New WC-Cu thermal barriers for fusion applications: high temperature mechanical behaviour

ABSTRACT: The combination of tungsten carbide and copper as a thermal barrier could effectively reduce the thermal mismatch between tungsten and copper alloy, which are proposed as base armour and heat sink, respectively, in the divertor of future fusion reactors. Furthermore, since the optimum operating temperature windows for these divertor materials do not overlap, a compatible thermal barrier interlayer between them is required to guarantee a smooth thermal transition, which in addition may mitigate radiation damage. The aim of this work is to study the thermo-mechanical properties of WC-Cu cermets fabricated by hot pressing. Focus is placed on the temperature effect and composition dependence, as the volume fraction of copper varies from 25 to 50 and 75 vol%. To explore this behaviour, fracture experiments are performed within a temperature range from room temperature to 800 degrees C under vacuum. In addition, elastic modulus and thermal expansion coefficient are estimated from these tests. Results reveal a strong dependence of the performance on temperature and on the volume fraction of copper and, surprisingly, a slight percent of Cu (25 vol%) can effectively reduce the large difference in thermal expansion between tungsten and copper alloy, which is a critical point for in service applications. The thermal performance of these materials, together with their mechanical properties could indeed reduce the heat transfer from the PFM to the underlying element while supporting the high thermal stresses of the joint. Thus, the presence of these cermets could allow the reactor to operate above the ductile to brittle transition temperature of tungsten, without compromising the underlying materials.info:eu-repo/semantics/publishedVersio

Behavior of Cu-Y2O3 and CuCrZr-Y2O3 composites before and after irradiation

ABSTRACT: The Cu-Y2O3 and CuCrZr-Y2O3 materials have been devised as thermal barriers in nuclear fusion reactors. It is expected that in the nuclear environments, the materials should be working on extreme conditions of irradiation. In this work the Cu-Y2O3 and CuCrZr-Y2O3 were prepared and then irradiated in order to understand the surface irradiation resistance of the material. The composites were prepared in a glove box and consolidated with spark plasma sintering. The microstructures revealed regions of Y2O3 dispersion and Y2O3 agglomerates both in the Cu matrix and in the CuCrZr. The irradiated samples did not show any surface modification indicating that the materials seem to be irradiation resistant in the present situation. The thermal conductivity values for all the samples measured are lower than pure Cu and higher than pure W, however are higher than those expected, and therefore, the application of these materials as thermal barriers is compromised.info:eu-repo/semantics/publishedVersio

WC-Cu thermal barriers for fusion applications

ABSTRACT: WC-Cu cermets have been devised for thermal barriers between the plasma facing tungsten tiles and the copperbased heat sink in the first wall of nuclear fusion reactors. Composite materials with 50 and 75 v/v% WC have been prepared by hot pressing at 1333 and 1423 K with pressures of 37 and 47 MPa, respectively. Microstructural changes have been investigated by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction. The materials consolidated have also been evaluated in terms of Archimedes' density, thermal diffusivity, Vickers hardness and elastic modulus. Implantation was carried out at room temperature with Ar+ at 100 keV ion beam with a fluence of 4 · 1020 at/m2. The materials consisted of homogeneous dispersions of WC particles in a Cu matrix and presented densifications of about 90%. Incipient swelling in copper-rich regions have been observed on the implanted surfaces, however no significant changes have been detected by X-ray diffraction. Higher WC content in the cermet materials increased hardness and the elastic modulus. The cermets' thermal diffusivity was significantly lower than that of pure copper or tungsten, as desirable for a thermal barrier.info:eu-repo/semantics/acceptedVersio

Improvement of Mechanical Properties with Non-Equimolar CrNbTaVW High Entropy Alloy

ABSTRACT: CrNbTaVWx with (x = 1 and 1.7) high entropy alloys have been devised for thermal barriers between the plasma-facing tungsten tiles and the copper-based heat sink in the first wall of fusion nuclear reactors. These novel materials were prepared by ball milling and consolidated by Upgrade Field Assisted Sintering Technology at 1873 K under an applied pressure of 90 MPa for 10 min. In this work, the structural and mechanical properties of these materials were evaluated. Consolidated samples presented a major phase with a bcc-type structure with lattice parameter value of 0.316 nm for CrNbTaVW and CrNbTaVW1.7 compositions. Moreover, observation of the microstructures evidences also two minor phases: Ta-Nb-Cr and Ta-V rich (in which carbon is detected). Despite the similarity in the structural properties of these two alloys, their mechanical properties are distinct. The flexural stress for the sample with higher amount of W (CrNbTaVW1.7) is higher by 50% in the 298-873 K range, with an increased strain to fracture, which can be associated with reduced brittleness caused by the additional W incorporation.info:eu-repo/semantics/publishedVersio

Role of beta-stabilizing elements on the microstructure and mechanical properties evolution of modified PM Ti surfaces designed for biomedical applications

Invited keynotes paper from EUROPM2017, Milan.This work focuses on the evaluation of modified surfaces on Ti produced by powder metallurgy. These newly designed surface modifications are achieved by deposition and diffusion of a stable aqueous suspension prepared in one case from micro-sized Nb powder (Ti beta-stabilizer element) and in another case from Nb plus the addition of ammonium chloride, NH4Cl, (thermo-reactive diffusion process). Different design parameters such as diffusion element (Nb or Mo), state of the Ti substrate (green or sintered) and the treatment process (diffusion or thermo-reactive diffusion) lead to all the surface-modified materials, GreenTi-Nb, SintTi-Nb and Ti-Nb-NH4Cl, GreenTi-Mo, SintTi-Mo and Ti-Mo-NH4Cl. The modified Ti surfaces present a gradient in composition and microstructure (beta / alpha+beta / alpha phases) resulting in an improvement in some of their mechanical properties: (1) higher micro-hardness in all the modified materials and (2) lower elastic modulus (more similar to that of the human bone) in those without NH4Cl.The authors would like to thank the funding provided for this research by the Regional Government of Madrid (program MULTIMAT-CHALLENGE-CM, ref. S2013/MIT- 2862), and by the Ministry of Economy and Competitiveness of Spain (program MINECO, ref. PCIN-2016-123 and Ramón y Cajal contract RYC-2014-15014)

