Biomedical Engineering Reference
In-Depth Information
13.3.1 Preparation
Several families of rare earth aluminosilicate (REAS) glasses possess the
properties listed in Section 13.2 and have been investigated [4-7] for
the
in situ
irradiation of diseased organs. These glasses have a simple
chemical composition, being composed of just three oxides, namely,
alumina (Al
2
O
3
), silica (SiO
2
), and the desired, neutron activatable rare
earth oxide (RE
2
O
3
). Unlike most common glasses, these glasses contain
only four elements, Al, Si, O, and the RE. Fortunately, the radioisotopes
formed from Al, Si, and O during neutron activation decay rapidly and
are of no consequence. These glasses will hereafter be designated as
REAS, where RE designates the rare earth, A denotes alumina, and S
denotes silica. Thus, a REAS glass containing samarium (a RE element)
would be designated as SmAS.
REAS glasses are prepared by mixing high-purity powders of the three
oxides and melting the homogeneous mixture in a platinum crucible for
4-8 hours at 1500-1600
◦
C. Care must be taken in choosing the raw
materials to ensure that they are of high chemical purity and do not
contain traces of unwanted neutron activatable elements.
The glass-forming region for several families of REAS glasses, which
can be melted below 1600
◦
C, is shown in Figure 13.2, which is a similar
style of diagram to Figure 2.1, the composition map of bioactive glasses.
RE
2
O
3
Y
Sm
Ho
Dy
AI
2
O
3
Weight %
SiO
2
Figure 13.2
Compositional diagram showing the glass formation range for rare
earth aluminosilicate (REAS) compositions that melt below 1600
◦
C [4, 6, 7].
