Synthesis and Raman Spectra of K–Ca Double Carbonates: K2Ca(CO3)2 Bütschliite, Fairchildite, and K2Ca2(CO3)3 at 1 Atm

Аннотация

Abstract—This paper reports the synthesis of double K–Ca carbonates at atmospheric pressure in closed graphite capsules. The mixtures of K₂CO₃ and CaCO₃ corresponding to the stoichiometry K₂Ca(CO₃)₂ and K₂Ca₂(CO₃)₃ were used as starting materials. The low-temperature modification of K₂Ca(CO₃)₂ was synthesized by a solid-state reaction at 500°C during 96 h. The high-temperature modification of K₂Ca(CO₃)₂ as well as K₂Ca₂(CO₃)₃ were synthesized by a solid-state reaction at 600°C for 72 h and by cooling of the melt from 830 to 650°C for 30 min. The obtained carbonates were studied by Raman spectroscopy. The Raman spectrum of bütschliite is characterized by the intense band at 1093 cm^–1 and several bands at 1402, 883, 826, 640, 694, 225, 167 and 68 сm^–1. The Raman spectrum of fairchildite has characteristic intense bands at 1077 and 1063 cm^–1, and several bands at 1760, 1739, 719, 704, 167, and 100 сm^–1. In the Raman spectrum of K₂Ca₂(СO₃)₃, the intense lines were found at 1078 and 1076 cm^–1 and several lines at 1765, 1763, 1487, 1470, 1455, 1435, 1402, 711, 705, 234, 221, 167, 125 and 101 сm^–1. The collected Raman spectra can be used to identify carbonate phases entrapped as microinclusions in phenocrysts and xenoliths from kimberlites and other alkaline rocks.