Fluorinated Carbon Fibers Research Articles

Characterization of fluorinated PAN-based carbon fibers by zeta-potential measurements

An alternative technique in order to increase the fiber surface polarity is the mild direct fluorination of carbon fibers. We studied the influence of various fluorination agents at different temperatures and pressures on the chemical surface composition, the bulk structure and the wetting behavior of two high tensile strength (HT) carbon fibers. Zeta (ζ)-potential measurements using the streaming potential method (applied in the EKA) were performed to characterize the electrokinetic properties of fluorinated carbon fibers. Since fluorine is able to form different kinds of chemical bonds with graphite like materials (ionic, semi-ionic or covalent CF bonds). The time dependence of the ζ-potential reflects the surface composition of the obtained fiber material, due to the dissociation of such ionic CF groups. The pH dependence of the ζ-potential of the fluorinated carbon fibers were determined in 10 −3 mol l −1 KCl electrolyte solutions indicating an increased acidic character of the fluorinated fiber surfaces compared to the unmodified carbon fibers. From the KCl-concentration dependence of the ζ-potential it is possible to acquire information about the degree of interaction between the solid surface and the ions of the electrolyte solution, based on specific or electrostatic interactions. The molar adsorption-free energies Φ K + for potassium and Φ cl − for chloride ions by the fiber surfaces were calculated from the concentration c max at the maximum ζ-potential ζ max.

Deintercalation Process of Fluorinated Carbon Fibres. Part I - Controlled Rate Evolved Gas Analysis

The intercalation of fluorine into graphite leads to graphite intercalation compounds (F-GICs) exhibiting potential properties such as the storage and transport of fluorine. Stage-1 compounds with C2.5F to C4F compositions are obtained by fluorination treatments at room temperature of ex-pitch, high-temperature treated carbon fibres under 10 bars F2 pressure in the presence of gaseous HF. The deintercalation process of fluorine species has been studied by evolved gas analysis: the F-GICs are decomposed using the Controlled transformation Rate Thermal Analysis (CRTA) method. The thermal analysis curve obtained for stage-1 F-GICs exhibits three decomposition steps. The first two steps correspond to a simultaneous deintercalation of atomic fluorine F and gaseous HF and the third step (above 460°C) to the degradation of the compound with formation of C2F4 and CF4 which further dissociate in the spectrometer to CFn (1 ≤ n ≤ 3) species.

Deintercalation process of fluorinated carbon fibres—II. Kinetic study and reaction mechanisms

The deintercalation process of fluorine species from fluorine-graphite intercalation compounds (F-GICs) has been investigated by evolved gas analysis. The controlled transformation rate thermal analysis method was used. In this way, the rate of production of the gaseous phase is permanently controlled at low pressure, so that both temperature and pressure gradients can be lowered at will, avoiding the overlap of the successive steps of the reaction. These experiments have been carried out on stage-1 F-GICs with C F ratios ranging from 3 to 4, which were obtained from high-temperature treated carbon fibres (ex-pitch) fluorinated at room temperature with P F 2 < 10 bar in the presence of gaseous HF. The thermal analysis exhibits three parts: the first two parts correspond to the deintercalation of fluorine and HF; and the third part (> 460 °C) to the degradation of the carbonaceous skeleton. The activation energies associated with the different parts have been determined by the rate-jump method. A kinetic study of the deintercalation/decomposition processes has been proposed. The first (deintercalation) part is apparently accompanied by a post-deintercalation reaction of evolving fluorine with carbon atoms of defects leading to the formation of covalent CF bonds. The deintercalation is achieved during the second part which can be described by a two-dimensional interfacial advancement process. The apparent activation energy of this deintercalation part has been evaluated to be 144 kJ mol −1. The degradation part, with 240 kJ mol −1 activation energy, can be ascribed to a two-dimensional nucleation and growth of nuclei mechanism.

Surface Modification of Pitch Based Carbon Fibers by Direct Fluorination Comparison with Anodic Oxidation.

We investigated the hydrophilicity of fluorinated carbon fibers at room temperature, that is a new method of surface treatment, and found that through this treatment, wettabillity of the surface of carbon fibers increased dramatically without decrease of tensile strength. Observation by scanning electron microscope (SEM) showed the same surface morphology of fluorinated carbon fibers as that of original fiber. On the other hand, of anodic oxidated fibers. In the case of anodic oxidation as the wettabillity of oxidated fibers increased, the surface roughness increased and resulted in the decrease of tensile strength.

Structure and properties of fluorinated carbon fibers

The fluorination of carbon fibers results in a partial or total conversion of the carbon layers into CF layers. In constrast to the formation of intercalation compounds of carbon fibers, the fluorination causes considerable changes in the fiber texture which results in a marked decrease of tensile modulus and mechanical strength. The relationship between the structural changes and the resulting mechanical properties is studied by small-angle and wide-angle X-ray scattering.

A study of fluorinated carbon fibers

A study of fluorinated carbon fibers