Yttrium silicate-based composites dispersed with silicon carbide particles have been proposed as a novel material concept of self-healing environmental barrier coatings applied for Si-based ceramics and their composites. Crack-healing effectiveness as well as high-temperature oxidation behavior of the yttrium silicate composites was investigated as functions of oxidation time and temperatures. Dense samples of the composites dispersed with 5 vol% SiC particles were fabricated by using the pulsed electric current sintering technique. Thermal oxidation for selfhealing was conducted at temperatures ranging from 1000°C to 1300°C for from 1 to 24 h in air. High-temperature oxidation experiments were carried out at temperatures ranging from 1200°C to 1400°C for from 1 to 60 h in air. As a result, the surface cracks with approximately 200 µm in length introduced on the sample surface were disappeared completely after heat treatment at 1300°C for 1 h in air. Crack-healing performance of SiC/Y 2 SiO 5 is better than that of SiC/Y 2 Si 2 O 7. The crack-healing performance of SiC/Y 2 SiO 5-Y 2 Si 2 O 7 is in the middle of that of SiC/Y 2 SiO 5 and SiC/Y 2 Si 2 O 7. The mechanism of crack healing was identified as the consequence of SiC oxidation into SiO 2 , which accompanies a volume expansion, and outward diffusion of Y 3+ cations caused the formation of Y 2 Si 2 O 7 outer layer. Oxidation of SiC particles within the matrix developed an oxidized zone. Growth of the oxidized zone obeyed the parabolic law, which meant diffusion process in the oxidized zone is the rate-controlling process.

Crack-healing effectiveness was investigated as functions of heat treatment time and temperature on 5 vol% SiC-dispersed Y 2 SiO 5 -based composites. Dense specimens of SiC/Y 2 SiO 5 composite were fabricated by the pulsed current sintering technique. Thermal oxidation for crackhealing was conducted at temperatures ranging from 1000 to 1300°C for from 1 to 24 h in air. Bending tests were carried out at room temperature on samples before and after heat treatment in order to clarify the crack-healing performance. The results show that SiC/Y 2 SiO 5 composites possess a considerable crack-healing ability. The surface cracks with approximately 200 µm in length introduced on the sample surface were disappeared completely after heat treatment at 1300°C for 1 h in air. Mechanism of crack-healing was considered as filling up of cracks by Y 2 Si 2 O 7 oxidation product which is formed by outward diffusion of cations. Bending strength of samples introduced surface cracks after heat treatment was recovered up to the level as high as that of as-sintered samples. [

Crack-healing effectiveness of Y2SiO5-based composites dispersed with 5 vol% SiC particles was investigated. Dense specimens of 5 vol% SiC/Y2SiO5 were fabricated by pulsed electric current sintering technique. Surface cracks were introduced by using a Vickers indenter to be a crack length of approximately 200 μm. Self-healing performance of SiC/Y2SiO5 composites via high-temperature oxidation in air was studied as a function of heat treatment temperature. As a result, surface cracks disappeared perfectly after heat treatment at 1300°C for 6 h in air.

No abstract

This article studied corrosion behavior of steel and sacrificial anode on ship's shell in the clean and polluted water of Thi Vai River at room temperature by mass loss, potentiodynamic polarization and electrochemical impedance spectroscopy methods. The experimental results showed that the life of ship's shell was dropped about two times by wastewater, which discharged into the Thi Vai River. Authors proposed some suggestions to resolve the serious problem.