Journal of Sol-Gel Science and Technology

“Sol paint” that yields yttrium-based compounds was prepared by mixing four chemical ingredients, yttrium acetate tetrahydrate precursor, diethanolamine, isopropyl alcohol, and hydrochloric acid, and then applied as oxidation/corrosion resistant coatings for Inconel 625 substrates. Annealing the coatings at 500°C developed a coalescent microstructure of coarse particles consisting of amorphous yttrium carbonate as the major component and crystalline yttrium oxide (Y2O3) as the minor one. At 700°C, the yttrium carbonate was transformed into Y2O3 by decarbonation. Increasing the annealing temperature to 900°C led to the formation of the YCrO3 phase yielded by interaction between Y2O3 and the Cr2O3 which had arisen from the oxidation of the underlying Inconel; the YCrO3 phase created a particle coating with a densified microstructure. There were two key factors in mitigating the degree of oxidation of Inconel at 900°C in air: (1) an uptake of oxygen by Y2O3 in the coatings, and (2) a densified coating layer that suppresses the diffusion and permeation of oxygen through it. Furthermore, inhibiting the rate of NaCl-caused corrosion was not only due to the excellent coverage of particle coatings over the entire surfaces of the substrates, but also may be associated with a good adherence of the coatings to the substrates.

Li3V2(PO4)3/C (LVP/C) composite materials have been successfully synthesized via a sol–gel method with oxalic acid as chelating agent and polyethylene glycol (PEG) as the supplementary carbon source, in which oxalic acid and PEG serve as double carbon sources. The X-ray diffraction patterns indicate that all of the samples are well crystallized. Transmission electron microscopy images reveal that the LVP/C sample prepared with 10 wt% PEG is uniformly coated by carbon layer with an appropriate thickness of 10–16 nm, resulting in a high electrical conductivity and a fast kinetics. The Li+ diffusion coefficient in the LVP/C sample prepared with PEG is 3.482 × 10−13 cm2 s−1, which is larger than that of the LVP/C sample prepared without PEG. In the range of 3.0–4.3 V, the LVP/C-10 electrodes exhibit good rate capability and excellent cyclic performance, which discharge capacities are 131.9 mAh g−1 at 0.1 C and 105.3 mAh g−1 at 5 C. The present work provides a valuable route for preparing lithium metal phosphates with double carbon sources to improve the conductivity and hence the electrochemical performance.

The structure of the silica aerogels was studied by Raman spectroscopy. The spectra of the solid network resembles that of bulk silica with additional bands related to organic groups and a large amount of OH groups. The typical bands due to ring breathing also called defect bands D 1 and D 2 located at 490 and 610 cm−1 are present. However, the evolution of the D 2 band compared to that of OH band (980 cm−1) seems apparently, in contradiction with the results previously reported in the literature. During heat treatments between 25 and 300°C the D 2 and the OH bands increase simultaneously. Generally, in silica glass the defect band D 2 grows at the expense of the OH groups. This result is explained by the oxidation of the organic compounds which, in this temperature range, leads to the formation of the both species (OH) and those related to siloxane rings. 29Si MAS NMR results are in agreement with the Raman study.

Porous thermochromic pure and tungsten (W)-doped vanadium dioxide (VO2) films have been prepared on silica substrates by spin coating via a sol–gel process and annealing in ammonia (NH3) atmosphere. NH3 with weak reducing capacity can prevent V4+ from further oxidization and contribute to the formation of porous structure. These films exhibit enhanced visible transparency and switching property at near-infrared wavelengths across the metal–insulator transition (MIT). The transmittance change in the VO2 film annealed at 2.0 × 103Pa is as high as 52.9 % at λ = 2000 nm, and its solar modulation efficiency reaches up to 9.4 %. W-doping shifts the MIT temperature of the VO2 films from 55 to 28 °C, while the films remain the excellent modulating ability in near-infrared region, and the decreasing efficiency of V0.99W0.01O2 film can achieve to 20 K/at.%, which will greatly favor the practical application of VO2-based smart windows. Transmittance spectra for pure VO2 film in the range of 250–2500 nm and the recorded transmittance–temperature hysteresis loop in the range of 20–90 °C of the W-doping VO2 films after annealing at 500 °C for 30 min (middle inset).

Magnetic bioglasses in the system CaO–SiO2–P2O5 were prepared by interaction of acetic acid vapors with iron nitrate dispersed on the surface of sol–gel derived porous silicate network. Upon pyrolysis, the created iron acetate species transform into magnetic iron oxide nanoparticles. X-ray diffraction (XRD), FT-infrared (FT-IR) spectroscopy and surface area measurements (BET) were employed to monitor the evolution of glass structural features during the synthetic pathway as well as the structure and the texture of the resultant glasses. XRD, Raman spectroscopy and vibration magnetic measurements (VSM) revealed the features of magnetic phases, developed in the form of γ-Fe2O3 and magnetite. The obtained glasses exhibit in vitro bioactivity, expressed by spontaneous formation of hydroxyapatite on their surface after immersion in SBF at 37 °C, confirmed with μ-Raman and FT-IR spectroscopies.

