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Effect of firing temperature on triaxial electrical porcelain properties made from Tanzania locally sourced ceramic raw materials

Authors:
Blasius Ngayakamo at Dar es Salaam Institute of Technology
Blasius Ngayakamo
S. Eugene Park
S. Eugene Park
S. Eugene Park
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építôanyag
§ Journal of Silicate Based and Composite Materials
Effect of firing temperature on
triaxial electrical porcelain properties
made from Tanzania locally
sourced ceramic raw materials
blaSiuS NGAYAKAMO § The Nelson Mandela African Institution of Science and Technology,
Department of Materials Energy Science and Engineering § henryblasius@gmail.com
S. eugene PARK § The Nelson Mandela African Institution of Science and Technology,
Department of Materials Energy Science and Engineering
Érkezett: 2018. 02. 16. § Received: 16. 02. 2018. § https://doi.org/10.14382/epitoanyag-jsbcm.2018.19
Abstract
The study has investigated the effect of firing temperature during the production of technical
triaxial electrical porcelain, for electrical insulation applications using Tanzania locally sourced
ceramic raw materials. The green triaxial porcelain samples containing 50 wt% of Pugu kaolin,
35 wt% of Same clay and 15 wt% of feldspar were produced and fired at 1200°C-1300°C with
a heating rate of 10°C/min (dwell time of 1.5h) and cooled at 100C/min to a room temperature.
X-ray diffraction technique was used to investigate phases developed in the triaxial electrical
porcelain after firing process. The main crystalline phases revealed were mullite and quartz. The
technological properties of the triaxial electrical porcelain such as water absorption, apparent
porosity, bulk density, bending and dielectric strength were determined for each porcelain sample
fired at high temperature. The optimum physical-mechanical and electrical properties were found
at 12500C. However, the triaxial electrical porcelain properties were found to decrease with the
increase in firing temperature.
Keywords: Firing temperature, triaxial electrical porcelain, physical-mechanical and dielectric
properties
Kulcsszavak: Égetési hőmérséklet, triaxiális szigetelő porcelán, fiziko-kémiai és dielektromos
jellemzők
Blasius NGAYAKAMO
MSc Materials Scientist and Engineer
at NM-AIST. Department of Materials Energy
Science and Engineering. Fields of interest:
ceramic raw materials, flux materials and high
voltage porcelain insulators.
S. Eugene PARK
Associate Professor and chair, Materials and
Energy Science and Engineering at NM-
AIST Department of Materials Science and
Engineering, Fields of interest: Ceramic and
sustainable Energy Engineering.
1. Introduction
Triaxial electrical porcelain is composed of clay, feldspar which
are locally sourced ceramic raw materials and other ller materials
such as quartz and alumina. e raw materials play specic
roles in inuencing the properties and performance of the nal
products. Clay [Al2Si2O5 (OH)4] provides plasticity, quartz (SiO2)
maintains the shape of the porcelain structure during ring, and
feldspar [KxNa1-x (AlSi3) O8] promotes vitrication. e three
ceramic raw materials place electrical porcelain in the phase
system [(K, Na)2O-Al2O3-SiO2)] in terms of oxide hence referred
as triaxial porcelain [1, 2]. Traditional ceramic raw materials are
the potential candidate materials for the production of triaxial
electrical porcelains. e use of traditional ceramics as raw
materials instead of industrial chemicals is highly preferred due
to the lower price of the raw materials [3].
e properties of triaxial electrical porcelain are contributed
to the variations in the composition of the raw materials, the
method of production, and the ring temperature adopted
[1]. e sintered triaxial porcelain product contains mullite
(Al6Si2O13) and undissolved quartz (SiO2) crystals embedded
in glassy phase which result from the liquid phase formed by
the melting of feldspar in the raw materials [4].
erefore the desired properties of triaxial electrical
porcelains are achieved particularly during the ring process
since the technological properties of clay-based ceramics
products depend on ring conditions such as temperature
[5, 6]. However, other technological properties which are
evaluated to determine the performance of the ceramic product
aer ring are water absorption, ring shrinkage and bending
strength [6]. During the ring process, the triaxial porcelain
body undergoes several phase transitions, during which both
composition and structure change signicantly which inuence
triaxial porcelain properties at the end of the ring process
[5]. Hence, the properties of the triaxial porcelain are mainly
inuenced by sucient development of mullite during ring
process since the development of mullite in the porcelain is
highly associated with ring temperature of the porcelain which
should not be below 1150 to 1200 °C for the mullite forming
processes to be completed [5, 7]. erefore, the development of
the physical-mechanical and dielectric properties of porcelain
are contributed by each phase developed during ring which
depends on the concentration and microstructural attributes
which are inuenced by temperature and the chemical
composition of the raw materials which is an important factor
because of its eects on porcelain properties [8-11]. Since the
eect of ring temperature on the electrical porcelain properties
made from Tanzania locally sourced ceramic raw materials
is not reported. erefore, the work intends to evaluate the
eect of ring temperature on the triaxial electrical porcelains
made from Tanzania locally sourced ceramic raw materials.
However, the study focuses also on the phase changes, surface
morphology development as well as the physical-mechanical
and dielectric properties of the triaxial electrical porcelain
sample due to change in ring temperature.
