796
BOLETIN DE LA SOCIEDAD ESPAÑOLA DE
ARTICULO
Ce ámica y Vid io
Acicula i on nanopa icles p o ec ed
agains sin e ing wi h aluminium oxide
R. PozAs1, M. P. MoRAles2, C. J. seRnA2, M. oCAñA1
1
Ins i u o de Ciencia de Ma e iales de Se illa (CSIC-UNSE), Amé ico Vespucio s/n, Isla de la Ca uja, 41092 Se illa, Spain.
2
Ins i u o de Ciencia de Ma e iales de Mad id (CSIC), Can oblanco, 28049 Mad id, Spain.
Acicula i on nanopa icles ha e been ob ained by he mal educ ion wi h hyd ogen o a goe hi e p ecu so p o ec ed agains sin e ing wi h
Al ca ions, ei he by doping du ing he syn hesis o by a u he coa ing and he ela ion be ween mic os uc u e and magne ic p ope ies o
he inal Fe pa icles has been s udied in o de o e alua e he e iciency o bo h p o ec ing me hods. Uni o m goe hi e and Al-doped goe hi e
p ecu so s we e p epa ed by oxida ion wi h ai o FeSO
4
solu ions, con aining Al(NO
3
)
3
when equi ed, p e iously p ecipi a ed wi h Na
2
CO
3
,
while he Al oxide coa ing on he undoped goe hi e p ecu so was ca ied ou by he e ocoagula ion. In bo h p o ec ing me hods, Al ca ions
we e mainly concen a ed in he pa icle ou e laye s o he goe hi e p ecu so s and he inal i on. Due o his Al en ichmen , he g ow h o
i on c ys als du ing he educ ion p ocess is minimised esul ing Fe pa icles wi h imp o ed coe ci i y and squa eness. Ne e heless, he
coa ing p ocedu e seems o be mo e e ec i e gi ing ise o he i on pa icles wi h he la ges coe ci i y, p obably due o a be e p ese a ion
o he acicula mo phology in his case.
Keywo ds: Aluminium, Goe hi e, I on nanopa icles, Magne ic p ope ies
Nanopa ículas acicula es de hie o p o egidas en e a la sin e ización con óxido de aluminio
Se han ob enido nanopa ículas acicula es de hie o po educción é mica con hid ógeno de un p ecu so acicula de goe i a que ue p o egido
en e a la sin e ización po la adición de ca iones Al median e dopado du an e su sín esis o po ecub imien o pos e io , es udiándose la
elación en e la mic oes uc u a y las p opiedades magné icas de las pa ículas inales de α-Fe con obje o de e alua la e icacia de ambos
mé odos de p o ección. Los p ecu so es uni o mes de goe i a y de goe i a dopada con Al se p epa a on po oxidación con ai e de disoluciones
de FeSO
4
o de FeSO
4
y Al(NO
3
)
3
, p e iamen e p ecipi adas po la adición de Na
2
CO
3
, mien as que el ecub imien o con óxido de aluminio
sob e las pa ículas de goe i a ue lle ado a cabo po un p ocedimien o de he e ocoagulación. En ambos mé odos de p o ección, los ca iones
aluminio es aban p incipalmen e concen ados en las capas más ex e nas de las pa ículas, an o de los p ecu so es de goe i a como del
hie o. Debido a es e en iquecimien o en Al, se minimiza el c ecimien o de los c is ales de hie o du an e el p oceso de educción esul ando
pa ículas de Fe con mayo es alo es de coe ci i idad y de cuad a u a de la cu a de his é esis. No obs an e, las pa ículas de hie o p o egidas
median e ecub imien o p esen aban alo es de coe ci i idad lige amen e mayo es, p obablemen e debido a la mejo conse ación de la
mo ología acicula en es e caso.
