Rheological characteristics of clay-kaolin aqueous suspensions were studied by a rotational viscometer to correlate their behavior with the properties of ceramic slips for casting containing quartz, feldspars, and other nonplastic materials. In particular, the effects of the different amounts of dry materials and deflocculant (mixture 1:1 of Na2CO3 and Na2SiO3) and of temperatures on the shear-time-dependent properties of suspensions were examined

Lapasin, R.

Lucchini, F.

English

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FNASA TECHNICAL MEMORANDUM
NASA TM-77363
RHEOLOGICAL STUDY OF CLAY-KAOLIN AQUEOUS SUSPENSIONS
Ro Lapasin and Eo Lucchinl
Translation of "studio Reologico di Sospensioni Acquose di
Argilla/Caolino" Ceramurgia, Volume ii, Number 2, 1981,
pp. 57-61.
(_ASA-T_-773_3) RdEOLGGICAL STUDY OF
CLA¥-KkOLIN K_U_OUS SUSPEhSIO_S (National
_erona_txc_ and Space Administr_tioa) 17 p
HC A02/_ A01 CSC& 07D
G3/25
N8_-23711
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. MARCH 1984
https://ntrs.nasa.gov/search.jsp?R=19840015643 2020-03-20T22:07:49+00:00Z
J_
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|. Rspe,f No.
NASA TM-77363
Tltlo_d_btltlo
RHEOLOGICAL STUDY OF
AQUEOUS SUSPENSIONS
2. Government Accession No.
nl
C LAY- K_:OL IN
SlrANDARD TITLE PAGE
3'. Reoipient'e Ceteleo No.
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4. Per|strain00,9onisoticn Code
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7. _me,(,) R. Lapasin and _. Lucchini.
Institute of _ppl_ed ,and Industrial
Chemistry of the University of Studies
. of Triestet Tri'ester Italy .
9. Pe,form:n 90rgmiaQt,en Ncme and A4drcs8
• L_o Kanner _ssociates
..Redwood City, California 94063
12. ;;9onsorin0 Agency Name and Address" ._ .
National Aeronautics and Space Adminis-
tration, Washington, D.C. 20546
J ,,
_5. Supplementers, Me_es
Translation .of "Studio Re_logico di Sospensioni
Argilla/Caoli.no", Ceramurgia, Volume ii, Number
pp. 57-61.
L Peflemdn90,0eaiHlien Repo_t Me.
10. Work Un_!He.
||. Con_rect o_ G_ont No.
NASw-3 541
13. _ypeel_epe,t0.dPeriod¢_c,._
Translation
14. Sponsoring; Agency, Co_e
Acquose di
2, 1981,
_. *b,,,_,
Reological characteristics of. clay-kaolin aqueous suspensions
were studied by a rotational v.iscometer .to correlate their
behavior with the'propertieS of ceramic slips for. casting
containing quartz,' f_id_pars, and other nonplastic materiels.
In particular, the'effects of the different amounts of dry
(mixture "lil" of Na2CO3 and Na2SiO3
shear-time-dependent properties of
m_terf_is and deflo'cculant
and o_ temperatures on the
suspensions were e x.amined:
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RHEOLOGICAL STUDY OF CLAY-KAOLIN AQUEOUS SUSPENSIONS
R. Lapasin and E. Lucchini
Institute of Applied and Industrial Chemistry
University of Studies of Trieste, Trieste, Italy
i. Introduction
The property of clay to give colloidal aqueous suspensions is
widely used by the ceramic industry. These suspensions to which kaolin,
fluxes and finely crushed quartz as well as deflocculants are added are
placed in suitable gypsum molds so as to obtain, after hardening and
drying, the object of desired shape.
/5__/7*
The rheological properties of such slips, which are deeply affected
by the dose of the different components, influence considerably the
casting speed. On the other hand, possible changes in their cQmposition,
meant for accelerating this phase of the production process, may alter
the drying speed and some characteristics of the objects such as, for
example, the crude mechanical resistance in the crude slate and the
appearance of the surfaces.
In general the slips are non-Newtonian inasmuch as the viscosity
depends on the speed gradient to which the material is exposed and on
the theological history of the material itself. Consequently it is nec-
essary to know their characteristics depending on shear and time and the
parameters affecting them.
