VOL.'3 DECEMBER 1938 Philips Technica.1 ·Rev.iew, DEALING WITH TECHl\'lCAL PROBLEMS RELATING. TO THE PRODUCTS,. PROCESSES ~D INVESTIGATIONS OF N.V...PHILIPS' GLOEILAMPENFABRIEKEN EDITED BY THE RESEARCH LABORATORY OF N.V. PHILIPS' GLOEll.AMPENFABRIEKEN, EINDHOVEN, HOLLAND ZIRCONIUM' AND ITS COMPOUNDSWITH A HIGH ·MELTING POINT by J. D. F~ST. In this article the preparation of zirconium and its mechanical, chemical and electrical properties are dealt with. The most important applications ofzirconium and its compounds with high. melting points are then discussed. Zirconium is often used in discharge tubes where its high melting point, small value of secondary emission and, when use'das f1 getter, its property pf being able to take up large quantities of oxygen, nitrogen and' hydrogen are of significance. Zirconium oxide and zirconium' carbide are 'important as refractory materials. Introduction . ; Even since the beginning of the development of tungsten as filament in incandescent lamps, and the the manufacture of electric incandescent lamps, use of this element in the place of all the other much research has been carried out on metals with substances which were used for that purpose. high melting points in the laboratories of such fac- Several others of the metals mentioned, such' as ,tories. The metals in the following groups of the Zirconium, tantalum and molybdenum, have also periodic system drew particular attention: found uses, although less important ones. 1) The platinum group: platinum, iridium and The aim of this article is to make several state- osmium, the last of which was used for some ments about the properties and. ~.applications. of time as filament in the sources of electric light. the element. zirconium an? severa_l~ts comi)Qun~s. 2) The fourth main group: titanium, zirconium, We shall discuss, successively the metal, the oxide hafnium and thorium. (Zr02) and the carbide (ZrC). 3) The fifth main: group: vanadium, niobium and The metal in the pure state is used chiefly in tantalum, the last of, which was used for some transmitting valves and other discharge tubes, time in so-called tantalum lamps. where use is made of its great chemical affinity 4), The sixth main group: chromium, molybdenum for various other elements such as oxygen, nitrogen, and tungsten. carbon and hydrogen. The oxide is chiefly used as a At the beginning óf the development of the elec- refractory and as an opacifier for glazes and tric incandescent lamp industry (around 1880) prac- enamels. The carbide is stilllittle used, but it shares tically nothing was known about the mechanical and the interest which has existed during the last ten or physical properties of the last th~ee groups men- fifteen years for the metallic car"bides with a very tioned, and very little about their chemical prop- high melting point and very great hardness. erties. The interest of this industry, however, contributed very much to the research which has Brittle and ductile zirconium led to the fairly extensive knowledge of these Twenty-four years ago the first scientific pub- metals which we now possess. This interest was at lication from the Philips Laboratory appeared 1). first chiefly directed toward the melting point It contained statements about the preparation of and the speed of evaporation, but when the electric metallic thorium, uranium, zirconium and titanium. lamp industry also began to manufacture X-ray Zirconium was prepared by reduction of zirconium tubes, transmitting and receiving valves for radio tetrachloride (ZrCla) with sodium. The metal was purposes, rectifier valves etc.v-It began to include 1) D. Lely and L. Hamburger, Herstellung der Elemente all the properties of the metals under consideration. Thorium, Uran, Zirkon und Titan, Z. anorg. allg, Chem. 87, The technical result was the present general use of . 209, 1914. -,.~,. fi PHILIPS TECHNICAL REVIEW Vol. 3, No. 12 s, ( i obtained in the form of a powder and the size detrimental influence on the mechanical properties j , of the grain depended upon the reduction tem- of metals, so that very small amounts are already perature, the nature of the chloride, etc. Later enough to make the metal brittle. Titanium which I the ~ethod was improved upon by previously can also contain considerable quantities of oxygen subliming the chloride in hydrogen and thus and nitrogen in solid solution, exhibits the same obtaining it in large compact pieces. If this sub- phenomena as zirconium. Thorium, however, which limed chloride is used, and if it is reduced in belongs to the same group of the periodic system as large porti~ns at a fairly high temperature, the titanium and zirconium, is found to have no ap- nietal is obtained in, the form of chunks with di- preciable dissolving power for oxygen and nitrogen. mensions