Reactive Metals Zirconium, H a f n i u m , a n d Tifaniurn
I
DONALD R. SPlNK The Carborundum Metals Co., Akron, N. Y.
Similar in chemical and physical properties these Group IVA metals
fill present specialty gaps and are counted on heavily for future use in severe services
ZTRCOSIUM,
HAFNUM, and titanium are sister metals in the Group IVA elements of the periodic table. As such, all three of these metals are chemically similar and possess similar physical properties. All a r e characterized by high melting points and all have high degrees of reactivity which result in the formation of extremely stable compounds such as oxides, nitrides, borides, and silicates. All three of these metals generally occur together in nature. Titanium is found as rutile or ilmenite, whereas zirconium and hafnium are usually found in zircon deposits. Ilmenite and rutile may be completely separated from zircon by physical means; however, separation of hafnium from zirconium in the zircon is a difficult chemical process. I n fact, properties of the two elements are so similar that the presence of hafnium in zirconium was not recognized for over a hundred years after zirconium had been isolated. Production of zirconium, hafnium, and titanium metals in commercial quantities has been greatly accelerated by the use of these metals in various defense efforts. Virtually all the zirconium and hafnium produced to date has been for the S a v a l Reactor Program. Consequently, although this program provided the incentive for preparing these new reactive metals, it has effectively restricted their availability. Titanium, produced on a large scale for high speed aircraft, became generally available a t a n earlier date, and a much more intensive effort has been applied to the development of its commercial applications than those of the other metals. Whereas both zirconium and titanium are now available in a complete line of mill products, hafnium has been restricted
Heat exchanger made by Pfaudler Permutit is a 130-square-foot unit for use in Exchanger contains 64 zirconium 70% hydrogen peroxide a t 70" to 80" C. tubes, 1 inch b y 0.049 inch wall, that are welded into a zirconium tube sheet. Shell side of the exchanger contains low pressure steam a t 240" F. Unit replaced a tantalum exchanger of similar size at a capital savings in excess of $ 1 0,000
Typical hairpin-shaped bar of hafnium as produced in the iodide crystal-bar process b y Foote Mineral Co.
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4 Titanium tube bundles are used in SUIfuric acid-slurry heaters a t Freeport Nickels' nickel-cobalt ore-concentrating plant. Heaters, manufactured b y Struthers-Wells use titanium tubing, inch in outside diameter, and titanium-lined heads. The tubes and heads handle 10 to 20y0 sulfuric acid at 400" F. a t 600 p.s.i. pressure. Slurry contains32 to 35% solids in the leaching section. Roughly 100,000 pounds of titanium have been used at this facility, including miles of pipe
COLRTESY TITANIUM METALS CORP.
A One of a number of zirconium trays being used in a large sieve-plate column. Column and trays are being exposed to 3 0 to 50'7, sulfuric acid at 100" to 1 4 0 " F. Trays, 9 feet in diameter, were fabricated from '/winch hot-rolled zirconium sheet b y Vulcan Manufacturing Co. Installation was used to replace a packed column and reduce pressure drop across the column, while increasing throughput threefold. Acceptable plastic trays would have to b e several inches thick
A Titanium fabricated piping assembly in 4-inch. Schedule 10 welded detail has replaced Type 3 0 4 L stainless in service in 65y0 nitric acid vapors a t 21 0" C. at 3 5 0 p.s.i. pressure. Titanium has proved to last approximately 4.3 times longer than Type 3 0 4 L stainless
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A Typical cathode of hafnium produced b y the fused-salt electro-refining process
INDUSTRIAL AND ENGINEERING CHEMISTRY
LESS COMMON E L E M E N T S
COURTESY DU PONT
A Titanium has replaced lead-covered copper coils a t an appreciable saving to National Lead, who use 25 to 30% sulfuric acid in production of paint pigments. Acid, along with other metal sulfates, i s heated to 380°F. b y steam coils. Titanium replaced silver a t a 35y0saving in cost in a similar application at Du Pont.
