STUDIA UNIVERSITATIS BABES-BOLYAI, PHYSICA, SPECIAL ISSUE, 2003
SILICA-LIME-PHOSPHATE VITROCERAMICS WITH IRON
D. Eniu1 and S. Simon2
1
University of Medicine and Pharmacy, Faculty of Pharmacy,
3400 Cluj- Napoca, Romania
2
Babes-Bolyai University, Faculty of Physics, 3400 ClujNapoca, Romania
Abstract
Glass transition and crystallisation temperatures determined from thermal
analyses indicate the structural evolution of samples in function of
composition. The glass stability is enhanced by Fe2O3 addition to silicalime-phosphate host glass up to 20 mol %. Electron paramagnetic
resonance and magnetic susceptibility results inform on the surrounding
and magnetic interactions between iron ions. The Fe3+-EPR data indicate
that the size of ferromagnetic particles increases after heat treatment and
their surroundings become more ordonated due to the partial
crystallisation of samples. The magnetic susceptibility increases by heat
treatment and depends on the treatment temperature.
1. Introduction
The use of calcium phosphate glasses and glass ceramics as bone substitutes has
become common in orthopedic surgery [1]. Ferromagnetic calcium phosphate glass
ceramics are successfully applied to reinforce the bone and to decrease the
recurrence of tumors by hyperthermic treatment [2]. In this samples is essential the
development of ferromagnetic crystallites in iron reach phases.
The aim of this paper is to evidence the structural effects caused by iron addition to
calcium-silica-phosphate glasses, the vicinity and magnetic interactions of iron ions
of CaO-P2O5-SiO2-Fe2O3 glass and glass ceramic samples.
2. Experimental
The starting materials used to obtain 45(3.34 CaOP2O5)(55-x)SiO2xFe2O3 glasses
were CaCO3, CaHPO42H2O, SiO2 and Fe2O3 of reagent grade purity. The oxide
mixtures corresponding to the desired compositions (0  x  30 mol %) were
melted in corundum crucibles at 1550oC for 10 minutes in an electric furnace
Carbolite type RHF 1600, in air, under normal conditions. The melts were quickly
undercooled by pouring onto stainless steel plates at room temperature. Specimens
of the glass samples were heat treated with a rate of 4 oC/min from the room
temperature to 1000, 1100 and 1200oC in air. They were maintained at the
treatment temperature for 30 minutes and then were slowly cooled in the furnace
down to the room temperature.
D. ENIU AND S. SIMON
The electron paramagnetic resonance (EPR) spectra were recorded on a 300 ESP
Bruker spectrometer, in X band, at room temperature on powder samples.
The magnetic susceptibility was measured between 80K and 300K with a 10 -8
emu/g sensitivity Faraday-type magnetic balance.
Thermal analysis measurements were carried out using a MOM derivatograph with
a rate of 10oC/min.
3. Results and discussion
The structural evolution of samples in function of composition was first checked by
determining the glass transition and crystallisation temperatures from differential
thermal analyses. The data obtained show that the glass transition temperature, T g,
increases by addition of iron to the calcium-silica-phosphate matrix up to 20 mol %
(Fig. 1). One observes that glass transition temperatures are very close for
the sample without iron and that with lowest iron content, while Tg has the
same value for the samples with 20 and 30 mol % Fe2O3 contents.
o
Tg ( C)
With respect to glass stability, expressed by the difference between the
crystallization temperature and glass transition temperature, it was found an
increase up to x = 20 Fe2O3 mol %.
The local atomic order and
the valence state of iron in
oxide glass matrices play a
major role in determining
400
the physical properties of
glasses, inclusively their
390
capability to aggregate in
clusters [3]. For glass
380
compounds
used
as
precursor
materials
of
370
ferromagnetic biomaterials
with
applications
in
360
hyperthermic treatments
the iron atoms segregation
350
in
clusters
is
very
0
5
10
15
20
25
30
important. Both cluster
x (mol %)
size and sample magnetic
Fig. 1 The composition dependence of glass
susceptibility are to be
transition temperature.
enlarged in view of this
therapy.
The EPR spectra of the investigated samples consist in a large, relatively
symmetric line. This feature is specific to disordered oxide systems with high
Fe2O3 content wherein spherical ferromagnetic monodomain particles are formed
[4], most probably magnetite particles. The resonance line at g ≈ 2.0 is shifted to
2
SILICA-LIME-PHOSPHATE VITROCERAMICS WITH IRON
lower values of the magnetic field when the iron oxide content increases. This
result could be assigned to the occurrence of ferromagnetic multidomain particles
in the samples with higher Fe2O3 content. The width of g ≈ 2.0 line increases with
Fe2O3 content from 830 Gs, for x =10, to 2780 Gs, for x = 30, and suggests that the
Intensity (a.u.)
(a)
Fig. 2
EPR spectra of
(a) glass ceramic and
(b) glass samples.
(b)
0
1000 2000 3000 4000 5000 6000 7000
B (G)
size of ferromagnetic particles are distributed on a relative large values range, but
on the other hand they are small enough to be not detected by X-ray diffraction
analyse. The size of these particles and the local order are increased by the
crystallisation heat treatment. This is also reflected by EPR spectra
evolution as can be seen from Figure 2. The spectrum of the heat treated
sample contains beside the line typical of untreated glass sample an
additional narrow line (B = 195 G) arising from Fe3+ ions disposed in the
crystalline phase well developed during the applied heat treatment.
The highest local concentration for iron inside the samples was obtained from
ESCA measurements [5] for the glass ceramic resulting by the treatment applied at
1000oC. The magnetic susceptibility, , increases by heat treatment, e.g. for the
sample with x = 10 mol %, at room temperature,  increases from 35 to 150 (10-3
emu/mol). The temperature dependence of the reciprocal magnetic susceptibility
for this composition is illustrated in Figure 3. The magnetic susceptibility reaches
the largest value after the heat treatment applied at 11000C.
Both SiO2 and P2O5 are glass formers. Pure vitreous SiO2 and P2O5 consist in a
continuos random network of quasi-tetrahedral SiO4 and PO4 units wherein silicon,
3
D. ENIU AND S. SIMON
respectively phosphorous is four coordinated. In these glasses CaO and Fe 2O3 act
as glass network modifiers.
Fig. 2
Temperature dependence of reciprocal susceptibility for
45(3.34 45(3.34 CaOP2O5)45SiO210Fe2O3 samples heat treated at
different temperatures: untreated (■), 10000C (●),11000C (▲,▽),12000C (▼).
The thermal diffusivity of these samples has a good stability in the temperature
range including the interval of interest for therapy by hyperthermia [6].
4. Conclusion
The glass stability is enhanced by Fe2O3 addition to silica-lime-phosphate host
glass up to 20 mol %. With increasing Fe2O3 content the samples contain beside
monodomain also multidomain ferromagnetic particles. The size of these particles
increases and their local structure becomes more ordonated in vitroceramic samples
obtained by heat treatment. The magnetic susceptibility rises up to five times in the
partially cristallised samples.
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