Chemistry of Detonation 2

8/3/2019 Chemistry of Detonation 2

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THE JOURNAL OF CHEMICAL PHYS ICS V O L U M E 48 , NUMBER 1 1 JANUARY 1968

Chemistry of Detonations. II. Buffered Equilibria:VIORTIMER J. KAMLET AND J. E. ABLARD

U. S. Naval Ordnance Laboratory, While Oak, Silver Spring, Maryland(Received 19 June 1967)

At low loading densities, values of N, M, and Q calculated from the H20-C02 "arbitrary" show poorindividual agreement with estimates of these quantities from the RUBY computer code. Nevertheless, whensubstituted into the equation P=15.58 NM1/2Ql/2pO', they lead to detonation pressures which correspondclosely to RUBY predictions. That incorrect in put information should yield results which are very nearly"correct" is rationalized on the basis that the equilibria whose shifting engenders the changes in N, M, andQare "buffered" in the sense that "errors" in N are offset by compensat ing "errors" in M and Q. As a consequence of the fact that most of the important equilibria in the detonation of C-H-N-O explosives arebuffered, calculated (and actual) mechanical properties of detonations appear to be extremely insensitiveto exact product compositions. A number of other interesting consequences of these buffered equilibria arediscussed.

1. INTRODUCTIONIn Paper I of this seriesl it was suggested that detonation pressures of C-R-N--O high explosives mightbe estimated by means of the simple empirical equation

P=15.58iVMl /2Qj,f2po2 (P in kilobars), (1)where iV is the number of moles of gaseous detonationproducts per gram of explosive, M the average molecular weight of these gases, Q the chemical energy of thedetonat ion reaction ( - t:..Ho per gram of explosive), andpo the initial density. In a preliminary test of this relationship, iVRUBY , MRUBY , and QRUBY (the computerestimates of these quantities) were subst ituted intoEq. (1) for a number of typical organic explosives atrepresentative loading densities. That this led to values of Peale which differed only nominally from pressurespredicted by the RUBY and STRETCH BKW computercodes2 confirmed that, given "proper" values of iV, M,and Q, the new equation leads to reasonable estimatesof P (Table III of Ref. 1) .

I t was then demonstrated that l\'"rh, ACrb, and Qurh,as easily calculated from the H 20-C02 arbitrary assumption of detonation product compositions, corresponded reasonably closely (i.e., to within 5%) toiVRUBY , MRUBY , and QRUBY at initial densities above1.40 glcc, but that differences became significantlylarger at lower loading densities (Table V of Ref. 1).The H20-C02 arbitrary represents N2, H20, and CO 2as being the only important gaseous products in thedetonation of most C-H-N-O explosives, with H 20having priority in formation over CO 2From these findings it was expected that, when used

1 M. J. Kamlet and S. J. Jacobs, J. Chern. Phys. 47, 23 (1967),Part I, preceding paper.'A s used herein, the term RUBY includes the results of computations at the Los Alamos Scientific Laboratory by theSTRETCH BKW computer code and at NOL by the LawrenceRadiation Laboratory's RUBY code. For the purposes of presentdiscussions, these codes differ only in minor regards and, unlessotherwise specified, RUBY computations shall be considered asbased on Mader's most recent covolume factors and the "moreappropriate" of his dual K-W parameter sets (Ref. 11 of Part I) ,with the heat of formation of solid carbon taken as zero. SeePart I for other leading references.

