ma e ials
A icle
C ys alliza ion and Quan i ica ion o C ys alline and
Non-C ys alline Phases in Kaolin-Based Co die i es
Ma a Valáško á1,* , Zdenˇek Klika 2, Bo is No osad 3,4 and Bedˇ ich Sme ana 5
1Ins i u e o En i onmen al Technology, VŠB-Technical Uni e si y o Os a a, 17. lis opadu 15,
708 00 Os a a-Po uba, Czech Republic
2Depa men o Chemis y, VŠB-Technical Uni e si y o Os a a, 17. lis opadu 15,
708 00 Os a a-Po uba, Czech Republic; [email p o ec ed]
3Nano echnology Cen e, VŠB-Technical Uni e si y o Os a a, 17. lis opadu 15,
708 00 Os a a-Po uba, Czech Republic; [email p o ec ed]
4Facul y o Elec ical Enginee ing and Compu e Science, VŠB-Technical Uni e si y o Os a a,
17. lis opadu 15, 708 00 Os a a-Po uba, Czech Republic
5Facul y o Ma e ials Science and Technology, VŠB-Technical Uni e si y o Os a a, 17. lis opadu 15,
708 00 Os a a-Po uba, Czech Republic; [email p o ec ed]
*Co espondence: [email p o ec ed]; Tel.: +420-597-327-308
Recei ed: 1 Augus 2019; Accep ed: 19 Sep embe 2019; Published: 23 Sep embe 2019


Abs ac :
Kaolin is mos o en used as adi ional aw ma e ial in ce amic indus y. The pu pose
o he s udy was o ob ain unde s anding o he s uc u al and chemical a iabili y o co die i e
ce amics in luenced by chemical and mine alogical p ope ies o six aw kaolins aken om di e en
locali ies when hey a e applied in ce amics mix u es wi h e miculi e and sin e ed up o 1300
◦
C.
The X- ay di ac ion and simul aneous he mog a ime ic and di e en ial he mal analysis we e used
o iden i y and cha ac e ize c ys alline mine al phases and he cou se o eac ions du ing he hea ing.
The pe cen ages o he c ys alline and non-c ys alline phases we e newly de e mined by ecalcula ion
o he bulk chemical analyses o kaolins and co die i e ce amics using Chemical Quan i a i e Mine al
Analysis (CQMA) me hod. Va ying amoun s o mine als in kaolins: kaolini e om 73.3 o 85.0,
musco i e om 4.2 o 9.9, and qua z om 6.0 o 19.5 (mass %) a ec ed amoun o co die i e/indiali e
om 75.2 o 85.1, ens a i e om 5.8 o 8.9 (when a e calcula ed as hei maximal possible pe cen ages),
and non-c ys alline phases om 8.8 o 15.1 (mass %) in co die i e ce amics. Reg ession analysis
p edic ed high ela ionship be ween quan i y o : (a) kaolini e in kaolins and c ys alline co die i e and
(b) qua z in kaolins and non-c ys alline phases in he ce amics. The mig a ion o po assium om
musco i e in o he co die i e s uc u e, mel ing poin and c ys alliza ion o co die i e/indiali e phases
and po e size a iabili y in ela ion o impu i y o kaolins a e documen ed and discussed.
Keywo ds:
awkaolins; co die i e/indiali e; he malcon e sions; X- aydi ac ion; chemicalquan i a i e
mine al analysis
1. In oduc ion
Co die i e (Mg
2
Al
4
Si
5
O
18
) has he oxide a io composi ion 2:2:5 o 2MgO
·
2Al
2
O
3·
5SiO
2
, and is
one o he phases, which a e p esen in he e na y glass–ce amic sys em MgO–Al
2
O
3
–SiO
2
[
1
].
Co die i e-like c ys als syn hesized below 830
◦
C we e e med
β
o m [
2
]. The
µ
-co die i e was
conside ed as a me as able p oduc c ys allizing om glass a empe a u es below 950
◦
C which
ans o ms i e e sibly upon hea ing o he
α
o m. The low empe a u e o ho hombic o m
is co die i e s able below 1450
◦
C. The high empe a u e hexagonal o m is diso de ed indiali e
s able abo e 1450
◦
C [
3
], which below 1450
◦
C ans o ms slowly o
β
phase [
4
]. The con en ional
me hods o he syn hesis o co die i e ce amics include solid-s a e sin e ing o magnesium, aluminum,
Ma e ials 2019,12, 3104; doi:10.3390/ma12193104 www.mdpi.com/jou nal/ma e ials
Ma e ials 2019,12, 3104 2 o 13
and silicon oxides in he mix u es co esponding o chemical composi ion o co die i e. Addi ion o
nuclea ing agen s (e.g., TiO
2
, Z O
2
, Fe
2
O
3
) e ec i ely inc eases he so ening and dec eases glass
ansi ion empe a u es.
