Novel co‐polymerization polyimide (PI) fibers based on 4,4′‐oxydianiline (ODA)‐pyromellitic dianhydride (PMDA) were prepared. 2‐(4‐Aminophenyl)‐5‐aminobenzimidazole (PABZ) containing the NH group was introduced into the structure of the fibers as the proton donor. The results of Fourier transform infrared (FTIR) and dynamic mechanical analysis (DMA) showed that hydrogen bonding occured between the NH group and chains, which strongly enhanced interchain interaction. This hydrogen bonding interaction increased the tensile strength and initial modulus of the PI fibers up to 2.5 times and 26 times, respectively, compared to those of homo‐PI PMDA‐ODA fibers with no hydrogen‐bonding interaction because of the absence of proton donors after the imidization process. In the mean time, glass transition temperature (Tg) of the modified PI fibers was found to be 410–440°C, which was higher than that of the homo‐PI PMDA‐ODA fibers. From the result, a novel access to molecular design and manufacture of high performance PI fibers with good properties could be provided. Copyright © 2009 John Wiley & Sons, Ltd.
A series of random copolyamic acid were synthesized from various ratios of two diamines 4, 4′‐oxydianiline (ODA) and 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (PABZ) by polycondensation with pyromellitic dianhydride (PMDA) in N‐methyl‐2‐pyrrolidone (NMP). Their inherent viscosities were in the range of 1.89–2.91 dl/g. The polyamic acid (PAA) solution drops were spun into fibers by the wet spinning process. The polyimide (PI) fibers were obtained from PAA fibers after drawn and treated in heating tube. The fibers were characterized by fourier transform infrared (FTIR), wide X‐ray diffraction (WAXD), scanning electron microscope (SEM), thermal gravimetry analysis (TGA), dynamic mechanical analysis (DMA), and tensile testing. WAXD showed these PI fibers were basically amorphous. The tensile strength and initial modulus of the PI fiber reached 1.53 and 220.5 GPa when diamine ratio of PABZ/ODA was 7/3, which were almost three times and 30 times over that of the PMDA/ODA PI fibers. TGA showed that the PI fibers were thermally stable with 10% weight losses recorded in the range of 492–564°C under nitrogen atmosphere, and their glass transition temperature (Tg) were found to be 410–440°C by DMA with increasing PABZ content from 30 to 70%. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Global Positioning System (GPS) currently fulfills the positioning requirements of many applications under Line-Of-Sight (LOS) environments. However, many Location-Based Services (LBS) and navigation applications such as vehicular navigation and personal location require positioning capabilities in environments where LOS is not readily available, e.g., urban areas, indoors and dense forests. Such environments either block the signals completely or attenuate them to a power level that is 10-30 dB lower than the nominal signal power. This renders it impractical for a standard GPS receiver to acquire and maintain signal tracking, which causes discontinuous positioning in such environments.In order to address the issue of GPS tracking and positioning in degraded signal environments, a novel architecture for ultra-tight integration of a High Sensitivity GPS (HSGPS) receiver with an inertial navigation system (INS) is proposed herein. By enhancing receiver signal tracking loops through the use of optimal estimators and with external aiding, the capabilities of the receiver can be substantially improved. The proposed approach is distinct from the commonly used ultra-tightly coupled GPS/INS approaches and makes use of different tracking enhancement technologies used in typical HSGPS receivers, multichannel cooperated receivers and the current ultra-tightly coupled GPS/INS methods. Furthermore, the effects of inertial measurement unit (IMU) quality, receiver oscillator noise and coherent integration time on weak signal tracking are also analyzed.Simulated test results in both static and dynamic testes show that, the designed INS-aided GPS receiver can track the incoming weak GPS signals down to 15 dB-Hz without carrier phase locked, or 25 dB-Hz with carrier phase locked. When there are multiple strong GPS signals in view, the other weak signals can be tracked down to 15 dB-Hz with carrier phase locked.
Catalytic removal of CO from industrial flue gases has been an increasing concern. One attempt is utilizing the tail part of an SCR unit to oxidize abundant CO and trace “slip NH3” synergistically. Herein, Ru/Cu-SSZ-13 was developed to conduct the oxidation of CO and the selective catalytic oxidation of NH3 (NH3-SCO) simultaneously and showed 10 times higher reaction rates than Ru/SSZ-13 on both oxidations. The RuO2 (110) surface was highly active for CO oxidation and NH3 dehydrogenation but would turn insensitive due to the accumulation of adsorbed NO species (NOcus), which derived from the peroxidation during NH3 dehydrogenation. With the assistance of Cu-SSZ-13, generated NOcus could be consumed in an internal SCR route conducted by the activated Cu2+/Cu+ redox cycle, which made NOcus available for the NH3 preferential oxidation rather than the blocked reactive surface. Also, it promoted NH3 transformation on the Cu-SSZ-13 side and boosted the regeneration of Ru-active sites from occupation by NOcus to enable simultaneous CO oxidation. Therefore, the reactivity of RuO2 was boosted after minimizing the interference between the transformation paths of CO and NH3. Furthermore, due to the high NH3-SCO sensitivity of Ru/Cu-SSZ-13, the trace “slip NH3” can be preferentially removed from CO-rich flue gas.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.