Prince BAWUAH^1*, Márton Zsolt KISS^2,3, Pertti SILFSTEN¹, Carl-Mikael TÅG⁴, Patrick A. C. GANE^5,6, and Kai-Erik PEIPONEN¹

¹Institute of Photonics, University of Eastern Finland, Joensuu Campus, P. O. Box 111, FI-80101 Joensuu, Finland
²Cellular Sensory and Wave Computing Laboratory, Institute for Computer Science and Control, Hungarian Academy of Sciences, H-1111 Budapest, Hungary
³Faculty of Information Technology and Bionics, Pázmány Péter Catholic University, H-1083 Budapest, Hungary
⁴(Former) Forest Pilot Center OY, Kerrolankatu 2, FI-21200, Raisio, Finland
⁵Department of Forest Products Technology, Aalto University, School of Chemical Technology, P. O. Box 16300, 00076 Aalto, Finland
⁶Omya Development AG, CH-4665 Oftringen, Switzerland

(Received September 24, 2013; Accepted December 3, 2013)

In this paper, far-infrared (FIR) spectroscopic techniques have been employed to detect different calcium carbonate crystal concentrations in powder mixtures. We have compared absorption spectral features of both pure and mixtures of natural ground calcium carbonate (GCC) and synthetic precipitated calcium carbonate (PCC). It is evident that the absorbance data differentiate clearly and unequivocally between calcite and aragonite in the spectral range of 2–18 THz. Also, from the absorbance measurement of two sets of mixtures, we have revealed a linear relationship between the ratio of some selected absorbance peaks of the mixtures and concentration of a particular pigment within the mixture. This innovative technique could be a novel, practicable technique for quality control or for analyzing coating and/or filler pigments and extenders in the paper making and printing industries. Finally, we have proven in the case of paper that, surface roughness and print color play no role as far as the locations and magnitudes of the absorbance spectral features are concerned.

Key words: aragonite, calcite, calcium carbonate, far infrared, polymorph

^*E-mail addresses: prince.bawuah@uef.fi, butadyne@yahoo.com