Study of the Gelling Process in the La-Co-Citric Acid System

The gelling process in the aqueous lanthanum-cobalt-citric acid system was studied using UV-VIS and IR spectroscopic methods, as well as viscosity measurements, to establish the gelling mechanism of transition metal ions (La3+ and Co2+) in the presence of chelating agent. Lanthanum and cobalt nitrates and lanthanum and cobalt acetates, respectively, were used as starting reagents, and the citric acid was used as chelating agent. The gelation process was investigated at room temperature and at 80°C. At elevated temperature, the gels were obtained after 30 h, whereas at room temperature, these were obtained in 1 month. Complex gels were formed for the both studied systems. The Co2+ ions mainly present an octahedral symmetry during the whole gelation process, whereas the citric acid acts as monodentate or bridging ligand depending on the metal precursors used. The mechanism of formation of the La- Co-CA based gels with the coordinative structures was proposed

Perovskite type nanopowders and thin films obtained by chemical methods

The review presents the contribution of the authors, to the preparation of two types of perovskites, namely BiFeO3 and LaCoO3, by innovative methods. The studied perovskites were obtained as powders, films and sintered bodies. Their complex structural and morphological characterization is also presented. The obtained results have underlined the important influence of the method of preparation on the properties of the synthesized perovskites

Phase formation and electrical properties of the LaCoO3 obtained by water-based sol-gel method with citric acid

In the present work the LaCoO3 formation from gel precursors obtained by water-based sol-gel method with citric acid was studied. As precursors La and Co nitrates were used. The obtained gels were analyzed by TG/DTA and TG/EGA. The decomposition of the gels takes place in two main steps with the evolution of the same volatile compounds (H2O, CO2 and NO2) leading to the conclusion that two types of bonding of the components in the gels occurred. The decomposition of the gels takes place up to 400°C. The gels thermally treated at 600°C lead to single pure perovskite rhombohedral phase of lanthanum cobalt oxide (LaCoO3). Some electrical properties of LaCoO3 measured in “operando” conditions, i.e. in gas fl ow, at atmospheric pressure (by using the differential step technique DST) are presented and discussed

Sol-gel synthesis and structure of La2O3–CoO–SiO2 powders

LaCoO3 powders are studied because they exhibit interesting electrical, magnetic and catalytic properties. In this paper, new synthesized La2O3-CoO-SiO2 powders with different quantity of silica were prepared via solgel method in aqua media, starting from metal nitrates with different chelating agents. The relation between the reaction in solution, crystallization pathway and morphology were discussed. In LaCoO3-SiO2 powders, depending on the content of SiO2 and the treatment temperature (700–1100°C), different crystalline phases (LaCoO3, Co2SiO4 and La9.31(SiO4)6O2) were observed with the crystallite sizes ranging from 50 to 100 nm. It was proved that chemical composition and nature of used additives has influence on the phase formation and structure of obtained nanomaterials

Thermal behaviour of the TiO2-based gels obtained by microwave-assisted sol-gel method

In order to establish the influence of the preparation method on thermal behaviour of gels obtained by the sol-gel and microwave-assisted sol-gel methods, a comparative thermal analysis study was conducted by the thermogravimetric and differential thermal analysis (TG/DTG/DTA) and evolved gas analysis (EGA) on TiO2 and V2O5-doped TiO2 gels, where TiO2:V2O5 molar ratio was set to 99.95:0.05 and 98.0:2.0. In contrast to TiO2 gels, for which the thermal behaviour was not significantly influenced by the preparation method, the microwave-irradiated binary samples showed a more complex and prolonged decomposition compared to their non-irradiated counterparts. This observation was correlated with influence of microwaves in enhancing the reaction rate between the Ti and V reagents leading to formation of more complex compositions of gels. Based on TG/DTG/DTA results, the temperatures of 300 and 450 A degrees C were chosen for the processing of powders in air. All samples thermally treated at 300 and 450 A degrees C crystallized in a single anatase phase except the TiO2:V2O5 with a molar ratio 99.95:0.05, obtained by microwave-assisted sol-gel method that contains also small amount of rutile phase. At 550 A degrees C all samples contain mixture of anatase and rutile phases

Layered Double Hydroxides (LDHs) as New Consolidants for Cultural Heritage Masonry

