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A contribution to the history of ductile titanium and zirconium
JOURNAL OF THE LESS-COMMON METALS
A CONTRIBUTION DUCTILE
TO THE
TITANIUM
AND
361
HISTORY
OF
ZIRCONIUM
W. J. KlZOLL Rhode St. GenZse (Belgium) (Received
December Ist, 1964)
SUMMARY
This account the equipment
describes
the lines of thought,
developed in the author’s
laboratory
the laboratory
experiments
in Luxemburg
between
and
19~3 and
1940, which led to the present-day production method for titanium by reduction from its chloride under noble gas. The various steps taken are shown in chronological order and a few sketches, the reduction
taken
equipment.
later in zirconium
from laboratory
The repercussions
reduction
at Albany,
evolution
of titanium
on the titanium
and zirconium
subsided, the present lull appears propitious may be of historical value, as a complement some years ago’. Perusal
of my diaries
follow the lines of thought methods
that
for the extraction
present
the evolution
directed
of
work accomplished
Oregon, for the U.S. government,
based on the author’s work in Luxemburg, and on private industry, are reported.
The stormy
journals,
of the development
project
which was
at Boulder
City
in the last decade having
for the publication of this note which to a first biographical report I wrote
and laboratory
books makes it possible
my steps in the elaboration
to
of workable
of both metals in ductile form from their ores*.
On setting up my research laboratory in Luxemburg in 1923 I established a program of investigation concerning the much neglected less-common metals, as far as they could be expected
to be cold ductile and available
in their ores. This put the
elements Ti and Zr at the top of a list which comprised also: Cr, V, Th, Be, Ta, Nb and U. Titanium, of course, took first place as regards the ore basis. This vast project,
begun singlehanded
and on a shoestring
may have appeared
to the compe-
tent metallurgist of that time as a manifestation of delusions of grandeur. Yet my success as a one-man orchestra proved that my conception was right, and I lived long enough to see my dreams become a reality. From the start of my career I came up against the inertia, if not the outright opposition of plant managers, in Europe as well as in the U.S.A., and convincing them was probably the hardest part of my task. The director of a German company to which. I had granted some rights in the * The author apologizes for using the personal form in the present report: this was unavoidable for the simplification of the phrasing. J, Less-Common
Metals, 8 (1965) 361~367
W. J.KROLL
362
results of my work, wrote on May 20, x939, with regard to titanium as follows: “I am afraid that nobody would be ready today to spend 3-5 months of work and the salaries of a good engineer or technician, or D.M. 30-50,000 ($IZ,OOO-~0,000) if he was not sure of selling at least one hundred or several hundred kilograms a year.” (my translation). As for America, the story of six companies that refused to consider ductile titanium in 1938, even after inspection of a fine sample display, has been told elsewherel. There has to be a market, otherwise “bold” capital would not move. My first experiments with titanium had to be delayed until they were sparked in 1928 by an incident relating to connections I had established with a German company interested in beryllium, and, more specifically, in a copper-beryllium alloy. I looked for possible substitutes for this alloy, which is age-hardenable, and I produced a copper-titanium alloy by reaction of alkali titanium double fluoride with coppermagnesium. This ahoy proved to be age-hardenable, but I had some doubts whether this property was attributable to the titanium, or to some residual magnesium. I therefore decided to produce first a high grade titaniummetal by the classical method of TiCL/Na reduction in a bomb. The granules obtained were alloyed with copper under argon. This identified titanium as the cause of aging in the copper alloy2. Then I proceeded to establish the high copper side of the binary equilibrium diagrama, and this obliged me to do some more bomb reductions. I thus became familiar with this process and with its treacheries. Some of the larger granules were hand-forged and were shown in the U.S.A. in 1932 on the occasion of a first visit. Then my interest shifted from the titanium alloy to the production methods for the metal, and, using a suggestion from Borchers (Aachen), I electrolyzed in 1932 a mixture of TiOzj CaFz/CaCIz with a contact cathode. I observed that the oxide was practically insoluble in the electrolyte and floated on the surface and that any reduction that took place was at the cathode tip, where some calcium was deposited. Then I electrolyzed TiOs in a KzTiFs bath with a