C. B. SAWYER AND 8 . R. KJELLGREN The Brush Beryllium Company, Cleveland, Ohio
Newer
A
in Beryllium
NYONE engaged in the extraction of berylliumfrom its ores must feel a continuing wonder a t the number of ore samples submitted, with determinations made by reputable chemists and showing considerable quantities of beryllium which cannot be subsequently verified. This suggests that the single greatest need of the industry is for a rapid foolproof method of determining beryllium. Accurat.eresults can he obtained with the existing hydroxyquinoline method (17)only by a skillful operntor, and the method is stiU tedious, though a great improvement oyer the earlier hicarhonate separation. But if a quick volumetric method were available to analytical laboratories, many more ores could be , examined and there would be less misdirected effort in consequence of faulty analysis. Moreover, such a method would
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Many minerals of beryllium exist other than the familiar beryl. Here again an easily applied method of analysis, not requiring special skill, would be of much service in discovering deposits of such unfamiliar minerals. Beryllium is said to occur in the earth's crust in the amount of 0.0005 per cent (2) and in this respect lies between tin and arsenic in abundance.
Extraction of the Oxide The element beryllium was discovered in 1798. Beryllium metal was obtained in 1828, but not until nearly a century later has it appeared substantially in the arts. Analytical difficulties have contributed much to this slow progress. For in spite of much promotional publicity emphasizing the so-called mystery of the element, it is just as susceptible to the laws of science and honest work as any other element. The literature generally states that powdered beryl is not attacked by any single acid except hydrofluoric (26). Con-, sequently for "opening the ore," alkaline fluxing is generally resorted to, with accompanying introduction of alkaline metals which complicate the remaining treatment. Beryllium oxide in powdered raw beryl, however, may be 76 per cent extracted by treatment at 265" C. with dilute sulfuric acid. This is considerably above the boiling point of the acid, and high pressure develops. But if the raw beryl is given a preliminary heating in a rotary kiln to temperatures above 1000" C., its susceptibility to sulfuric acid is greatly increased. The higher the temperature of heating, the more ready and complete is the extraction. Beryl which has been heated to its sintering point a t about 1450' C. yields 91 per cent of its beryllium on treatment with 56 per cent sulfuric acid a t only 250' C. If the beryl is heated hotter until melted and then quenched by being poured into water, it becomes very reactive with strong sulfuric acid a t atmospheric pressure. This is the method which the writers now employ (32). After the beryl is quenched in water, it is no longer optically active between crossed Nicols nor does it give an x-ray spectrum. The original crystalline structure has therefore been destroyed to bring about the accompanying increase in susceptibility to sulfuric acid. The melting point of beryl is indefinite and varies with its origin but generally lies between 1500" and 1600" C., which i s well within the range of open-hearth melting. Autoclave treatment with sulfuric acid will open the possibility of utilizing beryl heated only to the sintering point in a cement kiln; thus subsequent grinding will be greatly facilitated, and beryl can be utilized which has not been entirely cleaned from its gangue. This would be of special value for smaller beryl crystals. After the ore is sulfated, it is passed through Dorr leaching machines to extract all soluble sulfates, including those of aluminum, iron, and alkali metals as well as beryllium. The remainder of the process consists in simple evaporation and crystallization with dewatering in sugar centrifugals. Aluminum is crystallized and separated quantitatively as the ammonium alum by the use of excess ammonium sulfate in the strong beryllium sulfate mother liquors. The essential feature of the separation not heretofore recognized was the concentration of the beryllium sulfate in the hot mother liquor to such a point that the mother liquor would be just saturated, with respect to beryllium sulfate, a t its final crystallizing temperature, thus effecting a complete precipitation of the aluminum ( S I ) . The ammonium alum is recoverable in a high degree of purity and may be converted into anhydrous aluminum sulfate or aluminum oxide (16),and in large-scale operation this by-product should go far towards covering the cost of chemically processing the ore. Lithium, cesium, and rubidium, if present, may also be recovered as sulfates. All reagents employed in this process are cheap
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and standard, and may be largely recovered if the scale of the operations warrants it. Beryllium sulfate recovered by this process is fed into a rotary kiln fired by natural gas and there decomposed to beryllium oxide at a maximum temperature of 1450" C. This product is very pure and has a low bulk density in spite of having reached this high temperature. One ton of beryl valued a t the plant (Figure 2) a t about $54 contains about 240 pounds of beryllium oxide.
