Search results for "chemical engineering"
showing 10 items of 5892 documents
Hydration process and rheological properties of cement pastes modified by orthophosphate addition
2005
Abstract The use of cement by nuclear industry for confining low radioactive waste knows a constant increase. The interest bore to this material is due to its mechanical and chemical properties. However, these properties may be modified by the nature and the amount of wastes introduced with the mixing solution especially with large amount of phosphate. Precipitation of hydroxylapatite in the cement paste at the very beginning after mixing was emphasized from a particular concentration of orthophosphate. It was also found that this phenomenon leads to an early rigidification of the cement paste. From a kinetics point of view, the evolution of hydration was both delayed and slowed down accord…
Comparisons of processing and strength properties of two adhesive systems for composite joints
2007
Abstract In the present study rheological, static and impact tests are carried out on two adhesive resins usually employed in marine applications; then single lap joint tests are conducted on composites joints evidencing the effect of the curing time of both resins on the mechanical properties of the joint. The applicability and workability conditions of the adhesive resins are determined evaluating the curing evolution by a preliminary rheological analysis; then the relation of curing properties with the mechanical performances of the resins themselves and with ones of the composite joints is estimated. Static flexural and Izod impact tests are performed on the resins at increasing time af…
STABILITY AND ORGANOCATALYTIC EFFICIENCY OF N-HETEROCYCLIC CARBENES ELECTROGENERATED IN ORGANIC SOLVENTS FROM IMIDAZOLIUM IONIC LIQUIDS
2015
The kinetic of degradation of 1-butyl-3-methylimidazole-2-ylidene (selected as model N-heterocyclic carbene - NHC), generated in organic solvents by cathodic reduction of the parent 1-butyl-3- methylimidazolium salts BMIm-X, was studied by a simple voltammetric analysis. The effect of NHC degradation rate on the efficiency of an organocatalyzed reaction (the synthesis of g-butyrolactone from cinnamaldehyde and trifluoromethylacetophenone) was investigated. The nature of the solvent and of the anion X have a remarkable effect on the stability of the NHC, the bis(trifluoromethylsulfonyl) imide anion being the best for a long lasting carbene (while acetonitrile seems to be the worst solvent). …
Supramolecular Modification of ABC Triblock Terpolymers in Confinement Assembly
2018
The self-assembly of AB diblock copolymers in three-dimensional (3D) soft confinement of nanoemulsions has recently become an attractive bottom up route to prepare colloids with controlled inner morphologies. In that regard, ABC triblock terpolymers show a more complex morphological behavior and could thus give access to extensive libraries of multicompartment microparticles. However, knowledge about their self-assembly in confinement is very limited thus far. Here, we investigated the confinement assembly of polystyrene-block-poly(4-vinylpyridine)-block-poly(tert-butyl methacrylate) (PS-b-P4VP-b-PT or SVT) triblock terpolymers in nanoemulsion droplets. Depending on the block weight fractio…
Elongation and plasmonic activity of embedded metal nanoparticles following heavy ion irradiation
2023
Shape modification of embedded nanoparticles by swift heavy ion (SHI) irradiation is an effective way to produce nanostructures with controlled size, shape, and orientation. In this study, randomly oriented gold nanorods embedded in SiO2 are shown to re-orient along the ion beam direction. The degree of orientation depends on the irradiation conditions and the nanorod's initial size. SHI irradiation was also applied to modify spherical metallic nanoparticles embedded in Al2O3. The results showed that they elongate due to the irradiation comparably to those embedded in SiO2. Metallic nanostructures embedded in dielectric matrices can exhibit localized surface plasmon (LSP) modes. The elongat…
Surface modification of poly(ethylene-co-acrylic acid) with amino-functionalized silica nanoparticles
2011
In this work we studied the possibility to achieve a hybrid-surface through the modification, via a facile wet chemical process, of the surface of films of poly(ethylene-co-acrylic acid) (EAA) with amino-modified silica nanoparticles. Films of EAA were preliminarily activated by the introduction of -COCl groups on their surface. Silica nanoparticles were thereafter covalently bound on the polymeric surface as confirmed by FTIR, ATR-FTIR, XPS, NMR and SEM determinations. The nanoparticles formed a multilayer on the film surface and covered almost uniformly the whole film surface. Direct measurements of superficial amino groups by titration allowed us to detect a concentration of about 18 nmo…
Pb-PbOHCl Composite Nanowires Synthesized by Galvanic Deposition in Template
2019
In this paper, we report a detailed study on the synthesis of composite nanowires of Pb-PbOHCl via galvanic deposition into the pores of a membrane acting as a template. PbOHCl deposition quantitatively occurs as the solution pH exceeds the value of about 4.12. Simultaneously, owing to the galvanic coupling, electro-deposition of lead occurs, so composite nanowires were formed. The role of different parameters controlling the kinetic evolution of the process, such as oxygen bubbling, solution pH, surface area and type of sacrificial anode were investigated one at a time. The results suggest that every modification accelerating the alkalization of the solution inside the template pores favor…
Nanowire ordered Arrays for electrochemical sensing of H2O2
2016
In this work, we present the performance of nanostructured array of Cu for electrochemical sensors of hydrogen peroxide. Nanostructured sensors are obtained by template synthesis in commercial polycarbonate membranes. Arrays of Cu nanowires were fabricated through a displacement deposition reaction that permits to obtain nanostructures directly and without the use of an external power supply. To test the performance of nanostructured sensors, electrochemical experiments were carried out in an aqueous solution with different amounts of hydrogen peroxide. In order to obtain sensors with stable performance, we found that it is essential to increase wettability of the nanostructures through add…
Performance Evaluation for a Sustainable Supply Chain Management System in the Automotive Industry Using Artificial Intelligence
2020
Increasing the sustainability of a system can be achieved by evaluating the system, identifying the issues and their root cause and solving them. Performance evaluation translates into key performance indicators (KPIs) with a high impact on increasing overall efficacy and efficiency. As the pool of KPIs has increased over time in the context of evaluating the supply chain management (SCM) system&rsquo
Rearrangement of N-(3-pyridyl)nitramine
2009
AbstractContrary to other N-(pyridyl)nitramines, the title compound cannot be rearranged to 3-amino-2-nitropyridine or other isomers. Hypothetical products of its transformation under influence of concentrated sulphuric acid, viz. 3-hydroxypyridine, 3,3′-azoxypyridine and 3,3′-azopyridine, were obtained from 3-nitro- and 3-aminopyridine in oxidation and reduction reactions. N-(3-Pyridyl)nitramine was prepared and rearranged in concentrated sulphuric acid. 3-Hydroxypyridine and 3,3′-azoxypyridine were isolated from the reaction mixture, other products were identified by the HPLC and GCMS methods. The results indicate that N-(3-pyridyl)hydroxylamine is an intermediate formed from N-(3-pyridyl…