The oxide a io in composi ion o co die i e is economically p oduced om he aw kaolin
con aining kaolini e (Al
2
O
3·
2SiO
2·
2H
2
O), alc (3MgO
·
4SiO
2·
H
2
O) and a co ec ing componen alumina
(Al
2
O
3
). The ac ha he p ope ies o clay mine als used in he mix u e and he condi ions o
p epa a ion in luence sin e ing and p ope ies o ce amic body is widely known. S uc u al p ope ies
o co die i es p epa ed by he solid-s a e eac ion om he mix u es o alc, kaolin, and alumina as
well as om kaolin and e miculi e wi hou u he co ec ing addi i es a 1300
◦
C we e cha ac e ized
in he p e ious wo ks [
5
,
6
]. Raw kaolins con ain kaolini e, musco i e (whi e mica), qua z, and an
admix u e o silica es, mos ly eldspa s, bio i e, and accesso y mine als [
7
]. T ans o ma ion o kaolin
con aining kaolini e, qua z, and musco i e in he empe a u e ange o 980–1121
◦
C p oduced p ima y
mulli e wi h a Si-Al spinel [
8
,
9
]. Impu i ies in kaolins such as musco i e and K- eldspa , con aining
po assium in hei s uc u e, ac as lux ha acili a ed easy mel ing upon i ing and o ma ion o
non-c ys alline glassy phase [
10
–
12
]. Simila ly, Fe-impu i ies suppo ed c ys alliza ion o mulli e [
13
].
In e ac ion be ween kaolini e and musco i e in he empe a u e ange o dehyd oxyla ion o musco i e
be ween 800–900
◦
C was no decla ed [
14
]. The mine als o he mica g oups ans o med a 950
◦
C o
mulli e, K- eldspa and plagioclase [
15
]. A empe a u es below 1000
◦
C, musco i e was eplaced by
alkali eldspa s and qua z was p ese ed e en a 1100
◦
C, while c is obali e was iden i ied only in
qua z- ich clays [11].
The main aim o his wo k was o ob ain an unde s anding o he s uc u al and chemical
a iabili y o co die i e ce amics in luenced by chemical and mine alogical p ope ies o kaolins aken
om di e en locali ies. The e o e, he simple wo-phase ce amic mix u es o kaolin and e miculi e
wi hou co ec ing addi i es we e p epa ed in he mass a io 1:1, close o he oxide a io composi ion
2:2:5 o co die i e 2MgO
·
2Al
2
O
3·
5SiO
2
o he solid s a e eac ion up o 1300
◦
C. X- ay di ac ion and
simul aneous he mog a ime ic and di e en ial he mal analysis we e used o cha ac e ize c ys alline
mine al phases and decomposi ion and c ys alliza ion o phases om he mel . Quan i ica ion o
c ys alline and non-c ys alline phases is newly pe o med based on he elemen al bulk chemical
analysis using he Chemical Quan i a i e Mine al Analysis (CQMA) me hod [16].
2. Ma e ial and Me hods
2.1. Kaolin Samples
The g ani e-de i ed kaolins o he Ka lo y Va y egion and kaolins om K- eldspa - ich
sedimen a y ocks o he Pilsen egion ep esen wo main Czech kaolin deposi s [
17
,
18
]. The
h ee kaolin samples o igina ing om he Ka lo y Va y egion a e om pe sonal collec ion and a e
labeled as Bo (locali y Božiˇcany), Se (locali y Sedlec) and Po (locali y Podboˇ any). Kaolin samples
o igina ing om he Pilsen Basin we e ob ained om LB Mine als, L d., Czech Republic, and a e
labelled as Ka (KKN om locali y Kaznˇejo ), B (locali y Ho n
í
Bˇ
í
za) and Ch (DSF om locali y
Chlumˇcany). All kaolin samples we e subjec ed o sie ing h ough 0.04 mm sie e.
2.2. Kaolin–Ve miculi e Ce amic Mix u es
Ve miculi e om he Pa aiba egion o B azil (Ve ) [
19
] was supplied by G ena, L d., Vesel
í
nad
Lužnic
í
, Czech Republic. Sample (30 g) was milled using aga e plane a y mill F i sch Pul e ise e 5
and hen sie ed o he ac ion <40 µm.
The ce amic kaolin– e miculi e mix u es ma ked as C-Bo, C-Se, C-Po, C-Ka, C-B , and C-Ch
we e p epa ed in hei mass a io o 1:1, homogenized o 1 h (Heidolph Reax o e head shake , REAX
20/4, Me ck, Da ms ad , Ge many), and hen milled o 15 min a 550 pm in aga e plane a y mill
F i sch Pul e ise e 5. Samples we e p epa ed in a po celain combus ion boa and hen sin e ed in an
elec ical labo a o y u nace LH15/13 a he hea ing a es 10
◦
C min
−1
up o 1000
◦
C and 2
◦
C min
−1
o
Ma e ials 2019,12, 3104 3 o 13
1300
◦
C. The samples we e hen le a his empe a u e o 1 h and a e ha slowly cooled o he oom
empe a u e. The ce amic samples we e ma ked iden ically as hei pa en ce amic mix u es.
2.3. Me hods
Elemen al analysis was pe o med using he SPECTRO XEPOS ene gy dispe si e X- ay
luo escence (ED-XRF) spec ome e (Spec o Analy ical Ins umen s, Kle e, Ge many). The esul s
om he XRF analysis we e calcula ed o he s oichiome ic me al oxides concen a ions.
Simul aneous he mog a ime ic (TG) and di e en ial he mal analysis (DTA) o samples
was pe o med in pla inum c ucibles using he expe imen al sys em SETARAM SETSYS 18 TM
TG/DTA/TMA (Lyon, F ance) wi h an “S”- ype measu ing od ( icouple) in a gon a mosphe e (6N) a
a hea ing a e o 10
◦
C min
−1
om 25 o 1300
◦
C. The ansi ion empe a u es de e mined acco ding
DTA wi h an es ima ed e o o ±5◦C.