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2. Experimental procedures
Pugu Kaolin was collected from the Pugu hills, 35 km west of
Dar es Salaam, Same clay and feldspar from Same, Kilimanjaro
region in the northern zone of Tanzania. e ceramic raw
materials were crushed and ball milled to reduce their size.
e particle size less than106 µm was achieved by using sieve
shaker Model RX-29-10 digit. e chemical composition of
the raw materials was analyzed by using X-Ray Fluorescence
(XRF) PANalytical, Model: Minipal4 (PW4030)-Rh X-Ray
Tube, 30kV, 0.002mA and the results are presented in Table 1.
e examination of the surface morphology of the porcelain
sample was carried out by Scanning Electron Microscope
(SEM) Model: JEOL JSM-6335F having a resolution of 10µm
at 2kV. e crystalline phase analysis of the porcelain insulator
was analyzed by X-ray diractometer Model: Bruker D2-
PHASER-40Kv/44mA. Six triaxial porcelain samples were
produced by varying the composition of the locally sourced
materials by 50%wt of Pugu kaolin, 35%wt of same clay and
15%wt of feldspar. e powder mixtures were uniaxially
compacted into rectangular shapes at 10 MPa. e porcelain
green body samples were seasoned at a room temperature for
5 days and they were oven dried at the temperature of 110 °C
for 24 hrs. e sintering of porcelain samples was done at 1200,
1250 and 1300 °C for 1.5 hrs at the ramp rate of 10 °C/min
in each ring process. e sintered porcelain bodies were le
to cool at 10 °C/min to room temperature and were subjected
to physical-mechanical properties and dielectric strength
analysis.
3. Results and discussion
3.1 Chemical composition of the raw materials
e chemical compositions of the raw materials in form of
their oxides are presented in Tabl e 1 . e study results reveal
that both clays have the higher content of silica and alumina.
However, feldspar and Pugu kaolin have a higher content
of Hematite (Fe2O3) compared to Same clay. e literature
reports that small amount of coloring oxides such as Fe2O3
and TiO2 less than 0.9% may be accepted for porcelain wares
production [12]. However, a considerable high amount of
Fe2O3 in Pugu kaolin and feldspar may not be accepted as
they may impart yellowish and reddish color in porcelain
wares unless beneciated. Feldspar has considerable higher
alkaline oxide K2O than Pugu kaolin and Same clay. During
the sintering process, the alkaline oxide K2O melts and
forms the liquid phase that contributes to densication at
higher temperatures due to the formation of the glassy phase.
Nevertheless, the quantities of the alkaline oxides depend on
the mineralogical nature of the clays and their reactivity during
melting of the clay minerals [13]. e alkaline oxides(K2O
and Na2O) play a signicant role towards vitrication,
phase transformation and mullite grain growth [14, 15].
Oxides Pugu kaolin Same clay Feldspar
SiO260.0 60.4 57.1
Al2O330.3 13.9 14.0
Fe2O33.95 1.40 3.08
MnO 0.021 0.00 0.32
CaO 0.39 0.00 1.0
Na2O0.00 0.04 0.20
K2O2.14 2.6 12.09
Table 1. Chemical composition of raw materials
1. táblázat Alapanyagok kémiai összetétele
3.2 Mineralogical composition of the raw materials
e X-ray diraction patterns of the ceramic raw materials
before and aer ring are presented in Fig. 1 as reported by
[16]. e result shows phase compositions of both Pugu kaolin
and Same clay are kaolinite, however, Pugu kaolin showed the
development of crystalline phases of mullite and quartz at a
temperature of 1400 °C. In addition, Same clay was observed
to form cristobalite and sillimanite above 1200 °C. Feldspar
contains albite, and microcline, tridymite, and quartz. Since
the major components of interests are potassium feldspar
(K2OAl2O3O6SiO2) sodium feldspar (Na2O Al2O3O6SiO2);
and lime feldspar (CaOAl2O3O6SiO2). However, the results
indicate that feldspar deposit contains a high content of potash
feldspar compared to soda feldspar which is also supported by
the chemical composition by XRF that is K2O is 12.09% while
Fig. 1. X-ray diraction patterns of Pugu kaolin, Same clay and feldspar [16]
1. ábra Pugu kaolin, Same agyag és földpát röntgendiraktogramjai [16]
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Na2O is only 0.20%.So feldspar deposit is, therefore, a potash
feldspar. Feldspar promotes vitrication of the porcelain
insulator at the end of the sintering process.
3.2 Characterization of red triaxial porcelain samples
Fig. 2 presents the results of water absorption, apparent
porosity, and bulk density respectively for the porcelain
samples versus ring temperature. e gure shows that
the best values for physical properties for triaxial electrical
porcelain are achieved at the ring temperature of 1250 °C.
is might be due to the formation of the liquid phase and
densication at this ring range. However, the values of water
absorption, apparent porosity, and bulk density were observed
to decrease at higher ring temperature. is might be due to
the expansion of trapped water bubbles inside the porcelain
matrix and change in the composition of the glassy phase [1,
3]. e results of the study are in agreement with the works
of [1, 3, 13]. e authors reported that water absorption and
bulk density increased due to vitrication and densication of
the porcelain samples. However, the physical properties were
observed to vary due to the decrease of vitrication range
and an increase of ring temperature due to the expansion
of trapped water bubbles inside the porcelain sample at high
ring temperatures. Generally, the variation of the physical
properties of the triaxial electrical porcelain might have
been caused by the method of production, chemical and
mineralogical properties of the raw materials.
