Papers by Author: Li Zhang

Abstract: The corrosion behavior of Cu-Ni-Si alloy exposed to a nutrient-rich simulated seawater-based nutrient-rich medium in the presence of a deep-sea bacterial (Erythrobacter pelagi sp.nov) was investigated by metallographic microstructure observation, electrochemical impedance spectroscopy (EIS) measurement. It was demonstrated that the charge transfer resistance (Rct) and the resistance of oxide film (R_f) dramatically increased within 2 days then gradually decrease and becoming stable because of an patchy or blotchy biofilm formed on the surface of the alloy.

Abstract: The corrosion behavior of duplex stainless steel immersed in nutrient-rich simulated seawater without deep sea bacteria and with deep sea bacteria (Erythrobacter pelagi sp.nov) was studied. The effect of chloride ions and presence of deep sea bacteria on corrosion resistance was investigated. The occurrence of localized corrosion (Viz. pitting and crevice corrosion) was examined using visual inspection and SEM-EDX. Electrochemical impedance spectra were used to study the effects of deep sea bacteria on duplex stainless steel and inferences were made. Most significantly was the reduction of pitting resistance potential with increase in exposure time.

Abstract: Tributyltin (TBT) in water was photocatalytically decomposed in the presence of TiO₂ film photo-catalyst, which was prepared by coating TiO₂ on the industry pure titanium foil. The photocatalytic decomposition rate of TBT is up to 93.8% within 30 min. Photocatalytic decomposition of TBT was greatly enhanced with rate constant nearly 3 times as that by photolysis. TBT decomposed in a stepwise manner, and the main products were monobutyltin (MBT), which is further decomposed to inorganic tin in the system.

Abstract: This work screens electrode materials used in EDM and proposes some potential electrodes for future industrial applications. Traditional graphite, W, and Mo EDM electrodes have low TWR due to their high melting points; while, Zn, brass, and Cu often experience too much tool wear. As to some newly developed alloy and composite materials, their machining performances depend on not only their melting points but also their microstructures. Cu-W alloy has high wear resistance but it is susceptible to shape loss due to its internal porosity. By contrast, Cu-graphite, Cu-ZrB₂ and Cu-TiB₂ composites show good capabilities of removing material with little wear loss and therefore could be promising for future usages.

Abstract: Laser surface melting (LSM) of aluminum alloy 6013 was conducted using a high power Nd-YAG laser under nitrogen gas with the aim of improving the stress corrosion cracking (SCC) resistance of the alloy. The SCC behavior was studied in a 3.5% NaCl solution using a slow strain rate test (SSRT). A laser-melted layer in the order of 500µm thick was produced, which consists of fine dendritic and cellular structures with some Al-Si-Cu-Fe-Mn phase particles formed at interdentritic boundaries. The results of the SSRT test showed that the susceptibility of the alloy to SCC, in terms of total elongation to failure, was decreased after the laser surface modification. This was considered to be attributed to the presence of the laser-formed AlN film, which acted as a barrier to the ingress of the corrosive Cl- into the material and enhanced the pitting resistance of the material. An examination of the fractured surface indicated that the crack propagation path, in the early stage of SCC, was along the tortuous dendrite and cell boundaries. This caused the crack path deviated from the growing direction and resulted in a longer crack length covered before failure thus increasing the overall crack propagation resistance.

Abstract: An thin reagent containing optochemical film sensor for detecting and measuring free chlorine in water is described. The film sensor has been manufactured by immobilisation indicator of 3,5-dimethyl-4-hydroxybenzaldazine in a permeable transparent polymeric membrane. A linear calibration for free available chlorine can be obtained in the range between 0.05 and 3ppm. The limit of quantitation is 0.3 ppm, and the accuracy exceeds 7%. It takes about 150s to measure the relatively low occupational exposure concentration of 0.1ppm. The interference of combined chlorine has been studied. The sensor has no response to combined chlorine. And the stability of the sensors and the effect of external parameters like relative humidity (RH), temperature on the sensor response have been investigated. The sensor response is affected by varying the temperature; however, humidity in the range between 0 and 90% RH does not affect sensor response. The 3,5-dimethyl-4-hydroxybenzaldazine remained stable inside the polymeric film and no chemical reaction, crystallization or leaching occurred during 6 months of observation. Proper choice of indicator dye and polymeric material and successful application of kinetic evaluation method for the exposure experiments determine the desired features of the sensor. Introduction