molybdenum cathode, and finally with a fused lead cathode, again without success. The rather oxidized deposit in the first case was a black powder. I observed that the bath became increasingly stiff during the run and I suspected the formation of high melting lower Ti oxides. This provoked some experiments on the stability of TiOz which I reduced at 1300°C with hydrogen dried with liquid air. Under these conditions I observed a partial reduction corresponding to a weight loss of x1.4*/~. I then made a number of calcium reductions of oxide under argon, in a fairly large piece of equipment, sometimes adding alkaline earth chlorides as a flux, and resorting also to calcium hydride for a second reduction of the powder obtained. The metal after leaching, pressing and sintering i+z vacz+o proved to be hot malleable but coId brittle. From rg35 to 1937 I was diverted from titanium experiments by a task which was quite difficult, the production of getter grade barium, and the filling of fine nickel tubes with this metal. I produced it by aluminium reduction of its oxide in a high vacuum, which made me well acquainted with vacuum technology and gettering of noble gases. I also produced distilled calcium in kilogram quantities, which I used for reduction of the oxides of Cr, V, Th and the like under argon4, thus confirming the ductility of these metals. In 1937 I again tried to reduce carefully vacuum-dried KzTiFs with sodium under argon, but in vain. The salt proved to be incurably contaminated with oxide. Then, the same year, I received a sample of a black titanium sponge from the German company Degussa in Frankfurt; this was sold mainly to Japan for the production of magnet J. &wCommon
Met&.
8 (1~65) 361-367
HISTORY OF DUCTILE TITANIUM
AND ZIRCONIUM
363
steels. I did not know that this sponge was obtained by reduction of TiCL with sodium under hydrogen, with NaCl added as flux. As the patent specifications showed late+, the operating conditions were so unclean that oxide-free sponge could not be expected. Purification of sodium to free it of its oxide content was unknown at that time, but with slight modifications this process could nevertheless have yielded a quite acceptable grade of metal. On June 17, 1937, having recognized that TiOz could not be used as a raw material for the reduction, even with distilled calcium under noble gas, I reduced TIC14 with pure calcium turnings under gettered argon in a high frequency furnace. The chloride was dripped on the hot reducing agent. Later I used calcium lumps and the temperature rose in some cases to, or above, the melting point of the reactant (850” C). After that I reduced intentionally at temperatures at which the calcium was fused. The sponge obtained, after leaching with HCI and vacuum sintering, was ductile as cold. On July 30, x937, I made the decisive step of switching from costly calcium to magnesium. What followed was only the logical development. At times the temperature and the iron crucible alloyed with the sponge. A molybdenum sheet lining removed this problem. External heat was applied with larger
__.-TiCI.,
letter
Co chtps _TiC
‘4
-CO
Cl?iPS
_TiC
TICI,
Thermbcouple (a)
Thermbcouple (b)
Thern’kouple
Thermocouple
(Cf
Fig. I. Evolution
(d)
of the reduction equipment. J. Lsss-Common Mel&,
8 (~$5)
361-367
W. J. KROLL
364
size reactors made of stainless steel. The output rose from a few dozen grams to about one kilogram, and the best hardness obtained was 180 Brinell. The concept of reducing with magnesium under gettered argon of substantially atmospheric pressure was maintained as well as dripping of TiCL onto the fused reagent. The early difficulties with leaching of the sponge have been describedi, as well as the use of Von Bolton’s arc melting button furnacei, which I adapted to my purposes by making it all metal. Almost all the present alloys were superficially studied. All that remained to be done was to increase the size of my operations. Industrialization added very little to my small laboratory set up. At that time I had an advance of more than ten years over any titanium research in the world. The successive reactor constructions are shown in Fig. I. The zirconium reductions I made simultaneously were derived in principle from the method I used for titanium, with special regard to the different physical properties of the chloride, which is solid at room temperature. I immediately recognized that the chloride could not be mixed with the reducing agentr, but had to be reacted under control in the gas form. Any iron chloride contained was first reduced to the less volatile divalent form by distillation in hydrogen. These adaptations were put into operation in July 1938 (see Fig. 2). The heating of the vaporizer for ZrClJ
umps
Therm’ocouple
Fig. 2. Purification-reduction
of ZrClr.
