Biomedical Engineering Reference
In-Depth Information
cited study dealt with CDHA or HA; unfortunately, the necessary
data were found in just a few papers. Therefore, in many cases, I
was forced to mention just “apatites” without a further clarification.
Thus, the readers are requested to be understandable on this
uncertainty.
The greater part of the published reports on synthesizing of
nanodimensional and/or nanocrystalline apatites is focused on the
bottom-up approach. Among the available preparation techniques,
a wet chemical precipitation is the most popular one [63, 72, 74,
87, 101, 103, 141-143, 146, 152, 172, 173, 232, 241, 255-292].
Various authors discussed the effects of synthesis parameters,
such as temperature [267-270, 286], time [268], calcium ion
concentration [270], presents of surfactants [273], calcination [268],
and the use of different reagents on the morphological properties
of nanodimensional apatites. In general, the shape, stoichiometry,
dimensions, and specific surface area of nano-sized apatites appeared
to be very sensitive to both the reaction temperature (Fig. 3.4) and
the reactant addition rate [267, 280, 286]. Namely, particle sizes
of nanodimensional apatites were observed to increase in a linear
correlation with temperature [269, 286], which is a good indication
that sizes of nanodimensional apatites can possibly be tailored.
Furthermore, the initial pH values and reaction temperatures both
play important roles in the morphology of the precipitated apatites,
as well as on the phase formation and degree of crystallinity [290].
For example, significant differences in the chemical composition,
morphology, and amorphous character of nano-sized CDHA produced
through the reaction between aqueous solutions of Ca(NO
)
and
3
2
(NH
can be induced, simply by changing the pH of the reactant
hydrogen phosphate solution [291]. Thus, the solvent systems,
dispersant species, and drying methods appear to have effects
on the particle size and dispersibility. However, some conflicting
results have been obtained on how certain synthesis parameters can
affect the morphological properties of these nano-sized particles.
Nevertheless, it was commonly observed that nano-sized crystals of
apatites synthesized through the chemical precipitation were often
highly agglomerated; however, these agglomerates could be clusters
of ultra-fine primary particles [271].
A hydrothermal synthesis [58, 61, 131, 132, 224, 225, 255, 286,
287, 293-313] seems to be the second most popular preparation
)
HPO
4
2
4
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