NASA Technical Reports Server (NTRS) 20050060620: Performance of Ceramics in Severe Environments

1.3 MB·English

by  NASA Technical Reports Server (NTRS)

Performance of Ceramics in Severe Environments
Niuthon 3, Jacobson, Dennis 8. Fox, James 1. Smialet, and Christopher Dellacorte
‘NASA Glenn Research Conter
Cleveland, OFF 44135
Kang N. Lee
Cloveland Ssare LmiversiyiNASA Glenn Rewearch Center
Cleveland, OH 44135
Introduction

(Cevamics ue geuerally sab

higher emperatores than most metas aad alloys, Thus the
evelopment of high temperature srucaural ceraries has bec at atv of wiv researc: for amy
year, While the dream ofa cerur:c heat ergine sil fages may alleges, niche wares ne
dewelopiig Ibs these materials a igh temperatures, In hose applications ceaenics ae exposed
‘not culy to high reaperatares but abo agressive gus id.

ss. Tn this chapler we wise

the response of cecemic mailers (these envimarments. We discuss aces aueeunisans. he

sve impu-tonce of a pastivular coment, nd, whee avalabe, sososion nes

‘Most uf the available comasion infocwacon is on silicon vari

(SC) ane sicgu aide Sig
sauonfihie ceramies, These tcatorss foun a stable ia of siten (810.1 n amo ding,
environment. We bogin witha sigenston oF okidaiou of thee materials and proceed tothe
lets of ocher eormderts such as waccevapos ul al deposits. We ab: disouss oxication snd
ccorosion of othr ceramics _precureec dives cesunes,eeramie matrix compesites (CMC),
cinatcs whicl form oxide scales other thar. silica, and oxide cesauice, Many uf the vanosion

stneused ean be miigatod with rectory oxide ouatirys and we divense the current ta
‘of this ative area of esearch, Ultimately. dhe coacen of corrosion is Jos aed besring
ceapubility. We dlacnss the effots of couzosive eavisruuen.on che arength of cera, bath

‘monolithic ar composite, We conelude witha discus af high temperature wear of emis,

nother important Zorn of degradation st igh lemperatures

‘The durability of ceramics is suka with u variyy ef teshnignes, Tetheeal axidation sodics ia
sr usa be cured out in a simple box furnace. Harmetion of a astoolve stface maid esuls ius
‘weight ain. wth onidtion kinedes determined by sight gain as uation af me

Alternatively these kines cun e derived hom axis hckresses unease
via optia! (Ror. 1] and closson-optivalLecniques. Tube fumages allow the se of coualled
exposure envitonments, Thermegraviasic axalyyis (TGA) pormite weight chasge io be
nmtimuorsty monitor iRef. 2). Thermal eyeing can be introduced fe atone awvurate!y nnd

real aptication. High veloity,iydravarbun-tuels bummer sigs sibjoct potential engine materials
‘wan exvironmesc which closely upproximutes uctal aperatag comitions, After these expomures

samptes are rypically saalyaed with a variety of techniques ineludiag epi anieroseup

ay
aifrasion (XRD), and seaming ee-uon mvcroscupy (SEM) to deteemine companion and
morphology of the carosion pode,

High Temperature Oxidation and Corrosion of Silica-Forming
Ceramics

isothermal Oxidation

ea this section we discuss the kinetics of SiOz fonation on 8%, SiC, and SiN in ony ten:
SiC 1 0:60) = S108) a)

SiCts) + 02 Uxigl = 81036} + COL) co)
SiN) + 3 OL = 5 SIO) +2 EH 3

| illastestes the ormetiun of w aotective oxide scale, The cucu sis farm can be
describe in hoe differ way:

1 weight change ofthe sample. the thickness of the is
formed, and he recession ato the sting marl, Conversion of ese antes given in
Tabce I assuming the loss of Cor N from SiC ana 3M, rapectindy, Figure 2 llurates e-pical
‘TGA resulls for high purity SiC and SiN, ot 1309°C in pare oxygen. Tho ne at fr Mis plot
were taken we wight gain aud the plo isi the [orm of scale thickaoss to provide a vunpasison
heewoon the te aera
“Rial Seale Thickness Welght Gain | Revert”
qm cagiem’) (am

<r a Ta OFA

sisityiad” TT Eg Dae
TSicsiovam [1 az) Toaaait

‘SHC-SiOy Cy T DOTS DARKE a
SENSO fT OHRT6 Toes
T_T TaD ie

“Table Conversion af ealeigkagay To weight gan and To reestion Ze: Si, iC and SEN,

fom)

ssophons (er

cristae

8 goud deal can bo ‘eamed from the oxidation of pute slieorta form s.rfawe SiO, THis prucess
haa bsen extensively sic by The semiconductor iadcey Re. 3p ands eettvely well.
lnderstood. ‘The oxidation of silicor wil bs buoy summuized ly paovide a buss “er the

“Usowsn uf SiC ad SN dation.

Silicon oxidation is de

ered by reaction (1). Kiseie dala cat be uccuray described sith the
linear parsbolic model of Decl and Grove (Ref. 3:

sbtar,= Bitte) “8

ees 3, t8 the

inet of the oxide, fc dhe ime, «isa shift i ene to comet Cor Do ini

oxide layer, and A and. ure sanstons eluted te tne linear und porabotis rate constants. 8t short
enes,€9 ation @) eduwes te

a
a eSttor, a
qin

“Teas the yuentity 4/8 mths linear rate somstant. (cis goneraly agreed that inte eay tages of

‘exidion, the le controlling step in the chorea rausom (13, The linear rate constant canbe ft

to 9 standaed Acthenias expression

B_[B) asf 2} 6
$F (ie) °
‘isthe pre exponential, Q), is He atlvalin: energy forthe Hnear rte constant, Ris

le yu comslant and Wie the absolute teraperaracs, Table MU ss fi for sume ensured silicon

linear rae constants, A: longer times, oquaion (2) slmpliies to:

apr 0
Ure the quenty ithe parabolic ats cops. J heave the ral omg tpi eon
throng the ce sve, Silay the paaboi te comune san he expose wi an Area
sae eaicsion

(2,
ns ten Be :
of Se ©

Hove Bis the pre-expoueial and Qp isthe eetivacion energy forthe parabolic rae vnmatant,
These are gives in Tablet

Silica ens i veytalline ae well a gmonphovs fous, Censicer first the mmorphans tem whist

1005 or slivinin pure exygen at tomperatnes less than 1200°C “Ihe network af silicon acd

‘oxygen aloun is suliclendy open so chat here are chanel fr diskae xygen to pert

‘Based vt his eonvept, Deal and Cove (Ref. 3} deve the folloming expresion far the parchelic

tas const:
B 725 9)
7 “

ere Bays the eftztivediusion cvefliien for permeation, Cis the eyaiibriom conceatstion
of onidancin te oxi, and is the anaes of oxidast molecule incorporate inna wh
‘yalume of he ovis layer, Using the peemeation te of diatomic anygen tow anouphoes
sillea measured by Novton (Ref, 3), Deal sl Grove are able lesive tho exidaioa sates of Si,
“These caoulated tates show g00d upreement with mewsured para Tert,

Figur 3s astuadurd Arrsenius pl of silicon oxidation compaced to the waitin rates for
alloys which umm other encimon prtcrivscmidet—ahvai. AbO\(Ref. Spand ernie, Os

‘Rel. 6). This:itusrates the unique properties of the sca eae. Nowe that

rae of iit
Formation are very low. Mure importncy, dhe ativation eneegy For sifca sont i nw
peemealion af nxygenthroogh the ston naw: does nox nvalve bua Ereaking, a a lace
clffuson process wnuld. “iy the data inca hat SiO is une ofthe best promective odes ia a

ure oxygen cavitentent,
‘Oxidatina of SiC lay follies fneur-parubolckraetics, The inewr rate constant hag only een
eas hy a fow investigarar andi lite in Athens form in Table 1. Linear gies are
aly obeervatie at temperatures less than about 120U°C. Oxidation coors via te folowing
SiC) +3204)
Sic) +2 OF

