/

EA-6010-24

Dist. Category UC-90C

MATERIALS RESEARCH FOR THE CLEAN UTILIZATION OF COAL

QUARTERLY PROGRESS REPORT

April - June 1980

Samuel J. Schneider

Project Manager

Center for Materials Science

National Bureau of Standards

U. S. Department of Commerce

Washington, D. C. 20234

PREPARED FOR THE UNITED STATES

DEPARTMENT OF ENERGY

Office of Advanced Research and Technology

Under Contract No. EA-77-A-01-6010

"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,

expressed 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. Materials Performance and Properties 2

2. Creep of MHD Refractories 2

3. Electrical Transport Mechanisms in Slag 3

4. Corrosion of Downstream MHD Components 14

1

I. SUMMARY OF PROGRESS TO DATE

Brief Summary

1. Materials Performance and Properties

A large portion of the data for the book on construction materials

for coal gasification was assembled; final cost information was received

from computer vendors for services required for the data base computer

management; the Failure Information Center transmitted 791 abstracts, 27

tables, and one hard copy report to industry; a report on erosive failures in coal conversion pilot plants will be published as an NBS Internal

Report.

2. Creep and Related Properties of MHD Refractories

Work during the quarter was concentrated on assembling the 12 station

creep assembly. Compressive yield results were obtained on two materials,

magnesia excess spinel and a sodium doped alumina at 1400 °C, and 1500 °C.

Both materials were relatively creep resistant.

3. Electrical Transport Mechanisms in Slag

The ‘electrical conductivity of a slag containing 20 percent by weight

of Fe 304 has been completed. The data reinforces the suggestion that

the primary conducting mechanism in iron-containing slags at high

temperature is iron ion conductivity. A paper detailing the information

leading to this conclusion was given at the 7th International Conference

on MHD Electrical Power Generation, held at MIT, Cambridge, Mass.,

June 16-20, 1980.

4. Corrosion of Downstream MHD Components

Type 316 and Type 304 stainless steel tubes were exposed for 4 hours to

various oxygen/fuel ratios and K2 SO4 /K2 CO 3 seed combinations. These

data indicate that seed could cause tube fouling; fouling extent differs

under the various test conditions. Wastage evaluations, started last

quarter, indicate that Type 304 stainless steel corrodes (weight loss)

at the rate of about 4 mm per year.

1
II. DETAILED DESCRIPTION OF TECHNICAL PROGRESS

1. Materials Performance and Properties (H. M. Ondik, R. C. Dobbyn,

A. Perloff, W. S. Brower,

and W. A. Willard)

Progress : The normal collection and evaluation of materials performance

and properties data has continued along with preparation of data tables

for the book on construction materials for gasification use. At two

separate times during the quarter, the beginning, and two-thirds through,

the completed tables for the book were assembled. Currently, all of the

data available from the Failure Information Data Base has been tabulated

and arranged, and entered into the Plant Experiences subsections of

Section A of the book. Tables for Section B, containing data for DOE

research contractors' reports are not quite complete, but work is con- tinuing. The "Operating Requirements" portions of Section A are being

assembled.

The Failure Information Center received twelve requests for information during the quarter. In response to these requests a total of 791

abstracts, 27 tables and one hard copy report were transmitted. Also

during this quarter the final draft of a report addressing erosive wear failures was delivered to DOE; this report will also be published as a NBS Internal Report, NBSIR 80-2045.

Main Commerce is currently evaluating the final cost figures provided by computer vendors who have submitted bids for the services we wish to obtain. There have been a variety of delays during the quarter,

most of them due to vendors asking for time extensions. It should be a matter of days only and the winner of the award will be known. Perhaps

two months after that date the contract will be signed and in effect.

Training for Data Center personnel in the use of the Data Base Management System will then begin.

Plans : The book on construction materials for gasification is to be

completed; normal acquistion and dissemination of data will continue.

The computer services contract should be awarded and training in the use of the system will begin.

2. Creep and Related Properties of MHD Refractories (N. J. Tighe and

C. L. McDaniel)

Progress : Work during the quarter concentrated on assembling the 12

station creep assembly while continuing the creep yield experiments on the excess magnesia-spinel and the sodium doped alumina refractory.

