Warren B. Blumenthal
National Lead Company Niogoro Falls, New York
Zirconium Chemistry in Industry
T h e story of zirconium chemistry in industry starts in the molten rocks of the earth, for the evidence of the behavior of the zirconium atom in the rocks presages the behaviors encountered in the preparation and isolation of the element or its useful compounds. Zirconium is moderately abundant in magmas and the rocks derived from magmas, its concentration in the crust of the earth being roughly equal to that of carbon, i.e., about 0.0270. As siliceous magmas cool, one of the first phases to crystallize is zircon, Zr02.SiOz. Its formation is favored by a moderate excess of acidic oxides in the magma, and i t is particularly likely to crystallize from magmas which yield granites and syenites. Once the zircon has formed, it is extremely stable, and much of the zircon that has formed in nature has survived hundreds of millions of years of geologic change, through upheavals, weathering, and changes in physical and chemical environment. The tetrrh-dral crystals are easily recognized. Even in ancient times, well-formed colorless and colored zircon crystals which had been freed from the matric-s in which they had developed found their way into the arts and ornamentation. Mention is made of the zircon in both Old and New Testaments (Exodus 39: 12 and Revelation 21: 20), and it is freauentlv mentioned in ancient and medieval literature
ill.
"
Not all of the zircon in nature remained unchanged. I n hot alkaline environments, complex alkali or alkaline earth zireonylosilicates and zirconosilicates were formed. In the presence of fluorides, complex fluorinecontaining minerals were created, and reactions also occurred with other minerals of the environment, resulting in highly ramified crystalline structures containing a great diversity of metallic elements. Also, many of the complex silicates formed as original crystallizations from the magmas, without going through the intermediate formation of the zircon phase. Some of the natural zircon occluded or lay near to deposits of radioactive elements, particularly uranium and thorium, and bombardment of the zircon by their radiations degraded the zircon crystal structure to varying degrees, giving rise to some of the colored and otherwise altered zircons now distributed widely in the earth's rocks. Reheating of zircon in nature to approximately 1550°C led to breakdown of the unit cells of the zircon to their constituent oxides, zirconia and silica. The dissociated zircon is called "metamict." When the dissociation has not proceeded far, heating the mineral may cause reassocistion to true zircon. In other cases, crystals of the decomposition products have grown to appreciable size and their distribution is not suitable for rearrangement to zircon on heating. 604
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Once the zircon had formed in the rocks, it was capable of remainmg unchanged for eons, even under conditions which broke down the host rock formation to soil and silt. Often, when weathering and the action of streams corroded and eroded away the host rock, virtually unaffected zircon crystals were exposed and became subject to the play of forces on the surface of the earth. These crystals tended to be swept downstream and downhill, to be pulverized by pressure and by rubbing against materials with which they came in contact, and finally to be dropped in river deltas and along the Iitorals near the mouths of rivers. Sometimes geologic uplifts raised the deltas and the Iitorals, forming beaches in whose sands were relatively high concentrations of zircon grains. Lighter mineral grains were washed and blown away, while zircon and other heavy mineral grains remained in increasing concentrations. The stage was thus set for modern man to find beaches whose sands were sufficiently rich in zircon and other heavy minerals to permit economic mining and segregation of useful fractions. The chief exploitation of beach sands for their zircon content has been undertaken near Jacksonville, Florida, in the State of Kerala (formerly Travancore), India, and the eastern Australian coast near Byron Bay. Many other such beaches are known, and may eventually be worked for zircon. Processing Zircon
The Florida deposits of zircon sand extend for about six miles along the beach near Jacksonville. The sand of the area contains about 4% heavy minerals, of which about 40% is rutile and llY0 zircon. The recovery of these two minerals simultaneously is economically feasible. Physical separations, based on the differential responses of the components to gravitational, electrostatic, and electromagnetic fields, leads to the recovery of the z i w n a t a purity of about 99%. Zircon sand cannot be decomposed a t the ordinary temperature by any known reagent. Even hoiling acids and alkalies have little effect on the sand. (Some commercially unimportant metamict and otherwise altered zircons dissolve to varying extents in acids, such as hydrochloric acid.) When zircon is milled down to micron size, it is significantly attacked by boiling hydrofluoric or boiling sulfuric acid, but due to the high cost of such fine milling and the adverse effect on the economy of handling the silica content of the mineral, these procedures have not proved of industrial value. Zirconium Carbide
