Materials Science Forum Vol. 1007

Abstract: The objective of this research is to study the influence of temperature on drying and changes in carbohydrate composition during the drying. Chlorella pyrenoidosa was dried in oven at various temperatures and initial weight 2 g. The initial moisture content of Chlorella pyrenoidosa was 487.2% dry weight and the composition was hemicellulose (62.76), cellulose (2.39), and lignin (0.46% dry weight). Every 5 min, the moisture content was recorded. The critical moisture contents of Chlorella pyrenoidosa at 50, 60, and 70 °C are 7.2, 3.9, and 3.1% dry weight, respectively. Meanwhile, the equilibrium water contents are 0.53, 0.32, and 0.12% dry weight, respectively. The carbohydrate content in Chlorella pyrenoidosa cell as a result FTIR analysis indicates that the higher temperature of drying the carbohydrate content increases. Drying of Chlorella pyrenoidosa at temperatures of 50, 60, and 70 °C will decrease moisture content without disturb carbohydrate molecule, so the carbohydrate content increases. Therefore, drying of Chlorella pyrenoidosa before converting become bio-ethanol will give benefit to increase the carbohydrate content and initial rupturing of it’s cell.

Abstract: Al-Mg alloy strips were cast by an unequal-diameter twin-roll caster. It was found that cracks formed on the surface at grain boundaries. The grains near the surface were small in size, which likely contributed to crack formation. The use of a molten metal pouring method to increase the grain size near the surface is proposed to reduce cracks. In the previous method, molten metal is poured into a pool, which is on the lower roll surrounded by side-dam plates, a back-dam plate, and the upper roll. In this study, molten metal was directly poured onto the roll surface at a shallow angle using a launder. When the angle was smaller than 20°, cracks did not form. With the proposed method, the heat transfers between the molten metal and the roll surface decreased, as determined from the grain size and strip thickness. The cracks on the strip surface were color-checked and visually inspected.

Abstract: Si ranging from 0.2 mass% to 2.0 mass% was added to Al-5%Mg alloy (5182) and strip was cast by a vertical type high-speed twin-roll caster at a speed of 80 m/min. The as-cast strip was cold-rolled down to 1 mm thickness and annealed. The mechanical properties were investigated using cup tests and tension tests. The limiting draw ratio (LDR) of the 5182 alloy was 2.0 and the LDR became smaller as the Si content increased. When the Si content was 2.0 mass%, the LDR was 1.8, which shows that Si-added 5182 can be used for sheet forming, if the Si content is less than 2.0 mass%. The tensile strength and elongation were almost constant when the Si content was less than 1 mass%, but decreased at 2.0 mass% Si. However, the elongation was greater than 20% at 2.0 mass% Si. For die casting, 2.0 mass% Si was determined as the appropriate content from the results of the tension tests. When the Si content is in the range from 1.0 mass% to 2.0 mass%, then the Si added Al-5%Mg has the ability to be used for both die casting and sheet forming.

Abstract: The effects Si and Mn addition on the fluidity length, mechanical properties, and casting cracks of a die-cast Al-4.5%Mg alloy were investigated. The Si content was 1, 2, or 3 mass% and the Mn content was 0.3, 0.6, or 0.9 mass%. Both Si and Mn did not affect fluidity. Si content of more than 1 mass% improved casting crack resistance. The effect of Mn on casting cracks was weaker than that of Si. When Si content was 2 mass%, both tensile stress and elongation were good. Mn did not affect the mechanical properties.

Abstract: Casting of clad strip consisting of Al-40%Sn-1%Cu alloy and 1050 pure aluminum from molten metals was attempted using an unequal diameter twin-roll caster equipped with a scraper. The liquidus line and solidus line of the Al-40% Sn-1% Cu alloy are 620 °C and 220 °C, respectively. The liquidus line and solidus line of the 1050 are 657 °C and 646 °C, respectively. Therefore, solidification temperatures of the two aluminum alloys are much different. When an Al-40%Sn-1%Cu solidification layer was bonded to a solidification layer of the 1050 alloy, the temperature of the 1050 solidification layer surface was higher than the solidus line of Al-40% Sn-1% Cu. However, the Al-40% Sn-1% Cu alloy could be bonded to the 1050 strip and a two-layer clad strip could be cast. The interface between the two strips was very clear. Electron Probe Microanalysis (EPMA) indicated that Sn in the Al-40% Sn-1% Cu alloy did not diffuse into the 1050 alloy. Tensile shear tests were conducted using the as cast clad strip, and no breakage occurred at the interface between the strips but only in the Al-40% Sn-1% Cu layer. This result confirmed that the two strips were strongly bonded at the interface.

Abstract: Strip casting using a side dam plate produces a vertical burr at the strip edge. In the present study, changing this vertical burr into a horizontal burr using a burr changer is proposed. The burr changer was placed inside the side dam plate. The burr changer was made from mild steel and an insulator sheet and cut along the shape of the roll. The burr changer was placed so as to prevent exhaustion of semisolid metal between the side dam plate and the roll-side surface. When the position of the burr changer was appropriate, the vertical burr changed into a horizontal burr. The horizontal burr was flat. The width of the horizontal burr was affected by the lowest position of the burr changer and became narrower as the lowest position of the burr changer approached the roll gap position.

Abstract: This study investigated the crystallization position and formation mechanism of globular crystals at the center area in the thickness direction of aluminum alloy strips cast by a high-speed twin roll caster. Twin roll casters for single strips and clad strips were used, as well as twin roll casters equipped with a cooling slope. The globular crystals were formed from dividing arms of dendrites of the solidified layer facing the center area at the roll gap. The arms of isolated dendrite also divided. No globular crystals were formed at the interfaces of clad strips with different solidification temperatures because of the temperature gradient at the interface which inhibited division of the dendrite arms. It was demonstrated that globular crystals at the center area of the thickness direction were formed by dendrite-arm-dividing at the roll gap by the strip casting clad strip. Experiments by semisolid-strip casting with the cooling slope showed that globular crystals in the molten metal existed in the solidification layers.

Abstract: In this study, the two types of high-strength low-alloy steels were melted and cast in a vacuum induction furnace. Phase transition temperature of HSLA steel was calculated by JMatPro software. The calculation results show that the two different types of HSLA steels which have equal phase proportions of ferrite and austenite at a temperature of approximately 820 and 800 °C in HSLA-I and HSLA-II, respectively. In addition, the effect of chemical composition on the microstructure and mechanical properties of steels were studied. The results indicate that the ultimate tensile stress value of HSLA-II samples was greater than the HSLA-I samples by about 35%, and the yield stress and breaking strength value of HSLA-II were higher than HSLA-I as well.

Abstract: Antibacterial materials based on nanotechnology have been attracted considerable attention by the scientific community. In this study, the sol-gel method was applied to prepare of antibacterial materials from tetra-n-butyl orthotitanate, zinc nitrate and ethylenediamine tetraacetic acid (EDTA) as a complexing agent. The effects of the synthesis conditions on the properties of the Ag/ZnTiO₃ samples such as the calcination temperature, the calcination time, pH value and ethylene glycol volume, were investigated. The obtained materials were characterized by powder X-ray diffraction (XRD) and their antibacterial activity against Staphylococcus aureus (S. Aureus) was evaluated. The results showed that the optimum conditions for Ag/ZnTiO₃ synthesis were: calcination temperature of 650°C, calcination time of 2 h, pH value of 4.5 and ethylene glycol volume of 4.5 mL.