Characterization of Magnesium‐Doped Hydroxyapatite Prepared by Sol‐Gel Process

Pure and doped hydroxyapatite (HA) nanocrystalline powders (Ca_10‐xMg_x(PO₄)₆OH₂) were synthesized using sol‐gel process. For this, calcium nitrate tetrahydrate, magnesium nitrate hexahydrate, and phosphorous pentoxide were used as precursors for Ca, Mg, and P, respectively. Calculated amounts of magnesium ions (Mg⁺²) especially from 0 to 10% (molar ratio) were incorporated as dopant into the calcium sol solution. The structure and morphology of the gels obtained after mixing the phosphorous and (calcium + magnesium) sol solution were different, and their condensations in time depend on the quantities of magnesium added. The several powders resulting from the gels dried and sintered at 500°C for 1 h were characterized by thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and inductively coupled plasma (ICP). Additionally, their agglomeration, morphology, and particle size were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The specific surface area of each sample was measured by the Brunauer–Emmett–Teller (BET) gas adsorption technique. The results of XRD, FTIR, and ICP values ranged between 0.45 and 2.11 mg/L indicated that the magnesium added in the calcium solution was incorporated in the lattice structure of HA so prepared, while those obtained by SEM and TEM confirmed the influence of Mg on their morphology (needle and irregular shape) and crystallite size, which is about 30–60 nm. The as‐prepared powders had a specific surface area ranged between 6.37 and 27.60 m²/g.     

Catalysis with Doped Sol‐Gel Silicates

Silicates doped with catalytic species have only been slowly adopted by the fine chemicals and pharmaceutical industries, in spite of their remarkable and unique properties such as pronounced physical and chemical stability; high (enantio)selective activity and ease of materials production and application. This is now changing thanks to stricter safety regulations and to concomitant success of the first commercial catalysts. In this account we tell the story of these materials and identify some deficiencies in the innovation process that may serve as lesson in guiding the future management of innovation in these relevant industries.     

The Sintering Trajectory and Electrical Properties of Niobium‐Doped Titania Sputtering Targets

Nb‐doped TiO₂ (TNO) films, which are highly conductive and transparent, can be used as transparent conductive oxide (TCO) films. A predominant manufacturing method for TCO film is magnetron sputtering, and the material of the sputtering target affects the performance of the film. The objective of this study was to investigate the sintering densification, microstructure, and electrical properties of TNO and TiO₂ sputtering targets. The results showed that the segregation of Nb at the grain boundary in TNO helps to facilitate densification and inhibit grain growth. After 1200°C sintering, the sintered density of TNO target achieves almost 100% of the theoretical density. Moreover, the Nb₂O₅ additive greatly improves the electrical properties, decreasing the resistivity of TiO₂ from >10⁸ Ωcm to 4.6 × 10¹ Ωcm. Correlations between TNO sputtering target investigated in this study and TNO sputtered film reported in the literature are also preliminarily established. The resistivity of TNO film with an anatase structure is obviously lower than that of TNO target with a rutile structure.     

Sol‐Gel Synthesis and Spray Granulation of Porous Titania Powder

Bimodale poröse Titandioxidpulver mit kontrollierter Phasenzusammensetzung und ‐porosität, die nasschemisch hergestellt wurden, sind in unserem Labor umfassend untersucht worden. Diese Arbeit gibt eine Übersicht über experimentelle Parameter, die die Phasen‐ und Porenstruktur dieser Pulver beeinflussen. Außerdem wird der Einfluss von Lösungspeptisation auf die Packung und Anordnung der Partikel untersucht. Die unpeptisierte Sprühlösung und das peptisierte Sol wurden sprühgetrocknet, um Granulate mit kontrollierter Porosität und Morphologie herzustellen. Die Eigenschaften der Granulate waren abhängig von den Eigenschaften der verwendeten Lösung. Insbesondere die Granulate aus der unpeptisierten Sprühlösung zeigten eine bimodale Porengrößenverteilung mit rauen Oberflächen, die auf harte Aggregate zurückzuführen sind. Granulate vom peptisierten Sol zeigten eine monomodale Porengrößenverteilung mit glatten Oberflächen von gutgepackten Mikrostrukturen. Potentielle Anwendungen ergeben sich für diese Granulate als Adsorber, als Katalysatorträger und als Packung für chromatographische Trennkolonnen.     

