Search

To understand the effect of acid solution treatment on poly 1, 4-cyclohexylen dimethylene terephthalate(PCT) fiber, the surface morphology, mechanical properties, aging reaction activation energy and infrared spectrum of PCT fibers before and after sulfuric acid and nitric acid treatment were tested and analyzed by scanning electron microscope(SEM), single fiber strength machine, synchronous thermal analyzer(STA) and Fourier transform infrared spectrometer(FTIR). The results show that the acid immersion treatment can cause the shrinkage of PCT fiber, leading to the surface corrosion of the fibers and the occurrence of dents and cracks; The entering of water molecules into the fiber macromolecule gap of PCT fiber causes a simultaneous decrease in breaking strength and elongation at break; The breaking strength of PCT fiber decreased with the increase of acid solution concentration, treatment time and treatment temperature; Unless at a lower concentration and temperature, the sulfuric acid resistance of PCT fiber is better than that of nitric acid; The sulfuric acid resistance of PCT fiber is weaker than that of the polyphenylene sulfide(PPS) and the polytetrafluoroethylene(PTFE) fiber, and better than that of the polyimide(PI) and the Aramid 1313 fiber; Acid solution treatment can lead to a decrease in the activation energy of the aging reaction and molecular stability of PCT fiber. [ABSTRACT FROM AUTHOR]

The effects of tempering temperatures on microstructure and mechanical properties of the on-line quenched Q690q bridge steel were investigated through optical and scanning electron microscopes and tensile tests. The results show that the microstructure of the on-line quenched steel is primarily the lath bainite. After tempering at 540~650℃, the microstructure is the tempered sorbite. It is also found that with the increase of the tempering temperature, the lath width and the averaged grain size become larger, and the amounts of the carbide precipitations and large-angle grain boundaries increase. Meanwhile, with the tempering temperature increasing, the strength of the tested steel trends to be decreased, in contrast to the plasticity and toughness. At 620℃, the tested steels have the best mechanical properties, in which the yield and tensile strengths are 878 MPa and 992 MPa, the percentage elongation after fracture is 20%, and the impact absorption energy at -40℃ is 143 J. [ABSTRACT FROM AUTHOR]