/£, ft

MHD MATERIALS - SEED/SLAG INTERACTIONS AND EFFECTS

QUARTERLY PROGRESS REPORT

July 1 - September 30, 1980

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."

MHD MATERIALS - SEED/SLAG INTERACTIONS AND EFFECTS

QUARTERLY PROGRESS REPORT

July 1 - September 30, 1980

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

Page

I. SUMMARY OF PROGRESS TO DATE 1

II. DETAILED DESCRIPTION OF TECHNICAL PROGRESS 2

1. Thermochemistry of Seed and Slag 2

2. Electrical Conductivity and Polarization 24

3. Corrosion of Downstream MHD Components 37

i

I. SUMMARY OF PROGRESS TO DATE

1. Thermochemistry of Seed and Slag

Vapor pressure data of K over K 2 0-Ca0-Al 2 0 3 -Si02 samples are reported

and compared. The K pressure at equal K2 0 and CaO concentrations is

insensitive to variation in the A1 2 0 3 and Si

0

2 concentration (probably

within limits) if the sum of the A1 2 0 3 and Si

0

2 concentrations are constant. The K2 0 activity of two samples at equal K2 0 concentrations,

is reduced by increased A1 2 0 3 + Si

0

2 concentration and reduced CaO

concentration, but remains proportional at varying K2 0 concentrations.

Phase equilibria studies along the join K 2 C0 3 -KA10 2 have pointed to

the possibility of high temperature mesomorphic ("liquid crystal")

behavior. Also, as a supplement to experimental work in the system K2 0-

CaO-Al 2 0 3 -Si02 , liquidus diagrams have been calculated for selected

binary joins. These calculations reaffirm the marked non-ideality of

most silicate solutions with respect to molecular end members and point

up the need for accurate models of K2 0-Ca0-Al 2 0 3 -Si0 2 melts.

2. Electrical Conductivity and Polarization

Four probe AC electrical conductivity measurements are compared

with four probe DC measurements on slag from a coal burning steam plant

in Bow, NH. AC and DC data agree quite well with some anomalies existing

over the temperature range measured. The measurements support the

suggestion made in previous reports that above 1385 °C, ionic conductivity is the predominant transport mechanism in this particular slag

which contains a relatively large amount of iron.

3.

Corrosion of Downstream Components

Type 316 stainless steel tubes were exposed to an oxygen-rich and

fuel -rich environment seeded with K2 S 04 anc* K2 C0 3

. The samples

were maintained at 500 °C and 590 °C wall temperature using internal

air cooling. SEM and EDX analysis was performed on sections of the

samples showing the chemical nature of the reaction zone and salt

deposit. As seen in previous experiments the Fe penetrates the salt

deposit to the greatest extent followed by lesser penetration by Cr

while Ni is sometimes found in the metal at the interface. In the

coming quarter the plans are to continue the study of Type 316 stainless steels using SEM-EDX analysis and to collect and analyze x-ray

diffraction data on residue salt deposit material from fuel -rich and

oxygen-rich system. Also, the feasibility of using metal and ceramic

coatings on mild steel (with the testing of specific materials at

590 °C) will be examined.
II. DETAILED DESCRIPTION OF TECHNICAL PROGRESS

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

Progress :

A. Vaporization Studies (E. Plante)

Measurements of the K and 0 2 vapor pressures over a third sample in

the K2 0-Ca0-Al 2 0 3 -Si02 system were completed. These data were obtained

using a Knudsen-effusion, modulated beam mass spectrometric method. The

objective of these measurements is to produce sufficient experimental

results to provide a data base for the construction of a simple empirical

model for prediction of alkali seed retention of real slags produced by

combustion of Western sub-bituminous coals in an MHD seeded environment.

Previous reports have described and compared the potassium pressure

measurements on a K2 0-Al 2 0 3 -Si02 composition in the absence of CaO with

results obtained on two K2 0-Ca0-Al 2 0 3 -Si

0

2 samples. These results

showed that calcia has a major effect on K2 0 retention and increases the

K2 0 activity by orders of magnitude at calcia concentrations which would

be characteristic of Western slags obtained by combustion of Western

coals (for example, Rosebud) in a seeded MHD combustion process.

This report includes new data obtained on a third K2 0-Ca0-Al 2 0 3 - Si02 model slag. As in the previous work, this slag model is based on the 4 component phase diagram and has been selected so that the initial

composition lies close to an invariant melting point. We believe that

such compositions will tend to give rise to liquid solutions which will

have vaporization properties similar to slag solutions once melting has

taken place. Later work will be extended to include compositions in

which one or more solid phases may be present.

Table 1 lists the sample designations, mineral components and

starting composition for the 3 model slag systems studied to date.

The CaO concentrations in KCAS-VP-1 and KCAS-VP-3 are 27.5 and

28.0 wt% respectively and the observed K pressures at equal K2 0 concentrations

agree within reasonable experimental error (certainly ±30 percent).

This is true despite the changes in the A1 2 0 3 and Si

0

2 concentrations

which are 22.2 and 35.5 wt% respectively for the KCAS-VP-1 sample and

13.5 and 46.0 wt% respectively for the KCAS-VP-3 sample. This indicates

that within a limited composition range, A1 2 0 3 and Si

0

2 can be interchanged

on a wt% basis with essentially no effect on the K2 0 activity. Comparison

of the K pressures of KCAS-VP-2 and KCAS-VP-3 at equal K2 0 concentrations

shows that the KCAS-VP-3 pressures are about 2.3 times as great as the

KCAS-VP-2 pressures independent of the K2 0 concentration. This difference

is attributed to the lower calcia content of the KCAS-VP-2 sample but

part of the effect may also be due to the higher A1 2 0 3 + Si

0

2 concentration.

These results are illustrated in figure 1-a which shows the K pressure

as a function of wt% K2 0 at a temperature of 1667 K. The points for the

KCAS-VP-1 and KCAS-VP-2 data were calculated at the average K2 0 concentrations

from the least squares constants listed in Table 2 while the curve for

KAS-VP-3 was obtained from a fit of the data to an equation assuming a linear dependence of log P^ on the wt% K2 0 in the sample.

2
Table 2 lists experiment identification, K2 0 concentration range,

the slope and its standard error, and the intercept and its standard

error when the K pressure is fit to the equation:

log P = A/T + B.

Generally the observed slopes are in reasonably good agreement

except for the initial data for each sample. The initial data in each

series is subject to more error due to evaporation of unreacted

starting materials such as unreacted K2 C0 3 and is believed, therefore,

to be less reliable. The initial data in the KCAS-VP-1 series shows

slopes which are more characteristic of evaporation of K from KAlSi04 than from slag solutions. This may possibly be due to having a sample

which is somewhat off-composition.