COURTESY DU P O N T
A At one Du Pont plant titanium fabricated gate valves have been installed in different locations involving hot sodium hypochlorite, 6OY0 nitric acid, plus organic acid a t 260" F., and hot, polluted r a w river water. Previous materials included Type 3 16 and 304 stainless, and Durimet 20. Titanium has improved all service periods
in its application to use as a control-rod material in nuclear reactors because of its scarcity and high price. T h e inclusion of titanium and zirconium on the list of the less common metals can no longer be justified, Both are produced in tonnage quantities and current productive capacities exceed the predicted utilization for the next five years. I n addition, both of these metals can be worked on conventional mill equipment. As a result, both titanium and zirconium are available in a \vide range of mill products including ingot, billet, sheet. plate, strip, bar, rod, pipe, and tube. Both of these metals are also available in cast form. The cost of producing zirconium and titanium has fallen sharply during their short lives. This fact has opened u p many uses in which these metals a r e competitive with some of the more generally recognized materials of construction employed by the chemical industry. T h e most valuable single property of these metals to the chemical industry is their general inertness to a wide variety of corrosive agents. This inertness is the result of the formation of a tight, stable oxide film that protects the reactive metal from vastly different chemical exposures over \vide temperature ranges. I n chemical applications, titanium and zirconium are complimentary and someLvhat noncompetitive with each other; where one metal may fail, the other is almost certain to be recommended. I n general, zirconium is more applicable in extreme exposure conditions from the strong, hot, inorganic acids such as boiling 20% HCI or 6076 H2S04 to molten alkalies. \$'here zirconium is not recommended, such as in hot copper and iron chloride solutions, aqua regia, and wet chloride, titanium has proved to be remarkably successful. \%h' ere either metal serves \veil> such as in dilute sulfuric acid solutions, titanium is the normal choice because its cost per pound is somelvhat lolver than zirconium. Density of titanium is approximately two thirds that of zirconium, and therefore, titanium tvould also be recommended where either metal could be used. Very little up-to-date information has been accumulated on the resistance-tocorrosion of hafnium in various chemical agents. What little information we do have indicates that hafnium is superior to zirconium. For example, in pressurized water reactors, unalloyed hafnium exhibits a corrosion rate approximately one third that of the most satisfactory zirconium alloys. -4s hafnium supplies become more generally available, corrosion data for many severe conditions will be obtained. Methods of production, fabrication, analysis, or the physical and mechanical properties of these metals are not the concern of this paper. Such data is
now available from the prime producers or converters of the respective metals being covered here. However, as specific applications of these metals in the chemical industq- are revie\+.ed, conversion techniques will be apparent in many cases. Perhaps the most important thought prefacing a discussion of these applications is that each has weathered the stern test of comparative economics. Furthermore. often five or more \ears of preliminary corrosion testing habe preceded each application, during which time vast improvem.ents in metal quality and convertibility have been made. It is truly hard to appreciate the significant advances that have been made in reactive metals within the past ten years. I t has been within this period that the consumable electrode, cold-mold arcmelting technique was developed. Before this development, titanium and zirconium were available only as induction-melted products and contained several tenths of one per cent of carbon from the graphite crucibles used to hold the melt. The physical, mechanical, and corrosion resistance properties of inductionmelted zirconium (or titanium) are so vastly different from those of the coldmold arc-melted metals that early users refused to believe that the metals could actually be so nearly identical and yet have such different properties.
Titanium
In the case of titanium, much of the stress over the past few years has been placed on the development of highstrength alloys for aircraft and missile application. During this period, as in the case of zirconium, titanium quality was continually improving.
Titanium is most useful in equipment that handles
b Dilute sulfuric acid with oxidizing agents present b Hot concentrated nitric acid-35-65% above a bout 200" F.
b
Sodium or calcium hypochlorites, metal chlorides, and organic chlorides
b b b b
Wet chlorine gas Chlorine dioxide Urea Polluted sea water
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Titanium is a reactive metal with a characteristic tight, stable, oxide cost that protects the metal from corrosion by most oxidizing agents. Corrosion of titanium is thus retarded. rather than accelerated by oxygen. There are many less expensive materials that adequately resist most oxidizing solutions, but there are exceptions, and in these, titanium has established a firm hold on the market. Titanium shell and tube heat eschangers for nitric acid service have become fairly common in the chemical industrv and arescattered inmanydifferent plants. Titanium is used in hypochlorite solutions of many types. Wyandotte Chemical Corp. uses a hypochlorite cooler with titanium tubing and tube sheets that contains 48 tubes, 1 inch in outside diameter by 16 feet (approximately 200 square feet of cooling surface). The tube side is exposed to 2070 caustic containing a maximum of 150 grams per liter of chlorine a t 70" to 76" F. iVater at 50" to 55' F., and 75 p s i . pressure is on the shell side. T h e tube sheet is faced with 4-inch titanium sheet to which the tubes are welded. The corrosion resistance of titanium in wet chlorine gas or in chlorinated brine is unique. This application area
Titanium and zirconium are easily welded in an inert atmosphere and, in fact, are more readily welded than aluminum and some of the stainless alloys. The replacement of the stainless steels with titanium is becoming rather commonplace, especially as the price of titanium is lowered.
