N80鋼點蝕行為的研究-

1、 27N80鋼點蝕行為的研究姜文軍,陳振宇,郭興蓬(華中科技大學(xué)化學(xué)與化工系,湖北武漢430074摘要采用電化學(xué)噪聲(ECN 法,原子力顯微鏡(AF M 原位觀察,研究了N80鋼在以0.5mol/L NaHCO 3為基礎(chǔ)液加入NaCl 溶液中的點蝕行為。結(jié)果表明,點蝕的噪聲隨Cl -濃度增大,單位時間內(nèi)點蝕特征峰增多,峰值變大,壽命變長;N80鋼表面狀態(tài)的變化與電化學(xué)噪聲譜的特征有明顯相關(guān)性。關(guān)鍵詞N80鋼;電化學(xué)噪聲;原子力顯微鏡;點蝕中圖分類號TG172文獻(xiàn)標(biāo)識碼A 文章編號1001-1560(200708-0027-03收稿日期2007203208基金項目中國石油天然氣集團(tuán)公司中青年創(chuàng)新

2、基金資助項目(04E70140前言點蝕的發(fā)生首先是Cl -在表面活性點的吸附,吸附的Cl -與鈍化膜中的金屬陽離子形成配合物。當(dāng)Cl-濃度超過臨界值后,這種配合物從鈍化膜表面脫附,形成陽離子空位,即亞穩(wěn)態(tài)蝕點的“形核”。這時鈍化膜可能再鈍化造成亞穩(wěn)態(tài)蝕點的死亡?？缀艘部赡芾^續(xù)長大,當(dāng)孔核半徑達(dá)到臨界值后,這個孔核就不可能再鈍化,將成長為真正的孔蝕1。電化學(xué)噪聲(ECN 峰的出現(xiàn)與亞穩(wěn)態(tài)蝕點的形核或者再鈍化過程有關(guān)2,3。電化學(xué)噪聲法是根據(jù)腐蝕電極表面出現(xiàn)的電位或者電流隨機(jī)自發(fā)波動現(xiàn)象而產(chǎn)生的一種測試方法。此方法簡單,對腐蝕體系無擾動,故可廣泛應(yīng)用于腐蝕理論研究和工業(yè)腐蝕監(jiān)測。原子力顯微鏡(AF

3、 M 測試可以在大氣條件或溶液中進(jìn)行,并且觀察時只需很少或不需對樣品作前期處理,這樣就可以用AF M 直接觀察實際條件下動態(tài)過程4。利用AF M 可以在金屬腐蝕環(huán)境中進(jìn)行原子/分子水平上的實時原位觀察。因此,AF M 在金屬腐蝕研究領(lǐng)域得到了越來越多的應(yīng)用5。AF M 不僅可以觀察樣品表面的形貌,而且可以得到樣品表面的物理和機(jī)械性能等相關(guān)信息6,7。本工作采用電化學(xué)噪聲法并結(jié)合AF M 觀察,研究了N80鋼在以0.5mol/L NaHCO 3溶液為基礎(chǔ)溶液的不同濃度NaCl 溶液中點蝕過程的特征和規(guī)律。1試驗1.1電化學(xué)噪聲測試1.1.1樣品制備采用N80鋼制備研究電極,其成分見表1。試驗前,

4、除研究電極的一圓截面<=0.5c m 2作為工作面以外,其余部分緊密鑲嵌在聚四氟乙烯柱環(huán)中,研究電極另一端焊接銅絲導(dǎo)線并用環(huán)氧樹脂密封絕緣。工作面依次經(jīng)320,600,800號氧化鋁耐水砂紙打磨,再經(jīng)細(xì)金相砂紙打磨至光亮,蒸餾水清洗后,用無水乙醇、丙酮擦拭干凈。為了避免縫隙腐蝕,在研究電極與封裝的聚四氟乙烯之間涂一圈清漆,冷風(fēng)吹干。表1N80鋼的化學(xué)成分(質(zhì)量分?jǐn)?shù)%C Si Mn P S Cr Mo N i Fe 0.2400.2201.1900.0130.0040.0360.0210.028-基礎(chǔ)溶液為0.5mol/L NaHCO 3溶液,然后加入不同量的NaCl 使Cl -濃度達(dá)到規(guī)

