Tungsten Properties, Chemistry, Technology of the Element, Alloys, and Chemical Compounds Erik Lassner and Wolf-Dieter Schubert Vienna University of Technology Vienna, Austria Kluwer Academic / Plenum Publishers New York, Boston, Dordrecht, London, Moscow Library of Congress C a t a l o g i n g - i n - P u b l i c a t i o n Data Lassner, Erik Tungsten - properties, chemistry, technology of the element, a l l o y s , and c h e m i c a l compounds / Erik Lassner and Wolf-Dieter Schubert p cm Includes b i b l i o g r a p h i c a l references and index ISBN 0-306-15Q53-4 Tungsten I Schubert, Wolf-Dieter II Title QD181.W1L37 1998 620 ' 8934—dc21 98-45787 CIP ISBN 0-306-45053-4 © 1999 Kluwer Academic / Plenum Publishers, New York 233 Spring Street, New York, N.Y 10013 10987654321 A C.I.P record for this book is available from the Library of Congress All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher Printed in the United States of America To a group of pioneers in the field of Power Metallurgy and Tungsten Science: Friedrich Benesovsky, Gustav F Hiittig, Richard Kieffer, Tivadar Millner, Hans Novotny, Paul Schwarzkopf, and Karl Sedlatschek They educated a generation of scientists and technicians who spread their knowledge throughout the world And to our friend, the late Bernhard F Kieffer Preface Why does someone write a book about Tungsten? There are several reasons and precedents for this, the most important of which is that the last book on tungsten was written more than 20 years ago, in 1977, by St W H Yih and Ch T Wang During the intervening period there have been many new scientific and technological developments and innovations, so it was not only our opinion but the view of many other members of the "tungsten family" that it was time to start writing a new book about tungsten Preparations of the new book began in 1994 Further impetus to the project was provided by the realization that in spite of this new knowledge having been presented at seminars or published in the technical press, a general acknowledgement of it by the majority of technicians and scientists is still far from being realized It is our hope that this book will significantly contribute to a broader acceptance of recent scientific and technological innovations An important prerequisite for such a project is the availability of a recently retired, experienced person willing to devote his time and talents to the tedious part of the exercise Erik, who retired in 1993, was both highly motivated and eager to start; and it was a relatively easy task for Erik to persuade Wolf-Dieter to participate in the project The fact that both of us have for many years enjoyed a close cooperation in tungsten-related research projects leading to the publication of several joint papers only facilitated the decision Moreover, as authors of "Tungsten, Tungsten Alloys, and Tungsten Compounds" in the latest edition of Ullmann s Encyclopedia of Industrial Chemistry, we have also had some common experience in writing Another important prerequisite was that we both had extensive experience in tungsten-related research and technology during our professional work Wolf-Dieter's scientific career and extensive research activities combined with Erik's long-term industrial and development knowledge contributed to a fruitful cooperation in preparing the manuscript for this book Nevertheless, in the writing of this book we also learned a lot more about tungsten Richard Kieffer (the father of Bernhard Kieffer and for many years one of the leading experts on tungsten) always said: "If you want to inform yourself only roughly about something, present a paper about the subject; but, if you want to gain an in-depth knowledge about it — you have to write a book." So it seems that during the writing of this book (it is now February 1998) we grew into experts Encouragement, a very important aid in a project of this kind, was given to us first of all by Bernhard F Kieffer, who unfortunately passed away prematurely