Fig. 2. Physical properties of triaxial electrical porcelain sample versus ring
temperature
Fig. 2. Triaxiális szigetelő porcelán zikai jellemzői az égetési hőmérséklet
függvényében
Fig. 3 shows changes in the mechanical strength of triaxial
electrical porcelain with ring temperature. e trend shows
that the increase of mechanical strength of porcelain sample may
be due to increased densication, vitrication and in absence of
microcracks. e best mechanical strengths (both bending and
compressive strengths) were obtained at 1250 °C. However, the
mechanical strengths began to decrease above 1250 °C due to
closed pores development and a considerable amount of cracks
on the surface of the porcelain samples. e results of the current
study are in agreement with the previous studies as reported
in the works of Kitouni et al.,[13] and Olupot et al., [1]. e
authors have reported that the mechanical strength increases
due to increased densication with temperature and tends to
decrease due to development of pores at high ring temperature.
However, the mechanical strength was found to decrease with
the increase of the ring temperature due expansion of closed
pores and microcracks [1]. Hence the mechanical strength of a
porcelain sample is strongly dependent on the defects such as
pores and cracks [13].
Fig. 3. Variation of mechanical strength of triaxial electrical porcelain sample versus
ring temperature
Fig. 3. Triaxiális szigetelő porcelán mechanikai jellemzői az égetési hőmérséklet
függvényében
Fig. 4 shows the variation of the dielectric strength of
porcelain samples red at 1200, 1250 and 1300 °C. e trend
shows that the dielectric strength increases with an increase
in ring temperature and began to decrease with further
temperature rise at 1300 °C. e increase of the dielectric
strength of electrical porcelains is due to increased vitrication
range of the electrical porcelains samples. e results of the
current study are also reported by Olupot et al, [1]. e authors
evaluated ceramic raw materials from Uganda for electrical
porcelain production. e authors obtained the highest
dielectric strength of 19kV/mm at 1250 °C. However, above
1250 °C, the samples became more porous due to change in
the composition of the glassy phase. e dielectric strength
was found to decrease with the increase of ring temperature
which aected vitrication range and the dielectric properties
of the triaxial electrical porcelain.
Fig. 4. Variation of dielectric strength of triaxial electrical porcelain sample versus
the ring temperature
Fig. 4. Triaxiális szigetelő porcelán dielektromos jellemzői az égetési hőmérséklet
függvényében
In Fig. 5 the X-diraction pattern of triaxial electrical
porcelain is presented. e diractogram conrms that the
mullite and quartz phases are present in the porcelain insulator.
Both phases promote the mechanical and dielectric properties
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of the porcelain insulator. However, high peaks of quartz
may lead to high amount of glassy phase which may lower
the dielectric strength of the porcelain insulators but not the
mechanical strength of a porcelain insulator which is aected
by microcracks. e high amount glassy phase provides free
movement of mobile ions such as Na+, K+, and Al3+ which
increases the conductivity [17].
Fig. 5. X-ray diraction pattern of a porcelain insulator red at 1250 °C
Fig. 5. 1250 °C hőmérsékleten égetett szigetelő porcelán röntgendiraktogramja
Fig. 6 shows the examination of the surface morphology using
the Scanning Electron Microscope (SEM) Model: JEOL JSM-
6335F having a resolution of 10nm at 2kV. It was evidenced the
densication on the surface of the triaxial electrical porcelain
sample aer the ring process was completed.
Fig. 6. SEM micrographs showing densication of triaxial electrical porcelain sample
at 1250 °C
Fig. 6. 1250 °C hőmérsékleten égetett triaxiális szigetelő porcelán
elektronmikroszkópos felvétele
4. Conclusions
In this research work, the eect of ring temperature on
triaxial porcelain samples properties was investigated. At the
optimum ring temperature of 1250 °C, the best physical-
mechanical and dielectric properties were achieved. However,
ring beyond 1250 °C resulted in progressive deterioration of
the physical-mechanical and the dielectric properties of the
electrical porcelain samples. is might have been caused by
the development of microcracks and high content of glassy
phase caused by high peaks of quartz. So it is imperative to
be aware that, the actual ring temperature and its inuence
on the triaxial electrical porcelain properties depend on the
chemical composition of the materials under study. erefore,
the locally sourced materials need to be evaluated from time to
time in order to avoid deviation of the desired triaxial electrical
porcelain properties during the ring process.
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Ref.:
Ngayakamo, Blasius – Park, S.Eugene: Eect of ring temperature on
triaxial electrical porcelain properties made from Tanzania locally
sourced ceramic raw materials
Építő anyag – Journal of Silicate Based and Composite Materials,
Vol. 70, No. 4 (2018), 106–109. p.
https://doi.org/10.14382/epitoanyag-jsbcm.2018.19
Az égetési hőmérséklet hatása tanzániai helyben
bányászott kerámia alapanyagokból készült triaxiális
porcelán szigetelők jellemzőire
xxxxxxx
Kulcsszavak: égetési hőmérséklet, triaxiális szigetelő porce-
lán, fiziko-kémiai és dielektromos jellemzők
ÉPA 2018_4.indd 109 2018. 10. 20. 18:22:55
... The quality and quantity of the raw materials plays a significant role on the properties of blended green body and the fired body/microstructure of porcelain body that ultimately affect the performance of electrical porcelain insulators. The clay [Al 2 Si 2 O 5 (OH) 4 ] content when wet, acts as a binder for the other body ingredients in the green state which confirm plasticity of the body for easy molding and shaping, while feldspar [K x Na 1-x (AlSi 3 )O 8 ] serve as flux and alternative source of alumina and silica, whereas quartz (SiO 2 ) used as a filler material helps to maintain the shape of porcelain body at green state and during firing (Ngayakamo and Park, 2018). Various scholars designed efficient high quality porcelain insulator using ball clay as a plastic materials (Anih et al., 2005;Oladiji et al., 2010). ...
