The boron-containing phenolic fibers were prepared by melt-spinning a mixture of novolak resin and boron acid followed by curing the filaments with formaldehyde solution in the presence of an acid catalyst. The resulting fibers were heat-treated in N2 at elevated temperatures. The results show that the addition of 1.0 wt% boron acid in the precursor resin can greatly increase thermal stability, mechanical strength and flame resistance of the resultant fibers. In comparison the boron-containing phenolic fibers with the pure phenolic fibers, the weight loss of the boron-containing phenolic fibers (BPF-1.0), heat-treated at 240 °C for 2 h, decreases from 60.5 to 39.1% in N2, from 32.8 to 14.1% in air. Whereas, the limited oxygen index increases from 32.5 to 37.2%; the tensile strength increases from 129.3 to 163.4 MPa.

Tin oxide (SnO2) microspheres with an average 2.5 μm in diameters have been successfully synthesized through a rapid hydrothermal process heating by microwave in the presence of an ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate. X-ray diffraction, scanning electron microscopy and transmission electron microscopy are used to characterize the morphology and crystalline structure of the microspheres. The as-synthesized SnO2 microspheres exhibit a tetragonal rutile structure. The mechanism of the microspheres formation is proposed.Tin oxide (SnO2) microspheres with an average 2.5 μm in diameters have been successfully synthesized through a rapid hydrothermal process heating by microwave in the presence of an ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate.

Oxygen treatment after KOH corrosion of phenolic-based activated carbon fibers was conducted to explore the influence of oxygen functional groups on the performance of capacitors fabricated with the carbon fibers. Scanning electron microscopy analysis shows that KOH corrosion can increase the surface roughness. The result of temperature programmed desorption shows that the amount of surface oxygen functional groups increases with the extent of oxygen treatment after KOH corrosion, and reaches a maximum at 250 °C; the increase is contributed mainly by the formation of carbonyl- or quinone-type groups. The performance of the capacitors was tested in 7 M KOH using potential sweep cyclic voltammetry and constant current charge–discharge cycling. The results reveal that the specific capacitance increases from 163.5 F g−1 to 280.7 F g−1 at a current density of 50 mA g−1 with increasing the amount of oxygen functional groups. The oxygen functional groups can improve the wet ability of carbon surface and causes the quick faradic charge transfer reaction, which decreases the total resistance, and results in the enhancement of specific capacitance at high current density.

The microstructure evolution of phenolic fibers carbonized at different temperatures and the influence of the resulting microstructure on the mechanical and electrical behaviors were investigated using a combination of techniques including thermogravimetric analysis-mass spectroscopy (TG-MS), Fourier transform infrared spectroscopy (FT-IR), laser Raman spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 physical adsorption, tensile strength and electrical conductivity measurements. The results showed that below 500 °C aromatic union was crosslinked by aliphatic bridges; above 500 °C with increasing temperature the polymer network was destroyed, hexagonal carbon layers were gradually formed; above 850 °C the content of the hexagonal carbon layers was further increased due to the transformation of the amorphous carbons in the fibers; above 1500 °C slow evolution toward ideal graphite was occurred. The accessible micropores (<1.2 nm, 200–1040 m2/g) could be detected in the range of 600–950 °C. The tensile strength of the carbon fibers exhibited a maximum value of 640 MPa at 550 °C. The electric conductivity increased with increasing temperature and reached a maximum value of 2.45 × 104 S/m at 2800 °C.