O40) io)
SiO(9) + COxe) b>
-Mocrfld Get 7} wos dhe feo point out tat the enitavion ace of SIC shou be 5 to 2 times

slansne fan ts exten rates o slice dust dealin erygen use tn oilize the

carbon, a8 shots in reactions (Tahoe (Pui especivey, “Teis has been veil expedanentlly
(Refs 1.7). Futhot, 9s insleavod in Table 1 the seta eneray for te sural ute coastans
CF 8 avd SiC ar similar, enggesting s pemcerion mechanism Fr dif soa contol through the

SiO, see

Parahntie

constanrs for SiC ars s0 Tete in Tale (Refs 1,8}, Ons tinportaat observaioa
‘with SiCs the oxidation cete dependeace ow erystelegraphis vieulaion (Ref. 1), Therewuss
fortis ate controversial. Harris (Ref, 9) suggested this occurs only curing the linear oxidation
period and is dus to diffewnt chemical ection rates. Costello and Tessler (Ref. 1) and Zheng
‘tal. (Reb 11) observe tis ding he puabulis epime, Raoubery etal. (Ref 1)ree evidence fa
silicon oxyearbide subscale. whic may iofuece dhe lf sium rate, though is existenze hut not
‘bccn cleatly established.

108

Atshor ims and temperate

erally groin SiO Hm is aimomphons,

snuaber of Frew leas 1 crystallization of Si0s, inching longer times higher temperatures, sd
5 qxestion becomes the effet of exystlinity on uxidaton rates. Chul (Ref.

12) has pesinael enperimeats oa oxidation of SiC a 200°C walk an Sri, long-term ans to
‘usu scale lier amorp'ous Wo crystalline, Ox‘Uaioa rales de-reave by a facta af 20%

pon crystal earion, Facer, even though cestlline seale nceupies u portion ofthe tou seule,

Impucies. Ax

ow amorphous scele is conzually jrowing. ‘Thus erystelization decreases oxidation rates, bu
sank by 2 small urn. Thi contra with ALA, sacl: hore erpsallizatcm fn the ® use

1 tho «plier Jeads to arto axder of mised decrose in oxidation snes (Re. 1).

The disunsiog tus Za Ize been ou voupous aa pes of Siew SiC. Generally, the wxidation
rates of powders senie aeontingly with suntace ea (Ref 14). However, aano-partisles of Si (20
to SUD am) have been shown to onid:ze mote slowly than oxpecre (Rot. 15). The aheorvad rice
to mF he tanita sues Re 3) athe ee3sons or the stower eatin rams revain am

ioteresing question

“Table Mal Lists cide cates for CVD sin altive-comtaining Sty, (Refs R16). (his
SiC. The
‘oxidation cate of SiN i sluwer a iat of SHC EFlante [aa asa dfecent activation enerpy

‘nsrucive frst examine high puricy SiN, md compere tc to dut of Si ane

than that a Si und SiC. This sugets ata leven! oxidation provess oecurs,alough the
‘etoot mechs fa been st area of some controversy, High gurity SiN, forms an iuermedioee
‘ohcon oxynitride layer of composition SiNzO, Ths role ofthis ineemediats i il unclear
Some investgatur (Ref 17) believe sul a. dtfosion bates, Lsading to the sfower rection
tes: her investigators Ref. 18) believe it combats to mixed ditfs:oufchemies: reacion
con ofthe exidation process. Obi and Jayne (Ref 19; shore evidence thet the sicon
oxynitride, riven us SiN,.0.., sactudly a yraled composition du Sit 0 $10%, They
pone that idan oucurs in tss aes a a peogiessve oxygen-fot-nttogen subsintion
THOME FIES= UTNE HOsAxO Mp Uy!

