JOURNAL DE PHYSIQUE
Colloque
C1,
supplemen
au
n02,
Tome
47,
b ie
1986
page
c1-385
SINTERING AND CHARACTERIZATION STUDIES OF NiO
M.
JIM~NEZ-MELENDO,
A.
DOM~NGUEZ-RODR~GUEZ,
R.
M~RQUEZ
and
J.
CASTAING*
Depa amen o de Op ica, Facul ad de ~isica, Ap do.
1065,
41080 Se illa, Spain
~abo a oi e de Physique des Ma B iaux,
C.
N.
R.
S.
Belle ue,
F-92195 Meudon Cedex, F ance
Resume
-
Des polyc is aux de NiO de hau e pu e e on @ 6 6labo 6s pa
mge a ec e sans cha ge. 11s on B 6 ca ac 6 is6s pa mic oscopie
op ique e 6lec onique. Leu compo emen en luage a 6 6 6 udi6 au
dessus de 1200°C.
Abs ac
-
High pu i y NiO polyc ys als ha e been p epa ed by ho -
p essing and by sin e ing. They we e cha ac e ized
by
op ical and
elec on mic oscopy. Thei c eep beha iou was s udied abo e 1200°C.
I
-
INTRODUCTION
Nickel oxide polyc ys als ha e been p epa ed wi h he aim o s udying hei
plas ic de o ma ion. Fo mechanical es ing, ma e ials wi h s abilized
mic os uc u e (g ain size, po osi y,
...)
a e needed. We ha e p epa ed NiO
polyc ys als wo ways simila o hose p e iously used o NiO/l/ o
Co0/2,3,4/ and cha ac e ized he esul ing specimens by mic os uc u al
obse a ions and c eep es ing.
I1
-
PREPARATION OF POLYCRYSTALS
11-1
-
Ini ial sin e ing
The s a ing powde was high pu i y NiO p o ided by Johnson-Ma hey ( o al
impu i y con en below 15 ppm) wi h an a e age pa icle size o 0.1 Qm. The
powde was i s cold-p essed in a die unde 400 MPa. I was hen annealed 3
days in ai a 1200°C on a boa made o NiO o a oid con amina ion. The
densi y o he sin e ed body was 65
%
o
he heo e ical densi y aken as
6.8
g/cm3 and he g ain size o he o de o
1
m. Such a ma e ial is no app o-
p ia e o high empe a u e mechanical es ing and wo ypes o addi ional
ea men we e equi ed.
11-2
-
Ul a-high empe a u e sin e ing
Since mos o he c eep es s we e o be pe o med below 1400°C, sin e ing
ea men s be ween 1500°C and 1700°C (0.80
TM
and
0.88
TM
;
TM
=
2230
K,
mel ing empe a u e) we e pe o med in ai du ing 3 days. To a oid con amina-
ion, he specimens we e sepa a ed om he alumina c ucible by a bed o NiO.
A icle published online by EDP Sciences and a ailable a h p://dx.doi.o g/10.1051/jphyscol:1986157
JOURNAL
DE
PHYSIQUE
11-3
-
High empe a u e comp ession
The low densi y sin e ed bodies we e subjec ed o la ge c eep de o ma ion in
o de o s abilize hei mic os uc u e. The s a ing specimens, wi h 12 x
10
x 10 mm dimensions, we e placed in he comp ession c eep machine and s ained
a 1150°C
<
T
<
1300°C (0.64
<
TM
<
0.71 TM) in ai by applying s esses
be ween
5
and 24 MPa o 6 o 24 hou s. The o al s ain
E
was be ween 0.6 and
1.5.
Fo hese expe imen al condi ions, he a e con olling mechanism o
de o ma ion is di usional c eep /5/.
Specimen we e hen cu om esul ing body o he ac ual c eep es s wi h
s ess axis ei he pa allel o pe pendicula o he di ec ion o ho -p essing.
I11
-
SPECIMEN CHARACTERIZATION
We ha e de e mined a ious cha ac e is ics o he NiO polyc ys als
:
(i)
The densi y was deduced om he a io o weigh o olume. The densi y is
known wi h an accu acy o 0.2
%
which is con olled by he size measu emen s.
(ii)
The g ain size and mo phology we e de e mined om op ical and scanning
elec on mic og aphs. Fo ha pu pose, g ain bounda ies we e chemically
e ched (H3P04, 15 mn a 160°C)' on mechanically polished su aces.
We ha e used a semiau oma ic image analyse Kon on MOP-30 o a e age he da a
on up o 300 g ains o each polyc ys al. The g ain size wa aken as he
equi alen plana diame e , de ined as d
=
4
(g ain a ea)/
II)~.
We ha e also
de e mined a o m ac o , de ined as
F
=
4
IX
(g ain a ea)/(g ain pe ime e )z,
which gi es quan i a i e in o ma ion on g ain shapes and en a i ely made an
e alua ion o hei p e e en ial o ien a ions.
