Manufacturing of ceramic nanomaterials in Ti–Si–C–N system by sol–gel method

Problems concerning sol–gel synthesis of ceramic nanomaterials, methods of investigation of these materials and of processes proceeding with their participation have been presented. One-component nc-TiC, nc-TiN and multi-component TiC + SiC + C and Ti(C,N) + Si(C,N) + Si₃N₄, powders have been investigated. The sol–gel synthesis is carried out in two stages: low-temperature, in which the raw nc-TiC_x product is obtained, and high-temperature one. In the high-temperature stage carbonization of carbides and elimination of excessive organic compounds, being the source of carbon in carbonization process, take place. It has been demonstrated that the oxygen, present at trace level in argon, can react with components of the system in certain range of temperature, influencing the quality of obtained product. High-temperature oxidation resistance of investigated materials in dry air was also determined, applying kinetic methods. TG-DSC measurement data were used as the basis of kinetic analysis. The method of investigation has been presented at the example of TiC + SiC + C powder oxidation. Is has been demonstrated, that in case of multi-component materials, components were oxidized in temperature ranges characteristic for pure phases.     

Mesoporous and nanocrystalline sol–gel derived NiTiO3 at the low temperature: Controlling the structure,size and surface area by Ni:Ti molar ratio

Nanocrystalline nickel titanate (NiTiO₃) thin films and powders with mesoporous structure were produced at the low temperature of 500 °C by a straightforward particulate sol–gel route. The sols were prepared in various Ni:Ti molar ratios. X-ray diffraction and Fourier transform infrared spectroscopy revealed that the powders contained mixtures of the NiTiO₃ and NiO phases, as well as the anatase-TiO₂ and the rutile-TiO₂ depending on the annealing temperature and Ni:Ti molar ratio. Moreover, it was found that Ni:Ti molar ratio influences the preferable orientation growth of the nickel titanate, being on (202) planes for the nickel dominant powders (Ni:Ti ≥ 75:25) and on (104) planes for the rest of the powders (Ni:Ti: ≤ 50:50). The average crystallite size of the powders annealed at 500 °C was in the range 1.5–2.4 nm and a gradual increase occurred up to 8 nm by heat treatment at 800 °C. The activation energy of crystal growth decreased with an increase of Ni:Ti molar ratio, calculated in the range 24.93–37.17 kJ/mol. Field emission scanning electron microscope analysis revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 20–35 nm. Moreover, atomic force microscope images presented that the thin films had a hill-valley like morphology with roughness mean square in the range 41–57 nm. Based on Brunauer–Emmett–Taylor analysis, the synthesized powders showed mesoporous structure containing pores with needle and plate like shapes. The mesoporous structure of the powders was stable at high annealing temperatures and one of the highest surface areas (i.e., 156 m²/g) reported in the literature was obtained for the powder containing Ni:Ti = 50:50 at 500 °C.     

Experimental study and thermodynamic modeling of the MgO–NiO–SiO2 system

The MgO–NiO–SiO₂ system has been studied by a combination of thermodynamic modeling and experimental measurements of phase equilibria. A complete literature review, critical evaluation and thermodynamic modeling of phase diagrams and thermodynamic properties of all oxide phases in the MgO–NiO–SiO₂ system at 1 atm total pressure are presented. To resolve the contradictions in the literature data, a new experimental investigation has been carried out over the temperature range from (1400 to 1650) °C using an equilibration and quenching technique followed by electron probe X-ray microanalysis (EPMA). Tie-lines between olivine and monoxide, olivine and proto-pyroxene, liquid and olivine and liquid and cristobalite have been measured. The whole set of experimental data, including the new experimental results and previously published data, has been taken into consideration in thermodynamic modeling of oxide phases in the MgO–NiO–SiO₂ system. The Modified Quasichemical Model has been used for the liquid phase. A simple random mixing model with a polynomial expansion of the excess Gibbs energy has been used for the monoxide solid solution. The models for olivine and proto-pyroxene were developed within the framework of the Compound Energy Formalism. The optimized model parameters reproduce all available thermodynamic and phase diagram data within experimental error limits.     

