Physical Properties of Cobalt

Physical Properties of Cobalt are very simalar to many metals. Cobalt is a silver-white metal which, when pure, may be machined in a lathe as readily as pure nickel or pure iron. The commercial metal, containing small percentages of carbon, machines after the manner of mild steel. When under corresponding conditions cobalt is harder than nickel and iron. The effect of carbon between 0.06 and 0.37 per cent, is not sufficient to counteract that of slight variations in the heat treatment. The tensile strength of cobalt when pure, cast, and unannealed is 34,400 lb. per square inch, which value is increased to 59,700 lb. with a carbon content of 0.062 per cent.; and to 61,900 lb. when the carbon reaches 0.25 per cent.

The specific electric resistance of cobalt wires of great purity is 89.64×10^-7 ohms per cm. cube, but this value increases enormously by the addition of small quantities of impurities.

Physical Properties of Cobalt related to it magnetivity: Cobalt is magnetic at all temperatures up to about 1150° C., at which point it becomes non-magnetic. When placed in a magnetic field a bar of cobalt increases in length, and it is interesting to note in this connection that this magnetic elongation for both cast and annealed cobalt becomes practically nil between 1100° and 1200° C.

The density of pure cobalt containing 99.9 per cent, of the metal and a trace of iron, but no nickel or carbon, is given as follows:

Condition of metal.	Density
Cast from just above the melting-point (1500° C.)	8.7562 at 15° C.
Cast and swaged down to a thin cylindrical bar	8.9227 at 19° C.
Cast and annealed from 700° C.	8.8105 at 14.5° C.

From the foregoing it is evident that the mechanical history of the metal has an important influence upon its density, as is usually the case.

The density of pure electrolytic cobalt foil is given by Winkler as 7.9678 at 20° C.

The coefficient of linear expansion of cobalt is given by the expression:

α = 0.00001208 + 0.000,000,0128t

between 6° and 121° C.

The melting-point of cobalt has been determined by a considerable number of investigators, the most reliable results being between 1464 and 1491 ° C.

Physical Properties Cobalt of it boiling point: Cobalt boils at 2415° C. under 30 mm. pressure. Its specific heat has been determined by numerous investigators, the more important results being as follow:

Specific heat.	Temperature range, ° C.
0.10795	20-100
0.1053	15-100
0.1056	15-100
0.104	20-100
0.103	15-100

The specific heat at any temperature between 0° and 890° C. may be calculated from the equation:

Specific Heat = 0.1058 + 0.0₄457t + 0.0₇66t².

The most intense lines in the spectrum of cobalt are as follow: Arc: 3405.27, 3443.79, 3453.66, 3489.57, 3502.45, 3529.96, 3569.59, 3587.30, 3845.60, 3894.25, 3995.45, 4121.52, 4531.12, 5444.80, 5946.73, 5984.40, 5992.11, 6006.50, 6007.85, 6049.34, 6082.67, 6282.89, 6320.62, 6348.00, 6450.51, 6455.30, 6478.10. Spark: 2564.13, 2580.42, 2582.33, 2663.65, 3845.65, 3873.30, 3874.14, 3894.26, 3995.53, 4118.94, 4121.51, 4531.20, 4581.82, 4813.70, 4868.01.