Beryllium Oxide Beryllium oxide is easily fluxed by relatively small quantities of calcium oxide and alkali metal oxides as well as by fluorides. None of these is employed in the process here described, and a t no time has the highly adsorptive beryllium hydroxide been thrown down. Consequently, beryllium oxide produced by this process is especially suitable for refractory use. Caution must be used throughout to avoid contamination from dust and the like. Pure beryllium oxide has a melting point of 2570 " C. This is about 500" higher than that of alumina. Articles of beryllia may be extruded or pressed with or without binder into large or small forms (26,278) as shown in Figures 3 and 4. When properly prepared, they show excellent electrical insulating qualities a t high temperatures and also very good resistance to thermal shock (26, 278). This latter quality permits repeated heats t o be made from the same crucible. A German firm advertises ceramic products of beryllia which are entirely gastight a t 2200" C. (7). These products resist molten alkalies but are very susceptible to acid attack. They are hardly attacked, even a t high temperatures, by carbon, carbon monoxide, or hydrogen. On the other hand, oxides such as alumina, magnesia, etc., readily form slags with beryllia. An exception is zirconia which does not react even a t 1900" C . Especially noteworthy is the small loss in the presence of high-frequency waves. Standard-size pressed brick are available. They are fired a t 1500" C. and may be fabricated sufficiently soft to permit machining. Although these brick may be made to vary in bulk density from 1.42 to 2.09, the raw beryllium oxide from which they are manufactured has a density of about 3.02, which is practically identical with that of fused beryllia. Beryllia confers some of its good properties on ceramic mixtures containing other oxides. I n this connection there is some ceramic demand for raw beryl, whose beryllia contenb is thus obtained already combined with silica and alumina. Beryllia additions to glass show some possibilities (19). Beryllia is notable for its large infrared and blue radiationa a t elevated temperature (18).
Reduction of Metal Metallic beryllium may be produced in alloy form by direct reduction of its oxide by means of carbon (20)or hydrogen (40). It can be produced unalloyed by electrolysis of its anhydrous fluoride or chloride salts above (8, 36) or below (3, 22) its melting point, and by a chemical reduction of the same fluoride or chloride with sodium or magnesium (9,87, 3s). The writers are more or less familiar with all of these methods, and all of them show some commercial possibility. The first two utilize carbon or hydrogen and have the advantage of direct use of beryllium oxide but are best suited to alloys of beryllium. The reduction of the fluoride or chloride either electrolytically or by sodium or magnesium yields a product generally useful in alloys, whether rich or lean. Nevertheless, the use of the fluoride or chloride has disadvantages. If electrolysis or reduction by sodium or mag-
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nesium is carried out at high temperatiira above or approaching the melt.ingpoint of beryllium-namely, 1285"C.volatilization of the halides and contamination of the product are apt to result because of the extraordinarily high temperature. If these attempts are made at temperatures helow the meking point of beryllium metal, it is more or less finely divided and considerable loss may attend its coalescence. The basic methods mentioned above were either disclosed long ago or the patent protection obtained will expire in a relatively short time without, in certain instances, ever having been put into commercial use in this country. Consequently the protection remaining to newer developments in these methods is principally of a limited or improvement nature.