Palab as cla e: Aluminio, Goe i a, Nanopa ículas de hie o, P opiedades magné icas
1. INTRODUCTION
Comme cial me al pa icles o eco ding media a e usually
p oduced s a ing om di e en i on hyd oxide o oxide p ecu so s
which, h ough dehyd oxyla ion o hema i e (α-Fe2O3) when equi ed,
a e con e ed o α-Fe me al pa icles a e he mal educ ion. The
p oduc s a e subjec ed also o a passi a ion ea men o ming a
su ace laye o i on oxide a ound he pa icle in o de o p e en
u he oxida ion o he me al co e (1,2). Fo his applica ion acicula
nanopa icles o α-Fe a e equi ed due o he low alue o he
demagne iza ion ield along he majo axis, which d i es o highe
coe ci i y alues (3). Fo he p epa a ion o hese i on pa icles, goe hi e
ha g ow hs as elonga ed pa icles ollowing i s c ys allog aphic
habi , is usually used as p ecu so , which mus be ans o med o i on
p ese ing he acicula mo phology. In gene al, educ ion o hese
p ecu so s des oys he acicula mo phology, which has undesi able
e ec on he magne ic p ope ies o he inal e omagne ic me al co es.
Fo his eason, he addi ion o p e en ing sin e ing agen s, such as Al,
B, Si, P and Sn, o he s a ing goe hi e pa icles has been sugges ed o
p ese e hei acicula mo phology du ing he o ma ion o he me al
pa icles (4).
Recen ly, we ha e p epa ed acicula i on nanopa icles by
educ ion o uni o m goe hi e pa icles ob ained in he p esence o
ca bona e ions (5). Mo eo e , i was also shown ha he use o an
Al-doped p ecu so esul ed in an impo an imp o emen o he
magne ic p ope ies o he inal me al pa icles (6). In his wo k, Al
ca ions ha e been inco po a ed o he undoped p ecu so pa icles by
coa ing a e hei syn hesis h ough a he e ocoagula ion p ocess, and
he ela ionship be ween he mic os uc u al ea u es and he magne ic
p ope ies o he inal α-Fe pa icles was s udied and compa ed o
hose o he Al-doped sys em, in o de o e alua e he e iciency o
bo h p o ec ing me hods o p e en sin e ing.
2. EXPERIMENTAL PROCEDURE
2.1. P ecu so p epa a ion
Fo he p epa a ion o he acicula goe hi e, a 0.15 mol dm-3 Fe(II)
sulpha e (FeSO4·7H2O, Ald ich, 99%) aqueous solu ion was p ecipi a ed
by he addi ion o 0.225 mol dm-3 sodium ca bona e (Na2CO3, Ald ich,
Bol. soc. esp. Ce am. V., 43 [4] 796-800 (2004)
797
99.5%) and he esul ing dispe sion was hen oxidized a cons an
empe a u e (40ºC) by bubbling ai a cons an low a e (2 dm3min-1)
o 6 hou s, ollowing he me hod desc ibed ea lie (5). The p ecu so
syn hesized by his me hod is named as G.
Al(III)-doped goe hi e pa icles we e ob ained by adding he desi ed
amoun o Al(III) ni a e (Al(NO3)3·9H2O, Fluka, 99%) o he Fe(III)
sulpha e aqueous solu ion be o e he addi ion o sodium ca bona e (6).
The sample syn hesized by his me hod is named as GAl.
Undoped goe hi e pa icles (sample G), we e coa ed wi h aluminium
hyd ous oxide laye s. The coa ing p ocess in ol ed i s he dissolu ion
o he desi ed amoun o Al(NO3)3 in 150 ml o double dis illed wa e
and he addi ion o a 10% NaOH aqueous solu ion o each a pH o 12.5.
The goe hi e pa icles (150 mg) we e homogeneously suspended in his
solu ion using an ul asonic ba h and, inally, he pH was lowe ed o
8.5 by he slow addi ion o HNO3 (0.5 mol dm-3) in o he slu y (7). The
sample syn hesized by his me hod is named as G(Al).