3
Table 1

Mineral Constituents and Composition of Vaporization Samples

Composition Wt%

Sampl e Mineral Constituents (Wt%) k

2 o CaO A1

2 °3 SiO

KCAS-VP-1 KAlSi0

4 (49.8), Ca2

Si0

4 (16.5)

Ca

2 Al2 Si0

7 (16.5), Ca

3

Si

2 08 (17.2)

14.8 27.5 22.2 35.5

KCAS-VP-2 KA1 Si0

4 (28.6), KAlSi

2 06 (13.8) 11.5

Ca

2 Al2 Si07 (28.9), CaAl

2 Si2 00 (28.7)

17.6 33.7 37.2

KCAS-VP-3 KAlSiCL (42.0), CaSiOo (58.0) 12.5 28.0 13.5 46.0
Table 2

Slope, Intercept and Standard Deviations for K Pressure Data

Expt Id wt% k

2

o A a A B a B

KCAS-VP-1

3-13-80 14.8-12.4 -20047 391 8.144 .255

3-14-80 12.4-9.3 -19071 524 7.278 .334

3-18-80 9. 3-7.

2

-17429 452 6.058 .289

3-18-80 6. 2-4.8 -16372 210 5.068 .129

3-21-80 4. 8-4.0 -16896 279 5.289 .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

5
Potassium

Pressure

(atm)

Wt% K

2 0

Figure 1-a Potassi um pressure as a function of 1^0 concentration for

3 samples in the I^O-CaO-Al oOg-SiOg system at 1667. K.
B. Phase Equilibria (L. Cook)

Progress:

1. K2 C0 3 -KA102

Phase equilibrium behavior in the more K 2 0-rich parts of the system

K2 0-Ca0-Al 2 0 3 -Si02 is comparatively complex as outlined in the previous

three quarterly reports. During the past quarter, an attempt was made

to resolve the nature of the complex interaction between potassium

carbonate and potassium aluminate. Potassium carbonate, added as seed,

is expected to be an important phase in all MHD systems except possibly

those using the most sulfur-rich of coals. Potassium aluminate together

with silica comprises by weight the most important component of MHD slag

[1-3]. The carbonate/aluminate interaction, which is thought to be

interfacially controlled is potentially of prime importance to the

design and operation of downstream MHD components where the flow of slag

and condensed seed phases must be predictable. A preliminary investigation

showed a rather dramatic and surprising lack of evidence for fTowage or wetting in certain K2 C0 3 -rich mixtures at temperatures as high as 1300 °C.

Initially this was thought to be due to formation of intermediate solid

solutions. This troublesome phenomenon has been investigated further as follows.

Both K2 C0 3 and KA10 2 are extremely hygroscopic, necessitating the

use of special methods. Preparation, purity and handling procedures for

these materials have been described in ref. [3]. X-ray analysis was completed on a powder diffractometer equipped with a dry cell and graphite

monochromator using CuKa radiation. Additional characterization was done via a scanning electron microscope [SEM] with energy dispersive x- ray [EDX] analyzer.

Four principal types of experiment were performed on carefully

homogenized K2 C0 3 /KA102 mixtures. In the first, 25 to 50 mg pellets of

6.4 mm dia. were pressed, dried at 800 °C, weighed and heated for 5-15

min. in a covered 15 ml Pt crucible at 1150 °C. After noting weight loss

(always less than 10 percent), specimens were examined by x-ray, SEM and

EDX. In the second type of experiment, powders were placed in a 2.6 mm

i . d. Pt capsule with ends crimped loosely, which was in turn welded in

a 4.6 mm i.d. Pt capsule. Capsules were then maintained at constant

temperature for about one hour and quenched. By noting whether material

was present in the outer capsule, melting or lack thereof could be determined,

given the tendency of molten potassium carbonate to wet platinum. In

the third type of experiment, several hundred mg of powder were placed in

a Pt foil boat inside a covered 15 ml Pt crucible. This was heated in a muffle furnace, cooled in dry air, weighed and a portion was x-rayed.

The remainder was reweighed and used for the continuation of the series

of experiments, until all K 2 C0 3 was vaporized. This took from 2-6 hours.

The fourth type of experiment utilized a high temperature x-ray apparatus

of the type described in ref. [4]. Because of weight loss problems

associated with the presence of cold surfaces in this apparatus, it was necessary to use pressed pellets, introducing errors in the temperature

measurement and the lattice parameters. Therefore, only qualitative

observations could be made using the high temperature x-ray set-up.

7
Shown on Figure 1 are the conditions under which the four types of

experiments were performed. A lack of melting is evident for compositions

other than the most K2 C0 3 -rich, as judged by the criteria of change in

net shape of the sample and wetting of the Pt container. This is unexpected

because of the known fluxing effect of K2 C0 3 and also because of the lack

of reported high temperature compounds between K2 0 or K2 C0 3 and KA10 2

. i Figure 1 also shows a calculated liquidus diagram assuming ideal solution

behavior. 2 Copious melting would be expected for a large range of

compositions via any reasonable liqu.dus diagram in the absence of intermediate compounds or solid solutions.

Information from the pellet experiments can be summarzied as follows.

Potassium aluminate sinters readily in a short period of time to yield a dense pellet with few voids. Pellets of (K2 C03 /KA1

0

2 ) compositions 50/50,

60/40, 70/30, 80/20 and up to and including 90/10 retain their shape well

(see Fig. 2-a) and become only very loosely bonded to the Pt foil, if at

all, during the experiments. The outer surfaces in this composition range,

especially those of the 90/10 composition (Fig. 2-b) , show evidence of

coarse crystal! i ni ty . From EDX examination, aluminum appears to be

homogeneously distributed throughout. Voids are present in the interior

of these pellets. Some evidence of reaction with platinum was noted which

may be associated with a green color. Reaction with platinum is not

necessarily the cause of the color, however. Platinum appears to be

almost exclusively concentrated in small layered groups of platelets

between the larger grains. It does not appear to be an important chemical

constitutent of the major crystalline phase.

By contrast with the more KA102 -rich compositions, those in the range

92/08 to 100/0 show definite melting with extensive flowage and wetting

of the Pt foil (Fig. 3). However, for the 92/08 specimen, the suggestion is

of partial melting rather than complete melting: the melt has not coalesced

into the corners of the foil, and there is extensive topographic development

on the surface. Two types of surface can be discerned, one of which may

represent crystallized melt (Fig. 4). The latter occurs in areas where

obvious melting and flowage have occurred. This latter surface is apparently

a manifestation of a definite structural arrangement, i.e., ordered intergrowths

in the underlying K2 C0 3 lattice. A high surface tension is suggested by

the curious features shown in Figure 5-a. Their origin appears to require

a rather complicated explanation, but they are ubiquitous. The second type

of surface in the 92/08 pellet experiment is illustrated in Figure 5-b.

