Synthesis of SiO2 glass fibres from Si(OC2H5)4-H2O-C2H5OH-HCl solutions through sol-gel method

Various factors affecting the spinnability of the Si(OC₂H₅)₄-H₂O-C₂H₅OH-HCl solutions have been investigated in order to find appropriate experimental conditions for making gel-derived SiO₂ glass fibres. The molar ratios of H₂O, C₂H₅OH and HCl to Si(OC₂H₅)₄ were changed in the range from 0.5 to 10.0, 0.5 to 7.0 and 0.001 to 0.1, respectively. The solutions were reacted at 30 and 80° C. It has been reconfirmed that the most important factor determining the spinnability of the solution in the course of the hydrolysis reaction is the molar ratio of water to Si(OC₂H₅)₄ in the solution. The rise of the reaction temperature led to the remarkable shortening of the time required for drawing fibres. The increase of the amount of HCl decreased the upper limit of the H₂O/Si(OC₂H₅)₄ molar ratio range where the spinnability is found as well as reaction temperature. The solutions with a H₂O/Si(OC₂H₅)₄ ratio larger than 2.0 gave often fibres having a circular cross-section, while other solutions gave fibres with a non-circular one. The tensile strength of the gel-derived SiO₂ glass fibres was also reported.     

Effects of mono-substituting chelating agents on BaTiO3 prepared by the sol-gel process

BaTiO₃ of various grain size was prepared by the sol-gel process from Ti (OR)₄ (R = isoC₃H₇ or C₄H₉)+Ba(CH₃COO)₂+chelating agent CH₃COCH₂COR(R = CH₃ or OC₂H₅) in a composition of equal molar ratio. Fourier transform infrared and fast atom bombardment mass spectrometry analyses suggested that the chelating agent substituted for one of the OR groups in Ti (OR)₄ to form Ti (OR)₃ (CH₃COCHCOR). The gelation time varied from 3 to 5 months and diminished with increasing steric hindrance. The amorphous gel was crystallized into cubic phase BaTiO₃ upon heating above 650°C. The tetragonal phase was obtained after heating for 1 h at 1350°C with the theoretical Ba/Ti ratio and 1.0096 c/a value. The measured dielectric constants diminished with increasing grain size. The results illustrated the merits of altering the chemistry of the precursors to control the properties of the BaTiO₃.     

Synthesis and characteristics of near-stoichiometric barium titanate powder by low temperature hydrothermal reaction using titanium tetra(methoxyethoxide)

Near-stoichiometric BaTiO₃ powders with ultrafine particle size and high crystallinity were prepared by low temperature hydrothermal reaction of Ba(OAc)₂ and Ti(OCH₂CH₂OCH₃)₄. BaTiO₃ particles were synthesized in the spherical, metastable cubic crystalline grains with size distribution between 60–90 nm in diameter. Ultrafine particle size was resulted from the control of the hydration rate and the decrease of Ti-O-Ti cross-linking extent of titanium precursor, Ti(OCH₂CH₂OCH₃)₄, which gives electronic, steric, and weakly chelating effect to titanium ion. Increasing the Ba/Ti mole ratio in reactant could not overcome the notorious Ba-deficiency but, improved stoichiometry and produced finer and less agglomerated particles. Interestingly, adding a slight pressure to autogeneous hydrothermal condition (total 4–10 atm) has yielded near-stoichiometric, highly crystalline, and less agglomerated BaTiO₃ particles. These particles, which were in metastable cubic form as synthesized, initiated phasetransition to tetragonal form by calcination at below 400 °C.     

