Formation Behavior of Phosphoric Acid-Based Chemical Conversion Films Containing Alkaline Earth Metals on Magnesium Alloy*1

Akinori Nakamura1,*2, Satoshi Oue2, Hiroki Koga1,3 and Hiroaki Nakano2

1Department of Materials Process Engineering, Kyushu University, Fukuoka 819–0395, Japan2Department of Materials Science & Engineering, Kyushu University, Fukuoka 819–0395, Japan3Fukuoka Industrial Technology Center, Mechanics Electronics Research Institute, Fukuoka 807–0831, Japan

The phosphating of Mg alloy was performed in unagitated solutions containing 1 g·dm−3 of Mg, Ca, Sr, and Ba as alkaline earth metals (M) and 50 g·dm−3 of H3PO4 of pH 3 at 40°C for 3 min. The structure and formation behavior of the phosphate �lms were investigated. The X-ray diffraction patterns of phosphate �lms broadened irrespective of the type of alkaline earth metal, which was a characteristic of an amor-phous structure. XPS analysis revealed that the valence of P in the phosphate �lms was pentavalent. The pH in the vicinity of the Mg alloy during the phosphating, as measured using an Sb microelectrode, was approximately 10.4, 11.4, 10.7, and 12.0 in the solutions containing Mg, Ca, Sr, and Ba, respectively. This shows that phosphoric acid dissociates to the third stage during the phosphating, and the phosphate �lms comprising M3(PO4)2 containing an alkaline earth metal are formed. The phosphating was successively performed in two types of solutions containing different alkaline earth metals, and the cross section was analyzed. As a result, it was determined that the new phosphate �lms were formed at the interface between the Mg alloy substrate and phosphate �lms, and the previously formed phosphate �lms were boosted in the �lms. [doi:10.2320/matertrans.M2016463]

(Received December 26, 2016; Accepted April 4, 2017; Published May 12, 2017)

Keywords:　 phosphating, phosphate coating, magnesium alloy, phosphate �lm, alkali-earth metal, phosphoric acid, antimony microelectrode

1.　 Introduction

Because Mg alloys are lightweight yet strong, they have been applied for the parts of portable electronic devices, med-ical related science, automobile, and aircraft industries.1,2) However, the standard electrode potential (E0) of Mg is −2.36 V (vs. NHE), which is signi�cantly less noble than oth-er metals. As a result, its corrosion resistance is inferior. Therefore, anticorrosion coatings are generally applied to Mg alloys. In contrast, phosphating is performed to provide wear resistance, lubricating ability, electrical insulation, and deco-rativeness to metallic materials. Phosphating has been widely used for pre-paint surface preparation because of good adhe-sion between the phosphated and paint �lms.3) During the phosphating of Mg alloys, an alkaline earth metal, such as Ca, is employed as an additive.4–10) The phosphate �lms contain-ing alkaline earth metals are reported to show an excellent corrosion resistance and adhesion with paint �lms. However, there are many ambiguities with respect to the structure and formation mechanism of the �lms. Therefore, in this study, Mg, Ca, Sr, and Ba among the alkaline earth metals were add-ed to the solution for phosphating, and the structure and for-mation mechanism of the �lms were investigated. The analy-sis of the �lm structure was performed using X-ray diffrac-tion (XRD) analysis, XPS analysis, and differential thermo-gravimetric analysis. To investigate the formation mechanism of phosphate coating, the pH in the vicinity of Mg alloys during phosphating was measured, and the cross section of phosphate �lms formed in succession using two types of phosphate solutions was analyzed.

2.　 Experimental

AZ91 (mass%, 8.8% Al, 0.7% Zn, 0.16% Mn, 0.02% Si, 0.002% Cu, 0.001% Ni, 0.001% Fe, 0.0008% Be, rest Mg) from the Japan society of magnesium was used as a Mg alloy specimen. Prior to phosphating, Mg alloy was carefully pol-ished down with No. 1000 emery paper, and alkaline degreas-ing, pickling, and de-smutting were performed as a pretreat-ment under the conditions shown in Table 1. Table 2 shows the phosphating conditions. The phosphating solution com-prised 50 g·dm−3 (0.51 mol·dm−3) of H3PO4, and alkaline earth metals were added in the amount of 1 g·dm−3 metal composition in the form of nitrate [Mg(NO3)2·6H2O 10.55 g·dm−3 (0.041 mol·dm−3), Ca(NO3)2·4H2O 5.89 g·dm−3

*1 This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 80 (2016) 684–690.