The X- ay di ac ion (XRD) analysis o c ys alline mine al phases was ca ied ou on he X- ay
di ac ome e Ul ima IV (RIGAKU, Tokyo, Japan). The XRD pa e ns we e eco ded in he 8–60
◦
2
θ
ange (CuK
α
adia ion
λ
=0.15418 nm, a scin illa ion de ec o and a scanning a e o 2
◦
/min
a 40 kV and 40 mA). The po osi y o he d ied ce amic samples was measu ed using a me cu y
in usion po osime e Au oPo e IV 9500 (Mic ome i ics Ins umen Co po a ion, No c oss, GA, USA).
All me hods lis ed he e a e mo e ully desc ibed in he p e ious wo k [6,20].
The Chemical Quan i a i e Mine al Analysis (CQMA) me hod ecalcula es he elemen al bulk
chemical analysis (analy es SiO
2
, Al
2
O
3
, e c.) o he iden i ied mine als in XRD analysis and hei
c ys allochemical o mulas o he analyzed sample. The calcula ion o mine al amoun s is pe o med by
op imiza ion p ocedu es(e.g., he leas squa e and/o non-nega i e leas squa eme hod). Theaddi ional
mo e de ailed in o ma ion as well as ecalcula ion o he quan i a i e con en o mine als de e mined
by o he me hods o hei elemen al bulk chemical analysis has ecen ly been published [16].
3. Resul s
3.1. Kaolin Samples
The chemical composi ions o kaolin samples indica e no pu e kaolini es (Al
2
O
3·
2SiO
2·
2H
2
O)
(Table 1). The XRD pa e ns o kaolins (Figu e 1) showed kaolini e (PDF ca d no. 00-058-2005), musco i e
(PDF ca d no. 01-076-0668), qua z (PDF ca d no. 01-086-2237), and o hoclase (PDF ca d no. 01-075-1592)
in he kaolin sample Ch.
Table 1. ED-XRF analysis o kaolin samples.
Samples Hi 1Bo
0.93
Se
1.08
Po
1.22
Ka
1.57
B
1.59
Ch
1.30
Oxides (mass %)
SiO249.97 49.65 56.25 49.71 50.83 50.45
TiO20.16 0.07 0.38 0.66 0.93 0.72
Al2O334.62 35.17 30.07 34.80 33.61 33.94
Fe2O31.10 0.86 0.72 0.72 0.67 0.72
CaO 0.15 0.12 0.25 0.09 0.01 0.06
MgO 0.22 0.21 0.24 0.21 0.17 0.27
Na2O 0.03 0.03 0.03 0.06 0.08 0.07
K2O 1.18 0.93 0.84 1.21 1.41 1.88
L.O.I. 212.21 12.26 11.15 12.26 12.01 11.63
Sum 99.66 99.30 99.94 99.72 99.72 99.75
1Hinckley index [21]; 2Loss on igni ion a e hea ing a 1000 ◦C o 2 h =H2O+.
Ma e ials 2019,12, 3104 4 o 13
Ma e ials 2019, 12, x FOR PEER REVIEW 4 o 13
Figu e 1. XRD pa e ns o kaolin samples om 5 o 40° 2θ. Peaks o kaolini e (K) a e unlabeled; M—
musco i e, Q—qua z, and O—o hoclase.
The DTA/TG analysis (DTA cu es in Figu e 2) o kaolins hea ed o 1100 °C displayed he mal
e en s occu ing wi hin he empe a u e in e als cha ac e is ic o ans o ma ion o kaolini e and
micas (Table 2).
Table 2. TG/DTA o kaolin samples
Ranges: 1 2 3 4 To al Mass Loss
Kaolin
Sample
Mass
(mg)
ΔT1
(°C)
Δm1
(mg)
ΔT2
(°C)
Δm2
(mg)
T2min
(°C)
ΔT3
(°C)
Δm3
(mg)
ΔT4
(mg)
T4max
(°C)
ΔmTML
(mg) (%)
Bo 20.20 20–175 0.04 410–730 2.36 526 730–946 0.18 963–1031 988 2.58 12.8
Se 21.40 20–160 0.05 403–720 2.41 528 720–946 0.13 959–1041 990 2.59 12.1
Po 18.60 20–185 0.11 440–730 2.04 535 730–932 0.13 955–1041 993 2.28 12.3
Ka 20.90 20–200 0.06 450–725 2.32 535 750–946 0.16 961–1041 997 2.54 12.2
B 19.90 20–170 0.01 430–720 2.19 533 730–931 0.13 972–1051 999 2.33 11.7
Ch 27.90 20–160 0.12 410–715 2.88 534 720–939 0.11 976–1047 997 3.11 11.1
Figu e 1.
XRD pa e ns o kaolin samples om 5 o 40
◦
2
θ
. Peaks o kaolini e (K) a e unlabeled;
M—musco i e, Q—qua z, and O—o hoclase.
The DTA/TG analysis (DTA cu es in Figu e 2) o kaolins hea ed o 1100
◦
C displayed he mal
e en s occu ing wi hin he empe a u e in e als cha ac e is ic o ans o ma ion o kaolini e and
micas (Table 2).
Table 2. TG/DTA o kaolin samples.
