decomposition of Mg5(CO3)4(OH)2 5H2O to MgO.
Fig. 2 shows the N2 adsorption-desorption isotherms of MgO
calcined at 600 ° and 700 °C. It indicates type III isotherm with H3
hysteresis loop. The appearance of this type of hysteresis is due to
slit-like pores with nonuniform size and/or shape. The BJH pore
size distribution derived from adsorption data of the isotherm is
shown in the inset of Fig. 2, which also confirms the absence of
regular shape and size of the pores in the samples. The BET surface
area, total pore volume and average pore diameter of the 600 °Ctreated
particles were found to be 46 m2 g1, 0.34 cm3 g1 and
30.4 nm, respectively, and those of 700 °C-treated samples were
29.5 m2 g1, 0.30 cm3 g1 and 41.6 nm, respectively. BET study
indicates that with increasing calcination temperature, surface
area and pore volume are decreased and pore size is increased,
which is due to thermal sintering of MgO.
Fig. 3 shows the FESEM microstructures of (a,b) as-prepared,
and (c,d) 600 °C-treated samples. It is clear that the as-prepared
samples consist of rod-like microstructure with smooth surface.
The aspect ratio of the rod ranges from 30 to 150. Interestingly,
after calcinations, the smooth rod of Mg5(CO3)4(OH)2 5H2O with