Study of the topography and roughness of the glaze surface

Study of the topography and roughness of the glaze surface

MATERIA£Y CERAMICZNE /CERAMIC MATERIALS/, 66, 2, (2014), 121-125
www.ptcer.pl/mccm
Study of the topography and roughness of
the glaze surface as modi¿ed by selection
of raw materials grain size
JANSZ PARTYKA*, MARCIN GAJEK, KATARZYNA GASEK
AGH University of Science and Technology, Faculty of Material Science and Ceramics, Department of Ceramics and
Refractory Materials, al. A. Mickiewicza 30, 30-059 Kraków, Poland
*e-mail: [email protected]
Abstract
The presented paper shows a new, simple method for improving the surface properties, such as smoothness, gloss and whiteness,
of ceramic glazes. This method consists in making the intentional selective choice of the grain size of selected raw-material components.
In the investigation, the variable factor was the grain size distribution of hard raw materials, that is quartz, feldspar and zirconium silicate.
The obtained results indicate that the proper selection of the grain size of individual raw materials markedly improves the surface quality.
Keywords: Grain size, Glaze, Surface, Roughness, Whiteness degree
MODYFIKACJA TOPOGRAFII I CHROPOWATOĝCI POWIERZCHNI SZKLIWA
POPRZEZ DOBÓR UZIARNIENIA SUROWCÓW
Prezentowana praca pokazuje nową, prostą metodĊ poprawiania wáaĞciwoĞci powierzchniowych, takich jak gáadkoĞü, poáysk i stopieĔ
biaáoĞci szkliw ceramicznych. Metoda ta polega na Ğwiadomym selektywnym doborze uziarnienia wybranych skáadników surowcowych.
W badaniach czynnikiem zmiennym byáo uziarnienie surowców twardych, czyli kwarcu, skalenia oraz krzemianu cyrkonu. Uzyskane wyniki
pokazują, Īe odpowiedni dobór uziarnienia poszczególnych surowców znacząco poprawia jakoĞü powierzchni.
Sáowa kluczowe: rozmiar ziarna, szkliwo, powierzchnia, chropowatoĞü, stopieĔ biaáoĞü
1. Introduction
Glazes determine the most important usable and technical parameters of ceramic products. These properties
depend mainly on the quality of glaze surface. Two methods
of correcting the glazes parameters, including surface quality,
are functioning in the technology of manufacture of non-refractory ceramic goods. The ¿rst of them is the modi¿cation of
the molar oxide composition, which relies on the knowledge
of the properties of individual oxides and their effect on the
glaze parameters [1-3]. However, this method is often unreliable, as the role of oxides is only known for simple systems,
whereas contemporary glazes are multi-component systems,
in which the effects of either the synergy or weakening of
the force of interaction between individual oxides exist [4-5].
The second method involves changing the ¿ring parameters of glazed products by either increasing the maximum
temperature or elongating the ¿ring process. Such changes
are dif¿cult to accomplish, chieÀy due to economic reasons.
Few examples of other techniques of modifying the surface
properties of glazes can be found in literature. Methods of
multilayered deposition of ceramic glazes are known. Two
layers of raw glaze are applied onto the green body in two
stages and then jointly ¿red, or a thin layer of transparent
glaze is applied onto the ¿red coat of white opaque glaze,
after which the product is ¿red again [6]. None of the methods
brings about the expected results, mainly due to the dif¿culty
in producing the uniform thickness of the applied coatings,
but also because of the fact that the two glazes react with
each other during ¿ring. Studies on the effect of grain size
distribution on the quality of glazes have been performed by
Koenig and Henderson [7], Bernandin [9], and Danielson [10].
They concern the inÀuence of variations in the duration of
grinding in traditional ball mills on the wettability and reactivity
between the glaze and body, as well as on the occurrence
of defects, such as glaze crawling or rolling up.
Examination of the ceramic glaze surface is dif¿cult. The
high gloss of glazes, or their full or partial transparency, make
the determination of even their colour and shine dif¿cult.
Since recently, the study of the topography of ¿red glaze
surfaces has been enabled to be fully carried out owing to
the development of microscopic techniques. The techniques
most commonly used for this purpose include: AFM electron
microscopy and the confocal laser microscopy technique
[12-14]. The second technique in particular deserves special attention, as it enables satisfactory surface topography
121
J. PARTYKA, M. GAJEK, K. GASEK
images and surface ¿nish results to be obtained in an non-invasive technique and with no special sample preparation.