(iii) The p esence o disloca ions in he g ains was in es iga ed ei he by
chemical e ch pi ing (HNO3, 20 mn a 105°C) o ac u e su aces o by
ansmission elec on mic oscopy o hin oils p epa ed by mechanical,
chemical and ion hinning.
(i ) Mechanical da a p o ided addi ional cha ac e is ics o he ma e ials.
Tes s we e pe o med in a c eep machine desc ibed in-
/6/.
IV
-
RESULTS AND DISCUSSION
(i)
The densi y o he ho -p essed specimens was always highe han o he
sin e ed ones in spi e o he di e ence in empe a u es. Values up o
97
%
heo e ical densi y we e ound a e comp ession a 1300°C
(
0
=
20 MPa,
=
12 hou s); a e sin e ing be ween 1600°C and 1700°C, hey we e ne e abo e
88.1
%.
In ano he wo k, a ela i e densi y highe han 99.7
%
was achie ed
;
his was ob ained unde s esses much highe han he ones we used /I/.
Mos o he po es we e ound a he g ain bounda ies and especially a iple
poin s; his is analogous o obse a ions made o COO /4/. We did no ind
any in luence on po e placemen ela ed o he di e en p epa a ion
echniques.
(ii)
A minimum mean g ain size o 6.3 ;Im was ob ained o polyc ys als
ho -p essed a 1150°C du ing 12 hou s ( ig. I-a). Fo sin e ed specimens, he
g ains we e always la ge ( ig. I-b) and could each 20 pm a 1700°C. These
g ain sizes a e simila o hose ound o COO in simila condi ions /2,4/.
The shape o he g ain size dis ibu ions (Fig.
1)
a e consis en wi h a
logno mal law as o en obse ed
/7/.
Howe e , he polyc ys als p ocessed unde
s ess a low empe a u e showed de ec i e a eas which e ained oughly he
ini ial g ain mo phology (Fig. 2). The hi hes densi y o hese a eas was
2
ound a 1150°C and did no exceed 10-2 cm-
.
Fig.
1
-
His og ams o he g ain-size d dis ibu ion o polyc ys als ob ained
by
:
(a) ho -p essing,
T
=
1150°C,
0
=
16
MPa,
=
12 hou s and d
=
6.3
pm;
(b) sin e ing,
T
=
1600°C,
=
3 days and d
=
13.4 Dm. The plo shows he
pe cen age N o g ains e sus d.
Fig. 2
-
Scanning elec on mic og aph
(X
1300) o a ho p essed polyc ys al (T
=
1150°C,
o
=
17 MPa,
=
6 hou s) showing a de ec i e a ea wi h small
g ains.
We ha e insu icien esul s o make a quan i a i e s udy o he kine ics o
g ain g ow h, which is gene ally ound o ollow he law
:
d, do
=
g ain size a ime and
=
0
;
K
=
cons an
;
Q
=
ac i a i.on ene gy
A
alue o m
=
4 has been ound o alumina 181, bu m
=
3,
o MgO 191 and
COO /4/, is a mo e usual obse a ion o po ous ma e ials. I we i ou da a
wi h
m
=
3, we ind do
=
1
u n and an ac i a ion ene gy o 3.8 eV, much
la ge han he one o Ni sel -di usion 1101. This is an indica ion ha he
a e con olling mechanism o sin e ing be ween 1500°C and 1700°C is he
sel -di usion o oxygen, he slowes species in NiO 1101.
The g ains gene ally exhibi equiaxial shapes; he o m ac o s F a e la ge
han 0.7 (Fig. 3), he maximum alue o a ci cle being
1.
Fo ho -p essed
NiO, F is no smalle han o sin e ed ma e ials, a ac ha can be ela ed
o he mechanism o plas ic de o ma ion, o be discussed in a u he pape
(see also M. Jimgnez-Melendo, Tesis Doc o al, Uni e sidad de Se illa, 1985).
~1-388
JOURNAL DE PHYSIQUE
X- ay di ac ion was used o e eal he p esence o any p e e ed o ien a ion
o he g ains. A Phi lips ex u e goniome e was used
(1).
Random o ien a ions
we e ound o sin e ed polyc ys als as well as o ho -p essed ones, in spi e
o he la ge uniaxial comp ession.
Fig.
4
-
Scanning elec on mic og aph (x 2000) o a sin e ed specimen
(T=1700°C,
3
days) showing
(100)
clea ed aces on some g ains wi h disloca ion
e ch pi s.
60
40
N(%)
20
0
(I)
O.A. Ruano, CENIM, Mad id, is acknowledged o his help.
0
0.2
0.4
06
0.8
1.0
F
Fig.
