SYNTHESIS OF SUPER FINE ARAGONITE-TYPE CALCIUM CARBONATE BY PRECIPITATION IN ULTRASONIC FIELD
Chemical Product Design and Engineering (CPD&E)
Chemical Product Design & Engineering - Poster (CPD&E - P)
Keywords: aragonite, ultrasonic field, additives, alcohol
Calcium carbonate is a compound which was extensively studied due to its abundance in nature and its large number of industrial applications each one requireing specific qualities referring to purity, crystallization form, dimensions and grain size distribution, porosity, aggregation degree.
There are three stable polymorphs of calcium carbonate: rhombohedral calcite, needle or rod like aragonite and spherical vaterite.
Recently the interest for aragonite is increasing because new fields like biomaterials are developing.
The synthesis of calcium carbonate by precipitation in liquid-liquid reaction depends on many parameters as supersaturation, pH, temperature, reaction time, agitation speed, feeding order of the reacting solutions, the nature and the presence/absence of the additives. Usually a mixture of the three polymorph is formed.
We investigated the possibility of developing an aragonite type calcium carbonate with uniform particle size and submicron dimensions by precipitation in liquid-liquid reaction using as starting reagents 1M solutions of calcium nitrate and potassium carbonate :
Ca (NO3)2 + K2CO3 = CaCO3 + 2KNO3
The synthesis was carried out in a batch reactor placed in an ultrasonic field of 45 kHz. The optimum acoustic amplitude was established at 50% of the full amplitude of the ultrasonic device.
The influence of several additives as Tween 20, AOT and ethanol was investigated.
Other parameters, like pH, temperature, reaction time and feeding order were also varied.
All samples were examined by FT-IR spectroscopy, optical and electron microscopy and granulometry.
Aragonite was formed in the presence of ethanol, in the themperature range 40-60 °C, regardless of the feeding order of the reagents. The material has a high degree of uniformity, the particle size being in the submicron range and is only slightly impurified with calcite, as results from the FT-IR spectra.
In the presence of Tween 20 or AOT as additive the formation of aragonite is dependent of pH which must be adjusted at 10 and the particle size is in the range of 1-5 microns.
See the full pdf manuscript of the abstract.
Presented Wednesday 19, 13:30 to 15:00, in session Chemical Product Design & Engineering - Poster (CPD&E - P).
