Browsing by Author "Ahmed, R"

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    Desirable TiO2 compact films for nanostructured hybrid solar cells
    (Taylor & Francis, 2019-08-08) Yun, JH; Lyu, MQ; Ahmed, R; Triani, G
    Two different TiO2 compact films, fabricated by sol-gel spin-coating (SC) and spray-pyrolysis (SP) processes, were employed as an electron transport layer (ETL) to the nanostructured hybrid perovskite solar cells (PSCs), and they were comprehensively investigated through the various characterisation approaches using electrochemical and physicochemical approaches. With cyclic voltammetry and XPS results, the absence of pinholes on the SP-TiO2 compact films was indicated, and AFM and SEM results confirmed the SP-TiO2 compact films had lower surface roughness and more compact particle connectivity, offering a decent interface between the perovskite active layer and the adjacent TiO2 films. The performance of the SP-PSCs using the SP-TiO2 compact films was 7.06%, which was 3 times higher than that of the SC-PSCs. Voc decay measurement also confirmed that such pinhole-free and improved film interfaces of SP-TiO2 compact films contributed to elongating electron lifetime in PSCs by the enhanced hole blocking effect of the SP-TiO2 compact films. © 2020 Informa UK Limited
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    Measuring residual strain and stress in thermal spray coatings using neutron diffractometers
    (SSRN, 2020-10-14) Faisal, NH; Ahmed, R; Prathuru, AK; Paradowska, AM; Lee, TL
    During thermal spray coating, residual strain (or stress) is formed within the coating and substrates due to many processes (quenching stress, peening effect, deposition temperature, lamella structure) and micro-structural phase changes. It is also known that the residual stress values of thermally sprayed coatings are dependent upon the measurement method. Neutron diffraction technique can provide a non-destructive through-thickness residual strain analysis in thermally sprayed components with a level of detail not normally achievable by other techniques. Despite this advantage, the number of studies involving neutron diffraction analysis in thermal spray coatings remain limited, partly due to the limited number of neutron diffraction strain measurement facilities globally, and partly due to the difficulty is applying neutron diffraction analysis to measure residual strain in the complex thermal spray coating micro-structure. This paper provides a comprehensive guide to researchers planning to use this technique for thermal spray coatings, and reviews some of these studies. ENGIN-X at the ISIS spallation source in the UK is a neutron diffractometer (time-of-flight) dedicated to materials science and engineering with high resolution and versatile capabilities. The focus is on the procedure of using ENGIN-X diffractometer for thermal spray coatings with a view that it can potentially be translated to other neutron diffractometers. Neutron sources worldwide (e.g. Africa, Asia, Australia, Europe, and North America) have been used to measure strains in various materials, and here, we present few examples where thermal spray coatings have been characterized at various neutron sources worldwide, to study the residual strains and micro-structures. © Elsevier Inc.
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    Modern and historical engineering components investigated by neutron diffractionon ENGIN-X
    (Japan Society of Mechanical Engineers, 2012-06-29) Paradowska, AM; Tremsin, A; Kelleher, JF; Zhang, SY; Paddea, S; Burca, G; James, JA; Ahmed, R; Faisal, NH; Festa, G; Andreani, C; Civita, F; Bouchard, PJ; Krockelman, W; Fitzpatrick, ME; Grazzi, F
    The ENGIN-X beamline is mainly used to determine residual strains/stresses deep within the interior of bulk engineering components. It is mainly used by scientists and engineers for the development of modern engineering processes and structural integrity investigations. ENGIN-X diffraction and transmission mode can be a very useful tool to measure strain, phase transitions, texture and material composition in spatial resolution in historical or archaeological artifacts and modern materials. The complexity of the shapes and sizes of the samples measured on ENGIN-X varies significantly between experiments, and this required the development of better planning, simulation and control software, SScanSS. In this paper an overview of recent developments in strain scanning on ENGIN-X and a highlight of current scientific research are presented. © 2012 The Japan Society of Mechanical Engineers
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    Neutron diffraction residual strain measurements in nanostructured hydroxyapatite coatings for orthopaedic implants
    (Elsevir, 2011-11-01) Ahmed, R; Faisal, NH; Paradowska, AM; Fitzpatrick, ME; Khor, KA
    The failure of an orthopaedic implant can be initiated by residual strain inherent to the hydroxyapatite coating (HAC). Knowledge of the through-thickness residual strain profile in the thermally sprayed hydroxyapatite coating/substrate system is therefore important in the development of a new generation of orthopaedic implants. As the coating microstructure is complex, non-destructive characterization of residual strain, e.g. using neutron diffraction, provides a useful measure of through thickness strain profile without altering the stress field. This first detailed study using a neutron diffraction technique, non-destructively evaluates the through thickness strain measurement in nanostructured hydroxyapatite plasma sprayed coatings on a titanium alloy substrate (as-sprayed, heat treated, and heat treated then soaked in simulated body fluid (SBF)). The influence of crystallographic plane orientation on the residual strain measurement is shown to indicate texturing in the coating. This texturing is expected to influence both the biological and fracture response of HA coatings. Results are discussed in terms of the influence of heat-treatment and SBF on the residual stress profile for these biomedical coatings. The results show that the through thickness residual strain in all three coatings was different for different crystallographic planes but was on average tensile. It is also concluded that the heat-treatment and simulated body fluid exposure had a significant effect on the residual strain profile in the top layers of HAC.(C) 2011 Elsevier Ltd.