(1) Background: In time, stone monuments suffer a process of aging and loss of aesthetic and mechanical properties. In order to restore and stop the loss of their properties, various treatments are used, and in this context, a new class of discovered materials with interesting properties are layered double hydroxides, or LDHs. (2) Methods: The LDHs, prepared by a coprecipitation method, were characterized by the structure by X-ray diffraction, composition by FT-IR spectroscopy and X-ray fluorescence spectroscopy, size by diffuse light scattering, and porosity by N2 adsorption/desorption. Additionally, some microscopy techniques such as optical microscopy and SEM/EDAX were used for surface aspects and morphology, and finally, all these were checked with ImageJ software for representative roughness parameters of the treated surfaces by brushing or incorporation. (3) Results: The prepared materials show different degrees of crystallinity and textural properties, and the dispersion of the material presents good stability in time in water/ethanol mixtures. Treatment with the LDH dispersion applied by brushing led to improvements in the mechanical properties (about a 5% increase in compressive strength), to an increased surface stability (about 30%), and to an improvement in the resistance to freeze–thaw cycles. The textural properties of the specimens’ materials were not altered by these treatments. (4) Conclusions: The order of the consolidation efficacity was CaMgAl-LDH > MgAl-LDH > CaAl-LDH, better for application by brushing than by incorporation

Layered Double Hydroxides (LDHs) as New Consolidants for Cultural Heritage Masonry

(1) Background: In time, stone monuments suffer a process of aging and loss of aesthetic and mechanical properties. In order to restore and stop the loss of their properties, various treatments are used, and in this context, a new class of discovered materials with interesting properties are layered double hydroxides, or LDHs. (2) Methods: The LDHs, prepared by a coprecipitation method, were characterized by the structure by X-ray diffraction, composition by FT-IR spectroscopy and X-ray fluorescence spectroscopy, size by diffuse light scattering, and porosity by N2 adsorption/desorption. Additionally, some microscopy techniques such as optical microscopy and SEM/EDAX were used for surface aspects and morphology, and finally, all these were checked with ImageJ software for representative roughness parameters of the treated surfaces by brushing or incorporation. (3) Results: The prepared materials show different degrees of crystallinity and textural properties, and the dispersion of the material presents good stability in time in water/ethanol mixtures. Treatment with the LDH dispersion applied by brushing led to improvements in the mechanical properties (about a 5% increase in compressive strength), to an increased surface stability (about 30%), and to an improvement in the resistance to freeze–thaw cycles. The textural properties of the specimens’ materials were not altered by these treatments. (4) Conclusions: The order of the consolidation efficacity was CaMgAl-LDH > MgAl-LDH > CaAl-LDH, better for application by brushing than by incorporation

Preparation and Biocompatibility of Poly Methyl Methacrylate (PMMA)-Mesoporous Bioactive Glass (MBG) Composite Scaffolds

In recent years, the rising number of bone diseases which affect millions of people worldwide has led to an increased demand for materials with restoring and augmentation properties that can be used in therapies for bone pathologies. In this work, PMMA- MBG composite scaffolds containing ceria (0, 1, 3 mol%) were obtained by the phase separation method. The obtained composite scaffolds were characterized by X-ray diffraction, infrared spectroscopy, and scanning electron microscopy. UV–Vis measurement and EDX analysis confirmed the presence of cerium ions in the composite scaffolds. Evaluation of the in-vitro biocompatibility using MTT assay showed that composite scaffold containing 1 mol% of ceria presented higher viability than control cells (100%) for concentrations ranging between 5 and 50% after 96 h of incubation

Structural, Optical, and Sensing Properties of Nb-Doped ITO Thin Films Deposited by the Sol–Gel Method

The aim of the present study was the development of Nb-doped ITO thin films for carbon monoxide (CO) sensing applications. The detection of CO is imperious because of its high toxicity, with long-term exposure having a negative impact on human health. Using a feasible sol–gel method, the doped ITO thin films were prepared at room temperature and deposited onto various substrates (Si, SiO2/glass, and glass). The structural, morphological, and optical characterization was performed by the following techniques: X-ray diffractometry (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV/Vis/NIR spectroscopic ellipsometry (SE). The analysis revealed a crystalline structure and a low surface roughness of the doped ITO-based thin films. XTEM analysis (cross-sectional transmission electron microscopy) showed that the film has crystallites of the order of 5–10 nm and relatively large pores (around 3–5 nm in diameter). A transmittance value of 80% in the visible region and an optical band-gap energy of around 3.7 eV were found for dip-coated ITO/Nb films on SiO2/glass and glass supports. The EDX measurements proved the presence of Nb in the ITO film in a molar ratio of 3.7%, close to the intended one (4%). Gas testing measurements were carried out on the ITO undoped and doped thin films deposited on glass substrate. The presence of Nb in the ITO matrix increases the electrical signal and the sensitivity to CO detection, leading to the highest response for 2000 ppm CO concentration at working temperature of 300 °C