All p ecipi a es we e cen i uged and washed se e al imes wi h
deionised wa e o pu i ica ion. Finally, he powde ed solids we e
collec ed by il a ion and d ied a 50ºC be o e analyses.
2.2. The mal Reduc ion
To ob ain he inal me al pa icles, he goe hi e samples (~60
mg) we e dehyd a ed by hea ing in ai o 4 h yielding hema i e
which was hen educed, a cons an empe a u e in a hyd ogen
(99.9999%) s eam ( low a e = 20 l h-1) o 4 h. Dehyd oxyla ion and
educ ion empe a u es we e op imised in each case o ge comple e
educ ion, as well as o minimise pa icle sin e ing. A e educ ion,
he samples we e cooled down o oom empe a u e, unde he
hyd ogen a mosphe e, and, inally, passi a ed by exposing hem o
alcohol apou s o 1 hou , which we e gene a ed by bubbling N2 gas
(99.999%) a cons an low a e (40 dm3h-1) in o a lask con aining pu e
e hanol (99.8%). Me al samples p epa ed a e educ ion o G, GAl and
G(Al) powde s a e named as Fe, FeAl and Fe(Al) espec i ely.
2.3. Cha ac e isa ion Techniques
T ansmission Elec on Mic oscopy (TEM, Philips 200 CM)
was used o examine he mo phology o he pa icles. The pa icle
size dis ibu ion o he powde s was e alua ed om he elec on
mic og aphs by coun ing a ound one hund ed pa icles. F om hese
da a, he deg ee o polydispe si y, de ined as he s anda d de ia ion
(SD)/mean size (8), was e alua ed. The mean and he SD alues
associa ed wi h he axial a io (L/W) we e e alua ed om he L/W
a ios ob ained o each pa icle.
Phase iden i ica ion was ca ied ou by X- ay di ac ion (XRD) in a
Siemens D501 appa a us using CuKα adia ion and a di ac ed beam
g aphi e monoch oma o . An es ima ion o he c ys alli e size was
de e mined om he ull wid h a hal maximum o he XRD selec ed
e lec ion by using he Sche e equa ion (9). Di e en ial he mal
(DTA) and he mog a ime ic analyses (TGA) (Seiko, EXSTAR 6000)
we e ca ied ou in ai a a hea ing a e o 10ºC min-1.
The quan i a i e composi ion o he samples in e ms o he Al
and Fe con en s was de e mined by X- ay luo escence (XRF, Siemens
SRS 3000). Ene gy dispe si e X- ay analysis (EDX, Philips DX4),
ins alled in he TEM mic oscope, was also used o gain in o ma ion
on he homogenei y o he pa icles composi ion. The a ia ion o he
aluminium and i on concen a ions in he pa icle ou e laye s du ing
he ans o ma ion om goe hi e o hema i e, and inally o i on was
ob ained om he X-Ray Pho oelec on spec a (XPS), eco ded in a
VG Escalab 220 using he MgKα exci a ion sou ce. Calib a ion o he
binding ene gy scale o he spec a was done a he C1s peak o he
su ace ca bon con amina ion aken a 284.6 eV. A omic pe cen ages
o he elemen s we e calcula ed om he peaks a eas a e backg ound
sub ac ion (Shi ley backg ound). The a eas we e e e ed o he
sensi i i y ac o s o he elemen s as supplied by he ins umen
manu ac u es.
Tempe a u e p og ammed educ ion (TPR) expe imen s we e
pe o med in a con en ional appa a us connec ed o a compu e o
da a s o ing and p ocessing, using a he mal conduc i i y de ec o ,
(TCD) calib a ed using di e en amoun s o CuO, as p e iously
desc ibed (10). The eac i e gas (5% H2 in A , low a e = 50 cm3 min-1)
was passed h ough 5 mg o sample, which was hea ed up o 600ºC a
a cons an hea ing a e o 5ºC min-1.
