ELECTROCHEMICAL BEHAVIOR AND PASSIVITY 

OF TITANIUM GRADES 7 AND 29 UNDER 

IMMERSION CONDITIONS 

Prepared for 

U.S. Nuclear Regulatory Commission 

Contract NRC–02–07–006 

Prepared by 

Xihua He 

Center for Nuclear Waste Regulatory Analyses 

San Antonio, Texas 

September 2011
ii

ABSTRACT 

This report documents the results of experimental studies that were conducted to evaluate the 

difference in corrosion behavior between Titanium Grades 7 and 29 under immersion 

conditions. In the proposed Yucca Mountain repository, titanium alloys (Grades 7 and 29) 

would be used to fabricate the drip shield, which is one of the engineered barriers. Because of 

the lack of long-term corrosion rates data for Titanium Grade 29, the U.S. Department of Energy 

(DOE) assumed that the corrosion rates for the Titanium Grade 29 structural supports are the 

same as those for the outer surface of the Titanium Grade 7 plate. This work was conducted to 

understand the difference in electrochemical behavior and passive film properties between 

Titanium Grades 7 and 29. 

Cathodic and anodic polarization techniques were used to examine the electrochemical 

behavior of Titanium Grades 7 and 29 at 95 °C [203 °F] in a simulated crevice solution 

containing deaerated 5 M NaCl and 0.1 M HCl. The open circuit potential for Titanium Grade 29 

was about 50 mV lower than that for Titanium Grade 7, but it was about 390 mV higher than that 

of commercially pure titanium, suggesting that the ruthenium addition to titanium passivated the 

material significantly, but the passivity was slightly lower than that with palladium addition. Both 

palladium in Titanium Grade 7 and ruthenium in Titanium Grade 29 influenced the proton 

reduction kinetics resulting in enhancement of the crevice corrosion resistance; however, 

palladium and ruthenium appeared not to influence much of the anodic dissolution behavior. 

The electrochemical impedance spectroscopy tests were conducted to study the passive film 

resistance in Yucca Mountain repository-relevant chemistries. The results indicated high 

passivity for both materials, and the passive film resistance appeared to be independent of 

temperature. Compared to Titanium Grade 7, Titanium Grade 29 showed lower passive film 

resistance; however, the difference is not significant. 
iii

CONTENTS 

Section Page 

ABSTRACT ................................................................................................................................... ii 

FIGURES ..................................................................................................................................... iv 

TABLES ........................................................................................................................................ v 

ACKNOWLEDGMENTS .............................................................................................................. vi 

1 INTRODUCTION ................................................................................................................ 1-1 

 1.1 Background ................................................................................................................ 1-1 

 1.2 Objective .................................................................................................................... 1-2 

2 EXPERIMENTS .................................................................................................................. 2-1 

2.1 Cathodic and Anodic Polarization .............................................................................. 2-1 

2.2 Electrochemical Impedance Spectroscopy ................................................................ 2-1 

3 RESULTS AND DISCUSSION ........................................................................................... 3-1 

3.1 Cathodic and Anodic Polarization .............................................................................. 3-1 

3.2 Electrochemical Impedance Spectroscopy ................................................................ 3-3 

4 SUMMARY AND CONCLUSIONS ...................................................................................... 4-1 

5-1 REFERENCES ................................................................................................................... 5-1 
iv 

FIGURES 

Figure Page 

1-1 Schematic Illustrating the Polarization Curve for Titanium and its Relationship 

 To the Cathodic Polarization Curves for Proton Reduction on Unalloyed 

 Titanium and on a Platinum Group Metal Alloyed Titanium .......................................... 1-2 

3-1 Cathodic Polarization of (a) Titanium Grades 7 and 29 and 

 (b) Titanium Grades 2 and 7 .......................................................................................... 3-1 

3-2 Anodic Polarization Curves of (a) Titanium Grades 7 and 29 and 

 (b) Titanium Grades 2 and 7 in a Simulated Crevice Solution ....................................... 3-2 

3-3 Bode Plots of Electrochemical Impedance Spectra Recorded on 

 Titanium Grades 7 and 29 in Simulated Concentrated Water ....................................... 3-4 

