Chi Yuan Lee

Studies on Ni-Mo-P Coatings by Electroless Deposition

This paper describes the performance of Ni-P and Ni-Mo-P alloy coatings deposited by electroless plating on the aluminum alloy 5052 to evaluate the corrosion resistance, thermal stability and electro-conductivity of coating assemblies. Corrosion behaviors of the obtained deposits in a 0.5M H2SO4 environment were investigated. The crystalline state and morphologies of Ni-P and Ni- Mo-P alloys were examined by field emission scanning electron microscopy (FE-SEM). The experimental results indicate that the Ni-Mo-P coating operated at 70°C and pH 9.0 has a nanocrystalline structure and its corrosion resistance in a 0.5M H2SO4 environment can be enhanced by the co-deposition of Mo as compared to Ni-P films. It has also been found that the Ni-Mo-P ternary alloys reveal good thermal stability after annealing at 400°C. Based on the excellent performance of Ni-Mo-P ternary alloys, these alloys have a potential to be applied to precision mould, optical parts mould, and surface metallization of substrates.

in situ Measuring of Temperature and Humidity within the Membrane Electrode Assembly by Micro-Sensors

This study investigated the micro array sensors which were fabricated by micro-electro-mechanical-systems (MEMS) fabrication technology for monitoring the temperature and humidity distributions within the membrane electrode assembly (MEA) of fuel cells. The micro array sensors were embedded in parylene substrate, the sensors were made from chromium and gold. The advantages of micro temperature and humidity sensors are their small volume, which enables them to be placed on MEA with high sensitivity and accuracy. The dimensions of the temperature and humidity sensors are 180 µm × 180 µm and 180µm × 220µm, respectively. The operating conditions involve temperatures from 30 to 100°C and the resistance of temperature sensor varied from 31.685 to 36.798 Ω. The measuring results reveal that the temperature is almost linearly related to the resistance and the accuracy and sensitivity are less than 0.3°C and 2.3×10−3/°C. The humidity sensor showed that the capacitance changed from 12.14 to 15.03 pF, the relative humidity from 25 to 95 % RH, and the accuracy and sensitivity is less than 0.25 % RH and 0.04 pF/% RH.

The Structure and Properties of Electroless Ni-P and Ni-Mo-P Deposits

The structure and properties of electroless Ni-P and Ni-Mo-P alloys, including the as-plated and annealed deposits, on the aluminum alloy 5052, have been investigated to evaluate the corrosion resistance, thermal stability, electric conductivity, and mechanical characteristics of the coating assemblies. The corrosion behavior of the obtained deposits was examined in a 0.5M H2SO4 environment. The crystal structure of the electroless Ni-based alloys was analyzed by X-ray diffraction (XRD), and the surface morphology and microstructure of Ni-P and Ni-Mo-P alloys were examined by field emission scanning electron microscopy (FE-SEM). The experimental results indicate that the corrosion rate of the Ni-Mo-P coating produced at 70°C and pH 7.0 is almost equals that of the Ni-P film in a 0.5M H2SO4 environment. It is also found that the Ni-Mo-P ternary alloy reveal excellent thermal stability after annealing at 400°C for 1 hr. The electroless Ni-Mo-P deposits have a potential to apply to precision mould and surface metallization of substrates, based on the excellent performance of the ternary alloys.

Integration of Micro Temperature Sensor and Heater in a Stainless Steel-Based Micro Reformer

With advances in micro fuel cell development, the production of hydrogen for micro reformer has become increasingly important. However, some problems regarding the micro reformer are yet to be resolved. These include reducing the size, reducing the quantity of CO and combining the fuel cell, among others. Accordingly, in this investigation, a micro temperature sensor and a heater are combined inside a stainless steel-based micro reformer to measure and control the temperature and thus improve performance and minimize the concentration of CO. In this work, micro-electro-mechanical-systems (MEMS) of the micro channel type are fabricated on a stainless steel substrate to enhance the methanol conversion ratio. The micro temperature sensor and heater are made of gold and placed inside the micro reformer. Although the micro temperature sensor and heater have already been used to measure and control temperature in numerous fields, they have not been employed in micro reformer and commercial products. Therefore, this study presents a new approach for integrating a micro temperature sensor and heater in a stainless steel-based micro reformer to minimize the size and improve performance.

A Novel Integration Approach for Combining the Porous Silicon on a Micro Fuel Cell

This investigation employs porous silicon as the gas diffusion layer (GDL) in a micro fuel cell by micro-electromechanical-systems (MEMS) fabrication technology. Pt is then deposited on the surface of the porous silicon, to enhance the fuel cell conductivity. The porous silicon with different pore sizes of 10 µm, 30 µm, 50 µm to test performance for GDL, and the fuel cell performances are discussed. The GDL was replaced by porous silicon and used in a proton exchange membrane fuel cell (PEMFC). Dry etching is applied to a 500 µm-thick layer of silicon to yield fuel channels with a depth of 450 µm and a width of 200 µm. Accordingly, the GDLs of the fuel cell are fabricated using macro-porous silicon technology. Porous silicon was fabricated by deep reactive ion etching (DRIE). The experimental shows the results with different pore size, fuel flow rate and operation condition. The best performance was 9.37 mW/cm2 with dry gas flow rates of H2/O2 at 30/30 ml/min and 10 µm hole.

