Colloidal Particles: Spherical Yttrium Iron Garnet
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Afterwards, urea or ammonia was added in different concentrations for increasing pH and improving hydrolysis process. In some cases, it was added poly(vinylpyrrolidone) and ammonium iron (III) sulfate [NH 4Fe(S04) 2 12H 20 in w*/o to avoid aggregation 7 . The hydrolysis reaction (1) is:
5Fe(CI) 3 + 3Y(C1) 3 + 24H 20
-+
{x[Fe 5Y3O12] + (1-x)[5Fe(OH) 3] [3Y(OH) 3]}
(1)
After keeping the solution at the temperature of 900 C for 3 hours the resulting dispersion was filtered through 0.1 ptm pore size Nucleopre membrane. The powder was then dried in a desiccator under vacuum. The scheme of preparation of YIG particles is shown in
figure 1. Solution of FeCh3 in concentrations3 of 2 1.10 or 1.10-
Solution of YCI3 in concentrations 3 of 2 1.10 or 1.10-
Separation with membranes 0.1um 0
Heat the solution at 90 C
Urea or Ammonia
0
Aging 3 h, 90 C
I
Separation with membranes 0.1 ýLm and drying in desiccator
YI Heat at 1100IIC
Crystalline and magnetic Figure 1. Scheme of the process
Table I: Experimental conditions for YIG sample preparations. Sample 8 P1
Precipitation agent (moLL-1)
P2 P3 P4
Urea Urea Urea Urea
P5
NH3 (2)
P6
NH 3 (2)
P7 P8 P9 P10
NH3 (2) Urea (0.5) Urea (0.25)
Pl
(1) (2) (1) (2)
Urea (0.5) Urea (0.5)
Concentration of iron Addition of PVP chloride (moLL-1) (% w/w)
Addition of NH 4Fe(SO4)2 (% w/w)
10.2 10.2 . 1.7
1010.3 10.2 10.1 10-3 10. 10310-1 10"3
-
-
-
1.7
584
-
-
1
50% 50% 50%
RESULTS Precipitates were calcinated at 1100°C for 4 hours and yield, cubic YIG particles. The surface charge behavior was investigated by dispersing the precipitate in different solvents. Figure 2 demonstrates that there are variations in electrophoretic mobility in different alcohols depending2 on the added ammonium hydroxide volume. •2,0,5
-
-•-
a
•
Et
U
WW/2-Pro.peoW (11)
--A,- 2-prPW44
0
±'•1.0
-0,5 0 5o
...--. ----................... ..-..-.-.. ..-..-.-..-------0o -... --
-1,0
-0.1
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0.8
0,9
1,0
NH,OH / ml Figure 2. Dependence on the eletrophoretic mobility of yttrium iron particles in different alcohols, (A)ethanol, (m) 2-propanol and (6) water/2-propanol 1:1 mixed, for sample P3 at a constant ionic strength (0.001 mol L-' KNO3), depending on N-hO4H volume. The sample P3 was treated at 1100°C for 4 hours before the dispersion.
Organic solvents are used as dispersion medium for silica3 heterocoagulation in low dielectric constant media. The behavior of used alcohols demonstrated that ethanol is better solvent than other alcohols because the particle surface charge is more positive than that in 2-propanol/water mixture. Despite the low dielectric constant of the solvent, the results in figure 2 demonstrate that ammonium hydroxide exhibits strong basic property in alcoholic medium. The pH was evaluated by addition of phenolphthalein in these alcohols in which it changes color characteristic after small addition of ammonium hydroxide. Yttrium iron garnet samples obtained from different routes, showed in scheme of Table I,
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