Papers by Keyword: CaTiO₃

Abstract: Microbial resistance has become a threat that causes thousands of deaths yearly; therefore, efforts are required to address this problem. One of the promising methods used to inhibit bacterial growth is photocatalyst technology. In this research, CaTiO₃ compounds was synthesized using the molten salt method and tested for antibacterial activity in both UV-unexposed and UV-exposed conditions on Staphylococcus aureus bacteria. The diffractogram showed that the CaTiO₃ compound was successfully synthesized without impurities that indicated by the characteristic peaks at 2θ (^o) = 23.29; 33.18; 47.52; 59.33; 69.48; 79.17. The micrograph results showed that the CaTiO₃ compound had a regular polyhedral shape and was agglomerated with particle sizes in the 0.2941 ± 0.0144 µm range. The UV-Vis DRS spectra showed that the CaTiO₃ compound had a bandgap energy of 3.48 eV (315 nm). In the antibacterial activity test results under UV irradiation, the growth of Staphylococcus aureus decreased by 3.95, 0.91, and 1.45 CFU/mL.

Abstract: The nanostructured photocatalysts are the most promising materials for the degradation of toxic dyes. Particularly, CaTiO₃ has been used in several applications including catalytic, optical, biological and electronic. In this present study, perovskite structured CaTiO₃ nanomaterials have been synthesized by microwave irradiation method. The physico-chemical properties of the prepared CaTiO₃ nanomaterials were studied by various advanced characterization techniques. The XRD patterns confirm the presence of perovskite structure of the prepared nanomaterials. FT-IR analysis confirms the presence of Ca-Ti-O vibrational bonds. Micro Raman study display the existence of O-Ca-Ti-O with B_1g mode of vibrations. Morphological studies revealed the presence of truncated nanospheres. The dye degradation property of prepared CaTiO₃ was investigated by Malachite green (MG) by UV-light.

Abstract: Preparing titanium powders by calcium vapor reduction of titanium oxide directly is a new way with short flow sheet and CaTiO3 is the very important intermediate compound in this process. In this paper, the behavior of intermediate CaTiO3 in the reduction process of TiO2 was investigated. The thermodynamic calculation indicated that the Gibbs free energy change of the reaction to produce CaTiO3 by CaO and TiO2 was always negative below 1000 °C; The reaction Gibbs free energy change of the calciothermic reduction of CaTiO3 was lower than that of TiO, which would be the most predominant step from TiO2 to Ti. The experimental results showed that CaTiO3 phase derived from the reaction between TiO2 and the reduction by-product CaO, and the reaction between TiO2 and the decomposition product CaO from the additive of CaCl2 with crystal water as well in the calcium vapor reduction process of titanium oxide. But CaTiO3 could be reduced to Ti much easier than that of TiO2 by calcium vapor.

Abstract: Well dispersive and single crystal calcium titanate (CaTiO₃) whisker with a length of 50-100μm was synthesized by sintering the mixture of calcium chloride and titanium dioxide with improvement of adding the mineralization agent of Pb(Ac)₂.3H₂O. The as-prepared samples were characterized by XRD, SEM. The optimum synthesis condition and the effect of the mineralization agent were discussed respectively. In the end, the possible reaction process was given and a LS growth mechanism was proposed.

Abstract: The 0.95MgTiO₃-0.05CaTiO₃ (95MCT) powders and ceramics were prepared by a sol-gel method by using Mg(NO₃)₂•6H₂O, Ca(NO₃)₂•4H₂O and Ti(C₄H₉O)₄ as the starting materials. The effects of calcination temperature on phase formation, morphology and particle size distribution of the proposed powders were examined, and the microwave dielectric properties of 95MCT ceramics made from different size particles were investigated. The dried gels were calcined at 600 °C, 700 °C, 800 °C and 900 °C, and the derived particle sizes of powders were 10-20 nm, 50-100 nm, 60-120 nm and 120-150 nm, respectively. The proper sizes, which range from 50-150 nm, lowered the sintering temperature of 95MCT ceramics effectively from 1400 °C to 1175 °C due to the high surface energy. Sintered at 1175 °C, the 95MCT ceramic prepared from 50-100 nm size particles had compact structure and exhibited good microwave dielectric properties: εr = 21.33 and Q×f = 36,315 GHz.

Abstract: The CaTiO₃ compounds were prepared by sintering the mixtures of the TiO₂ and CaO in air. The compounds were used as cathode, the graphite as anode and the molten CaCl₂-NaCl as electrolyte. Electrolysis was performed at 800°C and constant-voltage 3.2V in dry argon atmosphere. The results showed that the electrolytic rate could be significantly enhanced because of the additive CaO. The electrolysis time was shortened efficiently than that of direct electrochemical reduction of solid TiO₂.

