Aldona Beganskiene

Evidence of the formation of mixed-metal garnets via sol–gel synthesis

A sol–gel method based on in situ generation of mixed-metal chelates by complexing metal ions with 1,2-ethanediol in aqueous media has been developed to prepare pure and substituted yttrium aluminium garnets: Y3Al5O12 (YAG), Y3Sc2Al1Ga2O12 (YSAGG-3212), Y3Sc1Al3Ga1O12 (YSAGG-3131), Y3Sc2Al3O12 (YSAG), Y3Al3Ga2O12 (YAGG), Y3Sc2.5Ga2.5O12 (YSGG). The XRD patterns of the powders sintered at 1000 °C showed the formation of monophasic garnet material except in the case of YSGG sample. The thermal behaviour, phase transformations, composition and micro-structural features in the gels and polycrystalline samples were studied by TG/DTA, XRD, FT-IR, SEM and EDX analysis. These new materials doped with different active elements could be potential candidates as laser materials for solid-state lasers.

pH impact on the sol-gel preparation of calcium hydroxyapatite, Ca10(PO4)6(OH)2, using a novel complexing agent, DCTA

Aqueous sol-gel chemistry routes — based on ammonium hydrogen phosphate as the phosphorus precursor, calcium acetate monohydrate as the source of calcium ions, and 1,2-diaminocyclohexanetetraacetic acid monohydrate (DCTA) as the complexing agent — have been used to prepare calcium hydroxyapatite (HA). The sol-gel process was performed in aqueous solution at different pH values followed by calcination of the dry precursor gels for 5 h at 1000°C. Phase transformations, composition, and structural changes in the polycrystalline samples were studied by thermoanalytical methods (TG/DTA), infrared spectroscopy (IR), X-ray powder diffraction analysis (XRD), and scanning electron microscopy (SEM). It was shown that pH adjustment has significant impact on the apatite formation process and on the morphology and phase purity of the ceramic samples.

Sol-Gel Derived Two-Dimensional Nanostructures of Calcium Phosphates

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.

SOL-GEL PREPARATION AND CHARACTERIZATION OF NOVEL MIXED-METAL COBALTATES-ALUMINATES

This article reports on the sol-gel synthesis and characteristic properties of novel mixed neodymium and neodymium-yttrium cobaltates and cobaltates-aluminates (NdCoO3, NdCo0.75Al0.25O3, NdCo0.5Al0.5O3, NdCo0.25Al0.75O3, (Nd0.5Y0.5)CoO3, (Nd0.5Y0.5)Co0.75Al0.25O3, (Nd0.5Y0.5)Co0.5Al0.5O3, and (Nd0.5Y0.5)Co0.25Al0.75O3). The polycrystalline powders were characterized by powder X-ray diffraction (XRD) analysis, Fourier transform-infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM). Single-phase solid solutions NdCo1-xAlxO3 and (Nd0.5Y0.5)Co1-xAlxO3 were obtained after annealing precursor gels for 10 h at 1000°C. From the results obtained, it could be concluded that the NdCo1-xAlxO3 and (Nd0.5Y0.5)Co1-xAlxO3 solids are composed of spherical grains with uniform size (from 100 to 500 nm). The surface morphology changes slightly with substitution of cobalt by aluminium and neodymium by yttrium. With increasing amount of aluminium the crystalline particles formed with more pronounced agglomeration. The possible application of synthesized compounds as blue cobalt-based pigments was suggested.

Sol-Gel Synthesis of Modified Silica Anti-Reflecting Coatings

The thickness of the modified silica coatings and their transparency at specified wavelength were easily controled by changing sol concentration and the parameters of the spin-coating formation process. It was demonstrated that the modification of sols changes the maximum of the transmittance for the certain range of wavelength. Using modification process of the sols in the technology of preparation of transparent coatings, their hydrophobic properties and resistance to humidity increased. The transmittance spectra of the 3% SiO2 coatings, which were applied on different glass substrates, showed that the usage of suitable sol and coating program will result a formation of films which possess antireflective properties

Synthesis of Silica-Carbon Nanotube Composite Materials and Their Application for Laser Systems

Currently, fabrication of CNT and polymer composites for saturable absorbers is very popular. But due to nature of organic polymer matrix, these composites are unstable on higher temperatures or in high energy light exposition. Therefore a sol-gel process for the fabrication for inorganic (i.e. silica) or semi-organic (organic-modified silica) matrix can be a promising way to produce photo-chemically and thermally stable CNT composites. In this work we investigated SWCNTs solubility in ethanol using different surfactants - Triton, polyvinylpyrrolidone, and Poly(4-vinylpyridine). Most stable colloidal solution was obtained using a P4VP as surfactant - solutions were stable up to 6 weeks. Therefore this surfactant was used for the fabrication of SWCNT/Silica composite coatings. SWCNTs was directly dispensed in a colloidal silica sol and coatings made by spin-coating technique. Samples were investigated under optical, atomic force microscopy methods, and optical non-linearity was measured. Thermal stability was investigated using Raman spectroscopy.