5、定值。在電化學(xué)噪聲測試前,工作電極先在0.5mol/L NaHCO 3溶液中鈍化,形成鈍化膜。控制溫度(40±0.5。試驗溶液均由分析純試劑與蒸餾水配制。1.1.2儀器ECN 測量采用兩支同材質(zhì)的研究工作電極(W E1和W E2以及一個參比電極(SCE ,為防止Cl -污染,SCE 通過雙液接鹽橋與被測溶液相接。為了提高信號精密度,設(shè)計中采用高輸入阻抗(>1012和低漂移的運算放大器I CL7650進(jìn)行信號前置放大,采用ADS1211P 高精度AD 轉(zhuǎn)換器(24bit 進(jìn)行模數(shù)轉(zhuǎn)換,測試過程由基于W indows 98的軟件Corrtest 控制。數(shù)據(jù)采樣頻率為3Hz 。第40

6、卷第8期2007年8月材料保護(hù)M a ter i a ls Protecti onVol .40No .8Aug .2007 281.2原子力顯微鏡觀測將N80鋼材加工成10mm ×10mm ×1mm 的薄片。用研磨膏和拋光布拋光至鏡面,再用蒸餾水、無水乙醇、丙酮清洗表面的污漬,冷風(fēng)吹干。儀器采用SP A400型原子力顯微鏡在輕敲掃描模式下進(jìn)行測試,原位觀察N80鋼在含不同濃度Cl -的0.5mol/L NaHCO 3溶液中的表面微觀形貌的變化情況。所用探針為Si 3N 4探針,彈性系數(shù)為0.14N /m ,掃描頻率2Hz 。2結(jié)果與討論2.1電化學(xué)噪聲測試N80鋼在0.5

7、mol/L NaHCO 3溶液中鈍化1h 后,再將N80鋼置于以0.5mol/L NaHCO 3溶液為基礎(chǔ)液的不同濃度NaCl 溶液中進(jìn)行試驗。在溶液浸泡5h 后,所測得的電化學(xué)噪聲譜見圖1。圖1N80鋼在0.5mol/L NaHCO 3+NaCl溶液中的電流、電壓噪聲將電流噪聲進(jìn)行數(shù)據(jù)處理,得到點蝕噪聲峰出現(xiàn)的頻率(1h 內(nèi)噪聲峰出現(xiàn)的個數(shù)、最大電流噪聲峰峰值、最大電流噪聲峰的寬度即最大壽命、電流噪聲峰的峰值均值、電流噪聲峰的平均壽命,結(jié)果見表2。表2點蝕電化學(xué)噪聲譜計算結(jié)果Cl -濃度/(mol L -1產(chǎn)生頻率/(個h -1電流最大峰值/nA平均峰值/nA 最大壽命/s 平均壽命/s0.

8、0811138.452.314.3 5.60.1615148.360.626.58.60.2417542.1127.933.113.10.40201022.6563.888.336.7由圖1和表2可知,隨Cl -濃度的增大,單位時間內(nèi)產(chǎn)生的噪聲峰個數(shù)增多,噪聲峰的最大峰值以及所有噪聲峰的平均峰值變大,噪聲峰的最大壽命以及平均壽命也延長。在Cl -濃度為0.40mol/L 時,最大峰值、平均峰值有明顯增大,最大壽命和平均壽命也明顯增大。在Cl -濃度為0.08,0.16,0.24mol/L 時,具有電流噪聲峰狹窄,電位噪聲下降快速回升緩慢的特征,由此可見,在這些條件下N80鋼處于點蝕亞穩(wěn)態(tài)階段;

9、在Cl -濃度為0.40mol/L 時,噪聲監(jiān)測后期電位噪聲峰與電流噪聲峰的壽命趨于一致,表明點蝕的“成核”已超過臨界尺度,點蝕進(jìn)入了穩(wěn)定發(fā)展階段。上述結(jié)果表明,Cl -濃度增大到一定值時,將促進(jìn)陽離子空位在鈍化膜/金屬界面的積累超過臨界值,鈍化膜會同基體金屬發(fā)生宏觀尺度上的脫離,鈍化膜穿孔后無法自我修復(fù)1,8。2.2原子力顯微鏡分析經(jīng)0.5mol/L NaHCO 3鈍化的N80鋼,在不同溶液中浸泡后的AF M 形貌見圖2。由于NaHCO 3能夠在N80鋼表面形成比較致密的鈍化膜,所以在圖中可以觀察到其表面光滑平整;在0.24mol/L NaCl +0.50mol/L NaHCO 3溶液中,由

