Papers by Keyword: Dip-Coating

Abstract: Polysilazane-based coatings were prepared on dense and porous substrates by dip-coating. Both the pure, liquid polymer and polymer solutions in cyclohexane were investigated. Relevant properties of the coating solutions, including rheological properties and surface tension, were determined and used to predict the resulting layer thickness as a function of dip-coating parameters on dense borosilicate glass substrates. A good correlation between existing model (Landau and Levich) and experiment was found for the pure polymer. In the presence of a solvent, evaporation phenomena led to a predicted coating thickness that is much less than the experimental value for all dip coating withdrawal spends. The introduction of a correction factor was found to adequately describe the deviation. In case of porous substrates, the coating thickness could not be predicted using the model due to infiltration of the base structure, resulting in an interpenetrating ceramic composite layer after pyrolytic conversion of the preceramic polymer compound. When preparing polymer-derived ceramic films on porous base materials, e.g. for membrane applications, this phenomenon has to be taken into account.

Abstract: The study evaluated the photocatalytic activity of TiO₂ supported on ceramic foams. In order to obtain these foams it was used a polymeric spongeprocess through replica method. Alumina ceramic foams were obtained with interconnected and open cellular structures allowing access of light through the material pores. The photocatalyst used was the commercial TiO₂ P25 Degussa impregnated into the ceramic foam by dip-coating method. These steps were used in the photodegradation of organic dye in an aqueous system. The photocatalytic tests showed 81 % efficiency in decolorizing the solution of Rhodamine B 20 mg L^{- 1} with a kinetic constant of 9.6 x 10^-3 min^{- 1}

Abstract: Multilayered thin films of aluminum-doped ZnO (Al:ZnO) have been deposited by the sol-gel dip coating technique. Experimental results indicated that the thermal annealing temperature affected the crystallinity of the Al:ZnO films. X-ray diffraction (XRD) analysis showed that thin films were preferentially orientated along the c-axis plane. The preferred orientation along (0 0 2) plane becomes more pronounced as the thermal annealing being increased. The film thickness ranges between 180 and 690 nm. In our experiments, the most optimum condition of Al:ZnO annealing temperature was both 500 oC.

Abstract:

Dip-coating is a conventional solution processing technology to prepare large-area films at a low cost and with cheap facilities. For semiconductor film processing, crystal orientation and thickness uniformity are the primary factors that determine the film quality and its electrical performance. These requirements are readily satisfied with the dip-coating method because the film morphology can be effectively optimized by tuning the withdrawal speed. This work optimizes the withdrawal speed for the dip-coating of patterned semiconductor films of 400×500 mm² as well as that for film dip-coating on the whole surfaces of the substrate. For both experiment, optimized electrical mobility is achieved at the same withdrawal speed, however, the random crystal orientation of the patterned films causes a remarkable decrease in device performance.

Abstract: Calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, CHAp), tricalcium phosphate (Ca₃(PO₄)₂, TCP) and calcium oxide (CaO) are the main components of inorganic part of human bones. Such synthetic nanocomposites could be very important implantable materials and using as substitute material for human hard tissues (bones and teeth). In this study, an aqueous sol-gel chemistry route has been developed to prepare nanostructured CHAp thin films on stainless steel substrate. For the preparation of thin films dip-coating and spin-coating techniques were used. The final samples were obtained by calcination of coatings for different time at 1000 °C. For the characterization of surface properties, the X-ray powder diffraction (XRD) analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM) and the contact angle measurements were recorded.

Abstract: Silica sol-gel membranes have been developed for moderate temperature (300 °C) separation of hydrogen (H₂) from nitrogen (N₂), methane (CH₄) and argon (Ar) gas molecules. Tubular ceramic support with 15 nm nominal pore diameter and 45% porosity was modified by dip-coating method. Gas permeation characteristics were evaluated. Defect free silica layer over the substrate for hydrogen gas separation was obtained. Hydrogen gas permeate flux of 4.82x10^-1 mol/sec m² at 1.0 barg feed pressure was obtained. Selectivities of H₂ over N₂, CH₄ and Ar of 3.07, 2.23 and 3.75 at 300 °C, 200 °C and 300 °C and 0.9 barg were obtained with the silica membranes. The gas permeation and the selectivity performance of the membrane were evaluated.

Abstract: Studies have been performed to improve the oxidation resistance of ferritic stainless steels at high temperatures because these materials have been proposed for the manufacture of interconnectors for solid oxide fuel cell (SOFCs) and solid oxide electrolysis cells (SOECs) operating at intermediate temperatures (IT-SOFCs). Among the coatings employed, ceramic spinel-type oxides have been the most frequently applied. In this context, Mn-Co-based coatings were deposited on ferritic stainless steel (AISI 430) in this study using a dip-coating technique. The obtained coatings were characterized with respect to their morphology by SEM, their elementary composition by EDS and their structure by XRD. It was possible to produce continuous and adherent Mn-Co-based coatings on the surface of the metallic substrates.

Abstract: Titanium dioxide (TiO₂) coating was prepared through dipping stainless steel net into titanium dioxide sol and then extracting it. The photocatalytic activities for all titanium dioxide coatings were tested by methyl orange degradation under ultraviolet and visible light irradiation. The photo-absorption property was determined by UV-Vis spectrophotometer. The titanium dioxide coating is photo-catalytically reactive for the degradation of methyl orange. The photo-catalytic activity is influenced by extraction times, degradation time, doping element and light source. La-doped titanium dioxide exhibits the best photocatalytic activity in comparison with undoped, V-doped and La-V-codoped ones. The degradation rate of methyl orange by La-doped titanium dioxide coating reaches 92% after 70 minutes irradiation under ultraviolet light.

Abstract: ZnO thin films have been prepared sol gel dip coating method using zinc acetate dehydrate (Zn(CH₃COO)₂·2H₂O, Merck) as cation source, 2-methoxyethanol (C₃H₈O₂, Merck) as solvent and monoethanolamine, MEA (C₂H₇NO, R&M) as sol stabilizer. Film deposition was performed by dip-coating technique at a fixed deposition rate on Corning 7740 glass substrate. The effect of sol concentration on the properties of the thin films is discussed. The effect of the sol concentration on produced ZnO films was found to be significant. X-ray analysis showed that thin films were preferentially orientated along the c-axis direction of the crystal. Besides, the films had a transparency of greater than 80% in the visible region for sol–gels with a zinc content of up to 0.8 M and exhibited absorption edges at ~375 nm.

Abstract: Honeycomb absorbing materials were measured using the method of free space in this paper. The reflectance of honeycomb absorbing materials was calculated and simulated, and it was verified based on the measured results. It was demonstrated that this test method was feasible. Through studying on absorbing properties of honeycomb, the results have showed that the radar absorbing properties of honeycomb are related to electromagnetic parameters, as well as thickness of the dip-coatings. With the increase of thickness of the dipping layer, the radar absorbing capability of high frequency and low frequency wave are significantly increased. It is worth noting that the resonance peak moved to the low frequency with the increase of dipping layer thickness. These results are useful for design of honeycomb absorbing materials.