irL<to '/fO

EA- 601 0-21

Dist. Category UC-90C

MATERIALS RESEARCH FOR THE CLEAN UTILIZATION OF COAL

QUARTERLY PROGRESS REPORT

July - September 1979

Samuel J. Schneider

Project Manager

Center for Materials Science

National Bureau of Standards

Washington, D.C. 20234

PREPARED FOR THE UNITED STATES

DEPARTMENT OF ENERGY

Under Contract No. EA-77-A-01 -601

0

"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 precess disclosed, or represents that its use would not infringe privately owned rights."

TABLE OF CONTENTS

PAGE

I. OBJECTIVE AND SCOPE OF WORK 1

II. SUMMARY OF PROGRESS TO DATE 1

Articles Published and Talks Presented 3

III. DETAILED DESCRIPTION OF TECHNICAL PROGRESS 4

1 . Metal Corrosion 4

a. Pre-Cracked Fracture Test 4

2. Ceramic Deformation, Fracture and Erosion 5

3. Chemical Degradation of Ceramics .6

a. Reactions and Transformations 6

b. Slag Characterization 6

c. Vaporization and Chemical Transport 9

4. Failure Prevention 16

a. Failure Information Center 16

b. Materials Properties Data Center 17

5. Creep of MHD Refractories 19

6. Electrical Transport Mechanisms in Slag Associated

with Electrochemical Degradation of Insulator

and Electrode Materials 22

7. Corrosion of Downstream MHD Components 33

I. OBJECTIVE AND SCOPE OF WORK

Coal gasification and other conversion processes require the handling and

containment of corrosive gases and liquids at high temperature and pressures,

and also the handling of flowing coal particles in these environments. These

severe environments cause materials failures which inhibit successful and

long-time operation. The project entails investigations on the wear, cor- rosion, chemical and electrical degradation, fracture, and deformation pro- cesses which lead to the breakdown of metals and ceramics currently being

utilized in test facilities and pilot plants. Studies will also be carried

out on new candidate materials considered for improved performance. Special

emphasis will be devoted to the development of test methods, especially

short-time procedures, to evaluate the durability of materials in the severe environments. These methods will focus on wear, impact erosion, stress

corrosion, strength, deformation, slow crack growth and chemical degradation.

A system has been initiated to abstract and compile all significant operating incidents from coal conversion plants as well as materials property and

performance information important to the design and operation of these

plants. This program will provide a central information center where probblems of common interest can be identified and analyzed to avoid unnecessary

failures and lead to the selection of improved materials for coal conversion

and utilization. Active consultation to DOE and associated contractors will

be provided as requested.

II. SUMMARY OF PROGRESS TO DATE

Brief Summary

1. Metal Corrosion

a. Pre-Cracked Fracture Test: Experimental verification of the

analysis for the change in stress-intensity ratio (Ky/K ) with temperaature was conducted for the tension-loaded DCB specimen? These tests

showed that the stress-intensity change with temperature is very sensitive to the thermal expansion of the loading fixture. The stressintensity can be made to increase substantially with temperature.

2. Ceramic Deformation, Fracture, and Erosion

The earlier part of this quarter was spent making repairs to the

apparatus for mechanical testing at elevated pressure and temperature.

Following these repairs, a series of experiments was begun on newly

formulated batches of an intermediate-alumina (56%) refractory concrete.

These experiments involved an in situ measurement of the modulus of

rupture following a 70 hour hydrothermal exposure. In addition, the

porosity and pore size distribution were measured for two intermediatealumina (50% and 56%) refractory concretes to examine the influence

of these properties on the modulus of rupture. Two additional experiments

are planned with the mechanical testing apparatus at elevated pressure

and temperature to complete the studies begun this quarter. Upon

completion of these experiments and analysis of the data, the final

report will be prepared.

1
3. Chemical Degradation

a. Reactions and Transformations

Additional data has been obtained on the behavior of CA2 and CA6 in

hydrothermal environments.

Preparation of a final report summarizing the work of this task is in

progress

.

b. Slag Characterization

As discussed in previous reports, it was decided to measure the

viscosity of the melt while extending its temperature to the

maximum achievable with the existing platinum heater until burn

out occurred. At this point a new heater would be constructed

from 60% Pt-40% Rh to increase the melt temperature. The melt which

is currently being investigated has the following composition:

Si

0

2 , 48.30%; A1 2 0 3 , 12.10%; Fe 2 0 3 , 12.00%; CaO, 14.90; MgO, 8.00%;

and Na 2 0, 4.70% (wt%).

Five experiments were conducted and each resulted in slag spills

and/or heater burn outs resulting in extensive rebuilding of the

viscometer vessel internals.

c. Vaporization and Chemical Transport

Vapor transport data, in the form of alkali species partial pressures,

have been obtained for the K2 slag system, of initial composition (wt%)

Si

0

2 47.3, A1 2 0 3 11.1, Fe 2 0 3 12, CaO 13.9, MgO 7.8 and K2 0 8.7, using

the transpiration mass spectrometric technique (TMS). Complementary

computer modeling calculations, using the S0LGASMIX program, have also

been made. Data obtained previously for the so-called slag, of

Initial composition (wt.%) A1 2 0 3 12.05, CaO 3.8, Cr 2 0 3 1.3, Fe 2 0 3 14.25, K2 0 1 9.54, MgO 1.03, Na 2 0 0.47, S0 3 0.21 , Si

0

2 46.82, and Ti

0

2 0.52, have been analyzed, and presented at an international symposium.

4. Failure prevention

a. Failure Information Center

Five additional reports of operating experiences and failure analysis

were entered into the Center's data base. Approximately 2,800 information

items were distributed to DoE contractors and newsletter readers during

this quarter. A draft report on erosive wear failures was completed and

a feature article for the Materials and Components Newsletter was submitted

for publication in the October, 1979 issue.

b. Materials Properties Data Center

The routine on-going data tasks of the Center have continued during the

quarter. A major emphasis has been the effort to expedite the acquisition

of computer vendors' services through contacts with the DOC ADP procurement

division, the vendors who have submitted proposals and the preparation

of benchmark test material.

2
5. Creep of MHD Refractories

Efforts this quarter were directed toward obtaining data on the deformation

of the chrome-iron spinel refractory. The reduced cross-section type of

creep specimen was evaluated in creep tests at 1400, 1500 and 1600°C. The

material was characterized using X-ray diffraction, light microscopy and

scanning electron microscopy. The results are reported In the text.

6. Electrical Transport Mechanisms in Slag Associated with Electrochemical Degradation of Insulator and Electrode Materials

The measurement of the electrical conductivity of YCr03 (.05 Ca)

as a function of oxygen pressure from 10° to 10" 15 atmospheres has

been started. Some difficulty has been encountered in the low pressure

regions because of hydrogen embrittlement of the platinum electrode

leadouts.