Barium titanate fabricated from fur-fibres

Long-fibrous barium titanate (BaTiO₃) particles were prepared by a hydrothermal reaction of potassium titanate hydrate (2K₂O·11TiO₂·3H₂O) and barium hydroxide (Ba(OH)₂). Effects of preparation conditions on crystal structure and powder morphology were examined. Fur-fibres of K₂O·4TiO₂, 1–10 mm long and 1–100 m in diameter, were obtained by heating a mixture of K₂CO₃ and TiO₂ powders at 1000 C for 100 h. Keeping the fur-fibres in ion-exchanged water for 4 days gave fur-fibres of 2K₂O·11TiO₂·3H₂O). Long-fibrous BaTiO₃, with fibres 100m–1mm long and 1–10 m in diameter, was obtained by a hydrothermal reaction of the hydrate and Ba(OH)₂ (Ba/Ti ratio of 1) at 150 C for 24 h. As-prepared long-fibrous BaTiO₃ was composed of fine crystallites (average size about 270 nm) of cubic phase. The cubic phase and morphology of fur-fibres were maintained up to 1250 C, but heat treatment at 1300 C brought about a growth of crystallites to a few micrometers and a phase transformation to tetragonal phase. It was found that the hydrothermal reaction was effective in producing crystalline BaTiO₃ powder at a low temperature of 150 C.     

Synthesis of single-crystalline perovskite barium titanate nanorods by a combined route based on sol-gel and surfactant-templated methods

The single-crystalline perovskite barium titanate nanorods were successfully synthesized by a combined route based on sol-gel and surfactant-templated methods at low temperature. The synthesis was accomplished by using barium acetate (Ba(CH₃COO)₂) and tetrabutyl titanate (Ti[O(CH₂)₃CH₃]₄) as the starting materials and laurylamine as the surfactant, respectively. Well-isolated single-crystalline cubic perovskite BaTiO₃ nanorods with diameters ranging from 20 to 80 nm and lengths reaching up to > 10 μm can be easily fabricated by this route. The crystal form and morphology of the nanorods were characterized by X-ray diffraction, TEM and HRTEM. The mechanism of the formation of the single-crystalline cubic perovskite BaTiO₃ nanorods was discussed based on the theory of oriented attachment.     

Preparation of NbN fibres by nitridation of sol-gel derived Nb2O5 fibres

Nbn fibres were prepared by nitriding sol-gel-derived Nb₂O₅ fibres. Precursor niobium-oxide-gel fibres were obtained by spinning viscous sots prepared through acid-catalysed hydrolysis of niobium penta-ethoxide, Nb(OC₂H₅)₅. It was found that the spinnability of the sols depended on the water/alkoxide and the acid/alkoxide ratios. The niobium-oxide-gel fibres thus obtained were converted to niobium nitride by heat-treatment in a NH₃ gas above 800°C. Characterization of these fibres was carried out using X-ray powder diffraction, Auger electron spectroscopy and scanning electron microscopy. The nitride fibres obtained at 1050°C were mostly of stoichiometric -NbN phase, and they showed a transition to a superconducting state at around 11 K.     

Surface,structural and electrical properties of BaTiO3 films grown on p-Si substrates by low pressure metal organic chemical vapour deposition

Metal organic chemical vapour deposition of BaTiO₃ using Ba(tmhd)₂, Ti(OC₃H₇)₄ and N₂O, where tmhd equals 2,2,6,6-tetramethyl-3,5-heptanedionate, via pyrolysis at relatively low temperatures (370C) was performed in order to produce BaTiO₃ insulator gates. Scanning electron microscopy showed that the surfaces of the BaTiO₃ films had very smooth morphologies. Atomic force microscopy showed that the BaTiO₃ thin film was polycrystalline. X-ray diffraction results indicated that BaTiO₃ crystalline films grew on Si(100) with [110] orientation. High resolution transmission electron microscopy measurements showed that the BaTiO₃ films were polycrystalline, and an interfacial layer in the BaTiO₃/Si interface was formed. The stoichiometry and atomic structure of the BaTiO₃ films were investigated by Auger electron spectroscopy and transmission measurements, respectively. Room temperature capacitance-voltage measurements clearly revealed metal-insulator-semiconductor behaviour for samples with BaTiO₃ insulator gates, and interface state densities at the BaTiO₃/p-Si interface were approximately high, 10¹¹ eV^–1 cm^–2, at the middle of the Si energy gap.     

