EARL A. WEILMUENSTER Olin Mathieson Chemical Corp., Niagara Falls, N.
Y.
Utilization of High-Energy Fuel Elements Boron-containing materials offer high promise as high-energy liquid propellants for military and perhaps also civilian use A L L AIRCRAFT FUELS are materials from which energy can be released in a controlled manner to provide for propulsion. Different applications make different demands on fuels, and so the criteria for choosing a fuel may vary widely. J. R. Cracknell, writing in the March 15, 1957, issue of Flight, said that the ideal fuel should possess the following characteristics : High energy content per unit weight High energy content per unit volume Easy handling Low cost “Unfortunately for most of the commonly used fuels, these requirements tend to be mutually exclusive. Today, however, a new class of ‘exotic fuels’ encompasses all these requirements.” Mr. Cracknell pointed out that “the first aviation fuels were hydrocarbons,
and with comparatively minor modifications they still hold the field today. They have given good service and appear to meet all the requirements. If this be the case, why the incentive to change and why the interest in new highenergy fuels, especially those of the lightweight elements?” He said also that “for the civilian operator there is at present no incentive, but for the military every last iota of efficiency and performance counts. With the increasing efficiency of miniaturized nuclear weapons, the weight of the fuel load becomes a critical factor in performance. Conversely, the defense must at all costs ensure that every bomber is intercepted well before it reaches the target, and that every interception will result in a certain kill. Thus, each is straining to the utmost in the performance race and today,
with the greatlyreduced numberof bombers now needed to deliver a crippling blow, even the rarest and most expensive fuels must be considered, if they will give the required performance.” One of the mcst important properties of a fuel for an air-breathing power plant is its B.t.u. per pound value, compounds of the lighter weight elements having higher heats of combustion than the hydrocarbon fuels. Liquid hydrogen immediately stands out, with its very high heat of combustion. However, its extremely low density would require a large storage system for a power plant and this, of course, would necessitate a large refrigeration or insulation system. Beryllium in nearly all of its compounds is extremely toxic and also is in short supply. For these reasons it was decided not to investigate these materials. V0L. 49, NO. 9
SEPTEMBER 1957
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Monufacturing Process
In general, the manufacturing proass being used ta prepare HEF fuels consiaS -c of tseating b o r o n a n t a i n i i o m in such a manner that they arc converted to me' f ~ l intrrmcdiate boron cornSubsequent reactions of these intcrmediates convat them to the final product. The entire operation is a completely integrated process, requiring 0 .5 1.0 1.C 2.0 2.5 3.0 3.5 4.0 1.5 only the s w n g boron chemicals and a Milllbos ol B.T.U./eu.ft. s m a l l amount of othm ma& for Heating value of elemenh chemical d b u p to compensate for minor losses. By-products of certain step8 in the proears are recyded fm usd as reactants in some carlia proceasing step. Although the en& procegl is completely integrated and is currently in we for the prodnction of HEF fucla, O h Mathiemn *is continuing te invrstigate altesnative routea for certain specific operations, with the vim of lowering w@and obtaining higher yieMs of+ncts and conversions of reactants. To illusaate, the company now has three competitive routea for the conversion of the boron-eontaining GW. In addition, every step of the process has one or more competitive and economically feasible alternative routes that could be used as the occasion demanded. From the standpint of use in liquid propellants, the boron-conaining materials evoking the most interest are penMillions ol B.T.U./cu.ft. taborane and decaborane. Heating value of possible fuels The replacement of hydragcn by an alkyl group results in a lowered heating value for the resultant compowd. Diborane, the simplest of all the boranes, can be prepared by reaction of stantially better than JP-4, the hydroAeswrch on Ihe Bomnn lithium hydride with boron pifluoride carbon currently in use. etherate. The product, being a gas, is For the reasons outlined, the field of The mast promising area for risearch, conveniently removed from the reaction boron chemistry w a s chosen as a pmmtherefore, appeared to be the boranes medium. The higher boranes, pentaising area for development of new fuels. (-%compounds of boron and hydrogen). borane and decaborane, are prepared Boron was djscovered as a separate Thge boranes, although of a lower heat in several ways. The mute mast muelement in 1606. The next step in the of combustion per pound than liquid hyally followed is through diborane. Simdevelopment of its chemistry was the much higher drogen, nevertheless posple application of heat is sufficientto conwork in Germany to prepare the boron hears of combustion than 'the hydrocarvert the diborane to pentaborane and dechydrides, characterize them, and *Ibon fuels. In fact pentaborane is about 6W0 better than JP-4, a commonly tablish some of theif properties. The aborane. The HEF fuels are believed to meet the American effort started in 1942 with exused hydmarbon fuel. requirements for future high speed mistensive studies on the chemistry of the In vim of Olin Mathieson's long insile and aircraft applications. Continued boron hydrides. In 1947 a survey was terest in explosives and ammunition, research and development are expected made hy the British, which encompased as well as the success achieved in develop to keep pace with the growing demand studies of boron matuials to be used as ing and producing hydrazine, it was only for superior performance high-energy ramjet fuels. At the same time Amerinatural that the corporation should be infuels in the liquid propdlaut field can effort started on combustion studies terested in a high-energy fuels progvm. The day may not be far off when these and the use of boron hydrides in rocket It therefore accepted a contract with the fuels will be available for civilian as well motom, ramjets, and air-breathing cnN a y Bureau of Aeronautics in 1952 on as military una. pines. The ZIP project started in 1952 the ZIP roject to prepare high-energy and ihtensive studies have been in progliquid h i s . The goal wan to develop a Commwciai Chemical Development Asr*u ever since that time. A hreaksociation,Frcnch Lick, Ind., May 14,1957. liquid fuel whidi would perform sub-
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through baa been made, and what are now known an the HEF fuels arc being synthesized. The% materials have been produced in test quantities andhave lived up to expectations of high density, low toxicity, and safe haodling in addition toa high energy content.
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INOUSTRIAL AND LNOlNEEllWO CHEMISTRY
