Applied Mechanics and Materials Vol. 302

Abstract: Moore’s law by scaling conventional CMOS involves huge lots of technology evolution in both aspects of electronics material and micromachining. One of the most promising modern innovations is the 3D IC and the key material to the 3D IC is the low-K (dielectric) materials. Since the new generation low-K material is rather porous and fragile in structure strength, conventional singulation methods including the dicing saw and nano-second laser can not be applied. New machine modality has to be used to avoid the cracking and excessive debris contamination. In this paper we demonstrate the application of pico-second laser on the grooving machining of low-K wafer. The results show that the removal of low-K material is up to the production standard: smooth groove bottom with minimal debris. However, as the groove line involves metal pads the laser power is partially consumed by the ablation of the metallic material the depth is not controlled ideally. With proper adjustment of the machine parameter such as laser power, focal depth and pulse energy the problem can be resolved.

Abstract: PZT thin film was fabricated by using RF-sputtering process, and platinum was used as bottom electrodes. The sputtering gases were Ar：O2＝25：0 sccm, Ar：O2＝20：5 sccm, or Ar：O2＝15：10 sccm. After sputtering, the PZT film was annealed for 5 minutes under O2 gas environment and at the temperature of 600 0C, 650 0C, 700 0C or 750 0C. To judge the quality of the deposited PZT film, its physical properties and electric properties were evaluated. The results indicate that the best crystallization temperature of PZT thin film is about 700 0C. Also, the roughness of the PZT thin film becomes larger with the increasing of annealing temperature. By adding more oxygen in the sputtering gas, one could have better crystallization of the PZT film. As for the electrical properties, the leakage current of PZT thin film increases with the increasing of annealing temperature. Furthermore, the ferroelectric property is affected by the crystallization amount of perovskite, the thickness of PZT thin film, and the diffusion situation between the bottom electrode and the PZT film.

Abstract: In order to evaluate the impact protection capacity of armor material quantitatively, direct impact testing loaded by modified Hopkinson bar was used to simulate the impaction between penetrator and armor. Protection coefficient k was defined to describe the protective performance. Using the direct impact testing, Ti-6Al-4V specimens with different microstructure and thickness were tested. Results show that k decreases with increased impact velocity and increases with increased thickness of specimen. Under a given loading condition, binary microstructure exhibits the highest k, indicating the best protective performance. Moreover, its k shows the most sensitivity to thickness (mt) and the least sensitivity to impact energy (me), which means that its protective performance can be improved most efficiently by increasing its thickness and it will exhibit good protective performance in a wider impact velocity range. This new method can evaluate the impact protective properties of armor materials efficiently, which may have a broad application prospect.

Abstract: A dynamic model of mass transfer was developed with mass transfer equation and mass transfer differential equation according to two film theory for the simultaneous transport of hydrogen sulfide through hollow fiber membrane (HFM) contactors while using N-methyldiethanolamine (MDEA) as the chemical solvent. The model results are in excellent agreement with the experimental data. The results indicate that the removal of H2S increased while increasing concentration of MDEA and gas pressure, however, the removal of H2S decreases while increasing gas velocity. The concentration of H2S increases at the same place in the lumen while increasing gas velocity. There is serious decreasing amplitude of axial concentration of H2S during the initial stage, but it slows down at half of the length and a great reduction of H2S concentration in radial direction with the increase of the length. The decreasing amplitude is dropped due to the concentration of H2S decreased in radial direction. The model can indicate H2S removal rate in given operational conditions and offer theory evidence for the design of membrane contactor. Natural gas is believed to play a vital role in the next few decades for industrial and domestic utilization. It is considered as one of the cleanest and safest of all energy sources. However, nature gas is not a pure hydrocarbon and sometimes it has some sour gases such as hydrogen sulfide which has high toxicity. Hydrogen sulfide can not only corrode equipment and transmission pipeline under aerobic and hot humid conditions but also cause catalyst poisoning, even serious threaten the safety of human. Wet desulphurization is widely used for natural gas treatment and aqueous solutions of alkanolamines are often used as absorption solvent. Among these alkanolamines, MDEA as an absorption solvent of acid gases is widely used today because it possesses the characteristics such as higher H2S selectivity, bigger absorption capacity, lower regeneration energy, smaller hot-degradation and lower circulating load. But desulphurization unit can be seriously corroded in the sulfur removal process. On the other hand, these conventional processes such as absorption towers, packed and plate columns possess many disadvantages such as flooding, foam formation, and demand high capital and operating costs. So the technology meets a certain obstacles. Recently, new processes using gas–liquid membrane contactors as gas absorption devices have been a subject of great interest. Among the diversity of membrane geometries available for membrane contactors, hollow-fiber membrane contactors are favored due to their high surface/volume ratio for separation which is 30-50 times compared with traditional absorbers. This type of process offers several practical advantages including low energy and operating costs, simplicity and occupying small area. In addition, membrane contactors as unit equipment can be combined according to actual need. [4~5] used polypropylene hollow fiber membrane as the absorber and MDEA as the chemical solvent for the absorption of H2S via changing operating conditions (e.g. temperature, pressure, the concentration of the solvent, flux of gas-liquid phase) and studied the influence of the changes to mass transfer coefficient and sulfur removal efficiency. The results indicate that the sulfur removal efficiency can be 95% above by optimizing the operating conditions. At home and abroad, comprehensive two-dimensional mathematical models were developed based on differential equation. Wang [6] simulated the absorption of CO2 using different absorption medium in hollow fiber membrane contactors. But they did not consider the effect of mixed gas. Chen [7] modeled the distribution of reactants and products concentration in the shell side in different typ es of reaction. However, the model can not obtain the concentration of H2S in the lumen. Rami Faiz [8] modeled the distribution of acid gas, but the mathematical model was not validated by the experimental work.

