P H I L I P 5 . H E S S I N G E R
BERYLLIA E N G I N E E R E D SPACE AGE M A T E R I A L Beryllium oxide, commonly called bevllia, possesse~
a combination of unique thermal, electronic, and nuclear Properties not found in other known materials
t was only a few years ago that references listed beryllia
I as an ingredient in gas lamp mantles and as high
temperature laboratory ware. Currently beryllia is experiencing an explosive growth in number and variety of applications. A combination of remarkable properties accounts for this rise in popularity. Consider berryllia's properties : relative light weight, high heat resistance, excellent electrical insulating properties, transparency to microwave radiation, practical immunity to nuclear radiation, high hardness, and high thermal conductivity. With credentials such as these, it is little wonder it appeals to the missile, electronic, and nuclear industries. I t is very much a space age material but it also offers much promise for more conventional applications. Beryllium oxide ceramic materials have been known for a number of years. But beryllium and its compounds are toxic and expensive. For example, a high alumina ceramic body can be formulated for about 25 cents per pound. Similar ceramic bodies made of beryllia cost $25.00 per pound until recently. However, in many cases, forming and fabrication of beryllia ceramic structures can now be accomplished by using standard ceramic methods :
-Dry pressing -Ram pressing
-Extrusion
-Slip casting
Other techniques developed for forming high alumina ceramic parts can be adapted to form beryllia ceramic parts. The isostatic technique, used by National Beryllia Corp. and Coors Porcelain, is one of these. Such an adaptation of processing procedures gives much promise for reducing the new high cost of processing beryllia shapes. 16
INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
l o o k at Some of the Current and Possible Future Uses
Beryllia answers the need for a high purity, high density refractory material. I t has a 4650" F. melting point, about 1000" above aluminum oxide and about 1000" below thorium oxide. But as a thermal conductor it is better than either. It also has superior shock resistance. Repeated heating to red heat followed by quenching in ice water has no effect on it. I n the nuclear field, beryllia combines its refractory properties, thermal properties, and ability to efficiently moderate and reflect neutrons to make it the best high temperature moderator and reflector material currently available. Combined with uranium oxide, it can be used as a matrix material for fuel elements. Parts made of beryllia with suitable nuclear poisons may be used in shiclding and control rod assemblies. High dielectric strength values, thermal shock resistance, thermal conductivity, and specific heat combine to make beryllia one of the best ceramic materials for electronic applications. Klystron tubes and powder tube components, antenna "window" elements, and heat absorbing and radiation resisting shields for electronic equipment take advantage of the excellent thermal and electrical properties of beryllia. High physical strength and thermal shock resistance, combined with chemical inertness, permit beryllia to be used extensively as a crucible material and as crucible lining in the melting of molten alloys where high temperature and high purity must be obtained. I t is expected to outlast graphite now being used extensive!y in this application. Beryllia crucibles and thermocouple protection tubes can be used repeatrdly at temperatures up to 4000" F.
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High heat capacity and thermal conductivity make it useful in applications such as rocket and missile re-entry bodies. Aeronautical uses where extreme high temperatures in supersonic aircraft are encountered focus on be@a as a refractory material for planes of the future. As the price of beryllia comes down, we will find nengovernment-8upporte.delectronic industries replacing more and more of the ceramic parts they are nowusing with heryllia, opening new markets. Several electronic CompanieB are presently evaluating beryllia for use in cnmmexial products where improved performance jusdfiesthe slight increase in total cost. inquiries have been received by processors as to the suitability of making beqllia tubing for piping molten aluminum. It has also been suggested that such tubing can be used for introducing material to or withdrawing sampks from moltem metal baths and other regions of hightemperature. ,I
ROUTES TO BERYLLIA
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Let’s look at a few of the processes that have been developed by the industry for beryllium oxide production.
