//e //- ^

MHD MATERIALS - SEED/SLAG INTERACTIONS AND EFFECTS

QUARTERLY PROGRESS REPORT

January 1 - March 31, 1981

Samuel J. Schneider

Project Manager

Center for Materials Science

U. S. Department of Commerce

National Bureau of Standards

Washington, D. C. 20234

PREPARED FOR THE UNITED STATES

DEPARTMENT OF ENERGY

MHD OFFICE

"This report was prepared as an account of work sponsored by the United

States Government. Neither the United States nor the United States

Department of Energy, nor any of their employees, nor any of their

contractors, subcontractors, or their employees, makes any warranty,

express or implied, or assumes any legal liability or responsibility

for the accuracy, completeness, or usefulness of any information,

apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights."

TABLE OF CONTENTS

I. SUMMARY OF PROGRESS TO DATE

II. DETAILED DESCRIPTION OF TECHNICAL PROGRESS .

1. Thermochemistry of Seed and Slag . . . .

2. Electrical Conductivity and Polarization

3. Corrosion of Downstream MHD Components .
,

-
I. Summary of Proyress to Date

1. Thermochemistry of Seed and Slag

An equation representing K-pressures covering the concentration

ranges: K^O, 3-14 wt%; CaO, 17-36 l\ and AKOo, 14-36 %: balance, S i Op was fit to the data previously obtained from four component simplified

"Western" channel slags. The equation uses three linear terms in

concentration variables, a term in 1/T and a constant. Increases in the

l<20 and A1

? 03

concentrations of one percent predict increases in the

K-pressure ot 20 and -4 percent, respectively, while the effect due to

CaO is negligible in this approximation. The standard deviation in the

fit is 34 percent. Differences between the model and data are probably

due to the assumption that bulk compositions represent the actual

concentration in the slag solutions.

Experiments were continued in the system I< 20 -Ca 0 -Al 203 -Si 02 . Evidence suggests lack of significant solid solution within the

compositional region investigated with the possible exception of

KA 1 S i ^ 0 6

.

2. Electrical Conductivity and Polarization

Data has been obtained to show a time- temperature relationship for

obtaining a stable conductivity measurement in slag derived from coal from

the Rosebud seam in Montana. Both AC and DC four probe conductivity

measurements on this slag have been completed. A series of quenching

experiments have also been completed but analysis of these experiments

will be made later.

Four probe AC measurements were made on a sample of Na beta alumina,

a known fast ion conductor, for comparison with the measurements made on the Rosebud slag also hypothesized to be at least a partially ionic

conductor.

3. Corrosion of Downstream MHD Components

Specimens of A213-T22 steel tubes were exposed to K^SCL seeded fuel

rich and oxygen rich hot gas streams. The wall temperature? of the specimens

were maintained at 400 °C, 500 °C and 590 °C, respectively. SEM and EDX

analysis were conducted on metallographically prepared sections of the

specimens to determine the extent and the chemical nature of the reaction

zone between the metal and the deposited salt coating. The distribution

of the metal cations in the reaction zone is detailed and the extent of

cation penetration into the deposited coating is described.

1
II. Detailed Description of Technical Progress

1. Thermochemistry of Seed and Slag (E. R. Plante and L. P. Cook)

A. Vaporization Studies (E. R. Plante)

Progress : An objective of the current work is to obtain K-pressure data

for selected compositions of the four component system, K2 0-Ca0-Al 2 0 3 - Si02

. These selected compositions correspond to the channel slag which

would be produced by the interaction of seeded combustion gases with

simplified "Western" coal ash. A second objective is to predict the Kpressure or K2 0 activity in melts with compositions not too different

from those studied by using the data base generated to develop an initially empirical model. Finally, it is planned to extend the model to

other coal ash compositions, including additional components, such as Fe2 0 3 and MgO. The basic use of such a model is to aid in determining

the magnitude of seed loss to slag in MHD systems and to suggest the

best method to minimize this effect.

Thus far, vapor pressure data have been determined for four different samples. Table 1 lists the initial mineral constituents and the

starting and final composition in wt% of each of the four components.

All vapor pressure measurements have been obtained using a Knudsen

effusion, modulated beam mass spectrometric method.

During the current quarterly period, further studies and analysis

of the KCAS-VP-4 measurements were made. As noted in the last report,

the vapor pressures were approximately a factor of two higher than

expected, and the decrease in volatility with composition was not as large as expected. We have now concluded that the initial analysis of

the data was in error because of an incorrect weight loss during the

first part of the experiment. In the final part of the experiment, the mass spectrometer constant was about a factor of two lower than in the

earlier part and the use of a mass spectrometer constant weighted toward

the latter value removes the apparent discrepancy.

Most effort during this period has been devoted to the development

of an empirical model to predict K vapor pressures or activities of K2 0

in molten slags. As a data base for this model, we have used the data

obtained in the KCAS-VP-1, KCAS-VP-2 and KCAS-VP-3 experiments. Table 2 lists the results of treating the basic data in the simplest way, that

is, separating the data into groups of limited composition and fitting

the equation,

log P

k = A/T + B ,

by least squares. Table 2 is reproduced from a previous report. A few

of the B terms have been altered slightly because of updated mass spectrometer constants in the final analysis. The basic data consists of

250 K-pressures at varying T, and compositions of K2 0, CaO, A1 2 0 3 , and

Si

2

. An examination of the slopes in Table 2 shows that they are generally close to 17,000, except for those near the beginning of the

2
KCAS-VP-2 and the KCAS-VP-3 measurements. These lower slopes may be

decreased by impurity evaporation (unreacted K2 C0 3 ). Also, at the

beginning of the KCAS-VP-1 experiment, the initial slopes are 20,000 and

19,000 until the K2 0 bulk composition has been reduced to about nine wt%

K2 0. These higher slopes may be due to increased K2 0 concentration in

the melt. Although all of the compositions have been calculated as though the sample is a homogeneous melt, this is probably not the case. Rather, it is more likely that a relatively homogeneous melt is in

equilibrium with crystalline KAlSi04 , which goes into solution as the

temperature is increased with a resulting increase in both the K2 0 and

A1 2 0 3 concentrations.

In spite of the uncertainties in the composition variables, we have

fit, by least squares, all of the data from the KCAS-VP-1, KCAS-VP-2, and

KCAS-VP-3 measurements to an equation of the following form;

log P (atm) = A/T + B + C(wt% K

2 0) + D(wt% CaO) + E(wt% A12 03

)

.

The values of the coefficients and their standard deviations are listed

in Table 3.

Table 3

Coefficients and Standard Deviations for Model Equation

Term Value Standard Deviation

A -16794 176

B 5.228 0.173

C 7.887 E-2 0.309 E-2

D 1.741 E-3 3.318 E-3

E -1.825 E-2 0.209 E-2

The coefficients in the equation show that each percent increase in the

K2 0 concentration increases the K-pressure by 20 percent, and each

percent increase in the A1 2 0 3 concentration decreases the K-pressure by

four percent. The effect of CaO on the K-pressure using this approximation is negligible. The standard deviation in the fit is 34 percent,

while maximum deviations in individual points generally do not exceed

100 percent. Because most of the data used to fit this model equation

are from data at lower concentration ranges (below about ten wt% K2 0),

it is to be expected that the model equation will predict too high a Kpressure for high "bulk concentrations" of K2 0, mainly because much of

the K2 0 at these compositions is tied up as KAlSi04 . The formation of

crystalline KAlSi04 in the melt can be thought of as a buffering process, whereby the slag can increase its bulk K2 0 content without as large an increase in K-pressure as would be observed if the K2 0 were in

solution.

