HIGH TEMPERATURE APPLICATIONS OF STRUCTURAL CERAMICS

QUARTERLY PROGRESS REPORT

July - September 1981

Samuel J.

Project

Schneider

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

Under Contract No. DE-A105-800R20679

’’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

INTRODUCTION 1

Sub task A. High Temperature Fracture of Structural Ceramics. . 2

Subtask B. Crack Growth Mechanism Maps 3

Subtask C. Microstructure and Phase Alteration 5

Subtask D. Microstructure and Fracture in Reactive

Environments 19
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NBS-5.2.10 - HIGH TEMPERATURE APPLICATIONS

OF STRUCTURAL CERAMICS

E. R. Fuller, R. J. Fields, T. J. Chuang,

A. Dragoo and S. J. Schneider

National Bureau of Standards

Center for Materials Science

Washington, D. C. 20234

INTRODUCTION

The achievement of higher efficiency thermochemical engines and

heat recovery systems requires the availability of high temperature,

high performance structural materials. Structural ceramics such as SiC, Si^N^ and certain Al^O^-Si^N^ combinations have received particular

attention for these applications due to their basic characteristics of

good strengths coupled with good corrosion and thermal shock resistances.

Even with these positive attributes, improved reliabilities and extended

lifetimes under service conditions are necessary for structural ceramics

to gain industrial acceptance and use. The problems are mechanical and/or

chemical in nature and are enhanced by the fact that these materials are

subjected to high temperatures, reactive environments and extreme thermal

gradients.

With an objective of improved performance for heat engine/heat recovery applications the NBS program on structural ceramics addresses these

problems through the determination of the critical factors which influence

mechanical and microstructural behavior. The activities of the program

are grouped under four major subtasks with each designed to develop key

data, associated test methods and companion predictive models. The status

of the subtasks are detailed in the following sections.
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NBS 5.2.10(A) - HIGH TEMPERATURE FRACTURE OF STRUCTURAL CERAMICS

RESULTS FROM PRIOR QUARTERS

Four-point bend tests on notched bars of Si^AlON^ were completed and

the results compared with previous work on an yttria-doped SiC (NCX34)

and with literature values for Si^N^. Reduced scale testing rigs using

SiC were manufactured to test small billets of experimental materials.

Fifteen different compositions of Si^N^ + Y.A.G. materials obtained from

Professor Tien of University of Michigan using these rigs were tested at

1300 “C in order to avoid oxidation. Further studies of Tien's Si_N,

3 4

were conducted to ascertain critical stress intensity factors and to

clarify some inconsistencies in earlier results. A literature survey of

available data on fracture toughness, crack growth behavior and creep

properties of SiC, Si^N^ and sialon was completed. Four-point bending

tests under constant displacement rate were performed on several SiC and

sialon specimens. For a-SiC tested in air, the results showed little

oxidation and high resistance to slow crack growth up to 1300 “C. For

sialon specimens (Si, A1 0 ) , it was found that as z increases, the

6-z z z 8-z

susceptibility to crack growth and oxidation decreases.

The asymptotic behavior of the stress intensity factor as a function

of crack length for 4-point bending at small and large crack lengths was

investigated in more detail. This work is useful for future numerical

solution schemes. Also, an analysis of load-deflection curves which

compute crack growth behavior (V-K) without requiring a knowledge of

Young's modulus or machine compliance was completed.

High temperature four-point bending tests under constant displacement

rate condition have been performed on notched reaction sintered SiC specimens. Several ways of initiating cracks were tried before a chevron notch

was utilized. This produced a stable crack growth period and a sharp crack.

A paper entitled "Slow Crack Growth in Sialon" was presented at the

International Symposium on Fracture Mechanics of Ceramics, University Park,

Pennsylvania July 17, 1981. A paper entitled "Effects of Deformation on the Fracture Behavior of Si^N^ and Sialons" was presented at the 2nd NATO
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Advanced Study Institute held at Falmer, England from the 27th of July to

the 7th of August, 1981. Both of these papers presented work which came

partly from this task.

DISCUSSION OF CURRENT ACTIVITIES

Further analyses of the four-point bend test were completed. One

analysis allows the determination of the tensile creep behavior from

flexural testing of trapezoidal cross-sections. A further analysis

deducing tensile behavior from bending and compression tests will be

finished shortly. These results will be written up and published. A

sensitivity analysis just performed on four-point bending allows us to

judge what type of crack growth behavior we may be able to measure

properly in flexure. Materials not having these crack growth characteristics require a mechanically more stable test specimen such as the

double-torsion specimen. This has proved to be the case for a-SiC and

we are now fabricating these sorts of specimens from this material. We

are still awaiting the delivery of 3-SiC to complete work on this material.

In the meanwhile, we are working ahead on the properties of the siliconized

silicon carbide.