3-4 One-Time Constant Analog Circuit Model for Fitting Electrochemical 

 Impedance Spectroscopy Data ...................................................................................... 3-5 

3-5 Bode Plots of Electrochemical Impedance Spectra Recorded on 

 Titanium Grades 7 and 29 in Aerated Simulated Concentrated Water .......................... 3-7 

3-6 Bode Plots of Electrochemical Impedance Spectra Recorded on Titanium 

 Grades 7 and 29 in Simulated Acidified Water .............................................................. 3-8 
v 

TABLES 

Table Page 

2-1 Chemical Composition of Titanium Grades 7 and 29 (in Weight Percent) ..................... 2-2 

2-2 Chemical Compositon of Simulated Concentrated Water and Simulated 

 Acidified Water ............................................................................................................... 2-2 

3-1 Open Circuit Potentials of Titanium Grades 7, 29, and 2 Measured from 

 N2-Deaerated 5 M NaCl and 1 M HCI at 95 °C [203 °F] (in VSCE) .................................. 3-2 

3-2 Passive Film Resistance of Titanium Grades 7 and 29 Obtained by Fitting 

 Electrochemical Impedance Spectroscopy Shown in Figure 3-3 (in Ohms cm2

) ........... 3-6 

3-3 Passive Film Resistance of Titanium Grades 7 and 29 Obtained by Fitting 

 Electrochemical Impedance Spectroscopy Shown in Figure 3-5 (in Ohms cm2

) ........... 3-6 
vi 

ACKNOWLEDGMENTS 

This report describes work performed by the Center for Nuclear Waste Regulatory 

Analyses (CNWRA) for the U.S. Nuclear Regulatory Commission (USNRC) under Contract 

No. NRC–02–07–006. The activities reported here were performed on behalf of the USNRC 

Office of Nuclear Material Safety and Safeguards, Division of High-Level Waste Repository 

Safety. This report is an independent product of CNWRA and does not necessarily reflect the 

view or regulatory position of USNRC. 

The authors gratefully acknowledge P. Shukla for his technical review, Y. Pan for his 

programmatic review, L. Mulverhill for her editorial review, and A. Ramos for his administrative 

support. Special thanks to B. Derby and G. Bird for their assistance in conducting experiments 

in this study. 

QUALITY OF DATA, ANALYSES, AND CODE DEVELOPMENT 

DATA: All CNWRA-generated original data contained in this report meet the quality assurance 

requirements described in the Geosciences and Engineering Division Quality Assurance 

Manual. Sources for other data should be consulted for determining the level of quality for 

those data. All data and calculations related to this report have been recorded in CNWRA 

Scientific Notebooks 794 (He, 2011a) and 1024E (He, 2011b). 

ANALYSES AND CODES: None. 

REFERENCES 

He, X. “Corrosion Tests of Titanium Alloys.” Scientific Notebook No. 794. San Antonio, Texas: 

CNWRA. pp. 66–92. 2011a. 

He, X. “Corrosion Tests of Titanium Alloys and Borated Stainless Steel.” 

Scientific Notebook No. 1024E. San Antonio, Texas: CNWRA. pp. 1–68. 2011b. 
1-1 

1 INTRODUCTION 

This report is part of the knowledge management activities for the U.S. Nuclear Regulatory 

Commission (NRC) high-level waste repository safety program. The report documents 

experimental work to assess the difference in electrochemical behavior and passive film 

properties between Titanium Grades 7 and 29. 

1.1 Background 

In the proposed Yucca Mountain repository (DOE, 2008), the titanium alloy (Grades 7 and 29) 

drip shields and Alloy 22 (Ni−22Cr−13Mo−3W−4Fe) waste package outer containers are 

components of the engineered barrier system. The drip shield is designed to divert water that 

could have entered the drift and prevent the water from contacting the waste package. DOE 

(2008) stated that the drip shield plates will be fabricated from Titanium Grade 7 (UNS R52400). 