in combination with the arbitrary method of estimating N, M, and Q, Eq. (1) might allow rough predictionsof detonation pressures of experimental explosives ator near their theoretical maximum densities. Such predictions would require as input information only theelemental composition of a C-H-N-O explosive, itsloading density, and an estimate of its heat of formation, and would require no other calculational aidsthan are available to the organic-synthesis chemist athis desk. I t was felt that the results would be meaningful where arbitrary and RUBY values of N, M, and Qdid not differ markedly, i.e., only at Po> 1.40 g/cc.When pu t to the test, however, the new methodshowed both higher precision and broader scope thananticipated. Comparisons between hand calculationsand machine computations (Table VI of Ref. 1) involved 103 data sets for 27 compounds and compositionsat loading densities from 1.00 to 1.96 glee. They coveredthe full gamut of N urt , Murb, Qarb, and Gurb (the weightfraction of explosive going over to gaseous detonationproducts) to be encountered among organic high explosives. The results3 showed good agreement betweenP eule [Eq. (l)J and P RUBY at the higher densities aswas expected. At Po> 1.45 glee, differences averaged1.6% and in only a single instance (of 66 data sets)was the "error" greater than 5%.

II. THE SEEMING ANOMALY

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Much to our surprise, however, it was also foundthat, although agreement between Peale and PRUBYwas indeed slightly poorer at the lower loading densities, the differences were still quite small and no trendcould be discerned. At po=1.40 glee, differences averaged 2.4% (12 data sets); at 1.20 glcc, differencesaveraged 2.1% (12 data sets); at 1.00-1.13 glcc,differences averaged 2.0% (13 data sets). Further,in no case was the "error" as high as 5% at the lowerclensi ties.

'The values of P oalo included a "correction" step which involved subtract ing 6'/(, where Garb, the weight fraction of explosivegoing over to gaseous products, was gr eater than 0.93. See Appendix C to Part I.

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CHEMISTRY OF DETONATIONS . I I 37Such precision at 1.00 g/cc was most unexpected inthe light of our earlier observation that at this lowdensity N arb, M arb, and Qarb for underbalanced explosives may differ by as much as 10-20% from thecorresponding RUBY values. With TNT at 1.00 g/ccas an example:

N,ub=0.0253 moles gas/g explosive, NRUBy =0.0293,difference = -13.7%,M arb=28.52 g gas/mole gas, MRUBy=26.38,

difference = +8.2%,Q rb = 1282 cal/g, QRUBY = 1104,

difference = +13.9%, butP eale=75.3 kbar, P RUlly =76.2,

difference = only -1.2%.Similarly, with tetryl at 1.00 g/cc, N arb (0.0270) differsfromNRuBy (0.0323) by -16.5%, bu t Peale (85.3kbar)differs from PRUBY (87.1) by only -2.1%. With picricacid at this density, N arb (0.0251) differs from NRUBY(0.0317) by -20.8%; Peale (84.4 kbar) differs fromPRUBY (87.9) by only -4.0%.The results may be summarized as follows. "Proper"values of N, M, and Q in Eq. (1), e.g., RUBY values orarbitrary values at the higher loading densities, leadto detonation pressures which agree well with RUBYpredictions. At the lower densities the H 2O-C02 arbitrary no longer provides "proper" estimates of N, M,and Q. This apparently makes little difference as concerns average agreement between Peale [Eq. (1) ] andP RUBY , however, and we are faced with the seeminganomaly that input information which is known to begrossly "incorrect" leads to predictions from Eq. (1)which are very nearly "correct."

The rationalization of this anomaly holds importantimplications about effects of product compositions oncalculations from Eq. (1). To whatever extent Eq. (1)successfully parallels RUBY and the KistiakowskyWilson equation of state, and to whatever extent thelatter in turn successfully describe actual phenomena,these implications may also serve toward a betterunderstanding of properties of explosives in real detonations and, eventually, certain types of damage effects.

