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At least 793 records · Page 44

Characterization of 430L porous supports obtained by powder extrusion moulding for their application in solid oxide fuel cells

The characterization of 430L stainless steel planar porous supports obtained by powder extrusion moulding was performed in this work. A thermoplastic multicomponent binder based on high density polyethylene and paraffin wax was selected for the process. Green supports were shaped by extrusion moulding, and subsequently the binder was removed by a thermal cycle previously optimized. Sintering was carried out at different temperatures in low vacuum. Density of sintered parts was measured by Archimedes' method and porosity was also evaluated through a microstructural analysis by optical microscopy. The porosity degree of samples sintered at low temperature was close to 35% which is a very suitable value for their application in SOFCs. Tensile tests were carried out in order to determine mechanical strength as a function of porosity degree. Based on these results, the best feedstock composition and processing parameters were selected. The oxidation behaviour in static air at high temperature was studied, and formed oxides were characterized in a scanning electron microscope equipped with energy dispersive analysis of X-rays. X-ray diffraction experiments were performed in order to identify the formed oxides based on formula Fe{sub 2−x}Cr{sub x}O{sub 3}. The results of these studies showed that this kind of ferritic stainless steel would be more suitable to be used as anodic supports where a rich hydrogen atmosphere is employed. Preliminary deposition tests allowed obtaining a homogeneous Ni–YSZ anode layer with a thickness of 10 μm on the porous metallic substrates. - Highlights: • 430L stainless steel porous supports were obtained by powder extrusion moulding. • Porosity degree was controlled sintering at different temperatures in low vacuum. • Tensile tests allowed determining mechanical strength of porous supports. • A study about its oxidation behaviour in static air at high temperature was realized. • After oxidation, formed oxides were characterized by EDS–SEM and XRD.

36 MATERIALS SCIENCE↗

Template preparation of strontium hexaferrite (SrFe{sub 12}O{sub 19}) micro/nanostructures: Characterization, synthesis mechanism and magnetic properties

Using electrospun thermoplastic ester elastomer (TPEE) micro/nanofibers as the template, strontium hexaferrite micro/nanostructures with different morphologies were prepared successfully by a combination process composed of sol-gel precursor coating technique and subsequent calcination. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) were used to characterize the morphology, crystalloid structure and the magnetic properties of samples. The relation between the fabricated structure morphologies and TPEE micro/nanofibers properties was studied. It was believed that the hydrogen bond effect competition between TPEE/precursors and precursors/precursors played an important role on the formation of the obtained structures. In addition, the influence of annealing time and annealing rate on the magnetic properties of the samples obtained was investigated. The structures thus fabricated can be potential materials in many fields, drug delivery and photocatalysts for example.

36 MATERIALS SCIENCE↗

Preliminary Results of Helical Tomotherapy in Patients with Complex-Shaped Meningiomas Close to the Optic Pathway

Meningiomas are the most common benign intracranial tumor. Meningiomas close to the optic pathway represent a treatment challenge both for surgery and radiotherapy. The aim of this article is to describe early results of helical tomotherapy treatment in complex-shaped meningiomas close to the optic pathway. Twenty-eight patients were consecutively treated. All patients were immobilized with a thermoplastic head mask and planned with the aid of a magnetic resonance imaging-computed tomography fusion. All treatments included daily image guidance. Pretreatment symptoms and acute toxicity were recorded. Median age was 57.5 years, and 92.8% patients had Eastern Cooperative Oncology Group performance status scale {<=}1. The most common localizations were the sella turcica, followed by the cavernous sinus and the sphenoid. The most common symptoms were derived from cranial nerve deficits. Tomotherapy was administered as primary treatment in 35.7% of patients, as an adjuvant treatment in 32.4%, and as a rescue treatment after postsurgical progression in 32.1% patients. Most patients were either inoperable or Simpson IV. Total dose varied between 5000 and 5400 cGy; fractionation varied between 180 and 200 cGy. Median dose to the planning target volume was 51.7 Gy (range, 50.2-55.9 Gy). Median coverage index was 0.89 (range, 0.18-0.97). Median homogeneity index was 1.05 (range, 1-1.12). Acute transient toxicity was grade 1 and included headache in 35.7% patients, ocular pain/dryness in 28.5%, and radiation dermatitis in 25%. Thus far, with a maximal follow-up of 3 years, no late effects have been seen and all patients have a radiological stabilization of the disease. Helical tomotherapy offered a safe and effective therapeutic alternative for patients with inoperable or subtotally resected complex-shaped meningiomas close to the optic pathway. Acceptable coverage and homogeneity indexes were achieved with appropriate values for maximal doses delivered to the eyes, lenses, and chiasm, despite the proximity of the tumor to these structures.

