Papers by Keyword: Alkaline Solution

Abstract: The dealloying technique has been a well-known process since antiquity, but recently it has started to be used to produce nonporous metals and metal oxide semiconductors for various electrochemical applications. The dealloying process is carried out in both acidic and basic solutions, depending on the base material and the desired application. In this study, Cu-based amorphous ribbons were dealloyed in alkaline aqueous solution at room temperature, keeping the temperature constant and varying the concentration of the solution. This process has the advantage that both dealloying of the ribbons and nanostructured copper oxide synthesis on their surface is obtained in one step. For the preparation of copper-based amorphous ribbons, the melt-spinning process was used, and the composite obtained consisting of nanopores decorated with Cu₂O/CuO nanoparticles makes it an ideal candidate for electrochemical applications. For the investigation of the structural, morphological, and optical properties of the obtained materials, X-ray diffraction (XRD) and scanning electron microscopy (SEM).

Abstract: Ordinary Portland cement (OPC) is the essential binding material to produce the OPC concrete. Production of OPC is recently attaining a rate of 2.6 billion ton per year worldwide and growing 5% annually. OPC contributes at rate of 5 – 8% of human-worldwide CO₂ emissions which are the greenhouse gases pollute the atmosphere. Geopolymer concrete (GPC) is a creative, sustainable, economical and eco-friendly material for construction industry, which is a suitable alternative to the OPC concrete, able to extensively curb the CO₂ emissions. To prepare this kind of concrete, a combination of pozzolanic material such as fly ash (FA), and/or ground granulated blast furnace slag (GGBS) rich with silica and alumina can react with alkaline activator solution producing aluminosilicate gel, acting as a superb binding material for fine and coarse aggregates under special conditions of curing. This study highlights the recent explorations on geopolymer mortars and concrete. Effect of chemicals such as sulphuric acid, effect of fly ash partial replacement with different binding materials, effect of concentration of alkaline activator solutions and the effect of temperature and time of curing variation have been discussed on durability and mechanical properties of geopolymer concrete. Results have shown superb resistance of geopolymer concrete to the detrimental effects of sulphuric acid on weight and compressive strength. Furthermore, fly ash partial replacement with silica fume, OPC or GGBS, or nanosilica inclusion in GPC has a positive effect on the GPC properties. Finally, using high concentration of sodium hydroxide has a detrimental effect on GPC properties.

Abstract: Production of Ordinary Portland Cement (OPC) requires huge quantity of natural resources and energy and it releases large amount of carbon - di - oxide to the environment. Therefore, enormous studies have been carried out throughout the world to establish geopolymer as an alternative binder material for the replacement of OPC to protect the environment. This study intends to explore the effects of alkaline solution on the properties of geopolymer produced with ground granulated blast furnace slag. Properties such as Standard consistency, setting time of slag based geopolymer paste has been determined using Vicat’s apparatus (according to the guidelines given by Indian Standards for OPC). In order to determine the effects of alkaline solution on the properties of geopolymers, the concentration of sodium hydroxide solution has been varied from 6M to 16M and the ratio of sodium silicate solution to sodium hydroxide solution is also varied from 1.0 to 2.0. Results indicate higher standard consistency and significant less setting time for slag based geopolymer paste than that of OPC paste. Compressive strength of the geopolymer paste and mortar cube samples, cured in ambient conditions till the day of testing, is increasing with the increase of the concentration of sodium hydroxide solution. Highest compressive strength is obtained for the samples prepared with alkaline solution having the ratio of sodium silicate solution to sodium hydroxide solution as 1.5. But when the concentration of sodium hydroxide solution is beyond 14M, decreasing trend in compressive strength is observed.

Abstract: Polyethylene (PE) is widely used as packaging materials in the form of plastic bags. After end-use, some of these plastic bags are not properly disposed and may persist in different kinds of environment. Oxo-biodegradable plastics are PE films incorporated with pro-oxidants to promote degradation. As part of the continuing study, changes on the tensile properties of oxo-biodegradable PE plastic bags immersed in alkaline solution at 60 °C are investigated. The effects of colorant additive (varied at two levels) and thickness (varied at three levels) on tensile properties of PE films are reported. Specifically, the tensile strength [MPa], strain at break [%], and elastic modulus [MPa] are monitored with time. It is observed that films undergo degradation which is exhibited by a decrease in all tensile properties after 1008 hours of immersion in alkaline solution. Analysis of variance (ANOVA) shows that the initial tensile strength and elastic modulus, as well as the strain at break and elastic modulus after 1008 hours of immersion, are all affected by colorant additive.