... A crystalline alumino-silicate mullite (Al 6 Si 2 O 13 ) compound primary originated from clay relictcalled primary mullite and has a cuboidal structure under SEM analysis (Carty and Senapati, 1998;Iqbal and Lee, 2000;Lee and Iqbal, 2001;Lee et al., 2008). Whereas, the glassy phase or liquid phase originated during sintering of feldspar, causes densification of the ceramic bodies (Ngayakamo and Park, 2018). But an excess amount of glassy phase promotes free movement of ions in the porcelain bodies that result in poor electrical insulation. ...
... As observed from Fig. 6d, the dielectric strength of porcelain insulators were found to increase with increasing firing temperature and reaches a maximum of 8 kv/mm at a firing temperature of 1300 C. The increasing of the dielectric strength may be due to increased vitrification range of the electrical porcelain samples at the optimized firing temperature (Ngayakamo and Park, 2018). Among the desired batch composition, the dielectric strength of batch-2, batch -3 and batch-4 found to fall in the specified range of 6.1-13 kv/mm for porcelain insulator (Olupot et al., 2010). ...
Fabrication of electrical porcelain insulator from ceramic raw materials of Oromia region, Ethiopia
Article
Full-text available
  • Aug 2019
Electrical porcelain insulator was fabricated from local ceramic raw materials, Bombowha kaolin/clay, Arero feldspar and Arero quartz available in Ethiopia. The raw materials mineralogy, chemical composition, and thermal properties were characterized by using x-ray diffractometer (XRD), atomic absorption spectrometer (AAS) and thermogravimetry (TGA), respectively. Plasticity of clay was determined according to Atterberg plasticity test. Based on the raw materials chemical composition, five different porcelain insulator test bodies were prepared at firing temperature of 1000 °C, 1100 °C, 1200 °C and 1300 °C. Water absorbance, apparent porosity, bulk density, dielectric strength and microstructure of fired porcelain insulators were studied as a function of firing temperature. The XRD and AAS results revealed that in Bombowha clay, kaolinite mineral was found to be a major mineral constituent with appreciable silica (46.84 wt%) and alumina (36.74 wt%) content with moderate plasticity (PI = 19–21%). The Arero feldspar belongs to anorthoclase feldspar minerals with less alkali content (Na2O + K20) of
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... Mullite (3Al 2 O 3 .2SiO 2 ), which is formed when clay is fired at an elevated temperature, is the primary objective in the production of porcelain insulators, and it is a characteristic constituent of all ceramic microstructures (Islam et al., 2004;Meng et al., 2012;Merga et al., 2019). Porcelain microstructure consists of coarse quartz particles and mullite crystals embedded in a glassy phase (Ngayakamo & Park, 2018a). The formation of crystalline mullite, the particle size of the quartz, the viscosity of the glassy phase, and their homogeneity throughout the body of the microstructure have the potential to tune the ultimate properties of the porcelain insulator. ...
... The micrographs in Batch-3 showed interconnected mullite phase and quartz particles of various sizes embedded in the glassy phase. This is a characteristic of porcelain microstructure (Ngayakamo & Park, 2018a). The quartz grain was retained from the raw materials as a result of partial sintering (Belhouchet et al., 2019), the reaction of metakaolinite with relics of feldspar formed the mullite phase, and the glassy phase was formed from feldspar melt (Iqbal & Lee, 2000;Meng et al., 2012;Merga et al., 2019). ...
Potential Uses of Local Clay Materials for the Production of Porcelain Electrical Insulators, Ethiopia
Article
  • Jun 2023
Clays are extremely variable materials with different mineral compositions, and they are the main ingredients in ceramics applications. Their properties play specific roles in influencing the technological properties and performance of ceramics products. Evaluating the various properties can help to determine the best way to utilize clay materials, such as the locally available Bombawuha (BC) and Denkaka (DC) clays mined from Ethiopia's Bombawuha and Denkaka areas, respectively. The objective of this study was to examine these materials for the purpose of using them to produce quality electrical porcelain insulators. The clay samples were characterized for their chemical composition, mineralogy, thermal properties, plasticity, and particle-size distribution, using atomic absorption spectrometry (AAS), X-ray diffractometry (XRD), differential thermal analysis coupled with thermogravimetric analysis (DTA-TGA), the Atterberg plasticity test, and sieve hydrometer analysis. Based on the characteristics, suitable clay materials were selected and mixed with feldspar and quartz to formulate various porcelain body compositions which were fired at three different temperatures (1200, 1250, and 1300°C) and dwell times (1.5, 2.0, and 2.5 h). The mineralogy, water adsorption, apparent porosity, bulk density, dielectric strength, flexural strength, and microstructure of the fired bodies were measured. The results revealed that, compared to DC, BC contains kaolinite as the major mineral with appreciable amounts of silica (46.72 wt.%), alumina (35.32 wt.%), and fluxing oxides but smaller amounts of CaO. BC contains greater clay fractions (20.58 wt.%); and has a middle-range plasticity index (PI = 11.2 wt.%), thus making BC suitable for producing porcelain insulators. A test-body composition of 40 wt.% BC, 40 wt.% feldspar, and 20 wt.% quartz, fired at 1250°C for 2 h, exhibited water adsorption of 0.17 wt.%, apparent porosity of 0.42 wt.%, bulk density of 2.45 g/cm3, a dielectric strength of 8.22 kV/mm, and flexural strength of 43.63 MPa and, thus, satisfied the required properties for quality porcelain insulators.
