Papers by Keyword: Sol-Gel Process

Abstract: The aim of this work was to synthesize eight samples of pseudoboehmite obtained by the sol-gel process under different conditions in a two level factorial experimental design consisting of three variables. It was observed how the properties of pseudoboehmites (crystallinity and morphology) were affected by the three analyzed variables, namely: aging temperature, aging time and addition of polyvinyl alcohol. The samples were characterized by x-ray diffraction, scanning electron microscopy with secondary electrons detector, differential thermal analysis, and thermogravimetric analysis. After being characterized, the pseudoboehmite powders were calcined in an electric furnace at 500°C. After calcination, the resultant powders were analyzed via x-ray diffraction. One of the most important results achieved in this work was the successful synthesis of gamma-alumina from pseudoboehmite, as well as high crystallinity in the pseudoboehmite samples aged at high temperatures.

Abstract: Soft chemistry (chimie douce) processes allow the design of multifunctional composite coatings tailoring the interfaces between phases. Instrumented indentation has become routinely used to characterize thin systems and allows for getting insight into interface mechanics. The paper illustrates both experimental approaches allowing for the fabrication PMMA based nanocomposites and their characterization employing nanoindentation.

Abstract: Polymeric nanocomposites are hybrid materials, where fillers with nanometric dimensions are dispersed in a polymeric matrix. The fillers have a high surface area, promoting better dispersion in the polymeric matrix and therefore an improvement in physical properties of the composite depending on the homogeneity of the material. In the present work, nanocomposites of polystyrene with different concentrations of pseudoboehmite obtained by a sol-gel process, and treated with octadecylamine were prepared. The nanocomposites were characterized by thermal and mechanical tests. The addition of pseudoboehmite caused a reduction of the melting flow during the production of the composites evidencing the interaction of pseudoboehmite with the polymeric matrix. The addition of pseudoboehmite promoted an increase in the melt flow index, in the the hardness of the nanocomposites obtained, practically does not affect the tensile strength and modulus and the impact strength decreases. The presence of pseudoboehmite causes increase in heat deflection temperature and Vicat softening point and the thermal decomposition occurred at a higher temperature than the pure PS.

Abstract: Weathering and air pollution compromise the preservation of historic buildings made of stone. The concept of the consolidation of materials is introduced to overcome this problem, or at least to reduce its severity. The consolidation consists of introducing a chemical substance into damaged stone for restoring its original mechanical properties, or into undamaged stone for preserving it. Silicon compounds, such as tetraethoxysilane, are frequently used for this purpose. Here, we present a time domain study of the sol-gel process using Dynasylan 40 with the addition of the nanoparticles of SiO₂, Al₂O₃, TiO₂ and CaCO₃.

Abstract: Hydrothermal method and sol-gel process were used to synthesize multiferroic BiFeO₃ ceramics. X-ray diffraction, scanning electron microscopy, vickers diamond indenter and three-point bending method were used to investigate the effects of methods on the phase structure, microstructures and mechanical properties. Cold isostatic pressing on the ceramics with two different loads (10 MPa, 200 MPa) was used to illustrate the influence of pressure in mechanical properties. The results show that all samples are crystallized in the perovskite phase. A few small traces of impurity are observed at a 2θ of ~28 ^o, which are found to be those of Bi₂Fe₄O₉. The SEM images depict that samples prepared by sol-gel process are more uniform and the grain size is slightly larger than that of hydrothermal processed samples. The investigations on the hardness and flexural strength demonstrate the ceramics prepared by hydrothermal method have better mechanical properties than that of sol-gel process, and the mechanical properties can be obviously enhanced by increasing pressure.

Abstract: The aim of this work is to improve the known methods of forming coatings on titanium implants: anodizing, plasma spraying, and ceramic one. For this purpose we use hydroxyapatite (HA) obtained from biological raw materials by roasting technology that preserves the microstructure of natural HA. The sol-gel method has been used to impart bioactivity to anodic coatings. In addition, criteria for evaluating the effectiveness of the methods for forming coatings, based on analysis of author data and expert opinions, are proposed. The evaluation of the methods used in this paper is presented.

Abstract: To improve the preparation technology and mechanical properties of carbon/carbon composites, a kind of Zirconium dioxide modified Carbon/carbon (C/C–ZrO2) composites were prepared by Sol-Gel Process combined with isothermal chemical vapor infiltration (ICVI) method. This method could shorten preparation cycle greatly to reduce the cost. The microstructures and mechanical properties of the C/C–ZrO2 composites were investigated. The results indicate that the ZrO2 modified phase is uniformly distributed in the carbon matrix, the bending strength and modulus of C/C–ZrO2 composites are much higher than unmodified C/C composites due to its particle toughening and fiber toughening.

Abstract: Porous Al₂O₃-SiO₂-ZrO₂ ceramic composite membranes were fabricated by the sol-gel method. The effects of constitution of the composite sol, dip-coating parameters and calcination parameters on the morphology, phase composition, pore size distribution and BET surface area of the membranes were investigated extensively. The thermogravimetric analysis (TGA)/differential scanning calorimeters (TG/DSC), scanning Electron Microscopy (SEM), XRD analysis and N₂ adsorption-desorption analysis was employed for the membranes characterization. TG/DSC curve shows that the suitable calcination temperature of Al₂O₃-SiO₂-ZrO₂ membranes is 1000°C. The SEM morphology displays a smooth and free-crack layer of Al₂O₃-SiO₂-ZrO₂ composite membranes on the surface of the support after calcination at 1000°C. Furthermore, the membranes were also successfully coated with a good adhesion to the support. The optimal composite membranes were obtained when the moral ratio of Al₂O₃-SiO₂-ZrO₂ was 10:2.3:1, the dip-coating parameters were four times dip-coating with every time of 60s respectively.

Abstract: When bioactive coatings are applied to medical implants by means of sol-gel dip coating technique, the biological proprieties of the implant surface can be modified to match the properties of the surrounding tissues. In this study, sol-gel method is used to synthesized organic-inorganic nanocomposites materials consisting of an inorganic titania matrix in which 10 wt% of a biodegradable polymer, the poly-ε-caprolactone (PCL), was incorporated. The synthesized materials, in sol phase, were used to dip-coat a commercially pure titanium grade 4 substrate in order to improve its surface biological properties. Materials were characterized using Fourier transform infrared spectroscopy (FT-IR) and a morphological analysis of the obtained films was performed via scanning electron microscopy (SEM). Coating bioactivity was investigated by soaking coated substrates in a fluid simulating the human blood plasma (SBF) and successively evaluating the formation of a hydroxyapatite layer on their surface by means of SEM/EDX (energy dispersive X-ray).

Abstract: As the key parts to fuel cells, proton conducting electrolytes decides the performance of fuel cells. SiO₂-P₂O₅-TiO₂ based glasses have been prepared by a sol-gel process in this experiment. Through TG、 XRD and SEM analysis, it was found that the membrane was existed in the form of amorphous structure. And most of the pores were in micro-pores of size less than 10μm. By the results of resistance, the conductivities were obtained by calculation. The influence of temperature to conductivity was discussed in detail. It was found that the conductivity was increased with the increased temperature .The membrane showed overall conductivities greater than 10^-2S·cm^-1 at 2000Hz in the temperature range of 70~140°C.