Sumei Li

Microfluidic approach for rapid interfacial tension measurement.

A novel microfluidic approach to measure interfacial tension of immiscible fluids rapidly is reported. This method rests upon quantitative force balance analysis of drop formation dynamics in a coaxial microfluidic device. The values of interfacial tension for several two liquids without/with surfactants are measured. These measurements compare well with those measured by the commercial interfacial tensiometry. The viscosity of water phase fluid can also be accurately measured in the same microfluidic device. Several model systems with interfacial tension from 1.0 to 10.0 mN/m and water phase viscosity from 1.0 to 10.0 mPa.s are tested in this work.

Low-temperature bonding of poly-(methyl methacrylate) microfluidic devices under an ultrasonic field

High bond strength at low temperature without shape distortion is a major goal in microfluidic device fabrication. In this paper, we present a new easy bonding method for poly-(methyl methacrylate) (PMMA) microdevices at low temperature in an ultrasonic field. The ultrasonic energy spot effect at an interface could lead to a high bond strength up to 30 mJ cm−2 at only 60 °C. This bond strength is tens of times higher than the typical value in the literature (Tsao et al 2007 Lab. Chip. 7 499). The benefit from the low bonding temperature is that no deformation of the channel was evident. Few changes in the substrate surface property were observed. The static water contact angle of the bonded substrates had a small decrease compared to that of the virgin ones. The bonded microchannel devices were not reduced in transparency and smoothness. This method is batch-production oriented because many microdevices could be bonded at one time.

Contamination and emission factors of PCDD/Fs, unintentional PCBs, HxCBz, PeCBz and polychlorophenols in chloranil in China

The production of chloranil is regarded as a potentially significant source of unintentional POPs. This research aimed to identify the contamination levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), hexachlorobenzene (HxCBz), pentachlorobenzene (PeCBz) and polychlorophenols in chloranil samples and identify the formation pathways. The toxicity equivalent (TEQ) values for PCDD/Fs in the chloranil samples ranged from 163 to 1540200 pg I-TEQg(-1), while the PCB TEQ values ranged from 1.9 to 3.3 pg WHO-TEQg(-1). High levels of HxCBz, PeCBz and polychlorophenols were also detected in the chloranil samples. The average emission factors were 522.2 mg I-TEQt(-1) (PCDD/Fs), 0.0026 mg WHO-TEQt(-1) (PCBs), 32.6 mg t(-1) (HxCBz), and 136.6 mg t(-1) (PeCBz). The PCDD/Fs and PCBs are thought to be formed from the polychlorophenols and polychlorobenzenes generated during the chloranil production process. Purification of the chloranil products can reduce the unintentional POPs releases and protect the environment.

Formation and contamination of PCDD/Fs, PCBs, PeCBz, HxCBz and polychlorophenols in the production of 2,4-D products

The concentrations and profiles of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), pentachlorobenzene (PeCBz), hexachlorobenzene (HxCBz) and polychlorophenols in 2,4-D were investigated in this study. Two 2,4-D acid and three 2,4-D butyl ester enterprises were selected as typical 2,4-D producers. The total concentrations of 2,3,7,8-PCDD/Fs in the 2,4-D samples ranged from 355 to 35080ngkg(-1) and the corresponding TEQ values were in the range of 13.4 and 694.6ng WHO-TEQkg(-1). The concentrations of total PCBs in the 2,4-D were in the range of 16.1 and 8023ngkg(-1), and the WHO-TEQ values of the PCBs were between 0.057 and 108.3ng WHO-TEQkg(-1), while total PCBs were between 1486 and 47342ngkg(-1). The average emission factors were 414.4μg WHO-TEQt(-1) for PCDD/Fs and 21.9μg WHO-TEQt(-1) for PCBs. The polychlorobenzenes and polychlorophenols impurities may play a key role in the PCBs and PCDD/Fs formation. The impurities of PCDD/Fs and PCBs in 2,4-D may increase the risk for the human and environmental health.