Figures 1 and 2 are shown as an example of how well the model

equation fits the data. Figure 1 shows the data from the KCAS-VP-1

measurements in the K2 0 bulk composition range from 14.8-12.4 wt% K 2 0.

3
The two reference lines show the K-pressures predicted by the model at

14.8 and 12.4 wt% K2 0, respectively. While it is clear that the data

itself would give a steeper slope, the model representation is quite

good. Figure 2 shows data for the KCAS-VP-2 data in the 11.4-10.7 K2 0

concentration range with the lines representing the upper and lower K2 0

contents, respectively. Again the model representation is quite good.

These examples are neither the best nor worst fit of the data.

Plans : Continue model development work, including application to other

slag compositions. Supplement model data with further measurements as deemed necessary. Investigate effect of solution concentration data

where available on the model.

4
Table 1

Mineral Constituents and Composition of Vaporization Samples

Initial/Final

Composition Wt%

Sample Mineral Constituents (Wt%) k

2 ° CaO A1 2°3 Si 0

2

KCAS-VP-1 KAlSi0

4 (49.8), Ca

2

Si

4

( 1 6 . 5

14.8 27.5 22.2 35.5

Ca

2

Al

2 Si0y(16.5) , Ca^Si2 0y (17.2) 1.6 31.8 25.7 40.9

KCAS-VP-2 KAlSi0

4 (28.6), KA1 S2

0

g

( 1 3 . 8

11.5 17.6 33.7 37.2

Ca

2

Al

2

Si0

7 (28.9), CaAl

2

Si

2

0

g

(28.7) 6.1 18.7 35.7 39.5

KCAS-CP-3 KA1 Si0

4

(42. 0) , CaSi0

3 (58.0) 12.5 28.0 13.5 46.0

1.8 31.4 15.2 51.6

KCAS-VP-4 KAlSi0

4 (66.9), Ca

2

Si0

4

(33. 119.9 21.6 21.6 37.0

2.7 26.2 26.2 44.9

5
Table 2

Slope, Intercept and Standard Deviations for K-Pressure Data

Expt Id wt% k

2o A SD,A B SD,B

KCAS-VP-1

3/13/80 14.8-12.4 -20047 391 8.062 .255

3/14/80 12.4- 9.3 -19071 524 7.196 .334

3/18/80 9.3- 7.2 -17429 452 5.976 .289

3/18/80 6.2- 4.8 -16372 210 4.986 .129

3/21/80 4.8- 4.0 -16896 279 5.207 .178

KCAS-VP-2

5/14/80 11.4-10.7 -14632 434 4.200 .278

5/15/80 10.7- 8.6 -16366 180 5.097 .112

5/16/80 8.6- 6.5 -17571 257 5.656 .158

5/19/80 6.5- 6.2 -16606 526 4.992 .321

KCAS-VP-3

8/13/80 12.5-10.8 -15052 775 4.983 .512

8/14/80 10.8-10.3 -17512 453 6.282 .298

8/14/80 10.3- 7.4 -15441 612 4.732 .374

8/15/80 7.4- 6.0 -16006 581 5.178 .362

8/15/80 6.0- 3.9 -15390 320 4.544 .197

8/18/80 3.9- 3.2 16948 801 5.417 .505

6
Potassium

Pressure

(atm)

4

Figure 1. Potassium pressure vs. 10

4

/T for KCAS-VP-1 sample in the 14 8-12 4 wt% K

2

0 bulk composition range compared to lines from empirical model equation.

7
Potassium

Pressure

(atm)

4 Figure 2. Potassium pressure vs. 10 /T for KCAS-VP-2 sample in the

11.4-10.7 wt% KpO bulk composition range compared to lines from empirical

model equation.

s 8
B. Phase Equilibria in the System K^O-CaO-Al ^C^-SiC^ (L. P. Cook)

Progress

In the previous quarterly report a series of three sets of experiments

were outlined for verification of proposed subsolidus equilibria in the

system K2 0 -Ca 0-Al 2 0 3 -Si 02 . Briefly these are: 1 ) 1000 hr subsolidus

equilibrations in which mixtures of the four crystalline phases cor- responding to each of 13 proposed equilibrium volumes are heated for

extended periods with periodic regrinding and x-ray analysis; 2 ) solid

state tie line reactions using unstable combinations of phases which

in principle should react to produce the stable pair; 3) glass crystallization experiments in which completely melted samples of the four

phase volumes are quenched to produce glass, powdered, sealed in Pt

capsules and crystallized at subsolidus temperatures. For convenience

a diagram of proposed subsolidus relations is shown in Figure 1.

1000 Hour Subsolidus Equilibrations

Specimens of extended equilibrations have been examined by x-ray

diffraction to determine if any changes in parameters have occurred which

might indicate significant solid solution. In general lattice parameter

shifts corresponding to more than .05°2e (CuKa radiation) can be detected

easily. During the last quarter KA1 Si 3 08 was successfully synthesized hydrothermally, making additional experiments possible. Results are summarized

in Table 1 below. In general there appears to be little evidence for

the existence of solid solutions from results of these experiments,

and the four phase assemblages shown in figure 1 appear to be substantiated

with the possible exception of KAlSi 2 06 /KAlSi 3 0 8 /3Al 2 03 *2Si02 /CaAl 2 Si 2 0 8

. Mullite and KA1 Si 2 06 in this assemblage apparently react to produce

a-Al 2 0 3 and an unidentified phase whose principle x-ray lines do not

correspond to any of the silica polymorphs. The possibility of a hydrated phase cannot be ruled out, as this experiment was performed

under a confining pressure of 7500 psi with ^5 wt % H^O in the capsule.

Solid State Tie Line Reactions

Table 2 below summarizes data accumulated to date on two-phase tie

line verification at 1200-1300 °C. Essentially all the tie lines involving

KA1 Si

O

4 shown in figure 1 have now been verified with the exception of

KA1SiQ4 /CaAl 2 Si 2 0 8 , which appears to be complicated by solid solution

relationships (see previous quarterly report).

9
Now that KA1 Si 3 0 8 is available as a starting material, additional

reactions will be tested in the near future to verify KA1 Si 2 0 6 /CaAl 2 Si 2 O 0 and KAlSi 2 0 6 /CaSi0 3 . Verification of KAlSi 3 0 8 /CaAl 2 Si 2 0 8 and

KAlSi 3 0 8 /CaSi0 3 will be done hydrothermal ly.

Glass Crystallization Experiments

Glasses from 8 of the 13 four phase volumes in figure 1 have been

crystallized, as shown in Table 3 below. It was necessary to crystallize

assemblages with KA1 Si 3 0 8 hydrothermal ly (^5 wt % water added; 7500 psi

confining pressure) due to the low temperatures required to maintain

subsolidus conditions. Glasses from the remaining five volumes have not

been successfully prepared due to their high melting nature and high

viscosity, despite heating to temperatures approaching 1900 °C. Results

of experiments in Table 3 are consistent with four-phase volumes

indicated in figure 1. The occurrence of cristobalite instead of

quartz is not surprising; however its lattice parameters do not indicate

substantial solid solution. Lattice parameters of potassium aluminosilicates from certain of the glass crystallization experiments are slightly larger than pure end members. The exact significance of this

is at present uncertain.

Plans

Complete experiments on subsolidus K2 0-Ca0-Al 2 0 3 -Si0 2 . Measure

compositions of invariant melts from four phase volumes. Begin experiments

with iron-containing compositions.