The analytical work on the electrochemical corrosion at 1343°C of

YCr0 3 in Bow NH slag with 20 % K2 S04 added has been completed. While the

cathode showed a sizeable attack zone, the anode attack zone was small.

The total reaction layer was about .03mm thick composed of a boundary

layer of Fe-Cr-Al spinel without Si and a zone near the undisturbed

electrode material composed of Fe-Cr-Al spinel but rich in silicon.

The electrical conductivity as a function of temperature of Bow NH

slag with 20% K2 S04 added to the melt has been completed. These measurements were done in air and at a reduced oxygen pressure but the latter

run must be repeated because of an experimental difficulty. Just as in

the measurements of the Bow NH slag without the K2 S04 added, this slag

was quenched from a higher s^a k temperature to below the softening point

in order to quench in the Fe 2 /Fe 3 ratio established at the higher

temperature. The two materials (with and without K2 S04 ) behave quite

differently, the latter showing a large ionic current down to low temperature.

7. Corrosion of Downstream MHD Components

Type 304 stainless steel tubes, maintained at 400°C, 500°C, and

590°C were exposed to K2 S04 seeded fuel rich and oxygen rich hot

gas streams. Optical and SEM examinations and EDX analysis of the

specimens revealed differences in the deposits formed on the tubing

(thinner in the fuel rich stream) as well as differences In nickel

distribution in the reaction zone of the metal-deposit interface.

In the coming quarter, a similar series will be run but with a mixture of 80% by weight K2 C0 3 and 20% by weight K2 S0 4 added to the

hot gas stream.

Articles Published and Talks Presented

R. C. Dobbyn, "How do we handle the Subjective Component of Inservice

Data Reporting and Analysis", ASME, Materials and Fabrication Committee

Meeting, San Antonio, Aug 1979.

W. S. Brower, R. C. Dobbyn, and C. R. Robbins, "Refractory C0 2 Acceptor

Gasifier Lining Reviewed", DOE Materials and Components Newsletter,

October, 1 979.

3
II. DETAILED DESCRIPTION OF TECHNICAL PROGRESS

1 . Metal Corrosion

a. Pre-Cracked Fracture Test (J. H. Smith and G. E. Hicho, 562)

Progress: Tests were continued to experimentally verify the analysis

for the change in stress-intensity ratio (Ky/K ) with temperature for

the tension-loaded DCB specimen. The loading fixture used was made of

type 347 stainless steel and the specimen grips were made of Inconel

600. Measurement of the increase in load-line displacement, V, with

temperature were made with a linear-voltage displacement transducer

( LVDT) . Measurement of the load-line displacement were made at temperatures

from 0 to 500 C.

Previous results indicated that a discrepancy existed between the measured

change in load-line displacement with temperature and the change in

displacement calculated from the differences in thermal expansion of the

loading fixture and loading grips. This discrepancy may result from 1)

unexpected variation in the thermal expansion of the specimen and loading

fixture and 2) errors associated with translating displacements measured

on the edge of the specimen to the displacement at the load-line position.

Experiments were conducted to assess the magnitude of these two sources of error.

The loading fixture was modified to permit direct measurement of the

displacement at the loading position for the specimen. Measurements

were then performed with the specimen removed from the loading fixture

to assess changes in the length of the test fixture and loading grips

with temperature. These measurements showed that the thermal expansion

of the test fixture was significantly larger than originally calculated.

This means that the loading fixture as designed would be over compensating,

that is, would cause the stress intensity, Ky, to increase with temperature,

rather than remained constant as required.

A sensitivity analysis indicated that the larger than anticipated thermal

expansion described above, may arise from small variations in the amount

of thermal expansion occurring in the loading fixture. Small variations

in the thermal expansion of the loading fixture and loading grips may

result in significant variations in the displacement of the test specimen

with temperature.

The discrepancy between the measured and expected load-line displacement

due to translation of the displacement measurements from the specimen to

the load-line were assessed by measuring the displacements at both

points on the test specimens. These results showed that the usual

procedure of using the method of similar triangles to make this required

measurement translation did not result in significant errors.

Pl_ans: Work on this research project is now discontinued and there are

no plans for further work.

4
2. Ceramic Deformation, Fracture, and Erosion (E. R. Fuller, Jr.,

S. M. Wiederhorn, D. E. Roberts, and L. Chuck, 562)

Progress : The earlier part of this quarter was spent making repairs to

the apparatus for mechanical testing at elevated pressure and temperature.

Following these repairs, a series of experiments was begun on newly

formulated batches of an intermediate-alumina (56%) refractory concrete.

These experiments involved an in situ measurement of the modulus of

rupture following a 70 hour hydrothermal exposure. In addition, the

porosity and pore size distribution were measured for two intermediatealumina (50% and 56%) refractory concretes to examine the influence of

these properties on the modulus of rupture. These studies are described

below.

At the end of last quarter, while testing the high-alumina refractory

concrete at a temperature of 1 01 0°C and a steam pressure of 1100 psia, a segment of the lower heater in our main furnace burned out. To replace

this heater segment, the apparatus had to be disassembled and the lower

furnace assembly had to be completely rebuilt. While the apparatus was disassembled for these repairs, a number of other minor repairs were undertaken: the subheater surrounding the lower loading bellows was replaced with a larger wattage heater; new gaskets were installed in the

lower flange of the inner environmental chamber; and the steel bolts

previously used in this flange were replaced with stainless steel bolts

to match better the thermal expansion of the flange. Towards the end of

the quarter, the system was again disassembled to replace the lower

loading bellows which had developed several pin-hole size leaks.

Following the repairs to the furnace assembly, a series of experiments

was begun on newly formulated batches of an intermediate-alumina (56%)

refractory concrete. The exposure conditions for these experiments were similar to those used last quarter for the high-alumina refractory. The

specimens were exposed at temperature and pressure to steam for at least

70 hours prior to an in situ measurement of the modulus of rupture.

Additional specimens were simultaneously exposed to the same environment;

but they were then cooled to room temperature and atmospheric pressure

before they were broken to determine their modulus of rupture. Experiments

thus far have been conducted at steam pressures of nominally 800 to 1000

psia and at temperatures of 360°C and 1 01 0°C . The experiment at 660°C

will be conducted next quarter.

In addition to these experiments, the influence of porosity and pore size

distribution on the modulus of rupture was examined for two intermediatealumina refractory concretes. A mercury porosimeter was used to determine

the open pore porosity and size distribution both in control specimens

and in specimens that had been exposed to hydrothermal conditions. The

hydrothermal ly exposed, and stronger, specimens had a greater porosity

than the control specimens, but the pore size distribution was skewed

towards smaller pore sizes.

5
Plans: Two additional experiments are presently planned.^ The first

experiment is to complete the series of in situ modul us-of-rupture

experirents on the intermediate alumina refractory concrete with a test

at 660

6

C. Time permitting, the high-alumina refractory concrete will be

tested in a simulated coal gasification environment at a temperature of

lOlCrC and a total pressure of 1000 psia (6.9 MPa). Following completion

of these experirents and analysis of the data, the final report will be

prepared.