Ranges: 1 2 3 4 To al Mass Loss
Kaolin
Sample
Mass
(mg)
∆T1
(◦C)
∆m1
(mg)
∆T2
(◦C)
∆m2
(mg)
T2min
(◦C)
∆T3
(◦C)
∆m3
(mg)
∆T4
(mg)
T4max
(◦C)
∆mTML
(mg) (%)
Bo 20.20 20–175 0.04
410–730
2.36 526
730–946
0.18
963–1031
988 2.58 12.8
Se 21.40 20–160 0.05
403–720
2.41 528
720–946
0.13
959–1041
990 2.59 12.1
Po 18.60 20–185 0.11
440–730
2.04 535
730–932
0.13
955–1041
993 2.28 12.3
Ka 20.90 20–200 0.06
450–725
2.32 535
750–946
0.16
961–1041
997 2.54 12.2
B 19.90 20–170 0.01
430–720
2.19 533
730–931
0.13
972–1051
999 2.33 11.7
Ch 27.90 20–160 0.12
410–715
2.88 534
720–939
0.11
976–1047
997 3.11 11.1
Ma e ials 2019,12, 3104 5 o 13
1
Figu e 2
Figu e 4
Figu e 2. DTA cu es o kaolin samples.
The empe a u e con e sions o kaolins con aining admix u e o musco i e and qua z p oduce
new phases ha will be in ol ed in he sin e ing and c ys alliza ion p ocess o co die i e-indiali e.
The empe a u e ange
∆
T
1
=20–200
◦
C co espond o he loss o adso bed wa e [
22
,
23
].
The empe a u e ange
∆
T
2
=400–730
◦
C was assigned o dehyd oxyla ion o kaolini e and con e sion
o me akaolini e (e.g., [11,22,24]), acco ding o he eac ion (Equa ion (1))
Al2Si2O5(OH)4
Kaolini e
400–730 ◦C
−−−−−−−−→ Al2Si2O7+2H2O
Me akaolini e (1)
The posi ion o he endo he mic minimum T
2min
mo ing om 526
◦
C o 535
◦
C was consis en
wi h s uc u al o de ing, exp essed by Hinckley index [20,25,26] (Table 1).
The empe a u e ange
∆
T
3
=720–946
◦
C o an endo he mal p ocess accompanied by he mass
loss
∆
m
3
abou 0.67
±
0.17% was assigned o dehyd oxyla ion o musco i e [
11
,
27
]. The ans o ma ion
empe a u e om musco i e in o dehyd oxyla ed musco i e we e epo ed in he a ious anges (e.g.,
300–1000 ◦C [27], 650–750 ◦C [28], 850–1000 ◦C [29]), acco ding o he eac ion (Equa ion (2))
KAl2(AlSi3)O10(OH)2
Musco i e
900 ◦C
−−−−−→ KAl2(AlSi3)O11
Dehyd oxyla ed musco i e
+H2O (2)
The empe a u e ange
∆
T
4
=955
◦
C–1051
◦
C and he exo he mic maximum om 988–999
◦
C
(ma ked as T
4max
in Table 2) was assigned o he ans o ma ion o me akaolini e o p ima y mulli e.
O he small di use exo he mic e ec s abo e 1050
◦
C we e a ibu ed o he seconda y mulli e [
29
].
The p ocesses o he o ma ion o p ima y and seconda y mulli es om he kaolin e ac o y clays
we e mos ly desc ibed by he eac ions (Equa ions (3)–(5)) [12,29,30]
Al2Si2O7
Me akaolini e
550–1200 ◦C
−−−−−−−−−→ (3Al2O3·2SiO2)
P ima y mulli e
+SiO2(amo phous)(3)
Depending on he s uc u al de ec s o kaolini es, me akaolini e s uc u e decomposes a abou
900 ◦C wi h seg ega ion o alumina and silica acco ding o he eac ion (Equa ion (4)) [31]
Al2Si2O7
Me akaolini e
900 ◦C
−−−−−→ γ−Al2O3
Alumina +2SiO2(4)
A e y di use DTA exo he mic peaks obse ed in he egion o 1100–1200
◦
C was a ibu ed o a
ecombina ion eac ion o he seg ega ed phases (Equa ion (4)) and hen o he o ma ion o seconda y
mulli e (Equa ion (5))
4SiO2+6γ−Al2O3
>1050 ◦C
−−−−−−−→ 2(3Al2O3·2SiO2)
Seconda y mulli e (5)

Ma e ials 2019,12, 3104 6 o 13
S uc u e o dehyd oxyla ed musco i e is uns able and easily mel s in he empe a u e o he
o ma ion s age o mulli e (Equa ion (6)). The ini ial s age o mulli e c ys als in SiO
2
—mel can be
suppo ed by he p esence o K
2
O eleased upon mel ing om he dehyd oxyla ed musco i e [
32
]
acco ding o he eac ion (Equa ion (6))
2KAl2(AlSi3)O11
Dehyd oxyla ed musco i e
1125–1150 ◦C
−−−−−−−−−−→ (3Al2O3·2SiO2)
Mulli e
+K2O+4SiO2(6)
3.2. Co die i e Samples
The elemen al composi ion o he ce amic samples p epa ed a 1300
◦
C was ecalcula ed o he
s oichiome ic oxides. Fe was ecalcula ed o Fe2O3(Table 3).
Table 3. The ED-XRF analysis o ce amic samples.