10
Table 1 . Summary of Extended Four-Phase Equilibrations.

Four

Phase Volume

Cumulative Treatment

(Temp °C) (Time, hr)

New Evidence for

Phases? Solid Solution?

KAlSi 0 4 /Al 2 0 3 /

CaAl 1 2 0 1 9 /CaAl 2 Si 2O8

1200 1000 No No

KA1 Si 0 4 /CaAl 12O19/

Ca 2 Al 2 Si 07/CaAl 2 Si 2 0 a 1200 1000 No No

KAlSi 0 4 /KAlSi 2 0 6 /

Ca 2 Al 2 S

i

0 7/ CaAl 2 Si 2 0 e 1200 1000 No No

KAlSi 0 4 /KAlSi 2 0 6 /

Ca 2 Al 2 Si 0 7 /CaSi 0 3 1200 1000 No No

KAlSi 0 4 /KAlSi 2 0 6 /

A1 20 3 /CaAl 2 Si 2O8

1200 1000 No No

KA1 Si 2 0 6 /Al 2 0 3 /

3A 1 2 0 3

- 2 Si 0 2 /

CaAl 2 Si 2 0 8 1200 1000 No No

KAlSi 2 06/Ca2Al 2 Si0 7 /

CaAl 2 Si 20e/CaSi0 3 1200 1000 No No

KA1 Si 2 0 6 / KA1 Si 3 0 8 /

CaAl 2 Si 20 8 /CaSi0 3 (p h

2o

700

= 7500 psi) 316 mon. CaSiOg No

KA1 Si 2 0 6 / KA1 Si 3 0 8 /

3A1 2 0 3

- 2 Si 02 /

CaAl 2 Si 2O8

^ p h

2o

700

= 7500 psi)

316 A1 2 0 3 + unident, phase

(mullite and

possibly KAlSi

disappeared)

No

2O6

KAlSi 3 0 8 / 3Al 2 0 3

- 2 Si 02 /

CaAl 2 Si 20 8 /Si0 2 ^ p h

2o

700

= 7500 psi

)

316 No No

KA1 Si 3 0 8 / CaAl 2 Si 2^0/

CaSi 0 3 /Si 0 2 (ph

2 o

700

= 7500 psi) 316 No No

KAlSi 0 4 /Ca 3 Si 2 0 7 /

Ca 2 Al 2 S

i

0 7 / CaSi 0 3 1200 1000 No No

KA1 Si 0 4 /Ca 3 Si 2O7/

Ca 2 Si0 4 /Ca2Al 2 Si 0 7 1200 1000 No No

11
Table 2. Suninary of Tie Line Reactions.

Tie Line

A1 ternative

Starting Materials

Tie Line

Verified?

KAlSi0

4

/Ca

2 Al

2

Si0

7

Ca

2

Si0

4

/KAlSi

2

0

e/CaAl

12

0

1 g Yes

KA1 Si0

4/Ca

2 Si04

Ca0/KAlSi

2

0

6

Yes

KAlSi0

4/Ca

3

Si

2

0

7

Ca

2

Si0

4 /KAlSi2 0g Yes

KAlSi0

4

/CaSi0

3

Ca

3

Si

2

0

7

/KAlSi

2 0g Yes

KAlSi0

4

/CaAl

12

0

ig

Ca

2

Al

2

SiO

y /3Al

2

0

3

• 2Si0

2 /KAl 02

Yes

KA1 Si

2 0g/Ca

2

Al

2

Si Oy KA1 Si

0

4

/CaAl

2

Si

2 0g/CaSi

0

3

Yes

12
Table 3. Summary of Glass Crystallization Experiments.

Four

Phase Volume

Heat Treatment

(Temp °C) (Time, hr)

Phases

Detected

Evidence for

Solid Solution?

KA 1 S i 0 / CaA

1

12 O 19 /

CaaAl 2 Si0 7 /CaAl 2 Si 2 0 8 1200 100 Same No

KAlSi0 4 /KAlSi 2 0 6 /

Ca 2 Al 2 S i 0 7/ CaAl 2 S

i

2 0 8 1200 100 Same No

KAlSi04 /KAlSi 2 0 6 /

Ca 2 Al 2 Si O7/ CaSi

O

3 1200 100 Same No

KA1 Si 2 0 6 /Ca 2 Al 2 S i 0 7 /

CaAl 2 S i 2 0 a/ CaSi 0 3 1200 100 Same Slight increase in

unit cell of KA1 Si 2 0 6

KA1 Si 2 0 6 /KAl Si 3 0 8 /

CaAl 2 Si 2 0 8 /CaSi0 3 700 316

(P

H 0 7500 psi)

KAlSi 2 0 6 /

KAlSi 3 0 8 /

CaAl 2 Si 2 0 8 /

monocl inic

CaSiO 3

No

KA1 Si 3 0 8 /CaAl 2 Si 2 0 e /

CaSi0 3 /Si02 700 316

(P

H 0

= 7500 psi)

Cristobal ite/

CaAl 2 Si 2 0 8 /

KAlSi 3 0 8 /

monoclinic

CaSiO 3

No

KA1 Si

0

4 /Ca 3 Si 2 0 7 /

Ca 2 Al 2 Si 0 7 /CaSi 03

1200 100 Same Slight increase in

unit cell of KA1 S i

0

4

KAlSi0 4 /Ca 2 Si04 /

Ca 3 Si 2 0 7 /Ca 2 Al 2 Si0 7 1200 100 Same Slight increase in

unit cell of KA1 Si

0

4

13
C 2 S = Ca2

Si°4

C3 S 2 = Ca3

S1 2°7

wo = CaSiO

_

ge = Ca^Al^SiO^

an = CaAl^Si^Og

Ca6 = CaA112°19

14

trd = Si02

ksp = KAlSi 0

lc = KAlSi 206

kls = KAlSi04

mu = 3Al 20 3 * 2 Si02

cor = a1 2°3

Figure 1 
Electrical Conductivity and Polarization (W. R. Hosier)

Progress

Introduction

In the last quarterly report (October-December 1980), AC and DC four

probe measurements on coal slag derived from the Rosebud seam in Montana

were described. This slag contains a minimal amount of iron (approximately

4 w/o) compared to a typical Eastern slag (approximately 12-16%).

During this quarter, work has continued on the investigation of the

conductivity mechanisms in the slag with low iron content. Emphasis has

been placed on the near equilibrium state required for a stable conductivity

at a given temperature and the relationship of the specific impedance of

resistance measured between the probe sets. This relationship when observed

over a frequency of range 40 kHz down to zero Hz (DC) can possibly give

information about the conducting process in the slag. The physical properties

of the near equilibrium state were established by quenching stabilized samples

with subsequent analysis by SEM and XRD techniques.

In the last quarterly report, measurements on a sample of Zr02 which is an oxygen ion conductor were described. These measurements were unsatisfactory

in showing the polarization effects of ionic conductivity because the platinum

electrodes as well as the near-electrode sample area were oxygen ion-exchanging

with the oxygen in the ambient atmosphere. A set of measurements (AC & DC four

probe) has been completed on Na-beta alumina received from Dr. John A. Bast

of the General Electric Co. in Schenectady, NY. Beta alumina properly prepared

is a nearly completely ionic conductor. The conducting ion, Na, K, Ag, etc.

moves through the material with higher than usual ionic mobility and research

at a number of laboratories indicates that the material shows promise as

a solid electrolyte for battery or other applications. For our measurements,

the purpose was again to establish the viability of using a combination of four

probe AC & DC measurements to establish a true bulk resistivity as well as

to show that these measurements can give some information as to the conductivity mechanisms of the material.

