Egg-shells of hen were collected in bulk. They were cleaned mechanically by de - ionized water
and boiled in water for 20 minutes. They were then placed in a furnace for a three-stage thermal
treatment. Heating rate and soaking time at these three stages are given in Table I. Experimental
setup for this synthesis is shown in Fig. 1.
In first stage the eggshell heated upto 450 0C at the heating rate 70C/min. followed by soaking for
two Hrs at 4500C. Similarly in second stage eggshells were heated from 450-6000C at heating rate 50C/min. and soaking at 6000C for two Hrs. In final stage the eggshell heated from 6000C to
9000C at the heating rate of 40C/min followed by soaking for one Hr at 9000C.
At the temperature 9000C, the eggshells transformed into calcium oxide by releasing carbon
dioxide (CO2) according to the following equation:
The CaO so obtained from the eggshells was then converted into HAp in a phosphate solution
following a procedure reported before by Roy [12], Eric M. Rivera et.al [8] and subsequently
used by others [13].
A stoichiometric amount of calcined eggshell was dispersed in well-degassed distilled water.
Under vigorous stirring reagent grade tri-calcium phosphate solution (Merck) was mixed into
calcined eggshell solution at a controlled into the suspension maintained at 900C temperature.
Mixing was continued for more time to achieve proper mixed solution. After completion of
mixing, the solution was subjected to aging treatment for 24 Hrs and then filtered. The filtered
solution was further heat treated in presence of steam atmosphere. The rate of heating was
150C/min. up to 6500C, 80C/min from 6500C to 9000C followed by soaking for 1 Hrs at
9000C.Steam is supplied to maintain H2O presence during reaction. The expected reaction is
given as: