Hydroxyde d'aluminium

Résumé

L'hydroxyde d'aluminium, de formule chimique , est la forme la plus stable de l'aluminium dans les conditions normales de température et de pression. L'oxyhydroxyde d'aluminium AlO(OH) et l'alumine ne diffèrent de l'hydroxyde d'aluminium que par la perte d'une ou plusieurs molécules d'eau. L'aluminium possède le même degré d'oxydation dans ces trois composés, qui constituent à eux trois la majeure partie du minerai d'aluminium, la bauxite. Il existe dans la nature plusieurs minéraux de composition : la gibbsite, la bayérite, la doyleite et la nordstrandite, dont le plus courant est la gibbsite. Propriétés chimiques La nature chimique exacte de l'hydroxyde d'aluminium est controversée. La représentation Al(OH)3, constituée d'un ion Al3+ lié à trois ions OH−, est très simplifiée, et le composé est généralement plus ou moins hydraté. Une représentation plus rigoureuse serait donc Al2O3.xH2O pour les trois oxydes/hydroxydes. L'hydroxyde d'aluminium est amphotère (il peut a

Source officielle

https://fr.wikipedia.org/wiki/Hydroxyde_d'aluminium

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molybdenum atomic-doping on bio-waste derived nitrogen-doped conductive carbon electrocatalyst was synthesized and investigated for the dinitrogen reduction to ammonia in alkaline media. The assessment of the catalytic activity was found to be non-trivial as nearly any external source can be the cause of ammonia contamination. In a closed-cell set-up using isotopically labelled 15N2 as feed gas for 48h chronoamperometry at -0.1 V vs RHE that the current density was correlated to the availability of the gas. Non-precious metals were incorporated in an oxidized carbon black conductive matrix and investigated for their activity towards oxygen evolution reaction in 0.1 M H2SO4, 0.5 M H2SO4 and 0.1 M HClO4. The stability of the deposited catalyst was insufficient and their deterioration was attributed to the oxidation of the carbon support as well as the dissolution of the metal ions upon high anodic potentials.The same metal-incorporated oxidized conductive carbon black agents were investigated for the enhancement of the performance of Si/C anodes in lithium-ion batteries. It was found that cobalt incorporation in the oxidized matrix displayed a significant influence in the electrochemical kinetics and consequent rate performances. With 0.8% cobalt ions by mass incorporated in oxidized KetJen Black the average capacity of the Si/C anode was increased by 180% at 1.5 A.g-1. This metal incorporation approach was extended to other ionic species (copper, iron and nickel) and other carbon conductive agents (SuperP). The electrolyte affinity, the desolvation process and the improved electronic conductivity synergistically improved the rate performance without compromising the gravimetric capacity of the electrode.The deposition of ultra-thin aluminium oxide by atomic layered deposition on the surface of LiNi0.5Co0.2Mn0.3O2 cathode material in lithium-ion batteries for the improvement of cyclic performances at high voltages (4.3-4.6 V) was investigated. One source of the failure mechanisms of the battery comes from unwanted side reactions between surface species and the electrolyte. The aluminium oxide layers of 1.42 nm and 2,36 nm were found to be beneficial at current densities exceeding 1.0 C (1 C = 170 mAh.g-1), and especially at 5.0 C with an increase of about 20 mAh.g-1 and 35 mAh.g-1 compared to uncoated NCM523, respectively. The capacity retention was found to be improved for all coated samples compared to pristine upon 140 cycles at 1.0 C. Mitigating side reactions and increasing the specific capacity at higher C-rates by atomically controlled layered deposition of inexpensive metal oxides is desirable for the implementation next-generation of safer and stable fast-charging high-voltage lithium-ion batteries.

EPFL2022

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Hydration reactions and stages of clinker composed mainly of stoichiometric ye'elimite

Mohsen Ben Haha, Emmanuelle Boehm Courjault, Frank Bullerjahn, Karen Scrivener

Ye'climitc (Ca4Al6O12SO4 or C(4)A(3)(S) over bar) is the main hydraulic mineral present in calcium sulfoaluminate cement (CSA). The hydration of ye'elimite is responsible for the early age cement properties. We identify 5 stages in the hydration of neat stoichiometric ye'elimite in suspensions with water to binder ratio 40 and 100. During stage I (initial period) there is a rapid rise of the solution concentration appears followed by a fast slowdown. Stage 11 (dormant period) shows a slow but steady fall of the concentrations. The rate of reaction increases again during stage III (acceleration period) as indicated by the rising pH and solution concentrations. This leads to stage IV (main hydration period) during which the rapid and massive dissolution of anhydrous phases and precipitation of hydrates occurs. With that stage V (final period) is reached during which the recrystallization of formed hydrates continues. The duration of each stage is directly linked to the evolution of the solution concentrations and the type hydration reaction. In particular, the crystallinity of aluminium hydroxide seems to play an important role. The findings obtained in suspension were successfully linked to experiments on paste.

PERGAMON-ELSEVIER SCIENCE LTD2019

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Chemical shrinkage of ye'elimite with and without gypsum addition

Mohsen Ben Haha, Frank Bullerjahn, Karen Scrivener

Ye'elimite (Ca4Al6O12SO4 or C(4)A(3)S) is the main hydraulic mineral present in calcium sulphoaluminate cement (CSA). Its reaction is responsible for the (early) hydration and associated cement properties such as the chemical shrinkage. This paper discusses the evolution of chemical shrinkage and related hydration reactions of stoichiometric ye'elimite in the absence and presence of gypsum. The measurements reveal a transitory chemical expansion followed by recovery to the original value for both binders. The shrinkage evolution is linked to the changes within the X-ray amorphous phases formed during hydration. This amorphous component is composed of several metastable hydrates such as aluminium hydroxide gel, which undergo subsequent recrystallization with time. This causes the release of some of the bound water and coincides with the period during which the chemical expansion occurs. (C) 2018 Elsevier Ltd. All rights reserved.

ELSEVIER SCI LTD2019

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EPFL2022