*2 Graduate Student, Kyushu University. Present address: JFE Steel Corpo-ration, Fukuyama 721–8510, Japan

Table 1　Chemical pre-treatment conditions for the phosphate coating for Mg alloy.

Process Conditions

Degreasing 200 g·dm−3 NaOH, 80°C, 5 min

Pickling Phosphoric acid-based solution, pH3, 40°C, 1 min

Desmutting 200 g·dm−3 NaOH, 80°C, 5 min

Table 2　Phosphate coating conditions for Mg alloy.

Bathcomposition

H3(PO4)2 50 g·dm−3

Mg(NO3)2·6H2O 10.55 g·dm−3

Ca(NO3)2·4H2O 5.89 g·dm−3

Sr(NO3)2 2.42 g·dm−3

Ba(NO3)2 1.9 g·dm−3

pH 3

Operatingconditions

Temperature 40°CImmersion time 5 min

Quiescent bath

Materials Transactions, Vol. 58, No. 7 (2017) pp. 1007 to 1013 ©2017 The Japan Institute of Metals and Materials

(0.025 mol·dm−3), Sr(NO3)2 2.416 g·dm−3 (0.011 mol·dm−3), and Ba(NO3)2 1.9 g·dm−3 (0.0073 mol·dm−3)]. The pH was adjusted to 3.0 using NaOH, and phosphating was performed for 3 min of immersion time in an unagitated solution at 40°C.

The phosphate �lms were exfoliated with a scraper, and the structure was analyzed via XRD (Cu-Kα, tube voltage of 40 kV, tube current of 30 mA). The exfoliated 10 mg phos-phate �lms were examined via differential thermogravimetric analysis (TG-DTA). The chemical bonding state of the phos-phate �lms was investigated using XPS. To elucidate the for-mation behavior of phosphate �lms, the phosphating was �rst performed in a solution containing Ca(NO3)2, following which, it was performed in a solution containing Sr(NO3)2. The cross section of the phosphate �lms was examined via EDX line analysis.

An Sb microelectrode11) was manufactured to investigate the pH change because of hydrogen evolution in the vicinity of Mg alloy substrate during phosphating. The Sb microelec-trode was �xed at a distance of 0.1 mm from the Mg alloy, and the potential of Sb electrode was measured during phos-phating. The distance between the capillary of the reference electrode and the Sb microelectrode was approximately 2 mm, and the distance between the capillary of the reference electrode and the Mg alloy was identical to that between the Sb microelectrode and the Mg alloy. Using the pH–potential calibration curve that was constructed in advance, we deter-mined the pH near the Mg alloy during the phosphating.

To investigate the effect of alkaline earth metal on the dis-sociation reaction of phosphoric acid, pH titration curves were measured by dripping 0.1 mol·dm−3 of NaOH at a speed of 2 ×  10−3 dm3·min−1 into the 0.12 dm3 solution containing both 0.01 mol·dm−3 alkaline earth metal and 0.01 mol·dm−3 phosphoric acid. Because the pH in the vicinity of Mg alloy was found to be 10.4 to 12.0 during phosphating via an Sb microelectrode, the pH titration curves were measured to ap-proximately pH 12, and the precipitations that occurred in the solution were analyzed via XRD. The precipitates that oc-curred during the pH titration curves measurement were col-lected using a centrifuge tube, and were separated from the supernatant liquid via centrifugal separation. Subsequently, each rinsing and centrifugal separation cycle was repeated 4 times, and the precipitates were dried at 80°C for 24 h (except for the addition of Mg: 48 h). The obtained powder sample was analyzed using XRD.

3.　 Results and Discussion

3.1　 Structure of phosphate �lmsFigure 1 shows the XRD patterns of phosphate �lms ob-

tained from the solution containing Mg, Ca, Sr, and Ba as al-kaline earth metals. In all the phosphate �lms, multiple peaks were observed. However, these resulted from the metallic Mg, which mixed from the Mg alloy substrate during the ex-foliation of phosphate �lms. Except for the peaks resulting from the metallic Mg, the diffraction patterns of all the phos-phate �lms broadened regardless of the type of alkaline earth metal, characterizing the �lms as amorphous structures.

