Encyclopædia Britannica, Ninth Edition/Titanium
TITANIUM (atomic weight[1] = 48 08, O = 16), designates in chemistry a relatively rare element, which is customarily classed with the metals, although it comes nearer in its character to silicon than to any of the ordinary metals. Its discovery as an element was due to William Gregor, who found in the mineral menaccanite a new earth, which was regarded as the oxide of a new metal, menachin. Independently of him Klaproth in 1793 discovered a new metal in rutile and called it titanium; he subsequently found that it was identical with Gregor's element. The latter name was, however, retained. Titanium, although pretty widely diffused throughout the mineral kingdom, is not found in abundance. The commonest titanium mineral is rutile (TiO2); anatase and brookite, though mineralogically different from rutile and each other, are forms of the same binoxide.
Metallic titanium is little known. In 1822 "Wollaston examined a, specimen of those beautiful copper-like crystals which are occa sionally met with in iron-furnace slags, and declared them to be metallic titanium. This view had currency until 1849, when Wohler showed that the crystals area compound, Ti(NC) 2 + 3Ti 3 N 2, of a cyanide and a nitride of the metal. Real titanium was made by Wohler and Deville in 1857 by heating to redness fluo-titanate of potassium (see below) in vapour of sodium in an atmosphere of dry hydrogen, and extracting the alkaline fluoride formed by water. The metal thus produced had the appearance of iron as obtained by the reduction of its oxide in hydrogen. When heated in air, it burns brilliantly, with the formation of binoxide. Its most curious property is the readiness with which it unites with nitrogen gas into a nitride. The exact composition of this nitride is not known; but when heated in hydrogen it loses part of its nitrogen as am monia, and becomes Ti 5 N 6, a metallic-looking yellow solid, and this when heated in nitrogen gas passes into higher nitrides, which are again available for the production of ammonia. Tessie du Mothay in 1872 proposed to utilize these reactions for the production of ammonia from atmospheric nitrogen. Of other titanium compounds the most important are those formed on the type of TiX 4, when X = Cl,Br, or 0, &c.
The binoxide TiOz exists as rutile. One method of preparing a } urer oxide from the mineral is to fuse it, very finely powdered, with six times its weight of bisulphate of potash in platinum, then extract the fuse with cold water, and boil the filtered solution for a long time. Titanic oxide separates out as a white hydrate, which, however, is generally contaminated with ferric hydrate and often with oxide of tin, Sn0 2 . A better method is Wohler's. He fuses the finely powdered mineral with twice its weight of carbonate of potash in a platinum crucible, pounds the fuse, and treats it in a platinum basin with aqueous hydrofluoric acid. The alkaline titanate first produced is converted into crystalline fluo-titanate, TiF 6 K 2, which is with difficulty soluble, and is extracted with hot water and filtered off. The filtrate, which may be collected in glass vessels if an excess of hydrofluoric acid lias been avoided, deposits the greater part of the salt on cooling. The crystals are collected, washed, pressed, and recrystallized, whereby the impurities are easily removed. The pure salt is dissolved in hot water and decomposed with ammonia to produce a slightly ammoniacal hydrated oxide; this, when ignited in platinum, leaves pure T10 2 in the form of brownish lumps, the specific gravity of which varies from 3 9 to 4 "25, according to the temperature at which it was kept in igniting. The more intense the heat the denser the product. The oxide is fusible only in the oxy-hydrogen flame. It is insoluble in all acids, except in hot concentrated sulphuric, when finely powdered. Sup posing the excess of vitriol to have been boiled away, the residue, after cooling, dissolves in cold water. The solution, if boiled, de posits its titanic oxide as a hydrate called meta-titanic acid, be cause it differs in its properties from ortho-titanic acid, obtained by decomposing a solution of the chloride in cold water with alka lies. The ortho-body dissolves in cold dilute acids; themeta-body does not. If titanic oxide is fused with excess of alkaline carbonate it expels C0 2 parts of carbonic acid for T10 2 parts of itself. The salt R.pT10 2 is decomposed by water with the formation of a solu tion of alkali free of titanium, and a residue of an acid titanate, which is insoluble in water but soluble in cold aqueous mineral acids.
The chloride TiCl4 is obtained as a distillate by heating to dull redness an intimate dry mixture of the binoxide and ignited lamp black in dry chlorine. The reaction may be carried out in a hard glass tube. For methods of purification we refer to the handbooks of chemistry. The pure chloride is a colourless liquid of 1 7604 specific gravity at 0., boiling at 136 4 under 753 3 mm. pressure (T. E. Thorpe). It fumes strongly in moist air. When dropped very cautiously into cold water it dissolves into a clear solution, which, however, when boiled, deposits most of its oxide in the meta- hydrate form. There are, at least, two lower chlorides of titanium, one of the composition Ti 2 Cl 6 and another of the com position TiCla, both solids and both extremely prone to pass into titanic compounds. A solution of the tetrachloride in water, as well as of the soluble hydroxide in dilute acid generally, when kept in contact with metallic zinc, is reduced to one of the lower chlorides with development of a violet colour. With regard to the detection of titanium we need not add much to what we have already given incidentally. Acid solutions of T10 2 are not precipitated by sulphuretted hydrogen; but sulphide of ammonium acts on them as if it were ammonia, the H 2 S being liberated. Oxide of titanium when fused with microcosmic salt (i.e., NaP03) in the oxidizing flame yields a bead which is yellowish in the heat but colourless after cooling. In the reducing flame the bead becomes violet, more readily on the addition of tin; in the presence of iron it becomes blood-red. Titanic oxides when fused on charcoal, even with cyanide of potassium, yield no metal.
- ↑ According to T. E. Thorpe's researches, published in 1883.