Stearic Acid Solution Research Articles

Structure and microwave properties of Fe75Si25 alloys produced by high-energy wet ball milling in organic media

Fe-Si alloys are known for excellent soft magnetic properties and are widely used as fillers of composite for microwave applications. A change in the size and the morphology of the powder particles has a significant influence on the microwave properties of composites filled with such powders. In this paper, Fe75Si25 powders were produced by wet ball milling. A solution of stearic acid in petroleum ether (a surfactant solution) and acetone were used as milling media. The influence of wet ball milling conditions on the morphology and the structure of the produced powders was studied by scanning electron microscopy, X-ray diffraction, Mossbauer spectroscopy and X-ray photoelectron spectroscopy. Wet ball milling of the alloy in an acetone leads to the formation of the particles of greater thickness and smaller size in comparison with the particles produced by wet ball milling in a surfactant solution. In both cases after milling the alloy is disordered. During the milling process Si concentration in the alloy decreases due to the formation of surface oxide layers enriched with silicon. The frequency dependence of microwave permittivity and permeability of composites filled with produced powders was studied. The depolarization factor, percolation threshold, and intrinsic permeability of produced powders particles were determined. The frequency dependence of intrinsic permeability of the particles was shown to depend strongly on the milling conditions. A change in the milling conditions makes it possible to produce Fe75Si25 powders with the required microwave properties.

Superhydrophobic Coatings on Aluminium Based on Carboxylic Acids

Development of new coatings for corrosion protection should be directed to environmentally friendly yet efficient technologies. Industrial applications additionally demand energy sustainability and cost effectiveness. Among varieties of new coatings being developed superhydrophobic coatings are also in the focus of current research in both academic and industrial sectors. The background of their use, inspired by effects in nature, is the prevention of ingress of electrolyte to underlying substrate and properties of self-cleaning and anti-sticking. Superhydrophic surfaces can be applied to different substrates, from metal, textile, plastics, etc. Superhydrophobicity can be related to surface texture or surface chemistry, e.g., use of silane-, fluoro-based or other compounds [1]. The basic idea of the current research study is to design multifunctional compounds by integrating corrosion inhibitors and hydrophobic agents with lipophilic or fluorous properties into hybrid matrices so as to produce a corrosion resistant hydrophobic coating that display good adhesion to Al substrates. The first step is to test potential candidates for (i) hydrophobic compounds and (ii) corrosion inhibitor compounds. Among hydrophobic compounds, carboxylic acids were tested since they offer environmentally friendly and cheap option. In order to adsorb carboxylic acids on metal surface an appropriate pre-treatment is required. In the present work we investigated the possibility to fabricate superhydrophobic surfaces on aluminium metal pre-treated by alkaline etching at 90 °C [2] which represents a green solution-phase method to produces hierarchical growth of the aluminium hydroxide array. After immersion in ethanol solution of carboxylic acid the surface turns superhydrophobic. In the present study we have investigated the effect of several parameters on the formation of superhydrophobic surface on aluminium pre-treated by etching: type of etching as a pre-treatment, length of carboxylic chain, time of immersion in carboxylic acid and concentration of carboxylic acid. The effect of these parameters on the water contact angle and corrosion properties in 0.5 M NaCl solution were determined. Depending on the type of carboxylic acid a remarkable decrease in both cathodic and anodic current density can be achieved. Optimal parameters were denoted as those achieving high water contact angle, and low corrosion current density combined with a broad passive range. XPS showed that after alkaline etching the aluminium surface was fully covered by an hydroxide layer. ToF-SIMS provided direct evidence of adsorption of octanoic and stearic acids. Coatings prepared on Al by self-assembling in carboxylic acids were tested also by long-term immersion in NaCl solution. Surface durability in terms of resistance in acid and alkaline solution, as well as sliding angle were determined. Morphology of self-assembled carboxylic layers on alkaline etched aluminium analysed by FE-SEM shows nano-rough surface with numerous micro-cones with steps or terraces giving the surface a dual roughness. Composition of the surface was investigated using various surface analytical methods, i.e. FTIR, XPS and SIMS. Adsorption bonding of carboxylic acids to hydroxylated Al surfaces is also being investigated by DFT calculations. We utilized periodic slab model of passivated surface with hydroxylated oxide-layer supported on Al metal. These calculations help us to scrutinize details of how carboxylic head-groups attach to hydroxylated surface and how lateral intermolecular interactions and their self-assembly depends on the length of the aklyl tail. The effect of the organic layer composition on the resulting electronic properties of the passive layer (band gap, electronic workfunction) is also investigated. Fig. 1. FE-SEM image of aluminium surface etched in NaOH and immersed in 5 mM ethanol solution of stearic acid. Detail: contact angle of water drop 156°. Acknowledgments: This work is a part of M.ERA-NET project entitled “Design of corrosion resistant coatings targeted for versatile applications”, acronym COR_ID. The financial support of the project by Ministry of Education, Science and Sport of Republic of Slovenia (Programmes of International Scientific Cooperation) and Agence Nationale de la Recherche, France, is acknowledged.