Unintentional production of persistent chlorinated and brominated organic pollutants during iron ore sintering processes

Iron ore sintering (SNT) processes are major sources of unintentionally produced chlorinated persistent organic pollutants (POPs), including polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), and polychlorinated naphthalenes (PCNs). However, few studies of emissions of brominated POPs, such as polybrominated dibenzo-p-dioxins/dibenzofurans (PBDD/Fs) and polybrominated diphenyl ethers (PBDEs), during SNT have been performed. Stack gas and fly ash samples from six typical SNT plants in China were collected and analyzed to determine the concentrations and profiles of PCDD/Fs, PCBs, PCNs, PBDD/Fs, and PBDEs, as well as any correlations among these compounds. The PCDD/F, PCB, PCN, PBDD/F, and PBDE emission factors were 2.47, 0.61, 552, 0.32, and 107μgt-1, respectively (109, 4.07, 10.4, 4.41 and 0.02ng toxic equivalents t-1, respectively). PCBs were the most abundant compounds by mass, while PCNs were the next most abundant, contributing 51% and 42% to the total POP concentration, respectively. However, PCDD/Fs were the dominant contributors to the chlorinated and brominated POP toxic equivalent concentrations, contributing 89% to the total toxic equivalent concentration. The PCDD/F and other chlorinated and brominated POP concentrations were positively correlated, indicating that chlorinated and brominated POP emissions could be synergistically decreased using the best available technologies/best environmental practices already developed for PCDD/Fs.

Formation and emission of brominated dioxins and furans during secondary aluminum smelting processes.

Secondary aluminum smelting (SAl) processes have previously been found to be important sources of polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs). It is crucial that the key factors that influence the formation and emission of PBDD/Fs are identified to allow techniques for decreasing PBDD/F emissions during SAl processes to be developed. In this study, stack gas samples were collected from four typical secondary aluminum smelters that used different raw materials, and the samples were analyzed to allow differences between PBDD/F emissions from different SAl plants to be assessed. The composition of the raw materials was found to be one of the key factors influencing the amounts of PBDD/Fs emitted. The PBDD/F emission factors (per tonne of aluminum produced) for the plants using 100% (Plant1), 80% (Plant2), and 50% (Plant3) dirty aluminum scrap in the raw material feed were 180, 86, and 14 μg t(-1), respectively. The amounts of PBDD/Fs emitted at different stages of the smelting process (feeding-fusion, refining, and casting) were compared, and the feeding-fusion stage was found to be the main stage in which PBDD/Fs were formed and emitted. Effective aluminum scrap pretreatments could significantly decrease PBDD/F emissions. Much higher polybrominated dibenzofuran concentrations than polybrominated dibenzo-p-dioxin concentrations were found throughout the SAl process. The more-brominated congeners (including octabromodibenzo-p-dioxin, octabromodibenzofuran, heptabromodibenzo-p-dioxins, and heptabromodibenzofurans) were the dominant contributors to the total PBDD/F concentrations. The results could help in the development of techniques and strategies for controlling PBDD/F emissions during metallurgical processes.

Deformation behavior of thermal aged duplex stainless steels studied by nanoindentation, EBSD and TEM

The cast duplex stainless steels were investigated in order to understand the plastic deformation behaviors and fracture mechanisms after thermal aging at 400°C for up to 10,000 h. Tensile strength has an obvious improvement, but the yield strength has a slightly increase after long-term thermal aging. Microcracks initiate in the ferrite and extend to phase boundaries, leading to the fracture of ferrite before the tensile failure of specimen. Nanoindentation tests indicate that hardness in ferrite continuously increases with aging time, but not strongly affected by deformation degree. Electron backscattered diffraction observations reveales that high-stress concentration on the phase boundaries causes the phase boundary separating. The dislocations pile-up at spinodal decomposition precipitates in ferrite phases and along G-phase boundaries, leading to the reduction of mechanical property of the ferrite.