Slag Conductivity

An elemental analysis of the slag from Rosebud seam coal is given in

the last quarterly report. Pol 1 i n a and Larsen 1

’ 2 have done extensive

measurements on slag from this coal but using a somewhat different experimental technique. The slag for this experiment has been altered by adding

20% K2 S04 to the melt in order to give a potassium content more representative of slag residing in a functioning MHD generator. Potassium rejection,

however, occurs when the sulfate is added so that a considerable amount less

of potassium ends up in the final material. In this case analysis for potassium

in the doped material was 5.8 w/o before the electrical measurements were

carried out and 5.0% after the measurements were completed so that loss of

potassium during the course of the measurements was not appreciable. The

potassium rejection upon initial doping is much less in an Eastern slag such

as that obtained from the Bow, NH steam generating plant where the calcium

content is low.

15
During the course of the electrical measurements, much more careful

attention was paid to attaining a stable conductivity at a given temperature

than had been done previously. Figure 1 shows time required at a given

temperature necessary for the conductivity to change by less than 1%/hour.

These changes were continuously monitored by the data acquisition system.

Methods for acquiring the data were described in previous quarterly reports.

Figure 2 shows the conductivity of this Western slag with 5 w/o

potassium as a function of inverse temperature. Both AC (40 Hz) and DC

data are shown and the measurements were done in an air atmosphere. At

each temperature point, stabilization times were allowed to correspond

to those shown in figure 1. At temperatures above 1200 °C the AC and DC

data are nearly the same but at lower temperatures the frequency dependance

of the conductivity becomes larger. Extrapolation to zero or low frequency

brings the AC and DC conductivities into near agreement. Specific impedances

were calculated for all probe sets. Definition of these probe sets was given in Quarterly Report July - September 1980, but a brief description

will be given again as an aid in reading this report. The slag is held

in an alumina crucible through which 4 probes are inserted into the slag

sample. The top probe labeled 1, and the bottom probe labeled 4, are electrodes through which current is introduced into the sample. Probes 2 and 3, second and third from the top, carry no current and are potential sensors along the sample length. Polarization effects when present should be

observed at current carrying probes only, especially when non ion exchanging

electrodes are used with an ionically conducting species. SEM micrographs

together with EDX analysis show no iron or potassium incorporated in the bulk

platinum of any one of the four probes. Specific impedances were calculated

between all probe sets. Specific impedance is the measured impedance

(resistance) between a probe set multipled by the area and divided by the

distance between the set. Thus Z 12 =Z-A/d 12 , Z23 = Z*A/d23 and Z 34 = Z*A/d 34 . The area A remains the same throughout the sample length. The distances

between probe sets is d 12 , d23 and d 34 . Z is the measured impedance between

each set. Z 23 is then the sample resistivity as measured at a particular

frequency. If Z32 does not vary with frequency over a frequency range then

capacitive reactance effects do not play a significant role in determining

the total impedance and the impedance •fs non -reactive. Figure 3 is a plot of

Z23 vs. frequency for several temperatures. At high temperature (above 1200 °C)

there is no frequency dependence at least below 10 kHz so AC (40 Hz) and DC

data agree quite well as shown in figure 2. The frequency dependence of Z ]?

and Z 34 is very small also for temperatures above 1200 °C but the magnitudes

are always larger than Z 23 at a given temperature.

Figure 4 is a plot of the F 34 (.V) values for this slag

function of temperature. The origin and significance of this value is given

in Quarterly Report July - September 1980. This value remains relatively

constant for the 40 Hz measurement over the temperature range plotted.

Since the variation in V 23 and V 34 with frequency is small, the variation

of F 34 (V) is also small with frequency. The DC value of F 34 (V) also shown

on the same figure, increased significantly above 1300 °C which indicates

that ionic conductivity is playing a significant roll in the total conductivity and that polarization effects are significant. This effect does not

appear to be as pronounced as that in the Bow, NH slag described in previous

quarterly reports.

16
This slag conductivity sample was sectioned into four pieces, each

containing a probe. These sections were examined using a scanning electron

microscope with EDX spectroscopy. X-ray diffraction analysis was done on pieces from several sections. The spectrum was identical for each section

which indicates that there were no gross differences in composition along

the sample length. The pattern was very strong in anorthite (CaAl 2 Si 2 0 8 ) or potash feldspar ( KA1 Si 3 0 8 ) and leucite ( KA1 S

i

2 04 ) with a small amount

of hercynite (FeAl 2 04 ). A very small amount of another unknown phase was also indicated. EDX analysis showed areas that appeared to have a crystalline

nature. Lighter areas always had Fe, A1 and Mg combinations which suggest

an magnesia-iron alumina spinel but none was detected in the XRD spectrum.

In these areas generally Ti and Ca were present. Other areas showed A1 , Si,

K and Ca combinations. Micrographs of the sample along with EDX spectra will

be given in a later report.

Quenching Experiments

One of the purposes of the electrical measurements and analysis is to

try to correlate the electrical conductivity with a component in the sample

at a particular temperature. One way to do this would be to quench each

sample very rapidly to low temperature just after the electrical measurement

at an elevated temperature and then make a possible correlation between

conductivity and component materials and physical state. This would be a very time consuming process requiring attachment of the platinum electrodes

through the alumina crucible walls thus constructing a new cell for each

temperature point. As shown in figure 1 , a certain time is required at

every temperature for the conductivity to become stabilized. A furnace was

so arranged that samples of slag in alumina crucibles identical to

conductivity samples but without the probes could be dropped into a water

bath. The furnace was programmed to hold a set temperature for the time shown

in figure 1 after which a sample was quenched; the programmed temperature

dropped to another set temperature for a specified time, another sample

quenched and so on. A series of quenched samples were prepared in this manner. These samples are in the process of being prepared for SEM and

XRD examination and will be reported later.

Conductivity Measurements on Na-beta Alumina

The beta alumina sample was prepared by cutting the bulk material

which was in the form of a tube 27 mm in diameter and 23 mm long into

samples 23 mm long, 3 to 4 mm wide and 1.5 mm thick (tube wall thickness).

XRD spectra in the tube material showed it to be all beta alumina. Leads

were attached in the usual manner, i.e., by drilling holes for the four

probes along the length of the sample and attaching the platinum lead out

wires with spongy platinum peened into the holes around the lead. Figure 5

shows a plot of the specific admittance ( 1 /Z2 3 ) times temperature at 40 Hz

vs. reciprocal of absolute temperature. Z23 is the resistance between the

center two probes (conductivity probes) multiplied by the cross sectional area (A) and divided by the distance between the probes d 23 . This should

represent the thue bulk conductivity of the material if the impedance is

independent of frequency in this range. The data shown in figure 5 agree

very well with that given by Wittingham and Huggins 3 where the sodium ion

17
transport in beta alumina was measured using reversible solid electrodes.

