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Mardān, Pakistan

Fawad U.,Kyungpook National University | Fawad U.,Kohat University of Science and Technology | Kim H.J.,Kyungpook National University | Khan A.,AWKUM | And 3 more authors.
Science of Advanced Materials | Year: 2015

This work is particularly dedicated to the synthesis of Li6Gd(BO3)3: Tb3+, Dy3+ (lithium gadolinium borate) phosphors by the well-known solid state reaction method and their X-ray and photoluminescence investigations. The optimal activator's concentrations (0.2 mol% for Tb3+ and 0.3 mol% for Dy3+) were determined and used for further analysis. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for analyzing the phases, crystallinities, grain sizes and the overall morphologies of the synthesized phosphors. The X-ray and UV-VIS induced luminescence were measured. The UV induced emission spectrum of Li6Gd(BO3)3: Tb3+ phosphor showed five major peaks corresponding to the characteristic Tb3+ transitions (5Dj →7Fj), whereas, Li6Gd(BO3)3: Dy3+ phosphor exhibited four major emission peaks that correspond to transitions from the ground state of f9(6H15/2) to some higher energy states of 4f9. The quantitative analyses of luminescence of the synthesized phosphors are vital for their applications in various fields. Hence, the X-ray induced light yields were measured for Li6Gd(BO3)3: Tb3+, Dy3+ phosphors to be 113% and 78% of that of gadox (gadolinium oxy sulfide, Gd2O2S: Tb3+), respectively. Hence these phosphors could be good candidates for X-ray imaging. According to Blasse's and Dexter's calculations, the dipole-dipole interaction is responsible for concentration quenching mechanism on concentrations of both phosphors. The chromaticity coordinates were measured for Li6Gd(BO3)3: Tb3+, Dy3+. © 2015 by American Scientific Publisher. Source

Ullah A.,Loughborough University | Naeem M.,AWKUM | Holdich R.G.,Loughborough University | Starov V.M.,Loughborough University | Semenov S.,Loughborough University
Progress in Colloid and Polymer Science | Year: 2011

Control of permeate flux is important in microfiltration processes as it influences trans-membrane pressure and fouling of a membrane. Particles of vegetable oil ranging from 1 to 15 mm were passed through a 4 mm slotted pore membrane at various flux rates. Various intensities of shear were applied parallel to the membrane by vibrating the membrane at different frequencies. At the lowest permeate flux rate (200 lm-2 hr-1) the membrane fouled because the drag force was too low to squeeze the deformable oil droplets through the membrane. At higher flux rates the drag force over the oil droplets increased and deformation, and passage, of oil droplets into the permeate was possible. Without any applied shear highest trans-membrane pressure was observed due to fouling, which could be modelled by a pore blocking model. A positive displacement pump was used in experiments which maintained nearly constant flow of permeate. Flux rates varied from 200 up to 1200 lm-2 hr-1, and the highest shear rate used was 8,000 s-1. The experimental system provided a simple technique for assessing the behaviour of the microfilter during the filtration of these deforming particles. © Springer-Verlag Berlin Heidelberg 2012. Source

Ullah A.,Loughborough University | Holdich R.G.,Loughborough University | Naeem M.,AWKUM | Khan S.W.,UET Peshawar | Starov V.M.,Loughborough University
Chemical Engineering Research and Design | Year: 2014

Size distribution of crude oil drops in the permeate has been predicted using the 'linear fit' approach with, and without oscillating the membrane. Without membrane oscillation (without shear rate), static and drag forces are taken into account and their balance is assumed as 100% cut-off or rejection point. With the membrane oscillation, 'inertial lift' model available in the literature is considered and in this case 100% cut-off is assumed when away migration and convection velocities becomes equal. Three types of crude oil drops with different °API values and interfacial tensions are analysed experimentally, the results are compared with the presented model and the model is an agreement with the experiments. The study has been validated with the genuine size distribution of oil drops obtained from oil companies operating at Kuwait at various locations in order to investigate the industrial applicability of the model. Overall oil concentration of the permeate can be calculated using the proposed model that provides an idea whether the concentration of oil in the permeate is within the standard set by international regulatory authorities. © 2014 The Institution of Chemical Engineers. Source

Ullah A.,Loughborough University | Holdich R.G.,Loughborough University | Naeem M.,AWKUM | Starov V.M.,Loughborough University
Journal of Membrane Science | Year: 2012

The effect of interfacial tension between two fluids, on the passage and rejection of oil droplets through slotted pore membranes is reported. A mathematical model was developed in order to predict conditions for 100% cut-off of oil droplets through the membrane as a function of permeate flux rate. Good agreement of theoretical predictions with experimental data shows that the model can be applied to the filtration of deformable droplets through slotted pore membranes. At high interfacial tension (40mN/m) with lower flux (200lm -2hr -1)droplets of crude oil (27 API) were 100% rejected at droplet diameter 4.3μm using a 4μm slotted pore membrane. At lower interfacial tension (5mN/m), with the same flux rate, 100% rejection occurred at 10μm droplet diameter using the same membrane. It was also found that the droplet rejection efficiency below the 100% cut-off was roughly linear with drop size, down to zero rejection at zero drop diameter. Hence, the model, coupled with this approximate correlation, can be used to predict dispersed oil drop concentration from a known feed drop size distribution. © 2012 Elsevier B.V. Source

Ullah A.,Loughborough University | Holdich R.G.,Loughborough University | Naeem M.,AWKUM | Starov V.M.,Loughborough University
Journal of Membrane Science | Year: 2012

Shear enhanced microfiltration of crude oil/water emulsion is investigated and the effect of an applied shear rate on the rejection of drops by the membrane is reported. Applying vibration provides shear at the membrane surface leading to shear-induced migration and an inertial lift of drops/particles. Both phenomena tend to move the drops away from the membrane surface. The shear-induced migration and inertial lift migration increase with increasing shear rates. A mathematical model is presented to account for the presence of both phenomena. The developed model is used for theoretical prediction of 100% cut-off of crude oil drops by the membrane with, and with-out, vibration applied. A satisfactory agreement of the model predictions with experimental data shows that the model can be successfully used for a theoretical prediction of 100% cut-off of drops by slotted pore membranes. When applying a shear rate of 8000s -1 and 200lm -2h -1 flux rate, 3-4μm radius drops were almost completely rejected; reducing 400ppm of crude in the feed to 7ppm in the permeate. © 2012 Elsevier B.V. Source

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