promises to be one of the greatest for titanium. Many large titanium heat exchangers are presently being used to cool wet chlorine cell gas a t approximately 180°F. Most of the titanium used in pulp and paper equipment is in chlorine dioxide mixers, in which a '8-inch thick liner provides the corrosion resistance necessary for this highly corrosive agent. Both titanium and zirconium will find potential applications in the food-processing industry. A 250-gallon titanium cooking kettle emerged corrosion free after 4000 hours of food-preparation tests
conducted by H. J. Heinz Co. for the following foods: Vinegar for kosher dill pickles Relish blending Savory salt Ketchup, basic sauce Strained junior food Titanium is completely impervious to sea water under all conditions. but for simple sea water applications the metal will not find widespread uses for some time because cupro-nickel alloys such as Monel, and aluminum brasses are adequate and less costly. Low concentrations of HpS, however, make sea water extremely corrosive to most commonly used metals, and titanium is superior in thisenvironment. T h e use of titanium for anodizing racks has been a n almost unnoticed giant, largely because secondary or nonaircraft quality metal is most generally used. In 1959, the aluminum industry alone used 100,000 pounds of titanium for anodizing aluminum. Titanium has excellent corrosion resistance to many corrosive plating solutions and does not build up electrical insulator films on racks. .4lthough the sulfuric
COURTESY T I T A N I U M M E T A L S CORP. OF AMERICA
A Solid titanium condenser insert for the inlet end of a stainless steel nitric acid cooler used to combat corrosion of tube sheet and tubes in high temperature nitric acid service
4
Calera Mining Co., a t Garfield, Utah, and Sherrit Gordon Mines, Canada, find that sulfuric acid leaching makes titanium necessary in some of their equipment in the cobalt-nickel refining process. Titanium agitators and shafts used in oxidation autoclaves are made by Struthers-Wells
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INDUSTRIAL AND ENGINEERING CHEMISTRY
LESS C O M M O N ELEMENTS acid most commonly used for anodizing baths attacks titanium ordinarily, the anodizing protects the metal, does not build up, and conducts electricity when pressed against another conducting metal. A titanium stream jet diffuser has been used in an environment of 125-p.s.i. steam \vith 170 hydrochloric acid and entrained inorganic solids. Titanium in this service has outlasted every other material ever tried. by a factor of 12. Previous materials included cast iron stainless steels, bronzes, and Hastelloy C.
It is often desirable to develop some quick and convenient method of testing a new material directly in a commercially established process. Certain applications illustrate some of the methods that have been found to be most convenient to test zirconium within the plant without drastically affecting the process. Although these applications may not be entirely fair because of possible induced electrolytic cell effects, they can normully be employed as gross screening tests.
Zirconium Many of the properties of zirconium are similar to those of titanium, which \\auld lead to the belief that application of these metals rvould overlap to a considerable extent. Such is not the case. The most outstanding characteristic of titanium’s corrosion behavior is its ability to withstand hot multi-valent chloride environments and certain hot oxidizing solutions and gases containing free chlorine. Titanium is vastly SLIperior to zirconium in these applications. However. when the complete spectrum of
corrosive environments is considered, zirconium is found to be vastly superior to titanium, especially in hot inorganic acids. molten alkalies, and many of the more common corrosive media at high temperatures. There has been more interest in and use of zirconium in sulfuric acid than in all other applications in the chemical industry put together. Whereas titanium has found much usage in sulfuric acid,
its application is limited to more dilute concentrations than is zirconium; oxidizing conditions must also be present for the proper application of titanium. Separation of hafnium from zirconium provides one of the most difficult proving grounds for corrosion-resistant metals. Free hydrochloric acid is present in all solutions and in many of the slurries. As a consequence. much of the equipment originally specified failed after a
A Zirconium casting replacements for original Hastelloy C pump parts indicate indefinite service life on the basis of several years of experience. Parts were made by Oregon Metallurgical Co.
4 In this iet after condenser, titanium has replaced Type 304 L stainless in an environment of mixed nitriq and organic acids, and hot, brackish water. Average life of stainless wcs six months; titanium has been in continuous service for 64 months with no signs of corrosion. Previous failures were due to stress-corrosion cracking of welds COURTESY OU PONT
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4 Single-shaft, titanium-lined chlorine dioxide mixer where pulp i s bleached b y mixing i t with a '/2% chlorine dioxide solution a t 160" to 195" F. Unit was fabricated b y Improved Machinery, Inc.
