Key Engineering Materials Vol. 608

Abstract: The use of zirconia dental ceramics has grown in recent years due to improvements in esthetics and biocompatibility. Zirconia is used in dental applications for its high strength and fracture toughness. In this research, the influence of sintering conditions on the strength and optical properties of zirconia was investigated. Spray dried granules of 3Y-TZP zirconia were die pressed into disc-shaped samples and cold isostatic pressed at 250 MPa. Sintering was conducted using either one step sintering at 1500 oC or two-step sintering, with pre-sintering at 1200 oC and final sintering at 1500 oC. Heating rates of 2 and 10 oC/min were used. The biaxial flexural strength, fracture toughness, density, microstructural characteristics and optical properties of the sintered samples were determined. It was found that the sintering conditions did appear to influence the mechanical and optical properties. The sintering conditions had no significant effect on the density. It was concluded that for the sintering conditions examined, the two-step sintering with a heating rate of 2 oC/min produced the best average mechanical and optical properties of 3Y-TZP zirconia.

Abstract: The effect of manganese doping on microstructure, piezoelectric and electromechanical properties of Pb_0.94Sr_0.06(Zr_0.52Ti_0.48)O₃ (PSZT) ceramics has studied. The PSZT ceramics doped MnCO₃ concentration in the region of 0-1.0 mol% were prepared by a solid-state reaction and conventional sintering process. Phase identification showed the formation of single phase perovskite structure in all compositions. Microstructure and fracture behavior were observed by scanning electron microscopy (SEM). The fracture behavior demonstrated the change of fracture type from trangranular to mix of trans-and inter-granular type with increasing the amount of MnCO₃. Dielectric constant (K), d₃₃ and k_p were increased when higher amount of MnCO₃ was doped. In addition, the mechanical quality factor (Q_m) was highest at 0.1 mol% MnCO₃ doping in PSZT ceramics.

Abstract: Dielectric capacitors can be utilized in powder conversion systems of applications such as hybrid-electric and fuel cell vehicles. In order to fabricate capacitors that are suitable for practical uses, the materials should have moderately high dielectric constants, while retaining low loss. In this study, strontium titanate and strontium titanate samples doped with 10, 20, 30 at% of Mg and Al were tested for dielectric permittivity and dielectric loss. The results indicated that an increase in the amount of dopants led to enhancement of dielectric constants. The value of dielectric constant of strontium titanate with 30 at% Mg was four times higher than that of the undoped strontium titanate, while the samples with 30 at% Al could achieve the dielectric constant five times higher than that of the undoped sample. Low dielectric loss, in the range between 0.001-0.024, was observed.

Abstract: This study aimed to use the zinc dust which is a waste from hot-dip galvanizing plant for the synthesis of ZnO nanoparticles using microwave-assisted process. The precursor solution was prepared by dissolved as received zinc-dust powder in nitric acid. Then it was precipitated by NaOH at required pH and microwave irradiated in a household microwave oven at power of 100W for 10-20 min. The effects of preparation conditions and an addition amount of poly ethylene glycol (PEG; MW2000) for synthesis of ZnO on its properties were investigated. The synthesized nanoparticles were characterized for their phase structure, morphology and surface area by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET), respectively. The photocatalytic activity was determined by the degradation of methylene blue solution under UV irradiation. It was found that microwave heat treatment and addition of optimum amount of PEG could enhance the photocatalytic activity of precipitated ZnO particles. The resultant ZnO particles prepared by an addition of 0.25wt% PEG and microwave irradiation for 20 min exhibited the highest photodegradation rate among other products.

Abstract: In this study, ceramics in ((K_0.5Na_0.5)_0.935Li_0.065)NbO₃ + xMnO₂ (mol%) ceramics (when x = 0.0025, 0.0050, 0.01 and 0.015) were successfully prepared by the conventional mixed-oxide technique. The structural phase formation and microstructure were characterized by x-ray diffraction technique (XRD) and scanning electron microscopy (SEM). The crystal structure was identified by XRD as a single-phase perovskite structure, with tetragonal symmetry. The microstructure shows different grain size with different composition x. This study clearly showed that the Mn has influence on the dielectric properties in ((K_0.5Na_0.5)_0.935Li_0.065)NbO₃ ceramics.

