NATIONAL BUREAU OF STANDARDS REPORT

9456

FLAME INHIBITION WITH ELECTRON ATTACHMENT AS THE FIRST STEP

Robert M. Mills

llvsKPort has been "prepared

for information and record -

Purposes and is not to be refer® m any publication.

NBS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

421 6221 February 20, 1967 9456

FLAME INHIBITION WITH ELECTRON ATTACHMENT AS THE FIRST SEEP

by

,R. M. Mills

IMPORTANT NOTICE NATIONAL BUREAU OF STA

for use within the Government. I and review. For this reason, the whole or in part, is not authori; Bureau of Standards, Washingto

the Report has been specifically |

Approved for public release by the

Director of the National Institute of

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accounting documents intended

ubjected to additional evaluation

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pies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

FLAME INHIBITION WITH ELECTRON ATTACHMENT AS THE FIRST STEP

by

Robert M. Mills

ABSTRACT

The suggestion is made that combustion inhibition

of the type observed with the use of most halogenated

hydrocarbons is due to a two-step process: (1) negative

ions and free radicals are formed by dissociative electron

attachment with the inhibitor molecules, and then (2) these

negative ions and/or free radicals react with the free

radicals found in flames. Considerable evidence from the

literature is presented which supports this idea. It is

concluded that, while the evidence is not conclusive, a serious consideration of the idea is justified.

FLAME INHIBITION WITH ELECTRON ATTACHMENT AS THE FIRST STEP

By

Robert M. Mills

1. Introduction

There is considerable evidence to show that nitrogen and carbon dioxide are effective as fire suppressants primarily through their action as diluents and cooling agents. For some time, however , it has been recognized that other agents are considerably more effective In inhibiting

combustion reactions. Many of the halogenated hydrocarbon compounds are

of this type. In spite of their high heat capacity, they do not, when

applied in less than extinguishing concentration, lower flame temperatures

appreciably, suggesting that another more effective mechanism is at work.

The inhibition mechanism currently receiving the most attentionstarts with the observation that large concentrations of H, OH, and 0

free radicals are generated in the reaction zone of a flame. These free

radicals are thought to be essential in the perpetuation of the flame.

Inhibition Is attributed to flame free radicals reacting in some way

with the inhibitor, making H, OH, and/or 0 unavailable for the combustion

process. Numerous authors have discussed this theory [1-5]. Spectroscopically, OH absorption lines have been observed to decrease as Fe(CO),-, one

of the best inhibitors known, is added to a hydrocarbon flame [6], Recently, Zeegers and Alkemade [7] studied recombination reactions of excess flame radicals and concluded that H, OH, and 0 concentrations are related

to one another. That is, a depletion of one free radical species would

also cause a reduction in the concentration of the others. If this is

true, it should not be important which flame radical reacts with the inhibitor .

The free radical depletion theory fails to provide a clear explanation for the observation by Creitz [8] and Lee [9] that there is a corre- lation between electron attachment cross section and inhibitor effectiveness. Good inhibitors also have large electron attachment cross sections.

The observed facts may be combined by proposing an electron attachment

process as the first step in an inhibition mechanism, the step that generates active species which then react with the flame free radicals. This

paper examined such a possibility. Most of the evidence presented was obtained from the literature.

2. Proposed Inhibition Mechanism

A typical flame inhibitor, CF^Br^, attaches low energy free electrons

by the dissociative attachment process [lOj [11]:
CF jBr + ( 1 ) e - Br + CF.

i 3

The negative ions and free radicals which result are very reactive. Inhibition could take place through the reaction of Q,OH, and/or H (or

possibly other molecular fragments from the fuel) with the negative ion

and/or the radical which remains after the negative ion detaches from the

parent inhibitor molecule. This radical will hereafter be referred to as the residual radical.

Consider first the possibility that inhibition is due to the reaction

between the residual radical and free flame radicals. Using the inhibitor

mentioned above, H, for example, could be removed as follows;

CF

3 + H - CF

3

H* (2)

The resulting molecule from this reaction is formed with excess energy

equal to the heat of formation. The excess energy would be lost by collision with a third body, Ms

CFj$* + M - CF-H4-M* (3)

3 3

Several other authors have mentioned the ability of these residual

radicals to inhibit, although their comments were not associated with

electron attachment. Rosser, Wise, and Miller [12] proposed in the Seventh Combustion Symposium that "the effectiveness of bromine-containing

inhibitors is essentially equal to that of an equivalent amount of bromine" in methane-air mixtures of maximum flame speed. Then, in comparing

the effectiveness of CF^Br and 1/2 Br^ , they concluded that the CF^ radical must contribute to the inhibition^process . Fenimore and Jones'' [3]

presented evidence which "suggests that methyl radicals from either methane or methyl bromide are powerful inhibitors" in CH/ -H^ - air mixtures.

