COMPARATIVE ANALYSIS OF THE MECHANOCHEMICAL HEM ACTIVATION EFFECT ON THE MICROSTRUCTURE AND PHASE TRANSFORMATIONS OF SEDIMENTARY APATITES

Abstract

High-energy-ball-milling (HEM) is a well-known approach for preparing various solid materials with increased reactivity. Such a manner of material activation is environmentally friendly and an alternative to the disadvantages of the traditional processing of phosphate raw materials that leads to pollution by solid phases and gaseous technological products.
This work investigates a natural CaO-P₂O₅-SiO₂ system with 46.5 - 48.4 % CaO, 29.0 - 29.6 % _Р2О5 with a different amount of SiO2 - from 1.9 to 7.3 %. 
The samples were activated with 20 mm Cr/Ni bodies using a planetary ball mill for different times - 150 and 300 min.
The structural, phase, and size transformations of the high-energy milled (HEM) samples in comparison to the raw samples were examined by chemical analysis low-temperature nitrogen adsorption (BET) method, powder X-ray diffraction (PXRD), and Fourier transform infrared (FT-IR) spectroscopy.
The obtained data indicate an increased defectiveness of the structure with prolonged HEM activation time leading to (i) the formation of XRD-amorphous particles, low-intensity and broadened peaks, (ii) increase of reactivity resulting in solid-phase crystallization of tri-calcium phosphates (TCP), pyro-phosphates (CPP), and (iii) isomorphic substitution of carbonate and hydroxyl ions for PO₄^3- and F- with formation of carbonate-fluorine-hydroxyl-apatite, types A and AB.