Monitoring of Temperature Distribution within a Silicon-Based Micro Reformer Using Array Micro Sensors

With advances in micro fuel cell development, the production of hydrogen for micro reformer has become increasingly important. However, some problems regarding the micro reformer are yet to be resolved. These include reducing the size, reducing the quantity of CO and combining the fuel cell, among others. Accordingly, in this investigation, array micro temperature sensors and heaters were combined within a silicon-based micro reformer to measure and control the temperature and thus improve performance and minimize the concentration of CO. In this work, micro-electro-mechanical-systems (MEMS) of the micro channel type were fabricated on a silicon substrate to enhance the methanol conversion ratio. Array micro temperature sensors and heaters were made of platinum and placed inside the micro reformer. Although the micro temperature sensor and heater have already been used to measure and control temperature in numerous fields, they have not been employed in micro reformer and commercial products. Therefore, this study presents a new approach for combining array micro temperature sensors and heaters within a silicon-based micro reformer to minimize the size and improve performance.

Integration of Micro Array Sensors in the MEA on Diagnosis of Micro Fuel Cells

The temperature and humidity conditions of a membrane electrode assembly (MEA) determine the performance of fuel cells. The volume of traditional temperature and humidity sensors is too large to allow them to be used to measure the distribution of temperature and humidity in the MEA of fuel cells. Measurements cannot necessarily be made where required. They measure only the temperature and humidity distribution outside the fuel cells and yield results with errors that exceed those of measurements made in MEA. Therefore, in this study, micro-electro-mechanical-systems (MEMS) fabrication technology was employed to fabricate an array of micro sensors to monitor in situ the temperature and humidity distributions within the MEA of fuel cells. In this investigation, an array of micro temperature and humidity sensors was made from gold on the MEA. The advantages of array micro gold temperature and humidity sensors are their small volume, which enable them to be placed on MEA and their high sensitivity and accuracy. The dimensions of the temperature and humidity sensors are 180μm × 180μm and 180μm × 220μm, respectively. The experiment involves temperatures from 30 to 100 °C. The resistance varied from 23.084 to 28.196 /. The experimental results reveal that the temperature is almost linearly related to the resistance and the accuracy and sensitivity are less than 0.3 °C and 3.2×10-3/°C, respectively. The humidity sensor showed that the capacitance changed from 15.76 to 17.95 pF, the relative humidity from 20 to 95 %RH, and the accuracy and sensitivity were less than 0.25 %RH and 0.03 pF/%RH.

Metal Bipolar Plate with Micro Sensors

The fuel cell has the potential to become an indispensable source of electric power. However, some problems have not yet been resolved. Measuring the temperature and humidity inside the fuel cells is currently difficult. Accordingly, in this study, micro sensors were fabricated within the fuel cell, in which the temperature and humidity distributions were measured. The substrate of the fuel cell was made of stainless steel (SS-304) and etching was employed to fabricate the channel on the stainless steel substrate. Then micro-electro-mechanical-systems (MEMS) technology was used to fabricate the array micro temperature and humidity sensors on the rib of channel of stainless steel. The advantages of array micro temperature sensors are their small volume, their high accuracy, their short response time, the simplicity of their fabrication, their mass production and their ability to measure the temperature at a precise location more effectively than the traditional thermocouple. The micro humidity sensors were made from gold and titanium as down and up electrodes in the channel. The performance curve of the single cell was operating at 41.54 °C and gas flow rates of H2/O2 at 200/200ml/min. The max power density of the bipolar with micro sensor was 56 mW/cm2.

Improving Machining Accuracy of the EMM Process through Multi-Physics Analysis

In this study, the parametric effects of the EMM process were studied by both numerical simulation and experimental tests. The numerical simulation was performed using commercial software, FEMLAB, to establish a multi-physics model which consists of electrical field, convection and diffusion phenomena to simulate the parametric effects of pulse rate, pulse duty, electrode gap and inflow velocity. From the simulated results, the relationship between parameters and the distribution of metal removal could be established. Proper process variables were also chosen to conduct the EMM experiments. After the experiments, the profile of the processed rectangular slot was measured by a Keyence digital microscope. Comparing profile of the processed rectangular slot with the profile of the cathode, the machining accuracy of EMM process could be determined. It could also verify the goodness of the multi-physics model for predicting machining accuracy. From this study, the effects of parameters such as pulse rate, pulse duty, electrode gap and inflow velocity are better understood. The simulation model could be employed as a predictive tool to provide optimal parameters for better machining accuracy and process stability of the EMM process.

The Electrochemical Micro-Fabrication Method for Micro-Scale Flow Channels

Due to lack of desirable mechanical properties of silicon substrate; the current trend of micro-fabrication technology is towards metallic materials. In this study, the electrochemical micromachining (EMM) technology is developed to fabricate micro-scale flow channels on thin metallic 316L stainless steel plate. The cathode electrode, the tool, is the mirror image of flow channels. It was produced by the MEMS and UV-LIGA technology and the size is 200μm in width and 500μm in height for the intension to fabricate a serpentine flow channel of 200μm in both depth and width. Because of the electrode size, the process control parameters and geometrical features surpassed conventional and CMOS methods. The flow channels on 0.6mm thick SS 316L plates were fabricated by EMM process within 30 seconds with effective area of 625mm2. The dimensions of flow channel were varying from 1504m to 5004m in width and about 2004m in depth. The results demonstrate the EMM technology produces good quality metallic flow channels efficiently.