Two methods for the conversion of zircon to other useful compounds have proven particularly satisfactory, each primarily for a particular series of derived
products. The most extensively used has beeu the treatment of a mixture of zircon and carbon in an arc furnace, so as to form zirconium carbide (2): ZrOz.SiOz
+ 4C
+ ZrC
+ SiO + 3 C 0
Zirconium carbide, ZrC, is not a compound in the same sense as sodium, calcium or aluminum carbides. These latter carbides are daltonide compounds and their reactions with water or dilute acids give hydrocarbons:
Zirconium carbide does not react with water or dilute acids, except hydrofluoric acid. Its reaction with the latter acid liberates hydrogen gas. Zirconium carbide looks like a metal, conducts electricity like a metal, and has alloying and other properties characteristic of a metal. It may be regarded as an allotrope of metallic zirconium containing dissolved carbon. While pure zirconium metal has a hexagonal crystal lattice a t the ordinary temperature, that of zirconium carbide has a face-centered cubic of the sodium chloride type. The distance between zirconium atoms in the carbide is only 8% greater than in the pure metal. If, during the preparation of zirconium carbide, less than the theoretical equivalence of carbon is available to react, a product of the same structure is obtained, except that lattice vacancies occur where carbon might have beeu. The same face-centered cubic zirconium can also be prepared with one or more species of atoms of about the same diameter as the carbon atom replacing the latter, e.g., oxygen, nitrogen, or boron. Thus, the composition and structural features do not reflect the valency of the element combined with the zirconium, as would be the case in a classical chemical compound, but rather are dependent on the presence of atoms of a certain size to fill vacant lattice positions. Zirconium carbide is extraordinarily refractory, melting a t about 3600°C and boiling a t about 5100°C. The compositions 4TaC lZrC, melting a t 4205'C, and 4TaC IHfC, melting a t 4215'C, are the highest melting substances known. The element hafnium, atomic number 72, located just below zirconium, atomic number 40, in the periodic table, bears a closer resemblance to zirconium than any other two elements do to one another. The atomic radii of zirconium is 1.442 I% and of hafnium, 1.454 A. All of the zirconium found in nature contains hafnium. In commercial zircon, the hafnium content is generally about 2 weight per cent of the zirconium content. Because of the extreme similarity of chemical properties, the hafnium is carried through the industrial processing of zirconium minerals and the derivative compounds with virtually no separation. Since there are no significant qualitative chemical differences between the two elements, the presence of hafnium in the zirconium compounds of commerce is regarded as of no consequence. Only from zirconium intended for use in atomic reactors must the hafnium be removed, because the larger capture cross section of hafnium is detrimental to thermal electrons. Hafnium, with nearly twice the atomic weight of zirconium, is probably as similar chemically to zirconium as deuterium is to hydrogen. Therefore, for chemical purposes hafnium
+
+
may be regarded as a double-weight isotope of zirconium. There are appreciable differences between the physical constants of pure hafnium and its compounds and those of zirconium and its analogous compounds, i.e., melting point, boiling point, and of course specific gravity. The occurrence of many hafnium and zirconium compounds as polymers, in which hafnium and zirconium are randomly interchanged, increases the difficulties involved in separating the elements. The most successful large scale separations have been achieved by liquid-liquid extraction techniques. Zirconium cyanonitride is an industrial product prepared by the same procedure as described for zirconium carbide, except the carbon is insufficient to provide one carbon atom for each zirconium atom in the product. During the preparation, the metal picks up oxygen and nitrogen from the air and these elements occupy some of the vacancies left by the deficiency of carbon. The formula of the product is represented as Zr(C,N,O). I t has a golden yellow to bronze color, and is somewhat more reactive with chemical agents such as chlorine or hot concentrated sulfuric acid than is zirconium carbide. Zirconium Chlorides