Titanium Grade 7 is a commercially pure titanium alloy with the addition of a small amount 

of palladium (approximately 0.2 wt%) to enhance its corrosion resistance. The drip shield 

structural supports will be fabricated from Titanium Grade 29 (UNS R56404), which is a titanium 

alloy composed of approximately 6 wt% aluminum and 4 wt% vanadium for strength, plus 

approximately 0.1 wt% ruthenium for corrosion resistance. 

Titanium is highly resistant to corrosion in a wide range of environments conferred by the 

naturally formed passive film on the surface. However, as pH decreases and temperature 

increases, titanium passivity decreases resulting in decreasing corrosion resistance, especially 

crevice corrosion resistance. One of the most effective strategies for enhancing the corrosion 

resistance, especially in a reducing acidic environment such as the crevice region, is through 

alloying with platinum group metals (platinum, palladium, rhodium, ruthenium, iridium, and 

osmium) (Schutz, 2003). Among the platinum group metals, platinum and ruthenium are 

commonly used as the alloying elements. It is generally accepted that the function of these 

noble metal elements is to create cathodic sites, which catalyze proton reduction in the 

reducing acidic environment. As schematically shown in Figure 1-1, this catalysis of proton 

reduction shifts the corrosion potential into the passive region, thereby enhancing the 

corrosion resistance. 

Although both palladium and ruthenium can enhance titanium corrosion resistance, Schutz 

(2003) indicates that for the same amount of alloying elements, palladium is more effective in 

enhancing corrosion resistance than ruthenium. Ruthenium content needs to be approximately 

twice that of palladium to achieve equivalent corrosion resistance. The difference could be 

because of the different catalysis capabilities of palladium and ruthenium. For titanium 

materials, because the ruthenium content in Titanium Grade 29 is less than the palladium 

content in Titanium Grade 7, the corrosion resistance of Titanium Grade 29 could be lower than 

that of Titanium Grade 7 based on the observation by Schutz (2003). 
1-2 

Figure 1-1. Schematic Illustrating the Polarization Curve for Titanium and its 

Relationship to the Cathodic Polarization Curves for Proton Reduction on Unalloyed 

Titanium and on a Platinum Group Metal Alloyed Titanium 

1.2 Objective 

Because of the presence of different alloying elements in Titanium Grades 7 and 29, 

and scarcity of data available in the literature to evaluate the corrosion behavior of 

Titanium Grade 29, the objective of this work is to investigate the possible different 

electrochemical behavior and passivity of Titanium Grades 7 and 29 under immersion 

conditions. The results are used to evaluate the difference in passive film properties between 

Titanium Grades 7 and 29. 

Log (current density) 

Potential 

Titanium anodic polarization curve 

Cathodic reaction (proton 

reduction) catalyzed by 

platinum group metals 

Cathodic reaction on 

Active region unalloyed titanium 

Passive region 
2-1 

2 EXPERIMENTS 

Electrochemical polarization and impedance spectroscopy were used to understand the 

possible difference in corrosion resistance properties of Titanium Grades 7 and 29. 

Experiments were carried out with cylindrical specimens 6.2 mm [0.24 in] in diameter and 

48 mm [1.9 in] in length machined from the same Titanium Grades 7 and 29 as for the dripping 

tests.1

 The Titanium Grade 7 is in mill-annealed condition with a single α-phase conforming to 

ASTM B265 (ASTM International, 2008). The Titanium Grade 29 is in the β-transformed 

(final processed above the β-transus temperature) plus subsequently annealed condition 

conforming to ASTM B861 (ASTM International, 2010). The Titanium Grade 29 has an α-plus-β

phase structure. Both titanium grades were used as in the as-received condition without any 

heat treatment. In the prototype drip shield design, DOE proposed to heat treat the drip shield 

assembly to relieve stress from the fabrication process at 593 °C [1,100 °F] for a minimum of 

2 hours (BSC, 2007). Heat treatment below the β-transus temperature is not expected to affect 

the corrosion properties. The chemical composition of the titanium specimens used in this study 

is shown in Table 2-1. All specimens were polished up to a 600-grit finish and cleaned 

ultrasonically in deionized water and acetone. At the completion of each test, the specimens 

were rinsed in deionized water and dried. 