Figure 2 shows the heat and mass variation using differen-tial thermogravimetric analysis of phosphate �lms obtained

from the solution containing Sr. In the heat variation curve, an endothermic peak at approximately 100°C and two exother-mic peaks around 500°C were observed. In contrast, the mass variation revealed that the mass of phosphate �lms decreased with increasing temperature and remained constant above 200°C. The inclination of curve of decrease in mass changed somewhat at approximately 100°C to show an endothermic peak. Because the mass of phosphate �lms was 10 mg before the experiment, the ratio of decrease in mass was 25% above 200°C. The phosphate �lms obtained from the solutions con-taining Mg, Ca, and Ba as alkaline earth metals showed al-most the same trend as that shown in Fig. 2. In contrast, the heat and mass variations of ammonium magnesium phos-phate (MgNH4PO4·6H2O) determined using differential ther-mogravimetric analysis has been reported. According to the

Fig. 2　Differential thermogravimetric analysis of phosphate �lms obtained from the solution containing Sr.

Fig. 1　XRD patterns of phosphate �lms obtained from the solutions con-taining Mg, Ca, Sr and Ba. [(a) Mg, (b) Ca, (c) Sr, (d) Ba]

1008 A. Nakamura, S. Oue, H. Koga and H. Nakano

report,12) the endothermic peaks were present at 90°C and 230°C. At these temperatures, the decrease in mass occurred in two steps, indicating that MgNH4PO4·6H2O changes to Mg2P2O7 via MgNH4PO4H2O.12) In addition, the exothermic peak is reported to be present at 600°C, which corresponds to the crystallization of Mg2P2O7. In this study, the endothermic peak at approximately 100°C seems to result from the desorp-tion of crystallization water, and the exothermic peaks at ap-proximately 500°C possibly corresponds to the crystallization of phosphate �lms. Therefore, XRD analysis was performed after heating the phosphate �lms at 200 and 600°C. However, there was no clear difference in XRD spectra between the before heating, shown in Fig. 1, and the after heating. This shows that the details of endothermic and exothermic peaks obtained via differential thermogravimetric analysis in this study are unknown.

XPS analysis was performed to elucidate the chemical bonding state of phosphate �lms obtained in this study. Fig-ure 3 shows the XPS spectra of phosphate �lms obtained from the solutions containing Ca, Sr, and Ba as alkaline earth metals. In all the phosphate �lms obtained from the solutions containing Ca, Sr, and Ba, the peak position of the P spectrum was almost constant inside the phosphate �lms after Ar sput-tering except for the outermost surface. In all the phosphate �lms, the binding energy of the peak in the P spectrum was in the range of 136.9–137.4 eV. The binding energy of the P2p orbital of Na2HPO4 is reported to be approximately 137 eV.13) This indicates that P of the phosphate �lms obtained in this study is present in a �ve-valence state. The peak at 136.9 to 137.4 eV in XPS spectra shown in Fig. 3 broadened, showing the possibility of mixing of a multi chemical bonding state.

3.2　 Formation behavior of phosphate �lmsFigure 4 shows the pH change with time in the vicinity of

Mg alloy during the phosphating in solutions containing Mg,

Ca, Sr and Ba. In all the solutions containing Mg, Ca, Sr, and Ba, pH changed signi�cantly due to a large quantity of hydro-gen evolution accompanied by the dissolution of Mg alloy during the initial stage of phosphating. However, the region of stable pH was observed with increasing time. During the initial stage of phosphating, pH does not seem to be accurate-ly measured because of the adhesion of hydrogen to the Sb microelectrode and capillary as a reference electrode. There-fore, the value in the region of stable pH after the �xed time was measured. The stable pH values in the vicinity of Mg al-loy during the phosphating in solutions containing Mg, Ca, Sr and Ba were 10.4, 11.4, 10.7, 12.0, respectively. These values were similarly high regardless of the type of alkaline earth metal.