Raw Mahrial Preparation
Mineral Concentrates & Chemical recently unveiled their process. Although it may appear to be very uneconomical through use of many recycling steps, it is said to compare favorably with other processes in use. Ninety per cent of all equipment is either stainless steel, plastic, glass, or glass-lined. Ore is unloaded from trucks directly into a 25-ton hopper and fed to 6 X 12 inch Cedar Rapids jaw msher by a Syntron and belt conveyor. Bucket elevators transfer crushed ore to an aufomatic sampler and storage bins. Each bin holds diffeFent grades of ore for proper blending M o r e concentration. A Jeffery hammer mill pulverizes ore to less than 100 mesh and either diverts it to direct storage or through a ball mill for flotation upgrading. The flotation ball mill grinds ore to less than 200 mesh and sends it on to special conditioning tanks and flotation cells for upgrading to 15 to No/,beryllia. Dry concentrates or high grade ore are ground to less than 320 mesh and ace transferred through a pneumatic conveyor to storage where it is weighed and fed to the mixing hopper. Flux in the form of sodium carbonate and sodium fluoride is added. Mixture is pelletized to approximately 1-inch VOL 5 4
NO. 3 M A R C H I962
17
diameter pellets and fed by conveyor to the sintering step, a large Sunbeam conveyor belt-type annealing furnace. Pellets are fused in the furnace at a temperature of 1750" to 1800" F., depending on the ore to be worked. As fused mass comes off cooling end of the furnace it is fed to a heavy duty screw conveyor which acts as a primary crusher while conveying to storage bin. Sinter is fed with a Syntron to a wet ball mill as water and peroxide are added. Acid or caustic is added here to keep a very close control of p H and to ensure lOOyoextraction. The slurry is then fed to the drag classifier and solids are removed on a 3 X 5 inch Denver drum filter. Pregnant liquor containing beryllium plus large quantities of impurities is pumped to a 5000-gallon settling tank for further clearing. The top liquor is removed to a 2nd 4000-gallon settling tank for additional clarification. Liquor is pumped to a surge tank through a series of Sparkler plate and frame filters into a large 20,000gallon storage tank. At this point the liquor contains from 15 to 20 grams per liter of beryllia plus approximately 1.57, iron, 2.57' silicon, 1.O% aluminum, 0.05% boron, 0.01% lithium, 0.17ophosphorous, 2.0% fluorine, 0.1 7,manganese, O . l 7 , magnesium, and comparative lesser amounts of other elements. Liquor thus begins its first and major purification step. It is pumped through a Precote process filter which removes all suspended particles greater than 0.5-micron size. From the filter it goes into the two large oxidation tanks where high pressure air and chemicals are added. The greatest per cent of the contaminants are floated off by very careful controlling p H at different phases during heating. Purified pregnant liquor is then pumped to the pri-
mary precipitation tank where it is contacted with caustic soda to make a fine beryllium hydroxide. 4 s this settles to the bottom it is pumped into the "wash" tank where it is scrubbed with water at a controlled p H to remove some of the remaining impurities. Beryllium hydroxide is them pumped to evaporators where it is concentrated to a thick paste. Nitric acid is added to redissolve the hydroxide. Silicon is removed by triple dehydration and filtration. Beryllium nitrate solution is concentrated and crystallized in a special unit designed to give a very fine crystal body. The crystals are filtered and dried at a very low temperature and in a controlled atmosphere. They are then redissolved with a mixture of alcohol and organic acid. The solution is pumped into a liquidliquid extraction unit where final purification takes place. At this point we have the purest beryllium product-it contains less than 50 p,p.m. total impurities. The beryllium is precipitated from the final solution by very careful p H control with gaseous ammonia under pressure and heat. The resulting beryllium hydroxide is of very high density and all particles are spherical in shape. This is then filtered in an Eimco Burwell filter and placed in a steam dryer. Proper drying of the hydroxide is as important to the final oxide as any step in the operation. A standard D.F.C. furnace rebuilt to Mincon specifications is used to calcine the oxide. The resultant oxide has very uniform physical properties if proper control is used in preparing the hydroxide. .4 special lined Spencer turbine vacuum system is used to pick up the oxide from the end o€ the furnace as calcination is completed. A very efficient ventilation system is used to maintain minimum air contamination during all operations.
Initial heat-sintering nuens roast raw beryllium oxide at 7800 OF. f o r seven hours. Careful control of time and temperature is most important. Sintering makes beryllium ore soluble, an important key to Mincon's~otation process of extraction
Final calcining o j bercllia is meticulous and demanding. The oxide is placed in large, specially built heat-treated containers on mine cars. The cars are rolled into sfiecially designed ovens where gas jets above the car calcine the oxide nt 1800" F.
