Jinling Liu

Highly stable anion exchange membranes based on quaternized polypropylene

A series of novel quaternized polypropylene (PP) membranes with ‘side-chain-type’ architecture was prepared by heterogeneous Ziegler–Natta catalyst mediated polymerization and subsequent quaternization. Tough and flexible anion exchange membranes were prepared by melt-pressing of bromoalkyl-functionalized PP (PP-CH2Br) at 160 °C, followed by post-functionalization with trimethylamine (TMA) or N,N-dimethyl-1-hexadecylamine (DMHDA) and ion exchange. By simple incorporation of a thermally crosslinkable styrenic diene monomer during polymerization, crosslinkable PP-AEMs were also prepared at 220 °C. PP-AEM properties such as ion exchange capacity, thermal stability, water and methanol uptake, methanol permeability, hydroxide conductivity and alkaline stability of uncrosslinked and crosslinked membranes were investigated. Hydroxide conductivities of above 14 mS cm−1 were achieved at room temperature. The crosslinked membranes maintained their high hydroxide conductivities in spite of their extremely low water uptake (up to 56.5 mS cm−1 at 80 °C, water uptake = 21.1 wt%). The unusually low water uptake and good hydroxide conductivity may be attributed to the “side-chain-type” structures of pendent cation groups, which probably facilitate ion transport. The membranes retained more than 85% of their high hydroxide conductivity in 5 M or 10 M NaOH aqueous solution at 80 °C for 700 h, suggesting their excellent alkaline stability. It is assumed that the long alkyl spacer in the ‘side-chain-type’ of 9 carbon atoms between the polymer backbone and cation groups reduces the nucleophilic attack of water or hydroxide at the cationic centre. Thus, PP-based AEMs with long “side-chain-type” cations appear to be very promising candidates with good stability for use in anion exchange membrane fuel cells (AEMFCs).

Processing and characterization of mechanically alloyed immiscible metals

Abstract A number of metal systems exhibit positive heat of mixing between the constituent elements and consequently they are immiscible and cannot form alloys. Some classical examples of these systems are Ti–Mg, Zr–Nb, W–Cu, Ni–Ag, and Cu–Fe. We have investigated the alloying behavior of the Ni–Ag, Ti–Mg, and Zr–Nb systems through two solid-state non-equilibrium processing techniques, viz., mechanical alloying and high-pressure torsion. Increases in solid solubility limits have been achieved in all the systems, although the magnitude of the increase is different in the different alloy systems. The results obtained are also different depending on the technique employed and the lattice strain introduced into the system. The extent of increase in solid solubility limits has been rationalized in terms of the heat of mixing between the constituent metals and it is shown that the solid solubility limit is higher the smaller the positive heat of mixing.

Experimental investigation on the machinability of SiC nano-particles reinforced magnesium nanocomposites during micro-milling processes

This paper experimentally investigates the machinability of magnesium metal matrix composites (Mg-MMCs) with high volume fractions of SiC nano-particles using micro-milling process. The nanocomposites containing 5 vol.%, 10 vol.% and 15 vol.% reinforcements of SiC nano-particles were studied and compared with pure magnesium. The milling was carried out at different feedrates and spindle speeds chosen according to design of experiment (DOE) method. Cutting forces, surface morphology and surface roughness were measured to understand the machinability of the four different materials. Based on response surface methodology (RSM) design, experimental models and related contour plots were developed to build a connection between material properties and cutting parameters. Those models can be used to predict the cutting force, the surface roughness, and then optimise the machining conditions with the required cutting forces and surface roughness.

Microstructure and Lattice Parameters of AlN Particle-Reinforced Magnesium Matrix Composites Fabricated by Powder Metallurgy

Magnesium matrix composites reinforced with AlN particles were fabricated by the powder metallurgy technique. The evolution of lattice constants and solid solubility levels of Al in α-Mg and the microstructure of Mg–Al/AlN composites were investigated in the present study. The results showed that the solid solubility of Al in α-Mg reached a relatively high level by the P/M process with a long time of milling. X-ray diffraction showed that the peaks of Mg phase clearly shifted to higher angles. The lattice constants and cell volume decreased significantly compared with those of standard Mg due to a significant amount of Al incorporated into α-Mg in the form of substitutional solid solution. The degree of lattice deformation decreased at a low sintering temperature and increased at higher sintering temperatures due to the presence of AlN. Microstructural characterization of the composites revealed a necklace distribution of AlN particles in the Mg matrix. Heat treatment led to precipitation of Mg17Al12 from the supersaturated α-Mg solid solution. The precipitate exhibited granular and lath-shaped morphologies in Mg matrix and flocculent precipitation around AlN particles.

Abnormal behavior of silica doped with small amounts of aluminum

Silica is the most abundant mineral in the crust of the Earth. It has been demonstrated that the aluminum concentration in silica plays a key role in determining many properties of silica-based components. Although the alumina-silica system has been intensely studied, the effect of very small amounts of aluminum on the structure and properties of silica remains unclear. We report results of first principles calculations showing that small amounts of aluminum could be metastable when located in the center of Si-O rings without breaking the silica network. In contrast, higher aluminum contents will result in the destruction of the Si-O bonds, leading to the formation of triclusters and a 4-, 5-, and 6-fold Al-O coordination, as observed in previous studies. Based on the silica structure obtained through geometric optimization, the properties of silica doped with small amounts of aluminum were calculated. The results can account for many ‘abnormal’ phenomena experimentally observed. The results benefit most areas such as geosciences, microelectronics, glass industry, and ceramic materials.

Magnesium nanocomposites reinforced with a high volume fraction of SiC particulates

Abstract The microstructure and indentation behavior of magnesium nanocomposites containing a high volume fraction (up to 15 vol.%) of nanometer-sized SiC was studied using X-ray diffraction, electron microscopy, and microindentation techniques. The indentation hardness and contact stiffness were found to increase with increasing volume fraction of the nanometer-sized SiC particles up to 10 vol.%. The magnesium nanocomposites with 15 vol.% SiC had a lower indentation hardness than that of 10 vol.% SiC. The strain rate sensitivity exponent of the Mg–SiC nanocomposites increased with increasing volume fraction of SiC. The decrease of the indentation hardness suggested that the deformation mechanism of the magnesium nanocomposites was likely altered when the critical volume percent of SiC nanoparticles was achieved, estimated at 10 vol.%.

Chemical Vapour Deposition Phase Diagrams for Zirconium Carbide

Thermodynamic equilibrium condensed phases for chemical vapor deposition (CVD) of zirconium carbide (ZrC) from C3H6-ZrCl4-H2 and CH4-ZrCl4-H2 were calculated by a method based on the minimization of the free energy of the reaction system. The deposition phase diagrams, which indicated the condensed phases, were then constructed from the calculation results. These diagrams demonstrated the effect of partial pressure of reactants, deposition temperatures, and the different carbon sources on the final condensed phases. Useful information can be provided from these diagrams to determine the process parameters for the deposition of ZrC coatings.