/£ 7f '/f^/

EA-6010-20

Dist. Category UC-90C

MATERIALS RESEARCH FOR THE CLEAN UTILIZATION OF COAL

QUARTERLY PROGRESS REPORT

April - June 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-01-6010

"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,

express or implied, or assumes any legal liability or responsibility

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

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

TABLE OF CONTENTS

PAGE

I. 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 5

1. Metal Corrosion 5

a. Pre-Cracked Fracture Text 5

2. Ceramic Deformation, Fracture and Erosion 8

3. Chemical Degradation of Ceramics 12

a. Reactions and Transformations 12

b. Slag Characterization 13

c. Vaporization and Chemical Transport 16

4. Failure Prevention 24

a. Failure Information Center 24

b. Materials Properties Data Center 26

5. Creep of MHD Refractories 28

6. Electrical Transport Mechanisms in Slag Associated

with Electrochemical Degradation of Insulator

and Electrode Materials 29

7. Corrosion of Downstream MHD Components 42

ii

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, corrosion, chemical and electrical degradation, fracture, and deformation processes 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 problems 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 analysis for the change in stress-intensity

ratio (1C,/K ) with temperature was conducted for the tension- loaded DCB

test fixture. The test specimen was 310 stainless steel, the loading

fixture was 347 stainless steel, and the loading grip was Inconel 600.

These tests demonstrated that the newly designed tens ion-loaded DCB

testing method produces a nearly constant stress- intensity with increasing

temperature, whereas, the currently used wedge- loaded/DCB testing method

shows an unacceptably large decrease in stress-intensity with increase

in temperature.

2. Ceramic Deformation, Fracture, and Erosion

Three studies were conducted this quarter in the apparatus for mechanical

testing at elevated pressure and temperature. The first study was a con- tinuation of some initial experiments that were begun last quarter. The

goal of these initial experiments was to establish the satisfactory operation

of the apparatus. The second study was conducted to calibrate the temperature profile inside of the environmental test chamber of the apparatus.

With the successful completion of these studies, the third study was a series of controlled experiments to determine the flexural strength of

1
newly formulated batches of a high alumina (94%) refractory concrete in

steam at elevated pressure and temperature. These studies are described

in the text.

A similar series of controlled experiments will be undertaken next quarter

on newly formulated batches of a low alumina (56/0 refractory concrete.

These specimens will be tested at nominally the same conditions that were

used this quarter for the high alumina refractory. Following these experiments, time permitting, both of these refractory concretes will be tested

in a simulated coal gasification environment at a nominal pressure of 1000

psia and a nominal temperature of 1010°C.

3. Chemical Degradation

a. Reactions and Transformations

In the simulated gasification environment, CC replaces hydrated calcium

aluminate phases in high purity refractories. CC is stable to about 1100°C

in dry CO^ (500 psig), and to at least 975°C (1000 psig) in the dry gasification atmosphere. It dissociates near 625°C (1000 psig) when steam is

added to the latter. AH dissociates at about 240°C (1000 psig).

b. Slag Characterization

Work continued on the measurement of viscosity of a slag having a composition of: SiO , 48%; A1„0 , 12.10%; Fe 0 12.00%; CaO, 14.90%; MgO, 8.00%

and Na_0, 4.7% (expressed in wt %) . In 50% CO and 50% steam at 97 psi

the viscosity (log^) was 1.46 at 1321°C, 1.72 at 1240°C, 1.73 at 1232°C

and 1.98 at 1161°C. Measurements will be attempted at higher temperatures

during the next quarter using a 60% Pt, 40% Rh heater.

c. Vaporization and Chemical Transport

Vapor transport data, in the form of alkali species partial pressure^ have

been obtained over a wide temperature (1500-1800 K) and pressure (10 - 1 atm)

range for two different slag samples and in atmospheres containing the coal

gas components of H^O and R (small concentration level only). As

expected, the presence of H^O or greatly increases the rate of K-release

from the slag samples.

Following completion of the H^O-slag system studies, the effects of higher

concentrations of on alkali release will be determined. Complementary

computer modeling of these experimental systems will also be attempted.

4. Failure Prevention

a. Failure Information Center

Ten additional reports of operating experiences and failure analysis were

entered into the Center's data base. Over 170 information items were transmitted to plant operators and fossil energy contractors. Progress is continuing towards the completion of reports on corrosion and erosion failures.

2
A first draft of one section of the construction materials handbook has

been completed. A feature article for the DOE Newsletter has been written

and will be submitted for approval.

b. Materials Properties Data Center

During this quarter materials for a section of the Construction Materials

Hankbook for Coal Gasification has been sent to DOE for approval, nine

computer vendors’ proposals for services have been received, reviewed, and

technically evaluated, and material prepared for the MHD state-of-the-art

review.

5. Creep of MHD Refractories

This task started during the quarter and the major efforts have been spent

in modifying an existing high temperature creep apparatus to use for initial

experiments in designing and ordering components for the complete 12-station

creep apparatus.

6. Electrical Transport Mechanisms in Slag Associated with Electrochemical

Degradation of Insulator and Electrode Materials

Yttrium chromite doped with Ca or Mg appears to be a viable electrode

material for a hot or semi-hot wall MHD generator. High density material has been made and the electrical conductivity measured over the temperature range from 25 to 1650°C. Preliminary measurements of its electrochemical corrosion resistance show that anode degradation is much less

than that of the cathode.

The electrical conductivity of Eastern coal slag (Bow NH) without added

potassium has been measured under carefully controlled conditions. The

low temperature conductivity, i.e. , conductivity below 900°C falls on

two definite curves depending on the temperature from which the sample

was quenched. Fe 3 C>4 appears to be the conducting medium in the high con- ductivity curve for samples quenched from above 1375°C. Samples quenched

from below this temperature have anorthite (CaA^S^Og) as the only detectable crystalline phase in a glassy matrix and have low conductivities.

7. Corrosion of Downstream MHD Components

Extensive changes were made to the extant burners rig, to provide more

control over test variables and to extend the testing capability to a longer term (> 100 hours) . Specimen size and preparation details were

worked out as well as the technique for making oxygen partial pressure

measurements in the hot gas zone in the immediate vicinity of the specimen.

Plans for the coming quarter include the start of four hour and one-hundred

hour tests on 304 and 316 stainless steel.

Articles Published and Talks Present

"Mechanical Property Testing of Refractory Concretes at High Pressure and

Temperature", E. R. Fuller, Jr., S. M. Wiederhorn, and D. E. Roberts, at

81st Annual Meeting of American Ceramic Society, Cincinnati, Ohio, April 29 - May 2, 1979.

3
F. A. Mauer and C. R. Robbins, "X-ray Powder Diffraction Measurements in

Reactive Atmospheres at 1000°C and 7 MPa (1000 psig)," in Advances

in X-ray Analysis , vol. 22 (1979).

Preparation and Properties of Yttrium Chromite Ceramics , T. Negas,

W. Hosier, National Bureau of Standards and L. Dominques, Trans-Tech,

Inc., 4th International CIMTEC Energy and Ceramic Conference, Faenza,

Italy, May 28-31, 1979.