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Isostatic Pressing
Dry Pressing
Starting as a dry powder with a consistency similar to talcum powder, an unfired ceramic shape is formed by pressure using the isostatic technique. Dry powder is poured into a rubber sac where it is deaired by vacuum. The sac is then sealed and placed in a water press where pressures in the neighborhood of 10,000 p.s.i. are exerted equally on all surfaces. Result is a compressed shape which can be handled and machined to desired dimensions. Inside contours are generally formed by using metal mandrels which have been first located in the rubber sac and around which the powder is poured. The isostatic technique permits forming of parts with a miniumum of internal voids or stresses. Allowance is made for the shrinkage which occurs during sintering operations following forming of the parts. Production of beryllia ceramic parts parallels the production of aluminum oxide ceramic parts in many plants. These operations are generally in separate facilities. One major difference in the production of beryllia is that all operations are performed within dry boxes. These dry boxes are all under vacuum so that beryllia dust from the variqus operations can be collected and not dissipated into the atmosphere of production areas. These precautions minimize the possible harm which might otherwise result from the handling of these toxic materials.
Many fabricators use a dry press and sintering process for volume production of large high purity beryllia parts. For example, Brush Beryllium uses totally enclosed dust-tight, semiautomatic slurry preparation system which is capable of slurrying 800 gallons of oxide, milling 20 gallons per charge, and storing 800 gallons of milled beryllium oxide. The oxide is bottom-discharged from the slurry tank to the mill, the mill being automatically filled to a preset height. After milling, the oxide is pumped directly to a storage tank. The material is then dried, vacuum unloaded, and screened. After screening, the material is charged to a 3 cubicfoot twin shell blender, using a closed materials-handling container. Intimate, homogeneous wet blending and granulation is accomplished. Additives and binders are charged to the blender slowly and at a constant rate to give a high degree of uniformity in blending. A very high percentage of moisture, in the range of 40 to 50%, must be added to form even, fairly dry granules approximately l / s inch in diameter. After binders and lubricants have been wet-mixed, the blender is discharged, with the apex down, through a ventilated flange into another material handling container. Material is dried to less than 0.75y0 moisture. Per cent moisture and loss of ignition must be accurately controlled to assure uniform pressing characteristics and fired shrinkage. The material is then rescreened and intimately reblended in the twin shell blender. Dried material is then discharged to pressing. A vacuum lifting plate is used to assist in removing the block from the pressing die to avoid creating undue stresses on the unfired shapes. After pressing, shapes are air-fired in two car-bottom electric kilns with 22 cubic foot setting capacity and capable of firing to 1550" C. and an electric elevator kiln using molybdenum disilicide heating elements capable of firing to a maximum temperature of 1650' C. A gas kiln and vacuum kiln are also available for use as required. At National Beryllia processing begins with ball milling of a slurry. After addition of organic binders, the slurry enters a continuous automatic system feeding through a spray drier from the mill and on to automatic drying presses as large as 100 tons. Or, spraydried granules can be removed from the system for manual conveying to and feeding of larger dry presses or isostatic presses. The continuous automatic system minimizes manual handling, eliminates dusting, and gives maximum granule uniformity. Sintering at National Beryllia is done by air-gas firing at temperatures up to approximately 1900" C. for maximum hardness, density, and purity. National Beryllia has recently installed equipment for production of high-purity beryllia and alumina shapes metallized and plated on one or more surfaces, printed circuits on beryllia or alumina, and brazed ceramic-to-metal assemblies.
Beryllia slurry is spray-dried to granules before feeding to dry presses or isostaticpresses at National Beryllia
VOL. 5 4
NO. 3
MARCH 1962
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A. An idea of the rangc of sius and shapes of bzryllio mode by Coon Porccloin can be obtm'wd by the s ~ a l cwith thepieccr shown
These UOX,pure bnyllia shapes, were ma& by Brush Beryllium's dry press and sinuring ploccrr. The shapes arc then dimnond-machined into many complicated and d i m l t configurations B.
