电化学

第 8 卷 　第 1 期 2002 年 2 月

Vol. 8 　No. 1 Feb. 2002

EL ECTROCHEM ISTR Y

Article ID :1006- 3471 ( 2002) 01- 0032- 08

Raman Spectroscopic Study on Mechanism of Aluminum Triphosphate Pigment GU Zhi-jun 3 , L IAO Yong- gui , ZHAN G Zhi- gang , GUO Qi-long , SU Fang- teng ( Fujian I nstit ute of Research on t he S t ruct u re of M atter , Chi nese A cadem y of Sciences , Xiamen 361012 , Chi na )

Abstract : The painted steel sample whose coating contained anticorrosive pigment

has been in2

vestigated by Raman spect roscopy. The protective mechanism of aluminum t rip hosp hate pigment for A3 steel is proposed as follows : Aluminum t rip hosp hate can be dissolved and arrive at t he sur2 face of t he steel. The dissolved t rip hosp hate ions can complex wit h ferric ions. And t he new prod2 uct s ,namely ferric t rip hosp hate ,can st rongly adhere at t he surface of t he steel by chemical bonds slowly. At last ,a compact protective film ,which effectively separates t he steel subst rate f rom t he aggressive media ,is formed at t he steel surface.

Key words : Raman Spect roscopy ,Mechanism ,Pigment ,Sodium chloride CLC number : O T G 172 ,O 646 　　　　　Document Co de : A 1 　Introduction In 1995 ,t he cost on corrosion of metal in t he U nited States has reached g300 billion or so per year. In order to reduce t he loss of corrosion ,many protection met hods have been used. Organ2 ic coating is one of t he most effective ,economical and popular met hods as yet . The various pig2 ment s in anticorrosive coatings protect t he metal subst rates by different mechanisms ,eit her by cre2 ation of alkaline environment s ,by passivation of t he active centers originating f rom geomet rical or st ruct ural defect s ,by decreasing t he oxygen permeation f rom t he environment or t he metal ion dif2 f usion t hrough t he coating ,or by buffering t he formation of hydrogen ions ,or by sacrificial metal powders in t he coating [ 1 ] . A small amount of inbhibitors can obviously retard corrosion , so in2 hibitors have been considered more and more important . Alt hough some t raditional anticorrosive pigment s ,such as lead-and chrome- based pigment s ,have good inhibitive performances ,but t hey Received date : 11 Oct . 2001

3 To whom correspondence should be addressed , Tel :86 - 592 - 6013060 , E - mail : zhjgu @ms. fjirsm. ac. cn Foundation item : Project supported by State Key Lab. for Phys. Chem. of Solid Surface ( 9703)

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have high toxicity too . They are st rictly limited ,or prohibited to use in many count ries and re2 gions. Thus t he application and research of new anticorrosive pigment s are bound to focus on t he highly effective ,multif unctional and environmentally f riendly pigment s. Aluminum t rip hosp hate is an anticorrosive pigment wit h good inhibitive performance when it is mixed in t he epoxypolyamide resin on A3 steel coupon [ 2 ] ,however ,it s mechanism is not clear yet . There have been lot s of st udies t hat have t ried to determine t he nat ure of corrosion species , especially on copper and iron , in t he presence of active inhibitors in solutions by Raman spec2 t roscopy [ 3～11 ] . Raman spect roscopy has been used to investigate corrosion under paint ,but wit h2 out anticorrosive pigment was in t he coating [ 12～14 ] . Therefore ,we report here using Raman spec2 t ra for st udies of t he corrosion species at t he artificial defect in t he coating ,in t he presence of anti2 corrosive pigment . It is helpf ul to better understand t he mechanisms of anticorrosive pigment s.

2 　Experimental 2. 1 　Preparation of t wo ferric compounds To synt hesize ferric p hosp hate [ 15 ] ,0. 02 mol ferric chloride ( FeCl3 ) ,0. 02 mol sodium hydro2 gen p hosp hate ( Na2 HPO4 ) ,and 0. 025 mol sodium acetate ( CH3 COONa ) were dissolved in 100 mL distilled water respectively ,mingled ,filtered ,drie. To synt hesize ferric t rip hosp hate , 0. 05 mol FeCl3 and 0. 03 mol sodium t rip hosp hate ( Na5 P3 O10 ) were dissolved in 100 mL distilled water respectively ,mingled ,filtered ,dried.