Optimization of MAO Process Parameters and Effect of Subsequent Sealing Treatment on Corrosion Resistance of Aluminum Alloy

Micro-arc oxidation (MAO) coatings were obtained on the substrate of AlSi12Cu aluminum alloy in Na2SiO3 electrolyte. Then, the MAO coatings were sealed in stearic acid and sodium silicate solution, respectively. Experiments were conducted by varying current density, oxidation time and the frequency. L9 (33) of orthogonal experiments were chosen to optimize the processing parameters in the process of MAO technique. Through the above orthogonal experiments, the optimal process conditions were determined: the current density of 30 A/dm2, the oxidation time of 20 min, and the frequency of 600 Hz. The results showed that the MAO coating consisted of α-Al2O3 and γ-Al2O3. There were lots of pores and micro-cracks on the coating surface. The corrosion current of the aluminum alloy after MAO combination with stearic acid sealing treatments was significantly reduced, decreased 100 times more than the substrate and the corrosion potential increased 272 mV, signifying enhanced corrosion resistance. The corrosion rate of the aluminum alloy after MAO treatment in the washing powder solution decreased 25 times more than that of the substrate.

The rheological response of carbonyl iron particles suspended in mineral oil solution of 12-hydroxy stearic acid

In this study, carbonyl iron based magnetorheological fluids (MRFs) with 12-hydroxy stearic acid (12-HSA) oil solutions as carrier were fabricated. Rheological performance of the magnetorheological fluid, including viscosity, yielding, magnetic hysteresis, dynamic modulus as well as thixotropic behavior, was investigated by using a rotational rheometer equipped with a magnetic device. It is found that the 12-HSA gave rise to an increase in the off-state viscosity and shear stress in the absence of magnetic field, indicating gel structure developed in the suspensions. This gel network associating with field-induced particle structure lead a substantial yield stress and dynamic modulus. The hysteresis test validated that the gel like network had a certain effect on maintaining the aggregation structure after removing the magnetic field. Dynamic oscillatory tests showed that 12-HSA solution based MRF exhibits solidlike property in the absence of magnetic field. The dependence of plateau value G′ on magnetic field showed relationship of natural logarithm. Regarding to the thixotropy, a longer recovery progress was observed in 12-HSA solution based MRF due to the restriction of gel network. The sedimentation measurements revealed that the strong flocculation could be formed by 12-HSA and enhances the stability of suspensions.

A green one-step fabrication of superhydrophobic metallic surfaces of aluminum and zinc

Abstract Superhydrophobic surfaces on metal materials play a significant role in considerable industries because of its eminent water-repel and anti-pollutant ability. A facile green methodology is proposed to in situ fabricate superhydrophobic surface on aluminum surface by simply immersing the plate in an aqueous mixture solution of HCl and stearic acid. Sample possesses high contact angle (150°) and low roll-off angle (8°), because the surface simultaneously combines rough structure with low surface energy. SEM images and contact angle measurements directly show the rough structures and contact angles. It did not require any toxic chemical agents, sophisticated techniques or equipments. The surface modification and ligand bonding of stearic acid on aluminum surface were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy. More importantly, the obtained superhydrophobic surfaces show remarkable stability in acidic and alkaline conditions, and the contact angle can stay above 150° without apparent fluctuation for water droplet with pH value ranging from 1 to 14. A prominent enhancement on the corrosion resistance capacity of the aluminum and zinc plates was achieved after the superhydrophobic treatment.

