Materials Science Forum Vols. 486-487

Abstract: It is generally well known that PCB (Printed Circuit Board) is a complex mixture of various metals mixed with various types of plastics and ceramics. Accordingly, it is very important to extract metallic components from used PCB’s from the point of view of recycling the used resources as well as the environmental protection. In this study, a high temperature pyro-metallurgical process was investigated to extract valuable metallic components from the used PCB’s. For this purpose, used PCB’s were shredded and oxidized to remove plastic materials, and then, a high frequency induction furnace was used to melt and separate metallic components in molten state from the remaining oxides. After the oxidation of the used PCB, 30.6wt% SiO2, 19.3wt% Al2O3 and 14wt% CaO were analyzed as major oxides, and thereafter, a typical composition of 32wt%SiO2-20wt%Al2O3-38wt%CaO -10wt%MgO was chosen as a basic slag system for the separation of metallic components Moreover, in order to understand the size effect on the extraction of metallic components, oxidized PCB’s were further milled, and then, melted. As a result, it was found that the size of oxidized PCB’s was needed to be less 0.9mm to make a homogeneous liquid slag and to recycle metallic components over 95%.

Abstract: To replace lead oxide glass, Bi2O3-SiO2-ZnO glass, as a Pb-free glass, was examined for optical properties for a transparent dielectric layer of a plasma display panel (PDP). The glass was evaluated for glass transition temperature (Tg) and thermal expansion coefficient (α). The transparent thick films produced with a screen-printing method were evaluated for optical properties. The transmittance of thick films fired at 560-620°C showed above 80%. The results suggest that the bismuth glass is a suitable candidate for one of the lead-free glasses compositions in a transparent dielectric layer.

Abstract: For the application of transparent dielectric layer of PDP (Plasma display panel), a Pb-free glass, ZnO-B2O3-SiO2 glass, was measured for thermal and optical properties after forming thick films. Glass frit of different size (d50=1.7, 4.3㎛) and different thickness film forming process (a die coater and a screen printer) were applied to a transparent dielectric. The coated layer was determined for pore contents, size, and transmittance. As a result, the screen printing method produced non-uniform surface and increased pores with multilayer. The die coater method, however, produced more uniform surface and less pore content compared to the screen printing method. Thus it shows that the increase of pore size and contents has detrimental effects on the transmittance of thick films made by a lead-free glass, ZnO-B2O3-SiO2 glass.

Abstract: To clarify the effects of parameters of porous ceramics form on the characteristics of composites fabricated by high-pressure infiltration, Alumina forms with different porosity (15~70vol %) and pore morphology were fabricated by Freeze and Dry Process and Partial Sintering Process. Alumina/aluminum composites were made by the squeeze casting. The composites contained the different volume fraction of aluminum depending on the initial porosity of the ceramics form. The coefficient of thermal expansion (CTE) and thermal conductivity of composites were measured. The results indicated clearly that variation of the structure of porous ceramics form fairly affected CTE but the effects on thermal conductivity were small.

Abstract: Mullite-alumina porous ceramics were fabricated by polymer-aided extrusion through using natural kaolin and alumina as starting materials. The physical and chemical properties of porous ceramics were investigated. The results showed that the approach of using kaolin as starting material offers many benefits such as low cost, big processing capacities, low mullitization temperature and unique microstructure. The porous ceramics with high strength, high porosity, narrow pore size distribution, high permeability and good thermal-shock behavior was obtained by modifying preparation conditions.

Abstract: The effects of reheating in solid-liquid region on the microstructure of electromagnetically stirred Al alloy have been investigated. The billet of Al alloy was produced at a various casting speed from 200 to 500 mm/min in a continuous casting machine with an electromagnetic stirring device. The microstructure of the billet, which was isothermally reheated in a solid-liquid region during holding for from 0.5 to 15 min, was examined. The roundness and size of primary α phase of electromagnetic stirred Al alloy was measured according to the reheating time. The roundness of primary α phase was obtained a minimum during holding for from 3 to 7 min at a holding temperature of 584°C and was deteriorated at a longer reheating time due to a dominant coalescence. Also the spheroidization of primary α phase during reheating in solid-liquid region was significantly dependent on initial microstructure of the billet.

Abstract: Microstructure and mechanical property at room temperature and at 1773 K of Nb-Si based refractory intermetallic alloys were investigated in terms of compression and fracture toughness test. Mo and V were chosen as ternary alloying elements because of their high melting points, atomic sizes smaller than Nb. Both ternary alloying elements were found to have a significant role in modifying the microstructure from dispersed structure to eutectic-like structure in Nb solid solution/Nb5Si3 intermetallic composites. The 0.2% offset yield strength at room temperature increased with increasing content of ternary elements in Nb solid solution and volume fraction of Nb5Si3. At 1773 K, Mo addition has a positive role in increasing the yield strength. On the other hand, V addition has a role in decreasing the yield strength. The fracture toughness of ternary alloys was superior to binary alloys. Details will be discussed in correlation with ternary alloying, volume fraction of constituent phase, and the microstructure.

Abstract: The anisotropy of hybrid composite such as Al/GFRP laminates made it possible to control the fiber orientation according to the loading patterns. Therefore, it is important to study the fatigue and delamination behaviors of Al/GFRP laminates by fiber orientation. Al/GFRP laminates of three different fiber orientations (0°, 45°, 90°) were chosen, and the progressive delamination behavior was examined through the fatigue tests. The effects of the fiber orientation on the crack length, the fatigue life, the delamination, the crack growth rate (da/dN), and the stress intensity factor range ( ΔK) were investigated and discussed. The findings led to a conclusion that the effect of fiber orientation should not be ignored in analyzing the progressive damage of Al/GFRP laminates.

Abstract: Ankle Foot Orthosis (A.F.O) should endure the uncountable repeating impact and fatigue loadings owing to the gait characteristics. This study investigates the impact deflection and relationship between the absorbed energy and the residual strength rate using the glass/epoxy and the aramid/epoxy for the leaf spring in A.F.O. In conclusion, an equation was suggested to evaluate the absorbed energy and the residual strength rate by the different impact velocities. When the glass/epoxy and the aramid/epoxy was selected for the leaf spring in A.F.O, it was reasonable to use the glass/epoxy of the cross-ply for the parts subject to the large impact and the aramid/epoxy of the woven type for the parts to require the high elastic energy such as the large deformation.

Abstract: This paper investigates the effect of the defect location on the stress concentration, the stress distribution, and the crack initiation behavior when the defects were made in the vicinity of the circular hole in the monolithic aluminum and the glass fiber reinforced laminates (GLARE). As the defect location in the vicinity of the circular hole was changed from ° = 90 4 q to ° = 0 1 q , the stress concentration was increased. Generally, the stress concentration of GLARE was about 15% greater than that of the monolithic aluminum. When the defect was at ° = 30 2 q , Multi Site Damage (MSD) crack was found in the monolithic aluminum, but just the main cracks existed in GLARE. The delamination instead of MSD crack was made in GLARE, and it resulted in the prevention against the second crack initiation.