ma e ials
A icle
De elopmen and P ope ies o New Mulli e Based
Re ac o y G og
Da id Zemánek 1,2 , Ka el Lang 2, Lukáš T dík2, Dalibo Všianský3, Lenka Ne ˇ i o á1,2, Pe Š u sa 2,3,
Pa el Ko ᡠ3, Lucie Ke šne o á3and Ka el D oˇ ák1,*


Ci a ion: Zemánek, D.; Lang, K.;
T dík, L.; Všianský, D.;
Ne ˇ i o á, L.; Š u sa, P.; Ko ᡠ, P.;
Ke šne o á, L.; D oˇ ák, K.
De elopmen and P ope ies o New
Mulli e Based Re ac o y G og.
Ma e ials 2021,14, 779.
h ps://doi.o g/10.3390/ma14040779
Academic Edi o : Mangiala di Te esa
Recei ed: 21 Decembe 2020
Accep ed: 26 Janua y 2021
Published: 7 Feb ua y 2021
Publishe ’s No e: MDPI s ays neu al
wi h ega d o ju isdic ional claims in
published maps and ins i u ional a il-
ia ions.
Copy igh : © 2021 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
1Facul y o Ci il Enginee ing, B no Uni e si y o Technology, Ve eˇ í331/95, 602 00 B no, Czech Republic;
[email p o ec ed].cz (D.Z.); [email p o ec ed].cz (L.N.)
2P-D Re ac o ies CZ JSC, Nád ažní218, 679 63 VelkéOpa o ice, Czech Republic;
Ka el.Lang@pd-g oup.com (K.L.); Lukas.T [email p o ec ed] (L.T.); pe [email p o ec ed] (P.Š.)
3Depa men o Geological Sciences, Facul y o Science, Masa yk Uni e si y, Ko lᡠská267/2,
602 00 B no, Czech Republic; [email p o ec ed] (D.V.); Pa el.Ko a @pd-g oup.com (P.K.);
Lucie.Ke sne o a@pd-g oup.com (L.K.)
*Co espondence: [email p o ec ed].cz; Tel.: +420-54114-7511 (ex . 8067)
Abs ac :
The p esen ed s udy is ocused on op imiza ion and cha ac e iza ion o a high-alumina
e ac o y agg ega e based on na u al aw ma e ials—kaolins, clays one, and mulli e dus by-p oduc
(used o inc ease he alumina and mulli e con en s, espec i ely). In o al, ou indi idual o mulas
wi h he Al
2
O
3
con en s be ween 45 and 50 w .% we e designed; he samples we e subsequen ly
i ed, bo h in a labo a o y o en and an indus ial unnel u nace. The e ec s o epea ed i ing we e
examined du ing indus ial pilo es s. Mine al and chemical composi ions and mic os uc u es,
o bo h he aw ma e ials and designed agg ega es, we e ho oughly in es iga ed by he means
o X- ay luo escence spec oscopy, powde X- ay di ac ion, and op ical and scanning elec on
mic oscopies. Po osi y, mine al composi ion, and mulli e c ys al-size de elopmen du ing he i ing
p ocess we e also s udied. Based on he acqui ed esul s, he o mula wi h he pe spec i e o be used
as a new mulli e g og, ea u ing simila p ope ies as he a ailable comme cial p oduc s, howe e ,
wi h educed p oduc ion expenses, was selec ed. The quali y o g og de e mines o a la ge ex en he
p ope ies o he inal p oduc . Hence, op imiza ion o agg ega es o speci ic e ac o ies is o a g ea
impo ance. The p oduc ion o enginee ed agg ega es p o ides he oppo uni y o u ilize indus ial
by-p oduc s.
Keywo ds: mulli e; e ac o y; high-alumina g og; kaolin; clays one
1. In oduc ion
Al hough nume ous scien i ic pape s dealing wi h ce amics and e ac o ies ha e been
published, ew au ho s ha e ocused on e ac o y g og so a . Mo eo e , in e ac o ies
enginee ing, he esea ch has mos ly been ocused on he ma ix; he a en ion has shi ed
o agg ega es only ecen ly [
1
]. Agg ega es a e an indispensable pa o e ac o ies, hey
enhance he o e all p ope ies, such as olume s abili y du ing i ing and high empe a u e
beha iou , and ep esen 50–100% o he aw mix o mos inal p oduc s. The p oduc ion o
e ac o ies is, among o he ac o s, con olled by he a ailabili y o g og [
2
,
3
]. Enginee ing
o agg ega es (i.e., he en i e p oduc ion sys em, including design, cus omiza ion, p ope ies
es ing, e alua ion o pe o mance o e ac o y p oduc s, and hei applica ion o desi ed
pu poses) is expec ed o b ing new b eak h oughs in e ac o ies echnologies. Design and
cus omiza ion o agg ega es comp ise designing o shape, su ace p ope ies, chemical
and phase composi ion, as well as op imizing mic os uc u e [
1
]. In he pas , e ac o y
ma e ials a end-o -li e we e dumped in land ills and new b icks we e made o new aw
ma e ials. Such was ing had a huge impac on he en i onmen , especially because o he
con inuous mining o aw ma e ials [
4
,
5
]. This a i ude has changed no only o ecological,
bu also o economic easons [6,7].
