[627] Vide Bull. Imp. Inst. 1911, 9, 134.
The preparation of alloys of titanium with almost all the commoner metals is protected by patent, but few of these are of technical importance. Small quantities of titanium are said to improve very considerably the properties of copper and its alloys, the brasses, bronzes, etc., especially in castings. The addition is usually made in the form of an appropriate titanium alloy, prepared by reduction of the mixed oxides with carbon in an electric furnace, or treatment of the mixed oxides, together with the alloying metal, with aluminium under similar conditions.[628] The titanium-silver alloys obtained in this way[629] are said to improve greatly the structure of silver, by preventing the familiar ‘spitting’ as the fused metal cools.
[628] Vide Rossi, U. S. P. 986505, March, 1911; 935863, October, 1909, etc.
[629] Rossi, U. S. P. 1024476 and 1025426, August, 1912.
An interesting process, which has been patented by Rossi,[630] recalls the method of formation of cementation steels. He has found that if a metal be loosely covered with its alloy with titanium, in a finely powdered condition, and the whole heated, the titanium diffuses into the metal, to a depth and concentration which vary with the temperature and the time of heating. He suggests that in this way a metallic body may be toughened and strengthened at any desired point, e.g. steel for armour-plate at the surface. Whether the process will be of any technical value or not can only be shown by experiment.
[630] U. S. P. 986504, March, 1911.
Application to Arc-lamp Electrodes.
—During the last fifteen years, innumerable efforts have been made to adapt titanium and its compounds to the manufacture of arc-lamp electrodes, or pencils.[631] The spark-spectrum of titanium is very rich in lines, and in respect of light efficiency, the element is very suitable for the purpose; the experimental difficulties, however, have been very great, and though electrodes containing titanium compounds have been on the market for some years, the problem cannot be said to have been satisfactorily solved. The best pencils contain titanium carbide, but successful attempts have been made to use the oxide. As early as 1904, Weedon[632] proposed an electrode prepared by heating 7 parts (1 mol.) of the dioxide with 1 part of carbon to 1500°-2000°C.; the ‘sub-oxide’ produced was powdered, worked up into a paste with a suitable binding material, and forced through a nozzle. The sticks so obtained, after drying and baking in the usual manner, were said to give satisfactory results, but consumption is very rapid, and troublesome deposits of the dioxide are formed at the end of the electrode. The dioxide, which alone is a very bad conductor, enters directly into the composition of the so-called ‘magnetite’ pencils, which are best made[633] by fusing together magnetite, rutile, and chromite, in suitable proportions, with a little potassium fluoride, powdering the brittle mass, and using this to form a paste from which the pencils may be obtained as usual. These electrodes are said to give a very efficient and fairly steady arc. They have the disadvantage that tiny glowing particles are thrown off, which soon render the globes opaque; the addition of sulphur[634] to the powder during manufacture is said greatly to diminish this inconvenience. Pencils made in a similar manner from powdered ferro-titanium[635] do not appear to have come into use.
[631] Vide, e.g. Ladoff, J. Ind. Eng. Chem. 1909, 1, 711.
[632] E. 26921, 1904.