Materials Science Forum Vols. 628-629

Abstract: In this paper, electrohydrodynamic atomization combined with a polymeric micromoulding technique was used to form PZT single element devices using a PZT sol-gel slurry without an etching process. The PZT single element device was initially designed to work as a piezoelectric ultrasonic transducer consisting of a circular or a square of various sizes, which was produced and used to evaluate the process. The resulting PZT device had a homogenous microstructure. It was observed that the relative permittivity of the circular and square single element devices was especially high at small size due to the fringe effect. The results show that the radius and width of the PZT single circular and square element devices with a thickness of 15µm should be bigger than 400µm in order to reduce the fringe effect.

Abstract: Micro hot embossing process is a cost-effective method for parallel replication of polymer microstructures. To study the effect of hot embossing and demoulding parameters on the replication accuracy of the polymer microstructure, densely patterned and high-depth channels on 50mm×50mm polymer substrates were fabricated by hot embossing in this paper. Experimental results showed that the replication accuracy of the microstructure increased with the increasing of hot embossing temperature and the thickness of polymer substrates. It can be found that demoulding became more difficult when replication accuracy increased. The reason was that higher replication accuracy resulted in larger contact area between the replica and the embossing mold. The demoulding problem could be solved by rising demoulding temperature. However, overhigh demouding temperature (110°C) would lead to round corners at the edges of the ribs. Experimental results also showed that very small channel widths and depths errors (less than 1.2%) of the microstructures with 2mm thickness substrates could be achieved, when embossing and demoulding temperatures were set to 120°C and 100°C, respectively.

Abstract: Compared with hot embossing, microfluidic chips injection molding is higher efficiency process and more suitable for mass production, but the quality control for injection molding is much more complex. Experiments indicate that the incomplete replication of the micro-channel and the sink mark for microfluidic chips are the chief defects to the molding. Simulation and theoretical analysis show that the stagnant flow of the melt in micro-channel and the shrinkage difference of the chips in different directions are the main reasons for molding defect. A set of new methods that how to control process parameter, design mold, and select polymer material is proposed to reduce or avoid the defects.

Abstract: . This paper presents the design, microfabrication and characterizations of a silicon based, single-cell μDMFC demonstrator for micro/portable electrical power applications. The flow field plates of the fuel cell were made on 2“silicon wafers utilizing wet-etching and sputtering techniques. The fuel cell was assembled in an epoxy-based packaging process. Results show that a lower internal ohmic resistance of the fuel cell can be achieved with a thicker current collecting layer (CCL). Influence of the operating conditions on the μDMFC performance was also investigated. It was found that 2M methanol can yield a better fuel cell performance because it provided a better compromise between the methanol crossover and mass transportation during operation. On the other hand, a 4-time increase of the peak power density of the fuel cell was achieved by increasing the methanol temperature from 20°C to 80°C.

Abstract: The rheological characteristics of four polymer melts (PS, PMMA, PP and HDPE) are investigated by a capillary rheometer with the die diameters from 1.5mm to 0.5mm.The effects of temperature on shear viscosity and the effects of both temperature and shear rate on non-Newton exponent of melts are discussed when the die diameter is 0.5mm. The results show that the shear viscosity of four polymers decreases with the rise of shear rate. The shear viscosity of PS and PMMA increases with the decrease of die diameter, the shear viscosity of PP and HDPE decreases with die diameter and minute differences of shear viscosity with different die diameters are observed with the growth of shear rate. When the die diameter is 0.5mm, Arrhenius equation is found to be suitable to describe the relations between shear viscosity and temperature for four polymer melts. The non-Newton exponents of four polymer melts increase with the temperature and decrease with the rise of shear rate.

Abstract: Carbon-MEMS (C-MEMS) have emerged as a new category of devices for micro/nano technology with many potential applications. Dielectrophoretic manipulation of micro/nanoparticles with C-MEMS is studied in this paper. Through electric field distribution modeling in carbon electrode array, we analyze the strongest simulation effect results of electric field in three dimensional (3-D) surface plots depicting the magnitude of electric field in various cross sections at different heights above the channel floor for 2, 10, 30 and 50 μm high carbon electrodes. It is represented here that maximum intensity of electric field generates with the equality between the height above the channel floor and the height of the electrodes. Simulation parameters involved are for dielectrophoretic manipulation of micro/nano particles based on 3-D C-MEMS. The advantages of using 3-D C-MEMS electrodes over other techniques of creating high-throughput systems for dielectrophoretic manipulation environment surrounded by micro/nano horizons are: (i) complex microscale 3-D electrodes with high-aspect ratios can easily be shaped and patterned using conventional lithography (ii) carbon has a high window of stability thus allowing application of higher voltages (iii) there is no need for bulk micromachining or patterning electrodes on multiple planes (iv) the distance between electrodes can precisely be controlled through the lithography process. FEMLAB 3.4 Multiphysics Modeling software (COMSOL, Stockholm, Sweden) is used for the modeling of electric fields and one-layer C-MEMS microelectrode array was fabricated with SU-8 photoresist.

Abstract: This article is pointed to the dimension accuracy analysis of the vacuum forming mold for plastic carrier tape. The dimension accuracy of the vacuum forming mold was decided by the dimension specification of the plastic carrier tape. After detail design of the parts which would be manufactured and assembled. The accuracy and performance of the mold had been tested subsequently. The dimension accuracy of the mold was conducted by the accuracy of the plastic carrier tape. Variation of dimensional accuracy of the plastic carrier tape was inspected to evaluate the performance of the vacuum forming mold. Mean and variance test was conducted under the significance level of α = 0.05.Through series of inspections, all the plastic carrier tape met the specification of dimension accuracy which indicated that the precision and performance of the developed vacuum forming mold also met the requirement.

Abstract: Laser cladding has been developed as a useful technology to modify material surface in industry. In this paper a new approach of surface modification is introduced. Depositional Laser Cladding (DLC) was developed and the different mechanisms were investigated during the manufacture. Basing on particular analysis of defects in the experiment, the relation between the quality of cladding layer and laser energy density is manifested. Depositional effect and thermal effect play their roles in different place and the depositional effect provides thin layers with the thickness of near mean particle size. Appropriate parameters of laser energy can promote high quality, avoiding pores and stacks in agglomeration and ebullition. Controllable low thickness near mean particle size and sharp edge make it possible to be used on producing certain shape in the surface engineering field, such as restoring and gradient materials.

Abstract: The simulation methods and application of different scales such as macroscopic, microscopic and nanoscopic in material design are primarily introduced. The essentiality of multi-scale coupling simulation of ceramic tool materials is analyzed. The research status of multi-scale coupling simulation of ceramic tool materials is also surveyed.

Abstract: A new WC matrix nanocomposite cermet was prepared by hot-press sintering. In the composite, certain amounts of VC is added to the composite as grain growth inhibitors. The consolidation is carried out under pressure 30～35Mpa and sintering temperature 1610°C for soaking 30min sintering. Microstructure of the nanocomposite cermet is scanned by SEM and mechanical properties are measured. It is detected that microstructure and fracture morphology is dissimilar to different particle sizes. Experimental results show that particle size of WC is important to the composite. Results show that relative density and hardness have the similar trend in growth. Meanwhile, the function of Al2O3 addition is also investigated in this paper.