Ma e ials 2021,14, 779. h ps://doi.o g/10.3390/ma14040779 h ps://www.mdpi.com/jou nal/ma e ials
Ma e ials 2021,14, 779 2 o 15
The gene al si ua ion in he e ac o y indus y has changed signi ican ly du ing he
las decades (especially in ecen yea s), which also a ec ed he p oduc ion o i ed clay.
Along wi h d op in demand o s anda d i ed clay caused by changes in he s eel manu ac-
u ing echnology, he p oduc ion o i ed clays one has dec eased. The eno mous changes
wo ldwide we e p ima ily gi en by he es ablishmen o new ecological egula ions in
China, exhaus ion o clays one deposi s in Eu ope (e.g., F ance, Poland, Czech Republic),
and lack o o he aw ma e ials used o g og p oduc ion, such as magnesi e, bauxi e, and
all ypes o aluminium oxides. Limi ed clays one esou ces led o he heap u iliza ion and
b ique ing echnology applica ion, bu he esul s o hese app oaches we e unsa is ac o y
ega ding shaping and i ing. These we e he impulses beyond he de elopmen o high
alumina e ac o y g og [8–10].
Mode n empe a u e-s able componen s ho -p oduced om me allic ma e ials based
on elemen s such as i anium [
11
], a e-ea h me als [
12
], o ungs en [
13
] in oduce he
necessi y o de elop du able empe a u e- esis an appliances o hei p oduc ion and
p ocessing. To esis high empe a u es and main ain he shape and unc ionali y, he
in e io o i ually any u nace is made o e ac o y ma e ials, which ha e become sophis-
ica ed p oduc s wi h ca e ully designed composi ions. The ce amic indus y cons an ly
de elops me hods o lowe he cos and inc ease he quali y and inal p ope ies o he
ma e ials [14,15].
Classi ica ion o e ac o ies acco ding o he chemical composi ion is based on he
anion: ca ion a io and consis s o h ee ypes o ma e ials: acidic, basic, and neu al. The
anion: ca ion a io highe han 1.5:1.0 indica es acidic e ac o y ma e ials, o example
SiO
2
con aining one ca ion and wo anions. The neu al a io is equal o 1.5:1.0, o example
Al
2
O
3
, and 1.0:1.0 indica es basic e ac o ies, o example MgO. This classi ica ion is widely
used in he me allu gic p oduc ion because he e ac o ies ha e o be compa ible wi h
alloys p ocessing. Ano he classi ica ion can be, o example, by me hods o ins alla ion—
shaped and unshaped, by me hods o manu ac u e— used and sin e ed, and by po osi y
con en —po ous and dense [14,16].
Each ype o e ac o y ma e ial, including g og, is applied in di e en indus ial sec-
o s gi en by hei cha ac e is ic p ope ies. Aluminosilica e e ac o ies, mulli e ma e ials,
and i eclay belong among acidic up o neu al e ac o ies. They a e usually applied in
elec ic u naces, coke o ens, annealing u naces, e c. They con ain silica and be ween
40 o 90 w .% o alumina. The dominan aw ma e ials o hese ypes o e ac o ies a e
clays [4,14,17].
The inal in e media e phase o he sin e ing p ocess is mulli e. The ea lies syn hesis
o mulli e was done by i ing kaolini e. Du ing hea ing o kaolini e, X- ay amo phous
me akaolini e is p oduced a i s . Subsequen ly, so called spinel phase and
γ
-alumina
a e o med, and inally, abo e 1000
◦
C, mulli e and amo phous silica a e p oduced. To
a oid he o ma ion o amo phous silica, addi ional alumina has o be added o he ini ial
aw ma e ial [
18
]. The chemical composi ion o mulli e in e ac o ies is usually close o
3Al
2
O
3·
2SiO
2
, which co esponds o he Al
2
O
3
con en o nea ly 72 w .%. The idealized
o mula o he mos commonly p oduced mulli e is 3Al
2
O
3·
2SiO
2
, howe e , he a io o
alumina and silica may a y om 2:1 o 3:2. Among he speci ic p ope ies o mulli e a e
high he mal esis ance up o 1700
◦
C in ai a mosphe e, low he mal expansion coe icien
6
×
10
−6
K
−1
and conduc ibili y 4–6 W/(m K) a 100–1400
◦
C, high c eep and co osion
esis ance, and, las bu no leas , a ou able physical and mechanical beha iou [
18
,
19
].
The i ing p ocess is ealized in sha , unnel, o o a ing kilns a he maximum empe a u e
usually no exceeding 1350
◦
C. In p inciple, a i icial mulli e can be ob ained in wo ways.
The majo i y o mulli e in indus ial condi ions is p oduced ia solid-s a e syn hesis by
i ing clay, Al
2
SiO
5
mine als (andalusi e, sillimani e, and kyani e), bauxi e, and o he solid
aw ma e ials. Ano he way is he sol-gel syn hesis. Solu ion-sol-gel-de i ed mulli es a e
cha ac e ized as chemical-mulli es. They a e syn hesized by chemical eac ion, py olysis,
and mulli iza ion [
18
,
20
]. Each o hese ways o mulli e o ma ion p o ides mulli e wi h
di e en p ope ies [16].