This is extremely useful in planning and determining the dimensions
of the spray dryer, unless drastic simplifications are adopted such as
that of disregarding the losses of load inside the centrifugal nozzles
or resorting to empirical types of relationships whose applications are
difficult to suspend suspensions with different contents of dry mater-
ial and deflocculant. Finally the paper industry which uses kaolin as
*Numbers in the margin indicate pagination in the foreign text.
kw
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i!
"filler" applied by means of a wet process is involved in very similar
problems.
All these considerations lead us to implementing a program of
research concerning the rheological behavior of suspensions containing
kaolin and clay; also because a literature search of the study convinced
us that in spite of the fact that there has been considerable scienti-
fic activity in the sector, many investigators used instruments which
did not make it possible to characterize completely, from the rheolog-
ical point of view, the systems examined or they used disputable pro-
cedures such as those of hysteresis loop or finally they confined
themselves to investigations of suspensions at very low concentrations
of solid material.
2. Materials and Experimental Procedures
The starting material used in our experiments consisted of a mix-
ture containing 52.5 % kaolin and 47.5 % of a crushed French clay of
the GSG type furnished by the Petra Company. The two components were
characterized from the chemical, mineralogical and granulometric point
of view by the traditional techniques (chemical weight analysis and by
atomic absorption, RX diffractometry, sedimentometric balance). The
results are given in Table i. The deflocculant used is the classic
mixture with a weight proportion 1 to 1 of sodium carbonate and sili-
cate, the percentages added, calculated with regard to dry material,
varied between 0.I and 1%.
The suspensions prepared by this method (altogether 1 kilogram)
were homogenized in a ball grinder with a capacity of 1.4 liter and
with a speed of rotation of 82 rpm.
2
Table 1. Chemical Composition and _anulometric Distribution of the
Materials Used
Chemical _omposition
(weight percentage)
Granulometric Distribution
(weight percentage)
clay kaolin d (_) clay kaolin
l.i. (*) 11.6 12.3 > 9.6 6.6 1.6
SiO 2 50.6 46.0
AI203 33.7 39.3
Fe203 1.5 0.8 9.6 t 3.0 6.7 10.1
TiO 2 i. 4 ---
K20 0.7 0.4 3.0 -. 1.6 6.7 31.1
Na20 0.1 0.4
CaO 0.3 0.i i 1.6 80.0 57.2
MgO 0.1 0.1
*firing loss; (@) equivalent diameter in um.
The experimental tests were carried out with a rotational viscosi-
meter of the type Rotovisko Haake, RV2, in the velocity gradient range
-i
between i0 and 2,000 s . The measurement system used is of the type
with coaxial cylinders (diameter ratio = 0.96). The experimental pro-
cedure adopted consisted of the application of the sequence of constant
velocity gradients; each gradient was applied until a stationary value
of the shear force was obtained. The tests were conducted at 25 + 0._ C.
3. Results and Discussion
At high concentrations of solids and low concentrations of the de-
flocculant, the experimental procedure makes it possible to reveal a
considerable thixotropic behavior, that is considerable variations of
the shear force in time with constant velocity gradient. These vari-
ations of the shear force in time are the result of processes of struc-
tural destruction or reconstruction taking place within the material
through the effect of variations of the kinematic conditions imposed.
ORIGINAL PAGE !_
OF POOR QUALrrY
Various approaches may be followed to describe the thixotropic
behavior and to give a theoretical interpretation. In previous pub-
lications [i, 2] some examples were given of application of the ap-
proaches of Cheng [3] and Camina [4] to the thixotropic behavior of
suspensions of kaolin and clay.
As regards the shear-dependent properties which are the subject
of this study, all the systems show a similar behavior in the range
of velocity gradients studied. This behavior depends to a considerable
extent, in quantitative terms, on the concentration of solids and de-
flocculant.
Figures I, 2 and 3 give the curves of the equilibrium flux of the
systems at three different concentrations of solid considered. The
above mentioned similarity of theological behavior and the drastic
reduction of viscosity resulting from the addition of deflocculant is
apparent.
