Comparison of chemical and physical activation processes at obtaining adsorbents from moroccan oil shale

Within the Moroccan natural resources valorisation scheme, new adsorbents have been prepared from oil shale by chemical and physical activation processes. The activation process the authors have developed in this study give effective adsorbent materials. In view of the physico-chemical properties of these materials and application to the treatment of water loaded with a metal (Cr6+ ion) or organic (methylene blue (MB)) pollutant, it is concluded that the chemical activation process of oil shale at low temperature (250 °C) affords the best material. The material’s yield is good in comparison with the physical activation at the same temperature and the process is energy saving differently from that at 450 °C. Moreover, the chemical activation of oil shale with phosphoric acid at 250 °C produces a material with a good yield (about 70%), a high specific surface area (approximately 600 m2 /g) and a highly porous structure, which gives it a high retention of methylene blue and the Cr6+ ion

Constraints on the structure and seasonal variations of Triton's atmosphere from the 5 October 2017 stellar occultation and previous observations

Context. A stellar occultation by Neptune's main satellite, Triton, was observed on 5 October 2017 from Europe, North Africa, and the USA. We derived 90 light curves from this event, 42 of which yielded a central flash detection. Aims. We aimed at constraining Triton's atmospheric structure and the seasonal variations of its atmospheric pressure since the Voyager 2 epoch (1989). We also derived the shape of the lower atmosphere from central flash analysis. Methods. We used Abel inversions and direct ray-tracing code to provide the density, pressure, and temperature profiles in the altitude range similar to 8 km to similar to 190 km, corresponding to pressure levels from 9 mu bar down to a few nanobars. Results. (i) A pressure of 1.18 +/- 0.03 mu bar is found at a reference radius of 1400 km (47 km altitude). (ii) A new analysis of the Voyager 2 radio science occultation shows that this is consistent with an extrapolation of pressure down to the surface pressure obtained in 1989. (iii) A survey of occultations obtained between 1989 and 2017 suggests that an enhancement in surface pressure as reported during the 1990s might be real, but debatable, due to very few high S/N light curves and data accessible for reanalysis. The volatile transport model analysed supports a moderate increase in surface pressure, with a maximum value around 2005-2015 no higher than 23 mu bar. The pressures observed in 1995-1997 and 2017 appear mutually inconsistent with the volatile transport model presented here. (iv) The central flash structure does not show evidence of an atmospheric distortion. We find an upper limit of 0.0011 for the apparent oblateness of the atmosphere near the 8 km altitude.J.M.O. acknowledges financial support from the Portuguese Foundation for Science and Technology (FCT) and the European Social Fund (ESF) through the PhD grant SFRH/BD/131700/2017. The work leading to these results has received funding from the European Research Council under the European Community's H2020 2014-2021 ERC grant Agreement nffi 669416 "Lucky Star". We thank S. Para who supported some travels to observe the 5 October 2017 occultation. T.B. was supported for this research by an appointment to the National Aeronautics and Space Administration (NASA) Post-Doctoral Program at the Ames Research Center administered by Universities Space Research Association (USRA) through a contract with NASA. We acknowledge useful exchanges with Mark Gurwell on the ALMA CO observations. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium).Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. J.L.O., P.S.-S., N.M. and R.D. acknowledge financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709), they also acknowledge the financial support by the Spanish grant AYA-2017-84637-R and the Proyecto de Excelencia de la Junta de Andalucia J.A. 2012-FQM1776. The research leading to these results has received funding from the European Union's Horizon 2020 Research and Innovation Programme, under Grant Agreement no. 687378, as part of the project "Small Bodies Near and Far" (SBNAF). P.S.-S. acknowledges financial support by the Spanish grant AYA-RTI2018-098657-J-I00 "LEO-SBNAF". The work was partially based on observations made at the Laboratorio Nacional de Astrofisica (LNA), Itajuba-MG, Brazil. The following authors acknowledge the respective CNPq grants: F.B.-R. 309578/2017-5; R.V.-M. 304544/2017-5, 401903/2016-8; J.I.B.C. 308150/2016-3 and 305917/2019-6; M.A. 427700/20183, 310683/2017-3, 473002/2013-2. This study was financed in part by the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior -Brasil (CAPES) -Finance Code 001 and the National Institute of Science and Technology of the e-Universe project (INCT do e-Universo, CNPq grant 465376/2014-2). G.B.R. acknowledges CAPES-FAPERJ/PAPDRJ grant E26/203.173/2016 and CAPES-PRINT/UNESP grant 88887.571156/2020-00, M.A. FAPERJ grant E26/111.488/2013 and A.R.G.Jr. FAPESP grant 2018/11239-8. B.E.M. thanks CNPq 150612/2020-6 and CAPES/Cofecub-394/2016-05 grants. Part of the photometric data used in this study were collected in the frame of the photometric observations with the robotic and remotely controlled telescope at the University of Athens Observatory (UOAO; Gazeas 2016). The 2.3 m Aristarchos telescope is operated on Helmos Observatory by the Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing of the National Observatory of Athens. Observations with the 2.3 m Aristarchos telescope were carried out under OPTICON programme. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 730890. This material reflects only the authors views and the Commission is not liable for any use that may be made of the information contained therein. The 1. 2m Kryoneri telescope is operated by the Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing of the National Observatory of Athens. The Astronomical Observatory of the Autonomous Region of the Aosta Valley (OAVdA) is managed by the Fondazione Clement Fillietroz-ONLUS, which is supported by the Regional Government of the Aosta Valley, the Town Municipality of Nus and the "Unite des Communes valdotaines Mont-Emilius". The 0.81 m Main Telescope at the OAVdA was upgraded thanks to a Shoemaker NEO Grant 2013 from The Planetary Society. D.C. and J.M.C. acknowledge funds from a 2017 'Research and Education' grant from Fondazione CRT-Cassa di Risparmio di Torino. P.M. acknowledges support from the Portuguese Fundacao para a Ciencia e a Tecnologia ref. PTDC/FISAST/29942/2017 through national funds and by FEDER through COMPETE 2020 (ref. POCI010145 FEDER007672). F.J. acknowledges Jean Luc Plouvier for his help. S.J.F. and C.A. would like to thank the UCL student support observers: Helen Dai, Elise Darragh-Ford, Ross Dobson, Max Hipperson, Edward Kerr-Dineen, Isaac Langley, Emese Meder, Roman Gerasimov, Javier Sanjuan, and Manasvee Saraf. We are grateful to the CAHA, OSN and La Hita Observatory staffs. This research is partially based on observations collected at Centro Astronomico HispanoAleman (CAHA) at Calar Alto, operated jointly by Junta de Andalucia and Consejo Superior de Investigaciones Cientificas (IAA-CSIC). This research was also partially based on observation carried out at the Observatorio de Sierra Nevada (OSN) operated by Instituto de Astrofisica de Andalucia (CSIC). This article is also based on observations made with the Liverpool Telescope operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. Partially based on observations made with the Tx40 and Excalibur telescopes at the Observatorio Astrofisico de Javalambre in Teruel, a Spanish Infraestructura Cientifico-Tecnica Singular (ICTS) owned, managed and operated by the Centro de Estudios de Fisica del Cosmos de Aragon (CEFCA). Tx40 and Excalibur are funded with the Fondos de Inversiones de Teruel (FITE). A.R.R. would like to thank Gustavo Roman for the mechanical adaptation of the camera to the telescope to allow for the observation to be recorded. R.H., J.F.R., S.P.H. and A.S.L. have been supported by the Spanish projects AYA2015-65041P and PID2019-109467GB-100 (MINECO/FEDER, UE) and Grupos Gobierno Vasco IT1366-19. Our great thanks to Omar Hila and their collaborators in Atlas Golf Marrakech Observatory for providing access to the T60cm telescope. TRAPPIST is a project funded by the Belgian Fonds (National) de la Recherche Scientifique (F.R.S.-FNRS) under grant PDR T.0120.21. TRAPPIST-North is a project funded by the University of Liege, and performed in collaboration with Cadi Ayyad University of Marrakesh. E.J. is a FNRS Senior Research Associate