Abstract: Steel corrosion is one of the main problems of concrete structure durability. Compared with the steel, GFRP rebar has the advantages of high strength, low density and good corrosion resistance. Therefore, GFRP becomes a good choice to replace steel bar in concrete structure. Since GFRP material is susceptible to the alkaline conditions, it is necessary to clarify the mechanical properties and corrosion mechanism of GFRP rebar in such an alkaline environment of interior concrete. In this study, the artificial accelerated corrosion tests of two kinds of GFRP rebar (epoxy and unsaturated polyester resin matrix) were conducted at 60 °C in alkaline solution up to 90 days. Then the tensile strength tests of GFRP rebar were carried out. The solution PH values, the tensile strength and mass loss of GFRP rebar were measured. The testing results show that the mass of GFRP rebar had rarely changed, but the tensile strength reduced about 30% after 90-day immersion test in alkaline solution. During the test, the PH value of the alkaline solution decreased from 13.62 to around 12.85, which indicated that the hydroxyl ions of the alkaline solution had been consumed. The ester bonds in resin matrix may hydrolyze in alkaline solution and the bonding interface between fiber and resin can be damaged progressively. It can cause the performance degradation of GFRP rebar. In addition, the relationship between the loss of tensile strength and the reduction of PH can be determined. That means the durability of GFRP rebar in concrete can be enhanced by controlling or limiting the alkalinity when producing concrete. Finally, the GFRP rebar of epoxy resin matrix shows higher retention values of tensile strength and better alkali resistance than those of UPR matrix rebar after 90d immersion in the alkaline solution. The obtained results in this paper can provide application reference of GFRP materials in civil engineering.

Abstract: The Ni+NiAl nanocomposite coatings were prepared by the electrodeposition under the galvanostatic conditions (j_dep = -250 mA cm^-2) from the nickel bath containing the suspension of NiAl nanopowder. For comparison, the Ni coatings were also obtained. The combined steady-state polarization and electrochemical impedance spectroscopy (EIS) investigations of hydrogen evolution reaction (HER) were carried out in 5 M KOH solution at room temperature. It was found that the Ni+NiAl nanocomposite coatings revealed higher apparent electrocataltic activity towards the HER as compared to the comparable Ni deposits due to the increase in the real surface area development and the intrinsic activity.

Abstract: Kinetics of hydrogen evolution reaction (HER) was investigated in 1 M NaOH solution at room temperature on a polycrystalline Fe electrode material which was electrochemically activated and unactivated. Studies of the HER were carried out using steady-state polarization and electrochemical impedance spectroscopy (EIS) measurements. It was found that for the Fe electrode material after activation at j = -320 mA cm^-2 for 24 h, the increase in the catalytic activity towards the HER was observed in comparison with that on the unactivated iron electrode material. Ac impedance behavior of the Fe electrode changed from a typical for smooth electrodes before activation (one time constant in the circuit) to that being characteristic for porous electrodes after activation (two time constants in the circuit). The reason for that is formation of solid products of the iron corrosion in alkaline solution which can cause passivation of the electrode surface and catalyse the HER.

Abstract: A slow strain rate tensile (SSRT) test was carried out to investigate the stress corrosion cracking (SCC) behavior of the sensitized 304L austenitic stainless steels (ASSs) in alkaline solution (0.5M NaOH). Mechanical properties and fracture morphology evolutions of the 304L ASSs were studied as a function of temperature through slow speed tensile tester and scanning electron microscopy (SEM). The results showed that the tensile strength and percentage elongation after fracture significantly reduced as the test temperature rose. Fractographic examination revealed both ductile and brittle fracture features for the specimens tested in different environments. However, the proportion of brittle fracture characteristics changed with the temperature.

Abstract: Electroreduction of Fe₂O₃ to Fe in sodium hydroxide solutions has been investigated. It is found that pure iron powder with uniform crystal particles can be obtained by electrolysis of Fe₂O₃ in alkaline solution. The porosity of the iron oxide (Fe₂O₃) pellet and the concentration of NaOH solution have significant influences on the electrolysis process. The deoxidation rate increases with increasing the concentration of NaOH solution, the grain size of iron products decreases with increasing the concentration of NaOH. The optimum NaOH concentration and pressure load used to fabricate Fe₂O₃ pellet are 60 wt% and 6 MPa, respectively. X-ray powder diffraction (XRD) analysis indicates that Fe₃O₄ was produced as the intermediate product during the electroreduction process.

Abstract: India is one of the Developing countries that needs to face the environmental pollution. Have many ways to reduce environmental pollution that causes by production of Portland cement and cause by the increasing of waste material. This paper studies the strength development in geopolymer mortar using industrial by-products. Geopolymer is the term used to represent the binders produced by polymeric reaction of alkaline liquid with silicon and aluminium as source materials. The by-product materials considered in this study are combination of GGBFS and Fly ash. The experimental program involves casting of geopolymer mortar cubes and testing them at 1 day, 3 days and 7 days for compressive strength. Different parameters considered in this study are ratio of sodium hydroxide to sodium meta silicate (1:1 & 1:2 ) and alkaline fluid to binder ratio Keeping 12-Molarity of the alkaline liquid as constant. It can be concluded that the strength increased with an increase in the quantity of GGBFS.