Oil/water mixtures and emulsions separation of stearic acid-functionalized sponge fabricated via a facile one-step coating method

Abstract Superhydrophobic and superoleophilic sponge was prepared by facile dip coating in a stearic acid (SA) solution and subsequent heat treatment. The obtained sponge exhibits excellent superhydrophobic stability and selectively sorption ability for oil pollutants on water surface. Also, the sponge is capable of separating huge amounts of oils from water continuously via a vacuum system and oil droplets in oil-in-water emulsions. After the separation by the coated sponge, the transparency for the emulsions (n-Hexane-in-water and toluene-in-water) can increase to over 80% from below 14.7%. The oil sorption capacity of as-prepared sponge for various types of oils and organic solvents can reach 17.4–41.6 times of its own weight, and the absorbed oils are easy to be recovered by a simple squeezing process. Moreover, the recovered sponge can repeatedly absorb/desorb the oils for at least 100 times, demonstrating slightly decrease in sorption capacities and hydrophobicity. The proposed approach for fabricating superhydrophobic sponges is simple and inexpensive so that the as-prepared sponge has great potential as an efficient sorbent in oily wastewater filtration and oil spill clean-up.

Fabrication of mechanically robust superhydrophobic aluminum surface by acid etching and stearic acid modification

The aluminium surface with multi-scale structure has been fabricated via a facile and rapid solution-phase etching method by HCl/H2O2 etchants. After modification with stearic acid solution, the wettability of the etched aluminum surface turns into superhydrophobicity with an optimal water contact angle of 160° ± 2° and a sliding angle of 4° ± 1°. The processing conditions, such as the etching time, modifier types and the concentration of H2O2 are investigated to determine their effects on the surface morphology and wettability. As a result, the obtained sample shows excellent anti-adhesion property and bouncing phenomenon of water droplet. It can withstand mechanical abrasion for at least 100 cm under 12.3 kPa, or hydrostatic pressure under 24 ± 1 kPa without losing its superhydrophobicity, suggesting superior mechanical durability. Moreover, the surface also remains superhydrophobicity even after contacting corrosive liquids or long-term exposure in air over 100 days. Such a mechanically durable superhydrophobic aluminum surface can provide a promising practical application in various fields.

The new method of modifying the hydrophobic properties of expanded perlite

The progressive industrialization and development of the automotive industry is the cause of the increasing demand for chemical products, especially oil products. Unfortunately, during processing, transportation or storage of these products, they get very often into the environment causing pollution. The removal of the results of accidents is still a current problem. The techniques which employ various types of sorbents deserve special attention among the several methods of eliminating the effects of pollutions. Moreover, expanded hydrophobic perlite is an interesting material among sorbents which are used on a large scale. The new method of modifying the hydrophobic properties of expanded perlite, with the use of solutions of stearic acid in organic solvents, was presented. The perlite that was used in research was produced by the PerliPol registered partnership in Belchatow. Hydrophobic properties of the obtained materials were determined on the basis of the results achieved due to the modified film flotation method, “floating on water” test and on the basis of the value of water retention for individual samples. All grain fractions of perlite obtained hydrophobic properties which were better than or comparable to the hydrophobic properties of the HydroPerl (PerlPol) commercial material used to remove petroleum product pollution. The hydrophobization process significantly improved the adsorption capacity of modified perlite to petroleum product pollution.

A novel and facile fabrication of superhydrophobic surfaces on copper substrate via machined operation

Practical application of superhydrophobic surfaces is often hampered by the sophisticated facilities, complex process, expensive cost and harmful solvents etc. This paper reports a novel method to prepare a superhydrophobic surface via machine operation and chemical modification. Superhydrophobic copper surfaces are obtained by machine cutting using 60° thread cutters followed by modification using stearic acid solution. The surface morphologies, chemical composition and wettability were characterized using scanning electron microscopy (SEM), Fourier transformed infrared (FT-IR) spectroscopy and water contact angle measurement. The as-prepared surface displays good superhydrophobic property. The formation mechanism of the microstructure is proposed. The rough surface depends on the cutter shape and feed rate provided.

