Dataset Information

Prediction of Mechanical Twinning in Magnesium Silicate Post-Perovskite.

ABSTRACT: The plastic properties of MgSiO₃ post-perovskite are considered to be one of the key issues necessary for understanding the seismic anisotropy at the bottom of the mantle in the so-called D" layer. Although plastic slip in MgSiO₃ post-perovskite has attracted considerable attention, the twinning mechanism has not been addressed, despite some experimental evidence from low-pressure analogues. On the basis of a numerical mechanical model, we present a twin nucleation model for post-perovskite involving the emission of 1/6 <110> partial dislocations. Relying on first-principles calculations with no adjustable parameters, we show that {110} twin wall formation resulting from the interaction of multiple twin dislocations occurs at a twinning stress comparable in magnitude to the most readily occurring slip system in post-perovskite. Because dislocation activities and twinning are competitive strain-producing mechanisms, twinning should be considered in future models of crystallographic preferred orientations in post-perovskite to better interpret seismic anisotropy in the lowermost lower mantle.

SUBMITTER: Carrez P

PROVIDER: S-EPMC5732224 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature

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Prediction of Mechanical Twinning in Magnesium Silicate Post-Perovskite.

Carrez Philippe P Goryaeva Alexandra M AM Cordier Patrick P

Scientific reports 20171215 1

The plastic properties of MgSiO<sub>3</sub> post-perovskite are considered to be one of the key issues necessary for understanding the seismic anisotropy at the bottom of the mantle in the so-called D" layer. Although plastic slip in MgSiO<sub>3</sub> post-perovskite has attracted considerable attention, the twinning mechanism has not been addressed, despite some experimental evidence from low-pressure analogues. On the basis of a numerical mechanical model, we present a twin nucleation model fo ...[more]

PMID: 29247231

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Project description:The EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) provides a scientific opinion re-evaluating the safety of calcium silicate (E 552), magnesium silicate (E 553a) and talc (E 553b) when used as food additives. In 1991, the Scientific Committee on Food (SCF) established a group acceptable daily intake (ADI) 'not specified' for silicon dioxide and silicates. The EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) recently provided a scientific opinion re-evaluating the safety of silicon dioxide (E 551) when used as a food additive. The Panel noted that the absorption of silicates and talc was very low; there was no indication for genotoxicity or developmental toxicity for calcium and magnesium silicate and talc; and no confirmed cases of kidney effects have been found in the EudraVigilance database despite the wide and long-term use of high doses of magnesium trisilicate up to 4 g/person per day over decades. However, the Panel considered that accumulation of silicon from calcium silicate in the kidney and liver was reported in rats, and reliable data on subchronic and chronic toxicity, carcinogenicity and reproductive toxicity of silicates and talc were lacking. Therefore, the Panel concluded that the safety of calcium silicate (E 552), magnesium silicate (E 553a(i)), magnesium trisilicate (E 553a(ii)) and talc (E 553b) when used as food additives cannot be assessed. The Panel considered that there is no mechanistic rationale for a group ADI for silicates and silicon dioxide and the group ADI established by the SCF is obsolete. Based on the food supplement scenario considered as the most representative for risk characterisation, exposure to silicates (E 552-553) for all population groups was below the maximum daily dose of magnesium trisilicate used as an antacid (4 g/person per day). The Panel noted that there were a number of approaches, which could decrease the uncertainties in the current toxicological database. These approaches include - but are not limited to - toxicological studies as recommended for a Tier 1 approach as described in the EFSA Guidance for the submission of food additives and conducted with an adequately characterised material. Some recommendations for the revision of the EU specifications were proposed by the Panel.

Dataset Information

Prediction of Mechanical Twinning in Magnesium Silicate Post-Perovskite.

Publications

Prediction of Mechanical Twinning in Magnesium Silicate Post-Perovskite.

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