III. BUFFERED EQUILIBRIAI t has been mentionedl that product compositionsin the Chapman-Jouguet condition and in the subse

quent expansion of the detonation gases depend moststrongly on the two important equilibria2 C O ~ C 0 2 + C ,

H 2 + C O ~ H 2 0 + C , t::..Ho= -41.2 kcal, (2)t::..Ho= -31.4 kcal, (3)

and that the H 20-C02 arbitrary is simply a conciserepresentation of the assumption that both equilibria

are predominantly to the right. From (H20/H2) ratiosin RUBY print-outs, it was shown that the computerpredicts Equilibrium (3) to be far to the right forC-H-N-O explosives at all loading densities underconsideration. The computer's (COdCO) ratios, onthe other hand, indicate that it finds Equilibrium (2)to be predominantly to the right, i.e., (C 02/CO) > 15,only at loading densities above 1.70 g/cc (see Table IVof Ref. 1 for specific data). At Po


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38 M . J . KAMLET A ND J . E . ABLARDTABU: 1. "Buffered" equilibria. N, M, Q, and

C02 +C , CO+H2->C+H,O

Arbitrary 2: H2O-CO-C02, 2 COC+H2OArbitrary 3: CO-H,O-C02, 2 CO


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CHEMISTRY OF DETONAT IONS . I I 39could cause methane to become a major rather thana minor product at the lower loading densities. Suchinput changes might involve assuming a positive heatof formation for solid carbon and assigning to CH4 alower covolume factor (k i ) in place of the value of 528currently used by RUBY. A ki/M i=13.760.15 proportionality was demonstrated for the "major" detonation species in Paper I of this series, 1 and k i = 528for CH4 does seem high in the light of this observation.9I t is therefore also of value to consider the effect on cpof shifting Equilibrium (5) completely to the left.Taking the detonation products assumed for TNTby Arbitrary 2 (Table I) and reacting the H20 withcarbon to form CH4 and additional CO according toReaction (5), we get the new set of products: 1.5moles N2, 5.83 moles CO, 1.17 moles CH4, and 0.17moles H20, for a total of 8.67 moles gas/mole TNT.N becomes 0.0382, M becomes 26.18, Q becomes 725,and cp becomes 5.263, an increase of 3.4% over thevalue of cp predicted from Arbitrary 2. Again, in Reaction (5), we encounter a buffered equilibrium whereinshifts from one extreme to the other cause markedchanges in N, M, and Q, but only nominal changes incpo The same holds true if carbon and hydrogen fromArbitrary 3 are reacted to form methane, or nitrogenand hydrogen to form ammonia.Indeed, since most of the equilibria which are believed to affect product compositions in actual detonations appear to be buffered, we have found that takingthe elements of a C-H-N-O explosive and recombiningthem to form any possible mixture of products fromamong N2, CO, CO 2, H20, CH" NHa, H2, and HCNgenerally leads to values of cp which differ betweenextremes by no more than 8-10%. Examples whichare highly unlikely in terms of actual detonation mixtures, bu t are nevertheless illustrative, involve converting the elements of TNT to the following sets of products: (a) 3.0 moles HCN, 3.0 moles CO 2, 0.5 moles CH"0.5 g atoms C; (b) 1.67 moles NH a, 0.67 moles N2,3 moles CO 2, 4.0 g atoms C. In the former case cp = 4.684,in the latter cp=4.775, which differ by -3.2% and-1.3%, respectively, from the value used in the presentcalculations.The above observations regarding the sensitivity ofN, M, and Qand the relative insensitivity of cp to exactcompositions of products from individual explosiveslead to a variety of interesting observations. Theseinvolve: (a) the present calculational method; (b) theRUBY code and similar computer-based methods of calculation; (c) effects of equilibria on actual detonationproperties and, eventually, on damage effects; and (d)methods which are widely used to intercompare thepredicted performance of explosives.

9 Unlike the k. values for N2, CO, CO" and H20, which have beenadjusted to accomodate experimental measurements, RUBY'scovolume factor for CH. remains the "geometrical" value based onmolecular dimensions as deduced from van der Waal's radii.Assuming a ki of 220 for CH, (13.76X16) might prove no lessrealistic. See Sec. II I of Part I.

