Search results for "engineering.material"
showing 10 items of 2352 documents
Electrochemical synthesis on boron-doped diamond
2012
Abstract Boron-doped diamond (BDD) is a novel and innovative electrode material. In protic media and particular aqueous electrolytes BDD exhibits a large over potential for the evolution of molecular hydrogen and oxygen. The large chemical window allows a variety of electrochemical conversions to be conducted. The anodic process treatment generates oxyl species directly which are known to be extremely reactive. Usually, the electrochemical mineralization of the organic components in the electrolyte occurs. However, with control of the reactivity of these intermediates the use in electroorganic synthesis can be realized. Until today mostly anodic conversions have been studied at BDD. Since h…
Hansen theory applied to the identification of nonhazardous solvents for hybrid perovskite thin-films processing
2018
Abstract Metal-halide perovskites have become the most studied material for efficient next-generation solar cells, in part because of the possibility of depositing high quality semiconducting perovskites by simple solution-based methods. However, the majority of solvent systems implemented in literature for deposition of lead halide perovskites are hazardous to handle. Investigation of alternatives perovskite processing methods are hence key to safely upscale the perovskite photovoltaic manufacturing. In this manuscript we use the Hansen theory to find suitable nonhazardous solvents to solubilize two lead salts, PbBr2 and PbI2, used to fabricate the corresponding methylammonium (MA) lead ha…
Transportation of complexing agents released by pulp and paper industry: A Finnish lake case
1996
Complexing agents (EDTA, DTPA) are used to bind metal ions in pulp and paper industry. Their role will increase significantly when the total chlorine free (TCF) processes will be applied to a larger extent. EDTA and DTPA were analysed in the waters from the southern part of the Lake Saimaa (SE Finland) influenced by the effluents of three pulp and paper mills. The samples were collected at different distances from the points of emission. The results of analyses suggest that EDTA can persist in lake water and is able to propagate for considerable distances, while DTPA can be detected only in the near surroundings of the site of release. Some EDTA was found even in the sampling points that we…
Sol–Gel Synthesis of Tunable Cerium Titanate Materials
2008
Cerium titanate structures present a high technological interest because of their optical and catalytic properties. This work reports the synthesis of these materials by a sol–gel methodology that allows mixed oxides with TiIV/CeIII, TiIV/CeIV or TiIV/CeIII–CeIV species to be obtained. Crystallization of CeO2–TiO2 mixed oxides and Ce2Ti2O7 pyrochlore phase was corroborated by XRD and Raman spectroscopy. Magnetic and EPR measurements were performed in order to clarify the oxidation state of the cerium ions in the system as a result of the easy oxidation of CeIII. The firing atmosphere is crucial for the CeIII/CeIV ratio, which is responsible for the different structure, but it also affects t…
Experimental set up for determining the temperature-oxygen partial pressure conditions during synthesis of spinel oxide nanoparticles
1997
Abstract Nanometric spinel oxide powders, Fe 3− x M x O 4 , where M is a transition element, have been synthetized by soft chemistry. This method generally leads to a non-stoichiometric phase, Fe 3− x M x O 4+δ where δ is the deviation from stoichiometry so that further annealing at low temperatures around 450°C and low oxygen partial pressure around 10 −25 Pa given by N 2 /H 2 /H 2 O gas mixtures is required: this enables a stoichiometric compound to be obtained and a nanometric size to be maintained. The complete set up consisting of a gas mixer, a thermogravimetric apparatus and a preparative furnace is described. Some results concerning the conditions of temperature and oxygen partial p…
Hybrid Materials Based on Magnetic Layered Double Hydroxides: A Molecular Perspective
2015
Design of functional hybrids lies at the very core of synthetic chemistry as it has enabled the development of an unlimited number of solids displaying unprecedented or even improved properties built upon the association at the molecular level of quite disparate components by chemical design. Multifunctional hybrids are a particularly appealing case among hybrid organic/inorganic materials. Here, chemical knowledge is used to deploy molecular components bearing different functionalities within a single solid so that these properties can coexist or event interact leading to unprecedented phenomena. From a molecular perspective, this can be done either by controlled assembly of organic/inorga…
Interactions between chemical evolution (hydration) and physical evolution (setting) in the case of tricalcium silicate
1994
This paper describes recent experimental results concerning investigation of the parameters which determine, on the one hand, the kinetics of hydration of tricalcium silicate and the thermodynamic, morphological and structural characteristics of C-S-H and, on the other hand, the evolution of the particle interactions at the origin of setting. It is shown that, in both cases, lime concentration in solution is the most important parameter. As a consequence, the chemical evolution of the system, which controls the lime concentration in solution, determines the nature of particle interactions and the physical evolution of the suspension or paste. In return, the contacts, between particles, resu…
Superatomic S2 Silver Clusters Stabilized by a Thiolate–Phosphine Monolayer: Insight into Electronic and Optical Properties of Ag14(SC6H3F2)12(PPh3)8…
2014
The electronic structure of two recently crystallographically solved, thiolate–phosphine protected silver clusters Ag14 and Ag16 are analyzed via density functional theory (DFT) and their optical excitations are analyzed from time-dependent DFT perturbation theory. Both clusters can be characterized as having the S2 free-electron configuration in the metal core, which is the first time such a configuration is confirmed for structurally known ligand-protected noble metal clusters. However, their different core shapes and ligand layer induce significantly different optical spectra. Performance of gradient-corrected DFT functionals is discussed and it is shown that the asymptotically correct L…
Interplay between Chemical Composition and Cation Ordering in the Magnetism of Ni/Fe Layered Double Hydroxides
2013
We report the synthesis of a family of ferrimagnetic NiFe layered double hydroxides (LDHs) with a variable Ni(2+)/Fe(3+) in-plane composition of [Ni(1-x)Fe(x)(OH)2](CO3)(x/2)·yH2O (x = 0.20, 0.25, and 0.33) by following a modified homogeneous precipitation. These layered magnets display high crystallinity, homogeneous hexagonal morphologies, and micrometric size that enable their quantitative exfoliation into single layers by sonomechanical treatment of the solids in polar solvents. This was confirmed by dynamic light scattering, UV-vis spectroscopy, high-resolution transmission electron miscroscopy, and atomic force microscopy methodologies to study the resulting steady suspensions. Our ma…
Room Temperature Magnetism in Layered Double Hydroxides due to Magnetic Nanoparticles
2013
Some recent reports claiming room temperature spontaneous magnetization in layered double hydroxides (LDHs) have been published; however, the reported materials cause serious concern as to whether this cooperative magnetic behavior comes from extrinsic sources, such as spinel iron oxide nanoparticles. The syntheses of crystalline Fe(3+)-based LDHs with and without impurities have been developed, highlighting the care that must be taken during the synthetic process in order to avoid misidentification of magnetic LDHs.