Possible Recycling of End-of-Life Dolomite Refractories by the Production of Geopolymer-Based Composites: Experimental Investigation

Production and characterization of geopolymers prepared by mixing metakaolin, end-of-life dolomite refractories, sodium silicate solution, and sodium hydroxide solution have been performed. The as-received refractory was crumbled in order to obtain products having, respectively, 250\ua0\u3bcm, 1 mm, and 2.5\ua0mm maximum particles size. Each batch of powder was added in different proportions to a blank geopolymeric matrix. It has been observed that the addition of waste refractory reduces workability of the reference refractory-free slurry. After hardening, only the set of samples prepared with powders with maximum size of 250\ua0\u3bcm maintain integrity while the others resulted affected by the presence of fractures caused by volumetric instabilities; samples with composition R100 showed the highest compressive strength, whereas higher refractory addition lowers strength. Specific surface area appears independent by materials composition; conversely pore volume slightly increases with the addition of dolomite refractory powder. During the thermodilatometric tests all compositions display a shrinkage of about 0.1% between 170 and 400\ua0\ub0C; however, sintering starts at higher temperature (above 600\ua0\ub0C) and samples melt in the range between 650 and 750\ua0\ub0C as a function of their composition, thus showing that the resulting materials loose refractoriness with respect to both the reference geopolymer and the dolomite refractory. Graphical Abstract: [Figure not available: see fulltext.

The Effect of the P/Si Ratio on the Preparation and Properties of Phosphoric Acid-Metakaolin Geopolymers

The present research deals with the production and characterization of geopolymers prepared by mixing metakaolin, different amounts of phosphoric acid solution and water. Hardening was performed by aging the geopolymeric pastes in a climatic chamber. The workability of the pastes has been improved while the H2O/total solid content has been kept constant and the P/Si ratio increased. However, such a benefit implies considerable heat output, which must be controlled in order to limit the formation of extended fractures. The compressive strength of the hardened materials increases with increasing P/Si ratio at a constant H2O/total solid content, whereas their strength decreases with increasing H2O/ total solid content at a constant P/Si ratio. The open macroporosity, which is directly dependent on the total amount of water added to the geopolymeric pastes, may explain the above results better than the nano/microporosity and/or chemical bonds that contribute to building up the materials\u2019 textural features

Synthesis, crystallographic characterization, and mechanical behavior of alumina chromia alloys

Powder mixtures of Alumina and Chromia, blended in different proportions (1, 3, 5 and 10%wt) by attrition milling, were fired either by pressureless sintering in air and hot pressing under vacuum. The resulting materials, characterized by X-ray diffraction, Raman spectroscopy, SEM, hardness and fracture toughness showed that all the compositions form complete solid solution which maintain the same crystal structures of corundum; chromia addition retards materials' densification of pressureless fired samples but not that of hot-pressed samples. Data from Raman spectroscopy and SEM/EDXS showed the appearance of Ti- and Mn-based impurities near the indentation print, in particular on fractured grains. The addition of chromia improves hardness, but does not affect toughness which is, on the other hand, greatly influenced by materials\u2019 residual porosity

The use of ALD and PVD coatings as defect sealants to increase the corrosion resistance of thermal spray coatings

Thermal spray coatings are widely used to improve the surface properties of materials, in particular the wear and oxidation resistance. Nevertheless, the corrosion resistance is slightly increased due to the fact that this type of coatings present some internal defects (pores, cracks) that allow the corrosive media to penetrate up to the substrate, that undergoes to corrosion degradation. The amount of these defects is strongly influenced by both the deposition technique and the material deposited. The aim of this work is to seal the internal porosities of the thermal spray coatings by the use of both PVD and ALD coatings or the combination of the two. The thermal spray coating analysed in this work is a pure alumina coating, deposited by Air Plasma Spray (APS) technique, that has been sealed with CrN coating, deposited by PVD (Physical Vapour Deposition) technique, and/or TiO2 coatings, deposited by ALD (Atomic Layer Deposition). The substrate used is a common medium C steel. The samples were then characterized in order to determine the microstructure (SEM+EDXS, light microscope) and the chemical composition (Rf-GDOES elemental profiling), that is important to determine the depth of penetration of the PVD and/or ALD coating inside the thermal spray deposit. Afterwards, a detailed electrochemical characterization in 3,5wt% NaCl aqueous solution was performed to verify the efficiency of the sealant treatment. In detail, a monitor in function of the time of the OCP potential was performed up to 24h of immersion time. In addition, potentiodynamic tests were performed using a 3 electrode electrochemical cell (CE: Pt wire, RE: Ag/AgCl). The same tests were then performed on the same samples that present an artificial defect produced by Rf-GDOES. The main goal of these tests is to determine the maximum depth of a defect that can allow the corrosive media to penetrate the thermal spray coating. Preliminary results showed that the use of PVD and ALD coatings as sealants can reduce the permeation of the corrosive media on the substrate

