The Study Of Microstructure Characteristics And Performances For Low Carbon MgO-C Refractories With The Ni Catalysis

In this paper,low-carbon MgO-C refractories were studied.The phase composition and microstructure evolution of specimens were analyzed by techniques of X-ray diffraction,scanning electron microscope,transmission electron microscope and energy dispersive spectrometer.The cold modulus of rupture,cold crushing strength,force-displacement curves,flexural modulus,and hot modulus of rupture and thermal shock resistance of specimens were tested.The effects of antioxidants?Mg-Al alloy and metallic Si powder?and the content of catalyst?Ni?NO₃?₂·6H₂O?on mechanical properties and microstructure characteristics of low-carbon MgO-C refractory samples were studied.The growth mechanism model of in-situ MgO whisker formation under the action of catalyst was established.The effects of Ni?NO₃?₂·6H₂O catalyst and antioxidants of Mg-Al alloy and metallic Si powder addition on the phase composition,microstructure evolution,mechanical properties and thermal shock resistance of the low-carbon MgO-C matrix specimens were studied.The results show that after 1200oC heating treatment,the Mg-Al alloy has been oxidized and turned into MgAl₂O₄ through reaction between Al₂O₃ and MgO,it is also found that MgAl₂O₄ whiskers with a diameter in the range of 400-500 nm and aspect ratio in the range of 30-40 were formed,and a Ni nanoparticle is located on the top of the MgAl₂O₄ whisker.After 1400oC heating treatment,some new phases of Al N and Si C whiskers were formed while metallic Si was totally disappeared.At the same time,the quantity of MgAl₂O₄ formation was increased significantly;however,there were no significant change both on the diameter and the aspect ratio of MgAl₂O₄ whiskers.When the amount of Ni?NO₃?₂·6H₂O addition is over 0.4wt.%,the thermal shock resistance and fracture toughness of specimens are improved significantly,which should be contributed to the formation of MgAl₂O₄ whiskers,AlN phase and SiC whiskers.The microstructure characteristics and mechanical properties of low-carbon MgO–C matrix specimens with Ni?NO₃?₂·6H₂O catalyst and antioxidants of Mg-Al alloy addition were investigated.The results indicated that in a reducing atmosphere,MgO whiskers and carbon nanotubes could be generated within low-carbon MgO–C matrix specimens at 1200oC.After cooked at 1400 oC,the length and diameter of MgO whiskers have no significant change.The magnitudes of the cold crushing strength,the cold modulus of rupture,the fracture displacement,and the residual cold crushing strength of the specimens are increased by 47%,66%,8% and 26%,respectively.The specimens with 0.6wt.% Ni?NO₃?₂·6H₂O addition result in better overall property.It is found that under the experimental condition,the particles of nano Ni derived from catalyst precursor of Ni?NO₃?₂·6H₂O encourage the formation of liquid phase,which can dissolve Mg?g?and CO?g?effectively.The MgO whiskers were generated via dissolution-diffusion-precipitation mechanism.The growth process of MgO whiskers should follow V-L-S growth mechanism.The microstructure and mechanical properties of the low-carbon MgO–C bricks with Ni?NO₃?₂·6H₂O catalyst and antioxidants of Mg-Al alloy addition were investigated.The results show that carbon nanotubes and MgAl₂O₄ whiskers could be generated within the matrix of specimens under a reduced atmosphere at 1200oC.After 1400oC heating treatment,the diameter of CNTs was increased and the length of CNTs was decreased.At this temperature,the quantity of MgAl₂O₄ whiskers was increased.The specimen with 0.6wt.% Ni?NO₃?₂·6H₂O addition exhibits better comprehensive property.