Bernhard not only encouraged us to write this book, but also encouraged Plenum Publishing Corporation to publish it Sometimes it was not easy to decide what should be included and what should be omitted; or the extent of detail to which each item should be discussed We decided in general to emphasize the technologically related matters and to refrain from discussing purely scientific principles Naturally, these decisions are always subjective and chapters dealing with those subjects with which we are more familiar are undoubtedly treated more precisely than others This is natural, because otherwise the individual chapters should each have been written by an expert on that particular topic As our original manuscript already exceeded the maximum allowed by the publisher, such an expert treatise would have exceeded the publisher's maximum several times over Nevertheless, we hope that our book gets a good reception from the reader Returning once again to the original question: "Why write a book?" somebody once said it is to establish a "monument" to the author(s) If this should be the truth, we want many people to come and glance at it However, besides constructing a monument, it is our intention to summarize the current status of the science and technology of tungsten for those interested in extending their knowledge of this subject A book always provides for easier and more efficient learning than searching for a large number of original publications, which must first of all be identified The preparation of this manuscript has sometimes exacted its toll on our families, we want to especially thank our wives for their patience and understanding Vienna and Graz, February 1998 Acknowledgments Without the support and help of numerous colleagues and friends as well as companies, it would not have been possible to write the book in its present form For valuable information, literature, photographs, data sheets, etc., we are kindly indebted to many people in many countries: Austria K Voigt and R Cantz, Bohlerit, Kapfenberg M Schwarzkopf, G Leichtfried, A Singer, and R Piircher, Plansee, Reutte H Wohrle, Plansee Tizit, Reutte P Putz, Sandvik Austria, Vienna F Sattler, Tamrock Voest-Alpine Bergtechnik, Zeltweg M Spross, B Zeiler, O Grau, and E Moos, Wolfram Bergbau-und Huttenges., St Peter i.S I Begsteiger, Porzellanfabrik Frauenthal GmbH Th Nagl, Austrian Energy and Environment F Koch, Bohler Edelstahl GmbH, Kapfenberg G Groboth, Austrian Research Center Seibersdorf E Hengge, Technical University Graz B Lux, P Ettmayer, H Danninger, and R Haubner, Vienna University of Technology Belgium D Lison, University of Louvain, Brussels China Zhao Quinsheng and Zou Zhiqiang, Central South University of Technology, Changsha Czech Republic V Dufek, Prague D Rafaja, Charles University Prague Germany K Dreyer, Widia, Essen D Ermel, ALD Vacuum Technologies, Erlensee H Frick, Kemmer Prazision, Schwabisch Gmiind J HoIz, Industrievertretungen GmbH., Wachtersbach H Kolaska, Fachverband Pulvermetallurgie, Hagen E Kubel, WI Hartmetall, Miinsingen G Marsen, Osram, Schwabmiinchen H Palme, University of Cologne D Pratschke, Gebr Leitz, Oberkochen G Gille, Starck, Goslar H Westermann, United Hardmetal, Horb; Elino Industrieofenbau, Diiren Hungary L Bartha, O Horacsek, and J Neugebauer, Hungarian Academy of Science, Budapest Israel R Gero, Ashot Ashkelon, Ashkelon R Porat and M Leiderman, ISCAR; Tefen Japan T Tanase, Mitsubishi Materials Corporation, Omiya T Nomura, Sumitomo Electric Industries, Itami Y Yamamoto, Tokyo Tungsten, Toyamaken K Kitamura, Toshiba Tungaloy, Iwaki City Luxemburg J P Lanners, Cerametal, Mamer Principality of Liechtenstein Th Kraus, Triesen Sweden L Rohlin, AB Sandvik Coromant, Stockholm U Fischer, AB Sandvik Rock Tools, Sandviken B Uhrenius, Sandvik Hard Materials, Stockholm C G Granquist, University of Uppsala The Netherlands F Mertens and G.vd Kerkhof, Philips Lighting, Maarheeze UK B Williams, EPMA, Shrewsbury S Jones, Royal Ordnance Speciality