Aqeel Khurram - Academia.edu (original) (raw)

Papers by Aqeel Khurram

Journal of Nanotechnology in Engineering and Medicine, 2015

Materials & Design, 2015

In this study, ultrafine grained (UFG) quenching and partitioning steels was achieved by using te... more In this study, ultrafine grained (UFG) quenching and partitioning steels was achieved by using tempered and deformed martensite as the pre-microstructure of the quenching and partitioning treatment. Compared with those manufactured through the conventional routine, superior mechanical properties were realized in UFG steels by using tempered and deformed martensite as the pre-microstructure of the quenching and partitioning treatment. The grain subdivision mechanism during deformation and the microstructure evolution during heating were investigated. Effect of carbide on the grain subdivision and its pinning effect against grain growth is highlighted. The proposed method produced UFG steels with considerable amount of retained austenite, which contributed to the enhanced mechanical properties of investigated steels.

Physica B: Condensed Matter, 2015

The excess conductivity analysis of resistivity versus temperature data of TlBa 2 (Ca 2 À y Mg y ... more The excess conductivity analysis of resistivity versus temperature data of TlBa 2 (Ca 2 À y Mg y )Cu 3 O 10 À δ (y¼ 0.5, 1.0, 1.5) superconductor samples have been performed in the light of Aslamasov-Larkin and Lawrence-Doniach theories before and after irradiation with a beam of gold (Au 4 þ ) ions of energy 20 MeV having a fluence of 1 Â 10 15 ions/cm 2 . The microscopic parameters such as zero temperature coherence length {ξ c (0)}, inter-plane coupling constant (α), and Fermi velocity (V F ) have been calculated from the ln-ln plot of excess conductivity (Δσ) versus reduced temperature (ε) using the Lawrence and Doniach model. The cross-over temperatures separating different fluctuation regions in the ln-ln plot are also determined. It is observed from the excess conductivity analysis that all the microscopic parameters have been decreased after the irradiations. Whereas, calculations have shown that critical magnetic fields (B c ) and critical current density (J c ) are increased after the ion irradiation, which, confirms the validity of the results because B c and J c are increased by the formation of artificial pinning centers after bombardment of energetic heavy ion beam.

Advances in Polymer Technology, 2015

The nanocomposite microwave absorbers are prepared from laminates of E glass/epoxy matrix with th... more The nanocomposite microwave absorbers are prepared from laminates of E glass/epoxy matrix with the incorporation of multiwalled carbon nanotubes (MWCNTs) and detonation nanodiamond (DND). Nanodiamond particles are used to effectively and uniformly disperse the carbon nanotubes in the polymer matrix, leading to a very homogenous mixture. The results showed that microwave absorption of nanocomposites increases with the increase in MWCNTs concentration in 11-17 GHz frequency range. The maximum loss of -28 dB was obtained at 14 GHz. The bandwidth corresponding to the reflection loss of −10 dB is 4.5 GHz. The mechanical properties are also improved after incorporating MWCNTs and DND in the composite. The tensile strength has been increased by ß113% after the addition of 1.0 wt% MWCNTs and 0.1 wt% DND. The morphological investigation demonstrated that coating of MWCNTs on the surface of the woven glass fibers in the presence of DND resulted in uniform dispersion of nanotubes throughout the matrix with the formation of connected networks that helps in electrical conduction and load transfer between the nanofillers and the matrix. The role of MWCNTs and DND particles in enhancing the electromagnetic absorption and mechanical properties of the nanocomposite laminates is explained. C

Superconductor Science and Technology, 2007

The high temperature superconductor thin films Cu1-xTlxBa2Ca3Cu4O12-delta (Cu1-xTlx- 1234) are po... more The high temperature superconductor thin films Cu1-xTlxBa2Ca3Cu4O12-delta (Cu1-xTlx- 1234) are post-annealed in a nitrogen atmosphere. The zero-resistivity critical temperature (Tc(R = 0)) of these thin films is increased from 92.3 to 104 K. The grain size is enhanced and their morphology is improved with the post-annealing. The enlargement of grain size is linked to fluctuation-induced conductivity (FIC) in the light of Aslamazov-Larkin (AL) theory. The FIC measurements have shown that the cross-over of three-dimensional (3D) to two-dimensional (2D) behaviour of fluctuations is shifted to higher temperature values with an increase of post-annealing temperature. These results have shown that the removal of oxygen and the increased grain size are the most likely sources of the increase in the cross-over temperature, T* to higher values.

