ISO 19613:2026

International
Standard
ISO 19613
Second edition
Fine ceramics (advanced ceramics,
2026-09
advanced technical ceramics) —
Measurement of viscosity of
ceramic slurry by use of a rotational
viscometer
Céramiques techniques — Mesure de la viscosité des céramiques
en suspension au moyen d'un viscosimètre rotatif
Reference number
© ISO 2026
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
4.1 Rotational viscometer with defined shear rate .3
4.2 Single cylinder viscometer .4
5 Apparatus . 4
5.1 General .4
5.2 Measuring system .4
5.2.1 General .4
5.2.2 Basic capacity of the instrument .4
5.2.3 Installation of rotational viscometer .4
5.3 Single cylinder viscometer. .5
5.3.1 Main body of single cylinder viscometer .5
5.3.2 Spindle .5
5.4 Temperature-control device. .5
5.4.1 Thermostat .5
5.4.2 Thermometer .5
6 Calibration of the rotational viscometer . 5
7 Measurement condition . 6
7.1 Temperature .6
7.2 Shear rate or angular velocity .6
7.3 Selection of geometry and/or spindle .6
8 Pretreatment of the sample . 6
8.1 Conditioning.6
8.2 Mixing .6
8.3 Degassing .7
9 Measurement procedures . 7
9.1 Sample loading . .7
9.2 Container sealing .7
9.3 Determination of a flow or viscosity curve .7
9.3.1 General .7
9.3.2 Measurement with a shear rate or angular velocity sweep . .7
9.3.3 Flow curve .8
9.3.4 Viscosity curve .8
9.4 Viscosity measurements .8
9.4.1 General .8
9.4.2 Measurement at fixed shear rate or angular velocity .8
9.4.3 Repeat and case of several measurements .9
10 Expression of the results . 9
11 Test report . 9
Annex A (informative) Coaxial double cylinder system . 10
Annex B (informative) Cone and plate system .13
Annex C (informative) Parallel plate system . 14
Annex D (informative) Single cylinder viscometer .16
Annex E (informative) Typical ranges of shear rate values . 19
Bibliography .20

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
This second edition cancels and replaces the first edition (ISO 19613:2018), which has been technically
revised.
The main changes are as follows:
— clarification added to the scope;
— paragraph addition in the Apparatus section on the use of different geometries;
— paragraph addition in the Measurement condition on the choice of the shear rate range;
— reorganisation of the Pretreatment of the sample section;
— rewriting the Measurement procedure section to include the identification of the fluid behaviour.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
International Standard ISO 19613:2026(en)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Measurement of viscosity of ceramic slurry by
use of a rotational viscometer
1 Scope
This document specifies a method for measurement of the viscosity of a ceramic slurry using a rotational
viscometer. The method only involves rotations with a monotonic angle variation. This document does not
apply to measurements using an oscillating rotation.
Ceramic slurry is used in ceramic processes such as dip coating, spray coating, screen printing, slip casting,
tape casting, spray drying and polishing. This document does not apply to dispersion of fillers in molten
thermoplastic polymers.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 20507, Fine ceramics (advanced ceramics, advanced technical ceramics) — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20507 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
shear stress
stress acting on planes parallel to the direction of flow when the fluid is subject to laminar flow
Note 1 to entry: The SI units are Pascal (Pa).
3.2
shear rate
gradient of laminar flow rate perpendicular to the fluid flow
−1
Note 1 to entry: The SI units are s .
3.3
viscosity
ratio of shear stress (3.1) to shear rate (3.2)
Note 1 to entry: This ratio is representative of the internal resistance of the fluid to flow.
Note 2 to entry: The SI unit of viscosity is Pa × s.
Note 3 to entry: mPa × s = 1 cP in terms of c.g.s. units [where 1P = 1 g/(cm × s)].