3. Chemical Degradation

a. Reactions and Transformations (F. A. Mauer and C. R. Robbins, 565) ** Progress: Analysis of forty in situ x-ray patterns of a test bar cf CA2 exposed to high pressure steam, and to a steam - carbon dioxide atmosphere

has been completed.

A test bar of CAe has been exposed to steam at 300°C (220 psig* ) for 700

hours. This compound with the s-A structure forms readily at 1400°C in

air but its stability under low temperature hydrothermal conditions is

not clear. S~al 1 amounts of 6 -A are commonly encountered in hydrothermal

exposure tests of high purity castables, but with compositions other

than that of pure CA&

.

Several tests bars of high and low AI 2 O 3 content refractory castables

fro- the exposure tests of Task 2 were examined by conventional x-ray

diffraction ~ethods.

All experimental data obtained during the in situ x-ray study of Task 3,

the x-ray characterization study of Task 2 specimens, and the light

microscope, SE l,‘ and x-ray diffraction analyses of core samples from the

’-e-Vactory lining of the Conoco Lignite Gasification Pilot Plant gasifier

^ave been reviewed and correlated. Preparation of a summary report is

in progress.

?'

r

s : A final report summarizing the work of this task will be prepared.

b. Slag Characterization (W. S. Brower, J. L. Waring, and

D. H. Blackburn, 565)

Progress : As discussed previously, it was decided to measure the

viscosity of the melt while extending its temperature to the

"axi-jr achievable wit k t

r e existing platinum heater until burn

out occurred. At this point a new heater would be constructed

fro~ 60cPt-40cRh to increase the ~elt temperature. The melt which

is currently being investigated has the following composition:

Si02 , 48.30?; A1 2 03 , 12 . 10 ?; Fe 2 0,, 12.00?; CaO, 14.90?; MgO, 8.00?;

and Na 2 0, 4.70? (wt?).

* In SI unit, 1 MPa = 145 psia.

** Cement notation

C = CaO

A = A1 2 03

6
In the first experiment prior to measuring viscosity, the platinum

heater was operating at about 1511 °C at ambient pressure. The

viscosity bob-thermocoupl e assembly was introduced into the melt.

The temperature of the melt was 1386°C which is well within the

fluid range of the composition. The physical position of the bob

is not visible and can only be approximated at these elevated

temperatures. Prior to generating steam pressure, the viscosity

at ambient pressure is usually checked. However, when the crucible

containing the melt was rotated no angular deflection was detected

on the magnetic position detector and the experiment was terminated.

Figure 1 shows the after-the-fact physical picture of the failure.

From the above it can be seen that the platinum crucible was lifted

from the pedestal and welded to the platinum heater.

Catastrophic failures result in the loss of many weeks since it is

necessary to rebuild the platinum crucible, remake the ceramic

pedestal, reshape the platinum heater, rebuild and recalibrate the

suspension.

Since it was thought that the bob was inadvertently introduced into

the liquid, experiment one was duplicated in experiment two. The

results were similar but not as disastrous. The crucible welded

to the heater but the suspension remained intact.

In experiment three the slag was melted out of the vessel in air

and the melt was observed. In the melting process the center of

the melt (coldest portion) remained solid and as the edges melted

the resulting liquid foamed up the sides and out of the crucible.

When a platinum rod positioned above the surface of the liquid

came into contact with the foaming material the rod served to bridge

and extract all of the liquid from the crucible. In experiment one,

the foaming liquid probably pushed the bob to the side where it welded

to the crucible after which, when the pedestal was rotated, the

crucible was lifted from the pedestal and welded to the heater.

This |oaming problem is probably due to evolution of oxygen gas

as Fe 3 is converted to Fe 2 on heating. From additional

experimentation it was found that the foaming problem could be

eliminated by annealing the starting melt at 1500°C for 4 hrs

before placing it into the viscometer.

In experiment four, a new batch of material previously heated as described above was placed in the viscometer for viscosity measurements. The platinum heater was controlling properly at 1 420 °C

but burned out prior to the introduction of the viscosity measuring

bob. From figure 1 it can be seen that the burn out pattern on the

platinum cylinder is near the position where the platinum electrode

fin had been welded to the heater. In the design the position of

the electrodes are fixed therefore fixing the platinum fins which

are clamped to the electrodes. Thus, thermal expansion is accomplished

by changes in the geometry of the platinum heater cylinder. It is

most likely that the platinum was "work hardened by repeated movement caused by such geometry changes and burned out where the metal

endured maximum flexing.

7
Figure X. Burn out pattern of the platinum heater.

8
These massive fins were removed from the cylinder and were welded

to a new cylinder of 60%Pt and 40%Rh. Two layers of insulating

material were cast about the heater. The Inner layer was fabricated

from green cast 97 and the outer layer from VSL 50.

In experiment five the 60%Pt-40%Rh heater was heated to 1480°C.

The doughnut shaped lid was removed for greater visibility of the

melt. The material maintained at the temperature for several hours

was visually observed to be melted. The bob was observed continuously

as it was lowered 1/4" at a time into the melt. At or near the

surface of the liquid the bob shifted position and welded to the

side of the crucible, which in turn welded to the 60/40 heater.

The run was terminated.

PI ans : The 60% platinum 40% rhodium heater will be used in an attempt to obtain viscosity at higher temperatures than those

obtainable with the pure platinum heater.

c. Vaporization and Chemical Transport (J. Hastie, D. Bonnell and

w. Horton)

Progress : Vapor transport data, in the form of alkali species partial

pressures, have been obtained for the K2 slag system, of initial composition (wt%) SI02 47.3, A1 2 0 3 11.1, Fe 2 03 12, CaO 13.9, MgO 7.8 and K2 0 8.7,

the transpiration mass spectrometric technique (TMS). Complementary

computer modeling calculations, using the S0LGASMIX program, have also

been made. Data obtained previously for the so-called K x slag, of

initial composition (wt.%) A1 2 0 3 12.06, CaO 3.8, Cr 2 0 3 1.3, Fe 2 0 3 14.25, K2 0 1 9.54, MgO 1.03, Na 2 0 0.47, S0 3 0.21 , Si

0

2 46.82, and Ti

0

2

0.

52, have been analyzed, and presented at an international symposium.

1. K2 + H 2 Slag-Gas System:

In the previous Quarterly Report (PQR), we presented vapor transport

data for the K2 synthetic slag (approximates an alkali enriched "Westerntype" basic slag) as a function of temperature and H 2 0 partial pressure.