Sharp outlines and jagged surface topography suggest but do not prove

crystal 1 inity at the temperature of the experiment. Chemistry appears similar

1 The synthesis of K 3 A10 3 has been reported in ref. [5], but this

compound apparently cannot be synthesized using K2 C0 3 and may not be

stable above 500-600 °C.

Thermodynamic properties for K2 C0 3 used in this calculation have been

obtained from ref. [6]. The melting point of KA1

0

2 is from ref. [7],

and its heat of fusion is from ref. [8].

8
to that of the bulk. An ordered arrangement of crystal platelets was usually apparent in these regions of the pellet. These platelets can be

differentiated by their morphology from the Pt-rich phases noted above.

In certain instances a suggestion of layering at right angles to the

platelet axes can be seen.

The degree of wetting and apparent melting increases with decreasing

KA1

0

2 content of the pellets to the point where complete coalescence of

the melt into corners of the foil occurs (Fig. 3-b). However, features

indicative of a strong interfacial effect can be seen also in the 100/0

composition. For certain grains in this experiment, an oriented intergrowth

of rod-like crystals within a medium of lower surface tension is suggested.

These rods appear to emanate from a point and spread radially outward,

terminating with rounded ends (Fig. 6-a). The presence of two phases in

these intergrowths or at least of two crystallographic orientations with

dramatically different surface tensions (Fig. 6 -b) is suggested. Only

certain of the K2 CO 3 grains show this structure. The amount of Pt in

all of these grains, regardless of structure, is uniformly low (est. <1 wt%)

.

In certain crystals the oriented structure is present only in the outer

portions. The 100/0 experiments invariably yield a dark gray product,

as opposed to the green color of the experiments which contain KA10 2

.

The results of the doubly encapsulated melting experiments (Fig. 1) are essentially in agreement with the results of the pellet experiments

discussed above, although the former are not as amenable to SEM characterization,

and so a comparison of the microstructures cannot be made at this time.

However there is no indication of any platinum reaction or change in

color in the sealed experiments. Thus, the anomalous melting behavior

appears to be independent of platinum reaction or interaction with air.

High temperature x-ray data for the 80/20 composition under dry

nitrogen show that the K 2 C0 3 in these mixtures goes through at least two

reversible subsolidus phase changes, and recrystal 1 izes extensively near the reported melting point of 901 °C (ref. [ 6 ]) to give strong preferred

orientation, thus making the actual determination of melting difficult.

The principal aluminate (220) peak can be observed at all temperatures

however and remains nearly constant in intensity. A phase change near

900 °C was observed visually through the port on the x-ray apparatus: a region of high thermal conductivity developed which upon further heating

slowly spread throughout the pellet. This suggests but does not prove

melting as recrystall ization and densi fication could produce the same

effect. Upon termination of high temperature x-ray experiments the

samples showed no visual evidence of melting.

For all experiments x-ray patterns of the results taken at 25 °C

show wel 1 -devel oped patterns of K2 C 03 and KA102 . In this respect the

patterns closely resemble those of appropriate mixtures of starting

materials. Important exceptions are the powder vaporization series of

experiments (Fig. 7). Extra lines occur in these patterns at 16.7°,

17.4°, 19.3° and ^29° values of 29 (CuKa radiation). These extra lines

do not occur in either pure K

2 C0 3 or pure KA1

0

2 subjected to similar

heat treatment. Of these lines those at 17.4 and 19.3° correlate

9
reasonably well with those of a potassium platinate phase reported by

ref. [9]. To a lesser degree this is true for the broad peak near 29°;

however, the intensity of this peak is not in keeping with the potassium

platinate pattern. Most importantly, it has not been possible to ascribe

the first and strongest peak at 16.7° to any known phase. All four

extra lines remain relatively constant in intensity until all of the

K2 C0 3 has evaporated (Fig. 7-d) - then they vanish abruptly along with

the coloration. Additionally, low angle lines have been detected for

certain compositions in this series, corresponding to periodicities in

the 50-100A range (Fig. 8). These are difficult to reproduce, they

appear to be very sensitive to methods of preparation, and they vanish

rapidly upon atmospheric exposure. Relatively high effective vapor

pressure of "K2 0" or K2 C0 3 is thought to be essential. It should be

noted that these low angle peaks have been detected only in K2 C0 3 /KA102 mixtures, and a considerable amount of time was spent in attempting to

differentiate what are judged to be genuine specimen diffraction effects

from machine-related artifacts. It is significant that lamellar features

can be seen on fracture surfaces in SEM micrographs of these experiments

(Fig. 9) which have dimensions approaching those indicated by the low

angle patterns.

Any reasonable hypothesis for correlation of the data presented

above must explain in particular the sudden change in apparent melting

behavior with composition (e.g. between 90/10 and 92/08 at 1150 °C).

Consequently, a phase change seems to be required. Two possibilities

can be suggested: 1) formation of unquenchable solids at high temperature

and 2) the existence of intermediate solid/liquid (mesomorphic) phases.

The occurrence of unquenchable high temperature solid solutions does

not appear to be supported by high temperature x-ray data, although

vaporization and recrystallization near the melting point make any such

interpretation difficult. It is perhaps significant in this regard that

Knudsen effusion measurements of K pressures over a 60/40 composition

give values very close to those for pure K2 C0 3 at 900-1100 °C [10],

indicating that any structural interaction with KA10 2 must be relatively

weak if it exists. An unusual type of structure would need to be proposed,

most probably of a mixed layer or intercalation type. It can be said

with certainty on the basis of the high temperature x-ray experiments

that the room temperature monoclinic form of K2 C0 3 [11] is not stable

above 500-600 °C, and that a transition to a hexagonal polymorph reported

in the pure end member [12] occurs in mixtures as well. Given the

existence of rapid reversible phase transitions in K2 C0 3 , the extra

lines on the room temperature powder patterns of Figures 7 and 8 must be

viewed with caution, as they are likely to represent metastable structures.

The possibility of mesomorphic behavior is at present perhaps the

strongest. While not a commonly observed high temperature phenomenon,

it has been reported in certain inorganic systems [13]. Furthermore,

pure K 2 C0 3 exhibits unexplained behavior near its melting point. This

is evidenced in the existence of anomalously high K pressures at the

melting point [10] and the suggestion of high viscosity as melts are

10
cooled through the crystal! ization temperature. In addition to chemical

similarity, the K2 C0 3 and KA10 2 structures possess a number of features

which would make such mutual intergrowth energetically possible, and

perhaps favorable, both as ordered liquids at high temperature and as intercalated or epitaxially intergrown solids in the subsolidus region.