Zirconium carbide and zirconium cyanonitride burn when heated in chlorine gas, with the formation of zirconium tetrachloride: Zirconium cyanonitride is usually preferred for this industrial chlorination because it is more easily crushed to suitable size for the chlorinator and reacts more readily. Zirconium tetrachloride is monomolecular in the vapor state, hut shows some peculiarities in the solid state that can only be interpreted by assuming some type of association of the molecules. The compound will melt a t 437' under 25 atmospheres pressure. It sublimes a t 331'C under 1atm pressure. The solid does not dissolve in any non-polar solvent, and is thus different from titanium tetrachloride, which is miscible with uon-polar solvents. In fact, zirconium tetrachloride appears to dissolve only in solvents with which it reacts chemically; t,herefore, the dissolved substance is something different chemically from zirconium tetrachloride. Zirconium tetrachloride dissolves readily in molten alkali chlorides, while titanium tetrachloride does not. In the molten alkali chlorides, chlorozirconates are formed: This and other behavior suggest that the chlorozirconate structure is already present in zirconium tetrachloride. This may be represented (8):
It is well known that phosphorus pentachloride has such a structure, that is, PCln+PCls-. In the system ZrC14-PCla there is evidence for the compounds PCI6.ZrCL, 2PCls.ZrC14, and PC16.2ZrC14, which might be represented
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The behavior of the system ZrCL-H,O is particularly interesting. Zirconium tetrachloride reacts vigorously with water or water vapor. When an aqueous solution of the reaction pr0ducts.i~evaporated, colorless tetragonal crystals of zirconyl chloride, empirically ZrOC12.8H20, are deposited. When the washed crystals are dissolved in water, the pH's of the solutions are about the same as those of hydrochloric acid solutions of the same molarity. This indicates complete release of one chlorine atom by hydrolysis. The basic zirconium ration is actually polymerized. Crystallographic study of zirconium oxychloride shows the unit structure to be a tetramer, the four zirconium atoms being a t the corners of a square, and each is linked to two others through two oxygen atoms, one above and one below the plane of the square (4). This tetramer appears to he present in the aqueous solution also, and one chloride ion tends to he held by coulomhic forces near the middle of each side of the square (5). But the composition and number of zirconium atoms of the ions in the aqueous solutions vary with concentxation, pH and temperature. Evidence for cationic, neutral, and anionic species has been adduced from ion exchange and electromigration studies. A full and definitive description of the aqueous zirconium chloride system will be long in forthcoming, hut a number of generalizations can be stated as practical guides for the industrial users of zirconium chlorides. The following are particularly noteworthy: 1. Aqueous aireongl chloride solution behaves as a solution of low polymers of hvdrsted ZrOOHt and chloride ion. 2. The pH of zirconyl chloride solutions is about equal to that of hydrochloric acid solution(s) of the same molarity. 3. . After preparing an aqueous solution of aircony1 chloride from the crystals, about three to twenty-four hours is required for a practical approximation of equilibrium to be established. In chemical processes making use of aqueous zirconyl chloride, a result. obtained using freshly prepared solution is likely to be different from that obtained with an aged solution. Even after the practical equilibrium has been achieved, relatively minute changes continue to go on for long periods of time, as reflected in changes in eleetriesl conductivity and in light scattering effects. The changes that go on in the solution are believed to consist of polymerizations and depolymerizstions, ohanges in hydration, and changes in the number of units of the prevailing species which are loosely held together through polarization attractions. A solution which is heated and then cooled may never return t o a state identical with that of asolution which hasnot been heated. 4. In the presence of other dissolved molecules and ions, the complex zirconium cation shows s tendenoy to relinquish molecules of water and to hond with the other molecules and ions. It exhibits little tendency t o cnmbine with monohydric alcohols hut appreeiahle tendency to combine with 1,2-dihydroxy alcohols. The tendency to combine with 1,2-dihydroxy aromatic campounds is even greater. There is a strong tendency to combine with carboxylste and even stronger with alpha-hydroxycarboxylate ions. With the latter, tri- and tetra-alpha-carboxylatoeirconic acidsprecipiipitsteiromthe solution:
Nitrate and even perchlorate ions are complexed t o some extent by zirconium chloride solutions (6).
