Abstract: PbZrO3-PbTiO3 (PZT)-based ceramics are playing a dominant role in piezoelectric materials, their evaporation of harmful lead oxide during the sintering process causes a crucial environment problem. It is necessary to search for lead-free piezoelectric materials that have such excellent properties as those found in the PZT-based ceramics. Therefore (Na0.5K0.5)NbO3-based solid solutions were studied to improve piezoelectric properties. In the present study, various quantities of Bi2O3 were added into 0.98(Na0.5K0.5)NbO3-0.02Ba(Sn0.02Ti0.98)O3 (0.98NKN-0.02BST) ceramics. It was found that 0.98NKN-0.02BST with the addition of 0~4.0 wt.% Bi2O3 exhibit relatively good piezoelectric properties. For 0.98NKN-0.02BST ceramic with the addition of 1.0 wt.% Bi2O3, the electromechanical coupling coefficients of the planar mode kp and the thickness mode kt reach 0.21 and 0.46, respectively, at the sintering of 1100oC for 3 h. The ratio of thickness coupling coefficient to planar coupling coefficient is 2.2. It is obvious that 0.98NKN-0.02BST solid solution ceramic by adding low quantities of Bi2O3 is one of the promising lead-free ceramics for high frequency electromechanical transducer applications.
Abstract: Gradient theories of plasticity play an important role in the description of inelastic behavior of materials. Usually, these theories involve space derivatives of stress or strain. On the other hand, conventional theories of plasticity can be divided into two groups, flow and deformation theories. Each of these groups has its own area of applications. The main conceptual difference between the theories belonging to the different groups is that the primary kinematics variables in deformation theories are displacements (or strains) whereas in flow theories velocities (or strain rates). Therefore, it is of interest to propose a gradient theory of plasticity involving space derivatives of a measure of strain rate (strain-rate gradient theory of plasticity) and to compare qualitative behavior of solutions for the strain-rate gradient theory of plasticity and an existing strain gradient theory of plasticity. One possible strain-rate gradient theory of plasticity is proposed in the present paper. The equivalent strain rate (second invariant of the strain rate tensor) is used as a measure of strain rate. The Laplacian operator is adopted to introduce the gradient term. An analytic solution for expansion of a hollow sphere is given for two strain-rate gradient theories of plasticity and one strain gradient theory. Comparison of the solutions shows that some qualitative features of the solutions for the strain-rate gradient theories are in better agreement with general physical expectations than those for the strain gradient theory.
Abstract: Subminiature fuel cell is a representative eco-friendly power source which possesses the merits of having the potential of being implemented in portable electronic devices and other subminiature devices, as well as having high energy density as compared to existing secondary cells. The size of the bipolar plate which is implemented in a subminiature fuel cell should be of a small size according to the size of the fuel cell, and the flow channel inside the bipolar plate also has be reduced to match the overall size of the bipolar plate. Therefore, a higher level of difficulty in the manufacturing process is involved in producing bipolar plate for subminiature fuel cells and mass production is extremely difficult. In this study, powder injection molding was applied to the production of subminiature metal bipolar plate to verify the possibility of mass production. For that, a bipolar plate and mold were designed and then a test injection forming was carried out. This was attempted to validate the feasibility of a subminiature metallic bipolar plate prepared through a debinding and sintering process by evaluating its electric conductivity and density.
Abstract: The effects of gellan gum and calcium ions concentration on gelation characteristics and rheological behavior were investigated using TA(texture analysis)and mechanical rheometer which monitored respectively press strength and the evolution of G′. At a premium gellan gum content of 0.02g in 100ml buffer solution, increasing calcium ions concentration led to an increase in the gelation strength, but when calcium ions content reached a critical concentration values range from 0.015% to 0.02%, gelation strength begin to decrease. While in the same content of calcium ions, calcium lactate exhibits grater effects on gelation strength than calcium chloride. The temperature at the onset of gelation and the gelation rates showed an increase with the increasing of gellen and calcium ions content. At the same calcium ions concentration, the evolution of modulus storage (G′), gel temperature and rate are higher with the addition of calcium lactate than using calcium chloride. Our study indicated exponential relationship between gelling temperature (gelling rate) and calcium concentration.
Abstract: Springback will occur when the external force is removed after bending process in sheet metal forming. This paper proposed an adaptive-network-based fuzzy inference system (ANFIS) model for prediction the springback angle of the SPCC material after U-bending. Three parameters were selected as the main factors of affecting the springback after bending, including the die clearance, the punch radius, and the die radius. The training data were obtained from results of U-bending experiment. The training data with four different membership functions – triangular, trapezoidal, bell, and Gaussian functions –were employed in the ANFIS to construct a predictive model for the springback of the U-bending. After the comparison of the predicted value with the checking data, we found that the triangular membership function has the best accuracy, which make it the best function to predict the springback angle of sheet metals after U-bending.
