Titania Ceramics Research Articles

Investigations into the cytotoxicity of titania ceramics surfaces

Investigations into the cytotoxicity of titania ceramics surfaces

High Voltage Screening on Ceramics Parts with Bimodal Strength Distribution

The effect of high voltage screening on ceramics parts composed of titania ceramics with relative densities of 60 and 90%, was examined. Before screening, strength distribution was clearly descriminated into two regions, high strength region and low strength region. The dielectric strength was measured on the low strength samples, and the electric field below which all of the low strength parts would break was estimated as a screening field. After electric screening, the mechanical strength was measured and compared with the original one. Ceramic parts composed of only high strength region were obtained by eliminating the low strength parts electrically.

Effect of Peptization on Densification and Phase‐Transformation Behavior of Sol–Gel‐Derived Nanostructured Titania

Porosity reduction, packing, pore‐size distribution, and anatase to rutile phase transformation behavior of nanostructured titania ceramics prepared from both peptized and unpeptized sols were studied and compared using XRD, DSC, and nitrogen‐gas physisorption techniques. Precursor gels prepared from the peptized sol had a green density of about 70% after drying at 40°C, whereas the samples prepared from the unpeptized sol had a green density of only 50%. Samples prepared from the peptized sol showed higher sintering and phase transformation rates compared to the unpeptized sols.

Effect of Powder Characteristics on Microstructures and Dielectric Properties of (Ba,Nb)‐Doped Titania Ceramics

The effect of powder characteristics on the microstructures and dieletric properties of (Ba,Nb)‐doped TiO2 ceramics was investigated. Two powders were prepared: one by coprecipitation and the other from mixing of reagent oxides. The powder characteristics were determined by TEM, X‐ray powder diffraction, SEM, and centrifugal particle analysis. Extensive abnormal grain growth is observed in samples sintered from coprecipitated powder, while it is not found in samples sintered from reagent oxide powder. The effects of crystallite size, agglomerate distribution, and chemical homogeneity on abnormal grain growth are discussed. A mechanism of abnormal grain growth is given, and chemical homogeneity is determined to be the main factor which caused abnormal grain growth. The effect of powder characteristics on dielectric properties is also described.

Chemical Strengthening of Polycrystalline Ceramics

The feasibility of strengthening polycrystalline ceramic bodies by low‐expansion solid solution surface layers was established. Failure, by shearing of the surface layers, was prevented by establishing gradual variations in composition and in thermal expansion coefficient which, in turn, resulted in gradual variations in stresses and reduction of the maximum shear stress. Titania ceramics were strengthened by TiO2‐SnC2 surface layers and alumina ceramics were strengthened by Al2O3‐Cr2O3 surface layers.

Dielectric properties of titania ceramics at microwave frequencies

The determination of the relative permittivity κ and the loss tangent tan δ of the ceramics titania (κ [similar, equals] 95, tan δ [similar, equals] 0.0004) and magnesium titanate (κ [similar, equals] 14.3, tan δ [similar, equals] 0.0001) by H01 mode and `ghost' mode cavity techniques is outlined. Results are presented for the frequency range 3 to 35 Gc/s at room temperature. It is noted that κ varies by 5% in both materials, and that tan δ rises significantly but remains at a relatively low value as the frequency is raised from 3 to 35 Gc/s. Experiments are described in which 1.8 cm wavelength cavities loaded with single glazed titania disks have been successfully operated at electric field strengths up to 10 MV m-1 with 20 kev axial electron beams. The use of these materials in slow-wave structures is briefly discussed.