Air-jet atomization for preparation of lipid nanoparticles: Dependence of size on solute concentration

Engineering nanoparticles for applications such as drug delivery, needs understanding of dependence of particle size on process and precursor parameters. The size of nanoparticles prepared through the aerosol route using solution droplet drying technique is traditionally governed by a 1/3rd scaling law between dry particle diameter and precursor solute concentration. Here, we experimentally investigate this relationship, for precursor solutions of lipids in organic solvents. Nanoparticles were prepared using air-jet atomization of precursor solutions of stearic acid in organic solvents (acetone, chloroform, methanol and ethanol), in a pulse heat aerosol reactor, at a process temperature of 50°C. The relationship between median mobility diameter of prepared nanoparticles (40–155nm) and solute concentration was governed by a scaling law exponent (SLE) in the range 0.104–0.182. The observed exponents showed significant deviations from the classical 1/3rd law. The experimental investigation indicated an unexpected increase in particle number concentration with increasing solute concentration for all solvents studied. Simulations with a critical super saturation based solute diffusion model and theoretical calculations of size dependent external factors such as coagulation and wall losses during transit, could not explain the deviation in SLE, nor the increased number concentrations. These considerations point to possible effects of solute concentration on the mechanism of droplet formation during the atomization process. A preliminary model based on an area conservation law has been proposed to explain the twin effects of deviation in SLE and increased droplet number concentration with increasing solute concentration. The present study provides empirical data on the relationship between dry particle diameter and solute concentration in the selected lipid-organic solvent systems. Also, it opens avenues for further understanding nanoparticle formation by air-jet atomization.

Corrosion performance of superhydrophobic nickel stearate/nickel hydroxide thin films on aluminum alloy by a simple one-step electrodeposition process

Superhydrophobic thin films are fabricated on chemically cleaned aluminum alloy substrates by a one-step electrodeposition process in the ethanolic solution containing Ni2 + ions and stearic acid (SA) under applied DC voltage. Morphological features observed by scanning electron microscopy (SEM), indicate that the thin films are composed of cauliflower-like structures with micro-nano scale particles. The chemical compositions of these films are characterized using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), which indicate that these films consist of low energy nickel stearate (Ni(SA)2). A schematic model of the electrodeposition process of Ni(SA)2 is also presented. Wetting analysis demonstrates that the surface of the film is superhydrophobic with a water contact angle (CA) of 160 ± 1° with contact angle hysteresis (CAH) of 2.1 ± 1°, which is obtained under optimum electrodeposition conditions based on a 0.4 molar ratio of Ni2 +/SA solution. The corrosion resistance properties calculated from the Tafel curve of superhydrophobic surfaces prepared in this solution are 280 times larger than the chemically cleaned aluminum alloy substrate. Furthermore, electrochemical impedance spectroscopy (EIS) analysis demonstrates that the charge transfer resistance is 1.63 × 107 Ω·cm2 for superhydrophobic films (Ni2 +/SA = 0.4) compared to that of chemically cleaned aluminum alloy substrates (1.56 × 103 Ω·cm2). Therefore, the superhydrophobic film of Ni(SA)2 on the chemically cleaned aluminum alloy substrate improves the corrosion resistance performance of aluminum substrates in corrosive environments.

Superhydrophobic surface fabricated on iron substrate by black chromium electrodeposition and its corrosion resistance property

The fabrication of superhydrophobic surface on iron substrate is carried out through 20min black chromium electrodeposition, followed by immersing in 0.05M ethanolic stearic acid solution for 12h. The resultant superhydrophobic complex film is characterized by scanning electron microscope (SEM), disperse Spectrometer (EDS), atomic force microscope (AFM), water contact angle (CA), sliding angle (SA) and X-ray photoelectron spectroscope (XPS), and its corrosion resistance property is measured with cyclic voltammetry (CV), linear polarization and electrochemical impedance spectroscopy (EIS). The results show that the fabricated superhydrophobic film has excellent water repellency (CA, 158.8°; SA, 2.1°) and significantly high corrosion resistance (1.31×106Ωcm−2) and excellent corrosion protection efficiency (99.94%).