Zirconium bromides and iodides behave much like the corresponding chlorides, but it should be noted that the iodides are very susceptible to atmospheric
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oxidation, with liberation of free iodine. Since the chlorides are the least expensive, they are used almost exclnsively in industrial studies and in manufacturing processes. However, zirconium tetraiodide is used in the manufacture of exceedingly pure zirconium metal by pyrolysis. This is the well-known van Arkel-de Boer "hot wire" process. Zirconium tetrachloride is the most important zirconium compound for the production of zirconium metal. In the Kroll process, zirconium tetrachloride is sublimed into a pool of molten magnesium, where it is reduced to metal sponge, according to the equation In another application, zirconium tetrachloride is dissolved in molten alkali chlorides? allowed to solidify, and the product added to molten magnesium and to molten aluminum as a means of introducing a small amount-about 0.2 to 0.3% by weight-of zirconium metal into the basis metal. I t has the effect of refining the grain size and markedly increasing the strength of the magnesium or aluminum. Zirconium tetrachloride is a strong Lewis acid, and as such is effective as a Friedel-Crafts catalyst. In some FriedelLCrafts syntheses zirconium tetrachloride has been found to give extraordinarily high yields and high purity products. I t is also a useful component of Ziegler-type catalysts for the condensation of ethylene. Zirconium tetrachloride is the starting material for the synthesis of a numher of organic derivatives of zirconium, such as alkoxides and zircocene, which will he discussed later in this paper. Zirconyl chloride is t,he most commonly used zirconium compound from which to derive other zirconium compounds: hydrous oxide, carbonated hydrous oxide, acetate, sulfate, glycolate, lactate, and others. Its solutions precipitate acid dyes, and can he used to prepare high quality pigment toners and to improve the properties of color lakes (7). Aqueous zirconyl chloride solution has considerable solvent action on sparingly soluble sulfates, such as calcium sulfate, due to the removal of sulfate ion from the solution by complexing with the zirconium atom. The free acid in zirconyl chloride solutions may he neutralized and a soluble compound of composition Zr00HCI .xH20 recovered. It is highly polymerized in solution and amorphous in the solid state. A similar product is obtained by dissolving precipitated zirconia in hydrochloric acid. This zirconyl hydroxy chloride, urhile still acidic in reaction, is relatively mildly acidic and has been used in the preparation of body deodorants. A chloride of the same empirical composition-hut judging from its different properties polymerized in a different pattern-has been obtained by neutralizing the free acid of zirconyl chloride solution with an alkali or alkaline earth carbonate. The latter chloride is represented as Zr203Clz~xH20.It has proved particularly suitable for the preparation of pigments from acid dyes. Zirconium Fluorides
The entire aqueous chemistry of zirconium compounds may be regarded as the manifestation of the tendency of zirconium to form covalent bonds with oxygen, to seek out preferred bonds with oxygen when
oxygen in more than one condition is available, and to realize as near an approach as sterically possible the attainment of the maximum coordination number of eight. In zirconyl chloride the zirconium atom is bonded to four oxygen atoms which serve as bridges in the tetramer structure, and three or four other oxygen atoms of water or hydroxyl ion, a total of seven or eight oxygen bonds. The aqueous chemistry of the fluorides is distinguished from that of the other halogenides of zirconium by the preference of the zirconium atom for fluorine over oxygen of water (but not of hydroxyl ion). Thus. in the absenre of appreciable hydroxyl ion concentration, the zirronium atom forms fluozirronic acids: ZrOOH+
+ 4F- + 3 H t + H.0 H2ZrOF4.2H.0 + 2F- + 2H H A F s + H 9 0
HZrOF4
+
-
-r
The arid H1ZrOF4.2H20 is very soluble and can be crystallized from the aqueous solution. No salts of this acid ale known. When it is neutralized, it breaks down to oxyfluozirconic acids of lower acidity until hydrous zirconia, ZrO?.xH20 is obtained as the final product of neutralization. On the other hand, the hexafluozirconic acid cannot be isolated from solution, and when it is neutralized with bases it forms well crystallized, anhydrous hexafluozirconates (8). The fluozirconic acids have no use as such, but the alkali fluozirconates are used in the preparation of zirconium metal and zirconium alloys. They react with alkali metals according to the equation: NsnZrF6
+ 4Na
-
6N;tIr
+ Zr
Alkali fluozirconates have also been reported to he useful as stabilizers for silicone rubber and alginate plastics, as welding fluxes, as additives to optical glass to promote durahilitv, and as agents that improve the bond between aluminum or steel and plastic coatings. Anhydrous zirconium tetrafluoride cannot be recovered from aqueous systems. I t is made by treating the metal or oxide with fluorine or an excess of hydrogen fluoride gas, by the thermal decomposition of ammonium fluozirconate, or by metathesis of zirconium tetrachloride with hydrogen fluoride.
