Research on Effect of Rare Earth Compounds in Phosphating Process

JOURNAL OF RARE EARTHSVol.22, Spec. , Dec. 2004, p.262.Research on Effect of Rare Earth Compounds in Phosphating ProcessKuang Juchi(邝钜炽)*，Zhu Hengxiang(朱恒祥)，Pang Xijie(庞熙杰), Xiao Xueyan( 肖雪燕), LuoYongjian(罗永坚), Zhang Weiqiang(张伟强)，Li Jinai(黎金爱)( Deptment of Chemistry and Chemical Engineering，Foshan Universirty, Foshan 528000, China )Abstract: The effect of REC on appearance，weight and coating corrosion resistance was discussed, of which resultssuggest that addition of a small quantity of the REC into phosphating bath is very advantageous in terms of coating re-sistance to corrosion and depositing speed, and the scale of optimizing doses of REC added in bath is 30 ~55 mg L~ '.Through analyses of configurations and components of films by SEM and EDS, it was ascertained that the samplesgained in bath added REC, relative to the sample got in bath without REC, improve the coating inoxidizability becauseof increasing of covering rate of sheet crystals in the surface, and the sequence of what elements P, Fe and Zn contib-ute to erosion resistance of films is Fe>P>Zn.Key words: phosphating ;corrosion resistance; accelerant; densifying agent;rare earthsCLC number :TG178Document code:AArticle ID :1002 - 0721 (2004) -0262 -04.Although phosphatisation up to now is still an1.2Proceeding parameterimportant method of protecting against corrosionwidely applied for iron and many iron-base alloys andpH 1 ~4. 5; temperature(T,C) 25 ~ 50; timeone of the most popular technics of surface treatment(t, min) 3~30.of the metals before painted (1.2not merely process1.3 Phosphating stepstemperature and velocity of phosphating but corrosionresistance of the obtained phosphate film is to be de-After cleanout of grease and rust on the sur-veloped. Some investigations of the rare-earth com-faces, the test strips of cold roll plates in size of 2posite additives in Phosphating Process resulted incmx4 cm x 0.2 cm had been dipped in the phos-positive outcomes 13-71 so that we were aroused tophatisation solution for specified time， then werediscuss the effects of REC on film's appearance, sed-measured the weight of the films and done for the ex-iment rate and corrosion resistance by using a field e-periments of corrosion resisting according to GBmission SEM with high resolving power and an EDS ,6807 -86，following washing with water and drying atand certain significative conclusions were achieved.100 C.1 Experimental1.4 Examination of films1.1 Basic composition of phosphatesationThe examination target consists of facies,solutionweight and corrosion resistance of the phosphatingfilms.(1) Solution characterizing nitritesPrescription1 (g●LI): ZnO 8 ~ 35;H,PO,，(1) Examination of facies: by the way of eye-40 ~ 90;HNO38~20; NaNO2 0.1 ~0.5; Light rareballing in accordance to GB/T 11376-1997,“Con-earth compounds (REC-1, REC-2) 0 ~0.12.version Film of Metal Phosphates" or GB 6807-86,“Phosphating technical specifications for steel work(2) Solution characterizing molybdatesPrescription2 (g. L"'): HyPO. 110 ~ 180;pieces before Painting”.ZnO,0 ~ 50; Zn(NO3)2 150 ~ 170; HOOC( 0H)(2) Examination of weight: by weighing meas-CHCH(OH)COOH 5~ 10; (NH4)2MoO4 0.8 ~Ire secundum GB 6807 -86，“Phosphating technical1.5; Light rare earth compounds ( REC-1 , REC-2 )中国煤化工es before Painting”.0~0.12._osion resistance: byTYHCNMHGReceived date; 2004 - 10- 10; rerised date: 2004-11 -08Biography: Kuang Juchi( 1955 - ) ,Male , Master，Associate professor* Corresponding author(E - mail:kjc2277@ 163. com)KuangJ Cetal. Research on Effeet of Rares Earth Compounds in Phosphating Process263dropping solution of copper sulfates according to GB6807- 86，“ Phosphatingtechnical specifications forsteel workpieces before Painting”.1.5 Parsing of configurations and2ABcomponents of filmsZn(1) The extermal configurations of the films口3-C__18.2____ 31.93__ 49.872A818.43 34. 7346. 