Oxides Samples
(mass %) C-Bo C-Se C-Po C-Ka C-B C-Ch
SiO252.88 52.82 56.01 52.71 53.29 52.95
TiO20.57 0.52 0.62 0.87 0.89 0.81
Al2O325.76 26.13 23.00 25.77 25.15 25.27
Fe2O34.68 4.53 4.48 4.45 3.99 4.44
MnO 0.06 0.06 0.05 0.05 0.05 0.05
CaO 0.81 0.75 0.86 0.73 0.70 0.70
MgO 13.25 13.24 13.19 13.28 13.22 13.26
Na2O 0.21 0.21 0.19 0.20 0.22 0.21
K2O 1.69 1.51 1.50 1.71 1.83 2.09
Sum 99.91 99.77 99.90 99.77 99.34 99.78
The XRD pa e ns o ce amic samples we e e y simila and wo ce amic samples C-Se and
C-Po a e gi en as examples (Figu e 3). The c ys alline indiali e (PDF ca d No. 01-082-1884), ens a i e
(PDF ca d no. 00-019-0768) and a b oad a ea o non-c ys alline phases we e iden i ied a all ce amic
samples. The TG/DTA esul s o kaolin– e miculi e mix u es (Table 4) and DTA cu es (Figu e 4)
we e e alua ed as ollows: dehyd a ion o e miculi e and kaolini e ha e occu ed in he empe a u e
ange
∆
T
1
=20–265
◦
C. The empe a u e ange o
∆
T
2
=407–437
◦
C, accompanied by a mass loss o
app oxima ely 6.58
±
0.30%, was assigned o dehyd oxyla ion o kaolini e and a con inuing dehyd a ion
and dehyd oxyla ion o e miculi e. Ve miculi e dehyd oxyla ed and c ys allized o ens a i e a abou
835
◦
C a he empe a u e ange
∆
T
3
=745–848
◦
C (ma ked E in Figu e 4) [
33
,
34
]. The exo he mal
eac ions in he ange
∆
T
4
=905–1017
◦
C and maximum peaks a T
4max
=960–972
◦
C ha e been
a ibu ed o he o ma ion o MgAl
2
O
4
spinel and
µ
-co die i e [
35
,
36
]. The empe a u e ange
∆
T
5
co esponds o he mel ing and c ys alliza ion o indiali e and ens a i e.
Table 4. TG/DTA o kaolin– e miculi e ce amic mix u es.
Ranges: 1 2 3 4 5 To al Mass Loss
Sample Mass
m (mg)
∆T1
(◦C)
∆m1
(mg)
∆T2
(◦C)
∆m2
(mg)
∆T5
(◦C)
∆T3
(◦C)
∆m3
(mg)
∆T4
(◦C)
T4max
(◦C)
∆T5
(◦C)
∆mTML
(mg) (%)
C-Bo 15.12
20–256
0.19
409–597
1.01
1084–1254 757–836
0.18
913–999
964
1084–1254
1.38 9.1
C-Se 15.00
20–226
0.18
416–610
1.01
1086–1255 755–843
0.19
906–1000
960
1086–1255
1.38 9.2
C-Po 15.11
20–233
0.19
407–631
0.93
1075–1252 753–838
0.18
905–1002
964
1075–1252
1.30 8.6
C-Ka 14.97
20–251
0.16
424–609
1.02
1080–1246 745–848
0.16
906–1017
960
1080–1246
1.34 8.9
C-B 15.14
20–239
0.17
434–603
0.95
1102–1258 745–835
0.16
905–999
970
1102–1258
1.28 8.5
C-Ch 15.15
20–265
0.17
437–650
1.04
1104–1243 748–848
0.12
907–999
972
1104–1243
1.33 8.8
Ma e ials 2019,12, 3104 7 o 13
Ma e ials 2019, 12, x FOR PEER REVIEW 6 o 13
S uc u e o dehyd oxyla ed musco i e is uns able and easily mel s in he empe a u e o he
o ma ion s age o mulli e (Equa ion (6)). The ini ial s age o mulli e c ys als in SiO
2
—mel can be
suppo ed by he p esence o K
2
O eleased upon mel ing om he dehyd oxyla ed musco i e [32]
acco ding o he eac ion (Equa ion (6))
2KAl
2
(AlSi
3
)O
11
 °
󰇒
⎯
⎯
⎯
⎯
⎯
⎯
⎯
⎯
󰇏
(3Al
2
O
3
·2SiO
2
) + K
2
O + 4SiO
2
Dehyd oxyla ed musco i e Mulli e
(6)
3.2. Co die i e Samples
The elemen al composi ion o he ce amic samples p epa ed a 1300 °C was ecalcula ed o he
s oichiome ic oxides. Fe was ecalcula ed o Fe
2
O
3
(Table 3).