was achieved by shifting the induction coil. In later experiments the reduction product was turned out on a lathe and vacuum distilled to separate the M&12. This is the basic knowledge I transmitted in 1945 to the U.S. Bureau of Mines. It permitted rapid advance of the Government project and is still embodied in the procedures used today. The 43 years between 1940-1945, which I spent at the Union Carbide Research Laboratories in Niagara Falls contributed to some extent to enriching my knowledge about Ti and Zr. In a process6 developed for rapid production of ZrClr from low grade (32%) Zr/Si by its reaction with FeClz under noble gas or hydrogen, and dissolution of the gaseous chloride obtained in fused KCl/NaCl which form a complex, purificaJ. Less-Common
Metals. 8 (1965) 361-367
HISTORY
OF DUCTILE
TITANIUM
AND ZIRCONIUM
365
tion was observed with respect to Fe, Al and Ti which make stabler compounds than does Zr. By reevaporation, the dissolved ZrCld could be recovered in the pure state. This could be achieved by using higher temperatures andior a vacuum, or by oversaturating the salt solvent. This method is used today in the purification of HfC14 and ZrC14 when very pure sponge is required. Oxides, of course, are also retained (mechanically) in the carrier salt. Then I refined various metals and alloys by anodic dissolution and electrolysis in a fused chloride bath?, paying special attention to the refining of iron and ferro-alloys such as ferro-manganese and ferro-chromium, as well as to the chemical equilibria that form between the solid cathode deposit and the bath. In the case of the iron electrolysis C, S and Si were eliminated. This method I used in 1947 at the Bureau of Mines in Albany, Oreg., in attempting to plate smooth layers of Zr on a metallic cathode under argon, as described later in an investigation report8. Dr. K. S. Dean, the then assistant Director of the Bureau of Mines used this process later on a semi-industrial scale to refine titanium. The background of knowledge I passed on to the Y.S. Bureau of Mines in early 1935,when I started working with this organization, was then as follows : reduction of TIC14 under clean argon with magnesium in a reactor, heated from the outside, followed by crushing and leaching of the sponge chips with HCl and either sintering the pressed powder in vacua, or arc melting the briquettes in vacua or under controlled argon pressure with a d.c. current, and using a thoriated tungsten tip; reduction of Hz-purified vaporized ZrC14 under similar conditions under argon, and separating the salts from the sponge by vacuum distillation. On the side of the Government there existed some knowledge of the use of my process in a reactor of a few dozen pounds of Ti sponge per batch. The salts were tapped, a procedure feasible only with larger batches; the sponge was turned out on a lathe in a low humidity room and the chips were leached with HCl in a refrigerated vat, then dried, crushed, pressed and vacuum sintered. By early 1944 the Government titanium project had bogged down because the vacuum sintering did not eliminate salt inclusions sufficiently, and plates of about one inch thick burst at the center when hot rolled. _4rc melting, initiated at my instigation by Albany and later followed up by private industry, saved the day. It removed all residual salts. I had adopted this in Albany in preference to leaching because of explosions that occurred when zirconium sponge was ground under water. Vacuum separation of the salts from the Zr sponge, followed by arc melting was the procedure we then followed. There was, however, an interruption in the development of this procedure. VVhen it became necessary to produce arc melted ingots instead of buttons I hesitated to use a water-cooled copper sleeve to contain the metal, because of the great risk of explosions I foresaw; events proved me to be right. I then discovered, that Zr picked up no more than about o.30ib carbon when fused in graphite, which impurity impaired malleability only a little. Consequently, we developed a split-tube low-voltage graphite resistor furnace9 which, built in a vacuum, permitted production of cast ingots of about 20 lb. This graphite melting of Zr had to be abandoned later because the C-contaminated metal corroded in hot water under pressure. Arc melting took over. In the meantime, the pilot reactor of 50 lb. sponge (later increased to 75 lb.) was put in operation and on April 24, 1947, 5 batches had been produced. On June 30 of the same year I left a copy of a paper’” on the hafnium separation from Zr in the hands of the chief metallurgist of the Bureau in Washington. It described the thiocpanate process of Fischer-Chalybaeus, in sulphuric acid solution with ether