61 RADIATION PROTECTION AND DOSIMETRY↗

Effect of intrafractional prostate motion on simultaneous boost intensity-modulated radiotherapy to the prostate: A simulation study based on intrafractional motion in the prone position

Although the prostate displacement of patients in the prone position is affected by respiration-induced motion, the effect of intrafractional prostate motion in the prone position during “simultaneous integrated boost intensity-modulated radiotherapy” (SIB-IMRT) is unclear. The purpose of this study was to evaluate the dosimetric effects of intrafractional motion on SIB-IMRT to a dominant intraprostatic lesion (IPL) using measured motion data of patients in a prone position, fixed with a thermoplastic shell. We obtained 2 orthogonal x-ray fluoroscopic images at the same moment every 0.2 seconds for 30 seconds before and after treatment, once weekly, from 7 patients with localized prostate cancer with detectable prostatic calcification. Prostate displacements in the left-right (LR), anteroposterior (AP), and superoinferior (SI) directions were calculated using the prostatic calcification as a fiducial marker. We defined the displacement between pretreatment and posttreatment as baseline drift (BD). An SIB-IMRT plan was generated in which each IPL + 3 mm received a dose of 94.5 Gy, whereas the remainder of the prostate + 7 mm received a dose of 75.6 Gy in 9 fields. A simulated plan of dose blurring was generated by the convolution of isocenter-shifted plans using measured motion data in 30 seconds and motion in 30 seconds + distance between pretreatment and posttreatment position (BD) for each of the 7 patients. The motion in 30 seconds mainly reflected respiration-induced motion. The mean displacements of BD were 1.4 mm (− 3.1 to 8.2 mm), − 2.2 mm (− 9.1 to 1.5 mm), and − 0.3 mm (− 5.0 to 1.8 mm) in the AP, SI, and LR directions, respectively. The differences in the target coverage with V{sub 90%} of the IPL and V{sub 100%} of the prostate between the simulated plan and original plan were − 3.9% to − 0.3% and − 0.6% to 1.1% for respiration-induced motion and 3.1% to − 67.8% and 3.6% to − 13.3% for BD with respiration-induced motion, respectively. The large motion of BD resulted in an inadequate coverage by the prescribed dose of the SIB-IMRT to the IPL. A 7-mm margin is recommended when real-time tracking techniques are not applied. The effect of respiration-induced motion was small, so long as a 3-mm margin was added.

61 RADIATION PROTECTION AND DOSIMETRY↗

Successful delivery of adjuvant external beam radiotherapy for ependymoma in a patient with Ondine's curse

Ondine's curse is a rare, potentially life-threatening disorder characterized by loss of automatic breathing during sleep and preserved voluntary breathing. It is seldom encountered in the radiotherapy clinic but can pose significant technical challenges and safety concerns in the delivery of a prescribed radiation course. We report a unique case of successful delivery of radiotherapy for ependymoma in a patient with Ondine's curse. A 53-year-old gentleman presented with vertigo when lying down. Brain magnetic resonance imaging revealed an enhancing mass in the floor of the fourth ventricle. He underwent maximal safe resection. Pathology revealed ependymoma. The patient was referred for radiotherapy. Computed tomography simulation was performed in supine position with 3-point thermoplastic mask immobilization. Sequential TomoTherapy plans were developed. At first scheduled treatment, shortly after mask placement, his arms went limp and he was unresponsive. Vitals showed oxygen saturation 83%, pulse 127, and blood pressure 172/97 mm Hg. He was diagnosed with Ondine's curse thought secondary to previous brainstem damage; the combination of lying flat and pressure from the mask was causing him to go into respiratory arrest. As supine positioning did not seem clinically advisable, he was simulated in prone position. A RapidArc plan and a back-up conformal plan were developed. Prescriptions were modified to meet conservative organs-at-risk constraints. Several strategies were used to minimize uncertainties in set-up reproducibility associated with prone positioning. He tolerated prone RapidArc treatments well. The report highlights the importance of applying practical patient safety and treatment planning/delivery strategies in the management of this challenging case.

61 RADIATION PROTECTION AND DOSIMETRY↗

Clinical implementation of radiosurgery using the Helical TomoTherapy unit

The American Society of Radiation Oncology has recently recommended the use of radiosurgery to manage brain metastases. For such a recommendation to be implemented in a widespread manner, radiosurgery must be accessible at community radiation therapy facilities. The work presented here describes our clinical experience in the implementation of radiosurgery using a Helical TomoTherapy unit. Helical TomoTherapy is a unique dose-delivery system designed to perform intensity-modulated radiation therapy (IMRT). The system built on the ring-based gantry has the tight machine tolerances required for radiosurgery. A frameless system consisting of a thermoplastic mask and a noninvasive ''stereotactic radiosurgery (SRS)-stereotactic radiotherapy (SRT)'' fixation device is used for patient immobilization. Treatment planning is performed using the TomoHD treatment planning system designed for IMRT. The image-guidance system on the Helical TomoTherapy is used for patient localization. Our clinical experience demonstrated that the radiosurgery procedure can be streamlined as we do for IMRT patients. The treatment time of about 10 minutes is comparable with that for IMRT patients. The same patient-specific quality assurance for IMRT is used for radiosurgery. As demonstrated, SRS using Helical TomoTherapy is not a whole-day event, unlike SRS using other dose-delivery systems or SRS performed in the past.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

Immobilization and image-guidance methods for radiation therapy of limb extremity soft tissue sarcomas: Results of a multi-institutional survey

Radiation therapy for limb-extremity soft tissue sarcoma (STS) requires accurate, reproducible dose delivery. However, patient positioning is challenging and there is a lack of existing guidelines to assist institutional standardization. Therefore, we conducted a multi-institutional international survey of STS immobilization, image guidance methods, and treatment protocols to investigate current practice. Seventy-three UK radiotherapy centers and 15 hospitals in 7 other countries completed a questionnaire on STS immobilization and image-guidance procedures. Specifically, the survey collated information on the current usage of immobilization equipment, including custom devices, patient setup tolerances, the use of written protocols, the modality and frequency of image guidance, the method of treatment, allocated treatment times, and the application of surgical clips. Multiple combinations of immobilization devices were reported. In the UK, 12%, 40%, 30%, 12%, and 5% use 1, 2, 3, 4, and 5 types of device for lower limb STS. Vacuum bag plus either foot or ankle support was most common (66%). Of 15 international centers, 27%, 60%, 7%, 0%, 7% use 1, 2, 3, 4, 5 devices, with vacuum bags (73%) and thermoplastic (47%) predominant, similar to UK values of 77% and 52%. For image guidance, in the UK, 37% use kV planar, 34% use MV planar, and 16% use cone-beam CT for the first 3 fractions and then weekly. Internationally, daily imaging was more prevalent with 33% using kV planar, 7% MV planar, and 40% cone-beam CT daily. Custom devices plus combinations of devices, along with 5- and 10-mm set-up tolerances, were most commonly reported. Less than half of centers have written treatment protocols. Conventional treatment is most common in the UK, with only 42% using conformal techniques. Treatment is allocated between 10 and 30 minutes. Twenty-six percent of UK centers and 53% of international centers use surgical clips. Across treatment centers, there is no consistent approach to STS immobilization, image-guidance methods, or treatment protocols assessed by this survey. A wide variety of immobilization devices and configurations are utilized, and the frequency and modality of imaging are similarly diverse. In the absence of guidelines, the creation of an online repository of example immobilization techniques could enable centers to compare a diversity of cases. The availability of a forum for viewing and discussing a range of cases could potentially lead to improved patient setup and reduce the time taken to devise an individual immobilization strategy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