Table 3. The ED-XRF analysis o ce amic samples
Oxides Samples
(mass %) C-Bo C-Se C-Po C-Ka C-B C-Ch
SiO
2
52.88 52.82 56.01 52.71 53.29 52.95
TiO
2
0.57 0.52 0.62 0.87 0.89 0.81
Al
2
O
3
25.76 26.13 23.00 25.77 25.15 25.27
Fe
2
O
3
4.68 4.53 4.48 4.45 3.99 4.44
MnO 0.06 0.06 0.05 0.05 0.05 0.05
CaO 0.81 0.75 0.86 0.73 0.70 0.70
MgO 13.25 13.24 13.19 13.28 13.22 13.26
Na
2
O 0.21 0.21 0.19 0.20 0.22 0.21
K
2
O 1.69 1.51 1.50 1.71 1.83 2.09
Sum 99.91 99.77 99.90 99.77 99.34 99.78
The XRD pa e ns o ce amic samples we e e y simila and wo ce amic samples C-Se and C-
Po a e gi en as examples (Figu e 3). The c ys alline indiali e (PDF ca d No. 01-082-1884), ens a i e
(PDF ca d no. 00-019-0768) and a b oad a ea o non-c ys alline phases we e iden i ied a all ce amic
samples. The TG/DTA esul s o kaolin– e miculi e mix u es (Table 4) and DTA cu es (Figu e 4)
we e e alua ed as ollows: dehyd a ion o e miculi e and kaolini e ha e occu ed in he empe a u e
ange ΔT
1
= 20–265 °C. The empe a u e ange o ΔT
2
= 407–437 °C, accompanied by a mass loss o
app oxima ely 6.58 ± 0.30%, was assigned o dehyd oxyla ion o kaolini e and a con inuing
dehyd a ion and dehyd oxyla ion o e miculi e. Ve miculi e dehyd oxyla ed and c ys allized o
ens a i e a abou 835 °C a he empe a u e ange ΔT
3
= 745–848 °C (ma ked E in Figu e 4) [33,34].
The exo he mal eac ions in he ange ΔT
4
= 905–1017 °C and maximum peaks a T
4max
= 960–972 °C
ha e been a ibu ed o he o ma ion o MgAl
2
O
4
spinel and µ-co die i e [35,36]. The empe a u e
ange ΔT
5
co esponds o he mel ing and c ys alliza ion o indiali e and ens a i e.
Figu e 3.
XRD pa e ns o ce amic samples C-Se and C-Po. The peaks o indiali e a e unma ked and
ens a i e is ma ked wi h a ow. A non-c ys alline phase a ea is sepa a ed om he backg ound by a
dashed line.
1
Figu e 2
Figu e 4
Figu e 4. DTA cu es o kaolin– e miculi e mix u es. E—ens a i e.
The ans o ma ion empe a u es o he mine al phases and he empe a u es p io o he
c ys alliza ion p ocess du ing he sin e ing o he kaolin– e miculi e ce amic mix u es on he TG-DTA
cu es (Figu e 4) we e de e mined a he i e anges (Table 4).
4. Discussion
The p ocess o he o ma ion o co die i e/indiali e om kaolin– e miculi e mix u es can be
gene ally desc ibed by he eac ions including ans o ma ion o e miculi e o ens a i e (Equa ion (7))
2 Mg3(Si3Al1)O10(OH)2
Ve miculi e
700–900 ◦C
−−−−−−−−→ 6MgSiO3
Ens a i e
+Al2O3+H2O (7)
and hen, he eac ion be ween ens a i e, mulli e and SiO
2
in o co die i e/indiali e o ma ion (Equa ion (8))
6MgSiO3
Ens a i e
+2(3Al2O3·2SiO2)
Mulli e
+5SiO21250 ◦C
−−−−−−→ 3Mg2Al4Si5O18
Co die i e/Indiali e
(8)
The p e ious li e a u e has con i med he ac s, ha he impu i y p oduc s eac wi h he liquid
phase in luencing c ys alliza ion. The e o e, he posi ion o he exo he mic peak shi s o he lowe
empe a u es, e.g., he p esence o 1.5 mass % K2O lowe ed empe a u e abou 25 ◦C [37].
The CQMA p ocedu e [
16
] calcula ed om he bulk chemical analyses c ys allochemical o mulas
and quan i y o mine als, which we e iden i ied using he XRD pa e ns (Figu e 1). In he case o
Ma e ials 2019,12, 3104 8 o 13
kaolin samples, he CQMA ecalcula ed all elemen s (Table 1) o he kaolini e Al
2
Si
2
O
5
(OH)
4,
qua z
SiO
2
, o hoclase KAlSi
3
O
8
and musco i e, whose c ys allochemical o mula has been e ined o
K
0.87
Na
0.07
(Al
1.43
Fe
3+0.07
Mg
0.50
Ti
0.02
)(Si
3.39
Al
0.61
)O
10
(OH)
2
, and esidual elemen s Fe and Ti o he
commonly occu ing mino phases in kaolins as limoni e Fe2O3·H2O and u ile TiO2(Table 5).
Table 5. Quan i a i e amoun s o mine als in kaolin samples de e mined using CQMA me hod.
Mine al
(mass %)
Samples
Bo Se Po Ka B Ch
Kaolini e 81.9 85.0 73.3 82.4 79.0 79.7
Musco i e 9.0 6.6 5.2 9.1 9.9 4.2
Qua z 7.2 6.7 19.5 6.7 9.0 6.0
Limoni e 1.2 0.9 0.8 0.7 0.7 0.8
Ru ile 0.1 0.1 0.3 0.6 0.9 0.7
O hoclase 0.0 0.0 0.0 0.0 0.0 8.0
Sum 99.4 99.3 99.1 99.5 99.5 99.4
The esul s in he Table 5 e ealed simila amoun s o kaolini es in kaolin samples Bo, Se, and Po
om he Ka lo y Va y egion (80.1
±
6.1 mass %) and kaolin samples Ka, B , and Ch om he Pilsen
a ea (80.4
±
1.8 mass %), excep he kaolin sample Po, which is poo in kaolini e (73.3 mass %) a he
expense o qua z (19.5 mass %). All kaolins con ain K-bea ing musco i e in amoun s lowe han
10 mass % and o hoclase (8 mass % in kaolin sample Ch).