The 4 creep furnaces are being fitted with a water-cooled drive rod

assemblies for the attachment to the load cells and to the pneumatic

cylinders. Preliminary tests with the one inch rods in place indicate

that the excessive heat loss through these rods reduced the maximum

temperature to < 1600 °C. With the 3/4 inch rods the desired furnace

temperature could be reached. Since both sizes of rods are in hand

the 3/4 rods will be used for the highest temperature. Modification

of the furnaces is being discussed with the manufacturer. The fixtures

should be in place in all the furnaces when the power supply console

is delivered in July.

2
Creep tests on selected refractories included:

Chrome-spinel - Results obtained on this material were presented in

the Refractories Division at the American Ceramic Society Meeting in

April. An NBSIR Report will be issued on this material.

Magnesia Excess Spinel - Creep yield tests on this material were carried

out at a constant loading rate of 2 x 10“^ in/mi n at 1400 °C, 1500 °C

and 1600 °C. The results indicate a moderate yield drop.

Sodium Doped Alumina : This material was received from K Keto of Montana

Tech in the form of cores taken from bricks installed in the test reactor

at Montana State U. Creep yield tests were carried out at 1400 °C

and 1500 °C at the constant load rate of .002"/min. At 1400 °C the

material is very creep resistant but there is a 3-fold drop in yield

stress at 1500 °C compared with the results at 1400 °C. The X-Ray

analysis of the material showed it to be composed of a and 3 alumina.

There is a gradual loss of 3 during the high temperature exposure.

Plans : During the next quarter the power supply should be delivered

and put in service with the 12 station creep assembly. A differential

displacement device will be evaluated for measuring the creep rate

in the new creep assembly.

The reaction of the sodium-doped material with slag in the Montana State

test rig will be evaluated and compared with the results obtained from

the creep tests.

The inclusion of an NBS representative on the air-preheater materials

selection committee will be explored. Although this committee was only

informally established in FY 79, its usefulness to the selection and

evaluation of air-preheater materials has been demonstrated by the progress obtained to date.

3. Electrical Transport Mechanisms in Slag (W. R. Hosier)

Progress :

Slag Electrical Conductivity

In order to further investigate the effect of iron on the electrical

conductivity of coal slag in relationship to other slag components, and

in relationship to the redox conditions surrounding the material, an additional batch of slag from the Bow, NH steam generating plant (but

containing extra iron) has been prepared. Iron was added in the form of

Fe 304 to bring the total iron content to 20 mass percent. This

material is difficult to form in the measuring crucible and must be

formed in a reducing atmosphere before contacts are attached. (See

below for an explanation of contacting procedure and four probe DC

measurements.) The conductivity measurements on this material have been

completed and the data is given in Figures 1 and 2. As in all previous

measurements on this slag, there is a break point in the curve above

3
1385 °C (1/T(K) ^ 6 X 10 and all samples show nearly the same slope of

conductivity vs. reciprocal temperature regardless of the iron or potassium content and regardless of the ambient oxygen pressure. It is

evident, however, that the magnitude of the conductivity in this temperature

range is larger than for the data on Bow, NH slag reported in previous

quarterly reports beginning April - June 1979 except for that slag

sample containing an even larger amount of iron (23.4%) reported in the

last quarterly report for Jan. - March 1980. Table 1 gives the conductivity

at 1450 °C of all the samples measured to date. The analyses shown are based on the original analysis of this slag as received from the Bow, NH

steam plant. This original analysis is given in Table 1, page 33 of QR

April - June 1979.

Table 1

Based on Ini

Mass % Fe

14.7

12.8

23.4

20.0

:ial Analysis Conductivit

Mass % K Air

0.43

( 0.066

8.4 0.058

7.5 0.31

0.40 0.16

5 ppm O2

0.062

0.066

0.16

The data shown in Figures 1 and 2 show the same general characteristics below

1385 °C as the previous data on this slag shown in QR April - June 1979

when the data is taken according to a prescribed routing whi^h was designed to freeze in a specific ratio of iron ions (Fe ^/Fe below

1000 °C. The previous sample contained only 14.7% iron and the conductivity on the lower branch of the conductivity curves (below 1000 °C) is

about an order of magnitude lower than for the data shown in Figure 1.

The high conductivity branch of the curves, however, are similar in

magnitude as well as shape. A preliminary investigation using SEM

analyses of material providing the data for these low temperature

branches of the curves (below 1000 °C| indicates that the conductivity

is not primarily a function of the Fe ^/Fe ^ ratio frozen in by the

quench to 900 °C (see QR April - June 1979) but is due mostly to the

crystalline component of the solidified slag. Scanning electron microscope micrographs show crystallite bridging in various degrees depending

on the history of the sample. It is possible that this bridging acccounts

for the somewhat unpredictable conductivity below 1000 °C particularly

since there does not seem to be a primary dependence of the conductivity

on the oxygen pressure (vis. Fig. 1 and

4
2). This concept is being investigated and will be reported on at a later time. A paper was presented at the 7th International Conference

on MHD, held at MIT in Cambridge, June 16 - 20, 1980, Session 5, Paper

No. D - 7 which gives a possible explanation for the high temperature

behavior (above 1385 °C) of iron-containing slags. It can readily be seen from Table 1 that the conductivity at 1450 °C depends on the iron

content and not on the amount of potassium (for the several amounts

shown in the table) and not on the oxygen partial pressure in the range

from 0.2 to 10"^ atmospheres. The conclusion drawn then is that for

this slag composition, the conductivity above 1385 °C is due primarily

to the iron ions.

Measurement Technique and Sample Preparation

Measurements of the physical properties of materials at high temperatures

are becoming increasingly important particularly with respect to emerging

energy technologies. A few examples include materials used in magnetohydrodynamics, fuel cells, and batteries for energy storage and conversion

of chemical to electrical energy. The electrical conductivity of some materials for these technologies is important as all require the passage

of current (ionic and/or electronic). For those materials that remain

solid with relatively simple chemistry in a device, the conductivity

measurement over the useful temperature range is not difficult. However,

for those materials that may be in a solid and/or liquid state, depending

on temperature, the measurement becomes more difficult. Measurements

are complicated further by chemical interaction of a material with the

containing crucible, by chemical /phase changes with temperature and

oxygen pressure, by thermal expansion or contraction problems upon

solidification or cooling, and by the requirement of electrical contacts

that will give reliable results without disintegration. A measurement

technique has been developed over the last year which can alleviate

these problems. A brief description of the sample preparation and

measurement technique both of which are extremely important for obtaining

valid results on high temperature materials such as coal slag follows.

Generally, only four probe DC conductivity measurements will be discussed.

Two probe DC measurements give erroneous results when ionic conductivity

is involved, especially when ion exchanging electrodes are not used. AC

measurements are useful for samples having relatively high resistances

where capacitive reactance components can be determined at reasonable

frequencies (< several megahertz). For most high temperature materials,

however, the electrical conductivities are high enough (^.01 to 10 ohm ^cm ^) so that the required frequencies are too high to resolve the capacitivereactive components of the total impedance which are due to contact

barrier layers or grain boundary effects. Four probe AC measurements,

however, are a viable option but usually require more instrumentation

than DC measurements.

For materials which can be cut to a suitable sample size and will not

flow over the temperature range of the measurement, contacts can be

applied directly to the material by drilling small holes (diamond dental

drill) in the sample to attach the contact lead wires. This is done by

5
peening spongy platinum around the leadout wires, which are usually

platinum to withstand the high temperature oxidizing atmospheres. A

schematic diagram of a typical contact is shown in Figure 3. Generally

the portion of the wire in the hole should have a non-symmetrical con- figuration on the end to prevent the wire from turning in the hole and

to prevent pull-out from the adjacent peened platinum. In the schematic,

an oval disk is shown. This was made by inserting the leadout wire with

a small ball on the end through a hole in a piece of metal and simply

hammering the ball flat. Any non-symmetrical shape formed in any way

will suffice. Measurements using this contacting method have been made

on many ceramic materials up to 1700 °C. No contact resistances were

apparent. For best results, the materials should be fully sintered up

to the highest measuring temperature to prevent further densification

during measurement. Figure 4 shows a radiograph of a sample of

Yq 95 ^^o osC >^03 with contacts applied as described above.

