Combination Mechanism Of In-situ Silicon Nitride Bonding MgO Ceramic Composites

Silicon Nitride (Si3N4) has a series of excellent high temperature properties, such ashigh strength, low density, good self-lubrication, wear resistance, thermal shock resistance,good thermal conductivity and so on. It can significantly improve the performance ofrefractory materials. Oxide-Carbon bonded with nitride materials sintered at hightemperature has excellent properties, which are high strength, oxidation resistance, goodslag resistance, thermal shock resistance, and small pollution to steel.Oxide-Carbon-Silicon Nitride refractory is a new-type composite refractory, MgO-Crefractory combined with silicon nitride is one of which. Now the research about MgO-Crefractories combined with silicon nitride is less.This article firstly prepared Si3N4/MgO samples, and observed the interface of Si3N4and MgO by high resolution transmission electron microscopy(HRTEM). Through theobservation, it can be found that in-situ columnar silicon nitride is combined closely withmagnesia particles, and Si3N4lattice fringes and MgO lattice fringes combined directly,also no glass phase in interface, so we can conclude that Si3N4and MgO are bonded bychemical bonds.Based on Material Studio Material simulation software platform, the lattice constantsis optimized by using the first principles method, and the β-Si3N4charge density and bondMulliken population are analyzed. Five kinds of surface structure models:β-Si3N4(1010)-Si, β-Si3N4(1010)-N, β-Si3N4(100)-NSi, β-Si3N4(0001) and β-Si3N4(1120)have been established. The surface models are optimized by molecular dynamics, thesurface structure changes is analysed, and the surface energy is calculated. The resultsshow that β-Si3N4(1010)-Si surface and β-Si3N4(0001) surface have obvious relaxationand reconstruction, surface energy is high and surface is not stable, so the two surfaces areeasily combined with heterogeneous to formate interface; β-Si3N4(1010)-N surface,β-Si3N4(1010)-NSi surface and β-Si3N4(1120) surface are more stable and has lowsurface energy, therefore, have relatively stable surface.Five kinds of interface models have been established, using the appropriate field andmolecular mechanics energy minimization method, the interface structure is optimized.The high-temperature interface structure is simulated with molecular dynamics.Theatomic bonding type and the interface atomic relaxation are analysed, and the ideal workof adhersion is calculated. The simulation results show that the order of the ideal work of adhesion of the structure models is β-Si3N4(0001)/MgO(111)-O＞β-Si3N4(1010)-Si/MgO(001)＞β-Si3N4(1010)-Si/MgO(1120)＞β-Si3N4(1120)/MgO(001)＞β-Si3N4(1120)/MgO(110). The greater the ideal work of adhesion, the higher interface bondingstrength is. The longitudinal relaxation of the atoms which are not involved in thesuspension of the bonding, adjusted the mismatch of the interface, ensured the interfacebalance and coordination between atoms in the interface, improved the interfacial latticedistortion, also enhanced the interface bonding strength.