Pitting Corrosion Behaviour of Monel-400 Alloy in Chloride Solutions

1-IntroductionPittingcorrosionisthemostdestructiveformamongthedifferentformsoflocalizedcorrosionofmetals.Thebreakdownofthepassivefilmbyag-gressiveionssuchaschlorideionscanleadtohighpenetrationrates.Copper-nickelalloysarewidelyusedascorrosionresistantmaterialsinmarineengineering.Theircor-rosionratesdecreasesharplywithincresingNicon-tent.AseriesofCu-Nialloyshavebeenwidely.tudi.d[1~12]innaturalseawaterandinNaClsolu-tionsusingdifferentelectrochemicalmethods.Con-tradictoryresultshavebeenobtained…     

Corrosion of Zinc-Containing Cabal Glasses by Various Leaching Solutions

The corrosion behavior of some cabal glasses (CaO-B₂O₃-Al₂O₃) containing ZnO was evaluated both as a bulk specimen and as grain powder. Different leaching solutions were used including HCI, H₂SO₄, and NaOH for varying temperatures or periods of exposure. Zinc oxide replacing calcium oxide in cabal glasses of constant 40 mol% B₂O₃, 30 mol% Al₂O₃, caused a decrease in chemical durability in all leaching solutions used. The corrosion was found to be linear with time in the limit of investigation (1–4 h) but with different rates depending on the type of leaching solution or temperature.     

Catalytic Oxidation of CO Gas over Nanocrystallite Cu x Mn1−x Fe2O4

The catalytic oxidation of CO over nanocrystallite Cu _x Mn_(1−x)Fe₂O₄ powders was studied using advanced quadruple mass gas analyzer system. The oxidation of CO to CO₂ was investigated as a function of reactants ratio and firing temperature of ferrite powders. The maximum CO conversion was observed for ferrite powders which have equal amount of Cu²⁺ and Mn²⁺ (Cu_0.5Mn_0.5Fe₂O₄). The high catalytic activity of Cu_0.5Mn_0.5Fe₂O₄ can be attributed to the changes of the valence state of catalytically active components of the ferrite powders. The firing temperature plays insignificant role in the catalytic activity of CO over nanocrystallite copper manganese ferrites. The mechanism of catalytic oxidation reactions was studied. It was found that the CO catalytic oxidation reactions on the surface of the Cu _x Mn_1−x Fe₂O₄ was done by the reduction of the ferrite by CO to the oxygen deficient lower oxide then re-oxidation of this phase to the saturated oxygen metal ferrite again.     

Effect of Ni+2-substituted Fe2TiO5 on the H2-reduction and CO2 Catalytic Decomposition Reactions at 500℃

CO2 is a major component of the greenhouse gases, which causes the global warming. To reduce CO2 gas,high activity nanosized Ni 2 substituted Fe2TiO5 samples were synthesized by conventional ceramic method.The effect of the composition of the synthesized ferrite on the H2-reduction and CO2-catalytic decomposition was investigated. Fe2TiO5 (iron titanate) phase that has a nanocrystallite size of ～80 nm is formed as a result of heating Fe2O3 and TiO2 while the addition of NiO leads to the formation of new phases (～80 nm)NiTiO3 and NiFe2O4, but the mixed solid of NiO and Fe2O3 results in the formation of NiFe2O4 only.Samples with Ni 2=0 shows the lowest reduction extent (20%); as the extent of Ni 2 increases, the extent of reduction increases. The increase in the reduction percent is attributed to the presence of NiTiO3 and NiFe2O4 phases, which are more reducible phases than Fe2TiO5. The CO2 decomposition reactions were monitored by thermogravimetric analysis (TGA) experiments. The oxidation of the H2-reduced Ni 2 substituted Fe2TiO5 at 500℃ was investigated. As Ni 2 increases, the rate of reoxidation increases. Samples with the highest reduction extents gave the highest reoxidation extent, which is attributed to the highly porous nature and deficiency in oxygen due to the presence of metallic Fe, Ni and/or FeNi alloy. X-ray diffraction (XRD) and transmission electron microscopy (TEM) of oxidized samples show also the presence of carbon in the sample containing Ni 2＞0, which appears in the form of nanotubes (25 nm).     

