A Study On The High Temperature Effect Of The Lanthanum-iron-arsenic Ternary System

China not only has a large amount of arsenic-containing iron ore,but also with the development of social economy,the cycle of scrap steel is gradually shortened.Purification,metamorphism and alloying are considered to be the widely used forms of rare earth elements in materials.The unsaturated outer electron layer of rare earth elements has unique structure and strong chemical activity,which can erupt various electronic energy levels.Rare earth elements can react with arsenic to form compounds with high melting point,thus improving the properties of steel such as thermoplastic and mechanical properties.In this paper,the rare earth metal elements lanthanum and arsenic are sealed in a cylinder made of industrial pure iron according to the atomic ratio of gram（1:1,1:2,1:3,1:5）,and at different constant temperatures（1173K,1223K,1273K）,under different constant temperature time（15h,20h,30h）,prepared ternary samples of lanthanum-iron-arsenic.And use the Miedema binary generation thermal model,Toop ternary thermal model,Bramfitt two-dimensional plane mismatch model and related lanthanum-iron binary system indoor test to influence the rare earth element lanthanum in the lanthanum-iron-arsenic ternary system Conducted a systematic discussion and research.The overall detection methods include metallurgical microscope,XRD analysis,thermal field emission scanning electron microscope and energy spectrometer,and the following main research conclusions have been obtained:The thermodynamic behavior of the rare earth element lanthanum in the lanthanum-iron-arsenic ternary system is studied by using the Miedema model and the Toop geometric model.Calculating the enthalpy of mixing the La-Fe-As related binary system and ternary system components,the excess free energy,entropy and excess activity.Within the overall concentration range,the three thermodynamic indicators（enthalpy of mixing,excess free energy and excess entropy）are all negative,and the calculated activity of La or Fe or As has a certain deviation from the theoretical ideal result.The rare earth element lanthanum is added to the cylinder and reacts preferentially with arsenic to form lanthanum-arsenic binary compounds such as La As.The two-dimensional mismatch of the lattice of the compound that lanthanum may generate with iron and arsenic is between 3.19%and 73.69%.In many compounds,the binary Fe₂As can theoretically be used as the non-uniformity of the ternary compound La Fe As,the nucleation base has a very small two-dimensional mismatch of 3.19%.For the microstructure,La-As gram atom ratio is 1:3,for the 1223K temperature,holding time was 20 hours,the distribution is the most uniform and complete.Rare earth element lanthanum,iron and arsenic have not been found to generate ternary compounds under high temperature conditions.The main binary compounds are Fe₂As and La As.Under different experimental conditions,La As₂ and Fe₁₂As₅ are formed.Regarding the chemical stability of ternary high products of lanthanum,iron and arsenic,the samples were statically placed in air,distilled water,weak acid,and weak base.Except for the sample in the weak base,the integrity of the tissue components was destroyed after 144 hours.The sample corrosion is the slowest in the weak alkali environment,and the oxidation corrosion is the most severe in the air environment.