Tannenbaum, Stanley

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RES
THE HEAT OF COMBUSTION OF TETRAETHYLDIBORANE
By Stanley Tannenbaum
Lewis Flight Propulsion Laboratory
G leveland, Ohio
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NATIONAL ADVISORY COMMITTEE
FOR AERONAUTICS
WASHINGTON
January 16, 1957
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TECH LIBRARY KAFB, NM
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NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
THE HEAT OF
RESEARCH MEMORANDUM
COMBUSTION OF TmmETmmlBoRANE
By Stanley T%neribaum
SUMMRRY
nL433a7
The net heat of combustion of a sample of tetraethyldlborane
found to be 20,400 +130 Btu per pound for the reaction of liquid
to gaseous carbon dioxide, gaseous water, and solid boric oxide.
was
fuel
The
measurements were made in-a Parr oxygen bomb calorimeter and the com-
bustion is believed to have been 99 percent con@ete. A more reasonable
value for the net heat of ccmibustionwould therefore be 20,600 + 130 Btu
per pound.
l INTRODUCTION
At the request of the Bureau of Aeronautics, Department of the
Navy, the NACA is participating in a project aimed at the discovery
and evaluation of certain high-energy fuels. A part of the work that
the NACA will perform in this project is the determination of the funda-
mental flame velocity, heat of combustion, and possibly other combustion
properties of fuel samples submitted by companies participating in the
project as contractors to the Bureau of Aeronautics.
A sample of tetraethyldiborane was received and the heat of com-
bustion of this material has been measured in a Parr oxygen bomb
calorimeter.
TEST SPECIMENS
Two grouys of samples (A and B), along with analytical data
(table I), were obtained from the manufacturer in sealed glass bulbs.
They were kept at dry-ice temperature until introduced into the bomb.
The liquid weight varied from 0.2 to 0.35 gram, and several samples
contained small amounts of dark insoluble material.
The A samples were used for preliminary investigations; the re-
ported values are for the B samples.
2 Commnmxwm NACA RM E53E11
APPARATUS AND PRCCEDtJRX
The apparatus consisted of a Parr adiabatic calorimeter equipped
with an Illium constant-volumebomb and a me~cury thermometer which
copld be read to +0 .005° F. The bomb was calibrated using standard
benzoic acid. The samples were contained.in”glass bulbs filled so that
at room temperature the Iiquid.occupied the entire volume. me method
used in making a determination was to attach:the bulb to the iron igni-
tion wire with a preweighed piece of cellulode tape, place a perforated
nickel cruicible around the bulb, and fill the bomb with 25 atmospheres
of oxygen. The heat generated by the burning of the ignition wire and
cellulose tape caused the liquid to rupture the glass bulb and burn.
Carbon dioxide formed in the combustionwas absorbed in Ascarite
after the gas had been dried by passage thro@ Anhydrone. When all ‘-
the gas had been flushed out with fresh oxygeh, the bomb was opened
and examined for signs of incomplete combustion. It was then washed ‘“
with distilled water and the washings were fiJ.tered. The filtrate
was then titrated to determine nitric acid formed during the combus-
tion. The last step was to titrate for boric acid (ref. 1).
RJZSULTSAND DISCUSSION
The results frcm four determinations of the heat of combustion d
sample B tetraethyldiborane and the analysis of the combustion products
are given in table 11. The heats of combustion are the gross uncorrected
values determined directly in the bonibwith gaseous carbon dioxide,
liquid water, and solid boric acid as the conibustionproducts and with
part of the boric acid &lssolved in the water present in the bonib. The
value for this gross heating value is 22,04S+130 Btu per pound. The
determined percent carbon, as carbon dioxide, was much below the theo-
retical and manufacturer’s values for tetraethyldiborane,whereas the