Metals, Wolverhampton M Maby, Secretary General, International Tungsten Industry Association, London USA B North, M Greenfield, and G J Wolfe, Kennametal, Latrobe B F Kieffer, M Ostermann, J Oakes, and K Horten, Teledyne Advanced Materials, Huntsville E Rudy, SINTEX, Oregon C L Conner, The Dow Chemical Company, Midland E A Amey, USBM J Stone, Denver Ch W Miller, Jr., Harper International, Lancaster We gratefully acknowledge the critical reading of various parts of the manuscript by the following people: M Spross and B Zeiler, Wolfram Bergbau- und Hiittenges., St Peter i.S., Austria G Leichtfried, Plansee, Reutte, Austria K Mereiter, E Zobetz, H Mayer, P Mohn, and J Redinger, Vienna University of Technology, Austria W Kiesl, R Stickler, and R Podloucky, University of Vienna, Austria M Shale, William Rowland, Sheffield, UK E Bennett, NPL, Teddington, UK H C Starck, Goslar, Germany O Foglar, Schladming, Austria A particular vote of thanks is due to A Bartl and W Prohaska (Institute for Chemical Technology of Inorganic Materials, Vienna, Austria) for the preparation of numerous drawings, tables, copies, and photographs We owe special thanks to Mrs Ann Stanly of Teledyne Metalworking Products for correcting the manuscript in regard to the English, which is not our mother tongue We gratefully acknowledge the financial support of Teledyne Advanced Materials^ Huntsville, AL, USA Contents Preface vii Acknowledgments ix The Element Tungsten: Its Properties 1.1 Analogous to Atom Related Physical Properties 1.1.1 Nucleus 1.1.2 Electron Configuration 1.1.3 Spectra 1.1.4 Thermodynamic Functions Bulk Tungsten Metal Related Physical Properties 1.2.1 Electronic Structure and Bonding 1.2.2 Structural Properties 11 1.2.3 Mechanical Properties 16 1.2.4 Thermal Properties 30 1.2.5 Electromagnetic Properties 34 1.2.6 Optical Properties 36 1.2.7 Electron Emission 40 1.2.8 Acoustic Properties 42 Chemical Properties of Tungsten Metal 42 1.3.1 General Remarks 42 1.3.2 Reactions with Nonmetals 46 1.3.3 Reactions with Metals 46 1.3.4 Reactions with Compounds 50 1.3.5 Reactions with Aqueous Solutions 53 1.3.6 Miscellaneous 55 1.3.7 Reactions with Organic Compounds 56 References for Chapter 56 1.2 1.3 This page has been reformatted by Knovel to provide easier navigation xiii xiv Contents Tungsten History: From Genesis to the 20th Century Products 61 2.1 The Formation of Tungsten Atoms 61 2.2 How Tungsten Atoms Came on Earth 63 2.3 Average Abundance 64 2.4 Geology: Formation of Ore Deposits 65 2.5 Minerals 69 2.6 Ore Deposits and Reserves 70 2.7 Early Discoveries of Ores, Compounds, and of the Element 77 2.8 Technically Important Discoveries 79 2.9 Industrial Evolution 80 References for Chapter 83 Important Aspects of Tungsten Chemistry 85 3.1 Oxidation of Tungsten Metal by Air or Oxygen 85 3.2 Reaction of Tungsten with Water 86 3.3 Reduction of Tungsten Oxides by Hydrogen 88 3.3.1 Introduction 88 3.3.2 Thermodynamic Considerations 89 3.3.3 Formation of a Volatile Tungsten Oxide Hydrate [WO2(OH)2] 91 3.3.4 Kinetic Considerations 91 3.3.5 Influence of Foreign Elements 103 Reduction of Tungsten Oxides by Carbon or CarbonContaining Compounds 107 Reduction of Tungsten Halides 110 3.5.1 Introduction 110 3.5.2 Reduction of WF6 111 3.5.3 Reduction of WCl6 by Hydrogen 113 3.5.4 Reduction of WCl6 by Carbon-Containing Reagents 113 3.4 3.5 This page has been reformatted by Knovel to provide easier navigation 420 Index terms Links Carbides of tungsten (Continued) preparation by CVD 113 in an auxiliary melt 118 in salt melts 119 WC 140 WC1-x 140 W2C 139 Carbon black properties 115 Carbothermic reduction of WO3 107 Carbothermic production (Ferro-W) 310 Carbo-silicothermic production (Ferro-W) 311 Carburization 114 direct 330 high temperature 329 Catalysis 365 Cathode reactions 124 Cathodes in x-ray tubes 297 334 330 332 324 Cemented carbides: see Hardmetals Chalkogenide catalysts 374 Chemical uses 148 164 365 153 166 155 173 100 101 Chemical vapor reaction 334 transport 96 Chemical vapor deposition: see CVD Chinese APT plants 201 Chlorides of tungsten 169 Chlorination of ore concentrates 110 Cleavage 15 Coating (of hardmetals) 351 Cobalt powder 344 This page has been reformatted by Knovel to provide easier navigation 421 Index terms Cohesive energy Links Coils, coiling 264 Cold isostatic pressing 232 Coldstream process 384 Cold work tool steels 317 Compacting of tungsten powder 231 Consumption and use 403 Coordination compounds 174 Corrosion of tungsten 53 Creep 28 Critical density 31 Critical pressure 31 Critical temperature 31 Crystallographic properties of tungsten 11 Crystallographic shear structures 348 125 151 CVD of tungsten 111 244 of tungsten carbide 113 334 D Deformation of tungsten 22 Deformation-mechanism map 28 Denox SCR catalyst 366 Density of tungsten of states 13 Die pressing (W) 231 Digestion of oxidized scrap 193 of scheelite 191 of wolframite 192 Direct carburization 109 Direct compaction (hardmetal) 348 This page has been reformatted by Knovel to provide easier navigation 330 422 Index terms Direct recycling Links 381 Discharge lamps: see Gas discharge lamps Discoveries of tungsten and its ores 77 Dislocations, movement of 15 Doped tungsten powder 22 229 chromium doping 230 lithium doping 229 NS/AKS doping 230 sodium doping 229 Ductile to brittle transition temperature 20 Ductilizing effect 22 E Ecology 387 Economy 395 Effective nuclear charge Elastic properties of tungsten 10 Electrical resistivity 34 Electrochemical treatment 126 Electrochemistry of tungsten 123 Electrochromic device 128 Electrochromism 126 Electrodialysis 196 Electroforming 126 Electrolytic dissolution 126 Electron affinity Electron-beam zone melting Electron configuration Electron emission Electron emitters (W, W-ThO2, W-La2O3, porous W) 244 39 289 Electronegativity Electronic structure and bonding Electropolishing 127 This page has been reformatted by Knovel to provide easier navigation 18 193 24 423 Index terms Links Enthalpy of fusion 30 of sublimation 30 Entropy effusion 30 Equilibrium lattice constants (calculated) 11 Equilibrium partial pressures (W-H-O system) 92 Evolution of the universe 61 Evaporation rate of tungsten 30 Evolution of massive stars 61 Extrusion (hardmetals) 348 F Fabrication of tungsten Ferberite 239 69 Ferrotungsten 309 Fiber-reinforced composites 278 Field emission Fischer Tropsch catalysts 42 371 Flotation of scheelite 183 of wolframite 184 Fluorescent lamps 285 Fluorides of tungsten 167 Foreign elements (influence on reduction) 103 Fusion electrolysis 126 Fusion reactor 293 168 G Gangue separation 195 Gas-discharge lamps 284 Geology of tungsten 65 Globular tungsten powder 245 This page has been reformatted by Knovel to provide easier navigation 287 424 Index terms Links Grain boundary diffusion 33 weakness 20 Gravity methods (beneficiation) 195 H Hafnium carbide, precipitation hardening 268 Halides of tungsten 110 Halogen lamps 284 Halogen cycle 285 Hardening (tungsten steels) 313 Hard metals: see Hardmetals Hardmetals 321 applications 353 coatings 351 granulation 347 hotpressing 351 nanocrystalline precursor 335 postsinter treatments 351 powder consolidation 348 milling 346 preparation of powder grades 345 sintering 348 straight grades 312 WC-(Ti, Ta, Nb)C-Co grades 359 Hardness 18 Heat sinks 290 Heavy alloys: see Heavy metals Heavy metals 270 Heteropolytungstates 157 Hexagonal tungsten bronzes 164 High-density liquid 156 This page has been reformatted by Knovel to provide easier navigation 254 425 Index terms Links High kinetic energy penetrators 271 High-performance switches 287 High-purity tungsten 247 High speed steels (HSS) 309 High temperature carburization 329 High temperature steels 317 High tension separation (beneficiation) 184 Hot strength of tungsten Hot work tool steels Huebnerite 257 302 314 27 317 69 Hydrodenitrogenation 365 Hydrodesulfurization 365 Hydrogen tungsten bronzes 164 Hydrometallurgical scrap conversion 189 Hydrometallurgy 184 192 380 I Immunity in aqueous systems 124 Impregnated tungsten 246 