Thermal expansion coefficient tailoring of LAS glass-ceramic for anodic bondable low temperature co-fired ceramic application

The Li–Al–Si glass-ceramics were prepared by conventional glass-ceramic fabrication method. The influences of Na₂O content on the sintering property, microstructure, and coefficient of thermal expansion were investigated. The results show that the coefficient of thermal expansion of LAS glass-ceramics can be tailored to match that of silicon by the addition of Na₂O content. Na₂O has a remarkable influence on the crystallinity of Li–Al–Si glass-ceramic. The coefficient of thermal expansion of Li–Al–Si glass-ceramic is thus tunable between that of glass phase and crystal phase. The Si–O bond length change in stretch vibration modes introduced by Na₂O also contributes to the variation of coefficient of thermal expansion of the Li–Al–Si glass-ceramics. The coefficient of thermal expansion of the Li–Al–Si glass-ceramic with 1.5 wt% Na₂O addition is about +3.34 ppm/°C at 350 °C and shows a good compatibility to that of silicon in a wide temperature range, which makes it a promising candidate for anodic bondable low temperature co-fired ceramic substrate applications.     

Improving sealing performance of borosilicate glass-ceramics for solid oxide fuel cell applications: Effect of AlN

Glass and glass-ceramic are one of the key sealing materials for solid oxide fuel cells (SOFCs) and they need to meet stringent requirements for long-term operation at high temperatures. Here, we report for the first time the incorporation of aluminum nitride (AlN) dopant into borosilicate glasses and glass-ceramics so as to tailor their basic properties and sealing performance. The results show the AlN-doped glass-ceramics exhibit remarkably enhanced thermal stability and chemical compatibility when adhering to Y₂O₃-ZrO₂ electrolyte. The electrical conductivity is also significantly reduced by the AlN doping, and the conductivity of 15 wt.% AlN-doped glass-ceramic is nearly two orders of magnitude lower than that of the undoped glass-ceramic. This work indicates that AlN doping is an effective strategy to obtain a reliable borosilicate glass-ceramics for SOFCs.     

Dynamic oxidation protective behaviors and mechanisms of HfB2-20wt%SiC composite coating for carbon materials

HfB₂-20%wtSiC composite coating was prepared by liquid phase sintering method. After modification of HfB₂ phase, the initial oxidation consumptions of the SiC coated samples were delayed from 500 ℃ to 800 ℃. Due to the higher oxidation activity of HfB₂, the sufficient generated B₂O₃ is capable of inhibiting oxidation consumption of carbon substrate in oxidation activation region (800 ℃-1000 ℃) and fastest oxidation region (1000 ℃-1280 ℃). The enhanced oxidation activity of SiC above 1000℃ leads to the increased generation of SiO₂, inhibiting the evaporation of B₂O₃ through the formation of Hf-B-Si-O glass layer, improving its stability and oxidation resistance above 1000℃. The heterogeneous refractory Hf-Oxides embedded in Hf-B-Si-O glass layer play role of reinforcement phases, restricting generation and spread of cracks. The inerting effect of Hf-B-Si-O glass layer strengthened with the increase of thermogravimetric analysis (TG) recycle oxidation times, indicating promising oxidation inhibition potential of the coating in dynamic aerobic environment.