Magnesium ions crystallization rates

Measurements of the specific surface area, SSA, of the products grown at various times indicate that the initial formation of a microcrystalline or amorphous precursor leads to a rapid increase in SSA. The development of these phases is also observed by scanning electron microscopy, and dissolution kinetic studies of the grown material have indicated the formation of OCP as a precursor phase ( , 7). The overall precipitation reaction appears to involve, therefore, not only the formation of different calcium phosphate phases, but also the concomitant dissolution of the thermodynamically unstable OCP formed rapidly in the initial stages of the reaction. In the presence of magnesium ion the overall rate of crystallization is reduced and lower Ca P ratios are observed for the first formed phases (51). 

Production of L- A spar tic Acid A solution of 1.5 M ammonium fumarate (pH 8.5) containing 1 mM of magnesium ions is passed through a 2.5 x 30 cm column packed with the immobilized cell preparation (for enhanced long-time stability treated with glutaraldehyde/1,6-hexanediamine41) at a flow rate of 90 mL/h at iT C. 1 L or the effluent is adjusted to pH 2.8 with 60% H2S04 at 90 °C and cooled to 15°C. The L-aspartic acid crystallizes out and is collected by filtration and washed with water yield 179.6 g (90%) [x]20 +25.5 (c = 8, 6 N HC1). 

The production rate P r in Equation (3) is calculated from Equation (4) from mass balance of magnesium ion, where M, Comr2+, Cm22+ and F are molecular weight, initial concentration of Mg, concentration of Mg in the crystallizer and feed rate, respectively. 

DCPA and DCPD are widely used as an initial precursor component of self-setting CaP bone cements (Barrere et al. 2006 Hofmann et al. 2009). It is reported that cells are able to rapidly resorb DCP ceramics (Gilardino et al. 2009). However, this structure is metastable under physiological conditions and transforms towards a more stable apatitic structure (Elliott 1994). Many attempts have been made to maintain its structure under conditions where the apatite formation is favored thermodynamically. It is reported that the presence of magnesium ions strongly reduces the transformation rate (Boanini et al. 2010). Absorbance of magnesium ions into DCPD crystal nuclei prevents crystallization and gradually decreases the mechanical properties (Lilley et al. 2005). However, maximally 0.3 wt.% Mg + can be replaced with Ca + atomic sites (Elliott 1994). 

In the present work, a constant composition method has been used to investigate the growth of HAP from solutions of low supersaturation and in the presence of different background electrolytes. The influence of magnesium and strontium ions both on the rate of crystallization and upon the electrokinetic properties of the crystallite surfaces has also been investigated. 

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