10、于加入的Cl -不斷地侵蝕鈍化膜,同時鈍化膜也在自我修復(fù),導(dǎo)致鈍化膜變得不光滑;進(jìn)一步將Cl -濃度增大到0.4mol/L 時,Cl -將鈍化膜破壞并產(chǎn)生點蝕坑。原子力顯微鏡觀測結(jié)果與所測的電化學(xué)噪聲特征譜的變化有一致性。圖2N80鋼在不同溶液中浸泡后的AF M 形貌圖AF M 相位圖主要通過記錄探針掃描時驅(qū)動信號和微懸臂的振動信號之間的差值而成像。在相同的試驗條件下,由相同的探針測得的相位圖,相位滯后的大小與樣品表面的局部黏彈性和硬度有關(guān)。例如對于較 29軟和黏性大的樣品表面,探針有被吸附的傾向,難以從試樣表面離開,導(dǎo)致更大的相位移;而對于較硬和彈性小的樣品表面,探針較易離開,相位移值減小。

11、形貌圖和相圖之間的差異為:當(dāng)表面為非均質(zhì)表面時,相圖可以從微納米尺度上分辨微觀物理性質(zhì)的差異9。相圖上最大相位移和最小相位移之間的差值即相位對比度deg ,根據(jù)相圖的成像原理,deg 的變化可以反映樣品表面物理性質(zhì)的相似程度。非均質(zhì)表面應(yīng)該比均質(zhì)表面有更大的deg 值,故deg 可以表征所觀察的樣品表面物理性能差異。試驗中隨著Cl -濃度的增大,deg 也有增大的趨勢。在未加Cl -的溶液中,deg 為21.3;在Cl -濃度為0.24,0.40mol/L 時,deg 則依次為162.4,167.8。未加Cl -的體系中,由于NaHCO 3鈍化產(chǎn)生鈍化膜,所以樣品表面趨于一致,deg 較小;加

12、入Cl -后,Cl -破壞了鈍化膜甚至導(dǎo)致膜穿孔,促使樣品表面不一致,deg 增大。Cl -在鈍化膜表面某些活性位置(夾雜、位錯或晶界吸附,并與表面膜內(nèi)的陽離子形成可溶性配合物,引起鈍化膜的減薄和破壞,造成基底金屬的溶解,但這種亞穩(wěn)態(tài)蝕點的生長過程受到溶液中過高的HCO -3/Cl -濃度比抑制,導(dǎo)致電流進(jìn)一步增加相當(dāng)困難,暴露的基體金屬很快被HCO -3鈍化。但當(dāng)Cl -濃度增大、HCO -3/Cl -濃度比變小時,將導(dǎo)致鈍化膜更易被破壞。3結(jié)論(1在0.5mol/L NaHCO 3基礎(chǔ)溶液中,隨著Cl -濃度增大,電流噪聲峰的產(chǎn)生頻率、最大峰值和平均峰值、最大壽命及平均壽命都變大。Cl -

13、濃度超過某一臨界值時,電流噪聲峰的峰值、壽命等均明顯增大,且電流噪聲譜特征發(fā)生變化。(2在本試驗條件下,當(dāng)Cl -濃度低于0.4mol/L時,只出現(xiàn)亞穩(wěn)態(tài)點蝕的噪聲譜特征;當(dāng)Cl -濃度達(dá)到0.4mol/L 時,點蝕形核將超過臨界尺寸,點蝕將進(jìn)入穩(wěn)定發(fā)展階段,電化學(xué)噪聲譜特征發(fā)生明顯變化。(3AF M 原位觀測的表面微觀形態(tài)的變化與電化學(xué)噪聲的譜特征具有良好的關(guān)聯(lián)性。AF M 測試結(jié)果表明,Cl -破壞了鈍化膜,導(dǎo)致原本致密的鈍化膜變?yōu)椴痪鶆?。隨著Cl -濃度進(jìn)一步增大,Cl -促使亞穩(wěn)態(tài)點蝕的孔核超出臨界值,孔核無法再自我修復(fù)鈍化,鈍化膜被擊穿。參考文獻(xiàn)1董澤華,郭興蓬,鄭家燊,等.16Mn

14、 鋼局部腐蝕中的電化學(xué)噪聲特征J .中國腐蝕與防護(hù)學(xué)報,2002,22(5:291293.2Roberge P R.Analysis of s pontaneous electr oche m ical noisef or corr osi on studies J .J App l Electr ochem,1993,23:12231231.3Hashi m ot o M ,M iyaji m a S,M urata T .An experi m entalstudy of potential fluctuati on during passive fil m breakdown and r