Ma e ials 2021,14, 779 3 o 15
The e a e wo ways o indus ial p oduc ion o ma e ials wi h high mulli e con en
(abo e ~50% o mulli e): sin e ing (>1500
◦
C), and using (>1830
◦
C, in some cases e en
>2000
◦
C). The e m sin e -mulli e e e s o mulli es syn hesized by hea ing o empe a-
u es below he mel ing poin ( o c ys allize and densi y he mulli e). Fused-mulli es a e
p epa ed by hea ing alumina and silica mix u es o empe a u es abo e he mel ing poin ,
ollowed by cooling, du ing which mulli es c ys allize. Mulli es p oduced by using ha e
highe Al
2
O
3
:SiO
2
a ios han hose p oduced by sin e ing om iden ical ini ial ma e ials.
The amoun o alumina in sin e -mulli es usually does no exceed 77 w .% [
3
,
21
]. Mulli e
con en s in i ed clays o clays ones a e usually below 65 w .% o he whole ma e ial,
including he amo phous phase. Ex eme mulli e con en s occu in so called used mul-
li es, which may be used as componen s o high alumina g ogs o enhance hei posi i e
p ope ies. F om he chemical poin o iew, posi i e pe o mance o mulli e based g og is
de e mined by high con en o alumina and low con en s o CaO, MgO, Fe
2
O
3
, and alkalis.
The p esence o de imen al elemen s, mainly alkalis, may signi ican ly dec ease he o e all
hea a igue esis ance [18,22].
The pape p esen s he enginee ing, cha ac e iza ion, and manu ac u ing possibili ies
o new mulli e based agg ega es wi h Al
2
O
3
con en be ween 45 and 50 w .%. The main
objec i e o he esea ch is o p esen new agg ega es ea u ing p ope ies simila o hose
o comme cially a ailable agg ega es, howe e , his solu ion is much cheape since we use
clays one and kaolins mixed wi h used mulli e by-p oduc .
2. Ma e ials and Me hods
2.1. Raw Ma e ials and Mixes
Raw mixes wi h he con en s o Al
2
O
3
be ween 45 and 50 w .% we e designed and p e-
pa ed in indus ial condi ions (P-D Re ac o ies CZ JSC, VelkéOpa o ice, Czech Republic).
To each such high alumina con en s, suppo ing aw ma e ials we e necessa y o be added
o he na u al clays one and loa ed kaolins (Tables 1and 2). Fo economic easons, MOTIM
Whi e Fused Mulli e p oduced by Elec oco undum L d., Mosonmagya ó á , Hunga y,
was chosen (0–1 mm ac ion; see Table 3 o he pa icle size dis ibu ion). MOTIM mulli e
is a by-p oduc om mechanical p ocessing o used mulli e blocks designed o glass
indus y applica ions. The e o e, i can be conside ed as a seconda y aw ma e ial. The
a io o 85% clays one–kaolin and 15% MOTIM mulli e was used o each he Al
2
O
3
con en
o a leas 45%. Fo he chemical and phase composi ions o he aw ma e ial see Table 4in
he Resul s sec ion.
Table 1. Lis o aw ma e ials.
Raw
Ma e ial
Clays one Kaolin Mulli e G og
W Supe KN-83 GP3 DS1 MOTIM
Si e/ Kaznˇejo si e,
Czech Republic/
Kosya in,
Uk aine/
Kosya in,
Uk aine/
Chlumˇcany si e,
Czech Republic/
Elec oco undum
L d.
P oduce Ke amos
company SOKA company SOKA company Sedleckýkaolin,
a.s. company
Mosonmagya ó á ,
Hunga y
Ma e ials 2021,14, 779 4 o 15
Table 2.
Calcula ed chemical composi ions o aw mixes (85% clay, 15% MOTIM mulli e) based on WDXRF analysis in w .%,
ounded o wo decimal places.
Fo mula
Designa ion Raw Ma e ials Al2O3SiO2Fe2O3TiO2CaO MgO K2O Na2O
WW supe clays one +
MOTIM 48.62 47.51 0.88 1.37 0.37 0.15 0.49 0.25
K KN83 kaolin + MOTIM 49.74 47.82 0.40 1.23 0.30 0.07 0.31 0.14
G GP3 kaolin + MOTIM 48.53 48.86 0.76 0.67 0.26 0.20 2.89 0.10
D DS1 kaolin + MOTIM 45.20 50.19 0.54 0.56 0.32 0.20 0.71 0.38
Table 3. Pa icle size dis ibu ion o MOTIM mulli e, 0–1 ac ion.
Sie e
Opening
[mm]
>1 0.5–1.0 0.2–0.5 0.2–0.09 <0.09
w .% 0 44 34.6 15 6.4
Table 4. Chemical and phase composi ion o aw ma e ials in w .%, ounded o wo and one decimal places espec i ely.