2.1 Cathodic and Anodic Polarization 

To understand the role of palladium in Titanium Grade 7 and ruthenium in Titanium Grade 29 on 

corrosion resistance properties of the alloys, the cathodic and anodic polarization behaviors of 

Titanium Grades 7 and 29 were examined at 95 °C [203 °F] in a simulated crevice solution 

containing 5 M NaCl and 0.1 M HCl deaerated with ultra high purity N2. The test solution and 

temperature were the same as those Brossia and Cragnolino (2004) and Brossia, et al. (2001) 

used to examine the electrochemical behavior difference between Titanium Grades 2 and 7 

(Titanium Grade 2 is commercially pure titanium without any noble alloy element addition). 

During the tests, about 38 mm [1.5 in] out of the 48 mm [1.9 in] cylindrical specimen was 

immersed in solution. The cathodic polarization tests were performed from 100 mV above the 

open circuit potential down to −0.8 VSCE at the same scan rate as the anodic polarization tests. 

In a separate test, anodic polarization tests were performed from 100 mV below the open circuit 

potential up to 1.0 VSCE at a scan rate of 0.167 mV/s. All the polarization tests were conducted 

in a glass cell with a 200-mL [0.053-gal] solution. The cells were fitted with a water-cooled 

condenser and a water trap to minimize solution loss at elevated temperatures and by air 

intrusion. The saturated calomel reference electrode was connected to the solution through a 

water-cooled Luggin probe with a porous silica tip, and the reference electrode was maintained 

at room temperature. A platinum flag was used as a counter electrode. 

2.2 Electrochemical Impedance Spectroscopy 

The electrochemical impedance spectroscopy tests were conducted in 2-L [0.53-gal] glass cells 

with polytetrafluoroethylene lids. The cell has the same configuration as that for the polarization 

tests. The groundwater chemistries relevant to the Yucca Mountain repository including 

simulated concentrated water and simulated acidified water were used in the test 

(Gordon, 2002). Table 2-2 summarizes the chemical composition of simulated concentrated 

 

1

Jung, H., X. He, T. Ahn, T. Mintz, and R. Pabalan. “Corrosion of Alloy 22 and Titanium Alloys Under Seepage Water 

Dripping Conditions.” San Antonio, Texas: CNWRA. 2011. Under NRC review. 
2-2 

Table 2-1. Chemical Composition of Titanium Grades 7 and 29 

(in Weight Percent) 

Material Ti* Pd* Fe* C* N* O* H* Al* V* Ru* 

Titanium Grade 7 

Heat CN2775 Balance 0.16 0.08 0.01 0.01 0.13 0.001 N/A N/A N/A 

Titanium Grade 29 

Heat 00192DB Balance NA 0.19 0.04 0.006 0.109 0.0021 5.62 4.16 0.10 

*Ti—titanium, Pd—palladium, Fe—iron, C—carbon, N—nitrogen, O—oxygen, H—hydrogen, 

 Al—aluminum, V—vanadium, Ru—ruthenium, N/A—not applicable

Table 2-2. Chemical Composition of Simulated Concentrated Water and Simulated 

Acidified Water 

Simulated Concentrated Water Simulated Acidified Water 

Chemical Reagents Concentration (g/L*) Chemical Reagents Concentration (g/L*) 

KCl 6.48 KCl 6.52 

NaCl 5.44 NaCl 34.92 

NaNO3 8.75 NaNO3 27.30 

Na2SO4 20.71 Na2SO4 50.8 

NaHCO3 96.40 MgSO4 • 7H2O 10.11 

NaF 3.10 Ca(NO3)2 • 4H2O 5.90 

 Na2SiO3 • 5H2O 0.20 

 H2SO4 

(specific density of 

1.84 g/cm3

) 

150 μL [0.0051 fl oz] 

*1 g/L = 8.35 × 10−3 lb/gal

water and simulated acidified water. Simulated concentrated water has a pH ranging from 

