Geoscience Reference
In-Depth Information
Figure 10.65 SEM photographs of the HAp
films formed on the surface of the iron
plates
[293]
.
Source: Courtesy of the Academic Press,
Orlando, FL.
chemistry, but the mesostructure of bone gives it two to six times more fracture
toughness than HA. This limits current HAp usage to small, unloaded implants and
coatings.
HA whisker-reinforced composites might solve the problem. Their production
requires hot pressing and/or HIP at 1000
1100
C. Even these processes fail to
achieve fully dense samples.
Unfortunately, they also give rise to a whole new set of problems. Many sinter-
ing additives form tricalcium phosphate, which increases HA biodegradability and
reduces implantation lifespan. Others form CaO, a reactive material whose volume