Magne ic cha ac e iza ion o he samples was ca ied ou in
a ib a ing sample magne ome e (MLVSM9 MagLab 9 T, Ox o d
Ins umen ). Magne iza ion cu es we e eco ded a oom empe a u e
by i s sa u a ing he sample in a ield o 3 T; hen, he sa u a ion
magne iza ion (Ms), he squa eness (M /Ms, whe e M is he emanen
magne iza ion) and he coe ci i y (Hc) we e de e mined o each
sample. The Ms alues we e e alua ed by ex apola ing o in ini e ield
he expe imen al esul s ob ained in he high ield ange whe e he
magne iza ion linea ly inc eases wi h 1/H.
3. RESULTS AND DISCUSSION
3.1. P ecu so s P epa a ion
Uni o m goe hi e pa icles (Fig. 1) o 118 nm in leng h wi h axial
a io o 5 (Table I) we e ob ained ollowing he me hod desc ibed
in expe imen al sec ion (Sample G). Unde he same condi ions,
he addi ion o Al ca ions up o a Al/Fe+Al mole a io = 5%
(Sample GAl) yielded single phase goe hi e pa icles (Fig. 1) wi h
an aluminium con en simila o ha ini ially added (Table I). The
p esence o aluminium yielded sho e pa icles (62 nm in leng h)
ha he undoped ones, keeping simila pa icle wid h, and b oade
size dis ibu ion (Table I). These mo phological changes ha e been
a ibu ed o isomo phous subs i u ion o Al3+ o Fe3+ in he goe hi e
s uc u e (11). I has been al eady epo ed ha he Al ca ions we e
mainly concen a ed in he pa icle ou e laye s in spi e o being in he
eac ion medium om he beginning o he goe hi e p epa a ion (6).
Table I.- ComposITIon and mo phologICal Cha aCTe IsTICs (lengTh,
wIdTh and axIal aTIo) obse ed o goeThITe p eCu so s (The ela-
TI e sTanda d de IaTIons a e InCluded In pa enThesIs).
Mo phological Cha ac e is ics Al/Fe+Al mole a io
Sample Leng h
(nm)
Wid h
(nm)
Axial
Ra io
Nominal
(%)
XRF
(%)
XPS
(%)
G118 (20) 24 (29) 5 (30) - - -
GAl 62 (28) 23 (33) 3 (33) 5 5 17
G(Al) 118 (20) 24 (29) 5 (30) 5 5 80
Goe hi e pa icles we e also coa ed wi h uni o m laye s o an
aluminium hyd ous oxide using an Al/Al+Fe a io simila o ha o
he doped sample (Al/Fe+Al mole a io = 5%). As i can be seen in
he TEM images (Fig. 1), only acicula pa icles we e p esen in he
coa ed sample, sugges ing ha all p ecipi a ed aluminium hyd ous
oxide was deposi ed on he su ace o goe hi e pa icles. The amoun
o aluminium inco po a ed on he goe hi e su ace was con i med o
be simila o ha ini ially added (Table I) and EDX analyses con i med
he p esence o Al in all analysed pa icles. Finally, XPS spec oscopy
ACICULAR IRON NANOPARTICLES PROTECTED AgAINST SINTERINg wITh ALUMINIUM OxIDE
Bol. soc. esp. Ce am. V., 43 [4] 796-800 (2004)
798
showed a mo e impo an en ichmen o Al (Al/Fe+Al mole a io =
80%) in he pa icle ou e laye s in compa ison wi h he Al(III)-doped
goe hi e sample (17% mole), which is as i should be expec ed om he
coa ing p ocedu e (Table I).