Importance of gelation and crystallization for producing superhydrophobic surfaces from mixtures of hydrogenated castor oil and fatty acids

Superhydrophobic surfaces were obtained easily from a mixed solution of hydrogenated castor oil (HCO) as an organogelator and a fatty acid as a crystalline compound by a casting method: a contact angle of 160° ± 2° and a sliding angle of 5° ± 1° were achieved on a surface prepared from the mixed solution of HCO and stearic acid (SA) at 6:4 weight ratios at 30 °C. The superhydrophobicity of the surface was attributable to a hierarchical structure which consisted of self-assembled nano-fibers of HCO and nano/micrometer-scale crystals of SA on hemispherical sub-structures having a diameter of several tens of micrometers. The hierarchical structure was formed under controlled conditions involving mixing ratios of HCO and a fatty acid, preparation temperatures, and fatty acid species. These results indicated that balance between gelation of HCO and crystallization of a fatty acid in the casting process was of importance in producing superhydrophobic surfaces.

Superhydrophobic aluminum alloy surfaces prepared by chemical etching process and their corrosion resistance properties

Superhydrophobic aluminum alloy surfaces are obtained by chemical etching using 1M NaOH solution followed by passivation using 0.01M ethanolic stearic acid (SA) solution. The formation of low surface energy aluminum stearate takes place during the passivation process between stearic acid and hydroxyl group-terminated aluminum alloy surfaces. A schematic model of the SA passivation process on the OH terminated Al-surfaces is presented in this work. The flake-like micro-nanostructure morphology of the low surface energy aluminum stearate increases the water contact angle by more than 150°, demonstrating the superhydrophobic properties. The corrosion current density reduces and polarization resistance increases systematically with increasing passivation time. The polarization resistance, calculated from the Tafel curve of the superhydrophobic surfaces prepared by stearic acid passivation for 60min, is determined to be 137 times larger than that of the as-received aluminum alloy substrate. Similarly, the modulus of impedance, as-determined from electrochemical impedance spectroscopy (EIS), is found to be 70 times larger for the superhydrophobic surfaces compared with the as-received aluminum alloy surface. These results demonstrate that the superhydrophobic aluminum alloy surfaces created by chemical etching followed by passivation have superior corrosion resistance properties than the as-receive aluminum alloy substrate.

Corrosion protection of brasses and zinc in simulated urban rain

Self‐assembled surface layers of benzotriazole (BTAH), 2‐mercaptobenzimidazole (2‐MBI) and stearic acid (SA), were studied as protective layers for brasses (Cu10Zn and Cu40Zn) and Zn in simulated urban rain (pH=5). Layers were formed by immersion of samples in ethanol solution of organic inhibitors BTAH, 2‐MBI and SA. The results of weight loss immersion tests, polarization measurements and electrochemical impedance measurements showed that SA layers provided the best long term corrosion protection of all tested inhibitors and exhibited the highest contact angles. 2‐MBI provided less protection than SA. BTAH can be ruled out as a corrosion inhibitor under tested conditions, because it performed poorly upon long term immersion. In the cases of Cu40Zn and Zn it even promoted corrosion.

Corrosion resistance of high-level-hydrophobic layers in combination with Vitamin E – (α-tocopherol) as green inhibitor

Modifications of Cu and Cu40Zn surfaces were achieved by their immersions in ethanol solutions of stearic acid with and without the additions of Vitamin E. The surface morphologies, wettability, and corrosion resistance were characterised by means of SEM, water contact-angle, potentiodynamic measurements and EIS. The corrosive media was artificially prepared acid rain at 25°C. Significant increase in the contact angle indicated that the biomimetic morphology effectively repelled water from the metal surface. Electrochemical measurements indicated that Vitamin E additionally improved the inhibitory properties of the as-prepared hydrophobic layer against corrosion. The inhibitive effectiveness increased to more than 99%.