Impurities influence on microstructure 15 influence on strength 28 Incandescent lamps 284 Indirect sintering 238 Infiltration (W-Cu, W-Ag) 276 Injection molding (hardmetals) 348 Intergrowth tungsten bronzes (pyrochlore) 165 Intermetallic phases and compounds International Tungsten Industry Association Interstitial impurities 45 135 406 15 21 Iodides of tungsten 172 173 Ion exchange 197 200 Ionic radii This page has been reformatted by Knovel to provide easier navigation 28 426 Index terms Links Ionization energy Ionization potential Iron powder 344 Isopolytungstates 121 Isotopes K Kinetics of the W-H-O system 91 L Lattice defects 14 Low temperature brittleness 20 Lubricants in grade powder milling 344 347 M Macro process Magmatic hydrothermal model Magnetic separation (beneficiation) 331 65 184 Magnetic susceptibility 36 Magnetoelectric effects 36 Magnetohydrodynamic power generation Mass absorption coefficient 293 Melting base 312 Melting metallurgy 307 Melting metallurgy scrap 381 Melting point 30 Menstruum WC 118 Mercury xenon arc lamp 286 Metal halide lamp 288 Metallic bonding Metallothermic production (Ferro-W) 311 Metal working of heavy metals 68 272 This page has been reformatted by Knovel to provide easier navigation 331 427 Index terms Links Metal working of (Continued) non-sag tungsten 262 P/M tungsten 240 W-ThO2 268 Meteorites 63 Metric ton unit (MTU) 399 Microplasticity 24 Microstructures of tungsten 16 Minerals 69 Mining districts 75 Mittersill scheelite mine 388 Mixed carbide powders 343 Mixed ligand compounds 173 Molybdenum separation 195 Monotungstates 153 Morphological changes (oxide reduction) 240 97 N Nickel powder 344 Nitrides of tungsten 143 Non-sag tungsten 259 Nuclear fusion reactions Nuclear magnetic resonance characteristics 62 O Ore deposits 68 sorting 181 Organometallic compounds 175 Oxide dispersion strengthened alloys 266 Oxides of tungsten 90 nonstoichiometric binary compounds 151 nonstoichiometric ternary compounds 160 This page has been reformatted by Knovel to provide easier navigation 371 145 428 Index terms Links Oxides of tungsten (Continued) stoichiometric ternary compounds 152 volatile oxide hydrate [WO2(OH)2] 92 WO2 150 WO2.72(W18O49) 149 WO2.9(W20O58) 149 152 WO3 146 212 Oxidation of soft scrap 190 of tungsten 85 Oxidation-reduction (heavy metal recovery) 384 Oxobromides of tungsten 171 Oxochlorides of tungsten 170 Oxofluorides of tungsten 168 Oxoiodides of tungsten 173 Oxygen adsorption on tungsten 85 Oxygen diffusion in tungsten 85 Oxygen permeation through tungsten 85 95 P Passivation of tungsten 124 Perovskite structure 161 Peroxotungstates 159 Phosphides of tungsten 144 Photoelectric emission 42 pH-sensitive tungsten electrodes 126 Physical vapor deposition 245 Plasticity 22 Plasitifier for extrusion (hardmetals) 344 Plasma spraying 244 Plutonic hydrothermal vein deposits 70 Polycondensation tungstate 120 Polytungstates 155 This page has been reformatted by Knovel to provide easier navigation 163 429 Index terms Links Porous tungsten 246 Preconcentration (beneficiation) 180 Pretreatment of ore concentrates 189 Primary tungsten sources 187 Primary tungsten supply 402 Proton absorption (P-process) 289 63 Pseudoalloys: see Tungsten copper (silver) Pyrometry 38 R Radiation shields 291 Rapid carbothermal reduction 332 Rapid neutron capture (R-process) 297 63 Reactions with acids and alkalis 46 with carbon: see carburization with ceramics 55 with elements 44 with glass melts 55 with metals 46 with metal compounds 51 with nonmetals 46 with nonmetal compounds 50 with organic compounds 56 with water and aqueous solutions 53 Recycling 86 377 Reduction mechanisms (oxide reduction) Reduction of tungsten halides 95 110 Reduction of tungsten oxides with carbon 107 doped tungsten 229 with hydrogen 88 push type furnace 221 This page has been reformatted by Knovel to provide easier navigation 215 299 430 Index terms Links Reduction of tungsten oxides (Continued) rotary furnace 223 Reduction sequence (oxide reduction) 93 