The dissolution of Na2O-MgO-CaO-SiO2 glass in aqueous HF solutions

The dissolution (or etching) of a multicomponent (Na₂O-MgO-CaO-SiO₂) silicate glass in aqueous HF solutions is studied. The solutions were chosen in the systems HF-HNO₃-H₂O, HF-HCl-H₂O and HF-H₂SO₄-H₂O, and the temperatures varied from 25 to 60° C. SEM micrographs of the glass surface after etching show an orange peel surface structure which develops during etching and which originates from surface flaws. The dissolution rate of the glass was found to increase with higher HF concentration, higher strong-acid concentrations and higher temperatures. The dissolution rate is determined by the reaction of HF molecules and HF₂ ions with the Si-O-Si grouping surrounding the SiO₄ tetrahedron. In the multicomponent glass some of these bonds are non-bridging due to the presence of Na₂O, CaO and MgO, increasing the dissolution rate significantly. H⁺ ions introduced by adding strong acids to the etch solution adsorb on the surface and catalyse the dissolution reaction. Several models used to describe the relation between the dissolution rate and the H⁺ concentration are discussed.     

Synthesis of Ternary Intercalation Compounds in the Graphite–HNO3–R (R = H2SO4 , H3PO4 , CH3COOH) Systems

The reactions of stage II–IV graphite nitrates with concentrated H₂SO₄, H₃PO₄, and CH₃COOH were studied at graphite : acid weight ratios from 3 : 1 to 1 : 1. The results demonstrate that the reactions in question follow different paths. In the graphite nitrate–H₂SO₄system, the reaction decreases the stage index and yields a ternary graphite intercalation compound. The contents of intercalated HNO₃and H₂SO₄are controlled by the amount of H₂SO₄and the stage index of the parent graphite nitrate. The reaction between graphite nitrate and H₃PO₄leads to partial replacement of HNO₃by H₃PO₄, increasing the identity period without changes in the stage index. The results for the graphite nitrate–CH₃COOH system provide no direct evidence for the formation of an intercalation compound with HNO₃and CH₃COOH. It is shown that varying the nature and amount of the second intercalate species opens up possibilities for preparing oxidized graphite with controlled physicochemical properties.     

A novel approach to prepare tetragonal BaTiO3 nanopowders

BaTiO₃ nanopowders were attempted to synthesize by using a novel straight-forward, solvent free reactions under autogenic pressure at elevated temperature (RAPET) approach. The as-prepared BaTiO₃ nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, high-resolution TEM, and convergent-beam electron diffraction. It was found that Ba(OH)₂·8H₂O and Ti(OBu)₄ could be appropriate starting materials to synthesize BaTiO₃ at 973 K for 2 h by using RAPET approach. Pure tetragonal BaTiO₃ nanopowders could be obtained by exceeding moderate amount of Ba(OH)₂·8H₂O in the starting materials. The obtained BaTiO₃ nanoparticles had well dispersion and crystallinity, possessed a tetragonal perovskite structure at room temperature and relatively narrow particle size distribution.     

Synthesis of M(NpO<Subscript>4</Subscript>)<Subscript>2</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O (M = Mg,Ca, Sr,Ba) Using Н<Subscript>3</Subscript>ВО<Subscript>3</Subscript> Solutions and Properties of These Salts

Two procedures for preparing the compounds M(NpO₄)₂·nH₂O (M = Mg, Ca, Sr, Ba) using boric acid were suggested. In the first procedure, samples of freshly prepared salts M₃(NpO₅)₂·nH₂O (M = Ca, Sr, Ba) are treated with excess 0.5 M H₃BO₃ with vigorous stirring. In the process, the initially light green salts rapidly transform into black products of the general composition M(NpO₄)₂·nH₂O. In the second procedure, a measured volume of a Np(VII) solution with a known LiOH concentration was added to excess 0.5 M H3BO3 solution containing a calculated amount of Mg, Ca, Sr, or Ba nitrate. The reaction yields black precipitates of the same compounds as in the previous case. After washing with water and drying in an oxygen stream, the final products contain a small impurity of Np(VI). The IR spectra suggest that the compounds obtained are structurally related to the previously studied salts MNpO₄ (M = K–Cs), i.e., in their lattices there are neptunium–oxygen layers built of NpO₂³⁺ cations and bridging O atoms. New data on the properties of the compounds M₃(NpO₅)₂·nH₂O with M = Ca, Sr, and Ba were also obtained.     

