Rocket Performance Has Come a Long W a ) Theoretical Isp (Sec.) H i g h e n e r g y chemicals w i l l g i v e 5 0 % m o r e perf or financée
Today's chemicals —good foi 2 5 % Derformance aain ν
1952
1956
Chemically Attainable
High Energy Chemicals
Hid
High Energy Chemicals
• Higl
Exotic n e w chemicals w i l l p o w e r t o m o r r o w ' s jets a n d rockets, o p e n t h e door to v o l u m e m a r k e t s for the chemical industry A. CHALLENGE to the chemical industry: L e a r n the missile industry's needs; develop tomorrow's rocket propellants and missile construction materials. Why? T h e Navy rocket airplane Skyrocket burned u p nearly 1800 p o u n d s of alcohol and liquid oxygen in 18
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a one minute flight. Multiply this many times, and it's easy to see t h e volume potential of some chemicals for use as propellants. Generally speaking, this vast amount of fuel will b e consumed by two types of vehicles— rockets and jets. This business is, or
should b e , business for the chemical industry. Other figures for thought: T h e Department of Defense will spend over $2 billion on missiles in fiscal 19-58 alone-more than t h e cost of developing the A-bomb. Propellants could take up to 5 % of this.
^ Rockets are used for many purposes other t h a n military. This t y p e , burning liquid oxygen a n d kerosine, will carry t h e earth satellite 37 miles u p , reaching a s p e e d of 4000 m.p.h. Other types will p r o p e l it to an altitude of 300 miles and a speed of 18,000 m.p.h. Knowledge of our upper atmosphere gained from Project Vanguard will help scientists prepare tomorrow's rockets for assaults on outer space
erformance
T h e chemical industry is doing something about getting its share of this melon. Last week at French Lick, Ind., Commercial Chemical Developm e n t Association held a symposium on W h a t the Rocket a n d Missiles Program Means to the Chemical Industry. Pur-
pose of the symposium, says CCDA, was to give t h e chemical industry more insight into t h e opportunities in the missiles business. Of course, m a n y chemical companies are already involved in the field. Right now, these companies tell C&EN, chemicals such as aniline, hydrazine, oxygen, hydrogen peroxide, fuming nitric acid, a n d JP-4 (a hydrocarbon mixture) are being moved in tonnage quantities for propellant use. But today's propellants aren't u p to tomorrow's big jobs such as t h e Intercontinental Ballistic Missile and outer space flight. T h e rocket industry needs propellants w i t h more "oomph." W h y ? Hotter chemicals will let a rocket carry its payload farther. Or, smaller medium-range rockets would be possible. Looming o n t h e horizon to challenge present compounds are high energy chemicals. A chemical or combination of chemicals t h a t gives specific impulse values over 2 5 0 seconds (at 3 0 0 p.s.i.) can b e considered in the high energy class. (Specific impulse—I sp —equals p o u n d s of t h r u s t available p e r pound of propellant p e r second.) This is w h e r e the chemical industry comes in. It has the knowledge of chemical properties and handling knowhow to find a n d tackle the highpowered new chemicals that can do the job. T h e challengers? Ozone, boron hydrides, fluorides, and hydrogen. Farther away a r e free radicals and nuclear propulsion. These are t h e chemicals t h a t industry is talking about right now. But t h e b i g questions are: H o w good are they? H o w can they be m a d e at low cost? H o w can they b e handled? H e r e are t h e answers, to the limits of security. First, though, some caution signs: • T h e s e chemicals, and the combinations described, haven't b e e n proved practical. S o m e may never work out. • Performance figures cited are purely paper calculations for hypothetical combinations.
• Specific impulse is only one measure of performance—albeit the most popular one. Factors such as density and molecular weight of combustion products may have significant bearing. Most propellants are a team—oxidizer and the fuel it will burn. Usually, two or three times as much oxidizer as fuel, on a weight basis, is needed to give the best results. Oxidizers, then, can be expected to get much of the attention in the search for high energy chemicals.