9.8 to 10.2. The pH of simulated acidified water is around 2.7. For one set of tests in simulated 

concentrated water, the solution was deaerated with ultra high purity N2. All other tests were 

open to air through the condenser. During the test, 41 mm [1.5 in] out of the 48 mm [1.9 in] 

cylindrical specimen was immersed in solution. Electrochemical impedance spectra were 

obtained at open circuit over a frequency range of 100,000 to 0.001 Hz at temperatures of 

60, 80, and 95 °C [140, 176, and 203 °F] sequentially. At each temperature the impedance 

spectra were measured about once each week up to several times. After the impedance 

measurements at each temperature, the solution was set to the next higher temperature. The 

total duration for each test was about 2 months. 
3-1 

3 RESULTS AND DISCUSSION 

3.1 Cathodic and Anodic Polarization 

Figure 3-1 shows the cathodic polarization curves for Titanium Grades 7 and 29 obtained from 

deaerated 5 M NaCl and 0.1 M HCl solution at 95 °C [203 °F]. Table 3-1 summarizes the open 

circuit potentials and cathodic Tafel slopes of Titanium Grades 7 and 29 obtained from this 

study and those of Titanium Grade 2 that Brossia, et al. (2001, Figure 4-19) previously obtained 

under the same conditions. The open circuit potential for Titanium Grade 29 was about 50 mV 

lower than that for Titanium Grade 7, but it was about 390 mV higher than that of Titanium 

Grade 2. This suggests that the ruthenium addition to titanium passivated the material 

significantly. For both Titanium Grades 7 and 29, an activation-controlled region was observed 

that was then followed by a mass-transport-limited region. In the activation-controlled region, 

Titanium Grade 7 exhibited a cathodic Tafel slope of −32 mV/decade (Figure 3-1), which is 

similar to −27 mV/decade Brossia, et al. (2001) measured. In this region, Titanium Grade 29 

appeared to show two subregions with a cathodic Tafel slope of −57 mV/decade at lower 

overpotentials followed by −22 mV/decade at higher overpotentials. The average value is close 

to that of Titanium Grade 7 suggesting palladium and ruthenium have a smiliar effect on 

cathodic behavior of titanium. The minor difference could be due to the difference in 

microstructure with Titanium Grade 7 exhibiting single phase and Titanium Grade 29 exhibiting 

two phases. The absolute value of cathodic Tafel slopes for Titanium Grades 7 and 29 was 

smaller than that of Titanium Grade 2 (−100 mV/decade), which suggests that the palladium or 

ruthenium facilitated the cathodic reaction (proton reduction) in this study (i.e., a small change in 

Figure 3-1. Cathodic Polarization Curves of Titanium Grades 7 and 29 in a Simulated 

Crevice Solution of Deaerated 5 M NaCl, and 0.1 M HCl at 95 °C [203 °F] 

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00

Ti Grade 7-cathodic polarization

Ti Grade 29-cathodic polarization

bc (Ti Grade 7)= -32 mV/decade

bc (Ti Grade 29)= -22 mV/decade

bc (Ti Grade 29)= -57 mV/decade

Current density, A/cm2

Potential, VSCE
3-2 

Table 3-1. Open Circuit Potentials and Cathodic Tafel Slopes of Titanium Grades 7, 29, 

and 2 Measured from N2-Deaerated 5 M NaCl and 0.1 M HCl at 95 °C [203 °F]

Titanium Grade 7 Titanium Grade 29 Titanium Grade 2 

Open Circuit 

Potentials, VSCE

−0.24 

(from Figure 3-1) 

−0.29 

(from Figure 3-1) 

−0.68* 

Tafel Slopes, 

mV/decade 

−32 

(from Figure 3-1) 

−57, −22( 

from Figure 3-1) 

−100* 

Open Circuit 

Potentials, VSCE

−0.05 

(from Figure 3-2) 

−0.11 

(from Figure 3-2) 

−0.68* 

*Brossia, C.S., L. Browning, D.S. Dunn, O.C. Moghissi, O. Pensado, and L. Yang. “Effect of Environment on the 

Corrosion of Waste Package and Drip Shield Materials.” CNWRA 2001-03. San Antonio, Texas: Center for Nuclear 

Waste Regulatory Analyses. 2001. 

potential applied to Titanium Grades 7 or Grade 29 leads to a large change in current). 