84were observed and parsed with JSM- -6330 scanningelectron microscope ( SEM) made by JEOL ( Ja-Fig. 1 Changes of various elements in flm versus RECpan).3-C: without REC;2AB;with mix of RECs(2) The components of the flms were analyzed(REC-1: REC-2=1:3)with OXFORD Incar energy dispersive spectrometer(EDS) made by 0XFORD (U. K).102 Results and Discussion2.1 Effect of REC on phosphating2.1. 1 Varieties of appearance and components of0 3.97 8.07 15.9 23.7 31.5 41.4 51.3 61.2coatings Addition of RECs induces evident varie-Conentraion ofREC (mg:L")ties of the phosphatisation coatings not only in facie-Fig.2 Change of film weights versus RECs contentsses but in components of RECs.( condition:pH=2.5, T=40 C, 15 min)(1 )Change of aspects It has been found in theexperiments that conversion of the bulky asymmetryphosphate coating, for example, in the condition ofcrystals on the plans gained in the solution withoutlower temperature T( T≤30C) and 5 min operationRECs into the even, close deep-color hopeites pro-time, a full even coating not to be able gained in theduced in the solution with RECs can take place repure nitrite-phosphate bath can be smoothly producedposefully, which affects the micro-aspect of nitrite-by adding the RECs to the bath ( Table 1).phosphate solution more greatly than that of molyb-More information about it shown in Fig. 2 re-date- phosphate solution( Table 1).veals clearly that the films grow fast till the adding a-Table 1 Change of flm faces versus REC contentsmount of the RECs reaches4 mg●L 1 , and then doSolutionthey somewhat slowly up to 30~55 mg .L- of theREC-2/(mg.[")characterizingRECs concentration accompanying in the meanwhileitritesmolybdatesformation of the closest films， after this, do theyFail to film fullyAsymmetry lightmore tardily not to change almost the coating weightsblue flmversus increase of the RECs amount instead of symp-Even light grey flm Even rainbow flmtom of film's faces going bad inchmeal, which is32Even and close grey Even and closefilmrainbow flmcharacterized dendrite.116Even grey film with Even rainbow fim2.1.3 Improving corrosion resistance of filmdeadriteAs shown in Fig. 3, coating corrosion resistance ,(2) Change of components Fig. 1 EDS indiwhich is expressed in time of resisting the standardcates that an accession of micro amount of the rare-test solution of CuSO, is greatly affected by additionearth compounds influenced indeed the relative pro-amount of the REC in the wide range of a micro aportion of different elements in the hopeites film. Formount to 115 mg .L-. Especially, when REC con-example, in Sample 2AB, addition of the mixture oftent overruns 30 mg L，the curve of coating CorTO-REC-1 and REC-2 (REC-1: REC-2 =1:3) inducedsion resistance zooms to the top value 230s versus a-the mass percentage in the film of P element went up)ou |中国煤化工nying with the heavi-to 18.43 from 18.20, and Fe up to 34. 73 from 31.lance at the position,93, but Zn down from 49. 87 to 46. 84, as seen invhYH. C N M H. Gening and worseningthe datasheet attached to Fig. 1.coating when the dosage of REC is over 602.1.2 Accelerating formation of filmsIt is vis-mg.L". It is reminded to pay at tention to the opti-ible for the RECs to speed up construction of themizing dose of REC to be 30 ~60 mg .L-'.264JOURNAL or RARE EARTHS, Vol 22, Spec. , Dec. 2004250 [:005000 I.昌500 8.07 23.7 41.4 61.2 97.5Concentraion ofREC/(mgL' )Fig.3 Change of corrosion resistances of films482253 SET 15.8V x1,00 10um H0D15wmnwith RECs contentsFig. 6 Film appearance of Sample 3 - C gained in bath2.2 Comparison between REC-1 and REC-2without RECTwo kinds of light rare-earth compounds hadbeen screened out from numerous RECs and were ex-amined for disposal of dye effluent to contrast theirworking capacities, which gave the results shown inFigs. 4 and 5. It suggests that the REC-2 is betterthan the REC-1 in accelerating formation of flms aswell as improving corrosion resistance of them.00[30 I482260 SEI 15.8EV x1.038 18m KD16m+①REC- ..②REC-2Fig.7 Film appearance of Sample2- B gained in bathadded 0.05 mg.L-' REC-1200 3.9 7.8 15.6 23.5 30.6Dosage ofREC1(mgL2)Fig. 4 Contrast of REC-1 with REC-2 in change offilm weights25。2004B22 SEI 15.8V x1,83 18m HD15m昌善。