Relationship to the Chemical Industry
I
IVOR E. CAMPBELL National Steel Corp., Weirton, W. Va.
For companies wishing to diversify, these metals ofFer a promising field. However, foreseeable markets may support only a limited number of producers
OUR
ABILITY TO achieve high temperatures and to generate intense power has outstripped our ability to control and to contain them. Recognition of this situation has stimulated a n intense materials research effort that received its first impetus during World War 11, and a shot in the arm with. the advent of the “race for space.” T h e substantial role that ceramics and quasi-ceramic materials will play in developing materials to meet these needs should not be minimized. However, it can be stated with assurance that the development of metallic materials capable of withstanding extremcs in temperatures and energy fluxes for varying lengths of time: dependent on the application involved, is of major concern. This concern has prompted investigation of rare, a n d / o r difficult to handle, and marginal materials, \vith the understandable philosophy that nothing should be overlooked. For example, boron has been evaluated as a structural material even though it is extremely brittle, except at high ten+ peratures, and cannot be justifiably called ductile, even a t high temperatures. Molybdenum has been investigated extensively for service at high temperatures in oxidizing atmospheres. even though its oxidation resistance is comparable to that of carbon, a major fuel. Rhenium has been investigated extensively even though the known reserves Xvould probably permit a maximum annual production of the order of 10 tons. These citations are not made in a critical vein. Sound judgment dictates that “no stone be unturned.” Further, special applications ma!- well require each of these materiais. For example, boron may be useful at low stresses and
1 12
certainly has interesting nuclear properties; molybdenum a1lo)s are still the best bet for high temperature service, particularly if continued progress can be made in developing methods of protecting i t against oxidation; rhenium alloys that have unique properties may very \vel1 be the anslcer to needs for special parts requiring limited quantities of material. The urgent need for new and improved materials has not stopped a t the research and development stage; rather, i t has led ro the forced-feeding and growth of several metal industries! particularly titanium, zirconium, and niobium (columbium), These industries, having grown at an abnormal rate, are hard put to find commercial markets. if and when special military markets disappear as the needs are met by other metals. or are diverted by other technological advances. T h e plight of the titanium industry, several years ago. is a n outstanding example. but its plight. to a lesser degree, may be the lot of other metal industries in the h t u r e . This possibility is cited as a Lvord of caution because the extractive metallurgy field has been a tantalizing area for many chemical companies uishing to diversify. \l:hile it is entirely logical that the chemical industry could contribute to the production of these metals, in which the techniques of the chemist and the chemical engineer are assuming increasing importance, it is obvious that the market can be sliced onlv so thin. Plant Capacity Important
T h e potential market in the foreseeable future will support only a certain number of producers with a reasonable profit to
INDUSTRIAL AND ENGINEERING CHEMISTRY
each producer. Separate and apart from military applications which failed to develop to the anticipated degrre. the titanium industry could not. and tvould not, support the number of producers and potential producers. Hoivever. the same is true of the neophyte niobium industry and may \veil be true of the silicon industry. There is need for improved processes for maltin? many of the refractory metals, and we may well look to the chemical industry for these processes. However, i t is also probable that in the long run, the production capacity of the individual plants must reach certain minimum levels if costs are to come down to the desired levels. These minimum plant capacities for low cost production and our anticipated capacity to use the metals \vi11 limit the total number of producers. At one time or another. at least 15 to 20 companies. many of them chemical companies, have given serious consideration to producing niobium. Some of these \vi11 undoubtedly enter the field as the market develops. However, it \could seem obvious that a far smaller number of plants \\.ill be required to produce at the most efficient plant capacity level. Significance of Melting Point
Within the composition limits available for commercial service. all of the metals can be strengthened by alloying. Although a high melting point alone does not necessarily indicate a useful base for high temperature alloys, there is a direct relationship betneen the high temperature strength of a pure metal and its melting point. In anv event. since all metals lose strength rapidly as
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LESS COMMON E L E M E N T S their melting points are approached. a high melting point is a minimum consideration for hiyh temperature service. Further, there are many applications where a high melting material may suffice even though it \vi11 not retain its strength for extended periods of time-e.g., in heat sinks or reinforcements for ablative materials. Effect of Nonmetallics
Mechanical properties of these metals are particularly influenced by nonmetallic impurities or alloy additions and many are rendered unworkable by small percentages of carbon, oxygen, and nitrogen. This is particularly significant because, except for molybdenum and tungsten and to a lesser extent tantalum and niobium, these metals are difficult to refine. In many cases, it is necessary or a t least desirable to prepare the primary metal in as pure a form as possible because refining is either impractical or impossible. For example, no knokvn method is available for removing oxygen and nitrogen from titanium or zirconium except electrorefining. The affinity of these tlvo metals for oxygen is such that the metal evaporates preferentially in vacuum. and oxygen is actually concentrated in the residual metal. It is true that nonmetallics are useful strengthening agents for the refractory metals. However, the substitutional alloys have more flexibility than the interstitial alloys, and are generally preferred. I n any event, even when nonmetals are used as strengthening agents, it is preferable to ha1.e the primary metal low in these impurities so that the composition of the alloy can he more readily controlled. In fact. it is frequently simpler to produce a pure metal than to hold nonmetallics a t ii controlled level. Perhaps the most significant reason for the interesi. in pure metals is the recognition that the maximum in properties is still to be achieved. At present purity leveis. further increases in purity result in decreases in strength. However, an ahsolutel) pure metal without crystal defects (if this uere attainable) should be much stronger than the strongest alloys produced to date. Therefore, further research is indicated. Interest in the pure metals has led to special techniques for refining both process materials and the metals themselves.
