Thermal, Mechanical, and Microstructural Study of PBO Fiber during Carbonization

Poly(p-phenylene benzobisoxazole) (PBO) fiber shows fascinating properties including excellent mechanical performance, high crystallinity, and fairly good heat resistance as a kind of polymer fiber. Its properties make it a possible candidate as a precursor of carbon fiber. This paper mainly investigates the possibility of yielding carbon fiber from PBO by direct carbonization using a continuous process and multiple properties of yielded fiber treated under different heat treatment temperature (HTT). The results show that PBO fiber was able to sustain an HTT as high as 1400 °C under the inert atmosphere and that the shape of fiber was still preserved without failure. Using thermal gravimetric analysis (TGA) and TGA coupled with mass spectroscopy (TGA-MS), it was found that a significant mass loss procedure happened around 723.3 °C, along with the emission of various small molecules. The mechanical performance first suffered a decrease due to the rupture of the PBO structure and then slightly increased because of the generating of graphite crystallite based on the broken structure of PBO. It was observed that PBO’s microstructure transformed gradually to that of carbonaceous material, which could be the reason why the change of mechanical performance happened.

Research of the Surface Changes in the Modification Process of Activated Carbon

This paper studied the changes in the surface morphology and microcrystalline structure of GAC modified using the original activated carbon, HNO3, FeCl2·4H20, KMnO4. The micro pore structure on the surface is damaged after being treated by HNO3, and the transition pores increase; after being treated by FeCl2·4H20 and KMnO4,the carbon surface is irregular, and there is a protuberance, which is due to the irregular loading of manganese ions on the activated carbon surface. Then the roughness of the activated carbon increases and the size of graphite crystallite of GAC is also greatly reduced, showing obvious trend of fine grains. Meanwhile, the studies of the effect of removing the trichlorophenol from water after modification indicate that the results basically match. On this basis, the modified model is put forward.

Photocatalytic Degradation of Alachlor on Fe-TiO2-Immobilized on GAC under Black Light Irradiation Using Box-Behnken Design

The aim of this work was focused on the photocatalytic degradation of alachlor from aqueous solution using 10%wt Fe-TiO2, as 0.1%wt of Fe doped into TiO2 structure, immobilized on granular activated carbon (GAC) under black light irradiation. The extended photocatalytic conditions were studied as functions of catalyst loading, number of black light, and initial pH of solution using Response Surface Method (RSM) based on Box-Behnken design (BBD). Characterizations of the photocatalyst by TGA-DTA, and XRD were investigated. Photocatalyst was calcined at 400°C under nitrogen atmosphere. As a Result of calcinations, photocatalyst consisted of only graphite crystallite while the crystallite phases of TiO2 were not observed. The degradation results showed that the photocatalytic process gave the highest percent degradation comparing with adsorption and photolysis processes. The effects of three operating variables which are catalyst loading, number of black light, and initial pH of solution on the degradation efficiency of alachlor were examined. Photocatalyst loading was only significant parameter effecting for photocatalytic degradation of alachlor. The photocatalytic degradation slightly increased with increasing of number of black light while pH of solution did not affect photocatalytic degradation of alachlor. The photocatalytic process and adsorption process were affected from the initial alachlor concentrations as well.

Impaction of Graphite Type on Performance of Polycrystalline Diamond Powder

Taking different types of graphite as raw materials ， polycrystalline diamond powder is prepared by shock wave synthesis through copper to absorb and transfer the heat in the article. Yield and abrasion resistance performance are tested, and impaction of graphite crystallite structure on the yield and abrasion resistance performance is researched. As the result, diamond yield and abrasion resistance synthesized from scale graphite is not as good as from earthy graphite. It is easy for polycrystalline diamond powder synthesized from artificial graphite which crystallite has parallel coke-base to graphitize and difficult to get diamond. Yield of artificial graphite which crystallite has disorderly carbon black base is higher than that of earthy graphite, there are more pores for the first baked artificial graphite of carbon black base, the abrasion resistance performance of synthesized diamond is worse than earthy graphite, and the abrasion resistance performance of the second baked polycrystalline diamond powder is better than earthy graphite.

Study of the Surface Morphology and the Microstructure of PAN-Based Carbon Fibers

The microstructure of two kinds of self-made PAN-based high-modulus carbon fibers (HMCF-1, HMCF-2) was studied by scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM), and was compared with that of T800 and M55J. The correlation of XRD and HRTEM in terms of graphite crystallite sizes and interlayer spacing of graphite layer was also investigated. The results show that the diameters of T800, HMCF-1 and HMCF-2 are almost the same (~5.20μm) and all of them are lager than that of M55J (~4.86μm). The crystal sizes and the degree of graphitization are in the order of HMCF-2>HMCF-1>M55J>T800, while the regularity of the lattice fringes of HMCF-2 is better than those of others.

Properties of Carbon Nanofibers Prepared from Polyacrylonitrile/Poly(methyl Methacrylate) Blend

The polyacrylonitrile(PAN)/poly (methyl methacrylate)(PMMA) blend fibers were prepared by wet-spinning technique and carbonized over the temperature range of 400-1000°C in nitrogen atmosphere. After carbonization of the blend fibers, the PMMA component removed and the PAN component left in the form of carbon nanofibers. Morphology of the carbon nanofibers were investigated via scanning electron microscopy (SEM), and the carbonization behavior of the fibers were examined via x-ray diffraction (XRD), Raman microspectrometry. The optimal condition made carbon fibers with great L/D ratio and diameter less than 200 nm. XRD and Raman spectra shows that the PAN/PMMA blend fibers treated at 600°C produced some graphite crystallite.

Clustering of water molecules on model soot particles: an ab initio study

Clustering of water molecules on model soot particles is studied by means of quantum calculations based on the ONIOM approach. The soot particles are modeled by anchoring OH or COOH groups on the face side or on the edges of a graphite crystallite of nanometer size. The quantum calculations aim at characterizing the adsorption properties (structure and adsorption energy) of small water aggregates containing up to 5 water molecules, in order to better understand at a molecular level the role of these OH and COOH groups on the behavior with respect to water adsorption of graphite surface modelling soot emitted by aircraft.

Analysis of Picosecond Pulsed Laser Melted Graphite

A Raman microprobe and TEM have been used to analyze the resolidified region of liquid carbon generated by picosecond pulse laser radiation. From the relative intensities of the zone center Raman-allowed mode for graphite at 1582cm−1 and the disorder-induced mode at 1360cm−1 , the average graphite crystallite size in the resolidified region is determined as a function of incident pulse energy density. By comparing with Rutherford backscattering spectra and Raman spectra from nanosecond pulsed laser melting experiments, additional information about the disorder depth in picosecond pulsed laser melted graphite is obtained. Comparisons of TEM micrographs for nanosecond and picosecond pulsed laser melting experiments show that the structure of the laser disordered regions in graphite are similar and exhibit similar behavior with increasing laser pulse fluence. The similarities in the resolidified regions under both irradiation schemes discourages a determination of the properties of liquid carbon after the liquid has resolidified.