Both these variables had a strong effect on the rate of vaporization of

K2 o from the slag, primarily in the form of K and 02 species. For

instance, an 100 K increase in temperature, or a two order of magnitude

Increase in H 2 0 pressure, led to about an order of magnitude increase in

slag vapor pressure, e.g., see Figs. 3 and 4 of PQR, respectively . The

most significant reactions giving rise to these dependences are considered

to be

K2 0 U) (in slag) = 2K + 1/2 0 2 (1 )

K2 0 U) (in slag) + H 2 = 2K + H 2 0 (2)

H 2 0 = H 2 + 1/2 02

. (3)

Also, relatively insignificant amounts of K0H were formed under these

conditions. In order to verify this reaction scheme, and to extend the

vapor transport conditions to reducing conditions close to those present

in coal gas, a series of measurements were made using H 2 as the initial

reactant gas. Compositions of H 2 -N 2 -H 2 0-0 2 gas up to 10. volume % H 2 were attained prior to corrosive loss of the transpiration reactor.

9
As H~ is introduced to the slag system the O2 concentration is

decreased~and H2 0 increases in accord with reaction (3). Typical data

are given in Fig. 1. Note that at relatively low H 2 concentration (< 5x10"'

atm) the 02 scavenging process provides a high concentration of H 2 0.

As there are three interdependent (through reactions (l)-(3)) reactive

gases simultaneously present; namely, H 2 , H 2 0 and 02 , the dependence of

K pressure on reactive gas pressure can be complex, as shown in Fig. 2.

For the decreasing pressure region of the run chronology, the one-half

power dependence of K pressure on H 2 0 pressure (resulting from reaction

(3)) is consistent with reactions (2) and (3).

2. K2 Slag System--Time Dependent Observations:

During the initial heating-vaporization phase, using a non-reactive

N- carrier gas, a periodic pressure burst phenomenon was noted for both

the K and 02 vapor species. As shown in Fig. 3, the rise time for such

a burst is almost instantaneous once the critical temperature is reached.

After about 20 min., at constant temperature, the K and 02 pressures

return to the expected level. This type of phenomenon has also recently

been observed in solar heating experiments of liquid oxides. The

explanation for this effect in our system is unclear but may be indicative of a non-homogeneous sample, perhaps containing residual K2 C0 3 used in the slag-synthesis. Alternatively, phase separation of an initially homogeneous sample may be possible.

A second type of time dependent phenomenon was observed for this

slag, as shown in Fig. 4. Once an isothermal condition has been achieved

the K pressure falls off with time. We believe that this results from

surface depletion of K (and 02 ) from the sample due to the bulk rate of

diffusion being too small relative to the surface vaporization rate.

This effect was found to be much less pronounced at higher temperatures

where the diffusion rates are probably higher.

3. Modeling of the K2 + H 2 Slag-Gas Systems:

An equilibrium model has been chosen to describe the chemical

interaction between gaseous environment and coal slag. To utilize the

model fully requires a knowledge of activity coefficients of the slag

constituents which may contribute to chemical interaction with the gas.

Also required is a computer program which gives equilibrium compositions

for systems containing not only a gaseous phase and pure condensed

phases but also solutions that are not ideal. A start on the problem of

the activity coefficient of K2 0 in slag has been made using vapor pressure

data obtained in this laboratory for K2 0-Si02 solutions. Redl ich-Kister

type equations have been developed and a choice among these has to be

made. A program known as SOLGASMIX, developed at the University of

Ume3, Sweden, has been received which handles the required systems

described above. It will solve both constant pressure and constant

volume problems at fixed temperature. To use the non-ideal solution

feature, an equation for the activity coefficient of a species is needed.

This will usually be a function of mole fraction and temperature. A few

trial runs of the program have been made.

10
Typical output data obtained from the SOLGASMIX program for the K2 slag in the presence of H 2 are given in table 1. Note that K is the

predominant alkali vapor species, in agreement with experimental observation. However, the 02 partial pressures are much less than observed

experimentally. It is also noteworthy that the K partial pressure is

relatively temperature insensitive in the presence of H 2 and H 2 0. This

agrees qualitatively with data presented in the previous Quarterly

Report for the Kj slag system (e.g., see Fig. 1 of previous report).

Table 1

Species partial pressures from non-ideal solution 3 multicomponent equilibrium calculations for K2 slag + H 2

Species Pressure

(1600 K)

(atm) Pressure

(1700 K)

(atm)

h 2 0.11 -3 b 0.63 -4

h 2 o 0.26 -3 0.27 -3

02 0.23 -9 0.77 -8

K 0.57 -3 0.60 -3

KOH 0.51 -4 0.55 -4

Si 0 0.54 -8 0.31 -7

a K2 0 activity coefficient specified as 10" 8 and independent of

temperature.

^Denotes e.g., 0.11 x 10" 3

11
APPLIED H2 PRESSURE (x|0 2 ATM)

1. Response of K2 slag system to added H ? , showing conversion of slag

0 2 to H 2 0. Conditions, 1655 K temperature, 0.18 atm M 2 carrier gas

pressure and capillary nozzle. -x:

12

ION

INTENSITY

(mV)
(wiv) aanssadd 2 o

sT lO CD

1

i i 2 2 o

( IMXV ) 3dnSS3Hd >1

2. K-pressure (open symbols) and 02 pressure (closed symbols) variation with

H 2 0 for added H 2 with K2 slag. Conditions, 1655 K temperature, 0.18 atm

N 2 carrier gas pressure and capillary nozzle.

13

PRESSURE

H

2

0

(ATM)
(A^)

A1ISN31NI

NOI

>1

TIME (MINUTES)

3. K-species pressure burst phenomenon expressed as K+ ion intensity versus

time, for K2 slag. Conditions, 1655 K temperature, 0.18 atm N2 carrier

gas pressure and capillary nozzle.

14
ISOTHERMAL

o

oo

o

to

o

o

CM

o

A1ISN31NI NOI H

4. Typical K + ion intensity signal decay with time for K2 slag. Conditions,

1570 K temperature, 0.21 atm. N

2 and capillary nozzle.

15

TIME

(MINUTES)
4. Failure Prevention

Failure Information Center (R. C. Dobbyn, W. A. Willard, 562, and

W. S. Brower, 565)

Progress: During the quarter the Failure Information Center received

five reports of operational experiences and materials and components

failures from coal conversion pilot plants and process development

units. To date, the percent contribution of failure incidents contained

in the data base is shown in Table 1.

These reports have been classified and evaluated for technical completeness and accuracy. Detailed summaries of this information have been

entered into the Center's computerized data bank.

The Center provided Battel 1 e-Col umbus with ten updated summaries and

three hard-copy reports for possible inclusion in the DoE Newsletter

feature on failure experiences. In addition, a feature article, sum- marizing the performance of refractory construction materials used in

the C0 : Acceptor Pilot Plant, was submitted to Battelle for publication

in the October, 1979 issue.

The Failure Information Center answered fourteen other requests for

information from DoE contractors. In response to these, 2,764 abstracts

and ten hard-copy reports were transmitted. The Center also received

one visitor.

A substantial reformatting of data base entries was completed during the

quarter. Completing this task will not only better facilitate information

exchange and analysis but will also speed the transfer of data to the new data base management system.