2. 2 　Materials To prepare t he coated coupon ,t he surface of t he A3 steel coupon ( 200 ×100 mm) was abraded wit h 60 # ,80 # sand clot h in succession ,cleaned ,degreased wit h et hanol ,covered by t he epoxypolyamide resin containing aluminum t rip hosp hate pigment ,air dried in ambient temperat ure for one week ,placed a plastic t ube (inner diameter = 90 mm) on t he coated coupon wit h 704 binder , air dried. The solution was made of distilled water and sodium chloride ( NaCl ,AR) ,and t he con2 cent ration was 3. 5 % ( wt %) .

2. 3 　Micro- Raman spectroscopy —Raman spect ra were obtained by LabRam I confocal microscopic Raman spect rometer ( Dilor) wit h a He- Ne laser ( 632. 8mm) in t he pore covered wit h 1 mm solution at ambient tem2 perat ure and air-open system. ( The Raman spect ra of ferric p hosp hate and ferric t hip hosp hate were obtained f rom t heir powder samples directly. )

3 　Results and Discussion 3. 1 　Two ferric compounds Fig. 1 and Fig. 2 show micro- Raman spect ra of synt hetic ferric p hosp hate and ferric t rip hos2 p hate ,respectively. In figure 1 , t he characteristic peak is at 1 010 cm - 1 . Additional feat ures are observed at 270 ,541 ,1 444 cm - 1 ,and a shoulder peak of 439 and 478 cm - 1 . In figure 2 ,t he char2

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acteristic peak is 1 107 cm - 1 . Additional feat ures are observed at 412 ,704 ,928 and 994 cm - 1 .

Fig. 1 　Micro- Raman spectrum of ferric p hosp hate

Fig. 2 　Micro- Raman spectrum of ferric trip hosp hate

( FePO4 )

( Fe TP)

3. 2 　Characterization of pa inted blank A3 steel coupon Table 1 summarizes t he Raman shift s and corrosion species for painted blank A3 steel coupon Tab. 1 　Nominal Raman frequencies ( cm - 1 ) of corrosion species observed wit h exposure time ( day) for painted blank painted steel coupon immersed in 3. 5 % NaCl solution. The underlined peaks exhibit strong intensities 1 day inner

2 days outer

Inner of

Outer of

yellow

yellow

252

256

6 days black

yellow

black

220 257

256

251

295 282

296

314

314

311

351

345

347 377

377

311 377

382 527 528

529 538

652 658

668

br

1304 γ- FeOOH + Fe3 O4 +γ- Fe2 O3 +α- FeOOH + FeCl3 ( s)

668

655 664

1293 Fe3 O4 γ- FeOOH + Fe3 O4 +α- Fe2 O3 +γ- FOOH +γ- Fe2 O3

+γ- Fe2 O3 + FeCl3 ( s)

670 br

br

Fe3 O4

534

Fe3 O4

1302 γ- FeOOH +γ- Fe2 O3

Fe3 O4 +γ- Fe2 O3

+ FeCl3 ( s) +αFe2 O3

+γ- FeOOH + FeCl3 ( s)

Assignment

α- Fe2 03 γ- FeOOH Fe3 O4 α- Fe2 O3 FeCl3 ( s) 3 γ- Fe2 O3 γ- Fe2 O3 α- FeOOH +γ- Fe2 O3 γ- FeOOH Fe3 O4 γ- FeOOH Fe3 O4 γ- FeOOH Corrosion species

　　3 br represents broad wave. 3 Wit hout illustrated particularly ,t he location measured was t he inner point .