I0
i/
Pa.s
0
lo
-1
lO
D
• 0
• o
• U
0 •
0
0
I
I
D
0
O
A •
C D 0.375
• 04
0 04_.
• 045
A05
A0c
006
eJ
ii
dl
G
( A
c.
o
<,
.. .
,0 ;o ;>
Figure l: Viscosityn against
velocity gradient Y for the systems
with concentration of solid C s
equal to 61%.
u_
I0_]
11
lPas'l
0
lO
n
I
c
&
41
A
ii
C: 0. "t
• 0.2
03
• 0 34
_. 0.375
& 0 45
,: C 6
II
II
::' l
_', 0 111
10 _ O •
, C I I
i • ,
:% • C, {., C._.,
'_ • • I •i "_ /"A
I
10 ':L_ 103 ;:' i5'',
ORIGINAL PAGE !8
OF POOR QUALITY
Figure 2: Viscosity q against velocity
gradient # for the systems with solid
concentration C S equal to 50 %.
II
C. _;
• 0.2
• 0.2'75
03
• ,: 45
-.', ',.,b
• 0.8
t, II
II
• II •
• iii • ,II
• "" :'II"
46646 il
lu 10 3 ; { ''- _;
Figure 3: Viscosity r, against velocity
gradient Y for the systems with solid
concentrations C S equal to 40 %.
m
iOF' POOR QUAL.F_Y
The similarities of the curves of flux makes it possible to qive
a compact representation of the shear-dependent behavior of all the
systems considered, accordinq to a procedure of superimposition by
translation of the curve [2,5] . The flux curve of a system (in the
present case the system with concentrations of solid C S - 61%, and
concentration of deflocculants equal to 0.375 %) is taken as reference
curve. The flux curves of all the other systems are translated over
the reference curve. The components of the translation vector determine
the translation factors a and _. The curve of the reference system
may be taken as characteristic curve of the family of systems (master
curve) in a diagram Logn R - log_ R in which r.R and _R are reduced
variables defined by _k_;;,,a ; _R=_, a
pa
IG z, a_.
16 ......................... -..... , •
0 tO' _t _, x
Figure 4: Characteristic flux curve
(master curve) in terms of reduced
viscosity nR against reduced velo-
city gradient YR"
Therefore the first result which is obtained with this procedure
is the plotting of the characteristic curve shown in Figure 4 in a dia-
gram icg_ R - log YR" Another advantage deriving from the application
of such a procedure is that in this way it is easy to obtain the char-
acteristic rheological parameters of this sytem. As regards these
parameters it is observed primarily that for each system it is possible
to determine both directly and/or through the above mentioned procedure
a critical velocity gradient @c below which the shear-dependent behavior
is plastic and may be described satisfactorily with the Bingham model.
t
Above Yc the behavior becomes dilating. Figure 4 shows the flux
curve described by the Bingham model and obtained through the fit hing
6
ORIGINAL PAGE I3
OF POOR QUALITY
of all the experimental points concerning the field of velocity gradients
o
less than Yc"
Therefore the shear-dependent rheological behavior of each system
is characterized by three parameters: the limit of slipping TB, the
plastic viscosity np and the critical velocity gradient Yc" The effect
of the concentration of the solid and the deflocculant on the shear-
dependent rheological properties of the suspensions may therefore be
described by the variations of such parameters.
03 .
i
t, ;
i
.o
1o'
,o
\
,,O
_ _ _- -_2 -_ •
--_- .... -UP"
kL."..
.... -, i,,-- - - ,_'r "
Figure 5: Limit of slipping _B against
concentration of deflocculants C.
_:C, 6_.,: _:C _ 50%; .', :C, _ 40°o) %
(J 02 _,4 I()
,0o
IPa s]
!.,
-1
2Io
I
%
_,, b
"eL,
, , :-','.)('JR QuAI_r_'_'
-1
lo
16:
t6 _ ,
0 0.2 0'4 0.6 08 C("} 10
D
\
Figure 6: Plastic viscosity rip against
concentration of deflocculant C.
(O:C,=61°/,; [];C,=50oi0: '. c,- 40%).
L
' %m
v
2_
0 0_, 04 06 08 _ . 10
Figure 7: Critical velocity gradient
9 against concentration of defloccu-
c
lant C.