A submerged, natural-gas burner of b zirconium i s used in a sulfuric acid con-
COUFTEEY TlTANlUM M E T A L S CORP. OF A M E R I C A
centration. Pfaudler-Permutit fabricated unit i s used to concentrate spent sulfuric acid to approximately 20% and i s normally exposed to higher concentrations of boiling sulfuric acid inside the unit. Burner shell i s made of 3/16-inch cold-rolled plate. The 700 pound unit has been in successful service for over a year
4 A commercially available gear Pump/ used in very severe acid services, i s made b y Eco Engineering
A Three-way, two-part zirconium valve which has been used for zirconyl chloride solutions of varying acidities along with high-pressure steam. Service life appears to b e indefinite whereas few other materials would last a month. Valve i s made b y Continental Mcnufacturing Co.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Co.
LESS COMMON E L E M E N T S few days or months. Many replacements \\ere made with zirconium a n d the following applications review some of these replacement items: a Hastelloy C plow was used to remove a cake of zirconyl chloride crystals from a n open-bottom basket centrifuge. T h e crystals were saturated with 6.t- hydrochloric acid a t 70' to 100' F. T h e plow was so severely cor1 oded after on11 31 days in service that small pieces of Hastelloy were breaking off and contaminating the pure crystal cake. A zirconium plow replacement was made and has been unaffected after more than 2 vears in the same service. T h e l', 2-inch Hastelloy shaft supporting the plow was replaced with zirconium after 6 months of service. A Hastello) C cake thickness detector used in this centrifuge corroded free of its support shaft after only 8 days in service. causing extensive damage to areas of the rubbei-covered centrifuge basket. T h e replacement of Hastelloy C parts in the centrifugal pumps used in the
zirconium plant in services ranging from hydrochloric acid, thiocyanic acid, sul[uric acid, acidified solvents, and 2070 caustic solutions was evolutionary. First, the Hastelloy C drain plugs on the casings were replaced with zirconium plugs; results led to zirconium sleeves and collars on the impeller shafts and mechanical seal parts. Finally. the pump housings and impellers \vere replaced. A s mentioned earlier, the application of any metal in the chemical process industry is predicted on the economics of the situation. T h e following two specific examples will give the reader some insight into the cost of zirconium compared to the cost of Hastelloy C. The Hastello) C unloading plow used in the basket centrifuge decrepitated after one month in service. A replacement Hastelloy C plow was quoted as costing $353. A replacement was made with zirconium a t a cost of $485 (expected selling price). T h e zirconium plow has been in service 24 months to date.
When a Broad Range of Corrosive Environments Is Considered, Zirconium Surpasses Practically All Other Metals , Especially in Hot Inorganic Acids and Molten Alkalies . Xedia Acetic acid Chromic acid Citric acid Dichloracetic acid Formic acid Hydrobromic acid Hydrochloric acid
Six-inch lined fee is used as a test piece in severely corrosive service at the Esso Standard Oil plant in Baton Rouge, La. Tee was made by Pfaudler Permutit, Inc.
4 Solid titanium shaft agitator is 1 2 feet long and 4 inches in diameter, and welded to 1 -inch thick flat-plate agitator blades. The hairpin coil is 7 feet in diameter and 6 feet high made of 2-inch pipe. Service is a slurry of hot inorganic metallic chlorides with traces of free hydrochloric acid. Titanium has proved satisfactory in this service for 2 years of continuous service; previous failures in Hastelloy C occurred in 3 to 4 months, through abrasion and corrosion
Hydrofluoric acid Lactic acid Monochloracetic acid Nitric acid Nitric acid, mixed fuming Nitric acid, red fuming Nitric acid, white fuming Oxalic acid Phosphoric acid
Concn., wt. % Acids 5-99.5 10-30 10-50 100 10-90 65 1-37 1-20 20-37 (sealed cont.) All 10-85 100 10-100 66 white 0.5-25 5-85 5-60 60-85 60-85
Sulfuric acid
10-70 10-40 80-96
Sulfurous acid Tannic acid Tartaric acid Trichloracetic acid
6
Aluminum chloride Ammonium chloride Aniline hydrochloride Barium chloride Calcium chloride Calcium hypochlorite Carhon tetrachloride Chlorine gas (dry) Chlorine gas (wet) Chlorine-satd. water Cupric chloride
25 10-50 100 Misc. Chlorides 1-30 1-satd. 5-20 5-20 10-65 5-25 50- 100
Temp, O
c.
