Phase Evolution And Nitrided Bonding Properties Of MgSiN₂/Si₃N₄ In MgO-C Refractories

MgO-C refractories are widely used in steel smelting,high-temperature furnace lining and other fields due to their excellent thermal shock resistance and erosion resistance.However,the presence of carbon in MgO-C refractories results in poor oxidation resistance,and how to improve the oxidation resistance of MgO-C refractories has been a research hotspot.MgSiN₂ has many excellent properties such as high hardness,high thermal conductivity,good fracture toughness,good thermal shock resistance and oxidation resistance up to 920 ?.Based on these properties of MgSiN₂,an attempt was made to add MgSiN₂ to the MgO-C refractory system and then studied its influence on the phase evolution,microstructures and physical properties of MgO-C refractory.This article first explored the preparation mechanism of MgSiN₂ powder and studied the effects of many factors such as molten salt system,additives,firing temperature and raw material ratio on the preparation of MgSiN₂ powder.Then the influence of sintering atmosphere on the properties of MgO-C refractories was investigated and the coupling relationship between the carbon-embedded atmosphere and nitrogen atmosphere on the phase reconstruction?MgSiN₂,Si₃N₄,etc.?and properties was revealed.Finally,the mechanism of the effect of MgSiN₂ on the properties of MgO-C refractories was clarified.The results showed that:?1?The reaction conditions had a great influence on the preparation of MgSiN₂ powder.The purity of the powder was higher when Na Cl-KCl was used as molten salt system,Y2O3 was used as additive,the sintering temperature was 1250 ? and the molar ratio of magnesium powder to Si₃N₄ is 3.5:1.Excessive sintering temperature would cause magnesium thermal reduction reaction in the system,affecting the purity of MgSiN₂ powder.?2?The sintering atmosphere had a significant effect on the densification process of MgO-C refractories.The samples prepared under the carbon-embedded atmosphere and the nitrogen atmosphere had similar amounts of liquid phases,the main factor affecting the densification process was the solid phase reaction process.Under the nitrogen atmosphere,more ceramic phases?such as Si₃N₄,Si C?were formed in the sample,which could obviously promote the solid-phase reaction.The columnar Si₃N₄ was more effective than the bulk Si₃N₄ in improving the mechanical properties of the sample,while the whisker-like Si C could form a network structure inside the sample to promote the densification of the material.?3?When MgSiN₂ powder was added to the MgO-C refractories,MgSiN₂ powder had a significant effect on the reactivity of Si and inhibited the reaction between Si and C to form SiC,which resulted in a reduction in the densification of MgO-C refractories and then affected the physical properties of the material.