For a material such as slag that becomes molten within the range of

temperatures involved in the measurement, a different procedure was

used. Alumina crucibles which are readily available and which show

minimal reaction with the slag were chosen for the experiments. A

crucible is carefully filled to just under one-half full by repeated

melting of additions of slag powder. This is necessary to prevent the

material with absorbed gases from bubbling over the top during the

initial filling process. Holes are then drilled through the crucible

sides and into the slag for the four probes. Leads are attached using

the same procedure as described above. Figure 5 shows a radiograph of

a typical crucible with leads attached and numbered for the discussion

to follow.

Spongy platinum is commercially available from several companies

specializing in platinum products. It can readily be made, however,

from powdered platinum which is sintered lightly at 1200 °C for 1/2

hour. The resulting spongy solid mass can be cut into pieces and can be

pressed into the holes surrounding the leadout wires. For small samples

such as described above, the contacting must be done under a binocular

microscope. The peening tools can be made from any hardened metal

material formed into a suitable tip for compaction of the spongy platinum.

This method yields a leak tight seal.

It can be seen (Fig. 5) that the size and shape of the molten sample

remains fixed during the course of the measurement. This is essential

for accurate determination of a conductivity. Furthermore, the electrodes

do not penetrate a surface exposed to the ambient atmosphere so that

oxidation-reduction conditions at the surface do not affect the conductivity

value.

The measurements are made using a constant current power supply. In

certain temperature ranges and under certain conditions the material is an ionic conductor. Under these circumstances, care must be taken

during data acquisition to avoid polarization on the conductivity probes

(two center probes). Since the current is maintained constant, the

voltage measured between the conductivity probes is a true measure of

the bulk conductivity of the material, i.e., a = 1/p = 23 where A is

6
the cross sectional area of the sample, z is the distance between the

conductivity probes 2 and 3, and V 23 is the potential developed between

the conductivity probes 2 and 3 at a constant current I. This conductivity

may be electronic and/or ionic depending on the chemical (bulk and

phase) and physical state of the material, but V 23 will remain constant

with time. If there is no potential drop at the current contacts

(contacts 1 and 4, Figure 5) due to a contact resistance and the conductivity

is entirely electronic, no polarization with time will be observed at a given temperature on all probe sets M 12 , V23, V34, or V14. If the

conductivity is ionic or partially ionic and probe measurements are taken in a reasonably short time at low electric fields (< IV/cm) such

that polarization effects do not extend far beyond the current carrying

contacts 1 and 4, probe voltage V 23 will remain constant but Vi 2 > V 34

and Vi 4 will change with time during the short interval that current is

flowing for the measurement. With the data acquisition system (D.A.S.)

used in this experiment, collecting a set of data points (i.e., Vi 2 » ^ 23 * V 34 , V 14 , temperature, current, and time) required about 40 seconds

for one applied voltage polarity. Since the current is reversed for

each data point at a given temperature to eliminate permanent polarization

build up at any current carrying electrode and to eliminate any thermoelectric voltage present due to a temperature gradient along the length

of the sample, the total time to scan all voltages for both current

directions is approximately 80 seconds. The D.A.S. consists of a programmable calculator-based system interfaced with appropriate electrometers

and voltmeters to measure the necessary parameters. The data can be

stored and calculations are made automatically after the current is off.

All conductivity curves reported during the last year were obtained

using this method. These are a reflection of the probe voltage V 23 versus the temperature. Each point on the curve is representative of

near equilibrium conditions for temperatures above 1000 °C. Since

diffusion of oxygen is relatively slow at temperatures below 1000 °C,

very long times are required, days or weeks, for compj^ete stabilization

and data below this temperature have a quenched-in Fe ^/pe ^ ratio and

crystalline content. In addition, for slag samples, precipitation and

re-solution of crystalline phases causes the conductivity to change with

time at a given temperature above 1000 °C. These processes generally

follow an exponentially decreasing curve. In order to be able to complete

the experiment in a reasonable time, a data point was considered close

enough to its final equilibrium value when the change in conductivity

was less than 1% over a ten minute period. At a given temperature, data

was taken at ten minute intervals with applied voltage off between

measurements. Above 1300 °C these conditions could be met in less than

1 hour while below 1300 °C durations as long as 20 hours were required.