366
W. j.KROLL
as a solvent, It is the great merit of the chemists of the U.S.-A.E.C. to have modified this method so that it could more easily be operated. There was no other use for Zr but in the atom pile, and hafnium separation and purity are an essential requirement in this application. At this point it is necessary to go back in history and to show the transfer of ideas, as worked out in Albany or by other people in the field. The vacuum separation of the M&l2 from the sponge was a great advance in Ti and Zr production. A report on this was submitted at the Boston meeting of the American Electrochemical Society on October 16, 194711, Private industry immediately took advantage of this method which did away with leaching, its oxide pickup and its hydrogen poisoning of the sponge. Some of the users of this procedure, however, made serious mistakes because they wanted to improve it. In one construction a central funnel was arranged in the batch, the latter consisting of turnings obtained in a dry room, thus cutting down on the sections through which the gases might escape. The large periphery should have been used as gas outlet. Furthermore, the same construction allowed the condensation of the MgClz upwards. Not only did this entail the possibility of some condensate dropping back in the distilled charge when opening the retort, and spoiling or burning up the batch, but there was also some refluxing of the gaseous MgClz which resulted in an extended distillation cycle. Another user of vacuum distillation put his very long reactor on two refractory pillars with the results, that the shell, heated externally with gas, folded by creeping so that after a while the deformed boat used in the reduction no longer fitted the distillation retort. Another failure was that of a company which tried to combine reduction and vacuum separation to speed up the cycle. The difficulties encountered in the elimination of leaks in the hot equipment, and the slow reduction-by creep-of the diameter of the vessel, exposed to the heat while evacuated, made this procedure impossible. The vacuum separation is in use in Japan, with batches of up to 13 tons of sponge (see Fig. 3). It is probably more expensive than leaching but the sponge obtained is of unsurpassed quality, giving arc melted buttons of less than IOO Brine11 over most of the batch, a higher yield, low hydrogen and MgCL content, and much less spattering on ingot making. The fact that MgCle escapes in. uacuo from the center of a sponge cake 4 ft. in diameter is amazing, especially when considering the raw sponge, whose very fine cavities are filled with chloride. I objected when starting this project to using the Pidgeon retort as a model, with its atmospheric pressure on the hot walls, which would have imposed a small diameter and thus made large batches impossible. External heating of the retort end in an electric vacuum furnace indeed proved to be a very successful idea. The industrial development of the Zr process from z lb. to 75 lb. batches took, with only three men on the project, little more than two years. This comprised the carbide production, chlorination, &-Cl4 purification, reduction and vacuum distillation. The titanium project, which skipped the ore to raw chloride phase, took twice as long. My able collaborators and the open-minded chief of the station, to whom credit has been givenl, made such success possible. Yet zirconium is far more difficult to produce than titanium, and stringent specifications of the atom energy for the purity of this metal impede the engineer. The methods developed in Albany spread to various other branches of technology and the use of a vacuum on a big scale in pyrometallurgical procedures, 1. Less-Common Met&, 8 (1965) 361-367
r Crude
TiCt,
Ti
spcmge cake
Ti sponge Fig.
3. Practical
flowsheet
for
WAC
for producing
titanium
sponge.
KROLL, A. W. SCHLECHTEN AND 1..A. YERKES, Tvans. Electrochem. Sm., 89 (1946) 317. JO W. FISCHER, 1%'.CHALYBAEUS AND M. ZUMBUSCH, Z. Anorg. Chem., ,255 (x948) 277. II W. J. KI‘;KOLL, A. W. SCHLECRTEN, W. I<.CARMODY, I-.A. YERKES, H. P. HOLMES AND H. I-. tfH,RE:RT,Trans. Ekctrockenz. .%c., qz (I$+?) t)g.