Metallic Beryllium Beryllium metal has about the same density as magnesium,
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cent highcr than Young's modulus for steel. This property has apparentlynever beenactuallyineasured(57), hut Young's modulus of elasticity for an 84 per cent beryllium-aluminum alloy was determined in an associated laboratory (41)from its natural frequency of vibration as being 23.7 per cent higher than that of steel; this is sufficiently close to the calculation above to act as confirmation of the remarkably high modulus. It follows immediately that the velocity of sound in the 84 per cent beryllium-aluminum alloy must he 120 per cent greater than the velocity of sound in steel and therefore over twice as great as t.hat of the next ncarest metal. This fact is of great importance in acoustical applications. The metallurgical handling of pure beryllium metal still remains an unsolved problem, according t o Kroll ( l a ) , who is inclined to class heryllium with silicon in alloy habit and
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Beryllium Copper
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The largest commercial outlet for beryllium a t present continues to be in various alloys with copper. It has been stated elsewhere that beryllium is to copper almost what carbon is to iron (299). That is, beryllium alloyed with copper in quantities resembling those of carbon in iron develops properties in copper close to those of steel. As is the case with steel, beryllium copper is hardenable by appropriate and broadly analogous heat treatment, and the tensile properties thus produced can cover a wide range, depending on the heat treatment. As has also proved to be the case with steel, third and fourth metal additions to the binary alloy have been found beneficial, so that, if history is repeating itself, the ternary and quaternary alloys of beryllium copper will come more and more to a dominant position. Historically the precipitation-hardening effect of beryllium in a ternary alloy of copper and some nickel was patented in this country by Corson (6),a United States research worker. The process for precipitation hardening by beryllium in binary alloy with copper was patented here by the Germans, Masing and Dahl (23). Both original applications were filed in 1926. As disclosed in the records of the United States Patent Office, an interference between the Corson application and that of Masing and Dahl terminated favorably to Corson, with the result that Corson won the fourth and broadest claim of his alloy patent, and that all reference to nickel additions was canceled from the Masing and Dahl patent. The claims of the Masing and Dahl patent were still further generally limited so that they cannot read on additions of third metals in amounts sufficient (‘to substantially alter the characteristic properties of the said alloys.” I n a subsequent patent application by Dahl (6) in which he originally sought generally to cover third-metal additions to beryllium copper, Corson’s work was cited against him and Dahl withdrew claims directed not only to third-metal additions in general but also to cobalt in particular. Dahl’s patent issued with a single claim covering the addition of chromium. It is surprising that Corson’s work and field have not received more attention because superior alloys are produced by third-metal additions; wherever this effect is substantial, as defined in the quotation from the Masing and Dahl patent, this patent does not cover the resulting beryllium-copper alloy or the heat treatment thereof. Lebeau and Moissan first produced binary beryllium copper as early as 1897 (22), and therefore the binary alloy of beryllium with large amounts of copper was disclosed a t an early,
date. Reference is again made to the analogy of beryllium copper with steel, but this time to point out an important difference. Whereas in steel, heat hardening is possible to some extent with diminishing carbon content down to 0.1 per cent, binary beryllium copper will not heat-harden when the beryllium content is less that about 1 per cent (1, 2 4 ) . But thirdmetal additions, such as iron, cobalt, nickel, and chromium, have the effect of permitting heat hardening with lower beryllium contents, sometimes as small as 0.1 per cent. The General Electric Company’s Trodalloys (14), or lowberyllium copper alloys, are in this class and are distinguished by their high electrical conductivity ranging from about 50 to 70 per cent that of copper, though a t a reduction of physical properties compared with high-beryllium copper. Thirdmetal additions to beryllium-copper ,alloys thus play an even more important part than in the case of carbon and iron because they take up the slack in the beryllium content, which is necessary in the binary alloy before heat hardening can begin. I n another important respect heat-hardening beryllium copper differs from heat-hardening steel, The hardening of both beryllium copper and steel requires a first heating to
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“cherry red,” followed immediately by quenching, from which ordinary steels emerge hard and brittle; but beryllium copper emerges from the quenching tank soft and ductile and capable of withstanding various cold-forming operations. It is the next step of reheating t o low temperatures which in steel tempers it, that in beryllium copper first hardens it. Continued heating or heating to a still higher temperature softens beryllium copper, just as it does steel. The important technological fact here is that the violent initial quenching from a high temperature leaves beryllium copper in a soft workable state where it can be finished by machining, stamping, or drawing. Hardening for final physical properties is brought about by gentle soaking a t a relatively low temperature. This gentle prolonged final hardening a t low temperature minimizes deformation and inequalities of treatment which would result in steel, especially where the final shape is complicated. A perfect illustration of the advantageous use of these heat-hardening properties of beryllium copper is found in a convoluted beryllium-copper bellows (Figure 5 ) which forms the pressure-sensitive element of a recording subsurface oil gage made