No polarization was observed in this voltage measurement (V23) at any

time during the run. Since polarization at current carrying contacts

can be expected for ionic conductors where the electrodes are not ion

exchanging, as is the case here, some information can be obtained by

comparing the voltages developed at the probe sets during the course of

the data acquisition. A complete description of the information that

can be obtained in this manner will be given in a later quarterly report.

For best results these scan voltages must be interpreted in conjunction

with x-ray diffraction and scanning electron microscope analytical

techniques.

7
Plans

Electrical conductivity measurements of various slags will continue with

particular attention to analysis of the results pointing closely to

understanding the conductivity process. The analytical methods described

in this report will be extended and hopefully will be applied to four

probe AC conductivity data if the equipment on hand will lend itself to

this measurement.

In the last quarterly report, an electrochemical study was reported

on a slag at 1250 °C. This temperature is below the break point in

conductivity (1385 °C) as shown in Figures 1 and 2 of this report on slag containing no added potassium. Voltage breakdown was seen to occur

at this temperature (1250 °C) in about 2 minutes in a constant current

mode at a current density of 0.2A/cm2. This experiment should be repeated

at a temperature greater than 1385 °C to determine the effect of decreased

viscosity, and hence, increased iron ion conductivity of slag on the

time for voltage breakdown.

8
C\J

O

O)

00

CD

Figure 1. Electrical Conductivity of Bow NH slag containing 20 %

Fe as a function of temperature in an air atmosphere.

9
I_(LU0-UJL|0) AllAllOnaNOO

Figure 2. Electrical conductivity of Bow NH slag containing

20 % Fe as a function temperature in an atmosphere

of 5 X 10“^ ppm in N,

10

T(K)
LEAD

OUT

AND

ANCHOR

CD

11

Figure

3.

Schematic

of

typical

leadout

wire

assembly

for

high

temperature

electrical

conductivity

measurements-
Figure 4. Radiograph of sample and leadout wires

mounted as illustrated in Figure 3.

12
#

Figure 5. Radiograph of slag sample contained

in alumina crucible with leadout wires

(numbers) extending through walls.

13
4. Corrosion of Downstream MHD Components (J. Smit and C. D. Olson)

Progress : Type 316 and Type 304 stainless steel tubular specimens were exposed to seeded oxygen-propane fired hot gas streams at various

seed compositions, fuel to oxygen ratios and tube wall temperatures

Exposure time for all specimens, exclusive of apparatus warm-up and*

cool-down time was four hours. Seeding took place for the first

twenty-five minutes of exposure during which approximately 250 grams of seed was added to the hot gas stream. For all specimens the gas stream temperature in the vicinity of the specimen was held at about

1300 °C. Tube wall temperatures, monitored by Pt/PtlORh thermocouples welded into the midpoint of the specimens, were maintained at either

500 °C or 590 °C by internal air cooling.

Six specimens of Type 316 stainless steel were exposed in the manner described above and to the specific conditions as indicated in Table 1.

Table 1.

Specimen No. Wall Temp (°C) Seed Gas Stream :

5-6 500 K2SO4 fuel rich

6-6 590 K2SO4 fuel rich

7-6 500 K

2 SO

4 + K

2 CO

3

* O

2 rich

8-6 590 K

2 SO

4 + K2 CO

3

*

O

2 rich

9-6 590 K

2 SO

4 + K2 CO

3

* fuel rich

10-6 500 K

2 SO

4 + K2 CO

3

* fuel rich

Ratio of K^SO^ to K^CO^ is 1 :4 by weight.

Following exposure, sections were taken from the specimens for optical,

SEM and EDX analysis. The sections, prepared using metal lographic

techniques, were cut from a location 10 mm away from the midpoint position

on the specimen. Because of the sensitivity of the deposited coatings

to moisture the tubular specimens were encapsulated immediately upon

removal from the test rig. All cutting, grinding, and polishing

operations were conducted using non-aqueous media. In addition the

sections were stored in vacuum dissicators except during intervals of

processing. Figures 1-6 are optical micrographs of specimens 5-6 through

10-6 so handled. The leading tube surface is at the top of each picture.