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... This suggests that the possibility of electric shock is low since the insulator has a good charge storage capacity. The samples exhibit electrical resistance that are above the recommended range 1.0x10 6 which is a quality of a good insulator [3,54]. Generally, this suggests that the fine nature of the talc powder helped to amplify the qualities of the other constituents in the porcelain insulators. ...
... The dielectric strengths of the samples were reported to reach a maximum of 13 kV/mm as the firing temperature increases. This is attributed to the increased vitrification range of the ECPI samples at the optimized firing temperature [54]. The XRD showed only feldspar and quartz peaks at 1000°C with no peak for the clay. ...
Production of Electrical Porcelain Insulators from Local Raw Materials: A Review
Article
Full-text available
  • Aug 2021
This paper reviewed the production of electric porcelain insulators utilizing from local raw materials from developing countries. The raw materials used were feldspar, quartz/silica and kaolin. The chemical composition, mineralogy, and thermal properties of the raw materials were characterized using AAS, XRD, and TGA respectively. Different weight percentage combinations of the individual raw materials were investigated by the authors. Most of the results showed relatively acceptable porcelain insulators properties such as low water absorption, poros-ity, high insulation resistance, dielectric strength and bulk density. The paper showed that electric porcelain insulators with good properties can be produced from available local raw materials in some developing countries using appropriate formulations. However, for production of improved porcelain insulators properties, suggestions were made on the areas for future research.
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... Furthermore, the electrical properties of a material are very different when it is in a liquid phase, and are also affected by the concentration and movability of K + and or Na + ions in the liquid phase [8]. Although the development of the liquid phase is essential for the sintering of ceramic bodies [9], the over-abundant quantities of the liquid phase encourage the free motion of ions in the ceramic bodies, which results in the materials exhibiting low dielectric properties. ...
... Raw materials from Ethiopia, such as kaolin, feldspar, and quartz have previously been used to fabricate electrical insulators [5], where the optimal dielectric strength of the produced insulators was achieved by increasing the sintering temperature up to 1300 º C. The enhancement in the dielectric strength was found to occur because there was an increase in the vitrification range of the insulator samples at the optimal sintering temperature [9]. ...
Self-glazing dielectric ceramic bodies fabricated from Egyptian rhyodacite and kaolin
Article
  • Jun 2021
  • MATER CHEM PHYS
Rhyodacite is a good source of major oxides, as these are contained in its essential mineral components, such as quartz, oligoclase, and albite. Thus, using natural rhyodacite and kaolin, dielectric self-glazing ceramic materials were prepared that exhibit excellent dielectric properties. The obtained materials were sintered at different temperatures to determine their vitrification ranges and optimal sintering temperatures. As well as determining the composition and microstructure of the phases obtained, their physical, thermal, and mechanical properties were also measured. The prepared materials exhibit low dissipation factors and stable dielectric constants at high frequencies, making them promising dielectric materials for use in high power circuits that operate at high speed.
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... In clay, the kaolinite and illite are present on high quantity. According to [13][14] these elements exploitation is favoured in the field of ceramics. Fig. 5 shows the variation of slip's flexural strength as a function of the clay's concentration on ceramic slip after firings 1140 °C at different pressures. ...
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... Triaxial siliceous porcelain is a highly densified ceramic product with a large compositional range primarily composed of non-renewable raw materials, such as kaolin/refractory plastic clay (as plastic material), feldspars (as fluxing material), and quartz (as filler) in varying amounts [16][17][18][19][20]. Chemically, in terms of oxide components, the starting raw materials place the siliceous porcelain in the phase system SiO 2 -Al 2 O 3 -(Na, K) 2 O. On firing, the interaction between the components of the siliceous porcelain formulation leads to the formation of a complex microstructure characterized by the presence of an extensive glassy phase, undissolved quartz, mullite, and residual porosity. ...
Effect of Firewood Ash Waste on the Densification Behavior of Electrical Siliceous Porcelain Formulations
Article
Full-text available
  • Mar 2022
This study focuses on the effect of firewood ash waste generated in the red ceramic industry on the densification behavior of electrical siliceous porcelain formulations. For this purpose, siliceous porcelain formulations added with up to 8.0 wt.% of firewood ash waste for partial replacing Na-feldspar were prepared. The siliceous porcelain specimens were produced by uniaxial pressing and fired at 1300 °C using a fast-firing cycle. The densification behavior of the specimens fired was monitored by measuring linear shrinkage, apparent density, water absorption, apparent porosity, and volume electrical resistivity. Microstructural and phase characterizations were carried out by SEM and XRD, respectively. The results showed that the densification behavior, properties, and microstructural evolution of siliceous porcelain formulations were influenced by the amount of firewood ash waste added. The firewood ash waste, on the other hand, had little effect on the phase evolution. The optimum densification and technical properties for manufacturing electrical siliceous porcelain using a fast-firing cycle were found between 3.15–4.20 wt.% of firewood ash waste as a renewable auxiliary fluxing material. The environmental and economic benefits of such electrical siliceous porcelain with potential application for low-tension electrical insulator should also be highlighted.