by Exline (IO). I n the development of this gage, efforts to produce a low-hysteresis spring bellows of chromemolybdenum steel encountered serious difficulty from the practical impossibility of producing uniform treatment in such a convoluted steel bellows. Probably the quenching medium would not properly enter the convolutions. But when the bellows was formed from previously quenched soft sheet or tube beryllium copper, and was then heat-hardened by a long low-temperature soak, inequalities of treatment yanished. Exline (11) found that he was limited to the use of nonferrous materials and that, of these, beryllium copper had by far the most favorable elastic characteristics, including a much lower mechanical hysteresis, This points to its use in Bourdon tubes. Lebeau (22) also noted the sonorous quality of beryllium copper, which is a property proceeding from its low hysteresis. Beryllium-copper alloys find applications in springs of all kinds. I n connection with springs, there comes to the front an outstanding quality of beryllium-copper alloys-namely, high (fatigue) endurance limit. Determinations of this property in air range from over 35,000 up to 44,000 pounds per square inch and therefore compare favorably with the heat-treated low-carbon steels. But a unique feature of beryllium-copper alloys is their ability to maintain their high endurance limit under conditions of corrosion. Thus Gough and Sopwith (13) found no diminution of the endurance limit of beryllium copper even in salt spray. They found that its endurance limit of 38,000 pounds per square inch under salt spray is higher than that of any other material tested, even including heat-treated alloy steels and stainless steel. Heat-hardened beryllium copper, especially in ternary alloys, has been exposed to temperatures of about 300” C. or more. It can without detriment be continuously exposed to temperatures of 150-200” or over. This range is sufficient to cause loss of temper in other work-tempered springs. The electrical conductivity of heat-hardened beryllium copper is more than twice that of steel and ranges from 18 per cent of that of copper up t o 70 per cent in some of the ternary alloys. These may have as much as 30 per cent of the electrical conductivity of copper even with beryllium contents for maximum tensile properties. Tensile strengths of wrought beryllium-nickel copper containing 2.25 per cent beryllium may reach values of over 200,000 pounds per square inch. The corresponding Brinell hardness can go to 385, and the Rockwell C hardness may I
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reach 42. Slightly higher beryllium contents can give Brinell hardness figures in excess of 400 and Rockwell C hardness values up to 45. Good castings of beryllium copper may be made in plaster and sand molds (Figure 6). I n this case, especially, third or fourth metal additions are very beneficial in preserving a small grain size. There is a considerable application indicated for cast dies or molds of beryllium copper, especially in the plastics industry where high thermal conductivity may be important. Success in this field, however, depends on the consistent direct production of cast surfaces free from blemishes and still remains in some doubt. Hurley’s patent (16) has claims drawn on the use of binary beryllium copper for dies and molds, but the application was rejected until the inventor had produced an affidavit that beryllium copper had an essential “greasy characteristic.” It is open to question whether such a greasy characteristic exists in beryllium copper and is necessary for the operation of the dieormold. Silliman (34) gave an excellent review of beryllium with special reference to beryllium copper.
Production Cost About 3 pounds of beryllium oxide are required to produce 1 pound of the metal. The price of beryllidm metal is now $23 per pound, alloyed with copper. This price corresponds to 52 cents for the beryllium in a pound of 2.5 per cent beryllium copper, and was established about a year ago by this company. The new price was a reduction from $30 per pound. Assuming adequate ore supply, further price reductions may be expected as the volume of output increases. Eight years ago (January, 1930) one of the authors (30) made the following statement: “On a large scale and with well-developed processes a production cost between $1.40 and $2.70 per pound of beryllium for labor and materials can ultimately be realized.” The succeeding eight years of additional experience with beryllium oxide and beryllium copper have not made these views seem incorrect, if one assumes a stable money and a continuing slight downward tendency in the price of ore.
Summary The ore supply continues to develop and is more than adequate at present. A better method of analysis is needed. Extraction of beryllium from the ore by sulfuric acid may be accomplished without fluxes to yield a very pure flux-free oxide. Beryllia with a melting point of 2570” C. is admirably adapted for refractories and may be formed with or without -binders. Articles made from it are characterized by resistance to thermal shock and high electrical resistance, even at high temperatures. Metallic beryllium and high-beryllium aluminum have a Young’s modulus greater than that of steel and will transmit sound at a velocity twice as great as in steel. Their use is indicated in acoustic applications. Beryllium copper resembles steel in many ways. I n ternary alloys it can be heat-hardened to develop tensile strengths in excess of 200,000 pounds per square inch with Brinell hardnesses of 385 or more. It has an electrical conductivity more than twice as great as steel, low mechanical hysteresis, and a salt-spray corrosion endurance limit higher even than stainless steel. The endurance limit in air is between 35,000 and 44,000 pounds per square inch. Beryllium copper presents a unique advantage for fabricators because its soft,
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workable condition after high-temperature quenching adapts it for forming into intricate shapes which may be subsequently uniformly hardened by a gentle reheating temperature. Assuming adequate ore supply, the price of beryllium will continue its downward trend and can ultimately reach much lower figures.
