ABSTRACT
Fourier Transform Infrared Spectroscopy (FT-IR) was used successfully for the simultaneous quantitative analysis of calcium carbonate phases (calcite, aragonite, vaterite) in ternary mixtures. From the FT-IR spectra of pure calcite, aragonite and vaterite powders with KBr, the absorptivities, alpha, of the absorption bands at 713 cm(-1) for calcite, 745 cm(-1) for vaterite, 713 and 700 cm(-1) for aragonite, were determined. In order to overcome the absorption band overlapping a set of equations based on Beer's law was developed. The detection limits were also established and found to be 1.1 x 10(-4) mg calcite per mm(2) of pellet at 713 cm(-1), 3.6 x 10(-4) mg aragonite per mm(2) of pellet at 700 cm(-1), 1.8 x 10(-4) mg aragonite per mm(2) of pellet at 713 cm(-1) and 3.1 x 10(-4) mg vaterite per mm(2) of pellet at 745 cm(-1). Analysis of a known ternary mixture of calcium carbonate polymorphs tested the validity of the method.
ABSTRACT
MATERIALS AND METHODS: A section of a metal stent consisting mainly of tantalum coated partially by strongly adhering calcium oxalate monohydrate (COM) crystals was immersed in supersaturated solutions prepared from calcium chloride and sodium oxalate at 37 degrees C and ionic strength 0.15 M in NaCl. Abstract OBJECTIVES: To investigate the kinetics of encrustation of a metall alloy urinary stent system in vitro by calcium oxalate and characterize the crystals forming from solutions supersaturated with respect to all calcium oxalate hydrates. RESULTS: The COM-coated stent mineralized upon immersion in the supersaturated solutions. The process was monitored with a calcium ion-selective electrode and the rates were measured at conditions of sustained solution supersaturation. COM crystals formed on the stent and the rate of COM crystal growth yielded a second-order dependence on the solution supersaturation. CONCLUSIONS: The deposition of COM crystals on the metal stents coated partially with COM crystals by adhesive forces was found to be most important for the acceleration of the encrustation process. The dependence of the rates on the solution supersaturation suggested absence of secondary nucleation and a surface-controlled process for the encrustation process.
