ROLE OF STARCH CHARACTERISTICS IN THE
PROPERTIES OF LOW-COST CERAMIC MEMBRANES
M-M. Lo en e-Ayza
a
, M. J. O s
a
, V. Pé ez-He anz
b
, S. Mes e
a,*
.
a
Ins i u o de Tecnología Ce ámica. Uni e si a Jaume I. Cas ellón (Spain).
b
IEC G oup, Uni e si a Poli ècnica de València (Spain).
*Co esponding Au ho ([email p o ec ed])
Abs ac
S a ch is used as po osi y gene a o in memb anes and o he po ous ce amics. The e a e
di e en p o ide s ha o e a wide a ie y o s a ches, which p oduce dis inc po e size
dis ibu ions. A s udy was conduc ed o e alua e he e ec s o he cha ac e is ics o
s a ches (impu i ies, pa icle size), ob ained om po a o, pea, maize and whea , on he
p ope ies o mic o il a ion memb anes o mula ed wi h adi ional aw ma e ials ( he
ce amic ma ix was composed o qua z, albi e and mulli e). The esul s indica ed ha
he po e size dis ibu ion and he pe meabili y coe icien o he memb ane can be
con olled modi ying only he pa icle size o s a ch. In his way, co ela ions we e
ob ained be ween su ace mean diame e o s a ch and memb ane p ope ies
(cha ac e is ic po e diame e s d
16
and d
50
, and pe meabili y coe icien ). Mo eo e , i is
necessa y o use a s a ch ha ing a mean pa icle size g ea e han abou 50 mic ons in
o de o ob ain a signi ican change in he po e size dis ibu ion and an inc ease in he
pe meabili y o he memb ane.
Keywo ds: memb ane, po osi y, pe meabili y, s a ch, pa icle size.
1 In oduc ion
Ce amic po ous ma e ials ha e been a subjec o esea ch due o hei po en ial
applica ions in di e en ypes o memb anes, as well as in o he ields as ca alys
suppo s
1
, acous ic o he mal insula o s
2
, and bioma e ials
3
among o he s.
The syn hesis o po ous ce amics equen ly includes a subs ance which disappea s
du ing he he mal ea men o sin e ing (by decomposi ion, e apo a ion, mel ing o
bu ning
4
), gene a ing an addi ional ne wo k o po es ha modi y he memb ane po e
size dis ibu ion ha could be ob ained wi h he ce amic composi ion by i sel . As
examples, he mel ing and e apo a ion o poly(me hylme ac yla e) desc ibed by Zeng e
al.
5
, he decomposi ion o u ea by Vijayan e al.
6
o he bu ning o lou by Slosa czyk
e al.
7
. The ange o ma e ials employed o c ea e po osi y in ce amics is b oad, as he
e iews abou his subjec ha e shown (Che alie e al.
4
).
The addi ion o a empe a u e sensi i e componen in o de o c ea e po osi y in he
suppo is applied in he manu ac u e o memb anes based on ad anced ce amics
(alumina, i ania, zi conia), and also o memb anes based on adi ional composi ions
8
o local aw ma e ials (clays
9,10
, pe li e
11
). Nume ous ma e ials ha e been used as po e
gene a o s, s a ing by chemically pu e subs ances (u ea
6
), going h ough p ocessed
subs ances (co n s a ch
11
), and ending in na u al p oduc s (poppy seeds
2
, ice b an
10
), o
e en in was es (sawdus
8
, ly ash
9,12
). S a ches a e b oadly employed as ma e ials o
gene a ing po osi y in ce amics as hey p oduce po es du ing bu ning ou a ound
500ºC
13-15
. In addi ion, hey a e easy o bu n, cheap and en i onmen ally iendly
4
.
Howe e , s a ch, as a subs ance de i ed om na u al sou ces (po a o, pea, co n, whea ,
e c.) and subjec ed o di e en p ocesses o ex ac ion and condi ioning, has a wide
ange o cha ac e is ics ha can a ec he inal p ope ies o he esul ing memb ane.
Usually, in each esea ch abou memb anes only one speci ic ype o s a ch is used as
po e gene a o . The e o e, his speci ic ype o s a ch i is a ixed pa ame e along he
in es iga ion. Howe e , he a ailabili y o di e en ypes o s a ch opens he doo o
modi y he p ope ies o memb anes wi hou changing he aw ma e ial’s p opo ions o
he p ocessing pa ame e s du ing he expe imen s, as shown G ego o a e al.
16
.