Raw Ma e ial/Composi ion Clays one Kaolin Mulli e G og
W Supe KN-83 GP3 DS1 MOTIM
Loss o Igni ion (1000 ◦C) −14.24 −13.47 −13.15 −12.46
Chemical Composi ion
Al2O342.15 43.53 42.04 37.93 76.38
SiO253.19 53.57 54.86 56.49 23.40
Al2O3:SiO2 a io 0.79 0.81 0.77 0.67 3.26
Fe2O31.03 0.43 0.87 0.61 0.01
TiO21.68 1.50 0.81 0.68 0.01
CaO 0.38 0.29 0.24 0.12 0.01
MgO 0.17 0.07 0.23 0.24 –
K2O 0.85 0.36 0.57 3.53 0.08
Na2O 0.45 0.15 0.28 0.1 0.1
Phase Composi ion and Gene al Fo mula
Kaolini e (Al2Si2O5(OH)4) 80.2 93.3 89.7 69.9 –
Illi e (K0.65Al2(AlSi3O10)(OH)2) 11.7 4.1 4.7 6.2 –
Smec i e (no gene al o mula
a ailable) 2.8 – –
Ana ase (TiO2) 2.5 0.8 0.7 0.6 –
Qua z (SiO2) 2.8 1.8 4.3 10.8 0.1
Feldspa s
(K
x
Na
y
Ca
1−(x+y)
Al
2−(x+y)
Si
2+(x+y)
O
8
)
- - 0.6 12.5 –
Mulli e
(Al(4 + 2x)Si(2 −2x)O(10 −x) whe e
x = 0.17 o 0.59)
– – – – 80.5
Co undum (Al2O3) – – – – 0.2
C is obali e (SiO2) – – – –
Amo phous phase NA NA NA NA 19.2
Fo he pilo indus ial expe imen s, p essed b ique es om he aw mixes wi h he
app oxima e dimensions o 7 cm
×
5 cm
×
3 cm we e p epa ed. The b ique ing echnology
enables p epa a ion o bodies o op imized sizes and posi i ely impac s educ ion in
was ing o aw ma e ials ( he ese es o kaolins and clays ones a e limi ed). Fo labo a o y
expe imen s, he mixes we e addi ionally homogenized wi h a wheel mixe o 10 min.
Ma e ials 2021,14, 779 5 o 15
Be o e p essing wi h he p essu e o 10 MPa in o cylinde bodies wi h 5 cm in diame e ,
10% o wa e was added o he d y mixes.
Th ee i ing expe imen s we e used:
1.
Fi ing in labo a o y o en—hea ing 10
◦
C/min o he maximum empe a u es o 1250,
1450, and 1550 ◦C, ollowed by 5 h soaking a he maximum empe a u e
2. One cycle o i ing in indus ial unnel kiln: 1480 ◦C wi h 5 h soaking
3.
Two cycles o i ing in an indus ial kiln wi h he egime iden ical as lis ed abo e
(ad 2)
2.2. Analy ical Me hods
Chemical composi ion analysis o he aw ma e ials was pe o med by wa eleng h-
dispe si e X- ay spec oscopy (WDXRF) using SPECTROSCAN MAKC-GV ins umen
(Spec on Company, S . Pe e sbu g, Russia) equipped wi h QUANTITATIVE ANALYSIS
4.0 so wa e. Samples we e analysed in o ms o used beads.
Powde X- ay di ac ion analysis o he aw ma e ials and enginee ed agg ega es was
conduc ed on Panaly ical Empy ean di ac ome e (Mal e n Panaly ical Company, Almelo,
The Ne he lands) equipped wi h Cu-anode, 1-D posi ion sensi i e de ec o a con en ion
B agg–B en ano e lec ion geome y. The se ing we e s ep size–0.013 2
θ
, ime pe s ep—
188 s, and angula ange 5–80 2
θ
. Con en s o he amo phous phase we e quan i ied using
he addi ion o 10 w .% luo i e (CaF
2
) as an in e nal s anda d. Quan i a i e phase analysis
was done ia he Rie eld me hod using Panaly ical High Sco e 3.0 plus so wa e.
Pola izing ligh mic oscopy (PLM) examina ion was pe o med on 30
µ
m hick pol-
ished hin sec ions using an Olympus BX 51 mic oscope (Olympus Company, Tokyo, Japan).
Scanning elec on mic oscopy wi h X- ay mic oanalysis (SEM/EDS) was conduc ed on
gold-coa ed mechanically b oken specimens ( o mo phological analyses) and on polished
ca bon-coa ed hin sec ions ( o chemical mic oanalyses) using TESCAN MIRA 3 (Tescan
Company, B no, Czech Republic) ins umen wi h he accele a ing ol age o 30 kV.
De e mina ions o bulk densi y, appa en densi y, appa en po osi y, and wa e ab-
so p ion we e done by he well-known hyd os a ic g a i y me hod (e.g., ˇ
CSN EN 993-1
s anda d [
23
]). Appa en po osi y and po e size dis ibu ion was de e mined by me cu y
po osime y using The mo Finnigan POROTEC Pascal 140–240 ins umen (The moFishe
Scien i ic, Wal ham, MA, USA).
3. Resul s and Discussion
3.1. Cha ac e iza ion o Raw Ma e ials
The alumina con en (be ween 42–44 w .%) and alumina:silica a io (0.77–0.81) was
simila o he clays one (W-supe ) and wo o he kaolin samples (KN-83 and GP3). In DS1
kaolin, bo h he pa ame e s we e signi ican ly lowe (37.93 and 0.67%). The Al
2
O
3
:SiO
2
a io in MOTIM mulli e g og (3.26) was much close o he mulli e alue o 2:1 (3.39), han
3:2 (2.54), which co esponds o he p oduc ion by using. The Fe
2
O
3
con en was be ween
1.03 (clays one) and 0.43 (KN-83), while in he MOTIM mulli e i eached only 0.01%. The
CaO con en s we e below 0.4% in all he clay and kaolin samples. The con en s o alkalis
in all he aw ma e ials we e ela i ely low wi h he excep ion o DS1 kaolin, whe e he
con en o K2O eached 3.53%.