Nonaqueous Sol–Gel Synthesis of Magnetic Iron Oxides Nanocrystals

Benzyl alcohol route, starting form Fe(III) acetylacetonate, was applied to obtain crystalline magnetite nanoparticles. In particular, the effect of synthesis parameters (time and temperature) and use of SOCl₂ on the physical and magnetic properties of the so‐obtained powders were evaluated. By means of this approach, monocrystalline magnetite particles with size ranging from 5 to 15 nm were obtained.     

Bioactive Sol‐Gel Coatings

Recent sol‐gel techniques enable bioactive composite layers to be prepared by the embedding of bioactive compounds, biomolecules (BMs) and cellular systems within inorganic layers. These novel bioactive layers offer interesting new applications, e.g. biocompatible coatings on implants and medical products, the preparation of biosensors and biocatalysts, and coatings that can release biocides in a controlled manner.     

A Simple Method for the Reinforcement of UV‐Cured Coatings via Sol‐Gel Photopolymerization

A difunctional methacrylate oligomer was mixed with a variable amount of a MAPTMS precursor in the presence of both a radical and a cationic photoinitiator. The simultaneous photolysis of both photosensitive molecules upon UV irradiation allowed the single‐step generation of a type‐II polymethacrylate/polysiloxane nanocomposite film. Methacrylate and methoxysilyl conversions during irradiation were efficiently monitored by FTIR spectroscopy. The inorganic structure of the resulting silica‐based hybrid films was characterized using ²⁹Si solid‐state NMR. Finally, the reinforcement ability of the resulting hybrid films was also assessed by using a unique range of characterization techniques: DMA, scratch test, and nanoindentation.

     

Magnetic and Dielectric Properties of Nanostructured BiFeO3 Prepared by Sol–Gel Method

Polycrystalline BiFeO₃ was synthesized at 400°C–700°C. Distinctive difference in the magnetic and dielectric properties was observed between the samples sintered at 400°C–500°C and those sintered at 600°C–700°C. The former showed ferromagnetic‐like hysteresis loops with an increased magnetization of 0.54 emu/g, whereas the later showed linear loops with a small magnetization of 0.065 emu/g. Although X‐ray did not identify any secondary phase, the suspected trace of some magnetic phase (Fe₃O₄) in the samples was conceded by the occurrence of an exchange bias. The difference in dielectric response between the two groups of samples arose mainly from a different conductivity at the grain boundaries. Owing to Fe₃O₄ coating at grain surface, the 400°C–500°C sintered samples behaved like a single parallel R–C circuit, whereas the dielectric response of the samples sintered at 600°C–700°C was represented by a series of two parallel R‐C units for grains and grain boundaries, respectively. Two dielectric relaxation peaks observed at <700 Hz and 0.3~6 MHz in the high‐temperature sintered samples were attributed to the Maxwell–Wagner relaxation and electron hopping, respectively.     

Characterization and Tribological Investigation of Sol–Gel Titania and Doped Titania Thin Films

Titania (TiO₂) and doped TiO₂ ceramic thin films were prepared on a glass substrate by a sol–gel and dip-coating process from specially formulated sols, followed by annealing at 460°C. The morphologies of the original and worn surfaces of the films were analyzed with atomic force microscopy (AFM) and scanning electron microscopy. The chemical compositions of the obtained films were characterized by means of X-ray photoelectron spectroscopy (XPS). The tribological properties of TiO₂ and doped TiO₂ thin films sliding against Si₃N₄ ball were evaluated on a one-way reciprocating friction and wear tester. The AFM analysis shows that the morphologies of the resulting films are very different in nanoscale, which partly accounts for their tribological properties. XPS analysis reveals that the doped elements exist in different states, such as oxide and silicate, and diffusion took place between the film and the glass substrate. TiO₂ films show an excellent ability to reduce friction and resist wear. A friction coefficient as low as 0.18 and a wear life of 2280 sliding passes at 3 N were recorded. Unfortunately, all the doped TiO₂ films are inferior to the TiO₂ films in friction reduction and wear resistance, primarily because of their differences in structures and chemical compositions caused by the doped elements. The wear of the glass is characteristic of brittle fracture and severe abrasion. The wear of the TiO₂ thin film is characteristic of plastic deformation with slight abrasive and fatigue wear. The doped TiO₂ thin films show lower plasticity than the TiO₂ thin film, which leads to large cracks. The propagation of the cracks caused serious fracture and failure of the films.     

