Biomimetic Modifications of Calcium Orthophosphates
155
Me2+/(Me2+ + Ca2+) ratios higher than 0.05 and mixture of the ion-modified HA and -TCP
calcium phosphates at ratios lower than 0.05. The SEM analyses revealed that Zn and Mg
substitutions influenced the morphology of the β-TCP grains (Fig 14). Sintering at 800-
1000 oC leads to zinc-modified-β-TCP powders of idiomorphic crystals with sizes ranging
from 500 to 5000 nm in all studied cases. Magnesium-modified-β-TCP fine powders with
spherical grains of smaller size (250 - 1000 nm) were obtained at a Mg2+/(Mg2+ + Ca2+) ratio
higher than 0.02 (Figure 13 and 14). The surface of the spherical grains of magnesium
modified samples was covered by blanket, while clean grain boundary was observed in the
zinc-modified samples.
(^)
Zn1
800 oC^1000 oC
P0
Zn3
Zn5
Zn10
Zn13
600
o
C
(^)
(^)
10 20 30 40 50
2-theta-Scale
10 20 30 40 50
10 20 30 40 50
a.
(^)
(^)
P0
Mg2
Mg5
Mg10
Mg16
10 20 30 40 50
10 20 30 40 50
10 20 30 40 50
2-theta-Scale
600 oC^800
oC 1000 oC
b.
Fig. 13. XRD powder data of Zn-modified (a) and Mg-modified (b) calcium phosphates at
different temperatures. (▄ - HAP; not marked – Me2+-β-TCP).
The calculated unit cell parameters showed that low ion substitution (Me2+/(Me2++Ca2+)
ratio up to 0.05) leads to a slight decrease in the parameter a and the volume V and to an
increase in the parameter c of the Me-β-TCP unit cell (Table 9). This tendency became more
pronounced at higher temperatures.
The inclusion of Mg2+ and Zn2+ ions into the crystal unit cell of the thermodynamically
stable HA proceeds through Ca 2+ ion substitution. As the ionic radii of Mg2+ (0.65 Å) and
http://www.ebook3000.com