A sligh inc ease in he he mal s abili y o he goe hi es p epa ed
in he p esence o aluminium wi h espec o he Al- ee goe hi es
was de ec ed by TG and DTA analyses as illus a ed o he coa ed
sample (Fig. 2). As obse ed, he s ong endo he mic peak, which is
due o he con e sion o goe hi e o hema i e, was displaced om
250ºC o sample G o 257ºC o sample G(Al). This highe empe a u e
o dehyd oxyla ion can be a ibu ed o he en ichmen o aluminium
in he pa icle ou e laye s since i could hampe he anspo o he
eleased wa e (12).
3.2. I on Me allic Pa icles
3.2.1. THERMAL REDUCTION OF SAMPLES
The goe hi e pa icles we e ans o med o me allic i on in wo
s eps, aiming o educe in e nal po osi y and a oid u he al e a ions
o he pa icle mo phology (1). Fi s , he goe hi e pa icles we e
ans o med o hema i e by hea ing up o maximum empe a u e so
ha he pa icle mo phology emained una ec ed in he unp o ec ed
sample (300ºC). The so-ob ained hema i e samples we e hen educed
o me al i on, o which he educ ion empe a u e was also op imized
in o de o minimize he possible pa icle mo phology al e a ion du ing
his ea men . Fo his pu pose, empe a u e p og ammed educ ion
(TPR) expe imen s we e ca ied ou . The TPR p o iles o he undoped
goe hi e samples (Fig. 3) clea ly showed ha he educ ion p ocess
ook place unde he non-iso he mal condi ions, om 250ºC o 550ºC
in wo well- esol ed educ ion s eps. The hyd ogen up akes ob ained
Figu e 1.- TEM images o goe hi e (G), Al(III)-doped goe hi e (GAl)
and Al(III)-coa ed goe hi e (G(Al)) samples and he co esponding i on
pa icles ob ained a e educ ion (Fe, FeAl and Fe(Al) samples).
Figu e 2.-TG and DTA analyses o goe hi e (G) and Al-coa ed goe hi-
e (G(Al)) samples.
Figu e 3.- TPR p o iles o he hema i e samples ob ained by hea ing
a 300ºC he undoped (G), Al(III)-doped (GAl) and Al(III)-coa ed (G(Al))
goe hi e p ecu so s.
R. POzAS, M. P. MORAALES, C.J. SERNA, M. OCAÑA
Bol. soc. esp. Ce am. V., 43 [4] 796-800 (2004)
799
by nume ical in eg a ion o he peaks a eas indica ed ha he i s
s ep (~340 ºC) was due o he ans o ma ion o hema i e o magne i e
(Fe3O4), whe eas he second one (~470 ºC), was due o he magne i e-
me al i on educ ion. Finally, he TPR p o iles also sugges ed ha he
p esence o aluminium ca ions in he hema i e p ecu so s (ei he in he
doped o coa ed samples) e a ds he educ ion p ocess (Fig. 3). In ac ,
an iso he mal ea men a 600 ºC was u he equi ed in bo h cases o
comple e he educ ion eac ion (Fig. 3). I has been epo ed ha he
educ ion a e o i on is mos ly con olled by he emo al o wa e (13).
The e o e, i seems ha he p esence o Al ions a he pa icle su ace
hampe he anspo o wa e , needing highe educ ion empe a u es
o i s o al elease. Fig. 3 also shows ha he only app eciable di e ence
in he educ ion beha iou be ween he doped (GAl) and coa ed (G(Al))
samples is ha he i s educ ion s ep (Fe3O4 o ma ion) akes place a
lowe empe a u e o he o me .
In iew o hese esul s, he hema i e samples we e educed unde
he iso he mal condi ions desc ibed in he expe imen al sec ion, a
inc easing empe a u es s a ing om 250ºC o ind he minimum
empe a u e equi ed o comple e educ ion which, as expec ed, was
highe o bo h Al-doped and Al-coa ed samples (400ºC) han ha o
he unp o ec ed one (325ºC).
