In order to improve the mechanical properties of the SiO 2f /SiO 2 composites, the uniform and complete Al 2 O 3 coatings were prepared on the quartz fibers via sol–gel method with aluminum isopropoxide as the precursor. The thickness of Al 2 O 3 coatings increases with concentration of aluminum isopropoxide precursor solution. The Al 2 O 3 coatings fabricated with 10 wt.% precursor solution were uniform and complete, and its thickness was approximately 430 nm. The SiO 2f /SiO 2 composites with Al 2 O 3 coatings achieve higher mechanical strength compared with the SiO 2f /SiO 2 composites without Al 2 O 3 coatings. The flexural strength of SiO 2f /SiO 2 composites increases with concentration of aluminum isopropoxide precursor solution. And the compressive strength shows a slightly decreasing trend with concentration of aluminum isopropoxide precursor solution. The mechanical performance of the SiO 2f /SiO 2 composites fabricated from fibers coated with 10 wt.% aluminum isopropoxide precursor solution was excellent, and its compressive strength was 57.1 MPa, flexural strength was 28.6 MPa. And the reason was that the Al 2 O 3 coatings effectively enhanced the interface isolation between the fiber and the matrix, optimizes the deflection path of the crack and increased the strength of the SiO 2f /SiO 2 composites. The mechanical strength of SiO 2f /SiO 2 composites with Al 2 O 3 coatings was increased after not only short-term but also long-term heat treatment.
In this paper, polymethylhydrosiloxane (PMHS) and ethanol were used as raw materials to synthesize the ceramic precursor of side ethoxy polysiloxane (PESO) using dehydration and a dealcoholization reaction, which had a ceramic yield of 87.15% and a very low residual carbon content. With the quartz fiber as a reinforcer, the silica matrix composites (SiO2f/SiO2) with a double-layer interface (PyC-SiO2/BNNSs) coating were manufactured using precursor impregnation pyrolysis (PIP). The as-prepared SiO2f/SiO2possessed an excellent mechanical property, which exhibited obvious fiber pull-out and debonding phenomena from a fracture morphology. The flexural strength and fracture toughness of SiO2f/SiO2reached 63.3 MPa and 2.52 MPa·m1/2, respectively. Moreover, the SiO2f/SiO2had suitable dielectric properties, with a dielectric constant of about 2.5 and a dielectric loss of less than 0.01. This work provides an important concept for the enhancement of the dielectric properties and mechanical properties of quartz fiber-reinforced ceramic matrix composites, as well as in the preparation of wave-transmissivity composites.
Joining is an indispensable process for expanding the application of ceramics and composites. Recently, glasses have been extensively explored for ceramic/composite joining owing to their unique functional needs. However, the difficulty in detecting amorphous materials and lack of enthalpy data make the interfacial reaction mechanism challenging to investigate. In this study, the interfacial reaction mechanism of joints of SiO 2f /SiO 2 composite-brazed bismuth glass was thoroughly explored. SiO 2 was dissolved from the matrix and used throughout the brazing process. In the initial stage, silica reacts with the brazing glass to form Bi 4 (SiO 4 ) 3 . Then, owing to the decomposition of Bi 4 (SiO 4 ) 3 , the silicate glass replaced the bismuth glass. Finally, some precipitation of SiO 2 occurred at the brazing seam owing to an entropy–enthalpy dominating mode. This study may instigate the design of brazing glasses for joining SiO 2f /SiO 2 composites.
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