On the plastic deformation of soda-lime glass - a Cr3+ luminescence study of densification

International audienceSilicate glasses are known to experience an anomalous plastic behavior at micron-scale: 1) they exhibit densification when flowing plastically and 2) hydrostatic pressure affects the yield point. We have previously shown (A. Perriot et al. J. Am. Ceram. Soc. 89 (2006) 596) that densification maps are useful to infer a reliable constitutive law for the plastic response of silicate glasses. It is shown here that for soda-lime glass Cr3+ luminescence microspectroscopy may be used for that purpose. We also show that the constitutive law we have previously developed for amorphous silica provides a qualitative description of normal glasses although it is unable to account for the finer details. More work is needed to quantitatively model normal-glass plasticity at the continuum length-scale

Cristallochimie des éléments traces dans les phases du manteau terrestre: Applications de la spectroscopie de luminescence à haute pression et haute température.

Mémoires de Géosciences Rennes, n°84 , 241p. ISBN: 2-905532-83-1La connaissance des coefficients de partage des éléments traces à haute pression et haute température est aujourd'hui requise afin de tester les différents modèles géochimiques d'évolution du manteau terrestre. Etant données les difficultés inhérentes à l'évaluation de ces coefficients de partage lors d'expériences d'équilibre dans différentes conditions (pression, température, composition chimique, ... ), la modélisation de la distribution de ces éléments traces est nécessaire. Cependant, celle-ci passe par la compréhension des phénomènes microscopiques qui contrôlent l'incorporation de l'élément. Ce travail a porté sur la détermination des différents sites d'accueil du chrome trivalent dans des minéraux du manteau à partir de l'étude de sa luminescence. Cette spectroscopie de luminescence, mise en oeuvre à haute pression en cellule à enclumes de diamant, permet de suivre l'évolution des niveaux d'énergie du cr3+ en fonction de la pression. Nous avons ainsi acquis des données de luminescence sur plusieurs phases cristallines de basse pression (spinelles, pyroxènes, forstérite), de haute pression (grenats, ilménite, pérovskites), et sur des verres silicatés de composition chimique simple. Les résultats obtenus sur les minéraux montrent que le Cr3+ s'incorporent majoritairement dans les sites octaédriques, ,nécessitant, dans certains cas, une compensation locale des charges. Les mécanismes de substitution", mais aussi l'énergie de stabilisation de l'élément trace dans la structure, dépendent alors fortement de la nature des cations disponibles pour assurer l'équilibre électrostatique. Dans les verres, nous mettons en évidence des variations importantes de la distribution de sites d'accueil en fonction de la composition chimique. La modélisation des paramètres thermodynamiques qui participent au partage du chrome à partir de nos données de haute pression est alors discutée.No abstrac

Tropospheric Ozone Assessment Report: Present-day distribution and trends of tropospheric ozone relevant to climate and global atmospheric chemistry model evaluation

International audienceThe Tropospheric Ozone Assessment Report (TOAR) is an activity of the International Global Atmospheric Chemistry Project. This paper is a component of the report, focusing on the present-day distribution and trends of tropospheric ozone relevant to climate and global atmospheric chemistry model evaluation. Utilizing the TOAR surface ozone database, several figures present the global distribution and trends of daytime average ozone at 2702 non-urban monitoring sites, highlighting the regions and seasons of the world with the greatest ozone levels. Similarly, ozonesonde and commercial aircraft observations reveal ozone’s distribution throughout the depth of the free troposphere. Long-term surface observations are limited in their global spatial coverage, but data from remote locations indicate that ozone in the 21st century is greater than during the 1970s and 1980s. While some remote sites and many sites in the heavily polluted regions of East Asia show ozone increases since 2000, many others show decreases and there is no clear global pattern for surface ozone changes since 2000. Two new satellite products provide detailed views of ozone in the lower troposphere across East Asia and Europe, revealing the full spatial extent of the spring and summer ozone enhancements across eastern China that cannot be assessed from limited surface observations. Sufficient data are now available (ozonesondes, satellite, aircraft) across the tropics from South America eastwards to the western Pacific Ocean, to indicate a likely tropospheric column ozone increase since the 1990s. The 2014–2016 mean tropospheric ozone burden (TOB) between 60˚N–60˚S from five satellite products is 300 Tg ± 4%. While this agreement is excellent, the products differ in their quantification of TOB trends and further work is required to reconcile the differences. Satellites can now estimate ozone’s global long-wave radiative effect, but evaluation is difficult due to limited in situ observations where the radiative effect is greatest