Investigation of the presence of KCl in the structure and morphology of V-amylose–inclusion complexes

Amylose–fatty acid inclusion complexes were prepared using amylose extracted from pea starch and fatty acids with different chain length. To form the complexes, amylose, dissolved in aqueous alkaline solution (0.1 Ν ΚΟΗ), was mixed with fatty acid potassium soap solution and after neutralization the complex was obtained as precipitate. To investigate the structure and morphology of V-amylose–inclusion complexes, a series of techniques such as X-ray diffraction, SEM-microscopy combined with elemental microanalysis, Differential scanning calorimetry and Fourier transform infrared spectroscopy were employed. XRD analysis of complexes, revealed that the complexes displayed the typical V-form pattern, with an extra peak at 2θ?=?28.2°. To identify the origin of that peak the complexes were examined by SEM microscopy combined with elemental microanalysis. The results indicated that the peak was due to the presence of potassium chloride, formed during the preparation of the complexes. Washing the complexes with water was sufficient to remove the salt.     

Corrosion inhibition of steel in molar HCl by triphenyltin2–thiophene carboxylate

The effect of triphenyltin2–thiophene carboxylate (TTC) on the corrosion of steel in hydrochloric acid medium was studied using gravimetric, electrochemical polarisation and electrochemical impedance spectroscopy (EIS) measurements. The percentage inhibition efficiency was found to increase with increasing concentration of inhibitor to reach 97% at 10^?3 M. Polarisation study shows that TTC is an efficient inhibitor and acts as a mixed-type inhibitor. EIS results indicate the increase of resistance transfer (R_T) and the decrease of double layer capacitance (C_dl) with TTC concentration. Triphenyltin2–thiophene carboxylate molecules lead to the formation of a protective layer on the surface of steel. The inhibitor is adsorbed on the steel surface according to Langmuir isotherm.     

Phase equilibria,crystal structure at 1373 K and properties of complex oxides in the Nd–Co–Fe–O system

Phase equilibria in the Nd–Co–Fe–O system were systematically studied at 1373 K in air. The homogeneity range and crystal structure of solid solution NdCo_1–xFe_xO₃ (0.0 ≤ x ≤ 1.0) have been studied by the X-ray powder diffraction method. The structural parameters of complex oxides have been refined by the full-profile Rietveld method. It was shown that all oxides reveal practically stoichiometric oxygen composition within the entire temperature range under investigation. The values of thermal expansion coefficients for the cobaltites NdCo_1–xFe_xO₃ (x = 0.3, 0.7) have been calculated within the wide temperature range in air. Chemical stability of NdCo_1–xFe_xO₃ (x = 0.3, 0.7) in respect to the solid electrolyte materials (Ce_0.8Sm_0.2O_2–δ and La_0.88Sr_0.12Ga_0.82Mg_0.18O3-δ) was examined. Electrical conductivity of NdCo_1–xFe_xO₃ (x = 0.3, 0.7) was measured as a function of temperature within the range 300–1373 K in air. It was shown that substitution of cobalt for iron leads to the decrease of conductivity. The isothermal-isobaric cross-section of the phase diagram for the Nd–Co–Fe–O system at 1373 K in air has been presented.     

Characterization and photocatalytic activity of TiO2 by sol–gel in acid and basic environments

Journal of Sol-Gel Science and Technology - The sol–gel synthesis of water-based sols of nanocrystalline TiO2 in a large pH range (1.3–10.6) was carried out by acid hydrolysis of...     

Influence of aging temperature and Mg/Zr molar ratio on transformation of C2H6 to C2H4 over VOx catalyst supported on Mg–Zr nanocomposite

Research on Chemical Intermediates - To identify active and selective catalysts for oxidative dehydrogenation of ethane in presence of CO2, MgO–ZrO2 supports with varying amounts...     

Synthesis and crystal structure of d–f heteronuclear Gd(III)–Co(II) system

A carboxylate-bridged Co(II)–Gd(III) complex, [(bipy)CoL₃Gd(NO₃)L₃Co(bipy)] (HL =?α-methylacrylic acid, bipy =?2,2′-bipyridine), was prepared and characterized. Single crystal X-ray analysis reveals that the complex assumes a carboxylate-bridged CoGdCo unit. Magnetic measurements showed χ_m T decreases when the temperature is lowered.     

