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Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 201 5. NATIONAL BUREAU OF STANDARDS REPORT

73^0

DRY POWDER DECOMPOSITION IN FLAMES

By

Ronald T® Gautreau

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U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March 3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and maintenance of the national standards of measurement and the provision of means and methods for making measurements consistent

with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials, devices, and structures; advisory services to government agencies on scientific and technical problems; invention and' development of devices to serve special needs of the Government; and the development of standard practices, codes, and specifications. The work includes basic

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Publications

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460, Publications of the National Bureau of Standards, 1901 to June 1947 ($1.25), and the Supplement to National Bureau of Standards Circular 460, July 1947 to June 1957 ($1.50), and Miscellaneous Publication 240,

July 1957 to June 1960 (Includes Titles of Papers Published iti Outside Journals 1950 to 1959) ($2 .25); avail- able from the Superintendent of Documents, Government Printing Office, Washington 25, D. C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1002-11-10121 September 12 , 1961 73^0

DRY POWDER DECOMPOSITION IN FLAMES

By

Ronald To Gautreau

Participant in

Junior Scientist and Engineer Programs

1961

IMPORTANT NOTICE

NATIONAL BUREAU OF STANDARDS REPORTS are usually preliminary or progress accounting documents

Intended for use within the Government. Before material In the reports Is formally published It Is subjected

to additional evaluation and review. For this reason, the publication, reprinting, reproduction, or open-literature

listing of this Report, either In whole or In part, is not authorised unless permission Is obtained In writing from

the Office of fho Director, National Bureau of Standards, Washington 25, D. C. Such permission Is not needed,

however, by the Government agency for which the Report has been specifically prepared If that agency wishes

to reproduce additional copies for Its own use.

U, S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

DRY POWDER DECOMPOSITION IN FLAMES

By

Ronald To Gautreau

ABSTRACT

The effects of passing dry powder inhibitors past a flame in the presence of

electric fields were studied- It was found

that the collection of powder residues on

plate electrodes is influenced by varying

the structure of the electric fields- An

explanation based on the action of induced

dipoles in non-uniform fields is proposed1« Introduction

Previous preliminary work had suggested that sodium bicarbonate, a dry powder inhibitor, acquired an electric charge

when it was passed around a flame in the presence of an electric

field- It was found that the powder could be collected on parallel plate electrodes placed close to the flame and that a

larger amount of powder collected on the positive electrode. A

sample taken from the positive electrode was analyzed and reported

to be sodium hydroxide- On the basis of these results it was

thought that the sodium, bicarbonate had acquired a negative charge

in the process of decomposition and recombination in the flame

gases- Preliminary work by T. G- Lee, of this laboratory, had

indicated, some other, different process, probably dipole formation

in the mo:l ten powder particles- The purpose of the experiments

described in this' paper was to investigate these phenomena more

thoroughlyII- Experiment

The apparatus used in the experiment is shown in Fig- 1.

Fuel gas was passed through the center tube of the three-tube,

metal burner; the flame size was controlled by a regulating

valve in the fuel line. The dry powders under observation were

conducted past the outside of the flame by using a controlled

vibrator to shake the powder thrqygh a screen in the hopper into

the air stream which flowed through the outer tube of the burner

past the flame- The rate of application of the powder was controlled by adjusting the variable vibrator- The speed at which

the powder passed by the flame was controlled by adjusting a regulating valve in the air supply; the air passing through the outer

tube also helped to stabilize the flame. The middle tube was not

used in the experiment.
2

The plate electrodes were separated by four Bakelite rods

whose lengths were accurate to t 0.003 inches; the plates could

therefore be assumed to be reasonably parallel.' These plates

were located slightly above the burner mouth and were aligned

parallel to and equidistant from the burner axis. A potential

greater than 600 volts was established between the two parallel

plates producing an electric field transverse to the burner axis.

An auxiliary wire was also available to connect the burner to

either of the electrodes.

