Preparation Of Transition Group Catalysts And Its Effect On The Mechanical Properties Of MgO-C Refractories

The transition catalyst was added to the MgO-C refractory binder phenolic resin,and various characterization methods such as X-ray diffraction analysis,scanning electron microscopy,transmission electron microscopy,infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize the catalyst and phenolic resin.The cold modulus of rupture,cold crushing strength and thermal shock resistance of MgO-C refractory samples were tested.The mechanism of synthesizing carbon nanotubes by pyrolysis of phenolic resin was investigated.The effects of catalysts（Fe-Mo catalyst and Fe-Ni catalyst）on the structure and mechanical properties of MgO-C refractories were investigated.The main findings are as follows:The Fe-Mo catalyst was prepared by co-precipitation method,and its effect on the synthesis of carbon nanotubes by pyrolysis of phenolic resin was investigated.The results show that the dispersibility of the Fe-based catalyst is improved with the addition of the promoter Mo.At the same time,the outer electron structure of Fe changes,some electrons are transferred from Fe to Mo,and Fe is in an electron deficient state,which improves the decomposition performance of the catalyst for hydrocarbon gas.In addtion,the catalytic activity of Fe-Mo catalyst increases first and then decreases with the increase of Mo content.The catalytic activity is optimal when the molar ratio of Fe-Mo in the precursor is 1:2.The initial temperature of carbon nanotubes synthesized by pyrolysis of phenolic resin Fe-Mo catalyst is700-800°C,and the diameter of carbon nanotubes is about 60 nm.As the pyrolysis temperature increases,the length of the catalytically synthesized carbon nanotubes increases remarkably,and the hydrocarbon gas generates carbon nanotubes according to the decomposition-dissolution-diffusion-precipitation process.The Fe-Ni catalyst with core-shell structure was prepared by electroless nickel plating,and its effect on the synthesis of carbon nanotubes by pyrolysis of phenolic resin was studied.The results show that the composition of the catalyst after electroless plating is Fe₂O₃ and amorphous Ni.The composition of the catalyst after annealing in reducing atmosphere evolves into Fe₃O₄ and crystalline Ni.On the one hand,Ni is uniformly distributed on the surface of the particles,and the dispersibility of Ni can be improved to exhibit the catalytic activity of Ni.On the other hand,the interaction of Ni and Fe on the core-shell interface causes electrons to transfer from Ni to Fe,while Ni is in an electron-deficient state,which improves the catalytic synthesis of carbon nanotubes by Ni.The experimental results show that the performance of Fe-Ni catalyst with core-shell structure is better than that of metal Ni catalyst with nanometer scale.Further,the initial temperature of the carbon nanotubes synthesized by the Fe-Ni catalyst is 500 to 600°C,and the diameter of the carbon nanotubes is about 50 nm.The length of the carbon nanotubes increases as the pyrolysis temperature increases.When the temperature exceeds 1000°C,the partial pressure of the hydrocarbon gas in the atmosphere is lowered to cause the diameter of the carbon nanotube to increase to about 160 nm.The above Fe-Mo and Fe-Ni catalysts were added to a low carbon MgO-C refractory matrix to study their effects on the structure and mechanical properties of MgO-C refractories.The results show that the Fe-Mo and Fe-Ni catalyst samples have more carbon content than the catalyst-free samples,and the main source is the catalytically synthesized carbon nanotubes.The content of carbon nanotubes synthesized by adding Fe-Ni catalyst is better than that of Fe-Mo catalyst.MgAl₂O₄whiskers were formed.The content of carbon nanotubes synthesized by adding Fe-Ni catalyst is better than that of Fe-Mo catalyst.It shows that Fe-Ni has better effect on improving the graphitization level of phenolic resin after pyrolysis.The bulk density of the MgO-C samples after heat treatment at 1200°C was higher than that of the catalyst-free samples.Compared with the non-catalyst sample,the cold modulus of rupture,cold crushing strength,hot modulus of rupture and residual cold crushing strength of the sample added with 0.5 wt%Fe-Ni catalyst after heat treatment at1400°C increased by 23.2%,33.4%,13.0%and 39.7%,respectively.