Physical Properties of Zirconium

Amorphous zirconium, prepared by the method of Berzelius, is a coal-black powder which is a bad conductor of electricity. According to Wedekind and Lewis the black, amorphous zirconium of Berzelius is not an individual substance but a gel, which retains water most pertinaciously. The gel has a density of 3.75, but after drying at 1000° C. in a high vacuum its density becomes 5.79. Amorphous zirconium appears to be the colloidal modification of the metal; and the two modifications of zirconium bear to one another the same relation as do amorphous and crystalline silicon. Crystallised zirconium, as prepared by Weiss and Neumann, is white, and resembles cast-iron. It forms broad, monoclinic plates, and has a density of 4.15 (Troost), 4.25 (Moissan), or 6.40 (Weiss and Neumann). It has a hardness of 7-8 on Moh's scale and scratches glass and the ruby; its specific heat is 0.0666 or 0.0804 (Weiss and Neumann); it melts at about 1530° C. The arc, spark, and absorption spectra of the metal have been studied by various observers. The most intense lines in the spectrum of zirconium are as follow:

Arc: 3392.14, 3496.38, 3890.49, 3891.53, 3929.71, 3973.63, 4081.40, 4227.94, 4239.49, 4282.36, 4507.32, 4535.90, 4575.69, 4634.20, 4687.99, 4688.63, 4710.23, 4739.68, 4772.50, 4815.80, 6127.64.

Spark: 3392.20, 3438.39, 3496.40, 3556.89, 3698.41, 3751.85, 3836.98, 3958.39, 3991.31, 3999.18, 4149.43, 4209.21, 4380.12, 4443.31, 4494.78, 4497.27.

The most persistent, i.e. the ultimate lines in the spark spectrum, are 3394.8 and 3392.4.

The crystalline metal is very stable in the air, and burns only slowly at a white heat, though more rapidly in the oxy-hydrogen blowpipe flame; when combustion is incomplete the product contains some sesquioxide, Zr₂O₃. The amorphous metal burns more readily. The heat of combustion of 1 gram is 1958-7 calories (Weiss and Neumann). When heated to dull redness in chlorine or hydrogen chloride the metal yields the tetrachloride, and it combines with hydrogen at a red heat to form the solid dihydride ZrH₂.

Zirconium is but slowly attacked when heated with hydrochloric, nitric, or sulphuric acid, but is rapidly oxidised by aqua regia. Hydrofluoric acid is the best solvent for this metal, the cold dilute acid easily dissolving it; caustic alkalis also dissolve zirconium with evolution of hydrogen. Zirconium preparations sometimes show radioactivity, owing probably to the presence of thorium as an impurity.