Journal of Superconductivity and Novel Magnetism, 2014

Journal of Applied Polymer Science, 2014

Honeycomb cores (HCs) coated with graphite and multiwalled carbon nanotubes (MWCNTs) filled in a ... more Honeycomb cores (HCs) coated with graphite and multiwalled carbon nanotubes (MWCNTs) filled in a thermoplastic resin are proposed as microwave absorbers. The MWCNT contents varied from 0.2 to 0.6 wt % in a graphite-filled (15 wt %) thermoplastic resin. The HCs were coated with three different types of coating materials for the sake of comparison: graphite, MWCNTs, and graphite plus MWCNTs. The dielectric properties [the real and imaginary parts of complex permittivity (e 0 and e 00 , respectively)] and reflection loss (RL) of all of the coated HCs were measured and compared. We observed that the permittivities and RL increased significantly with increased weight percentage of the MWCNTs in the graphite-filled thermoplastic resin. The RL measurements showed a maximum loss of 220 dB around 7 GHz and a bandwidth of 2.7 GHz at 210 dB in the HCs coated with the 0.4 wt % MWCNT plus graphite. There was also a shift in the RL peak position from the x band to the c band after the increase of MWCNT content. We also observed from the measurements that a combination of graphite and MWCNTs resulted in a broadband microwave absorber; a bandwidth of 13 GHz was observed for 80% RL when the MWCNT content increased to 0.6 wt % in the graphiteincorporated resin. The possible mechanism that increased RL with the incorporation of MWCNTs in the graphite-mixed thermoplastic resin is discussed.

2013 International Conference on Aerospace Science & Engineering (ICASE), 2013

Sandwich structures comprising para-aramid paper honeycomb core and carbon fiber epoxy matrix com... more Sandwich structures comprising para-aramid paper honeycomb core and carbon fiber epoxy matrix composite facesheets were fabricated for aerospace applications. For the adhesion of honeycomb core and composite facesheets, two different types of adhesive films were used. The curing parameters for adhesive films, including temperature and time, were optimized for maximum bonding strength.

Physica C: Superconductivity, 2004

The effects of post-annealing conditions on the apical oxygen phonon modes have been investigated... more The effects of post-annealing conditions on the apical oxygen phonon modes have been investigated and their correlations with the critical temperature of the Cu 1Àx Tl x Ba 2 Ca 2 Cu 3 O 10Àd (Cu 1Àx Tl x -1223) superconductor thin films have been developed. The samples were annealed in different ambient environments, such as air, N 2 , O 2 and vacuum and their FTIR absorption spectrum has been taken. Three absorption peaks observed between 455-440, 665-648 and 1240-1246 cm À1 are assigned to apical oxygen vibrations, the chain axis O(3) vibrations and to C-O single-bond, respectively. The frequency of the mode at 655 cm À1 is sensitive to the concentration of O(3) in the charge reservoir layer, which in turn controls increase or decrease of the bond length of apical oxygen. The softening of the apical oxygen mode is possibly linked with the reduction of thallium, which in turn is associated with the amount of oxygen [O(3)] in the charge reservoir layer. In as-prepared material and annealed under oxygen, the state of thallium is not reduced from Tl þ3 to Tl þ1 and sufficient number of carriers are not supplied to CuO 2 planes, the material remains in the region of carrier under-doping. The softening of apical oxygen mode positioned at 455 cm À1 is associated with the formation of low T c phases. The C-O related IR mode is softened with the post-annealing in air at 780°C and annealing in N 2 ambient at 400°C. The critical transition temperature is found to decrease with the post-annealing at 400°C in N 2 , which is possibly due to the under-doped CuO 2 planes of the material. However, the post-annealing at 780 and 650°C

