Solid State Phenomena Vol. 345

Abstract: Nanosilica is a nanotechnology product with many substantial functions in many industries. Previous research showed that nano silica can be synthesized from geothermal silica, that caused silica scaling in injection well and turbine in geothermal power plant, reducing its power plant capacity by 40%. This research used geothermal silica as a precursor for nanosilica production with co-precipitation to recover amorphous silica from silica geothermal to reduce scaling while also increasing its economic value. The objectives of this study were to determine the model to represent the co-precipitation method for nano-silica by using nucleation and growth modelling, therefore help the scale-up process of nanosilica production. The experiment was conducted in four steps. (1) Silica washing utilized distillate water with a ratio of water to silica of 10:1 and sulfuric acid of 20% with a ratio of acid to silica of 4:1, both as a washing agent. (2) Preparation of HCl with concentrations of 3% and 9%. (3) Preparation of sodium silicate solution by reacting washed silica and NaOH to obtain sodium silicate. (4) Preparation of primary and secondary sodium silicate by diluting sodium silicate by two and four times to obtain primary and secondary sodium silicate, respectively. (5) Precipitation of sodium silicate with HCl consists of two steps using primary and secondary sodium silicate. The result showed that the model fit concentration data, with Sum of Squared Error (SSE) 1.9297.10-4, mass transfer coefficient rate is 9.8.10-3 dm/min, and the average relative error is 3.5%.

Abstract: For the miniaturization of the structures of semiconductor device fabrication, high uniformity of side-flatness and edge roll-off of 300 mm wafers are required. In this study, the formation of light point defects (LPDs) on silicon (Si) wafer surface due to an edge gripper handling system was investigated. The relationships between the generation of LPDs with respect to flatness, edge profile, and edge roll-off of Si wafers were analyzed. It was found that the variation of tradition facet parameters and near-edge geometry metric, such as edge site front surface-referenced least squares/range (ESFQR), have no impact on the formation of surface LPDs. By contrast, the performance of Z-height double derivative (ZDD), allowed an accurate prediction of formation of surface LPDs. Additionally, for a 300mm silicon wafer, the surface LPDs occurred with frontside ZDD obtained at a radius of 149.2 mm, ranging above -954 nm/mm² . The surface was LPDs free when ZDD was below -1235 nm/mm². Surface LPD formation occurred randomly and was not predictable when ZDD ranged from -954 nm/mm² to -1235 nm/mm². The result indicates that the LPDs caused by wafer handling is proportional to the performance of ZDD at the edge roll-off area of silicon wafer, this is consistent with the requirement of edge roll-off considering wafer geometry.

Abstract: AISI H13 material finds wide use as screw shafts and screw elements in Twin Screw Extruders for Polymer Compounding applications owing to its high strength, excellent thermal shock resistance, high wear resistance and good fatigue strength. However, two AISI H13 shafts used in the Twin Screw Extruder supplied for fluoropolymer application experienced breakage after two years of service. Visual examination of broken shafts revealed deposits of processing material, rust marks and grooves at multiple locations on the shaft spline at the element to element butting zone. The location of breakage of the shaft was noted at Barrel No.5, which happens to be the vent zone of the extruder. The fracture surface was observed to be almost perpendicular to the rotating axis of the shaft. Macro-examination of the shafts showed abnormal wear at the groove areas and significant reduction in the diameter of the screw shafts with complete absence of spline in the zone adjacent to fracture. Hardness survey revealed values of 25-27 HRC that was 18-20 HRC lower than the hardness in supply condition. Microstructural examination on the failed shafts showed fine spheroidized carbides with ferrite in tempered martensitic matrix. SEM Analysis on samples from fracture surface revealed presence of multiple micro-voids and indicated coalescence of these voids. Based on the investigation & analyses it was inferred that the predominant mode of failure of the shafts had been “Corrosion Assisted Ductile Rupture” in elevated temperature operating conditions. Finally, recommendation to prevent occurrence of such failures has been proposed.