(:__):C 61_o; _'G .: SO°o; " C - 40%]
__m_ -_ _
Figures 5, 6 and 7 give the variations of TB, Fip and _c with the
variation of the concentration of deflocculant. The progressive ad-
dition of deflocculant causes a drastic reduction of the parameters,
a reduction which is maximum in case of saturation conditions. This
condition is achieved for different values of concentration at the
three levels of solid concentration studied. Beyond these conditions,
subsequent conditions of deflocculant do not cause considerable effects
of overdoping. Figures 8, 9 and i0 show the effects of the variation
of the solid concentration on TB, np and _c' evaluated in accordance
with three different values of concentration of deflocculant.
/6__£
,0_]
TB !
,Pa,I
q
u
Io
0
I0 ,
/
/
/
/
/
1
Figure 8: Limit of slipping TB against
solid concentration
Cs (0:C=.4%: _:C=,45°o: O:C 6%).
p •
I0
_Ip
IO
0 ¸
/
,/
,is" •,1_
' 4o _o '_,., E,o
Figure 9: Plastic viscosity n
solid concentration C S.
{O:C-_.4°,o: A:C-- ,4S°o: O:C ,6%),
p against
:0
6
O
•_2 --
e
i/
/
Figure 10: Critical velocity gradient
%c against solid concentration C s-
[e :C.. ,4%; A:C - ,4_'_; _;C .6%).
_o_L ...........
40 bo
_,,, L
10
The variation of the parameters with the concentration of defloc-
culants is derived from the variations of the state of agqregation of
the particles obtained from the absorption of deflocculant and the
variation of potential. Actually the adsorption and the development
of the double layer are the main mechanisms by means of which we explain
the effect of the deflocculant used which frees by hydrolysis Na +
cations and colloidal silica.
The high concentrations of solids and the considerable variations
inside the family of systems studied, of the conditions o_ aggregation
of the dispersed phase makes it difficult to apply extensively the
analyses and models proposed by various authors [6-12] to interpret
the theological behavlor of suspensions of kaolin, clay and similar
materials. At the present time it was considered suitable to reexamine
some interpretations proposed by Firth and Hunter [9] concerning the
flow properties of colloidal suspensions to evaluate the possibility
of extending them to the systems in question.
According to those authors and according to what was already indi-
cated by Thomas [8], it is possible to obtain from the data on plastic
viscosity, an estimate of the effective value of the concentration of
the dispersed phase and its variation with the variation of the concen-
tration of deflocculants.
From the value of the relative viscosity nR (defined by the ratio
np/n s with K s the viscosity of the dispersing medium) and from the
equation of Thomas [13], valid for suspensions of spherical particles
without mutual interaction:
] ' "_ ; _1' ; 1 _" _'J_ 'i'" _ 2.73 1.,, '_',,,,,1_ [']616,I. j
it is possible to obtain the value of the effective volumetric fraction
of the dispersed phase assuming the flux units present in conditions of
high velocity gradients as spherical.
ii
): OHIGINAL PAGE IS
OF POOR QUALITY
The ratio CFp = CEff/¢p, in which CEff is the effective volumetric
fraction calculated by this means and _ is the nominal volumetric
P
fraction, gives a measure of the increase of volume of the dispersed
phase resulting from the aggregation of particles. Table 2 gives the
values of CFp for three different concentrations of solids (C S = solid
concentration, C = concentration of deflocculant. It is apparent that
according to the conditions of maximum reduction of the plastic vis-
cosity of the systems, the deflocculation of the dispersed phase is
not complete, the minimum values of CFp being equal to 1.99, 1.62 and
1.43 for the three different concentrations of solids considered.
/6__!i
Table 2: Values of CFp c al_c_ulated o__n the b__aasis of equations of Thomas
c.- 40
c [(,..)