Fluorine Ranks High High on the list of chemicals of interest as high energy oxidizers are the fluorine compounds. While compounds such as oxygen difluoride, nitrogen trifluorine have many desirable properties, the top performer in the fluorine family is liquid elemental fluorine, F 2 . Fluorine burned with JP-4 gives a theoretical I s p of 265 seconds. Compare this with the I s p of 225 seconds reached using red fuming nitric acid as the oxidizer. Burning fluorine with hydrazine gives a theoretical I gp of 298 seconds; with hydrogen 352 seconds. High energy indeed. An added feature—fluorine has a relatively high density. T h e missile development program could gobble u p large amounts of fluorine. Right now, the only substantial producer is the Atomic Energy Commission. Total production figures are classified. Pennsalt Chemicals has a large hydrogen fluoride plant at Calvert City, Ky., which could serve a large fluorine generating plant. General Chemical is among other companies showing interest in liquid fluorine. Raw material for fluorine is acid grade fluorspar, C a F 2 , which yields about half its weight in fluorine. U. S. production of acid grade fluorspar is about 200,000 tons a year, equivalent to nearly 100,000 tons of fluorine. Cost? A direct figure for large quantities of liquid fluorine isn't available. An Air Force source says $4.50 to $6.00 a p o u n d for moderate quantities, depending on destination. Industry sources tell C&EN that cost could drop to $1.00 a p o u n d for daily multiton shipments if demand ever reaches these proportions. Handling liquid fluorine presents some problems. Since it boils at —306° F., it must be kept cold. It is corrosive, b u t nickel alloy containers seem to b e Suitable. A mobile liquid fluorine carrier has been developed. MAY
27,
1957
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formed as a combustion product light and not too persistent.
is
Ozone Goes One Better
T o m o r r o w ' s Jet A i r l i n e r s W i l l Fly Faster a n d Further, Thanks to the " Z i p " Fuels...Here's
Why:
H e a t v a l u e o f f u e l is the o n l y factor that can be changed v e r y m u c h ·
W Range of airplane = N 0 A H ( L / D ) Log rrf
(Berguet Formula)
N 0 = Propulsion efficiency Δ Η = Heat value of the fuel L/D = Ratio of lift to d r a g Ratio of weight of fuel to gross weight of aircraft
The fluorine is kept cold in transit by a jacket of liquid nitrogen. Thus fluorine is not under pressure unless the nitro gen accidentally boils away. General Chemical, among others, operates such carriers.
If a liquid fluorine tank should burst there would be a fire at the spot, but it would probably be localized, say fluo rine men. Accidentally spilled fluorine should dissipate readily into the sur rounding air. Similarly, the toxic H F
Another hot candidate for future ideal oxidizer is liquid 100% ozone, a "super oxidizer." Here's how it com pares with its close relative oxygen: Oxygen and JP-4 give a theoretical I s p of 248 seconds; ozone and JP-4 give an I s p of 266 seconds. Even a com bination of 7 0 % oxygen and 3 0 % ozone with JP-4 helps give the system a boost—I sp 253 seconds. And ozone has a higher density than oxygen. Liquid 100% ozone isn't being made commercially yet. Only research amounts have been made for military use. It's made by passing oxygen through an ozonator where high volt ages convert about 2 % by weight to ozone. The ozone is separated from the lower boiling oxygen by condensa tion and then cooled until liquid. Newer ozonators developed by Welsbach with a capacity of 600 pounds per day per unit make large-scale plants possible. Ozone costs more than oxygen, but is still not too high. While no firm prices are available for liquid 100% ozone, Welsbach says about 10 cents a pound in multiton quantities is possible. But there's one drawback—high con centrations of ozone tend to be explo-
H i g h Energy Chemicals W i l l Be Fuels of t h e
tyMmmEm
Theoretical | sp ( 3 0 0 p.s.i.a.), Sec.
These are today's rocket nron^llrmt combinations
Current workhorse
20
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High energy comes in above 250 sec. with fluorine and ozone providing the boost
sive. Concentrations of about 2 5 % ozone dissolved in oxygen are relatively safe. T h e trouble comes with hig^-r concentrations or with liquid ozt Minute traces of impurities can toucn it off. One path toward a more stable 100% ozone: Start with extra pure oxygen and use scrupulously clean ozone-generating equipment. Using this method, scientists at Temple Research Institute have handled, burned, and even premixed 100% ozone gas with organic fuels "without incident." Ozone has always been considered a toxic chemical, even at 0.1 p.p.m. But there is a report of a. man breathing 8 p.p.m. and surviving. Fortunately, ozone doesn't form toxic combustion products.