3
-
His og am o he o m ac o F dis ibu ion o he polyc ys al wi h
g ain size depic ed
in
ig Ib
;
F
=
0.8
(iii)
The p esence o high disloca ion densi ies may be expec ed in polyc ys-
als which ha e unde gone plas ic de o ma ion. F ac u e su aces displayed
la ge amoun s o
(
100) clea ed aces ( ansg anula ac u e) whe e disloca-
ions can be e ealed by chemical e ch-pi ing /!I/. Pi densi ies we e
ema kably low in bo h ypes
polyc ys als (Fig.
4).
TEM obse a ions we e
also pe o med; disloca ions we e obse ed. Thei small densi y occasionally
is an indica ion ha plas ic de o ma ion occu s essen ially by a disloca ion-
ee mechanism in he condi ions used o he p epa a ion o he ho -p essed
polyc ys als.
-
-
1
-
-
-
-
-
-
111
(i )
The aim o ou wo k is he s udy o high empe a u e plas ic de o ma ion
o NiO polyc ys als. We discuss he mechanical da a ob ained o bo h kindso
ma e ials. C eep cu es a e shown in he igu e 5. Since he es s a e
pe o med a cons an load, he s ess a dec eases a inc easing
E
acco ding
o
5
=
aoexp(-
E)
o homogeneous de o ma ions, whe e a is he alue
displayed in ig.5. I on, he ela ion be ween In
E
and
E
is linea . The
slope o he s aigh line is equal o n; we ound alues be ween
1
and 2, in
ag eemen wi h s ess exponen s de e mined o he wise
/5/.
Fo small
e
,
ansien s ha e been obse ed ( ig.5, cu e A) o ho p essed
specimens when he c eep s ess is pe pendicula o he one o specimen
p epa a ion (see sec ion 2.3). This is p obably due o a sligh change o he
mic os uc u e which canno be de ec ed by o he cha ac e isa ion echniques.
Such ansien s we e no obse ed o sin e ed specimens. Thei mechanical
da a showed a small sca e o iden ical a and T, he a io o maximum o
minimum
6
was
2,
when o ho p essed polyc ys als, i could each 10. The
la e ones gene ally de o med as e ( ig.5) han he o me by a ac o
5
o
10. These di e ences in beha iou mus e y likely be asc ibed o he
exis ence o andomly dis ibu ed de ec i e a eas wi h small g ain-sizes ound
in ho p essed NiO ( ig.2). Al hough his p epa a ion is easie (low T) and
gi es high densi y bodies, his echnique is no as aluable as he high T
sin e ing o p o ide NiO polyc ys als o medium
T
ange c eep es s.
Acknowledgemen s
The au ho s a e indeb ed o
F.
Be nie , F. Cumb e a and B. Pellissie o
hei assis ance in he expe imen al wo k.
Fig. 5
-
C eep cu es o polyc ys als ob ained by (A) ho -p essing, T=l 300°C,
a
=
10 MPa,
=
12 hou s wi h d
=
10 pm (B) sin e ing, T=1500°C, 3 days wi h
d =9 pm.
lo-'
Re e ences
/
11
No is, M.R., U ick, P.A. and Sp iggs, R.M., in Ma e ials Science Resea ch
(edi ed by G.C. Kuczinsky), ol.6, p.409. PIenum P ess, New Yo k, 1973.
/
21
U ick,
P.A.
and No is, M.R., J. Ame . Ce am. Soc. 56 (1973) 570.
/
3/
Kuma , P. and Johnson,
D.L.,
J. Ame . Ce am. Soc.
37
(1974) 62.
/
4/
Kuma , P. and Johnson,
D.L.,
J. Ame . Ce am. Soc.
5
(1974) 65.
d
22
MPa
I
I I
I
0.45 0.10 0.7s
aao
E

C1-390
JOURNAL
DE
PHYSIQUE
/
5/ Ji nenez-Melendo, M., Cab e a-Cano,
J.,
Do ninguez-Rod iguez, A. and
Cas aing, J., J. Phys. Le . 44 (1983) L339.
/
61
Ge ais,
H.,
Pellissie ,
B.
aK3 Cas aing,
J.,
Re . In . Hau es Tempe .
Re ac . 15 (1978) 43.
/
71 Ku z, S.K and Ca pay, F.M.A.,
J.
Appl. Phys. 51 (1980) 5725.
/
8/ F idez, J.D., Ca y, C. and Mocellin, A., in AdKnces in Ce amics (edi ed
by
W.D.
Kinge y), ol.10, p. 720. The Ame ican Ce amic Socie y,Ohio, 1984.
/
91 C ampon, J., These dlE a , p. 122. Uni e si b des Sciences e Techniques,
Lille, 1983.
/lo/ Mon y, C., Rad. E ec s
74
(1983) 29.
/?I/ Guibe eau, F., Domingue?Rod iguez, A., Spendel, M. and Cas aing,
J.,
o be published.