Effect of anodic oxidation of coal tar pitch-based carbon fibre on adhesion in epoxy matrix: Part 2. Comparative study of three alkaline solutions

Anodic oxidation of coal tar pitch-based carbon fibre was performed in various alkaline solutions, such as NaOH, NaHCO₃ and Na₂CO₃, to examine the effect of various kinds of electrolytes on the surface chemical nature of treated fibres and the adhesive strength between treated fibres and epoxy resin. Evaluation of the oxygen concentration and surface functional groups of the carbon fibre surface was conducted by X-ray photoelectron spectroscopy (XPS). A fragmentation test was adopted for evaluation of the adhesive strength between the carbon fibre and epoxy matrix. As a result, it was shown that the highest O_1S/C_1S value was obtained in NaOH aqueous solution, and the highest interfacial shear strength (IFSS) was also obtained from the carbon fibre oxidized in NaOH solution. It was recognized that the IFSS values increase with increasing of O_1S/C_1S in every solution at the initial stage of oxidation below 1.0 × 10⁻³ C mm⁻². However, above this level of electrical charge in NaOH solution, decreasing IFSS values may occur, regardless of an increasing O_1S/C_1S value. SEM analysis inferred that in the case of the fibre treated in NaOH solution, grooves on the carbon fibre surfaces had become deeper over 1.0 × 10⁻³ C mm⁻². Presumably, the amorphous part of the carbon fibres could be oxidized intensively, and the remaining graphite layer become very thin and easy to break when a shear stress is loaded on its interface.     

Effects of anodic oxidation in H2SO4 electrolyte on the biocompatibility of NiTi shape memory alloy

Effects of anodic oxidation in H₂SO₄ electrolyte on the biocompatibility of NiTi shape memory alloy (SMA) were investigated by characterizing surface structure, blood compatibility, wettability, release of harmful Ni ions of anodized NiTi SMA. Although titania film resulting from anodic oxidation in H₂SO₄ electrolyte has a porous structure, it can effectively block out-diffusion of Ni from NiTi SMA to simulated body fluid (SBF). Comparing with chemical polishing, anodic oxidation in H₂SO₄ electrolyte can also improve the wettability, blood compatibility, thromboresistance of NiTi SMA.