I
.2
.25
275
3
45
.6
8
C, = 5_ . c, L;'
C,,. c [°,,) C,, c {",,; C,,,
2 73 1 2 16 .'_,75 1.91
2 44 .2 2.06 .4 1.78
2.36 .3 1.92 425 1.70
2 31 34 1 78 45 1.59
2 26 .375 1 74 5 1.54
2 07 .45 1.60 £, 1 4G
1 99 6 1.62 .8 1.43
2 03 8 1'.65 I 0 1.48
As regards the dependence of iB on CFp, the linear correlation
given by Hunter and Frayne [12] may be considered valid only in the
first approximation. The decrease of Yc with the addition of defloc-
culation means that in conditions of greater deflocculation, the expan-
sive behavior of the kaolin/clay suspensions is manifested at lower
velocity gradients. We refer to the article by Beazley [.14] for a pos-
sible interpretation.
From an examination conducted on a restricted series of systems
within the range from 20 to 30°C, it was found that the variations of
viscosity with temperature are more marked at high velocity gradients.
As regards the characteristic rheological parameters, this is manifested
in a considerable variation of the plastic viscosity np , while the
12
IJ
i
limit of slipping _B remains approximately constant in the cases
studied. If we analyze the data in terms of relative viscosity,
it is observed that under this aspect too no considerable v_ria-
tions are observed with the temperature, and the conclusion must
therefore be drawn that in the range of temperature considered
and for the systems studied, the decrease of the viscosity of
the suspensions with the temperature is derived substantially
from the decrease of viscosity of the dispersing agent.
4. Conclusions
a) At high solid concentrations and low concentrations of
deflocculant, a substantial thixotropic behavior may be noted
experimentally. In a subsequent study we will present the results
of a detailed investigation of the effect of the temperature on
the rheological properties of the suspension in question.
b) All the systems studied show a similar shear-dependence
behavior which may be described synthetically through a character-
istic flux curve (master curve).
c) It is possible to determine a critical velocity gradient
_C and consequently to differentiate two regions of different
shear-dependent behavior (plastic for gradients less than 9C'
expanding at higher gradients). The plastic behavior may be
described with the Bingham behavior.
d) Three rheological parameters (TB, np and 9C ) are suf-
ficient to characterize the shear-dependence of the systems studied
and to describe the effects of the variations of the contents of
solid and deflocculant.
e) For the three levels of solid contents studied, values
of concentrations of deflocculant were determined beyond which
further additions of deflocculant do not cause perceptible varia-
tions of the rheological behavior.
13
f) It is possible to extend partly to the systems examined
the interpretations suggested by Firth et al. for similar systems
with low solid concentration.
i!
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14
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REFERENCES
Lapasin, R., A. Alessandrini and F. Sturzi, Proc. VIII Int.
Congr. on Rheology, Naples. Vol. 2: Fluids, Naples, 1980,
p. 563.
Alessandrini, A., R. Lapasin, E. Lucchini and F. Sturzi,
Proc. 2nd Yugoslav-Italian-Austrian Chemical En@ineerin@
Conference, Bled, 1980, p. 558.
Cheng, D.C.H. and F. Evans, Brit. J. Appl. Phys. 16, 1599 (1965).
Camina, M. and C.G. Roffey, Rheol. Acta i__O0,606 (1971).
Lapasin, R., A. Papo and G. Torriano, Proc. XIV FATIPEC Contr.
Budapest, 1978, p. 653.
12.
6. Michaels, A.S. and J.C. Bolger, Ind. En@. Chem. Fund. _, 24 (1962).
7. Thomas, D.G., A.I.Ch.E. Journal 9, 310 (1963).
8. Thomas, D.G., A.I.Ch.E. Journal i__0, 517 (1964).
9. Firth, B.A., J. Colloid Interface Sci. 57, 248 (1976)•
Firth, B.A., J. Colloid Interface Sci. 57, 257 (1976).
Firth, B.A. and R.J. Hunter, J. Colloid Interface Sci. 5_/7,
266 (1976)•
Hunter, R.J. and J. Frayne, J. Colloid Interface Sci. 71,
30 (1979).
13. Thomas, D.G., J. Colloid. Sci. 2__0, 267 (1965).
14. Beazley, K.M., Trans. Brit. Ceram. Soc. 63, 451 (1964).
Presented at the Fifth International Technical Symposium on the
Production of Ceramics, Rimini, October 1980.
15 )


Rheological study of clay-kaolin aqueous suspensions

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