Drying process in the formation of sol-gel-derived TiO2 ceramic membrane

Accurate drying data for thin titania gel layers dried at 40°C and 20% relative humidity (RH) are given. The drying rate versus free moisture content diagram should show three regions as predicted by the classical drying theory. They are the constant rate period, the first falling rate period and the second falling rate period. The second falling rate period was not observed in the present case, because at 40°C and 20% RH the equilibrium moisture content will be enough to provide a continuous fluid network in the gel. The total drying time in the falling rate period increases with layer thickness. The drying mechanism in the first falling rate period was identified as capillary flow

Measuring and modeling broadband magnetic losses versus temperature and aging effects in CoO-doped Mn-Zn ferrites

We analyze the physical mechanisms associated with addition of CoO to sintered Mn-Zn ferrites and the ensuing stabilization versus temperature of their magnetic properties. We determine, in particular, the value and behavior of the magnetic anisotropy as a function of doping and temperature and we model in physical terms the evolution of the energy loss in the investigated frequency (DC - 1 GHz) and temperature (20 degrees C - +130 degrees C) ranges. We show that magnetic aging by long exposure of the CoO-doped ferrites at 200 degrees C is minimized by additional TiO2 doping. This is observed to restrain the increase of the extra-anisotropy induced by directional ordering of the Co2+ cations

Magnetic losses versus sintering treatment in Mn-Zn ferrites

partially_open5sìpartially_openBeatrice, Cinzia; Tsakaloudi, Vasiliki; Dobák, Samuel; Zaspalis, Vassilios; Fiorillo, FaustoBeatrice, Cinzia; Tsakaloudi, Vasiliki; Dobák, Samuel; Zaspalis, Vassilios; Fiorillo, Faust

Green synthesis and characterization of silver nanoparticles produced using 'Arbutus Unedo' leaf extract

Metallic nanoparticles have received great attention from chemists, physicists, biologists and engineers who wish to use them for the development of a new generation of nanodevices. In the present study silver nanoparticles were synthesized from aqueous silver nitrate through a simple and eco-friendly route using leaf broth of Arbutus unedo, which acted as a reductant and stabilizer simultaneously. The aqueous silver ions when exposed to the leaf broth were reduced and stabilized over long periods of time resulting in the green synthesis of surface functionalized silver nanoparticles. The bio-reduced silver nanoparticles were appropriately characterized. The results revealed the formation of single crystalline Ag nanoparticles with a narrow size distribution for each sample. The particles, although discrete, were predominately coated with the organic leaf extract forming small aggregates, which makes them stable over long time periods and highly appropriate for coatings or biotechnology applications.Publicad

Catalysis with inorganic membranes

Catalytic inorganic membranes are among the most challenging and intriguing porous materials. Consisting of a thin film of mesoporous or microporous inorganic material deposited on a macroporous material, catalytic membranes are multifunctional materials that must be engineered for both chemical and physical properties. New approaches to carrying out chemical reactions are possible by tailoring the membrane catalytic activity and selectivity, permselectivity, and other thin film properties. Readers are referred to several recent reviews of inorganic membranes, in particular, Zaspalis and Burggraaf, Armor, Gellings and Bouwmeister, Hsieh, Stoukides, and Tsotsis et al. Inorganic membranes are most conveniently classified according to pore size (see introductory article). Of particular importance is the ratio of the pore size to the molecular mean free path (MFP). Decreasing pore dimensions lead to increased selectivity with corresponding loss of permeability. Macroporous membranes have a pore size much larger than the MFP, leading to molecular (bulk) diffusion or viscous flow. Knudsen diffusion dominates in the mesoporous regime, where the pore size is comparable to the MFP. In addition, surface diffusion of the molecules along the pore walls may contribute, leading to an enhanced flux of the adsorbed species along the walls. The microporous regime is encountered when the pore size is comparable to the molecules. This regime makes possible much higher permselectivities, which depend on both molecular size and specific interactions with the solid. Finally, in dense membranes, molecular transport occurs through a solution-diffusion mechanism, which also involves specific interactions between the solute and membrane

Magnetic loss, permeability, and anisotropy compensation in CoO-doped Mn-Zn ferrites

Mn-Zn ferrite samples prepared by conventional solid state reaction method and sintering at 1325 °C were Co-enriched by addition of CoO up to 6000 ppm and characterized versus frequency (DC – 1GHz), peak polarization (2 mT – 200 mT), and temperature (23 °C – 120 °C). The magnetic losses at room temperature are observed to pass through a deep minimum value around 4000 ppm CoO at all polarizations values. This trend is smoothed out either by approaching the MHz range or by increasing the temperature. Conversely, the initial permeability attains its maximum value around the same CoO content, while showing moderate monotonical decrease with increasing CoO at the typical working temperatures of 80 – 100 °C. The energy losses, measured by a combination of fluxmetric and transmission line methods, are affected by the eddy currents, on the conventional 5 mm thick ring samples, only beyond a few MHz. Their assessment relies on the separation of rotational and domain wall processes, which can be done by analysis of the complex permeability and its frequency behavior. This permits one, in particular, to calculate the magnetic anisotropy and its dependence on CoO content and temperature and bring to light its decomposition into the host lattice and Co2+ temperature dependent contributions. The temperature and doping dependence of initial permeability and magnetic losses can in this way be qualitatively justified, without invoking the passage through zero value of the effective anisotropy constant upon doping

Catalytic membrane reactor for Suzuki-Miyaura C-C cross-coupling: Explanation for its high efficiency via modeling

A polymeric catalytic membrane was previously prepared that showed remarkable efficiency for Suzuki-Miyaura C-C cross-coupling in a flow-through configuration. A mathematic model was developed and fitted to the experimental data to understand the significant apparent reaction rate increase exhibited by the catalytic membrane reactor compared to the catalytic system under batch reaction conditions. It appears that the high palladium nanoparticles concentration inside the membrane is mainly responsible for the high apparent reaction rate achieved. In addition the best performance of the catalytic membrane could be achieved only in the forced flow-through configuration, that, conditions permitting to the reactants be brought to the catalytic membrane by convection

Assessing the role of bed sediments in the persistence of red mud pollution in a shallow lake (Kinghorn Loch, UK)

Red mud is a by-product of alumina production. Little is known about the long-term fate of red mud constituents in fresh waters or of the processes regulating recovery of fresh waters following pollution control. In 1983, red mud leachate was diverted away from Kinghorn Loch, UK, after many years of polluting this shallow and monomictic lake. We hypothesised that the redox-sensitive constituents of red mud leachate, phosphorus (P), arsenic (As) and vanadium (V), would persist in the Kinghorn Loch for many years following pollution control as a result of cycling between the lake bed sediment and the overlying water column. To test this hypothesis, we conducted a 12-month field campaign in Kinghorn Loch between May 2012 and April 2013 to quantify the seasonal cycling of P, As, and V in relation to environmental conditions (e.g., dissolved oxygen (DO) concentration, pH, redox chemistry and temperature) in the lake surface and bottom waters. To confirm the mechanisms for P, As and V release, a sediment core incubation experiment was conducted using lake sediment sampled in July 2012, in which DO concentrations were manipulated to create either oxic or anoxic conditions similar to the bed conditions found in the lake. The effects on P, As, and V concentrations and species in the water column were measured daily over an eight-day incubation period. Phosphate (PO4-P) and dissolved As concentrations were significantly higher in the bottom waters (75.9 ± 30.2 μg L−1 and 23.5 ± 1.83 μg L−1, respectively) than in the surface waters (12.9 ± 1.50 μg L−1 and 14.1 ± 2.20 μg L−1, respectively) in Kinghorn Loch. Sediment release of As and P under anoxic conditions was confirmed by the incubation experiment and by the significant negative correlations between DO and P and As concentrations in the bottom waters of the lake. In contrast, the highest dissolved V concentrations occurred in the bottom waters of Kinghorn Loch under oxic conditions (15.0 ± 3.35 μg L−1), with the release from the bed sediment apparently being controlled by a combination of competitive ion concentrations, pH and redox conditions