C. Centcrlcss grinding of typical helix support rod is shown h e . Rods can be ground to tolerances of +O.WOZ-inch diametn by B m h Bnyllium
D. Thsc rods, bars, plates, tubes, radomes, and nose cows art typicd Bmloz shapes made by National Bmllia
n
limitations to Size
There have been in the past limitations to the PO& ble confiwations of beryllia shapes. H~~ and cold pressing were used to form green blanks. Extensive and costly diamond grinding followed to obtain shapes which could not be Dressed. Sliu casting and extrusion have since been added to production methods, permitting much greater flexibility in configuration. This has reduced the amount of machining that must be done. Fabrication technology of beryllia has had to deal with a wide variety of shapes in sizes ranging from several grams to 25 pounds. Typical of the large parts fabricated by conventional economic techniques have been blocks approximately 6.3 X 6.3 X 1.5 inches. Some of the smallest parts produced to date have been approximately 0.020 inch in diameter by 0.010 inch thick. Tolerancea on such parts have been as close as +0.0001 inch and have been achieved by means of precision diamond grinding techniques. Larger parts have been produced by hot pressing with the maximum size to date being approximately 7 inches in diameter by 8 inches high. Larger sizes could be produced by this technique ifrequired. The current limit on size in the upper range is dictated by equipment capacity. At present 200-ton presses are available in industry capable of producing parts up to approximately 8 inches square by 2 inches thick. Larger parts could undoubtedly be produced but would require either a modification of the existing equipment w prccurement of higher capacity presses. For extruded work the length is limited primarily by the hot zone ofthe available kilns. Here again it is only a matter of increasing equipment capacity to produce larger shapes. Undoubtedly there is a point beyond which the iarge shrinkages involved would impose severe technical problems. This point, however, can only be determined empirically.
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There has been some hesitancy to use beryllia ceramics because of the problems thought to be associated with beryllia dust. The dust is dangerous. I t can cause reactions in the lungs similar to those of silicosis and anthracosis. Elaborate precautions are needed even when it is suspected that very small amounts of beryllia dust may be present. However this is a problem for the beryllia producer, not the user. The ceramic can be fired to such a hard surface resistant to abrasion that no dust will be created through normal handling. Of
AUTHOR
P. S.Hcssingn is the Vice-Presi&nt and Manager
of Research and Deuelopmcnt f m National Beryllia Cap.,
€€askell, N . J. He has authmcd many arlules on the mnmt and possible future uses of beryllia. Mr. Hessingcr wishes
course, sawing and grinding create dust, but these can be performed the than the Purchaser. The supplier and the manufacturer are more familiar with the precautions to be taken. Future
The future market success ofberyllia rests primarily in its fabricated form. Present and future needs of two of its biggest users, electronics and nuclear industries, must be constantly studied. Certainly the military and space industries will continue to use beryllia in its many shapes. But here cost is not as important as it might be with commercial applications. I t is believed that commercial applications will grow rapidly, particularly where additional cost can be justified through increased performance and reliability. The trend toward size reduction in consumer electronic products will also speed commercial use of beryllia parts.
Two major problems fadng the beryllium industry today are: -Fully exploring dl of the properties of beryllium oxide in ceramic form and develop volume fabrition methods for maximum reduction of cost, thus increasing the range of usage -Finding adequate a n d dependable long range domestic supplies of beryllium ore that can b e e e o n o m i d y mined, milled, and processed into ceramic grade beryllium oxide Ore is mined or has been found in Colorado, South Dakota, New Mexico, Nevada, Utah, and New Hampshim. I t is believed that these deposits will eventually answer the need for a domestic supply. Beryl ore fmm which beryllia is obtained is now being imported from Brazil and Argentina in South America, India, and a number of African nations. It should be noted that 1 ton of beryl yields only 200 to 280 pounds of beryllia which must satisfy all of the need for the metal as well as the oxide. It has been proposed that beryllia could be used in combination with metals and other oxides. The general rule, however, has been that anything which is added to pure Be0 is detrimental to its thermal and electrical properties, and in some cases its mechanical properties. The tendency in the industry today is to use a 99% purity Be0 or better where maximum properties of the material are obtained.
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to express his appreciation to The Brush Beryllium Co., The Bnylliwn Cmp., Mineral Concentratcs C3 Chemic01 Co., Inc., and Corns Porcelain Co. frn their comments on the uses of beryllia and pmnission to use &scriptions of thir processes. V O L 5 4 NO. 3 M A R C H 1 9 6 2
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