Their measurements were made, however, on single crystals and in a direction perpendicular to the c axis. The material used in this experiment

was high density ceramic. Figure 6 is a plot of Z 23 as a function of

frequency for several temperatures. It can be readily seen that the

specific impedance remains constant over the frequency range from 40 Hz to

40 kHz for this probe set. On the other hand the specific impedances

measured between probe sets 1 and 2 and between 3 and 4, i.e., Z 12 and Z 34

did not remain constant with frequency but increased by nearly an order of

magnitude with decreasing frequency from 40 kHz to 40 Hz. This indicates

that a capacitive reactance x^ = ^ was a contributing factor to the total

impedance between these probe sets. This behavior is in contrast to the

impedances Z 12 and Z 34 as measured in the slag sample discussed previously

where these values did not vary significantly with frequency but the

magnitudes were higher. As might be expected then, from the increase in

impedance as the frequency is lowered even to 40 Hz, a DC measurement

between these probe sets is not possible. The current carrying probes

act like the plates of a condensor where charge builds up until breakdown

occurs. The final result is that this material cannot be used to demonstrate

the comparison of F(V) values discussed previously because DC values

cannot be measured due to the fast ion conductivity. On the other hand

it does demonstrate that even in a fast ion conductor such as beta

alumina, a four probe AC measurement with non-ion exchanging electrodes

gives accurate electrical conductivity values.

References

1. R. Pollina and R. Larsen, 17th Symposium on Eng. Aspects of MHD , C.6.I.,

Stanford University, Stanford, CA (March 27029, 1978).

2. R. Pollina, W. Anderson, R. Larsen, 7th Inti. Conf. on MHD Electrical

Power Generation, D-8, Vol . 1, p. 226-232, MIT, Cambridge, MA (June 16-

20, 1980).

3. M. S. Wittingham and R. A. Huggins, J. of Chem. Phys. 54, No. 1, 414 (1971).

18
1500

si* OJ

cvj

(\J

O

cvj

go

CVJ

o

CD

<0

si*

CVJ

O

(Do) 3Un±Vd3dl/\l3±

TIME(HOURS)
Figure 2. Electrical conductivity in air as a function of reciprocal

temperature. 40 Hz AC and DC data are shown. Slag from Rosebud coal.

Jo

0
905°C

953 1003 1046

(UJO-iULjO) 30NVG3dl/MI 0UD3dS

KZ

N

a:

Li.

ro

c\j

cuu

fO -a

<uQ- r- eao

u u

4- "O

•r- 13

(_> J

D

0) O) Q. i/I oo o

DC

• £

ro o

S- a; 4—

S-n oi

CD fD

•r— i Ll. 00

,2 /

vs.

frequency

for

several

temperatures

.
! O 5*

JX

Mgure

4.^

34 vV;

values

(40

Hz

AC

and

DC)

asa

function

of

temperature.

Slag

from

Rosdbud

coal.
SPECIFIC

ADMITTANCE

•T(ohm-cmf

l

TOO

Figure

5.

Specific

admittance

(conductivity)

-T

vs.

reciprocal

temperature

for

Na-beta

alumina.

These

measurements

were

done

in

air.
(uuo-wqo) 30NV03dlAII DI3l03dS

o

2

LU

Z>

Li.

c.o

4-> CJ

03

</) 03

03c1 r—E

=3

03

QJ X3

I 03

OO

rvj "O oo c cu

03 t-o

OOM

CNJTO

rvj i.a»

Oj Q. o E

c: <u 03 4-> TJ

QJQ. 03 E S-

•r- Ol>

U QJ

•i— oO 4-

•r- i- U O

aj <+- a. CO >,a

c

• aj

>X> 13cr

qj a;

s_ i. 3 4—

03

•r- 4-

Ll- o
3. Corrosion of Downstream MHD Components (J. Smit, 561 and C. D. Olson, 565)

Introduction : The examination and evaluation of various metals subjected . to a corrosive hot gas stream is being undertaken to determine the suitability of the materials to function in heat exchangers in the bottoming

unit of a combined magnetohydrodynamic (MHD)-steam power electrical

generating system. Selected metal specimens are being exposed to fuel

rich and oxygen rich, metal salt seeded hot gas streams which reproduce

some of the expected characteristics of the harsh environment existing

downstream in the heat exchanger region of the steam bottoming plant.

The resistance to corrosion and erosion of the Materials in the described

environments gives an indication, to a first approximation, as to their

potential suitability for service.

1 . Progress

A. Characterization of ASTM A213-T22 Steel : Samples of boiler pressure

tubing, ASTM A213-T22 containing 1.95% chromium, 0.44% molybdenum, 0.44%

manganese, 0.12% carbon, 0.015% sulphur, 0.35% silicon with the balance

iron, were analyzed with respect to surface condition and homogeneity.

The specimens were characterized: a) in the as received condition, b) after

cleaning, and c) after exposure to a seeded hot gas stream. A scanning

electron microscope (SEM) with an energy dispersive x-ray analyzer

(EDX) was used to conduct the analysis on sections taken from the

specimens and prepared for examination, with slight variation, using

standard metal lographic techniques.

The material, in the as received condition, was covered with a smooth,

semi-gloss black coating. Closer examination. Fig. 1, revealed surface

striations with some voids paralleling the longitudinal axis of the tube.

Higher magnification, Fig. 2, shows a rather rough but seemingly homogeneous

top layer, however. Fig. 3, shows particles embedded in the surface. EDX

analysis of the area in general indicated no gross abnormalities in the

bulk composition.

All of the specimens in the series covered by this report were cleaned to

constant weight prior to test in an ultrasonic bath at 50 °C in a 10%

by weight ammonium citrate solution adjusted to neutral pH. The surface

of the cleaned specimen, Fig. 4, showed the same type of striation as seen on the uncleaned surface as well as areas of varying contrast,

Fig. 5. Closer examination of these discolored regions, Figs. 6 and 7,

showed also the presence of particles embedded in the surface. The

chemical composition of these particles varied from the bulk and a slight

chemical shift was also observed in the bulk material surrounding the

particles, Figs. 8 and 9. Other areas were observed. Figs. 10, 12 and 15

where particles are embedded in the bulk and whose composition varies from

that of the bulk. Figs. 11, 13, 14, 16 and 17. These areas of inhomogeneity

have been found throughout the sample. The possibility exists that corrosion

may be enhanced in these regions, manifested as pitting or crack propagation.

25
It is not known if these particles were embedded in the melt or embedded

during fabrication. However, knowledge of their existence aids in understanding the presence of unexpected metal cations such as Cu, Zn and A1

in the EDX examination of specimens exposed to the hot gas streams. Their

presence also complicates attempts to understand the behavior of the system.

B. Examination of the ASTM A213-T22 Steel : The boiler pressure tubing,

(about 1 2 . 4 mm in diameter, wall thickness about 1.5 mm) was cut into

0.30 m lengths for test purposes. Six specimens in all were used to

complete this series. Each tube was thoroughly cleaned as described.

At the midpoint of the tube a Pt/Ptl 0%Rh thermocouple was welded in place

to monitor tube wall temperature. The thermocouple output signal is

also used in a feed back loop to control the tube wall temperature by

adjusting the cooling air flow rate.

The tubular specimens were subjected to either an oxygen rich or propane

rich hot gas stream seeded with K2 SO 4 (see Table 1). All specimens

were exposed, exclusive of apparatus warm up and cool down, for a period

of approximately four hours with seeding of 250 g of salt occurring in

the first 25 minutes. Six specimens were exposed under these general

conditions, two at 590 °C, two at 500 °C, and two at 400 °C. The gas

stream temperature, in all cases, was held at approximately 1300 °C as indicated by a Pt/Ptl 0%Rh thermocouple placed in the vicinity of

the test specimen in the hot gas stream. The test specimens, following

the exposure runs, were analyzed using an SEM/EDX system.

Table 1.