Preparation of the BaTiO3–SiO2 hybrid particles for the catalyst of methane steam reforming process

BaTiO₃ nano-coated SiO₂ (BaTiO₃–SiO₂) hybrid particles were prepared by liquid phase deposition and sol–gel process. The obtained BaTiO₃–SiO₂ hybrid particles have relatively high surface area (20 m² g⁻¹) at 600 °C annealing temperature. Ni component was impregnated to the obtained BaTiO₃–SiO₂ hybrid particles, and the obtained catalyst was used for the methane steam reforming process to consider the effect of the surface area on the catalytic activity. The catalytic activity of the Ni/BaTiO₃–SiO₂ catalyst was approximately three times as large as that of the reported Ni/BaTiO₃ catalyst, even in the lower process temperature. However, the limitation temperature for methane steam reforming process of this hybrid material was 600 °C, because of the diffusion of the Ba component.     

Stress evolution of sol-gel-derived silica coatings during heating: The effects of the chain length of alcohols as solvents

The effects of the solvent on in-plane stress evolution were studied on sol-gel-derived silica gel coatings during heating. Si(OC₂H₅)₄-H₂O-HNO₃-ROH (ROH = CH₃OH, C₂H₅OH, n-C₃H₇OH, and n-C₄H₉OH) solutions were prepared where the mole ratio Si(OC₂H₅)₄:H₂O:HNO₃ = 1:8:0.01 and the volume ratio Si(OC₂H₅)₄:ROH = 1:1.1. Silica gel films were deposited by spin coating on Si (100) wafers 4 in. in diameter, and heated at 5 °C/min up to 500 °C, where in situ stress measurement was conducted by measuring the substrate curvature. The stress was tensile and increased with increasing temperature. The stress was found to be identical below 200 °C between the films prepared with different alcohols while the stress above 200 °C was larger in the order, n-C₄H₉OH < n-C₃H₇OH ≈ C₂H₅OH < CH₃OH, namely in the order of the boiling points of the solvents.     

Investigations related to the incorporation of Ca2+ ions into the BaTiO3 lattice

Dependence of the composition of (100–x) BaTiO₃ +xCaTiSiO₅ precursor (x = 2–16 mol%) mixtures on calcination temperature was investigated by means of X-ray diffraction and differential scanning calorimetry. The formation of a secondary phase, fresnoite (Ba₂TiSi₂O₈), starts at about 900 °C. The resulting Ba and O vacancies and the produced microstress stabilize the pseudocubic phase of BaTiO₃ at room temperature. Temperatures higher than 1200 °C are necessary to incorporate Ca ions into the BaTiO₃ crystals forming (Ba, Ca) TiO₃ solid solutions. As a result the lattice becomes free of tension and the BaTiO₃ based ceramics transform into thermodynamically stable tetragonal phases at room temperature.Dedicated to Professor Kurt Issleib on the occasion of his 75th birthday.     

Photoelectrochemical properties of donor doped BaTiO3 electrodes

The photoelectrochemical behaviour of donor-doped BaTiO₃ ceramic anodes has been investigated in comparison with that of H₂-reduced BaTiO₃ and SrTiO₃. Donor-doped BaTiO₃ has response to visible light without mechanical polishing and is unaffected by chemical etching or etching followed by polishing. H₂BaTiO₃ also has photoresponse in the visible; it is, however, modulated by mechanical polishing. Whereas, H₂SrTiO₃ has response in visible light, only on mechanical polishing. The visible photoresponse of BaTiO₃ is due to the mid-band gap states arising from lattice defects such as Ti³⁺V_O and Ba-vacancies. The differences between BaTiO₃ and SrTiO₃ is explained in terms of the changed characteristics of V_Ba(Sr)-energy states.     

Effect of temperature and time on solvothermal synthesis of tetragonal BaTiO<Subscript>3</Subscript>

Tetragonal BaTiO₃ nanoparticles are synthesized via solvothermal route in an ethanol water mixture. Ba(OH)₂·8H₂O is used as Ba precursor and TiO₂ (P25 Degussa ∼25 nm, 30% anatase, 70% rutile) is used as Ti precursor in the Ba : Ti molar ratio 2 : 1. Effect of temperature and time study on solvothermal synthesis of BaTiO₃ revealed that a moderate reaction temperature i.e. 185°C and longer reaction time favour tetragonal phase stabilization. Dissolution–precipitation appears to be the transformation mechanism for the crystallization of BaTiO₃ from particulate TiO₂ precursor.     