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t hat was exposed in 3. 5 % NaCl solution wit h immersion time. At different point s ,t he corrosion species are different . Namely , t he special dist ribution of corrosion species is inhomogeneous. The corrosion species for painted blank A3 steel coupon are iron oxides and iron oxyhydroxides. Immersion 1 day ,t he corrosion species at inner point are mainly γ- FeOO H , Fe3 O4 γ , - Fe2 O3 ,

α- FeOO H ,and scare FeCl3 in solution. Alt hough α- Fe2 O3 exhibites mode in t he 1 300 to 1 310 cm - 1 range ,no peak is observed at t he f requency t hat it s most intense mode ( 290 cm - 1 ) is expect2 ed. It indicates t hat t his species is not present in detectable concent ration. The corrosion species at outer point is mainly Fe3 O4 . Figure 3 shows t heir Raman spect ra. Immersion 2 days ,yellow and black spot s can be observed by naked eyes. Only Fe3 O4 can be detected at t he black. However , γ- FeOO H ,Fe3 O4 and γ- Fe2 O3 at t he inner of t he yellow ,γ- FeOO H , Fe3 O4 ,α- Fe2 O3 and scare γ- Fe2 O3 and FeCl3 in solution at t he outer of t he yellow , can be detected. Immersion 6 days ,

γ- FeOO H α , - Fe2 O3 γ , - Fe2 O3 and scare FeCl3 in solution at t he inner of t he yellow ,Fe3 O4 γ , - Fe2 O3 γ α and scare - FeOO H , - Fe2 O3 ,FeCl3 in solution at t he inner of t he black ,can be detected. Figure 4 shows t he micro- Raman spect ra of corrosion species for painted blank A3 steel coupon immersed in 3. 5 % NaCl solution for 6 days at inner of yellow point ( a) ,and at inner of black point ( b) .

Fig. 3 　Micro- Raman spectra of corrosion species for

Fig. 4 Micro- Raman spectra of corrosion species for

painted blank A3 steel coupon immersed in

painted blank A3 steel coupon immersed in

3. 5 % NaCl solution for 1 day at inner point

3. 5 % NaCl solution for 6 days at inner in yel2

( a) ,and at outer point ( b)

low point ( a) and at inner in black point ( b)

Because of t he artificial defect ,” large cat hode ,little anode”is formed ,t he defective area be2 comes t he anode relative to t he ot her. When t he blank painted A3 steel coupon is immersed in 3. 5 % sodium chloride solution ,t he corrosion occurs at t he surface of t he defect . Furt hermore ,at t he surface of t he defect ,geomet rical and p hysical st ruct ures are different . Different point s have different activities. Their corrosion rates are different too . The point s whose corrosion rates are quicker grow quicker because t he volume of iron corrosion species is larger t han t hat of t he metal. The corrosion species immersed can be oxidized wit h time ,and t he stable species can be formed. So

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t he special dist ribution of corrosion species is inhomogeneous , and t he corrosion species for t he painted blank A3 steel coupon are iron oxides and iron oxyhydroxides.

3. 3 　Characterization of the pa inted A3 steel coupon whose coating conta ined alu2 minum triphosphate pigment Table 2 shows t he Raman shift s and corrosion species for t he painted A3 steel coupon ,ex2 posed in 3. 5 % NaCl solution ,whose coating contained aluminum t rip hosp hate pigment ,wit h im2 mersion time. Figure 5 shows t he micro- Raman spect ra of corrosion species for t he sample im2 mersed in 3. 5 % NaCl solution for one day ( a) ,and for two days ( b) at inner point s. Tab. 2 　Nominal Raman frequencies (cm - 1 ) of corrosion species observed wit h exposure time ( day) for t he painted steel coupon whose coating contained aluminum trip hosp hat pigment immersed in 3. 5 % NaCl solutions. The underlined peaks exhibit strong intensities 1 day

2 days

19 days

21 days

α- Fe2 O3

225 251

245

247

α- Fe2 O3 +γ- Fe2 O3

288 377

376

γ- Fe2 O3 γ- Fe2 O3 +γ- FeOOH

376 408

α- Fe2 O3

499

α- Fe2 O3 + FeCl2 γ- FeOOH

534

α- Fe2 O3

611

γ- Fe2 O3

642

γ- Fe2 O3 + Fe3 O4

658 710

715

br

Fe TP 3 PO4 3 -

840 990- 1100

1090br

1314

1077br

Fe TP 3

1309

γ- FeOOH α- Fe2 O3

br

1342br

　3

γ- FeOOH FePO4

272

br

assignment

Fe ( OH) 3

γ- Fe2 O3 +γ- FeOOH

γ- FeOOH

γ- Fe2 O3 +α- Fe2 O3 +

γ- FeOOH + γ- Fe2 O3

+ FePO4

+γ- Fe2 O3 + FeTP

Fe3 O4 + FeCl2 + FeTP

+ FeTP

Corrosion species

represents broad wave. 3 Fe TP represents ferric trip hosp hate.