Acknowledgment The authors acknowledge with thanks the kindly review and valuable criticism of this paper by C. H. Davis and H . E‘. Silliman of the American Brass Company.
Literature Cited (1) American Brass Co., Anaconda Publication. B-21,4th ed., p. 3
(1937). (2) Behrend, F., and Berg, G., “Chemische Geologie,” p. 9, Stuttgart, Ferdinand Enke, 1927. (3) Borchers, W., 2. EEektrochem., 2, 7 (1895). (4) Cooper, H. S., U. S. Patent 1,254,987 (Jan. 29, 1918). (5) Corson, M. G., Ibid., 1,893,984 (Jan. 10, 1933), 1,990,168 (Feb. 5, 1935). (6) Dahl, O., Ibid., 1,847,929 (March 1, 1932). (7) Deutsche Gold- und Silber-Scheideanstalt vorm. Roessler. “Degussa Gerate aus reinen Oxyden” (Catalog), p. 7 (1936). (8) Dickinson, S. J., U. S. Patent 1,511,829 (Oct. 14, 1924). (9) Dobray, H., Compt. rend., 38, 784 (1854). (10) Exline, P. G., paper presented a t fall meeting of Am. SOC. Mech. Engrs., 1937. (11) Exline, P. G., private communication, Dec. 23, 1937. (12) Fahrenwald, F. A., U. S. Patent 1,333,965 (March 16, 1920). (13) Cough, H. J., and Sopwith, D. G., J . Inst. Metals, 60, 143-53 (1937). (14) Harrington, R. H., Trans. Am. I n s t . Mining Met. Engrs., 124, 172-86 (1937). (15) Hurley, R. T., U. S. Patent 1,920,699 (Aug. 1, 1933). (16) Kjellgren, B. R., E. S. Patents 1,752,599 and 1,752,641 (April 1, 1930). (17) Knowles, H. B., Natl. Bur. Standards, Research Paper 813 (1935). (18) Kroll., W... Metals & A l l o m . 8. 349 (1937). (19) Lai, C. F., and Silverman, A.; J. Am. Ceram. Soc., 11, 535-41 (1928); 13, 393-8 (1930). (20) Lebeau, P., Compt. rend., 125, 1172 (1897). (21) Ibid., 126, 744 (1898). (22) Lebeau, P., and Moissan, H., Ibid., 125, 1172 (1897). (23) Masing, G., and Dahl, O., U. S. Patent 1,975,113 (Oct. 2, 1934). (24) Masing, G., and Dahl, O., Wiss. Ver6.fent. Siemens-Werken, 8, 105 (1929).‘, (25) Mellor, J. W., Treatise on Inorganic and Theoretical Chemistry,” Vol. IV, p. 208, London and New York, Longmans, Green and Go., 1923. (26) Navias, L., J. Am. Ceram. SOC.,15, 234 (1932). (27) Nilson, L. F., and Pettersson, O., Wieds Ann. P h y s i k , 4, 554 (1878). (28) Phillips, M. L., P h g s . Rev., 32, 834, 836 (1928). (29) Sawyer, C. B., M i n i n g and Met., 15, 93 (1934). (30) Sawyer, C. B., S. A. E. Journal, 26, 98 (1930). (31) Sawyer, C. B., and Kjellgren, B. R., U. S. Patent 2,018,473 (Oct. 22, 1935). (32) Ibid., Reissue 20,214 (Dec. 22, 1936). (33) Schwerber, P., Metallborse, 18, 704 (1928). (34) Silliman, H. F., IND.ENG.CHEM., 28, 1424 (1936). (35) Sloman, H. A., J . Inst. Metals, 49, 381 (1932). (36) Stock, A., U. S. Patent 1,427,929 (Sept. 5, 1922). (37) Stott, L., Trans. Am. Inst. M i n i n g Met. Engrs., 122, 57 (1936). (38) Swanger, W. H., and Caldwell, F. R., Natl. Bur. Standards, Research Paper 327, 1141 (1931). (39) Veaeey, W., U. S. Patent 1,515,082 (Nov. 11, 1924). (40) Warren, H. N., Chem. News, 70, 102 (1894). (41) Williams, A. L., private communication, Dec., 1937. .
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RECEIVED January 27, 1938. Presented
as part of the Symposium on the Less Familiar Elements a t the Second Annual Symposium of the Division of Physical and Inorganic Chemistry, American Chemical Society, held in Cleveland, Ohio, December 27 t o 29, 1937.