V. CONSEQUENCES OF BUFFERED EQUILIBRIAIN THE DETONATIONA. Present Calculational Methods

I t follows from the relative insensitivity of cp toequilibrium positions that the present calculationalmethods do not stand or fall with the validity of ourestimating N, M, and Q by means of the H 20-C02arbitrary. Using an H20-CO-C02 or even a CO-H20 -CO 2 decomposition scheme or any combination of theseto supply N, M, and Qfor Eq. (1) would not have ledto values of Peale differing appreciably from those whichwe have reported.Since the H20-C02 arbitrary was chosen in the present study because it best reproduced RUBY'S estimatesof these quantities at the higher densities, the aboveobservation becomes important in reconciling the success of the simplified calculations with our current beliefthat the computer's predictions regarding the positionsof the various equilibria involving carbon are open toserious question. RUBY'S computations are based onthe input assumption that carbon takes the form ofsolid graphite with zero heat of formation. 2 I t hasnever been established that sufficient time is available in the C-J state for carbon to assume orientationin an ordered crystal lattice of any appreciable sizeand it seems fair to suggest that, lacking evidence inthis regard, the tJ.H,=O assumption must be consideredas suspect. Similar considerations have led to the useof +15 kcaljg-atom as the heat of formation of carbonin RUBy-type computations at the Lawrence RadiationLaboratories of the University of California, this valuebeing considered the "heat of subdivision" of finelydivided graphite. lOAs is discussed in the Appendix RUBY'S estimate ofthe position of Equilibrium (5) is strongly influencedby the input heat of formation of carbon; similar considerations are likely to apply as regards Equilibria(2) and (3). Thus, the possibility exists that RUBY'Sestimates of N, M, Q, and the various Ni bear littlerelationship to the values of these quantities in actualdetonations.

I t follows that the H20-C02 arbitrary must be considered similarly suspect as regards estimates of actualN, M, and Q. In consequence of the buffered equilibria,however, this arbitrary may nevertheless be completelyadequate for the estimation of a c t u a l ~ cp, and henceactual detonation pressures and velocities.

B. Computer-Based Methods of CalculationWe have already questioned RUBY'S input assumptions regarding the tJ.Hj of carbon, the k i of the "minor"

10 Dr. E. Lee, Lawrence Radiation Laboratory (privatecommunication). The referee has pointed out to us that Maderexperimented with a positive AH, in the course of his BKW studies.While using a positive AH , for carbon was a help in calculatingP and D, it caused troubles in calculations involving the isentropicexpansion of the detonation products, perhaps because it was notallowed to change during this process.



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40 M . J . K A M L E T A N D J . E . A B L A R Ddetonation species, and the parameters in the K-Wequation (Appendix C of Ref. 1). Other of the inputdata may be at least as suspect in that they are basedon inherently inexact measurements or involve extrapolations to pressures far beyond experimentally accessible ranges.

In seeming contradiction, however, RUBY does infact succeed in predicting detonation pressures over alimited range of compositions and loading densities,which accommodate the body of inherently inexact andoften contradictory measurements about as well asmight be expected of any computational method. Further, the computer's estimates of detonation velocitiesshow reasonably good agreement with more accurateexperimental information over the same limited rangeof compositions and densities.Again we feel that a rationale for "correct" resultsfrom "incorrect" input information may be found inthe phenomenon of compensating "errors" such as havealready been shown to minimize the effects of differences between arbitrary and RUBY N, M, and Q inEq. (1). I t is no less likely that, even where the computer grossly misjudges the N;'s, the buffered equilibriamay introduce mutual cancellations which also tend tolessen the effects on RUBY'S pressure and velocity of"errors" in the various quantities which interact toproduce these predictions in the computer's multiiterative machinations. Thus relatively large differences between RUBY values and actual values of pJ,p g (or Vg) , T, the tJ.H/s, Lx.k., CvdT, N, Q, EJ-Eo, ,,(,etc., may offset one another and lead to values of PRUBYand ~ U B Y which are very nearly "correct." In consequence, RUBY'S P and D predictions may parallel thoseof Eq. (1) in being insensitive to exact product compositions and hence to inaccuracies in large segments ofthe input information.