H y d r o g e n Is Tops—Theoretically Oxidizers are only half the story. For a really super propellant you need a high energy fuel to pair off with the oxidizer. Liquid hydrogen, from a performance point of view, probably is the ideal chemical fuel. White fuming nitric acid with hydrogen gives a theoretical I s p of 298 seconds; hydrogen and oxygen push the I s p to 342 seconds. Combining a couple of these supers, hydrogen and ozone, would
Even small missiles Nike getting a load major U. S. cities. even more emphasis
have a large appetite for chemical propellants. This early of liquid chemicals is similar to hundreds now protecting Hard-to-handle high energy chemicals coming up will put on protective clothing
raise the theoretical I s p to 369 seconds. While this is impressive in theory, all isn't a bed of roses where hydrogen is concerned. Hydrogen is the lightest element known. This means a large container is needed to carry a useful payload of hydrogen. The size and weight of such a container might make hydrogen impractical. Going to liquid hydrogen helps a little. A liquid hydrogen trailer could carry 14 times more liquid hydrogen than pressurized gas on a weight basis. But liquid hydrogen opens the door to a few tough new problems. Hydrogen liquefies at —424° F., a h a r d temperature to reach. One approach uses helium for cooling. The liquid hydrogen cost picture is a bit cloudy. Studies show that liquid hydrogen for less than 50 cents a pound should be possible in a large-scale plant. Liquid hydrogen is dangerous only because it can produce large volumes of flammable gas. Oxygen has to be present to make liquid hydrogen explode, and techniques are available to keep out oxygen. A hydrogen fire would probably be confined to a limited area because the gas is so
light.
There'd be no persistent fumes.
Boron—Key to Z i p p i e r Fuels If hydrogen alone is too light to be used as a fuel, the next approach might be to tie it up with a slightly heavier element. Boron is the lightest elemexit (besides lithium) which can combine with hydrogen. It forms gaseous, liquid, or solid hydrides with relatively high hydrogen content. Among these compounds are diborane ( B 2 H 6 ) , pentaborane (B5H9), and decaborane ( B 1 0 H 1 4 ) . Another advantage: Boron itself releases 25,000 B.t.u. per pound when burned. T h e new Zip fuels, combinations of boron, hydrogen, and carbon, are getting attention as fuels for jet engines. (Zip is the Navy's code name for its high energy fuel program.) They would replace hydrocarbon fuels. Some reasons: high heat values, up to 4 0 % higher efficiency than fuels such
as JP-4. Industry activity in boron is high. Olin Mathieson operates its own plant for making these high energy boron MAY
27,
1957
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Theories Fuel Researchers B e a r in Mind Rocket fuels form gaseous combustion products which are under pressure within the reaction chamber. Part of the heat content of these gases is converted to kinetic energy as the gases expand through a nozzle and out the open end of the rocket. These escaping gases produce a forward thrust that propels the vehicle. High thrust is produced by high heat values coupled with high efficiency in converting this heat to kinetic energy. To get maximum heat the propellants should: • Have large positive heats of formation, on a unit mass basis. This limits the selection to light elements such as hydrogen, oxygen, fluorine, nitrogen, beryllium, boron, carbon, lithium, aluminum, and magnesium. • Form combustion products with large negative heats of formation, since the total heat content of the system is the difference between the heat of formation of the propellant and the heat of formation of the combustion products. How efficiently the heat is converted to kinetic energy depends on the molecular weight of the combustion products. Low molecular weight reaction products such as hydrogen, carbon monoxide, nitrogen, and water make for higher efficiency. Generally, no solids should be present in the exhaust because they don't expand on passing through the nozzle and so do no work. Propellants can be liquids or solids. Usually, the system is of the bi-propellant type, made up of a separate oxidizer and fuel. A good propellant should: • • • •
Be stable to allow it to be stored and handled easily. Have a high density to hold down container and vehicle size. Be nontoxic to permit humans to handle it. Be noncorrosive to simplify materials problems.
The performance of a propellant system is measured as specific impulse, IS{), defined as pounds thrust provided by a pound of propellant per second. No combination of chemicals known today satisfies all the thermodynamic and physical criteria. Propellant systems are a compromise: Highest Temperature System Cvanogen + Ozone T( = 9467 c F.; IS1) = 270 seconds (est.) Lowest Molecular Weight System Hydrogen -+- Fluorine M.W. = 8.9; I s| , = 352 seconds Lowest c p /c v System Alcohol -+- Hydrogen Peroxide k = 1.20 I s p = 230 seconds Today's operational rocket propellants give I s p values in the range of 200 to 250 seconds at 300 p.s.i. chamber pressure. Higher chamber pressures raise these values somewhat. An I s p over 250 seconds at 300 p.s.i. qualifies the system as high energy. The highest theoretical I s p obtainable with molecular chemical fuels is around 400 seconds. This is the domain of rocket fuels of the future.