The high temperature x-ray data suggest that the thermal expansivities

of K2 C0 3 and KA10 2 may be similar, making close association of the

lattices along an interface reasonable, provided minor structural readjustments

are possible. Such interfacial association of these compounds has been

investigated by treating idealized lattices of K2 C0 3 (primitive hexagonal)

and KA10 2 (m3m) via the computer program MATCH 1 (ref. [14]). Results

indicate that intergrowth along an interface defined by K2 C0 3 (001) and

KA102 (111) is both possible and likely. The former plane is preferred

by the author over others in potassium carbonate, as this is the plane

in which the carbonate ions are aligned. Figure 10 shows one way of

superimposing the two lattices such that negligible cumulative mismatch

results for distances of several hundred angstroms, largely eliminating

the need for dislocations (potassium ions have been positioned by analogy

with the Na 2 C0 3 structure [15] and the ideal cristobalite structure

[16]). A hexagonal symmetry is evident in the pattern of site coincidences.

It is suggested that ordered interfacial intergrowths of this type

[possibly along the (110) or (100) planes of KA10 2 ] could be responsible

for the unaccounted-for extra lines in Fig. 7. If an ordered or partially

ordered planar arrangement is present in a mesophase at high temperatures,

solidification might tend to preserve this arrangement insofar as structurally

possible. Additional effects such as intercalation of Pt and K or ordering of vacancies might also occur, especially in association with a planar interface. This could account for the coloration and the low

angle periodicities observed in the powder patterns.

2. K2 0-Ca0-Al 2 0 3 -Si0 2

As an aid to experimental investigation, the development of models

for calculation of MHD slag liquidus surfaces was continued. Following

the approach outlined in the previous quarterly reports, ideal solution

calculations were first performed to establish a basis for the calculation of excess functions eliminating the difference between ideally

calculated and observed liquidii. Results of ideal solution calculations

for several binary joins within the quaternary system are shown in

Figures 11-13. These diagrams have been drawn using an iterative program

developed by the author which first solves the following equations for

convergence:

-In Y mel tX A

In yXtAX A

AH

fusion

A

R T

-L

) Tfusion / 'A

-In Y mel t

X B In

X£B

B +

AU fusion

iH

B

R T T fusion^

'b

11
where X is mole fraction, A and B refer to etjid members, R is the gas

constant, T the temperature kelvin and An the enthalpy of melting.

Following this the program plots liquidus curves and measured eutectic

points as shown in the illustrations. Measured values are taken from

previous reports and from ref. [17]. The agreement between calculated

and observed is not good, reaffirming the marked non-ideality of these

silicate solutions with respect to molecular end members. The sole

exception appears to be KA1 S i 0z+ - KA1 Si 2 06 (not shown); however, this may

be in part fortuitous since the thermodynamic data were derived from the

phase diagram [8].

An attempt will be made during subsequent quarters to develop the

quasi chemical melt polymerization model outlined in ref. [2] for detailed

application to the system K2 0-Ca 0-Al 2 03 -Si 02 , in conjunction with continued

experimental work. Also, it is hoped that soon a program recently

written by the author for quasi chemical calculation of multicomponent

liquidus surfaces can be applied.

Plans : Extend K pressure measurements to additional compositions in the

K2 0-Ca0-Al 2 0 3 -Si02 system. Analyze existing data for model slags obtained

thus far in an attempt to obtain unifying relationships between K pressure

and composition.

Continue experimental work in K2 0-Ca0-Al 2 0 3 -Si0 2

. Develop program

for calculation of liquidus surfaces according to quasichemical model.

References

1. E. R. Plante and L. P. Cook, Proc. 17th Symp. Eng. Aspects

Magnetohydrodynamic Electrical Power Generation, Stanford,

C. 1.1. (1978).

2. L. P. Cook, 7th Int. Conf. on Magnetohydrodynamic Electrical

Power Generation, Cambridge, Mass., V. 1, 212 (1980).

3. L. P. Cook, R. S. Roth, H. S. Parker, and T. Negas, Am. Mineral.,

62 1180 (1977).

4. D. K. Smith, Norelco Reporter, ]_0 19 (1963).

5. A. Bon, C. Gleitzer, A. Courtois and J. Protas, C. R. Acad. Sci

.

Paris, 278C 785 (1974).

6. JANAF Thermochemical Tables, 2nd Ed., NSRDS-NBS 37, U.S. Dept.

Corrmerce (1971 )

.

7. R. S. Roth, Advances in Chemistry Series , Amer. Chem. Soc.,

Washington, D.C. (in press )

.

8. F. E. Spencer, J. C. Hendrie, Jr., and D. Bienstock, 6th Int.

Conf. on Magnetohydrodynamic Electrical Power Generation, Washington,

D. C., V. 2, 181 (1975).

9. C. L. McDaniel, Nat. Bur. Stand., pers. comm. (1980).

12
10. E. R. Plante, Nat. Bur. Stand., pers . comm. (1980).

11. P. M. deWolff, File No. 16-280, JCPDS Int. Centre for Diff. Data,

Swarthmore, PA.

12. S. J. Schneider and E. M. Levin, J. Amer. Ceram. Soc., _56 218

(1 973)

.

13. P. G. de Gennes, The Physics of Liquid Crystals , Oxford Univ.

Press, London (1 974)

.

14. B. Dickens and L. W. Schroeder, Mat. Bur. Stand. Tech. Note 893,

71 p. (1976).

15. G. C. Dubbeldam and P. M. deWolff, Acta. Cryst., B25 2665 (1969).

16. M. O'Keeffe and B. G. Hyde, Trans. Amer. Crystallog. Assoc., 115

65 (1979).

17. E. M. Levin, C. R. Robbins, and H. F. McMurdie, Phase Diagrams

for Ceramists , Columbus, Ohio, The American Ceramic Soci ety ( 1 964)

.

13
1300

— Calculated Ideal Liquidus • Wetting

| O No Wetting

j B Wetting

No Wetting » No Wetting

»«• — Wetting

Pellet Expts.

Double Capsule Expts.

Vaporization Expts. •••• High Temp. X-Ray

90 80 70 60 50 40

K2C03 Mol % K2C

O

3

30 20 10

KAI

0

2

Fig. 1. Experimental data for K2CO3-KAK32, with calculated

(ideal) liquidus for comparison.

14
Fig. 2. SEM micrographs of 90/10 pellet heated at 1150°C, 5 min.

Bars represent 100. um. Note sharp upper edge of pellet

visible in Fig. 2 -a, which suggests lack of melting.

Fig. 2-b illustrates the development of coarse crystallinity on the surface.

Fig. 3. SEM micrographs of melted 92/08 (a) and 100/0 (b) pellets

heated at 1150*0, 5 min. 3ars represent 100 pm and 1 mm. Melt (dark areas on lighter ?t foil) has not coalesced

into corners of foil in (a) as it has in (b)

.

15
Fig. 4. SEM mosaic of surface of melted 92/08 pellet. Fig. 3-a.

Bar represents 10 um.

a b

Fig. 5. Surface of melted 92/08 pellet, Fig. 3-a. 3ars represent

10 and 1 urn.