The con en s o mine als p esen in he aw ma e ials e lec ed hei chemical com-
posi ions: he highes kaolini e con en (o e 93%) was iden i ied in he KN-83 sample,
and he lowes one (below 70%) in he DS1 kaolin. The mos di e se associa ion o clay
mine als was ound he W-supe clays one, whe e, besides kaolini e and illi e, smec i e
was also p esen . The highes con en s o “impu i ies”, qua z and eldspa s, we e ound
in he DS1 kaolin. The high pe cen age o eldspa s co esponds o he high con en s o
po assium in his sample. Chemical and phase composi ions o he used aw ma e ials a e
gi en in Table 4.
Mo phology o he aw ma e ials was obse ed using SEM. The size o kaolini e
pseudohexagonal pla ele s no mal o (0 0 1) was appa en ly he la ges (up o 5
µ
m) in

Ma e ials 2021,14, 779 6 o 15
he DS1 kaolin, whe e also he c ys al size was he mos uni o m. The smalles kaolini e
c ys als (<1
µ
m) we e obse ed in W-supe clays one, and GP3 kaolin samples. I can
be assumed ha kaolini e c ys al size, i s dis ibu ion and, hence, speci ic su ace may
a ec eac i i y. Fo compa ison o mic os uc u es see Appendix A. The SEM obse a ion
o MOTIM mulli e (Figu e A5) co esponds o he sie e analysis esul s. The pa icle
size o he MOTIM suppo ing aw ma e ial was below 1 mm wi h he mean alue o
0.28 µm (Table 3).
3.2. Tailo ed Agg ega es
3.2.1. Phase Composi ion
The bulk phase composi ion, including amo phous (“glassy“) phase, o all he ag-
g ega es p epa ed in bo h he labo a o y and indus ial condi ions was analysed by XRD
(Table 5, Appendix B). The c is obali e and amo phous phase con en s o well homogenized
samples i ed in a labo a o y o en di e ed signi ican ly (Figu e 1). In agg ega e samples
K and D, c is obali e did no appea a any o he i ing empe a u es (1250, 1450, and
1550
◦
C). The con en o he amo phous phase was ela i ely high al eady a 1250
◦
C and
inc eased negligibly wi h inc easing empe a u e. Fo sample D, such a se e e mel ing
al eady a lowe empe a u es can be explained by he abundance o po assium in he
o mula (2.89%, Table 2). Howe e , o sample K, he chemical composi ion did no p o ide
any clea explana ion o he cou se o he mel ing p ocess. In samples W and G, he con en s
o he amo phous phase and c is obali e co ela ed nega i ely wi h each o he . C is obali e
mel ed below 1450
◦
C in sample W, and abo e his empe a u e in sample G. Residual
qua z in he amoun s abo e 1% emained in samples W and G a 1450
◦
C. On he o he
hand, qua z did no ans o m o c is obali e bu mel ed di ec ly in samples K and D.
Ma e ials 2021, 14, x FOR PEER REVIEW 7 o 15
Figu e 1. C is obali e and amo phous phase con en s in labo a o y- i ed samples; no c is obali e
was de ec ed in K-L and D-L samples.
Figu e 2. Con en s o mulli e in syn he ised samples and e e ence ma e ial; L =l abo a o y i ing,
T,TT = one and wo cycles o i ing in indus ial unnel kiln.
Table 5. Phase composi ion o p epa ed g og samples (L = labo a o y o en, T = indus ial unnel kiln one i ing cycle, TT = indus-
ial unnel kiln wo i ing cycles) and e e ence ma e ial – Re e ence ma e ial. The o mulas wi h simila composi ion as he e e -
ence ma e ial a e highligh ed by ed colou .
Sample Fi ing
Mulli e Co undum C is obali eQua z Amo phous
Phase
Designa ion Tempe a u e[°C]
WL
1250 74.5 0.0 16.1 4.0 5.5
1450 75.6 0.0 7.4 3.8 13.1
1550 71.2 0.0 0.5 0 29.7
W−T 1550 58.5 0.5 20.3 0.9 19.8
W−TT 1550 54.9 0.7 14.6 0.4 29.4
G−L
1250 69.5 0.0 19.6 3.0 7.9
1450 70.7 0.0 24.8 1.0 3.5
1550 71.7 0.0 0.6 0.0 27.7
G−T 1550 56.9 0.1 21.8 0.1 21.1
G−TT 1550 55.9 0.1 23.2 0.0 20.8
K−L
1250 59.1 0.0 0.0 3.9 36.8
1450 57.2 0.0 0.0 0.0 42.8
1550 54.9 0.0 0.0 0.0 45.1
Figu e 1.
C is obali e and amo phous phase con en s in labo a o y- i ed samples; no c is obali e was
de ec ed in K-L and D-L samples.
Ma e ials 2021,14, 779 7 o 15
Table 5.
Phase composi ion o p epa ed g og samples (L = labo a o y o en, T = indus ial unnel
kiln one i ing cycle, TT = indus ial unnel kiln wo i ing cycles) and e e ence ma e ial–Re e ence
ma e ial. The o mulas wi h simila composi ion as he e e ence ma e ial a e highligh ed by ed
colou .
