Surface cleanliness of steel is important in avariety of applications. Any time a metal surface isinvolved in a reaction or process,the characteris-tics of the surface can have a great influence.These processes include electroplating,chemicalplating,phosphating and painting. In any of theseprocesses a poorly prepared,or otherwise" dirty"surface,may have adverse effects on the quality ofthe final product.Electrocleaning is a fastand effective cleaningprocess used in metal pretreatment,especially inpreplate cycles.The work being processed may beused as anode or cathode,or periodic reverse elec-trode. Typical reverse electrocleaning ( PR) set-tings include1 0 sec cathodic then 1 0 sec anodic,etc. Passing large amounts of current through thesolution to the work piece results in intense bub-bling on the surface. This bubbling causes a scrub-bing action which literally knocks off contaminantsfrom the surface. Furthermore,there isa chemicaleffect associated with the high current density atthe interface<1> .Anodic cleaning is desirable because the posi-tive charge creates an oxidizing condition on thework piece.This is advantageous because it pre-vents the deposition of metals from the bath. Itfurther acts to remove more active non- ferrousmetals or oxides which may be present on the sur-face,and may prevent buildup of“smut”on thesurface.Finally,hydrogen is notabsorbed into themetal during anodic electrocleaning.But oxygenon an anode makes metal coloured or passivated.In some cases,the metal surface needs to be acti-vated.Cathodic electrocleaning also has some advan-tages.The scrubbing action of the bubbles is moreeffective because twice as many are formed com-pared with anodic cleaning.This is a direct conse-quence of the fact that hydrogen is monovalentwhile oxygen is divalent.The negatively chargedsurface tends to repel organic materials in the solu-tion which frequently have a net negativecharge<2 > .However high strength steel used onplane construction material is sensitive to hydrogenbrittleness.For high strength steel,it is difficultto remove hydrogen absorbed by short- term anodeelectrolysis,so cathodic and typical PR electro-cleaning are not suited<3> .The purpose of this investigation is to studypulse electrocleaning:first,the effectof pulse cur-rent frequency and current density on the cleaningeffectiveness and hydrogen permeation,and thenthe description of cyclic voltammagramsto evaluatesurface cleanliness<4 > .1 Experimental Method1 .1 Specimen preparationAll samples were prepared from batch an-nealed drawing quality steel.Sampleswere shearedto a size of( 2 .2± 0 .0 1 ) cm× ( 2 .2± 0 .0 1 ) cm.Each sample was degreased by thorough rinsingwith acetone three times.After degreasing,thesamples were further cleaned using acetone in aSoxhlet stripping apparatus for two times.Eachtime is for four hours.The back and edges of thesamples,as well as the lead strips,were stoppedwith insulating lacquer.Finally,the sample sur-faces were intentionally contaminated with a 1 0microliter aliquot of a 1 0× 1 0 - 6 solution ( byweight) of rolling oil in toluene.1 .2 Cleaning conditionsThe electrocleaning conditions can be seen inTable1 .In all cases the total cleaning time wasmaintained at four seconds.Pulse cleaning wasdone using a square wave.The power source wasapplied ascurrentsource and was of the same mag-nitude in both the anodic and cathodic cycles.Thepulse frequency was0 ,0 .2 5 ,0 .5 ,5 ,1 0 ,2 0 and1 0 0 Hz.The current density was1 0 0 and 2 0 0m A/cm2 .The electrocleaner formulation has highconductivity( 35 g/L Na OH) .In addition to these cleaning cycles,a sample( No.1 1 ) which had been intentionally contaminat-ed but not electrocleaned was evaluated as a base-line for contamination.A sample ( No.1 2 ) whichhad been cleaned in Soxhlet but not contaminatedas a baseline for cleanliness. A polished sample( No.1 3) was evaluated as a comparison for partic-ular treatment.1 .3 Evaluation of surface chemistry and clean-liness( 1 ) C
More abstracts about the 脉冲频率和电流密度对钢板表面洁净度和渗氢的影响(英文)