Effect of microstructure and chemical composition on subcritical crack growth in SiC-based fiber tows

SiC-based fibers, a key component for the reinforcement of thermostructural ceramic matrix composites, are subjected to subcritical crack growth (SCG) causing their delayed failure. Stress exponents <10 were reported for various fiber types, standing out from other types of ceramic or glass. The continuum of silicon oxycarbide (SiCO) and carbon free phases is suspected to govern the environmentally assisted crack growth phenomenon, highlighted by relationships between SCG parameters and oxygen or carbon free contents. Metallic heteroelements (Ti or Zr, found in Tyranno® fibers) play a critical role on this sensitivity as well. The existence of 2 distinct groups of fiber types, possibly associated to different SCG mechanisms, is discussed

Self-organized nano-scale multilayer coating on SiC fibers obtained by phosphating

Ceramic matrix composites (CMC) combine refractory and structural properties, with a damage-tolerant behavior ensured by an interphase material, usually deposited on fibers. Unfortunately, surface deposition does not prevent contacts between fibers, which are responsible for the premature collective failure of fiber clusters and therefore for limited lifetime. Recently, a workaround has been proposed by transforming the surface of the fibers itself into a continuous monolayer coating. Here we describe an SiC fiber etching process by phosphoric acid vapors at atmospheric pressure and intermediate temperature (600–700 °C), leading to an in situ multilayer transformation into a (carbon/silicophosphate)n coating, n ranging from unity to tens and layers thickness from 100 to 300 nm. The carbon layers are micro/mesoporous carbide-derived carbon (CDC) tubes with micrometric radii. This one-step etching process gives opportunity to create layered materials containing CDC even on complex geometries such as fabrics

