Hume-Rothery, William

(b . Worcester Park, Surrey, England, 15 May 1899; d. Iffley, Oxfordshire, England, 27 September 1968)

metallurgy, chemistry.

Hume-Rothery was the son of Joseph Hume Hume-Rothery, a lawyer, and Ellen Maria Carter. Most of his childhood was spent in Cheltenham, and while he was a schoolboy attending Cheltenham College (1912–1916) he decided on a military career. Early in 1917, a few months after he had entered the Royal Military Academy, Woolwich, he suffered an attack of cerebrospinal meningitis which left him totally deaf. He was therefore discharged from the army and subsequently entered Magdalen College, Oxford, where (following the influence of his Cheltenham science master, George Ward Hedley) he read chemistry, receiving a first-class honors degree in 1922.

Graduate work at the Royal School of Mines (under Sir Harold Carpenter) at London University turned his interest to metallurgy and led to a highly original paper on intermetallic compounds, published in 1926, the year in which he received his London Ph.D. degree. Returning to Magdalen in December 1925, he stated that he proposed “to carry on research at Oxford in intermetallic compounds and problems on the borderland of metallography and chemistry.” Chemical research and the city of Oxford formed the center of his activities for the remainder of his life, although the “chemistry” in time became closer to physics.

On 28 March 1931 he married Elizabeth Alice Fea, with whose understanding help he overcame many difficulties associated with his deafness. He learned to modulate his voice, which he of course could not hear, and became an excellent lecturer. Students often served as his “ears” at large conferences, but in individual conversation his skill in lip reading, aided on occasion by his visitor’s use of a pad and pencil, made his handicap almost unnoticeable. His great zest for life, combined with his ready, often puckish, sense of humor, made it easy and pleasant to exchange ideas with him on both casual and complex topics.

Hume-Rothery was an ardent fly-fisherman and an accomplished watercolorist. In the closing years of his life he began to cultivate exotic cacti, and did so with the same engrossing enthusiasm with which he took rugged country walks to seek subjects for his brush.

His work at Oxford University was supported by external research grants. Although he had many students, either undergraduate or in research, he did not have an official university appointment until 1938, when he became lecturer in metallurgical chemistry. In 1957, under pressure from the metallurgical profession, the School of Metallurgy was established at Oxford with Hume-Rothery as the first professor.

Hume-Rothery’s scientific contributions are related to the principles underlying the crystal structures of alloy phases. In 1925, although the existence of various types of intermetallic phases had been shown (see summaries by Desch¹ and Giua²), no theory accounted for their formation. Many phases extended over a wide range of compositions (and hence were unpalatable to chemists who, a century after Dalton believed in simple molecules), while many welldefined combinations ignored the normal rules of valency; however, the new determination of atomic arrangement in crystals by X-ray diffraction, as well as the new views of the nature of the atom and electron, had prepared the ground for a new approach.

Hume-Rothery, in 1924, saw that electrically conducting compounds must have “loose” electrons and therefore could not conform to valency rules; in his 1926 paper he pointed out—almost as an aside, sandwiched between an experimental report on the constitution of certain alloys of tin and an animadversion against the misuse of the phase rule—that body centered-cubic β solid solutions of copper with B subgroup elements occur only when the ratio of valence electrons to atoms was in the neighborhood of 3:2; for example, CuZn, Cu₃Al, Cu₅Sn. With this first glimpse of a new field, the phrase “electron compounds” became current. The concept was soon extended by A. J. Bradley to the complex-cubic γ phases at a ratio 21:13 and by Arne Westgren to the close-packed hexagonal phases at 7:4, and thereafter to many others.

In 1934, in his most influential single paper, written with two students, Hume-Rothery pointed out that the melting points and solid solution ranges of alloys of copper or silver with many different elements became nearly identical when considered as a function of the added valence electrons (that is, atomic fraction of the solute multiplied by its valence). Moreover, making use of V. M. Goldschmidt’s analysis of the structures of the elements, he showed, for the first time, the significance of the atomic size factor: Solid solutions did not form between pairs of elements whose atomic radii differed by more than 15 percent. Finally, Hume-Rothery observed that the size-related group of compounds identified by F. H. Laves (1933) or the saltlike intermetallic compounds identified by E. Zintl (1931) appeared only when the constituent elements differed greatly in electronegativity. In succeeding decades, he studied in electronic and size factors in many alloy systems, notably those of the noble metals and the transition metals.

Hume-Rothery’s three rules of alloy formation related immediately to theoretical work on the electron theory of metals,³ and in particular they supported the idea of interaction between Brillouin zones and expanding spherical Fermi surfaces. Jones’s calculation⁴ of electron momenta at various electron concentrations in body-centered-cubic and face centered-cubic alloys seemed to give the fundamental reason behind the observed electron to atom ratios in the α and β phases. Further refinement of the theory, however, has led to continually increasing complications, so that Hume-Rothery’s original rules are still (1972) more useful as a guide to alloying behavior than is any basic mathematical theory.

Hume-Rothery was a fine experimentalist, especially noted for his accurate pyrometry on reactive materials at high temperature. Although he preferred the microscope for studying the constitution of alloys, he developed refined X-ray methods and did much to improve their interpretation.