Table 1. Molar composition of tested glaze.
CaO
MgO
ZnO
2. Experimental procedure
Opaque glaze for a ¿ring temperature of 1210-1220 °C,
with molar composition as shown in Table 1, was used
for testing. The raw materials used included quartz, two
feldspars (a mixed alkaline oxide and a potassium oxide
types), zirconium silicate, wollastonite, talc and kaolin. The
chemical analysis of the raw materials is given in Table 2.
The preparation of glaze sets involved regrinding of individual raw-material groups in a MicrCer laboratory bead mill
supplied by Netzsch. Quartz, which was classi¿ed to the ¿rst
raw-material group, was ground down to four different grain
sizes. The second group included both feldspars, which were
jointly ground down to three grain sizes. Zirconium silicate
was used both in the commercial form and as ground in the
MicroCer mill. The remaining raw materials, i.e. kaolin, wollastonite and talc, were ground jointly in a Gabbrielli planetary
mill for a duration of 15 minutes. Particle size distributions
of raw materials were determined by an X-ray analyzer
Sedigraph 5100 from Micromeritics. The grain size parameters of all raw-material groups are presented in Table 3.
Individual groups were combined as per the recipe (Table
1) and homogenized in the planetary mill for 10 minutes.
The grain size composition of all glazes are shown in Table
4. Homogenization was conducted in the planetary mill with
a small addition of grinding media to avoid any change in the
grain size distribution of the components, but only to achieve
a high degree of homogeneity. The glaze suspensions, immediately prior to application, were additionally homogenized
for 10 minutes using ultrasounds. The above-mentioned
methodology was employed to take control over the grain
size distribution of the glazes. The glaze, in the amount of
6 grams, was applied onto disks of 50 mm in diameter made
of Vitreous China sanitary body from Sanitec Company
(preliminarily bisque ¿red at a temperature of 1000 °C).
Glazing was carried out using a standard spray gun. The
test samples were ¿red jointly in a laboratory electric furnace
0.78
Na2O
0.22
K2O
Al2O3
0.45
SiO2
4.41
ZrSiO4
0.26
Table 2. Chemical analysis of the raw materials.
Name
Oxide composition [wt%]
Al2O3
CaO
MgO
Feldspar
76.06 14.59
0.20
0.10
Feldspar
66.37 18.47
0.40
Quarz
SiO2
99.70
0.30
Wollastonite 51.79
0.42
Talc
65.95
Zirkon
silicate
5.44
Kaoline
59.30 39.73
Na2O+K2O ZrSiO4
9.05
14.76
46.26
1.22
0.60
33.45
0.31
0.76
0.35
0.09
0.14
93.45
0.74
Table 3. Characteristics of the grain size distribution of the raw
materials used.
Raw
materials
Quartz
Feldspars
ZrSiO4
Remaining
raw materials
Residue below grain size [%]
d50
[—m ]
10 —m
1 —m
0.2 —m
8.33
58.6
5.0
0.0
1.44
89.6
16.5
5.6
0.37
92.5
23.6
18.6
0.27
94.6
86.4
41.2
3.99
76.7
16.2
1.1
0.43
99.4
91.6
24.2
0.15
96.0
96.3
59.5
1.37
99.6
36.8
11.7
0.25
99.2
94.9
37.4
4.68
81.2
31.9
1.1
Table 4. Grain size compositions and surface parameters of glazes modi¿ed by grain size selection.
Surface parameters
Grain size glaze compositions d50
Glaze name
Quartz
Feldspar
ZrSiO4
Remaining raw
materials
Whiteness
L
CIELAB
Glossy
[%]
Roughness: linear / surface
de¿ne in experiment
[—m]
GL-1
8.33
GL-2
1.44
GL-3
0.37
GL-4
0.27
GL-3
GL-5
GL-6
8.33
GL-7
0.37
GL-7
GL-8
122
0.37
0.37
0.43
0.43
0.15
3.99
0.15
[—m]
1.37
1.37
0.25
1.37
1.37
MATERIA£Y CERAMICZNE /CERAMIC MATERIALS/, 66, 2, (2014)
2.68
92.70
77.87
2.69
2.62
93.59
80.35
0.73
0.82
94.99
80.05
0.79
0.52
95.01
82.66
0.25
0.27
94.99
80.05
0.79
0.52
95.93
86.21
0.28
0.28
92.70
79.58
0.60
0.66
93.23
80.75
0.28
0.30
93.23
80.75
0.28
0.30
93.55
81.51
0.22
0.27
STUDY OF THE TOPOGRAPHY AND ROUGHNESS OF THE GLAZE SURFACE AS MODIFIED BY SELECTION OF RAW MATERIALS GRAIN SIZE
Table 5. Characteristic temperatures of glazes modi¿ed by grain
size selection.