One o he mos in e es ing p ope ies o a memb ane is he pe meabili y coe icien ha
is ela ed wi h he geome y o he memb ane’s po e ne wo k. Many models ha e been
p oposed, based on di e en app oxima ions, in o de o ela e he pe meabili y o a
po ous solid wi h he cha ac e is ics o i s own po e ne wo k. Some models a e simple
like he Hagen-Poiseuille o he Kozeni-Ca man equa ions
17
. Howe e , he complexi y
o he model g ows as he desc ip ion o he po e ne wo k geome y became mo e
igo ous (as examples, he applica ion o g ain models
18
o digi ized s uc u e models
19
).
In consequence, he phenomenological app oaches emain o unique use ulness o he
quan i ica ion o memb ane’s inal p ope ies
20
.
This esea ch was ocused on analyzing he e ec s o di e en ypes o s a ches, wi h
dis inc cha ac e is ics, on he p ope ies o low-cos ce amic mic o il a ion
memb anes. The aim was o ex end he ange o memb ane ea u es (po osi y,
pe meabili y), wi hou modi ying he p opo ions o he aw ma e ials o he p ocessing.
Addi ionally, an a emp was made o ela e memb ane’s pe meabili y wi h he pa icle
size o he speci ic ype o s a ch used as po e gene a o h ough a simple model.
2 Expe imen al
The aw ma e ials o he ce amic memb anes we e clay (UA-50, Mine a ia, Spain),
mic onized sodium eldspa (cou esy o Pamesa, S.A. Spain) and eldspa ic sand (AFS-
125, Ime ys, Spain). They we e p opo ioned by weigh in 40:40:20 a ios espec i ely.
As a esul , he global mix u e was app oxima ely 72.0 SiO
2
, 17.6 Al
2
O
3
, 4.2 Na
2
O, 1.5
K
2
O, 0.6 TiO
2
, 0.5 Fe
2
O
3
, 0.3 CaO and 0.2 MgO, wi h a loss on igni ion o 2.9 (w %).
Six di e en s a ches we e selec ed as po e gene a o s: S1 (po a o s a ch, Roque e
F e es S.A., F ance), S2 (po a o s a ch, Sigma-Ald ich Co. USA), S3 (whea s a ch,
Roque e F e es S.A., F ance), S4 (pea s a ch, Roque e F e es S.A., F ance), S5 (pea
ibe L50M, Roque e F e es S.A., F ance), and S6 (maize s a ch ex a pu e, Fishe
Chemical, USA). The abo e aw ma e ials we e p ocessed as ecei ed, in powde y
s a e. In addi ion, a supplemen a y po e gene a o was p epa ed by sie ing he S6 s a ch
h ough a 200 mic ons mesh ha was named S7.
The pa icle size dis ibu ion o he s a ches was ob ained by d y lase di ac ion
(mas e size 2000, Ma e n Ins umen s L d. UK) and he cha ac e is ic diame e s D
10
,
D
50
, D
90
, D
V
and D
S
we e calcula ed. The pa ame e s D
90
, D
50
and D
10
a e he cu o
pa icle size below which 90%, 50% and 10% o he o al pa icle olume lies. The
pa ame e s D
V
and D
S
a e espec i ely he olume mean diame e and he su ace mean
diame e . The humidi y was ob ained om he weigh loss a e d ying a 110 ºC in an
elec ical o en (kg o wa e by 100 kg o d y solid). The ue densi y o he d ied
s a ches was measu ed by helium pycnome y (Ul apycnome e 1000, Quan ach ome
Inc., USA.) and he ash con en was de e mined by ea ing e e y s a ch a 1000 °C.
Finally, he chemical analysis o he ashes was pe o med by EDX (Genesis 7000
SUTW, EDAX, USA), connec ed o a FEG-SEM (Quan a 200F, FEI Co, USA).
The ce amic aw ma e ials we e p opo ioned by weigh and hen d y mixed in a blade
mill (Mul i io, Moulinex In e na ional, F ance). Once homogenized, he chosen s a ch
was added g adually o he blade mill o a oid he o ma ion o la ge agglome a es. All
expe imen s we e pe o med using mix u es calcula ed o con ain 85 w % o ce amic
ma e ial and 15 w % o d y s a ch (Table 1), excep he e e ence mix u e wi hou s a ch
(whose ue densi y was measu ed by helium pycnome y). The olume ac ion o
s a ch was be ween 23 % and 25 % in all he aw ma e ial mix u es, and he e o e
beyond he pe cola ion h eshold o 18 % indica ed by G ego o á e al
21
.
