| dc.description.abstract | The discovery of new composites by integrating materials of different physical
properties with optimal control is of immense interest to researchers at present.
Today, there are several composites being used for several applications. The list of
composites and their applications is endless from toys to space applications in today's
life, as it is a very broad area of research. Composites are made up of the
combinations of two or more materials in which one of the materials, so called
reinforcing phase in the form of fibers, tubes and particles which are incorporated in
the other called matrix phase. The main functions of the matrix are to transfer the
stresses between the reinforcing fibers or particles, and to protect them from the
mechanical and environmental damage. This enhances their mechanical properties
like strength and stiffness. A composite is therefore one synergistic combination of
two or more phases which is superior to their individual phases due to more physical
and chemical properties. Ceramic composites have successfully replaced many
traditional ceramics and metals in several applications due to their light weight and
high strength, high tensile strength at elevated temperatures, high creep strength and
toughness. Typically, composites can be properly designed and manufactured, by the
appropriate combination of the strength of the reinforcing phase and the toughness of
the matrix. Such ceramic composites can be more capable to give the desirable
properties, which is not possible with a single conventional ceramic.
Polymer matrix composites and metal matrix composites have a large
number of applications in many fields. However, there are certain issues such as
homogeneity of fillers (particles or fibers), recycling, lack of stability, low
mechanical and thermal strength, very high coefficient of thermal expansion, etc. The
disadvantages of these composites are the difficulty in the production of fiberreinforced
composites and their increased labor cost. Ceramic matrix composites are
more significant over single phase ceramics, metals matrix and polymer matrix
composites in some applications due to their high fracture toughness and high
resistant to thermal shocks. They are used in the field of automotive industry,
renewable or alternative energies, healthcare, electronics and telecommunications,
aerospace, gas sensors and in many high temperature applications. These are based on
the combination of physical properties and are referred to as bio-ceramics, electroceramics,
magneto˗ceramics, opto˗ceramic, multiferroics and catalysts, etc. Several
materials like carbon, graphene and metal oxides have been used to produce
composites with different combinations to get superior physical properties.
In the present work, the conducting and magnetic metal oxide mixtures were
preparation and examined as metal oxide composites. The electrically conductive
lanthanum nickelate (LNO) was prepared as the conducting matrix. Ferrites of spinel
cubic structure like CoFe2O4, Ni Fe2O4 and barium hexaferrite BaFe12O19 were
prepared as magnetic phase. The synthesis, structural, morphological and
compositional studies of lanthanum nickelate (LaNiO3) and Co, Ni, Ba ferrites were
carried out. The electrical conductivity of LaNiO3 and the magnetic properties of
ferrites were investigated at room temperature.
Three nanocomposite systems of LaNiO3 with different ferrites were
prepared. All composites were investigated for their structural, morphological and
compositional studies. The electrical and magnetic properties of composites were
investigated. The study of these composites was further extended for electromagnetic
interference (EMI) shielding to test shielding effectiveness. The main results on
electrical conductivity, magnetic properties and EMI shielding of nanocomposites are
briefly summarized. In the thesis, major findings on this work are discussed. The
composites of conducting and magnetic metal oxides have not yet been studied and
reported. The electrical and magnetic properties of composite materials can be finely
tuned by varying concentration of reinforcing phase into conducting matrix and these
materials are explored in order to search possible application. This work mainly
focuses on the i) Preparation of new composites using conductive and magnetic metal
oxides, ii) Tuning of electrical conductivity and magnetic properties, iii) To study
composites for EMI shielding, iv) To check the possibilities of applications in the
field of electronics and v) To explore the surface and interface physics of hetero
structure.
Electromagnetic interference (EMI) is a fast growing problem in the modern
era of electronics, telecommunication and in various instruments. It has become a
critical area to be considered in electronic design and packaging. The increasing
usage of large number of electronic devices and the need of increasing processor
frequencies, the environment is becoming noisy due to the increasing electromagnetic
fields. Therefore, it is necessary to prevent the unwanted EM waves with the adequate
EMI shielding. The desire of high performance shields with the reduction in size,
weight and price had been a great interest of researchers to discover new materials as
suitable candidate for electronic housing. Presently, there are several types of
housings and EMI shields are made up of polymer composites and thin metal or
metal-alloy sheets work to protect devices from electromagnetic waves.
As a part of present thesis work, we have studied all above composites for
the EMI shielding measurements in the frequency range of 8 to 18 GHz. It is
observed that each composite system showed a very high shielding effectiveness. | en_US |