Abstract: Anodic oxide film on titanium alloy (Ti-6Al-4V) substrate was prepared by anodization. The reaction was done by applying low current densities from 0.25 to 2 mA/cm² for 30 minutes using monocalciumphosphate monohydrate (MCPM) solution as an electrolyte. Essential parameters which affected to the formation of anodic oxide film were studied. The properties of the anodic oxide film would be optimized when the parameters were appropriately controlled. Increasing of the current density and the concentration of MCPM electrolyte could promote hydrophilicity and surface roughness of the film. After anodization, the anodic oxide film formed at 2 mA/cm² in 1M MCPM showed the best hydrophilicity (lowest water contact angle) and the film formed at 0.25 mA/cm² in 0.5M MCPM showed the lowest hydrophilicity (highest water contact angle). XPS analyses confirmed that the chemical species of as-anodized film formed at 2 mA/cm² in 1M MCPM changed. Ti2p spectra scarcely changed while the O1s spectra significantly changed due to the presence of chemisorbed water and Ti-OH formed during anodization. The SEM micrographs also revealed the biocompatibility from the growth of the cementoblast cell on anodized surface. It was indicated that anodization using MCPM as an electrolyte at 2 mA/cm² in 1M MCPM could modify the surface roughness and chemical species and that both are likely to be crucial key factors for enhancing of hydrophilicity of as-anodized film which would enhance the biocompatibility of Ti-6Al-4V as a result.

Abstract: Effects of titanium dioxide nanoparticles on thermal stability of polymeric thin film are investigated in this study. Polystyrene with molecular weight of 52,000 g/mol is used as a base polymer. The concentrations of titanium dioxide nanoparticles in polystyrene are varied from 0-0.20 wt.%. Films are fabricated by spin casting on Si wafer substrate and annealed at 180 °C and 190 °C for various times in order to study dynamics of dewetting. Film morphologies are analysed by optical microscopy and atomic force microscopy. Dewetting areas of each film as a function of annealing time are determined. It is found that addition of titanium dioxide nanoparticles suppresses dewetting in polystyrene film with thicknesses of ~30 nm and ~100 nm. The same titanium dioxide amounts, on the other hand, accelerate dewetting process in the film with thickness of ~265 nm. Mechanisms of dewetting suppression in polymeric film by titanium dioxide nanoparticles are discussed.

Abstract: A visible-light responsive CdS/ZnO nanocomposite photocatalyst was successfully synthesized by precipitation of CdS nanoparticles, using Cd (NO₃)₂ and Na₂S as starting materials, on ZnO nanoparticles and then calcined at 400°C for 2 hours. The effects of the mole ratio of CdS and ZnO in the composites on their phase, morphology, and surface area were investigated by X-ray Diffraction (XRD), scanning electron microscope (SEM), Brunauer Emmett Teller method (BET), respectively. The photocatalytic degradation of methylene blue solution in the presence of composite products under visible-light irradiation was investigated. The results showed that the mole ratio of CdS and ZnO played a significant role on photocatalytic performance. The highest photocatalytic activity was obtained from the CdS/ZnO nanocomposite with mole ratio of 1:4, which is higher than that of pure CdS and pure ZnO.

Abstract: In this work, properties of tungsten carbide (WC) particulate reinforced alumina matrix composites fabricated by powder injection moulding (PIM) technology were reported. The 90 wt% of Al₂O₃ and 10 wt% of WC powders were mixed with a composite binder, composed of 85 wt% polyethylene glycol (PEG) and 15 wt% polyvinyl butyral (PVB). Feedstocks of alumina and alumina-tungsten carbide composites having powder loading from 44 to 52 vol% were prepared and injected into a mould of rectangular shape. The binders in the mouldings were leached by water and then thermally debinded prior to sintering at 1600 °C for 2 hours in argon atmosphere. Strength, Density, hardness and density of the alumina and alumina composites’ bodies were compared and reported. It was found that the properties of sintered specimens, both Al₂O₃ and Al₂O₃/WC composites, increased with increasing powder loadings. The properties enhancement was also presented in the WC reinforced alumina composites. The composite of 52 vol% powder loading had flexural strength and hardness of 253.8 MPa and 12.5 GPa, respectively.

Abstract: Silicon carbide (SiC) ceramics were prepared by carbothermal reduction together with in-situ reaction bonding. Raw rice husk was carbonized in an incineration furnace. The carbonized rice husk was ground and was then treated with hydrochloric acid by varying concentrations. The sample powders were mixed with silicon metal powder and pyrolyzed at various temperatures in either argon or nitrogen atmosphere. Silicon carbide phase was found in all pyrolyzed samples. Cristobalite was found in argon atmosphere pyrolyzed samples while silicon oxynitride was found in the samples pyrolyzed in nitrogen atmosphere at lower than 1500 °C. Silicon carbide whisker is the main phase on the surface of pyrolyzed sample. Increasing pyrolysis temperatures decreased the amount and size of silicon carbide whisker but increased the silicon carbide particle. Porosity and weight loss of samples after pyrolysis were increased with increasing temperatures due to the reaction in the system.