made to determine the linear roughness, Ra, and the surface
roughness, Sa. The roughness results given (Table 4) are
mean values obtained from scanning two 1.28 mm side square areas on each sample. The images of the topography of
the examined modi¿ed glaze surfaces are shown in Figs. 1-3
(of which Figs. 1-2 are two-dimensional and Fig. 3 is three-dimensional). In addition, the characteristic temperatures of
the examined glazes were determined using a Misura HSM
3M high-temperature microscope, by heating glaze pellets
on the top of an alumina stand until they melted. The values
of the characteristic temperatures (of sintering, softening, the
sphere, the halfsphere, and melting) are shown in Table 5.
Temperature
Glaze
name
Softening
Sphere
Half sphere
Melting
[°C]
GL-1
GL-2
GL-3
GL-4
1178
1288
1326
1373
1175
1287
1325
1371
-3
-1
-1
-2
1166
1273
1322
1369
-12
-15
-6
-4
1155
1268
1315
1354
-23
-20
-11
-19
3. Results and discussion
In the research procedure, emphasis was laid on systematic examinations based on the variability of a single
factor only. Constant molar composition, the identical and
averaged grain size distribution of each raw-material group, the consistent glaze preparation procedure, the same
amount of glaze applied on the biscuit and the joint ¿ring
process, ensure the correctness of the scheduled methods
of research. Any changes of the surface parameters result
only from the pre-planned modi¿cations to the grain size
distributions (Tables 3 and 4). A general conclusion drawn
from the comparison of the surface parameters: brightness,
gloss and roughness is unequivocal. Selective modi¿cation
to the grain size distribution of individual glaze components
at a temperature of 1220 °C for a total duration of 14 hours,
consisting of 7 hours heating, 60 minutes soaking and 6 hours
cooling. The above sample preparation procedure was aimed
at eliminating any additional factors favouring the formation
of surface defects. On the glaze surfaces of the ¿red samples, the determinations of gloss and whiteness were ¿rst
made using a Elcometer 406L and Konica-Minolta CM-700d
spectrophotometer respectively. The measurement results
are shown in Table 4. Then using an OLYMPUS Lext 4000
confocal laser microscope, glaze surface examinations were
a)
b)
d)
c)
e)
Fig. 1. Images of the surface of glazes modi¿ed by grain size selection, a) GL1/(quartz d50 – 8.33 —m); b) GL2/(quartz d50 – 1.44 —m); c)
GL3/(quartz d50 – 0.37 —m, ZrSiO4 d50 – 1.37 —m); d) GL4/(quartz d50 – 0.27 —m), e) GL5/(ZrSiO4 d50 – 0.25 —m)), produced using a LEXT
4000 confocal microscope.
MATERIA£Y CERAMICZNE /CERAMIC MATERIALS/, 66, 2, (2014)
123
J. PARTYKA, M. GAJEK, K. GASEK
a)
a)
b)
b)
Fig. 2. Images of the surfaces of glazes modi¿ed by grain size selection, a) GL7/(feldspar d50 – 3.99 —m); b) GL8/(feldspar d50 – 0.15 —m)),
produced using a LEXT 4000 confocal microscope.
may signi¿cantly enhance the surface quality of the ¿red
glazes. The description of the glazes is based on providing
the value of the median grain size, d50, of the raw material
being characteristic of a given glaze (quartz, feldspars or
zirconium silicate, respectively).