Dataset on fractographic analysis of various SiC-based fibers

International audienceThis data article reports a systematic fractographic analysis of SiC-based filaments aiming at stress intensity factors assessment. A total of 11 fiber types (as-received or chlorinated Nicalon® and Tyranno® of all three generations) where therefore repeatedly tensile tested to generate the fracture surfaces. The tensile strengths were found to be independent to defect location (surface or internal). The well-known linear square root dependence of strength on mirror, mist or hackle outer radius was reaffirmed. These measurements reveal some residual tensile stresses on Nicalon® fibers, statement however questioned by the broad data scattering. Moreover, it is shown the surface etching treatment didn't affected (generating or releasing) such residual stress. A null y-intercept was consequently adopted to assess the characteristic stress intensity factors (KIC, mirror, mist or hackle constants). The toughness (KIC) estimated this way ranges from 1.0 to 1.9 MPa m1/2 and shows a clear dependency to substrate composition: higher values were extracted on oxygen-free fibers. The Am/KIC ratio, estimated to equal 1.8 and independent to substrate type, is a key parameter that would assist further fractographic investigations

New insight into subcritical rupture of SiC-based filaments at intermediate temperatures (400–900 °C) under air

The delayed failure of SiC fibrous reinforcement has continuously been investigated to warrant the long term performances of Ceramic Matrix Composite (CMC). Chiefly assessed on multifilament tow samples to alleviate some handling difficulties, subcritical crack growth (SCG) parameters are however ruled by structural artifacts which hinder the identification of intrinsic filament behavior. In this paper, we propose to estimate the true filament parameters for 5 fiber types from bundle behavior using a recently communicated Monte Carlo algorithm integrating flaw and stress distributions through a deterministic fracture mechanics law under Paris’ formulation. So computed tow lifetime are broadly dispersed, encompassing raw data, and show a structure-dependent scale effect, revealed by nfilament>ntow where n is the stress exponent. The relationship between SCG coefficient and chemical composition of the substrate is discussed and highlights the major effect of doping elements (Ti or Zr), oxygen or hydrogen content

Predicting the failure by slow crack growth of SiC-based multifilament tows: Batch-to-batch discrepancies as linked to fiber slack

This work investigates the scale effect observed on slow crack growth parameters for SiC-based fibers (Nicalon® and Tyranno® ZMI) and how it can be affected by the variability from a batch of tow to another one. A 10% difference on the stress exponents (nt) was numerically estimated using a dedicated Monte Carlo simulation. This effect is however marginal when compared to the lifetime scatter itself. This partly originates from the fiber slack in used tow specimen, assessed by tensile test completing the experimental work. The number of tensile tests to be performed is discussed. Specimen gauge length is an additional and significant source of discrepancies affecting the fiber alignment and subsequently the tow stress exponent

Dataset on fractographic analysis of various SiC-based fibers

International audienceThis data article reports a systematic fractographic analysis of SiC-based filaments aiming at stress intensity factors assessment. A total of 11 fiber types (as-received or chlorinated Nicalon® and Tyranno® of all three generations) where therefore repeatedly tensile tested to generate the fracture surfaces. The tensile strengths were found to be independent to defect location (surface or internal). The well-known linear square root dependence of strength on mirror, mist or hackle outer radius was reaffirmed. These measurements reveal some residual tensile stresses on Nicalon® fibers, statement however questioned by the broad data scattering. Moreover, it is shown the surface etching treatment didn't affected (generating or releasing) such residual stress. A null y-intercept was consequently adopted to assess the characteristic stress intensity factors (KIC, mirror, mist or hackle constants). The toughness (KIC) estimated this way ranges from 1.0 to 1.9 MPa m1/2 and shows a clear dependency to substrate composition: higher values were extracted on oxygen-free fibers. The Am/KIC ratio, estimated to equal 1.8 and independent to substrate type, is a key parameter that would assist further fractographic investigations

Delayed failure under static fatigue of Hi-Nicalon bundles: The role of stress dispersion on scale effect

SiC-fibers are subjected to a predictable premature failure, consequence of a slow crack growth mechanism. This has chiefly been studied through static fatigue testing of multifilament tows. The discrepancy existing between experimental results, broadly dispersed, and the bundle theory (solely considering the filament strength distribution) has been interpreted by discrete stochastic phenomena. In this work, the uncertainty on applied stress caused by fiber misalignment (slack) was rather investigated through Monte Carlo simulation, ascribing to each filament of the tow a strength and a stress among established distributions. If a coherent lifetime range could this way be obtained, a scale effect on stress exponent was also revealed: equal to 12.6 on filament it falls to 8.4 on bundle, in agreement with experimental results. The same would apply to larger scale (woven tow).Graphical abstract - Download full-size image : https://ars.els-cdn.com/content/image/1-s2.0-S0167577X21005024-ga1.jp

Delayed failure prediction of SiC-based bundles: The impact of sampling size

The present paper deals with sampling size related uncertainties for the delayed failure of SiC-based bundles under static fatigue condition. It is shown that 75 tests are required to assess the median lifetime with a 20% error at a given stress/temperature. Extending this work at different stress highlights the error on prediction parameters (classical power law model) for different testing strategies: stress scanning with little repetition or conversely extensive repetition at few stresses. It is shown, for a fixed total number of tests, a mixed approach (inconstant number of repetition) should be preferred to reduce the error