Figure 5 shows the pH titration curves measured for the solutions containing each 0.01 mol·dm−3 of alkaline earth metal and phosphoric acid titrated with 0.1 mol·dm−3 NaOH. In the solution only containing phosphoric acid, the increase in pH stagnated at three regions of pH 2 to 3, 6 to 7 and 10.5 to 11.5. This is attributed to three steps of dissociation reac-tions described by eqs. (1)–(3)14)

H3PO4 H2PO4− + H+ K1 = 7.5 × 10−3 (1)

H2PO4− HPO4

2− + H+ K2 = 6.2 × 10−8 (2)

HPO42− PO4

3− + H+ K3 = 2.2 × 10−13 (3)

The ratio of activity of H3PO4 and H2PO4− in eq. (1) is 1:1 at

pH 2.12. Similarly, the ratio of activity of H2PO4− and HPO4

2− in eq. (2) is 1:1 at pH 7.21. The ratio of activity of HPO4

2− and PO4

3− in eq. (3) is 1:1 at pH 12.66. These pH values were almost identical with those at which the increase in pH stag-nated, as shown in Fig. 5. In solutions containing an alkaline earth metal, the increase in pH stagnated at three pH regions as well as in solution only containing phosphoric acid. The

Fig. 3　XPS spectra of P in phosphate �lms obtained from the solutions containing Ca, Sr and Ba. [(a) Ca, (b) Sr, (c) Ba]

1009Formation Behavior of Phosphoric Acid-Based Chemical Conversion Films Containing Alkaline Earth Metals on Magnesium Alloy

precipitate began to form above pH 6, and the formation amount of precipitate increased signi�cantly above pH 10.5. The precipitate above pH 6 is caused by the formation of hy-drogen phosphate salt [MHPO4, M: alkaline earth metal] con-taining alkaline earth metal due to dissociation of phosphoric acid to second stage. However, the precipitate above pH 10.5 is caused by the formation of phosphate [M3(PO4)2] contain-ing alkaline earth metal due to dissociation of phosphoric acid to third stage. As shown in Fig. 4, the pH in the vicinity of Mg alloy during the phosphating was more than 10, indi-cating that phosphoric acid dissociates to third stage during the phosphating, and the phosphate [M3(PO4)2] containing

alkaline earth metal is formed. Focusing on the region above pH 9 in the pH titration curve shown in Fig. 5, the increase in pH stagnated at approximately pH 9.5 in the solution contain-ing Mg. The degree of the increase in pH was second moder-ate in the solution containing Sr. As shown in Fig. 4, pH in the vicinity of Mg alloy during the phosphating was lowest in the solution containing Mg, and was second lowest in the solu-tion containing Sr. The stagnation of increase in pH at the lowest pH in the solution containing Mg is attributed to the formation of Mg3(PO4)2 at the lowest pH. The second moder-ate increase in pH in the solution containing Sr seems to be caused by the formation of Sr3(PO4)2 at lower pH next to Mg.

The structures of precipitates that occurred in solutions during the measurement of pH titration curves that are shown in Fig. 5 were investigated via the XRD analysis. Figure 6 shows the XRD patterns of precipitates that occurred in solu-tions containing Mg, Ca, Sr, and Ba. Prior to the XRD analy-sis, the precipitates were dried for 24 h at 80°C. Because the precipitate obtained from the solution containing Mg showed no peak in the XRD pattern, the precipitate containing Mg was dried for 48 h at 80°C. By evaluating the crystallinity of the precipitates from the XRD pattern, the crystallinity was highest for the precipitates obtained from the solution con-taining Ba and lowest for the precipitates obtained from the solution containing Mg. Table 3 shows the result of the XRD pattern obtained using the XRD analysis software of JADE. All the precipitates that occurred in solutions containing Mg, Ca, Sr, and Ba were found to be phosphate [M3(PO4)2] con-taining alkaline earth metals. The phosphate including OH radical was observed in solutions containing Mg, Ca, and Sr, and apatite [Ca5(PO4)3(OH)] was detected in the solution

Fig. 4　pH change with time in the vicinity of Mg alloy during the phosphate coating in solutions containing Mg, Ca, Sr and Ba. [(a) Mg, (b) Ca, (c) Sr, (d) Ba]

Fig. 5　pH titration curves for solutions containing H3PO4 and Mg, Ca, Sr and Ba. [(a) Mg, (b) Ca, (c) Sr, (d) Ba, (e) H3PO4 only]

1010 A. Nakamura, S. Oue, H. Koga and H. Nakano

containing Ca. From the XRD analysis of precipitates, the signi�cant increase in precipitates above pH 10.5 in the pH titration curve shown in Fig. 5 was demonstrated to be at-tributed to the formation of phosphate [M3(PO4)2] due to the dissociation of phosphoric acid to third stage.