They suggest that methyl radicals react mostly with oxygen atoms in air

or 0

^ flames [33], making the oxygen radical unavailable for the normal

combustion reaction.

Return now to the possibility that the negative ion formed in the

electron attachment process is the important agent in removing flame free

radicals. For example, H could be removed by;

B + Br -» HBr he (4)

In this case, a stabilizing reaction similar to (3) is not necessary

since the excess energy can be carried away by the electron.

Regardless of whether the residual radicals or negative ions are the

important agents, the overall result is the same as in the inhibition

theories mentioned in [1-5], i.e., there is a reduction in concentration

of active free radicals in the inhibited flame. The uniqueness of the

mechanism proposed here is reaction (1). Electron attachment may be

necessary to supply the residual radicals and/or negative ions which then

react with the flame radicals, thereby explaining the electron attachment

correlation.

2
3. Supporting Observations

3 . 1 Electron Attachment in Inhibited Flame

One of the first questions which arises when examining the validity

of the proposed inhibition mechanism is whether negative ions are found

in a flame when inhibitors are added. Several experimenters report that

they are. Feugier and Van Tiggelen [15] observe that Cl~ions appeared with

addition of the slightest trace of chlorine compounds. Calcote et al [16]

reports Cl'resulting from addition of PCl^^and Miller observed [14] that

negative ions can be detected when CCI4 is added to a flame.

In order to further substantiate the idea that inhibitors are good

electron attachers and to study the type of attachment taking place, a qualitative study was made in this laboratory of the predominant negative

ions formed from (each) of 20 compounds in an electron bombardment ion source using a time-of-.f light mass spectrometer [11]. Most, but not all,

of the compounds studied are considered to be good flame inhibitors. The

energies of the bombarding electrons in the source were distributed

roughly over the same range as those believed to exist in flames, i.e.,

0 to 1 electron volts. Table I summarizes the results. Without exception,

all effective inhibitors formed negative ions by the dissociative attachment process. Most of the halogenated inhibitors detached one of the

halogen atoms.

Malcolm rates SF,. as only slightly more effective than CQ^ [20]. Yet

it is one of the bes ^electron attachers known. In Table I, SF , is one

of the few compounds for which simple attachment (attachment without dissociation) was observed. The ratio of SF^”/SF^“ was less than 1/20,

which is in agreement with Hickam and Fox [21] , and it is tempting to ex- plain the ineffectiveness of SF, as an inhibitor by the fact that too few

residual radicals are formed. However, this may not be a valid explanation, since Hickam and Berg [22] found that the ratio of SF,-"/SF^“ depends on temperature, being .25 at 80 °C and 1.5 at 280 ^C. The SF^“ ion is formed

with excess energy and is unstable. Since the SF,. molecule is large and

has many bonds, it is able to hold together for a time in its excited

state. But eventually some SF,-" ions stabilize by ejecting an electron

or F atom. The fact that SF^ does not inhibit combustion suggests one or more of the following:

1) Most SF,~ ions are stabilized in flames by ejecting an electron

(i.e., SF ” and F are not formed);

2) The delay between attachment and dissociation to SF^~ is sufficient for the negative ion to pass out of the reaction zone;

3) The increased ratio of SF^/SF^ at flame temperature, which is

expected from the work of Hickam and Berg, does not materialize;

4) The residual free radical, F., for some unknown reason does not

react with the free radicals in the flame;

5) The negative ions, SF^~ and SF,." , do not react with the free

radicals in the flame.