The geometry of the deposited coatings is consistent with that observed

on the Type 304 stainless steel tubes at the same conditions and reported

on previously.

14
The nature, size and shape of the deposited coatings is of importance

to both the heat and seed recovery aspects of the bottoming steam

plant operation. These characteristics will effect not only the heat

transfer properties of the system but will also have a major influence

on fouling conditions particularly in the main heat exchanger. Further,

the removal of this material and its subsequent transport downstream

will prove an added burden to the seed recovery system.

Figures 7-18 are micrographs of sections of Type 304 stainless steel

reported on earlier showing the deposited coatings. The leading tube

surface is at the top of each picture. These specimens were prepared

in the same manner as the Type 316 stainless steel tubing described in

a succeeding paragraph. The conditions of exposure are given in Table 2

and some conclusions regarding these coatings follow.

Table 2

Figure No. Wall Temp. (°C) Seed Gas Stream

7 400 °C K

2

SO

4

O

2

rich

8 500 °C K2SO4 O

2

rich

9 590 °C K2SO4 O

2

rich

10 400 °C K2SO4 fuel rich

11 500 °C K

2

SO

4

fuel rich

12 ^ 590 °C K2SO4 fuel rich

13 4

^ OO

o O K2SO4 + K2CO3* O

2

rich

14 500 °C K2S0^ + K2CO3 O

2

rich

15 590 °C K2S0^ + K2CO3* O

2

rich

16 400 °C K2SO4 + K2CO3* fuel rich

17 500 °C K2SO4 + K2CO3* fuel rich

18 590 °C K2SO4 + K2CO3* fuel rich

j Ratio of K^SO^ to K^CO^ is 1:4 by weight.

i

i

I

15
Generally a compact seed deposit forms on the leading surface of the tube,

being thinnest at the midpoint and broadest at the compact depositpowdery deposit merge zone. A thinner somewhat powdery deposit forms

on the trailing surface. The leading surface deposit is independent of

temperature (400 °C - 590 °C) for the case of K2 SO 4 in O2 rich hot gas

streams. For all other cases the deposit thickness decreases with

increasing tube wall temperature. Leading surface deposits are generally

thicker in O2 rich hot gas streams while trailing surface deposits are generally thicker in fuel rich hot gas streams. The combination of

K2 SO4 with K2 CO 3 results in a thinner deposit at all temperatures for

the O 2 rich hot gas stream case than for the K2 SO4 alone.

From the preceeding then it may be argued that fouling in the heat

exchanger area would probably be least and the heat transfer efficiency

greatest at the higher temperature, i.e., above 500 °C, with a K2 SO 4 + K2 CO 3 mixture probably in an oxygen rich hot gas stream.

The gravimetric studies initiated in the last quarter were continued

during this reporting period. Three specimens of Type 304 stainless

steel tube were exposed at 590 °C to conditions indicated in Table 3.

Prior to exposure the specimens were cleaned with ethanol and weighed.

Immediately following exposure the specimens were rinsed with warm water

and then ethanol to remove the seed deposit. The specimens were then

cleaned in a ultrasonic bath with 10 %F1 N 03 at 50 °C for twenty minutes

and reweighed. The weight change is noted in Table 3. Even by the most

conservative treatment the weight loss translates to a wastage of 4 mm

per year which is not acceptable and would virtually eliminate Type 304

stainless steel as a candidate material.

Plans : Specimens of Type 316 stainless steel previously exposed and

prepared will be analyzed by SEM and EDX techniques for signs of both

incipient and gross corrosion. In addition deposit samples obtained

from specimens exposed for gravimetric analysis will be analyzed using

x-ray diffractometer techniques. The purpose of this analysis is to obtain

more information on the corrosion process involved and on the possible

transformation of the seed compounds during deposition.
Specimen

Gas

Stream

Specimen

Weight

in

Weight

in

Change

in

Specimen

Stainless

Seed

State

Temp.

°C

Grams

Before

Grams

After

Weight

in

No.