A CONTRIBUTION DUCTILE
TO THE
TITANIUM
AND
361
HISTORY
OF
ZIRCONIUM
W. J. KlZOLL Rhode St. GenZse (Belgium) (Received
December Ist, 1964)
SUMMARY
This account the equipment
describes
the lines of thought,
developed in the author’s
laboratory
the laboratory
experiments
in Luxemburg
between
and
19~3 and
1940, which led to the present-day production method for titanium by reduction from its chloride under noble gas. The various steps taken are shown in chronological order and a few sketches, the reduction
taken
equipment.
later in zirconium
from laboratory
The repercussions
reduction
at Albany,
evolution
of titanium
on the titanium
and zirconium
subsided, the present lull appears propitious may be of historical value, as a complement some years ago’. Perusal
of my diaries
follow the lines of thought methods
that
for the extraction
present
the evolution
directed
of
work accomplished
Oregon, for the U.S. government,
based on the author’s work in Luxemburg, and on private industry, are reported.
The stormy
journals,
of the development
project
which was
at Boulder
City
in the last decade having
for the publication of this note which to a first biographical report I wrote
and laboratory
books makes it possible
my steps in the elaboration
to
of workable
of both metals in ductile form from their ores*.
On setting up my research laboratory in Luxemburg in 1923 I established a program of investigation concerning the much neglected less-common metals, as far as they could be expected
to be cold ductile and available
in their ores. This put the
elements Ti and Zr at the top of a list which comprised also: Cr, V, Th, Be, Ta, Nb and U. Titanium, of course, took first place as regards the ore basis. This vast project,
begun singlehanded
and on a shoestring
may have appeared
to the compe-
tent metallurgist of that time as a manifestation of delusions of grandeur. Yet my success as a one-man orchestra proved that my conception was right, and I lived long enough to see my dreams become a reality. From the start of my career I came up against the inertia, if not the outright opposition of plant managers, in Europe as well as in the U.S.A., and convincing them was probably the hardest part of my task. The director of a German company to which. I had granted some rights in the * The author apologizes for using the personal form in the present report: this was unavoidable for the simplification of the phrasing. J, Less-Common
Metals, 8 (1965) 361~367
W. J.KROLL
362
results of my work, wrote on May 20, x939, with regard to titanium as follows: “I am afraid that nobody would be ready today to spend 3-5 months of work and the salaries of a good engineer or technician, or D.M. 30-50,000 ($IZ,OOO-~0,000) if he was not sure of selling at least one hundred or several hundred kilograms a year.” (my translation). As for America, the story of six companies that refused to consider ductile titanium in 1938, even after inspection of a fine sample display, has been told elsewherel. There has to be a market, otherwise “bold” capital would not move. My first experiments with titanium had to be delayed until they were sparked in 1928 by an incident relating to connections I had established with a German company interested in beryllium, and, more specifically, in a copper-beryllium alloy. I looked for possible substitutes for this alloy, which is age-hardenable, and I produced a copper-titanium alloy by reaction of alkali titanium double fluoride with coppermagnesium. This ahoy proved to be age-hardenable, but I had some doubts whether this property was attributable to the titanium, or to some residual magnesium. I therefore decided to produce first a high grade titaniummetal by the classical method of TiCL/Na reduction in a bomb. The granules obtained were alloyed with copper under argon. This identified titanium as the cause of aging in the copper alloy2. Then I proceeded to establish the high copper side of the binary equilibrium diagrama, and this obliged me to do some more bomb reductions. I thus became familiar with this process and with its treacheries. Some of the larger granules were hand-forged and were shown in the U.S.A. in 1932 on the occasion of a first visit. Then my interest shifted from the titanium alloy to the production methods for the metal, and, using a suggestion from Borchers (Aachen), I electrolyzed in 1932 a mixture of TiOzj CaFz/CaCIz with a contact cathode. I observed that the oxide was practically insoluble in the electrolyte and floated on the surface and that any reduction that took place was at the cathode tip, where some calcium was deposited. Then I electrolyzed TiOs in a KzTiFs bath with a molybdenum cathode, and finally with a fused lead cathode, again without