Carbonate de sodium

Résumé

Le carbonate de sodium est un composé chimique de formule NaCO et correspondant à l'espèce minérale naturelle dénommée natrite. Il s'agit d'un sel de sodium de l'acide carbonique. Il représente un des grands produits polyvalents de la chimie moderne. Dans le langage courant, ce solide ionique, le plus souvent sous forme poudreuse, et ses solutions aqueuses sont dénommés communément respectivement cristaux de soude et soude, du nom ancien de cet alcali minéral, utilisé précocement dans l'industrie verrière antique. Il ne faut pas confondre le carbonate de sodium NaCO avec l'hydroxyde de sodium NaOH, dit « soude caustique », ni avec le bicarbonate de sodium NaHCO, autrefois nommé communément « bicarbonate de soude ». Obtention Le carbonate de sodium peut être obtenu à partir de gisements de natron , souvent stocké en réserve géologique sous forme de thermonatrite , ou encore de trona NaCO • NaHCO • 2HO. En Égypte antique, on le trouvait dans la fleur de natron des lacs Amer

Source officielle

https://fr.wikipedia.org/wiki/Carbonate_de_sodium

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Biomimetic apatite coatings - Carbonate substitution and preferred growth orientation

Biomimetic apatite coatings were obtained by soaking chemically treated titanium in SBF with different HCO3- concentration. XRD, FTIR and Raman analyses were used to characterize phase composition and degree of carbonate substitution. The microstructure, elemental composition and preferred alignment of biomimetically precipitated crystallites were characterized by cross-sectional TEM analyses. According to XRD, the phase composition of precipitated coatings on chemically pre-treated titanium after exposure to SBF was identified as hydroxy carbonated apatite (HCA). A preferred c-axis orientation of the deposited crystals can be supposed due to the high relative peak intensities of the (0 0 2) diffraction line at 2 theta = 26 degrees compared to the 100% intensity peak of the (2 1 1) plane at 2 theta = 32 degrees. The crystallite size in direction of the c-axis of HCA decreased from 26 nm in SBF5 with a HCO3- concentration of 5 mmol/l to 19 nm in SBF27 with a HCO3- concentration of 27 mmol/l. Cross-sectional TEM analyses revealed that all distances correspond exactly to the hexagonal structure of hydroxyapatite. The HCO3- content in SBF also influences the composition of precipitated calcium phosphates. Biomimetic apatites were shown to have a general formula of Ca10-x-yMgy(HPO4)(x-z)(CO3)(z)(PO4)(6-x)(OH)(2-x-w)(CO3)(w/2). According to MR and Raman analyses, it can be supposed that as long as the HCO3- concentration in the testing solutions is below 20 mmol/l, only B-type HCA (0 < z < 1; w = 0) precipitates. At higher HCO3- concentration, it can be assumed that AB-type HCA (z = 1;0 < w < 1) is formed. (C) 2007 Elsevier B.V. All rights reserved.

2007

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Method for Measuring Chromium Evaporation from SOFC Balance-of-Plant Components

Josef Andreas Schuler

Cr poisoning is a well-identified performance degradation process in solid oxide fuel cells (SOFC). While stainless steel (SS) interconnects have been identified to be a significant source of Cr, the Cr contribution from balance-of-plant (BoP) components located upstream of the cathode still needs to be ascertained. A method to measure Cr concentration level from BoP components was developed in this work. The volatile Cr species were collected by air sampling through a quartz tube coated with sodium carbonate. SEM observations enabled to correlate changes in the oxide layer microstructure of BoP alloys to their Cr evaporation rate. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.022203esl] All rights reserved.

Electrochemical Society2012

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Adsorption of N-2 at 77 K and scanning electron microscopy have been used to measure the changes in the support morphology, at nano- and microscale level, along the processes involved in the preparation of a supported Pd catalyst: Pd deposition, doping, and thermal treatments. Among the investigated supports, viz., activated carbons, gamma-Al2O3, SiO2, and SiO2-Al2O3 (SA), the SA one was found particularly sensitive to these processes, as a result of its high plasticity and reactivity. Involved processes can be summarized as follows: (i) During the I'd deposition, the support itself is partially dissolved and removed as a result of both the basicity of the precipitating agent and the final washing. (ii) When the undoped sample is thermally treated up to 823 K, only modest phenomena are observed. (iii) Upon doping with potassium carbonate, the support dissolution continues, and the greater the carbonate concentration, the greater the dissolution extent. In this case the dissolved material is not removed, but reprecipitates (partially outside the pores), during the subsequent drying at 393 K. (iv) When doped samples are thermally treated, the reaction between carbonate and support causes the mobilization of the support itself, with sintering phenomena that can reach the total collapse of the porous structure. The starting temperature of the pore collapse decreases with increasing potassium carbonate concentration. The modification of the support influences, directly or indirectly, the surface properties and the availability of Pd particles that can be doped or even covered by materials from support and made more or less accessible or even inaccessible by pore narrowing, widening, or blocking.

2009

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