[en] A series of reinforced composite membranes were prepared from Nafion 212 and crosslinkable fluorine-containing polyimide (FPI) with various crosslinkers. The crosslinkable FPI reacts with the crosslinkers and forms semi-interpenetrating polymer networks (semi-IPN) structure with Nafion 212. The water uptake, swelling ratio, mechanical properties, thermal behavior, proton conductivity, and chemical oxidation stability of the composite membranes are studied. The degree of crosslinking is characterized by gel fraction of the composite membranes. Compared to pure Nafion 212, the composite membranes exhibit excellent thermal stability, improved mechanical properties and dimensional stability. The tensile strength of the composite membranes is in the range of 37.3-51.2 MPa. All the composite membranes exhibit high proton conductivity which ranges from 1.9 x 10^-2 to 9.9 x 10^-2 S cm^-1. The proton conductivity of the composite membrane with 2-propene-1-sulfonic acid sodium salt (SAS) as the crosslinker is 9.9 x 10^-2 S cm^-1 at 100 ^oC which is similar to that of Nafion 212 under the same condition.

[en] The microstructure evolution and micro-mechanical behavior of secondary carbides at grain boundary in a Fe–Cr–W–Mo–V–C alloy for cold work roll were systematically investigated in this study. The typical microstructures at the characteristic temperature of 1240 °C, 1200 °C and 1150 °C were observed by Optical Microscope and Field Emission Scanning Electron Microscope. The hardness values of secondary carbides were predicted and measured by first-principles calculation, Vickers hardness tester and nanoindentation technique. The fracture toughness (K_C) values were calculated by a method known as Indentation Microfracture. Single-pass scratch tests were carried out to investigate the micro-scale wear behavior of secondary carbides. The macroscopic pin-on-disk test was also performed. The results show that the secondary carbide at grain boundary contains secondary MC, M₂C and M₇C₃. The formation of secondary MC and M₇C₃ belongs to the precipitation and growth process, while secondary M₂C is the result from the growth of eutectic M₂C. In the studied alloy, M₇C₃ is a dominant carbide in quantity, and has higher hardness than secondary M₂C and the matrix, and processes the better toughness than secondary MC, whose hardness almost reaches 30 GPa, and can also effectively resist the crack initiation and propagation, which therefore makes a significant contribution to the wear resistance of the alloy.

[en] Most of the anhydrous proton conducting membranes are based on inorganic or partially inorganic materials, like SrCeO₃ membranes or polybenzimidazole (PBI)/H₃PO₄ composite membranes. In present work, a new kind of anhydrous proton conducting membrane based on fully organic components of PBI and tridecyl phosphate (TP) was prepared. The interaction between PBI and TP is discussed. The temperature dependence of the proton conductivity of the composite membranes can be modeled by an Arrhenius relation. Thermogravimetric analysis (TGA) illustrates that these composite membranes are chemically stable up to 145 deg. C. The weight loss appearing at 145 deg. C is attributed to the selfcondensation of phosphate, which results in the proton conductivity drop of the membranes occurring at the same temperature. The DC conductivity of the composite membranes can reach ∼10^-4 S/cm for PBI/1.8TP at 140 deg. C and increases with increasing TP content. The proton conductivity of PBI/TP and PBI/H₃PO₄ composite membranes is compared. The former have higher proton conductivity, however, the proton conductivity of the PBI/H₃PO₄ membranes increases with temperature more significantly. Compared with PBI/H₃PO₄ membranes, the migration stability of TP in PBI/TP membranes is improved significantly

[en] Poly(1,2,4-vinyltriazole) (PVTr) and poly(1,2,4-vinyltriazole-co-5-vinyltetrazole-co-acrylonitrile) (P(VTr-VT-AN)) were prepared by normal free radical polymerization and click chemistry, respectively. The structure of the polymers was characterized by FTIR spectra, H NMR spectrum and elemental analysis. Compared with polybenzimidazole (PBI) which is one of the most widely studied anhydrous proton conducting polymers, the solubility of vinyltriazole-based polymers is improved significantly. They are soluble in a lot of polar solvents. The glass-transition temperatures of such kind of polymers are between 70 and 85 ^oC, thus indirectly indicating the improvement of fabricating properties. In phosphoric acid doped membranes, the higher the basicity of the vinyltriazole-based polymers is, the higher the proton conductivity is. The temperature dependence of the proton conductivity of the acid doped membranes can always be fitted by a simple Arrhenius equation. Transmittance of phosphoric acid doped vinyltriazole-based polymers is above 80% in the range of visual spectra and changes a little with the different structure and basicity of the copolymers

[en] The reinforced composite membranes based on Nafion^® membranes attract a lot of attention as proton exchange membrane (PEM) for polymer electrolyte membrane fuel cells (PEMFCs). Fluorine-containing polyimide (FPI), end-capped with alkynyl, is synthesized from 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 2,2′-bis(trifluoromethyl)- 4,4′-diaminobiphenyl (TFMB), and 3-aminophenylacetylene (APA). The chemical structure of FPI is characterized by ¹H-NMR. The reinforced composite membrane based-on semi-interpenetrating polymer network (semi-IPN) is prepared via solution casting of FPI and Nafion^®212, and crosslinking thereafter. During the membrane preparation, alkynyl in FPI reacts with azide and itself via click chemistry and addition polymerization. The water uptake, swelling ratio, mechanical properties, thermal behavior, proton conductivity, and oxidative stability of the composite membranes are investigated. Compared to Nafion^®212, the composite membrane shows improved thermal stability, mechanical properties, and dimensional stability. The tensile strength of the composite membranes is in the range of 35.0–55.6 MPa, which is much higher than that of Nafion^®212 membrane. The composite membranes show considerable proton conductivity from 2.0 × 10⁻² S cm⁻¹ to 9.9 × 10⁻² S cm⁻¹ at a temperature range from 30 °C to 100 °C, depending on FPI content

[en] Fluorine-containing polyimide (FPI) with hydroxyl groups is synthesized from 4,4′-(hexafluoro isopropylidene) diphthalic anhydride (6FDA), 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP), and 4,4′-diaminodiphenyl ether (ODA) via high temperature polycondensation. Thereafter, alkynyl groups are introduced into FPI. During the preparation of the composite membrane, alkynyl groups on FPI react with azido methyl of 4,4′-bis(azido methyl) biphenyl via click chemistry and form semi-interpenetrating polymer network (semi-IPN) structure within the composite membranes. The mechanical properties, thermal behavior, water uptake, swelling ratio, proton conductivity, oxidative stability, as well as the performance in single cell operation are investigated. Compared to pure perfluorosulfonic acid (PFSA) polymer membrane, the composite membranes based on semi-IPN of FPI and PFSA exhibit improved mechanical properties, excellent thermal and dimensional stabilities, and suitable proton conductivity. The tensile strength of the composite membranes ranges from 28.0 to 67.0 MPa. With increasing FPI content in the membranes, the dimensional stability of the composite membranes increases. The composite membranes have the proton conductivity from 4.3 × 10⁻² S·cm⁻¹ to 1.0 × 10⁻¹ S·cm⁻¹ at 100 °C and also have good performances as proton exchange membrane (PEM) in single cell at 80 °C