16
a b

rig. 6. Surface of melted 100/0 pellet. Fig. 3-b. 3ars represent

10 urn.

17
15* 20* 25* 30* 35*

Fig. 7. X-ray powder patterns (29 vs. intensity). Fig. 7-a is

from pure K 2 CO 3 starting material dried at 160°C under

vacuum. Figs. 7-b,c,d are from vaporization experiments

• at j- 250°C. Compositions determined by weight loss are

as follows: b) 60/40, c) 10/90, d) 0/100. . Arrows in

b) show extra lines.
Fig. 8 . Low angle portions of powder patterns (29 vs. intensity)

from 50/50 powder heated in the presence of excess K2 CO 3 at 1250°C. Beginning with the right, cumulative heat

treatments are 30, 45, 60, 90 and 120 min.

Fig. 9. SEM micrograph of fracture surface of vaporization

experiment near 65/35. Note lamellar structure, upper

right. Bar represents 100 run.

19
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Fig. 10. hatching of potassiun sites in K2 CO 3 along hypothetical

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2 . Electrical Conductivity and Polarization (W. R. Hosier)

Progress

Slag Electrical Conductivity

In the last quarterly report (April - June 1980), a detailed description

of the sample preparation and measurement technique was presented.

Figure 5 of the corresponding section of that report shows a radiograph

of a typical slag sample with the leads attached and numbered. Figure 1 is a reproduction of that radiograph in this report for the convenience

of the reader. The measurement technique and the data acquisition

system have been extended to include the potential measurements between

all probe sets, i.e. V 12 , V 23 , V 34 and V 14 . This has the advantage of

being able to detect where polarization or abnormalities exist along the

length of the sample with respect to the center of the sample. The

center of the sample, monitored by probes 2 and 3, is the area where the

bulk conductivity is measured and where it is assumed little or no polarization exists because no current is being drawn through the two

contacts involved. This is because the potential between probes 2 and

3, as well as the other probe sets, is measured by a voltmeter whose

input impedance is high compared to the sample resistance between those

two probes. At the same time, current is introduced to the sample

through probes 1 and 4, and it is at these areas where polarization and

other effects may be observed. Consider the equation

where d 14 and d 23 are the distances between probe 1 and 4 and between 2

and 3 respectively. The denominator of the first term in equation 1 is

the potential between 1 and 4 normalized to the value between 2 and 3.

This, of course, presumes that the cross-sectional area of the sample

remains the same along the entire length of the sample. If it does not,

these adjustments must be made in the normalization factor. If the

value of equation 1 is zero or near zero, no polarization or inhomogeneities

exist along the sample length except in the possible case that a deviation

of V 12 from the norm is equal to the negative deviation of V 34 from the

norm. This can be detected by use of the relationships:

fl4(V) =

( 1 )

V 23 di 2 /d23

( 2 )

and

24
f 3 4 (V) 1 (3)

V34

V 2 3d 34 /

d

23

which again represent the deviation from the norm of the potential

value between probes 1 and 2 (equation 2) and between 3 and 4 (equation

3). If f 12 (V) and f 34 (V) are near zero, no polarization or inhomogeneities

exist along the sample. If either or both of these values deviate

widely from zero, polarization and/or inhomogeneities may exist.

Figures 2 and 3 show plots of the values for equations 1, 2, and 3 for a slag sample measured with increasing temperature (Figure 2) and with

decreasing temperature (Figure 3). These datawere taken using a constant

DC current and with equilibrium established at every point. This equilibrium was established by monitoring the potential between probes 2

and 3 as a function of time. When this value changed over a period of

15 minutes by less than 1 percent, datum for the temperature point was

taken.

It is apparent that there are substantial differences between the curves

for increasing and for decreasing temperatures below 1300 °C. This will

be discussed later. It should be noted, however, that at temperatures

above 1300 °C both figures show a marked increase in the f(V) values

(with the exception of f 12 (V)) which indicates an increase in the polarization

effects because of enhanced ionic conductivity. Electric fields along

the sample were kept at approximately 1 volt/cm in order to avoid possible

permanent polarization. A more dramatic increase in the f(V) values

would be observed using higher electric fields.

This result is in agreement with the argument set forth in several

previous quarterly reports that above 1385 °C the conductivity in this

particular coal slag (derived from ash products of a Bow, NH steam

generating plant) is predominantly ionic.

AC Conductivity Measurements (Four probe)

At each equilibrated temperature AC conductivity measurements were made

along with the DC measurements described above. The data at each temperature

pointwere taken as a function of frequency from 40Hz to 40KHz, This

limitation of frequency was imposed because of the AC voltage sensing

instrument's limited frequency response. The accuracy over this frequency

range was 0,3 percent of the reading plus 0.04 percent of the 10V range

used. For these AC measurements, however, a constant current was not

used. The AC signal generator output voltage was adjusted to obtain

nearly one volt on the conductivity probes for every temperature point.

The current was measured as the potential drop across a standard (adjustable)

resistor in series with the sample. The data scans were made in the same sequence as in the DC case described previously.

Figure 4 shows the data at 40Hz for f(V) values of the equations 1, 2,

and 3 for increasing temperature, while Figure 5 gives the data for

decreasing temperature. Since this was the same sample as the DC case

and measured at the same time, the sample conditions should be the same.

25
Below 1300 °C, the corresponding AC and DC curves are similar. Since

this is the case, it seems likely that the deviations from the near zero values expected for an ideal sample with no polarization, cracks, or inhomogeneities are caused primarily by inhomogeneities or microcracks.

Polarization effects would not show up in the AC data at 40Hz, but would

be apparent in DC data if ionic conductivity was prevalent.

On the other hand, there is a decided difference in the data for increasing

temperature compared to those for decreasing temperature and this difference

is evident for both DC and AC measurements. The reason for these differences

may be attributed to the difference in sample treatment. The relatively

rapid cooling of the sample from 1500 °C after the final filling process

before contacts were applied probably results in some microcracks as well as some variation in crystalline components along the sample lengths.

These effects show up in the f(V) data of Figures 2 and 4 differently

than the f ( V ) data of Figures 3 and 5 for which the sample was cooled very

slowly from high temperatures where microcracking should be minimized.

It is interesting to note that f 34 (V) is negative and nearly constant in

Figure 5 over the entire temperature range below 1300 °C while f 12 (V)

is positive and monotonical ly increasing as the temperature decreases.

This indicates that the condition of the sample in the volume between

probes 3 and 4 is not changing appreciably as the sample is cooled, but

in that volume between probes 1 and 2 it is changing. Under this situation,

an analysis of the two ranges under a scanning electron microscope might

reveal the nature of the different behaviors. This also demonstrates a case where a negative f 34 (V) partially compensates for a positive f 12 ( V

)

and gives a f i4 ( V ) value nearer zero than it should be. The conclusion

is that, since the AC and DC data are in relatively close agreement,

polarization effects do not play a large role in the measurements and

the conductivity in this temperature range is not predominantly ionic in

nature.