body deodorants is presumed to depend on similar interaction with malodorous acids. It is also thought that hydrous zirconia sequesters components of the perspiration which nourish microorganisms, and prevents their growth and the formation of malodorous substances which are by-products of their metabolism. In commenting on pharmaceutical applications of zirconium compounds, i t should be emphasized that zirconium is a non-toxic element. Extensive tests on animals and humans have shown that large amounts of zirconium compounds may be eaten or applied topically without, ill effects. I t should be further noted, however, that even non-toxic elements may be put into harmful combinations. The strongly acidic compounds of zirconium must be treated with the cautions that apply to any strong acids. All heavy metals have toxic properties when introduced into animal organisms intravenously; soluble zirconium compounds are no exception, but intravenous injections of insoluble compounds of zirconium have been found to be harmless. It has been noted that even the soluble compounds of zirconium tend to he less toxic than most heavy metals on intravenous injection. Again, foreign bodies of many types, including some zirconium compounds, injected intracutaneously or subcutaneously tend to stimulate the formation of granulomas. A non-toxic substance must be regarded as one which, under ordinary conditions of ingestion or contact does not give rise to bodily disorders. iYo case of zirconium poisoning has ever been reported to result from the industrial handling of zirconium compounds. A somewhat more reactive variant of hydrous zirconia is obtained by precipitating with sodium carbonate rather than with an alkali hydroxide. When suitably prepared, the precipitated product approaches the composition 2Zr02.C02.8H20. I t is known in the indus ry as zirconium carbonate and as carbonated hydrtus zirconia. It has the same pharmaceutical uses as hydrous zirconia, and in addition it finds use in the manufacture of a number of soluble salts of zirconium, such as zirconyl acetate, zirconyl nitrate, and ammonium zirconyl carbonate. Zirconyl Acetate
Hydrous Zirconia
When alkalies are added to aqueous solutions of zirconium halogenides, protons are removed from the complex zirconium cation and hydrous zirconium oxide or hydrous zirconia is precipitated. This is generally most suitably accomplished in a solution of a chloride of zirconium. The reaction is essentially ZrOOH+
+ OH- + (z - 1) H?O
-
ZrOs.zHsO
Hydrous airconia is very insoluble in water and weak acids, hut it dissolves slowly in hydrochloric acid (fairly rapidly if hot) and rapidly in hydroflunric acid. The chief use of hydrous zirconia has been in pharmaceuticals, in which its affinityfor oxygen compounds makes it suitable for sequestering and rendering innocuous certain irritants and malodorous substances. For example, the irritant exuded by the poison ivy plant, Rhus lozicodendron, is a catechol derivative. The catechol hydroxyl groups form a chelate ring with the zirconium atom. The effectiveness of hydrous zirconia and certain other zirconium compounds as
Zirconyl acetate or diacetatozirconic acid, HZrOOH(C2Ha02)a, is readily obtained as an aqueous solution hy adding acetic acid to an aqueous slurry of carbonated hydrous zirconia. Evaporation of the solution under reduced pressure gives the solid compound. It is resinous or glue-like in appearance, and is amorphous to the X-ray. Its properties indicate it to be a highly polymerized product. The powdered solid readily dissolves when added slowly to rapidly swirling water. On heating, the solution yields a solid hydrolysate, a more basic acetate of composition ZrOOHCzHa02. When the mixture is allowed to cool and stand a t the ordinary temperature, the precipitate slowly redissolves. Zirconyl acetate has been widely used as a waterrepellent agent for textiles. I t is usually mixed with a proprietary wax emulsion. I t is easy to apply, has no adverse effect on the hand or appearance of the textile, and its use is economical. It is not permanent, however, and a new application is necessary after each laundering or dry-cleaning of a treated garment. Zirconyl acetate has been shown, in a wide variety Volume 39, Number 12, December 1962
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of formulations, to be a highly desirable curing catalyst for silicone water-repellent films, such as are used on textiles and leather. These water-repellent finishes are permanent and will withstand vigorous laundering with powerful detergents surprisingly well. Ammonium Zirconyl Carbonate
