De vervaardiging van grondstoffen voor de bereiding van tetraaethyllood resp. "Ethyl fluid"

Document(en) uit de collectie Chemische ProcestechnologieDelftChemTechApplied Science

Influence of reaction gases on the structural and optical characteristics of Ce-oxide thin film coatings

Poster presentatio

Influence of reaction gases on the structural and optical characteristics of Ce-oxide thin film coatings

Oral Presentatio

Electronic properties, mechanical stability and reduction reaction energies for cubic lanthanide oxide composites: A computational modelling approach

Lanthanide(Ln) oxides represent an array of materials which exhibit unique properties, such as, superior mechanical, thermal, optical and magnetic properties, derived by their unfilled semicore 4f orbitals. Two forms of cerium oxide(CeO2 and Ce2O3) for instance have been the subject of numerous studies aiming to elucidate chemical and physical characteristics of their bulk and thin film properties. Cerium oxides have been widely deployed as catalysts in the preparation of active metal nanoparticles, as electrolytes or anode support materials. On the theoretical side, density functional theory(DFT) investigation has elucidated structures and electronic properties by utilizing hybrid DFT methods. Studied compounds include the A-type hexagonal structure and CeO2 with the cubic fluorite structure (space group Fm-3m). This study presents a comprehensive DFT + U account into electronic structures, mechanical properties of C-type lanthanide sesquioxides and thermodynamic (redox) properties. The aim of this work is fourfold: (1) to evaluate the effects of the Hubbard U parameter on the electronic and structural properties of C-type lanthanide sesquioxides (Ln2O3), (2) to assess the mechanical stability of all C-type lanthanide sesquioxides, (3) to elucidate the thermodynamic feasibility of CeO2 to undergo a redox reaction at temperatures relevant to catalytic applications, and (4) to underpin the effect of adding Hf and Zr to CeOδ [ δ=2-1.5] on reduction energies. We find that a Ueff value of ~ 5 eV reproduces the analogous experimental band gap of Ce2O3. Bader’s charge distributions on the C-type Ln2O3 have verified the ionic bonding nature of these compounds. Our analysis for the reduction energy of CeO2, in a wide range of temperatures, demonstrates that transfer cerium oxide between the two + 4 and + 3 oxidation states exhibit a temperature independent behavior. Preliminary results indicate that CeO2 alloyed with Hf or Zr results in enhancing its redox characteristics by lowering reduction enthalpies

Physico-chemical properties of CrMoN coatings - combined experimental and computational studies

In this study, Cr−Mo−N thin films with different Mo contents were synthesised via closed field unbalanced magnetron sputtering ion plating. The effects of Mo content on the microstructure, chemical bonding state, and optical properties of the prepared films were investigated by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy, and ultraviolet-visible spectrophotometry. XRD results determined the face centered cubic (fcc) structure of pure CrN film. The incorporation of molybdenum (Mo) in the CrN matrix was confirmed by both XRD and XPS analyses. The CrMoN coatings demonstrate various polycrystalline phases including CrN, γ-Mo2N, Cr with oxides layers of MoO3, CrO3, and Cr2O3. Microstructural results of the Cr-Mo-N coatings show that the grain size increased with an increase in Mo content due to the formation of MoN phase, in which the Mo atoms interact with N atoms around the grain boundaries of the CrN phase. XPS investigations confirmed the presence of Cr, Mo, N, C and O elements in the studied coatings. The optical results revealed that the synthesised coatings exhibit low reflection magnitudes in the visible region of the solar spectrum indicating good antireflection surfaces. Mo doped thin coatings improve the solar absorptance by ~76% in the wavelength range of 200–800 nm with a low thermal emittance of ~ 20% in the infrared range (up to 4000 nm). Furthermore, by applying density functional theory, the computational simulation provides similar trends as the experimental finding of absorption coefficient in the wavelength range