Advances in Applied Ceramics: Structural,Functional and Bioceramics

The material properties and damage characteristics of lead zirconate titanate(PZT) ceramics were investigated at various temperatures. A positive voltage was obtained when the sample was cooled from 20°C to −190°C, while a negative voltage was obtained when the sample was heated from −190°C to 180°C. The difference between the positive and negative values depended on the thermal stress. Compressive stress generated a more positive voltage in the cooling process, while tensile stress led to a more negative voltage in the heating process. The voltage values also depended on the cooling (or heating) rate of the sample, e.g. the greater the cooling (or heating) rate, the greater the voltage. When cyclic loading was conducted mechanically at −190°C, the voltage reduced, but it was recovered after heating to 20°C. Damage of the PZT ceramic (90° domain switching) was detected when the sample was cooled to −190°C due to the high thermal stress.

In this study, the impinging stream-rotating packed bed and precipitation method were used to continuously prepare Fe and Co co-doped Titanium Dioxide by in-situ modification. With TiOSO₄ solution containing Fe and Co₂₊ and NH_3·H₂O were sprayed on the packing and sheared by the packing that rotated at a high speed, resulting in improvement of microscopic mixing. The prepared catalyst is anatase with a particle size of 14 nm and a specific surface area of 194.34 m²/g. The photoresponse range is extended to 550 nm with a band gap of 2.5 eV. The photoluminescence results show that doping of Fe and Co can effectively inhibit the recombination of photogenerated electron-hole pairs. The percentage decomposition of 100 mg/L phenol under UV and visible light irradiation for 2.5 h is 88.71% and 24.58%, which is 1.59 and 2.07 times that for pure TiO₂.

Silicon carbide (SiC) fibres are widely used as promising reinforcement in ceramic matrix composites due to their excellent mechanical and thermal properties. In this work, sub-micrometer SiC fibres were prepared by electrospinning using polycarbosilane as the precursor, followed by curing in air and pyrolysing at high temperatures. The effect of the microstructure of SiC fibres on mechanical properties was investigated and the SiC fibre mats prepared at 1300°C for 2 h exhibited a mechanical strength of 184.5 ± 19.4 MPa. Hot-drawing was conducted on as-spun fibres during the curing process and the strength, Young's modulus, and flexibility of SiC fibre mats were improved. The strength with a drawing ratio of 200% reaches 243.0 ± 17.5 MPa. The enhancement of mechanical strength after hot-drawing is mainly attributed to the reduced defects in fibres, improvement in the orientation of the precursor fibres as well as the alignment of the molecular chains in the precursor fibres.

In this study, paste backward extrusion is introduced for fabrication of sodium beta-alumina electrolyte closed-end tubes (with a wall thickness of 1 mm and external diameter of 8.0 mm). For this purpose, the two-piece extrusion die was designed and extrudable water-based paste was prepared by using sodium beta-alumina powder, polyvinyl pyrrolidone, as a binder, and ethylene glycol as a plasticizer. The effect of solvent content on the rheological parameters of the paste and the ram extrusion velocity on the liquid phase separation are investigated. The results indicate that the optimum solvent content for making the extrudable paste is in the range of 30–35 wt-%, and the liquid phase separation is obviously occurred when the ram velocity is lower than 1.2 mm s⁻¹. It was also shown that by using backward extrusion, and by applying optimum conditions, closed-end tubes with high density (about 97%) and good surface quality could be fabricated successfully.

The R₂O–CaO–MgO–Al₂O₃–SiO₂–Fe₂O₃ glass ceramics was prepared using granite wastes and Fe₂O₃. The effect of Fe₂O₃ on crystallisation and properties of glass ceramics was studied. Results show that the crystalline phases were Fe₂TiO₅ and K(NaCa)Mg₅Si₈O₂₂F₂ when the content of Fe₂O₃ was low. The main crystalline phase was Fe_1.5Ti_0.5O₃ when the content of Fe₂O₃ was high. With the increase of Fe₂O₃, the crystal size of K(NaCa)Mg₅Si₈O₂₂F₂ reduced and the atomic ratio of Si to Mg increased. The colour of sample varied from greyish green to black with different additions of Fe₂O₃. The flexural strength with a maxim (101.02 MPa) when the content of Fe₂O₃ was 4.7 mol-%. Given the low cost of granite wastes and Fe₂O₃, this new type of black glass ceramics is expected to meet the increasing demand from the market of building decoration due to its excellent properties.

Tooth discolouration and the existence of metallic substrates increase the difficulty of restoration to reproduce natural and aesthetic appearance. The commonly used veneered zirconia restorations have a high risk of porcelain chipping, and the monolithic zirconia restorations cannot always achieve satisfying aesthetics. The newly developed self-glazed monolithic zirconia restorations digitally manufactured by additive technique have colour- and translucency-gradient characteristics. They could mask the different coloured substrates and achieve a natural look simultaneously. This clinical report describes the prosthodontic treatments of two patients with different coloured substrates in the anterior region. Both functional and aesthetic outcomes are satisfactory after 1–3 years of follow-up.

Porous Yb₂O₃ ceramic (55%) was pressureless sintered at 900°C for four hours in air. The crystal structure of Yb₂O₃ was confirmed to be cubic ( ) with c = 10.43731 Å by neutron diffraction. The spectral vibrational signature of Yb₂O₃ was also confirmed by micro-Raman spectroscopy. Yb₂O₃ is an amphoteric oxide with both acid and base character, which presents the potential for producing different hydrocarbons when used as a Fischer–Tropsch (FT) catalyst. It was found that Yb₂O₃ is indeed catalytically active and can be used to convert syngas (CO + H₂) into useful hydrocarbons. Production of methane, ethene, and ethane was detected in the catalytic experiment performed at 500°C, but propane, propene, butane, and methanol were also detected in the experiment performed at 250°C. Hydrocarbons heavier than C₄ were not observed. The limited data show deviation from a Flory–Schulz distribution suggesting additional surface processes are occurring beyond chain growth and termination.

The enhancement of surface acidity for tungsten-doped CeTiO_x was investigated through electronic structure. Tungsten doping increased the ratio of Ce³⁺ from 12.0% to 29.6%, which was confirmed by XPS. The doped tungsten was present as W⁵⁺ in a ratio of 71.5%. In O K-edge XAS spectra, increase in indicated the formation of oxygen vacancies through tungsten doping. The decrease in W 5d-e_g peak intensity demonstrated the occupation of the W 5d orbital by electrons formed at the oxygen vacancies. The enrichment of W⁵⁺ was owing to transfer of electrons to 5d-e_g orbital of tungsten rather than to cerium ions. The acid sites were analysed using FTIR and NH₃-TPD. The peak intensity of Brønsted acid sites and amount of NH₃ desorption increased from 66.2 to 136.1 µmol g⁻¹ with tungsten doping. The doped tungsten formed Brønsted acid sites and led to enhanced surface acidity and catalytic activity.