RUBY and Eq. (1) probably both reflect the fact that,as is discussed in the next section, actual mechanicalproperties of detonations are also insensitive to exactproduct compositions. It is also possible that the success of the K-W equation of state with other parameters and covolumes,2,7.11 other equations of state,12and other computer-based methods over limited rangesof explosive composition and density may be attributedto similar buffering phenomena. A necessary corollaryis that, as has already been pointed out in part byJ ones,13 good agreement between predicted and expenmental P and D do not necessarily justify: Ca) theform of the equation of state, (b) the equation-of-stateparameters except over limited ranges of composition,(c) covolume factors of the detonation products, (d)assumptions regarding the form and properties taken

11 R. D. Cowan and W. Fickett, J. Chern. Phys. 24, 932 (1956).12 For a review of the various equations of state, see S. J.Jacobs, ARS (Am. Rocket ~ o c . ) J. 30, 151 (1960). .13 H. Jones, Third S y m p o s ~ u m on Flame and Exploston Phenom-ena (The Williams and Wilkins Co., Baltimore, 1949), pp. 590-594.

by carbon and other solid products in the detonation,(e) other input information, and (f) predictions ofother detonation properties which are not subject toexperimental verification.C. Actual Mechanical Properties of the DetonationFrom an analysis of computer results not unlike our

own, Johansson and PerssonI4 have recently suggestedthat detonation pressures might vary with the squareof the loading density, i.e., for individual explosivesK=2.0, (6)

where A is a constant depending on the nature of theexplosive. l The proportionality was demonstrated forfive materials over the important range 1.0


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CHEMISTRY OF DETOXATIONS . I I 41Detonation velocity measurements also support thisconclusion. In Part I we reported that the equation

A = 1.01, B= 1.30 (7)allowed calculation of detonation velocities D whichagreed well with RUBY predictions. In still another paperof this series we shall show that Eq. (7) also accommodates a large body of ideal (infinite diameter) experimental detonation-velocity results to within less than 1.5% average difference and less than 1.0% as a90% confidence limit (26 explosives, Po from 0.95 to1.90 glcc, more than 100 individual measurements).That equilibria are buffered in actual detonations isagain a likely explanation for the fact that a single setof A and B in Eq. (7) serves equally well for nearCO2-balanced explosives and for hiahly underbalancedexplosives. b

Price has suggested" that an explosive's abilitv todo some types of work is a simple function of itsdetonation pressure. We shall offer supporting evidencein this regard in a subsequent paper, since it followsfrom Price's observation that the quantity cf>arb mayalso provide the basis for predicting the relative a b i l i t ~ of C-H-N-O explosives to effect certain types of d a ~ -ag : . That such measures of performance (e.g., theablhty to push a plate or expand a cylinder) show thesame dependence on cf>arb for near-C02-balanced andhighly underbalanced explosives again reflects the imp o r t a n ~ e of buffered e q u i l i b r ~ a . Such buffering may~ e u t r a h z e the effects of changmg product composition

at .least the early stages of the detonation gas expanSlOn m the same sense as has been demonstrated forthe C-J condition.

I t seems necessary at this time to emphasize thatthe above generalizations may pertain only as concernsC - H - ~ - O explosives and that diametrically opposedconcluslOns may apply to aluminized mixtures. Evidence is available that kinetic factors (which extendfar beyond the time of the C-J condition), rather thanthermodynamic factors, govern the extent of utilization of aluminum in the detonation. If, as seems reasonable, the rates of the aluminum reactions are highlytemperature dependent, and if aluminum reacts at differ:nt rates w i ~ h . H 20, CO, and CO 2, detonation propertIes of alunumzed explosives should depend verystrongly on exact equilibrium compositions of thesespecies in the C-J condition and in the early stagesof the gas expansion. For such reasons, Eqs. (1) and(7) may be inapplicable for use with aluminized mixtures.D. Some Comments Regarding "Heats of Detonation". Many explosives chemists have for many years conSIdered "heat of detonation" as the primary measureof efft;ctiveness. "Figures of merit" of experimentalexploslVes have most often been expressed in terms of