3
Of course, reaction (1) cannot take place in flames which have no free electrons. Such is the case in Hydrogen flames, Bulewicz and

Padley [17] found no measurable trace of ionization in Hydrogen, Carbon

Monoxide, Hydrogen Sulfide and Carbon Disulfide flames burned with Oxygen. They conclude that the electron density is at least three orders of

magnitude less than in hydrocarbon flames. Ion formation in H^-O, flames

is directly proportional to hydrocarbon impurity concentration [18]. It

Is also true that, as a rule, inhibitors are less effective when used with

Hydrogen-Oxygen flames than in Hydrocarbon-Oxygen flames. Lask and Wagner [5], for example, published curves showing that 35% by volume of

C

2

F

3

CI must be added to H0

" air mixture to make it non-flammable for all

H^-^air mixtures, but that only 14% is needed for n-hexane ~ air mixtures,

and 9% for Benzene - air. They also note that "with R as fuel, Fe (CO)

is less effecti\T e (as an inhibitor) than with hydrocarbons." Creitz [ 8

]'' has published curves showing that, for a given oxygen concentration, much

more CF^Br and CH_Br is needed to extinguish hydrogen flames than hydrocarbon flames. This inhibitor ineffectiveness in hydrogen flames cannot

be due to a dearth of flame free radicals, eince it is known [19] that

large amounts of H, OH, and 0 are produced in the reaction zone of the

hydrogen flame. It must be due to a deficiency in electrons.

The situation Is not so clear with CO - 00 flames. Simmons and

Wolfhard [13] report that in CO and air flames, "the amount of methyl

bromide which can be introduced into carbon monoxide before the flame is

extinguished is very large." Creitz [ 8 ] agrees that CH^Br is ineffective

in CO flames, but found CF^Br to be quite effective.

If reaction (1) is the first step in inhibition, the inhibiting com- pounds must not only exhibit high electron attachment, but the attachment

cross section must be high at the electron energies characteristic of

electrons in a flame. As mentioned before, the average electron energy in

flames is thought to be below 1 electron volt. This is also the energy

range where the attachment cross sections are high for inhibitors [22] [24],

Compounds such as Cli Br, CF^Br, and CF^Cl are inhibitors [25] [26],

and attach at the right energies [27] [10]. It is surprising, then, that

CH^Cl is not an effective inhibitor [26]. In terms of electron attachment, the explanation is clear. No negative Ions are produced in CH^Cl

until an electron energy of lOev Is reached (well above the energies of

flame electrons). Thus attachment similar to equation (1) cannot take

place. The same can be said for CH^F (negative ion appearance potential

of 12.4 volts [27]) and CF (negative ion appearance potential of 4.5

volts [10]). Neither CF,^ nor CH^F are chemical inhibitors.

Attachment cross section curves generally have a narrow peak at low

electron energy, indicating a resonance attachment process. With some inhibitors, there is a second, somewhat broader peak which follows the

initial one [22] [24]. In terms of the flame system, this means that a significant number of electrons must have energies at which the cross section peaks occur if reaction ( 1 ) is to be important.

- 4 -
From the definition of cross section it can be shown that:

00 attachments

3

mole fraction of inhibitor . CT(v)p(v) v dv

J o

( 5 ) cm where

3

sec

18 3 n = 4 x 10 molecules /cm at 1800 and atmospheric pressure

o

ct(v) = attachment cross section, which is a function of velocity, v„

p(v) dv - number of electrons having Velocity between v and v-fdv

per cm . If reaction (1) is the first step in inhibition, then the effectiveness of a particular inhibitor depends on the electron energy distribution in the

flame to which the inhibitor is added. There are several observations

in the literature which seem to support this idea.

Creitz [8] shows graphs in which the effectiveness of CF-Br and

CH^Br can be compared in Hydrogen- air and Hydrocarbon- ( i . e . , Ethane, Propane, and Butane) air flames. CH^Br is the better inhibitor in the hydrogen flame, but CF^Br is more efficient in the Hydrocarbon flames. The

hydrogen flame temperature is greater than that for the hydrocarbons [28],

and it is reasonable to expect the electron velocity distribution, p(v),

to be shifted to higher values of velocity. Thus the greater efficiency of

CH^Br in the Hydrogen flame can be accounted for if the attachment cross section peak for this compound occurs at slightly higher velocity (or

energy) than for CF^Br. The energy required for attachment to take place

is D(x-y)-EA4£, where D(x-y) is the dissociation energy of the xy bond,

EA is electron affinity, and E is the kinetic energy and energy of excitation of the products of reaction. In comparing the attachment process

for CH^Br and CF Br, EA is the same since the electron attaches to a Br

atom in both cases, and it is assumed that E is also similar for the two

compounds. However, Dibeler et al [10] have reported that

D(CH^~BrJ -D(CF^-Br) = 3 kcal 0 Thus electron attachment in CH.,Br does take

place at slightly higher electron energy.

