Preparation And Properties Of Corundum-Lanthanum Aluminate Composite Materials

Corundum material possess many excellent properties including high melting point,high hardness,chemical stability,corrosion resistance and other excellent performances,but it's also has poor toughness,high thermal conductivity,difficult to sintering.Lanthanum hexaaluminate and lanthanum magnesium hexaaluminate have the characteristics of low thermal conductivity,high thermal expansion coefficient,strong oxidation resistance,structural stability and thermochemical stability at high temperature.In order to improve the properties of corundum materials,lantha num aluminate was introduced into corundum material as the second phase.In this paper,the preparation of lanthanum aluminate,the effect of lanthanum aluminate on the sintering behavior of corundum,the fracture behavior and thermal shock stability of corundum-lanthanum aluminate composite refractories were systematically studied.The results were as follows:LaAlO₃ precursors containing La-O-Al bond complexes were prepared by low temperature solid state reaction method.The LaAlO₃ phase begins to form at 700?.With the increase of calcination temperature,the grain size gradually increased and the powder particle size decreased gradually.When the temperature rise to 1300?,the lanthanum hexaaluminate precursor transform to lanthanum hexaaluminate with a form plate-like structure,and the pure lanthanum hexaaluminate powders were synthesized at1500?.When the calcination temperature is 1300?,the lanthanum magnesium hexaaluminate with a plate-like structure starts to form.The particle size of the lanthanum magnesium hexaaluminate powders is gradually increased with the increase of the calcination temperature.The addition of a small amount of lanthanum oxide and magnesium oxide can promote the sintering of alumina.La₂O₃ and MgO can partly dissolve in Al₂O₃ lattice in the form of La³⁺(or La³⁺and Mg²⁺)to cause lattice expansion,and the residual parts reacted with Al₂O₃ to form lanthanum hexaaluminate?or lanthanum magnesium hexaaluminate?,which were located at the grain boundary of alumina.Lanthanum hexaaluminate has some influence on the sintering behavior of alumina by introducing through three different methods of La₂O₃,LaAlO₃ and pre-synthesized lanthanum hexaaluminate.When the La AlO₃ is introduced,the materials have a relatively high densification degree.In-situ formation of lanthanum magnesium hexaaluminate in alumina can effectively promote sintering.With the introduction of lanthanum oxide and basic magnesium carbonate,the densification degree of the material is relatively high and the grain development is better.The formation of lanthanum hexaaluminate or lanthanum magnesium hexaaluminate in alumina decreases the thermal conductivity coefficient of the materials and decreases with the increase of the formation amount.Through in-situ formation of plate-like lanthanum hexaaluminate and lanthanum magnesium hexaaluminate in the corundum refractory material,the flexural strength and the hot flexural strength of the material can be improved by 23.2?33.2%and34.5?68.6%,respectively.The enhancement can be attributed to the increasing crack propagation path and transgranular fracture.The formation of lanthanum hexaaluminate and lanthanum magnesium hexaaluminate reduces the thermal conductivity of the materials and increases the elastic modulus of the material,which improves the thermal shock resistance of corundum refractory material.