success. The rather oxidized deposit in the first case was a black powder. I observed that the bath became increasingly stiff during the run and I suspected the formation of high melting lower Ti oxides. This provoked some experiments on the stability of TiOz which I reduced at 1300°C with hydrogen dried with liquid air. Under these conditions I observed a partial reduction corresponding to a weight loss of x1.4*/~. I then made a number of calcium reductions of oxide under argon, in a fairly large piece of equipment, sometimes adding alkaline earth chlorides as a flux, and resorting also to calcium hydride for a second reduction of the powder obtained. The metal after leaching, pressing and sintering i+z vacz+o proved to be hot malleable but coId brittle. From rg35 to 1937 I was diverted from titanium experiments by a task which was quite difficult, the production of getter grade barium, and the filling of fine nickel tubes with this metal. I produced it by aluminium reduction of its oxide in a high vacuum, which made me well acquainted with vacuum technology and gettering of noble gases. I also produced distilled calcium in kilogram quantities, which I used for reduction of the oxides of Cr, V, Th and the like under argon4, thus confirming the ductility of these metals. In 1937 I again tried to reduce carefully vacuum-dried KzTiFs with sodium under argon, but in vain. The salt proved to be incurably contaminated with oxide. Then, the same year, I received a sample of a black titanium sponge from the German company Degussa in Frankfurt; this was sold mainly to Japan for the production of magnet J. &wCommon
Met&.
8 (1~65) 361-367
HISTORY OF DUCTILE TITANIUM
AND ZIRCONIUM
363
steels. I did not know that this sponge was obtained by reduction of TiCL with sodium under hydrogen, with NaCl added as flux. As the patent specifications showed late+, the operating conditions were so unclean that oxide-free sponge could not be expected. Purification of sodium to free it of its oxide content was unknown at that time, but with slight modifications this process could nevertheless have yielded a quite acceptable grade of metal. On June 17, 1937, having recognized that TiOz could not be used as a raw material for the reduction, even with distilled calcium under noble gas, I reduced TIC14 with pure calcium turnings under gettered argon in a high frequency furnace. The chloride was dripped on the hot reducing agent. Later I used calcium lumps and the temperature rose in some cases to, or above, the melting point of the reactant (850” C). After that I reduced intentionally at temperatures at which the calcium was fused. The sponge obtained, after leaching with HCI and vacuum sintering, was ductile as cold. On July 30, x937, I made the decisive step of switching from costly calcium to magnesium. What followed was only the logical development. At times the temperature and the iron crucible alloyed with the sponge. A molybdenum sheet lining removed this problem. External heat was applied with larger
__.-TiCI.,
letter
Co chtps _TiC
‘4
-CO
Cl?iPS
_TiC
TICI,
Thermbcouple (a)
Thermbcouple (b)
Thern’kouple
Thermocouple
(Cf
Fig. I. Evolution
(d)
of the reduction equipment. J. Lsss-Common Mel&,
8 (~$5)
361-367
W. J. KROLL
364
size reactors made of stainless steel. The output rose from a few dozen grams to about one kilogram, and the best hardness obtained was 180 Brinell. The concept of reducing with magnesium under gettered argon of substantially atmospheric pressure was maintained as well as dripping of TiCL onto the fused reagent. The early difficulties with leaching of the sponge have been describedi, as well as the use of Von Bolton’s arc melting button furnacei, which I adapted to my purposes by making it all metal. Almost all the present alloys were superficially studied. All that remained to be done was to increase the size of my operations. Industrialization added very little to my small laboratory set up. At that time I had an advance of more than ten years over any titanium research in the world. The successive reactor constructions are shown in Fig. I. The zirconium reductions I made simultaneously were derived in principle from the method I used for titanium, with special regard to the different physical properties of the chloride, which is solid at room temperature. I immediately recognized that the chloride could not be mixed with the reducing agentr, but had to be reacted under control in the gas form. Any iron chloride contained was first reduced to the less volatile divalent form by distillation in hydrogen. These adaptations were put into operation in July 1938 (see Fig. 2). The heating of the vaporizer for ZrClJ
umps
Therm’ocouple
Fig. 2. Purification-reduction
of ZrClr.