4
II. DETAILED DESCRIPTION OF TECHNICAL PROGRESS

1. Metal Corrosion

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

Progress : Tests to experimentally verify the analysis for the change in

stress- intensity ratio (K^/K^) with temperature for the tension-loaded

DCB specimen were continued. The redesigned loading fixture for stressing

the tension-loaded DCB specimen that was described in reference 1 was

used. The loading fixture was made of type 347 stainless steel, the

loading grips were made of Inconel 600 and the specimen was made of

type 310 stainless steel.

The experimental verification of the predicted change in stress-intensity

ratio, (K^,/K

q

) with temperature requires that the displacement at the

specimen crack line, V^, be measured as a function of temperature.

Previous attempts to measure this change in crack line displacement, V^, as a function of temperature have proven to be insufficiently accurate

to verify the analytical equation for the change in stress-intensity

ratio, (K

t

/K ) with temperature. Therefore, an experimental apparatus

was designed and set up to determine the crack-line displacement, V , changes with a linear-voltage displacement transducer (LVDT) . The

results of these tests are shown in Figure 1. These tests showed that

the stress- intensity ratio, (K /K ) , for the 310 specimen in the tensionloaded DCB fixture increases slightly (less than 7% on heating to

275°C. That is, this particular specimen-loading fixture is nearly

thermally compensated so as to produce a nearly constant stress-intensity

with temperature. In contrast, a conventional wedge-loaded DCB specimen

decreases by over 10% as the temperature is increased from 0°C to 275°C

as shown in Figure 1. The analysis developed in reference 2 predicts

that the K /K ratio will increase by about 13% as the temperature is

increased to 275°C, as shown in Figure 1. Therefore, the present experiments show that the tension-loaded DCB specimen maintains nearly constant

stress- intensity factor with increasing temperature. However, the

predicted change in stress- intensity ratio (K^/K^) given in reference 2

may not be accurate and will require modification to agree with the

present experimental results.

Plans : Additional experimental tests will be conducted to determine the

change in stress- intensity ratio (K^/K ) with temperature. Refinements

will be made in the measurement of crack-line displacement and temperature in these experiments. The verification experiments will be extended

to higher temperatures. Attempts will be made to conduct tests up to

600°C but these may be limited to a lower temperature if substantial creep

occurs in the specimen or loading fixture. The analysis for predicting

the change in stress- intensity ratio (K /K ) with temperature will be

modified to agree with the results of the experimental verification

tests.

In itial laboratory testing of specimens of 310 and 304 stainless steel

and of Incoloy 800 which have been prepared will be initiated. Preparation of a summary report of results obtained to date will be initiated.

5
-A.

TEMPERATURE/

°C

Effect

of

Temperature

on

Stress-Intensity
References

1. NBS Quarterly Report to DOE: January 1, to March 31, 1979

"Materials Research for Clean Utilization of Coal." EA-6010-20,

Dist. Cat. UC-90C.

2. NBS Quarterly Report to DOE: January 1 to March 31, 1978

"Materials Research for Clean Utilization of Coal." EA-6010-20,

Dist. Cat. UC-90C

7
2. Ceramic Deformation, Fracture, and Erosion (E. R. Fuller, Jr.,

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

Progress : Three studies were conducted this quarter in the apparatus

for mechanical testing at elevated pressure and temperature. The first

study was a continuation of some initial experiments that were begun

last quarter. The goal of these initial experiments was to establish

the satisfactory operation of the apparatus. The second study was conducted to calibrate the temperature profile inside of the environmental test chamber of the apparatus. With the successful completion of

these studies, the third study was a series of controlled experiments to

determine the flexural strength of newly formulated batches of a high

alumina (94%) refractory concrete in steam at elevated pressure and

temperature. These studies are described in detail below.

To establish the elevated pressure and temperature operation of the

mechanical testing apparatus, two additional experiments were conducted

at the beginning of the quarter. In the first experiment, which was on- going from last quarter, specimens of a high-alumina refractory concrete

were exposed to steam at a pressure of 4.55 MPa (660 psia) and at a temperature of 410°C for 110 hours. The specimens were then broken at

the elevated pressure-temperature conditions. The strength of these

specimens was only slightly weaker than the strength of untreated, or control, specimens. See Table 1. In the second experiment, highalumina refractory specimens were tested after exposure to steam at a pressure of 4.86 MPa (705 psia) and a temperature of 510°C for 90 hours.

The strength of these specimens was similar to that of the specimens

exposed at 410°C. Results of both of these initial experiments are tabulated in Table 1. Also listed are the crystalline mineral phases that

were determined for each specimen after the exposure and strength measurement at elevated pressure and temperature.

Following these initial experiments, a short study was undertaken to

establish the temperature profile inside the environmental test chamber

for various nominal temperatures and pressures. To measure the temperature profile, a modified internal fixture was devised to replace the

upper loading assembly. This fixture consisted of a blank flange through

which four high-pressure thermocouple "feed-thrus" was made. The

specimen loading fixture was attached to the inside of this flange, and

refractory concrete specimens were positioned on the first and last

loading stations of the fixture. Each of these specimens had two sheathed

thermocouples embedded inside the refractory; one in a hole at the

center of the specimen and the other in a hole near one end of the

specimen. Results showed that at thermal equilibrium a slight temperature^gradient could exist along the length of each specimen (approximately

to 5 C, maximum, with the direction of the gradient being dependent on the specimen position) and that the specimen temperature was approximately 25 C different than the heater-element temperature. Another important result of these experiments was that a mode of heating was established that allows the specimens to increase in temperature and pressure

along the saturated vapor cure. Previous experiments have shown that

these heating conditions help establish crystalline phase equilibrium

more rapidly than when the specimens were heated under drier conditions.

8
Having determined the temperature conditions at the specimens for various

furnace settings, a series of experiments were conducted on newly formulated

batches of a high-alumina (94%) refractory concrete. These experiments

consisted of a measurement of the flexural strength at pressure and

temperature following a 100 hour exposure in high-pressure steam at

temperatures of nominally 360 C, 660 C, and 1010 C. To complement these

strength measurements at temperature and pressure, additional refractory

specimens were exposed simultaneously with the strength specimens.

These additional specimens were then tested at room temperature and

atmospheric pressure after the elevated pressure-temperature exposure.

Initial results from these experiments are illustrated in Figure 1 where

the fracture loads are plotted for specimens broken at various exposure

temperatures and for similar specimens broken after the exposure. The

greatest discrepancy in these strength measurements was observed for

1010 C experiment. Under these exposure conditions, the strength measured

at temperature and pressure was approximately 2 to 3 times greater that

the strength measured after exposure. X-ray diffraction analysis and

examination of the specimens with scanning electron microscopy is currently

in progress.

