Dilip K. Sarkar

Superhydrophobic Aluminum Alloy Surfaces by a Novel One-Step Process

A simple one-step process has been developed to render aluminum alloy surfaces superhydrophobic by immersing the aluminum alloy substrates in a solution containing NaOH and fluoroalkyl-silane (FAS-17) molecules. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and water contact angle measurements have been performed to characterize the morphological features, chemical composition and superhydrophobicity of the surfaces. The resulting surfaces provided a water contact angle as high as ∼162° and a contact angle hysteresis as low as ∼4°. The study indicates that it is possible to fabricate superhydrophobic aluminum surfaces easily and effectively without involving the traditional two-step processes.

Chemical Nature of Superhydrophobic Aluminum Alloy Surfaces Produced via a One-Step Process Using Fluoroalkyl-Silane in a Base Medium

Various surface characterization techniques were used to study the modified surface chemistry of superhydrophobic aluminum alloy surfaces prepared by immersing the substrates in an aqueous solution containing sodium hydroxide and fluoroalkyl-silane (FAS-17) molecules. The creation of a rough micronanostructure on the treated surfaces was revealed by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRRAS) confirmed the presence of low surface energy functional groups of fluorinated carbon on the superhydrophobic surfaces. IRRAS also revealed the presence of a large number of OH groups on the hydrophilic surfaces. A possible bonding mechanism of the FAS-17 molecules with the aluminum alloy surfaces has been suggested based on the IRRAS and XPS studies. The resulting surfaces demonstrated water contact angles as high as ~166° and contact angle hystereses as low as ~4.5°. A correlation between the contact angle, rms roughnesses, and the chemical nature of the surface has been elucidated.

Synthesis of Monodisperse Fluorinated Silica Nanoparticles and Their Superhydrophobic Thin Films

Monodispersive silica nanoparticles have been synthesized via the Stöber process and further functionalized by adding fluorinated groups using fluoroalkylsilane in an ethanolic solution. In this process, six different sizes of fluorinated silica nanoparticles of varying diameter from 40 to 300 nm are prepared and used to deposit thin films on aluminum alloy surfaces using spin coating processes. The functionalization of silica nanoparticles by fluorinated group has been confirmed by the presence C-F bonds along with Si-O-Si bonds in the thin films as analyzed by Fourier transform infrared spectroscopy (FTIR). The surface roughnesses as well as the water contact angles of the fluorinated silica nanoparticle containing thin films are found to be increased with the increase of the diameter of the synthesized fluorinated silica nanoparticles. The thin films prepared using the fluorinated silica nanoparticles having a critical size of 119 ± 12 nm provide a surface roughness of ∼0.697 μm rendering the surfaces superhydrophobic with a water contact angle of 151 ± 4°. The roughness as well as the water contact angle increases on the superhydrophobic thin films with further increase in the size of the fluorinated silica nanoparticles in the films.

Fabrication of Superhydrophobic Surfaces on Aluminum Alloy Via Electrodeposition of Copper Followed by Electrochemical Modification

Superhydrophobic aluminum surfaces have been prepared by means of electrodeposition of copper on aluminum surfaces, followed by electrochemical modification using stearic acid organic molecules. Scanning electron microscopy (SEM) images show that the electrodeposited copper films follow “island growth mode” in the form of microdots and their number densities increase with the rise of the negative deposition potentials. At an electrodeposition potential of −0.2 V the number density of the copper microdots are found to be 4.5×104 cm−2 that are increased to 2.9×105 cm−2 at a potential of −0.8 V. Systematically, the distances between the microdots are found to be reduced from 26.6 μm to 11.03 μm with the increase of negative electrochemical potential from −0.2V to −0.8V. X-ray diffraction (XRD) analyses have confirmed the formation of copper stearate on the stearic acid modified copper films. The roughness of the stearic acid modified electrodeposited copper films is found to increase with the increase in the density of the copper microdots. A critical copper deposition potential of −0.6V in conjunction with the stearic acid modification provides a surface roughness of 6.2 μm with a water contact angle of 157°, resulting in superhydrophobic properties on the aluminum substrates.

Review of Different Techniques to Study the Interactions Between Coke and Pitch in Anode Manufacturing

The quality of carbon anodes, consumed in electrolysis during the primary aluminum production, has an important impact on the electrolytic cell performance. Coke and pitch are the raw materials used in anode manufacturing. The raw material properties and the process parameters during production determine the anode quality. A plant receives these materials from different sources, and the variability in their properties is usually a major concern during anode production. The interaction between coke and pitch influences strongly the anode properties. Study of coke and pitch individually as well as the interactions between them using different techniques (spectroscopic, optical, etc.) such as XRD, FTIR, XPS, and SEM help identify their compatibility. Each technique gives information on different aspects of the raw materials. In this article, the use of a number of these techniques for studying coke, pitch, and their interactions will be discussed. Results will be presented for a number of cases.