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17、ce m icr oscopy:backgr ound,devel opment and ap 2p licati on t o electr odeposited ceriu m oxide fil m s J .Ap 2p lied Surface Sci,1998,126(12:2133.編輯:童敏(上接第26頁13魏同波,郭寶剛,梁軍,等.鋁合金微弧氧化陶瓷膜的性能研究J .材料科學(xué)與工程學(xué)報,2004,22(4:564567.14Yao Z P,J iang Z H,Xin S G,et al .Electr oche m ical i m 2pedance s pectr osco

18、py of cera m ic coatings on Ti 26A l 24V by m icr o 2p las ma oxidati on J .Electr ochi m ica Acta,2005,50:32733279.15Bai A,Chuang P Y,Hu C C .The corr osi on behavi or of N i 2Pdeposits with high phos phor ous contents in brine media J .Materials Che m istry and Physics,2003,82:93100.編輯:童敏N80鋼點蝕行為的

19、研究 ids was investigated using metall ography,weight l oss test and elec 2tr oche m istry .It was f ound that the passivati on ti m e had remarkable effects on the corr osi on resistance of the tin coated steel sheet .Na mely,the corr osi on resistance of the tin coated steel in acidic cor 2r osive s

20、 oluti ons increased with the increasing passivati on ti m e .How 2ever,its corr osi on resistance in neutral corr osive s oluti ons increased with the increasing passivati on ti m e in the early stage,due t o the for 2mati on of tin oxide fil m ,and it decreased there with after a certain pe 2ri od

21、 of passivati on,owing t o the diss oluti on of tin oxide fil m .Key words:tin coated steel sheet;passivati on ti m e;corr osi on resist 2ance;electr ochem istryEffect of S i on A t m ospher i c Corrosi on of Carbon SteelZHANG Q i sheng 1,2,WANG Xiang dong 1,Y U Yong si 2,J I A NGShe m ing 1,CHE N X

22、iao p ing 1(1.Central Ir on &Steel Research I n 2stitute,Beijing 100081,China;2.Dalian University of Technol ogy,Dalian 116024,China .Cailiao B aohu 2007,40(08,2123(Ch .Accelerated corr osi on tests in laborat ory,involving cyclic wet alter 2nate corr osi on in S O 2containing envir on ment (0.0

23、1%NaHS O 3were done t o investigate the effect of Si on the corr osi on resistance of carbon steel in at m os phere .Thus the surface and cr oss secti on mor 2phol ogies of the corr oded sa mp les were observed using a scanning e 2lectr on m icr oscope .The cr oss secti onal ele mental compositi on

24、of the rusted layer was deter m ined by means of energy dis persive s pectr osco 2py .And the phase compositi on of the corr oded p r oducts was analyzed by means of X ray diffracti on .It was found that the rusted layer on the corr oded steel samp les was mainly composed of Fe OOH,Fe OOH and Fe 2O

25、3.Cu and P were beneficial t o increasing the corr osi on resistance of the carbon steel in industrial envir on ment,but Si was har mful t o the corr osi on resistance of the steel t o s ome extent .Key words:Si;at m os pheric corr osi on;accelerated corr osi on test;rusted layerEffect of Electr i c

26、 Curren t D en sity on Structure and Properti es of M i croarc O x i da ti on Ca ti n gs on M agnesi u m A loyL I A NG Jun 1,2,HAO J ing cheng 1(1.State Key Laborat ory of Solid Lubricati on,Lanzhou I nstitute of Che m ical Physics,Chinese Acade 2my of Sciences,Lanzhou 730000,China;2.Graduate School

27、,Chi 2nese Acade my of Sciences,Beijing 100039,China .Cailiao B aohu 2007,40(08,2426(Ch .Current density is one of the key fac 2t ors influencing the structure and p r operties of m icr oarc oxidati on coatings .Thus m icr oarc oxidati on coatings were p repared on AM60B magnesiu m all oy fr om a si

28、licate electr olyte at different current densi 2ty .The effects of the current density on the structure and corr osi on resistance of the m icr oarc oxidati on coatings were investigated using a thickness meter,scanning electr on m icr oscope,and electr ochem ical device .The results showed that the

29、 coating thickness increased line 2arly with the increasing current density .The m icr o structure of the coatings was highly dependent on the current density .The nu mber of the m icr opores on the coating surface decreased and the m icr o cracks were enlarged with increasing current density .Moreo

