| TiB2 material with good electrical conductivity,aluminum liquid wetting and anti-corrosion resistance to molten aluminum electrolytic become inactive in recent years to develop a hot cathode material.TiB2 composites based on its exposed aluminum industry practice in poor adhesion,easy to fall off and so on, using plasma spraying TiB2 inert preparation of new cathode coating on the carbon cathode,and the spraying and coating performance research.(1) Obtained by orthogonal design influence TiB2 coating bond strength of the primary and secondary factors as: auxiliary gas (H2) flow (ie spray voltage)> main gas (Ar)flow>spraying distance>spray current;the optimum parameters are:spray voltage: 72V(i.e.,H2 flow rate 224L/h),the primary gas (Ar) flow rate:1800L/h,spraying distance:90mm,spray current:550A. Through experiments it is concluded that:After parameter optimization TiB2 coatings partially melted lower than the column area, effectively reducing the large number of holes and pores,coating the internal organizational structure is more compact, more uniform particles, porosity decreases, lower resistivity, conductivity changed for the better, the bond strength significantly increased; wetting angle difference caused by oxidation products of TiB2 droplet spreading, flat with optimization, improved wettability is good.(2) Four point probe method is used to measure the coating resistivity, through SEM explores the spray particle size influence on TiB2 cathodic coating resistivity, further explores the spraying powder particle size of TiB2 coating bond strength and the influence law of porosity and hardness etc.The following conclusions: ①TiB2 powder size too large or too small are detrimental to the conductive properties of the coating, with decreasing particle size TiB2 powder coating resistivity showed a decreasing tendency to increase after the first, when the powder particle size speed and impulse when -325～+400 mesh,plasma flame stream longerjet energy concentration,good TiB2 particles deform,TiB2 droplet impact substrate surface is large,crystallization and tile better porosity compared to 0.019Ω.cm.②The oxidation of TiB2 particles in the coating can lead to coating porosity increases, the density decreased.TiB2 particle size distribution, the greater the degree of internal oxidation coating, the greater the organization bulky and uneven;The smaller the particle size distribution,the smaller the degree of oxidation,dense and uniform coating.Granularity when -325-+400 mesh is least oxide coating, oxidation products impact on the porosity is low,minimum coating resistivity, the conductivity is best.③TiB2 resistivity of the coating increases with increasing thickness; with decreasing particle size,the bonding strength first increases and then decreases particle size of-325-+400 mesh when the bonding strength up to 7.4MPa,spray coating the best powder particle size;with decreasing particle size,porosity coating monotonically decreasing,while the smaller dispersion of micro-hardness value,high average microhardness.(3) Preparation of the optimal parameters and the optimal size of TiB2 cathode coating,Determination of the basic properties of the coating results:①nder the dual optimization TiB2 coating particles forming better combination between the inner coating layers closer; TiB2 coating average porosity of 12.23%;average bond strength of 7.63MPa;average microhardness of 817.6HV;average resistivity of the coating at room temperature:0.108Ω.cm;double coating optimize overall performance is more excellent.②TiB2 coating is increased from 25 ℃ to 200 ℃ process,The resistivity reduce large range;After 400℃ resistivity increases gently;800℃ when the resistivity of TiB2 coating 0.3174Ω.m.③TiB2 coating layer after 6 times of psychro-thermal cycles started to crack, damage phenomenon;electrolyte coating after 48h after corrosion by hot molten cryolite coating surface erosion caused by slight corrosion, corrosion coating after pyramid-shaped particles in part,but the internal structure of dense TiB2 coating thickness variation measured rate 0.00033mm/h,good corrosion resistance. |
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