Purification of Meetiyagoda Kaolin for boron free glaze manufacturing
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Date
2015
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Uva Wellassa University of Sri Lanka
Abstract
A tile is a manufactured piece of hard-wearing material such as ceramic, stone, metal, or even
glass for covering of roofs, floors, walls, or other objects. Tiles are often made from ceramic with
a hard glaze finish. But sometimes with other materials such as glass, marble, granite and slate are
also used to produce tiles. Among them, floor tiles are commonly made of ceramic, porcelain and
stones due to their attractiveness, durability, and easiness to clean. The main components of a tile
are tile body, glaze layer, and printed layer. The raw materials used to form a tile consist of clay
minerals, quartz, feldspar which is used to lower the firing temperature and chemical additives
required for the shaping process. Tile decoration is mainly depending on the glaze layer. Sodium
feldspar, potassium feldspar, quartz, wollastanite and kaolinite are abundantly used materials in
glaze production. Even through Sri Lanka contains most of the above raw materials; at present all
required glaze materials as imported to the country due to the cost, lack of technology and some
quality problems of raw materials. So this research aims to manufacture a low cost glaze medium
mainly using local mineral materials and few imported materials.
Methodology
The current study was carried out at Uva Wellassa University, Badulla, Sri Lanka and Lanka Tiles
PLC, Jaltara, Sri Lanka. First, the raw materials were purified to make frit and glaze. The acid
leach process was carried out for purification of kaolin and the magnetic process was carried out
feldspar, wollastanite and quartz. The clay sample selected for investigation was kaolinite clay
obtained from Meetiyagoda area. Then the clay sample was ground using a laboratory ball mill to
–149 μm (100 meshes). The ground clay sample was placed on the sieve, and then mechanically
shacken for 5 min. The oversize was further grounded followed by sieving with the same sieve.
The procedures were repeated till the entire clay sample passed through the sieve. After that
ground clay sample passing 100 mesh was subjected to calcination. The sample was heated at
C ) to activate the
clay before acid treatment (Al-Zaharani and Abdulmajid, 2009). Calcineated clay sample passing
100 mesh were leached using 3M hydrochloric acid for different periods of time (10-150 min) and
at different leaching temperatures (25ºC to boiling temperature) using a constant temperature
shaking water bath at a fixed shaking rate of 160 cycles/min and using boiling under reflux
(Hulbert and Huff, 1970). At the end of leaching, the resulted slurry was filtered to separate
undissolved materials and, washed in distilled water. The filtrate and washings were continued
until ions were removed in the sample. The resulting sample was dried for 24 h in Laboratory
oven. Likewise the feldspar and wollastanite were purified by magnets. The purity and quality of
leached kaolinite were tested using common base (CS 100) in tile industry. After that the frit was
made using 80g of sodium tetraborate pentahydrate (Na2B4O7.10H2O), 100g quartz, 160g of
kaolin, 40g of wollastonite, 20g of zirconium silicate and 5g sodium chloride. The raw material
was mixed in a pot mill. Water was added slowly step by step until the mixture forms in to a
crumb. The crumb was heated at 100 C until it was completely dry. Then the dried product was
transferred to porcelain cups and it was placed in a laboratory muffle kiln. The kiln was heated at
a rate of 4 C per minute up to a 1050 C and kept at same temperature for 90 minutes (Simon et al,
2007). The furnace was switched off and the crucible was allowed to cool down to ambient
temperature in the furnace. The product was removed, wrapped in a plastic film hammered to
break in to small pieces. Then the base formula was generated by using it. Glass formation and
formulation mechanisms (fluxes, vitrifying agent, opecifier), thermal expansion of the materials
and melting point (softening temperature) were considered for base making. The materials in the
base thermal expansion were adjusted according to frit thermal expansion. Frit (30g), kaolin (8g),
sodium feldspar (30g), wollastanite (32g), zirconium silicate (10g), aluminium oxide (2.5g), zinc
oxide(1.5g), C.M.C (0.2g) and S.T.P.P (0.2g) were added to the base formula and it was grind
with 100 ml water in pot mill for about 20 minutes. Resulted base medium was sieved using a 100
µm sieve and it was sprayed by spray gun on to engobe green tile. Base density and base viscosity
was measured before spraying. Based tile was fired in the kiln. Finally fired tile surface properties,
thermal shock, abrasion, strain, cracking and acid resistance were checked to ensure the quality.
Description
Keywords
Mineral Sciences, Materials Sciences, Mineral, Ceramic, Chemistry