Variación de 13C en el ambiente de Madrid (atmósfera, aguas superficiales y aguas subterráneas)

Stable isotopes of carbon are studied in atmosphere, freshwater (rivers) and groundwater of the region of Madrid. Sampling and analytical techniques are adapted for the isotopic study of carbon in the environment. The atmosphere samples show δ13C values from -13.92 to -15.67 ‰, closely related to the polution level of air. The water from wells, to the Tertiary detritic aquifer, with δ13C among -13.92 and -15.67 ‰. The dissolution of carbonatic rocks and the biologic activity could be the origin of the wide variations δ13C from -7.07 to -11.85 %0) found in the waters from rivers Jarama, Guadalix and Guadarrama.Se analizan el 13C de la atmósfera, ríos y pozos del área de Madrid, al objeto de evaluar su distribución y origen, mediante adaptación y desarrollo de técnicas de muestreo y análisis. Las muestras atmosféricas presentan valores de δ13C situados entre -9,81 y -14,64 ‰, que se corresponden gradualmente con los puntos de menor a mayor grado de polución por aportes principalmente de C02 procedente de la quema de combustibles fósiles. Las aguas de los pozos analizados, pertenecientes al acuífero terciario del detrítico, muestran un estrecho margen de variación, entre δ13C -13,92 y -15,67 ‰, relacionado con los procesos geoquímicos naturales. Las aguas de los ríos Jarama, Guadalix y Guadarrama, presentan una amplia variación en su composición isotópica (δ13C entre -7,07 y -11,85 ‰) debido a la disolución de carbonatos a su paso por las formaciones de calizas del Mesozoico y, en menor medida, a los aportes de efluentes contaminados

Inhibition of Akt sensitises neuroblastoma cells to gold(III) porphyrin 1a, a novel antitumour drug induced apoptosis and growth inhibition

Background:Gold(III) porphyrin 1a is a new class of anticancer drug, which inhibits cell proliferation of wide range of human cancer cell lines and induces apoptosis in human nasopharyngeal carcinoma cells. However, the underlying signalling mechanism by which gold(III) porphyrin 1a modifies the intracellular apoptosis pathways in tumour cells has not been explained in detail in neuroblastoma cells.Methods:Cell proliferation and apoptosis were determined by measuring 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Annexin V binding, respectively. Western blot assay was used to detect proteins involved in apoptotic and Akt pathways. In vivo tumour growth was assessed by inoculating tumour cells to nude mice subcutaneously, and gold(III) porphyrin 1a was administrated intravenously.Results:This study assessed the antitumour effect and mechanism of gold(III) porphyrin 1a on neuroblastoma in vitro and in vivo. Gold(III) porphyrin 1a displayed a growth inhibition and induction of apoptosis in neuroblastoma cells effectively in vitro, which was accompanied with release of cytochrome c and Smac/DIABLO and caspases activation. Further studies indicated that gold(III) porphyrin 1a inhibited X-linked inhibitor of apoptosis (XIAP). However, we found that gold(III) porphyrin 1a can induce a survival signal, Akt activation within minutes and could last for at least 24 h. To further confirm association between activation of Akt and the effectiveness of gold(III) porphyrin 1a, neuroblastoma cells were treated with API-2, an Akt-specific inhibitor. API-2 sensitised cells to gold(III) porphyrin 1a-induced apoptosis and growth inhibition.Conclusion:These results suggested that Akt may be considered as a molecular brake that neuroblastoma cells rely on to slow down gold(III) porphyrin 1a-induced apoptosis and antiproliferation. Gold(III) porphyrin 1a is a mitochondrial apoptotic stimulus but also activates Akt, suggesting an involvement of Akt in mediating the effectiveness to growth inhibition and apoptosis by gold(III) porphyrin 1a and that inhibition of Akt can enhance the anticancer activity of gold(III) porphyrin 1a in neuroblastoma. © 2009 Cancer Research UK.published_or_final_versio

Mechanisms of hypoxic up-regulation of versican gene expression in macrophages

Hypoxia is a hallmark of many pathological tissues. Macrophages accumulate in hypoxic sites and up-regulate a range of hypoxia-inducible genes. The matrix proteoglycan versican has been identified as one such gene, but the mechanisms responsible for hypoxic induction are not fully characterised. Here we investigate the up-regulation of versican by hypoxia in primary human monocyte-derived macrophages (HMDM), and, intriguingly, show that versican mRNA is up-regulated much more highly (>600 fold) by long term hypoxia (5 days) than by 1 day of hypoxia (48 fold). We report that versican mRNA decay rates are not affected by hypoxia, demonstrating that hypoxic induction of versican mRNA is mediated by increased transcription. Deletion analysis of the promoter identified two regions required for high level promoter activity of luciferase reporter constructs in human macrophages. The hypoxia-inducible transcription factor HIF-1 has previously been implicated as a key potential regulator of versican expression in hypoxia, however our data suggest that HIF-1 up-regulation is unlikely to be principally responsible for the high levels of induction observed in HMDM. Treatment of HMDM with two distinct specific inhibitors of Phosphoinositide 3-kinase (PI3K), LY290042 and wortmannin, significantly reduced induction of versican mRNA by hypoxia and provides evidence of a role for PI3K in hypoxic up-regulation of versican expression