Q/QTNT. I t deserves comment that, as concerns "heatsof detonation," equilibria such as (2), (3), and (5)engender two types of situationsPOn the one hand, a CO2-balanced explosive likeBTNEU produces no carbon to participate in suchequilibria and the "heat of detonation" mav be considered to be a reasonably constant prope;ty of theexplosive, relatively independent of the conditionsunder which calculated or measured (Table I). Anunderbalanced e?,plosive like TNT, on the other hand,produces appreciable amounts of carbon in the detonation state. At the successively lower pressures as thegases expand, this carbon reacts first with CO 2 to formCO [Equilibrium (2) ] and then with H 20 to form COa.nd H2 [Equilibri,:m (3) ] or CO and CH4 [Equilibnum (5) J, successively greater amounts of detonationenergy being "soaked up" in these reactions. In consequence, the "heat of detonation" of TNT becomes acontinuously varying property which can differ b\- asmuch as 107% depending the initial density,' thee x t e ~ t . to which the gases haye expanded, ar:d thecondltlOns under which the equilibria "freeze." To agreater or lesser extent, the latter considerations alsoapply to any explosive with Garb < 1.00.If R U B ~ ' S (C02/Co) ratios come near to being correct, ArbItrary 1 (Table I) approximates the detonatio.n c o n ~ i t i o n for high-density explosives at the C-Jpomt w ~ l l e , f.rom the correspondence with usual typesof calonmetnc measurements,5 it is likely that Arbitrary 2 represen ts a condition after the gases haveexpanded to several (possibly 2-20) charge diameters.Arbitrary 3 might correspond to a situation much farther down the isentrope.Using Q/QTNT from Table I as the basis for intercomparison, and depending on the arbitrary used tocompute the Q's, a "figure of merit" for BTNEUmight equally well be 1.15 (Arbitrary 1), 1.54 (Arbitrary 2) , or 2.14 (Arbitrary 3) . In the first case thecomparison would be at the top of the isentrope inthe second case a relatively short distance down'theisentrope, the third case a relatively longer distancedown the lsentrope. From similar considerations it ispossible to take one's choice: PETN is 3% more ~ o w e r -ful than BTNEU (Arbitrary 1) or BTNEU is 6%more powerful than PETN (Arbitraries 2 or 3).

Even more important, however, a judicious choiceof sets of experimental conditions might provide evidence for any such calculational intercomparison in17 Very strict}y speaki?g, the term heat of detonation should referto the a ~ p r o p n a t e l y adjusted chemical energy difference betweenthe startl?g e x p } o S l v ~ and the products formed in the C-J state.The term c a l o n m e ~ ~ c h e ~ t of de!onation, " which usually involvesat least some reeqUlhbratlOn dunng the expansion of the productgases from the C-J state, is therefore almost necessarily a misnomer. ~ h e same . l l O l d ~ true .for .most other usages of the term byexplosl\:es ~ h e m l s t s , IncludIng .ltS usages in the present paper. Toeml?haslze I ~ e x a c t n e s s of termInology, "heat of detonation" is setoff In quotatIOn marks where appropriate. We are grateful to DrDonna Price for pointing this out. .



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42 M . J. K A M LET AND J. E . ;\ B L A R Dthe form of accurately measured "calorimetric heats ofdetonation." Such a choice might involve changes in(calorimeter volume/explosive weight) ratios or, asfirst shown by Sutton18 and convincingly confirmed byApin and co-workers,4 varying charge densities or thedegree of confinement of the charge within the calorimeter.

