Effect Of Additives On Solid Phase Synthesis Of Magnesium-alumina Spinel Materials

Magnesia alumina spinel is a kind of synthetic spinel refractory,which is indispensable in the high-temperature industry.However,the synthesis of magnesium-alumina spinel requires a higher sintering temperature and a higher energy consumption,which is easy to cause a waste of resources.In order to promote the development of high-temperature industry,it is necessary to continuously improve the preparation method of magnesium-alumina spinel,so as to make magnesium-alumina spinel at a lower temperature,so as to reduce energy consumption.In this paper,magnesium alumina spinel was synthesized by solid phase sintering with light magnesium oxide and analytical pure alumina as the main raw materials and Al₂O₃:Mg O=2.55:1 mass ratio.Mn O₂,V₂O₅,B₂O₃and H₃BO₃with different contents were added into the mixed raw materials and were sintered in solid phase at 1200℃～1600℃.XRD,SEM,EDS and performance tests were used to analyze the influence of additives on the solid-phase synthesis of magnesium-alumina spinel.The experimental results are as follows:（1）magnesium aluminum spinel can be synthesized with magnesium oxide and alumina as raw materials.Magnesium aluminum spinel with close to theoretical content has been generated before 1200℃,but a high sintering temperature is required.The samples sintered at 1600℃are still in the initial state of sintering.At 1600℃,the bending strength of MA sample was117.63MPa,the volume density was 3.17g/cm³,and the apparent porosity was10.17%.（2）The four additives can promote the synthesis of magnesia-alumina spinel.After the addition of additives,the initial stage of sintering began at 1300℃.Compared with the sample MA without additives,the sintering process was advanced by 300℃,indicating that all four additives could reduce the sintering temperature.The addition of additives can promote the discharge of pores in the sample.Among them,Mn O₂and V₂O₅activated the lattice through the solution defect reaction,provided more channels for internal ion diffusion,greatly increased the ion diffusion rate,and thus promoted the sintering.The optimal addition amount of Mn O₂and V₂O₅was 5%.The average grain size of sample M5 at 1600℃was about 10um,and that of sample V5 was about 9um.After the addition of B₂O₃,the diffraction peak of Mg Al BO₄appeared,and the appearance of such a eumelt accelerated the diffusion of ions and promoted the sintering.The optimal addition amount of B₂O₃was 3%,and the average grain size of sample B3 at 1600℃was 12um.After the addition of H₃BO₃,the boron liquid phase will increase the contact between raw materials,accelerate the diffusion and transfer of materials,and thus promote sintering.The optimal addition amount of H₃BO₃is 7%,and the average grain size of sample HB7 at1600℃is 15um.（3）The four additives greatly improved the performance of the sample.After the addition of the additives,the flexural strength and volume density of the sample were higher than that of the sample MA and gradually increased with the increase of temperature,while the corresponding porosity was lower than MA and gradually decreased with the increase of temperature.Among them,the properties of the samples with B₂O₃and H₃BO₃added increased first and then decreased,because the production of too many liquid phases was mismatched with the thermal expansion of other phases,resulting in defects and decreased performance.（4）Through the above comprehensive analysis,it is concluded that the four additives can promote the synthesis of magnesium-alumina spinel in solid phase:H₃BO₃>B₂O₃>Mn O₂>V₂O₅.