Abstract: The synthesis process of the fused silica glass uses chemical vapor deposition (CVD) method in a furnace. The synthesis process involves complicated physical-chemical phenomena such as turbulence, combustion, radiation, two-phase flow, and so on. A CFD simulation has been carried out for an industrial furnace and process. The simulation result including temperature and major species concentration then is input to CHEMKIN to calculate the radical equilibrium concentration on the fused silica surface. The trend of the simulated fused silica surface temperature is consistent with the measured refraction index showing that the surface temperature is one of the most important parameters influencing the refractive index uniformity of the fused silica product.
Abstract: With the advantage of simplicity and low cost, ink jet printing has the potential to replace the traditional chemical and physical deposition technology in thin film fabrication. In this work, silver conductive thin films are deposited on glass and polyimide substrates by ink jet printing, where some major characteristics of the printed thin films are investigated and compared to those deposited by sputtering. The micro texture and residual stresses of the thin films are measured with X-ray diffractometry (XRD). Using thin film scratch tester, the adhesion of thin films deposited by both ink jet printing and sputtering is studied. Further observations on electric and optical performance by using visible wavelength photospectrometry, four-point probe, and surface profiler are also discussed. The result shows that the micro texture of the printed thin film behaves as good as the sputtered thin film. Furthermore, the micro scratch result illustrates that the adhesion of the printed thin film is even better than the sputtered thin film. It emphasizes that, after certain baking process, the ink jet printing has the possibility to replace sputtering in thin film deposition, especially for the polymer substrates.
Abstract: Polymer nanocomposites have been attracting attention among researchers as electrical insulating application from energy storage to power delivery. However, partial discharge has always been a predecessor to major faults and problems in this field. In addition, there are a lot more to explore as the characteristic of partial discharge in nanocomposites is not clearly understood as well as the electrical properties of the nanocomposites. By adding a few amount of weight percentage (wt%) of the nano fillers, the physical, mechanical and electrical properties of polymers can be greatly enhanced. This is due to its amazing characteristic of having large specific area as a consequential from its nano sized particle that could enhance the electrical properties of the insulator. For instance, nano fillers in nanocomposites such as silica (SiO2), alumina (Al2O3) and titania (TiO2), play big role in providing good approach to increase dielectric breakdown strength and partial discharge resistance of nanocomposites. Such polymer nanocomposites will be reviewed thoroughly in this paper based on previous experimental works and studies. This paper provides reviews from related publications from year 1997 to 2011 including the results of experimental works which have been conducted by the authors with main focus on partial discharge characteristics in polymer nanocomposites, which demonstrates that research and utilization of polymer nanocomposites has well developed from past decades and will possess a high demand in future as electrical insulating material.
Abstract: In the structural analysis of mechanical elements, both in the design and testing phase, the Young’s modulus value influences the precision of the results and must be taken into consideration during the calculation. The E value is usually shown in tables that do not report precise values, but ranges of values that are characterized by a certain amplitude. In the structural calculation analytically or numerically developed, an approximate reference E value that is hypothesized constant in the material is usually used. Moreover, this value does not take into consideration possible thermal-chemical-mechanical treatments used on the material. A mechanical designer needs to know the precise E value of the material in the final operation state in order to develop a structural analysis. According to what has been specified above, it is necessary to know the value of the elastic characteristics for every point of material in order to associate a value in the development of a correct and deepened numerical analysis for every zone in examination. We have developed a finely tuned experimental system having the following main steps: - measurement of the penetration of a metallic microsphere, as a function of the applied load, in a single point of the analyzed material; - determination of Young's modulus. This procedure allows for E to be measured, if necessary, at points very close to each other in such a way as to be able to take into consideration, when performing structural analysis requiring a high degree of accuracy, the influence of the gradient of the longitudinal elastic modulus. The precision of the punctual values obtained for E is comparable with that of traditional experimental methodologies (e.g. tensile test), since the proposed procedure expects the use of the experimental calibration curve, which is precisely constructed based upon the data obtained through the above methodologies.
Abstract: Activated carbon fibers (ACFs) are widely used adsorbents due to their small fiber diameter, uniform pore size distribution and rapid adsorption/desorption rate. In addition, carbon nanotubes (CNTs) have received much attention recently because of their excellent mechanical and electrical properties and being candidates for adsorption. Thus, it should be highly interested as grafting CNTs onto ACFs to form a hybrid adsorbent. Therefore, the objective of this paper is to investigate the physicochemical properties of ACFs grafted with nitrogen-doped CNTs (CNs) and determine the adsorption and desorption performance of toluene vapor on this hybrid adsorbent. The chemical vapor deposition method was used for growth of CNs directly onto ACFs. The resulting materials were characterized by several techniques. Next, the adsorption breakthrough behaviors of toluene on the samples were measured in a continuous flow-type fixed-bed system. And then the temperature programmed desorption system was utilized to observe the desorption characteristics of toluene from the samples. Results show that the CNs have been grafted homogeneously onto the ACFs. The attachment of CNs on ACFs was believed to block part of the active surface area, causing the decrease in specific surface area and pore volume, but lead to the increase in microporosity. The adsorption of toluene on ACFs or the hybrid adsorbent was physical adsorption. At higher adsorption temperatures, the hybrid adsorbent could maintain high enough capacities of toluene and even exceed the performance of ACFs. Moreover, toluene could be desorbed completely from ACFs and the hybrid adsorbent up to 400 oC with the highest desorption efficiency at about 180 oC.