was achieved by shifting the induction coil. In later experiments the reduction product was turned out on a lathe and vacuum distilled to separate the M&12. This is the basic knowledge I transmitted in 1945 to the U.S. Bureau of Mines. It permitted rapid advance of the Government project and is still embodied in the procedures used today. The 43 years between 1940-1945, which I spent at the Union Carbide Research Laboratories in Niagara Falls contributed to some extent to enriching my knowledge about Ti and Zr. In a process6 developed for rapid production of ZrClr from low grade (32%) Zr/Si by its reaction with FeClz under noble gas or hydrogen, and dissolution of the gaseous chloride obtained in fused KCl/NaCl which form a complex, purificaJ. Less-Common
Metals. 8 (1965) 361-367
HISTORY
OF DUCTILE
TITANIUM
AND ZIRCONIUM
365
tion was observed with respect to Fe, Al and Ti which make stabler compounds than does Zr. By reevaporation, the dissolved ZrCld could be recovered in the pure state. This could be achieved by using higher temperatures andior a vacuum, or by oversaturating the salt solvent. This method is used today in the purification of HfC14 and ZrC14 when very pure sponge is required. Oxides, of course, are also retained (mechanically) in the carrier salt. Then I refined various metals and alloys by anodic dissolution and electrolysis in a fused chloride bath?, paying special attention to the refining of iron and ferro-alloys such as ferro-manganese and ferro-chromium, as well as to the chemical equilibria that form between the solid cathode deposit and the bath. In the case of the iron electrolysis C, S and Si were eliminated. This method I used in 1947 at the Bureau of Mines in Albany, Oreg., in attempting to plate smooth layers of Zr on a metallic cathode under argon, as described later in an investigation report8. Dr. K. S. Dean, the then assistant Director of the Bureau of Mines used this process later on a semi-industrial scale to refine titanium. The background of knowledge I passed on to the Y.S. Bureau of Mines in early 1935,when I started working with this organization, was then as follows : reduction of TIC14 under clean argon with magnesium in a reactor, heated from the outside, followed by crushing and leaching of the sponge chips with HCl and either sintering the pressed powder in vacua, or arc melting the briquettes in vacua or under controlled argon pressure with a d.c. current, and using a thoriated tungsten tip; reduction of Hz-purified vaporized ZrC14 under similar conditions under argon, and separating the salts from the sponge by vacuum distillation. On the side of the Government there existed some knowledge of the use of my process in a reactor of a few dozen pounds of Ti sponge per batch. The salts were tapped, a procedure feasible only with larger batches; the sponge was turned out on a lathe in a low humidity room and the chips were leached with HCl in a refrigerated vat, then dried, crushed, pressed and vacuum sintered. By early 1944 the Government titanium project had bogged down because the vacuum sintering did not eliminate salt inclusions sufficiently, and plates of about one inch thick burst at the center when hot rolled. _4rc melting, initiated at my instigation by Albany and later followed up by private industry, saved the day. It removed all residual salts. I had adopted this in Albany in preference to leaching because of explosions that occurred when zirconium sponge was ground under water. Vacuum separation of the salts from the Zr sponge, followed by arc melting was the procedure we then followed. There was, however, an interruption in the development of this procedure. VVhen it became necessary to produce arc melted ingots instead of buttons I hesitated to use a water-cooled copper sleeve to contain the metal, because of the great risk of explosions I foresaw; events proved me to be right. I then discovered, that Zr picked up no more than about o.30ib carbon when fused in graphite, which impurity impaired malleability only a little. Consequently, we developed a split-tube low-voltage graphite resistor furnace9 which, built in a vacuum, permitted production of cast ingots of about 20 lb. This graphite melting of Zr had to be abandoned later because the C-contaminated metal corroded in hot water under pressure. Arc melting took over. In the meantime, the pilot reactor of 50 lb. sponge (later increased to 75 lb.) was put in operation and on April 24, 1947, 5 batches had been produced. On June 30 of the same year I left a copy of a paper’” on the hafnium separation from Zr in the hands of the chief metallurgist of the Bureau in Washington. It described the thiocpanate process of Fischer-Chalybaeus, in sulphuric acid solution with ether