Progress was also made in the preparation of the Construction Materials

Handbook for Coal Gasification, a joint project with the Materials

Properties Data Center at NBS (see section b).

A draft summary report on erosive wear failures in coal conversion

process plants was completed by project staff and is currently in

review. Several sections of a similar report on corrosion have also

been completed.

Camera-ready copy of the final report on the performance of materials

and components at the CO2 Acceptor pilot plant was transmitted to DoE

during the quarter. This completes the project.

PI ans : Liaison with pilot plants and failure analysis laboratory staff

will continue, as will work on the construction materials handbook.

Review of the draft report on erosive wear will be completed and com- pletion of the draft report on corrosion failures is also scheduled.

The regular information and data gathering, analysis and dissemination

activities of the center will continue.

16
Table 1

FAILURE INCIDENTS IN COAL CONVERSION SYSTEMS

PROCESS NO OF INCIDENTS PERCENT

Bi gas 16 3.61

BMI 35 7.91

Carbonate 5 1 .13

Clean Coke 27 6.10

C02 52 11.76

CPC 1 0.22

Cresap 20 4.52

Exxon 3 0.67

GFETC 2 0.45

Hygas 45 10.18

Letc 3 0. 67

Lignite 18 4.07

Mete 13 2.94

Mi sc. 15 3.39

Pete 2 0.45

SRC 22 4.97

SRC-W 17 3.84

Synthane 114 25.79

Synthoil 2 0.45

Westinghouse 30 6 .78

Total Number of Incidents = 442

b. Materials Properties Data Center (H. M. Ondik, T. A. Hahn, and

A. Perloff, 565, and I. J. Feinberg, 562)

Progress : The Data Center staff has continued normal operation

along with work on the Construction Materials Handbook for Coal

Gasification and the paper on the Current Status of Materials

for Open-Cycle MHD Power Generation.

During the quarter we received responses from computer vendors

to the questions raised in our technical evaluations of their

proposals for computer services. Two of the nine vendors who

submitted proposals have withdrawn from competition since they

could not meet our requirements. The other seven vendors have

responded satisfactorily and are eligible to participate in

benchmark testing sessions, although conferences had to be held

with two vendors to verify their ability to comply with the

specifications. The benchmark base, containing some eighty data

entries and a list of the types of operations to be performed,

has been prepared and delivered to the Commerce ADP procurement

group for distribution to the vendors. Benchmark test sessions

will be scheduled by the Commerce ADP management.

17
PI ans : It is expected that the Center staff will be occupied

chiefly with the benchmark test sessions and evaluation of the

results during the first poition of the next quarter. If all

goes smoothly, this next quarter should see the establishment

of a contract for a computer vendor's service. Draft sections

of the MHD paper and further sections of the gasification handbook will be delivered.
5. Creep of MHD Refractories (N. J. Tighe, C. L. McDaniel, S. M.

Wiederhorn, 562.00)

Progress : Work during this quarter concentrated on evaluating the

refractory designated Corhart RFG, a rebonded fused grain chrome spinel.

Specimens received from Harry Townes at Montana Tech were (1) cores cut

from bricks used in the test rig and (2) sections of refractory brick

removed from the test rig after a test run of 250 hours.

Experimental Procedure : The cores were machined into creep specimens three

inches long with reduced cross section 1/2 inch in diameter and 1 inch long.

These specimens were tested at 1400, 1500 and 1600°C in the deadweight creep

apparatus. Measurements were made of the swelling during exposure at 1400,

1500, and 1600°C using cylinders 1/2 inch in diameter by one inch long. Changes

in structure as a result of heating were monitored by X-ray diffraction.

The brick sections were examined using light microscopy and scanning

electron microscopy. Phases were identified by X-ray diffraction and through

energy dispersive X-ray analysis (EDAX) in the scanning electron microscope.

Resul ts : The as-received RFG refractory consists of a Cr rich and an Fe rich

spinel solid solution plus MgO. After heating at 1400°C, or above the material

equilibrates to a single spinel plus MgO. This oxidative phase change is

accompanied by a weight loss and a swelling of the specimen. The measured

changes are shown in Table 1.

Table 1. Dimensional Changes During Heating of Cr-Fe Spinel Refractory

RFG.

Temperature

°C

Time

hr

Length

% Change

Diameter

% Change

Wei ght

% Change

1 400°C 23 +0.3 +0.2 -0.6

1 500°C 26 +0.3 +0.4 -0.6

1 600°C 18 +0.2 +0.2 -0.9

Some of the weight loss can be attributed to volatization of the material.

Some swelling could be attributed to void growth during heating as well as

to the phase changes.

The RFG cores exhibited considerable creep at 1400, 1500 and 1600°C.

Examples of the deformation are shown in figure 1 which shows (a) an as ground core (b) a specimen after 133 hours at 92 psi which crept 8.4% and

(c) a specimen after 63 hours at 51 psi which crept 9.1%. These loads are heavier than those which might occur during service and were used to accelerate

the deformation rate.

The brick specimens were taken at different positions in the air preheater stack

at Montana. Interaction with the coal slag was evident visually on all specimens.

The scanning microscopy and EDAX measurements are not complete at this time

but with these techniques the slag penetration could be tracked easily in the

specimens. The powder diffraction analysis showed that the type of phase

transformations observed in the creep specimens occurred in specimens in

the stack. The complete analysis of both sets of specimens will be presented

in a later report.

19
PI ans : The creep testing and analysis of exposed specimens of the

chrome-iron spinel refractoi j will be completed during the coming quarter.

Specimens of the magnesia-rich, alumina spinel brick (Corhart) X-317 have

been machined and will be tested in creep and examined microscopically.

The furnace control system has been ordered and should be delivered in

4-5 months so that the long time creep tests can be started in early 1980.

20
Fig. 1 Refractory (RFG) specimens from creep tests (a) as received (b) 1500°C, 133 hr, 92 psi, 8.4% deformation

(c) 1600°C, 63 hr, 51 psi, 9.1% deformation.

21
Task 6: Electrical Transport Mechanisms in Slag Associated with Electrochemical Degradation of Insulator and Electrode Materials

(W. Hosier, T. Negas)

Progress :

a . Electrical Conductivity of YCrO^

In the last quarterly report (April-June 79), a discussion of the

proposed conductivity mechanism in YCr03 doped with a divalent metal

such as Ca or Mg was given. Electrical data was also presented for both

magnesia and calcia doped material as a function of temperature at

several partial pressures of oxygen. It is evident from this data and

from the model presented that the conductivity especially at low temperatures (lOOO^C to 25hC) is a strong function of the state of reduction

obtained at higher temperature where oxygen diffusion is more rapid. It

is desirable to know the conductivity as a function of oxygen pressure

in this high temperature range not only because it dictates the conductivity magnitude in the low temperature range when oxygen diffusion is

low, but also because it is probable that some part of this electrode

system may be operating in the oxidation-reduction range of temperature

(1200%C to 1600%C) in a functioning MHD generator. Oxygen pressures at

the anode and cathode of a generator under load may be many orders of

magnitude different.

