INVESTIGATION OF THERMO-ELECTROMAGNETIC MATERIALS IMPLEMENTED IN HARVESTING OF THERMOELECTRIC ENERGY IN ELECTRICAL MACHINES by Muhammid Hamid Al-Baghdadi A thesis submitted to Cardiff University in candidature for the degree of Doctor of Philosophy Wolfson Centre for Magnetics College of Physical Sciences and Engineering Cardiff University Wales, United Kingdom July 2016 The work has not previously been accepted in substance for any degree and is not being concurrently submitted in candidature for any degree. Signed ……………………....…… (Muhammid Hamid Husein Al-Baghdadi) Date …………………………… STATEMENT 1 This thesis is being submitted in partial fulfilment of the requirements for the degree of PhD. Signed: ……………………………. (Muhammid Hamid Husein Al-Baghdadi) Date: ……………………………….. STATEMENT 2 This thesis is the result of my own investigations, except where otherwise stated. Other sources are acknowledged by the provision of explicit references. Signed ……………………....…… (Muhammid Hamid Husein Al-Baghdadi) Date …………………………… STATEMENT 3 I hereby give consent for my thesis, if accepted, to be available for photocopying and for inter-library loan, and for the title and summary to be made available to outside organisations. Signed ……………………....…… (Muhammid Hamid Husein Al-Baghdadi) Date …………………………… I This work was carried out at the Wolfson Centre for Magnetics, School of Engineering, Cardiff University and financially supported by the Iraqi Ministry of Higher Education and Scientific Research Scholarship. I would like to express my highest gratitude and appreciation to them for providing the opportunity to attain the PhD, financial support and resources required in my study to complete this project. First of all, I am deeply grateful to my academic supervisors, Dr Fatih Anayi and Dr. Gao Min for their excellent guidance, encouragement, care, patience, constructive criticism and insight during this project. Similarly, I would like to express my special thanks to Dr. J. J. Bomphrey, Dr. Jorge Garcia Canadas, and Dr. Phil Buckle, Cardiff School of Physics, for their encouragement and invaluable guidance and continual support. I wish thank the other members of the Wolfson Centre, Dr. Jeremy Hall, Dr Turgut Meydan, and Dr Yevgen Melikhov for their advice and comments at all levels of my research. Special thanks go to all the members of the thermoelectric group at Cardiff University for their friendship and making my study life a memorable one. I would also like to acknowledge Dr. Mike Harbottle, Dr. Richard Marsh, and Anthony Oldroyd, members of the research office, electronic workshop, and mechanical workshop, for taking time out from their busy schedule to help and support my project during my study in Cardiff University. My greatest thanks are reserved for my family: especially my mother and father for their unconditional love, support and encouragement throughout my life, and to my wife for her constant care, love, support and standing beside me during happy and sad moments and to my sons and daughter who have suffered the most during my absence at their most needed times. II Many researchers have tried to exploit waste heat to generate electrical power. There are two phenomena that are related to the conversion of heat into electrical power: thermoelectric (TE) and thermomagnetic (TM) phenomena. In this work the latter (TM phenomenon) deals with the conversion of waste heat to generate electrical power. TM effect began in the 1960s due to the difficulties in induction of a strong magnetic field in the past. The work presented in this thesis focuses on the preparation of polycrystalline indium antimonide (InSb) bulk materials and investigation of their TM properties. The research was motivated by their anticipated application in technologically important regions of reducing energy losses and in operating conditions of electro-magnetic machines, such as motors, generators and transformers, by incorporating such energy conversion devices into the machines at carefully chosen locations. When a thermomagnetic sample is subjected to both temperature gradient and magnetic flux density concurrently, it will produce electrical output. A high electrical power output will be produced when the sample has similar numbers of both charge carriers, and, in addition, when the sample is subject to high temperature difference and high magnetic flux density across it. A new technique has been developed in this work to make undoped and doped InSb polycrystalline bulk materials with tellurium Te, based on open quartz tube instead of the traditional method requiring sealing of the quartz tube. A modification in the raw materials ratio was adjusted to obtain pure InSb sample. The X-ray diffraction (XRD) and the inter-planar spacing analysis were carried out