NBS 5.2.10(B) - CRACK GROWTH MECHANISM MAPS

RESULTS FROM PRIOR QUARTERS

Preliminary maps for Si^N^ have been drawn. A computer program for

automatically drawing maps from K-V data has been written. Data for SiC

has been collected with the aim of constructing a crack growth mechanism

map. An evaluation of K was made because its definition by ASTM E-399

X w conflicts with common usage in the ceramic community. A preliminary

crack growth mechanism map for a commercial hot pressed SiC was constructed

from published information. The literature survey of fracture and crack

growth mechanisms was completed for SiC, Si^N^ and sialon.
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A crack growth model based on diffusion mechanisms was developed.

The model entails a grain-boundary crack growing in steady state due to

applied stress by stress assisted surface and grain-boundary diffusion. By

further assuming the grain on either side of the crack behaves elastically,

the model predicts a unique K-V relationship and a threshold K below which

no crack growth will take place. A comparison of this prediction to a set

of creep crack growth data on sialon at 1400 ®C showed good agreement.

The paper entitled "A diffusive crack growth model for creep fracture"

(NBSIR 81-2255) was accepted for publication in J. Am. Ceram. Soc.

An investigation into the energy release rate of this crack growth

model was included in this paper. The results show that J is the

total amount of energy consumption rate which consists of a portion

consumed in the creation of new crack surfaces and the remaining portion

dissipated in the matter transport processes.

The theoretical prediction of V-K functional relationship based on diffusion-controlled crack growth was mapped into K-T space in order for

the future data to fit in the diffusive crack growth area of the mechanism

maps.

A paper entitled, "Crack Growth Mechanism Maps" was published in

Advances in Fracture Research. This paper describes the concept of crack

growth mechanism maps and details their construction.

DISCUSSION OF CURRENT ACTIVITIES

Data obtained in part A above is being analyzed here in order to

construct a crack growth mechanism map for NCX34. Since this material

(i.e., ^20^ doped silicon carbide) is one of the most promising nitrogen

ceramics, the map may prove very useful.

Due to the work performed in this DoE sponsored research project, the

investigators were invited to participate in a recent NATO Advanced Study

Institute on nitrogen ceramics. Also, we have been invited to present our work on time dependent failure mechanisms in silicon carbide to next

summer's Gordon Conference on ceramics. Much of the work to be presented

directly emanates from this DoE project. Our main emphasis in the review
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and evaluation of crack growth theories has been in diffusive crack growth

theories. We believe that this is the long term mechanism of failure and,

hence, the one of technological importance.

NBS-5.2.10(C) - MICROSTRUCTURE AND PHASE ALTERATION

RESULTS FROM PRIOR QUARTERS

X-ray analyses were performed on various sialon and as-received

silicon carbide samples. Also, preliminary x-ray data were obtained on alpha silicon carbide oxidized in the temperature range from 1200 to 1500 “C.

A literature survey was begun to collect references on the oxidation

and the high-temperature thermal and mechanical properties of silicon

carbide.

A concept for a high-temperature x-ray furnace was developed in

which the sample serves as the heating element.

DISCUSSION OF CURRENT ACTIVITIES

Phase Analysis

The various SiC polytypes, including 3-SiC, can be indexed on

hexagonal unit cells which differ principally in the stacking in the

c-axis direction. In considering the structural polytypes of SiC,

it is convenient to focus on the placement of Si-atoms, since the

C-tetrahedra can be referenced with respect to the Si-sub lattice . The

Si-atoms can assume either a cubic packing or a hexagonal packing in the

c-axis direction. The SiC polytypes are a consequence of various combinations of these two types of packing [1].

In view of the number of potential structures, it appears advisable

to use a structural analysis procedure which takes account of these structural variations in a fundamental manner. Such a procedure is one that

assigns occupation probabilities to each lattice site in the (001) planes

above the first two fiducial planes for which the site occupations are
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defined, a priori. This procedure recognizes that the x-rays inherently

average over many unit cells so that occupation probabilities are consistent with the method of measurement. The resulting theoretically calculated structure factors and predicted diffraction pattern will have

diffraction maxima which correspond to the range of structural polytypes,

but each maxima will have a weight, or composite probability, assigned to

it. Among peaks characteristic of a given poly type, relationships between

the composite probabilities are to be expected. Comparison of observed

peaks and peak intensities with the predicted pattern will establish the

set of polytypes which are consistent with the data and will indicate

those peaks which are assignable to impurities. It is also expected that

this analysis can be employed in oxidation studies to target groups of peaks

for observation during the oxidation process. Such an approach may identify

those polytypes which are most subject to oxidation.

Theoretical calculation of the structural factors and predicted

x-ray diffraction pattern are now in progress.

Structural Ceramics Bibliography

A structural ceramics bibliography is attached. Although SiC

and oxidation studies were emphasized in the literature search, references

also were collected for Si^N^ and Si^N^-oxide systems and for other

properties.

High-Temperature X-ray Diffraction

Designs for a high-temperature x-ray diffraction furnace were prepared.

These include drawings for the furnace housing (cover and endplate) and the

ceramic insulation.

