107 research outputs found
Optimization of chitosan-based scaffolds obtained via cathodic polarization
No full textCathodic polarization is a powerful technique largely used for the deposition of thin films on metallic substrates; it offers the distinctive advantage of an easy control over the composition, thickness, and morphology of the films by simply adjusting the process parameters such as the electrolyte bath composition, the applied potential (or current density), and the process duration. In this work, electrochemical deposition (ECD) was exploited to engender biopolymer blends composed by chitosan/collagen and chitosan/poly(ethylene oxide) and deposited at different weight ratios (5:1, 3:1) and compared to pristine material. Our findings demonstrate that ECD is an effective technique for the preparation of scaffolds made of chitosan blends in which morphology and mechanical properties can be optimized via scaffold compositio
Electrophoretic deposition of liquid templates
No full textRecent developments demonstrated that liquid templates in the form of solid particles stabilized emulsions can be used to produce porous materials. The use of such emulsions offers the possibility to control the porous properties over a wide range of pore sizes and porosities for a variety of materials. In addition, the liquid nature of the template enables the formed products to be sintered without a low temperature debinding step. In this work, the electrophoretic deposition (EPD) of these liquid templates for the production of porous alumina is reported. The experimental parameters needed to obtain stable emulsions, their influence on the final porous properties, as well as the influence of the deposition parameters are discussed.status: Publishe
Aqueous electrophoretic deposition at high electric fields
No full textFrom an environmental, safety and economic perspective water should be the solvent of choice for electrophoretic deposition under industrial circumstances. However, because of the electrolytic decomposition of water under the influence of direct current, the majority of EPD is carried out in non-aqueous solvents. In this work, experiments prove that deposits can be obtained from aqueous alumina suspensions while avoiding electrolysis of the medium by using unbalanced alternating current fields [1]. In addition it is shown that the formed deposits have a green density which is intrinsically higher than those formed by traditional DC EPD from ethanol based suspensions. A theoretical basis for both electrophoretic deposition by means of unbalanced alternating fields and the higher density of deposits formed by application of such fields is provided.status: Publishe
Study of the deposit resistance during electrophoretic deposition
No full textDeposition experiments in a Hull cell showed that high conductivity suspensions yield uniform deposits while low conductivity suspensions result in non-uniform deposits. This difference in deposition behavior is related to the resistance increase of the deposit during EPD. Impedance measurements during EPD showed that the ratio of the deposit resistance to the suspension resistance increases much more for high than for the low conductivity suspensions. They also showed that the total resistance of the EPD cell dropped almost to the suspension resistance after the electric field was turned off. This means that the deposit has no inherent resistance, but that its resistance during polarization is caused by the interaction of ions with the deposit and by the depletion of ions at the deposition electrode. The change in ion concentrations near the deposition electrode changes the acid/base properties of the particles in the deposit, as proven by adsorbed pH indicators on the particles. The change in acid/base behavior is quasi irreversible and results in a memory effect of the deposit resistance when the voltage is reapplied.status: Publishe
Textured α-alumina through electrophoretic deposition and templated grain growth
No full textThe development of texture was studied during electrophoretic deposition in alumina suspensions containing plate shaped alumina particles. The mechanism of platelet orientation during EPD was examined with respect to the influence of the electric field, gravity and hydrodynamic forces. This was realized by using two different deposition cells, with vertically or horizontally positioned deposition electrode. The texture of the green deposit was further enhanced during sintering by templated grain growth in which the platelet shaped alumina particles were growing at the expense of the fine grained matrix. The sharp 'fiber texture' obtained after templated grain growth during sintering of the deposit was characterized by means of x-ray diffraction and Electron Backscatter Diffraction (EBSD).status: Publishe
Microlocal analysis of partial differential operators with irregular singularities
Get PDFWe denote the variables in by x=(x_0 ,x^\u27), where and x^\u27 \in R^n. We consider partial differential operators of the form P(x,\partial /\partial x) = \sum\limits_{\left｜ \alpha \right｜ \leqslant m} {a_\alpha } (x)x_0^{\kappa (\left｜ \alpha \right｜)} (\partial /\partial x)^\alpha , where is some integer , is real analytic in a neighborhood of , and . We define the irregularity and the characteristic exponents of the operator P at the point \mathop x\limits^ \circ ^* = (0;\sqrt { - 1} ,0, \ldots ,0) \in \sqrt { - 1} T*R^{n + 1}. It will be proved that if and all the characteristic exponents of P are distinct, then P is equivalent microlocally to the operator in a neighborhood of \mathop x\limits^ \circ ^*
Alignment of TiO2 particles by electrophoretic deposition in a high magnetic field
No full textTextured titania thick films were fabricated by applying external electrical and magnetic fields. X-ray diffraction (XRD) results and scanning electron microscopy (SEM) images revealed that the titania grains in the c-axis direction were orientated along the high magnetic field (10 T) even though the anisotropic susceptibility of titania ceramic is quite weak. (C) 2004 Elsevier Ltd. All rights reserved
Chemical and physical pressure effects in the A-site spinel antiferromagnets CoM2O4 (M = Al, Co, and Rh)
No full textMagnetic phase transitions under high pressure are reported for the diamond lattice antiferromagnet Co _3−x Rh _x O _4 in the range of 0 ≤ x ≤ 2.0, which is an isostructural S = 3/2 system for the well-known frustrated antiferromagnet CoAl _2 O _4 . In the Co _3−x Rh _x O _4 system, magnetic and specific-heat measurements at ambient pressure revealed that a second-order antiferromagnetic transition occurred at the Néel temperature ( T _N ) which exhibits a nonmonotonic x -variation. The physical pressure variations of T _N were determined by ac-calorimetry under hydrostatic pressures up to p = 2.6 GPa for Co _2 RhO _4 and CoRh _2 O _4 . The rates of change of T _N with pressure (i.e., the pressure coefficients), 1.93 and 1.61 K GPa ^−1 , respectively, were comparable to those for CoAl _2 O _4 and Co _3 O _4 , respectively. The pressure coefficients of magnetic ordering temperature for these A-site spinel compounds were considerably larger than those for other spinel and iron-garnet compounds which follow the empirical ‘10/3 law’. Simple analysis of the chemical and physical pressure coefficients of T _N revealed that T _N depended on both the lattice volume and the oxygen positional parameter u
Electrophoretic deposition of bilayer based on sacrificial titanium dioxide and lead zirconate titanate on bare silicon wafer
No full textBilayer thick films of sacrificial titanium dioxide and Nb-doped lead zirconate titanate (PZTN) have been deposited on bare silicon wafers using electrophoretic deposition (EPD) technique. Deposition of such ceramic particles, dispersed ethanol-based suspensions, on semiconductor substrate has been made possible after preparation of alloyed junctions Al/Si characterized by ohmic behaviour. Sintering of green TiO2/PZTN films was performed at 900 ◦C for 1 h. The composition of the films, the thickness and relative density of the deposited materials have been analysed by EDS-SEM analysis. The lead diffusion through the silicon wafer has been reduce
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