Abstract: Metallic uranium is a fundamental raw material for producing nuclear fuel elements for research reactors and irradiation targets for producing 99Mo, as U3Si2, UMo alloy, UAlx, and uranium thin foils. Magnesiothermic reduction of UF4 is a possible route in the nuclear fuel cycle for producing uranium as a metal ingot. The main concern about the reducing scale to produce low-enriched (metallic) uranium (LEU) (around 1 kg) is the relatively low yield compared to calciothermic reduction. Nevertheless, the magnesiothermic reduction has the advantages of having lower cost and being a safer method for dealing with uranium processing. The magnesiothermic process, as a batch, is closed inside a sealed crucible. In the present study, in order to have a qualitative idea of the kinetics during the ignition moment, the slag projected over the lateral inner face of the crucible was used to sketch the general magnesiothermic evolution. The methods used were metallographic observation and X-ray diffraction followed by Rietveld refinement. The results of these analyses led to the conception of a general reaction development during the short time between the ignition of the reducing reaction and final settlement of the products. Relevant information from this study led to the conclusion that uranium is not primarily present in the lateral slag projection over the crucible during the reaction, and the temperature level may reach 1500°C or more, after the ignition.

Palavras-Chave: fissionable materials; fuel cycle; fuel cycle centers; magnesium; reduction; nuclear fuels; nuclear materials management; management; uranium; metallography; x-ray diffraction

DURAZZO, MICHELANGELO; SALIBA-SILVA, ADONIS M.; GARCIA, RAFAEL H.L.; CARVALHO, ELITA F.U. de; RIELLA, HUMBERTO G. Analysis of slag formation during UF4 magnesiothermic reduction. Nuclear Technology, v. 200, n. 2, p. 170-176, 2017. DOI: 10.1080/00295450.2017.1353870. Disponível em: http://repositorio.ipen.br/handle/123456789/28564. Acesso em: $DATA.

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Abstract: Bone fractures are a common clinical event related to trauma, aging or diseases. Since bone repair is complex, abnormal consolidation may occur or, even, non-union. Biomaterials have a key role in this context, since they can stimulate bone cell differentiation, accelerating the healing process. Bioactive glasses (BG) represent a promising class of biomaterials due to its high bioactivity and osteogenic potential. Nevertheless, the osteoconductive properties of BG may not be enough to stimulate consolidation in critical situations. Thus, it was hypothesized that enriching BG with other materials such as collagen (Col) and magnesium (Mg), trying to make a composite with similar properties to bone tissue, would constitute a more suitable graft for tissue engineering. This work aimed at obtaining BG/Col/Mg composites and evaluating their physicochemical features. Moreover, L929 and MC3T3-E1 cell culture studies were done to investigate the cytotoxicity of the composites. The results showed that Mg could be successfully introduced, at different percentages (1, 3 and 5%), into BG and BG/Col composites, improving mechanical properties and retaining the bioactivity of BG. Ca assay measurements demonstrated that reactions in the Mg/solution interface, i.e. reactions between Mg and the ions in the simulated body fluid (SBF) have led to an increased Ca uptake for compositescontaining 3 and 5% Mg compared to plain BG and BG/Col. In vitro studies showed that BG and BG/Col containing 1% of Mg were non-cytotoxic and biocompatible. This percentage of Mg is promising for forward works. Our data on the present BG/Mg and BG/Col/Mg-based composites are encouraging and may lead to further molecular and cell culture studies, and in vivo investigations to clarify the biological performance of these new biomaterials.

Palavras-Chave: skeleton; toxicity; collagen; magnesium; glass; composite materials; skeletal diseases; biological repair; biological materials

GABBAI-ARMELIN, P.R.; FERNANDES, K.R.; MAGRI, A.M.P.; SILVA, A.C. da; FORTULAN, C.A.; RENNO, A.C.M. Characterization and cytotoxicity evaluation of bio-inspired bioactive Glass/Collagen/Magnesium composites. Materials Chemistry and Physics, v. 228, p. 201-209, 2019. DOI: 10.1016/j.matchemphys.2019.02.072. Disponível em: http://repositorio.ipen.br/handle/123456789/30060. Acesso em: $DATA.