Schutz (2003) indicated that this facilitated cathodic depolarization shifts the alloy potential in 

the noble direction where oxide film passivation is possible. This study shows that both 

palladium and ruthenium influenced the cathodic reaction kinetics and both Titanium Grades 7 

and 29 will have higher crevice corrosion resistance than Titanium Grade 2. 

Figure 3-2 shows the anodic polarization curves of Titanium Grades 7 and 29 obtained from 

deaerated 5 M NaCl and 0.1 M HCl solution at 95 °C [203 °F]. The open circuit potential is 

summarized in Table 3-1 along with that of Titanium Grade 2 Brossia, et al. (2001, Figure 4-20) 

previously obtained under the same conditions. Consistent with the cathodic polarization 

behavior, Titanium Grade 7 exhibited slightly higher open circuit potential. Both materials 

exhibited essentially passive behavior at all potentials above the corrosion potential. Titanium 

Grade 29 showed slightly higher anodic current at lower potential, but it decayed to values close 

Figure 3-2. Anodic Polarization Curves of Titanium Grades 7 and 29 (Brossia, et al., 2001, 

Figure 4-20) in a Simulated Crevice Solution of Deaerated 5 M NaCl and 

0.1 M HCl at 95 °C [203 °F] 

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01

Ti Grade 7-anodic polarization

Ti Grade 29-anodic polarization

Current density, A/cm2

Potential, VSCE
3-3 

to that of Titanium Grade 7. The anodic behavior of both Titanium Grades 7 and 29 was similar 

to that of Titanium Grade 2 (Brossia, et al., 2001) suggesting that palladium and ruthenium in 

Titanium Grades 7 and 29 are unlikely to influence anodic dissolution behavior of the alloys. 

3.2 Electrochemical Impedance Spectroscopy 

Figure 3-3 shows the Bode and Nyquist plots of the frequency response of the Titanium 

Grades 7 and 29 as a function of temperature in N2-deaerated simulated concentrated water. 

The Nyquist plots are typical for passive materials with high passive film resistance, which did 

not show a semicircle. At each temperature the impedance measured was reproducible, and 

the impedance response was not affected by temperature. The phase angle spectra in the 

Bode plots seem to suggest that the oxide had two layers, one possibly transformed from the 

original passive layer upon contact with solution. However, the two layers were not very 

distinctive. For simplification, the spectra were fit to an analog equivalent circuit with one-time 

constant shown in Figure 3-4. The polarization resistance corresponding to the passive film 

resistance from fitting the spectra is summarized in Table 3-2. The average film resistance from 

all three temperatures for Titanium Grade 7 was almost two orders of magnitude higher than 

that of Titanium Grade 29, indicating lower passivity for Titanium Grade 29 under the same 

test conditions. After the test the specimen appeared darker, but no localized corrosion 

was observed. 

Tests were also conducted in simulated concentrated water and simulated acidified water under 

aerated condition. Similar to what was observed from Figure 3-3, the impedance response was 

not affected by temperature. (The spectra from aerated simulated concentrated water are not 

shown, because they were similar to Figure 3-3.). The Titanium Grade 7 specimen showed 

higher film resistance suggesting higher passivity for Titanium Grade 7 under the test 

conditions. The spectra were also fit to the analog equivalent circuit shown in Figure 3-4, and 

Table 3-3 summarizes the passive film resistance from fitting the spectra. The average film 

resistance for Titanium Grade 7 is less than one order of magnitude higher than that of 

Titanium Grade 29. 

The Bode plots of the frequency response of the Titanium Grades 7 and 29 specimens in 

aerated simulated acidified water at 60 °C [140 °F] are shown in Figure 3-5 (data from other 

temperatures were not included because they were too noisy). In the impedance 

magnitude spectra, the spectroscopy for Titanium Grade 7 was slightly greater than that for 

Titanium Grade 29 indicating that Titanium Grade 29 has slightly lower passive film resistance. 

