Concentrations Of NaOH Aqueous Solutions Research Articles

Organosilane-functionalized hydrothermal-derived coatings on titanium alloys for hydrophobization and corrosion protection

This work focuses on the structure, wettability and corrosion behaviors of Ti-6Al-4 V alloy after roughening treatments in different concentrations of NaOH aqueous solutions followed by low surface energy hexadecyltrimethoxysilane (HDTMS) coating. In this regard, scanning electron microscopy, contact angle measurements, potentiodynamic polarization and electrochemical impedance spectroscopy were used to characterize the samples. In contrast to hydrophilicity caused by the hydrothermal alkaline treatments, the subsequent HDTMS coating donated considerable hydrophobicity. Typically, the highest sessile water contact angle (about 147°) was obtained for the sample treated in 3 M NaOH solution followed by the HDTMS coating. In addition, the alkaline treatment reduced the corrosion resistance of the surface in a NaCl aqueous solution; however, the HDTMS hydrophobization process improved it significantly. It is eventually concluded that the coupled use of alkaline treatment and HDTMS functionalization can be further considered for moisture-exposed applications of Ti-based alloys.

Effects of NaOH Concentration on the Microstructure and Morphology of TiO2Precursor Nanobelts Prepared in a Hydrothermal Process

Unlike most previously reported experiments in which nanobelts were prepared using 10 M sodium hydroxide, a series of TiO2 precursor nanobelts with diameters ranging from 60 to 600 nm were successfully synthesized in our laboratory via a hydrothermal process using different concentrations of NaOH aqueous solutions and a commercial TiO2 powder (P25) as the raw materials. The reaction temperature was unexpectedly high at 260 °C. The formation process of TiO2 precursor nanobelts was investigated in terms of the morphological variations during a particle-to-nanobelt transition. Based on the detailed structural analysis of TiO2 precursor nanobelts, a rational mechanism has been proposed for the growth of the nanobelts. In addition, X-ray diffraction (XRD) of the nanobelts and degradation-efficiency test of a Rhodamine B (RhB) dye solution revealed that the precursor nanobelts should be heat-treated at 650 °C to produce highly crystalline anatase materials.

Effects of Alkaline Concentrations on the Tensile Properties of Napier Grass Fibre

This paper presents an experimental investigation of the effects of alkaline treatment on the tensile properties of Napier grass fibres. The effect of different concentrations of NaOH aqueous solutions on the morphology and structure of the fibres were studied. The fibres were treated with 5%, 10%, and 15% of Sodium hydroxide (NaOH) concentration for 24 hours of soaking time. The single fibre tests were then performed in accordance with ASTM D3822-07 standard. The morphology of the fibres before and after alkali treatment was observed with a Metallurgical Microscope MT8100. The results show that the physical properties were varied after the treatments and 10% concentration of NaOH treatment yield the maximum tensile strength and elongation of the fibre at 172 MPa and 5.7% respectively. Morphology observation found that the fibre became thinner, and the surface roughness of the fibres increased with the increment of NaOH concentration.

A simple way to synthesize anatase with high thermal stability

A simple and cost-effective method was proposed to synthesize nano-crystallized pure anatase titanium dioxide (TiO2) photocatalysts with a high thermal stability. The initial TiCl4 was reacted with a NaOH aqueous solution to form an amorphous sodium titanate, which was then transformed into an amorphous titanium dioxide hydrate through the replacement of Na+ by H+ using a HCl aqueous solution. After annealing, the pure nano-crystallized anatase TiO2 particles possessed a high thermal stability up to 900 °C. The high concentration of NaOH aqueous solution played an important role in preventing the precipitation of rutile TiO2 during hydrolysis process and promoting the formation of the nano-crystallized anatase TiO2. Samples calcined at 800 °C exhibited a significantly higher repeatable photocatalytic activity compared to the standard commercial photocatalyst P25 for the degradation of Rhodamine B in an aqueous suspension. This could be attributed to the synergistic effect of high crystallinity and mesoporous structure. The method is very simple, template-free, and cost effective, which makes it potential for the large-scale production.