tional crystallization, fractional distillation, vacuum melting and refining, and fluid bed processing. As new techniques for purifying metals are developed, improved methods are needed, both for rapid analyses in process control and for accurate analyses of pure metals. Better methods are needed for determining oxygen: and particularly in certain cases of analysis of some metals for the determination of sulfur and phosphorus, t\vo impurities frequently omitted from analytical specifications. In the case of sulfur. lo\v level analyses have proved to be so difficult that neutron activation has been explored as a means of analysis. Although the need for methods of determining nonmetals has received the most publicity, it has also been necessar!. to develop special concentration techniques for determining metallic impurities since in many cases the impurity levels are below those determined by normal spectrographic standards. For example. as purer and purer metals become available, analyses at the parts per billion level will be required. Other areas where chemists and chemical engineers can be expected to contribute to the technology are such fields as coating and decoration, recovery of scrap metals, development of techniques for rapidly identifying metals and alloys, and cost reduction through continuous operation. In some applications. the metals \vi11 require coating and/or decoration: fields
Supply and Price Status
3Ietal Re
dbundance, P.P.11.
Nb Cr Zr Ti
001 2 5 15 70 70 200 250 5,000
cu
100
Ta Hf Mo
W
*
Free n'orld
Reserve\'
11ill Product Price, 8/lb
1,000 800-1000 50-100 100,000 350,000 10-50 1,500,000 10-100 1,400,000 7,000,000 25-100 9,000,000 10-50 17,000,000 5-2 5 140,000,000
200 Ni 20,000 Mg a Tons of contained metal.
in which the chemist can make many contributions. If these metals are to be competitive. they must be used efficiently-Le.. scrap must be utilized and scrap values must be recovered from alloys. This area \vi11 also present problems of interest to the chemist because, in many cases. techniques will have to be devised for removing alloying elements in reprocessing scrap. The major obstacle to be overcome in obtaining high volume consumption of these metals in peacetime applications is cost reduction, so that these metals will not have to be restricted to uses where price is no object or where an extended service life is required to
Further Advances Needed in the Field of Refractory Metals:
b b
Exploration to supplement known reserves
Improved techniques and hardware to decrease production costs
b
N e w structural materials to bridge the g a p between metals and ceramics
b b
Commercial availability of larger sizes and shapes
Alloys of improved oxidation resistance at high temperatures
b Improved protective coatings for wider usage of such metals as molybdenum and niobium b
Chemical Techniques Stressed
The techniques employed are, in manv cases. more "normal" to the chemical industry than to the metal industry and involve such processes as ion exchange. solvent extraction: frac-
Improved methods for producing and using thin skins or coatings of refractory metals on less expensive metals
b Better understanding of the solid state so that the potential properties of the metals can be realized VOL. 53, NO. 2
FEBRUARY 1961
113
All of These Metals Are Considered Refractory, Although Some Are Disappointing as Alloy Bases for High Temperature Service Metal
Physical Properties
la
Corrosion resistance; electrical properties; melting point; workability
Nb
Nuclear properties; workability
Re
High melting point; strength; spark resistance
Mo
High melting point; high temperature strength; oxid a tion resistance
W
High melting point; high temperature strength; directional properties
Cr
Low ductility; properties
Ti Zr Hf
Low density; corrosion resistance
corrosion resistance;
oxidation resistance;
low
high temperature
Nuclear properties; corrosion resistance Nuclear properties; high density
justify the cost. Price reductions \
