Materials Science Forum Vols. 510-511

Abstract: Nickel powders were prepared by the reduction of hydrazine of Ni(OH)2 reactant slurries from non-aqueous media. The morphological characteristics of nickel powders were investigated under various processing conditions. Nickel powders were characterized by using scanning electron microscope (SEM), X-ray diffractometer (XRD), thermal gravitational analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The size of nickel powders was increased as the reaction temperature and time increased because of the thermal agglomeration of nuclei and/or increased growth rate. The surface of nickel powders composed of both Ni and Ni(OH)2 was oxidized in the temperature range of 400-600°C.

Abstract: Nickel powders were synthesized by the reduction of hydrazine of nickel salts from diethanolamine (DEA) solution, and the morphological characteristics of nickel powders were investigated with various process conditions such as the addition of hydrazine, reaction temperature, the composition of mixed solvents. The addition of hydrazine in DEA solution largely affected the size control of nickel powders. Under N2H4/Ni2+molar ratio= 1.5 and 2.0 conditions, spherical nickel powders in the submicron range were obtained owing to higher the reduction rate. An increase of temperature increased the size of nickel particles. At 220°C for 40min, the nickel powders were composed of polyhedral particles with a high crystalline in the submicron range. The mixed volume ratio of TEA to DEA solvent improved the inhibition of agglomerate between particles.

Abstract: The polystyrene spheres coated with a slurry, consisting of copper (I) oxide powder, water and PA (poly acrilamide), were reduced to form copper (Cu) hollow spheres at sintering temperatures ranging from 650 to 950 °C under a hydrogen atmosphere. The microstructural evolutions and mechanical properties of the Cu hollow spheres were investigated with the sintering temperature. The increase in the sintering temperature led to the increase in the density and grain size of the spheres. The amount of the residual copper oxide in the samples decreased with increasing sintering temperature. The electrical conductivity, hardness, and compression strength of the hollow spheres increased with increasing sintering temperature.

Abstract: Many micro technology researches have been concentrated in the field of materials and a process field. But the properties of micro materials should be understood to give still more advanced results. Among the various material properties, mechanical material properties such as tensile strength, elastic modulus, etc., is the basic property. To measure mechanical properties in micro or nano scale, actuating must be very precise. Piezo is a famous actuator, frequently used to measure very precise mechanical properties in micro research field. But piezo has a nonlinearity called hysteresis. Not precision result is caused because of this hysteresis property in piezo actuator. Therefore feedback control method is used in many researches to prevent this hysteresis of piezo actuator. Feedback control method produces a good result in processing view, but causes a loss in a resolution view. In this paper, hysteresis is compensated by using an open loop control method. To apply the open loop control method to piezo actuated nano scale material testing machine, hysteresis property is modeled in a mathematical function, and a compensated control input is constructed using inverse function of original data. The reliability of this control method can be confirmed by testing nickel, aluminum, and copper micro thin foil that is used in MEMS material broadly. If these MEMS material properties are used in a MEMS research field, more economical and high performance MEMS materials can be obtained.

Abstract: The effect of indium on the microstructures and mechanical properties of a Au-Pt-Cu alloy was investigated. The Au-Pt-Cu-xIn alloys heat-treated at 550°C for 30 min revealed a maximum hardness value of 207 HV, irrespective of the heat temperature and In contents. Also, the hardness of the Au-Pt-Cu-xIn alloys (x = 0.5, 1.0, 1.5, 2.0) aged at 550 °C rapidly increased with increasing aging time, and it reached an almost constant value after 30 min. The hardness of the Au- Pt-Cu-xIn alloys aged at 550°C for 30 min increased with increasing In content until 1.5wt%, but it slightly decreased with more increasing In content. Also, a variation of the tensile strength of the alloys with In contents showed a similar trend of hardness change with In contents. Analysis of EDS and TEM revealed that the microstructure of Au-Pt-Cu-xIn alloys is composed of solid solution with fcc structure and intermetallic InPt3 precipitate with L12 structure. Based on this investigation, it can be concluded that an increase in hardness of Au-Pt-Cu-xIn alloys is ascribed to a complex effect of the precipitation hardening of InPt3 and the grain size refinement.