Another observation indicating the possible importance of the relative

values of p(v) and c(v) has been made by Bonne, Jost and Wagner [6], They

report the effectiveness of Fe(C0)^ on hydrocarbon-air flames is much

greater than on hydrocarbon-oxygen flames, which of course, are hotter and

probably have a higher average electron velocity. It would be interesting

to know if the attachment cross section peak for Fe(CO),. occurs at the low

side of the electron velocity distribution so that the product of CT(v)p(v)

under the integral sign in (5) decreases as p(v) shifts to higher values

of velocity for the hotter oxygen flame.

Bonne et al also published data showing that flame speed does not

change significantly with pressure in the 0.1 to 1.0 atmosphere range.

This suggests that flame temperature, and thus average electron energy,

also remains essentially unchanged. At pressures below 0.1 atmosphere,

the flame speed of Bonne's methane-air flame did increase. However, it has

5
been reported [29] that the relative effectiveness of 7 inhibitors is the same at both 1 atmosphere and 0.01 atmosphere flames, suggesting that even

at 0.01 atm, the electron energies in flames have not changed by a large

amount

.

Although the relative effectiveness of inhibition does not seem to

change with pressure, the absolute value of effectiveness has been found

to change. Bonne et al [6] report that the efficiency of Fe(CQ) as an inhibitor decreases with decreasing pressure in the 1.0 to 0.1 atmosphere

range. This effect can be explained by a reduction in reaction rate. The

electron concentration is proportional to pressure [17], so the relative

concentrations of inhibitor and electrons is unchanged. However, the

reaction rate of both the electron attachment process and the reaction with

the flame free radicals which follows is reduced, thereby diminishing

inhibition.

3 . 2 Linearity of Inhibited Flame Speed Curves

Define an average attachment cross section c, so that;

[ e] v^ a = a (v) p (v) v dv

where

Jt p (v) v dv

Then:

[e] = electron density = p(v)dv

v = average electron velocity =

f* P (v) dv

a (v) and p (v) are the same as defined in equation (5)

1 a (v) p (v) v dv

- J or p (v>

« o v dv

If inhibitor concentration (n x percent inhibitor added) is written as [l], then equation (5) can be written as:

attachments

3 cm . sec

= k [e] [I] ( 6 )

where k = v a. Equation (6) has the form of a rate equation for

reaction (l5 with [ l] being the general term for [CF Br] . Equation (6)

also gives the number o| residual radicals (and negative ions) being produced per second per cm . Since it is proposed that the residual radicals

(and/or negative ions) are responsible for inhibition by reacting with

flame free radicals, it is reasonable to assume that the speed of an inhibited flame is equal to the uninhibited flame spe^d minus a term which

is proportional to the number of attachments per cm per sec:

S = S - k [e] [I] (7)

o

I where S is the speed of an uninhibited flame and k is a new constant.

- 6 -
As long as [ i] is small so that [ e] in equation (6) remains essentially

constant, the attachment per volume per second is linear with [i] . The

reduction in flame speed is thus also a linear function of inhibition

concentration. However, at higher inhibitor concentrations, the rate

of electron attachment becomes comparable with the rate of electron production. When this happens, an increase in inhibitor concentration, [ i] , results in a decrease in electron concentration, making equations (6)

and (7) nonlinear.

This behavior is observed experimentally. Garner, Long, Graham, and

Badakhshan [30] found that "the reduction in burning velocity is almost

linear with increase in concentration of additive (although there is some evidence of a slight falling off in effectiveness as the concentration

increases)." Bonne, Jost and Wagner [6] reported linear decrease in flame

speed with addition of up to 0.3 Mole % of Fe(C0)_, and up to 0.95 Mole %

of Br„. Lask and Wagner [5] used large enough inhibitor concentration

for the non-linearity to be clearly evident. The interesting thing is

that generally the best inhibitors at low additive concentrations also

become nonlinear at the lowest inhibitor concentration. The sketch in

Figure 1 illustrates this point. Compound "A" is the best inhibitor

at low additive concentrations, since it leaves the flame speed axis with

the greatest negative slope. Compound "A" also becomes nonlinear at

smaller concentrations than either "B" or "C". Data presented in Lask and

Wagner's report actually shows this behavior.

