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Solid State Metathesis Preparations of Hard Refractory Ceramics

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Solid State Metathesis Preparations of Hard Refractory Ceramics S o u p S t a t e M e t a t h e s is P reparations OF H a r d R e f r a c t o r y C e r a m i c s A thesis presented by: Artur Marek Nartowski BSc in partial fulfilment for the award of Ph. D. U n iv e r s it y C o l l e g e Lo n d o n D e p t , o f C h e m is t r y ProQuest Number: 10014877 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest 10014877 Published by ProQuest LLC(2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. Microform Edition © ProQuest LLC. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 Acknowledgements This work was supported by EPSRC and was completed under very helpfiil and encouraging supervision of Dr. I. P. Parkin. Grateful acknowledgement is due to members of staff, especially Dr. C. Carmalt, Prof. A. J. Craven, Dr. M. MacKenzie and the departmental microanalyst. I am also indebted to my fellow students, in particular, L. Affleck, L. Price, M. Fields and W. Cross for help and advice. I would like to thank my parents Renata and Luciano for support and hurrying me up with the completion of the work. I also fill grateful to my fi*iends Rafal, Matthias and Jens for their support. Abstract This thesis presents the synthesis of binary and ternary transition metal borides, carbides, nitrides and silicides the solid state metathetical processes. The reactions were initiated both in bulk and in the propagation modes. Rapid solid state metathetical reactions of Group 3-5, 13 and rare earth metal halides with nitriding agents such as LigN, MggN], Ca]N 2 and NaNg lead to formation of crystalline nitrides and co-product salts of Group 1 or 2 metals. Similarly, crystalline transition metal borides, carbides and silicides of Groups 4-8 have been synthesised using the halides and AIB 2, CaC2, SPC2, AI4C3, L%SL Mg 2Si or CaSi 2. The rates of these reactions and their final product crystallinity were related to the reagents used and the mode of reaction initiation. Thermally unstable transition metal nitrides of Group 6 transition metals, manganese, iron and cobalt have been synthesised using their halides and magnesium nitride with the aid of magnesium chloride as an inert heat sink. This work also reports the SSM (Solid State Metathesis) synthesis of highly crystalline transition metal carbides and silicides fi'om the transition metal oxides and CaC 2, SrC2, Mg 2Si, CaSi2. All the co-products fi“om the various reactions were removed using solvents such as THF, methanol, water or dilute acids. The final products were analysed using X-ray powder diffraction, FT-IR and SEM/EDXA. A selected group of carbides and nitrides were analysed using TEM and PEELS/ELNES (photoelectron energy loss spectroscopy/energy loss near-edge structure). Besides the identification of the final products, the main objectives in these analyses were to determine the elemental composition (and oxygen contamination) of these interstitial compounds. The compounds formed by SSM processes were shown to be useful in standardising ELNES measurements. Contents Page Title Acknowledgements Abstract Contents List of Tables List of Figures 13 Chapter I; Introduction 20 1.1 What are ceramics? 20 1.1.1 History of ceramics 20 1.1.2 Classification of ceramics 21 1.2 Carbides and nitrides 22 1.2.1 Properties 22 1.2.2 Applications 27 1.3 Transition metal silicides 32 1.4 Transition metal borides 36 1.5 Commercial preparations of transition metal borides, carbides and nitrides 38 1.6 SHS (self propagative higb-temperature syntheses) Reactions 40 1.6.1 Background and history 40 1.6.2 Synthesis of pore-free materials, items and coatings by SHS 42 1.6.3 Industrial applications of SHS products, materials and items 43 1.7 What are the SSM (solid state metathesis) reactions? 