The effect of the incorporation of rare earth cations and fluoride anions into the ceria fluorite lattice has been studied. Ternary Ln-Ce-O (Ln = La, Pr, Nd) oxide gels of target Ln : Ce ratios of 1 : 4, 1 : 1.86 and 1 : 1, with and without added fluoride ion, have been prepared, and the oxide materials obtained after calcination at 1223 K examined. Incorporation of Ln results in the formation of Ln/CeO2 solid solutions at low Ln levels, but a microscopic mixture of two cubic phases, pure ceria and a Ln-Ce-O phase of composition Ce0.35La0.65O1.67, is obtained when a 1 : 1 ratio is employed. With fluoride pure CeO2 and LaF3 are the only phases present and no mixed Ln-Ce-O phase is formed. TEM shows that the microstructure of this material is complex. The nature of analogous Pr- and Nd-substituted ceria materials is also described.

The application of ammonium carbonate (AC) as catalyst for the preparation of RF-aerogels leads to organic aerogels without metallic impurities in contrast to conventional catalysts like sodium carbonate. To synthesize the AC catalyzed RF aerogels we varied the catalyst and formaldehyde concentration in wide ranges. The nanostructure varies accordingly over an order of magnitude. The particle sizes in the dry aerogel network, determined by scanning electron microscopy, are in the range of 0.15–4 μm. The aerogel densities are in the range of 370–420 kg m−3. The specific surface measured by nitrogen adsorption (BET) varies from 0.5 to 13 m2 g−1 which equals a specific surface area from 0.7 to 20 μm−1. Thermogravimetry is employed to study the drying process, annealing reactions and decomposition of the aerogel into a carbon aerogel.

Silica aerogels are utilized in the industry and scientific investigations. However, most silica aerogels are brittle, which hinders their development and application. In this paper, we reported the design and synthesis of a silica aerogel composite reinforced with silica nanowires by using two silicon sources: propyltriethoxysilane and tetraethoxysilane. The effects of varying silica nanowires contents on the properties of the silica aerogel composites were studied and compared with those of neat silica aerogel under identical conditions. The composites were obtained by mixing silica nanowires with hybrid silica sol without surface modification and dried in ambient atmosphere. The samples showed low density (0.172 g cm−3), high porosity (over 90%), and super hydrophobicity (the water contact angle reached 153°). The cross-linked silica aerogel composites showed excellent mechanical behavior and can be compressed by as high as 70% of their initial length before they were broken. The maximum completely recoverable compressive strain reached 50%. The elastic modulus of the optimal silica nanowires/silica aerogel composite increased by 67% (from 0.21 to 0.35 MPa) compared with that of the neat silica aerogel. The cross-linked propyltriethoxysilane and tetraethoxysilane can be used to synthesize new types of elastic silica aerogels, and the excellent performance of the silica nanowires/silica aerogels composite will enable its application in various fields.

Boron Neutron Capture Therapy (BNCT) is a promising therapy for the cure of diffuse tumors. The successful clinical application of BNCT requires finding new boron-based compounds suitable for an efficient 10B delivery to the cancerous tissues. The purpose of this work is to synthesize borosilicate nanoparticles by a sol–gel recipe, and to functionalize them with folic acid in order to promote their capture by the tumor cells. Whereas sol–gel is a promising technique for the synthesis of nanoparticles, in case of borosilicate systems this approach is affected by significant boron loss during preparation. Here we show that functionalization of borosilicate nanoparticles with folic acid can reduce the boron loss. Moreover, preliminary biocompatibility tests indicate that functionalization strongly changes the reactivity of NPs towards blood cells, so favouring the potential use of these materials for clinical applications.

A lower operating temperature below 600 °C of the solid oxide fuel cells (SOFCs) is a key determinant of device performance. With this in mind, the roles of dispersing agents were investigated for synthesizing a cathode material made of La0.6Sr0.4Co0.2Fe0.8O3−α (LSCF) for application in intermediate temperature solid oxide fuel cells (IT-SOFCs). In the present study, LSCF was synthesized following a sol–gel method with the aid of an activated carbon and ethylene glycol as dispersing agents. X-ray diffractometer measurements indicate that a single perovskite phase of LSCF started to develop at the temperature of 500 °C and completely formed at 700 °C. Scanning electron microscope analysis confirmed that a well dispersed LSCF powders were successfully synthesized achieving a surface area of 12.05 m2 g−1 as corroborated by the BET surface area analysis. This finding shows significant improvements of modifying the structural properties of cathode material and could be used to fabricate the next generation of SOFCs.