If reaction (1) is important, the best inhibitors should become non- linear first. They are the best electron attachers , and therefore they cause an exhaustion in free flame electrons first, resulting in the non- linearity.

The next question is whether the nonlinearity occurs at the expected

additive concentration, i.e., the concentration at which the electron

density is significantly reduced. In order to show that this is, in fact,

the case, a short discussion of the origin of electrons and negative ions

in hydrocarbon flames is necessary.

It is generally agreed that Ionization in a flame occurs by the

chemi-ionization process. In chemi- ionization, ions are produced simultaneously with some chemical rearrangement of the reacting bodies. The

reaction most often mentioned is:

CH + 0 - CHO

4’ + e“

Calcote et al [16], in a study of the origin of negative ions in flames,

concludes that "The main source of negative ions is dissociative attachment of electrons to C

9 H_0*, with possibly, some contribution from electron

attachment to 0 ?

, 0 and/or OH." The important point here is that negative

ions probably are not formed in the primary ionization process of the fuel

fragments

- 7 -

FLAME

SPEED

ADDITIVE CONCENTRATION

Fig. 1. A sketch showing how the onset of nonlinearity occurs at

lower additive concentrations for the better inhibitors.

See report by Lask and Wagner [5] for actual data.

7a
Calcote [16] observed that negative !, ions appear in addition to, not

in place of, the ions previously observed in the clean flame." Presumably this is at additive concentrations of less than 1%, because Feugier

and Van Tiggelen report [15] that when chlorine compound concentration

reaches the order of 1%, all negative ions which appear in normal flame

are replaced by Cl . It would appear that negative ions normally found

in hydricarbon flames are formed by attachment in clean flames, where

the supply of electrons is abundant. But they are unable to form when

all or most of the free electrons have attached to additives. Therefore,

based on Feugier and Van Tiggelen's observation, most of the electrons

are used up at about 1% additive concentration. This conclusion fits

Lask and Wagner's [5] data. The flame speeds of most of the compounds

which they studied become nonlinear in the 0.5 to 1% range of additive

concentration.

The idea that the free electron density in hydrocarbon flames is

significantly reduced with the order of 1% inhibitor added (i.e., rate

of electron attachment is comparable to rate of electron production at

1% additive) can be confirmed somewhat quantitatively by using equation

(6). First a reasonable value for [e] will have to be found. If the

conclusion drawn above is correct, that the primary ionization process in

hydrocarbon flames involves positive ions and electrons (no negative

ions) and that the negative ions found in a clean flame are formed only

if the electron supply is not depleted by additives, then it can be con- cluded that the number of electrons per cm which are available for attachment to inhibitor molecules is equal to the number^of positive ions

pej^cm . Th^s number varies ijji^the literature fr^m 10 ions /cm to

10 ions/cm [31] [34], so 10 electrons per cm will be used as a reasonable value for [e] in equation (6).

The reaction constant, k, in equation (6) was found to equal the

average electron velocity times the average electron attachment cross

^ section. Using p|^.us£ble values for v^ (0.2 el^tr^n volts or about 10

cm/sec and cj^(10 cm [24^), k is equal to 10 cm /sec. Then at [I]

equal to 10 mole^yles/cm (or about 1% inhibitor at flame temperature),

there are about 10 attachments per sec per cm .

This is comparable to the rate of election (or positive ion) production found ij^ the literature. Calcote published a production rate of

10 ions/cm ^ec [32|^ With some reservations, V|n Tiggelen arrives at

a value of 10 to 10 ions (or electrons) per cm per sec [31]. The

agreement seems close enough to support the proposition that the non- linearity in flame speed reduction curves beginning at about 1% is due

to the reduction in the free electron supply.

3 . 3 Some Inhibitors Burn

In the 6th Combustion Symposium, Garner, Long, Graham, and Badakhshan

[30] observed "The presence of halogenated methane as additive in the

fuel/air mixture leads to two effects; the first is that of additional

fuel (when part of the additive molecule is combustible) which causes an apparent shift in the position of the burning velocity vs mixture strength

- 8 -
curves, while the second is the marked inhibiting effect on flame propagation,,” Others have also noted that some inhibitors acted as fuel, especially in lean flames [8] [26], These observations clearly support the

theory presented. The residual radical from CH Br-, for example, would be

CH^. Upon reaction with H radicals in the flame, CH, would be formed.