Abstract: The durability of a concrete structure is most significantly influenced by the corrosion of reinforcing bars, rather than by the deterioration of concrete itself. The corrosion of reinforcement bars due to chloride serves as a main deterioration factor at the interface between the bars and the concrete in the concrete structure. Accordingly, the corrosion inhibitors are widely used to improve the resistance to chloride penetration into reinforced concrete. Corrosion inhibitors are generally divided into the anode-type inorganic inhibitors and anode-cathode-type organic inhibitors, in terms of the reaction type. It is known that when the Cl-:OH- concentration ratio exceeds 0.6%, film on passive state metal on the bar-concrete interface is damaged and local corrosion starts regardless of the chloride ion content. In this study, the performance of the corrosion inhibitor was examined using a potentiostat, with chloride ion contents of 1.2kg/m3 (as reference), 2.4kg/m3, and 4.8kg/m3. The variables were the inhibitor type, Cl-:OH- molar ratio according to the addition of anode-type inorganic corrosion inhibitor (four ratios: 0.0%, 0.3%, 0.6% and 1.2%), and ratio compared to the standard anode-cathode-type organic corrosion inhibitor liquid (four ratios: 0.0, norm 1/2, norm, norm 2 times). As a result, with the anode-type inorganic nitrite corrosion inhibitor, the corrosion inhibition performance was verified with a corrosion potential of -0.30V at a molar ratio of 0.3% or higher when the chloride ion content was 1.2kg/m3, and at a molar ratio of 0.6% or higher when the chloride ion content was 2.4kg/m3 or 4.8kg/m3. With the anode-cathode-type organic corrosion inhibitor, the corrosion inhibition performance was very good at half the standard quantity (0.42kg/m3) regardless of the chloride ion content. From the added corrosion inhibitor quantities, the anode-cathode-type organic corrosion inhibitor had a better corrosion inhibition performance than the anode-type inorganic nitrite corrosion inhibitor.
Abstract: One prospective method to retard the speed of climate change is Carbon Capture and Storage (CCS). It is known that reducing emissions through CCS on point sources can only slowdown the rate of increase of atmospheric CO2 concentration and not able to mitigate the CO2 that are already in the atmosphere by previous emissions. Hence, a complimentary method would be to extract CO2 directly from air – Direct Air Capture (DAC). This paper addresses a novel concept of DAC whereby an additional phase of axial compression is introduced to adapt atmospheric air to a level suitable for capture. An axial compression model was developed so that fluid simulation studies can be performed. These information are then utilized in a feasibility study to address several key issues: the additional energy penalty when applying axial compression and whether or not, increasing the capture input by compression would displace the elevated energy consumption.
Abstract: The bioactive properties of hydroxyapatite [HA, Ca10(PO4)6(OH)2] have been demonstrated to be akin to osseous tissue, and provide quick fixation in prosthesis and orthopedics. In this study, sol-gel preparation of hydroxyapatite were arranged for Ca/P=1.67 molar ratio in calcium nitrate [Ca(NO)3.4H2O ] and triethylphosphate [TEP, C6H15PO4] and then dilute in the solvent of ethylene glycol mono-methyl ether [HOCH2CH2OCH3]. Consequently, sintering process was carried out at different temperature for various sintering time to materialize this inorganic polycrystalline phosphate. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) are applied to investigate the as dried amorphous and calcined hydroxyapatite. Results reveal calcinations at 1000oC prolonged for 30 minutes in air can exhibit crystalline hydroxyapatite.
Abstract: The fine combination of biomaterial and essential cells determines a successful artificial graft. With high biocompatibility, chitosan is a choice of materials for regeneration medicine. In the peripheral nervous system, Schwann cells are critical for nerve regeneration. Schwann cells not only help to conduct the nerve pulse but also guide the nerve extension, especially the injured nerve for recovery. Studies showed that chitosan can be a bridge material for damaged nerve regeneration. The interactions between chitosan and Schwann cells may provide important information for designing the chitosan grafts applied in medical applications. For this purpose, the chitoson was made into conduits by lyophilization. The conduit has porous 3D scaffolds and seeded with rat Schwann cells. The harvested cells were labeled with PI fluorescent dye and analyzed with flow cytometry. The results showed that the rates of DNA replication (S-phase) and cell division (G2 phase) of the cells grew on chitosan scaffolds were higher than the ones grew on the plane substrate. This indicates that the cells grew on chitosan scaffolds were more active than those on the plane substrate in cell proliferation, and the biocompatibility of chitosan can be sustained in this quantitative analysis. Therefore, chitosan scaffolds are efficient for cell expansion of rat Schwann cells and may be beneficial for the purpose of tissue engineering. This study proves that cell cycle analysis is a new point of view in disclosing the cell-material interactions.