The eigh mix u es we e mois ened up o a wa e con en o 5.5 kg H
2
O/100 kg d y
solid. Cylind ical es specimens o 50 mm diame e and 3-4 mm hickness we e o med
by uniaxial d y p essing a 300 kg·cm
-2
and d ied in an o en a 110 ºC no less han 24
hou s. The bulk densi y o he g een samples, and la e o he sin e ed ones, was
measu ed by me cu y displacemen .
The g een specimens we e sin e ed in wo s eps ( igu e 1). Ini ially, he s a ch was
oxidised in a mu le u nace wi h a slow ea men cha ac e ised by a maximum
empe a u e o 500 ºC and a soaking ime o 1 hou (K60L, Nanne i Spa. I aly). Finally,
he specimens we e sin e ed in a as elec ic kiln (pi ome ol S.A. Spain). This las
he mal s ep was designed o balance he po osi y and mechanical s eng h in he
sin e ed memb anes, and was cha ac e ized by a soaking ime o 1 hou a 1100 ºC.
The po e size dis ibu ion o he memb anes was measu ed by me cu y in usion
po osime y (Au oPo e IV 9500, Mic ome i ics Ins umen s Co, USA), and he open
olume o po es and cha ac e is ic po e diame e s (d
16
, d
50
, and d
84
), we e calcula ed.
The wa e up ake was measu ed by he boiling wa e imme sion me hod and he
pe meabili y coe icien o wa e was ob ained wi h a liquid pe meame e (LEP101-A,
PMI, USA). Addi ionally, he ue densi y o he memb anes was measu ed by helium
pycnome y o milled samples, he mine alogical composi ion was ob ained by XRD
(D8 Ad ance, B uke Co, USA), and he mic os uc u e o some memb anes was
analyzed by FEG-SEM.

3 Resul s and discussion
3.1 Cha ac e iza ion o s a ches
The humidi y o he s a ches co e ed a ai ly wide ange (Table 2). In h ee o hem,
humidi y was a ound 15 w %, while in o he was clea ly abo e, and in he wo
emaining, humidi y was below. The ue densi y o he s a ches S1, S2, S3, S4 and S5
was almos he same conside ing he unce ain y o measu emen (Table 2), while his
physical magni ude was signi ican ly lowe o s a ch S6. In spi e o hese di e ences,
he p ocessing o he aw ma e ial mix u es was accomplished as in he C0 composi ion.
The ash con en o he s a ches was less han 1 w %, excep in he case o S5 which was
ma kedly highe (Table 3), possibly due o i s own p oduc ion p ocess, which
inco po a es g ea e p opo ion o impu i ies. By con as , S2, S3 and S4 s a ches s and
ou o i s low ash con en . The ash con en combined wi h EDX analysis p o ided he
ype and con en o impu i ies. The esul s indica ed ha he s a ch S5 con ains he
g ea es amoun o impu i ies, ollowed by he s a ch S6 a a g ea dis ance. By con as ,
s a ch S2 con ained he lowes amoun o impu i ies. The elemen s ounded in g ea e
p opo ions in he ashes we e po assium, sodium, phospho us and calcium. These
elemen s could ac as luxes du ing he sin e ing o samples.
Pa icle size dis ibu ions o s a ches co e ed a a he b oad ange (Figu e 2). The ines
s a ches we e S3 and S4, he coa ses we e S5, S7 and S6, while pa icle size
dis ibu ions o S1 and S2 occupied an in e media e posi ion. The shape o he pa icle
size dis ibu ions was symme ical, excep o S5, S6 and S7, which possessed a ail in
he in e al o lowe diame e s. The cha ac e is ic diame e s indica ed ha he se en
selec ed s a ches spanned an o de o magni ude in pa icle diame e , aken as D
50
(Table 4). F om hese esul s, i can be in e ed ha s a ch S3 should gene a e po es
wi h diame e app oxima ely one en h o s a ch S6. Va ious op ions exis ed o D
50
alues less han hal o he co esponding o S6 s a ch, bu a gap in D
50
alues was
de ec ed be ween he ob ained o S6 sample and he ollowing comme cial s a ch in
size (S5). In o de o co e his gap in D
50
alues, he s a ch S7 was p epa ed.
