Sol-gel derived silica possess many promising features, including low-temperature preparation procedure, porosity, chemical and physical stability. Applications exploiting porous materials to encapsulate sensor molecules, enzymes and many other compounds, are developing rapidly. In this paper some potential applications, with emphasis on biomedical and environmental ones, are reviewed. The material preparation procedure is described and practical remarks on silica-based sol-gels are included. It is reported that sol-gels with entrapped various molecules may be used in construction of implants and coatings with bioactive properties. It is shown how to exploit the sol-gel production route for construction of sol-gel coated fiberoptic applicators for lasertherapy. The applications of bioactive materials are discussed, as well. It is demonstrated that it is possible to immobilize photosensitive compounds in sol-gel matrix without loosing their photoactivity. Some examples of sol-gel based biosensors are demonstrated, as well, showing their potential for detecting various gases, toxic substances, acidity, humidity, enzymes and biologically active agents.
This study is devoted to synthesis and characterization of uranium dioxide microspheres (Ø < 100 µm) and pellets by application of powder-free process called the Complex Sol-Gel Process. The precursors of prepared sols were ascorbic acid solution with dissolved a freshly precipitated ammonium diuranate. The microspheres of uranyl-ascorbate gel were obtained using the ICHTJ Process. The pellets were formed by pressing and sintering of uranium dioxide powder. Studies allowed determining an optimal heat treatment of calcination, reduction and sintering processes at temperatures of 700°C, 900°C and 1300°C, respectively. The main parameters which play a key role in the process of synthesis method and features of the pellets and microspheres of uranium dioxide are described in this article.
Crystal structure and phase composition of stainless steel substrates (AISI 304 type) was studied and it was found that they adopted the cubic symmetry. The calculated elementary cell parameter for the mayor Fe-Ni phase (weight fraction 99%) was a = 3.593 Å, whereas the mean grain size was <D> = 2932 Å. Morphology of the stainless steel substrate surface was studied with profilometry. Mechanical properties of the stainless steel substrates and stainless steel substrates coated with ceramic layer of barium strontium titanate were studied with microhardness tester. For measurements performed according to the Vickers method the average microhardness was found HV = 189 or HV = 186 for the “in-line” and “mapping” measurement pattern, respectively. The sol-gel method was used to coat the surface of the stainless steel substrate with a thin ceramic layer of the chemical composition Ba0.6Sr0.4TiO3. It was found that the stainless steel substrate covered with sol-gel deposited ceramic coating exhibited the average hardness within the range HV = 217 up to HV = 235 for loading force F = 98 mN and F = 0.98 N, respectively. The Knopp method was also used and it was found that the stainless steel substrate with Ba0.6Sr0.4TiO3 coating exhibited hardness HK = 386.
Titania dioxide (TiO2) layers were synthesized via the acid-catalysed sol-gel route using titania (IV) ethoxide, and then annealed at temperatures varying in the range of 150–700 °C. The research concerned the effect of annealing temperature on the structure of TiO2 layers, their surface morphology, and their optical properties. Further, X-ray diffractometry, and Raman spectroscopy were used to determine the structure of TiO2 layers. Scanning electron and atomic force microscopy were used to study the surface morphology of TiO2 layers. Transmittance, reflectance, absorption edge, and optical homogeneity were investigated by UV-VIS spectrophotometry, while the refractive index and thicknesses of TiO2 layers were measured using a monochromatic ellipsometer. Chromatic dispersion characteristics of the complex refractive index were determined using spectroscopic ellipsometry. Structural studies have shown that the TiO2 layers annealed at temperatures up to 300 °C are amorphous, while those annealed at temperatures exceeding 300 °C are polycrystalline containing only anatase nanocrystals with sizes increasing from 6 to 20 nm with the increase of the annealing temperature. Investigations on the surface morphology of TiO2 layers have shown that the surface roughness increases with the increase in annealing temperature. Spectrophotometric investigations have shown that TiO2 layers are homogeneous and the width of the indirect optical band gap varies with annealing temperature from 3.53 eV to 3.73 eV.
Worldwide commercial interest in the production of cerium doped yttrium aluminium garnet (YAG:Ce) phosphors is reflected in the widespread use of white light emitting devices. Despite of the fact that YAG:Ce is considered a “cool phosphor” it is the most important in white LED technology. This article reviews the developed techniques for producing phosphors with superior photoluminescence efficiency, including solid-state reaction, sol-gel and (co)precipitation methods. Also, by co-doping with rare earth elements, a red/blue shift is reached in the spectrum. The characteristics of YAG:Ce phosphors are investigated because the properties of the phosphors are strongly influenced by the synthesis routes and the sintering temperature treatment. After the phase analysis, morphology and emission studies of the phosphors there may be seen the conditions when the transition from the amorphous phase to the crystalline phase appears, when luminescent properties are influenced by the crystalline form, purity, average size of the particles, co-doping and so on.
This paper discusses the influence of the direction of applied deformation on the ability to gelation of thermosensitive chitosan hydrogels. The application of the shear rate equal in value to the classically performed oscillatory measurements leads to significantly different shapes of experimental curves. It was found that the type of mechanically applied deformation has a significant impact on the gelation ability of colloidal chitosan solutions and conditions of sol-gel phase transition. Simple shear leads to a phase transition at a lower temperature or in a shorter time compared to oscillatory tests. Moreover, based on the final values of dynamic viscosity in rotational measurements, it was found that stronger crosslinking of the polymer structure was observed.
The paper presents the influence of ZrO2 coating on Ti6Al7Nb titanium alloy depending on the method of deposition. The coatings were made by sol-gel method and atomic layer deposition (ALD). Wettability tests, pitting corrosion assessment and electrochemical impedance spectroscopy (EIS) were carried out in the paper. Complementary macro- and microscopic observations, roughness analysis by profilometric method and atomic force microscopy (AFM) were made. Based on the results obtained, it can be concluded that the type of method of depositing the layer on the surface of the material has a significant influence on its properties and that it should be taken into account during the process of the material improvement. Drawing on the findings presented, it can be inferred that roughness has a significant impact upon the surface wetttability of the tested surfaces and their related corrosion resistance. The obtainment of hydrophobic surfaces is for smaller rougidity values.