Plans ; A similar series of controlled experiments will be undertaken

next quarter on newly formulated batches of a low alumina (56%) refractory

concrete. These specimens will be tested at nominally the same conditions

that were used this quarter for the high alumina refractory. Following

these experiments, time permitting, both of these refractory concretes

will be tested in a simulated coal gasification environment at a nominal

pressure of 1000 psia and a nominal temperature of 1010 C.

9
Figure

1.

Fracture

load

of

a

high-alumina

refractory

concrete

as

measured

both

at

temperature

and

pressure

in

steam

(up

triangles

and

solid

line),

and

after

exposure

(down

triangles

and

dashed

line).
Table 1. In-Situ Strength of a high-alumina refractory

concrete in elevated pressure-temperature steam.

Exposure

Condition

Median Mineral

Strength Phases *

Control

(dried at 110°C and

fired at 1010°C)

14.8 MPa a-alumina,

2,150 psi CaO • AI 2 O 3 , and

CaO • AI 2 O 3

110 h at 410°C

and 4.55 MPa

10.9 + 0.3 MPa a-alumina, and

1,590 + 50 psi CaO • 2A12 0 3

90 h at 510°C

and 4.86 MPa

11.2 + 1.2 MPa a-alumina,

1,630 + 170 psi CaO • 2 AI 2 O 3 , and

CaO • AI 2 O 3

* Mineral phases were determined at room conditions after the elevated

pressure-temperature exposure and strength measurement.

11
3. Chemical Degradation of Ceramics

a. Reactions and Transformations (F. A. Mauer and C. R. Robbins, 565)

Progress: A test bar of unfired calcium aluminate binder was exposed to

the simulated gasification environment in a series of three experiments.

Chemical reactions were monitored by the in situ x-ray method as temperatures and pressures were varied.

Formation of hydrated calcium aluminates was suppressed by the presence

of CO in the environment. The phase assemblage at 270°C/1000 psig* was

a-A, CA, AH and CC. With increasing temperature, AH started to dissociate

at about 240°C/1000 psig. Small amounts of this compound persisted to

'v* 100°C above the dissociation temperature, as previously observed in

this work. At near 625°C/1000 psi, CC began dissociating, and this

reaction was accompanied by the formation of CA2

. Growth of bonding

phase CA2 was moderate at 800°C, but rapid in the temperature interval

900-1000°C (1000 psig)

.

In the simulated gasification environment, CC replaces hydrated calcium

aluminates as the bonding phase coexisting with AH or a-A. In Situ

experiments using a test bar of CC in dry CO2 (500 psig) show that CC

is stable to about 1100°C. In the dry gasification atmosphere it appears

stable at 975°C/1000 psig. With the addition of steam to this environment, the dissociation temperature of CC is lowered by about 400°C.

An experiment is in progress involving exposure of a test bar of calcium

aluminate binder to steam in order to delimit regions of temperature in

which the various phases encountered are stable. Forty energy dispersive

x-ray patterns have been recorded.

<• Phase analysis of refractory specimens from a modulus of rupture study

were made by conventional x-ray methods for Task 2. Results will be

given under that section.

Plans : Test bars of A-56 and CAS2 will be studied in the simulated

gasification atmosphere.

* In SI units, 1 MPa = 145 psia.

12
b. Slag Characterization (W. S. Brower, J. L. Waring, and D. H. Blackburn,

565)

Progress: Work was continued on the measurement of viscosity of a slag^

with the following composition: SiC> 2 , 48%; AI 2 O 3 , 12.10%; Fe203 , 12.00%

CaO, 14.90%, MgO, 8.00%, Na 2 0, 4.7% (expressed in wt percent). As reported

previously, an attempt was made to determine the viscosity of this material

in CO2 and steam. Ten psi of C02 pressure was added to 55 psi of steam in

the viscometer. Earlier the material was heated briefly in CO2 and some crystals had apparently formed on the surface of the melt. When the bob

was introduced into the melt it apparently contacted the crystalline mass,

moved off center and was effectively welded to the side of the crucible.

This ruined the crucible containing the melt and the suspension. The

old crucible was unwelded from the platinum heater with a hammer and

chisel and the heater was then reshaped. A new torsion wire was fabricated and calibrated. This wire was added to a new thermocouple and to

a bob to form the suspension.

Using a new crucible and a new batch of the quenched glass slag, the

viscosity was measured in 50% CO 2 and 50% steam at 97 psi total pressure.

At 1321°C, 1240°C, 1232°C, and 1161°C, the viscosity was found to be log

n = 1.46, 1.72, 1.73, 1.98 respectively. The results are related to previous data as shown in Figure 1.

At this point it was decided not to continue viscosity measurement in

mixed gaseous environment but to increase the temperature of viscosity

measurements with the existing heater in steam until burn out occurred.

When this occurs the heater will then be replaced with 60%Pt-40%Rh in

hopes of obtaining higher temperatures. Therefore, the melt previously

heated in CO 2 and steam was heated to a melt temperature of 1386°C in an attempt to remove the CO2 and any residual crystallites. The viscosity

bob was re-introduced into the melt and steam was generated up to 75 psi.

When the crucible was rotated no deflection was indicated on the magnetic

position detector. The run was again aborted; the crucible which lifted

from the pedestal and welded to the heater was again removed from the

heater with a hammer and chisel and the entire process described previously

was duplicated.

In all the earlier experiments each crucible had a large bottom fin

welded to the bottom. This crucible was potted to a ceramic pedestal

and fired to 1400°C. The procedure took about a week. For the present

experiments this process was shortened to save time by reducing the size

of the bottom fin and attaching the crucible to the pedestal with "alumina

cement." The "alumina cement" was fired in place during the course of the

run. However, the presence of high pressure steam apparently did not

allow the maturing of the cement. In the current experimental setup, the

size of the bottom fin has again been increased, and the original groove

in the ceramic pedestal cleared with a diamond saw. The crucible and

pedestal are held together with a lower temperature "green-cast" cement.

This experimental procedure should now be sufficient to hold the crucible

to the pedestal during rotation.

13
While attempting to make the final run at temperatures higher than

1380°C, a malfunction developed in the temperature controller. When

the system was taken apart once again, a heavy oxide coating and

remnants of residual arc melting were seen on the contacts of the

copper feed through which supply power goes to the platinum heater.

Plans : Rebuild the apparatus and gain as much viscosity information

as possible with the existing heater until burn out occurs. Then

attempt to extend the temperature in steam by using a new heater

fabricated from 60%Pt-40%Rh.

14
o«ai

aZD

UJCu2UJI15
c. Vaporization and Chemical Transport (J. W. H. Hastie, D. W. Bonnell,

and E. R. Plante, 561)

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

pressures, have been obtained over a wide temperature (1500-1800 K) and

pressure (10-6 - 1 atm) range for two different slag samples. The effect of

H 2 0 vapor and small H2 concentrations on the alkali transport process was

also determined.

We have found that it is necessary to establish the chemical reactions

and characteristic mass spectral fragmentation patterns for each individual coal gas component before proceeding with complex multicomponent

gas mixtures. Without such a data base it will not be possible to

interpret the observations made with actual coal gas atmospheres, even though such data could be obtained. Of the two slag systems studies one

is the so-called Ki system (based on Illinois No. 6 coal), discussed in

the previous (Jan. -Mar. 1979) Quarterly Report, and the other is a synthetic "Western type" coal slag of composition (wt%) , Si02 (47.3),

A1 2 0 3 (11.1), Fe 2 0 3 (12), CaO (13.9), MgO (7.0) and K2 0 (8.7) denoted as K2

. Complementary computer modeling of these systems has also been

initiated

1. Ki slag + H2 0 System:

The Kj slag system, of initial compositon A1 2 0 3 (12.06), CaO (3.8),

Cr 2 0 3 (1.3), Fe 2 03 (14.25), K2 0 (19.54), MgO (1.03), Na 2 0 (0.47), S0 3 (0.21), Si02 (46.82), and Ti02 (0.52) wt%, has previously been characterized by vaporization in a N2 atmosphere (see previous Quarterly

report). In the present study, the effect of added H2 0 on the release

of alkali to the gas phase was monitored with the transpiration mass spectrometer (TMS) from 1280-1419 °C and 10“ 3 - 10-1 atm H2 0 vapor in

^0.5 atm N2

. Typical data are given in Figures 1 and 2. Note in

Figure 1 the relatively small dependence of K-pressure on temperature

at a constant H2 0 pressure. However, as is shown in Figure 2, at constant temperature, the K-pressure is strongly dependent on the H2 0-pressure.

The following reactions are believed to be responsible for this effect.

K2 0 U) (in slag) + H2 0 = 2K0H (1)

K2 0 (£) (in slag) + H2 = 2K + H2 0 (2)

H2 0 = H2 + 1/2 0 2 . (3)

We believe that reaction (2) is the predominant mechanism for H2 0-

induced alkali release under the conditions pertaining to Figure 2 and

that the thermal dissociation of water (reaction (3)) provides the

necessary H2 . However, as is shown in Figure 2, the reactions do not

appear to have attained equilibrium.

Future experiments with added H2 gas are planned to test this interpretation.

16
2. K2 slag System

A lower melting, more basic, (as compared with the Kj sample) synthetic

slag was prepared for studies analogous to those performed for the Kj

system.

Under free vaporization (KMS) or ^-atmosphere (TMS) conditions the

predominant vapor species in this system are K and O2 ; pressures are

shown in Figure 3. The initial excess of O2 present in this slag is

believed to result from the preparation procedure where melting and

pouring in room air led to oxygen absorption by the sample. Pressure

bursts of K and O2 were noted in the initial phase of the TMS experiments, e.g., at 1500 K in Figure 3 suggesting that trapped gas was released from the slag.

3. K2 slag + H2 O system

The appreciable effect of H2 O vapor on the release of K from the K2 slag is demonstrated in Figure 4. The data are consistent with reaction

(2) as the primary process leading to the enhanced release of alkali.

Also, as the data agree with the thermodynamic pressure dependence (slope

0.5 for curve of Figure 4), the system appears to be at equilibrium. In

addition to this process, reaction (1) was also observed, but to a much

lesser degree than reaction (2) , by the presence of KOH as shown in

Figure 5.

4. Thermodynamic modeling

Previous attempts at modeling complex multicomponent systems, including

slags, have either assumed ideal solution behavior or an ideal mixing of

hypothetical complex species. However, it is well known, and our experimental data confirm this, that slags form highly non-ideal solutions. Accordingly, we have applied, for the first time, a non-ideal

solution multicomponent equilibria computer program to a slag system.

The program known as SOLGASMIX is based on the development by Eriksson

[(G. Eriksson, Chemica Scripta, 8^, 100 (1975)]. As a test case we have

taken the K2 slag system with a atm H2 present. Typical data are given

in Table 1 where the effect of non-ideal solution behavior is clearly

demonstrated. Also at 1500 K, the K species is much more significant

than KOH; 87% of the alkali is released as K under these conditions.

Plans: Following completion of the H2 O slag interaction studies, moderate

levels of H2 will be added to the atmosphere and vapor transport measurements made on the same slag systems. The amount of H2 added will

be determined mainly by the durability of the Pt reactor components to

the reducing atmosphere. Using a computer based non-ideal solution

model, the experimentally observed effect of H2 and H2 O on alkali vapor

transport will be analyzed thermodynamically and the results extended

to the pressure and temperature regime of slagging coal gasifiers.

17
Figure 1. Dependence of K-pressure on temperature in the presence

of HO 3x10 2 atm) and N

2 (0.5 atm) for the slag.

The following ionization cross sections were used to

convert intensities to partial pressures: N (1.46),

K (7.5), H

2

0 (3.2).

18
oCM X

UJtcZ58LUacQ.

Figure 2. Dependence of K-pressure on HO content in (0.35 atm)

at 1400 K for the slag. The dashed curve of slope 0.5

represents the theoretical (thermodynamic equilibrium)

dependence for reactions (1) and (2) (see text) . At

1400 K, the slag is a solid.

19
. TEMPERATURE (K) 1818 1538 1333

lOVT(K)

Figure 3. Vaporization of K and from the slag, expressed as log P vs 1/T plots: open circles - 0 (KMS) , closed circles -C>2 (KMS), closed circles -0 (TMS) , open triangles K

(KMS) , closed triangles K (TMS) . Chronological order of

data taken with increasing temperature except for arrowed

data points where the temperature was decreasing.

20
(wiv) x aanssaad

Figure 4. Dependence of K-pressure on H O-Pressure at contant temperature for the K slag (TMS data). The curve of slope 0.5

represents the

2 theoretical pressure dependence for reaction

(2) (see text)

.

21
(lNlV)3tinSS3tid

Figure 5. Dependence of KOH-pressure on H^O apparent pressure at

constant temperature for the K slag (KMS data) . The

curve of slope 0.5 represents the theoretical pressure

dependence for reaction (1).
Table 1

EXAMPLE OF THERMODYNAMIC MODEL OUTPUT

3

Ideal Solution Non- ideal Solution

P(acm)

T(K) 1000 1500 1000 1500

K 6.7 E-3 1.8 E-2 3.3 E-8 4.6 E-6

KOH 1.4 E-2 3.3 E-3 8.2 E-8 6.7 E-7

h2 0.96 0.95 0.97 0.97

h2o 2.3 E-2 3.4 E-2 2.7 E-2 2.7 E-2

°2 4.2 E-24 4.5 E-15 5.7 E-24 2.7 E-15

aSystem K2 slag wt%; Si02 (47. 3), A120 3 (11.1), Fe 20 3 (12), CaO (13.9)

MgO (7.0), K20 (8.7).

^Activity K20 experimental input (K20 + S102 data used).

23
4. Failure Prevention

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

W. S. Brower, 565)

Progress ; During the quarter the Failure Information Center received ten

reports of operational experiences and materials and components failures

in 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 I.

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 continued to aid Battelle-Columbus in their preparation of the

DOE Materials and Components Newsletter. Two updated statistical summaries

of operating experiences were supplied to Battelle for inclusion in the DOE

Newsletter feature on failures.

The Failure Information Center answered twelve requests for information

during this quarter. The response to these inquiries resulted in the

dissemination of 120 abstracts and 51 hard copy reports. In addition,

three visitors received detailed briefings on the Center's present and

planned activities.

Work is continuing on the reformatting of the data base and should be

completed during the next quarter. In addition, the Failure Information

Center's work with the Materials Properties Data Center on the Performance

and Properties Handbook of Construction Materials for Coal Gasification

is continuing. A draft of the first section of the handbook has been

completed (see section 4b)

<• Progress is continuing in the analysis of reported corrosion and erosion

failures. A draft report on corrosion problems is being prepared and

the analysis of erosive wear failures is continuing.

A feature article for the DOE Materials and Components Newsletter relating

the performance of the CO2 Acceptor Pilot Plant gasifier refractory lining

was completed and will be submitted to the DOE staff for approval.

The Morgantown Energy Technology Center was visited and additional information

on solids valves was obtained for inclusion in the construction materials

handbook.

Plans ; Plans for the next quarter include: completion of the draft report

on corrosion failures in the coal conversion industry; completion of

reformatting of failure information data base; visits to selected pilot

plants; continuation of work on coal gasification construction materials

handbook.

24
Table I

Failure Incidents in the Coal Conversion Industry

Process

No. of

Incidents Percent

BIGAS

BMI

CARBONATE

CLEAN COKE

co2

CRESAP

EXXON

GFETC

HYGAS

LETC

LIGNITE

METC

MISC.

PETC

SRC

SRC-W

SYNTHANE

SYNTHOIL

WESTINGHOUSE

16 3.6

35 8.0

5 1.1

26 5.9

52 11.8

20 4.5

3 0.7

2 0.5

45 10.2

3 0.7

18 4.1

13 3.0

15 3.4

2 0.5

22 5.0

16 3.6

115 26.1

2 0.5

30 6.8

440 = Total Number of Incidents t

25
!

'

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

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

Progress: A section on solids valves for the Construction Materials

Handbook for Coal Gasification has been sent to the DOE project monitor

for comments and approval of style, format, and content. The materials

sent to the monitor corresponds to the items marked with asterisks in

the following partial outline of the Handbook

Section A. Construction Considerations and Performance Data

1. Coal Handling and Preparation Equipment

11. Valves

11.3

Solids Valves

11.3.1 Operating Requirements***

11.3.2 Performance Data

11.3.2.1 Materials Evaluation Tests***

11.3.2.2 Component Test and Development***

11.3.2.3 Plant Experience***

11.3.3 Candidate Materials

The information contained in the "Materials Evaluation Tests" portion

includes the results of testing of samples of materials considered for

possible use as trim components in valves. The testing included resistance to erosion and abrasion of a large variety of materials and the

effect of thermal shock and temperature cycling on the properties of

some refractories. The "Component Test and Development" portion currently

contains the results of seat leakage tests performed on actual valves

mounted on a test stand. The "Plant Experience" portion includes inservice performance information gleaned from the NBS-DOE Failure Information Data Bank. The "Candidate Materials" section will not be written

until further information has been gathered and entered into the "Performance Data" section so that the most reasonable and best possible

selections based on all available data can be made for the possible

candidate materials.

Nine proposals for computer vendors' services were received from vendors

in mid-May. About seven full days of the Center staff's time were

required for the technical evaluation and review of the proposals. Four

of the proposals were rejected as not meeting the mandatory requirements

as stated in our request for proposals. The other five were acceptable

with the proviso that the vendors clarify or expand various statements

26
in the proposals. Since the vendors of the four rejected proposals

may appeal our evaluation and since it is possible that not all of the

five partially acceptable proposals will be clarified to our satisfaction,

we cannot yet know how many of the vendors' proposals will be eligible for

benchmark testing. As yet, no responses have been received from any of

the vendors.

The normal operations of the Data Center continue with regard to handling

of materials research contractors' reports and data, and work on the

Hankbook and the state-of-the-art review of MHD materials.

Plans : It is expected that during the coming quarter benchmark testing

will be conducted to determine which computer vendor's services will be

contracted, normal data operations of the Center will continue, further

sections of the Construction Materials Handbook for Coal Gasification

will be prepared, and the MHD materials state-of-the-art review will be

completed.

27
5. Creep of MHD Refractories (N. J. Tighe, S. H. Wiederhorn and

C. McDaniel, 562)

Progress: An existing deadweight loading apparatus was modified to

measure deflection of a specimen with a linear variable differential

transducer. The creep testing apparatus has SiC loading rams and is

equipped with a furnace capable of operation up to 1650 C.

Samples of the refractories designated X-317* and RFG* were obtained from

from Fluidyne and Montana State University. These samples were cores taken from the refractory bricks used in the air-preheater test rigs.

Because these materials react with the SiC rams it was necessary to find

a non—reactive materials for separating pads. A series of tests showed

that alumina was most compatible with both rod and specimen. However, some of the alumina compositions showed considerable creep at 1600 C

and a design modification must be made.

The first modification will be to make longer specimens with a reduced

cross-section. With this type of specimen the portion having the reduced

cross-section will be in the hot zone and the ends will extend beyond

the hot zone where the pads do not exhibit creep.

A few preliminary creep runs were made with the Corhart X-317 with

^ .08" (2 mm) thick alumina pads. The specimens were 3/4" in diameter

and 1" long. Specimens were weighed and measured before and after test runs at 1400°C, 1500°C and 1600°C. Specimens were held at: 1400°C for

68 hr. at 31 psi; 1500°C for 74 hr at 31-56 psi; and 1600°C for 86 hr

at 31-124 psi. Although some sintering occurred between the alumina

and the X-317, there was no evidence for creep in the X-317.

Furnaces and other components have been ordered for the 4-furnace creep

test assembly. In these assemblies three specimens can be tested in

each furnace. A process control system will be used to control and

program each furnace for times up to 1000 hours in both temperature

cycling and constant temperature modes. This system should be operable

by early 1980.

Plans : The modified creep specimens will be tested in both the deadweight creep apparatus and the constant strain-rate machine to determine

their suitability for use in extended creep tests. Bids for the furnace

process control system should be received and started through the procurement system. The anticipated delivery time for the control systems

is early 1980; by which time, the assembly of the creep stations should

be complete.

* X-317: Mg-Spinel with excess MgO

RFG: Cr- spinel

28
6. Electrical Transport Mechanisms in Slag Associated with Electrochemical Degradation of Insulator and Electrode Materials,

(W. Hosier, T. Negas, and G. White)

Progress ;

a. Electrical Conductivity of YCrC>3

In order to assess the viability of an electrode material for an MHD

generator its physical properties should be investigated. This includes

its microstructure and phase composition after material preparation as well as electrical, thermal, and mechanical properties. LaCrC>3 doped

with either Sr, Ca or Mg has been a leading contender 1 for an electrode

and/or lead out material for a hot or semi-hot wall generator. While

this material is a good refractory it is also a good conductor even at

room temperature. Problems sometimes are encountered, however, due to

hydration of the rare earth (La) oxide when the material is either not

fully reacted on preparation (or non stoichiometric) or when the transsition metal (Cr) evaporates at high temperatures leaving excess La.

Another member of the perovskite family has been developed in this

laboratory and at Trans Tech Inc., which is slightly less refractory but

has other properties similar to LaCrC> 3

. This material (YCrC> 3 ) 2 doped

with Ca or Mg does not, however, have the hydration problem associated

with the lanthana based perovskites.

The electrical conductivity is dependent on the oxidation state of the

chromium. Substitution of a divalent material either on the yttrium or chromium site in the orthorhombic lattice makes it possible t<£ change the

chromium valence from +3 in pure YCrC>3 to a combination of Cr 3 and

Cr*

4 depending on the compensation and oxidation of the material.

• fo , Consider the divalent element M ^ on the Y site. Then

(Y M

+2

) (Cr

+4 Cr+3

1“X X z >0

1 -Z 3-X + z T T

When z = 0, the material is fully reduced. All chromium

+

is in th<=i +3

state and no electron exchange can take place between Cr 3 and Cr 4 ions, thus inhibiting hole migration. This results in a low conductivity

material as can be seen in the lower curve of Figure 1.

Consider the effect of oxidizing the material to a state such that x = z. No more oxygen can be incorporated into the lattice to preserve charge

neutrality and all M

+2 is compensated for b^ Cr+l

* formation. Now

electron exchange can take place between Cr 4 and Cr 3 allowing hole

migration and resulting hole conductivity. TEP measurements near room

temperature show p type conduction. The upper curve in Figure 1 shows

29
such a situation for at least partially oxidized YCrC>3 doped with Ca on

the Y site. Figure 2 shows the same effect for material with Mg on the Y

site. The same argument can be made for the dopant placed on the chromium or transition metal site.

Y (Cr+4 M

+ 3 Cr+3

)0

z x i -x-z 3 -x + z^ 2 2

In the reduced state, as the material is made, z is 0 or very small. All

chromium is in the Cr 3 state. The divalent ion is charge compensated

for b^; y oxygen vacancies (one oxygen vacancy can charge compensate fcj>r

two M

2 substitutions since the valence difference between M

2 and Cr 3 is only 1). Low conductivity material results. Here again, the con- ductivity depends on the oxidation state of tljie material. At higher

oxygen pressures z increases allowing some Cr 3 to change to Cr 4 with

resulting electrical conduction. At full oxidation z = x

Y(Cr+3

M

+2 Cr+4

)0

1 —

x x x 3

with resulting highest electrical conductivity. The electrical conductivity of the YCr03 material was measured by the DC four probe technique

on samples approximately 3mm square and 25mm long. These samples were contacted with platinum electrodes which were attached by specially prepared platinum material forced into holes drilled in the sample to accept

the platinum lead outs. The leads become locked into the holes firmly

with resultant zero or undetectable contact resistance. The data was gathered using a Keithley data acquisition system. At each data point,

time, TC voltages, current and appropriate voltage drops across the

electrodes were recorded and stored in system memory. At the same time,

the system was programmed to calculate and print conductivity derived

from the current voltage relationship and sample dimensions. The temperature was calculated by the system using stored constants for linearization obtained from NBS Monograph 125, Thermocouple Reference Tables,

based on the IPTS- 68 . All data points shown in Figures 1 and 2 are taken

at equilibrium conditions with respect to temperature and oxidationreduction at high temperatures (>1200 °C) where oxygen diffusion is

large. Equilibrium times in this temperature range vary from a few

minutes to several hours depending on the temperature and oxygen pressure. Further work is being done on temperature and oxygen pressure

dependence of the conductivity.

b. Corrosion of YCr03 in Slag

Electrochemical corrosion of MHD electrode materials is probably the most

severe problem facing the duct portion of the MHD power producing systems. This problem is made more severe when operating at high temperatures. It may be possible however, to offset the disadvantages of

accelerated corrosion due to high temperature by the advantages of oper30
ation in the diffuse current mode. Operation at lower temperatures where

corrosion is decreased may lead to severe arc damage to the electrode

material, thus affecting generator performance. Figure 3 shows a schematic diagram of an electrochemical cell constructed to show the electrochemical degradation of an electrode material when in contact with slag and

when carrying current. In an initial experiment. Eastern (Bow, NH) slag

was used with 20 % K2 SO4 added to the melt and the electrode material was

YCr03 (.05 Mg). This cell was run for a total time of 16 hours in a constant voltage mode since the purpose of the experiment is to determine

the degradation process and electrochemical products formed. The cur- rent-time relationship is shown in Figure 5. The YCrC>3 electrodes were

rectangular prisms 3mm on a side and 10mm long and contacted on the ends

not immersed in the slag bath. The temperature was held constant at

1343 °C . Figure 4 is a photograph of a lengthwise cross section of the

tested cell. The drop off in current to 20% of the initial value (Figure

5) is most probably due to the build up of a silica rich layer near the

anode. This effect had been demonstrated earlier using platinum and

LaCrC>3 electrodes immersed in coal slag . 3 ' 4 It is obvious that the

cathode has been severely attacked but the anode is relatively undamaged.

Reaction products at the slag-electrode interfaces have not yet been

completely identified. It seems possible however that YCr03 , properly

made, may be used as an electrode and/or lead out material dependent on

the slag composition and the slag electrode interface temperature. More

work will be done on the reaction zone products and temperature effect on electrochemical processes.

c. Slag Electrical Conductivity

A number of measurements have been made on the electrical conductivity of

coal slags 5

, both natural and synthetic. A question still remains, howeve^ of what specifically is the charge transport mechanism for a given

slag at a specific temperature. How much of the conductivity is ionic

and how much is electronic? Electrical conductivity measurement on slags

is difficult for several reasons. 1. Slags are difficult to hold in any

crucible used in a conventional experiment because, when molten, the slag

tends to creep out of the vessel thus casting doubt as to the volume

content measured; a parameter necessary in the calculation of conductivity values. 2. The chemical state of many components in slag may

contribute to the conductivity and this depends on the oxidation or reduction condition which in turn is a function of temperature and

,

possibly, applied potential. 3. The conductivity can also depend on the

phase composition of the slag particularly when solid, i.e. , whether the

slag is primarily crystalline or glassy or a combination of both. 4.

When ionic conductivity is involved, measurement must either be done by

AC methods, a difficult and time consuming process because they must be

done for each point as a function of frequency, or they may be done by a four probe DC technique providing adequate precautions are taken to

eliminate errors due to polarization at the current carrying electrodes.

When practical, both methods should be used to complement each other.