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Abstract: The calcium substitution for magnesium on fluorapatite is attractive because this element is a natural substitute in biological apatites. There are several published stoichiometries for calcium substituted by magnesium fluorapatites and most works point out that the formation and fixation of biomimetic Ca-P coatings in Ringer’s solution were strongly related to Mg2+ content and furthermore the Mg replacement improves the bioactivity of apatite. In the present study, fluorapatite (FA) and fluorapatite substituted with 6% and 7% of magnesium were obtained by deposition via sol-gel coating on substrates of AISI 316L stainless steel to investigate the effect of magnesium substitution on fluorapatite with not yet investigated stoichiometry. Characterization of coating thickness, chemical composition and crystalline structure was performed using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The coating adhesion was evaluated using the pull-out test and the corrosion resistance was undertaken using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The electrochemical results showed improvement in the corrosion resistance of magnesium-fluorapatite compared to fluorapatite coated on AISI 316L stainless steel substrates. The improvement corrosion protection and adhesion performance indicate that such magnesium fluorapatites coatings are very interesting candidates as bioactive coatings for implants.

Palavras-Chave: stoichiometry; apatites; biological materials; implants; magnesium; coatings; hydroxides; sol-gel process; corrosion

FERREIRA JUNIOR, J.M.; RAJENDRAN, V.; SIMONELLI, G.; SILVA, A.C.M.; SANTOS, L.C.L.; MATTEDI, S.; PONTES, L.A.M.; COSTA, I.; ROSSI, J.L.; BAKER, M.A. Deposition and characterization of a sol-gel Mg-substituted fluorapatite coating with new stoichiometries. Applied Surface Science, v. 505, p. 1-13, 2020. DOI: 10.1016/j.apsusc.2019.144393. Disponível em: http://repositorio.ipen.br/handle/123456789/31080. Acesso em: $DATA.

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Abstract: The present work describes the optically stimulated luminescence (OSL) of a tissue equivalent crystal, the magnesium tetraborate, doped with dysprosium or cerium and co-doped with lithium due to the lack of materials with characteristics suitable for several dosimetric applications. In the present work, MgB4O7:Dy,Li and MgB4O7:Ce,Li were characterized through their OSL and radioluminescence emissions. Our results indicate that MgB4O7:Ce,Li has a strong emission peaked at 420 nm that is connected to the Ce3+ electronic transitions, while the emission of MgB4O7:Dy,Li has several peaks connected to the Dy3+ transitions. The OSL decay curves from both materials are composed by two components: a slow one and a fast one. MgB4O7:Ce,Li is 10 times more sensitive than MgB4O7:Dy,Li, especially due to the wavelengths of the emission peaks. The dose response for both materials were sublinear from 0.2 Gy to 100 Gy, for MgB4O7:Ce,Li, and from 0.2 Gy to 40 Gy, for the MgB4O7:Dy,Li. The OSL signal from MgB4O7:Ce,Li showed good stability over 40 days (with a fading < 1%), while MgB4O7:Dy,Li presented a complete fading of the signal after 40 days. These results suggest a clear potential of MgB4O7:Ce,Li for radiation dosimetry purposes using OSL technique.

Palavras-Chave: luminescence; optical activity; magnesium; borates; dysprosium; cerium; doped materials; lithium; dosimetry; radioluminescence

SOUZA, L.F.; SILVA, A.M.B.; ANTONIO, P.L.; CALDAS, L.V.E.; SOUZA, S.O.; DERRICO, F.; SOUZA, D.N. Dosimetric properties of MgB4O7:Dy,Li and MgB4O7:Ce,Li for optically stimulated luminescence applications. Radiation Measurements, v. 106, p. 196-199, 2017. DOI: 10.1016/j.radmeas.2017.02.009. Disponível em: http://repositorio.ipen.br/handle/123456789/27361. Acesso em: $DATA.

