In this study, melamine-urea-formaldehyde/nano-Al2O3 (MUF/nano-Al2O3) composite gel foams were produced by foaming with CO2 generated by CaCO3 and phosphoric acid. Nano-Al2O3 was introduced to the MUF matrix based on the optimum formulation obtained by the response surface methodology based on Box–Behnken design, and the effects of nano-Al2O3 on the cell structure, apparent density, compressive strength, pulverization ratio, thermal stability, and thermal conductivity were investigated. The results revealed that the introduction of nano-Al2O3 could improve the foaming and mechanical properties of MUF with smaller cell sizes, a narrower cell size distribution, decreased apparent density, higher compressive strength, and a decreased pulverization ratio. MUF/nano-Al2O3-1.5 with the most uniform cell size distribution had a 21% increased compressive strength, but its apparent density and pulverization ratio decreased by 10% and 13%, respectively. Although the char yield decreased with the introduction of nano-Al2O3, MUF/nano-Al2O3 composite foams still presented improved thermal stability under 300 °C, with a thermal conductivity of 0.068 W/(m·K) and a limiting oxygen index of more than 30%. Therefore, MUF/nano-Al2O3 composite gel foam could be employed in coal mines as thermal insulation sealing material due to its better cell structure and mechanical properties.
Shaobo Yang,Chun Guo,Yuan Wang,Jiali Li,Yujie Chen,Sijie Kou,Juanli Deng,Bo Chen,Shangwu Fan
A glass-ceramic derived from a high-yttrium aluminosilicate (HYAS) composition was developed for joining silicon carbide fiber-reinforced silicon carbide (SiC f /SiC) composites. The as-prepared powder exhibited a high softening point (∼1396 °C), good wettability, and a thermal expansion coefficient (3.79 × 10 −6 /K) well matched to that of SiC f /SiC. Dense joints were fabricated at 1420 °C for 60 min, achieving an average lap shear strength of ∼54 ± 2 MPa. The joining mechanism involved crystallization-assisted sintering, liquid-phase densification, and atomic-scale interdiffusion without interfacial reaction layer formation. Hydrothermal corrosion was evaluated in water containing ∼8 ppm dissolved oxygen, approximately three orders of magnitude higher than typical pressurized water reactor (PWR) conditions, to simulate long-term degradation. After 15 days, the joints retained a lap hear strength of ∼37 ± 2 MPa, with corrosion confined to the residual glass phase while interfacial integrity remained intact, demonstrating the promising durability of HYAS glass-ceramic as a durable sealant for SiC f /SiC composites under accelerated hydrothermal conditions.
危险品化学品经营许可证（带存储）