Calcium Titanate from Food Waste: Combustion Synthesis, Sintering, Characterization, and Properties

Abstract

Calcium titanate (CaTiO 3 ) was combustion synthesized from a calcium source of waste duck eggshell, anatase titanium dioxide (A-TiO 2 ), and magnesium (Mg). e eggshell and A-TiO 2 were milled for 30 min in either a high-energy planetary mill or a conventional ball mill. ese powders were then separately mixed with Mg in a ball mill. After synthesis, the combustion products were leached and then sintered to produce CaTiO 3 ceramic. Analytical characterization of the as-leached combustion products revealed that the product of the combustion synthesis of duck eggshell + A-TiO 2 that had been high-energy-milled for 30 min before synthesis comprised a single perovskite phase of CaTiO 3 . e high-energy milling of the reactant powder had generated a large reactive surface area and induced structural defects, both of which drove the completion of the combustion reaction and the phase conversion of the reactants into the product. A calcium titanate ceramic, fabricated by sintering as-leached powdered combustion product at 1350°C for 180 min, achieved a maximum density of 3.65 g/cm 3 and a minimum porosity of 0.54%. e same fabricated calcium titanate ceramic product also exhibited the highest dielectric constant (∼78) and the lowest dielectric loss (∼0.02), which resulted from the simplified charge polarization process.

Calcium titanate ceramics obtained by combustion synthesis and two-step sintering

“…Subsequently, as-prepared calcium titanate powder was processed by single-and two-step sintering to produce dense calcium titanate ceramics.The microstructures, densities and dielectric properties of the calcium titanate ceramics were compared and analyzed as-sintered. XRD analysis in our previous study [23] confirmed that the as-received duck eggshell was composed entirely of calcium carbonate. XRF data of the duck eggshell after heating (Table I) showed a major compound of calcium oxide (CaO) from the decomposition of CaCO 3 to form CaO and CO 2 gas.…”

“…Powdered duck eggshell and A-TiO 2 were high-energy milled with Si 3 N 4 balls in a jar (Fritsch GMBH, Pulverisette 6, Germany) for 30 min at 400 rpm. This procedure was adapted from reference works [23,24]. The high-energy milled powder mixtures were then mixed with magnesium powder by ball milling for 120 min using zirconia (ZrO 2 ) balls and a nylon vial.…”

“…Following our previous research [23], conventional, single-step sintering (SST) was performed at a heating rate of 10 °C/min with a holding time of 180 min at 1350 °C. In the case of two-step sintering, green pellets were first heated to 500 °C at a heating rate of 5 °C/min, and held at this temperature for 60 min to completely remove the organic binder.…”

“…The sintered density and apparent porosity of the calcium titanate ceramics were measured according to Archimedes' principal, and were calculated using equation (1) [23],…”

“…Moreover, except for certain commercial grade chemical components, the reactants used in combustion synthesis can be sourced from waste materials from activities such as agriculture, food production and from mineral tailings. Interestingly, calcium titanate was recently prepared by combustion synthesis using reactants from waste materials [22][23][24]. Self-propagating high-temperature synthesis (SHS) is one of combustion reaction modes mostly found to synthesize numerous advanced materials at temperatures above 4000 K. At room temperature, only small external ignition energy is required to initiate the reaction and then, the combustion generated extremely exothermic heat for the reaction to be self-sustaining.…”