3.2 Memb ane cha ac e is ics
The ue densi y o s a ches and he mix u e o ce amic aw ma e ials (2.64±0.02 g·cm
-
3
), plus he da a o bulk densi y o he g een memb anes allowed he es ima ion o hei
po osi y (ε
G
) (Figu e 3). The addi ion o s a ch causes a educ ion in he bulk densi y o
he g een memb ane. This is he esul o lowe ue densi y o s a ch, oge he wi h he
smalle compac ion du ing p essing, as he po osi y inc eases espec o he alue
co esponding o composi ion C0. In addi ion, s a ches’ ue densi y da a allowed o
discoun he olume occupied by e e y s a ch in he g een memb anes simula ing hei
s a e once he oxida ion s ep o he he mal cycle has inished (ε
GT
in Figu e 3). I was
ound ha ε
GT
was p ac ically independen o he s a ch employed. Acco dingly, he
po osi y o he memb anes a he s a o he sin e ing s ep was nea ly he same o all
composi ions excep C0. This ac acili a ed he assessmen o he e ec s o s a ch’s
cha ac e is ics on he p ope ies o memb anes.
A e sin e ing, memb anes we e ob ained ee o de ec s and wi h su icien s eng h o
pe o m cha ac e iza ion es s. I should be men ioned ha o he me hods o p epa ing
he mix u e o aw ma e ials caused de ec s in he memb anes and hus we e disca ded
(speci ically, we mixing and g anula ion we e in es iga ed). The sin e ed memb anes
we e composed by qua z, albi e and mulli e (Figu e 4), and showed a b oade ange o
bulk densi ies han ha o he g een ones, which indica ed ha he e ec s o he oids
le by s a ches du ing sin e ing had been di e en (Figu e 5). The po osi y and
densi ica ion (de ined as he change o po osi y o he specimen as a consequence o
sin e ing, di ided by i s ini ial po osi y
22
) o syn hesized specimens we e calcula ed
om he measu ed ue densi y o he sin e ed memb anes (2.59±0.02 g·cm
-3
). The
esul s indica ed ha he addi ion o s a ches inc eased po osi y and educed
densi ica ion in ela ion o he e e ence composi ion C0, bu di e ences exis ed
depending on added s a ch. The eby, he e is an app oxima ely linea ela ionship wi h
nega i e slope be ween densi ica ion and he pa icle size o s a ch ( aken as D
50
, Figu e
6), which is consis en wi h he inc eased di icul y in emo ing he la ges po es du ing
sin e ing. On he o he hand, he impu i y con en o he s a ches did no seem o exe a
signi ican e ec on sin e ing, which is consis en wi h he high p opo ion o luxes
p o ided by he aw ma e ials, bu i could be an impo an ac o o memb anes based
on high-pu i y oxides. In addi ion, SEM images ( igu e 7) showed ha he
mic os uc u e o he suppo s conside ably changed depending on he speci ic added
s a ch. As an example, he S2 s a ch (D
50
nea he lowe limi o he ange explo ed)
gene a ed abundan ounded po es, and appa en ly wi h li le di ec in e connec ions
(black a eas in he image), while he coa ses s a ch S6 p oduced bigge po es, bu less
egula and appa en ly in e connec ed by openings o highe a ea.
The o al po e olume, calcula ed om he bulk densi y o he ce amic ma ix and he
ue densi y o he memb anes, showed a e y good co ela ion wi h he wa e up ake
(Figu e 8). The alue o he slope, e y close o 0.01, indica es ha p ac ically all he
po osi y o he memb anes was open. By con as , me cu y in usion po osime y
always esul ed in lowe alues o he open olume o po es, indica ing ha a ac ion o
he open po osi y was below he de ec ion limi o he equipmen used (0.005 mic ons).
This ac ion o he open po osi y was also a unc ion o he added s a ch. Ob iously,
he employed s a ch a ec s he po e size dis ibu ion o he memb ane modi ying,
among o he ea u es, he ac ion o po es whose inle is below he limi achie able by
me cu y in usion. B oadly, he ine s a ches end o inc ease he ac ion o po es
unde ec able by me cu y in usion, bu a di ec co ela ion has no been iden i ied,
sugges ing ha he mixing p ocess can a ec o some ex en he po e size dis ibu ion
gene a ed in he sin e ed memb ane.
Memb ane’s po e size dis ibu ion showed bigge di e ences han hose o po osi y as a
consequence o he e ec o he s a ch (Table 5 and Figu e 9). In gene al, he
monomodal dis ibu ion o e e ence memb ane C0 shi ed o la ge diame e s and
showed a end o become bimodal o he memb anes syn hesized employing s a ch.
