SYNTHESIS AND CHARACTERISATION OF Mn3O4 – La2O3 NANO COMPOSITES FOR THERMISTERS

Abstract

In the present study, Synthesis of nano materials of Mn3O4 , La(OH)3 and Mn3O4 - La(OH)3 nanocomposite have been carried out following bottom up approach (reduction Process) by selecting several combinations of precursors, reducing agent and stabilization agents. Reaction conditions have worked out for synthesis to have monodisperse nanomaterials of nearly uniform dimensions. Mn3O4 - La(OH)3 nanocomposite was transformed into Mn3O4 - La2O3 following sintering process. These materials have been characterized for their morphology, crystalline structure, composition and optical properties using, TEM, XRD, FTIR, UV-Visible. Thermisters from these ceramic powder were fabricated in the form of thin wire compacted in a stainless steel tube having two sensing wires encapsulated parallel to each other have been fabricated. To work out the negative temperature coefficient (NTC) and NTC cut off temperature each thermister was kept in temperature controlled furnace for measuring resistivity values with respect to change in temperature. From these results parameters such as thermister constant, activation energy and temperature coefficient of each thermister were derived. Such thermisters will find applications to monitor and control the critical systems like aero engine, armor tank and other strategic devices from overheating and fire conditions. The complete work of the thesis is presented in the six chapters. Chapter 1 deals with challenges and applications of nanotechnology, properties of nanoparticles, type of thermisters. Chapter 2 covers literature which defines a number of methods used for the preparation of Mn3O4, La(OH)3 and Mn3O4 - La(OH)3 nanocomposite and also defines scope of the present work. Chapter 3 deals with methodology followed for synthesis and characterisation of Manganese Oxide (Mn3O4) Nanoparticles, Lanthanum Hydroxide Oxide (La(OH)3) nanomaterials, Mn3O4-La(OH)3 nanocomposites and Conversion of Mn3O4 - La(OH)3 into Mn3O4 - La2O3. It also covers experimental details on various techniques used for characterisation of these nanomaterials. Chapter 4 covers the detail description of results and discussions on synthesis and characterisation of nanomaterials, their composite for crystal structure, morphology, chemical structure, thermal stability and light interaction with radiations. Chapter 5 covers the electrical characterisation of nano materials and their nano composite, negative temperature coefficient (NTC) parameters has been worked out Mn3O4 alongwith composite of Mn3O4 - La2O3 (La2O3) for thermister applications. Chapter 6 includes the conclusion, summary of the results and significance of the study.