Sample Fi ing
Mulli e Co undum C is obali e Qua z Amo phous
Phase
Designa ion Tempe a u e
[◦C]
WL
1250 74.5 0.0 16.1 4.0 5.5
1450 75.6 0.0 7.4 3.8 13.1
1550 71.2 0.0 0.5 0 29.7
W-T 1550 58.5 0.5 20.3 0.9 19.8
W-TT 1550 54.9 0.7 14.6 0.4 29.4
G-L
1250 69.5 0.0 19.6 3.0 7.9
1450 70.7 0.0 24.8 1.0 3.5
1550 71.7 0.0 0.6 0.0 27.7
G-T 1550 56.9 0.1 21.8 0.1 21.1
G-TT 1550 55.9 0.1 23.2 0.0 20.8
K-L
1250 59.1 0.0 0.0 3.9 36.8
1450 57.2 0.0 0.0 0.0 42.8
1550 54.9 0.0 0.0 0.0 45.1
K-T 1550 67.2 0.0 31.1 0.1 1.6
K-TT 1550 66.5 0.0 24.4 0.0 9.1
D-L
1250 56.6 0.0 0.0 4.0 39.4
1450 55.3 0.0 0.0 0.7 44.2
1550 54.9 0.0 0.0 0.6 44.5
D-T 1550 51.2 0.0 1.6 0.0 47.2
D-TT 1550 49.5 0.0 1.8 0.1 48.6
Re e ence
Ma e ial 70.1 2.4 21.1 0.3 6.0
Mulli e con en s did no signi ican ly change be ween 1250 and 1550
◦
C in he
labo a o y-p epa ed samples (Figu e 2). In he samples i ed a 1250
◦
C, bo h he s uc u es
o mulli e—close o 3:2 and 2:1—we e p esen . A highe empe a u es, he 3:2 s uc u e
became dominan . Based on he mulli e peak p o iles, i is appa en ha he c ys allini y o
mulli e inc eased be ween 1250 and 1450
◦
C. The mulli e peaks’ alues o ull wid h a hal
maximum (FWHM) we e signi ican ly highe in he samples i ed a 1250
◦
C compa ed o
hose exposed o highe empe a u es.
A e i ing a an indus ial unnel kiln, mulli e con en was simila as in analogous
labo a o y-p epa ed sample o sample G. In samples W and D, he acqui ed mulli e
con en s we e lowe , and in sample K i was highe (Figu e 2). Mulli e con en s in he
indus ial samples can be a ec ed by inhomogenei y o he aw mix. The highe mulli e
con en in sample K co ela ed wi h he low amo phous phase con en (below 10%), in
compa ison o he same o mula i ed in labo a o y condi ions (o e 36–44%). I may be
assumed ha seconda y mulli e o med by c ys alliza ion o he mel du ing slow cooling
in he unnel kiln. In all he o mulas, mulli e con en sligh ly dec eased a e he second
cycle o indus ial i ing, which may be a ibu ed o co osion by mel . Fi eclay e ac o ies
a e usually no exposed o such high empe a u es (1550
◦
C) du ing hei li ecycle. The
common maximum exposi ion empe a u e does no exceed 1400
◦
C. The e o e, he isk o
he occu ence o co osion by mel du ing hei wo king li e ime is limi ed.
Ma e ials 2021,14, 779 8 o 15
Ma e ials 2021, 14, x FOR PEER REVIEW 7 o 15
Figu e 1. C is obali e and amo phous phase con en s in labo a o y- i ed samples; no c is obali e
was de ec ed in K-L and D-L samples.
Figu e 2. Con en s o mulli e in syn he ised samples and e e ence ma e ial; L =l abo a o y i ing,
T,TT = one and wo cycles o i ing in indus ial unnel kiln.
Table 5. Phase composi ion o p epa ed g og samples (L = labo a o y o en, T = indus ial unnel kiln one i ing cycle, TT = indus-
ial unnel kiln wo i ing cycles) and e e ence ma e ial – Re e ence ma e ial. The o mulas wi h simila composi ion as he e e -
ence ma e ial a e highligh ed by ed colou .
Sample Fi ing
Mulli e Co undum C is obali eQua z Amo phous
Phase
Designa ion Tempe a u e[°C]
WL
1250 74.5 0.0 16.1 4.0 5.5
1450 75.6 0.0 7.4 3.8 13.1
1550 71.2 0.0 0.5 0 29.7
W−T 1550 58.5 0.5 20.3 0.9 19.8
W−TT 1550 54.9 0.7 14.6 0.4 29.4
G−L
1250 69.5 0.0 19.6 3.0 7.9
1450 70.7 0.0 24.8 1.0 3.5
1550 71.7 0.0 0.6 0.0 27.7
G−T 1550 56.9 0.1 21.8 0.1 21.1
G−TT 1550 55.9 0.1 23.2 0.0 20.8
K−L
1250 59.1 0.0 0.0 3.9 36.8
1450 57.2 0.0 0.0 0.0 42.8
1550 54.9 0.0 0.0 0.0 45.1
Figu e 2.
Con en s o mulli e in syn he ised samples and e e ence ma e ial; L = l abo a o y i ing,
T,TT = one and wo cycles o i ing in indus ial unnel kiln.