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... , but for A sample sintered at 1200°C show lower dielectric strength because of disappearing of mullite phase and high ratio of quartz that means a high amount of glassy phase which may lower the dielectric strength of the porcelain insulators but not the mechanical strength of a porcelain insulator which is affected by micro cracks. The high amount glassy phase provides free movement of mobile ions such as Na + , K + , and Al 3+ which increases the conductivity [17]. The dielectric strength of porcelain sample C with nano alumina additive shown in Fig. 17 it is observed that nano-alumina has a positive effect on the dielectric strength of the electric porcelain. ...
Manufacture of porcelain insulator from Iraqi raw material and studying the effect of nano alumina additives on the dielectric properties
Conference Paper
Full-text available
  • Mar 2020
Porcelain was prepared from local raw materials; five mixtures (A, B, C, D, and E) were produced with a different weight percentage of kaolin, feldspar and silica sand. The powders were compacted as disk samples with the diameter (13 mm) by semi-dry pressing with (2 ton) applied pressure for (2minute). The specimens were sintering of (1200°C) and (1250°C) and the socking time was (2 hrs.) with the rate of rising of temperature (8°C) per minute. Physical properties (apparent porosity, water absorption, bulk density and shrinkage), mechanical properties (compressive strength and hardness) and dielectric properties were measured. with increasing of feldspar percentage the porosity, dielectric constant decrease while dielectric strength increase. the best physical, mechanical and dielectric properties which observed is the C mixture (50% kaolin, 25% feldspar,25 %silica sand). The nano alumina were additives to porcelain samples for mixture C with different weights percentage (0.5,1.0,1.5,2.0)%, dielectric properties were measured, with improvement dielectric properties and dielectric strength which were observed.
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Evaluation of Pozzolanic Reactivity of Thermally Activated Pugu Tanzania Kaolin as Supplementary Cementitious Materials for Oilfield Well Cement
Article
  • Mar 2025
  • SPE J
Portland cement (PC) is commonly used in oil fields to seal the space between the casing and the formation during oilwell drilling. However, the production of PC in industries raises concerns about environmental pollution and energy consumption. Notwithstanding, PC proves inadequate in enduring the downhole conditions of oil wells, potentially impacting well integrity. To surmount these challenges, supplementary cementitious materials (SCMs) such as fly ash (FA), silica fume (SF), blast furnace slag (BFS), and metakaolin (MK) are being extensively researched. FA, SF, and BFS are relatively less available and associated with environmental pollution. Besides, MK is a greener SCM produced at lower energy as compared to PC and is suitable for oil and natural gas well cementing applications. However, MK is relatively expensive due to the scarcity of high-grade kaolinite rocks in some areas. Consequently, more research is necessary to assess the viability of utilizing locally available kaolin rocks, which have never been researched as SCMs for oilwell cementing. The kaolin deposits in Pugu Tanzania are noted to be among the largest deposits in the world. However, they have yet to be been researched as SCMs for oilfield applications. Our research evaluates the pozzolanic reactivity of thermally activated Pugu Tanzania kaolin. In this research, raw kaolin (RK) was thermally activated at 700 °C, 750 °C, 800 °C, and 850 °C for 1.5 hours, 3 hours, 4.5 hours, 6 hours, and 24 hours at a heating rate of 10°C/min. The results show that RK and MK were composed of SiO2 and Al2O3 as major oxides and other trace oxides. RK was composed of kaolinite and quartz, which transformed to MK after thermal treatment. The optimal reduction of CaO in the Frattini test was 86.46% after 3 hours for thermally activated RK at 800 °C. Likewise, MK modified cement paste cured for 72 hours at 80 °C developed an optimal compressive strength of 36.25 ± 0.93 MPa. X-ray diffraction (XRD) results confirmed the presence of portlandite, larnite, calcium silicate, and calcium iron aluminum oxide, which hydrated to form products for compressive strength enhancement of cement paste. This was assisted by the highest Brunauer-Emmett-Teller (BET) surface area, which facilitated the dissolution reaction of MK during the hydration of cement. The results affirm that MK prepared from thermal activation of Pugu kaolin at 800 °C for 3 hours is suitable as an SCM for the replacement of 30% of oil well cement.
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Improving the functional properties of locally sourced porcelain insulators by heat treating and adding SnO2 nanoparticles
Article
  • Oct 2021
In the present work, we fabricated and studied the characterization of the industrial porcelain insulators using local Egyptian raw materials: Aswan Kalabsha ball clay, kaolin, feldspar from the Red Sea, and Zafarana quartz. Additionally, the chemical compositions of these local raw materials were studied. Porcelain samples were prepared using the conventional ceramic method, and different proportions of SnO2 nanoparticles were added to the porcelain preparation procedures. The dies produced from the standard batch were heat treated at different temperatures (900 °C–1200 °C). The effect of adding different proportions of SnO2 nanoparticles on the physical properties, including the bulk density, porosity, and water absorption as well as the electrical properties (mainly the dielectric constant, loss tangent and dielectric loss factor), of porcelain was determined as the functions of temperature. An improvement in the dielectric properties was achieved by increasing the percentage of SnO2 nanoparticles addition. The fired porcelain bodies were better than when they were sintered at a lower temperature. When the dielectric constant decreased, the AC resistivity increased, and thus, the dielectric loss decreased, which are useful features for many technological applications.