of several, centimetres, which are, how- The result is that this last metal does not exhibit ever, porous. This method of preparation pro- the phenomenon mentioned': thorium rods can also duces metal of great purity and is still one of the be obtain~d in the ductile state by compression best methods of preparing zirconium in the form and sintering of the powder. of a powder or of porous chunks. The best We must assume that grains of metal obtained samples we1;~ fo~nd upon analysis to have a by the reduction of the chlorides of the three metals purity of 100 per cent. The separate grains showed in question are covered with a film of oxideand (or) a certain ,ductility (mechanical deformability). It nitride. In the sintering of rods pressed from the was, however, very remarkable that when a rod was powders, the oxygen and nitrogen dissolve in the pressed from the pure metal powder, according to metal in the, case of zirconium and titanium, and the method used in working tungsten, and when the metal thus becomes brittle, while in the case this rod was sintered at a high temperature in a of thorium,' the oxide and nitride remain present as very high vacuum, '1;he, rod showed practically such in the rod. It is true that in the sintering of .~.. no sign of ductility. Working to sheet or wire by pressed thor~um rods a change in the structure also rolling, hammering and drawing was' therefore app,ears, but this change in the structure has a .impossible. Since however chemical analysis indi- favourable influence on the mechanical properties . cated a very highdegreeof purity, as was mentioned It consists namely in the fact that the oxide or above, it was for many years generally assumed nitride is collected into separate grains, which are, that zirconium is a very brittle metal and must be then ,present after sintering surrounded by a considered to belong to the so-called half-metals. coherent basic mass of ductile metal. This makes However, thirteen years ago an entirely new it understandable that much greater quantities of method of preparing zirconium in the form of oxygen and nitrogen are required to render thorium rods was discovered in this lahoratory 2), namely brittle than in the case of zirconium and titanium. by thermal decomposition of zirconium tetraiodide The grains of zirconium and titanium obtained on a glowing filainent (see below) and the rods as by reduction usually contain small traces of oxygen ! and nitrogen already dissolved, so that each in- I prepared were fouhd to possess a high degree of I ductility. The d~f~r~~bility is' so great that it dividual grain has a ductility considerably lower is now even possible', to cold-work rods of 7 mm than that of the absolutely pure metals, but con- \ i thickness to very thin .wire and sheet. The crystal siderahly higher than that of the pressed and sin- i structure of duétil~ zirconium was found to be the tered rods. ! same as that of brittle Zirconium, so that it was j' 'I not a question of, two allotropie modifications. Preparation of ductile zirconium in rod form It has therefore' 1;0 be assumed that the brittle Ductile zirconium is prepared by thermal deeoni- zirconium contained one or more impurities of position of zirconium tetraiodide. At a temperature of which chemical analysis gave no indication. 431°C the vapour pressure of this compound reaches Only in recents years has it become possible to a value o~ one atmosphere. If the gaseous iodide arrive at a, reasorîably satisfactory explanation comes into contact with a surface whose temperature of this phenomenon. .I't has been found that zir- is higher than 1l00°C, it decomposes partially into conium is able to ,tàke' up quantities of oxygen zirconium and iodine. When the process is carried and nitrogen in solid solution. When these elements out in practice the decomposition takes 'place are present in the dissólved state they have a very on a thin wire which is heated by the passage' of current to a, suitable temperature, for instance I ,2) J. H. de Boer und J. D. Fast, Über die Darstellung der 1300°C. Tlie reaction takes place in an apparatus reinen Metalle der Titangruppe durch thermische Zerset- I" zung ihrer Jodidè, I. Zirkonium, Z. anorg. allg, Chem. 153, made of pyrex' glass into which thick tungsten I' 1, 1926. terminals are fused. The required amount of crude I: - '_ '.,~ ',." . DECEMBER 1938 ZIRÇONIUM . 347 zirconium is introduced into this apparatus in the For practical uses zirconium is made in rods form of porous chunks (obtained by the reduction about 7 mm thick which weigh about 200 gr. of zirconium tetrachloride or of sodium zirconium The oven .temperature is kept at 250° to 350°C fluoride with sodium) together with a relatively, during the preparation. A tungsten wire 40 microns small amount of iodine.