Some textile plants prefer not to use even weakly acidic substanres for the surface treatment of textiles. This led to the development and use of ammonium zirconyl carbonate in place of zirconyl acetate. The compound is prepared by allowing carbonated hydrous zirconia to react with ammonium hydrogen carbonate: Ammonium zirconyl carbonate (or ammonium tricarhonatozirconate) crystallizes from aqueous solution in large, beautiful, colorless prisms. The crystals readily redissolve in water. The solid is unstable in air, gradually giving off carbon dioxide and ammonia. The aqueous solution is moderately stable a t room temperature, although after standing for a month or so i t is likely to begin depositing hydrous zirconia from the solution. At temperatures above 60°C, it decomposes rapidly. When ammonium zirconyl carbonate solution is evaporated on a textile surface, it leaves an invisible film on each fibre, which is moderately water-repellent. If suitable soaps and waxes are mixed into the ammonium zirconyl carbonate solution before it is applied to the textile, a highly water-repellent film is obtained. Perhaps it was the excellent water-repellent effect on textiles that caused a number of chemists to experiment on the action of ammonium zirconyl carbonate in water-base (latex) paints. When the films obtained from these treated paints were tested, they were found to be quite resistant to the destructive action of rainfall shortly after they were applied. The dried film was also found to exhibit outstanding resistance to wassing. In addition to the above, ammonium zirconyl carbonate has proved to he a convenient and effective reagent to incorporate into solutions such as carboxymethylcellulose, which will leave insoluble protective films on a variety of surfaces, including textiles, paper, cardboard, and wood. The convenience of providing a zirconium residue after the evaporation of ammonia and carbon dioxide, without leaving other cations or anions, has been particularly attractive. Zirconium Sulfates
Sulfates of zirconium can be prepared from chloride solutions, or directly or indirectly from zircon. If calculated amounts of alkali sulfates are added to zirconyl chloride solution and the solution is boiled, insoluble basic sulfates are formed. Variations in procedure will give basic sulfates of different compositions. A typical product of industrial importance has the empirical formula 5Zr02.3S03.15.5H20. The terminology "basic sulfate" has limited justification, for the acidic component, SO3, is stoichiometrically less of the total composition than the relatively basic component, ZrOn. The basic zirconium sulfates are precipitated from fairly strongly acidic solutions, and very nearly all impurities remain in the solution while the exceedingly pure basic zirconiumsulfateprecipitates. This has been of particular value in getting rid of iron 608
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which has been carried through from the mineral into the zirconium chloride. The basic sulfates of zirconium can be dissolved in the calculated amount of aqueous sulfuric acid to give the sulfate of composition Zr(SOI)1.4H10, "zirconium sulfate," or alternatively, H2ZrO(SOI)2~3H20, disulfatozirconic acid. The latter formula and name are more in keeping with the properties of the compound. Disulfatozirconic acid is soluble in water to the extent of 52.5 per 100 g m of solution a t lS°C. The aqueous solutions have about the same pII as sulfuric acid solutions of the same molarity. Electromigration studies of the solution show the zirconiunl to he in an anion, and hence the compound is a complex acid. Salts of the acid, such as ?rTa2ZrO(S04)2.3H20are known. Both disulfatozirconic acid and some of its hydrolysis products are precipitants of amino acids and proteins, and will tan hide, gelatine, and glue. High grade white leather has been made by zirconium sulfate tannage since the early nineteen thirties, and in recent years the availability of less expensive sulfates of zirconium has extended their use in industrial tanning to leather not specifically intended for use as white leather. Disulfatozirconic acid can be prepared from zircon of micron-size particles by reaction with hot concentrated sulfuric acid, or by the reaction of zirconia, hydrous zirconia, or zirconium oxychloride with the same reagent. A low cost crude grade of a sulfate of zirconium suitable for tanning is prepared by (1) heating zircon with soda ash to form sodium zirronylosilirate
and then (2) treating this product with concentrated sulfuric acid:
A complex water-soluble sulfate of zirconium can also be prepared by heating zirconium dioxide with ammonium carbonate:
The sulfates of zirconium exhibit very complex hydrolysis reactions, which give rise to a considerable number of basic sulfates (9-11). These basic sulfates are more properly regarded and treated as heteropolyacids. They generally consist of molecular chains which may be straight or branched. -4n ordinary solution of disulfatozirconic acid a t room temperature deposits a solid on standing: the more dilute the solution the more rapid the deposition. The composition of the solid is 4Zr02.3S03.1.5HSO,and it is known as Hauser's ealt since the publicatious by 0. Hauser of studies of the compound (12). But a disulfatozirconic acid solution which will deposit Hauser's salt loses this capacity if heated to 64T, held a t this temperature for a time, and allowed to cool to room temperature. In general, the hydrolysis of disulfatozirconic acid solutions is sensitive to the thermal history, the concentration, and the presence of foreign ions (notably chloride and bromide ions). Typical hydrolysis products have compositions and chemical behaviors that are explainahle on the following types of molecular structure:
Chauvenet: Addition of potassium sulfate to disulfatosirconic acid solution (9-11)
room temperature or higher temperatures, with formation of alkoxides or amides. These processes are often promoted by the presence of a base that will combine with the liberated HC1: Leuchs: Sulfuric acid sdded to dilute zirconyl chloride solution (9-11).