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Differences in phase, microstructural, and electrical characteristics of quartz-substituted alumina porcelain insulator
Article
  • Nov 2020
In the present study, total quartz content (30 wt%) of a standard porcelain body was progressively substituted with two different kinds of aluminas (active alumina and calcined alumina) keeping active alumina constant at 5 wt% and varying calcined alumina content to the extent of 5–25 wt%. The alumina incorporated compositions (AP1 to AP7), along with the standard quartz containing porcelain body (SP0), were processed following common ceramic processing techniques. Two types of forming techniques were used to make samples, namely extrusion of plastic mass to get cylinder of desired dimensions and the other one was hydraulic compaction to produce rectangular bars. The extruded and compacted samples were properly dried and then heated in an electrically operated furnace in the temperature range of 1170–1260 °C. The fully densified samples heated at 1260 °C were subjected to various tests, namely phase identification by X-ray diffraction (XRD) pattern studies; scanning electron microscopic (SEM) analysis; and measurement for electrical properties such as dielectric strength (kV/mm), dielectric loss (tanδ), electrical resistivity (ohm-cm), and dielectric constant to confirm suitability of the samples for application in high-tension power transmission system. The results revealed that the body AP6, wherein 25 wt% quartz was substituted by 5 wt% active alumina and 20 wt% calcined alumina and heated at 1260 °C, may be considered the most suitable sample for porcelain insulator.
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Effect of flux content and heating rate on the microstructure and technological properties of Mayouom (Western-Cameroon) kaolinite clay based ceramics
Article
Full-text available
  • Oct 2017
Four mixtures of kaolinite clay and feldspar (Western-Cameroon) were prepared and sintered at 1200 °C for 2 h at the heating rate of 5 °C/min, 10 °C/min, 15 °C/min and 20 °C/min. The main new crystalline phase was mullite associated with quartz, anatase and cristobalite for all heating rates. By increasing the feldspar content, both the amounts of mullite and of glassy phase increase which promotes the densification of the samples. Heating rate has less influence on the formation of new mineral phases, while this process is sensitive to flux content. Both heating rate and flux content have an effect on the microstructure of the fired bodies as well as technological properties. The specimens with 30% feldspar content sintered at 1200 °C from 5 °C/min to 20 °C/min exhibited water absorption values <10% and bending strength >12 MPa. These materials are suitable as wall tiles. Thus, these samples can be sintered at a heating rate of 20 °C/min instead of 5 °C/min which leads to a saving in firing time and in energy.
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Sintering and dielectric properties of a technical porcelain prepared from economical natural raw materials
Article
Full-text available
  • Dec 2016
In this study, the production of a technical porcelain, for the ceramic dielectric applications by using economical natural raw materials, was investigated. The basic porcelain composition was selected consisting of 30 wt% kaolin, 45 wt% potash-feldspar and 25 wt% quartz. The obtained phases in the sintered samples were investigated by X-ray diffraction, Fourier transform infrared spectroscopy analysis, and scanning electron microscopy images. It has been confirmed by these techniques that the main crystalline phases were quartz and mullite. Dielectric measurements of technical porcelains have been carried out at 1 kHz from room temperature to 200 °C. The dielectric constant, loss factor, dielectric loss tangent, and resistivity of the porcelain sample sintered at 1160 °C were 22-25, 0.32-1.80, 0.006-0.07, and 0.2-9 × 10¹³ Ω.cm, respectively. The value of dielectric constant was significantly high when compared to that of conventional porcelains which did not exceed generally 9. © 2016, Associacao Brasileira de Ceramica. All rights reserved.
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The Effect of the Firing Temperature on the Hardness of Alumina Porcelain.
Article
Full-text available
  • May 2014
  • MATER TEHNOL
Green alumina porcelain samples containing kaolin (27 %), Al2O3, grog (50 %) and feldspar (23 %) were fired at temperatures between 300 °C and 1250 °C with a heating and cooling rate of 5 °C/min. The Shore hardness and the Vickers hardness of the fired samples were measured at room temperature. Both hardnesses of the green alumina porcelain samples are low and remain approximately constant up to 400 °C when dehydroxylation begins. Between 400 °C and 700 °C both hardnesses slightly increase. Above 700 °C, they increase exponentially. This is explained by sintering and high-temperature reactions in metakaolinite. The dependencies between both hardnesses, Shore and Vickers, and the firing temperature are very similar, i.e., the Shore hardness and the Vickers hardness reflect changes in the sample in the same manner. The Vickers hardness is much more sensitive to the firing temperature. Its values after firing at 1250 °C are 130 times higher than those measured at room temperature. However, the values of the Shore hardness are only four times higher. The relationship between the Young's modulus and the Shore hardness and the Vickers hardness can be fitted by power-regression functions.