Barium zirconate titanate nanoparticles synthesized by the sonochemical method

A new route for preparing barium zirconate titanate nanoparticles (BaZr0.3Ti0.7O3 (BZT)) has been developed by ultrasonication of BaCl2·2H2O, ZrOCl2·8H2O and TiCl4 precursors in a high concentration of NaOH aqueous solution. The as-prepared powders were identified by X-ray diffraction (XRD) as cubic perovskite BZT. The phase formation was confirmed by FT-IR and Raman spectroscopy. The increase of NaOH concentration resulted in BZT powders with smaller particle size and less BaCO3 contamination. The microstructure of BZT powders prepared in 20 M NaOH examined by scanning electron microscopy (SEM) showed nanosized spherical morphology with the average particle sizes of 51±6 nm.

In situ Precursor-Template Route to Semi-Ordered NaNbO3 Nanobelt Arrays.

We exploited a precursor-template route to chemically synthesize NaNbO3 nanobelt arrays. Na7(H3O)Nb6O19·14H2O nanobelt precursor was firstly prepared via a hydrothermal synthetic route using Nb foil. The aspect ratio of the precursor is controllable facilely depending on the concentration of NaOH aqueous solution. The precursor was calcined in air to yield single-crystalline monoclinic NaNbO3 nanobelt arrays. The proposed scheme for NaNbO3 nanobelt formation starting from Nb metal may be extended to the chemical fabrication of more niobate arrays.

Solvation of Dimethyl Succinate in a Sodium Hydroxide Aqueous Solution. A Computational Study

Molecular dynamics simulations were carried out to study dimethyl succinate/water/NaOH solutions. The potential of mean force method was used to determine the transport mechanism of a dimethyl succinate (a diester) molecule across the aqueous/vapor interface. The computed number density profiles show a strong propensity for the diester molecules to congregate at the interface, with the solubility of the diester increasing with increasing NaOH concentration. It is observed that the major contribution to the interfacial solvation free-energy minimum is from electrostatic interactions. Even at higher NaOH concentrations, the increasing electrostatic interaction between the diester and ions is not large enough to favor the solvation of diester in bulk solutions. The calculated solvation free energies are found to be -2.6 to -3.5 kcal/mol in variant concentrations of NaOH aqueous solutions. These values are in qualitative agreement with the corresponding experimental measurements. The computed surface potential indicates that the contribution of diester molecules to the total surface potential is about 25%, with the major contribution from interfacial water molecules.

Compressive stress-strain properties of natural materials treated with aqueous NaOH

Abstract Physical and cushioning properties of wood samples treated with various concentrations of NaOH aqueous solutions have been investigated based on compressive stress-strain curves. The shapes of curves changed essentially at NaOH concentrations above 10% as a threshold concentration. The stress-strain curves were analyzed based on the assumption that a rule of mixtures is applicable in the case of a very small range of displacement. The form factor n was also calculated. The values of n of the wood samples treated with NaOH whose concentration was higher than 10% were different from those of the wood samples treated with NaOH whose concentration was less than 10%. The shape changes, longitudinal contraction and twisting of the wood samples are related to NaOH concentration. The energy-absorption efficiency parameter E and ideality parameter I were calculated based on stress-strain curves according to the literature. Also, these parameters change above the threshold concentration of 10%. It was concluded that the cushioning properties of wood treated with alkali concentrations higher than 10% are improved. Due to the shape change of wood samples, the efficiency of energy-absorption properties is higher.

Effects of system parameters on making aluminum alloy lotus

In the present article, stable biomimetic superhydrophobic surfaces on aluminum alloy are obtained by wet chemical etching following modification with crosslinked silicone elastomer, perfluorononane (C9F20), and perfluoropolyether (PFPE), respectively. The formation and structure of superhydrophobic surfaces were characterized by means of scanning electron microscopy (SEM), water contact angle measurement, Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The effects of surface roughness resulted from the etching time, and the concentration of NaOH aqueous solution on the superhydrophobicity of the surfaces have been discussed in detail. The optimal surface roughness of starting material is about 0.05–0.5 μm and the resulting surface roughness should be controlled between 2.7 and 5.8 μm in order to realize the superhydrophobicity on aluminum alloy; if the concentration of NaOH aqueous solution is about 4 wt%, the best treatment time is between 2 and 4 h to form a surface roughness changing from 2.7 to 5.8 μm. The trapped air with the binary structure plays a key role in fabricating superhydrophobic surface on aluminum alloy. In other words, the unusual structure on the surface, which has a binary structure consisted of microprotrusions and nanoparticles, plays a very vital role in constructing of the stable biomimetic superhydrophobic surface on aluminum alloy.