percent boron was somewhat higher than the theoretical value.
In all cases, slight amounts of black titerial were found among
the combustion products. However, experience indicates that such an
amount of residue is associated with a combustion efficiency of per-
haps 99 percent. It is therefore difficult to understand the discrep-
ancy in the analytical data of tables 1 and II other than by the assump-
tion that some chanae occurred in the material between the time it was
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NACA RM E53Ell 3
analyzed and the time the glass bulbs were filled. In previous studies
of Wmethylaminodiborane (ref. 2) and alkylsilanes (refs. 3 ad 4),
excellent agreement was obtained between the calculated carbon content
of the compounds and that recovered as carbon dioxide after conibustion.
The determined gross heating value-from table II is 22,048+130 Btu
per pound, which is equivalent to 1715.3 kilocalories per mole. The
—
following corrections were then made:
(1) Conversion from a constant-volume process to a constant-
. pressure process, +2.1 kilocalories per mole
(2) Correction for the heat of hydration of boric oxide to boric
acid and the heat of solution of part of the acid so formed,
-16.0 kilocalories per mole (ref. 5)
Corrections (1) and (2) result in a value of 1703.4 kilocalories
per mole or 21,892 Btu per pound for the reaction
‘2H2(C2H5)4(2) +15 02(g)-8 c02(g) ‘U H20(2) ‘B203(s)
A further correction is needed to yield the net heat of combustion.
(3) Correction for the latent heat of vaporization of the water
formed during conibustion,assuming that the sample contains the theo-
retical concentration of hydrogen (15.9 percent), -1488 Btu per pound
of tetraethyldiborane
Thus, the heat of combustion to gaseous water, gaseous carbon
dioxide, and solid boric oxide beccmes 20,404~130 Btu per pound, which
is rounded off to 20,400+lXl Btu per pound. If the combustion is
assumed 99 percent complete, a more reasonable value would be
20,600+130 Btu per pound.
‘TWOdeterminations were recorded for samples A, which showed a
heating value 615 Btu per pound lower than the value for ssmples B.
Letis Flight Propulsion Laboratory
National Advisory Committee for Aeronautics
Cleveland, Ohio, May 11, 1953
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4REFERENCES
NACA m E53E11
1. Blumenthal, Herman: Determination of Bororiin Metal Borides. Anal.. .
Chem., vol. 23,*no. 7, July 1951, -pp.99Z-994.
2. Hibbard, Robert R., and Dugger, Gordon L.: Fundamental Flame Veloc-
ity, Wat of Cmbustion, and Spontaneous Ignition Temperature of
Dimethylaminotiborane. NACA RM E52L23, 1952. .=
3. Tannenbaum, Stanley, and Murphy, Maurice F.: The Preparation, Phys-
ical Properties, and Heats of Combustion of Four Alkylsilanes.
NACA RME5U05, 1951.
4. Tannenbaum, Stanley, Kaye, Samuel, and Lewenz, George F.: Synthesis
and Properties of Same Alkylsilanes. Jour. Am. Chem. Sot., vol. 75,
no. 15, Aug. 5, 1953, pp. 3753-3757.
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5. Long, L. II.,and Norrish, R. G. W.: The Strengths of Certain
Covalent Metal Bonds. Phil. ‘Mans. Roy. Sot. (London), ser. A,
vol. 241, no. 838, Apr. 1949, pp. 587-61.7.
.
.
NACA RM E53Ell c..,.UU,.-m
TABLE 1. - ANALYSES OF ~IBoRANE SAMPLES
REPORTED BY MANUFACTURER
Sample Carbon, percent Boron, percent
Mfr. Theory M&. Theory
E
A
T
c
n
L
A 70.0 68.7 15.2 15.5
B 72.0 68.7 15.5 15.5
TABLE II. - HEAT OF COMBUSTION DATA FOR
SAMPLE B TE~lBORANE
kperiment Gross uncorrected Analysis of
heating vslues, combustion products
Btu/lb Carbon, Boron,
percent percent
1 21,996 66.03 16.4
2 22,170 6#3 16.2
3 22,105 . 16.4
4 21,920 66.05 16.3
.verage 22,048 65.9 m
+130
theoretical 68.7 15.5
orrected 20,400
Letvalue *MO
%as lost during analysis. --5=’
5
NACA -Langiey FleId, Vd.


The heat of combustion of tetraethyldiborane

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