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Sintering and mechanical properties of porcelains prepared from algerian raw materials
Article
Full-text available
  • Dec 2011
  • Cerâmica
Porcelain is a type of ceramics highly valued for its beauty and strength. The overall goal of this work is to utilize local raw materials within the following fractions: 37 wt.% kaolin, 35 wt.% feldspar and 28 wt.% quartz. This composition has been selected on the basis of the ternary phase diagrams (kaolin-feldspar-quartz). The densification behaviour indicated that specimens sintered at 1200 °C for 2 h with a heating rate of 5 °C/min, have a bulk density of about 2.50 g/cm3. This value is slightly higher than that reported for the conventional porcelain products (2.45 g/cm3). Porcelain specimens with and without calcination sintered at 1200 °C for 2 h have tensile strength values of about 45 and 73 MPa, respectively (equivalent flexural strength values of about 122 and 197 MPa, respectively). The flexural strength values of both specimens are much higher than those reported for conventional porcelains (ranged between 60 and 80 MPa). Furthermore, the value of micro-hardness of the fired samples without calcination at 1200 °C is 9.3 ± 0.2 GPa which is higher than the commercial porcelain products (5.5 GPa).
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Structure–property relationship in high-tension ceramic insulator fired at high temperature
Article
Full-text available
  • Jan 2004
  • MAT SCI ENG B-SOLID
Ceramic insulators are widely used in microelectronic devices. In this paper, the mechanical and electrical properties of porcelain ceramic insulator fired at 1350°C have been investigated along with microstructural characterization using scanning electron microscopy (SEM) in order to understand the structure–property relationship of ceramic insulator. The bending and the dielectric strength were measured on various samples fired at 1350°C. The bending strength (757.3kg/cm2) and the dielectric strength (28.36kV/mm) was found short of the desired value. The microstructural features developed clearly describe why the dielectric strength and the bending strength are not up to the mark. EDAX analysis, X-ray fluorescence (XRF) and X-ray diffractometry (XRD) techniques were also done to support the results. XRD pattern shows 70% mullite and 20% quartz peak intensity and the XRF results shows 22.64% Al2O3 that indicates low mullite formation and hence it is confirmed that it is mullite, the crystalline phase, which contribute together with quartz particle to the dielectric and mechanical strength. SEM image shows large number of microcracks that also hinder the high electrical and mechanical properties of porcelain ceramic insulator.
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Differences in Densification Behaviour of K–and Na–Feldspar–Containing Porcelain Bodies
Article
Full-text available
  • Nov 2003
Porcelain bodies fabricated from triaxial mixtures of clay, quartz and feldspar with different amounts of Na2O and K2O were investigated to study their densification behaviour on thermal treatment at which the bodies achieve full vitrification. The high temperature dilatometric study has shown a distinct behaviour in their densification rate. The degree of vitrification of the densified samples and samples separately heated at different temperatures was determined by measuring the shrinkage, bulk density (BD), percent water absorption (%WA) and flexural strength. It was found that Na-rich feldspar containing body composition achieve full vitrification at lower temperature compared to K-rich feldspar containing composition with improved flexural strength. Differential thermal analysis–thermogravimetric analysis (DTA–TGA) confirms similar reaction steps for both the compositions up to 1000 °C, beyond which feldspar forms eutectic melt and starts reacting. As the purity of raw materials has a strong influence on the colour of the fired bodies, the bodies were also subjected to colour measurement and their differences in whiteness also compared, and is discussed in this paper. The scientific and technological importance of such vitrified porcelain products has also been touched upon, highlighting their industrial application.
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Effects of mixing proportions and firing temperature on properties of electric porcelain from Ugandan minerals
Article
  • Apr 2008
  • IND CERAM
Five sample mixtures of Ugandan kaolin, ball clay, feldspar and flint were formulated and porcelain samples fabricated by extrusion through a vacuum pugmill. Samples were evaluated for formability. The degree of densification of sintered specimens fired at 1200 to 1350 °C was evaluated by measuring the firing shrinkage, bulk density, water absorption and bending strength. Crystalline phases and mullite morphology were studied using XRD and SEM respectively. Dielectric strength measurements were carried out on disc specimens. Dielectric and bending strength properties deteriorated at high temperatures because of pore formation and decreasing amount of undissolved quartz in the crystalline phase. An optimum composition of 30% kaolin, 15% ball clay, 30% feldspar and 25% quartz yielded an unglazed body with highest bending strength of 72MPa and dielectric strength of 19MVm-1 after firing at 1250 °C. The body consisted of small, closely packed mullite needles and undissolved quartz crystals embedded in a glass matrix.
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Influence of Mineralizers on the Constitution of Hard Porcelain: I. Mineralogical Compositions
Article
  • Feb 1974
  • AM CERAM SOC BULL
Mineralogical compositions of hard porcelain bodies have been studied with special reference to the influence of some mineralizing agents, viz. ZnO, TiO//2 and Fe//2O//3 on the development of the crystalline and glassy phases at higher temperatures. The dependence of recrystallization of mullite crystals from the glassy phase on the chemical composition of the glass has also been investigated. A mechanism of induced mullitization of feldspathic glass in hard porcelain by mineralizers is suggested.
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Electrical resistivity of porcelain in relation to constitution
Article
  • Jan 1999
  • CERAM INT
The electrical resistivity of porcelain samples has been measured from room temperature to 1200°C and it was found to depend on the concentration of the phases as well as the size and size-distribution of mullite crystals. The resistivity of porcelain was found to decrease with increase in amount, size and asymmetry of size-distribution of mullite crystals but increase with increase in quartz, cristobalite and glass content. Irrespective of constitution, resistivity of porcelain decreased with rise in temperature from about 1013 ohm-cm at room temperature to about 104 ohm-cm at 1200°C. The change in electrical resistivity of porcelain was primarily controlled by the defect structure of mullite and the composition and viscosity of the glassy phase.
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