Oxidation Studies

SiC sample holders and setter plates were prepared and conditioned

at 1500 ®C. Currently, two furnaces for this study are being relocated

to another laboratory, and work on this study is suspended until suitable
-e?

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electrical power is installed.

1. Parthe’ , Erwin, Crystal Chemistry of Tetrahedral Structures , NY,

Gordon and Breach, 1964.

STRUCTURAL CERAMICS BIBLIOGRAPHY

A. Oxidation and Other Reactions

[1] Bremen, W. , Naoumidid, A.; nickel, H.

Oxidationsverhalten des pyrolytisch abgeschieden b-SiC

unter einen atomsphaere aus C0-C02-gasgemischen. J.

Nucl. Mater. 71: 56-64; 1977. CA 88 : 12080684F

[2] Schlichting, Juergen; Kriegesmann, Jochen.

Oxidationsverhalten von heissgepresstem Siliciumcarbid

Ber. Dt. Keram. Ges. 56(3-4); 72-75; 1979. CA

91:06043522T.

[3] Costello, J. A.; Tressler, R. E. Oxidation kinetics

of hot-pressed and sintered a-SiC. J. Am. Ceram. Soc.

64(6): 327-331; 1981.

[4] Heuer, A. H. ; Ogbuji, L. U., Mitchell, T. E. The

microstructure of oxide scales on oxidized Si and SiC

single crystals. J. Am. Ceram. Soc. 63(5-6);

354-355; 1980.

[5] Costello, J. A.; Tressler, R. E.; Tsong, I. S. T.

Boron redistribution in sintered a-SiC during thermal

oxidation. J. Am. Ceram. Soc. 64(6): 332-335; 1981.

[6] Smith, C. L. SiC-fission product reactions in HTGR

TRISO UC2 and UCxOy fissile fuel: I, Kinetics of

reactions in thermal gradient. J. Am. Ceram. Soc.

62(11-12): 600-606; 1979.

[7] Smith, C. L. SiC-fission product reactions in HTGR

TRISO UC2 and UCxOy fissile Fuel: II, Reactions under

isothermal conditions. J. Am. Ceram. Soc. 62(11-12):

607-613; 1979.

[8] McDonough, W. J. ; Wu, C. Cm.; Morgan, P. E. D.

Internal phase changes in dense Si3N4 associated with

high-temperature oxidation. J. Am. Ceram. Soc., Comm.

64(3): C45-C47; 1981.

[9] Hirai, Toshio; Niihara, Koichi; Goto, Takshi.

Oxidation of CVD Si3N4 at 1550 deg to 1650 deg C. J.

Am. Ceram. Soc. 63(7-8): 419-423; 1980.
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[10] Lewis, M. H. ; Barnard, P. Oxidation mechanisms in

Si-Al-O-N ceramics. J. Mater. Sci. 15: 443-448; 1980.

[11] Lange, F. F. Phase relations in the system

Si3N4-Si02-Mg0 and their interrelation with strength and

oxidation. J. Am. Ceram. Soc. 61(1-2): 53-56; 1978.

[12] Land, P. L.; Wimmer, J. M. ; Burns, R. W.;

Choudhury, N. S. Compounds and properties of the system

Si-Al-O-N. J. Am. Ceram. Soc. 61(1-2): 56-60; 1978.

[13] Lange, F. F.; Davis, B. I. Development of surface

stresses during the oxidation of several Si3N4/Ce02

materials. J. Am. Ceram. Soc. 62(11-12): 629-631; 1979.

[14] Guzman, I. Ya. ; Litvin, Yu. N.; Gerasimov, V. I.;

Ochagova, I. G. Oxidation of ceramics based on silicon

carbide with nitride and oxynitride binders at high

temperatures in various oxygen-containing gaseous media.

Issled. Nitridov. , 3rd Mater. Vses. Nauchn. Semin.

Metodam Poluch. , Svoistvam Obi. Primen. Nitridov, 1973.

Kiev: Akad. Nauk Ukr. SSR, Inst. Probl.

Materialoved. ; 124-129; 1975. CA 87:12089340C.

[15] Hinze, J. W. ; Tripp, W. C.; Graham, H. C. The

high-temperature oxidation of hot-pressed silicon

carbide. Mater. Sci. Res. 9: 409-419; 1975. CA

86:26195750A.

[16] Pasechnik, Yu. A.; Getsko, 0. M.; Bantser, S. G.;

Snitko, 0. V. Luminescence of a silicon carbide surface

during anodic oxidation. Opt. Spektrosk. 43(2):

372-374; 1977. CA 87 : 18143593C

.

[17] Keys, Lewis H. The oxidation of silicon carbide. Proc.

Electrochem. Soc. 77-1 (Proc. Symp. Prop. High Temp.

Alloys, 1976): 681-696; 1976. CA 89 : 08063732Y

.

[18] Rzechula, Jerzy; Pielak, Anna. Effect of feldspar

fluxes on the oxidation of silicon carbide at 1273-1622

K. Szklo Ceram. 29(3): 68-70; 1976. CA 89 : 08063732Y

.

