Papers by Keyword: Soaking Method

Abstract: Nanostructured TiO₂ films were prepared by a one-step soaking method, which has many advantages, such as simple fabrication, a short reaction time, and fast growth. We have investigated the growth of TiO₂ films by the substrate orientation of the soaking method, which had an effect on the nanostructure of the TiO₂ films. The TiO₂ films prepared by this method had various structures: particulate-flat structure and sphere-flat structure. To determine the effect of the nanostructure of TiO₂ films on the photovoltaic characteristics of solar cells, solar cell devices using the inorganic semiconductor Sb₂S₃ as a sensitizer were fabricated by chemical bath deposition (CBD). Our solar cell device, using TiO₂ film with a sphere-flat structure as a photoelectrode, exhibited J_SC, V_OC, FF, and η values of 11.82 mA / cm², 0.49 V, 30.27 %, and 1.74 %, respectively.

Abstract: In order to improve fracture toughness of ceramics, an intrinsically small frontal process zone (FPZ) size must be expanded. An intra-type nano-structure, where nano-particles are embedded within matrix grains, yields dislocations around the dispersed particles due to residual stresses. These dislocations become sessile dislocations at room temperature, operate as origins of small stress concentration in the matrix, and create nano-cracks in the FPZ. To produce the intra-type nano-structure, we developed a soaking method. This method makes it possible to produce nano-sized metallic particles dispersed within ceramic powders. In this research, alumina-nickel nanocomposite powder was obtained using the soaking method. The powder mixed with α-alumina as a seed was sintered using a pulse electric current sintering technique. The sintered nanocomposites are then annealed to disperse dislocations around the nanoparticles into alumina grains. Results showed that the maximum fracture toughness was 7.6 MPam1/2, which was two times higher than that of alumina.

Abstract: Nickel dispersed alumina matrix nanocomposites were fabricated using a novel soaking method. Secondary particles were introduced into the nano-pores of a porous matrix grains by a soaking method, such that γ-alumina powder was soaked in nickel nitrate solution under vacuum. During pre-calcination, nickel oxide particles were created inside of the nano-pores of γ-alumina. The alumina powders were then reduced under hydrogen atmosphere to obtain nano-sized metallic nickel embedded in γ-alumina grains. The alumina-nickel composite powders were sintered by pulse electric current sintering (PECS) technique with α-alumina seeds. The maximum strength of the alumina-nickel nanocomposites was 984 MPa after sintering at 1,450 °C with α-alumina seeds, where the specimen size was 2
2
10 mm3. The maximum fracture toughness was 5.5 MPa·m1/2 after sintering at 1,350 °C with seeds measured by the single edge V-notched beam (SEVNB) method.

Abstract: To improve fracture strength and fracture toughness in ceramic materials, we focused our attention on an intra-type structure of nanocomposites. We proposed new processing method for fabricating intra-type nanocomposites. In this work, Al2O3/Ni nanocomposites were fabricated using a soaking method and sintered by PECS(Pulse Electric Current Sintering) method. We also estimated seed effects on this system. Seeded nanocomposites showed high fracture strength and higher fracture toughness than non-seeded nanocomposites and monolithic alumina. The fracture strength of the seeded nanocomposites was more than 800MPa in all sintering temperature range. The maximum value of the fracture toughness was 5.5 MPa⋅m1/2 for the specimen sintered at 1350°C. The sintered specimens with high fracture strength and high fracture toughness were annealed from 800°C to 1000°C for 0 to 10 min. The specimen annealed at 800°C for 5 min showed the highest fracture toughness of 7.6 MPa⋅m1/2. This value is two times higher than that of the monolithic alumina.