Figure 6 is a plot of the conductivity as a function of frequency for

the data taken with increasing temperature points while Figure 7 is for the same experiment taken with decreasing temperature. The increase in

conductivity with increasing frequency at lower temperature in each case may

be due to the capacity of the twisted lead pair from the sample to the data

acquisition system. A rough calculation of this capacity leads to an impedance value at 40KHz of the same order of magnitude as the resistance

observed between the conductivity probes. A room temperature measurement

of the capacitative reactance of the lead pairs has confirmed this calculation.

At temperatures above 1300 °C, the 40Hz AC data shown in Figures 4 and 5 remain near zero in contrast to that data for the DC case (Figures 2 and

3). Polarization effects are not observed at 40Hz or over the frequency

range measured and as a result, the f(V) values remain near zero.

Figure 8 shows the AC (40Hz) and DC conductivity taken with increasing

temperature. The maximum at about 1100 °C and the minimum at 1150 °C are distinct although the AC and DC values at the minimum differ by nearly a factor of two. However, they are in near exact agreement above 1385 °C

26
where ionic conductivity is predominant and nearly equal below 100 °C

where the slag is solid and electronic conductivity is probably predominant.

Figure 9 shows the AC (40Hz) and DC conductivity as a function of decreasing

temperature. In this case, there is only an inflection point near 1150 °C

and the AC and DC values differ again by about a factor of two. Since

for both the increasing and decreasing temperature curves (Figure 9 and 9)

careful attention was paid to obtaining equilibrated values, the reason

for the difference in the curve shapes with increasing and decreasing

temperatures is not clear. This should be investigated by SEM methods in an effort to determine the sample conditions under the two different situations.

It should be pointed out that previous electrical conductivity measurements on coal slag reported in previous quarterly reports were done by

quenching the sample from some temperature above the softening point to

a temperature (900 °C) below the softening point in order to quench in an established Fe+2 /Fe+ 3 ratio at lower temperature. These measurements

were taken under equilibrated conditions so that the Fe+2 /Fe+ 3 ratio

could change, depending on the temperature, at least above 900 °C.

From the results described above, obtained by the methods of measurement

and s'ample preparation described previously, it is possible to arrive

at certain conclusions about sample conditions during the course of the

measurement. These conclusions are stated in the text. The main result

is that these measurements support the viewpoint stated previously:

that the electrical conductivity of slag from coal burned at the Bow, NH

plant is predominantly ionic above 1385 °C. In addition, these measurements

demonstrate that four-probe DC measurements are valid for obtaining a bulk conductivity of ionic conductors under certain conditions.

PI ans : The electrical conductivity measurements reported over the last

year have been for slags containing relatively large amounts of iron.

These measurements will be extended to those slags containing less iron

and more calcium which is typical of slags from Western coals. SEM

investigations will be started in an effort to understand some of the

anomalies described in the text of this report.

27
Figure 1. Radiograph of a typical slag sample. Platinum probes 1,

2, 3, and 4 are shown with probes 2 and 3 being the conductivity pair; and probes 1 and 4, the pair where current is

introduced to the sample.

28
III[i

29

Figure

2.

Plot

of

the

DC

values

for

equations

1,

2,

and 3

asa

function

of

temperature

for

increasing

temperature.
TEMPERATURE
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in

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8

Figure

4.

Plot

of

40Hz

AC

values

for

equations

1,

2,

and

3

as

a

function

of

temperature

for

increasing

temperature.
500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

TEMPERATURE

°C
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6.

Conductivity

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a

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frequency

over

a

range

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increasing

temperatures.
34

Figure

7.

Conductivity

as

a

function

of

frequency

over

a

range

of

decreasing

temperatures

.
(013 uJM0)AllAllDnaNO0

35

Figure

8.

DC

and

40Hz

AC

conductivity

as

a

function

of

increasing

temperature

after

sample

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i-(ujo omo)AliAllOnaNOO

Figure

9.

DC

and

40Hz

conductivity

as

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decreasing

temperature

from

above

1500

0

C.
3. Corrosion of Downstream MHD Components (J. Smit and C. D. Olson)

Progress : Exposures of tubular specimens. Type 316 stainless steel,

were performed under varied conditions of K 2 S0 4 , K2 S0 4 -K2 C0 3 seed

and oxygen rich or propane rich hot gas streams. All samples

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. Four stainless steel specimens

were exposed under these general conditions, three at 590 °C and one at 500 °C. The sample temperatures were maintained using air

to internally cool the tubular walls and the wall temperature was monitored using Pt/Pt- 1 0%Rh thermocouple welded into the wall at the

mid-length point. The gas stream temperature, in all cases, was held at approximately 1300 °C as indicated by a Pt/Pt-1 0%Rh thermocouple placed in the vicinity of the test specimen. The test

specimens, following the exposure runs, were analyzed using SEM/EDX.

SEM/EDX Analysis of the Metal -Salt Deposit Interface - Test specimens

were removed from the test rig 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. Metal lographic specimens were selected from

the tubular specimen, 10 mm from the mid-length point. The specimens

were cut, ground, and polished using non-agueous media and stored in

evacuated desiccators prior to SEM/EDX analysis.

Test specimens numbers 8-6, 9-6, and 6-6 were exposed at 590 °C and

number 5-6 was exposed at 500 °C. All specimens exhibited similar

salt deposit characteristics. The surface facing the gas stream was thinner than the deposit an the side portion of the tube (drip zone),

and a thin fume deposit was found on the underside of the tube. The

thickness of the top surface deposit was found to be consistent with

previous samples in that, the surface salt deposit is thinner as the

wall temperature increases. Also, under fuel rich conditions the

deposit is thinner than in the o ygen rich environment.

An evaluation of specimens 8-6 (Figure 1) and 9-6 (Figure 24) can be

made simultaneously. Both samples were seeded with 80% by weight

K2 C0 3 and 20% by weight K2 S04 , with wall temperatures of 590 °C,

however, 8-6 was in an oxygen rich fuel environment and 9-6 was in a fuel rich environment. The variations in the salt deposit can readily

be observed with the oxygen rich specimen (8-6) exhibiting a top deposit

of 0.3 mm, drip deposit of 2 mm and a slight fume deposit. The fuel

rich specimen (9-6) shows a top coating of 0.1 mm, drip deposit of

1.6 mm and a very unusual fume deposit region, dendritic in nature.

Photos (Figures 2 and 3) show a banding property in the deposit with

K + S near the surface of the steel followed by a high K region with a thin band of K + S on the surface. This phenomena is also seen in the

37
fuel rich specimen coating. The bulk of both coatings, however-, is

generally high in potassium (K) with moderate to low amounts of sulfur

(S) found.

