`INFLUENCE OF ANNEALING TEMPERATURE ON OPTICAL PROPERTIES OF LIMESTONE COLLECTED FROM OBAJANA, KOGI STATE.

Abstract

Limestone is a common sedimentary rock composed primarily of the mineral calcite (CaCO 3 ). Though it is generally used in building industry, it has found little use in the technological industry in the form of CaCO 3 nanoparticles. Few works abound on the optical properties of Calcium Carbonate, and they do not extensively cover the optical properties in the IR-VIS-UV electromagnetic spectrum range. This dearth of information over the whole electromagnetic spectrum for Calcium Carbonate makes this research pertinent. Limestone (calcium carbonate) from Obajana, Kogi State were collected and grounded into powdery form. A portion of the powder was then placed on substrates and annealed at various temperature ranging from 50 to 500oC while the rest served as the unannealed sample. The annealed and unannealed samples were irradiated in the range of 300 nm to 1100 nm in UV-Vis Spectrophotometer. The results shows that there was increase in the absorption and transmittance of radiation in the annealed sample than in the unannealed sample. Also, their exist a slight increase in the band energy gap with a value of 0.07 eV due to annealing, and reduction in the values of refractive index and optical conductivity. All these improved optical properties making the annealed calcium carbonate material useful in solar application like anti-reflection coatings for solar-thermal devices, thermal control window coatings and heat mirror coatings in building industry.