　3 Wit hout illustrated particularly ,t he location measured was t he darker point .

Immersion 1 day ,t he mode at 272 cm - 1 is exhibited ;alt hough t he mode at 1 010 cm - 1 can2 not be distinguished obviously ,it can be regarded to be covered by t he very broad wave in t he 900

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to 2 700 cm - 1 range. Moreover ,t he oxides and hydroxides of iron have not characteristic peaks at 270 cm - 1 or so . So t he mode at 272 cm - 1 can be regarded as t he mode of ferric p hosp hate. Immer2 sion 2 days ,an intense peak at 710 cm - 1 ,a broad wave in t he 990 to 1 100cm peak at 270 cm

- 1

1

range ,and no

are exhibited. So t hey can be regarded as t he modes of ferric t rip hosp hate. Im2

mersion 19 days ,t he cent ric wave number t hat t he ferric t rip hosp hat is at 1 107 cm t he lower f requency ,1 090 cm

- 1

. Immersion 21 days ,it moves to 1 077cm

- 1

1

moves to continuously. ( See

figure 6)

Fig. 5 　Micro- Raman spectra of corrosion species for

Fig. 6 　Micro- Raman spectra of corrosion species for

t he painted A3 steel coupon whose coating

t he painted A3 steel coupon whose coating

contained aluminum trip hosp hate pigment im2

contained aluminum trip hosp hate pigment im2

mersed in 3. 5 % NaCl solution for one day

mersed in 3. 5 % NaCl solution for 19 days ( b)

( a) ,and for two days ( b) at inner points

and 21 days ( c ) , contrary to ferric trip hos2 p hate powder ( a)

The corrosion species for t he painted A3 steel coupon whose coating contained aluminum t rip hosp hate pigment are iron oxides and oxyhydroxides ,besides ferric p hosp hate at first and ferric t rip hosp hate which st rongly adheres at t he surface of t he iron by chemical bonds. Aluminum t rip hosp hate can dissolve and reach t he surface of t he steel. The t rip hosp hate ions can be hydrolyzed ,so t he p hosp hate ions are formed. The latter can react wit h iron corrosion prod2 uct s ,e. g. ,Fe2 + and Fe3 + ,so t he ferric p hosp hate can be detected by Raman spect roscopy initial2 ly. Wit h t he increase of t rip hosp hate ions and iron corrosion product s at t he surface ,t he t rip hos2 p hate ions cannot be hydrolyzed in time ,and t hey can complex wit h t he latter. Furt hermore ,t he produt ,ferric t rip hosp hate can st rongly adhere at t he surface of t he iron by chemical bonds slowly. So t he cent ric wave number of ferric t rip hosp hate moves to t he lower f requenies. At last ,a com2 pact protective film , which effectively separates t he steel subst rate f rom t he aggressive media ,is formed at t he steel surface.

4 　Conclusions ( a) The corrosion species for t he painted metal ,such as A3 steel ,whose coating contained an2

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ticorrosive pigment ,can be obtained , and much information for mechanism of anticorrosive pig2 ment can be provided by Raman spect roscopy st udy. ( b) The special dist ribution of corrosion species is inhomogeneous. ( c) The corrosion species for painted blank A3 steel coupon are iron oxides and iron oxyhy2 droxides. The corrosion species for painted A3 steel coupon whose coating contained aluminum t rip hosp hate pigment are iron oxides and oxyhydroxides ,besides ferric p hosp hate at first and ferric t rip hosp hate. ( d) The protective mechanisms of aluminum t rip hosp hate pigment for A3 steel are as fol2 lows . aluminum t rip hosp hate can dissolve and arrive at t he surface of t he steel. The dissolved t rip hosp hate ions can complex wit h ferric ions. And t he new product s ,namely ferric t rip hosp hate , can st rongly adhere at t he surface of t he iron by chemical bonds slowly. At last ,a compact protec2 tive film ,which effectively separates t he steel subst rate f rom t he aggressive media ,is formed at t he steel surface.