Abstract: The present study is aimed at investigating the effect of acid etching durations on the surface roughness and birefringence of lightweight mirrors made of ZERODUR® glass ceramic. Four acid etching durations (15, 20, 25 and 30 min) have been chosen at a fixed concentration. By using the photoelasticity, surface profiler and laser microscope, the results before and after acid etching have been obtained. It is found the maximum value of the retardation for the polished lightweight ZERODUR® mirror is up to 30 nm. In addition, residual stresses induced by the grinding process with an average grain size of 149 μm are relived after removing ZERODUR® material of a thickness of 60 μm.
Abstract: K2CO3-doped 0.98(Na0.5K0.5)NbO3-0.02(Na0.5Bi0.5)TiO3 [abbreviated as 0.98NKN-0.02NBT] lead-free piezoelectric ceramics were prepared by the conventional mixed oxide process. The effects of K2CO3 additions on the crystalline structures and electrical properties of the 0.98NKN-0.02NBT ceramics were investigated. The specimens of 0.98NKN-0.02NBT ceramics added with K2CO3 maintain an orthorhombic phase. In the case of low K2CO3 content (≤ 0.3 wt%), the grain growth became remarkable. The increase of grain size favors improving the piezoelectric properties, which is known as grain size effect. The grain size effect compensates the decrease of the electromechanical coupling factor due to the hard doping effect. For 0.98NKN-0.02NBT ceramics by doping 0.3 wt% Na2CO3, the electromechanical coupling coefficients of the thickness mode kt and the planar mode kp reach 0.51 and 0.33, respectively, after sintering at 1100 oC for 3 h. Our results show that 0.98NKN-0.02NBT with the addition of 0.3 wt% K2CO3 is a good lead-free piezoelectric ceramic.
Abstract: In this work, the effect of PE-g-MAH as compatibilizer in polyethylene/ natural rubber/ water hyacinth fibers composites were prepared and characterized in terms of tensile properties, morphology properties, swelling behavior and FTIR characteristic. Water hyacinth fibers (WHF) was used as reinforced fiber in the composites incorporated into the LDPE/NR matrices with different fiber loading. LDPE/NR/WHF composites were prepared with Z-blade mixer at 180°C with rotor speed of 50 rpm for 10 minutes. The presence of PE-g-MAH increased the tensile strength and Young’s modulus while reduced the elongation at break of LDPE/NR/WHF composites. The molar sorption of the composites decreased as the fiber loading increased. SEM morphology showed a better fiber dispersion and fiber distribution indicated PE-g-MAH improved the interfaces between water hyacinth fiber and LDPE/NR matrices. The absorption peak at 1741.52cm-1 indicated ester carbonyl group in LDPE/NR/WHFPE-g-MAH composites.
Abstract: The objective of this study is to investigate the mechanical behavior of copper thin film with different thicknesses subjected to varying strain rates. A micro-force tensile testing machine (MTS Tytron 250) was used to test the polyimide samples coated with different thicknesses of copper (500 nm, 750 nm, 1000 nm, and 1500 nm). The experiments were conducted by applying test vehicles to different strain rates (1.6×10-4 s-1, 1.6×10-3 s-1, and 1.6×10-2 s-1). The experimental results showed the strain rate and the thickness have obvious influence upon the mechanical properties of Cu thin film. The yield stress increases as increasing the strain rate or decreasing the thickness of Cu film. For considering the strain rate sensitivity m, the strain rate sensitivity m is found that it increases as decreasing the thickness to imply that Cu film has high strain-rate response at low thickness.
Abstract: The carbon (C) co-implantation and advanced flash anneal were employed to form the ultra shallow junction (USJ) for future nano CMOS technology applications. The effects of the C co-implantation process on dopant transient enhanced diffusion (TED) of the phosphorus (P) doped nano USJ NMOSFETs were investigated in details. The USJ NMOSFETs were prepared by a foundry’s 55 nano CMOS technology. Various implantation energies and doses for both C and P ions were employed. Results show the suppression of the TED is strongly dependent on both C and P implantation conditions. Besides, the mechanisms of P TED and suppression by C ion co-implantation were illustrated comprehensively with schematic models.