The posttest specimens are shown in Figure 3-6. For the test from simulated concentrated 

water, the surface was covered by a layer of white deposits from the solution. For the test from 

simulated acidified water, deposits were only shown at the interface of solution and vapor. No 

pitting corrosion was observed from either test. 

Both the polarization and electrochemical impedance spectroscopy show that Titanium 

Grade 29 had lower passive film resistance than Titanium Grade 7. The dripping tests1

 at 95 °C 

[203 °F] and 75 percent relative humidity showed that Titanium Grade 29 had higher corrosion 

rate, which could be attributed to the lower passive film resistance. The observation from this 

study is different from that Andresen and Kim (2006) reported whereby the corrosion resistance 

for Titanium Grades 7 and 29 was nearly identical. 

 

1

Jung, H., X. He, T. Ahn, T. Mintz, and R. Pabalan. “Corrosion of Alloy 22 and Titanium Alloys Under Seepage Water 

Dripping Conditions.” Under NRC review. San Antonio, Texas: CNWRA. 2011. Under NRC review. 
3-4 

(a) 

Figure 3-3. (a) Bode Plots and (b) Nyquist Plots of Electrochemical Impedance Spectra 

Recorded on Titanium Grades 7 and 29 in N2-Deaerated Simulated Concentrated Water at 

60, 80, and 95 °C [140, 176, and 203 °F] 

1

10

100

1000

10000

100000

1000000

10000000

0.001 0.01 0.1 1 10 100 1000 10000 100000 1000000

lZl (Ohms·cm2)

Frequency (Hz)

Ti7, 60°C

Ti7, 60°C

Ti7, 60°C

Ti7, 60°C

Ti7, 80°C

Ti7, 80 °C

Ti29, 60°C

Ti29, 60°C

Ti29, 60°C

Ti29, 80°C

Ti29, 80°C

Ti7, 95°C

Ti29, 95°C

Titanium Grade 7

Titanium Grade 29

-120

-100

-80

-60

-40

-20

0

20

40

60

0.001 0.01 0.1 1 10 100 1000 10000 100000 1000000

Phase angle (degrees)

Frequency (Hz)

Ti7, 60 °C

Ti7, 60 °C

Ti7, 60 °C

Ti7, 60 °C

Ti7,80 °C

Ti7, 80 °C

Ti29, 60 °C

Ti29, 60 °C

Ti29, 60 °C

Ti29, 80 °C

Ti29, 80 °C

Ti7, 95°C

Ti29, 95°C

Titanium Grade 7

Titanium Grade 29
3-5 

(b)

Figure 3-3 (continued). (a) Bode Plots and (b) Nyquist Plots of Electrochemical 

Impedance Spectra Recorded on Titanium Grades 7 and 29 in N2-Deaerated Simulated 

Concentrated Water at 60, 80, and 95 °C [140, 176, and 203 °F] 

Figure 3-4. One-Time Constant Analog Circuit Model for Fitting Electrochemical 

Impedance Spectroscopy Data 

Note: Rs⎯Solution resistance; Rp⎯Polarization resistance; CPE⎯Constant 

Phase Element 

-100000

400000

900000

1400000

1900000

2400000

2900000

-100000 400000 900000 1400000

Ti7, 60°C

Ti7, 60°C

Ti7, 60°C

Ti7, 60°C

Ti7, 80°C

Ti7, 80°C

Ti29, 60°C

Ti29, 60°C

Ti29, 60°C

Ti29, 80°C

Ti29, 80°C

Ti29, 80°C

Ti7, 95°C

Ti29, 95°C

RealZ (Ohm·cm2)

-ImZ (Ohm·cm2)

Titanium Grade 7

Titanium Grade 29

Rs CPEp

Rp
3-6 

Table 3-2. Passive Film Resistance of Titanium Grades 7 and 29 Obtained by Fitting 

Electrochemical Impedance Spectroscopy shown in Figure 3-3 

(in Ohms·cm2

) 