The corrosion process exhibited in both specimens seem to follow the same general corrosion mechanism. In sample 8-6 (oxygen rich) at the

leading edge, salt-stainless interface (Figures 1, 4-12) we find the

bulk stainless followed by a reaction zone area where high nickel is

found with chromium and iron followed by an area of high chromium, high

iron, nickel and potassium. Chromium and iron are then found penetrating

the salt deposit with the iron being the most mobile species and moving

far into the salt deposit. Nickel being the least mobil or least

reactive species is generally not found to penetrate the salt deposit

except at the interface where chromium and iron move rather readily

through the salt.

In 8-6 (Figure 13), the corrosion or reaction zone can be seen at

the drip zone salt deposit stainless steel interface region. This

darker band region, as analyzed using EDX, Figures 13-20, shows high

chromium, iron, low nickel, and potassium, indicating a reacted area

on the metal surface. Analysis above and below this region again

shows cation mobility. We find concentrations of the cations as follows:

a) bulk stainless steel, b) higher nickel -chromium-iron, c) higher chromiumiron-nickel-potassium, d) chromium-high iron-potassium, e) iron-potassium,

f) high potassium. Traces of sulfur are found in the coating and reaction

areas, also, indicating some sulfur-cation reaction. Therefore, the

SEM/EDX analysis seems to indicate a preferential leaching of the metal

cations from the bulk materials (Type 316 stainless steel) in a somewhat

orderly fashion as in the case of the 304 stainless steel. This can

be corroborated by wastage (weight loss) experiments described in

previous reports. The chromium and iron cations appear to be the

more reactive species in the stainless steel and are preferentially

leached by the potassium-sulfur salt. As these cations migrate from

the bulk stainless steel composition to the salt deposit the relatively

non-reactive nickel is left and what appears as layering is observed.

Figures 21-23 shows a portion of the fume deposit region where the cor- rosive process appears to be evident. On the edge, areas of low nickel are found, while areas of chromium, iron, potassium, and sulfur are found in the reaction zone. However, in the fume deposit region there

is not as great a separation of the cations, as found by EDX, possibly

due to the fact that no direct contact of the salt is made in this area during deposit but rather collected on the underside by vaporization.

In sample 9-6, fuel rich, at the leading edge of the stainless steel

(Figures 24-34) we again find the bulk stainless steel followed

by a reaction zone area. As in the fuel rich sample (8-6), what

appears to be a distinctive corrosion banding appears using EDX

analysis. The corrosive process in the oxygen rich fuel environment

38
appears to follow the same general pattern as found in the fuel rich

environment. The cations are found again in a general order of mobility

where: a) bulk stainless steel, b) higher nickel -high chromium-iron,

c) chromium-iron-nickel-potassium, d) chromium-higher-iron-potassium

e) iron-potassium, f) high potassium. Again sulfur is found in small

amounts in the reaction zone area and coating.

In the fuel rich environment the reaction zone area does not appear to

be as distinct as in the oxygen rich environment. The fuel rich system

shows no areas of high nickel above the bulk stainless steel but shows

high nickel associated with high chromium. There is, in general, more

sulfur present when higher nickel is found, possibly forming nickel -sul fur

compounds. As shown previously in the oxygen rich environment, the

fuel rich environment shows that chromium and iron are the most mobile

cation species that penetrate the salt deposit.

The drip zone region also exhibits a reaction band area in the fuel

rich system. The same corrosion process is observed in this area as previously describe for the top of the tube. The fume deposit region

examined exhibits a reaction zone area while the salt deposit shows high

potassium content. Again iron and some chromium is found in the fume

deposit, indicating the relative ease for these cations to migrate.

In sample 6-6, the tube wall was maintained at 590 °C but the corrosive

salt used was K 2 S0 4 in a fuel rich environment. As found in previous

fuel rich systems the coating was thin on the leading edge of the tube,

0.1 mm, while the drip zone region built up, 1 mm. The fume deposit

exhibited an unusual formation of material build up similar to what was observed in 9-6. The coating appears to have a more columnar nature

which has been observed with previous samples using K2 S0 4 salt exclusively.

The reaction zone area in 6-6 (Figures 35-43) is not well delineated

in the fuel rich system as compared to the oxygen rich system, however,

corrosion is observed. SEM/EDX analysis indicated that the reaction

bands above the stainless steel bulk composition have the following

sequence: a) low chromium-nickel-iron, b) high chromium-iron-no nickel,

c) chromium-iron-potassium, d) high potassium-chromium-iron, e) high

potassium-iron, f) high potassium. Traces of sulfur are associated

with the potassium but the bulk of the salt coating is high in potassium.

As found' in previous specimens, nickel is absent in high concentration.

At the interface no nickel is detected whether this be through loss of

the nickel or its displacement to other areas not readily detectable

is not apparent. However, the migration of chromium to the edge of the

stainless steel is seen with iron and chromium penetrating the salt deposits.

Examination of the drip deposit region show similar results as previously

discussed with the absence or near absence of nickel at the metals edge, and

with chromium and iron moving into the salt layer region. The fume deposit

region showed minimal corrosion while the coating contained high potassium.

39
At a lower temperature 500 °C, corrosion is still observed in Type 316

stainless steel, 5-6, using K2 S04 salt in a fuel rich environment.

Figures 44-49 shows the reaction zone area at the metal -salt interface

at the leading edge. In this area we find, using SEM/EDX: a) bulk

stainless steel, b) low nickel-high chromium-iron-potassium-sulfur,

c) potassium-iron-chromium-sulfur, d) potassium-iron-sulfur, 3) potassiumsulfur. An area of high nickel is not detected while areas of high

chromium and iron are readily decernable in the reaction zone. This

corrosion mechanism is also found in the drip zone area and the fume

deposit region, though both to a lesser degree.

Concl usion : The variances between fuel rich and oxygen rich environments in the presence of K2 S0 4 and K2 C0 3 are minimal. Corrosion of the

Type 316 stainless steel seems to occur readily in both instances. The

oxygen rich system, however, does seem to exhibit a more definable

corrosion band area than the fuel rich system. Both systems show that

iron and chromium are the more mobile species and that nickel is relatively

unreacted. In the oxygen rich system the nickel can be followed from

the bulk composition to the interface due to the migration of iron and

chromium upwards from the bulk to the surface and then into the coating.

In the fuel rich system nickel does not seem to be left behind or found

in high concentrations even though iron and chromium are found to migrate

into the salt deposit. In previous samples, nickel was found infrequently

,

but localized, in high concentrations in the high chromium region.

In general, therefore, both systems indicate the same metal cation movement from the bulk stainless steel into the salt deposit.