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Abstract: Hypereutectic Al-Si alloys can be used in applications that require high wear resistance. Such wear resistance is achieved by the presence of hard primary silicon particles, allied to the formation of Mg2Si intermetallic phase when magnesium is added in this alloy. Centrifugal casting generates a gradient in the microstructure of hypereutectic Al-Si alloys that can favor such applications. Cylindrical components of Al-19%Si alloy containing added copper and magnesium contents were processed by centrifugal casting. The purpose of this study is to investigate the formation and segregation of particles of primary silicon (β) and Mg2Si in Al-19%Si alloy containing additions of copper and magnesium. Because the density of silicon (2.33 g/cm3) and Mg2Si (1.88 g/cm3) is lower than that of aluminum (2.67 g/cm3), centrifugal casting causes primary silicon (β) and Mg2Si particles to concentrate more at the outer wall of the centrifuged pipe. In this study, primary silicon (β) and Mg2Si particles were found to be retained at the outer wall of the pipe. It is believed that the rapid cooling of the molten metal in the region of contact with the mold, whose temperature is lower than that of the molten metal, allied to the centrifugal force, prevented the particles from migrating to the inner wall of the pipe. The microstructure shows a gradient in the distribution of these phases, enabling the production of a functionally graded material. The addition of copper and magnesium leads to the formation of Mg2Si and Al5Cu2Mg8Si6 phases, reducing the amount of primary β phase (Si) particles. In all the evaluated conditions, a tendency is also observed for a gradual increase in the segregation of silicon towards the inner wall along the entire length of the centrifuged pipe.

Palavras-Chave: aluminium alloys; silicon alloys; wear resistance; copper; magnesium; casting; microstructure

CONTATORI, CHESTER; COUTO, ANTONIO A.; VATAVUK, JAN; BORGES, ARNALDO A.C.; LIMA, NELSON B. de; BALDAN, RENATO. Effect of copper and magnesium on the microstructure of centrifugally cast Al-19%Si alloys. Materials Science Forum, v. 930, p. 484-488, 2018. DOI: 10.4028/www.scientific.net/MSF.930.484. Disponível em: http://repositorio.ipen.br/handle/123456789/29286. Acesso em: $DATA.

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Abstract: The 6061 Al–Mg–Si alloy is used in nuclear fuel plates of nuclear research reactors which are fed with fuel in plate shapes. The production of these plates is based on the picture frame technique (PFT). The picture frame technique (PFT) is a manufacturing process for the fabrication of nuclear fuel plates where the nuclear fuel is encapsulated by Al alloy plates and thermomechanically processed to generate a set with reduced thickness. The effects of PFT on the corrosion resistance of the 6061 aluminum alloy were evaluated in this study by immersion and electrochemical tests in 0.005 mol L−1 NaCl solution. The results showed that the PFT fabrication process increases the corrosion resistance of the 6061 alloy in relation to the conventional 6061-T6, due phase dissolution and lower content of β’’ phase. Also, corrosion propagation gradually changes, with an increasing number of processing steps, from intergranular to intragranular corrosion attack.

Palavras-Chave: aluminium alloys; corrosion; fuel elements; pitting corrosion; differential thermal analysis; magnesium; silica; fuel plates

MILAGRE, MARIANA X.; DONATUS, UYIME; MOGILI, NAGA V.; MACHADO, CARULINE S.C.; ARAUJO, JOAO V.S.; KLUMPP, RAFAEL E.; FERNANDES, STELA M.C.; SOUZA, JOSE A.B. de; COSTA, ISOLDA. Effects of Picture Frame Technique (PFT) on the corrosion behavior of 6061 aluminum alloy. Journal of Nuclear Materials, v. 539, p. 1-13, 2020. DOI: 10.1016/j.jnucmat.2020.152320. Disponível em: http://200.136.52.105/handle/123456789/31618. Acesso em: $DATA.

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