INCORPORATED C70 IN SOL AND GEL

C₇₀ is incorporated in gel by a sol-gel process with using 3-amino-propyltriethoxysilane (NH₂(CH₂)₃Si(OC₂H₅)₃, APTS) and 3-glycidoxypropltrimethoxysilane (CH₂OCHCH₂O(CH₂)₃Si(OCH₃)₃, GPTMS) as precursors. C₇₀ is firstly mixed with APTS to form C₇₀-NH₂(CH₂)₃Si(OC₂H₅)₃ compound by the reaction between C₇₀ and amino-group of APTS, and then the compound is hybridized with GPTMS to form solid gel. The linkage of C₇₀ and APTS is estimated and confirmed with FT-IR spectra, and the UV/Visible spectra of the sol and gel are measured.     

Preparation of Y-TZP ceramic fibers by electrolysis-sol-gel method

Polycrystalline yttria stabilized tetragonal Zirconia (T-ZrO₂) fibers were obtained by pyrolysis of gel fibers using zirconium oxychloride octahydrate as raw material. The spinnable zirconia sol was prepared by electrolyzing the zirconium oxychloride octahydrate solution in the presence of acetic acid and sugar (sucrose, glucose or fructose), in which the molar ratio of CH₃COOH/ZrOCl₂ · 8H₂O and sugar/ZrOCl₂ · 8H₂O was in the range of 1.0–4.0 and 0.2–0.4, respectively. The relation of spinnability to the shape of colloidal particle was discussed. The as-prepared zirconia fibers sintered at different temperatures show smooth and crack-free surface with the diameter of 5–10 μm. Slow heating rate below 600 °C and then sintering at 1,400 °C for 30 min were necessary to obtain the dense tetragonal zirconia ceramic fibers, the particles composed the fibers had the size of ∼150 nm.     

Effect of Ba/Y Molar Ratio on Superconducting Properties of BaTiO<Subscript>3</Subscript>-Doped YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript><Emphasis Type="Italic">O</Emphasis><Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript> Films

YBa₂Cu₃ O _7?δ (YBCO) films with BaTiO₃ (BTO) nanostructures were prepared by using the precursor solutions with different cationic molar ratios of Y:Ba:Cu = 1.0:1.6–2.0:3.0 in the TFA-MOD process. These YBCO films were deposited on (00 l)-oriented LaAlO₃ single-crystal substrates using a spin coater. The high superconducting critical current density (J _C) (77 K, self-filed) of more than 10 MA/cm² for the final BTO-doped YBCO film was obtained. Moreover, the effect of different Ba/Y molar ratios in the precursor solution on superconducting properties of BTO-doped YBCO films was investigated. Compared with the BTO-doped YBCO film deposited by using the precursor solutions with Ba/Y molar ratio of 2.0, an enhancement of J _C in a magnetic field for the film from the solution with Ba/Y molar ratio of 1.9 was achieved. For Ba/Y molar ratios of 1.6 and 1.7, a reduction of J _C in a magnetic field occurred. The J _C enhancement may be mainly ascribed to the enhanced flux pinning by the Y₂Cu₂ O ₅ nanostructures with the optimal number dispersing in YBCO matrix.     

Pyroelectric properties of alanine and deuterium substituted TGSP and TGSAs single crystals

Alanine and deuterium substituted (NH₂CH₂COOH)₃ · (1 - x)H₂SO₄ · xH₃PO₄ (TGSP) and (NH₂CH₂COOH)₃ · (1 - x)H₂SO₄ · xH₃AsO₄ (TGSAs) single crystals were grown. Pyroelectric figure of merit $\text{p}\text{K}$ and polarization P_s of ADTGSP and ADTGSAs were measured and are of the same order as those obtained on ATGSP and ATGSAs, respectively. In both deuterated crystals, T_c was 10°C higher than the T_c values observed on either pure TGS or ATGSAs and ATGSP single crystals.