A comparison of dielectric properties of eggshells from free-range system and control-range system

Abstract

Calcium oxide (CaO) powders were prepared from eggshell’s calcium carbonate (CaCO3) obtained from control-range system (a supermarket) and free-range system (opened natural farm) hens. The CaO powders were sieved at 140 µm, put into porcelain crucible, and calcined under air atmosphere in a muffle furnace at 500, 600, and 900 °C for 2 h with heating rate 5 °C/min. All samples were molded by a homemade press machine. Several characterizations were carried out. LCZ impedance meter was used to measure dielectric properties, X-ray diffraction (XRD) was used to examined the structure and the average crystal size of the eggshell’s calcium carbonate, and Scanning electron microscope (SEM) was used to study surface morphology of the eggshells. The results show that after calcined, eggshell’s calcium carbonate CaCO3 phase was transformed to CaO. For the open natural farm eggshells calcined at 900 °C, the dielectric was 1.009 × 105, loss tangent was 1.6192, resistance was 7.16 kΩ, capacitance was 11.03nF when measured at frequency of 0.4 kHz, and average crystal size 1664.1 Å. For supermarket eggshells calcined at 900 °C, dielectric was 1.256 × 104, loss tangent was 2.335, resistance was 103.42 kΩ, capacitance was 1.8837 nF when measured at frequency of 0.4 kHz, and average crystal size 10370.7 Å. It is also found that the composite materials (D2) consisting of Ca(OH)2, TiO2 powder, chitosan, and SiO2 powder exhibits the electrical properties is nearby comparable to the supermarket eggshells.