Effect of polymer-nanoparticle interactions on the glass transition dynamics and the conductivity mechanism in polyurethane titanium dioxide nanocomposites

We report on the glass transition dynamics and the conductivity properties of a nanodielectric system composed of pre-synthesized TiO{sub 2} nanoparticles embedded in thermoplastic polyurethane. Increase of TiO{sub 2} loading results in enhanced segmental mobility of the composites and less steep temperature dependence, i.e., lower fragility index. The decrease in the fragility index and glass transition temperature is discussed based on the FTIR results. We observe different behavior of conductivity for temperatures above and below the glass transition temperature. At high temperatures the composites exhibit conductivity values more than 2 orders of magnitude higher than those in the pristine matrix. At the same time, at sub-Tg temperatures composites are characterized by superior electrical insulation properties compared to pristine matrix material. Such drastic temperature dependence of the conductivity/insulating ability of the flexible and light-weight, low-Tg composite material can be utilized in various applications including sensing and temperature switching materials.

36 MATERIALS SCIENCE↗

Investigation of thermal treatment on selective separation of post consumer plastics prior to froth flotation

Highlights: • Both PET and PVC have nearly the same densities. • The best pH value will be 4 for optimizing pH values. • Malic acid gave the best results for selective separation of PET and PVC. - Abstract: Plastics have become the widely used materials because of their advantages, such as cheapness, endurance, lightness, and hygiene. However, they cause waste and soil pollution and they do not easily decompose. Many promising technologies are being investigated for separating mixed thermoplastics, but they are still uneconomical and unreliable. Depending on their surface characteristics, these plastics can be separated from each other by flotation method which is useful mineral processing technique with its low cost and simplicity. The main objective of this study is to investigate the flotation characteristics of PET and PVC and determine the effect of plasticizer reagents on efficient plastic separation. For that purpose, various parameters such as pH, plasticizer concentration, plasticizer type, conditioning temperature and thermal conditioning were investigated. As a result, PET particles were floated with 95.1% purity and 65.3% efficiency while PVC particles were obtained with 98.1% purity and 65.3% efficiency.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

Combating oil spill problem using plastic waste

Highlights: • Up-cycling one type of pollution i.e. plastic waste and successfully using it to combat the other type of pollution i.e. oil spill. • Synthesized oil sorbent that has extremely high oil uptake of 90 g/g after prolonged dripping of 1 h. • Synthesized porous oil sorbent film which not only facilitates in oil sorption but also increases the affinity between sorbent and oil by means of adhesion. - Abstract: Thermoplastic polymers (such as polypropylene, polyethylene, polyethylene terephthalate (PET) and high density polyethylene (HDPE)) constitute 5–15% of municipal solid waste produced across the world. A huge quantity of plastic waste is disposed of each year and is mostly either discarded in landfills or incinerated. On the other hand, the usage of synthetic polymers as oil sorbents, in particular, polyolefins, including polypropylene (PP), and polyethylene (PE) are the most commonly used oil sorbent materials mainly due to their low cost. However, they possess relatively low oil absorption capacities. In this work, we provide an innovative way to produce a value-added product such as oil-sorbent film with high practical oil uptake values in terms of g/g from waste HDPE bottles for rapid oil spill remedy.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗

Synthesis Characterization and Electrospinning of Architecturally-Discrete Isotactic-Atactic-Isotactic Triblock Stereoblock Polypropene Elastomers