A facile method to fabricate functionally integrated devices for oil/water separation.

In this paper, we present a facile method for the fabrication of a functionally integrated device, which has the multi-functions of the oil-containment boom, oil-sorption material, and water/oil-separating film, through a single immersion step in an ethanol solution of stearic acid. During the simple immersion process, the two dominant factors of superhydrophobicity, surface roughness and low-surface-energy coatings, could be accomplished simultaneously. The as-prepared functionally integrated device with superhydrophobicity/superoleophilicity displayed a lower density than that of water, such that it could float on water and act as an oil-containment boom; an efficient oil-absorbing property, which was attributed to the capillary effect caused by micrometer-sized pore structures and could be used as oil-sorption materials; a high oil/water separating efficiency which was suitable for water/oil-separating film. In this way, the functions of oil collection, absorption, and water/oil separation are integrated into a single device, and these functions could work independently, reducing the cost in terms of energy consumption and being versatile for a wide range of applications.

Superhydrophobic surfaces on diverse metals based on ultrafast sequential deposition of silver and stearic acid

In the presence of NaF, silver (Ag) was galvanically deposited onto aluminum (Al) substrate quickly (typically 10s) from dilute aqueous AgNO3 solution. Subsequent immersion into ethanolic solution of stearic acid (SA, for 30s) rendered Al superhydrophobic. The deposition and morphological evolution of Ag were investigated in detail. It was found that NaF was indispensable to initiate the Ag galvanic deposition by dissolving the barrier oxide layer. Moreover, as reaction time prolonging, surface morphology and surface wettability varied synchronously. This strategy to fabricate superhydrophobic surface (coded as SHS) was also applicable to many other metals, such as Fe, Co and Mo with oxide passivation layer (NaF was needed) or Mg, Zn, Sn, Pb, and Cu with no apparent oxide passivation layer (NaF was not needed). In summary, the strategy to fabricate SHS based on Ag deposition and SA modification was quite impressive for its time-saving benefits and wide substrate applicability.

A novel solution-controlled hydrogel coated mesh for oil/water separation based on monolayer electrostatic self-assembly

Solution-controlled hydrogel coated materials for oil/water separation have been successfully fabricated. The as-prepared mesh can switch between superhydrophilicity/underwater superoleophobicity and superhydrophobicity/superoleophilicity through self-assembly and dis-assembly pathways. The PDMAEMA hydrogel coated mesh is firstly prepared via photo induced free radical polymerization. A facile monolayer electrostatic self-assembly method was involved by immersing the hydrogel coated mesh in an ethanol solution of stearic acid for a few minutes. The stearic acid modified mesh converts to superhydrophobicity/superoleophilicity. More importantly, the mesh can return to the original state swiftly after the dis-assembly of the monolayer by immersion in a NaOH aqueous solution. The unique superiority of this material is that the transition of wettability can be achieved in situ, so that oil and water can pass through the mesh in sequence through the control of the NaOH solution. Therefore, the as-prepared meshes have great potential in practical applications dealing with both water-rich and oil-rich oil/water mixture separation with high separation efficiency (>99.3%). The synthetic method is simple, time saving and cost saving.

A facile solvent-manipulated mesh for reversible oil/water separation.

A controllable oil/water separation mesh has been successfully developed and easily manipulated by immersion in a stearic acid ethanol solution and tetrahydrofuran with a very short period of time. The superhydrophilic and underwater superoleophobic mesh is first obtained via a one-step chemical oxidation and subsequently converts to superhydrophobic after it is immersed in an ethanol solution of stearic acid for 5 min. The surface wettability is regained to superhydrophilic quickly by immersion in tetrahydrofuran for 5 min. More importantly, the reversible superhydrophobic-and-superhydrophilic switching can be repeated multiple times with almost no visible morphology variation. Therefore, this approach provides potential application in controllable oil/water separation and opens up new perspectives in manipulation of various metallic oxide substrates.