This end culmina es in memb anes C6 and C7, whose po e size dis ibu ion is
bimodal. Despi e his clea end, a di ec co ela ion was no de ec ed be ween pa icle
size dis ibu ion o he employed s a ch and po e size dis ibu ion gene a ed in he
memb ane. I p obably was due o di e ences in he physical basis o each measu emen
(ligh di ac ion o pa icle size and me cu y in usion o po e size, and in his me hod
he measu ed diame e co esponds o he po e inle and no he eal diame e o he
po e). Howe e , some co ela ions we e iden i ied be ween he cha ac e is ic diame e s
o pa icle and po e, which could be used o es ima e he a e age po e size ha a
pa icula s a ch could gene a e in he memb ane. Speci ically, he bes esul s we e
ob ained by ela ing D
S
and po e diame e s d
16
o d
84
wi h a quad a ic polynomial
(Figu e 10). In addi ion, he D
50
diame e o s a ches also showed a quad a ic ela ion
wi h he same cha ac e is ic po e diame e s, bu wi h sligh ly lowe eg ession
coe icien s ( hey we e no included by his eason). This pa abolic end means ha o
gene a e la ge po es in he memb ane, o mo e co ec ly la ge po es whose inle is also
la ge, i is necessa y o use s a ches wi h la ge pa icle size ( o example, a s a ch wi h a
D
S
o 60 mic ons would be equi ed o gene a e a memb ane wi h a d
50
o 5 mic ons).
Howe e , he a e age pa icle size o mos comme cial s a ches is less han 40 mic ons,
Table 3: Ash and impu i y con en s o he s a ches.
Impu i ies (mg/kg o d y s a ch) S a ch Ash
con en
(w %)
Na K Mg Ca Zn P Cl Cu Si Al
S1
S2
S3
S4
S5
S6
0.71
0.17
0.37
0.29
3.53
0.83
7
9
52
74
368
274
48
37
28
46
1198
14
12
3
3
4
119
5
100
6
15
6
207
17
9
2
10
1
0
23
145
38
74
24
108
38
-
-
-
-
41
38
12
2
15
2
-
26
2
1
1
3
9
2
-
-
-
-
3
-
Table 4: Pa ame e s o pa icle size dis ibu ions o he s a ches.
S a ch D
10
(µm)
D
50
(µm)
D
90
(µm)
D
V
(µm)
D
S
(µm)
S1
S2
S3
S4
S5
S6
S7
26
22
12
17
16
57
43
46
39
20
24
75
190
145
76
67
31
34
184
393
274
49
42
21
25
90
211
154
41
35
18
23
35
95
79

Table 5: Po e size dis ibu ion pa ame e s, wa e up ake and pe meabili y coe icien o memb anes.
Re . d
16
(µm)
d
50
(µm)
d
84
(µm)
Wa e up ake
(%)
K
P
·10
16
(m
2
)
C0
C1
C2
C3
C4
C5
C6
C7
1.5
6.3
6.1
4.4
4.7
6.4
17.6
13.2
1.2
3.7
3.6
3.2
2.9
3.8
9.5
7.2
0.8
1.6
1.6
1.3
1.5
1.8
2.5
2.1
8.4
23.9
22.4
24.4
23.4
24.2
28.9
26.3
≈ 0
1.6 ± 0.4
1.4 ± 0.2
2.29 ± 0.10
1.67 ± 0.12
2.55 ± 0.16
23 ± 2
13.8 ± 1.4
Figu e 1: The mal ea men employed o oxidizing he s a ch and sin e ing he
memb anes.
Figu e 2: S a ches’ pa icle size dis ibu ions.
Figu e 3: Measu ed bulk densi y (ρ
G
) and po osi y (ε
G
) o g een memb anes, and also
calcula ed po osi y excluding he s a ch (ε
GT
).
Figu e 4: Di ac og am o memb ane C0.
Figu e 5: Bulk densi y (ρ
S
) and po osi y (ε
S
) o sin e ed memb anes.
Figu e 6: Rela ion be ween densi ica ion o sin e ed memb anes and D
50
o he
employed s a ch.
Figu e 7: Mic os uc u es o he memb anes ob ained om s a ches S2 and S6.

Figu e 8: Rela ions be ween memb anes’ wa e up ake and he open po e olume
measu ed by me cu y po osime y, and also he calcula ed o al po e olume.
Figu e 9: Di e en ial po e size dis ibu ions o he memb anes.
Figu e 10: Rela ions be ween he cha ac e is ic po e diame e s o he memb anes and
he su ace mean diame e o he employed s a ch.
Figu e 11: Rela ions be ween he pe meabili y coe icien o he memb anes and hei
cha ac e is ic po e diame e s.
Figu e 12: Rela ions be ween he pe meabili y coe icien o he memb anes and wo
cha ac e is ic pa icle diame e s (D
S
and D
50
) o he employed s a ch.