As estimated visually, an equal amount of powder was

collected on each electrode when the burner was not connected

to either electrode. When the burner was connected to one of

the electrodes, it was observed that a greater amount of powder

collected on the unconnected electrode; this effect was the same

regardless of which electrode the burner was connected to--a

greater amount of powder always collected on the electrode which

was not connected to the burner. With the flame extinguished

and the potential across the plates maintained, powder collected

equally on both electrodes, but the amounts collected were much

smaller than with a flame present; connecting the burner to

either electrode with the flame out seemed to have no effect on

the collection of powder.

To test if the observed effects were due to the heating of

the powders, an electrical heater about the size of a flame

(see Fig. 2J was placed in the fuel opening of the burner and

powder was passed around it. The powder collected in the same

manner as with a flame, showing that the observed effects were

caused by the heating of the powder and not by any reaction with

the flame c*

It is believed that the observed effects occurred as a result of dipoles induced in the powder particles when they were

decomposed by the heat from the flame in the presence of an electric field. When the burner was not connected to either of the

plates, the field was symmetric about a plane through the burner

axis parallel to the plate electrodes, but the field was not uniform. since the metal burner and flame were close to the electrodes

causing the field lines to bend downward with some of the lines

going from the positive terminal to the burner and then to the

negative terminal. The_force on a dipole of moment p in a nonuniform electric field E is given by

F = V (E 0 p )

.
- 3 -

Since the electric field is symmetric about a plane through

the burner axis parallel to the plate electrodes, the force field

acting on the induced dipoles should also be symmetric about the

same plane causing an equal amount of particles to be collected

on each plate. When the burner is connected to one of the electrodes, however, the electric field is no longer symmetric about

the previously described plane. If the burner is connected, for

example, to the positive plate, field lines will run from the

positive to the negative plate and from the burner and flame to

the negative plate with no lines running from the positive plate

to the burner or flame. The resulting asymmetry would tend to

deflect the dipole particles toward the negative plate where the

field line density is greatest.

The above effects were observed for three different powders;

sodium bicarbonate (NaHCCh), potassium bicarbonate (KHCCh), and

potassium oxalate (XpCqOqj. Samples were taken from each electrode after running the powder past the flame with the burner not

connected to either electrode. A chemical analysis performed on

the residue from the sodium bicarbonate and potassium bicarbonate

powders showed that carbonate and bicarbonate salts were collected

on both electrodes. An X-ray diffraction analysis verified this

result and also indicated that no hydroxide was present. (Hydroxide cannot be detected chemically in the presence of an excess

of bicarbonate since the bicarbonate neutralizes the hydroxide

when the powders are put into solution. ) An X-ray diffraction

analysis performed on the potassium oxalate powder residue showed

that the residue was mainly potassium oxalate ; no other substances

were identified.

III. Summary

Since the collection of powder on the electrodes can be

influenced by varying the shape of the electric field, the previous observation that the powder collects mainly on the positive

electrode, as mentioned in the introduction, can probably be

attributed to the grounding (either intentionally or unintentionally) of both the burner and the negative electrode when the

preliminary experiments were performed. The collection of powder

on the electrodes was apparently caused by induced dipoles rather

than by the formation of negative ions. The observation that the

residue collected on the positive electrode was sodium hydroxide

is considered invalid. The results of the present study indicate

that, the residue was composed of carbonate and bicarbonate salts

with an equal amount collecting on both electrodes.
If further work is to be done along the lines described

in this report, certain modifications of the apparatus would

be desirable. Different material, perhaps teflon, should be

used as separators for the plates. The Bakelite rods were

found to conduct electricity with the conductivity increasing

as the temperature of the rods increased from heat conducted

along the metal plates. This caused a current (10-30 pa) to

flow in the circuit resulting in a voltage drop of up to 600

volts across the resistors which protected the ammeter. For

this reason the total voltage of 1300 volts from the power

supply was not impressed across the plate electrodes. The

plate electrodes should also be made larger in size with the

burner opening in the middle of the plates instead of at the

edges as was done in these experiments. It would also be

advisable to use a glass burner rather than a metal one so

that the field between the plates would not be disturbed to

such a large extent.

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U. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., and

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