Table 5shows he e ec o he i ing empe a u e on he phase composi ion o
labo a o y-p epa ed samples, he compa ison wi h indus ial samples p oduced by one
and wo i ing cycles, and he e e ence ma e ial. The phase composi ion o sample K i ed
in he indus ial unnel kiln was he closes o he comme cial e ac o y mulli e agg ega e
used as he e e ence ma e ial. In labo a o y condi ions, simila composi ion was acqui ed
o he sample wi h o mula G (Table 5).
The he e ogeneous mic os uc u e o he indus ially p epa ed samples was obse ed
by pola izing ligh mic oscopy (PLM). Physical-mechanical p ope ies o he composi e
p oduc s a e usually s ongly a ec ed by he in e aces o di e en used ma e ials. Fi ed
clay nodules, locally o he size o e 1 cm, we e su ounded by mix u es o well-dispe sed
clay binde and MOTIM mulli e pa icles in all he examined samples ( o examples
see Figu e 3). The in e aces o hese egions we e ela i ely sha p (Figu e 4) wi h no
subs an ial po osi y possibly dec easing he physical-mechanical p ope ies o he samples.
G ey colou ing o he nodules nea he in e aces was caused by mig a ion o i on oxides
owa ds hei cen al pa s. In some cases, i on oxides o med isola ed ci cula spo s in
he i ed clay nodules. The ims o MOTIM mulli e did no exhibi any se e e co osion
(Figu e 3).
Ma e ials 2021, 14, x FOR PEER REVIEW 8 o 15
K−T 1550 67.2 0.0 31.1 0.1 1.6
K−TT 1550 66.5 0.0 24.4 0.0 9.1
D−L
1250 56.6 0.0 0.0 4.0 39.4
1450 55.3 0.0 0.0 0.7 44.2
1550 54.9 0.0 0.0 0.6 44.5
D−T 1550 51.2 0.0 1.6 0.0 47.2
D−TT 1550 49.5 0.0 1.8 0.1 48.6
Re e ence Ma e ial 70.1 2.4 21.1 0.3 6.0
The he e ogeneous mic os uc u e o he indus ially p epa ed samples was ob-
se ed by pola izing ligh mic oscopy (PLM). Physical-mechanical p ope ies o he com-
posi e p oduc s a e usually s ongly a ec ed by he in e aces o di e en used ma e ials.
Fi ed clay nodules, locally o he size o e 1 cm, we e su ounded by mix u es o well-
dispe sed clay binde and MOTIM mulli e pa icles in all he examined samples ( o ex-
amples see Figu e 3). The in e aces o hese egions we e ela i ely sha p (Figu e 4) wi h
no subs an ial po osi y possibly dec easing he physical-mechanical p ope ies o he
samples. G ey colou ing o he nodules nea he in e aces was caused by mig a ion o
i on oxides owa ds hei cen al pa s. In some cases, i on oxides o med isola ed ci cula
spo s in he i ed clay nodules. The ims o MOTIM mulli e did no exhibi any se e e
co osion (Figu e 3).
Figu e 3. Sample K-T– i ed clay nodules su ounded by mix u e o i ed clay and mulli e; PPL =
plane pola ized ligh , XPL = c ossed pola ized ligh .
Figu e 4. Sample G-T–in e ace o la ge, i ed clay nodule and mix u e o i ed clay and agmen s
o used mulli e.
3.2.2. Mulli e C ys al Size De elopmen
The de elopmen o mulli e c ys als‘ mean size along c c ys allog aphic axis wi h
i ing empe a u e (5 h soaking) in he clay pa o he g og was obse ed and calcula ed
using SEM (Figu e 5; mulli e was iden i ied by EDS analysis). Simila end was obse ed
in all he samples (Table 6). The slowes g owing o mulli e c ys als was obse ed in DS1
kaolin, which was he mos alkali- ich one. Howe e , he alues we e simila o each o he
Figu e 3.
Sample K-T– i ed clay nodules su ounded by mix u e o i ed clay and mulli e; PPL =
plane pola ized ligh , XPL = c ossed pola ized ligh .
Ma e ials 2021,14, 779 9 o 15
Ma e ials 2021, 14, x FOR PEER REVIEW 8 o 15
K−T 1550 67.2 0.0 31.1 0.1 1.6
K−TT 1550 66.5 0.0 24.4 0.0 9.1
D−L
1250 56.6 0.0 0.0 4.0 39.4
1450 55.3 0.0 0.0 0.7 44.2
1550 54.9 0.0 0.0 0.6 44.5
D−T 1550 51.2 0.0 1.6 0.0 47.2
D−TT 1550 49.5 0.0 1.8 0.1 48.6
Re e ence Ma e ial 70.1 2.4 21.1 0.3 6.0
The he e ogeneous mic os uc u e o he indus ially p epa ed samples was ob-
se ed by pola izing ligh mic oscopy (PLM). Physical-mechanical p ope ies o he com-
posi e p oduc s a e usually s ongly a ec ed by he in e aces o di e en used ma e ials.
Fi ed clay nodules, locally o he size o e 1 cm, we e su ounded by mix u es o well-
dispe sed clay binde and MOTIM mulli e pa icles in all he examined samples ( o ex-
amples see Figu e 3). The in e aces o hese egions we e ela i ely sha p (Figu e 4) wi h
no subs an ial po osi y possibly dec easing he physical-mechanical p ope ies o he
samples. G ey colou ing o he nodules nea he in e aces was caused by mig a ion o
i on oxides owa ds hei cen al pa s. In some cases, i on oxides o med isola ed ci cula
spo s in he i ed clay nodules. The ims o MOTIM mulli e did no exhibi any se e e
co osion (Figu e 3).