ur

co wonesre

gna pu our

warcurt
s aia apse,
cesT
cuanonroe V4ta 1 ¥9°z suis cans
| cemonscar ite
suit eutt
8 aur He SBE
wu
1] arwoonceeio,o1 8268 | . og
7 CLOT
fl 1 {rouest-s9 6 607
! euetiot euer-ils
ec! ammonset-xie soc € igh 2 ILE | 8
; ‘of ames ‘og sani,
PE Cox (gp onan Pa Aa mods)
‘Most commercial forms of SiN enntain additives, typ'cally rtietoxy oxides, Ws promote

unsrfcation. Ichas heen shown that he sets of these impecties donate oxidation (Re. 20

22), Ime oases mevemnt ofthe aAditve ction eg, Ma" or Y) onan! into he erasing,

‘olde il isthe rats-conaolling step tev oridtiog, Typically theve aateials usidlize Cater than
high pacity SicNqas show in Table IL, Many commetcist foes of SiC ule concainaelives. In
general horen ancl eatbnr additives in SiC Toad 19 marerils with anidsion ree comparable to

jh purity Si: Qe
rapid mddarion rates (R23),

those 0

s however rlracony oxids alive ‘ea wo uteri with ore

Gyelic Oxidation

“The disexssion thus fr as dealt with tcubermal wxiduls. However, many aplicacions inwae
femperacue.

yeling, This leads 0 stress frou the erm! expansion sssccutch hoewecen the
subtate aad the guowing onide sale, Figus iv plo of the thecal expunnion of eryaltine
‘SIO; (tistcbalte), SIC, SiyN,, sad arcorphous SiO, (Ref. 24}. As ante, fr most practical

sppCaliogs the scale will eytsin ot leas some amount uf yale SiC, suming asitess-
lige sale al leprae, da arg there eparnion of she erytalline SiO, means tha on

valing the selon 2 SiC or Si,N: subaru wilf hein mension. This rads oecteks oa cooking,
but

rvks heal in the nest teroperatuce increas. "This behaviae is ip eoutast w supe Toys
‘whee the oaide is io compression on zoulng, leading to oxige buskling sud splat, Thus
cystic oxidation behavior of SiC und SiN, tends co he goad, as ilostate ia Figure S (Res
25.28).

Corrosion of Siica-Farming Ceramics by Water Vapor

: temperate envingnmasescoatain wate, vaser, In gous, eubunlion of
nylon fuels in ir leads to an environment with “1G water vapor ‘Ref. 24). AL one bar
total presse tis is ~0 1 bee wate vapor eu it scars accordingly tu higher ute pressures
(Clearly the el7scts of water vapar on sicafoxuiny vecunis must be urdertiod to wile these

ruler. in auch enviroments

‘The fundurcenaal suis of pure Si are again helpful to underscand the effec f water vepne an

SiCunu $i, oxidetiom, Deal und Gnuve (Ref. 3 have dhown thu silicon oxidizes mare rapaly
in rater vapor. The diffusivity of wale: vapor in silce is less than the diffuovity of oxygen in
silica: however the solubility of water vapur in sli is conaideruly higher ham tha af oxygen,
Accotig to equation (9). tis leads 1 a wet increase in oxidation me. A simar oe is
berved fon SiC oxidating (Ref. 27.