Effects of Solution History on Sol‐Gel Processed Tin‐Oxide Thin‐Film Transistors

Antimony‐doped tin‐oxide (SbTO) thin films deposited by solution processing methods represent a promising avenue toward low‐cost transparent and flexible electronics, but reproducibility and performance homogeneity of devices prepared from these thin films have been seldom investigated. In this study, the role of sol‐gel precursor aging is investigated by comparing SbTO thin‐film transistors (TFT) fabricated from two different sol‐gel solutions: the first one was aged for 4 years, whereas the second was prepared freshly. For each of the solutions, a set of TFT was assembled on the same chip, to investigate the distinct roles of aging and sample inhomogeneity on the electronic and transport properties of SbTO. Higher electron mobility, but lower on/off ratios, was found in TFTs assembled from freshly prepared solution, an effect that may be assigned to larger size of SbTO grains. This study demonstrates the critical role of the solution “history” in determining the properties and reproducibility of SbTO TFTs, over other factors, including local film inhomogeneity and local fluctuations of the annealing temperature.     

Determination of Heat Treatment Temperature for Completing Polycondensation of Vinyl Substituted Silica Particles Prepared by Sol‐Gel Method

The completion of the polycondensation of sol‐gel derived organic‐inorganic hybrid silica by heat treatment was studied for powder samples prepared from vinyltrimethoxysilane and vinyltriethoxysilane. The appropriate temperature for the completion of the prepared submicron powdery samples from both starting compounds was determined through thermogravimetric analysis. The completion or incompletion of the polycondensation was elucidated by means of several instrumental methods in addition to a light scattering test. The lowest heat treatment conditions for the particles from vinyltrimethoxysilane and vinyltriethoxysilane are 170 °C and 180 °C, respectively, for 24 h. The morphologies of the heat treated samples were found to be slightly different depending on the starting material used.     

High‐Temperature Capture of CO2 on Lithium‐Based Sorbents Prepared by a Water‐Based Sol‐Gel Technique

A convenient water‐based sol‐gel technique was used to prepare a highly efficient lithium orthosilicate‐based sorbent (Li₄SiO₄‐G) for CO₂ capture at high temperature. The Li₄SiO₄‐G sorbent was systematically studied and compared with the Li₄SiO₄‐S sorbent prepared by solid‐state reaction. Both sorbents were characterized by X‐ray diffraction, scanning electron microscopy, nitrogen adsorption, and thermogravimetry. The CO₂ sorption stability was investigated in a dual fixed‐bed reactor. Li₄SiO₄‐G exhibited a special Li₄SiO₄ structure with smaller crystalline nanoparticles, larger surface area, and higher CO₂ adsorption properties as compared with Li₄SiO₄‐S. The Li₄SiO₄‐G sorbent also maintained higher capacities during multiple cycles.     

Preparation of Mesoporous Silicon Nitride via a Nonaqueous Sol–Gel Route

A silicon diimide gel Si(NH) _x (NH₂) _y (NMe₂) _z was prepared by an acid-catalyzed ammonolysis of tris(dimethylamino)silylamine. Pyrolysis of the gel at 1000°C under NH₃ flow led to the formation of an amorphous silicon nitride material without carbon contamination. All of the gel and pyrolyzed products exhibited a mesoporous structure with a high surface area and narrow pore-size distribution. The effective surface area of the pyrolyzed silicon nitride residues decreases with increasing temperature, but the heating rate during pyrolysis has little influence on the surface area and pore-size distribution of the final mesoporous ceramic Si₃N₄ products because of the highly cross-linked structures of the precursor silicon diimide gel.     

