Texas center for
Superconductivity (TCSUH)
Department of Civil and
Environmental Engineering
Abstract
Nanoscale iron particles are expected to
have practical uses in many engineering fields and there are several potential
methods of preparing of nanoscale iron particles. Some of the methods currently
used are chemical reduction, sol-gel method, and thermal decomposition. These
methods are critically reviewed.
1. INTRODUCTION
Nanoparticles display novel physical
properties due to (1) finite-size, and (2) surface/interface effects. Every
known materials will yield a new set of properties, dependent on the size, such
as optical properties, magnetic properties, catalyst and crystal morphologies.
In recent years, studies in the ultra-fine iron particles are expected to have
uses in the field of powder metallurgy, magnetic recording, ferrofluids, and
water treatment. Some common chemical methods of preparation of nanoscale iron
particles are viewed next.
2.
OBJECTIVES
Evaluating methods to produce nanoscale
iron. Specific objectives are (1) Review methods of producing nano iron; (2)
Verify methods to produce nano iron.
REVIEW OF LITERATURES
(a) Chemical Reduction method
Nanoscale iron can been prepared by the
reaction of Fe(III) chloride, and sodium borohydride in aqueous solution1.
X-ray diffraction, Mossbauer spectroscopy and elemental analyses can be used to
confirm the compositions and structure of the product. The reaction can be
reprented as:
Fe(H2O)63+
+ 3BH4- + 3H2O→Fe(s) + 5H2 +
3B(OH)3
This approach can also be used to
fabricate nanocrystalline Fe-Cu alloy, and Fe-P-B ultrafine amorphous particles.
In addition, it does not require extensive processing equipment and the cost of
production can be relatively low compared with other methods.
(b) Sol-gel Method
Glass-metal nanocomposites incorporating
ultra-fine particles of iron can be prepared by heat treatment of a gel derived
from a sol containing silicon tetraethoxide and a metal compound, such as
Fe(Cl)3. In the process,
spherical-shaped metal particles are isolated and with diameters ranging from
3-10 nm. The optical absorption and electrical conductance of such films have
been measured. The resistivity values in the range 0.0001-0.0039 Ωcm have
been obtained depending on the particle diameter. The rate of resistivity
change increased as the metal particle diameter becomes smaller.
(c) Thermal Decomposition
In this method, iron pentacarbonyl can be
thermally decomposed in an organic liquid. The mixture is refluxed and stirred
for 5-6h initially at 390K rising to 460 K as the reaction proceeded.
Mossbauer-spectroscopy and X-ray-diffraction studies show that the sample
contains small particles of a metallic glass. Annealing the particles at 523K
results in crystallization of the particles into a mixture of α-Fe and
χ –Fe5C2, of 8.5 median diameters. This method of
carbonyl decomposition has been used to prepare small particles suitable for
use in ferrofluids.
PRELIMINARY RESULTS
The chemical reduction method for
preparing nano iron was selected for experimental verification. Fe(Cl)3
and NaBH4 solution are being used.
5.
CONCLUSIONS
1)
Chemical
preparation of nanoscale particles permits the manipulation of matter at the
molecular level and has good chemical homogeneity; the role of such method has
been rapidly growing.
2)
Chemical
preparation of nanoparticles of iron is of great interest because of its
merits, such as low cost, better control of particle size and size
distribution.
6. ACKNOWLEDGEMENT
This study supported by funding form the
Texas Center for Superconductivity at the University of Houston.
7. REFERENCES
1)
George N.
Glavee, Kenneth J. Klabunde, Inorganic Chemistry, vol. 34, 28 (1995)
2)
Jianyi
Shen, Zheng Hu, etc., Applied Physical Letters, 59(20), 2510(1991)
3)
A.Chatterjee,
D.Chakravorty, Journal of Materials Science, 27, 4115 (1992)
4)
Jacques van
Wonterghem, Steen Morup, Physical Review Letter, Vol. 55,410(1985)
If you have any questions, please contact Dr. C.Vipulanandan
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