Influence of SrO content on microstructure and crystallization of glazes in the SiO2–Al2O3–CaO–MgO–K2O system

The effect of the SrO addition on the microstructure and structure of the glazes from the SiO₂–Al₂O₃–CaO–MgO–K₂O system was investigated in this study. The results were obtained by testing the ability of the frits crystallization, the stability of the crystallizing phases during the single-step fast-firing cycle depending on their chemical composition and the effect of addition of strontium oxide. Differential scanning calorimetry (DSC) curves showed that all glazes crystallized, and diopside and anorthite were mainly identified as dominant phases in the obtained glazes, while the size and amount of each depended on the amount of SrO introduced. The thermal characteristic of the frits was carried out using DSC, and crystalline phases were determined by X-ray diffractometry. The glaze microstructure was investigated by scanning electron microscopy and transmission electron microscopy. Additional information on the microstructure of frits was derived from spectroscopic studies in the mid-infrared range.

     

Erratum to: Nanoscale composite materials in the system SiO2–TiO2

Nanoscale composite materials based on the SiO₂–TiO₂ system were prepared in the form of co-precipitated composites and core SiO₂–shell TiO₂ composites, with specific surface area 150–650 m²/g and sorption volumes 0.1–1.0 cm³/g. It is shown that variation of phase composition and morphology permits to change their structural-adsorption properties and nanocrystallites size after thermal treatment. It is discovered that co-precipitated composite materials differ from core SiO₂–shell TiO₂ composites by a component interaction degree. It determines the difference of the titan-containing component crystallization process and alteration of their structural-absorption properties after thermal treatment. The results of the tests of composites as photocatalysts for Rhodamine B decomposition reaction, as catalysts of Hantzsch and Biginelli reaction, and as fillers in electrorheological fluids are shown.     

Structure and mechanism formation of polyelectrolyte complex obtained from PSS/PAH system: effect of molar mixing ratio, base–acid conditions, and ionic strength

Colloidal dispersions of polyelectrolyte complexes were prepared in aqueous solutions. We have used mixtures containing the strongly charged anionic polyelectrolyte sodium polystyrene sulfonate (PSS) and the weak cationic polyelectrolyte polyallylamine hydrochloride (PAH). Both polymers have the same molecular weight. The complexes were obtained by adding drop by drop a solution of the anionic polyelectrolyte to excess cationic polyelectrolyte. In these conditions, sodium polystyrene sulfonate and polyallylamine hydrochloride self-assembled in nanometer-range complexes; the self-assembly is driven by electrostatic interactions, as well as by entropy changes due to counterion release. The electrostatic interactions were controlled in several ways: by changing the C _PSS/C _PAH concentration ratio, by modifying the pH (and thus the protonation degree of polyallylamine hydrochloride), and by adding sodium chloride (screened interactions). Dynamic light scattering experiments demonstrated that the hydrodynamics radius of the polyelectrolyte complex increases, changing from soluble to insoluble complex formation, when some physicochemical parameters are increased: the concentration ratio between polyelectrolytes, the sodium chloride concentration, and pH. Zeta potential measurements, as a function of the C _PSS/C _PAH concentration ratio, as well as of pH and ionic strength, allow us to state that the resulting particles have a structure constituted by a neutral core surrounded by a positively charged shell. The polyelectrolyte complexes have globular shapes, as observed by electron microscopy.     

Investigation of photocatalytic and low-emissivity properties of TiO2:F films featuring columnar structure prepared on SnO2:F substrate by sol–gel method

Fluorine-doped TiO₂ thin films featuring columnar structure were prepared on fluorine-doped tin oxide (SnO₂:F) substrate using a sol–gel method. The F doping ratios were varied in the range of 0–8 %. The effect of [F]/[Ti + F] ratio on the structural, morphological, optical, photocatalytic and low-emissivity properties has been investigated in detail. X-ray diffraction studies revealed that all the composited films are mainly composed of anatase TiO₂ and rutile SnO₂ without other phases. The prepared TiO₂:F films possessed the columnar morphology with the single layer thickness ranging from 28 to 31 nm. The best photocatalytic activity was obtained for the films with 4 % F doping ratio which is mainly attributed to the highest crystallization and crystallite size. The transmission and hemispherical emissivity of the composite films could still reach approximately 70 % and 0.20, which match the requirements of the Chinese National Standard (GB/T18915.2-2002), promoting the films for the practical applications.     