Physica C: Superconductivity, 2005

ABSTRACT A very simple method for the direct synthesis of Cu0.5Tl0.5Ba2Ca2Cu3O10-y superconductor... more ABSTRACT A very simple method for the direct synthesis of Cu0.5Tl0.5Ba2Ca2Cu3O10-y superconductor is discovered. A predominant single phase of Cu0.5Tl0.5Ba2Ca2Cu3O10-y is achieved by the solid state reaction of Ba(NO3)2, CaCO3 and Cu(CN) at 840 °C. The material after firing in air was ground and mixed with Tl2O3 in appropriate ratios and palletized. Pellets were wrapped in aluminum foil and were heat treated at 840 °C for 5 30 min. Predominant single phase of Cu0.5Tl0.5Ba2Ca2Cu3O10-delta was achieved with a very small amount of impurity phase. The onset Tc of the material is 110 K and Tc(R = 0) = 103 K. The critical temperature is confirmed by resistivity and magnetic susceptibility measurements. The composition of the material was measured by EDX technique. The as-prepared material was found to be in the carrier over-doped region and after post-annealing in air/N2, material was promoted to the region of carrier optimum doping. The zero resistivity critical temperature of the material was increased to 103 K with the post-annealing in air/N2 atmosphere. FTIR absorption measurement manifested the formation of optimum doped material after post-annealing.

Physica C: Superconductivity, 2008

A comparison of X-ray photoemission spectroscopy of Mg doped Cu 0.5 Tl 0.5 Ba 2 Ca 1.5 Mg 0.5 Cu ... more A comparison of X-ray photoemission spectroscopy of Mg doped Cu 0.5 Tl 0.5 Ba 2 Ca 1.5 Mg 0.5 Cu 3 O 10Àd and Mg free Cu 0.5 Tl 0.5 -Ba 2 Ca 2 Cu 3 O 10Àd superconductor samples have been made. The main objective of these studies is to see the effect of Mg doping in developing better inter-plane coupling among the CuO 2 planes and its effects on the chemical shift of the bonding species. Through these studies it is observed that thallium is in Tl +1 oxidation state in the Cu 0.5 Tl 0.5 Ba 2 O 4Àd charge reservoir layer in both Mg doped and Mg free samples, however, the XPS line related to Ba atoms are shifted to higher binding energy side by 0.32 eV in Mg doped sample. This chemical shift is most likely due to presence of Ba atoms in the immediate vicinity of Mg atoms in Cu 0.5 Tl 0.5 -Ba 2 (Ca 0.5 Mg 1.5 )Cu 3 O 10Àd samples. Moreover, the binding energy of Cu atoms observed in XPS measurements is significantly shifted in magnesium substituted samples, which has provided an unequivocal evidence of enhanced inter-plane coupling. The enhanced inter-plane coupling promotes the enhancement of k F , n c , V F , and hence the superconductivity parameters.

Physica C: Superconductivity, 2005

X-ray photoemission spectroscopy (XPS) of Cu1−xTlxBa2Ca2Cu3O10−δ (Cu1−xTlx-1223) superconductors ... more X-ray photoemission spectroscopy (XPS) of Cu1−xTlxBa2Ca2Cu3O10−δ (Cu1−xTlx-1223) superconductors thin films is studied. These films were prepared by amorphous phase epitaxy method on the SrTiO3 substrate. This compound has Cu1−xTlxBa2O4−δ charge reservoir layer and three CuO2 planes. The atoms in the CuO2 planes have strong covalent bonding, while the some of the atoms in Cu1−xTlxBa2O4−δ charge reservoir, such as oxygen (Oδ)

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2013

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.