Abstract: Foamed metal is a kind of porous material with pores in the metal matrix. One of the possible process routes is to blow gas bubbles into liquid metals. However, many metallic foams produced by this foaming method have coarse and irregular cell structures. The industrial aim is to fabricate foams with more uniform structure and cell size. It is important to understand the mechanisms and factors controlling. The rheological characteristics are the most important factors in the metal foam manufacturing. Thus this study investigated the bubble behavior of the molten metal and its two most important two parameters: surface tension and liquid viscosity. The surface tension (by the ring method) and the viscosity (by the rotation method) of Mg-Al alloy (AZ91, AM60) have been measured under pure Ar and SF6 + CO2 atmosphere. The results show that the surface tension and the viscosity of these alloys decrease with increasing temperature. The addition of Ca and SiC to Mg alloys decreases the surface tension and increases the viscosity. This anomalous behavior is related with the preferential adsorption of high activity elements on the surface.

Abstract: The performances of an electrochemical detector (ECD) using Prussian blue (PB) modified indium tin oxide (ITO) electrode were investigated. PB is one of the well-known catalytic materials. PB offers electrocatalytic reaction between electrode and analytes (dopamine and catechol). We optimized the PB film thickness that would catalyze redox reaction efficiently using surface topography from atomic force microscopy (AFM). Capillary electrophoresis (CE) and amperometric method were used to separate and detect the testing analytes. The results showed that the PB film could serve as an excellent mediator, which catalyzes electron transfer. We measured electropherograms for the testing analytes consisting of catechol and dopamine with their concentrations of 100 µM and 10 µM, respectively.

Abstract: Activated carbon fibers were prepared from stabilized PAN-based fibers by chemical activation using hydroxides at different concentrations. The experimental data showed variations in specific surface area, microstructure, pore size distribution, and amounts of iodine adsorbed by the activated carbon fibers. Specific surface area of about 2244m2/g and iodine adsorption of 1202mg/g were obtained in the KOH 1.5M. However, the use of NaOH in the activation process rather than KOH and using the same time/ temperature profiles resulted in a carbon with a much lower surface area. KOH is a more developed pore structure than NaOH, which means that KOH is a better activation agent in producing ACF than NaOH.

Abstract: Porous hydroxyapatite (HAp) scaffolds were successfully prepared by using the HAp slurry based on the replication of polymer sponge substrate. The effect of HAp content in slurry on the pore morphology and size, and density, porosity, and mechanical strength of porous scaffolds was investigated. The scaffolds with average pore sizes ranging from 200 to 400 µm had an open, relatively uniform, and interconnected porous structure. As the HAp content increased, the porosity of scaffold decreased while the density increased. These phenomena were attributed to the fact that the pores became interconnected with more dense and thicker pore walls with increasing HAp content in slurry. The results suggest that the density, porosity, and compressive strength of the porous HAp scaffold were significantly affected by the content of the HAp powder in the slurry.

Abstract: Biodegradable β-tricalcium phosphate (β-TCP)/poly (lactide-co-glycolide) (PLGA) composites were synthesized by in situ polymerization with microwave energy. The influence of the β-TCP content in β-TCP/PLGA composites on the molecular weight, crystallinity, microstructure, and mechanical properties was investigated. As the molecular weight of composites decreased, the β-TCP content increased up to 10 wt%, while further raising of the β-TCP content above 10%, the molecular weight increased with increasing β-TCP content. This behavior may be ascribed to the superheating effect or nonthermal effect induced by microwave energy. It was found that the bending strength and Young’s modulus of the β-TCP/PLGA composites were proportional to the molecular weight of PLGA. The bending strength of the β-TCP/PLGA composites ranged from 18 to 38 MPa, while Young’s modulus was in the range from 2 to 6 GPa.