron spectroscopy depth profiling. It has also been shown that the IBM of the Si/C system can be well described by TRIDYN simulation. By combining these two findings, it is possible to design protective layers for various arrangements of layer structure and irradiation conditions. Three different multilayer structures (with individual layer thicknesses falling in the range of 10-20 nm) have been irradiated by Ar⁺ and Xe⁺ ions at room temperature in the energy and fluence ranges of 40-120 keV and 0.25 × 10¹⁶ to 6 × 10¹⁶ ion/cm², respectively. The carbon and silicon depth distributions have been calculated by TRIDYN simulation. From these profiles applying a simple rule for compound formation, the SiC in-depth distributions were calculated. The resulting corrosion resistance has been measured by potentiodynamic corrosion test in 4 M KOH solution. Excellent correlation between these results and the in-depth distribution (calculated by TRIDYN simulation) of SiC has been found. Thus, the design of a protective SiC coatings operating in harsh environments is possible by applying fast and cheap simulation techniques.