Thermoelectric β-FeSi₂ Prepared By Self-propagating High Temperature Reaction Synthesis And Annealing Treatment

For energy and photoelectric conversion,β-FeSi₂ is a well known new material.This disilicide is non-poisonous,highly resistant against oxidation.Raw material source is abundant and the price is very cheap,better absorbing ability for infrared rays.Academic photoemission obtaining efficiency is high;its characteristic section happens to correspond with transparence of silicon.The section is FDDI communications important wave band,so it is propitious to combine a new type of an apparatus with FDDI.Currently,we have the following preparation methods ofβ-FeSi₂ materials:Solid Phase Epitaxial,Mechanical Alloying,Ion Beam Synthesis,Rapid Solidification,Compression Method,Spark Plasma Sintering(SPS),Chemical Vapor Transport and Temperature Gradient Solution Growth.Using the above methods to makeβ-FeSi₂ thermoelectric materials,it needs a long production cycle,great energy consumption and high cost.Therefore,it is not suitable for mass production,and we have the necessity to seek better ways.Since the Self-propagating High Temperature Reaction Synthesis has many advantages:rapid reaction,save energy and easily improve product purity,great applicability,and small investment,we study the single-phase P-FeSi material with Self-propagating High Temperature Reaction Synthesis and Annealing Treatment.The technical can improve the practical application value ofβ-FeSi₂ and make it used widely.Moreover,it can bring about direct investment in manufacturing production and lower costs.With such materials as Powders of Fe,Powders of Si,KNO₃;we have a study of the mechanical activation process,the influence of different dosage of KNO₃ on the amount of FeSi₂ and the effect of annealing treatment on combustion synthesis products.The study shows that:in the process of the ball mill mixing,the reaction powders store some mechanic energy.In the same conditions,the original powders are milled for 3 hours through Self-propagating High Temperature Reaction Synthesis.That material is the most ideal. Compared with the ball mill 1h combustion synthesis products,theα-FeSi₂ content improves, and the Eutectic chondrules size ofε-FeSi andα-FeSi₂ also increases.KNO₃ can induce the production of iron silicon metal compounds.Different dosage of KNO₃ are responsible for different products of self-propagating high-temperature synthesis.With further intensified combustion synthesis,the amount ofα-FeSi is synchronous growing;when the dosage reaches 40%,in the combustion synthesis products,the amount ofα-FeSi₂ is obviously improved,but without anyβ-FeSi₂..Put Fe-Si combustion synthesis products with different dosage of KNO₃ in a vacuum furnace,and give them 880℃annealing treatment for 2 hours, allα-FeSi₂ will be turned intoβ-FeSi₂,but there is no influence onε-FeSi.In the whole process.the dosage of KNO₃ is very important,which not only affects how muchα-FeSi₂ you will find in combustion synthesis products,but also indirectly influences the amount ofβ-FeSi₂ after heat treatment.The powders and compacts of combustion synthesis products go through ball milling and anneal processes.Driven by the reduction of surface free energy, particles are combined into the internal porous morphology.With such materials as powders of Fe,powders of Si,KNO₃,we adopt a unique method of controlling combustion heat release to study the structural transformation process of the combustion synthesis Fe-Si intermetallic compound.The reaction of Fe-Si intermetallic compound synthesized through Self-propagating High Temperature can be roughly divided into the following several processes:the decomposition of KNO₃ and the melting dissolvation of powders of Si and Fe,the growing process of Combustion synthesis Fe-Si eutectic organization and FeSi-FeSi₂ eutectic particle coarsening.Then put forward the idea that the reaction of Fe-Si intermetallic compound through self spreading combustion synthesis can be described as diffusion-dissolution-precipitation.The decomposition of KNO₃ releases a lot of heat,which led directly to the first melting of Si particles,then spreading in the powder billet gaps.The tiny powders of Fe dissolve into the melting Si, intensifying the diffusion.Along with the liquid diffusion,it reaches saturation concentration,which will have Fe-Si eutectic granular separation,causing the formation and growth of eutectic embryos.