Thus, the net result of adding CR Br would be a decrease in H concentration

and an increase in methane concentration (i.e., an increase in fuel con- centration) .

4 . Summary

None of the observations which have been discussed in this paper are conclusive. However, taken together they appear to justify serious con- sideration of the theory that electron attachment is a necessary first

step in Inhibition. It appears that the limiting factor in inhibitor effectiveness at higher concentrations is the supply of electrons in flames.

This is not the total supply of electrons, but only those which ha ve the

proper energy for electron attachment to the inhibitor molecule.

An experiment can be performed which, if successful, should provide

evidence on the importance of electron attachment in inhibition reactions.

At the same time, such information should have practical value by suggesting more effective, extinguishing agents. If two inhibitors can be

found with (a) slightly different electron attachment energies yet still

within the energy distribution of flame electrons, and (b) which can be

mixed without reacting with one another, then two "slices" of electrons

would be removed from the electron energy distribution instead of one. A mixture of these compounds used to inhibit a flame should thus result

in the flame speed reduction vs inhibitor concentration curve remaining

linear for larger concentrations than if the compounds had been used

separately, thereby resulting in a greater reduction in flame speed.

9
T.A !>L SUMMARY UF RESULTS

SAMPLE NEGATIVE IONS SAMPLE PURITY REFERENCE

OBSERVED AND SUPPLIER

1

.

CC1

4

Cl" (Bakar 1512) (B) (2) (3) (10)

2. ®2tr

2

Br CP_Br„ - 98.9%

2 2

CFCl^Br ~ 1.1% (M)

3

.

®JC12

Cl" C3? 2C1 - 99.8%

Hydrocarbons - 0.1% <M) (3)

4. CF,Br Br" CF,Br - 99.8%

3

(4)

3 C CM) - 0.1%

4 5

5. CHBr n Br Stabilised vi ch

3 Oipliany lamina

(Eastman 45) (E)

6. CHC 1 „ Cl‘ Spectro Grads (S)

J (Eastman S 33)

7. CHFC1 r . s Cl" CHFC1

2

- 99. n, CC1 F -0.1% (3)

CHCIF -f Cli.F^ - 0.2%

2 s 2

(M)

8. CHRr

tL Br (Eastman 1903) (E)

9. CH.RrCl

2 Br (Eastman 5698) (E)

10. CH0 Br Br" CH^Br - 99.7%

QkCl - 0.3%

3

(M)

(5)

11. CM. 1

o I (Eastman 164) (E) (5)

12. C H BrC.1

Jm 4

Br (Eastman 567) (E)

13. CHBr 3r Ethar Free (S)

A j (Eastman 114)

10
TABLE I: SUMMARY OF RESULTS (continued)

SAMPLE NEGATIVE IONS

OBSERVED

14 • C

8

F

I6°

C F, 0

8 lb

15. CU! F

i

0 ) 0 ,

16. Fa (CO) . Fa (CO)”

3 4

SAMPLE PURITY REFERENCE

AND SUPPLIER

3M Chemical Co. label FC-75 (6)

Reported to be a cyclic ether

C10

3

F - 98%

Inerts (including Moisture)-2% (2) (3)

Obtained from City Chemical Co.

17. PC1

3

Cl SO -0.0005%. Fe- 0.0003%

4

Heavy Metals - 0.0005%

18. POCX

3

19. SF

6

20 . TiCi

4

?oct

2

SO “0 .01%, Fe4

0.001%

Ci Heavy Metals - 0.002%

SF . - 98%

5

(M) (3) (7) (8)

SF

5

Cl" (Fisher T 308) <F) O)

(B) Obtained from Baker Chemical Co.

(E) Obtained from Eastman Distillation Products Industries.

(F) Obtained from Fisher Scientific Co.

(M) Obtained front Matheoon Co.

11
References

[1] H. Wise and W. A, Rosser, Ninth Symposium (International) on Combustion, p. 733, Academic Press, New York (1963).

[2] M. C. Burden, T. H. Burgoyne, and F. J. Weinberg, Fifth Symposium

(International) on Combustion, p. 647, Reinhold Publ. Corp.

,

New York (1955)

.

[3] C. P. Fenimore and G. W. Jones, Combustion and Flame _7, 323 (1963).