To investigate the formation behavior of phosphate �lms, the phosphating was �rst performed in a solution containing Ca, and it was subsequently performed in another solution containing Sr. The cross section was analyzed using EDX and backscattered electron image. The result is shown in Fig. 7. The backscattered electron image (a) revealed that cracks oc-curred in phosphate �lms. The Ca content in phosphate �lms increased from the Mg alloy substrate toward the top of the �lms. On the contrary, the Sr content in phosphate �lms de-creased from the Mg alloy substrate toward the top of the �lms. That is, the phosphate �lms containing Ca were formed �rst and were concentrated on the upper area of the �lms, and the �lms containing Sr, which were formed later, were con-centrated at a lower area.

Figure 8 shows the backscattered electron image and EDX pro�les of the cross section of Mg alloys that were acquired, respectively, from the phosphate �lms containing Sr and Ba. The Sr content in phosphate �lms increased from the Mg al-loy substrate toward the top of the �lms, while Ba content in

the phosphate �lms decreased from the Mg alloy substrate toward the top of the �lms. That is, the phosphate �lms con-taining Sr were formed �rst and were concentrated on the up-per area of the �lms, and the �lms containing Ba formed later and were concentrated at lower area. From the results shown in Figs. 7 and 8, during phosphating, it was found that new phosphate �lms were formed at the interface between the Mg alloy substrate and phosphate �lm, and the former phosphate �lms were boosted up toward the upper area of the �lms.

During phosphating, during the dissolution of Mg alloy substrate accompanied by hydrogen evolution, phosphoric acid dissociates to third stage, and PO4

3− ions are formed on Mg alloy. These PO4

3− ions diffuse from Mg alloy substrate to the top of phosphate �lms. In contrast, alkaline earth metal ions in solution diffuse in phosphate �lms from the solution to the Mg alloy substrate. Comparing the diffusion rates of PO4

3− ions in phosphate �lms with those of alkaline earth metal ions, the phosphate �lms seem to be formed at the up-per area of �lms in the case of higher diffusion rate of PO4

3− ions, whereas the phosphate �lms are formed at the interface between the Mg alloy substrate and the phosphate �lms in the case of higher diffusion rate of earth metal ions. In this study, phosphate �lms containing an alkaline earth metal are formed at the interface between the Mg alloy substrate and phosphate �lms. This indicates that the diffusion rate of alkaline earth metal ions in phosphate �lms is higher than that of the PO4

3− ions. As determined from the pH change with time in the vi-cinity of Mg alloy during phosphating (Fig. 4), the dissolu-tion of Mg alloy continues even after the formation of phos-phate �lms. This is because H2O migrates in phosphate �lms and always contacts the Mg alloy. In the case of defect-free phosphate �lms, the diffusion of PO4

3− and alkaline earth metal ions in phosphate �lms seems to be extremely slow at room temperature. However, the cracks are reported to be present in phosphate �lms,4) and the diffusion of PO4

3− and alkaline earth metal ions in phosphate �lms seems to occur

Fig. 6　XRD patterns of the precipitates that resulted from the solutions containing Mg, Ca, Sr and Ba after measuring the pH titration curves shown in Fig. 5 [(a) Mg, (b) Ca, (c) Sr, (d) Ba]

Table 3　Precipitates analyzed via the X-ray diffraction (XRD) patterns shown in Fig. 6.

Alkaline earth metals Precipitates

MgMg3(PO4)2, Mg3(PO4)2(H2O)8

Mg3(PO4)2(H2O)4, Mg2PO4OH·4H2O

CaCa3(PO4)2, Ca3(PO4)2·H2OCa5(PO4)3(OH)

SrSr3(PO4)2, Sr5(PO4)3(OH)Sr10O(PO4)6

Ba Ba3(PO4)2

1011Formation Behavior of Phosphoric Acid-Based Chemical Conversion Films Containing Alkaline Earth Metals on Magnesium Alloy

Fig. 7　Composition pro�les in the depth direction of phosphate �lms. (The phosphate coating was performed �rst in the solution containing Ca, and succes-sively was performed in the solution containing Sr)

Fig. 8　Composition pro�les in the depth direction of phosphate �lms. (The phosphate coating was performed �rst in the solution containing Sr, and succes-sively was performed in the solution containing Ba)