In he case o ce amic samples, he CQMA ecalcula ed all elemen s o he bulk chemical
analyses (Table 3) o he quan i a i e amoun s o c ys alline mine als indiali e/co die i e and
ens a i e (MgSiO
3
), iden i ied by XRD pa e ns (Figu e 2). The e ined c ys allochemical o mula
Ca
0.1
Mg
1.90
Fe
3+0.40
Al
3.60
Si
5.00
O
18
o co die i e/indiali e includes all con en o Fe and Ca de e mined a
he six ED-XRF analyses o ce amic samples (Table 3). I should be no ed ha a simila c ys allochemical
o mula o indiali e was epo ed by Balassone e al. [
38
]. The excess Si and all pe cen ages o Ti, Na,
and K we e calcula ed as he oxidic non-c ys alline phases based on 10SiO
2
(Table 6), while conside ing
all elemen s—Al, Fe, Mg, andCa (Table 3)—al eady included in c ys allochemical o mulas o c ys alline
co die i e/indiali e and ens a i e.
Table 6. Quan i a i e amoun s o mine als in ce amic samples de e mined using CQMA me hod.
Mine al
(mass %)
Samples
C-Bo C-Se C-Po C-Ka C-B C-Ch
Co die i e 84.0 85.1 75.2 84.1 81.7 82.3
Ens a i e 6.2 5.8 8.9 6.5 6.8 6.7
O he s (1) 9.4 8.8 15.1 9.3 11.1 10.6
Sum 99.6 99.7 99.2 99.9 99.6 99.6
(1)
The calcula ed oxidic o mulas o esidual—non-c ys alline phases based on 10SiO
2
: C-Bo: 0.29Na
2
O
·
1.52K
2
O
·
0.61TiO
2·
10SiO
2
; C-Se: 0.31Na
2
O
·
1.45K
2
O
·
0.60TiO
2·
10SiO
2
; C-Po: 0.15Na
2
O
·
0.65K
2
O
·
0.36TiO
2·10SiO2; C-Ka:
0.28Na
2
O
·
1.72K
2
O
·
0.96TiO
2·
10SiO
2
; C-B : 0.26Na
2
O
·
1.41K
2
O
·
0.82TiO
2·
10SiO
2
; C-Ch: 0.27Na
2
O
·
1.72K
2
O
·
0.81TiO2·10SiO2.
The quan i a i e amoun s o mine als in ce amic samples de e mined using CQMA me hod
(Table 6) can hen be conside ed as he calcula ed pe cen ages o he highes possible c ys alline
phases and he lowes possible non-c ys alline phases. In six co die i e samples, he amoun o
co die i e/indiali e a ied om 75.2 o 85.1 mass %, ens a i e om 5.8 o 8.9 mass % and non-c ys alline
phases om 8.8 o 15.1 mass %, depending on he pu i y o kaolins, i.e., con aining kaolini e om 73.3
o 85.0, musco i e om 4.2 o 9.9 and qua z om 6.0 o 19.5 (mass %). The empe a u e co esponding
o he mel ing and c ys alliza ion o indiali e a he s age
∆
T
5
a ied om 177 o 139
◦
C (Table 4) in he
ela ion o he amoun o K
2
O om 1.50 mass % o 2.09 mass % (Table 3). The ela ion in Figu e 5a
Ma e ials 2019,12, 3104 9 o 13
be ween he empe a u e
∆
T
5
(Table 4) and he amoun o K
2
O in he ce amic mix u es (Table 3) was
desc ibed by he linea eg ession unc ion (Equa ion (9))
∆T5(◦C) =263.86 −58.68 ×K2O, he co ela ion coe icien R2=0.891 (9)
The ela ionship makes i possible o de e mine he maximum K
2
O di e ence o 0.59% by mass
be ween C-Po and C-Ch and co esponding o he ∆T5 empe a u e educed by 42 ◦C.
A high co die i e, gene ally p epa ed by ce amic p ocedu es a 1300
◦
C, c ys allizes in a
pseudohexagonal symme y (space g oup P6/mcc) (e.g., Beni o e al. [
39
]). The ea lie wo ks ha e
shown ha alkalis can be inco po a ed in o he s uc u al channels o co die i e. In his case,
a cha ge o he Al/Si a io in he amewo k balances acco ding o he equa ion
(K, Na)++Al3+→Si4+
,
causing dis o ion o he hexagonal symme y (e.g., [
40
–
43
]). Di usion o po assium ions was
documen ed du ing he dehyd oxyla ion p ocesses o musco i e and kaolini e and de ec ed in
me akaolini e laye s abo e 900
◦
C [
14
]. The ela ion in Figu e 5b shows a sligh ly la ge la ice
pa ame e s aand co indiali es iden i ied in ce amic samples in compa ison wi h pu e indiali es
designa ed as 1: Mg
2.00
Al
4.00
Si
5.00
O
18
[
4
] and 2: Mg
2.00
Al
4.00
Si
5.00
O
18
[
44
]. The simila ly o he
pa ame e s o K-subs i u ed indiali es, designa ed as 3: (K
0.17
Mg
1.94
Fe
0.06
Ca
0.04
)Al
4.25
Si
4.75
O
18
[
38
]
and 4: (K
0.25
Mg
1.75
)Al
4.25
Si
4.75
O
18
[
43
] can be conside ed as he esul o a possible mig a ion and
subs i u ion o po assium ions in o hei s uc u e.