Plans : 1) Continue the study of Type 316 stainless steel using SEM/EDX

analyses, 2) analyze collected x-ray diffraction data of residue salt

deposit materials from fuel rich and oxygen rich system, and 3) examine

the feasibility of using ceramic and metal coating on mild steels with

testing of specific materials at 590 °C.

40
Fig. 1

Fig. 2,

Optical micrograph of a section of Type 316 stainless steel tubing after

exposure to an oxygen rich hot gas stream seeded with K^SO^ and I^COg.

Tube temperature 590°C. Note deposit on upper surface of tube.

SEM micrograph, 45 X, of region T of optical micrograph Fig. 1 showing

metal -salt deposit interface in the drip zone.

41
Fig. 3. SEM micrograph, 92 X, of region T of optical micrograph Fig. 1 showing

netal -salt deposit interface in the drip zone.

316 SS

Fig. 4. SEM micrograph, 5460 X, of region 1Z of optical micrograph Fig. 1 showing

reaction area at metal -salt interface. Lettered regions correspond to

labeled EDX spectra Fig. 5-12.

42
Fig. 5. EDX spectra of regions A and B of Fig. 4 showing slight increase

in Ni concentration at metal -reaction zone interface (spectrum B).

Specie position and designations of all spectra in this section

of the report are as indicated above.

EDX spectra of regions C and D of Fig. 4 showing bulk spectra.

4 3

Fig. 6.
Fig. 7. EDX spectra of regions E and F of Fig. 4 showing high concentrations of Cr.

Fig. 8. EDX spectra of regions G and H of Fig. 4 showing low concentration of Ni
Fig. 9. EDX spectra of regions I and J of Fig. 4 showing high concentrations

of K.

EDX spectra of regions K and L of Fig. 4 showing high Fe and K

concentrations

Fig. 10.

i! 45
Fig. 11. EDX spectra of regions M and N of Fig. 4 showing high K concentrati

Fig. 12. EDX spectra of regions 0 and P of Fig. 4 showing Fe and trace Cr

in salt deposit.

46
316 SS

Fig. 13 SEM micrograph, 1300 X, of region T of optical micrograph Fig. 1 showing reaction area at drip zone (fume deposit-salt depo:i t-metal

interface). Lettered regions correspond to labeled EDX spectra,

Fig. 14-20.

Fig. 14. EDX spectra of regions A and B of Fig. 13 showing high Cr concentration.

47
Fig. 15. EDX spectra of regions C and D of Fig. 13 showing high Cr concentration.

Fig. 16. EDX spectra of regions E and F of Fig. 13 showing high Cr concentration.

48
' Fig. 17. EDX spectra of regions G and H of Fig. 13 showing high concentrations

of both Ni and Cr.

f Fig. 13.

I

i

!

EDX spectra of regions I and J of Fig. 13 showing high concentrations

of bcth Ni and Cr.

49
Fig. 19. EDX spectra of regions K and L of Fig. 13 showing high concentrations

of both Ni and Cr.

Fig. 20. EDX spectra of regions M and N of Fig. 13 showing high S and K

and a trace of Fe.
r ig. 22. EDX spectra of regions A and 3 of Fig. 21 showing high Cr concentrations

: ig. 21. SEM micrograph, 1800 X, of region Y of optical micrograph Fig. 1 showing

reaction area at metal -fume deposit interface. Lettered regions correspond to labeled EDX spectra, Fig. 22 and 23.

51
Fig. 23. EDX spectra of regions C and D of Fig. 21 showing absence of Ni.

Fig,. 24. Optical micrograph of a section of Type 316 stainless steel tubing after

exposure to a fuel rich hot gas stream seeded with K^SCL and I^CO^. Tube

temperature 590°C. Note deposit on upper surface of tube. “

J

52
B

336 SS

Fig. 25. SEM micrograph, 1720 X, of region 2Z of optical micrograoh Fig. 24 • Lettered regions correspond to labeled EDX spectra Fig. 26-34.

Fig. 26. EDX spectra of regions A and B of Fig. 25 showing high Cr and Ni con- centrations .

53
Fig. 27. EDX spectra of regions C and D of Fig. 25 showing high Cr and Ni

concentrations.

Fig. 28. EDX spectra of regions E and F of Fig. 25 showing high Cr con- centrations.

54
Fig. 29. EDX spectra of regions G and H of Fig. 25 showing high Cr con- centrations .

Fig. 30. EDX spectra of regions I and J of Fig. 25 showing high Fe con- centrations.

55
Fig. 31. EDX spectra of regions K and L of Fig. 25 showing high Fe con- centrations .

Fig. 32. EDX spectra of regions M and N of Fig. 25 showing Fe.
Fig. 33. EDX spectra of regions 0 and P of Fig. 25 showing trace of Fe

in the salt deposit.

Fig. 34. EDX spectra of regions Q and R of Fig. 25 showing trace of Fe

in the salt deposit.

57
Fig. 35. Optical micrograph of a section of Type 316 stainless steel tubing

after exposure to a fuel rich hot gas stream seeded .»/ ith K«S0».

Tube wall temperature 590°C. Note deposit on upper surface of tube.

Fig. 36. SEM micrograph, 1720 X, of region 3Z of optical micrograph, Fig. 35.

Lettered regions correspond to labeled EDX spectra Fig. 37-43.

58 11
Fig. 37. EDX spectra of regions A and B of Fig. 36 showing high concentrations

of Cr and absence of Ni

.

Fig. 33. EDX spectra of regions C and D of Fig. 36 showing high concentrations

of Cr and absence of Ni

.

59
Fig. 39. EDX spectra of regions E and F of Fig. 36 showing high concentrations

of Cr and absence of Ni

.

Fig. 40. EDX spectra of regions G and H of Fig. 36 showing high concentrations

of Cr and absence of Ni

.
Fig. 41 EDX spectra of regions I and J of Fig. 36 showing high concentrations

of Ni and absence of Cr.

Fig. 42. EDX spectra of regions K and L of Fig. 36 showing high concentrations

of K with a trace of Fe and Cr.
Fig. 43. EDX spectra of regions M and N of Fig. 36 showing high concentrations,

of K with a trace of Fe and Cr.

Fig. 44. Optical micrograph of a section of Type 316 stainless steel tubing

after exposure to a fuel rich hot gas stream seeded with K^SO^. Tube

wall temperature 500°C. Note deposit on upper surface of tube.

62
Fig. 45. SEM micrograph, 1160 X, of region 4Z of optical micrograph Fig. 44

showing reaction area at metal-salt interface. Lettered regions

correspond to labeled EDX spectra Fig. 46-49.

Fig. 46. EDX spectra of regions A and B of Fig. 45 showing high Cr and low Ni

concentrations.

63
EDX spectra of regions E and

F of Fig. 45 showing high concentrations

of Fe with

a slight trace of Cr.

Fig. 48.
Fig. 49. EDX spectra of regions G and H of Fig. 45 showing Fe with a trac

of Cr.

65