Papers by Keyword: Ion Migration

Abstract: Molecular dynamics are applied to simulate molecular motions in an aqueous solution of two soluble derivatives of a 100-ring polythiophene chain – one with sidechains terminating in a SO₃^– group, the other in NMe₃⁺. Each chain is in a helical conformation defining a water-containing central channel along whose axis the dynamics of ions from the solution to the channel’s axial electrostatic potential is simulated. The profiles of these potentials distinguish the tendencies of the two channel species to occlude water molecules on their surfaces. Invoking the conductive polymer characteristics of polythiophene that can accomplish the transfer of electrons between the aromatic rings and redox reagents in the solution, the effect of this transfer on the axial potential and migration is followed. The electrostatic potential monitors differences in the association of the solvent molecules with the two species of helical polymer and shows that while Na⁺ and Cl^– ions do not enter the channel in the absence of the redox changes, an ion with a selected charge does so spontaneously when appropriate electric charge is transferred to the channel. This enables the selected ion to travel about 10 – 20Å in the channel without the application of an external electric field.

Abstract: In reinforced concrete structures constructed on the coastline of the hypersaline Arabian Gulf water, corrosion of reinforcing steel causes cracking, delamination and spalling of concrete, within a time span of a few years. The King Abdullah Civic Center (KACC), being constructed on a reclaimed land off the coastline in the Eastern region of Saudi Arabia, is a major complex with wharves, quay walls, and breakwater and commercial buildings. To ensure the durability of buildings in the harsh marine environment and to provide a minimum service life of 35 years, a concrete mix in which 70% of Portland cement is replaced by granulated ground blast furnace slag (GGBFS) was recommended based on durability modeling conducted using the software STADIUM^®. Concrete with 70% GGBFS provides for the dual objective of achieving a green concrete and an enhanced service life of the building. Based on durability modelling it was concluded that corrosion inhibitor should be used preferably in the concrete. A detailed experimental program was conducted to assess the durability and strength properties of the 70% GGBFS concrete, with and without corrosion inhibitor. This paper presents the results of experimental investigations and durability modeling conducted for the project. A 70% GGBFS concrete mix without corrosion inhibitor was adopted for the raft foundation and subsequently for the entire building to make it a green concrete building.

Abstract: Electrokinetic has proven to be alternative technique to remediate pollution and increase soil strength for soft soil. This remediation method has been applied to remediate the hydrocarbon and heavy metal contaminant. Phytoremediation is a technique used to remediate the hydrocarbon and heavy metal contaminant. Both of this remediation technique has been proven as attractive alternative to clean up polluted soils. Although barren acidic soil is not categories as hazardous, the necessity of covered soil surface is on demand in order to minimize the surface erosion. Other than that, this remediation technology also helps in horticulture in order to enlarge the plantation and farming area. This paper will explain the formation of barren acidic soil, principles electrokinetic remediation for remediation of barren acidic soil and application of phytoremediation in order to sustain the process of remediation. Correlation of both remediation methods will minimize the acidic ion migration and sustain the pH value on soil surface for grass, vegetable or palm oil plantation.

Abstract: A molecular dynamics simulation is conducted to describe the behaviour of sodium and chloride ions as they enter a synthetic ion channel (mounted in a bilayer membrane) from aqueous NaCl solutions on either side of the membrane. The channel consists of an α-helical peptide chain scaffold with six aligned crown ether (CE) rings (18-CE-6) as side groups, forming a molecular chamber between each neighbouring pair. Responding to the channel’s axial −2 to −1 V electric potential, the Na⁺ ions, but not Cl⁻, enter the channel spontaneously but they do not proceed beyond the first chamber formed between CE rings 1 and 2. The application of an axial electric field promotes the entry of a Na⁺ ion and its migration over the internal length of the channel. The forces that drive the migration phenomena are predominantly coulombic. Although the same electric field simultaneously allows a Cl⁻ ion initially to access the channel the ion is subsequently expelled from the first chamber into the bilayer. Although a Na⁺ ion may make a facile or even spontaneous entry to the channel it requires an energy estimated from Coulomb forces as ~5 eV to pass subsequent CE rings, and considerably more to exit the channel. An important role is found for the vibrational activity of the ether rings’ C-O-C units in their facilitating contribution to the migration of Na⁺ in the channel.