Abstract: Simvastatin, as one of the HMG-CoA reductase inhibitors for lowering lipids, has been demonstrated its potential benefit in bone formation, which was, however, conflicting and inconclusive in vivo studies. Thus, we performed this study to assess the in vivo effects of simvastatin on bone formation. Six-week old rats were administered with simvastatin (20 mg/kg/d) or vehicle for 6 or 9 weeks. All animals were sacrificed one day after the final administration. The left femora were removed for the measurement of bone histomorphometry and bone mineral density (BMD).Compared to the control groups, on both 6th week and 9th week, bone mineral density and bone histomorphometry detected no significant differences in bone mass and microarchitecture in simvastatin treatment group, as well as bone formatin/resorption parameters. These results indicate that simvastatin had no positive effect or impact on bone in rats administered with high dose simvastatin (20 mg/kg/d) for 6 or 9 weeks.

Abstract: Highly-ordered TiO2 nanotube arrays were successfully fabricated by electrochemical anodization of titanium. The morphology of TiO2 nanotube arrays, the length and pore size were represented by field emission scanning electron microscopy (FE-SEM). The parameters of various anodization including F- concentration, reaction temperature and anodization voltage were investigated in detail. The results show that as-prepared TiO2 nanotube arrays possess good uniformity and well-aligned morphology in mixture of ethylene glycol and 0.3 wt% NH4F electrolyte at 40 V for 25 °C. The growth rates of TiO2 nanotube arrays can show activation energy.

Abstract: In this work, a modified two-step reaction kinetics model for methane-oxygen combustion is used to predict oxy-combustion characteristics and permeation rate characteristics inside a stagnation flow simple symmetric ITM reactor. New coefficients oxygen permeation equation model is introduced herein this work by fitting the experimental data available in the literature for a LSCF-1991 ion transport membrane. Using CH4 as fuel plus CO2 as sweep gas, the effects of reactivity is analyzed using the same sweep gases (CH4 plus CO2) is investigated here by comparing the same cases with and without considering reactions in the permeate side. Also the influences of the percentage of CH4 in the sweep gases mixture on the permeation and combustion processes are included in this work. It was found that the oxygen permeation flux increases with activating chemical reactions in the permeate side of the membrane and this is due to increased partial pressure driving force across the membrane surface as a result of disappearance of oxygen molecules in the permeate side because of combustion. Another reason for this is the increase in the membrane temperature which affects the activation energy of the membrane and so the permeation rate. More details about the models used and the oxy-fuel combustion characteristics in the permeate side of the membrane are included in the present study.

Abstract: In this work, both dimensional analyses using Buckingham Pi-theorem and scaling of the energy equation have been applied successfully in fluid to fluid modeling for post dry out to model the Freon (R-134a) data available in the literature and convert it to water equivalent data. Also the results are compared with the available data in the literature for water. Experimental data sets in two fluids are assumed to be equivalent if the values of the dimensionless groups are equal for both fluids. Both methods are used and the results are compared with the experimental data at different operating conditions. The Katto and the Ahmad modeling dimensionless parameters coming from the analysis using Pi-theorem predicted successfully the equivalent data of water at moderate mass fluxes. However, at too high or low mass fluxes, this method deviated from the experimental data. However, the fluid to fluid modeling using the scaling of energy equation is applicable at any operating conditions and the results are too close to the experimental data.

Abstract: The importance of thermal radiation in heat transfer mechanism in many micro combustion systems has been well identified in the past few years. There is currently lack of quantitative understanding on the radiation heat transfer in relatively small scale laminar diffusion flames in microchannels. In the present study a two dimensional model is considered to investigate the effects of radiation on oxy-fuel combustion characteristics in microchannels. The discrete-ordinates radiation model is used for the study. It is observed that excluding radiation model results in the over-prediction of combustion temperatures in the micro-reactor. It has also been observed that the overall reaction rate and its peak value increase when accounting for radiative heat transfer, despite the decrease in temperature caused by radiation. Therefore, it is important to incorporate a radiation heat transfer model in combustion micro-systems in order to predict their characteristics accurately.