fuels, and two other plants, for the Air Force and Navy, will be operating by fall, says Olin. Total government investment here is $40 million. Callery Chemical looms large in the boron fuels picture. Callery will produce its Zip fuel, HiCal, for the Navy in a new $38 million plant. American Potash & Chemical, a basic producer of boron, just started first known commercial 22
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production of decaborane. This venture is privately financed. Add Stauffer Chemical to the list of private investors in boron, with a sizable investment in laboratories and plant for making and evaluating high energy boron compounds. Biggest basic producer of borax, a fundamental raw material, is Pacific Coast Borax. Metal Hydrides makes intermediates for the exotic
boron compounds used as propellants. The boranes are hard to make. In the academic synthesis, costly chemicals such as boron trichloride and lithium hydride are involved as intermediates. Low yields are the rule. Costly intermediates and difficult syntheses add up to expensive products. Diborane costs several hundred dollars per pound; decaborane several thousand dollars per pound. Handling doesn't seem to be a big problem with the boranes. Pentaborane can be shipped under ICC labels as a flammable liquid. Diborane, a gas, is shipped packed in cylinders and cooled with dry ice, under special ICC permit. These new boron compounds are toxic. Diborane, for example, is toxic above 0.1 p.p.m. However, boron oxide, B 2 0 3 , a combustion product, is relatively nontoxic. Solids N o t Forgotten On the other side of the fence, development isn't standing still in the solid propellants field. Solids have some advantages over liquids. You don't have to pump a solid propellant, so the rocket motor can be much simpler. Reliability is thus sometimes higher. There are problems, though, tough ones. Once ignited, a solid propellant engine cannot be stopped and restarted. Further, all the desirable properties of a propellant have to be prebuilt into the solid charge. To make it extra tough, there is no way to predict accurately beforehand the properties a new combination of solids might have. This problem makes it difficult for chemical companies to get into the solid propellant field. Explosives handling experience is a must; so is an explosives plant, since the whole propellant is put together there. From the H a n d b o o k Official secrecy surrounds any solid propellant system that might qualify as high energy. Keeping in mind the parameters for liquid systems though, one can speculate on some solid systems using available handbook data. As fuels, the light metals, for instance, look good on paper. Boron and beryllium release high B.t.u. per pound when burned. Beryllium's extreme toxicity is a factor against it. Powdered light metal fuels with solid oxidizers suggest themselves.
I n the oxidizer field the perchlorates seem to b e favorites. Perhaps the t o p prospect h e r e is lithium perchlorate, with about 6 0 % available oxygen. It may turn out t h a t a combination of liquid oxidizer and solid fuel, alone or in a slurry, will show up best. Solid fluorine compounds may b e worth some thought. T h e field is w i d e open.
Missiles A r e Big Business, Getting Bigger Dept. o f D e f e n s e Spending for Missiles I
| Procurement
EBH
R & D
%
Def
e n s e Budget
2500 Millions:of Dollars ^Fiscal; ; Year)Jfg 2000
Into the W i l d Blue Yonder 1500
Right now it looks like molecular chemical propellants—liquid or solid— won't do m u c h better than a n I s p of 4 0 0 seconds. But the experts have their eyes on ultra energy chemicals w h e r e I gp 's can run 1000 seconds and higher. H e r e they talk about free radicals. F r e e radicals, created w h e n heat or some other form of energy breaks apart a molecule, constantly t e n d to recombine. W h e n they do, the energy that went into dissociation is released. H a r ness this energy, and you have a whole n e w concept of propulsion. For example, hydrogen fragments recombining give off about 90,000 B.t.u. p e r pound, good for a theoretical I s p over 1000 seconds. T h e problem is to make free radicals in large amounts and then to keep them from recombining u n d e r storage conditions. Some possible approaches: • Supercooling to near absolute zero. This works b u t lots of heavy cooling e q u i p m e n t is needed. • Mixing with inert gases, helium for instance. This might work, but it di-
1000
1957 (est.)
lutes
t h e free
radical
concentration.
Add another b i g problem: Temperatures can reach 12,000° F . Today's materials can't withstand this heat, b u t workable answers will b e well worth t h e effort. T h e atom, too, may have a place in propulsion. Fission of U 2 3 5 produces 1 billion B.t.u. p e r pound. Putting this energy to work to expand hydrogen, for example, could give a theoretical I s p near 9 0 0 seconds. T h e problems, of course, are many. H i g h temperatures are t h e rule, so new construction materials will be needed.
1958 (est.)
Among other problems: getting rid of fission products which poison the reaction. O r nuclear power could b e used directly. Fission particles exhausted at high velocities could propel a rocket. The profclems here are about the same —materials and control. T h e technology i s known in principle. Regardless of which chemicals finally m a k e the grade, missiles programs give n e w chemicals a chance to get started. It's up to the companies making the prociuct to find civilian outlets for their chemical during the missiles testing period.
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