| MnZn ferrite ceramics have a wide application today with the rapid development of 5G microwave technology because of its magnetic properties of high permeability and low loss.In the process of using ceramic materials,it is inevitable to encounter some problems because of its own brittleness and easy to fall off with other materials,especially metal materials.But by surface modification,these problems can be solved,and even some characteristics of ceramic materials can be improved.Ti oxide is rich in kinds and different in properties.It is widely used as a functional material.Al2O3 ceramics have unique properties such as corrosion resistance,high temperature resistance and oxidation resistance.It is used in various fields from daily life to aerospace.At present,it is one of the most widely used materials in oxide ceramics.The study of obtaining Ti oxide films on Al2O3 ceramics has a certain foundation,but how to control the film growth and post-treatment conditions to accurately control the composition of Ti oxide films still has its research value.316L stainless steel is an austenitic stainless steel material doped with molybdenum element.It has an irreplaceable position in chemical materials,industrial production and other industries.Stainless steel will be corroded by molten salt when used in molten salt energy storage containers.But some of its corrosion products have special properties such as catalytic properties.So it can be considered to use the interaction between molten salt and stainless steel to prepare some structures with good catalytic performance.However,molten salt reaction is an efficient method to realize the surface modification of materials because of the advantages of rapid thermal diffusion in high-temperature environment,low cost,simple operation and outstanding effect.In this paper,the surface of MnZn ferrite and Al2O3 ceramics was successfully modified by molten salt reaction in chloride environment to obtain Ti oxide coating.The effects of film properties and experimental conditions were explored,and the mechanism of film formation was analyzed.Meanwhile,using molten salt reaction,the Ni-Fe nanowire structure with catalytic effect was obtained by 316L stainless steel surface modification.The related electrochemical catalysis was tested,and the mechanism of catalytic effect obtained by surface modification was analyzed.Finally,the future development and application of molten salt reaction are considered and prospected.The specific work of this paper is as follows:(1)Using NaCl-KCl-K2TiF6 molten salt system,adding elemental Ti powder as Ti source,the surface modification of MnZn ferrite can be realized in glove box inert gas environment,and the interface structure of Ti oxide/MnZn ferrite can be obtained.The thickness of Ti oxide film increases from 10 μm to 40 μm and tends to be saturated.The composition of Ti oxide is semiconductor TiO2 at first,and changes to conductive phase Ti2O3 after the immersion time of molten salt increases to 20 min.The corresponding surface resistance decreases from 103 Ω/□ to 10-1 Ω/□,which has the potential to combine with metal electrode.The corresponding film formation mechanism is also analyzed:using the disproportionation reaction of Ti and the thermal diffusion in molten salt.The ferrite surface modification by molten salt reaction has the advantages of low cost,good effect and simple operation.It provides a new technology of ferrite surface coating and has the prospect of industrialization.(2)Using NaCl-KCl-K2TiF6 molten salt system,adding elemental Ti powder as Ti source,the surface modification of A12O3 can be realized in glove box inert gas environment,and Ti2O film can be formed on the surface of Al2O3.As the immersion time of molten salt increases from 1 min to 30 min,the smaller Ti2O particles increase and agglomerate,and the proportion of Ti increases from 8%to 20%and tends to be saturated,and the resistance increases from 7 Ω to 22 Ω.Then,the changes of surface modified Al2O3 after annealing at different temperatures were studied.The particle size of Ti oxide decreased significantly after annealing,and the content of O element increased significantly after annealing.Next,the effects of annealing at different temperatures in nitrate environment were studied.With the increase of temperature,the smaller particles also gathered and wrap the larger particles,and the content of Ti showed an increasing trend.At first,Ti2O was transformed into TiO,and finally into TiO2.Finally,the influence mechanism of nitrate and annealing treatment on the surface modification of Al2O3 by molten salt reaction was analyzed and the characteristics of surface modification of materials by molten salt reaction are further understood.(3)Using NaCl-KCl molten salt system,the surface of 316L stainless steel was modified in boron nitride crucible under atmospheric environment.After molten salt corrosion modification,nanostructures which has the potential of electrochemical catalysis were obtained on the surface of stainless steel.Besides,the effects of molten salt modification conditions such as temperature,modification time and voltage on the formation of nanostructures were studied.The output of nanostructures can be increased by temperature rise,modification time increase and voltage supply.The principle of nanostructure formation is further explored:because of the different electronegativity of Ni,Fe and Cr,Cr will first release in molten salt environment and forms a large number of vacancies on the material surface.Then,Ni and Fe will release and tend to rearrange in a certain direction,so as to form nanostructures.Because nanostructures have many vacancy defects,large specific surface area and high surface activity,they have good catalytic potential.(4)After summarizing the three works,we have obtained some comprehends and understandings on the surface modification of materials by molten salt reaction.Molten salt reaction has the characteristics of high-temperature and liquid solution environment,which can promote the flow and diffusion of atoms and is conducive to the surface modification of materials.Moreover,the cost of molten salt is low and there are no special requirements for materials.These characteristics are very suitable for mass production in industry.And the effect of surface modification can be simply controlled by changing the conditions such as temperature,time and molten salt composition ratio,so as to achieve the expected goal. |