Reserves of tungsten 76 ROMP catalysts 371 S Scavenging circuit (beneficiation) Scheelite 181 70 Secondary tungsten sources 189 Selenides of tungsten 167 Self diffusion 32 Semidirect recycling 384 Shaping of tungsten 242 Share in minable tungsten deposits 396 Short ton unit (STU) 399 Silica precipitation 195 Silicides of tungsten 143 Single crystal preparation 246 Sintering activated sintering 235 direct 235 of doped tungsten 235 of hardmetals 348 of heavy metals 271 indirect 238 stages 234 of tungsten 233 of tungsten copper (silver) alloys 277 Slip, slip systems 15 Slow neutron capture (S-process) 63 Sodium tungstate 153 Sodium tungsten bronzes 162 This page has been reformatted by Knovel to provide easier navigation 24 431 Index terms Solar system formation Links 63 Solid-solution alloys: see Substitutional alloys Solvent extraction 197 Solvents in grade powder milling 344 Spectral emissivity 36 Spray conversion of WC 335 Sputtering 245 Standard potentials 124 Steels: see Tungsten alloyed steels Stellites 318 Stress-strain curves of tungsten 25 Strength 22 theoretical 27 of wires 27 of whiskers 27 Structural energy Structural properties 11 Substitutional alloys 256 Subvolcanic vein deposits 70 Sulfides of tungsten 165 Superalloys 317 Superconductivity Supply and demand 319 35 401 Surface diffusion 15 Surface tension 15 T Telluride of tungsten 167 Tempering of tungsten steels 313 Tetragonal tungsten bronzes 163 Texture 17 Thermal conductivity 33 coefficient 34 This page has been reformatted by Knovel to provide easier navigation 316 21 432 Index terms Links Thermal diffusivity 33 Thermal expansion 31 coefficient 31 Thermionic emission 40 Thermocouple electromotive forces 37 Thermocouples 36 293 Thermodynamic functions atom bulk 31 Thermodynamics of W-H-O system 89 Thermoelectric effect 36 Thoriated tungsten 40 Total energy 374 Tungsten alloyed steels 312 Tungsten blue oxide 212 Tungsten bronzes 160 Tungsten carbide: see Carbides of tungsten 334 Tungsten heating elements 288 Tungstate catalysts Tungsten consumption by end use 266 82 291 Tungsten heavy metal alloys: see Heavy metals Tungsten hexacarbonyl 142 Tungsten losses 378 Tungsten metal powder production conditions 215 Tungsten metal powder properties 218 Tungsten ore reserves 76 Tungsten oxide hydrate (volatile) WO2(OH)2 91 225 Tungsten oxides: see Oxides of tungsten Tungsten oxygen system 145 Tungsten price 397 399 22 243 Tungsten rhenium 269 Tungsten scrap materials 372 This page has been reformatted by Knovel to provide easier navigation 256 433 Index terms Links Tungsten steels: see Tungsten alloyed steels Tungsten thin films 290 Tungsten tree 81 Tungsten world production (1910-1996) 81 Tungstic acids Twinning 152 214 15 V Vapor pressure 30 Volcanogenic-sedimentary deposits 73 W W contacts 286 W-Ag contacts 287 W-Cu contacts 287 WC catalysts 370 properties 140 WC-Ag contacts 287 WC-TiC 344 WC-TiC-Ta(Nb)C 344 W2C catalysts 370 properties 139 W3O: see Beta-tungsten Welding 243 Wire drawing 262 Whole flotation 180 Wolframite minerals 69 Work function 39 World mine production 396 Wrought P/M tungsten 240 This page has been reformatted by Knovel to provide easier navigation 266 286 434 Index terms Links X X-ray absorption spectrum X-ray diffraction diagrams (α-W, β-W) X-ray emission spectrum 12 X-ray tubes 297 Xe-arc lamps 286 Z Zinc process 382 Zirconium tungstate 155 This page has been reformatted by Knovel to provide easier navigation ... 4.2.11 Tungsten and Fluorine 167 4.2.12 Tungsten and Chlorine 169 4.2.13 Tungsten and Bromine 171 4.2.14 Tungsten and Iodine 172 Mixed Ligand and Coordination Compounds of Tungsten. .. 129 3.6 Tungsten Compounds and Their Application 133 4.1 4.2 Tungsten and Metals: Intermetallic Compounds and Phases 135 Tungsten and Nonmetals 138 4.2.1 Tungsten and Boron... papers only facilitated the decision Moreover, as authors of "Tungsten, Tungsten Alloys, and Tungsten Compounds" in the latest edition of Ullmann s Encyclopedia of Industrial Chemistry, we have also