Chapter XII: Zirconium

BY H. C. MORRIS

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.

GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION

Zirconium occurs in nature in commercial quantities as a mixed oxide and silicate known as baddeleyite, sometimes called brazilite, and as the silicate, zircon. Baddeleyite, as supplied to the trade, usually carries 80 to 85 per cent. ZrO₂. The silicate, zircon, carries about 65 per cent. ZrO₂. The oxide deposits, containing as they do a higher percentage of zirconium and the ore being more pure and easier to reduce, will in all probability become the principal source of zirconium.

The principal known deposits of zirconium ores are in Brazil, India and the United States, the countries being named in the relative order of their commercial importance.

=The Natural Oxide.=--The natural oxide, baddeleyite, or brazilite, occurs only in _Brazil_ in commercial quantities and is described in _Mineral Foote-Notes_ by Meyer,[99] who writes as follows:

[99] MEYER, H. C., _Mineral Foote-Notes_, November, 1916, p. 29.

There are but few commercial deposits of the unusual ores which
present more interesting geologic as well as economic features than
do the deposits of natural zirconium oxide in Brazil. The Caldas
region (visited in 1915 by the writer) in which these zirconia
deposits occur, is situated partly in the State of Minas Geraes and
partly in the State of Sao Paulo, approximately 130 miles north
of the city of Sao Paulo. It is a mountainous plateau, the main
elevation of which is about 3,600 feet. The surface is undulating,
presenting differences in level of from 300 to 600 feet.

The whole area is bounded on all sides by ridges rising abruptly
from 600 to 1,200 feet above the general level and forming a roughly
elliptical enclosure with a major axis of approximately 20 miles
in length and a minor axis of 15 miles. This peculiar arrangement
of the higher ridges is very significant when coupled with the
fact that the predominant rock of the plateau is a phonolite and
the presence of highly mineralized thermal water of considerable
medicinal value.[100] No thorough geological survey has been made of
this area with a view to determining the origin of the zirconia. The
character of the ore, however, and the formation, seems to point to
pneumatolitic agencies. A careful study of the relationship of the
large masses of coarsely crystalline nephelite-syenite in this area,
with pronounced segregations of eudialyte, might throw some light
upon this subject.

[100] DERBY, O. A., “Nepheline-rock in Brazil:” _Quart. Jour. Geol.
Soc._, August, 1887.

Zirconia ore can be roughly divided into two classes:

First, alluvial pebbles ranging in size from one-half inch to three
inches in diameter, generally carrying about 90 per cent. to 93 per
cent. zirconium oxide. These pebbles, known as favas and having a
specific gravity ranging from 4.8 to 5.2, are found along small
stream beds and on the talus slopes of low ridges.

Second, zirconia ore proper, or zirkite (a trade name), which ranges
in shade from a light gray to a blue black, the lighter colored
material carrying a higher percentage of zirconium silicate, as
evidenced by analyses, which in some cases show a minimum of 73 per
cent. zirconium oxide. The blue-black ore generally carries from
80 per cent. to 85 per cent. zirconium oxide. By careful sorting,
however, a uniform grade carrying about 80 per cent. is produced.

Prior to the investigations of Derby and Lee, this ore was considered
identical with baddeleyite. It has now been shown, however, that
it is a mechanical mixture of three minerals; namely, brazilite,
zircon, and a new and unnamed zirconium silicate carrying about 75
per cent. zirconium oxide. This new mineral has the same crystal form
as zircon (67 per cent. ZrO₂) but is readily soluble in hydrofluoric
acid, while zircon is not affected, this being a characteristic
differential test. The finely powdered mineral, on being treated
with a weak solution of hydrofluoric acid, leaves a residue of
minute, perfect, pyramidal crystals of zircon, the brazilite and new
zirconium silicate going into solution. Several large outcrops of the
ore occur on the extreme westerly edge of the plateau, one or two
isolated boulders weighing as much as thirty tons. This very cursory
examination of the zirconia deposits makes it unsafe to venture any
conjecture as to the quantity of ore available. Suffice it to say,
however, that the deposits have been traced for a distance of fifteen
miles between Gascata and Caldas, and if surface indications are of
any significance, are of vast extent.

