Mechanism Of High Temperature Phase Transformation And Interfacial Migration Of Tourmaline Particles And Their Effects On Ceramic Properties

Tourmaline is widely used in various fields with its good infrared radiation and piezoelectric properties.However,due to the special high-temperature heat-change behavior of tourmaline,the application of tourmaline is restricted to some extent.In order to expand the application of tourmaline,the characteristics of phase transition,interfacial behavior and ion transport mechanism in the process of schorl and dravite were studied in this work.At the same time,the effect of rare earth on the high temperature phase transition of tourmaline was explored by combining cerium oxide with schorl.The influence of the phase transition behavior of tourmaline on the ceramic matrix was also analyzed by the preparation of tourmaline ceramics.The results show that the factors that affect the high temperature phase transition of tourmaline are heat treatment temperature,holding time and phase transition medium.The high temperature phase transition of tourmaline occurs in the solid state,which belongs to the non-homogeneous reaction.The transfer of energy and matter is carried out at the interface of the phase.The temperature of the tourmaline is destroyed,the X and Y metal cations are broken.Interface at the spread of the new phase of the nucleation,to provide the basis for growth.When the schorl is kept at850°C for 1 h,the bridging oxygen between the Si-O tetrahedra is disconnected to form an island structure.The free metal cations are connected to the non-bridged oxygen in the Si-O tetrahedron and Al-O octahedron,then mullite has been formed,1000°C insulation 1 h,the schorl all converted to mullite.When dravite is kept at850°C for 1 h,Si-O tetrahedral composition of the six-ring by Mg²⁺connected to form cordierite,950°C insulation 1 h,dravite completely transformed into cordierite.The cerium nitrate,which is attached to the surface of the tourmaline particles,produces cerium oxide under the action of high temperature,and the cerium atoms can enter the lattice of the tourmaline crystal,leading to the lattice distortion of the tourmaline crystal,which makes the tourmaline structure more destructible,causing the surface tourmaline.The crystal first undergoes phase change.With the progress of the reaction,CeO₂,which does not participate in the reaction,moves with the surface to the interior of the tourmaline particles.Under the action of the cerium atoms,the tourmaline crystal changes phase by layer,and the newly formed mullite exhibits the structure of the surface nanocrystals.The optimization of the preparation process of tourmaline ceramics.Ingredients?weight percentage?:glass 45%,tourmaline 30%,kaolin 20%,iron tailings 5%.Firing process:heating rate of 10°C/min,firing temperature 900°C,holding time 1 h.Tourmaline in ceramic matrix has high-temperature phase transition,but the phase transition temperature becomes higher.This is due to the high temperature of the ceramic in a large number of liquid phase can be separated from the tourmaline particles,so that the exchange of material at the contact angle of the tourmaline blocked,phase change difficult.Tourmaline can produce high temperature phase mullite at 900°C,which contributes to the occurrence of porcelain reaction,making the ceramic structure more compact and higher.