Electrochemical behaviour of iron—chrome alloys in relation to pitting corrosion

The polarization behaviour and pitting corrosion of Fe-Cr alloys of 7, 13, 18, 24 wt% Cr were studied. Potentiodynamic and galvanostatic measurements were performed in the absence and presence of Cl^–. As the Cr content increases the active dissolution current densities decrease while the passive range and transpassive current densities increase. Polarization parameters gave for the passive transition of the alloys a Cr concentration of -13%. An increase of Cl^– concentration causes the progressive destruction of passivity. It interfered with O₂ evolution, and then destroyed the transpassive region. Still higher Cl^– concentrations initiated pitting corrosion as shown by the oscillations in potential of the galvanostatic polarization curves supported by visual observation. Results are discussed on the basis of competitive adsorption between the aggressive and inhibitor anions for the active sites on the alloys' surface.     

Adaptive and Dynamic Mechanism for Round Length Determination in Cluster Based Wireless Sensor Networks

The resource-constrained nature of WSNs require efficient use of resources, especially energy, to prolong their lifetime. Clustering is one of the popular approaches to allocate the resources efficiently among the WSN nodes. In this work, we analyze the problem of round length determination in cluster based WSN which has severe impact on the energy efficiency. This problem is very important since round length determines how often the cluster head (CH) rotates or re-clustering process occurs. A longer round length will cause the CH nodes to operate for a long time and drain their energies faster than other nodes resulting in uneven energy consumption in the network, while a shorter round length results in considerable wastage of energy due to frequent running of the setup phase. Hence, we propose an adaptive and dynamic mechanism for round length determination in cluster based WSNs by adapting Behavior Curve Function modeled by quadratic Bezier curves, where we associate the remaining energy level of the cluster to its round operation length and to its assigned criticality which is defined based on network energy level. This helps to determine the number of frames in a round or how many times the data collection occurs in a cluster in a round and the criticality of the energy in the WSN. Simulation results reveal that the proposed mechanism has effectively reduced the energy consumption and improved the WSN lifetime in both homogeneous and heterogeneous network settings.

     

EDGO: UAV-based effective data gathering scheme for wireless sensor networks with obstacles

Wireless Networks - One of the most important requirements for effective UAV–WSN operations is to perform data collection in timely and safe manner. Identifying an effective path in an...     

Grey Wolf based compressive sensing scheme for data gathering in IoT based heterogeneous WSNs

Wireless Networks - Sensor node energy constraint is considered as an impediment in the further development of the Internet of Things (IoT) technology. One of the most efficient solution is to...     

Opportunistic channel allocation decision making in cognitive radio communications

The global spread of wireless devices with mobile Internet access and the increasing demand of multimedia‐based applications are fueling the need for wireless broadband networks. IEEE 802.16 and 802.20 are standards for a broadband wireless access with promising cognitive radio features to support mobile Internet access. However, because of the fast changing radio environment and the demand for dynamic spectrum allocation mechanisms, these standards must continuously readjust different radio parameters. The cognitive radio makes decisions based on its built‐in inference engine, which also in time can adapt itself to different situations through the process of learning from experience. In this paper we present an automated opportunistic decision making and learning process for cognitive radio based on uncertainty reasoning algorithms. This novel approach is well suited in fast changing wireless environments with vague, incomplete, and heterogeneous information. Theory and simulations prove that decision making and learning of the cognitive radio based on the proposed approach cope with the changes in the radio environment. In this work we use fuzzy logic for the learning and decision making of the cognitive radio. Simulation also show that our approach provides accurate and precise decisions on allocating spectrum to mobile Internet users even in fast varying radio conditions. Copyright © 2012 John Wiley & Sons, Ltd.