Papers by Keyword: Calcium Titanate

Abstract: Calcium titanate (CaTiO₃) was synthesized through combustion in air from calcium sources of raw minerals (lime-stone and calcite), anatase titanium dioxide (A-TiO₂) and magnesium (Mg). The syntheses were divided into two reactant systems (lime-stone/A-TiO₂/Mg and calcite/A-TiO₂/Mg. Before synthesis, the raw minerals and A-TiO₂ were high-energy milled for 30 min. These powders were then separately mixed with Mg by ball milling. After synthesis, the as-combusted products were leached with 2 M HCl solution to remove by-products and impurities. A sequential mechanism for the in-situ combustion was proposed by using data from simultaneous thermal analysis (STA) together with thermodynamic values calculated with HSC^ software. XRD results showed that the as-leached products from both reactant systems mainly contained CaTiO₃. FT-IR spectroscopy indicated that the as-leached products had Ca-Ti-O and Ti-O functional groups. In addition, SEM observation of the as-leached products revealed cuboid-like crystals with a particle size of about 100 nm.

Abstract: It has been generally accepted that doping of dielectric materials could significantly contribute to compositional and microstructural evolution, which consequently lead to alteration in dielectric properties. In this study, the effects of adding magnesium (Mg) at 5,10 and 20at% on the chemical composition, microstructure and dielectric constant of calcium titanate (CaTiO₃) synthesized by solid state reaction was assessed. Chemical composition analysis using an X-ray diffraction technique CaTiO₃ doped with 5 at% Mg has been found to contain a single phase whereas samples doped with 10 and 20 at% Mg both exhibited apparent secondary phase (MgO). Microstructural examination however, revealed that no significant variation in particle size, grain size and density were evident among the samples of different Mg contents. Average dielectric constants obtained from the entire samples ranged from 245.9 to 387.6 (at 1 MHz) and the sample with the highest dielectric constant was that doped with 5 at% Mg. Enhancement of dielectric constant in the samples with the lowest level of Mg doping has been attributed largely to the homogeneity of its chemical composition.

Abstract: Alkaline earth titanates and zirconates and their binary systems are of interest for their temperature in sensitive dielectric properties. Calcium titanate and calcium zirconate perovskite ceramics find applications in pulse discharge, energy storage and microwave capacitors. These dielectric materials have been used in electric hybrid and fuel cell vehicles. In the present work, fine crystalline compound powders of calcium titanate and calcium zirconate were prepared by a single step molten salt synthesis. Calcium oxide and titanium dioxide/zirconium oxide were used as precursors to obtain the calcium titanate and calcium zirconate compound powders respectively. The prepared calcium titanate and calcium zirconate compound powders were characterized by TGA, FTIR, XRD, SEM and EDS analysis.

Abstract: Powder samples of (Ca,Sr)TiO₃:Er were prepared by a solid-state reaction method. Photoluminescence due to f-f transitions of Er³⁺ was not induced by band-gap excitation of (Ca,Sr)TiO₃ but by f-f transitions of Er³⁺. An electroluminescent device in which thin films of Ca_0.6Sr_0.4TiO₃:Er and SnO₂:Sb are stacked alternately was prepared by sol-gel and spin-coating methods. Very weak electroluminescence due to f-f transition of Er³⁺ was observed in the device.

Abstract: The CaTiO₃ samples were prepared by high-energy ball milling process followed by sintering process from 1040 to 1200°C. X-ray diffraction (XRD), microstructural analysis, and dielectric properties over a wide range of frequency varying from 0.01 Hz to 1 GHz at room temperature were investigated. The formation of a single phase CaTiO₃ with orthorhombic structure was achieved at 1120°C and above. From a morphological point of view, sintering temperature promoted grain growth. Dielectric properties in the frequency range 0.01 Hz - 1 MHz revealed a relaxation-type process. Interfacial phenomena were the possible physical mechanisms that gave rise to these relaxation-type plots. Extending the frequencies above ~1 MHz yielded a frequency-independent characteristic of dielectric constant (ε'). These turned out to the relatively small dielectric loss (tan δ) values. The origin of the dielectric responses in the frequency range 1 MHz - 1 GHz was attributed to the domination of dipolar polarization. The grain size effect in sintered CaTiO₃ samples was prominent, notably in dielectric responses above ~1 MHz. Increase in sintering temperature remarkably led to an enhancement in dielectric constant values and reduction in dielectric loss values. Therefore, a significant correlation existed between microstructural features and dielectric properties.

Abstract: Titanium-based composites containing Ti_xP_y phase (s) or CaTiO₃ and Ti_xP_y phase (s) were produced by a non conventional method using suitable mixtures of TiH₂ powder and phosphoric acid (TiH₂/P), or TiH₂ and 10 vol.% of calcium phosphate (TiH₂/CP), respectively. The composites were produced with the same phosphor molar concentration. The mixtures were prepared by ultrasound in water, dried in a rotary evaporator, pressed at 600 MPa and vacuum-sintered at 1200 °C for 2 hours. The mixtures were well dispersed by ultrasound and agglomerate-free. The analyses show that titanium particles were coated with Ti_xP_y phase (s) for the TiH₂/P composite or with an intermediary layer of Ti_xP_y phase (s) and an external deposit of calcium titanate for the TiH₂/CP composite. The TiH₂/P composite presented higher compressive strength and about the same contact angle compared to the TiH₂/CP composite. However, both materials displayed lower contact angle than that of pure titanium.