X- ay di ac ion pa e ns o all he samples educed a he abo e
empe a u es a e shown in Fig. 4. Samples Fe and Fe(Al) display a
simila pa e n wi h di ac ion peaks only due o α-Fe. Howe e , in
addi ion o he main di ac ion peaks due o α-Fe, sample FeAl shows
a b oad and e y weak peak a ound 35º (2θ), which could be due o he
p esence o small c ys alli es o an i on oxide wi h a spinel s uc u e
(14). This oxide could be o med du ing he passi a ion p ocess ca ied
ou o s abilize he pa icles. The highe amoun o oxide in his sample
could be due o i s smalle pa icle size (Fig. 1), and he e o e highe
su ace a ea. The c ys al size measu ed om he (100) e lec ion o i on
was obse ed o dec ease o he Al(III)-p o ec ed me al samples (Table
II). These da a sugges ha he p esence o aluminium minimises he
g ow h o i on c ys als du ing he he mal educ ion p ocess, and
clea ly e idence i s ole in p e en ing sin e ing.
Table II.- magneTIC p ope TIes (Ms = saTu aTIon magneTIzaTIon, Hc =
Coe CI ITy, M = emanenT magneTIzaTIon and M /Ms = squa eness)
and C ysTal sIze obTaIned o I on (Fe), al-doped I on (FeAl) and Al-
CoaTed I on (Fe(Al)) samples.
Sample Reduc ion
Tempe a u e (ºC)
C ys al Size
(nm)
Hc
(Oe)
Ms
(emu/g) M /Ms
Fe 325 200 110 205 0.05
FeAl 400 30 920 125 0.5
Fe(Al) 400 35 1050 120 0.4
Me al pa icles ob ained om he goe hi e samples show di e en
mo phological cha ac e is ics. Thus, in he absence o aluminium
(sample Fe), he pa icles sin e ed du ing he educ ion p ocess
losing he elonga ed shape (Fig. 1), which is in acco dance wi h he
highe c ys al size measu ed o his sample (Table II). Howe e , his
p ocess ook place in a lesse ex ension o he FeAl and Fe(Al) samples,
in which mo e elonga ed pa icles emained, especially in he case
o sample Fe(Al) (Fig. 1). I is clea ha in his sample, he aluminium
oxide coa ing is he esponsible o p e en ing sin e ing. Fo a
be e unde s anding o he beha iou obse ed o sample FeAl, he
a ia ion o he Al(Fe+Al) a io a he pa icle ou e laye s du ing he
ans o ma ion om goe hi e o hema i e and hen, o me al i on, was
ollowed by XPS inding ha he mola pe cen age o Al(III) inc eases
om 18% (goe hi e) o 36 % (i on) (Fig. 5). Thus, he e is a u he
clea Al en ichmen in he pa icle ou e laye s du ing educ ion,
which explains he absence o a signi ican sin e ing obse ed o
his sample, in which hese ca ions we e in oduced in o he goe hi e
p ecu so du ing i s syn hesis (6). This en ichmen was highe o he
Al(III)-coa ed pa icles ( om 80% o goe hi e, o 95% o i on) (Fig. 5),
which would explain he be e acicula mo phology obse ed o his
sample (Fig. 1). I should be no ed ha he posi ion o he Fe2p3/2 peak
obse ed in he XPS spec a (710.1 eV) (da a no shown) was consis en
wi h he p esence o he abo e men ioned oxidized i on in he pa icle
ou e laye s, which seems o be consis o a e imagne ic oxide simila
o Al(III)-doped maghemi e, as i has been sugges ed om Mössbaue
s udies ca ied ou on he FeAl sample (6).
Figu e 4.- X-Ray di ac ion pa e ns o samples Fe, FeAl and Fe(Al)
me al samples.
Figu e 5.- Va ia ion o he aluminium concen a ion in he pa icle
ou e laye s ob ained om XPS spec a du ing he ans o ma ion
om goe hi e o hema i e and inally o me al i on o Al-doped
goe hi e (GAl) and Al-coa ed goe hi e (G(Al)) samples.