Specimen Material Corrosive Salt Tube Wall Gas Stream

T °C State

Cr 1 . ASTM A213, T-22 k

2 so

4

590 0

2

rich

Cr 4. ASTM A213

,

T-22 k

2 so

4

500 0

2 rich

Cr 3. ASTM A213, T-22 k

2 so

4

400 0

2 rich

Cr 2 . ASTM A213

,

T-22 k

2 so4

590 Propane rich

Cr 5. ASTM A213

,

T-22 k

2 so

4

500 Propane rich

Cr 6 . ASTM A213, T-22 k

2 so

4

400 Propane rich

C. SEM/EDX Analysis of the Metal -Salt Deposit Region : Test specimens

were removed from the test apparatus upon cool down to approximately

40 °C and encapsulated immediately in epoxy to prevent any possibility

of contamination and to reduce the possibility of hydration occurring

in the salt coatings. Metallographic specimens were selected from the

26
tubular specimen, 10 mm from the midpoint. These specimens were cut,

ground, and polished using nonaqueous media and stored in evacuated

desiccators prior to SEM/EDX analysis.

Test specimens Cr-1 and Cr-2 were exposed at 590 °C, Cr-4 and Cr-5 at

500 °C, and Cr-3 and Cr-6 at 400 °C. All samples exhibited similar

salt deposit characteristics in that the coating was generally a compact

deposit of K2 S0 4 . A few areas were found where dissociation of the

coating deposit occurred leaving high potassium or high sulfur concentrations.

Figures 18-20 (Cr-1, Cr-4, Cr-3) oxygen rich show the coating formed in

the hot gas environment seeded with K2 S0 4 . These samples retain a very

thick salt deposit ranging from 2.3 mm to 3.2 mm in thickness on the

leading edge of the tube surface facing the gas stream. The fume deposit,

underside of the tube is approximately 0.2 mn in thickness (Table 2). This

type of deposit is typical of that produced by K2 S0 4 seeding in 02 rich

environment and has been seen on previous test specimens.

Table 2. Coating Deposition on Tubular Specimens.

Specimen Top (mm) Bottom (mm)

Cr-1 2.3 0.18

Cr-4 3.2 0.2

Cr-3 3.2 0.2

Cr-2 0.65 0.32

Cr-5 0.82 0.33

Cr-6 0.47 0.31

Figures 21-23 (Cr-2, Cr-5, Cr-6) show the result of K2 S0 4 seeding in a fuel

rich hot gas stream. The leading edge is much thinner ranging from 0.5 mm

to 0.8 mm. These samples also exhibit a thicker fume deposit region than

the oxygen rich environment, approximately 0.3 mm.

An evaluation of specimens Cr-1 (Fig. 18) and Cr-2 (Fig. 19) can be made

simultaneously. Both samples were seeded using K2 S04 with wall temperatures

maintained at 590 °C, however Cr-1 was in an oxygen rich fuel environment

and Cr-2 was in a fuel rich environment. The variations in, the salt deposit

can readily be observed with the oxygen gas stream specimen (Cr-1) exhibiting

a top deposit of 2.3 mm and a fume deposit 0.2 mm. The fuel rich gas stream

sample (Cr-2) shows a top deposit of 0.65 mm and a fume region of 0.3 mm.

27
The bulk of both coatings is predominately K + S, however, some areas

are depleted with one or the other species.

The corrosion process exhibited in both samples seems to follow the same general corrosion mechanism. In sample Cr-1 (oxygen rich) at the

leading edge, salt-steel interface (Figs. 24-31) we find the bulk steel

followed by a metal reaction band region where high chromium is found

at the metal reaction band-bulk steel interface. Associated with this

region is lower iron (compared to the bulk) and traces of potassium and

sulfur. Chromium is found to be depleted towards the top of the metal

corrosion band and not found to penetrate into the salt corrosion band

area. Iron is found to be the major cation in the metal corrosion band

and also is found to penetrate into the salt corrosion band region above

it. Potassium and sulfur increase in concentration from the metal

corrosion band/steel interface region towards the salt coating. Figures

32-36 shows an area where the corrosion bands can be seem to overlap.

Depletion of the iron is observed through the use of x-ray mapping.

Figures 37-41 support the previous data, indicating: a) bulk steel,

b) high chromium, iron, low potassium and sulfur, c) iron, low chromium,

potassium and sulfur, d) iron, potassium, sulfur, e) potassium, sulfur,

iron, f) potassium and sulfur.

In Cr-1 (Fig. 42), the metal corrosion or reaction can be observed at

the drip zone salt/steel interface region. The darker band region, as analyzed by EDX, Figs. 43-47, indicate that the corrosion mechanism in

the drip zone region follows that of the upper part of the tube. We find

concentrations of the cations as follows: a) bulk steel (iron, chromium),

b) high chromium, iron, low sulfur and potassium, c) low chromium, iron,

sulfur, potassium, d) iron, sulfur, potassium, e) sulfur, potassium,

iron, f) potassium and sulfur. SEM/EDX analysis seems to indicate a preferential leaching of the metal cations from the bulk material in a somewhat orderly fashion.

The iron cations appear to be the more reactive species in the steel.

The iron is preferentially leached by the corrosive salt from the bulk

while chromium appears to form a concentrated layer in the corrosion zone

of the metal. Whether this layer retards corrosion growth or accelerates

it is not clear, however, from previous work chromium has been found not

to be as mobile as iron.

Figure 48 shows a portion of the fume deposit region where the corrosive

process appears to be evident. Figure 49 shows the iron x-ray map of the area indicating lower iron on the tube edge (iron migration into salt) and

Figure 50 shows potassium penetration into the steel. EDX (Figs. 51, 52)

supplements (Figs. 49,50) analysis of cation migration in this area.

28
In sample Cr-2, fuel rich, at the leading edge of the ASTM A213 T-22

steel (Figs. 53-60) we again find the bulk steel followed by a reaction

zone area. As in the oxygen rich sample (Cr-1), there appears using

EDX analysis to be distinctive corrosion banding. The corrosive process

in the fuel rich environment seems to follow the same general order as found in the oxygen rich environment. The ordering is such that:

a) bulk steel (iron, chromium), b) high chromium, iron, low sulfur and

potassium, c) low chromium, iron, potassium, sulfur, d) iron, potassium,

sulfur, e) potassium, sulfur, iron, f) potassium and sulfur.

It should be noted that in Fig. 53, Cr-2 there appears to be mechanical

separation in the corrosion zone (i.e., cracking). This apparent lifting

from the bulk represents a scaling of the tube surface.

The drip zone region. Fig. 61, exhibits a reaction band area similar to

the leading edge, including what appears to be scale formation breaking

off Of the bulk composition. Figure 62 shows the area under higher

magnification while Figs. 63-71 indicate the same cation pattern in the

reaction zone as found at the leading edge.

The fume region (Fig. 72) exhibits a reaction area including cracking or scaling of the upper tube surface. Photomicrographs of x-ray mapping

show cation concentrations of iron (Fig. 74), potassium (Fig. 73),

sulfur (.Fig. 75), and chromium (Fig. 76). Again iron is found to drop

off in concentration near the edge of the metal reaction band (top of

tube surface) where it reacts and penetrates the salt deposit. Figure 77

is a higher magnification of this region, EDX analysis (Figs. 78-86) indicate

that the fume region corrosion is similar to that of the leading edge

and drip zone.

At lower temperatures of 500 °C and 400 °C corrosion is still observed in

the ASTM A213, T-22 steel. In Cr-4 (Fig. 19) 500 °C, oxygen rich hot

gas stream, corrosion as well as scaling is observed (Fig. 87). Analysis

(Figs. 88-90) of this corrosion region follow previous observations found

in sample Cr-1. In Cr-5 (500 °C, fuel rich hot gas stream) corrosion again

follows previous observation (Figs. 91-97). In Cr-3 (400 °C, oxygen rich

hot gas stream) and Cr-6 (400 °C, fuel rich hot gas stream) analysis has

shown similar cation positioning and layering, though to a lesser degree.