Glazebrook, et nl.: Disulfatozirconic acid plus hydrachlario acid brought to pH 1.5 (9-11).
These three structures depict zirconium species which are respectively anionic, neutral, and cationic. Because of the long chain structure, crystallization of the basic sulfates is difficult and the solid compositions are often recovered as amorphous substances. Phase studies by Hauser, Falinski, and d'Ans and Eick have made E good start toward delineating the system ZrOrS03-H20, but little has beeu done in the area of structural studies of the various phases that have beeu found. A great deal of chemistry remains to be learned from comprehensive study of this system. Zirconium in Organic Chemistry
Currently, a great deal of work is being reported on zirconium compounds with organic radicals and on the catalytic effects of zirconium compounds in organic reactions. Certainly much of the industrial interest in zirconium chemistry in the years immediately ahead will center on o r g a ~ reactions c involving zirconium. In the most restricted sense of the word, there are no organozirconium compounds, since zirconium has never been observed to form a stable sigma-bond with carbon. There are no zirconium analogues to the alkyls and aryls of silicon, mercury, arsenic, lead, tin, magnesium, etc.; but there are numerous compounds known in which zirconium is linked through oxygen or nitrogen to organic groups, and there are also the compounds of the so-called "sandwich" type, in which zirconium is bonded to rings of cyclopentadiene, indene or fluorene through delocalized electrons. Zirconium tetrachloride is the compound most commonly used as the starting material for the preparing of zirconium derivatives of organic compounds. The tetrachloride readily forms coord'mate bonds with oxygen or nitrogen atoms in organic molecules. Thus, with ethers ZrCL.2C2H60C2Hs and with amines: ZrCL.2(C2H5),N. If the oxygen or nitrogen atoms are bonded to hydrogen, as in alcohols, ketones (en01form), and primary and secondary amines, HCl is evolved a t
I n the case of the zirconium alkoxides, zirconium tends strongly to high coordination numbers by polymerization and by solvation with the parent alcohol. The alkoxides are reactive chemical substances. They promptly hydrolyze in the presence of water, forming hydrous zirconia and alcohol. They react with fatty acids to form alkoxyzirronium carboxylates. The alkoxides have been shown to be of value in the curing of silicone plastic films, and as additives to other types of plastics. Their use as catalysts and as waterrepellent agents have been described. The alkoxyzirconium carboxylates are also said to be useful in the water-repellent treatment of textiles and other fibrous materials. No uses for zirconium amides have been established. Zirconium tetrachloride reacts with fatty acids to form tetrmcylates. I t is difficult to disengage all traces of hydrogen chloride from the reaction product. Aqueous zirconyl and basic zirconyl chlorides react with alkali soaps to form zirconium soaps, generally containing one zirconium atom per fatty acid radical. These zirconium acylates or soaps are soluble in nonpolar solvents, and can be used to increase the viscosity of oils and to form greases. Such products have been examined as lubricants and die release agents, but have no industrial market a t present. Reference has already been made to the waterinsoluble complex acids formed by the reaction in aqueous medium of zirconyl chloride with alphahydroxycarboxylic acids ( I S ) . These acids are alkalisoluble, and the neutral or slightly alkaline solutions formed by their dissolution in aqueous alkali have been used extensively in body deodorants. During the past decade, the metallocenes have hecome subjects of much academic as well as industrial research. They constitute a class of metallic derivatives of cyclopentadieue and other compounds containing the cyclopentadiene ring. The metal atom is sandwiched between two five-membered rings in which there is a resonating system of electrons. The metallocenes are more or less aromatic in their properties, and this has given rise to their name (benzene--toluene--xylene--metallocene). Ferrocene is relatively highly aromatic in its chemical behavior, and zircocene shows a minimum of aromatic properties (14). Among the metallocenes, zircocene is unique in being colorless. Studies of the metallocenes in general, and zirocene among them, have been directed largely toward structure studies and toward applications as anti-knock Volume 39, Number 12, December 1962