43 1.7.1 Background 43 1.7.2 Initiation and product formation 44 1.7.3 Comparison of SHS and SSM processes 44 1.7.4 Future and advantages of SSM reactions 45 1.8 Aims of this work 48 Chapter 2; Preparations of metal nitrides 49 2.1 Introduction 49 2.1.1. Potential nitriding reagents 49 2.1.2. Aims and background 51 2.2 Synthesis 52 2.3 Characterisation 54 2.3.1 X-ray powder diffraction 54 2.3.2 SEM/EDXA 58 2.3.3 TEM 61 2.3.4 ELNES/PEELS analysis 65 2.3.5 ELNES of CrN and Cr 2N 67 2.4 Discussion 69 2.4.1 Level of nitridation in transition metal nitrides prepared by SSM 72 2.4.2 Decomposition of transition metal nitrides prepared using SSM routes 73 2.4.3. Formation of solid solutions 79 2.5 Thermodynamic considerations 82 2.6 Summary 84 2.7 Experimental 85 Chapter 3; Preparations of transition metal carbides 89 3.1 Introduction 89 3.1.1 Potential carbiding reagents 89 3.1.2 Aims and background 90 3.2 Synthesis 91 3.3 Characterisation 94 3.3.1 X-ray powder diffraction 94 3.3.2 SEM/EDXA 97 3.3.3 TEM 101 3.3.4 ELNES/PEELS analysis 105 3.4 Discussion 107 3.4.1 Level of carburisation in transition metal carbides 111 3.4.2 Formation of bimetallic transition metal carbides and transition metal carbonitrides 113 3.5 Thermodynamic considerations 119 3.6 Summary 121 3.7 Experimental 122 Chapter 4; Preparations of transition metal silicides 125 4.1 Introduction 125 4.2 Synthesis 126 4.3 Characterisation 131 4.3.1 X-ray powder diffraction 131 4.3.2 SEM/EDXA 135 4.4 Discussion 139 4.4.1 Control of stoichiometry in transition metal silicides 141 4.5 Thermodynamic considerations 144 4.6 Summary 145 4.7 Experimental 146 Chapter 5; Preparations of metal borides 149 5.1 Introduction 149 5.1.1 Potential boride precursors 149 5.1.2 Aims and background 150 5.2 Synthesis 150 5.3 Characterisation 151 5.3.1 X-ray powder diffraction analysis 151 5.3.2 SEM/EDXA analysis 153 5.4 Discussion 154 5.5 Thermodynamic considerations 156 5.6 Summary 156 5.7 Experimental 157 Chapter 6; Preparations of transition metal carbides and silicides using metal oxides as metal precursors 159 6.1 Introduction 159 6.1.1 Some commonly available oxides containing transition metals 159 6 .1.2 Aims and background 160 6 .2 Synthesis 161 6.3 Characterisation 165 6.3.1 X-ray powder diffraction 165 6.3.2 SEM 167 6.3.3 EDXA 169 6.3.4 TEM 172 6.4 Discussion 173 6.5 Thermodynamic considerations 174 6 .6 Summary 175 6.7 Experimental 176 er 7; Control of crystallite size in products formed using SSM 179 7.1 Introduction 179 7.1.1 Aims and background 179 7.2 Control of product crystallite size 180 7.2.1 Spreading the reagents 180 7.2.2 Varying the reaction scale 181 7.2.3 Mode of initiation 183 7.2.4 Using a diluent 184 7.2.5 Selection of SSM precursors 189 7.2.6 Increase in pressure 190 7.2.7 Annealing the as prepared SSM products 191 References 193 Publications 202 List o f Tables 1.1 Principal applications of metal carbides typified by several examples. 24 1.2 Melting/decomposition points of selected hardmetals compared with their parent metals, °C. 26 1.3 Microhardness properties of selected transition metal carbides. 27 1.4 Worldwide (unless stated) consumption of carbides and nitrides. 28 1.5 Melting points, °C, of selected transition metal silicides. 32 1.6 Principal properties of selected metal borides. Melting points of the parent metals are in brackets next to the melting points for their borides. All data taken fi*om references [20] and [76]. 37 2.1 Selected reactions of metal halides with lithium nitride or sodium azide initiated with flame (fl), filament (fil) or performed in bulk under vacuum (bkv) or nitrogen pressure (bkp).* Literature lattice parameters were taken from reference [ 152] and [159]. 56 2.2 Selected reactions of metal halides with Group 2 nitrides performed using flame (fl) or filament (fil) initiation, or as a bulk reaction under vacuum (bk).* Literature lattice parameters were taken from references [152] and [159]. 57 2.3 Samples analysed using EELS/ELNES and TEM techniques. 63 2.4 Conditions used to test oxidative stability of a selection of transition metal nitrides prepared using solid state metathesis discussed in this chapter. 76 2.5 Microanalytical data obtained for the samples of aluminium nitride annealed for different periods at 550 °C. 77 3.1 Selected bulk reactions of transition metal halides with calcium and strontium carbide.* Literature lattice parameters were taken from references [18], [159] and [175]. 93 3.2 Selected bulk reactions of transition metal halides with aluminium carbide.* All the literature lattice parameters were taken from reference [18], except for iron carbide, FegC, which was taken from reference [175]. 94 3.3 Reactions of transition metal halides with calcium and strontium carbides initiated with flame.* Literature lattice parameters were taken from references [18] and [175].
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