to check the structure of the samples and the result confirmed that the material was pure InSb. Measurements were taken under direct magnetic field, which was produced from direct current (DC) supply, and alternative magnetic field, which was induced from alternative current (AC). The design procedure involved determining the longitudinal, transverse and hybrid transverse voltages. Modifications in design of the measurement III system have been made to minimise the effect of AC magnetic field on these parts, such as the heat sink being made of copper plate and K-type thermocouples. In addition, magnetic shielding was used for wires in the vicinity to minimise the induced voltage that affects measurements of transverse voltage. The induced voltage was still higher than the transverse voltage, even with the use of magnetic shielding. For this reason, the research performed in this work relating to the thermomagnetic parameters under AC magnetic field did not obtain appropriately good results. The thermomagnetic parameters of samples under DC magnetic field have been improved by doping them with Te at different levels of 0.1% and 0.25%. The resistivity and Seebeck coefficient of the doped InSb with 0.25% Te was lower than those for undoped InSb single crystalline, which was used as a reference sample. The resistivity was lower, around 24% and 38% at the magnetic flux density 0 T and 1 T respectively, and the Seebeck coefficient was about 8% lower for various magnetic flux densities. In contrast, the Nernst, Righi-Leduc voltages and thermomagnetic power of the doped InSb with 0.25% Te were higher than those for undoped InSb single crystalline. The Nernst voltage was around 2% and 0.5% for the magnetic flux density of 1 T and temperature difference 30 °C and 80 °C respectively, while the Righi-Leduc voltage was higher, around 2.6% and 0.9%, and thermomagnetic power was higher around, 2.9% and 1% respectively for the same magnetic field and temperature differences. IV Abbreviations: TE Thermoelectric phenomena TM Thermomagnetic phenomena InSb Indium antimonied Te Tellurium element XRD X-ray diffraction DC Direct current AC Alternating current TME Thermo-magneto electric phenomena n-type Negative type semiconductor (the majority carriers are negative charge) C Carbon element Ge Germanium element In Indium element Sb Antimony element O2 Oxygen molecular In2O3 Indium trioxide P-type Positive type semiconductor (the majority carriers are positive charge) III-V Three-five semiconductor group LPE Liquid phase epitaxy process MBE Molecular beam epitaxy process MOVPE Metal-organic vapour phase epitaxy process MOCVD Metal-organic chemical vapour epitaxy process THM Travelling heater method VDS Vertical directional solidification process FZM Floating zone melting TSM Traveling solvent method HgSe Mercuric selenide BiSb Bismuth antimonied CdAs Cadmium arsenide Bi Bismuth e.m.f Electro motive force CdTe Cadmium tellurium ZT Dimensionless figure of merit InAs Indium arsenide GMT Geometrical magneto-thermo power Ni Nickel element Ag Silver element HgTe Mercuric tellurium (hkl) Lattice plane CP4 Etching solution PCB printed circuit board K-type Thermocouple type K (magnetic materials) V EM Electromagnetic IH Induction heating T-type Thermocouple type T (non-magnetic materials) r.m.s The root means square of voltage Nomenclatures: µe Mobility of charge carriers B Magnetic flux density m* Density of states effective mass Thermal conductivity 훿 Seebeck coefficient Δ푉 Voltage difference Δ푇 Temperature difference 풬 Generated heat ∏ Peltier coefficient I Electrical current 훽 Thomson coefficient 풥 current density ∇푇 Temperature gradient 푁 Nernst coefficient 푑푇⁄푑푦 Temperature gradient in y-axis 퐸 Electrical field 푆 Righi-Leduc coefficient 푑푇⁄푑푥 Temperature gradient in x-axis hLe Longitudinal potential difference coefficient 퐻 Magnetic field strength 푥 The distance between two points 푄 The heat transfer rate 퐴 Area 푞̇ Distance derivative of heat flux 푊 Width 피 The energy ℎ Thermal convection Resistivity 피 g Band gap energy KB Boltzmann’s constant 푛 The electron density 푝 The hole density ni Intrinsic carriers density The wave length of X-ray ℕ Diffraction order 푑 Lattice inter-planar spacing The angle between the plane wave and lattice plane 푉 The voltage VI 푅 The resistance 픸 The cross-section area 퐿 Length 핟 The turn density for the winding 휏 The thermal time constant 푣 The sample volume 푐 The specific heat capacity 퐴푠 The sample area that attached to the media 퐿푐 The ratio of the solid’s volume to surface area F The Lorenz force 휗 The charge carrier velocity 푚푒 The electron mass The flux linkage 풩 The number of turns The angular frequency The frequency µ0 The permeability of the free space g The air gap length VII Chapter 1: Introduction