NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1002-12-10421 December 3, 1963 3134

Seventeenth Quarterly Progress Report

on the

Mechanisms of Fire Ignition and Extinguishment

by

E. C. Creitz

Covering the period August 1, 1963 to October 31, 1963

for

Bureau of Ships

Department of the Navy

Code 638

Seventeenth Quarterly Progress Report

Mechanisms of F . re Ignition and Extinguishment

by

E. C a Creitz

Covering the period August 1, 1963 to October 31, 1963

1 . Summary

A review of background information leading up to the construction of

the mass spectrometer is given, Negative ion masses produced from SF^,

CCl^ and CIO.^F have been measured. Increased accuracy in the calibration

factor has been attained altho drift has not been completely eliminated.

2. Review of Background Information

Reactions between elecfcrophylic and electrophobic species in flames are believed to be important from the standpoint of the mechanisms of

extinction of flames. This view is the result of the work of Creitz (1)

who noticed the correlation between the efficiency of halogenatea hydrocarbons as extinguishing agents and the yield of negative ions by electron

attachment in the mass spectrometer, and that of Lee (2) who studied a large number of compounds including non-halogen compounds, such as iron

pentacarbonyl and lead tetroethyl, and concluded that all compounds which

are known to be inhibitors will attach low energy electrons. However,

there are other compounds such as SF^ which attach electrons and which

are known to have little or no effect on flame reactions. The present

work in construction of the new type of mass spectrometer is directed

toward its eventual use in determining the differences in the attachment mechanism between inhibiting and non-inhibiting electron attaching

gases. There is some evidence in the literature that attachment of

electrons by compounds which dissociate to give negative halogen ions

produces inhibition reactions in flames. In this case the energy of

the attaching electron is at least as large as the dissociation energy

and the electron ends up attached to the halogen atom which was dissociated from the original molecule, as in the following:

CF^Br e (1 .5 ev) .^CF^ + Br

The detachment of the electron from the Br icn requires in the order

of 3.5 ev energy so that the above reaction is, essentially irreversible.

On the other hand, compounds like SF^ can form molecular negative ions

such as SF^ and SF,. which have detachment energies comparable to those

for attachment. The mass spectrometer is to be used to try to connect

an attachment mechanism such as ne of the above, to the inhibition

process

.
* -x
2

Other work of interest which is not financed from this project includes, (1) further studies of the attachment f elec.tr uas by measurement

of the temperature coefficient of attachment and (2) a study of the products

of combustion of inhibited flames. The latter study is an attempt to trace

the history of inhibitor molecules in passage thru a flame. Private con- versations with others working in the field of chemical kinetics has

elicited the opinion that ionic processes are indeed important in the

inhibition of flame reactions.

3. The Mass Spectrometer

Optimum focusing settings vie re determined and no difficulty was ex- perienced in measuring the masses of negative ions obtained from SF^, CC1

/+ and CIO^F. The data indicated that it would not be necessary to shield

the filament from the gas to avoid thermal decomposition of the gas, as had

previously fewest thought might be necessary. Electrons were removed from

the stream of negative ions by the use of a weak magnetic field from a permanent magnet,

A better way for determination of the calibration factor was worked

out, with the help of data analysts of the NBS, so that it is now believed

that an error of ±0,1 can be achieved, exclusive of drift, which has nod

yet been measured.

When appearance potentials measurements are made, it is important

that the electron current from the filament remain constant. Efforts

are being made to automatically control the filament current. This seems not to be as simple as it appears and efforts are being continued

to produce such a regulator.

4. References

(1) E. C. Creitz, "Inhibition of Diffusion Flames by Methyl Bromide and

Trifluoromethyl Bromide Applied to the Fuel and Oxygen Sides of the

Reaction Zone", J. Res. NBS, 65A , 389 (1961).

(2) T. G. Lee, "Electron Attachment Coefficients of Some Hydrocarbon

Flame Inhibitors", J. Fays. Chem. , 67_, 360 (1962).

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