1012 A. Nakamura, S. Oue, H. Koga and H. Nakano

through the cracks.Focusing on the effect of the type of alkaline earth metal on

the structure and formation behavior of phosphate �lms, there was some difference in pH in the vicinity of Mg alloy during phosphating, and the pH was lowest in a solution containing Mg and highest in a solution containing Ba. The thickness of phosphate �lms is reported to be the largest in a solution con-taining Mg and the smallest in a solution containing Ba,4) which corresponds to the pH in the vicinity of Mg alloy during phosphating, i.e., in a solution containing Mg, the phosphate �lms are formed at a lower pH, and therefore, the thickness appears to increase. In the precipitation that oc-curred during the measurement of pH titration curve, only Ba3(PO4)2 with the highest crystallinity was formed in a solu-tion containing Ba (Fig. 6, Table 3), which seems to be relat-ed to the smallest thickness of phosphate �lms. The corrosion resistance of phosphate �lms is reported to be the worst in a solution containing Mg,4) which is attributed to the formation of cracks because of the increase of phosphate �lm thickness.

4.　 Conclusion

The structure and formation behavior of phosphate �lms of Mg alloy obtained from phosphating solutions containing Mg, Ca, Sr, and Ba as alkaline earth metals were investigated. XRD patterns of all the phosphate �lms broadened irrespec-tive of the type of alkaline earth metal, which characterizes the �lms as amorphous structures. XPS analysis revealed that P in phosphate �lms existed in the �ve-valence form. The pH in the vicinity of Mg alloy during the phosphating was mea-sured using an Sb microelectrode. The pH of Mg alloy in solutions containing Mg, Ca, Sr, and Ba was 10.4, 11.4, 10.7,

12.0, respectively, indicating that phosphoric acid dissociates to third stage and that phosphate [M3(PO4)2] containing alka-line earth metal (M) is formed during phosphating. The cross section of phosphate �lms obtained repeatedly from the two types of solution was analyzed. As a result, the new phos-phate �lms were found to be formed at the interface between the Mg alloy substrate and the phosphate �lm, and the former phosphate �lms were lifted toward the upper area of the �lms.

REFERENCES

1) The Japan Magunesium Association: Handbook of Advanced Magne-sium Technology, (Kallos Publishing Co., Tokyo, 2007) p.411.

2) Robert S. Busk: Magnesium Products Design, (The Japan Magunesium Association, Tokyo, 1988) p.15.

3) R. Morita and K. Osita: J. Surf. Finish. Soc. Jpn. 53 (2002) 182–184. 4) H. Koga, A. Nakamura, S. Oue and H. Nakano: J. Surf. Finish. Soc.

Jpn. 66 (2015) 108–113. 5) T. Ishizaki, I. Shigematsu and N. Saito: Surf. Coat. Tech. 203 (2009)

2288–2291. 6) S. Shadanbaz and G.J. Dias: Acta Niomaterialia 8 (2012) 20–30. 7) F.Z. Cui, J.X. Yang, Y.P. Jiao, Q.S. Yin, Y. Zhang and I.S. Lee: Front.

Mater. Sci. China 2 (2008) 143–148. 8) L.Y. Niu, J.X. Lin, Y. Li, Z.M. Shi and L.C. Xu: Trans. Nonferrous Met.

Soc. China 20 (2010) 1356–1360. 9) J.X. Yang, F.Z. Cui, Q.S. Yin, Y. Zhang, T. Zhang and X.M. Wang:

IEEE Trans. Plasma Sci. 37 (2009) 1161–1168. 10) Y. Zhou, Q.Y. Xiong and J.P. Xiong: Int. J. Electrochem. Sci. 10 (2015)

2812–2824. 11) H. Fukushima, T. Akiyama, J.H. Lee, M. Yamaguchi and K. Higashi: J.

Met. Finish. Soc. Jpn. 33 (1982) 574–578. 12) K. Shimamura: Doctoral thesis, Waseda University, (2006) p.15–16. 13) Shimadzu Corporation: X-ray Photoelectron Spectroscopy- ESCA

spectra database (Shimadzu Co., Kyoto, 1990) p.14. 14) K. Nagashima and I. Tomita: Analytical Chemistry, revised edition

(Shokabo, Tokyo, 2002) p.209.

1013Formation Behavior of Phosphoric Acid-Based Chemical Conversion Films Containing Alkaline Earth Metals on Magnesium Alloy