[4] W. E. Wilson, Jr., Tenth Sumposium (International) on Combustion,

p. 47, The Combustion Institute, Pittsburgh, Pa. (1965).

[5] C. Lask and H. C. Wagner, Eighth Symposium (International) on Combustion, p. 432, Williams and Wilkins Co., Baltimore (1962).

[6] U. Bonne, W. Jost and H. C. Wagner, Fire Research Abstracts and

Reviews, 4, 6, (1962).

[7] P. J. Zeegers and C. J. Alkemade, Combustion and Flame, 9_, 247 (1965).

[8] E. C. Creitz, J. Research NBS 65A , 389 (1961).

[9] T. G. Lee, J. Phy Chem _67, 360 (1963).

[10] V. H. Dibler, R. M. Reese, F. L. Mohler, J, Research NBS 57 , 113 (1956).

[11] R. M. Mills, Paper presented at 13th Annual Conference on Mass Spectrometer and Allied Topics (1965). Sponsored by ASTM Committee E-14.

[12] W. A. Rosser, H. Wise and J. Miller, Seventh Symposium (International)

on Combustion, p. 175, Rutterworths Scientific Publications,

London, Eng. (1959).

[13] R. F. Simmons and M. G. Wolfhard, Trans. Faraday Soc . 52,53,(1956).

[14] Wm. J. Miller, Third Quarterly Report on "Flame Ionization and Combustion Reactions", Aero Chem Research Lab., Inc,, Princeton, N.J.

(June 1966).

[15] A. Feugier and A. Van Tiggelen, Tenth Symposium (International) on Combustion, p. 621, The Combustion Institute, Pittsburgh, Pa. (1965).

[16] H. F. Calcote , S. C. Kurzius, and W. J. Miller, ibid, p.605.

[17] E. M. Bulewicz and P. J. Padley, Ninth Symposium (International) on Combustion, p. 638, Academic Press, New York (1963).

[18] J. C. Sternberg, W. S. Galloway and T.L. Jones, Pittsburgh Conference

on Analytical Chemistry and Applied Spectroscopy (Feb 1961).

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[19] J. A. Green and T. M. Sugden, Ninth Symposium (International) on Combustion, p. 607, Academic Press, New York (1963).

[20] J. E. Malcolm Engrs. Res. and Dev. Labs. Report 1177. Also in

final report on fire extinguishing agents for period Sept. 1947

to June 1950, covering research conducted by Purdue Res. Found,

and Dept, of Chem. under contract M44-009 eng 507 with Army Engrs

Res. and Dev. Lab., Ft. Belvoir, Va.

[21] W. M. Hickam and R. E. Fox, J. Chem Phys 2_5, 642 (1956).

[22] W. M. Hickam and D. Berg , "Advances in Mass Spectrometry", p. 458.

Pergamon Press, New York (1959).

[23] J. von Holne and W. M. Hickam, J. Chem Phys 3^2, 876 (1960).

[24] I. S. Buchel' nikova, J. Exptl. Theoret.Phys (U.S.S.R.) 35 , 1119

(1958).

[25] C. Halpern, J. Reseaxch, NBS 67A , 71 (1963).

[26] C. Halpern, ibid, 70A , 133 (1966).

[27] V. H. Dibeler and R. M. Reese, ibid, 54, 127 (1955).

I [28] B. Lewis and G. von Elbe, "Combustion, Flames and Explosions of Gases"

p. 706, Academic Press, New York, (1961).

[29] Wm. J. Miller, Second Quarterly Report on "Flame Ionization and

Combustion Reaction," Aero Chem Res .Lab. , Inc ., Princeton, N. J.

(March 1966).

[30] F. H. Garnez, R. Long, A. J. Graham, and A. Badakhshan, Sixth Symposium (International) on Combustion, p„802, Reinhold Publishing

Corp., New York (1957).

[31] A. Van Tiggelen "Ionization in Flames and Identification of the

Negative Flame Ions" University of Louvain, Scientific Report

No. 4, Astia Doc. No. 600456 (May 1964).

[32] H. F. Calcote, Combustion and Flame, _L, 385 (1957).

[33] C. P. Fenimore and G. W. Jones, J. Phy Chem 65, 1532 (1961).

[34] H. F. Calcote, Ninth Symposium (International) on Combustion, p.622

Academic Press, New York, N. Y. (1963).

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