31
We have devised a measuring technique that allows us to eliminate, minimize, or examine these four difficulties. The slag is held in a cylindrical high AI2 O 3 crucible 5cm long and 6mm inside diamter. Pre-cast

slag cylinders are placed in the crucible and heated to a temperature in an induction furnace such that the slag is melted and takes the form of

the crucible. This procedure prevents slag creep over the crucible

walls usually encountered when slag powders and chunks are used in

crucible loading. After cooling to room temperature the slag is con- tacted with four platinum probes carefully spaced along the length of

the crucible with the top probe (current) well below (> 5mm) the slag

surface. This prevents oxidation-reduction conditions from affecting

the bulk conductivity values during a measurement as a function of

temperature for temperatures where oxygen diffusion is low (solid) . A

horizontal boat measurement may be in error due to surface oxidation or reduction because the contacts penetrate the exposed surface.

The slag contact is made by drilling a small hole through the crucible

wall into the slag and inserting the platinum wire lead-out with a small

platinum ball on the end. This wire is then locked into place by specially prepared platinum pressed in the hole around the wire. This

method of contacting provides leak free seals for the conductivity

probes. The conductivity cell is then placed in a special holder for

insertion into the vertical tube furnace for measurement.

One objective is to determine the electrical conductivity of slag and

its direct dependence on the ratio of Fe 2 /Fe 3

. This ratio may be

determined by wet chemistry methods which involves the material solution

in hydrofluoric and hydrochloric acid in the absence of oxygen and

titrating with potassium dichromate. Preliminary measurements indicate

that the Fe 2 can be determined to a precision of better than ±0.5% by

weight. To get the Fe 2 /Fe 3 ratio, the total iron content must be

known. This method promises to give the ratio within 10% accuracy

especially in Eastern slags where the iron content is high.

In order to accurately determine the conductivity dependence on the iron

oxidation state, the ionic ratio must be maintained constant during the

temperature run. To accomplish this the slag was heated to a temperature above its softening or melting point. While holding the temperature constant the conductivity is monitored using the data acquisition

system and computer described briefly in section "a" of this task report.

When equilibrium is attained (no change in resistance as a function of

time) the sample is quenched to a temperature below its melting or softening point where no oxidation or reduction can take place in a reasonable time. Conductivity measurements are then made ^s a function

of temperature below this quench temperature. The Fe 2 /Fe 3 ratio

should be constant.

A new high temperature equilibrium is established with a subsequent

quench to low temperature where conductivity measurements are made with

32
a different Fe VFe 0 ratio. The curves shown in Figures 6 and 7 are taken in this manner. Both figures show data for Eastern slag (Bow, NH)

without potassium added to the melt. The chemical analysis is given in

Table 1.

The dashed portion of the curve represents the conductivity data with

increasing temperature which probably reflects the solution of the

conducting phase in the high conductivity material into the glassy

matrix in the low conductivity material. Many data points were taken in

this range (with increasing temperature) but the magnitude in each case depends on the equilibration time or time of solution of the conducting

phase Fe 3

C> 4

.

Table 1

Component Weight %

oxide

Si02 Fe 203 A120 3 CaO

K2 0

Na20

MgO

40.65

20.95

22.00

6.70

0.52

0.85

1.70

The main constituent amounts are typical of an Eastern slag; however, in

this analysis they do not add to 100%. Sulfur was found to be about 41

ppm. The component discrepancy is under investigation. Figure 6 is the

data taken in an air atmosphere while Figure 7 shows data taken in

5 ppm okygen in nitrogen. There appears to be little or no oxygen

pressure dependence of the conductivity. This slag quenched from a soak

temperature about 1375 °C to 900 °C has a conductivity below 900 °C

independent of the soak temperature and the conductivity is high. X-ray

diffraction measurements show Fe 3 C>4 to be a predominant crystalline

phase with a slight amount of some other unidentified spinel.

This slag quenched to 900 °C from a temperature below 1375 °C, which is

the point at which the slope of the high temperature equilibrium con- ductivity curve changes, has a conductivity below 900 °C independent of

the equilibrium soak temperature below 1375 °C. X-ray diffraction

measurements show the only crystalline phase to be anorthite, CaAl 2 Si 2 0g,

a nonconducting material. The conductivity of the slag in this state is

low.

The quench times from the soak temperature to 900 °C vary from 22 minutes

for a soak temperature o| 1510 °C to 15.5 minutes for a soak temperature

of 1278 °C . The Fe 2 /Fe 3 ratios for slag treated under these conditions

have not been measured. Scanning electron microscope analysis will be

33
done in the near future and should give information as to the phase

distribution of the iron. The fact that there is a sharp point which

is nearly oxygen pressure independent which determines the conductivity

state (high o£ low with nothing intermediate) at low temperature is not

completely understood.

Plans: The conductivity of YCr03 doped with Mg or Ca will be determined

carefully as a function of oxygen pressure at several high temperatures.

The oxygen pressure will be determined by a zirconia oxygen cell inserted

into the sample holder area.

The effect of slag containing potassium on YCrC>3 will be determined at

several temperatures and the reaction products and damage to the electrodes will be determined by SEM and XRD analysis where possible.

The work on conductivity mechanisms in slag will be continued. Eastern

slag containing potassium introduced as potassium sulfate will be investigated as well as, eventually, Western slag (Montana Rosebud) with and

without potassium.

Acknowledgements : Special acknowledgements should be given to H. Parker

and R. Roth of the Crystal Chemistry section for X-ray diffraction work

and helpful discussions on the chemistry of the slag conductivity.

34
References

1. Performance of U. S. Electrodes - Insulators Tested in the US-USSR

U-02 PhaseUI Experiment, J. L. Bates and J. L. Daniel, Pacific

Northwest Laboratory, Richland, Washington; B. Rossing and

J. W. Sadler, Westinghouse Electric Company, Pittsubrgh, Pennsylvania; W. Hosier and T. Negas, National Bureau of Standards - 18th

Symposium on Engineering Aspects of MHD, June 18-20, 1979, Butte,

Montana

.

2. Preparation and Properties of Yttrium Chromite Ceramics , T. Negas,

W. Hosier, National Bureau of Standards and L.Dominques, TransTech Inc. 4th International CIMTEC Energy and Ceramic Conference,

Faenza, Italy, May 28-31, 1979.

3. Development, Testing and Evaluation of MHD Material, NBS Quarterly

Report, October-December 1977, p. 40, DOE Contract

No. EA-77-A-01-6010

.

4. Electrochemical Corrosion of MHD Electrodes in Coal Slags,

L. Cadoff, B. Rossing and H. Smith, 17th Symposium on Engineering

Aspects of MHD, Stanford, California, March 27-29, 1978.

5. Open-Cycle Magnetohydrodynamic Electrical Power Generation, Edited

by M Petrie (USA) and B. Ya Shumyatsky (USSR) - pages 559-567.

Argonne National Laboratory, Argonne, Illinois, 1978.