Note 4 to entry: Viscosity is sometimes called ‘dynamic viscosity’ or ‘shear viscosity’ for clarification. The measured
viscosity is conventionally called ‘apparent viscosity’ since the gradient of shear rate is not identical for all parts of the
spindle.
3.4
Newtonian fluid
fluid in which shear stress is proportional to shear rate
Note 1 to entry: The ratio of shear stress to shear rate is viscosity.
3.5
non-Newtonian fluid
fluid in which shear stress is not proportional to shear rate
Note 1 to entry: The non-Newtonian behaviour can be determined by measuring shear stress using varying shear rate
(or angular velocity). Viscosity of the non-Newtonian fluid changes with the shear rate, in contrast with Newtonian
fluid, which has constant viscosity with the shear rate.
3.6
thixotropy
flow behaviour of fluid that shows time dependence, such that the apparent viscosity decreases with time
for a constant shear rate, and recovers slowly with withdrawal of the shear force
3.7
shear thickening
increase of shear viscosity of fluid when the shear rate (or stress) is increased
3.8
shear thinning
decrease of shear viscosity of fluid when the shear rate (or stress) is increased
3.9
Bingham plastic
linear shear stress/shear rate relationship starting from a finite yield stress value below which the fluid
does not flow
Note 1 to entry: The linear relationship is usually valid on a limited rage of shear rate.
3.10
flow curve
curve showing the relationship between shear rate and shear stress
Note 1 to entry: See Figure 1 a).
3.11
viscosity curve
curve showing the relationship between shear rate (or shear stress) and viscosity
Note 1 to entry: See Figure 1 b).

a) Flow curve b) Viscosity curve
Key

γ shear rate
τ shear stress
η viscosity
1 Bingham plastic
2 shear thickening (dilatant)
3 newtonian
4 shear thinning (pseudoplastic)
5 thixotropy (time dependent)
Figure 1 — Summary of rheological behaviours
3.12
ceramic slurry
suspension of grinding frit, clay or ceramic powders mixed or dispersed in water or other liquid. It includes
colloidal suspension, slip and paste
Note 1 to entry: The category may include low-viscosity colloids with small particles with sizes in the nanometre or
micrometre range, and high-viscosity pastes with inhomogeneous mixtures.
4 Principle
4.1 Rotational viscometer with defined shear rate
The viscosity, η, of a ceramic slurry measured using a rotational viscometer with a defined shear rate is
determined using Formula (1):

  (1)


where
η is the viscosity, in Pa × s;
τ is the shear stress, in Pa;
−1

γ is the shear rate, in s .
NOTE Symbols are in accordance with ISO 80000-4.

4.2 Single cylinder viscometer
A spindle of cylindrical or disk-like shape is driven in the ceramic slurry at a fixed angular velocity. Torque
is developed from the fluid resistance, and it depends on the viscosity of the slurry. Theoretically, shear rate
(or shear stress) cannot be determined, but viscosity can be measured as a function of angular velocity.
NOTE The gradient of shear rate is not identical for all parts of the spindle. Therefore, the measurement result is
conventionally called apparent viscosity because it is not the viscosity determined from the gradient of a known shear
rate.
5 Apparatus
5.1 General
Rotational viscometers have various measuring geometries. Representative rotational viscometers having
a defined shear rate are a coaxial cylinder system (see Annex A), a cone and plate system (see Annex B), and
a parallel plates system (see Annex C). In contrast, single cylinder viscometers without a defined shear rate
(see Annex D) are able to give an apparent viscosity relatively quickly and reproducibly, and to provide a
comparison between samples.
Contrary to coaxial cylinder and cone and plate geometries, the shear is not homogeneous in a parallel plates
system. The nature of geometry shall be reported and taken into consideration when comparing different
sets of results. Rotational viscometer with defined shear rate
5.2 Measuring system
5.2.1 General
The measuring system shall consist of two rigid, symmetrical, coaxial surfaces between which the fluid
whose viscosity is to be measured is placed. One of these surfaces shall rotate while the other remains
at rest. The measuring system shall be such that the shear rate can be defined for each measurement. A
torque-measuring device shall be connected to one of the surfaces, thus permitting determination of the
torque required to overcome the viscous resistance of the fluid. Suitable measuring systems are the coaxial
double cylinder system (see Annex A), cone and plate system (see Annex B), and parallel plate system (see
Annex C), as prescribed by JIS 8803 and ISO 20507. The dimensions of each measuring system are detailed
in Annexes A, B, and C, which are designed to ensure a geometrically similar flow field for all types of
measurement and all common types of basic instrument.
5.2.2 Basic capacity of the instrument
The basic instrument shall be designed to permit alternative rotors and stators to be fitted, for the generation
of a range of defined rotational frequencies (stepwise or continuously variable), and for measuring the
resulting torque, or vice versa (i.e. measurement of the necessary angular velocity to generate a defined
torque). The apparatus shall have a torque-measurement accuracy of 2 % of the full-scale reading. Within
the regular working range of the instrument, the accuracy of rotational-frequency measurement shall be
2 % of the measured value. The repeatability of viscosity measurement shall be ±2 %.
NOTE By using different measuring systems and rotational frequencies, most commercial instruments cover a
−2 3
viscosity range of at least 10 Pa × s to 10 Pa × s.
5.2.3 Installation of rotational viscometer
5.2.3.1 Coaxial double cylinder viscometer
a) The axis of rotation of the viscometer is installed vertically.
b) The surface of the sample is maintained at a lower position than the surface of the thermostat or the top
of the liquid jacket in the outer cylinder.