[19] Pampuch, R. ; Jonas, S. New aspects of the oxidation of

silicon carbide. Sci. Ceram. 9: 300-307; 1977. CA

90:04028078P.

[20] Sanders, William A.; Johnston, James R. High velocity burner rig

oxidation and thermal fatique behavior of silicon nitride and

silicon carbide base ceramics to 1370 deg C. NASA Tech. Memo.

NASA-TM-79040, E-9842. 'Cleveland: Lewis Res. Cent., NASA; 1978

44 pp. CA 91:06043550A.

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[21] Hayakawa, Junshiro; Isshiki, tokuichiro. Oxidation

resistance of oxide bonded silicon carbide refractories.

Part 1. Taikabutsu. 259: 394-400; 1979. CA

91:26215512H.

[22] Lauche, J. ; Tairov, Yu. M.; Tsvetkov, V. F.;

Szczepanski, F. Study of the kinetics of oxidation of

silicon carbide single crystals. Izv. Akad. Nauk SSSR

Neorg. Mater. 17(2); 254-257; 1981. CA 94:16128135F

[23] Krivoshein, D. A.; Maurakh, M. A.; Dergunova, V. S.

Petrov, Yu. N.; Lebedev, Yu. N. ; Artem'eva, S. P.

Mechanism of forming protective glassy films on the

surface of the system zirconium diboride-zirconium

carbide-silicon carbide-carbon during its oxidation.

Poroshk. Metall. , Kiev. 8: 58-62; 1980. CA

94:12088954P.

[24] Grinshpunt, A. G. ; Kashkul, V. V.; Anelok, L. I.

Study of high- temperature transformations in electrode

materials. Metallurgiya i Koksokhimiya. 69: 78-80;

1980. CA 93:222091060.

[25] Pampuch, R. ; Ptak, W. ; Jonas, S. ; Stooch, J.

Formation of ternary silicon-oxygen-carbon phase (s)

during oxidation of silicon carbide. Mater. Sci.

Monogr. 6 (Energy Ceram.): 435-448; 1980. CA

93:18172469W.

[26] Bantser, S. G.; Getsko, 0. M.; Pasechnik, Yu. A.;

Snitko, 0. V. Electroluminescence of different silicon

carbide polytypes in anodic oxidation. Ukr. Fiz. Zh.

25(1): 41-48; 1980. CA 92 :14119048M.

[27] Schlichting, Juegen. Silicon carbide as an

oxidation-resistant refractory material. I. Oxidation

and high- temperature corrosion behavior. Ber. Dtsch.

Keram. Ges. 56(8); 196-200; 1979. CA 92 :04027217N

.

[28] Schlichting, Juegen. Silicon carbide as an

oxidation-resistant refractory material. II. Oxidation

and high-temperature corrosion behavior. Ber. Dtsch.

Keram. Ges. 56(9): 256-261; 1979. CA 92 : 08063327G

.

[29] Knoch, H. ; Gazza, G. E. Effect of carbon impurity on the thermal degradation of an Si3N4-Y203 ceramic. J.

Am. Ceram. Soc. 62(11-12): 634-635; 1979.
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B. Strength

[1] Seshadri, S. G. ; Srinivasan, M. Estimation of fracture

toughness by intrinsic flaw fractography for sintered

alpha silicon carbide. J. Am. Ceram. Soc., Comm.

64(4): C69-C71; 1981.

[2] Quinn, G. D.; Katz, R. N. Time-dependent

high-temperature strength of sintered a-SiC. J. Am.

Ceram. Soc. 63(1-2): 117-119; 1980.

[3] McHenry, K. D.; Tressler, R. E. Fracture toughness

and high- temperature slow crack growth in SiC. J. Am.

Ceram. Soc. 63(3-4): 152-156; 1980.

[4] Lankford, James. Uniaxial compressive damage in a-SiC at

low homologous temperatures. J. Am. Ceram. Soc.

62(5-6): 310-312; 1979.

[5] Rice, R. W. ; Pohanka, R. C. ; McDonough, W. J.

Effect of stresses from thermal expansion anisotropy,

phase transformations, and second phases on the strength

of ceramics. J. Am. Ceram. Soc. 63(11-12): 703-710; 1980.

[6] Bilby, B. A. Tewksbury lecture: putting fracture to

work. J. J. Mater. Sci. 15: 535-556; 1980.

[7] Karunaratne, B. S. B.; Lewis, M. H. High-temperature

fracture and diffusional deformation mechanisms in

Si-Al-O-N ceramics. J. Mater. Sci. 15: 449-462; 1980.

[8] Lange, F. F. ; Davis, B. I.

;

Clarke, D. R.

Compressive creep of Si3N4/MgO alloys—Part 1 Effect of

composition. J. Mater. Sci. 15: 601-610; 1980.

[9] Lange, F. F. ; Clarke, D. R. ; Davis, B. I.