Stereochemically homogeneous and architecturally discrete isotactic-atactic-isotactic triblock stereoblock PP (sbPP) thermoplastic elastomers in which the block lengths for each domain type can be varied in programmed fashion while keeping total molecular weight and molecular weight polydispersity the same has been achieved for the first time. Five sbPP materials were prepared: sbPP-1 (6iso-88a-6iso), total isotactic content, 12%; sbPP-2 (12iso-76a-12iso), 24%; sbPP-3 (18iso-64a-18iso), 36%; sbPP-4 (24iso-50a-26iso), 50%; and sbPP-5 (20iso-64a-33iso), 53%. All five sbPP materials were successfully processed by solution-based electrospinning to provide fiberous mats with feature sizes on the nanometer to micrometer length scale. Extensive characterization by analytical (SEM, AFM, tensile testing, DSC,), spectroscopic (FT-IR, FT-Raman), and synchrotron X-ray diffraction techniques of bulk samples, electrospun fibers and solvent cast films of the sbPP samples revealed well-defined trends in elastic properties, morphologies and crystallinity that are associated with a higher degree of crystallinity that emerges with higher isotactic contents. The results of these investigations serve to provide an important foundation that can be used to potentially identify the best combination of stereoerror level incorporation within the isotactic domains and total isotactic content for these architecturally discrete sb-PP materials for maximizing desirable elastomeric traits and solution-based (electrospinning) processing methodology with the goal of achieving the best possible structural forms for potential product applications.

36 MATERIALS SCIENCE↗

Dynamic behavior of reversible oxygen migration in irradiated-annealed high temperature superconducting wires

Large-scale extrusion-based additive manufacturing of high-performance thermoplastic composites like fiber reinforced polyphenylene sulfide (PPS) is well-suited for tooling applications to lower manufacturing costs and lead times. Autoclave tooling requires good mechanical performance at temperatures even above the glass transition temperature (T g ). In this work, the authors have investigated a post-process isothermal annealing technique to improve the mechanical properties of various grades of carbon fiber reinforced PPS components printed on the Big Area Additive Manufacturing (BAAM) system. Since PPS is a semi-crystalline polymer, crystallinity can change during annealing and affect the mechanical properties of the part. In addition, isothermal annealing can also lead to solid-state structural changes in the form of thermal and oxidative branching and/or crosslinking reactions in some grades of PPS which can alter the crystallization process. This work reports the effect of annealing on dynamic mechanical properties of BAAM printed components, along with studies to determine the effect of annealing on crystallinity and the occurrence of oxidative reactions. Results showed that isothermal annealing at 250 °C for 18 h improved the storage modulus of all selected grades (neat and reinforced) of PPS at temperatures above T g . Annealing led to an overall increase in the degree of crystallinity, with secondary crystallization taking place. Although oxidative structural changes were observed to occur more on the surface of the PPS parts, they primarily influenced the size of crystals formed and did not significantly alter the degree of crystallinity at various regions within the sample.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Melt state behaviour of PEEK and processing window interpretation for fast compression moulding process

Fast mould heating is nowadays possible by using induction technology for example with the Cage System registered developed by RocTool. It allows heating and cooling kinetics of about 100 deg. C per minute and new perspectives are thus possible to optimize the compression moulding process of long fibre reinforced thermoplastic composites. Indeed, a high forming temperature may favour polymer creep and so on composite consolidation. Nevertheless, the processing time of PEEK composite above melt temperature must be reduced to a few minutes due to the fast thermal degradation of the matrix. On the other hand, high cooling rates may have negative effect on matrix crystallinity. The proposed procedure consist in performing a few minutes isotherm around 300 deg. C during the fast cooling. It would favour a high degree of crystallinity of PEEK without extending the cycle time.

36 MATERIALS SCIENCE↗

Room temperature homogeneous flow in a bulk metallic glass with low glass transition temperature

We report a high entropy metallic glass of Zn{sub 20}Ca{sub 20}Sr{sub 20}Yb{sub 20}(Li{sub 0.55}Mg{sub 0.45}){sub 20} via composition design that exhibiting remarkable homogeneous deformation without shear banding under stress at room temperature. The glass also shows properties such as low glass transition temperature (323 K) approaching room temperature, low density and high specific strength, good conductivity, polymerlike thermoplastic manufacturability, and ultralow elastic moduli comparable to that of bones. The alloy is thermally and chemically stable.

