Study On Si₃N₄ Wave-transmitting Material Fabricated By Reaction-sintering

With the developing of aviation, aerospace and military technology, the various aircraft flying speed getting higher and higher, therefore, we must develop new radome materials that can be used under the worse conditions. Si₃N₄ ceramic is one of the structure ceramic material which has the best comprehensive performance, and its electric, thermal conductibility and mechanical properties are very excellent, it can be used in the oxidation atmosphere at 1400℃and in the neutral or reducing atmosphere at 1850℃around. Therefore, as a potential ultra-high speed of sound missile radome material, Si₃N₄ has been made more and more extensive attention by domestic and foreign scholars.Refering to the materials science theory and domestic and foreign advanced technology, this paper combine the advanced gelcasting technology and low-cost reaction sintering technology at first time, and then exploit their own advantages to overcome the inadequate aspects for prepareing the missile radome materials with traditional preparation methods. With the combination of Si₃N₄ reaction sintering technology and non-pressure sintering technology, we prepared Si₃N₄ wave-transmitting material with adding different proportion silicon nitride in starting silica fume.With the controling parameters in gelation: MAM accounted for 15wt% of suspension liquid, MAM: MBAM is 1:6 in mass, TMAH accounted for 2.0～3.5% of total mass of raw materials powder, 5%Ammonium peroxydisulfate solution(APS) and N'N'N'N-tetramethylethylendiamine(TEMED) as initiator and catalyst accounted for 0.8～1.0vol%, 0.08～0.1vol% based on suspension respectively, gelation at 50～60℃for 30～60 min, we have prepared 50vol% solid content, high-quality Si₃N₄/Si bodies with.It is suggested that the proportion of Si₃N₄ starting powder in raw materials is a very important factor for the Si₃N₄ sintered products performance. When the Si₃N₄ starting powder content is not more than 50wt%, the sintered materials have a high density and low porosity. 35wt%Si₃N₄-5wt%Sintering-additives(SA)-Si sintered samples had the greatest average density 2.08g/cm³; the smallest average porosity 37.85%; the highest average bending strength 108.1MPa. 65wt%Si₃N₄-5wt%SA-Si sintered samples have the best average dielectric constant and dielectric loss value, which is 4.91 and 1.13×10^-2 respectively. changes in law of each group samples' properties. When 35wt%Si₃N₄-5wt%SA-Si samples were sintered at 1450℃, soaking time four hours, the density and bending strength reached to the highest values 2.13g/cm³ and 129.5Mpa respectively. At the same time, the nitrification results of silica improved effectively with sintering temperature increaseing. when the sintering temperature was over 1450℃, soaking time four hours, silica power in green bodies has a good nitrification which can meet the experimental equirement for Si₃N₄ preparation.