A new batch of YCr03 doped with 5% Ca on the Y site was prepared by

thermal sintering at 1700%C in an atmosphere of forming gas (5% H 2

- 95% N 2 ).

From this piece a sample was cut and electrical contacts mounted using

platinum leads attached by a special peaning process. The oxygen partial

pressure in an atmosphere of forming gas is 10~ 14 to 10' 15 atmospheres

of 02 as measured by a zirconia oxygen sensor. Partial pressures of a few parts per million (10~ 6 atmospheres) are obtainable by direct mixing

of nitrpgen and oxygen. In order to obtain pressures in the range 10~ 7 to 10 11 atmospheres 02 in N 2 a special gas blender is used to mix

forming gas, used as a carrier gas, with a 1 ppm 02 in N 2 gas mixture

used as a component gas.

Since YCr03 must be thermally sintered in a very low oxygen pressure,

initial conductivity measurements were made at the corresponding low

partial pressures ( 1

0

- 1

4

- 10” 15 atmos 02 ) used in the sintering process.

An initial soak temperature was chosen as 1300%C. The conductivity

increased with time for the first 45 minutes (data points taken at 5 minute intervals) and then monatonical ly decreased over the next 6 hour

period when a new soak temperature was selected. One would expect that

the conductivity would increase with time until an equilibrium value

would be established. Since this material was formed at 1 700%C in

forming gas (most reducing condition), the sample would oxidize slightly

(thus increasing the equilibrium conductivity) at 1300^0. The data at

1400^0 showed the same anomalous effect. However, several leads to the

sample became open circuit after about 7 hours at this temperature.

22
Upon dismantling the apparatus, it was apparent that the platinum leads

had melted and portions of platinum remaining intact had become very

brittle. It may be that the platinum has alloyed with chromium to form

a lower melting eutectic and this together with the embrittlement due to

hydrogen caused the failure. No silica was present in the system. The

decrease in conductivity could also have been caused by loss of chromium

by diffusion into platinum near the contacts causing an ever increasing

sample resistance. The cause of this failure is under investigation

using the scanning electron microscope.

The platinum in the sample holder was replaced as well as the leads

to the sample. Since the highly reducing atmosphere caused the problem

of platinum embrittlement and melting we decided to do the high oxygen

pressure equilibration experiments next. At 1300%C and 1400%C in air an apparent equilibrium was reached after about 30 minutes. At 1500^0, the

conductivity increased nearly linearly with time for 3 hours with a total change in conductivity of about 5*. At 1600%C, the conductivity

increased about 10% in the first 40 minutes and about 50% in the next 50

minutes. While one would expect an increase in conductivity under these

conditions, it is reasonable to assume that the rate of increase would

diminish with time. Other effects must be present and these too are under investigation.

b . Corrosion of YCrO3 jn_ SI ag

In the last quarterly report, an experiment on the electrochemical

effects at 1 343%C on yttrium chromite in contact with a high iron content

slag with 20% K2 SO4 added was described. Figure 1 shows the boundary

between the anode YCr0 3 (.05 Mg) (light grey) and the slag (dark) and

Figure 2 shows a portion of this join at a magnification of 800X; the

YCr03 is on the right. The grain structure in the bulk material is

identical to that of the original in a tested sample. Figure 3 shows

the same join area at a magnification of 1600X. The dark diagonal

stripe at the lower left is the YCr03 - slag void and is caused by the

difference of expansion of the two materials on cooling the test cell.

Figure 4 is a Si X-Ray map of the area shown in Figure 3 and Figure 5 is

a dual spectra of elements of different zones in the YCr03 just inside

the void area. Note the three distinct zones labeled 1, 2, and 3 in

Figure 3. Zone 3 is the bulk YCr0 3 and is undisturbed. Zone 1 is a reaction layer formed at the anode surface of an FeCrAl spinel without

silica (see Figure 4 and lower spectra of Figure 5). Zone 2 is a densified area of Fe, Cr, A1 , but high in silica with some yttria which may

act as a protective layer in the cell. (Upper spectra, Figure 5) The

usual silica rich layer in the near electrode slag was evident (Figure

4). The reaction layer (Zones 1 and 2) penetrated about 0.03mm into the

YCr03 material.

The cathode reaction was greater. The attack zone is approximately

1.2mm into the sample. Figure 6 is a micrograph at 40X showing this

attack zone (upper portion) and its relationship to the undisturbed

sample. Figure 7 is a micrograph at 800X of a portion of this uniform

23
attack zone with Figures 7a and 7b showing the K and Ca map of this

area. Potassium penetrated into the yttrium chromite with pullout of

the perovskite grains of considerably smaller size than those of the

original material. Unfortunately, the slag tended to pull away from the

cathode electrode so that the cathode electrode analysis is limited in

scope.

This test was carried out at 1343°C where the slag is molten and of

adequate conductivity. Anode attack was minimal but still present.

More tests should be made at lower temperatures where slag conductivity

is still adequate (see next section) but where the narrow reaction zone may be diminished or eliminated. The cathode reaction zone may also be

reduced if the slag temperature is lowered at the boundary, but with the

slag still remaining in the high conductivity regime.

c. Slag Electrical Conductivity

The electrical conductivity data for Eastern Bow NH slag without

added potassium was presented in the previous quarterly report. In this

quarter, measurements were made on this same slag (analysis Table 1,

page 39 QR Apr-June, 1979) but with 20 % K2 S04 added to the melt. In the

experimental procedures of loading the crucible with the slag, bubbles

sometimes form in the melt. Much time may be wasted making measurements

on a crucible containing a bubble in a critical area. Because of the

difficulty, each crucible is now radiographed prior to contacting to

make sure no bubbles remain in the bulk melt. Figures 8, 9 and 10 show a series of radiographs taken to show this effect. Figure 8 shows the

crucible after being heated to above the slag melting point in a RF

furnace after being filled with chunks and powders of the slag raw material. Figure 9 shows the contacted crucible; the contacts placed

below the bubble. Figure 10 shows the same crucible after being held at

1500°C for 5 minutes in a muffle furnace. Note that the bubble has

risen further to the crucible top and should present no difficulty in

the conductivity experiment.

Electrical conductivity measurements of the potassium containing

slag were made both in air and in a reduced oxygen partial pressure.

However, in the latter experiment, a slight leak developed in the upper

conductivity probe resulting in some slag coating on the outside surface

of the crucible. This makes the validity of the data doubtful so the

experiment must be repeated. Figure 11 shows the conductivity data for

the potassium containing slag in air. Here, just as in the previous

measurements on slag containing no added seed, the slag was quenched

from some high temperature (above melting point) to 900°C where the slag

is solid and then cooled slowly to about 500°C. The electrical data was taken then with increasing temperature up to the next high temperature

point from which it was quenched again. Only the inverted delta (v)

data was taken with decreasing temperature. Unfortunately, the data

does not fall into two distinct conductivity curves as did the data for

slag without added potassium. The two curves showing the lowest conductivity are derived from quenches from the greatest difference in soak

24
temperatures, 1383°C and 1489°C or 1500°C. The remaining curves show

higher conductivities, the relative conductivity decreasing with decreasing

soak temperatures. The quench times are given in Table 1 and are listed

in sequential order as the data was taken from day to day.

