Hussein, Abbas Ibrahim
(2018)
Synthesis of nano calcium oxide from cockle shells as stabilizer for fabrication of zirconia.
Masters thesis, Universiti Sains Malaysia.
Abstract
Various studies suggest that cockle shells hold great potential as a rich source
of natural calcium oxide (CaO). Different oxides have been used to stabilize zirconium
oxide (ZrO2) in a stable phase. Use of CaO as a stabilizer has been studied previously;
however, commercially prepared CaO has been utilized for these purposes. The aim
of the current study was to derive CaO from cockle shell waste and to utilize cockle
shell derived CaO for stabilizing ZrO2 and then to compare it with ZrO2 stabilized with
commercial CaO. The physical and mechanical properties of the CaO stabilized
zirconia derived from both sources were also investigated. CaCO3 samples were
characterized using scanning electron microscopy, Brunaur-Emmett-Teller surface
area analysis, X-ray diffraction analysis and energy dispersive X-ray analysis. The
CaO was obtained through calcination process at a temperature range from 300-750
°C. Themorphology of CaCO3 were controlled by manipulation of reaction parameters
such as DDW concentration, K2CO3 feeding rate, concentration of organic solvents,
and the drying methods. The calcium oxide was used to stabilize zirconium sintering.
(A) 9.2 g of commercially purchased zirconium oxide was mixed with 0.8 g of calcium
oxide derived from cockle shells. (B) 9.2 g of commercially purchased zirconium
oxide was mixed with 0.8 g of calcium oxide which was commercially purchased.
Each specimen mixture was pressed in stainless steel mold using hydraulic press under
5 tons (60MPa) pressure and sintered for various times (one, two, three, and fourhours) at different temperatures (1200 °C, 1300 °C, 1400 °C, and 1500 °C) to fabricate
pellets/blanks of CaO stabilized zirconia. SEM characterization of zirconia stabilizedusing cockle shells had an average particle size of 61.13 nm as compared to zirconia
stabilized using commercial CaO that had an average particle size of 64.37 nm. It was
noted that the nanoparticles had spherical shape and they were evenly distributed with
no visible agglomeration. EDX composition analysis revealed that percentage of
zirconia was higher in zirconia stabilized using nano CaO derived from cockle shells
in comparison to zirconia stabilized using commercial nano CaO. XRD analysis
revealed that the highest peak for the nano CaO stabilized zirconia crystals in the XRD
pattern was noted at an angle 2θ=30° depicting spherical crystals of zirconia. Flexural
strength test, compressive strength test, Vickers hardness test and density test were
performed for each sample. These tests concluded that nano CaO stabilized zirconia
from cockle shell is comparable to zirconia stabilized by commercial nano CaO and
had superior mechanical and physical properties when sintered at 1400 °C for 2 hours
holding time. It can be concluded from our study that the cockle shell waste is a rich
source of nano CaO. Mechanical and physical tests prove that nano CaO stabilized
zirconia derived from cockle shell can be considered suitable for dental applications.
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