Yao Lu

One-step electrochemical machining of superhydrophobic surfaces on aluminum substrates

A superhydrophobic surface on an aluminum substrate was fabricated by one-step electrochemical machining using the sodium chloride (NaCl) aqueous solution containing fluoroalkylsilane as the electrolyte. The resulting superhydrophobic surfaces showed a static water contact angle of 166° and a tilting angle of about 1°. The morphological features and chemical compositions were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electron probe micro-analyzer (EPMA), and Fourier-transform infrared spectrometer (FTIR). It shows that the binary micrometer–nanometer-scale rough structures and the low surface energy coating were present on the aluminum surfaces. The resulting surfaces have good properties of anti-adhesion and self-cleaning. The durability of the superhydrophobic surfaces on aluminum substrates was also investigated. This preparation method is advantageous as it does not require acid electrolyte or a separate process to lower the surface energy, uses simple steps, and is environmental friendly and highly efficient.

Fabrication of superoleophobic surfaces on Al substrates

An easy method of fabricating superoleophobic surfaces on Al substrates by constructing reentrant structures is reported. The reentrant micro/nanometer-scale structures comprise micrometer-scale, rectangular-shaped, and step-like Al structures obtained by electrochemical etching and nanometer-scale Ag grains resulting from immersion in [Ag(NH3)2]+ solution. Surface energy is reduced by perfluorooctanoic acid (PFOA) containing –CF3 and –CF2– groups. The PFOA-modified micro/nanometer-scale rough structures enable the formation of a composite solid–liquid–air interface with peanut oil. These structures show good superoleophobicity with a peanut oil contact angle of 160.0 ± 2° and a sliding angle of 8°. Nanometer-scale structures can effectively transform the micrometer-scale non-reentrant structures into reentrant structures. With the aid of suitable low surface energy materials such as PFOA, fabricating superoleophobic surfaces on Al substrates can be easier.

A rapid two-step electroless deposition process to fabricate superhydrophobic coatings on steel substrates

The present study reports a simple, highly effective, and safe two-step electroless deposition process for rapidly fabricating superhydrophobic Ag coatings on steel substrates. The steel plates were first immersed in the 1xa0mol/L aqueous CuSO4 solution for 20xa0s, and then immersed in the 0.03xa0mol/L aqueous AgNO3 solution containing 1xa0wt% fluoroalkylsilane (FAS) for 2xa0min. The sample surfaces were characterized by energy-dispersive x-ray spectroscopy, Fourier transform infrared spectrophotometry (FTIR), x-ray diffraction, scanning electron microscopy, step profiler, and optical contact angle measurements. The results show that, after the two-step electroless deposition process, the Ag coatings composed of the binary micro/nanometer-scale rough structures containing the FAS molecules with a low surface energy are formed on the steel surfaces. The as-prepared Ag coatings exhibit a good superhydrophobicity with a 163.4xa0±xa01.8° water contact angle and 1.5xa0±xa00.5° rolling angle.

Fabrication of Low-Adhesive Superhydrophobic Al Surfaces via Self-Assembled Primary Cell Assisted Etching

In this work, we present a novel etching method to fabricate the superhydrophobic Al surfaces in a salt solution. Hierarchical rough structures composed of micrometer-scale pits, protrusions, and rectangle plateaus and nanometer-scale step-like structures are formed on the Al surfaces by the self-assembled primary cell assisted etching and the preferential corrosion of grain boundaries and dislocations. After fluoroalkylsilane modification, the superhydrophobic Al surfaces with a 166.4° water contact angle and a 1° rolling angle are obtained. The developed method does not use any strong acids and has a smaller harm to the environment and operators.

Fabrication of Superhydrophobic Surfaces on Aluminum Substrates via Electrochemical Etching and Re-Deposition

Superhydrophobic surfaces on metal substrates are often prepared via roughing the surfaces and lowering their surface energy. The superhydrophobic aluminum surface with a water contact angle of 162.5° and rolling angle less than 6° was fabricated via electrochemical etching and re-deposition using the alkalic Na3PO4 electrolyte and then fluorination treating. The surface morphology and chemical composition were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results show that the surface consists of the micrometer-scale lumps and protrusions, and many nanometer-scale mastoids are filled in these protrusions. These hierarchical micro/nanometer-scale binary structures, which are similar to the micro-structures of lotus leaf surfaces, play an important role in achieving superhydrophobicity. The main components of the binary geometric structures are Al2O3, AlPO4, and H2O. The effects of the processing time and processing voltage on the macro-morphology were also investigated. The macro-rough structures appeared on the edge of the aluminum surface firstly, and then spread gradually to the entire surface.

The formation of reacted film and its influence on tribological properties of extruded Al-Si-Cu-20-25Pb alloy under dry sliding

The friction and wear characteristics of AlSiCuPb alloys, especially antiseizure, have been investigated under dry sliding for a wide range of load. It is shown that hot extrusion considerably improved antiseizure properties of stircast AlSiCuPb alloys, and a stable wear rate with the lowest level of coefficient of friction are found to be controlled by the formation of a reacted film covering almost the entire worn surfaces of specimens under high applied load. The reacted film consists of compounds containing Al, Si, Pb and O. The reacted film is generally found to play significant role in improving the ability to resist seizure for AlSiCuPb alloys containing 20 wt% and 25 wt% lead.