ACICULAR IRON NANOPARTICLES PROTECTED AgAINST SINTERINg wITh ALUMINIUM OxIDE
Bol. soc. esp. Ce am. V., 43 [4] 796-800 (2004)
800
3.2.2.
MAGNETIC PROPERTIES OF IRON NANOPARTICLES
The magne ic pa ame e s ob ained om he magne iza ion cu es
ep esen ed in Fig. 6 a e summa ized in Table II. All alues ob ained
o sa u a ion magne iza ion (Ms) a e lowe han i is expec ed o bulk
Fe (~220 emu/g) (15), due o he p esence o i on oxide on he pa icle
su ace esul ing om passi a ion (6). The la ges Ms alues ob ained
o he Fe sample when compa ed wi h he Al(III)-p o ec ed samples,
can be explained by he highe c ys al size o he o me , which
he e o e in ol ed a lowe ela i e oxide amoun in he passi a ion
laye , and ob iously by he p esence o non-magne ic aluminium
oxide on he pa icle su ace in he p o ec ed samples (16).
I should be no ed ha he inc ease in he M /Ms (Squa eness)
alues obse ed o he Al(III)-p o ec ed pa icles ( om 0.05 o sample
Fe o 0.4 and 0.5 o samples Fe(Al) and FeAl, espec i ely) sugges s a
change om a mul idomain beha iou o he Al(III)- ee samples o
a monodomain beha iou o Al(III)-p o ec ed samples, acco ding o
he dec ease in he Fe c ys al size obse ed by X- ay di ac ion om
200 o 30-35 nm (Table II) (17).
The inco po a ion o aluminium ca ions o he p ecu so pa icles
ei he by doping o coa ing, also had posi i e e ec s on he coe ci i y
(Hc) o he inal me al samples (Table II). Thus, he coe ci i y inc eases
om 110 Oe o he unp o ec ed sample (Fe) o 920 and 1050 o
samples FeAl and Fe(Al), espec i ely. This inc ease seems o be due o
he minimisa ion o sin e ing, p ese ing he acicula mo phology o
he pa icles, since i is well known he main ac o ha con ibu es
o he inc ease o coe ci i y in hese ma e ials is shape aniso opy.
Sligh ly highe Hc alue (1050 Oe), was ound o he sample p o ec ed
by coa ing (Fe(Al) sample), indica ing ha his p o ec ing p ocedu e
is sligh ly mo e e ec i e o p oduce i on me al pa icles wi h be e
magne ic p ope ies.
4. CONCLUSIONS
Bo h p o ec ing me hods o goe hi e pa icles, Al(III)-doping and
Al(III)-coa ing, d i e o an Al-en ichmen on he goe hi e pa icles
su ace, which is inc eased du ing he ans o ma ion o i on. This
en ichmen minimises he g ow h o i on c ys als and be e p ese es
he acicula shape in he inal i on pa icles, which has a a ou able
e ec on he squa eness and coe ci i y o bo h me al samples. This
beha iou indica es he e ec i eness o bo h me hod o p o ec he
acicula i on nanopa icles agains sin e ing and he e o e o ob ain
ma e ials wi h imp o ed magne ic p ope ies. Ne e heless, he
coa ing p ocedu e seems o be sligh ly mo e e ec i e gi ing ise o he
i on pa icles wi h he la ges coe ci i y.
ACkNOWLEDGMENTS
This wo k was suppo ed by he Spanish CICYT unde p ojec s
MAT2002-04001-C02 and MAT2003-01479. The ellowship o R. Pozas
om he Spanish Minis e io de Ciencia y Tecnología is g a e ully
acknowledged.
Figu e 6.- Magne iza ion cu es a oom empe a u e o samples Fe,
FeAl and Fe(Al) me al pa icles ob ained by he mal educ ion o he
goe hi e p ecu so s.
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