Compressive creep of Si3N4/MgO alloys—Part 2 Source of

viscoelastic effect. J. Mater. Sci. 15: 611-615; 1980.

[10] Lange, F. F.; Davis, B. I.; Clarke, D, R.

Compressive creep of Si3N4/Mg0 alloys—Part 3 Effects of

oxidation induced compositional change. J. Mater. Sci.

15: 616-618; 1980.

[11] Lange, F. F. Compressive surface stresses developed in

ceramics by oxidation- induced phase changes. J. Am.

Ceram. Soc. 63(1-2): 38-40; 1980.
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C. Phases, Polytypes and Microstructures

[1] Parthe’ , Erwin. Crystal Chemistry of Tetrahedral

Structures. New York: Gordon and Breach; 1964. Book.

[2] Smith, David J. ; Jepps, N. W. ; Page, T. F.

Observations of silicon carbide by high resolution

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[3] Jepps, N. W. ; Page, T. F. Electron microscopy of

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[4] Vodakov, Yu. A.; Mokhov, E. N.; Roenkov, A. D.;

Saidbekov, D. T. Effect of crystallographic orientation

on the polytype stabilization and transformation of

silicon carbide. Phys. Stat. Solidi. A51(l):

209-215; 1979.

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Mitchell, T. E.; Shinozaki, S. b-.a transformation in

polycrystalline SiC: I, Microstructural aspects. J.

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[7] Mitchell, T. E. ; Ogbuji, L. U.; Heuer, A. H. b-.a

transformation in polycrystalline SiC: II, Interfacial

energies. J. Am. Ceram. Soc. 61(9-10): 412-413;

1978. CA 89:24202847E.

[8] Ogbuji, L. U. ; Mitchell, T. E.; Heuer, A. H. The

b-.a transformation in polycrystalline SiC: III, The

thickening of a plates. J. Am. Ceram. Soc. 64(2):

91-99; 1981. CA 94:20165839J.

[9] Ogbuji, L. U. ; Mitchell, T. E.; Heuer, A. H.;

Shinozaki, S. The b-.a transformation in polycrystalline

SiC: IV, A comparison of conventionally sintered,

hot-pressed, reaction-sintered, and chemically

vapor-deposited samples. J. Am. Ceram. Soc. 64(2):

100-105; 1981. CA 93 : 04030735F.

[10] Shinozaki, Samuel S.; Sato, Hiroshi. Microstructure of

SiC prepared by chemical vapor deposition. J. Am.

Ceram. Soc. 61(9-10): 425-429; 1978.
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[11] Clarke, David R. High-resolution techniques and

application to nonoxide ceramics. J. Am. Ceram. Soc.

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[12] Schneider, G.; Gauckler, L. J. ; Petzow, G.; Zangvil,

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Am. Ceram. Soc. 62(11-12): 574-576; 1979.

[13] Robertson, Wayne M. Thermal etching and grain-boundary

grooving of silicon ceramics. J. Am. Ceram. Soc.

64(1): 9-13; 1981.

[14] Greskovich, C. Microstructural observations on hot-pressed

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microstructure and distribution of impurities in

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Discussion of "Grain Phases in a Hot-Pressed MgO Fluxed

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462-463; 1978.

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Sci. 15: 791-793 (1980).

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J. Mater. Sci. 15: 103-113; 1980.

[19] Clarke, D. R. Microstructure of a 12H Mg-Si-Al-O-N

Polytype alloy: intergranular phases and compositional

variations. J. Am. Ceram. Soc. 63(3-4): 208-214; 1980.

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diffraction data for the sialon X-phase. J. Mater. Sci.

15: 788-790; 1980.

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B. Crystallization of Mg-containing phases in

b'-Si-Al-O-N ceramics. J. Mater. Sci. 15: 438-442; 1980.

[22] Land, P. L.; Wimmer, J. M. ; Burns, R. W. ; Choudhury, N. S. Compounds and properties of the system

Si-Al-O-N. J. Am. Ceram. Soc. 61(1-2): 56-60; 1978.
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[23] Gauckler, L. J. ; Weiss, J. ; Tien, T. Y.; Petzow, G.

Insolubility of Mg in b-Si3N4 in the system Al-Mg-Si-O-N.

J. Am. Ceram. Soc. 61(9-10): 397-398; 1978.

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phases in hot-pressed Si3N4. J. Am. Ceram. Soc.

61(9-10): 392-396; 1978.

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in part of the system Si,Al,Y/N,0. J. Am. Ceram. Soc.

62(11-12): 642-643; 1979.

[26] Mitomo, M. ; Yajima, Y. ; Kuramoto, N. Thermal

decomposition of Si-Al-O-N ceramics. J. Am. Ceram.

Soc. 62(5-6): 316-317; 1979.

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Si3N4-Si02-ZrN-Zr02. J. Am. Ceram. Soc. 62(11-12):

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system Si-Ti-O-N. J. Am. Ceram. Soc. 63(1-2):

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by Fulrath, Richard M. ; Pask, Joseph A. Boulder:

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.