Reference s : [ 1 ] 　Th Shoulividis ,et al. Correlation between protection of steel from corrosion and t he conductivity of n- semicon2 ductor pigments[J ] . Corrosion ,1998 ,54 ( 5) :386. [ 2 ] 　Yong- gui Liao ,et al. Electrochemical impedance spectroscopy studies on inhibitve performance of aluminum trip hop hate pigment [J ] . Electrochemistry ,2001 ,7 ( 1) :126. [3 ] 　Bunding K A ,et al. Surface-enhanced raman scattering by pyridine on a copper electrode [J ] . J . Elextroanal. Chem. ,1985. 184 :405. [ 4 ] 　Thierry D ,et al. Simultaneous raman spectroscopy and electrochemical studies of corrosion inhibiting molecules on copper[J ] . J . Electrochem. Soc. ,1985 ,132 ( 5) :1 009. [5 ] 　Da Costa S L F A ,et al. Inhibiting action of benzotriazole on copper corrosion in deaerated sulfuric acid con2 taining ferric ions by t he rotating disc electrode ,fluorescence ,and raman spectroscopies[J ] . Corrosion ,1987 ,43 ( 3) :149. [ 6 ] 　Youda R ,et al. A SERS study on inhibition mechanisms of benzotriazole and its derivatives for copper corrosion in sulp hate solutions[J ] . Corrosion Science ,1988 ,28 ( 1) :87. [7 ] 　Aramaki K ,et al. A SERS study on adsorption of some organic compounds on iron [J ] . J . Electrochem. Soc. , 1989 ,136 ( 5) :1 299. [ 8 ] 　Youda R ,et al. SERS and impedance study of t he equilibrium between complex formation and adsorption of benzotriazole and 4- hydroxybenzotriazole on a copper electrode in sulp hate solutions [J ] . Electrochim. Acta , 1990 ,35 ( 6) :1 011. [ 9 ] 　Aramaki K ,et al. In situ raman spectra of pyridinium chloride adsorbed on iron in K2 SO4 and H2 SO4 solutions [J ] . J . Electrochem. Soc. ,1992 ,139 ( 6) :1 525. [ 10 ] 　Oblonsky L J , et al. Adsorption of octadecyldimet hylbenzylammonium chlorede to two carbon steel mi2 crostructures as observed wit h surface-enhanced raman spectroscopy[J ] . Corrosion ,1995 ,51 ( 12) :891. [11 ] 　Aramaki K ,et al. Surface-enhanced raman scattering spectroscopy studies on t he inhibition mechanisms of

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propargy1 alcohol for iron corrosion in hydrochloric acid[J ] . Corrosion ,1996 ,52 ( 2) :83. [ 12 ] 　Thierry D ,et al. In situ determination of corrosion species formed on painted galvanized steel by raman spec2 troscopy[J ] . J . Electrochem. Soc. ,1991 ,138 ( 3) :879. [ 13 ] 　Bernard M C ,et al. Underpaint corrosion of zinc-coated steel sheet studied by in situ raman spectroscopy[J ] . Corrosion Science ,1993 ,35 ( 5～8) :1 339. [ 14 ] 　Bernard M C ,et al. In situ Raman study of t he corrosion of zinc-coated steel in t he presence of chloride[J ] . J . Electrochem. Soc. ,1995 ,142 ( 7) :2 167. [ 15 ] 　Shou-chun Chen. Some Important Inorganic Reactions[ M ] . Shanghai :Shanghai press of science and technol2 ogy. 1963 :380.

防锈颜料三聚磷酸铝的拉曼光谱研究 辜志俊 3 ,廖永贵 ,张志刚 ,郭琦龙 ,苏方腾 ( 中国科学院福建物质结构研究所 ,福建 厦门 361012)

摘要 : 　应用拉曼光谱研究了含有防锈颜料涂装特性的钢样 ,在此基础上探讨了三聚磷酸铝防锈 颜料对 A3 钢的保护机理 . 三聚磷酸铝溶解后能到达钢样表面 ,其离子可与铁离子化合形成三聚磷 酸铁 . 三聚磷铁能缓慢地通过化学键牢固地附着在钢样表面 , 最终在钢表面形成一层隔绝腐蚀介 质和钢样的紧蜜保护膜阻止了腐蚀的继续发生从而达到保护的目的 .

关键词 : 　拉曼光谱 ;机理 ;颜料 ;氯化钠