30、ver,the coatingfor med at a current density of 9.0A /d m 2had the best corr osi on re 2sistance,which was attributed t o its compact m icr ostructure .Key words:magnesiu m all oy;m icr oarc oxidati on;current density;m icr ostructure;corr osi on resistanceP itti n g Corrosi on Behav i or of N80Steel

31、 J I A NG W en jun,CHE N Zhen yu,G UO Xing peng (Depart m ent of Che m istry and Che m ical Engineering,Huazhong University of Science and Technol ogy,W uhan 430074,China .Cailiao B aohu 2007,40(08,2729(Ch .The p itting corr osi on behavi or of N80steel in a 2queous NaCl s oluti on containing 0.5mol

32、/L NaHCO 3was investigated making use of electr oche m ical noise (ECN measure ment and at om ic force m icr oscop ic (AF M observati on .It was f ound that the nu mber of the p itting peaks,the peak value and the life of the peak increasedwith the increasing concentrati on of Cl -.Moreover,there ex

33、isted ob 2vi ous correlati on bet w een the characteristics of the measured electr o 2che m ical noise s pectr oscopy and the change on the surface state of the N80steel .Key words:N80steel;electr oche m ical noise;AF M;p itting corr osi onProcess for Chro m i u m Electropl a ti n g of St a i n less

34、 Steel i n the Presence of Co m plex Add iti vesCHE N Hai yan,Z HU You lan,HE Xiao ying (School of Materials and Energy S ources,Guangdong University of Technol ogy,Guang 2zhou 510006,China .Cailiao B aohu 2007,40(08,3033(Ch .The p r ocess for the chr om iu m electr op lating of stainless steel fr o

35、m a l ow concentrati on chr ome acid bath in the p resence of comp lex addi 2tives containing nano sized Ce O 2was established,ai m ing at getting rid of the seri ous polluti on of the envir on ment by hexavalent chr om i 2u m.The op ti m ized p r ocess para meters were deter m ined based on modific

36、ati on of the corres ponding orthogonal test results .It was sug 2gested that the op ti m ized p lating bath composed of 80.00g/L Cr O 3,0.70g/L H 2S O 4,3.00g/L Cr 3+,3.00g/L CeO 2,2.00mL /L HC OOH,and 0.15mol/L Na 2C O 3.And the op ti m ized p r ocess pa 2rameters were recommended as te mperature

37、of 30,current densityof 30A /d m 2,and electr op lating ti m e of 120m inutes .The intr oduc 2ti on of the comp lex additives was hel pful t o decreasing the concentra 2ti on of the chr ome acid and energy consu mp ti on as well .A t the sa me ti m e,the comp lex additive was als o beneficial t o in

38、creasing the anode polarizati on rate and the dis persi on capability of the p lating bath as well .Key words:comp lex additives;rare earth;stainless steel;chr ome e 2lectr op lating;orthogonal testFactors I nfluenc i n g the D epositi on Ra te and Co m positi on and Properti es of Electroless N i P

39、 C O Coa ti n g L I U Shao you,T ANG W en hua (I nstitute of App lied Che m istry,Kaili College,Kaili 556000,China .Cailiao B aohu 2007,40(08,3437(Ch .The changes in the concentrati ons of N i 2+and HP O 2-3in electr oless N i P C O p lating bath were deter m ined by means of UV vis s pectr ophot o

40、metry and high perf or mance liquid i on chr o mat og 2raphy,which was ai m ing at p r omoting the industrializati on of the tech 2nol ogy f or electr olessN i P C O p lating .The compositi on and m icr o 2structure of the coating were analyzed .The effects of rare earth metali on (La 3+、Nd 3+、Ce 4+

41、,pH value,te mperature,and by p r oductsHP O 2-3on the depositi on rate and compositi on and m icr ostructure of the N i P C O coating were investigated .The results showed that there existed positive correlati on bet w een the depositi on rate and pH value and te mperature,while the depositi on rat

42、e of the coating wasnegatively correlated t o the concentrati on of rare earth Nd 3+i ons .Mo 2reover,the depositi on rate of the N i P coating increased at a La 3+and Ce 4+concentrati on (volu me fracti on of 2.5mL /L,while the intr o 2ducti on of Ce 4+and Nd 3+in the p lating bath led t o increased bright 2ness of the coating and l ower content of P in the coating .Besides,the content of C and O,the resistance t o salt attack,hardness,and brit 2tleness of the N i P coating i