35

o

(ulid lul|0) AllAl 10DQN00

37

T(K)
$o

0) T>o

rH JZ

<0 4J c

-H

•g3 TJ

4J

C

•H

o>C 0) 0 TJ l o

(0 < X rH

04 a>

<Tj o

O' 4-> o to

4-> Q) O V

X!

a, (0

4-1 • Oc0

•H

XI o> o

•H 0) fa to

38

are

YCrOj

with

0.05

Mg

fully

oxidized

to

be

in

high

conductivity

state.

Slag

is

Eastern

(Bow

NH)

with

20%

S04

added

to

the

melt.
EASTERN

SLAG(BOW.NH) 3OX

LUF

39

Figure

5.

Current-time

relationship

of

the

test

cell

shown

in

Figure

The

test

temperature

was

constant

at

1343°C.
40
juuo-uuqo) AllAllOnaNOO

41
7. Corrosion of Downstream MHD Components (J. Smit, 561)

Progress : The objectives of this program are: 1) to develop a test

method for assessing the relative corrosion resistance of alloys in

downstream components of MHD systems; 2) to screen alloys for corrosion

resistance under some simulated downstream conditions, 3) to evaluate

the materials subjected to the tests in (2) to determine the conditions

under which screened alloys may be suitable candidates for incorporation

in the design of downstream components. In order to achieve these objectives, the first sub-task of the program called for extensive changes to

be made to an extant test rig. The changes were made to provide more

control over test parameters and to extend the testing capabilities

of the rig to a longer term (>_ 100 hrs.). To provide this control and

to extend operating times, automatic equipment was installed, and a gas

handling and storage unit was constructed. The additions and changes

detailed below were completed this quarter.

The rebuilt rig, Figure 1, is composed of: 1) a gas handling and storage

unit, Figure 2, for oxygen and propane, 2) an instrument unit, Figure 3,

containing a two gas blender-controller, a mass flow controller, a thermocouple amplifier unit and digital voltmeters, 3) a vertical test

chamber, Figure 4, which houses in descending order: a salt reservoir,

burner, combustion chamber, specimen support, and an exhaust duct.

The hot zone temperature of the rebuilt rig is now controlled by a modified

two gas blender-controller located between the gas supply and the burner

in the oxygen and propane supply lines. This unit, which permits control

of both the total flow rate and the oxygen-propane ratio, is interfaced

with a thermocouple output amplifier. The output from a monitoring thermocouple (Pt-Pt 10% Rh) , which is in close proximity to the specimen in the

hot zone, is fed to this amplifier. From the amplifier, the signal goes

to the gas blender-controller, which automatically maintains the hot zone

gas temperature at a preset fixed value by trimming values in the oxygen

and propane lines. During trimming, however, the oxygen-propane ratio

remains fixed. Measurements to date indicate a stability of +10°C at 1200°C.

The specimen temperature is controlled, again automatically, by a mass

flow controller located in the cooling air line between the test specimen

and the air source. This controller is also interfaced with a thermocouple

output amplifier. In operation, the amplifier receives a signal from a thermocouple, Pt-Pt% 10 Rh, which is welded into the test specimen. It

amplifies this signal and sends it to the mass controller. The controller

maintains the specimen temperature at a preselected value by trimming a valve in the cooling air line. Stability is in the order of +5°C at 550°C.

The thermocouple amplifiers have provisions for voltage read out so that

the hot zone and specimen temperatures may be monitored continuously.

The gas storage and handling unit has the capacity to hold six 1-a 220

cu. ft. oxygen cylinders and two 100 lb. propane cylinders. At anticipated flow rates, it is expected that this capacity will be sufficient

to allow about seventy- two hours of operation. However, this unit has

42
been set up with manifolds, control valves and check valves which will

permit the removal and replacement of oxygen or propane cylinders without interrupting the supply to the burner. Test duration from this standpoint then is unlimited. All lines in the system, for safety purposes,

are metallic, i.e., either copper, stainless steel or heavy walled steel.

In addition, again for safety reasons, flash arrestors are located in

the oxygen and propane lines just before these gases enter the burner

.

The piping has been laid out with by-passes so that there is the greatest

degree of flexibility for operation. The blender-controller, mass flow

controller and flow meters may be bypassed singularly or in combination

if necessary or if desired.

Modifications were made to the test chamber itself, Figure 1. Inlet and

vents have been placed in the top of the chamber. This allows the front

opening to be covered by a sliding, plexiglass window. Easy access to

the interior is maintained while improving air flow paths.

One of the test parameters of this program is the oxygen partial pressure

near the specimen surface. A Nernst probe is being prepared to make these

measurements. The probe, fabricated from a high density zirconia tube,

closed on one end, is approximately 0.30 m long and 19 mm in diameter

with a wall thickness of approximately 3 mm. An electrode was formed on

the exterior of the closed portion of the tube by covering that portion

with a platinum gauze and bonding it to that surface with platinum paste.

A 0.38 mm platinum lead out wire was spot welded to the gauze prior to

bonding. Platinum gauze, to which a 0.38 mm lead out wire was spot

welded, was shaped and bonded with platinum paste to the interior of the

tube surface directly under the exterior gauze, forming the second electrode. The unit was slowly heated, 2°C/min to 900°C, held for 8 hours

and copied at 2°C/min to room temperature to complete the bonding.

Calibration of the Nernst probe will be done in a furnace at varying

oxygen partial pressures.

In excess of a dozen specimens of 304 stainless steel, ASTM A 269, have

been prepared for test. The specimens are 0.25 m long, 12.7 mm in diameter and have a wall thickness of 0.89 mm. A 0.76 mm diameter hole has

been Eloxed in one place at the midpoint of each piece. The hole is the

receiver for a Pt-Pt 10% Rh thermocouple which will be welded into place.

The specimens have been cleaned according to ASTM Gl-72. Three test pieces

were cleaned three times according to that schedule and weighed prior to

cleaning and after each cleaning to determine weight loss if any through

that procedure. The loss was negligible being of the order of 1 to 3 mg

for specimens weights around 65.4 grams. This cleaning procedure will

also be used in those experiments in which corrosion weight loss determinations will be made.

Plans : In the coming quarter, CL partial pressure measurements of the

hot gas stream in the vicinity of the specimen will be undertaken, and

test specimens of 316 stainless steel, ASTM A 269-75, will be prepared.

Four hour and one-hundred hour tests of the 304 stainless steel specimens prepared in this quarter will begin as will some testing of the

316 stainless steel specimens. Evaluation of the tested specimens will

be carried out using, singularly or in combination, various metallographic

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and analytical techniques. The evaluation will be based on data obtained

from corrosion rate (uniform weight loss or wall reduction (mesurements and

pit depth measurements and on optical and scanning electron microscopy

examinations and on EDX and x-ray diffraction analysis where appropriate.

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Fig. 1. Test rig showing from left to right the vertical test

chamber, an instrument unit and the gas handling and

storage unit.

Fig. 2. Gas handling and storage

unit.

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Fig. 3. Instrument unit showing two gas blender controller (large

unit center right) and mass flow controller (below blender).

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Fig. 4. Vertical test chamber showing from the top salt reservoir

burner, combustion chamber and specimen support.

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