The oxides have also been found in the State of _Montana_, and in _Ceylon_, _Sweden_, and _Italy_, but none of these occurrences are of commercial importance.

=The Silicate.=--The simple silicate, zircon, is found in seashore and river concentrations of monazite sands, associated with ilmenite, garnet, rutile, and various other heavy minerals usually found in such places.

An important concentration of zircon occurs along the coast of _Brazil_, in the states of Bahia, Espirito Santo, and Rio de Janeiro, where cusps of the beaches are protected on the north by granite headlands and bordered by Tertiary bluffs, which are cut by various streams and lagoons that constantly furnish fresh material for the concentrating action of the tides and waves.

Probably the next most important occurrence of zircon is in _India_, in the beach sands of the province or state of Travancore at the extreme southwestern end of the Hindustan peninsula.

Next in importance is an occurrence in the _United States_ at Pablo Beach, Florida, where not only the beach sands, but the dunes bordering them, contain appreciable quantities of the following minerals in their relative order of abundance: ilmenite, garnet, epidote, zircon, rutile, and other heavy minerals including monazite.[101]

[101] HESS, FRANK L., Letter of May 1, 1918.

Other occurrences in this country, most of which are of academic interest only, are in Colorado, at St. Peter’s Dome, near Pike’s Peak; in Idaho, in the Clearwater region and elsewhere in black sands and in certain granitic rocks; in Sussex County, New Jersey, at the Williams mine, where zircon occurs abundantly in magnetite; in New York at Lyon Mountain, Clinton County; at a few places near Crown Point; abundantly in pegmatite at Old Red Mines, Mineville, Essex County, and in numerous places in Orange County on the south, and St Lawrence County on the north. In North Carolina, in Burke, McDowell, and Rutherford counties, zircon occurs in monazite sands, and also in Henderson County near Zirconia and in Fredell County near Sterling.

Large crystals of zircon occur in a small pegmatite area in Comanche County, Oklahoma, in the southwestern portion of the Wichita National Forest. Oregon has many localities in which the presence of zircon has been noted, chiefly in black sands, old and present beaches, placer gravels, etc., and the same is true of Washington. In Virginia, zircon is found in pegmatite in Aurelia County, and in sandstone near Ashland, not far from Richmond.

Zircon is also found in _Norway_, the _Ural Mountains_, _Ceylon_, _Australia_, and _British South Africa_.

POLITICAL CONTROL

The important zirconium resources of the world are controlled politically, in the order of their commercial importance, by Brazil, Great Britain, and the United States.

=Brazil.=--A number of years ago John Gordon, an American mining engineer, became interested in deposits of monazite sand on the coast of Brazil in the vicinity of Prado, Bahia. A thorough investigation of all the known monazite deposits of the world showed that those in Brazil were by far the most desirable, and that those in Travancore, India, were second in commercial importance.[102]

[102] See Chapter XIII.

Other firms exporting zirconium minerals from Brazil, in addition to Gordon & Rogers, of 141 Broadway, New York, are Suffern & Co., of 135 Broadway, New York; S. R. Scott & Co., 39 Broadway, New York; Foote & Co., Philadelphia, Pa.; P. S. Nicholson & Co., Caixa 91, Rio de Janeiro; E. J. Lavino & Co., Bullitt Building, Philadelphia, Pa.; Luiz de Rezende & Co., Rua Ouidor, Rio de Janeiro, Brazil; and Chas. Spitz, also of Rio de Janeiro, who is agent for the Société Minière, a French company in which Rezende & Co. are said to have a considerable interest. Sometime ago the firm of A. C. de Freitas & Co. of Hamburg, Germany, had a contract from the Brazilian government on monazite sands and agreed to export at least 1,200 tons annually. How much zircon that company exported is not known. The de Freitas properties are now being worked by the Société Minière (French).[103]

[103] Production figures 1902-1916 for the United States and Brazil
are given in Table 34.

