University of Plymouth PEARL https://pearl.plymouth.ac.uk 04 University of Plymouth Research Theses 01 Research Theses Main Collection 1970 The Formation and Reactivity of BORON CARBIDE and related materials JONES, JAMES ALFRED http://hdl.handle.net/10026.1/1880 University of Plymouth All content in PEARL is protected by copyright law. Author manuscripts are made available in accordance with publisher policies. Please cite only the published version using the details provided on the item record or document. In the absence of an open licence (e.g. Creative Commons), permissions for further reuse of content should be sought from the publisher or author. The Formation and Reactivity of I BORON CARBIDE and related materials A Thesis presented for the Research Degree of DOCTOR OF PHILOSOPHY of the COUNCIL FOR NATIONAL ACADEMIC AWARDS London by JAMES ALFRED JONES Department of Chemistry Plymouth Polytechnic Plymouth, Devon- February^ 1970o F'.V flCCH. i'iC. 1 CLASS, T Shi LJl JoH 13' ABSTRACT 1 The formation of boron carbide, (CBC)*B^^0*^(3^0 is re• viewed with special reference to newer production methods and fabrication techniques. Its crystal structure and the nature of its bonding are discussed in relation to those of other borides and carbides. Information so far available on the sintering of this material is summarised in relation to its reactivity. Sintering into monolithic compoaentBcan only be achieved by hot pressing at pressures between 200 and 300 Kgcm'^ and at temperatures above 2000°C preferably at about 2,300^0 for the most rapid achievement of theoretical density, i.e. pore free. High purity, stoichiometric boron carbide produced by the magnesium thermal reduction of boric oxide in the presence of carbon, and of submicron average particle size, has been oxidised by heating in air. The work indicates that there is preferential oxidation of boron at temperatures below SOO^C; any oxidation of the resultant carbon is inhibited by the product ^2^^ phase. The measured acti• vation energy of 23*9 Kcals per mol supports this view. Formation of mixed systems of titanitim borides are described, including both orthorhomic and cubic monoboride together with the hexagonal diboride. These are formed when titanium alloys (alpha, beta, and mixed alpha and beta) are coated with boron carbide and heated to l400^C under vacuum or inert atmosphere. (ii) ACKNOWLEDGMENTS The author wishes to express his sincere thanks to Dr« O.K. Glasson for his supervision and guidance throughout the course of this work. He is grateful to Mre Lo Bullock, Managing Director, Bullock Diamond Products Ltd., Torpoint, Cornwall, and to Dr. A.B. Meggy, Head of the Chemistry Department, Plymouth Poly• technic, for the use of facilities and the supply of materials* His thanks are also due to Noel Pearman, Andrew Johnson and Margaret Sheppard for their technical assistance and to Miss Loraine Ash who typed the manuscript. He is indebted to his wife, Dorothy, for her constant help and encouragement. -V- CONTENTS SECTION Page(s) 1o Introductory Survey and Review o» o» o o 1-77 lele General discourse oo oo o. oo o« 1 1o2» The classification of borides, carbides and related materials oo oo oo oo oo ^ 1o3o The structural properties of the boron carbides and related materials oo oo oo 8 lo^o The crystallo-chemical structure of the boron carbides oo oo oo oo oo oo 13 1o5o Boron-carbon system in detail oo oo oo 22 1o6(a}« Compounds of general boron carbide structure type oo oo oo oo oo oo 29 1o6ol(a) Boron-oxygen system oo oo oo oo oo 31 1o6o2(a) Boron-silicon system oo oo oo oo oo 31 1o6o3(a) Boron-carbon-silicon oo oo oo oo oo 33 1o6o^(a) Boron-carbon-nitrogen oo oo oo oo oo 3^ .1o6(b) Compoxmds of boron with other non- metals having low boron content oo oo oo 3^ 1o6ol(b) Boron-oxygen system oo oo oo oo oo 3^ 1o6o2(b) Boron-nitrogen system oo oo oo oo oo 3^a 1o7o Systems of boron with metals oo oo oo 33 1o7(a) Lower borides oo oo oo oo oo oo 33 1o7(b) Higher borides oo oo oo oo oo oo 38 1o7ol(b) Boron-aluminium system oo oo oo oo 38 1o7o2(b) Boron-al\iminium-carbon system oo oo oo 39 1o8. Chemical thermodynamics and kinetics of the production <f boron carbide and related materials oo oo oo oo oo ^0 (iv) SECTION Page(e) 1o9<. The sintering of boron carbide and other refractory materials oo oo oo 55 lolOo The chemical reactivity of boron carbide and related compounds oo oo oo 72 Idlo The applications of boron carbide and related refractories oo oo oo oo 76 2, Experimental techniques for the production and analysis of boron carbide oo o© o© oo oo ©o ©o 7^ ^ 98 2o1o The production of boron ceurbide ©© ©o o© 78 2©2(a) The chemical analysis of boron carbide and related compounds ©© ©© ©o ©o o© 79 2©2(b) X-ray diffraction identification of phases ©© ©© ©© ©o ©© ©© ©© ©© 82 2©2(c) Electron microscopy and diffraction «© ©© 86 2o2(d) Surface area measurement by gas sorption ©© 90 2o2(e) Thermometric analysis ©© ©© ©© ©© ©© 95 3o Experimental results obtained on the prepared boron carbide etnd on related materials ©© ©© ©© ©© ©© ©© o© 99-117 3o1o The analysis of the prepared boron carbide 99 3©1(a) The chemical emalysis of B^C o© ©o o© 99 3©1(b) Phase identification of B^C by X-ray diffraction ©o ©o ©© ©© ©© ©© o© 100 3©l(c) Particle size analysis by X-ray line broadening, by BoEoT* surface sorption . ^ and by electron microscopy ©© ©© ©© o« 103 3o2o The vacuum sintering of boron carbide©* ©© 112 3o3o The hot pressing of the prepared B^C ©© ©o 113 3o^© The ball-milling of the prepared B^C «© ©© 116 (v) SECTION Page(s) 4o The oxidation of bo^o;! carbide oo oo oo 1l8 ~ 127 4o1o General discussion oo oo oo .o. oo 118 ko2. Thermometric and particle size results oo 120 5o The formation of titanium boride oo oo 128 - l40 5e1o General discussion on titcmium and its alloys oo oo oo oo oo oo oe 128 5o2o The titanixun-boron system in detail .o oo 130 5o3o Experimental technique for the production of titanium boride oo oo oo oo oo 132 5o4o Identification of titanium-boron phases oo 133 5o5o Discussion of results oo o« oo oo 138 5o6. Formation of a hard surface on titanium alloys oe oo oo oo oo oo oo oo 139 6. Concluding summary oo oo oo oo oo 1^1 - 1^6 6e1o Preparation of boron carbide oo oo oo 1^1 6o2. Sintering of boron carbide oo oo o© 1^1 6o3o The oxidation of boron carbide in air oo l43 6o^o Formation of titanium boride coatings oo 1^3 6o3o Phenomologlcal theory of boron carbide formation oo ©o oo oo oo oo oo 1^^ 6o6o Proposed further work oo oo oo oo oo 1^5 REFERENCES oo oo oo oo oo oo oo oo oo viii - xvi APPENDICES oo oo oo oo oo oo oo oo oo XVii - XX (vi) SECTION 1, INTRODUCTORY SURVEY AND REVIEW I•I. General discourse. In spite of early historical applications, long history of investigation and use, boron and its compounds have not been extensively investigated until recent years. Studies of their inorganic chemistry and metallurgical science have been limited by the relatively low concentration of the element in the earth's crust, the specifity of its raw material sources. Also there are difficulties in conducting the appropriate investigations due to the unique character of boron which occupies an intermediate position between the metals and nonmetals in the Periodic classi• fication. Boron, Latin name borax, is already mentioned in the ancient works on chemistry, and metallurgy dating from 800 A.D. in connection with its use as a flux. In 1702, Ve Goldberg described the production of an acid from borax (sodium tetraborate) but believed this acid to be a salt. In 17^8, F. Baron proved that borax is a salt of boric acid. In 1777, this boric acid was dis• covered by G. Hoeffer in one of the lakes of Tuscany. The high affinity of boron for numerous elements, especially for oxygen, made It impossible to isolate pure boron and its alloys. Ultimately, elementary boron was obtained, independently in l8o8, by Sir Humphry Davy and by the French chemists Gay-Lussac and Thenard. By far the most important investigations of boron and its compounds were by Henri Molssan. In l892, Moissan developed a method for producing boron by reducing boric anhydride with mag• nesium, a method which is still in use at the present time. In l899f he obtained a compound of boron with carbon, vizo, boron carbide, and subsequently the borides of chromium, titanium and tungsten and those of silicon and boron steels. In 1909f Moissan's research was continued by V/eintraub who discovered the semiconductor properties of boron, and by Wedekind and Kroll who produced all the refractory borides known at present. A number of works on boron and borides were conducted in the I930's and 19^0*s by Becker, Agte, Moers and Andriexix. These investigations developed the production of boron and borides by deposition from the dissociated gaseons halides and by the elec• trolysis of fused mediso However, the basic research on boron and borides has been stimulated over the past two decades, by the interest in heat resistant alloys containing boron and refractory boridee^ fundamental work has been done by Kiessling (Switzerland) Kieffer, Benesovsky, Hovak, Nowotny (Austria), Glaser, Schwarzkopf, Binder, Bliunenthal, Moskowitz, Post, Brewer (United States), and Samsonov, Neshpor, Umanskll, (U.S.S.R.).