Large-scale Cd X ( X=S, Se) microtube arrays on glass substrate: transformation of CdOHCl microrod arrays by a simple template-sacrificing solution method

Large-scale arrayed Cd X ( X=S, Se) microtubes have been successfully prepared on glass substrate by a simple solution route. In this process, cadmium hydroxyl chloride (CdOHCl) microrod arrays, which could be directly grown on glass surface in solution of CdCl 2 and methenamine, were used not only as a source of cadmium but also as a new reactive template to fabricate these highly ordered cadmium chalcogenide tube arrays, and the orientation of CdOHCl microrods on glass substrate could be easily achieved by pretreating the glass surface with appropriate concentration of NaOH aqueous solution. The transformation from arrayed CdOHCl rods to CdS and CdSe microtube arrays were conducted in thioacetamide and Na 2SeSO 3 solution, respectively. The conversion was convenient, and no CdOHCl crystallites were detected in the final products measured by X-ray powder diffraction. The hexagonal prismatic morphology and orientation of CdOHCl rods were perfectly maintained in the as-prepared cadmium chalcogenide films according to scanning electron microscopy. Transmission electron microscopy was used to further characterize these microtube structures. The effect of NaOH pretreatment on CdOHCl orientation and the formation of tubular structures were also discussed.

Preparation and characterization of nanofiltration composite membranes using polyacrylonitrile (PAN). I. preparation and modification of PAN supports

AbstractPolyacrylonitrile (PAN) supports useful for the formation of nanofiltration (NF) composite membranes were prepared from PAN solutions in N‐methylpyrrolidone (NMP), using a phase‐inversion method. The compositions of the PAN/NMP solutions used were as follows: 10/90, 15/85, and 20/80 (in wt %). The PAN supports were treated with various concentrations of NaOH aqueous solutions (0.1, 0.5, 1, and 2 mol) for certain periods of times (0.5, 1, 2, and 3 h) in order to modify their surface chemically and morphologically. The characteristics of the supports, modified or unmodified, were carefully studied. The morphology of those were observed with field‐emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The change of the chemical structure of those by the NaOH treatment was studied using FTIR–ATR spectroscopy and ESCA. The permeation properties of those were also determined at 1–5 bar of operation pressure using a PEG 35,000 aqueous feed solution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1854–1862, 2001

Structure of molecular association of curdlan at dilute regime in alkaline aqueous systems

Small-angle X-ray scattering (SAXS) and static light scattering (SLS) measurements were carried out to clarify the fine structure of a molecular association of curdlan at the dilute regime in various concentrations of NaOH aqueous solutions. The SAXS data shows that the molecular association at higher concentrations of NaOH seems to exist in a rod-like structure at 25°C and 60°C. The cross sectional radius of gyration, R gc, for the rod-like molecular association, which is determined from the cross sectional Guinier plot, was evaluated in higher concentrations of NaOH aqueous solutions. In contrast, the rod-like structure cannot be detected in lower concentrations of NaOH. The rod length of the rod-like molecular association can be calculated from the radius of gyration, and also evaluated from the dissymmetry method for shape-identified particles. These values, for higher concentrations of NaOH, calculated from both the above methods show a good coincidence, and the rod length is estimated as about 300 nm at 25°C and 60°C. The distance distribution function for curdlan in higher concentrations of NaOH aqueous solutions also showed a typical profile of the helical conformations at both the temperatures.

Effect of framework aluminum on the dissolution process of ZSM-5 zeolite crystal

The effect of framework aluminum on the dissolution behavior of ZSM-5 zeolite crystal was systematically studied using an interferometric technique. We succeeded in the three-dimensional measurement of the dissolution rates of aluminum-containing ZSM-5 zeolite crystal, namely the (010) face of ZSM-5 zeolite crystal as well as the (100) and (001) faces. The dissolution rate was dependent strongly upon the amount of framework aluminum of the zeolite crystal and the concentration of NaOH aqueous solution used. It was also found that the aluminum-containing ZSM-5 zeolite crystal is convex and that the inclination of the (010) face at the edge of the ZSM-5 zeolite crystal is steeper than that of silicalite crystal.