Sol‐Gel Ormosils Doped with TEMPO as Recyclable Catalysts for the Selective Oxidation of Alcohols

Organically modified silicas doped with TEMPO prepared via the sol‐gel method are highly recyclable catalysts of the selective Montanari‐Anelli oxidation of 1‐nonanol; They show a notable ”positive feedback” effect of matrix alkylation on the catalyst activity which is typical of doped sol‐gel materials and markedly differentiates the behaviour of these materials from that of analogous silica‐supported TEMPO.     

Application of Taguchi Method for Characterization of Corrosion Behavior of TiO2 Coating Prepared by Sol‐Gel Dipping Technique

Titanium oxide (TiO₂) nanoparticle coatings were deposited on the 316L stainless steel substrates by sol‐gel method. The morphology, structure, and corrosion resistance of the coating were analyzed using SEM, AFM, X‐ray diffraction, and electrochemical techniques. The deposition parameters employed to realize the anticorrosion performance including calcinations temperature, polyethylene glycol (PEG) content, pH value, and number of dipping cycles were investigated. Taguchi statistical experiments were carried out to determine the influence of the deposition variables on anticorrosion properties and optimal conditions. The results indicated that a higher anticorrosion performance of TiO₂ films could be achieved using 1 g of PEG in a sol with pH in range of 7–9, six cycles of dipping, and calcination temperature at 400°C. The Tafel polarization measurements indicate that i_corr value decreases about 200 times and the R_corr value increases around 57 times compared with uncoated 316L stainless steel.     

Properties of Phosphorus‐Doped Silicon‐Rich Amorphous Silicon Carbide Film Prepared by a Solution Process

Using a polymeric precursor synthesized from a mixture of cyclopentasilane, white phosphorus, and 1‐hexyne, we deposited phosphorus‐doped silicon‐rich amorphous silicon carbide (a‐SiC) films via a solution‐based process. Unlike conventional polymeric precursors, this polymer requires neither catalysts nor oxidation for its synthesis and cross‐linkage. Therefore, the polymeric precursor is sufficiently pure for effective doping and fabricating semiconducting a‐SiC. This study presents the results of a detailed study of the effect of carbon and phosphorus concentrations on the structural, optical, and electrical properties of a‐SiC films. The lowest activation energy for these films is 0.39 eV, which leads to an optical gap and a dark conductivity of 2.1 eV and 10⁹ Ω cm, respectively. Moreover, these films satisfy the Meyer–Neldel rule for thermally activated conductivity, which indicates that white‐phosphorus doping of solution‐processed a‐SiC produces films with the same characteristics as phosphine‐doped vacuum‐processed a‐SiC.     

Magnetic Properties of Mn‐doped SnO2 Thin Films Prepared by the Sol–Gel Dip Coating Method for Dilute Magnetic Semiconductors

Manganese‐doped tin oxide (SnO₂:Mn) thin films were deposited on glass substrates by the sol–gel dip coating technique. The effect on structural, morphological, magnetic, electrical, and optical properties in the films with different Mn concentrations (0–5 mol%) were investigated. X‐ray diffraction patterns (XRD) showed the deterioration of crystallinity with increase in Mn‐doping concentration. Scanning electron microscopy (SEM) studies showed an inhibition of grain growth with an increase in Mn concentration. X ray photoelectron spectroscopy (XPS) revealed the presence of Sn⁴⁺ and Mn³⁺ in SnO₂: Mn films. SnO₂: Mn films show ferromagnetic and paramagnetic behavior. These SnO₂:Mn films acquire n‐type conductivity for 0–3 mol% (SnO₂ ‐ Sn_0.97Mn_0.03O_{2) ‐}doping concentration and p type for 5 mol% Mn‐doping concentration(Sn_0.95Mn_0.05O₂) in SnO₂ films. An average transmittance of > 75% (in UV‐Vis region) was observed for all the SnO₂:Mn films. Optical band gap energy of SnO₂: Mn films were found to vary in the range 3.55 to 3.71 eV with the increase in Mn‐doping concentration. Photoluminescence (PL) spectra of the films exhibited an increase in the emission intensity with increase in Mn‐doping concentration which may be due to structural defects or luminescent centers, such as nanocrystals and defects in the SnO₂. Such SnO₂:Mn films with structural, magnetic and optical properties can be used as dilute magnetic semiconductors.