First-principles investigation of the binary AB2 type Laves phase in Mg–Al–Ca alloy: Electronic structure and elastic properties

First-principles calculations have been carried out to investigate the electronic structure and mechanical properties of the main binary Laves phase CaMg₂, CaAl₂ and MgAl₂ with C14, C15 and C36 structures in Mg–Al–Ca alloy, respectively. The optimized structural parameters were in very good agreement with the experimental values. The calculated heat of formation and cohesive energy showed that the C15-CaAl₂ Laves phase was of the strongest alloying ability and structural stability. The electronic density of states (DOS) and charge density distribution were given. The elastic parameters C_ij were calculated, then the bulk modulus, shear modulus, Young's modulus, Possion's ratio and anisotropy value were derived. The ductility and plasticity were discussed in comparison with the previous experimental and theoretical data. The results showed that C14-MgAl₂ is of the best ductility and C15-MgAl₂ is of the best plasticity in the investigated binary alloys.     

Modification of the MgO–Al2O3–TiO2–SiO2 Glass by Silver Diffusion for the Formation of Luminescent Molecular Clusters

Doklady Chemistry - The capabilities of diffusion treatment of alkali-free MgO–Al2O3–TiO2–SiO2 glass using Ag-containing salt melts or special pastes for the formation of...     

Kinetics and Mechanism of 2,3,6-Trimethylphenol Oxidation by Hydrogen Peroxide in the Presence of TiO2–SiO2 Aerogel

The product and kinetics studies of 2,3,6-trimethylphenol (TMP) oxidation by 30% aqueous ₂₂ in the presence of a heterogeneous catalyst, TiO₂–SiO₂ aerogel, are performed in an MeCN medium. The main reaction products are 2,3,5-trimethyl-1,4-benzoquinone and 2,2",3,3",6,6"-hexamethyl-4,4"-biphenol. The reaction is first-order in ₂₂ and fractional order (1–0) in TMP. The reaction rate is proportional to the catalyst amount and depends on the water concentration in the reaction mixture in a complex manner. The results suggest the formation of an active intermediate on the titanium center. In this intermediate containing both a TMP molecule and the hydroperoxide group, inner-sphere one-electron oxidation of TMP occurs to give the phenoxyl radical.     

Hydration behavior of C2S and C2AS nanomaterials, synthetized by sol–gel method

Hydration behavior of dicalcium silicate (C₂S) (Cement chemistry nomenclature is used where C=CaO, S=SiO₂, A=Al₂O₃, S=SO₃) and gehlenite (C₂AS), synthesized by sol–gel method was investigated by means of isothermal heat flow calorimeter at different temperatures. These phases were obtained by crystallization processing at different temperatures from their xerogels (nano-crystalline) prepared by the sol–gel method at ambient temperature. The crystallization of C₂S begins below 600°C and it is well crystallized at 900°C. X-ray diffraction patterns reveal that β-C₂S is formed and it remains stable since after slow cooling. The crystallization of C₂AS xerogels starts with the formation of C₂S, then it reacts with alumina to form mineral C₂AS at 1100°C. The effect of hydration temperature upon the hydration reaction of C₂S obtained at 600 and 900°C and C₂AS annealed at 600 and 1100°C was investigated by means of isothermal calorimeter. An increase in the temperature of hydration brought about initial acceleration of all samples, as indicated by the increased magnitude of peak of calorimetric curves. The microstructure of the samples cured at hydrothermal condition after 1 and 7 days has been examined by means of scanning electron microscopy (SEM). Fine crystals of calcium silicate hydrate (C–S–H) were developed in C₂S samples, while C₂AS has been hydrated to form gehlenite hydrate supplemented by C–S–H.     

Effect of zinc oxide on microhardness and sintering behavior of MgO–Al2O3–SiO2 glass–ceramic system

Glass–ceramic in the MgO–Al₂O₃–SiO₂ system with crystallization ability of gahnite (ZnO·Al₂O₃) and mullite were synthesized. It was found that the glass–ceramic containing gahnite phase had desirable mechanical behavior and reached to an acceptable hardness and density. The compositions were designed based on magnesium oxide replacement (from MgO–Al₂O₃–SiO₂ glass–ceramic system) with zinc oxide. Glass–ceramics were characterized by DTA, X-ray diffraction and scanning electron microscopy. Heat treatment at 1100 °C cause form gahnite crystals in glass–ceramic. Microhardness increased with increasing gahnite crystals. To achieve good mechanical properties, the initially formed high gahnite phase must transform.