Material 60 °C [140 °F] 80 °C [176 °F] 95 °C [203 °F] Average 

Titanium Grade 7 

7.3 × 106

1.3 × 107

1.3 × 107

9.9 × 106

1.9 × 107 1.4 × 107

 1.3 × 107

Titanium Grade 29 

6.5 × 105

8.0 × 105

6.8 × 105

5.5 × 105

5.5 × 105 5.5 × 105

 6.3 × 105

Table 3-3. Passive Film Resistance of Titanium Grades 7 and 29 Obtained by Fitting 

Electrochemical Impedance Spectroscopy From Aerated Simulated Concentrated Water 

(in Ohms·cm2) 

Material 60 °C [140 °F] 80 °C [176 °F] Average 

Titanium Grade 7 4.7 × 106

8.7 × 106

8.3 × 106

6.1 × 106 6.4 × 106

Titanium Grade 29 3.5 × 106

2.2 × 106

2.2 × 106

3.0 × 106 2.7 × 106
3-7 

Figure 3-5. Bode Plots of Electrochemical Impedance Spectra Recorded on 

Titanium Grades 7 and 29 in Aerated Simulated Acidified Water at 60 °C [140 °F] 

0.1

1

10

100

1000

10000

100000

1000000

10000000

0.001 0.01 0.1 1 10 100 1000 10000 100000 1000000

lZl (Ohms·cm2)

Frequency (Hz)

Ti7-SAW-60°C

Ti29-SAW-60°C

-100

-80

-60

-40

-20

0

20

40

60

0.001 0.01 0.1 1 10 100 1000 10000 100000 1000000

Phase angle (degrees)

Frequency (Hz)

Ti7-SAW-60 °C

Ti29-SAW-60°C
3-8 

 

Titanium Grade 7 Titanium Grade 29 Titanium Grade 7 Titanium Grade 29

(a) (b) 

Figure 3-6. Posttest Titanium Grades 7 and 29 Specimens From (a) Simulated Concentrated 

Water and (b) Simulated Acidified Water 
4-1 

4 SUMMARY AND CONCLUSIONS 

In the proposed Yucca Mountain repository (DOE, 2008), the titanium alloy (Grades 7 and 29) 

drip shield is an engineered barrier designed to divert water that enters the drift and prevent it 

from contacting the waste package. The corrosion resistance of Titanium Grades 7 and 29 is 

enhanced by adding a small amount of palladium and ruthenium, respectively. This work was 

conducted to understand the difference in electrochemical behavior and passive film properties 

between Titanium Grades 7 and 29. 

To understand how palladium affects the electrochemical behavior of Titanium Grade 7 and 

ruthenium affects Titanium Grade 29, the cathodic and anodic polarization behaviors of 

Titanium Grades 7 and 29 were examined at 95 °C [203 °F] in a simulated crevice solution 

containing deaerated 5 M NaCl and 0.1 M HCl. The open circuit potential for Titanium Grade 29 

was about 20 mV lower than that for Titanium Grade 7, but it was about 390 mV higher than that 

of Titanium Grade 2, suggesting that the ruthenium addition to titanium passivated the material 

significantly, but the passivity was lower than that with palladium addition. Both palladium and 

ruthenium influenced the cathodic reaction kinetics and both Titanium Grades 7 and 29 will have 

higher crevice corrosion resistance than Titanium Grade 2. Palladium and ruthenium did not 

appear to influence much of the anodic dissolution behavior compared to Titanium Grade 2. 

The electrochemical impedance spectroscopy tests were conducted to study the passive film 

resistance. The groundwater chemistries relevant to Yucca Mountain including simulated 

concentrated water and simulated acidified water were used in the test. The impedance 

response from both materials was typical for passive materials with high oxide film resistance. 

The passive film resistance was not affected by temperature. The Titanium Grade 7 specimen 

showed higher film resistance indicating higher passivity for Titanium Grade 7 under the 

test conditions. 

In summary, both polarization and electrochemical impedance spectroscopy show that Titanium 

Grade 29 had lower passive film resistance than Titanium Grade 7. However, both tests show 

that Titanium Grades 7 and 29 had high passivity. Compared to the difference between 

Titanium Grade 7 and commercially pure titanium, the difference between Titanium Grades 7 

and 29 is not significant. 
0 

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