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interface in reaction-sintered silicon carbide. J. Am.

Ceram. Soc. 60(11-12): 539-540; 1977. CA

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Taranets, V. A. Investigation of phase transformations

and polytype stability of beta-silicon carbide. Phys.

Status Solidi A. 43(1): 363-369; 1977. CA

87:22175793J.

[32] Kinsman, K. R. ; Shinozaki, S. An uncommon mode of

morphological development among coherent phases (silicon

carbide). Scr. Metall. 12(6): 517-523; 1978. CA

89:18151332Y.

[33] Dubey, Madan; Singh, G. Use of lattice imaging in the electron

microscope in the structure determination of the 126R polytype of

silicon carbide. Acta Crystallogr. A34(l): 116-120; 1978.

CA 88:12082192T.
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[34] Heuer, A. H. ; Lou, V.; Ogbuji, L.; Mitchell, T. E.

Lattice resolution studies of engineering ceramics:

silicon carbide and silicon nitride. J. Microsc.

Spectrosc. Electron. 2(5): 475-480; 1977. CA

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Recrystallization and phase transformation in

reaction-sintered silicon carbide. J. Am. Ceram. Soc.

61(5-6): 237-242; 1978. CA 89:02010821V.

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Thermodynamic analysis of solubility and transformation

coefficient of boron in silicon carbide. Svoistva

Legirovan. Poluprovodnikov. pp. 53-58; 1977. CA

88:26198570U.

[37] Pandey, Dhananjai; Lele, S.; Krishna, P. Mechanism of

the 2H -. 6H solid state transformation in silicon

carbide. J. Cryst. Growth. 42: 644-650; 1977. CA

88:24180565M.

[38] Vodakov, Yu. A.; Mokhov, E. N. ; Roenkov, A. D.;

Saidbekov, D. T. Effect of crystallographic orientation

on the polytype stabilization and transformation of

silicon carbide. Phys. Status Solidi. A51(l):

209-215; 1979. CA 90 : 18144403Q

.

[39] Ogbuji, L. U. ; Mitchell, T. E. ; Heuer, A. H.

;

Shinozaki, S. Discussion of "Microstructural

characterization of ’REFEL’ (reaction-bonded) silicon

carbides." J. Mater. Sci. 14(9): 2267-2271; 1979.

CA 91:22180126F.

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177-188; 1980. CA 93 : 16159319C

.

[41] Pandey, Dhananjai; Lele, Shrikant; Krishna, P. X-ray

diffraction from one-dimens ionally disordered 2H crystals

undergoing solid state transformation to the 6H

structure. III. Comparison with experimental

observations on silicon carbide. Proc. R. Soc.,

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.

[42] Lubrovskii, G. b. Natural superlattices in crystals. Probl.

Tekhnol. Shirokozonnykh Poluprovodn. , Vses. Soveshch.

Shirokozonnym Poluprovodn., 2nd, 1979. Leningrad: Akad . Nauk

SSSR, Fiz.-Tekh. Inst.; 1980; pp. 150-164. CA 94 : 0402074IM.

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[43] Inomata, Yoshizo; Uemura, Yohichiroh; Inoue, Zenzaburo;

Tanaka, Hidehiko. Energy stored in a grain boundary

formed by rotation along a hexagonal lattice plane in

silicon carbide crystals. Yogyo Kyokaishi. 88(10):

628-633; 1980. CA 93 : 22213576Z

.

[44] Singh, S. R. ; Singh, G. Lattice- imaging studies on intergrowth structures of silicon carbide. Acta

Crystallogr. A36(5): 779-784; 1980. CA 93 : 16159331A.

[45] Guo, Chang-Lin. Crystal structure of silicon carbide

polytype l47R(b) . K'o Hsueh T’ung Pao. 24(23):

1080-1083; 1979. CA 92 : 10086296K.

[46] Lange, F. F. Eutectic studies in the system

Si3N4-Si2N20-Mg2Si04 . J. Am. Ceram. Soc. 62(11-12):

617-620; 1979.

D. Preparation

[1] Ando, Yoshinori; Uyeda, Ryozi. Preparation of ultrafine

SiC particles by gas evaporation. J. Am. Ceram. Soc.,

Comm. 64(1): C12-C13; 1981.

[2] Suzuki, Hiroshige; Hase, Teizo. Boron transport and change of

lattice parameter during sintering of b-SiC. J. Am. Ceram. Soc.

63(5-6): 349-350; 1980. CA 93 : 12119065K.

[3] Sekercioglu, I. ; Wills, R. R. Effect of Si3N4 powder

reactivity on the preparation of the Si2N20-A1203 silicon

aluminum oxynitride solid solution. J. Am. Ceram.

Soc. 62(11-12): 590-593; 1979.

[4] Guha, J. P. ; Goursat, P. ; Billy, M. Hot-pressing and

oxidation behavior of silicon nitride with ceria additive.