Soak temp.

1 500°C

1440

1408

1383

1489

1420

Quench time (min.)

21.0

19.0

20.0

20.0

23.5

21.0

In contrast to the data on slag containing no added potassium, all this

data showed strong polarization effects at all temperatures. As explained

in the previous report, the data is taken using a power supply in the constant

current mode. Polarization was observed in the current carrying probes only;

an increase in applied voltage with time to maintain a constant sample current

No polarization effects were observed on the conductivity probes during the

measurement time which was approximately 25 seconds.

No explanation of the data can be given at this point. X-Ray diffraction

measurements show little variation in crystalline content on samples quenched

to duplicate the conductivity samples. Quench times with the exception of the

fifth run were nearly the same. One might attribute the changes as being due

to a variation of the potassium or sulfur content as the experiment

continued but the last run (1420°C soak) showed a high conductivity

again similar to that obtained early in the experiment for the 1440°C

soak.

Plans : A study of the effect of oxygen pressure on the electrical

conductivity of YCr03 - (.05 Ca) will continue. A new approach to the

low pressure (< 10"7 atmospheres 02 in N2 ) experiments will be tried in

order to eliminate the reaction of H 2 and/or chromium on platinum mentioned

in the text.

The effect of slag containing potassium and sulfur on YCr03 will

be determined at temperatures lower than 1343°C under current carrying

conditions. This decreased temperature may lessen the electrochemical

boundary layer effects between YCr03 and slag.

The work on the conductivity mechanisms of slag will continue.

Eastern slag containing potassium introduced as potassium sulfate will

be investigated at a reduced oxygen pressure and initial experiments

started to determine the conductivity process of Western (Montana Rosebud)

slag with and without added potassium.

25
Figure 1 - Anode boundary between YCr0 3 (0.05 Mg) and Bow NH

slag with 20% K2 S04 added. (100X)

Figure 2 - Anode boundary - YCr0 3 on right (800X)

26
Figure 3 - Anode-slag boundary (1600X) showing three compositional

zones. Dark diagonal strip on lower left is a void

caused by difference in expansion of YCrOg and coal slag.

Figure 4 - Si x-ray map of area shown in Figure 3.

27
Figure 6 - Micrograph of cathode attack zone (upper half) of

Bow NH slag with 20% Ko S0, added on YCrO, (.05 Mg).

(40X) d 4 3

28
Figure 7 - Micrograph of a section of the cathode uniform attack

zone. (800X)

Figure 7a - Potassium x-ray map of area shown in Figure 7.

29
Figure 7b - Calcium x-ray map of area shown in Figure 7.

rigure 8 - Radiograph of crucible containing slag after being

heated in an RF furnace to above the softening point.

Note bubble formation.

30
a> o +-> o O O S3 oun . <u a> o o u n

•P (C 4- E E

T3 S- 3

11 3 1/1 +->4-

(O

O

a> a> +-> 4- CO

C~/4— E E E •>-

•r—*=(/)

ai •<— _q «o e E E >i

ai*-- r-

+-> 2

4— or,

C

fC

D i

+-> on jr e

O- E 00 rs-i— -I— E E

cr. ai c on i

•r— -Q

“OS 2

nsO E

CC4- -2 I

Cle—

a>

+-> u

ns +Jco

cr. E

®t

C

32E

QJ +J

rDC

JEi

OEEo • on

cu <u E*0

(O o

0O E

+-> 4- O o a

-e ai CL

rts E E E

DIE

O-r-

•i- +J -a (a

fO i

23 Cl I

O'!

<uE

CO 31
^wo-iugo) AllAllOnaNOO

32

T(K)

Figure

11

-

Conductivity

of

Bow

NH

slag

with

20%

K^SO.

added

in

air

asa

function

of

temperature

after

being

quenched

to

below

900°C

from

the

soak

temperatures

noted

in

the

figure.
Task 7.. Corrosion of Downstream MHD Components (J. Smit, 561,

and C. D. Olson, 565)

Progress : Exposure tests and SEM and EDX analysis were conducted

on Type 304 stainless steel tubular specimens. The tubes were exposed to K2 SO4 seeded propane fuel rich or oxygen rich hot gas

streams. Propane and oxygen gas flow rates and ratios and gas

stream color determined the gas stream condition, i.e., either

fuel rich or 0 2 rich. A Nernst probe was constructed to obtain

0 2 partial pressure data. The probe (fabricated from a high

density, closed on one end zirconia tube, platinum and platinum

paste) was fired to 900°C at 2°C/mm and cooled at the same rate.

It was then calibrated with 02 and air in a static furnace system.

Measurements of 02 partial pressure in the hot gas stream were undertaken for both the fuel rich and oxygen rich conditions.

In this dynamic system the probe initially withstood the thermal

stresses created by bringing it from room temperature to 1000°C

in minutes and also cooling it through the same interval in

minutes. It also withstood heating to about 1450°C in the hot

gas stream. However, the probe failed, i.e., cracked, before

sufficient data was collected. At present, another design is

being considered.

Gas stream temperature in the vicinity of the test specimen was maintained at approximately 1300°C while the specimen temperature

in that zone was adjusted by internal air cooling to a fixed value

between 400°C and 590°C. Total exposure time was four hours.

During the first 25 minutes of this period the gas stream was seeded with reagent grade K2 SC>4 at a rate of about 10 grams/minute.

Six specimens were tested under these general conditions. Three

of the specimens were exposed to the oxygen rich gas stream with

the tube temperature fixed at 400°C, 500°C, and 590°C respectively.

The remaining three were exposed to the fuel rich gas stream also

at 400°C, 500°C, and 590°C respectively. Each specimen was seated

in the test rig with an internal Pt/Pt 10% Rh thermocouple heli arced

into its wall. An external Pt/Pt 10% Rh thermocouple was placed

directly into the hot gas stream slightly above and to the side of

the specimen. With these strategically placed thermocouples

temperatures were monitored with digital volt meters continuously

during the test run. Tube wall temperatures were maintained at ±5°C.

To minimize contamination and moisture uptake in the coatings formed

during the test, the specimens were removed from the test rig upon

cooling down to about 40°C and potted immediately in epoxy. Metal - lographic specimens were prepared from sections taken at the midpoint

position in the hot zone and at approximately 10 mm away from that

position. The specimens were cut, ground and polished using non- aqueous media.