Hume-Rothery’s influence on metallurgical education was worldwide. Although his own original contributions were based on extensive knowledge of facts and an intuitive insight into their meaning, he was also an excellent interpreter of advanced work in mathematical physics. All but the first of his books were directed at undergraduate and industrial metallurgists and were expertly simplified texts, making clear to nonphysicists the new science that metallurgy was about to become. His book The Structure of Metals and Alloys (first published in 1936) was particularly important, and he took pride in keeping each new edition completely up to date, with the aid of collaborators in the fourth and fifth editions.

A historical essay by Hume-Rothery (1965) is revealing both of the state of the field and of his personal approach to science. Objecting to the contemporary tendency to restrict the term theory to work of a mathematical nature, he remarked that “Mendeleev’s Periodic Table as a theory of chemistry... is more accurate than, and certainly no less fundamental than a mathematical theory of alkali metals such as that of Wigner and Seitz.” He concluded

... the electron theory of alloys is in an unsatisfactory state.... Practically nothing has been predicted by à priori calculation methods in advance of the facts, whilst the simple theories which seemed so satisfactory 20 years ago are now in great doubt. On the other hand, there is a considerable theory or generalization of facts in the form of empirical rules or principles and these have permitted some predictions to be made. The theory of alloys is thus at the stage of Kepler and not of Newton (“The Development of the Theory of Alloys,” p. 346).

The empirical rules were nearly all the result of Hume-Rothery’s work.

NOTES

1. C. H. Desch, Intermetallic Compounds (London, 1914).

2. M. Giua and C. Giua-Lollini, Chemical Combination Among Metals (London, 1918).

3. N. F. Mott and H. Jones, The Theory of the Properties of Metals and Alloys (Oxford, 1936).

4. H. Jones, “The Phase Boundaries in Binary Alloys, II. The Theory of the α, β Phase Boundaries,” in Proceedings of the Physical Society, 49 (1937), 250–257.

BIBLIOGRAPHY

A full bibliography of Hume-Rothery’s 178 papers is given in G. V. Raynor, “William Hume-Rothery, 1899–1968,” in Biographical Memoirs of Fellows of the RoyalSociety, 15 (1969), 109–139). Only the most influential are listed below:

“Researches on the Nature, Properties, and Conditions of Formation of Intermetallic Compounds....” in Journal of the Institute of Metals, 35 (1926), 295–361; “The Electronic Energy Levels of the Elements, With Special Reference to Their Connexion With the Sizes and Electronic States of Atoms in Metallic Crystals,” in Philosophical Magazine, 11 (1931), 649–678; “The Freezing Points, Melting Points, and Solid Solubility Limits of the Alloys of Silver and Copper with Elements of the B Sub-Groups,” in Philosophical Transactions of the Royal Society, 233 (1934), 1–97, written with G. W. Mabbott and K. M Solid Solutions is Silver and Copper,” in Proceedings of the Royal Society, 157A (1936), 167–183, written with G. F. Lewin and P. W. Reynolds; “Atomic and Ionic Radii, II. Application to the Theory of Solid Solubility in Allyos.,” in Philosophical Magazine, 26 (1938), 143–165, written with G. V. Raynor; “The Application of X-Ray methods to the Determination of Phase-Boundaries in Metallurgical Equilibrium Diagrams,” in Journal of Scientific Instruments, 18 (1941), 74–81, written with G. V. Raynor; “Electrons, Atoms, Metals and Alloys,” in Transactions of the American Institute of Mining Engineer, 171 (1947), 47–62; “Applications of X-ray Diffraction to Metallurgical Science,” in P. Ewald, ed., Fifty Years of X-ray Diffraction (Utrecht, 1962), pp.190–211; “The Development of the Theory of Alloys,” in C. S. Smith, ed., The Sorby Centennial Symposium on the History of Metallurgy (New York, 1965), pp. 331–346.

His books include: The Metallic State (Oxford, 1931); The Structure of Metals and Alloys (London, 1936; 2nd ed. 1944; 3rd ed. 1954; 4th ed. [with G. V. Raynor], 1962; 5th ed. [with R. E. Smallman and C. W. Haworth], 1969); Atomic Thory For Students of Metallurgy (London, 1946; 2nd ed., 1952; 3rd ed., 1960; 4th ed., 1962); Electrons, Atoms, Metals and Alloys (London, 1948; 2nd ed., 1955; 3rd ed., New York, 1963); Metallurgical Equailibrium Diagrams (London, 1952), written with J. W. Christian and W. B. Pearson; Elements of Strutural Metallury (London, 1961); The Structures of Alloys of Iron: An Elementary Introduction (London, 1966).

Good accounts of the present state of understanding in the field opened by Hume-Rothery are T. B. Massalski, “Structure of Solid Solutions,” ch. 4 in Robert W Chan, ed., Physical Metallurgy, 2nd ed., rev. (Amsterda, 1970); and G. V. Raynor, “Hume-Rothery and the Development of the Science of Alloy Formation,” in Journal of the Institute of Metals, 98 (1970), 321–329.

Cyril Stanley Smith