J. Am. Ceram. Soc. 63(1-2): 119-120; 1980.

[5] Loehman, Ronald E. ; Rowcliffe, David J. Sintering of

Si3N4-Y203-A1203. J. Am. Ceram. Soc. 63(3-4):

144-148; 1980.

[6] Rahaman, M. N. ; Riley, F. L. ; Brook, R. J.

Mechanisms of densif ication during reaction hot-pressing

in the system Si-Al-O-N. J. Am. Ceram. Soc.

63(11-12): 648-653; 1980.

[7] Wills, R. R. ; Sekercioglu, I.; Niesz, D. E. The

interaction of molten silicon with silicon aluminum

oxynitrides. J. Am. Ceram. Soc. 63(7-8): 401-403; 1980.
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^ 4^8<?a . : .»o3 'i; .io*7»3 »cA ,6 .fc*bl73.tfl'C*»
[8] Galasso, F. S.; Veltri, R. D. Sintering of Si3N4-Y203

under nitrogen pressure. J. Am. Ceram. Soc., Comm.

64(1); C15-C16; 1981.

[9] Greskovich, C.; Prochazka, S. Stability of Si3N4 and

liquid phase(s) during sintering. J. Am. Ceram. Soc.,

Comm. 64(7): C96-C97; 1981.

[10] Yajima, S.; Hasegawa, Y.; Hayashi, J. ; limura, M.

Synthesis of continuous silicon carbide fiber with high

tensile strength and high Young's modulus. Part 1.

Synthesis of polycarbosilane as precursor. J. Mater.

Sci. 13(12): 2569-2576; 1978. CA 90: 10072495W.

[11] Bind, Jean Marie. Phase transformation during

hot-pressing of cubic silicon carbide. Mater. Res.

Bull. 13(2): 91-96; 1978. CA 88:221618202.

[12] Ruska, J.; Gauckler, L. J. ; Petzow, G. Phase

transformation of cubic silicon carbide during

hot-pressing with aluminum and aluminum oxide additions.

Sci. Ceram. 9: 332-338; 1977. CA 90:080598480.

[13] Enomoto, Ryo; Tanaka, Hiroyuki. Oxidation resistant

silicon carbide refractories. Japan. Kokai. Patent

No.: 78 64213. Applic. No.: 76/139719. Date:

11/19/76. CA 89:22184650D.

[14] Tomibe, Tadayoshi; Kamiko, Michiharu; Kimoto, Gohei;

Ohnuki, Hideo. Oxidation-resistant silicon carbide

heating elements. Jpn. Kokai Tokkyo Koho. Patent No.:

7964512. Applic. No.: 77/130868. Date: 11/2/77. CA

91:24195059K.

[15] Yanagi, Hiroki. Prevention of oxidation for graphite or silicon carbide refractories. Jpn. Kokai Tokkyo Koho.

Patent No.: 79 47712. Applic. No.; 77/114933. Date;

9/24/77. CA 91:181449640.

[16] Enomoto, Ryo; Tanaka, Hiroyuki; Hara, Kazuhisa.

Silicon carbide-based oxidation-resistance coating for

refractories. Jpn. Kokai Tokkyo Koho. Patent No.: 79

43911. Applic. No.: 77/111073. Date: 9/14/77. CA

91:18144960Q.

[17] Inomata, Kichizo; Tanaka, Hidehiko. Silicon carbide sintered

body with high strength and oxidation resistance. Jpn. Kokai

Tokkyo Koho. Patent No.; 80 20269. Applic. No.; 78/93328.

Date: 7/31/78. CA 93 : 08078282H.
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[18] Taguchi, Akira. Recrystallization-type silicon carbide

refractory material with improved oxidation resistance.

Jpn. Kokai Tokkyo Koho. Patent No.: 79 95614. Applic.

No.: 78/1699. Date: 1/11/78. CA 92:04027361E.

[19] Seiter, H. Preparation and doping of epitaxial layers of

silicon carbide. Report. BMFT-FB-T-79-125 ; Order No.

81-10878; 1979; 44 pp. CA 94 : 22183552Q.

E. Properties

[1] Ziegler, G. ; Bentsen, L. D. ; Hasselman, D. P. H.

Orientation effects on the thermal diffusivity of

hot-pressed silicon nitride. J. Am. Ceram. Soc.,

Comm. 64(2): C35-C36; 1981.

[2] Ehlert, Thomas C. Thermal decomposition of the oxynitrides of

germanium and the heat capacity of the oxynitrides of silicon and

germanium. Am. Ceram. Soc., Comm. 64(2): C25-C26; 1981.

Correction. 64(8): C114; 1981.

[3] Moon, Kenneth A.; Kant, Arthur; Croft, William J., Heats and

free energies of formation of two sialons by mass spectrometry.

J. Am. Ceram. Soc. 63(11-12): 698-702; 1980. Correction.

64(2): 124; 1981.

[4] Leedecke, C. J. Electrical properties of some Y-Si-Al oxynitride

glass-ceramics. J. Am. Ceram. Soc. 63(7-8): 479-480; 1980.