Journal of Superconductivity and Novel Magnetism, 2009

Synthesis of micro-pipes of YBa2Cu3O7−δ superconductor has been carried out for the first time by... more Synthesis of micro-pipes of YBa2Cu3O7−δ superconductor has been carried out for the first time by using chemical method. The shape, size and length of these micro-pipes depends upon dimensions of growth matrix and structure of geometry, i.e., circular, square, rectangular and hexagonal, etc., which could be uniformly coated with superconductor. The onset temperature of diamagnetism of the material is found

Journal of Nanoparticle Research, 2013

ABSTRACT Zinc oxide (ZnO) nanowires (NWs) are exposed to energetic proton (H+), nitrogen (N+), ph... more ABSTRACT Zinc oxide (ZnO) nanowires (NWs) are exposed to energetic proton (H+), nitrogen (N+), phosphorus (P+) and argon (Ar+) ions to understand the radiation hardness and structural changes induced by these irradiations. High-resolution transmission electron microscopy (HRTEM) is utilized to see the irradiation effects in NWs. Multiple doses and energies of radiation at different temperatures are used for different set of samples. The study reveals that wurtzite (crystalline) structured ZnO NWs experience amorphization, degradation and morphological changes after the irradiation. At room temperature, deterioration of the crystalline structure is observed under high fluence of H+, N+ and P+ ions. While for ZnO NWs, bombarded by Ar+ and P+ ions, nano-holes are produced. The ZnO NWs surfaces also show corrugated morphology full of nano-humps when irradiated by Ar+ ions at 400oC. The corrugated surface could serve as tight-holding interface when interconnects it with other NWs/nanotubes. These nano-humps may have the function of increasing the surface for surface-oriented sensing applications in the future.

Journal of Materials Science & Technology, 2014

Nanodiamond (ND) powder was successfully activated by wet chemical method and by exposure of UV/O... more Nanodiamond (ND) powder was successfully activated by wet chemical method and by exposure of UV/O 3 in a chamber followed by mixing in triethylenetetramine (TETA) solution. The reinforcement role of activated ND in the mechanical properties of epoxy matrix was studied. Both treatments, i.e. acid and UV/O 3 provide ND surface with chemical functionalities for adhesion with epoxy resin. Fourier transform infrared spectroscopy was utilized to confirm the attachment of surface groups to the ND particles. The low content of acid and UV/O 3 activated ND was dispersed ultrasonically in the epoxy matrix separately to make nanocomposites. The mechanical properties of the nanocomposites were investigated under three point bending. The strong interactions among activated ND particles and the epoxy resin provide efficient load transfer interfaces, which enhances the mechanical properties of the composites. It was found that the flexural strength, modulus, and toughness of 0.1 wt% ND loaded nanocomposites have been enhanced up to 85%, 57%, and 39%, respectively for UV/O 3 treated ND powder. It is also found that the optimum ND concentration to achieve maximum reinforcement is 0.1 wt% while higher concentrations lead to decrease in mechanical properties. The significant improvement of the mechanical properties of the ND/epoxy nanocomposites is attributed to the good dispersion of the functionalized ND in epoxy matrix.

