Capping Groups Induced Size and Shape Evolution of Magnetite Particles Under Hydrothermal Condition and their Magnetic Properties

Three simple capping molecules (urea, 3-aminopropanol, and polyethylene glycol) with different functional groups (−NH₂ for urea, −NH₂ and −OH for 3-aminopropanol, and −O− for polyethylene glycol) have been designed to prepare magnetite (Fe₃O₄) particles with various shapes. The crystal structure, morphologies, and magnetic properties of the products have been characterized by X-ray diffraction, electron microscopy, and vibrating sample magnetometer. The results indicate that the capping functional groups play a major role in determining the size, shape, and thus magnetic properties of the magnetite nanocrystals. The morphology evolution of the magnetite under the hydrothermal condition is discussed in detail, particularly for the interaction between the various capping groups and surface structure and chemistry of the nanocrystals.     

Modeling of a continuous rotary reactor for carbon nanotube synthesis by catalytic chemical vapor deposition

The modeling of carbon nanotube production by the CCVD process in a continuous rotary reactor with mobile bed was performed according to a rigorous chemical reaction engineering approach. The geometric, hydrodynamic, physical and physicochemical factors governing the process were analyzed in order to establish the reactor equations. While the study of the hydrodynamic factor suggests a co‐current plug‐flow approximation, the physical factor mainly deals with the phenomena of transport and the transfer of mass, which can be neglected. Concerning the physicochemical factor, the modeling is based on knowledge of the expression of the initial reaction rate, and takes into account catalytic deactivation as a function of time, according to a sigmoid decreasing law. The reactor modeling allows obtaining the evolution of partial pressure, carbon nanotube production and catalytic deactivation along the reactor for given initial operating conditions. The comparison between experimental and calculated production highlights a very good fit of data. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Modeling of coupled mass and heat transfer through venting membranes for automotive applications

Experimental and theoretical approaches based on a mathematical model, have been developed to study the evolution of environmental parameters (temperature, total pressure, relative humidity, and water vapor partial pressure) inside a housing of an electronic device with a window containing a macroporous membrane. The model was based on the coupling of mass and heat transfer taking into account the effects of polarization of concentration in boundary layers. Membranes have been characterized by mercury porosimetry, liquid entry pressure measurements, scanning electron microscopy, and gas permeation. Once the model was experimentally validated, it was applied to investigate the influence of membranes on heat and mass transfer and to study the impact of the boundary layers on the global mass transport. The results demonstrated the importance of the membrane choice and dimensions to get the best temperature regulation and avoid water condensation inside an automotive electronic control unit (ECU). © 2008 American Institute of Chemical Engineers AIChE J, 2009     

Spontaneous grafting of diazoates on metals

Hydroxyl ions react with diazonium salts to give transient diazohydroxides, which are deprotonated to diazoates. The latter react spontaneously with Fe and Au to give surfaces modified with aryl groups. These surfaces are characterized by XPS and IR spectroscopies. The mechanism involves the homolytic reduction of the diazoate to give a radical that binds to the substrate.     

Effects of ferrocene derivative on the physico-chemical and electrocatalytic properties of ordered mesoporous carbon

This work reports effects of ferrocene derivative on the properties of an ordered mesoporous carbon (OMC). A novel method for the incorporation of iron oxide species in the carbon framework of OMC without any decrease in the surface area is also reported. The decomposition of ferrocene derivative yields iron species that facilitate the formation of the carbon framework. The performance of ordered mesoporous carbon containing iron oxide (OMC-Fe) is compared to OMC and the properties of the new material are found to be improved. OMC-Fe combines electrochemical properties of OMC and iron oxide species. Electrocatalytic properties towards H₂O₂ are enhanced because of synergetic effect of ordered mesoporous carbon and iron oxide species. The electrochemical determination of H₂O₂ at the OMC-Fe modified electrode is more sensitive than that at OMC electrode. A sensitive and stable H₂O₂ sensor was developed based on OMC-Fe electrode with a large determination range and a good reproducibility.     

Multiscale physical characterization of an outdoor-exposed polymeric coating system

Surface topography and gloss are two related properties affecting the appearance of a polymeric coating system. Upon exposure to ultraviolet (UV) radiation, the surface topography of a coating becomes more pronounced and, correspondingly, its gloss generally decreases. However, the surface factors affecting gloss and appearance are difficult to ascertain. In this article, atomic force microscopy (AFM) and laser scanning confocal microscopy (LSCM) measurements have been performed on an amine-cured epoxy coating system exposed to outdoor environments in Gaithersburg, Maryland. The formation of the protuberances is observed at the early degradation stages, followed by the appearance of circular pits as exposure continues. At long exposure times, the circular features enlarge and deepen, resulting in a rough surface topography and crack formation. Fourier Transform Infrared Spectroscopy (FTIR) study indicates that the oxidation and chain scission reactions are likely the origins of the surface morphological changes. The relationship between changes in surface roughness and gloss has been analyzed. The root mean square (RMS) roughness of the coating is related to nanoscale and microscale morphological changes in the surface of the coating as well as to the gloss retention. A near-linear dependence of RMS roughness with the measurement length scale (L) is found on a double logarithmic scale, i.e., RMS ∼ L ^f. The scaling factor, f, decreases with exposure time. The relationship between surface topography, on nano- to microscales, and the macroscale optical properties such as gloss retention is discussed. Moreover, a recent development in using an angle-resolved light scattering technique for the measurement of the specular and off-specular reflectance of the UV-exposed specimens is also demonstrated, and the optical scattering data are compared to the gloss and the roughness results.

Evaluation of a permeability–porosity relationship in a low-permeability creeping material using a single transient test

A method is presented for the evaluation of the permeability–porosity relationship in a low-permeability porous material using the results of a single transient test. This method accounts for both elastic and non-elastic deformations of the sample during the test, and is applied to a hardened class G oil well cement paste. An initial hydrostatic undrained loading is applied to the sample. The generated excess pore pressure is then released at one end of the sample while monitoring the pore pressure at the other end and the radial strain in the middle of the sample during the dissipation of the pore pressure. These measurements are back-analysed to evaluate the permeability and its evolution with porosity change. The effect of creep of the sample during the test on the measured pore pressure and volume change is taken into account in the analysis. This approach permits to calibrate a power law permeability–porosity relationship for the tested hardened cement paste. The porosity sensitivity exponent of the power–law is evaluated equal to 11, and is shown to be mostly independent of the stress level and of the creep strains.