Bi-substituted Mg 3 Al–CO 3 layered double hydroxides

Magnesium–aluminium–bismuth-layered double hydroxides (LDH) intercalated with carbonate were studied in respect of maximal rate of substitution of Al3+ by Bi3+ for the first time. LDH with the nominal compositions of Mg3Al1 - xBix–CO3 (x = 0 to 0.5) were prepared using both the conventional super saturation co-precipitation method and sol–gel processing via hydration of the mixed oxide powders in carbonate-containing solutions. The mixed oxides were obtained either by calcination of the LDH (prepared by co-precipitation) or by using a novel alkoxide-free sol–gel method. All the LDH products were characterised using the methods of X-ray diffraction, scanning electron microscopy and thermogravimetry. The observed values of the lattice parameters of LDH phases were compared with the calculated values. It has been found that, regardless of the preparation method used and the conditions (pH, temperature, time) applied, the maximum rate of substitution of aluminium by bismuth in LDH is about 20 mol.%.Graphical abstractA schematic representation of LDH structure of a 3R polytype [4, 5] where the lattice parameter c and the basal spacing d relate to each other as c = 3d.

Structural, morphological, and magnetic characterization of bulk and thin films Y3Al5–xFexO12 (YAIG): From the perspective of aqueous sol–gel processing

ABSTRACT An aqueous sol–gel method was used for the preparation of bulk Y3Al5–xFexO12 (yttrium aluminum–iron garnet, YAIG) with the composition of x = 0.0, 1.0, 2.0, 2.5, 3.0, 4.0, 5.0 and thin films with the composition of x = 0, 3.0, 4.0, 5.0. The dip-coating technique was used for the preparation of Y3Al5–xFexO12 films on a silicon (Si) substrate. The phase composition and surface morphology of both bulk and coatings were determined and compared. The synthesized powder samples were investigated by X-ray diffraction analysis, infrared spectroscopy, scanning electron microscopy, and Mössbauer spectroscopy. The data provide evidence that some sol–gel-derived powder specimens consist of magnetically ordered component, while others show paramagnetic behavior depending on the composition of the product. It was also shown that sol–gel processing route could be successfully used for the preparation of mixed-metal YAIG thin films.

Sol-Gel Derived Ferrites: Synthesis and Characterization

In the present work, the sinterability and formation of nanosized yttrium iron garnet (Y3Fe5O12), yttrium perovskite ferrite (YFeO3), cobalt, nickel and zinc iron spinel (CoFe2O4, NiFe2O4 and ZnFe2O4, respectively) powders by an aqueous sol-gel processes are investigated. The phase purity of synthesized nano-compounds was characterized by powder X-ray diffraction analysis (XRD). The microstructural evolution and morphological features of obtained transition metal ferrites were studied by scanning electron microscopy (SEM). The possible application of these nanosized transition metal ferrites as ceramic pigments was demonstrated.

Silica-carbon nanotubes composite coatings as saturable absorbers

Currently, fabrication of CNT and polymer composites for saturable absorbers is very popular. But due to nature of organic polymer matrix, these composites are unstable on higher temperatures or in high energy light exposition. Therefore a sol-gel process for the fabrication for inorganic (i.e. silica) or semi-organic (organic-modified silica) matrix can be a promising way to produce photo-chemically and thermally stable CNT composites. In this work was investigated SWCNTs solubility in ethanol using different surfactants - Triton, polyvinylpyrrolidone (PVP), and Poly(4-vinylpyridine) (P4VP). Most stable colloidal solution was obtained using a P4VP as surfactant - solutions were stable up to 6 weeks. Therefore this surfactant was used for the fabrication of SWCNT/Silica composite coatings. SWCNTs was directly dispensed in a colloidal silica sol and coatings made by spin-coating technique. Samples were investigated under optical, atomic force microscopy methods, and optical non-linearity was measured. Thermal stability was investigated using Raman spectroscopy.