9875

SILICON-BRONZE

§ 74. In 1881 M. Weiller of Angoulême performed a series of experiments with phosphor-bronze wire, to test its suitability for telegraphic and telephonic conductors, and his results went to show that it possessed a conductivity one-third that of copper, but 2 times that of iron and steel. The conductivity not being sufficient for telegraphic purposes, he invented silicon-bronze, which is an alloy of copper and tin containing silicon. He thus obtained a wire presenting the same resistance to rupture as phosphor-bronze wire, but with a much higher degree of conductivity, rendering it applicable for telegraph purposes. Mr. W. H. Preece

states that phosphorus has a most injurious influence on the electrical conductivity of bronze, and that silicon-bronze is far superior, and has entirely replaced phosphor-bronze for telegraphic purposes. It is also important to note that, although wires made from this alloy are very much lighter than ordinary wires, they are of equal strength; and it is affirmed that, if broken, they will not fall to the ground as the ordinary wires do; but by reason of their high elasticity they spring back and coil up close to the standards. The same is also true of phosphor-bronze. The following table shows the comparative properties of different wires :

E. van der Ven1 conducted a series of experiments to determine the value of phosphor-bronze and silicon-bronze for electrical purposes, chiefly as materials for telephone wires, and came to the conclusion that phosphor-bronze has about 30 per cent of the conductivity of copper, and siliconbronze about 70 per cent, while that of steel has only 10.5 per cent the conducting power of copper. Comparing their tensile strengths with that of steel, he finds that a steel wire, 2 millimetres diameter, with quadruple security, and the conventional "sag" of 0·7 millimetre, can have a stretch from pole to pole of 130 metres. The stretch of a phosphorbronze wire, 1 millimetre diameter, under the same conditions would be 106 metres, and for silicon-bronze 91 metres. These alloys, with a diameter of 1∙18, and 0.77 millimetres respectively, have the same electrical resistance as a steel wire 2 millimetres diameter.

Silicon-bronze is valuable on account of its great strength and tenacity, high conductivity, and resistance to corrosion by atmospheric influences; and is therefore one of the very best mediums for transmission of electrical force. It can be made nearly as strong as steel, and yet possess treble its conductivity. The manufacture of this alloy has been greatly improved since its introduction, the latest kinds possessing less conductivity for electricity, but a higher tensile strength, which allows the wire to be more tightly stretched, and the supports wider apart. Wires of silicon-bronze are largely used on the continent for telephone purposes, and will stand the force of violent storms remarkably well, which is in some measure due to the small diameter of the conductor. In one case, at Rheims, a line having a span of 1000 feet was exposed to the action of the wind blowing directly across it, and stood the test admirably. The Italian General Telephone Company have employed silicon-bronze wires for some time without an accident occurring. Railway engineers have proved its efficacy for resisting a weight of snow in cold and hilly districts. When the wires have been 1 Musée Teyler, and Electrotech. Zeitsch. 1883.

covered with snow, and "sagged" considerably, they have immediately assumed their normal deflections when the snow has been removed. The poles of an Austrian railway company, using silicon-bronze, are from 328 to 720 feet apart across flat country, and from 160 to 500 feet apart in hilly districts. 1 Mr. Robey states that the blizzard, which did so much damage to telegraph wires in the United States in 1887, did not break those made of siliconbronze.

Silicon-copper and silicon-bronze are made, according to Weiller, the inventor of these combinations, in the following manner. He recommends the following proportions: potassium silico-fluoride 450 parts by weight, powdered glass 600 parts, common salt 250 parts, carbonate of soda 75 parts, carbonate of lime 60 parts, and dried chloride of calcium 500 parts. The mixture is heated in a covered plumbago crucible to a temperature a little below the point when they begin to act on each other, when the mixture is added to the molten copper or bronze, as the case may be; the reduced silicon combining with the metal or alloy.

The action of silicon on copper and bronze is similar to that of phosphorus. It acts as a deoxidiser, and the silica formed being an acid, is a valuable flux for any metallic oxides remaining unreduced. Silicon also enters into chemical combination with the alloy.

MANGANESE-BRONZE

§ 75. This is a new combination introduced by Mr. P. M. Parsons, to whom the author is indebted for much of the following information.2 Copper and iron unite at high temperatures in various proportions, forming alloys of great

1 Paper read before the Cleveland Inst. of Engineers, December 2 Brit. Assoc. Report, 1883.

1888.

hardness, and when the iron is present in certain proportions the tenacity and elasticity of the copper is increased. The same remarks apply to brass and bronze. It should be stated, however, that the above properties are acquired at the expense of ductility and toughness. The effect of iron being so decided, led some metallurgists to try the influence of manganese by reducing oxide of manganese with carbon in the presence of copper. Mr. Stirling and Mr. A. Parkes both used manganese to alloy with copper, brass, and other alloys. Mr. Everitt of Birmingham has introduced manganese into yellow - metal for sheathing and similar purposes.

No comparative experiments as to the strength, hardness, and ductility, or other qualities of these alloys, appear to have been published. The effect of manganese is to add somewhat to the ductility and toughness of copper alloys and allow copper, zinc, etc., of commoner quality to be used for definite purposes. In 1876 Mr. Parsons introduced his method of manufacturing manganese brass and bronze by mixing ferro-manganese with copper, and using this triple alloy for making various copper alloys, such as brass and bronze.

§ 76. Cupro-Manganese.--Copper and manganese unite in various proportions, forming alloys which may be red like copper, or silvery-white in colour, depending upon the amount of manganese present. They possess considerable hardness and tenacity, some are very ductile, and more fusible than ordinary bronze. They are distinguished by the property of soundness when cast into moulds, the castings being free from blow-holes. The great difficulty in producing alloys containing much manganese is owing to the great affinity that this metal has for oxygen, and the high temperature required for the reduction of manganese from its oxides, which are used as a source of the metal. This renders the production of homogeneous alloys, with a required amount of manganese, very difficult.