36 MATERIALS SCIENCE↗

Morphology and properties of recycled polypropylene/bamboo fibers composites

Polypropylene (PP) is among the most widely used thermoplastics in many industrial fields. However, like other recycled polymers, its properties usually decrease after recycling process and sometimes are degraded to poor properties level for direct re-employment. The recycled products, in general, need to be reinforced to have competitive properties. Short bamboo fibers (BF) have been added in a recycled PP (RPP) with and without compatibilizer type maleic anhydride polypropylene (MAPP). Several properties of composite materials, such as helium gas permeability and mechanical properties before and after ageing in water, were examined. The effects of bamboo fiber content and fiber chemical treatment have been also investigated. We showed that the helium permeability increases if fiber content is higher than 30% because of a poor adhesion between untreated bamboo fiber and polymer matrix. The composites reinforced by acetylated bamboo fibers show better helium permeability due to grafting of acetyl groups onto cellulose fibers surface and thus improves compatibility between bamboo fibers and matrix, which has been shown by microscopic observations. Besides, mechanical properties of composite decrease with ageing in water but the effect is less pronounced with low bamboo fiber content.

36 MATERIALS SCIENCE↗

Numerical simulation of multi-layered textile composite reinforcement forming

One important perspective in aeronautics is to produce large, thick or/and complex structural composite parts. The forming stage presents an important role during the whole manufacturing process, especially for LCM processes (Liquid Composites Moulding) or CFRTP (Continuous Fibre Reinforcements and Thermoplastic resin). Numerical simulations corresponding to multi-layered composite forming allow the prediction for a successful process to produce the thick parts, and importantly, the positions of the fibres after forming to be known. This paper details a set of simulation examples carried out by using a semi-discrete shell finite element made up of unit woven cells. The internal virtual work is applied on all woven cells of the element taking into account tensions, in-plane shear and bending effects. As one key problem, the contact behaviours of tool/ply and ply/ply are described in the numerical model. The simulation results not only improve our understanding of the multi-layered composite forming process but also point out the importance of the fibre orientation and inter-ply friction during formability.

36 MATERIALS SCIENCE↗

Friction in Forming of UD Composites

Inter-ply and tool/ply friction play a dominant role in hot stamp forming of UD fiber-reinforced thermoplastic laminates. This research treats friction measurements of a PEEK-AS4 composite system. To this end, an in-house developed friction tester is utilized to pull a laminate through two heat controlled clamping platens. The friction coefficient is determined by relating the clamp force to the pull force. The geometry of the gap between the clamping platens is monitored with micrometer accuracy. A first approach to describe the relation between the geometry and frictional behavior is undertaken by applying a standard thin-film theory for hydrodynamic lubrication. Experimental measurements showed that the thin-film theory does not entirely cover the underlying physics. Thus a second model is utilized, which employs a Leonov-model to describe the shear deformation of the matrix material, while its viscosity is described with a multi-mode Maxwell model. The combination of both models shows the potential to capture the complete frictional behavior.

36 MATERIALS SCIENCE↗

Integrating Materials, Manufacturing, Design and Validation for Sustainability in Future Transport Systems

The predictive methods currently used for material specification, component design and the development of manufacturing processes, need to evolve beyond the current 'metal centric' state of the art, if advanced composites are to realise their potential in delivering sustainable transport solutions. There are however, significant technical challenges associated with this process. Deteriorating environmental, political, economic and social conditions across the globe have resulted in unprecedented pressures to improve the operational efficiency of the manufacturing sector generally and to change perceptions regarding the environmental credentials of transport systems in particular. There is a need to apply new technologies and develop new capabilities to ensure commercial sustainability in the face of twenty first century economic and climatic conditions as well as transport market demands. A major technology gap exists between design, analysis and manufacturing processes in both the OEMs, and the smaller companies that make up the SME based supply chain. As regulatory requirements align with environmental needs, manufacturers are increasingly responsible for the broader lifecycle aspects of vehicle performance. These include not only manufacture and supply but disposal and re-use or re-cycling. In order to make advances in the reduction of emissions coupled with improved economic efficiency through the provision of advanced lightweight vehicles, four key challenges are identified as follows: Material systems, Manufacturing systems, Integrated design methods using digital manufacturing tools and Validation systems. This paper presents a project which has been designed to address these four key issues, using at its core, a digital framework for the creation and management of key parameters related to the lifecycle performance of thermoplastic composite parts and structures. It aims to provide capability for the proposition, definition, evaluation and demonstration of advanced lightweight structures for new generation vehicles in the context of whole life performance parameters.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