稀土元素_La_Ce_對鎂合金電偶腐蝕的影響_圖文

1、稀土元素(La,Ce對鎂合金電偶腐蝕的影響趙艷娜1,朱元良2,齊公臺2(11南陽理工學(xué)院生物與化學(xué)工程系,河南南陽473004;21華中科技大學(xué)化學(xué)系,湖北武漢430074摘要針對鎂合金化學(xué)和電化學(xué)活性較高,與其他金屬材料接觸時易產(chǎn)生電偶腐蝕的特點,主要研究了其電偶腐蝕特性及環(huán)境因素的影響規(guī)律。采用電化學(xué)方法通過測定電偶電流密度,研究了添加約1%混合稀土RE (45%La,50%Ce 的AZ91合金在NaCl 溶液中與A3鋼、紫銅偶接時的電偶腐蝕行為,探討了溶液中氯離子濃度、偶接金屬種類以及陰陽極面積比對電偶電流密度J M gg 的影響。結(jié)果表明:Cl -濃度增大,J M gg 變大;陰陽極面

2、積比越大,J M gg 也越大;偶接金屬A3鋼比紫銅更易促進(jìn)鎂合金的腐蝕;稀土La,Ce 的添加使電偶腐蝕有效距離變窄。關(guān)鍵詞電偶腐蝕;鎂合金;混合稀土中圖分類號TG172文獻(xiàn)標(biāo)識碼A 文章編號1001-1560(200512-0014-03收稿日期200508050引言鎂合金是一種輕型結(jié)構(gòu)材料,有著廣泛的應(yīng)用前景。鎂合金的電位比較負(fù),在使用過程中如果與其他種類的金屬材料接觸,易出現(xiàn)電偶腐蝕。鎂合金為腐蝕電池的陽極,其他材料為腐蝕電池的陰級,因此,鎂合金的腐蝕速率要比其單獨存在時的腐蝕速率大13。近年來,汽車輕型化要求使鎂合金的研究和應(yīng)用得以迅速發(fā)展,在AZ91鎂合金中添加混合稀土RE 能改善

3、其在中性氯化鈉溶液中的耐蝕性46。通過測定AZ91,AZ91+RE 合金分別與A3鋼、紫銅等構(gòu)成電偶對時的電偶電流密度,研究了氯離子濃度、偶對中陰極材料、陰陽極面積比等對電偶電流的影響以及電偶腐蝕電池中陽極電流的分布情況。1試驗材料和方法合金熔煉:在5kg 電阻坩堝爐中進(jìn)行,爐料為鎂錠(9919%Mg 、鋁錠(9919%A l 、鋅錠(99192%Zn 、混合稀土金屬RE (50%Ce,45%La ;覆蓋劑為RJ 2,精煉劑自制;熔煉溫度為780,澆注溫度700;金屬型鑄造,自然冷卻。所用鎂合金的化學(xué)成分見表1(質(zhì)量分?jǐn)?shù)。表1鎂合金的化學(xué)成分%合金RE A l Zn Mn 和Fe MgAZ91

4、081931136<0110余量AZ91+RE110481851131<0110余量試驗介質(zhì):NaCl 溶液由二次去離子水和分析純的氯化鈉試劑配制而成。電偶電流密度測定:將鑄件鎂合金加工成端面積為1c m 2的電極,偶接金屬有效面積分別為1,5,20c m 2,其余部分用黃色膠帶紙密封。然后,將鎂合金電極與偶接的金屬用自制的夾持器固定,電極間距離保持1c m 。電極偶接后浸泡于試驗介質(zhì)中,用零電阻電流計每1h 測1次電偶電流I g (鎂合金的電偶電流密度J M gg 在數(shù)值上與之相等,介質(zhì)溫度為20,試驗時間為72h,試驗結(jié)果取3個平行試樣的平均值。2結(jié)果與討論2.1C l -濃度

5、及偶接金屬的影響在不同Cl -濃度下,當(dāng)陰陽極面積比S c S a =51時,AZ91和AZ91+RE (陽極與A3鋼(陰極或紫銅偶接后的陽極電偶電流密度J M gg 值見表2。表2電偶對中鎂合金陽極的電偶電流密度mA/c m2電偶對NaCl濃度/% 0015315g較小,含Cl-時,J M gg 則較大;當(dāng)Cl-濃度增髙時,J M gg的值也增大,說明Cl-加速了電偶對中鎂合金的腐蝕。一方面是電解質(zhì)溶液導(dǎo)電能力增強的結(jié)果;另一方面是Cl-能破壞鎂合金表面的保護(hù)膜,促進(jìn)其離子的水化。Cl-濃度越大,在鎂表面吸附越多,越有利于降低鎂離子化反應(yīng)的過電位,促進(jìn)鎂離子的水化,使鎂離子轉(zhuǎn)移到水溶液中引起

6、更強烈的腐蝕。同時,還可看到,在電偶腐蝕裝置中,當(dāng)Cl-濃度、偶接金屬和陰陽極面積比都相同時,電偶對中AZ91合金比AZ91+RE合金電偶電流密度大,即J M g g(AZ91>J M g g(AZ91+RE,說明RE的加入有利于減緩鎂合金的電偶腐蝕。表2還顯示,在其他條件相同時,AZ91+RE合金與A3鋼偶接后的J M gg 和與紫銅偶接后的J M gg不同,且J M gg (A3鋼>J M gg(紫銅,表明A3鋼比紫銅更容易引起鎂合金的電偶腐蝕。這是由于A3鋼和紫銅表面的陰極反應(yīng)(主要是析氫反應(yīng)速度不同造成的,析氫反應(yīng)受陰極金屬過電位的影響,析氫過電位越低,析氫反應(yīng)越容易,而過

7、電位又與金屬材料的材質(zhì)有關(guān)。A3鋼表面析氫過電位小于紫銅,但析氫速度大于紫銅表面7。212陰陽極面積比的影響AZ91,AZ91+RE兩種合金與A3鋼在015% NaCl溶液中偶接,不同陰陽極面積比的J M g g值見表3。由表3可見,J M g g值隨著陰陽極面積比的增大而增大。這是因為隨著陰極面積增大,總的陰極電流增大,導(dǎo)致陽極腐蝕加快。在其他條件相同時,電偶電流密度J M gg (AZ91>J M gg(AZ91+RE,這與前面討論的RE的添加改善了鎂合金耐電偶腐蝕的結(jié)果是一致的。表3不同陰陽極面積比的電偶電流密度mA/c m2 S cS a1151201鎂合金作為電偶對中的陽極,腐

8、蝕電流的分布是不均勻的。AZ91+RE鎂合金與A3鋼偶接浸在不同濃度NaCl溶液中腐蝕2h后的形貌見圖1。從圖1可見,在同一鎂合金的腐蝕表面上腐蝕電流的分布是不均勻的。距離接合部位越近,腐蝕痕跡越深,相反,離接合部位越遠(yuǎn),腐蝕痕跡越淺。說明陽極腐蝕電流越接近異金屬接觸部位,電流越大,反之越小,因為電流的流動要克服電阻4。隨著氯離子濃度的增加,同一種鎂合金腐蝕后相連接的螺母的痕跡增大,即有效距離增大。這是因為氯離子濃度越大,溶液的電阻越小,電流越大。但是,在同一氯離子濃度下,AZ91和AZ91+RE的腐蝕圈痕跡卻依次減小(見圖2。這也就是說,按上述順序,有效距離越小。這說明稀土元素的加入,改變了

9、AZ91鎂合金的內(nèi)部結(jié)構(gòu),使電流的流動受到阻礙 。圖1不同濃度NaCl時AZ91+RE鎂合金的電偶腐蝕形貌(2h 圖2AZ91,AZ91+RE在315%NaCl溶液中的腐蝕形貌(8h3結(jié)論(1氯離子的濃度對電偶電流密度有影響,氯離子濃度越大,電偶電流密度J M gg也愈大,變化也愈明顯。(2不同的偶接金屬材料,對電偶電流密度有不同的影響。與A3鋼偶接的電偶電流密度J M gg大于與紫銅偶接的值,因為在此條件下A3鋼表面的析氫過電位小于銅的過電位。(3同一種鎂合金與A3鋼偶接時的電偶電流密度J M gg隨陰陽極面積比增大而增大。(4同一種鎂合金的陽極腐蝕電流的分布是不均勻的,距離接合部位越近,腐

10、蝕越強烈。有效距離與溶液中的氯離子濃度有關(guān),氯離子濃度越大,有效距離也愈大。(5相同的離子濃度、相同的偶接金屬、相同的陰陽面積比,兩種鎂合金的電偶電流密度J M gg的值按AZ91,AZ91+RE的順序遞減。參考文獻(xiàn)1段漢橋,王立世,蔡啟舟,等.稀土對AZ91鎂合金耐腐蝕性能的影響J.中國機械工程,2003,4(20:1789.2馬全友,王振家,王璐科,等.壓鑄鎂合金AZ91D在酸性NaCl溶液中的腐蝕行為J.表面技術(shù),2004,33(4:16.3樊昱,吳國華,高洪濤,等.鎂合金腐蝕的研究現(xiàn)狀及發(fā)展趨勢J.鑄造技術(shù),2004,25(12:941. 4張永君,嚴(yán)川偉,王福會,等.鎂的應(yīng)用及其腐蝕

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15、cti on(Monthly,Started in1960Contents&AbstractsEffect of Rare Earth Cerium Dop i n g on Electroca t a lytic Activ ity of Coa ti n g AnodeKey words:coating anode(DS A;rare earth cerium;electr ocatalytic ac2 tivityM easure of Electro2Brush Plati n g Solution Tem perature Usi n g Vir2 tua l I n str

16、um en t Based on I nfrared Irrad i a tionJ I N G Xue2dong1,2,XU B in2shi2,WANG Cheng2tao1,DONG Shi2yun2 (1.School of Mechanical Engineering,Shanghai Jiaotong University, Shanghai200030;2.Laboratory of NationalDefense Science and Technol2 ogy for Equipments Remanufacture,Beijing100072Cailiao B aohu 2

17、005,38(12,0407(Ch.It is essential to monitor solution tempera2 ture during the p r ocess of brush p lating of nano composite coating s o as to meet the requirement of quality control.Thus a virtual instrument(V I was developed to measure the s olution temperature around the contract ar2 ea of the an

18、ode wrap and the p lating zone of a workpiece in real ti m e, based on the p rinciple of infrared radiation.T wo app r oacheswere adopted to i m p r ove the measurement accuracy.Namely,the random interferences were eli m inated by moving the average filtering,while non2model calibra2 tion was used t

19、o correct the measurement result.It was found that the so2 lution temperature could be measured with a high accuracy making use of those t w o app r oaches.The s olution temperature was dis p layed on the vir2 tual panel during the brush plating p r ocess,and it would be alar med as the temperature

20、exceeded the per m itted value.Moreover,the app lied re2 sults indicated that the established approaches were feasible to the meas2 urement of the brush p lating s olution temperature.Key words:electro2brush plating;nano composite coating;virtual instru2 ment;s olution temperature;infrared radiation

21、;measurement Electrochem ical Properties of Copper Electrode Coa ted with Sn2I n Alloy Electrochem ica l Pla ti n g i n KO H SolutionL I Jun2hua,FE I Xi2m ing,X I A NG Cui2li(College of Chem istry,Central China Nor mal University,Wuhan430079,ChinaCailiao B aohu2005,38 (12,0810(Ch.Sn,In,and Sn2I n al

22、loy coatings were deposited on the surface of current collector copper electrode via electrochem ical r oute. The hydr ogen evolution electrochem ical properties and electr ochem ical stabilities of the copper electrodes coated with electr ochem ical Sn,In,and Sn2In alloy in1mol/L K OH s olution wer

23、e studied,based on the measure2 ment of the circular volt2ampere curves and electr oche mical i m pedance s pectroscopy.It was found that the copper electr odes coated with I n and Sn 2I n alloy coatings had higher hydrogen evolution potentials than the uncoat2 ed copper electrode,i.e.,the hydr ogen

24、 evolution potentials for the coated copper electr odes were larger than that of the uncoated one by569mV and 488mV,res pectively.In other words,the coated copper electrodes were ca2 pable of restricting hydr ogen evolution more effectively than the uncoated e2 lectr ode.It was therefore anticipated

25、 that the cost2effective Sn2In alloy coa2 ted copper electrode of better ability to resist hydr ogen evolution could find pr omising application in mercury2free battery industry,as the replacement of conventional I n2coated copper electr ode.Key words:electr odeposition;Sn2I n alloy;copper electr od

26、e;hydr ogen evolution;electr ochem ical p r opertiesFactors Affecti n g the Adhesion Force of Carbon Nitride F il m on H igh2Speed Steel SubstrateB I Kai1,L I U Jun2,CHEN Chun2(1.Depart m ent of Physics,Zhenjiang Watercraft College,Zhenjiang212003;2.College of Material Science and Engineering,Jiangs

27、u University,Zhenjiang212003,ChinaCailiao B aohu 2005,38(12,1113(Ch.W ith a view to the excellent mechanical and tribological properties of carbon nitride(CNxfil m and it p r om ising app lication as wear resistant material and solid lubricant,carbon nitride fil m was p repared on high2speed steel s

28、ubstrate using magnetron sputte2 ring technique.The adhesion force of the resulting carbon nitride fil m was measured making use of scratch test.A s the results,it was feasible to greatly increase the adhesion force of the CNx fil m by introduction of Ti N inter mediate layer.It was i m perative to

29、fully clean the substrate surface, app ly p r oper negative bias,select desired sputtering parameters,and intro2 duce suitable inter mediate layer s o as to ensure good adhesion strength of the target CNx fil m to the substrate.Key words:magnetron s puttering;carbon nitride fil m;adhesion force; aff

30、ecting factorsEffect of Rare Earth(La,Ceon Galvan ic Corrosion of AZ91Mag2 nesium AlloyZHAO Yan2na1,ZHU Yuan2liang2,Q I Gong2tai2(1.Depart m ent of B io2 logicaland Chem ical Engineering,Nanyang I nstitute of Technology,Nan2 yang473004;2.Depart m ent of Chem istry,HuazhongUniversity of Science and T

31、echnology,W uhan430074,ChinaCailiao B aohu2005,38(12,14 16(Ch.The galvanic corr osion behavior ofAZ91magnesium alloy and its dependence on envir onmental factors were investigated with respect to the high chem ical and electrochemical activity of the Mg alloy.Thus the effect of m ixed rare earth(45%La,55%Ce,mass fractionaddition by 1%on the corr osion behavior of AZ91magnesium alloy coup led with A3 steel or copper in NaCl s olution was