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.
Research of Oxidation Resistance of Short Carbon Fiber Reinforced SiC Composite by Hot-pressing
Short carbon fiber reinforced SiC(Csf/SiC) composite was prepared by hot-pressing method.XRD,SEM and isothermal oxidation test were used to study the isothermal oxidation property of Csf/SiC composite.The results show that the oxidation weight loss of the composite is the most at 900℃.The weight loss decreases with the oxidation temperatures rising.Below 900℃,the oxidation weight loss of the composites is caused by the carbon fibers oxidation.Above 1450℃,the composites gain weight.Between 900-1450℃,short carbon fibers on the composite surface are oxidized and the SiC matrix forms a protecting film.The inner short carbon fibers still have the strengthen effect for the oxidation layer and matrix protecting them from oxidation,and the composites have good self-resistance oxidation property.When the composites oxide at 1600℃,the composite surface is destroyed badly and lose the resistance oxidation capacity.
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.