33
On each of the three Type 304 stainless steel tubes run under

oxygen rich conditions a thick white, somewhat columnar deposit

was formed on the upper surface of the specimens, figures 1, 2,

and 3, while a thin powdery deposit formed on the remainder of

the surface. ~he columnar deposit was approximately 2 mm thick;

the powdery deposit 0.1 mm to 0.2 mm thick. SEM examination and

EDX analysis of the metal -deposit interface showed what appears

to be corrosion or reaction bands that increase in thickness with

temperature and vary in thickness with respect to location; the

thickest band being noted in the merge region of the columnarpowdery deposit at 590°C. The reaction band thicknesses range

from 3 pm to 20 pm.

SEM micrograph (figure 4) is typical of the reaction bands formed

in the metal -columnar deposit interface. The accompanying EDX

spectra, figures 5, 6, 7, and 8 indicate a narrow band immediately

adjacent to the stainless steel that is high in Ni . In this band

and beyond it, going away from the metal, is a region high in Cr

followed by a band high in Fe with virtually no Ni . Figure 9 shows

the reaction bands in the metal interface columnar deposit powdery

deposit merge zone. Figures 10 and 11 are the EDX spectra for those

bands. The analysis is the same as given above. It should be

noted that sulfur is markedly present in the bands adjacent to

the metal showing high Ni and high Cr peaks.

Under fuel rich conditions, a thin (compared to oxygen rich conditions) less columnar type deposit formed on the upper surface of

the specimens. Deposit thicknesses ranged from 0.3 mm to 0.8 mm.

By contrast the powdery deposit formed on the under surface was thicker than in the oxygen rich condition, being about 0.3 mm

thick, figures 12, 13, and 14. It was noted that the deposits

were of a grayish cast indicating the possible presence of carbon.

It was also observed that with an increase in specimen temperature

the upper deposit appeared to thin, the merge region of the upper

deposit with the powdery deposit appeared to descend and the powdery

deposit appeared to increase in thickness. Again the metal deposit

interface showed what appears to be corrosion or reaction bands

that increase in reaction width with temperature and vary in

thickness with location. These reaction bands range in thickness

from 7 pm to perhaps 160 pm. SEM micrographs, figures 15 and 16,

taken at a metal -col umnar deposit interface show two distinct

reaction sub-bands. EDX spectra on this region, figures 17, 18, 19,

20, 21, and 22 show high Cr peaks in the sub-band immediately

adjacent to the metal -deposi t interface with very little, if any,

Ni present. The other sub-band shows high Fe peaks with some Ni

rich zones or Cr rich zones. It should be noted that high sulfur

peaks are associated with the Ni rich zones and moderate K peaks

in the Fe rich zones.

34
Plans : Specimens of Type 304 stainless stee' will be evaluated

by SEM and EDX analysis after exposure to K2 C0; + <2 S0i_ seeded

fuel rich and oxygen rich hot gas streams. As with the past

series, specimen wall temperatures will be held at 400°C, 50C°C,

and 590°C. Exposure times for these tests will be 4 hours. At

the conclusion of this series, 100 hour exposure tests with seeding

every 24 hours will be initiated under conditions based on the

results of these tests and the previous tests.

35
Figure 1. Section of Type 304 stainless steel tubing after exposure

to K^SO^ seeded oxygen rich hot gas stream. Note formation

of thick deposit, 2 mm, on upper surface and thin powdery

deposit on lower surface. Tube temperature 400 C. 6 X.

36
Figure 2. Section of Type 304 stainless steel tubing after exposure to

K2SO4 seeded oxygen rich hot gas stream. Note formation of

thick, 2 mm, deposit on upper surface. Tube temperature

500°C . 6 X.

Figure 3. Section of Type 304 stainless steel tubing after exposure

to K?S0 a seeded oxygen rich hot gas stream. Note formation

of tn ick deposit on upper surface. Tube temperature 590 C. 6 X.

37
Figure 4. SEM micrograph, 4500 X of reaction bands formed in the metalcolumnar deposit interface. Lettered regions correspond to

labeled EDX spectra, Figures 5, 6, 7, and 8.

Figure 5. EDX spectra of regions A and B of Figure 4 showing absence or trace of Ni.

38
Figure 6. EDX spectra of region C and D of Figure 4 showing high Ni

immediately adjacent to the stainless steel (C) and high

Cr beneath it (D).

Figure 7. EDX spectra of regions E and F of Figure 4 showing stainless

steel spectrum (E) and high Ni immediately adjacent to it (F).

39
gure 8. hDX spectrum of region G of Figure 4 showing high K and S with

a trace of Fe.

g-re 9. SEF micrograph, 1800 X, of reaction bands formed in the metal

interface—columnar deposit powdery merge zone, location

X or : igure 3. Lettered regions correspond to EDX spectra

of Figures 10 and 11.

40
Figure 10. EDX

the

the

spectra

absence

absence

of regions H and 1 of Figure 9 showing Fe with

of both Cr and Ni (H) and high Cr and Fe with

of Ni(L)

.

Figure 11. EDX spectra of regions K and J of Figure 10 showing high Ni

and Cr with Fe (J^ and high Cr with Fe and a trace of Ni K .

41
Figure 12. Section of Type 304 stainless steel tubing after exposure

to K^SO^ seeded fuel rich hot gas stream. Note formation

of thin solid deoosit on upoer surface. Tube temperature

400°C. 6 X.

42
Figure 13. Section of Type 304 stainless steel tubing after exposure

to K2 SO4 seeded fuel rich hot gas stream. Note thinner

solid deposit on upper surface. Tube temperature 500 C.

6 X.

43
Figure 14. Section of Type 304 stainless steel tubing after exposure to

K9SO4 seeded fuel rich hot gas stream. Note thin solid

deposit, about 0.3 mm, on upper surface. Tube temperature

590°C . 6 X.

rigure 15. SEX micrograph, 190 X of reactionbands formed in the metal

deposit interface of region Y of Figure 14.

44
Figure 16. SEM micrograph, 450 X, of the same area as Figure 15.

Lettered regions correspond to labeled EDX spectra of

figures 17, 18, 19, 20, 21, and 22.

Figure 17. EDX spectrum of region L of Figure 16 showing high Cr

with Fe and low Ni

.

45
Figure 18. EDX spectra of regions M and N of Figure 16 showing high

Cr with Fe and low Ni (N) and absence of Ni (M)

.

Figure 19. EDX spectrum of region 0 of Figure 16 showing high Cr and

Fe and absence of Ni.

46
Figure 20. EDX spectra of regions P and Q of Figure 16 showing high

Fe with Ni and Cr (Q) and Fe with absence of Ni and Cr (P).

Figure 21. EDX spectra of regions R and S of Figure 16 showing Cr

and Fe with a trace of Ni (S) and high Fe with Ni with no

Cr, also high S and K, (R)

.

47
Figure 22. EDX spectra of regions U and T showing high Fe and Ni

with no Cr and high S and K (U) and K and S with a trace

of Fe (T)

.

43