A Study on Universal Factor Determining the Evolution of Surface Roughness During Electrochemical Polishing

Electrochemical polishing (ECP) is widely used for scratch- and damage-free finishing of metal components. Though the polishing effect of ECP has been confirmed in many researches, the influence of polishing parameters on evolution of surface roughness is still ambiguous owing to the use of different ECP systems. In this paper, the universal factor determining the evolution of surface roughness during ECP is studied by theoretical analysis as well as experiments. Theoretical analysis based on viscous layer mechanism demonstrates that the material removal thickness is the key parameter governing the roughness evolution of the polished surface regardless of other parameters including the voltage, current and electrolyte concentration and so forth. A series of experiments were designed and carried out to verify the proposed hypothesis. Both the experimental results and already published researches proved the validity and universality of the newly developed hypothesis on surface roughness evolution. This work is of great significance for further understanding the finishing mechanism of ECP and process control for its practical applications.

Reducing the Self-Discharge Rate of Supercapacitors by Suppressing Electron Transfer in the Electric Double Layer

Designing supercapacitors with suppressed self-discharge for long-term energy storage has been a challenge. In this work, we demonstrate that substantially reduced self-discharge rate can be achieved by using highly concentrated electrolytes. Specifically, when supercapacitors with 14 M LiCl electrolyte are charged to 0.80 V, the open circuit voltage (OCV) drops to 0.65 V in 24 h. In stark contrast, when the electrolyte concentration is reduced to 1 M, the OCV drops from 0.80 to 0.65 V within only 0.3 h, which was 80 times faster than that with 14 M LiCl. Decreased OCV decay rate at high electrolyte concentration is also confirmed for supercapacitors with different electrolytes (e.g., LiNO3) or at higher charging voltages (1.60 V). The slow self-discharge in highly concentrated electrolyte can be largely attributed to impeded electron transfer between the electrodes and electrolyte due to the formation of hydration clusters and reduced amount of free water molecules, thereby faradaic reactions that cause fast self-discharge are reduced. Our study not only supports the newly revised model about the formation of electric double layer with the inclusion of electron transfer, but also points a direction for substantially reducing the self-discharge rate of supercapacitors.

Optimum parameters for humic acid removal and power production by Al–air fuel cell electrocoagulation in synthetic wastewater

Although humic acid (HA) is a complex natural organic matter, it can potentially harm the environment and human health. In this study, aluminum–air fuel cell electrocoagulation (AAFCEC) was used to remove HAs from water while generating electricity. Initial pH, electrolyte concentration, HA concentration electrode distance and external resistance were investigated to determine the power generation and removal efficiency. The results showed that the better performance of power generation has been acquired in the alkaline solution and larger electrolyte concentration and short electrode distance. Further, Al–Ferron complexation timed spectrophotometry was used to determine the Al speciation distribution in the solution under different parameters. The power density of the cell reached 313.47 mW/cm2 for the following conditions: 1 g/L NaCl concentration, 3 cm electrode distance, 20 Ω external resistor, and pH 9. After about an hour electrolysis, the optimum removal rate of HA was above 99%. The results demonstrated that the AAFCEC is an efficient and eco-friendly water treatment process, and it could be further developed and disseminated in the rural areas and households.

Studying the Insulating Properties of Oxide Films Obtained on the Ti6A14V Alloy in Tartaric Acid Solutions Using the Method of Electrochemical Decoration by Copper

The investigation data of the formation peculiarities of oxide films on the Ti6A14V alloy in tartaric acid solutions have been given. It is shown that the behavior of alloy forming dependences is conditioned by the anode current density. At ja < 0.5 A∙dm-2 the continuous oxide film is not formed on the alloy surface and the preset value of the final voltage on the cell is not reached. With an increase in ja > 0.5 A∙dm-2, alloy forming dependences show a linear behavior that is indicative of the formation of low porous films. In these conditions, the oxide film formation rate is in direct proportion to the value of ja. The electrochemical oxidation of Ti6A14V alloy in tartaric acid solutions results in the formation of interference-colored oxide films. The oxide film ultimate thickness and color are defined by the preset voltage and are independent of the current density and electrolyte concentration. The isolating properties of obtained films were studied by the way of the cathode polarization of oxidized specimens in the sulfate copper-plating electrolyte. The research done allows us to make a conclusion that electrochemical copper deposition is a convenient tool for the detection of defective spots in oxide films. It is shown that due to the specific features of the reduction kinetics of Cu2+ ions on the oxidized titanium it is reasonable to use for the studies the initial sections of polarization dependences that correspond to ΔE = 0.2–0.25 V. The alloy polarization dependences allow us to establish unavailability of apparent dependences between the oxidation current density, the electrolyte concentration, the cell final voltage value and the polarization that occurs during the Cu2+ ion reduction. The anodic connection of copper-coated specimens conditions the reversible dissolution of a greater portion of the specks of copper deposits. It is indicative of the electron conduction of film defects. The obtained data allow us to vary the electrolysis parameters in a wide range with no significant influence of the treatment mode of Ti6A14V alloy on the quality of oxide coatings.

Electrochemical Studies of Chlorine Containing Silanes

The reduction potentials of a series of mono-, di- and trichloro alkyl and aryl substituted silanes was investigated by cyclic voltammetry. It was shown that chlorosilanes can be reduced in two one electron steps at potentials more positive than -1V vs SCE. The solvent type (THF, MeCN), silane type and polymerization and electrolyte concentration were varied and found to greatly impact the reduction potential.

Designing an ideal alcohol-based hand sanitizer: in vitro antibacterial responses of ethanol and isopropyl alcohol solutions to changing composition

This study aimed to achieve an in vitro quantification of the effects of composition and formulation factors on the killing rates of alcohol-based hand sanitizers. The killing rates of 85% ethyl alcohol (ET) and isopropyl alcohol (IPA) were studied under different conditions such as pH, electrolyte concentration, or inclusion of herbal extracts (cucumber, carrot, and aloe vera), a quaternary ammonium compound, or thickener over different time intervals. Changes in the activities were retested after 3 months as an indication of stability. From two-way ANOVA, both the time of exposure and the sanitizer type affected the activity against Staphylococcus aureus (P = 0.001 for both alcohols), whereas for Escherichia coli, time of exposure was significant (P = 0.027), while sanitizer type was less significant (P = 0.063). Extreme pHs, the presence of ions, and the inclusion of additives such as benzalkonium chloride (BAC), plant extracts, or carbomer impacted the 3-month activity of the samples differently. Important differences existing in the activities of ET and IPA, as a function of formulation factors or use conditions have been quantified using in vitro methods. Formulations should best be tailored for particular purposes and the all-purpose hand sanitizer may not exist. Graphic Abstract