Improving the anti-oxidation and water wettability of graphite through the design of coating structure for the preparation of Al2O3–SiC–C castables

SiC‐based lining refractories used in incinerators faced serious hot water vapor corrosion. The pores in SiC‐based refractories played a crucial role in corrosion resistance because both the penetration of water vapor and the expulsion of corrosion products depended on diffusion channels provided by pores. The in situ microporous Yb2Si2O7 bonding phase formed in the SiC bricks after sintering at 1550°C under air atmosphere, which simultaneously decreased the apparent porosity and pore size. The optimization of pore structures reduced the permeability to gases of SiC bricks by 37.5%, which prevented the penetration of hot water vapor into SiC bricks. The microporous Yb2Si2O7‐bonded SiC bricks presented only .15% permanent linear change and showed good thermal shock resistance after corrosion at 1000°C for 100 h under hot water vapor atmosphere. Some SiC particles in the refractories could be adopted as high‐temperature pore‐forming agents; the gaseous oxidation products of SiC bricks, including SiO(g) and CO(g), contributed to the generation of microporous Yb2Si2O7 (pore size ≤5 μm) and SiC whiskers during sintering, which obviously improved mechanical properties and water vapor corrosion resistance of SiC bricks.

Section: Introductionmentioning

confidence: 99%

Improved water vapor corrosion resistance of SiC bricks via in situ formation of microporous Yb₂Si₂O₇ bonding phase

Zhang,

Chen,

Xue

et al. 2024

“…23 Besides, many methods were proposed to improve the mechanical properties of ceramics. 24,25 It is necessary to study the ratio of rare earths to alkaline earths for the production of dense…”

Section: Introductionmentioning

confidence: 99%

“…found that by adjusting the ratio of Y 2 O 3 /MgO, a densified sample with a bimodal microstructure could be obtained, exhibiting a bending strength of 875 MPa and a thermal conductivity of 98.04 W/(m K) 23 . Besides, many methods were proposed to improve the mechanical properties of ceramics 24,25 . It is necessary to study the ratio of rare earths to alkaline earths for the production of dense Si 3 N 4 ceramics.…”

Section: Introductionmentioning

confidence: 99%

Effect of Er₂O₃/MgO ratio on mechanical and thermal properties of Si₃N₄ ceramics

Han,

Liu,

Wang

et al. 2024

Si3N4 ceramics with high mechanical properties and thermal conductivity, exhibiting fine and bimodal microstructure, were prepared by adjusting the Er2O3/MgO ratio and hot‐pressing sintering at 1800°C for 4 h. The microstructure, grain distribution, lattice oxygen content, mechanical properties, and crack propagation process of the sintered bulk samples were systematically investigated. It was found that a low Er2O3/MgO ratio contributed to the densification of Si3N4 ceramics, whereas a high Er2O3/MgO ratio favored the grain growth of Si3N4 ceramics. In this research, the grain size distribution and average diameters as well as their impact on mechanical properties were examined. When the ratio of Er2O3/MgO was 3:1, Si3N4 had a larger average diameter and higher thermal conductivity, but the mechanical properties were somewhat reduced. When the ratio of Er2O3/MgO was 2:2, the sample displayed enhanced mechanical performance, which can be explained by the formation of a bimodal structure. The research indicates that it is feasible to control the microstructure and optimize the mechanical properties of Si3N4 ceramics by tailoring the sintering additives.

“…Additionally, due to the low-melting point, solubility in water, absence of impurities, and low price introduced during the preparation process of molten salts (such as chlorides and fluorides), they have been widely used in the preparation of various products. [35][36][37][38] Notably, molten salt assisted method exhibits favorable results, especially in the field of ceramics. Flaky α-Si 3 N 4 and Si 3 N 4 whiskers were prepared in the molten salt environment of NaCl-NaF.…”

Section: Introductionmentioning

confidence: 99%

Preparation of high‐purity α‐Si₃N₄ powder via multifunctional synergistic catalysis and pretreatment method

Yuan,

Zhao,

Sun

et al. 2024

At present, the Si3N4 powder prepared is not pure enough. Therefore, this work introduces a novel method of preparing high‐purity α‐Si3N4 powder. Si3N4 powder with high α phase content was prepared via a unique two‐stage temperature‐rise (TSTR) process, using KCl and metal Co as dual catalysts through low‐temperature pretreatment for silicon powder and subsequent high‐temperature nitriding reaction. Molten KCl insulates silicon particles in three contact modes during low‐temperature pretreatment, promoting complete and uniform nitriding and absorbing the heat released during the reaction. In addition, Co forms a Co–Si liquid phase, causing the reaction to transition into a gas–liquid–solid reaction with lower potential energy, thereby reducing the reaction temperature. Through the synergistic effect of the two catalysts and optimized unique TSTR process, Si3N4 powder can be obtained at 1250°C, boasting a remarkably high α phase content of 99.1%, distinguished by its layered, needle‐like, and spherical structures. The detailed experiments first provide a comprehensive explanation of the growth mechanism of α‐Si3N4. This innovative method for preparing Si3N4 powder offers a new approach to the facile production of high‐purity phase ceramic powder.