[5] Wright, R. B.; Varma, R. ; Gruen, D. M. Raman scattering and

SEM studies of graphite and silicon carbide surfaces bombarded with

energetic protons, deuterons and helium ions. J. Nucl. Mater. 63

415-421; 1976.

[6] Gruber, P. E. Mechanical properties of silicon carbide

filaments. Proc. Int. Conf. Mech. Behav. Mater.,

2nd. 1330-1334; 1976. CA 87 : 266203761T

.

[7] Singh, T. N. ; Roy, B. N. Lattice dynamics of

beta-silicon carbide. Nuovo Cimento Soc. Ital. Fis.

B. 41B(1): 198-204; 1977. CA 87 : 22175852C

.

[8] Berry, T. Accurate measurement of lattice parameters

using a Bragg-Brentano x-ray diffractometer applied to neutron

irradiated silicon carbide. North. Div. Rep ND-R - U. K. At.

Energy Auth. ND-R-143(D). Risley /Warrington, Engl.; 1979; 20 pp.

CA 91:12100270K.

Glagovskii, A. A.; Ivanov, S. N. ; Makletsov. , A. N.

Absorption of ultrasonic waves by silicon carbide. Fiz. Tverd. - Tela, Leningrad. 19(11): 3467-3468; 1977. CA 88 : 08055173F

.

[ 9 ]
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[10] Lyubimskii, V. M. Elastic constants of silicon carbide

polytypes. Fiz. Tverd. Tela, Leningrad. 18(10):

3111-3112; 1976. CA 86:080493045.

[11] Leedecke, C. J.; Loehman, Ronald E. Electrical

properties of yttrium-aluminum-silicon oxynitride

glasses. J. Am. Ceram. Soc. 63(3-4): 190-193; 1980.

[12] Fegley, M. Bruce, Jr. The thermodynamic properties of silicon

oxynitride. J. Am. Ceram. Soc., Comm. 64(9): C124-C126; 1981.

F. Reaction Products

[1] EerNisse, E. P. Stress in thermal Si02 during growth.

Appl. Phys. Lett. 35(1): 8-10; 1979.

[2] Lora-Tamayo, A.; Dominguez, E.; Lora-Tamayo, E.

;

Llabres, J. A new model of the thermal growth of a silicon dioxide layer. Appl. Phys. 17: 79-84; 1978.

[3] Heubner, K. Structure and properties of silicon dioxide

and silicon oxide (SiOx) . Phys. Halbleiteroberf laeche.

11: 1-12; 1980. CA 94 : 18148780R.

[4] Varshal, B. G.; Shvorneva, L. I.; Danishevskaya , E.

D.; Pavlova, G. A. Thermal expansion of the

cristobalite-like 0.06 titanium dioxide-0.94 silicon

dioxide solid solution. Izv. Akad. Nauk SSSR, Neorg.

Mater. 17(1): 180-182; 1981. CA 94 : 14112754W.
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19

NBS-5.2.1Q(D) - MICROSTRUCTURE AND FRACTURE IN REACTIVE ENVIRONMENTS

RESULTS FROM PRIOR QUARTERS

An apparatus for mechanical testing structural ceramics in gaseous

combustion products at temperatures up to 1400 °C has been designed, and

the components required to construct the apparatus have been ordered from

commercial suppliers. The apparatus includes a laboratory box furnace

which is gas tight, a gas blending system which can control the flow and

composition of a mixture of 5 gases (SO

2

, H^O, CO^, 0^ , and N^) , and an existing, displacement rate controlled, loading machine. The furnace will

provide a 6 inch cube cavity that is heated electrically by molybdenum

disilicide elements. The gas mixture at nominally one atmosphere pressure

will flow through the furnace cavity. The gas blending system controls

the flow of each gas component by the thermal conductivity of its mass.

DISCUSSION OF CURRENT ACTIVITIES

The furnace system is under construction by its manufacturer. We

have conferred with the manufacturer to have the furnace modified so that

load bearing rods can be introduced through top and bottom ports of the

furnace. Regular access to the furnace cavity for placement of a test

specimen between the bearing rods is made through a sealed, water-cooled

front door.

Gas tight fixtures were designed for attachment to the top and bottom

furnace posts so that loading could be transferred from the test machine to

a specimen in the furnace. Commercial flanges and bellows required for the

fixtures were obtained. Accessory components are presently being machined

to hold the bearing rods. All of these parts will then be welded together

to make the fixtures.

The commercial gas blending system was delivered. The system includes

separate controllers which maintain the flow of each gas individually over

a specified flow range before blending. Unfortunately, the supplier

inadvertently transposed the ranges requested for SO

2

and N^. The units

for these two gases were returned for recalibration.
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Alteration of the laboratory room facilities were initiated to

provide power and cooling-water to the furnace and to exhaust the flow

of gas from the furnace out of the room. Although construction of the apparatus is not yet completed, we

expect that its assembly will soon be underway and its operation will

be verified on schedule by December 1981.
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