The lamellar preparation of continuous porosity-graded Si3N4 ceramics without obvious interfaces for broadband radome application

Traditional layered broadband radomes are challenging to meet the needs of the high-temperature application, due to thermal mismatch between their layers. In this study, porous Si3N4 ceramics with a novel continuous porosity gradient from 54.7% to 82.4% were achieved by lamellar gel-casting, freeze-drying, and subsequent sintering process. The porosity-graded structure in Si3N4 ceramics shows no failure or cracks after sintering, benefiting from the low shrinkage after sintering at 1900 degrees C with the rapid sintering rate. The continuous porosity-graded structure without obvious interfaces was architected by ice crystal growth during solidification and the growth of rodlike beta-Si3N4 grains across the interfaces during sintering. This approach can be beneficial to designing high wave transmission performance at specific broadband for radome.