366
W. j.KROLL
as a solvent, It is the great merit of the chemists of the U.S.-A.E.C. to have modified this method so that it could more easily be operated. There was no other use for Zr but in the atom pile, and hafnium separation and purity are an essential requirement in this application. At this point it is necessary to go back in history and to show the transfer of ideas, as worked out in Albany or by other people in the field. The vacuum separation of the M&l2 from the sponge was a great advance in Ti and Zr production. A report on this was submitted at the Boston meeting of the American Electrochemical Society on October 16, 194711, Private industry immediately took advantage of this method which did away with leaching, its oxide pickup and its hydrogen poisoning of the sponge. Some of the users of this procedure, however, made serious mistakes because they wanted to improve it. In one construction a central funnel was arranged in the batch, the latter consisting of turnings obtained in a dry room, thus cutting down on the sections through which the gases might escape. The large periphery should have been used as gas outlet. Furthermore, the same construction allowed the condensation of the MgClz upwards. Not only did this entail the possibility of some condensate dropping back in the distilled charge when opening the retort, and spoiling or burning up the batch, but there was also some refluxing of the gaseous MgClz which resulted in an extended distillation cycle. Another user of vacuum distillation put his very long reactor on two refractory pillars with the results, that the shell, heated externally with gas, folded by creeping so that after a while the deformed boat used in the reduction no longer fitted the distillation retort. Another failure was that of a company which tried to combine reduction and vacuum separation to speed up the cycle. The difficulties encountered in the elimination of leaks in the hot equipment, and the slow reduction-by creep-of the diameter of the vessel, exposed to the heat while evacuated, made this procedure impossible. The vacuum separation is in use in Japan, with batches of up to 13 tons of sponge (see Fig. 3). It is probably more expensive than leaching but the sponge obtained is of unsurpassed quality, giving arc melted buttons of less than IOO Brine11 over most of the batch, a higher yield, low hydrogen and MgCL content, and much less spattering on ingot making. The fact that MgCle escapes in. uacuo from the center of a sponge cake 4 ft. in diameter is amazing, especially when considering the raw sponge, whose very fine cavities are filled with chloride. I objected when starting this project to using the Pidgeon retort as a model, with its atmospheric pressure on the hot walls, which would have imposed a small diameter and thus made large batches impossible. External heating of the retort end in an electric vacuum furnace indeed proved to be a very successful idea. The industrial development of the Zr process from z lb. to 75 lb. batches took, with only three men on the project, little more than two years. This comprised the carbide production, chlorination, &-Cl4 purification, reduction and vacuum distillation. The titanium project, which skipped the ore to raw chloride phase, took twice as long. My able collaborators and the open-minded chief of the station, to whom credit has been givenl, made such success possible. Yet zirconium is far more difficult to produce than titanium, and stringent specifications of the atom energy for the purity of this metal impede the engineer. The methods developed in Albany spread to various other branches of technology and the use of a vacuum on a big scale in pyrometallurgical procedures, 1. Less-Common Met&, 8 (1965) 361-367
r Crude
TiCt,
Ti
spcmge cake
Ti sponge Fig.
3. Practical
flowsheet
for
WAC
for producing
titanium
sponge.
KROLL, A. W. SCHLECHTEN AND 1..A. YERKES, Tvans. Electrochem. Sm., 89 (1946) 317. JO W. FISCHER, 1%'.CHALYBAEUS AND M. ZUMBUSCH, Z. Anorg. Chem., ,255 (x948) 277. II W. J. KI‘;KOLL, A. W. SCHLECRTEN, W. I<.CARMODY, I-.A. YERKES, H. P. HOLMES AND H. I-. tfH,RE:RT,Trans. Ekctrockenz. .%c., qz (I$+?) t)g.