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additives to motor fuels, components of plastics, and catalysts, particularly for hydrocarbon condensations. Zirconium Compounds in Catalysis
Zirconium compounds have been found to have value in a large number of catalytic applications. Although the element and its compounds are not oxidation-reduction catalysts, they exhibit spectacular ability to promote the effectiveness of other substances which are oxidation-reduction catalysts. Zirconium soaps greatly enhance the effectiveness of cobalt or manganese paint driers and of nickel hydrogenation catalysts. Zirconium dioxide is a powerful catalyst for vapor phase esterification and is an active component of petroleum-cracking catalysts. The behavior of zirconium tetrachloride as a FriedelLCrafts catalyst has already been discussed in this paper; in general, zirconium halogenides behave as Lewis acids and serve in all the capacities of Lewis acids in catalysis. Outstanding results have been obtained in the fluorination of chlorine-containing hydrocarbons to produce specific fluorocarbons in good yield and satisfactory purity. A vast literature on zirconium compounds in catalysis includes applications to Fischer-Tropsch synthesis, hydrogen cyanide synthesis, hydration and dehydration of hydrocarbon chains, hydrolysis of chlorohenzene to phenol, polymerization, pyrolysis, and isomerization (15). Conclusion
The vast number of ramifications of zirconium chemistry, their elucidation and exploitation are mentioned in some fifteen hundred abstracts each year in Chemical Abslracts. Although only the surface of the
science and technology of zirconium chemistry has been penetrated, enough of valid interest has been uncovered to sustain the efforts of academic and industrial investigators in numerous laboratories the world over. I t seems likely that the present decade will yield a t least twenty thousand reports containing scientific and technological data on some aspect of zirconium and its compounds, with far-reaching effects in science and industry. Literature Cited ( 1 ) MELLOR,J . W . , "A Comprehensive Treatise on Inorganic and Theoretical Chemistry," The Macmillan Co., New York, 1930, Vol. 7 , pp. 9&9. A. W., CARMODY, W. R., $2) KROLL,W . J., SCHLECHTEN, YERKES,L. .4., HOLMES,H. P., AND GILBERT,H. L., T ~ a n sElecl~ochem. . Soc., 92,99-113 (1947). ;3) BLUMENTHAL, W. B., Znd. Eny. Chem.,46,530(1954). A., A N D VAUGHAN, P. A,, Acla C ~ y s t . ,9, ( 4 ) CLEARFIELD, 555-8 (1956). (5) MUHA,G. >I., AND VAUGHAX, P. A., J.Chem. Phys., 33, 1 9 4 4 (1960). (6) N ~ s m ~ v ~B.r I., s ,Z h w . A'eorg. Khim.,6,11504(1961). W . B., Znd. Eng. Chem.,40,510-2(1948). ( 7 ) BLUMENTHAL, ( 8 ) BLUMENTHAL, W . B., "The Chemical Behavior of Zirconium," 11. Van Nostrmd Co., Princeton, 1958, pp. .. 13544. ( 9 ) D ' A N ~ , J . , ASU EICR,H., Z. Elektrochem.,55.19-28(1951). . 4nn.ehim.. 16.237-32511941). ( 1 0 ) FALIN~KI. ,M . , B ~ M E N T H A L , W. B., Chemicsl Behavior of Zirconium," pp. 1 3 W 4 . HIUSER, O., A N D HERZFELD, H., Z. anmg. allgem. Chem., 67,369-75 (1910). OESPER,R. E., AND KLIKGENRERG, J. J., Anal. Chem., 2 1 , 1509-11 (1949). WILKINSOK, G., ET AL., J . .4m. Chem. Soe., 74, 2125-6 (1952); 75,1011 (1953). JOSEPH. P. T.. "Zirc~nium Comuounds Catalvsts and . Pr&oters," The Titanium Alloy Mfg. Div. of "the Nat. L a d Co., 1960,33 pp.
Technical Report on Sorption and Vacuum Technique Available The Institute of Science and Technology of the University of Mirhigan has prepared Teehnieal Report Number 661W-2-X on "Adsorption and Vacuum Technique" by Paul A. Faeth. A limited number of copies of this report are available gratis to teachers and technicnllibrariantna. A volumetric sdsorntion s ~ ~ a r a t and u s s sravimetric one are described. The discussion of -*,he vnh~rnet,rirmethod includes n detailed deserintion of the comtructirm and calibration of the ~
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Ken and krypton, and of calculating true density, are presented step hy step. The measurement of pore volumedistribution is also discussed. The gravimetria technique uses a qusrta beam microbalmre. The construction, manipulation, and calibration of the b&mce are described, dong with procedures and ca,lcleulations for typical measurements based on mass increases. These teehnioues include the measurement of som-
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Journol of Chemical Education