Burst strength of BIOLOX\uaedelta femoral heads and its dependence on low-temperature environmental degradation

Zirconia-toughened alumina (ZTA) currently represents the bioceramic gold standard for load-bearing components in artificial hip joints. ZTA is long known for its high flexural strength and fracture toughness, both properties arising from a microscopic crack-tip shielding mechanism due to the stress-induced tetragonal-to-monoclinic (t\u2192m) polymorphic transformation of zirconia. However, there have been concerns over the years regarding the long-term structural performance of ZTA since the t\u2192m transformation also spontaneously occurs at the material's surface under low-temperature environmental conditions with a concomitant degradation of mechanical properties. Spontaneous surface degradation has been extensively studied in vitro, but predictive algorithms have underestimated the extent of in vivo degradation observed in retrievals. The present research focused on burst-strength assessments of 828 mm ZTA femoral before and after long-term in vitro hydrothermal ageing according to ISO 7206-10. An average burst strength of 52 kN was measured for pristine femoral heads. This value was 3c36% lower than results obtained under the same standard conditions by other authors. A further loss of burst strength 3c13% in ultimate load) was observed after hydrothermal ageing, with increased surface monoclinic content ranging from 3c6% to >50%. Nevertheless, the repetitively stressed and hydrothermally treated ZTA heads exceeded the minimum burst strength stipulated by the US Food and Drug Administration (FDA) despite severe test conditions. Lastly, Raman spectroscopic assessments of phase transformation and residual stresses on the fracture surface of the femoral heads were used to clarify burst-strength fluctuations and the effect of hydrothermal ageing on the material's overall strength degradation

Research activities on radioactive waste management and on the back-end of the nuclear fuel cycle performed by the Joint Research Centre of the European Commission

The Euratom Research and Training Programme contributes, within its portfolio of activities, to establish and improve the scientific basis of knowledge for the safe management of spent nuclear fuel and radioactive waste. This includes research and innovation activities undertaken by the Joint Research Centre (or JRC, the European Commission’s science and knowledge service) in its laboratories. This paper provides an overview and some highlights of the Joint Research Centre (JRC) activities which are dedicated to the safety of spent fuel and high level radioactive waste forms. The fields of experimental and modelling research address various stages of spent fuel management after discharge from the reactor core: cooling in the spent fuel pool; handling, transport, extended interim storage and retrieval thereafter; disposal in a deep geological repository and long term behaviour of the spent fuel/waste form after disposal. The safety of the “back-end” of nuclear fuel cycles which include U-Pu recycling and/or a “fully closed” cycle with minor actinides separation and transmutation is also a major area of research. Both normal operation and accident scenarios, which cause fuel degradation/melting, are investigated. Possible applications for legacy waste management, decommissioning, and safeguards are considered. The relevance of the research is linked to the possibility of investigating “real” spent fuel and highly radioactive compounds using JRC’s research infrastructure, which includes hot cells and shielded facilities, and state of the art experimental methods that are (in some cases) rare or even unique. The activities are performed in collaboration with partners and/or in the context of international initiatives. Opportunities and perspectives for enhanced cooperation, including access and sharing of infrastructure are being developed

Organically modified silicate coatings for optical fibers

ABSTRACT Three kinds of UV-curable organically modified silicates have been prepared to be used as protective coatings for optical fibers. The synthesis involves the reaction of the thiol group of 3-mercaptopropyltrimethoxysilane with a C =C bond in one of the acrylic groups of three commercially available aliphatic triacrylates. The methoxysilyl groups of the synthesized diacrylate methoxysilanes were subjected to hydrolysis and condensation to form Si-O-Si units. Transparent, viscous, solvent-free resins were obtained that hardened in seconds when exposed to UV radiation. The coating derived from the reaction with glycerol propoxy triacrylate (GPTA) proved to adhere the best of the three to both plastic and glass substrates. It was then tested as a protective coating for silica fibers. Reliability tests were carried out including bending strength and fatigue tests at pH 7 and 10. The results show improved water resistance of the coated fiber in neutral conditions. INTRODUCTION Present formulations for UV-curable coatings applied to protect optical fibers consist of several components. Generally, the formulations include (1) a high viscosity reactive oligomer (epoxy acrylate, urethane acrylate, polysiloxane acrylate), (2) a reactive diluent (mono or multiacrylate monomers), (3) a photoinitiator, and (4) an adhesion promoting agent. The final properties of the cured coating such as hardness, flexibility, toughness, abrasion, optical transparency, adhesion and glass transition (Ta) are determined directly by the chemistry and composition of the liquid formulation. There are several commercially available UV-curable materials to satisfy a variety of applications. All of these materials are highly toxic in the liquid state. We are therefore investigating formulations which contain no volatile components in order to reduce the hazards related to their removal. Ideally, a coating formulation would be one component, nonvolatile, highly reactive, sufficiently viscous, with good wetting to the substrate. In addition, the resulting coating should have the desired mechanical, optical and physical properties after curing under dynamic conditions (in a high speed fiber drawing operation). We would like to be able to tailor these properties simply by controlling the synthesis parameters of this one component system. A promising class of materials for this kind of "ideal" coating is inorganic-organic hybrid materials with organics chemically linked to inorganics. In particular, organically modified silicates were investigated. In the search for new UV curable materials combining both good optical and protective properties, we synthesized three different types of diacryloalkoxysilanes. Upon hydrolysis and partial condensation of alkoxysilyl groups, they formed viscous, one component UV-curable liquids containing photoinitiator. The acrylosilicate coatings were synthesized by the method used previously by Wolter et al.1 in which 3-mercaptopropyltrimethoxysilane was coupled via its S-H group to the C =C bond of the acrylic group of aliphatic triacrylate. Three commercially available triacrylates commonly used as reactive diluents in UV curing technology were O-8194-1339-9/94/$6.OO SPIE Vol. 2074 / 13