Until very recently, zirconium has been of minor interest in this country, the monazite sands having been exploited for their thorium contents only, not for zirconium. However, Germany and Austria seem to have placed considerable value upon zirconium-bearing sands, and, as shown by the attached table, more was produced in 1913 than in all the time prior, and practically all the material produced during that year went to Germany. This is in accord with the efforts of Germany, just before the war, to obtain tungsten and molybdenum, and is an evidence of preparations long before hostilities began.

=India.=--Before the war, the German users of monazite were in control of the Travancore, _India_, deposits. That control of course ceased and the contracts were cancelled. The India Office decided that, in the future, all directors of the company must be British born, and that the company must be ready at all times to sell monazite sand to British firms, direct, at a fair price.

=United States.=--It is hardly probable that the deposits in the _United States_ will be able to compete, on a commercial basis, with the Brazilian ores; but, if the necessity should arise, this country can produce, within its own borders, enough zirconium to manufacture many thousand tons of zirconium steel. The cordial commercial relations between the United States and Brazil will probably protect this country from any undue restraint on exports from South America.

=General.=--All of the large countries interested have facilities for making the ferro-alloy. Numerous alloys of zirconium have been made, and a number of patents, both foreign and domestic, have been issued covering various alloys, both ferrous and non-ferrous. No secret processes, as such, are known to the writer.

TABLE 34.--PRODUCTION OF ZIRCONIUM MINERALS IN THE UNITED STATES AND BRAZIL, 1902-1916[104]

----+------------------+--------------------
| United States | Brazil
+------------+-----+------------+-------
| Quantity |Value| Quantity | Value
Year|(short tons)| |(short tons)|
----+------------+-----+------------+-------
1902| ... | ...| 12 |$ 3,947
1903| 1¹⁄₂ |$ 570| 7 | 1,947
1904| ¹⁄₂ | 200| 9 | 3,935
1905| 4 | 1600| 18 | 5,506
1906| ¹⁄₂ | 248| 26 | 5,041
1907| | 46| 38 | 8,756
1908| 0 | 0| 275 | 15,151
1909| 1 | 250| 117 | 11,838
1910| 0 | 0| 128 | 23,271
1911| 1¹⁄₂ | 802| 45 | 16,169
1912| 0 | 0| 43 | 14,772
1913| 0 | 0| 1,119 | 54,767
1914| 0 | 0| 237 | 14,903
1915| 0 | 0| 8 | 2,915
1916| 0 | 0| 104 | 16,647
----+------------+-----+------------+-------

[104] Adapted from _Mineral Resources_, U. S., 1916, Part II, U. S.
Geol. Survey, 1917, pp. 377-386.

SUMMARY

The principal use for zirconium ores at present is determined by the refractory properties of the oxide, zirconia. Refractory bricks and shapes for furnace linings, chemical ware, and other heat, acid, and alkali resisting articles are made of zirconia, and are finding a limited market.

The recent interest in zirconium is due to the remarkable properties which it is said to impart to steel. Its real worth, or function, in that direction is yet to be definitely determined, and tests conducted by the Bureau of Mines, Bureau of Standards and others are being made to ascertain the facts.

The best and most available source of supply at present is Brazil, where the natural oxide, baddeleyite, occurs in considerable quantities in the states of Minas Geraes and Sao Paulo. The deposits have not been explored sufficiently to make any reliable estimate of tonnage possible, but, judged from their surface showing, they are of vast extent. The silicate, zircon, is found in Brazil, India and in the United States in commercial quantities.

The important deposits of zirconium minerals are controlled by Brazil, Great Britain and the United States, but the actual ownership of many of the deposits is unknown. This is particularly true of the oxide ores.