In luence o kaolin on he quan i y o c ys allizing indiali e/co die i e and qua z admix u e in
kaolin on he o mula ion o he non-c ys alline phase is decla ed in Figu e 6. The amoun s o indiali e/
co die i e in he ce amic samples (Table 6, Figu e 6a) co ela e wi h he amoun o kaolini e in kaolins
(Table 5), as i was desc ibed by he linea eg ession unc ion (Equa ion (10))
Indiali e/co die i e (mass %) =11.91 +0.87 ×kaolini e (mass %), R2=0.939 (10)
Simila ly, he good ela ion be ween he amoun s o non-c ys alline phases in he ce amic samples
(Table 6) and he amoun s o qua z in kaolins (Table 5, Figu e 6b) was desc ibed by he linea eg ession
unc ion (Equa ion (11))
Non-c ys alline phases (mass %) =6.39 +0.46 ×qua z (mass %), R2=0.942 (11)
Ma e ials 2019, 12, x FOR PEER REVIEW 9 o 13
The quan i a i e amoun s o mine als in ce amic samples de e mined using CQMA me hod
(Table 6) can hen be conside ed as he calcula ed pe cen ages o he highes possible c ys alline
phases and he lowes possible non-c ys alline phases. In six co die i e samples, he amoun o
co die i e/indiali e a ied om 75.2 o 85.1 mass %, ens a i e om 5.8 o 8.9 mass % and non-
c ys alline phases om 8.8 o 15.1 mass %, depending on he pu i y o kaolins, i.e., con aining
kaolini e om 73.3 o 85.0, musco i e om 4.2 o 9.9 and qua z om 6.0 o 19.5 (mass %). The
empe a u e co esponding o he mel ing and c ys alliza ion o indiali e a he s age ΔT5 a ied om
177 o 139 °C (Table 4) in he ela ion o he amoun o K2O om 1.50 mass % o 2.09 mass % (Table
3). The ela ion in Figu e 5a be ween he empe a u e ΔT5 (Table 4) and he amoun o K2O in he
ce amic mix u es (Table 3) was desc ibed by he linea eg ession unc ion (Equa ion (9))
ΔT5(°C) = 263.86 − 58.68 × K2O, he co ela ion coe icien R2 = 0.891 (9)
The ela ionship makes i possible o de e mine he maximum K2O di e ence o 0.59% by mass
be ween C-Po and C-Ch and co esponding o he ΔT5 empe a u e educed by 42 °C.
A high co die i e, gene ally p epa ed by ce amic p ocedu es a 1300 °C, c ys allizes in a
pseudohexagonal symme y (space g oup P6/mcc) (e.g., Beni o e al. [39]). The ea lie wo ks ha e
shown ha alkalis can be inco po a ed in o he s uc u al channels o co die i e. In his case, a cha ge
o he Al/Si a io in he amewo k balances acco ding o he equa ion (K, Na)+ + Al3+ → Si4+, causing
dis o ion o he hexagonal symme y (e.g., [40–43]). Di usion o po assium ions was documen ed
du ing he dehyd oxyla ion p ocesses o musco i e and kaolini e and de ec ed in me akaolini e
laye s abo e 900 °C [14]. The ela ion in Figu e 5b shows a sligh ly la ge la ice pa ame e s a and c
o indiali es iden i ied in ce amic samples in compa ison wi h pu e indiali es designa ed as 1:
Mg2.00Al4.00Si5.00O18 [4] and 2: Mg2.00Al4.00Si5.00O18 [44]. The simila ly o he pa ame e s o K-subs i u ed
indiali es, designa ed as 3: (K0.17Mg1.94Fe0.06 Ca0.04)Al4.25Si4.75O18 [38] and 4: (K0.25Mg1.75)Al4.25Si4.75O18 [43]
can be conside ed as he esul o a possible mig a ion and subs i u ion o po assium ions in o hei
s uc u e.
In luence o kaolin on he quan i y o c ys allizing indiali e/co die i e and qua z admix u e in
kaolin on he o mula ion o he non-c ys alline phase is decla ed in Figu e 6. The amoun s o indiali e
/co die i e in he ce amic samples (Table 6, Figu e 6a) co ela e wi h he amoun o kaolini e in kaolins
(Table 5), as i was desc ibed by he linea eg ession unc ion (Equa ion (10))
Indiali e/co die i e (mass %) = 11.91 + 0.87 × kaolini e (mass %), R2 = 0.939 (10)
Simila ly, he good ela ion be ween he amoun s o non-c ys alline phases in he ce amic
samples (Table 6) and he amoun s o qua z in kaolins (Table 5, Figu e 6b) was desc ibed by he
linea eg ession unc ion (Equa ion (11))
Non-c ys alline phases (mass %) = 6.39 + 0.46 × qua z (mass %), R2 = 0.942 (11)
Figu e 5.
Rela ionsships be ween: (
a
) empe a u e
∆
T
5
s. amoun o K
2
O in ce amic samples and
(
b
) uni cell pa ame e s c s. ao indiali es. The pa ame e s labeled as: 1: Mg
2.00
Al
4.00
Si
5.00
O
18
[
4
];
2: Mg
2.00
Al
4.00
Si
5.00
O
18
[
44
]; 3: (K
0.17
Mg
1.94
Fe
0.06
Ca
0.04
)Al
4.25
Si
4.75
O
18
[
38
]; and 4: (K
0.25
Mg
1.75
)Al
4.25
Si4.75O18 [43].