2. Conclusion

The variances between fuel rich and oxygen rich hot gas environments in

the presence of I^SO* are minimal. Corrosion and scaling of ASTM A213,

T22 steel seem to occur readily in both instances. Both systems seem

to exhibit a discernable corrosion area, however, the fuel rich system

seems to advance corrosion. Comparative measurements of reaction band areas (Table 3) seem to indicate that more degradation of the steel tube

is taking place under a reducing environment, i.e., fuel rich, at the

higher temperatures. Reaction zones seem to be comparable at the lower,

i.e. 500 °C and 400 °C, temperatures.

29
Table 3.

Fuel Rich Series

Reaction Zone Thickness in ym

Sample Top Drip Zone Fume Deposit

Cr-2

590 °C

45 19 24

Cr-5

500 °C — 5 4

Cr-6

490 °C

4* 4 5

Oxygen Rich Series

Cr-1

590 °C

14 19 28

Cr-4

500 °C

14 40 10

Cr-3

400 °C

7 3 5

*4ym reaction depth during test translates to approximately 9 mm/year

Both systems indicate the same general corrosion banding and cation

movement from the bulk steel to the corrosive salt deposit. If the

corrosion is translated to longer periods of time this steel will not

stand up to the demand as a heat exchange material in the environments

anticipated in the MHD-steam bottoming generator.

Plans: 1. Continue SEM/EDX analysis of arc-plasma sprayed coatings

initiated previously to include additional cycling tests in both air

and forming gas. 2. Conduct exposure tests on arc plasma sprayed mild

steel tubing.

30
Fig. 1 SEM photomicrograph, 24x showing surface of ASTM

213-T22 steel as received.

Fig. 2 SEM photomicrograph, 125x showing same region as in Fig. 1.

Note Striations

U
Fig. 3 SEM photomicrograph 2430x showing particles imbedded in

the surface.

Fig. 4 SEM photomicrograph, 20x, showing surface of ASTM

21 3 -22 T steel after cleaning.

21-
Fig. b SEM photo micrograph, lOOx, showing same region as in

Fig. 4. Note Striations.

Fig. 6 SEM photomicrograph, 25x, showing surface of ASTM

213- 22T steel after cleaning. Note imbedded particle.

35
Fig. 7 SEM photomicrograph, 115x, of mid region of Fig. 6.

Note imbedded particle. Lettered regions correspond to

labeled EDX spectra Figs. 8 and 9.

Fig. 8 EDX spectra of regions A and B of Fig. 7 showing species

present in the embedded particle and species present

adjacent to it. Specie positions and designations of all

spectra in this section of this report are as indicated

above.
Fig. 9 EDX spectra of regions C and D of Fig. 7 showing species

in bulk and in region adjacent to the embedded particle.

Fig. 10 SEM photomicrograph, 1 1 40x showing presence of another

embedded particle. This one of high Si content .Lettered

regions correspond to labeled EDX spectra of Fig. 11.

3?
Fig. 11 EDX spectra of regions A and B of Fig. 10 showing

species present in the bulk and the presence of Si

in the embedded particle.

Fig. 12 SEM photomicrograph 117 Ox showing presence of still

another embedded particle .Lettered regions correspond

to labeled EDX spectra of Figs. 13 and 4.
Fig. 13 EDX spectra of regions A and B of Fig. 12 showing the

composition of the particle compared to the bulk.

Fig. 14 EDX spectra of regions C and D of Fig. 12 showing the

composition of the particle compared to the bulk.

>7
Fig. 15 SEM micrograph 1150x of an embedded particle in the

bulk. Lettered regions correspond to the labeled EDX

spectra of Figs. 16 and 17.

Fig. 16 EDX spectra of regions A and B of Fig. 15 showing

presence of several species with a near absence of

chromium. Specie positions and designations of all

spectra in this section of this report are as indicated

above

3 %
r

Fig. 17 EDX spectra of regions C and D of Fig. 15 showing high

Si peak.

Fig. 18 Optical micrograph of a section of ASTM 213-22T steel tubing

after exposure to an oxygen rich hot gas stream seeded with

K

2 SO4

. Tube temperature 590°C. Note deposit on upper sur- face of tube. Top position faces gas stream.

31
Fig. 19 Optical micrograph of a section of ASTM 213-22T steel tubing

after exposure to an oxygen rich hot gas stream seeded with

K2 SO4

. Tube temperature 500°C.

Fig. 20 Optical micrograph of a section of ASTM 213-22T steel tubing

after exposure to an oxygen rich hot gas stream seeded with

K2 SO4

. Tube wall temperature 400°C.
Fig. 21 Optical micrograph of a section of ASTM 213-22T steel tubing

after exposure to a fuel rich hot gas stream seeded with

K2 SO4 . Tube wall temperature 590°C. Note relatively thin

deposit on upper surface of tube.

Fig. 22 Optical micrograph of a section of ASTM 213-22T steel tubing

after exposure to a fuel rich hot gas stream seeded with

K2 SO4

. Tube wall temperature 500°C
Fig. 23 Optical micrograph of a section of ASTM 213-22T steel tubing

after exposure to a fuel rich hot gas stream seeded with

K2 SO4

. Tube wall temperature 400°C.

Fig. 24 SEM photomicrograph 405x, of region, top, of optical micrograph, Fig. 18, showing reaction area at metal -salt interface.

Lettered regions correspond to labeled EDX spectra Fig. 25 . 31 . 4

^
Fig. 25 EDX spectra of regions A and B of Fig. 24 showing high

chromium concentration at bulk-reaction zone interface

region. Specie positions and designations of all spectra

in this section of the report are as indicated above.

Fig. 26 EDX spectra of regions C and D of

of chromium at salt-reaction zone

Fig. 24 showing depletion

interface region.
Fig. 27 EDX spectra of regions E and F of Fig. 24 showing

penetration of iron into the salt coating.

Fig. 28 EDX spectra of regions G and H of Fig. 24 showing limit

of iron penetration into the salt coating.
Fig. 29 EDX spectra of regions 1 and J of Fig. 24 showing depletion

of chromium in the reaction zone--salt deposit interface

region.

Fig. 30 EDX spectra of regions K and L of Fig. 24 showing depletion

of chromium in the reaction zone--salt deposit interface

region.
Fig. 31 EDX spectra of regions M and N of Fig. 24 showing potassium

penetration into the bulk-reaction zone interface region.

Fig. 32 SEM photomicrograph 830x, of mid region of Fig. 24.

Figs. 33-36 are specie maps of area of Fig. 32.
FE MAP

Fig. 33 EDX specie map of region shown in SEM photomicrograph

Fig. 32, showing distribution of iron.

K MAP

Fig. 34 EDX specie map of region shown in SEM photomicrograph.

Fig. 32, showing distribution of potassium.

V7
CR MAP

Fig. 35 EDX specie map of region shown in SEM photomicrograph.

Fig. 32, showing distribution of chromium.

MAP

Fig. 36 EDX specie map of region shown in SEM photomicrograph,

Fig. 32, showing distribution of sulfur.
s

m

Fig. 37 SEM photomicrograph 1650x, of top region of Fig. 18

showing corrosion zone. Lettered region correspond to

labeled EDX spectra Fig. 38-41.

Fig. 38 EDX spectra of regions A and B of Fig. 37 showing high

chromium peak at the bul k--corrosion zone interface.
Fig. 39 EDX spectra of regions C and D of Fig. 37 showing

potassium in the corrosion zone.

