Study on carbon fiber surface treatment based on surface oxidation method
Surface conditions of carbon fibers severely effect on the bonding strength between the fibers and the matrix, even on the mechanical properties of the composites when carbon fibers were used as reinforcement on the preparation of ceramic matrix composites. Surface treatment of carbon fibers was carried out based on the air oxidation method and the liquid oxidation method with concentrated nitric acid (68%) as the oxidizing solution. It could remove impurities from the surface of carbon fibers and increase the degree of the surface concavoconvex, so the active surface area were increased and then improved the bonding strength between fibers and matrix. The surface topographies of carbon fibers after surface oxidation were characterized by SEM. The results illustrate that, impurities on the surface of carbon fibers are decreased and there are many longitudinal grooves evenly distributed on the surface in favor of increasing the bonding strength between the fibers and matrix.
SURFACE TREATMENT OF CARBON FIBER
A review of the surface structure and perfomance of carbon fiber is presented. Two general surface treatment method of carbon fiber is introduced: electrochemical and plasma oxidation; The adhesion mechanisms contributing to the improvements in the interface of carbon fiber/resin composties are also summarized.
Thermal incompatibility analysis of metal-ceramic systems based on flexural displacement data.
The feasibility of simple tests or analytical methods for prediction of residual stress states in metal-ceramic (MC) prostheses has not been demonstrated. Biomaterial metal-ceramic strips have been proposed to provide sensitive measures of transient and residual stress states through the measurement of midpoint deflection after cooling from the ceramic sintering temperature. The objective of this study was to apply the elastic-viscoelastic analogy to calculate transient and residual midpoint deflections in MC biomaterial strips and to compare these values with deflections measured with a beam-bending viscometer (BBV). Calculations and measurements were made for five MC systems that were found from a clinical study to be "thermally compatible" systems. Metal strips, 64 mm in length, 3 mm wide, and either 0.5 mm, 1.0 mm, or 2.0 mm in thickness, were veneered with four 0.25-mm thick layers of opaque porcelain. Midpoint deflection of the MC strips (ceramic oriented in the posterior position) was measured during cooling from an initial temperature of 700 degrees C. In general, the directions of the measured residual deflections did not agree with the "textbook" convention that negative deflections are associated with positive thermal contraction mismatch (alpha(M) - alpha(c) > 0) regardless of metal thickness. For a metal thickness of 0.5 mm, the residual midpoint deflection for all thermal contraction mismatch cases, except one, was positive (upward deflection) whereas the residual midpoint deflections were all negative when the metal thickness was increased to 1 or 2 mm, independent of the thermal contraction mismatch. The best agreement between calculated and measured values of residual midpoint deflection (+16 microns vs. +14 +/- 2.3 microns, respectively was obtained for MC biomaterial strips with a Ni-Cr alloy (0.5 mm thick) while the largest difference (+346 microns vs. +61 +/- 43.8 microns) was obtained for MC bimaterial strips with a Au-Pd allow (0.5 mm thick). In all but one case, changes in deflection direction as a function of metal thickness were correctly predicted by the viscoelastic analysis. The results of this study indicate that a viscoelastic model is useful for estimating thermal compatibility conditions of MC systems.