By reducing the grain size of quartz from the value of d50
= 8.33 —m down to the ¿nest grain size of d50 = 0,27 —m, at
a constant feldspar grain size of d50 = 0.43 —m, an almost
tenfold reduction in roughness, and an enhancement of whiteness by 2,5% and gloss by 5% were achieved. In contrast,
reducion of the particle size of the quartz from d50 = 1.44 —m
to d50 = 0.27 —m, at the constant grain size of feldspars d50 =
0.43 —m, leads to the surface roughness which is decreased
approximately 3 times with a small improvement of whiteness
and gloss (Table 4).
The surface parameters are also greatly inÀuenced by
the grain size of zirconium silicate. With a low grain size of
quartz of d50 = 0.37 —m and feldspar of d50 = 0.43 —m, the
reduction of ZrSiO4 grain size from the average value of 1.37
—m (commercial powder) to 0.25 —m reduces the roughness
almost by three times and considerably (by 6%) improves
the gloss (Table 4).
The least signi¿cant effect on the surface parameters of
glazes is shown by the change in feldspar grain size. Table 4
indicates that with ¿ne quartz of d50 = 0.37 —m used, reducing
the feldspar grain sized from d50 = 3.99 —m to d50 = 0.15 —m
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MATERIA£Y CERAMICZNE /CERAMIC MATERIALS/, 66, 2, (2014)
c)
Fig. 3. 3D images of the surfaces of glazes modi¿ed by grain size
selection, a) GL6/(quartz d50 – 8.33 —m); b) GL7/(quartz d50 – 0.37
—m, feldspar d50 – 3.99 —m)), c) GL8/(feldspar d50 – 0.15 —m)), produced using a LEXT 4000 confocal microscope.
results in a reduction in roughness by mere than 20%, with
a slight improvement in gloss and whiteness.
The explanation of these phenomena can be grounded
on the melting points of the basic components of the glaze.
Pure feldspars, the sodium and potassium types, melt at
temperatures of 1118 °C and 1150 °C, respectively, and their
grain size distribution can only inÀuence the melting kinetics.
The liquid phase in aluminosilicate systems starts to form at
a temperature slightly above 1000 °C due to the presence
of feldspar-quartz eutectics, or even below 1000 °C in the
presence of iron oxide, Fe2O3, which occurs in raw materials as an impurity. In this case, the grain size distribution,
particularly of quartz, may be of signi¿cance for accelerating the melting. Similar phenomena might occur at higher
temperatures during the dissolution of quartz particles in the
aluminosilicate melt formed by molten feldspars. The quartz
grain size distribution may also have a signi¿cant effect on
the initiation and kinetics of this process. This is con¿rmed
by the characteristic temperature determination results
presented in Table 5 for the glazes from GL1 through GL4.
In these glazes, the average quartz grain size is changed
from 8.33 —m for GL1 to 0.27 —m for GL4. The differences
in characteristic temperatures between the glazes to which
the coarsest and the ¿nest quartz was introduces range from
11 °C to 23 °C. A change in characteristic temperatures may
also indicate a reduction of glaze viscosity at the maximum
¿ring temperature, which means a better glaze spreading
STUDY OF THE TOPOGRAPHY AND ROUGHNESS OF THE GLAZE SURFACE AS MODIFIED BY SELECTION OF RAW MATERIALS GRAIN SIZE
and easier elimination of surface defects. All of these factors
favour the formation of smoother glazes of lower roughness,
as con¿rmed by the results presented in the paper.
4. Conclusions
References
[1]
[2]
[3]
The presented results allow us to drow the following
conclusions:
– selective grinding and choosing the grain size distribution
of hard raw materials, especially quartz and feldspars,
make it possible to effect some surface properties of
ceramic glazes;
– this method allows the degree of surface defecting to be
reduced to a large extent;
– the greatest effect on the change in the surface parameters of glazes is exerted by quartz grain size reduction;
– the effect of enhancing the surface quality of glazes results primarily from the change in glaze behaviour in the
¿ring process, namely the reduction of the characteristic
temperatures and viscosity;
– the increasingly common use of high-energy Àow mills
allows this method to be used in a tailor-made manner
to optimize the manufacturing costs and product quality.
Acknowledgements
The study has been carried out within the framework
of Research Project No. N N508 477734 ¿nanced by the
National Research and Development Committee (NCBiR).
The method is protected by the polish patent law, under
Patent Application No. PL 390244 A1.
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i
Received 18 October 2013, accepted 9 December 2013
MATERIA£Y CERAMICZNE /CERAMIC MATERIALS/, 66, 2, (2014)
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