USES OF ZIRCONIUM
As early as 1830 an attempt was made to use zirconia buttons, heated to incandescence, for lighting the streets of Paris. In 1885 an incandescent gas mantle of zirconium oxide was patented, but was replaced in a few years by thorium. About 1900 zirconia was used in the Nernst glower, and it has also been used in place of lime and magnesia as the incandescing material in the Drummond light. It is also said to be used in the Bleriot light, and its use in flares has been suggested.
During the past few years Dr. C. M. Johnson has succeeded in manufacturing laboratory ware made from zirconium minerals mixed with other refractories. Filtering crucibles, muffles, combustion tubes and boats, pyrometer protection tubes, and Kipp generators are now on the market, competing in price with German porcelain and fused silica. Zirconia crucibles are made from the fused material ground in a suitable mill. The powder is pressed or molded into shape with an organic binder, such as starch, or perhaps, better still, with a plastic cement made by grinding the fused material to 20 mesh, when it becomes colloidal in the presence of water. After drying, the articles are burned at a very high temperature (2300 to 2400°C.) until contraction ceases.
Fused zirconia has a high thermal endurance; is not affected when heated to redness and plunged into cold water, its coefficient of expansion being as low as 0.00000084; and its resistance to crushing is many times that of quartz glass. Its hardness is between that of corundum and quartz; its specific gravity 5.89, and porosity below 1 per cent. Its melting point is 2950°C, but 0.5 per cent. impurity reduces that by 100°C. Platinum, with a melting point of about 1750°C., can be melted to a mobile liquid in zirconia crucibles, and it is claimed that the boiling point of pure iron has been determined in similar crucibles.
Chemically, zirconia is very inert, being highly resistant to acids, fused alkalies, fused quartz, or molten glass. Possibly no other material known to chemists possesses such a combination of desirable refractory properties. Its one undesirable characteristic is its tendency under certain conditions at high temperatures, in the presence of nitrogen or carbon, to become converted into nitride or carbide.
An instructive paper entitled “Zirconia as a Refractory,” by E. H. Rodd, was published in the Journal of the Society of Chemical Industry, June 15, 1918.
Zirconium oxide as an opacifier has been thoroughly investigated by Hartman[95] and by Grunwald[96] with promising results; and a number of foreign patents have been granted on the use of the oxide in white ceramic enamels. Zirconia seems to be especially suitable for the manufacture of refractory bricks, or it can be applied as a lining or surfacing to other less desirable refractories. Continental practice along this line is said to have been much more highly developed than practice in this country, one example quoted being actual practice tests of a Martin Siemens furnace with a zirconia-lined hearth. After four months of continuous operation at high temperatures the hearth was still in good condition and gave promise of lasting at least an equal length of time without renewal. Statistics compiled from these tests showed a saving of about 50 per cent. in actual maintenance costs in favor of zirconia over the other refractories ordinarily used for such purposes. Bradford[97] quoted Podszus[98] as claiming to have made a furnace with the pure oxide which had first been fused in an arc furnace and then ground; and in which temperatures of 2400° to 2500°C. were obtained by firing with gas and oxygen.
[95] Hartman, Augustus, Zirconemail: Dissertations Arbeit: Techn. Hochschule, Munich, 1910.
[96] Ueber Zirkonoxyd in der Emailindustrie: Sprechsaal, No. 5, 1911.
[97] Bradford, Leopold, Birmingham Metallurgical Society (British).
[98] Podszus, Zeitsch. angew. Chem., Jahrg. 30, 1917, 1, pp. 17-19.
The most important question regarding zirconium at the present time has to do with the remarkable properties that some of its advocates claim it imparts to steel. That the Germans have had this use in mind for some time is evidenced by the numerous patents they have obtained covering the use of zirconium and its alloys.
Zirconium has been obtained in the amorphous and the graphitic state; and Wedekind has produced a metal of 99.8 per cent. purity resembling white cast iron in appearance, with a hardness of 7.8 (Mohs); specific gravity 6.40; specific heat, 0.0804; heat of combination, 1958 calories; and melting point, 1530°C.
Numerous alloys of zirconium have been made and a number of foreign and domestic patents have been issued covering various alloys, both ferrous and non-ferrous. It is stated that ferrozirconium is finding a limited application in the steel industry as a scavenger for removing nitrogen and oxides. An English patent, No. 29,376, covers the use of zirconium as a scavenger, the alloy containing 20 per cent. of the element and being used in an amount equal to about 1 per cent. of the weight of steel treated.
Another alloy containing 40 to 90 per cent. zirconium, the rest being mainly iron, is said to be free from metalloids and oxides, and malleable and ductile. Alloys covered by United States Patent No. 1,151,160 are claimed to be highly resistant to oxidation and chemical reagents. They have a metallic lustre and take a high polish, are readily malleable and ductile, and it is suggested that they may find an important application in filaments for electric lamps, as they are said to have the property of selective radiation. A typical analysis of some of the alloys claimed to have been produced under this patent shows Zr. 0.65 per cent., Fe 26 per cent., Ti 0.12 per cent. and Al 7.7 per cent.
A widely circulated statement to the effect that zirconium has been used in Germany in the production of steel for armor plates and armor-piercing projectiles has not been substantiated, so far as the writer knows, by any records of analyses.
The use of zirconium for alloying in steel is so new that, pending definite determination by disinterested competent authorities of the exact properties, if any, which zirconium imparts to steel, judgment as to its value for this purpose should be withheld.
Zirconium carbide has been patented for filaments for incandescent electric lamps and it has also been used as an abrasive. Tried as a pigment, zirconia has been found to have good covering power and should be considered where protection from acids, alkalies, or gases is particularly desired. The basic acetate has been used for weighting silk, and the pure oxide is used as a substitute for bismuth subnitrate in X-ray work.