12-01-2011, 01:50 PM
[attachment=8167]
PRESENTED BY:
ROHAN SAMKARIA
DEPARTMENT OF PHYSICS
NATIONAL INSTITUTE OF TECHNOLOGY, HAMIRPUR (HP)-177005
PROPERTIES OF ALUMINATES
An Aluminate is a compound containing aluminum and oxygen.
Spinel – MgAl2O4, after which this class of minerals is named.
Aluminates possesses a high melting point.
Good mechanical strength .
Excellent chemical resistance.
High thermal conductivity.
APPLICATIONS
Used as catalyst support, sensor technology and fuel cells.
Aluminates are used as tunable dielectric materials.
High resistivity, a low dielectric constant and a small loss tangent at low frequency make Aluminates suitable for application as
Insulators and electromagnetic radiation absorbers in the electronics industry.
Insulating and structural material in fusion reactors.
Apart from the above properties aluminates has been extensibly used as a dielectric materials at microwave frequencies. Most of the microwave based device systems are located in the frequency range 300 MHz-300 GHz .29
The low permittivity ceramics are used for millimeter wave communications and also as substrates for microwave integrated circuits.
The medium permittivity ceramics in the range 25-50 are used for satellite communications and in cell phone stations.
The high permittivity materials are used in mobile phones, where miniaturization of the device is very important.
For millimeter wave and substrate application a temperature stable low permittivity and low loss materials are required for high speed signal transmission with minimum attenuation.
Nano Aluminates
In order to meet the specifications of the current and future systems, improved or new microwave components based on dedicated dielectric materials and new designs are required.
Nano crystalline spinel ceramics represent an attractive class of materials which owing to their small size, exhibit novel properties different from bulk materials.
The different but often desirable behavior of nano scaled materials is attributed to the large amount of atoms located on the grain boundaries of the crystallites.
Size-dependent properties.
Surface to volume ratio
A 3 nm iron particle has 50% atoms on the surface
A 10 nm particle 20% on the surface
A 30 nm particle only 5% on the surface
Methods for preparation of Nano Aluminates
Nano Aluminates, when prepared via different routes, would demonstrate different properties , even with the same starting compositions.
A variety of chemical routes have been developed to prepare Nano Aluminates because the traditional solid-state method could not meet particle size requirements and versatility of synthesis process.
The disadvantage of solid state routes such as in homogeneity, lack of stoichiometry control, high temperature and low surface area are improved when the material is synthesized by a solution based method.
Wet chemical methods are preferred for aluminate preparation since they show high sinterability, high surface area with required stoichiometry.
Among wet chemical techniques, sol-gel using alkoxides, hydrothermal and colloid emulsions are time consuming and involve highly unstable alkoxides and difficult to maintain reaction conditions.
Co – precipitation is one of the more successful techniques for synthesizing nano sized particles.
This process avoid complex steps such as refluxing of alkoxides, resulting in less time consumption compared to other techniques.