Abstract: Bioactive Ti metal able to release Sr ions was prepared by chemical and heat treatments of Ti metal. Ti metal was initially soaked in 5M NaOH solution to form sodium hydrogen titanate. It was soaked in a mixed solution of CaCl₂ and SrCl₂ to replace its Na ions with Ca and Sr ions at a given range from 0.18 to 1.62 in Sr/Ca ratio. When it was heat-treated at 600 oC, it formed Sr-containing calcium titanate (SrCT) and rutile. The apatite formation in SBF of the treated metal was low, but increased markedly by subsequently soaking the metal in 1 M SrCl₂ solution at 80 oC. Thus, the treated metal gradually released Sr ions into phosphate-buffered saline up to 0.9 ppm. It is expected that the Ti metal formed with the bioactive SrCT layer could release Sr ions in a living body to promote bone formation, and bond to a living bone through an apatite.

Abstract: In this paper, a manual-controlled injection nanometer calcium titanate based on glass fiber filter enricher (MICTE) was prepared, and its application in speciation of Cr (III) and Cr (VI) was studied. The optimum experimental parameters for separation of the Cr (III) and Cr (VI) have been investigated. The results showed that the MICTE had adsorption capacity towards the Cr (III) and Cr (VI). And two forms of chromium show different adsorption capacities at different pH values, Cr (III) could be adsorbed at pH 9, but Cr (VI) cant be adsorbed. Whereas Cr (VI) retained at pH 3, but Cr (III) cant be adsorbed. Therefore, it is possible that the two forms of chromium are complete separated. The Cr (III) and Cr (VI) could be completely eluted with 1 mol·L¹ HCl and 1 mol·L¹NaOH, respectively. The chromium concentration was measured by atomic absorption spectroscopy. A new method for determination of the speciation of chromium in environmental water samples based on the manual-controlled injection enricher and atomic absorption spectroscopy determination was proposed. The method was successfully applied for the determination of Cr (III) and Cr (VI) in environmental waters with satisfactory results.

Abstract: Preparation of bioactive titanium (Ti) metal able to release Zn²⁺ ions was attempted by chemical and heat treatments of Ti metal. Ti metal was soaked in 5M NaOH solution at 60 °C to form sodium hydrogen titanate (SHT) on its surface. Then, it was soaked in a mixed solution of 100 mM Ca(CH₃COO)₂ and 0.01 - 1 mM Zn (CH₃COO)₂ at 40 °C for 24 h to replace Na⁺ ions in SHT with Ca²⁺ and Zn²⁺ ions at given range of 0.15 to 2.95 in Zn/Ca ratio. When it was heat-treated at 600 °C for 1 h, zinc-incorporated calcium titanate (ZCT) and rutile were formed on the surface of Ti metal. The ZCT partially replaced its Ca²⁺ and Zn²⁺ ions with H₃O⁺ ions by subsequent soaking in 1 mM acetic acid solution at 80 °C. Thus treated Ti metal formed apatite on its surface in a simulated body fluid (SBF) within 3 days, and slowly released Zn²⁺ ions into phosphate-buffered solution (PBS) up to 0.03 ppm. The Ti metal formed with this kind of bioactive ZCT layer on its surface is expected to be useful as orthopedic and dental implants, since it could bond to living bone sooner, by promoting formation of the surrounding bone.

Abstract: SrTi_0,65Fe_0,35O_3-δ, Ca_0,5Sr_0,5Ti_0,65Fe_0,35O_3-δ, CaTi_0,65Fe_0,35O_3-δ ceramic powders were synthesized by the polymeric precursor technique using CaCO₃, SrCO₃, C₁₂H₂₈O₄Ti and Fe (NO₃)₃.₉H₂O. After calcination, each powder was heat treated at temperatures chosen according to data collected on thermogravimetric-differential thermal analysis experiments. The compositions were analyzed by X-ray diffraction for structural phase evaluation (either perovskite cubic or orthorhombic), laser scattering for determination of particle size distribution and average particle size, transmission electron microscopy (TEM) for observation of particle shape and average true size. Pressed powders sintered at 1250°C were analyzed by X-ray diffraction and X-ray fluorescence; their surfaces were observed by scanning probe microscopy (SPM) for topographical analysis of grains and grain boundaries. TEM results show that the powders consist of agglomerated nanoparticles. Sr-based compounds have cubic perovskite phases whereas Ca-based compounds are orthorhombic. SPM images show intergranular features which might be responsible for reported blocking of charge carriers observed in impedance spectroscopy diagrams.