c) The inner cylinder is placed with its axis coinciding with the axis of the outer cylinder; the distance
from the bottom of the inner cylinder to the bottom of the outer cylinder is more than 5 mm. The upper
surface of the inner cylinder is more than 5 mm below the surface of the sample.
5.2.3.2 Cone and plate viscometer
a) The axis of rotation of the viscometer is installed vertically, and the plate horizontally.
b) The surface of the sample is maintained at a lower position than the surface of the thermostat or the top
of the liquid jacket in cone and plate.
c) The cone is adjusted so its tip lies on the axis of rotation, and the centre of the parallel plate is also
positioned on the axis.
NOTE The tip of the cone can cause friction if it is in contact with the plate. The tip means the imaginary tip of the
cone obtained by extrapolation if the end is cut flat.
5.3 Single cylinder viscometer.
The single cylinder viscometer has two main components relevant to this standard.
5.3.1 Main body of single cylinder viscometer
It is necessary to select the proper model of viscometer for the viscosity to be measured, each model being
suited to a specific range of viscosities. Brookfield provides single cylinder viscometers that are classified
as LV (low viscosity), RV (medium viscosity) and HA/HB (high viscosity), as prescribed in ISO 2555. Other
manufacturers also provide equivalent systems. The suitable uses of cylinder-type viscometers are also
determined by special spindles such as Krebs or vane types. Some single cylinder viscometers do not have a
demarcation point between the body/shaft and spindle to define the amount of rotating surface submersed,
so the shear rate is not fully determined in that case.
5.3.2 Spindle
Do not use spindles that are corroded or show eccentric rotation. Choose the spindle taking into account the
value of viscosity to be measured, based on the model of viscometer and angular velocity. It is preferable to
use the same spindle to compare samples, even when the measured value is outside the spindle’s optimum
range, rather than change spindles and rely on instrument accuracy. For an unknown sample without any
prior information, choose the proper exchangeable spindle that gives a proper magnitude of torque when
tested through the full range of angular velocity.
5.4 Temperature-control device.
5.4.1 Thermostat
The circulation temperature of a constant temperature bath or electric heated wall temperature of a
constant temperature bath shall be maintained within ±0,2 °C for temperatures between 0 and 50 °C. Wider
tolerances (e.g. ±0,4 °C) are often sufficient outside this temperature range. Closer tolerances (e.g. ±0,1 °C)
may be necessary for precise measurements.
5.4.2 Thermometer
The accuracy of the thermometer shall be ±0,2 °C or the apparatus shall contain a device to measure
temperature with equivalent accuracy.
6 Calibration of the rotational viscometer
Viscometers shall be calibrated periodically, e.g. by measuring the torque characteristics or by using
reference liquids of known viscosity (Newtonian fluids). Standard pre-mixed liquids are preferable to

the use of distilled wat
...