Test

Test

Grams r—

CO CM o o O • . • o o o

<T> 1

00 CO CD

r— CM CO

• « * CD CD

CD CD CD

CO O 00 CO CM

CM CO CO

• • • 1^ CD CD CD CD CD

O o o CTt cr> in LO CD

JZo o

•r*s- S- o•1—

I

1— iCL) O) 3 3 CM

Cf- O

CO CO o oo CM CM + + o o o C>0 oo oo

CM CM CM

'd" o o o CO CO CO

1 1

1 LO1 CD

17
Fig. 1. Section of Type 316

stainless steel tubing

after exposure to K

2SO4

seeded fuel rich hot gas

stream. Note deposit on lower surface. Tube

temperature 500 °C. 6 X.

Fig. 2. Section of Tyne 316

stainless steel tubing a after exposure to K2 SO4

seeded fuel rich hot gas

stream. Note thin deposit

on upper surface. Tube

temperature 590 °C. 6 X.

18
Fig. 3. Section of Type 316 stainless steel tubing after exposure to

K

2SO4 seeded O 2 rich hot gas stream. Note thick

deposit on upper surface. Tube temperature 500 °C. 6 X.

Fig. 4. Section of Type 316 stainless steel tubing after exposure to

a K2 SO4 + K2 CO 3 seeded 0^ rich hot gas stream. Tube

temperature 590 °C. 6 X.

19
Fig. 5. Section of Type 316 stainless steel tubing after exposure to

a K2 SO4 + K2 CO3 seeded fuel rich hot gas stream. Note deposit

on lower surface. Tube temperature 500 °C. 6 X.

Fig. 6 . Section of Type 316 stainless steel tubing after exposure to

a K2 SO4 + K 0 CO 3 seeded fuel rich hot gas stream. Tube temperature

590 °C. 6 X.

20
/

Fig. 7. Section of Type 304 stainless steel tubing after exposure

to K0 SO4 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.

21
Fig. 8 . Section of Type 304 stainless steel tubing after exposure to

K

2 SO4 seeded oxygen rich hot gas stream. Note formation of

thick, 2 mm deposit on upper surface. Tube temperature 500 °C.

6 X.

Fig. 9. Section of Type 304 stainless steel tubing after exposure to

K2SO4 seeded oxygen rich hot gas stream. Note formation of

thick deposit on upper surface. Tube temperature 590 °C. 6 X.

22
Fig. 10. Section of Type 304

stainless steel tubing

after exposure to K

2 SO4

seeded fuel rich hot gas

stream. Tube temperature

400 °C. 6 X.

Fig. 11. Section of Type 304

stainless steel tubing

after exposure to KoSO^

seeded fuel rich hot

gas stream. Tube

temperature 500 °C. 6 X.

23

I
Fig. 12. Section of Type 304 stainless steel tubing after exposure to

K2 SO4 seeded fuel rich hot gas stream. Tube temperature

590 ^C. 6 X.

Fig. 13. Section of Type 304 stainless steel tubing after exposure to

K

2 SO

4 + K

2 CO

2

seeded O

2 rich hot gas stream. Note formation

of thick, 1.7 mm, depost on upper surface. Tube temperature

400 °C. 6 X.

24
Fig. 14. Section of Type 304 stainless steel tubing after exposure

to K

2SO4 + K

2 CO

2

seeded oxygen rich hot gas stream. Note

formation of thick, 1 mm, deposit on upper surface. Tube

temperature 500 °C. 6 X.

Fig. 15. Section of Type 304 stainless steel tubing after exposure to

K 2SO4 + K

2 CO3 seeded oxygen rich hot gas stream. Note

formation of thinner deposit on upper surface. Tube temperature

590 °C. 6 X.

25
Fig. 16. Section of Type 304 stainless steel after exposure to K2 SO4 + K

2 CO3 seeded fuel rich hot gas stream. Note formation of

0.8 mm thick deposit on upper surface. Tube temperature

400 °C. 6 X.

Fig. 17. Section of Type 304 stainless steel tubing after exposure

to K

2SO4 + K2 CO3 seeded fuel rich hot gas stream. Tube

temperature 500 °C. 6 X.

26

vsmmssmmm.
i'

Fig. 18. Section of Type 304 stainless steel tubing after exposure

to K 2S 0

^ + K

2 CO3 seeded fuel rich hot gas stream. Note

deposit on lower surface. Tube temperature 590 °C. 6 X.

I

27