Ita t i n go
35-100 35-100 35-100 35-100 35-100 35 35 107 107 Any 35-100 100 35-100 35 20-70 20-70 35-100 35 100 100 210 35 100 35-100 100 35-100 35-100 100
AA AA AA A-B AA C-D AA AA A D AA AA AA A AA A AA A A B-C C-D A A D A AA AA AA
35 Boil 35-100 35-100 35--100 20-100 35-100 35-100
AA AA A A AA AA AA
A 25 Rt. AA 35-60 A 35-100 C-D (Continued on next pcige)
1 >1 ~~
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4 Cruciform nuclear reactor control rods of hafnium are currently being used to control power levels on all of our nuclear submarine reactors. In addition, these neutron-absorbing control rods are being used in several of the domestic commercial power reactors
One of the most convenient methods for testing a new material in a process stream i s b y inserting a thermowell in the system. A thermowell of zirconium provides an inexpensive test piece. Zirconium tubing or pipe can also b e made into live-steam bayonet heaters, and simple heat transfer data may b e obtained a t the same time the corrosion resistance of zirconium i s being determined
Afedia Ethylene dichloride Ferric chloride Manganous chloride Mercuric chloride Nickel chloride Sodium chloride Sodium hypochlorite Stannic chloride Stannous chloride Substitute sea water Tetrachlorethane Tetrachlorethylene Trichlorethylene Alum Ammonia Ammonium hydroxide Barium hydroxide Magnesium carbonate Potassium hydroxide Sodium hydroxide
Concn., wt. %
Temp.,
50
Boiling 35-60 100 35 100 55-100 35-100 35-100 35-100 35-100 35-100 35-100 Boil Boil Boil
1-5 5-15 > 15
20
1-satd. 5-20 3-satd. 0.5
5-25 15-75 50 50 50
Alkalies To 90 30
28-40 5-50 5
10-40 10-73
c.
&-Boil 35 35-100 35-100 100 35-100 35-100
Flanged, 2-inch zirconium pipe failed in hot hydrochloric acid service because of pitting in the heat-affected zone adjacent to the welds. This particular type of corrosion was traced to minor amounts of iron and chromium in the zirconium. For such severe corrosive conditions, a special lowiron-low-chromium grade of zirconium will give excellent service. Pipe was made b y Pfaudler Permutit, Inc.
Rating" AA A C
D AA AA AA AA AA AA A AA AA AA AA
A AA
AA A A AA AA
Misc. A 99.5 Boil Acetic anhydride C-D 20-80 Concd. Aqua regia A 2 100 Bromine water A 500 Carbon dioxide AA 50 Boil Chloroform A Boil Ethyl alcohol 95 A 35 Hydrogen peroxide 10-70 250 AA Lithium D 90 Mercury A Boil Methyl alcohol 99 D 145 Silicon tetraiodide A 20 Silver nitrate 0.8 AA 500 Sodium A 190 Urea Rating in mils/yr. AA = < 1 ; A = 1-5; B = 5-10; C = 10-25; D = > 25. This type of laboratory data is not entirely conclusive. Inhibiting agents, presence of impurities, and changing environments may affect corrosion resistance. Therefore, field tests under mtual service conditions are recommended prior to developing designs where zirconium is used.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
T h e zirconium pump casings that replaced Hastelloy C casings cost $630 each compared to a cost of $450 per casing of Hastelloy C. The zirconium pumps have given three times as much service to date as Hastelloy and are expected to last indefinitely in this severe service.
Hafnium There are presently no commercial applications employing this metal other than as a control-rod material in nuclear reactors. T o make a ductile product, all hafnium being produced as sponge must be refined. This may be accomplished in several ways: the iodidecrystal-bar process, electron-beam melting, a n d a n electro-refining process conducted in a fused-salt electrolyte. T h e future of hafnium appears bright. Hafnium will never be abundant, but some of its outstanding properties should always keep it in demand. Whereas the metal melts a t 1975' C. Hafnium carbide melts just shy of 4000' C.; thus, it is one of the most refractory materials known. Hafnium nitride is the most refractory nitride known; it melts a t 3300' C. Hafnium boride and hafnium silicate are also refractory materials with interesting properties. Materials with properties such as these will find increasing demand in tomorrow's advanced materials technology. RECEIVED for review November 16 1960 ACCEPTED November 18, 1960 DiviFion of Industrial and Engineering Chemistry, 138th Meeting, ACS, September 1960.