.

-

:

' l f *r, .

i

- \ V««*

f

l J J 1 » i. ill I .1 I l I

Fig. 40 EDX spectra of region E and F of Fig. 37 showing iron

penetration into the salt coating.
Fig. 41 EDX spectra of regions G and H of Fig. 37 showing high

chromium peak at bulk-corrosion band interface.

Fig. 42 SEM photomicrograph 840x, of drip zone region of Fig. 18

showing corrosion zone. Lettered regions correspond to

labeled EDX spectra Figs. 43-47.

iTJ
Fig. 43 EDX spectra of region A and B of Fig. 42 showing high

chromium peak at bulk-corrosion zone interface.

Fig. 44 EDX spectra of regions C and D of Fig. 42 showing

chromium depletion at corrosion zone-salt deposit

interface.
Fig. 45 EDX spectra of regions E and F of Fig. 42 showing iron

penetration into the salt deposit.

Fig. 46 EDX spectra of regions G and H of Fig. 42 showing

potassium penetration into the corrosion zone.
Fig. 47 EDX spectra of regions 1 and J of Fig. 42 showing iron

penetration at the salt deposit-corrosion zone interface.

Fig. 48 SEM photomicrograph 435x, of fume deposit region of

Fig. 18 showing corrosion zone. Figs. 49 and 50 are specie

maps of the area of Fig. 48. Lettered regions correspond

to labeled EDX spectra, Fig. 51 and 52.

si
FE MAP

Fig. 49 EDX specie map of region shown in SEM micrograph Fig. 48

showing distribution of iron.

K MAP

Fig. 50 EDX specie map of region shown in SEM micrograph

Fig. 48 showing distribution of potassium.

ss
Fig. 51 EDX spectra of regions A and B of Fig. 48 showing

chromium depletion in the corrosion zone.

Fig. 52 EDX spectra of regions C and D of Fig. 48 showing iron

pentetration into the fume deposit.

5(o
Fig. 53 SEM photomicrograph 444x, of top region of Fig. 21 showing

corrosion zone. Lettered regions correspond to labeled

EDX spectra Figs. 54-60.

Fig. 54 EDX spectra of regions A and B of Fig. 53 showing high

chromium peak at the bulk-corrosion zone interface.

57
Fig. 55 EDX spectra of regions C and D of Fig. 53 showing potassium

penetration in the corrosion zone.

Fig. 56 EDX spectra of regions E and F of Fig. 53 showing chromium

depletion at corrosion zone-salt deposit interface.
Fig. 57 EDX spectra of regions G and H of Fig. 53 showing iron

penetration into the salt deposit.

Fig. 58 EDX spectra of regions I and J of Fig. 53 showing

potassium penetration into the corrosion zone.
Fig. 59 EDX spectra of regions K and L of Fig. 53 showing chromium

depletion in mid region of the corrosion zone.
Fig. 61 SEM photomicrograph 1070x, of drip zone region of Fig. 21

showing corrosion band.

Fig. 62 SEM photomicrograph 2120x, of mid region of Fig. 61 showing

corrosion band. Lettered regions correspond to labeled EDX

63-71 .
Fig. 63 EDX spectra of regions A and B of Fig. 62 showing high

chromium peak at bulk-corrosion zone interface.
Fig. 65 EDX spectra of regions E and F of Fig. 62 showing chromium

depletion at the corrosion zone-salt deposit interface,

Fig. 66 EDX spectra of regions G and H of Fig. 62 showing iron

penetration into the salt deposit.
Fig. 67 EDX spectra of regions I and J of Fig. 62 showing iron

penetration into the salt deposit.

Fig. 68 EDX spectra of regions K and L of Fig. 62 showing iron

penetration into the salt deposit.
Fig. 69 EDX spectra of regions M and N of Fig. 62 showing iron

penetration at the corrosion zone-salt deposit interface.

Fig. 70 EDX spectra of regions 0 and P of Fig. 62 showing chromium

depletion in the corrosion zone.
Fig. 71 EDX spectra of regions Q and R of Fig. 62 showing potassium

at the bulk-corrosion zone interface.

Fig. 72 SEM photomicrograph 545x, of fume deposit region of Fig. 21

showing separation of corrosion band. Figs. 73-76 are specie maps of the area of Fig. 72.

fab
Fig. 73

Fig. 74

K MAP

EDX specie map of region shown in SEM photomicrograph Fig. 72

showing distribution of potassium.

FE

FE MAP

EDX specie map of region shown in SEM photomicrograph Fig. 72

showing distribution of iron.

(ff'l
Fig. 75 EDX specie map of region shown in SEM photomicrograph Fig. 72

showing distribution of sulfur.
Fig. 77 SEM photomicrograph of 1050x, of mid region of Fig. 72.

Lettered regions correspond to labeled EDX spectra Figs. 78-86.

Fig. 78 EDX spectra of regions A and B of Fig. 77 showing chromium

peak in the bulk.
Fig. 79 EDX spectra of regions C and D of Fig. 77 showing chromium

depletion in the corrosion zone.

Fig. 80 EDX spectra of region E and F of Fig. 77 showing iron

penetration into the fume deposit.
Fig. 81 EDX spectra of regions G and H of Fig. 77 showing iron

penetration into the fume deposit.

Fig. 82 EDX spectra of regions I and J of Fig. 77 showing chromium

depletion at corrosion zone-fume deposit interface.

n\
Fig. 83 EDX spectra of regions K and L of Fig. 77 showing high

chromium peaks at the corrosion zone-fume deposit interface.

Fig. 84 EDX spectra of regions M and N of Fig. 77 showing potassium

penetration at the bul k-corrosion zone interface.
Fig. 85 EDX spectra of

penetration at

regions 0 and P of

the bulk-corrosion

Fig. zone

77 showing potassium

interface.

Fig. 86 EDX spectra of regions Q and

sulfur in the bulk-corrosion

R of Fig. 77 showing potassium and

band break.

73
Fig. 87 SEM photomicrograph 1760x, of the top region of Fig. 19 showing

seperation in the corrosion band. Lettered regions correspond

to labeled EDX spectra Figs. 80-90.

Fig. 88 EDX spectra of regions A and B of Fig. 87 showing high chromium

peak and penetration of potassium and sulfur at the corrosion

zone-bulk interface.

11
Fig. 89 EDX spectra of regions C and D of Fig. 88 showing high sulfur

peaks in the mid corrosion band region.

Fig. 90 EDX spectra of regions E and F of Fig. 88 showing chromium

depletion in the upper portion of the corrosion zone.

15
Fig. 91 SEM photomicrograph lOOOx, of drip zone region of Fig. 22 showing

corrosion zone. Lettered regions correspond to labeled EDX spectra

Figs. 92-97.

Fig. 92 EDX spectra of regions A and B of Fig. 91 showing iron

and chromium peaks at the bulk-corrosion zone interface.

7k
Fig. 93 EDX spectra of regions C and D of Fig. 91 showing depletion

of chromium above bulk-corrosion zone interface.

Fig. 94 EDX spectra of regions E and F of Fig. 91 showing sulfur and

potassium penetration in the mid region of the corrosion band..

ll
Fig. 95 EDX spectra of regions G and H of Fig. 91 showing iron penetration

In to the salt deposit.

Fig. 96 EDX spectra of regions I and J of Fig. 91 showing high

chromium peak at the bulk-corrosion zone interface.
Fig. 97 EDX spectra of region

K and

L of Fig. 91 showing chromium

depletion above region I and J.