Abstract: Molecular dynamics investigations of ions in certain non-bulk media predict that they are capable of significantly greater mobilities than when in the liquid state. The entries of Li⁺, Na⁺, and K⁺ ions from electrolyte media into proposed synthetic channels consisting of fourteen 15-crown-ether-5 (CE) rings bonded in stacked conformations are described and their subsequent dynamics in the channel discussed. The importance of channel flexibility is established by investigating two CE channels that are structurally similar but vary in the rigidity with which their rings are connected. The dynamics of cation channel migrants are simulated across a bilayer membrane between two bulk aqueous salt solutions and also when the channel floats freely in an aqueous medium. Various features of ion behaviour are investigated in the presence, and in the absence, of an electric field applied along the channel axis. The novel oscillatory behaviour of the ions in the channel is investigated, together with the possibility of their exits into the liquid medium. The frictional forces opposing the ion trajectories are calculated, found to be ~10 nN and attempts to formulate frictional laws for nanoscale systems are discussed.

Abstract: In this paper, different silicon oxide-based films and electrode materials were deposited onto the W/Si substrates by sputtering to investigate the resistive switching characteristics of the conductive-bridging RAM cells via the ion migration. A room-temperature constant-voltage stressing has been used to examine its effects on the resistive switching behaviors of the RAM cells in this work. Our experimental results show that the constant-voltage stressing can effectively affect the current conduction behavior and stabilize the resistive switching of the memory cell. After the electrical stressing, the current conduction mechanism in the HRS during the set process of the Cu/Cu:SiO₂/W cell can be changed from the Ohm’s law and the space charge limited conduction to the single Ohm’s law.

Abstract: In this paper, intrinsic nanocrystalline silicon thin films were deposited onto the ITO/glass substrates by PECVD and were used as the conduction material for the conductive-bridging random-access memory devices. The resistive switching characteristics of the nanocrystalline silicon thin films were investigated. Experimental results have shown that the stable bipolar resistive switching of the nc-Si films and retention time over 10⁴s. In addition, the current conduction mechanism of the nanocrystalline silicon films was examined with XPS depth file analysis. It clearly indicates that the conduction mechanism for the resistive switching is formation metallic bridges come form metal cation migration in the nanocrystalline silicon films.

Abstract: Multiple copper-zinc alloy was used to treat water in order to restrict the formation of hard scale during heating process. Trace amounts of metal ions were dissolved from the alloy under the action of tiny battery corrosion, which took part in the crystallization of calcium carbonate crystal. The ion migration rules and its effect on the crystal structure of water scale were studied. The ICP test results show that after immersion in the water for 20 min, the zinc ion concentration increased to 0.35 mg•L-1 compared with contrast group. The simulating experiment of the scale crystal growth demonstrated that the calcium carbonate scale after treated with the alloy showed a transformation from calcite to aragonite, and the ratio of calcite to aragonite changed from 1:0.125 to 1:2.30. Meanwhile, the heat transfer efficiency was increased to 2.19%.

Abstract: The effects of the thermally annealing of Bi-Mn-Co-Sb2O3-added ZnO varistors on their electrical degradation were investigated. For the samples with 0.01mol% Sb2O3added and without Sb2O3, no marked difference in the non linearity index of the voltage-current (V-I) characteristics was observed upon electrical degradation for the annealed and nonannealed samples. Upon increasing the amount of Sb2O3 added, the values of  increased after electrical degradation for the annealed samples. Moreover, the value of  after electrical degradation was proportional to the full width at half maximum (FWHM) of the X-ray diffraction peak for Zn2.33Sb0.67O4-type spinel particles under various annealing conditions. The added Sb2O3 did not dissolve in the ZnO grains but became segregated at grain boundaries. Therefore, it is speculated that the increase in the FWHM for the spinel particles is due to the increase in the numbers of fine spinel particles at grain boundaries and triple points.

Abstract: The effects of SnO2 addition on the electrical degradation characteristics of Bi2O3-MnO2-Co3O4 -added ZnO varistors were investigated by field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and voltage-current (V-I) characteristics. The ZnO grain size was made uniform by the addition of SnO2 or Sb2O3. The nonlinearity index α of the V-I characteristic for Bi-Mn-Co-SnO2-added samples was approximately 50 and the varistor voltage was 120~140V/mm. The value of α after the electrical degradation showed a local maximum at approximately 0.1mol% added SnO2 and then showed a local minimum at approximately 0.5mol%, similar to the relative integral intensity of the XRD diffraction peak for the (004) plane for a small amount of SnO2 added. It is suggested that the diffusion of oxygen ions through the grain boundary is affected by the change in crystal orientation of ZnO grains at the grain boundary induced by the addition of a small amount of SnO2.