Journal of Low Temperature Physics, 2012

The fluctuation induced conductivity ͑FIC͒ of ͑Cu 0.5 Tl 0.5−x K x ͒Ba 2 Ca 3 Cu 4 O 12−y ͑x=0,0.... more The fluctuation induced conductivity ͑FIC͒ of ͑Cu 0.5 Tl 0.5−x K x ͒Ba 2 Ca 3 Cu 4 O 12−y ͑x=0,0.25͒ superconductor has been studied after potassium substitution at thallium site in the charge reservoir layer ͑Cu 0.5 Tl 0.5 Ba 2 O 4−y ͒. The samples were also post-annealed in oxygen to change the carrier density in CuO 2 planes. The zero resistivity critical temperature T c ͑0͒ was found to increase after K +1 substitution at Tl +3 sites in the Cu 0.5 Tl 0.5 Ba 2 O 4−y charge reservoir layer. However, T c ͑0͒ has been suppressed after post-annealing the samples in oxygen. The FIC analysis was performed in the frame work of Aslamasov-Larkin theory. The results of FIC analysis have shown three-dimensional ͑3D͒, two dimensional ͑2D͒ and short wavelength fluctuations ͑SWFs͒ in the order parameter. It has been also observed that there is an increase in the 3D-2D and 2D-SWF cross-over temperatures after potassium substitution along with an increase in T c ͑0͒. However, after post-annealing in oxygen, the dimensional cross-over has been shifted to lower temperatures. A direct correlation between the cross-over temperatures, the T c ͑0͒ as well as carrier doping level has been observed.

Journal of Applied Polymer Science, 2013

Diamond-epoxy composites reinforced with low content of submicron diamond powder 0.1, 0.4, 0.7, a... more Diamond-epoxy composites reinforced with low content of submicron diamond powder 0.1, 0.4, 0.7, and 1.0 wt % were synthesized. As received diamond powder was acid treated to purify and functionalize diamond particles. Fourier Transform Infrared Spectroscopy was utilized to study the moieties attached to the diamond particles. The trace elemental analysis of impurities in diamond powder before and after acid treatment was performed using ion beam techniques. The mechanical properties of the epoxy matrix were enhanced with the addition of purified and functionalized diamond powder. The Dynamical mechanical analysis results revealed that storage modulus of the prepared composites has been increased by $ 100% with diamond loading of 0.7 wt %. The Vickers's hardness of the diamond-epoxy composite was $ 39% higher than that of pure epoxy for the loading of 1.0 wt % diamond powder. Mechanisms responsible for the enhancement of the mechanical properties are discussed.

Journal of Applied Physics, 2012

With climbing worldwide oil prices and global warming, energy crisis poses a threat to living sta... more With climbing worldwide oil prices and global warming, energy crisis poses a threat to living standards, economy, and even global environment. Nanodielectrics become one of the new materials activated to play a unique role in sustainable and clean energy production, energy transportation, energy storage, and end usage. Based on our recent research on frequency-dependent dielectric properties of BaTiO 3 (BT) single domain, BT/parylene nanodielectric composites have been examined in wide-ranging frequency at room temperature by several theoretical models. The projected models combined with Debye type of dissipation and soft mode theory to obtain more precise frequency dependent dielectric spectrum. Among the others, Wiener mixture rule, Lichtnecker model, Rayleigh model, Yamada rule, Maxwell-Wagner model, modified Kerner model were used to find frequency dependent nanocomposites dielectric spectrum. The predicted results are compared with our experimental results and explored the frequency dependent dielectric behavior of nanodielectric composites. The dielectric constant decreases while dielectric loss increases with increasing frequency due to at very high frequency, only electronic polarization can occur. This investigation provides the fundamental knowledge on dielectric properties of nanocomposites with a wide frequency range instead of trial-and-error strategy of experiments for the future development of energy storage devices.

Journal of Nanotechnology in Engineering and Medicine, 2015

Materials & Design, 2015

Physica B: Condensed Matter, 2015

Advances in Polymer Technology, 2015

Superconductor Science and Technology, 2007

Journal of Superconductivity and Novel Magnetism, 2014

Journal of Applied Polymer Science, 2014

2013 International Conference on Aerospace Science & Engineering (ICASE), 2013

Physica C: Superconductivity, 2004

Physica C: Superconductivity, 2005

Physica C: Superconductivity, 2008

Physica C: Superconductivity, 2005

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2013

Journal of Superconductivity and Novel Magnetism, 2009

Journal of Nanoparticle Research, 2013

Journal of Materials Science & Technology, 2014

Journal of Low Temperature Physics, 2012

Journal of Applied Polymer Science, 2013

Journal of Applied Physics, 2012