Formation and mechanism of carbon coating on carbon fibers through glucose-to-carbon conversion and its effect on the mechanical properties of Cf/ZrB2-SiC composites

The protection for carbon fibers is crucial for carbon fiber-reinforced materials. Carbon coatings were prepared on carbon fibers through gelation, hydrothermal caramelization and pyrolysis, with glucose as precursor of carbon. The glucose-to-carbon conversion mechanism was explored, as well as the effect of high pressure in hydrothermal reactor and the catalytic role of KCl. The high pressure suppressed gas escape and was beneficial to the formation of dense carbon coating. The KCl promoted the generation of 5-HMF, thereby accelerated the glucose-to-caramel conversion. C f /ZrB 2 -SiC composites were prepared by introducing ZrB 2 -SiC slurry into the carbon fiber preform and hot press sintering. The carbon coating protected the carbon fibers from damage during sintering at high temperature. The carbon coating significantly improved the flexural strength, fracture toughness, and fracture work of C f /ZrB 2 -SiC composites from 122 MPa, 3.24 MPa‧m 1/2 , and 231.6 J/m 2 to 321 MPa, 5.87 MPa‧m 1/2 , and 567.1 J/m 2 , respectively.