Abstract: The microwave properties and microstructures of (ZnMg)TiO3-based dielectric prepared by conventional solid-state method were investigated as functions of CaTiO3 and CaO-B2O3-SiO2 additions. The effects of CaTiO3 on the crystal phase and the evolution of microstructure of (Zn0.65Mg0.35)TiO3 were studied. The result indicated that CaTiO3 secondary phase coexists with (ZnMg)TiO3 main phase in the ZMT-CT ceramics, which confirmed by EDS analysis. Because of CaTiO3 with large τf value (τf = 800 ppm/°C), the temperature coefficient of resonant frequency (τf) of ZMT-CT with biphasic structure was adjusted to near zero value. The microwave properties of (Zn0.65Mg0.35)TiO3 ceramics doped with 5wt% CaTiO3 sintered at 1150°C were ε ≈ 24, τf ≈ ±10 ppm/°C, Q×f > 45,000 GHz. Further, it was found that the CaO-B2O3-SiO2 additive could successfully reduce the sintering temperature of (Zn0.65Mg0.35)TiO3–CaTiO3 ceramics from 1150 to 950°C, and significantly improve the densification of this system, which were densified below 1000°C. This was due to the formation of liquid phases during the sintering observed by SEM. The (Zn0.65Mg0.35)TiO3–0.05CaTiO3 dielectrics with 1 wt% CaO-B2O3-SiO2 sintered at 950~1000°C exhibited the optimum microwave properties: ε ≈ 22, Q×f ≈ 20,000 GHz and τf ≈ ±10 ppm/°C.

Abstract: A conventional solid phase reaction method was followed to prepare (1−x)BaTiO3-xCaTiO3 based ceramics with content fractions ranging from x = 0.00 to 1.00. Phase segregation was observed when x exceeded 0.10. DC breakdown voltage (DC-BDV) abruptly changed at x = 0.30 and 0.85. Furthermore, the DC-BDV values of insoluble compositions (x = 0.30−0.85) were much higher than those of solubility limit (x = 0.20 and 0.90). Results obtained by investigation of the amount of absorbed current and the dependence of the rate of voltage increase for DC-BDV and AC-BDV confirmed the formation of space charge in insoluble compositions. This suggests that the dependence of the DC-BDV value for (1−x)BaTiO3-xCaTiO3 based ceramics was affected by the formation of space charge.

Abstract: The local structure and the spin Hamiltonian parameters g factors gi (i =x, y and z) and the hyperfine structure constants Ai for Co2+ in orthorhombic CaTiO3 are theoretically investigated from diagonalization of 6 × 6 energy matrix within the 4T1 ground state for a 3d7 ion in orthorhombic symmetry. In the calculations, the contributions from the admixtures of various J states (J=1/2, 3/2, 5/2), the ligand orbitals and spin-orbit coupling and the fourth-order orthorhombic field parameter, which were usually neglected in the previous works, are taken into account. The crystal-field parameters are determined from the superposition model in consideration of the suitable lattice distortion due to the charge and size mismatching substitution of Ti4+ by Co2+. Based on the studies, the bond lengths R1 and R2 in the xy plane are estimated to suffer the relative alternation R ≈ 5.4%, yielding more significant orthorhombic distortion in the impurity center as compared with that for the host Ti4+ site in pure crystal. The calculation results based on the above local lattice distortion show reasonable agreement with the observed values. The various contributions to the spin Hamiltonian parameters are discussed. Present studies may theoretically verify that the impurity Co2+ occupies the 6-fold coordinated Ti4+ site rather than the 12-fold coordinated Ca2+ site, associated with the enhanced orthorhombic distortion due to the mismatching substitution.

Abstract: (1–x)CaTiO3–xNdAlO3 (CTNA) microwave dielectric ceramics have a high Q value and a low temperature coefficient of resonant frequency ( τf ). CTNA ceramic powder was synthesized using a polymeric precursor derived from a mixed-metal ethylenediaminetetraacetic acid (EDTA) / ethylene glycol solution. The precursors and derived oxide powders were characterized by thermogravimetric analysis and X-ray diffraction. When x = 0.3, CTNA was synthesized at 900°C for 3 h in air. Compared with that prepared by the solid-state reaction method in literatures, the CTNA ( x = 0.3 ) ceramics with better microwave properties could be obtained at lower calcination and sintering temperatures by EDTA chelating method.