Physical Properties of Titanium

The impure titanium prepared by Berzelius and Wohler was a grey powder; the almost pure metal obtained in fused masses by Moissan's method is brittle, breaking with a white fracture, and sufficiently friable to be powdered in an agate mortar. It is nevertheless hard enough to scratch quartz and steel. Crystalline titanium is isomorphous with zirconium and silicon; Moissan's metal has a density of 4.87. The specific heat of titanium is variable, and the atomic heat of the impure metal examined by Nilson and Pettersson exceeded 6.4 at high temperatures, as the following figures show:

Temperature Interval.	Specific Heat.	Atomic Heat.
0 to 100	0.1125	5.40
0 to 211	0.1288	6.18
0 to 301.5	0.1485	7.13
0 to 440	0.1620	7.77

The melting-point of titanium is given as 1795° C. The spark spectra obtainable from solutions of titanium compounds have been studied by Pollok; and the long-waved portion of the spectrum has been mapped by Fiebig.

The most intense lines in the spectrum of titanium are as follow:

Arc: 3948.87, 3989.94, 3998.80, 4306.09, 4533.40, 4536.16, 4981.93, 4991.24, 4999.68, 5007.35, 5014.39, 5193.12, 5210.59.

Spark: 2516.10, 3361.40,* 3372.92,* 3383.87, 3505.10, 3510.99, 3685.37,* 3759.46,* 3900.81, 3913.72, 4163.90, 4395.20, 4549.90, 4572.27.

The four lines asterisked, together with 3761.5 and 3349.2, constitute the most persistent, i.e. the ultimate spark lines of titanium.

Chemical Properties. - Titanium is stable in the air, very little oxidation taking place even at 100°-120° C.; but it burns brilliantly in oxygen at 610° C., forming titanic oxide, and in nitrogen at 800° C., producing the nitride TiN. This is the only known case of vigorous combustion in nitrogen gas. By combustion in air a mixture of oxide and nitride results; nitride is also formed when the metal is heated in ammonia gas. The heat of combustion of the metal is 24,432 calories per equivalent. Chlorine combines with titanium at 350° C., forming the tetrachloride TiCl₄; bromine forms the tetrabromide TiBr₄, at 360° C., iodine forms the corresponding iodide TiI₄, at a still higher temperature. Carbon, silicon, and boron combine with molten titanium in the electric furnace; the crystallised borides and silicides are as hard as diamond. Alloys of titanium with copper, tin, iron, aluminium, chromium, cobalt, molybdenum, and tungsten are known. Pyrophoric titanium decomposes steam at 700°-800° C. Titanium dissolves slowly in cold, dilute sulphuric acid, and in hot concentrated hydrochloric acid, with evolution of hydrogen, and formation, according to Moissan, of violet solutions of salts of the sesqui-oxide. Nitric acid and aqua regia form titanic acid.

"The whole of the properties of titanium bring it clearly near to the metalloids and more especially to silicon" (Moissan).