Laboratory production of enriched BF₃ from CaF₂ . Bf₃

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Material Information

Title:
Laboratory production of enriched BF₃ from CaF₂ . Bf₃
Series Title:
United States. Atomic Energy Commission. MDDC ;
Physical Description:
5 p. : ill. ; 27 cm.
Language:
English
Creator:
Zedler, R. E
Luman, R. I
Oak Ridge National Laboratory
U.S. Atomic Energy Commission
Publisher:
Atomic Energy Commission
Place of Publication:
Oak Ridge, Tenn
Publication Date:

Subjects

Subjects / Keywords:
Boron trifluoride   ( lcsh )
Neutron counters   ( lcsh )
Genre:
federal government publication   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Restriction:
Date Declassified: July 18, 1947
Statement of Responsibility:
R.E. Zedler, R.I. Luman.
General Note:
Manhattan District Declassified Code
General Note:
Date of Manuscript: June 13, 1947

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 005023695
oclc - 465256594
System ID:
AA00009504:00001


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MDDC 1155


UNITED STATES
S" ATOMIC ENERGY COMMISSION
....OAK RIDGE
TENNESSEE












H. E. Zedier
Ko










R. I. Luman










Oak Ridge, Tennessee.
a'::" "*:> 'LABORATORY PRODUCTION
,...... ,O F
"....*'+++ ENRICHED BF3 FROM CaF2 BF3

document by reason of deletions necessary to accomplish declassification, this copy does

which may bear the same titl R.E. Zedler
, R. I. Luman


i|::.. .:?. C linton Laboratories



.Published for use within the Atomic Energy Commission. Inquiries for additional copies
*:+" a ":: n- ~ad any questions regarding reproduction by recipients of this document may be referred
...... ..', .... to the Technical Information Division, Atomic Energy Commission, P. 0. Box E,
P Oak Ridge, Tennessee.
.... ::. Inasmuch as a declassified document may differ materially from the original classified
M.":... : document by reason of deletions necessary to accomplish declassification, this copy does

MR.
i :.: not constitute authority for declassification of classified copies of a similar document
Rwh, i ::... vhlch may bear the same title and authors.


".': Date of Manuscript: June 13, 1947


Document Declassified: July 18, 1947

This document consists of 5 pages.


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1 MDDC-1155

LABORATORY PRODUCTION
OF
ENRICHED BF3 FROM CaF2 BF3




By R. E. Zedler
R. I. Luman



INTRODUCTION:

Boron trifluoride (BF3) is the gas commonly used in slow neutron counters. As furnished
by the AEC Isotope Branch, the boron in the complex CaF2* BF3, is 96% B10, as compared
with the normally occurring B10content of 20%. Since counter action results only on the
slow neutron capture by B10, counters 5 times as efficient may be obtained by filling
them with enriched BF3 generated from this complex.

The boron trifluoride gas is generated by heating the complex and collecting the gas in
a closed evacuated system.

CaF2 *BF3 -- CaF2 + BF3

A 250PC.

6.5 grams of the complex produce 1 liter (3 grams) of BF3 at'S.C.T.P.

EQUIPMENT:

The equipment is described in order from generator to receiving flasks. (See generating
system sketch.)

The generator (see generator sketch) is a flanged lid stainless steel container. A 1/4
O.D. :stainless steel thermocouple well is welded into the lid and extends nearly to the
bottom of the chamber. A nichrome heating element (40 ohms) is, wound around the gen-
erator, being insulated from the generator by mica. The unit is wrapped with asbestos
to minimize heat loss. A thermocouple hooked to a Leeds & Northrup Micromax is used
as the temperature measuring device.

The generator is connected to the glass system through a short length of copper tubing
which is sealed to the glass.with de-Kotinsky cement. A small copper can is soldered
around the copper tube near the cemented joint. This is filled with cold water to keep the
cement cool during the generation process.

Next in line are two glass traps and i glass wool filter in series to catch condensable
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impurities and entrained solids. ?:9.

Following the traps is the capillary flow meter. The manometer legs on each side of thBell'
.5 mm capillary tube are about 80 cm long, and extend into a mercury reservoir. With thgj!ij
capillary by-pass stopcock closed, the difference in mercury levels in the two legs is a i .r.I
indication of the rate of flow. The height of mercury in either leg indicates the static ..
pressure in the system. The flow meter also serves as a safety valve. :- :

A four-way stopcock follows the flow meter. The bottom outlet goes to the vacuum
pump through a cold trap. The four stopcock positions allow the following: 1) to evacuate
the generator side of the system, 2) to evacuate the receiving side of the system, 3) to .
connect both parts of the system and isolate the vacuum pump, 4) to isolate all sections aw ,: '
the system from each other. : .i

Following this stopcock are two outlets to which receiving flasks may be connected, bae. ;'.
of which has a stopcock. A manometer is attached to the receiving system to enable the
observation of static pressure readings and to act as a safety valve when the receiving
system is isolated from the rest of the system. On a side arm is a liquifying chamber maCb:_
from 30 mm pyrex glass tubing 1 foot long. BF3 from the generating system is ca densed..i
in this at the end of the generating process.

The collecting flasks used are the standard two liter pyrex glass type in which spectro- r"
scopically pure gases are distributed. :

PROCEDURE:

After introducing the complex in the generator, evacuate the entire system for several ::
hours. The system is tested for leaks with a spark coil. The stark coil produces a pale -
blue glow in a well evacuated system and a purple glow in a poorly evacuated system. The :,
thermos full of liquid nitrogen should be placed an the vacuum pump cold trap after an
indication of a good vacuum has'been obtained.....

Place the thermos bottles of acetone-dry ice mixture an the generator cold traps and
begin heating the generator (a variac is used to regulate the current through the heating -
coil). Continue evacuation of the system until the temperature reaches 1709C. t which" .::
temperature the vacuum pump is isolated by use of the fear-way stopcock. Increase th 1
current through the coil to maintain a steady temperature rise. '

The BF3 gas begins to. generate in appreciable quantity at 250oC. When the temperatMre-4
reaches 380C. (after 3 hours from the starting time of the heating process), most of th0 iem
BF3 will have been evolved.

When the manometer indicates that there is W0 cm pressure in the first receivl.g flaS ,I
the flask is removed and the stopcock sened into the second flask When all the BFs ::in j
been evolved (3 to 4 hours) a thermos of liquid nitrogen is placed as the liqufig che. '"
This condenses all the BFg in the system. g generating system is isolated fr .

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receiving: system by means of the four-way stopcock and the thermos removed. The BF3
-'vaporizes into'the second collecting flask which is then removed.


*RESULTS:

The BF3 thus collected should be 97.2% pure, 75% of the impurity being air. Final
Purification of the BF3 is done on the system used to evacuate and fill counters. The proc-
.ea: is simply that of solidifying the BF3 in a liquid nitrogen trap in an evacuated system
.aid then re-evacuating the system to remove the non-condensable air impurity from the
'solidified BF3.

This method, used at Clinton Laboratories, is essentially that given in an extract from
SAM-Report A-4121, but the system was modified to make the generation process simpler
/samd safer,
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