Fig.8 Film appearance of Sample 2 - B gained in bath青②REC-2added mixture of0.05 mg.L-1 RECs3.97.815.23.5 30.6(REC-1: REC-2=1: 3)Dosage ofREC (mgL')each coating (Figs.6~8), of which reason may beFig. 5 Comparision of corrosion resistance of REC-1 and REC-2that the working acidity is so high (pH =2.32) thatthe crystal seed of hopeite is too diffluent to survive.2.3 REC's optimizing quality of phospha-It is obvious that the surface of the sample withouttingREC is enveloped by lamellar crystals much less thanthat of each of ones added REC. In other words, the2.3. 1 Parsing of external configurationshigh-precision field emission SEM ( JEOL: JSM-covering rate of sheet crystals in the surface of Sam-6330F) was used to observe the external configura-ple 3-C ( without REC) is only about 25%，but thattions of the films got in the condition of prescriptionof Samg1 _hat of 2-B over65%.中国煤化工e cystal, Zn,Fe1(pH=2.32, T=50 C, t=30 min), and some(PO4)2TYHC N M H Ghe primary safe-pictures (Figs. 6~8) were gained.What is worth regarding is why no needle-shapeguard against corrosives for the phospha-tizing mem-crystal (Zn; (PO4)2● 4H2O) that was customarilybrane，8 it is . foreseeable that the order of coatingreported to be found in congener tests'3] is seen incorrosion resistance is 2AB > 2-B > 3-C，of whichKuangJCetal. Research on Effet of Rares Earth Compounds in Phosphating Process265conclusion complies with the experimental result re-3. Since the covering rate of sheet crystals in thepresented in temms of time of resisting CuSO, solutionsurface is increased, relative to the sample got in(Table 2).bath without REC, the samples gained in bath added2.3.2 Analysis of compositions The componentsREC improve the corrosion resistance of the films.of fims obtained by EDS are listed in Table 3.4. The sequence of what elements P, Fe and ZnThrough comparison of Tables 2 and 3, and the con-contribute to corrosion resistance of the flms is Fe >tribution of elements P, Fe and Zn to corrosion reP >Zn.sistance of the flms can be approximately expressedReferences :as Fe>P> Zn.[1] Kubicki J. In: Pracownia Techniki Przeciwkoro-ZyjnejTable 2 Comparison of inoxidizability of films[M]. WSiP( in Polish), Warszawa, 1977.Samples3-C2-B2AI[2] Ang K F, Turgoose S. Development of phospbate coat-ings on mild steel[J]. Trans. IMF, 1991 ,69 (2): 58. .Time of resistingCuSO, solution 1 min4.336.388.58[3] Ghali EL , Potvin RJ A. The mechanism of phospha-ting of steel [J]. Corrosion Science, 1972, 12: 583.Table 3 Components of flms (by EDS) "[4] Chen Tongyun, Hu Keliang. Preparation and propertiesof a normnal- -temperature extra- -thin type phosphatingElementsPercentage by weight /t%solution [J]. Corrosion & Protection, 2001, 22 (6):2AB244.PK18.2019. 1718. 43[5] Yan Huizhong ，Kong Fanqing ，Zhao Zengqi, et al.31. 9331.8834.73Research on phospbating technology of FeCrAIY materi-49.8748. 9546.84al for catalytic support [J]. Jourmal of the Chinese RareREC K0.00Earth Society, 2002, 20 (Spec. ): 46.Total100.00100. 00[6] Zhu Liqun, Wang Jianhua, Liu Feng, et al. Study of， concentration of REC in bath (g.L-1):3-C- 0.00;phosphating at room temperature with accelerant contai-2-B-0.05 (REC-1);2AB - 0.05 (REC-1:0.03 REC-2ning rare earth compound [J]. Electroplating & Finish-= 1:3)ing, 2001, 20(4): 8.3 Conclusions7 ] Zhang Jingshuang, Wang Shuanglin, Yang Zhelong, etal. Invetigation of the rare-earth composite additive in1. Addition of a small quantity of the RECs ad-phosphating process at medium temperature [J]. Elec-ditives into phosphating bath is very advantageous introplating & Pollution Control, 2000, 20(5): 25.terms of coating corrosion resistance and depositing[8] Kang Cuirong, Meng Qingying, Yang Zhian, et al. Thespeed. And the scale of optimizing doses of RECelectron microstructure analysis of zinc system phosphatecoating[J]. Joural of Tianjin University， 1996, 29added in the bath is 30~55 mg●L-'.(5) :740.2. The REC-2 is better than the REC-1 in accel-erating formation of coatings as well as improvingcorrosion resistance of them.中国煤化工MYHCNMHG