While such flexibility in calculation and measurement of Q for underbalanced explosives conforms withthe general observation that different explosives areindeed better for different applications, the "state ofthe art" has not yet reached the stage where an application and a calculational method based only on Qcan be unambiguously matched. For such reasons, wefeel that citing the "heat of detonation" (note quotesI7)as a unique property of an under balanced explosive isoften apt to be misleading. Where "figures of merit"are based on this property alone, intercomparisons ofexplosives should be taken cum grana salis unless allthe assumptions in the calculations or the exact conditionsof the calorimetric measurements are clearly spelled out.

ACKNOWLEDGMENTSThe authors wish to thank Mr. H. Hurwitz of thislaboratory for making available to us unpublished RUBYresults upon which much of the above is based. We arealso particularly grateful to Dr. Donna Price and Dr.

S. J. Jacobs for their very substantial contributions tothe effort. The work was done under NOL Foundational Research Task FR-44.APPENDIX: EFFECT OF RUBY'S INPUTINFORMATION ON THE POSITION ITPREDICTS FOR EQUILIBRIUM (5)

Changes in the K-W parameters do not markedlychange the equilibrium position. Using TNT parameters in the STRETCH BKW code, Mader predicted an(H20/CH4) ratio of 178 for TNT at 1.00 g/cc. Usingthe RDX parameter set in RUBY, Hurwitz at NOLreported (H 20/CH4) =144 for the same explosive atthe same density.2

In marked contrast, the equilibrium position is influenced strongly by input heats of formation andcovolume factors (k i ) . Following Le Chatelier's prin-18 T. C. Sutton, Trans. Faraday Soc. 34, 992 (1938).

ciple, more negative heats of formation or, at the highpressures encountered in detonations, lowered k/ s forindividual species shift equilibria toward those species.Less negative !::..H/s and higher k;'s shift equilibriaaway.Current RUBY computations at NOL, using 250 asthe k i for H20, 390 for CO, and 528 for CH4, andassuming zero heat of formation for solid carbon, predict (H20/CH4) =445 for TNT at 1.47 g/ce. Hurwitz,19using somewhat different values of (3 and K in earlierRUBY computations at NOL (but which differences,as mentioned above, should effect the equilibrium position relatively slightly) and taking the same k/ s forCO and CH4 but 360 rather than 250 as the ki forH20, reported the following results for TNT at 1.47g/cc: Assuming !::..Hj=O for solid carbon, (H20/CH4) =14.8; assuming !::..H j=+15 kcal/g-atom for solid carbon, (H20/CH4) =2.53.Thus a 44% change in the ki of the single speciescaused a 30-fold change in the product ratio. Assuminga positive !::..Hj for carbon such as is currently preferredby at least one highly knowledgeable group of researcherslO caused a further sixfold change.Similar effects are observed with RDX at 1.60g/cc. Current STRETCH BKW computations predict(H 20/CH4) =1.08 X 104 Earlier RUBY computationspredicted (H20/CH4) = 18.1 when !::..H j (carbon) wastaken as zero and 3.93 when !::..Hj (carbon) was takenas + 5 kcal.Correspondingly large shifts of Equilibrium (5) inthe direction of CH4 would therefore not be unexpectedat densities as low as 1.00 g/cc if a positive !::..Hf wereassigned to carbon and if the ki for CH4 were adjusteddownward in current RUBY computations.9 Methanecould become a "major" rather than a "minor" detonation product. The extreme sensitivity of productcompositions and the relative insensitivity of predicteddetonation properties to input information which is souncertain at the present "state of the art" shouldemphasize the critical importance to RUBY of the factthat equilibria are buffered. It should also emphasizethe potential pitfalls in performance predictions basedon "heat of detonation" alone, since the latter propertyis highly dependent on exact product composition.

19 H. Hurwitz, "Calculation of Detonation Parameters with theRUBY Code," U.S. Naval Ordnance Laboratory Rept., NOLTR63-205 (1965).

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