The Effect Of Aluminum Source On The Structure And Mechanical Properties Of Solid-phase Synthesized Magnesium Aluminum Spinel Materials

A synthetic magnesium aluminum spinel materials have the advantages of high melting point,low thermal conductivity,good thermal stability,good slag resistance,strong alkali corrosion resistance,and good chemical stability.There are some questions in the preparation process,for example,high cost of raw material,high sintering temperature,high energy consumption,low density and low strength.In order to reduce the cost of material synthesis and improve the sintering performance and strength of the material,and to obtain excellent magnesium aluminum spinel products,this paper has conducted a systematic study on magnesia-aluminum spinel materials with different raw material ratios,mainly including the following three parts:（1）In order to explore the sintering performance and strength mechanism of spinel materials,alumina is used as the aluminum source to prepare spinel materials with different mixture ratios.The molar ratios of Al₂O₃and MgO are respectively 3:1,1:1 and 0.2:1,the properties of three materials（aluminum-rich spinel,magnesia aluminum spinel,and magnesium-rich spinel）and the mechanism are studied.（2）In order to reduce the cost of raw materials,bauxite is used as an aluminum source to prepare spinel materials with different mixture ratios.The spinel materials prepared by Al₂O₃and MgO with the molar ratios of 3:1,1.5:1,1:1,0.6:1 and 0.2:1 are studied to explore the feasibility of bauxite.（3）In order to obtain the products with relatively low cost and good performance,bauxite and industrial alumina are used as aluminum sources to adjust the relative content of impurities in the raw materials.Taking SiO₂as an example,accounting for 4%and 2%of the total mass of the aluminum source,the influence of the relative content of impurities on the properties of spinel materials is researched.The samples of different components are prepared by solid-phase sintering method,and the density and apparent porosity are measured to analyze the densification of the materials,and the flexural strength is tested to study the mechanical properties of the materials.The elements,phases and microstructures of the materials are analyzed by EDS,XRD and SEM.The results are as follows:（1）Among the three spinel materials prepared by using alumina as aluminum source,magnesium aluminum spinel materials have the best densification,followed by magnesium-rich spinel,and aluminum-rich spinel is the worst.Sintered at 1550℃,the porosity and flexural strength of magnesium aluminum spinel are 0.45%and 112.62 MPa,respectively.（2）After the materials prepared by bauxite as the aluminum source are sintered at 1400-1500℃,the magnesium aluminum spinel and aluminum-rich spinel samples have good densification,while the magnesium-rich spinel samples have poor densification.The flexural strength of the magnesium aluminum spinel samples is greater than that of the aluminum-rich spinel samples,which is greater than that of the magnesium-rich spinel samples.The flexural strength of the magnesium aluminum spinel samples sintered at 1450℃reaches the maximum（106.48 MPa）.（3）Bauxite and industrial alumina are used as aluminum sources to prepare the spinel materials.When SiO₂accounts for 4%of the total mass of the aluminum source,the flexural strength of the aluminum-rich spinel materials sintered at 1450℃is the maximum（205.4 MPa）;while SiO₂accounts for 2%of the total mass of the aluminum source,the flexural strength of the magnesium aluminum spinel materials sintered at 1550℃is up to the maximum（133.41MPa）;while SiO₂accounts for 4%of the total mass of the aluminum source,the flexural strength magnesium-rich spinel materials sintered at 1550℃is the maximum（101.12 MPa）.（4）The densification of the two aluminum-rich spinel materials prepared with bauxite and alumina as the aluminum source are better.Compared with the aluminum-rich spinel materials prepared by bauxite or alumina as the aluminum source,the flexural strength of the former is stronger.The densification of the two magnesium aluminum spinel materials prepared by bauxite and alumina as the aluminum source are better,and their maximum flexural strength is higher than that of the magnesia aluminum spinel materials prepared with bauxite or alumina.Magnesium-rich spinel prepared from bauxite has good densification at1550℃,with the maximum flexural strength of 113.24 MPa.Compared with other magnesium-rich spinel materials,it has the highest flexural strength.