Microhardness and Young's modulus of high burn-up UO2 fuel

Vickers microhardness (HV0.1) and Young's modulus (E) measurements of LWR UO2 fuel at burn-up > 60 GWd/tHM are presented. Their ratio HV0.1/E was found constant in the range 60-110 GWd/tHM. From the ratio and the microhardness values vs porosity, the Young's modulus dependence on porosity was derived and extended to the full radial profile, including the high burn-up structure (HBS). The dependence is well represented by a linear correlation. The data were compared to fuel performance codes correlations. A burn-up dependent factor was introduced in the Young's modulus expression. The modifications extend the experimental validation range of the TRANSURANUS correlation from unirradiated to irradiated UO2 and up to 20% porosity. First simulations of LWR fuel rod irradiations were performed in order to illustrate the impact on fuel performance. In the specific cases selected, the simulations suggest a limited effect of the Young's modulus decrease due to burn-up on integral fuel performance

Factors affecting adherence to guidelines for antithrombotic therapy in elderly patients with atrial fibrillation admitted to internal medicine wards

Current guidelines for ischemic stroke prevention in atrial fibrillation or flutter (AFF) recommend Vitamin K antagonists (VKAs) for patients at high-intermediate risk and aspirin for those at intermediate-low risk. The cost-effectiveness of these treatments was demonstrated also in elderly patients. However, there are several reports that emphasize the underuse of pharmacological prophylaxis of cardio-embolism in patients with AFF in different health care settings. AIMS: To evaluate the adherence to current guidelines on cardio-embolic prophylaxis in elderly (> 65 years old) patients admitted with an established diagnosis of AFF to the Italian internal medicine wards participating in REPOSI registry, a project on polypathologies/polytherapies stemming from the collaboration between the Italian Society of Internal Medicine and the Mario Negri Institute of Pharmacological Research; to investigate whether or not hospitalization had an impact on guidelines adherence; to test the role of possible modifiers of VKAs prescription. METHODS: We retrospectively analyzed registry data collected from January to December 2008 and assessed the prevalence of patients with AFF at admission and the prevalence of risk factors for cardio-embolism. After stratifying the patients according to their CHADS(2) score the percentage of appropriateness of antithrombotic therapy prescription was evaluated both at admission and at discharge. Univariable and multivariable logistic regression models were employed to verify whether or not socio-demographic (age >80years, living alone) and clinical features (previous or recent bleeding, cranio-facial trauma, cancer, dementia) modified the frequency and modalities of antithrombotic drugs prescription at admission and discharge. RESULTS: Among the 1332 REPOSI patients, 247 were admitted with AFF. At admission, CHADS(2) score was ≥ 2 in 68.4% of patients, at discharge in 75.9%. Among patients with AFF 26.5% at admission and 32.8% at discharge were not on any antithrombotic therapy, and 43.7% at admission and 40.9% at discharge were not taking an appropriate therapy according to the CHADS(2) score. The higher the level of cardio-embolic risk the higher was the percentage of antiplatelet- but not of VKAs-treated patients. At admission or at discharge, both at univariable and at multivariable logistic regression, only an age >80 years and a diagnosis of cancer, previous or active, had a statistically significant negative effect on VKAs prescription. Moreover, only a positive history of bleeding events (past or present) was independently associated to no VKA prescription at discharge in patients who were on VKA therapy at admission. If heparin was considered as an appropriate therapy for patients with indication for VKAs, the percentage of patients admitted or discharged on appropriate therapy became respectively 43.7% and 53.4%. CONCLUSION: Among elderly patients admitted with a diagnosis of AFF to internal medicine wards, an appropriate antithrombotic prophylaxis was taken by less than 50%, with an underuse of VKAs prescription independently of the level of cardio-embolic risk. Hospitalization did not improve the adherence to guideline