Figu e 3. Sample K-T– i ed clay nodules su ounded by mix u e o i ed clay and mulli e; PPL =
plane pola ized ligh , XPL = c ossed pola ized ligh .
Figu e 4. Sample G-T–in e ace o la ge, i ed clay nodule and mix u e o i ed clay and agmen s
o used mulli e.
3.2.2. Mulli e C ys al Size De elopmen
The de elopmen o mulli e c ys als‘ mean size along c c ys allog aphic axis wi h
i ing empe a u e (5 h soaking) in he clay pa o he g og was obse ed and calcula ed
using SEM (Figu e 5; mulli e was iden i ied by EDS analysis). Simila end was obse ed
in all he samples (Table 6). The slowes g owing o mulli e c ys als was obse ed in DS1
kaolin, which was he mos alkali- ich one. Howe e , he alues we e simila o each o he
Figu e 4.
Sample G-T–in e ace o la ge, i ed clay nodule and mix u e o i ed clay and agmen s o
used mulli e.
3.2.2. Mulli e C ys al Size De elopmen
The de elopmen o mulli e c ys als‘ mean size along c c ys allog aphic axis wi h
i ing empe a u e (5 h soaking) in he clay pa o he g og was obse ed and calcula ed
using SEM (Figu e 5; mulli e was iden i ied by EDS analysis). Simila end was obse ed
in all he samples (Table 6). The slowes g owing o mulli e c ys als was obse ed in DS1
kaolin, which was he mos alkali- ich one. Howe e , he alues we e simila o each o he
(in compa ison o comme cial samples, o which hey a e app oxima ely by one o de o
magni ude la ge ).
Ma e ials 2021, 14, x FOR PEER REVIEW 9 o 15
(in compa ison o comme cial samples, o which hey a e app oxima ely by one o de o
magni ude la ge ).
Figu e 5. Compa ison o mulli e c ys als size in ma ices o K and G samples a e wo cycles o
indus ial i ing wi h he e e ence ma e ial ( i ing empe a u e 1480 °C/5h soaking).
Table 6. Mean size o mulli e c ys als [μm] on ma ix o labo a o y-p oduced samples, MOTIM
mulli e and e e ence ma e ial based on SEM obse a ion.
Fi ing Tempe a u e [°C]
/
Sample 1250 1450 1550
W-L 0.2 0.6 4.0
G-L 0.2 1.0 6.0
K-L 0.5 2.0 10.0
D-L 0.1 0.4 2.0
Comme cial Mulli e Based P oduc s
Re e ence Ma e ial 3.0
MOTIM 283.0
3.2.3. Po e Size Analysis
The e ec o i ing empe a u e on po e-size dis ibu ion de elopmen in labo a o y-
p epa ed samples is shown in Figu es 6 and 7. The o al olume o open po es wi h he
diame e s below 1 μm was signi ican ly lowe in all he samples i ed a 1450 °C (in com-
pa ison o hose i ed a 1250 °C). The o al olume o small po es also dec eased be ween
1450 and 1550 °C in he G-L and W-L samples. In he K-L and D-L samples, sligh inc ease
in open po osi y be ween 1450 and 1550 °C can be obse ed. The labo a o y-p epa ed
g og samples based on kaolins ea u ed lowe o al olumes o po es wi h he diame e s
be ween 1 and 40 μm han he sample based on clays one (W-L), his po e size o which
was dominan . A e i ing a 1250 °C, all he kaolin-based samples displayed simila po e-
size dis ibu ions wi h app oxima ely 85 ol.% o po es below 1 μm in diame e . The low-
es o al po osi y a e all he i ing egimes was obse ed in D-L sample. The inc ease in
he i ing empe a u e om 1250 o 1450 °C led o signi ican clinke ing o K-L and D-L
samples, which mani es ed by he dominance o small po es (below 1 μm).
Figu e 5.
Compa ison o mulli e c ys als size in ma ices o K and G samples a e wo cycles o
indus ial i ing wi h he e e ence ma e ial ( i ing empe a u e 1480 ◦C/5h soaking).
Table 6.
Mean size o mulli e c ys als [
µ
m] on ma ix o labo a o y-p oduced samples, MOTIM
mulli e and e e ence ma e ial based on SEM obse a ion.
Fi ing Tempe a u e
[◦C]/Sample 1250 1450 1550
W-L 0.2 0.6 4.0
G-L 0.2 1.0 6.0
K-L 0.5 2.0 10.0
D-L 0.1 0.4 2.0
Comme cial Mulli e
Based P oduc s
Re e ence Ma e ial 3.0
MOTIM 283.0
3.2.3. Po e Size Analysis
The e ec o i ing empe a u e on po e-size dis ibu ion de elopmen in labo a o y-
p epa ed samples is shown in Figu es 6and 7. The o al olume o open po es wi h
he diame e s below 1
µ
m was signi ican ly lowe in all he samples i ed a 1450
◦
C (in
compa ison o hose i ed a 1250
◦
C). The o al olume o small po es also dec eased