Biomedical Engineering Reference
In-Depth Information
4
3−
3
2−
4
3−
[65]; ions of hydroxide, chloride, bromide,
carbonate and oxide may to a certain extent substitute fluoride in the
crystal lattice of natural apatites [47]. Furthermore, various organic
radicals have been found in natural apatites [66, 67]. In principle,
the crystal structure of apatites can incorporate half the Periodic
Chart in its atomic arrangement. In medicine, this property might be
used as an antidote for heavy metal intoxication [68]. Ease of atomic
substitution for apatite leaves this mineral open to a wide array
of compositions. This might be related to the fact that the apatite
structure type displays porous properties [69]. The substitutions in
apatites are usually in trace concentrations but large concentrations
and even complete solid solutions exist for certain substituents (e.g.,
F
AsO
, CO
and VO
). To make things even more complicated, some ions in
the crystal structure may be missing, leaving the crystallographic
defects, which leads to formation of non-stoichiometric compounds.
Figure 1.2 shows examples of polycrystalline and single-crystalline
samples of natural FA.
−
and OH
−
Figure 1.2
Polycrystalline (left) and single-crystalline (right) FA of a
geological origin. The single crystal has a grey-green color due
to incorporated ions of transition metals.
Manufacturing of elementary phosphorus (white and red)
[70, 71], phosphoric acids [36, 72-75], various phosphorus-
containing chemicals and, especially, agricultural fertilizers (namely,
superphosphate [76-78], ammonium orthophosphates [79] is the
major industrial application of natural calcium orthophosphates.
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