A sscondiempontantefTeet af water vapar i hal ican range impurities fromm the envonctont
lw Cre sample tel. 2. As wil be discusiec, the oxidation a slcs-ormarg coves i quite
susvopsfle to sevondary elements. Thes the suey of water veper effets reqies a clean famace,

2. asilica furauce tube und pre-healng amy alumina purse remanve sedan fg es

Peelaps de mont impurtzal effec: of waler vapur at igh temperatures is dhe Formation nf soll
species from the Weemally grows: SiO, seule Refs. 28,29)

SiO,G+ T,0@)= SiO AR) an
SIO-() + 2TLOW) = SHO) re)

“Thus as dee seal wrows ibis also voluilzed hy tho woter vapor i the eam This Teas to

aclinesr kinetics where the swale oss wccording to a parabolic rete aw ant ce sale

woluilizes according a

ate. The purabolie rate constant, yas been sc ussed In aa
‘earlier stim. Tn a Mowing gu, votaion is Him

The se of eile

Se horny I

‘eral sline ith cme agcorcng to the Following expession fr Iauznar Now even afk
plate Ref. 30%:

«arin so" PR an

Here div the Hnger ste constant, eis the Reynolds rine, Se ss Sebi, 1s the

Jmerditfasion coeticien af the veal‘ spece (primarily SitOH ug) inthe boundary Hayes yi
(he censity ofthe volatile specie inthe boundeuy ayer, and Li a characterise diuension of the

speciaen, Co

inal parabolic esvwth Klctics and liner volatilization kinetes leads to:

ah

14
aoe °

Hore i de see thiczmese and ris tine, Figne 6 Mlnstates tis bebvioe via TOA
cesurerrene in a 9 ChiSO% H4O environment (Ret, 28) at L20°C. The SiDk sgoninen
shows a lineae weight loss, Roth the SiC and Shs niely show a weight gain allowed by 4
‘vght oss rate sina otha of the S10» specimen, Note the inal weight gaia of SIC is

rear than that of SigDL due u the Later uxidaton rae uf SiC. IL is impumtart to nate hat over
10

tong tes, de SiC and SiN, scbstrate will echt greater recession a8 avec ofthis

‘oxidativolui

ron proces rlacve tn natin atone.

‘The above Uescrption uf soate voluity ean bo oxtanded to a hydocarbon fuel bumer (Refs. 3
233), Figure 7 ilusttes seme kinetic results foe SiC nner these conditions, “These wengh losses

ee primarily Uue ws the volt of thes

film according to reaetion (12), Frou equation (3)

Ute key dependences on velocity, vs emporaure, 75 ane pressure, P ean be entrastel:

PASH), Jo 9 PS 5)

Hone cr: gus wloeite, Pyne he al pressure, and #SHOH)| i patal pressu uf
SWOH{@i- Avcording Yo equation £123, ae pslal pranure of SHOM)4 fs 2roporticnal tobe
‘jure of water vapor pressure, which is proportional te ttl proseure For hyeecacbon fie]

burns. This tae Teds cot

iempliied expression onthe -ight and sd of quation (15). The
linear rate constant would be expecta to have un expunencial dependsncy ot temperate us the
‘vapor pressure. PrSi(OH). varies exponeatilly with semper,

“The nonialied Annheuius representtia of ky in Fig, 8 wa obtained fram zauliple Heer
regression ovar a ange of presser, gus velocity, and tompersinee teat conltions,yrelding an

‘empirical eight Loss equation in furm simtart equation (15

coon) hahaa a9)

Hee Tis temperature in degrees K, is pressure in atmosphotss, aay is velovity i meteniev

Byulveleut celutiunships were meaaured (snd derived) for eoession of SiC in am br, represents
Dy multiplying squutinn (26) by 2.9 (2.1, foe the dovived equton). Rates for three types of SC?
composites sere fund ta he egzivalent 9 CVD SIC x sialeced SiC Ref. 34). The volaigy
rates dstermined for CVD an intro Si

1 sare bo found 1 be 1.8 times tase oF SC, wit
ro appar cfbe: of altives ar “he oxyde inlenfuce Layer (ef. 5).

qation (16) must be mudfied uo include lightly aifocn: water vapor conte ia actual eebie
‘engines (Chiges in fuel-to-sirraio andor water yeetion}. By normalizing tthe ealealasd
‘qilbvium wster vouteal i the burner i (0.10-0.12 sim.) equation (J6) can he se wate ia
general foam as: