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Identification of Iron Oxides Qualitatively/Quantitatively Formed during the High Temperature Oxidation of Superalloys in Air and Steam Environments

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Journal of Materials Science & Technology 2009年第4期25卷 479-482页

作者： M. Siddique N. Hussain M. Shafi Physics Division PINSTECH Materials Division PINSTECH

Mossbauer spectroscopy has been used to study the morphology of iron oxides formed during the oxidation of superalloys, such as SS-304L （1.4306S）, Incoloy-800H, Incoloy-825, UBHA-25L, Sanicro-28 and Inconel-690, at 1200℃ exposed in air and steam environments for 400 h. The basic aim was to identify and compare the iron oxides qualitatively and quantitatively, formed during the oxidation of these alloys in two environments. The behaviour of alloy UBHA-25L in high temperature oxidation in both environments indicates that it has good oxidation resistance especially in steam, whereas Sanicro-28 has excellent corrosion resistance in steam environment. In air oxidation of Inconel-690 no iron oxide, with established Mossbauer parameters, was detected.

关键词： Superalloys Mossbauer spectroscopy Oxidation Corrosion products

Schamel equation in an inhomogeneous magnetized sheared flow plasma with q-nonextensive trapped electrons

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Chinese Physics B 2018年第2期27卷 428-434页

作者： Shaukat Ali Shan Qamar-ul-Haque Theoretical Physics Division (TPD) PINSTECH

An investigation is carried out for understanding the properties of ion–acoustic（IA） solitary waves in an inhomogeneous magnetized electron-ion plasma with field-aligned sheared flow under the impact of q-nonextensive trapped electrons. The Schamel equation and its stationary solution in the form of solitary waves are obtained for this inhomogeneous plasma. It is shown that the amplitude of IA solitary waves increases with higher trapping efficiency（β）, while the width remains almost the same. Further, it is found that the amplitude of the solitary waves decreases with enhanced normalized drift speed, shear flow parameter and the population of the energetic particles. The size of the nonlinear solitary structures is calculated to be a few hundred meters and it is pointed out that the present results are useful to understand the solar wind plasma.

关键词： sheared flow plasma density inhomogeniety electron trapping

Effect of Firing Temperature on the Electromagnetic Properties of Electronic Transformer Cores Developed by Using Nanosized Mn–Zn Ferrite Powders

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Acta Metallurgica Sinica(English Letters) 2015年第2期28卷 159-163页

作者： Hassan Waqas Ammad Hussain Qureshi Muhammad Shahzad Materials Division Directorate of Technology PINSTECH

Current investigation deals with the effect of grain growth process as a function of sintering temperature on the electromagnetic properties （initial permeability, impedance, and gain） of Mn-Zn ferrite （MZF） cores （toroids）. By employing auto combustion process, nanosized [（20 ± 5） nm] MZF powders were synthesized and toroid shape cores were obtained after subsequent calcination and firing （sintering） process. It was observed that the submicron structure （0.5 μm） achieved in the ferrite core sintered at 1,000 ℃ was gradually transformed into micron size grains by increasing the firing temperature i.e., 1,100, 1,200, and 1,350 ℃. The results reveal that MZF core sintered at low temperature （1,000 ℃） showed high impedance, low initial permeability, and narrow working frequency range i.e., 3-15 MHz. However, the improvement in initial permeability, sintered density, and operational frequency range （100 kHz-17 MHz） was observed at high temperature （1,350 ℃） firing in the inert environment. This synthesized MZF core is more suitable for miniaturized switch mode power supply applications.

关键词： Mn-Zn ferrites Nanosized powders Impedance Sintering

Effects of Ni doping on the structural properties and collapse of magnetic ordering in NdFe_(1-x)Ni_xO_3(0.1 ≤x≤ 0.7) orthoferrites

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Chinese Physics B 2016年第2期25卷 496-503页

作者： I.Ahmad M.J.Akhtar M.Siddique Department of Metallurgy and Materials Engineering PIEAS Physics Division PINSTECH

Nd Fe_（1-x）Ni_xO_3（0.1 ≤ x ≤ 0.7） orthoferrites are synthesized by solid state reaction method, and the structural properties of these materials are investigated by employing x-ray diffraction（XRD）, scanning electron microscopy（SEM） and M o¨ssbauer spectroscopy. The orthorhombic structure is observed in all systems; however, with the increase in Ni doping,the increase in tolerance factor and the decrease in the cell volume are observed. Orthorhombic distortion decreases with Ni content increasing up to 50%, while above 50% Ni doping it increases. SEM examination indicates the increases in grain size and intermixing of grains with increase in Ni concentration. Comparison between bulk and theoretical densities shows that in each of all samples porosity is less than 2%. M？ssbauer spectroscopic investigations are performed to explain local structure, Fe oxidation states and collapse of the magnetic ordering. In these samples the Fe oxidation state remains＋3 and there is no considerable increase in hole states observed; however due to mismatch of the ionic radii between Fe^（3＋） and Ni^（3＋）, octahedral distortions, sagging and distribution of hyperfine parameters increase with increase in Ni concentration. The major factors behind the collapse of magnetic ordering in the Ni-doped systems are the weakening of the super-exchange interactions, decrease in the Neel temperature, increase in spin–spin relaxation frequency and high spin to low spin transition.

关键词： ceramic crystal structure electron microscopy Mossbauer spectroscopy

Magnetosonic Shocks in Ultra-Relativistic Dissipative Degenerate Plasmas

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Chinese Physics Letters 2016年第8期33卷 77-80页

作者： S.Hussain N.Akhtar N.Mustafa Theoretical Physics Division PINSTECHP.O.Nilore

Magnetosonic shock structures in dissipative magnetized degenerate electron ion plasma are studied. The two fluid quantum magnetohydrodynamic equations for non-degenerate ions and ultra-relativistic degenerate electron fluids with the Maxwell equations are presented. Using the reductive perturbation technique the Korteweg de Vries Burgers （KdVB） equation is derived and its solution is presented with the tanh method. Astrophysical plasma parameters are used to study the effects of variation of plasma density, magnetic field intensity and kinematic viscosity on the propagation characteristics of nonlinear shock structures in such plasma systems.

关键词： in on is et de of that

Comparison of Fission Induced by Protons and Pions

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Chinese Physics Letters 2011年第8期28卷 58-60页

作者： Zafar Yasin M.Ikram Shahzad Physics Division PINSTECHP.O.NiloreIslamabadPakistan

We compare the properties of fission induced by protons and *** different methodologies are used to make this ***,it is shown that pion-induced fission cross sections are not much different in magnitude from proton-induced fission cross sections at the same beam kinetic ***,across the pion-nucleon(3,3)resonance so prominent with free nucleons,it has been observed that there is no significant change in the reaction mechanism in the case of ***,it is noted that an empirical expression used for evaluations of proton-induced fission cross sections is also valid for positive pion-induced fission cross sections,at least for actinide *** cross sections computed using a cascade-exciton model code for ^(209)Bi and ^(238)U are also compared with the experimental data available.

关键词： energy beam kinetic

Formation of Charged Particle Tracks in Solids

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Chinese Physics Letters 2006年第6期23卷 1448-1451页

作者： Mukhtar A. Rana Physics Research Division PINSTECH PO Nilore Islamabad Pakistan

A criterion for formation of etchable tracks in solids is suggested using the well-known concepts of ionization and thermal spikes, diffusion process with useful and justified assumptions, and present or published experimental and theoretical investigations on the same subject. The suggested criterion is useful for a wide spectrum of researchers including development and applications of track recording materials, ions implantation, sputtering and other areas, which include interactions of charged particles with solids.

关键词： RADIATION-DAMAGE ACTIVATION-ENERGY AUGER ELECTRONS CR-39 DETECTORS

Total Fragmentation Cross Section of 158A GeV Lead Projectiles in Cu Target

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Chinese Physics Letters 2008年第9期25卷 3208-3211页

作者： Mukhtar Ahmed Rana Shahid Manzoor Physics Division Directorate of Science PINSTECH PO Nilore Islamabad Pakistan

Total fragmentation cross section for the reaction 158A Pb ions ＋ Cu target is measured using the most sensitive track detector CR-39. Measured values are compared with calculations. Exposures of target-detector stack with 158A P5 projectiles are made at CERN-SPS beam facility. Results of calibration of CR-39 detector in a charge region （63 ≤ Z ≤ 83） are also reported, which can be used for high energy particle identification using CR-39 and in determination of partial charge changing cross sections. The charge resolution δz achieved by this technique is about 0.2e. A systematic dependence of total fragmentation cross section on target properties is revealed and the corresponding results are presented.

关键词： the power-law exponents precipitation durative abrupt precipitation change

NO-CO-O2 Reaction on a Metal Catalytic Surface using Eley-Rideal Mechanism

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Chinese Physics Letters 2008年第10期25卷 3728-3731页

作者： Waqar Ahmad Physics Division PINSTECH P.O. Nilore Islamabad Pakistan

Interactions among the reacting species NO, CO and O2 on metal catalytic surfaces are studied by means of Monte Carlo simulation using the Eley-Rideal （ER） mechanism. The study of this three-component system is important for understanding of the reaction kinetics by varying the relative ratios of the reactants. It is found that contrary to the conventional Langmuir-Hinshelwood （LFI） thermal mechanism in which two irreversible phase transitions are obtained between active states and poisoned states, a single phase transition is observed when the ER mechanism is combined with the LH mechanism. The phase diagrams of the surface coverage and the steady state production of CO2, N2 and N2O are evaluated as a function of the partial pressures of the reactants in the gas phase. The continuous production of CO2 starts as soon as the CO pressure is switched on and the second order phase transition at the first critical point is eliminated, which is in agreement with the experimental findings.

关键词： the power-law exponents precipitation durative abrupt precipitation change