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Synthesis of rare-earth oxide mesoporous structures by combustion synthesis
2009 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

This work aims at characterizing the properties of rare earth oxides (ReO) produced by combustion synthesis. Three different studies are investigated. The first one consists in the study of ReO by the mean of thermogravimetry analysis. A mass spectrometer was used too, to get more information. Two different ReO are studied: yttrium oxide (Y2O3) and gadolinium oxide (Gd2O3). The ReO have been synthesized changing the most important initial parameter regarding the changes in the properties obtained. This parameter is the ratio glycine to rare earth nitrates (G/N), the two reactants used for the synthesis. The conclusions for this part are the following: for an excess of nitrates, the impurities in the oxides are mostly due to carbon residues, nitrates and carbonates. The amount of carbonates seems to scale with the specific surface area of the powder, while nitrates decrease when less in excess. The synthesis is carried out at 500 ¢XC in this study but the conclusion is that carrying out the synthesis at 600„aC or increasing the temperature to 600„aC after synthesis might allow for complete removal of nitrate without altering the structure too much. For the stoichiometric ratio, nitrates and carbonates can hardly be resolved by DTG. However, 46% of the total weight loss occurs above 460„aC for Y2O3. For an excess of glycine, unreacted glycine is found. A major difference in the chemical properties of the two oxides has been found as well. It is the heat of reaction released during the synthesis which does not show the same trend if we look at its evolution increasing the G/N ratio. The second part of this work consists in the study of the changes of some parameters in the synthesis on the ReO properties. Two parameters are tested: the mixing changing its speed and glycine from different brands (one aged of 20 years). It does not show major differences looking at adsorption and desorption of nitrogen measurements. Nevertheless, other ways have to be investigated like the concentration of rare earth nitrates solution for example. The last part is the study of the aging of ReO. Y2O3 for a G/N ratio of 0.56 is studied. The conclusions are the following: X-ray analyses, adsorption and desorption of nitrogen measurements and thermogravimetry showed that the fresh rare-earth oxides have a metastable structure. Moreover, this fresh powder structure seems to change to a stable one with time. And we could have noticed that the moistening seems to increase a lot the speed of this structure evolution.

Place, publisher, year, edition, pages
Keyword [en]
Physics Chemistry Maths, Rare-earth oxides, combustion synthesis
Keyword [sv]
Fysik, Kemi, Matematik
URN: urn:nbn:se:ltu:diva-57254ISRN: LTU-PB-EX--09/114--SELocal ID: df0576d2-b9d0-4c9c-b461-2501fbb992adOAI: diva2:1030641
Subject / course
Student thesis, at least 30 credits
Educational program
Chemical Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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