Memorandum from A. W. Waltner to Dr. Clifford K.Beck
1 p.

TO: Dr. Clifford K. Beck
FROM: A. W. Waltner
CC: Reactor Committee
SUBJECT: Preparation of Uranium Foils

"Rossi and Staub"a suggest the following procedure in preparing
U235 foils for spiral fission:

Preparation of Foils

"Uranyl nitrate is dissolved in a minimum quantity of alcohol.
A solution of 1 or 2 per cent of Zapon lacquer in Zapon thinner is
prepared and added to the first solution until the concentration of
uranyl nitrate is about 50 mg/cu cm. The nitrate concentration may be
much lower, but the value mentioned should not be greatly exceeded.

This solution is applied to an aluminum foil in a thin layer by
means of a soft brush. The brush should not touch again any portion of
the foil from which the solvent has evaporated. The foil is then baked
for three for four minutes at about 550°C to burn off the Zapon lacquer
and to convert the uranyl nitrate to U3O8. If platinum foil is used,
the baking temperature may be 800 or 900°C. The higher temperature
will result in more nearly complete elimination of Zapon and quanti-
conversion of uranyl nitrate into U3O8.

When the foil has cooled, it is rolled flat between sheets of paper
and the coated side is rubbed smooth with a soft tissue. Initially,
the coated surface will exert considerable frictional drag on the tissue
but this rapidly diminishes, without apparent removal of oxide, and a
smooth lustrous surface is produced.

A single layer of U3O8 applied by this method is, and apparently
must be, quite thin. However, the procedure may be repeated until
the desired surface density is reached. The coating is very tenacious
and will withstand sharp bending of the foil.

If the foil is to be coated on both sides, as it must be for the
preparation of spirals, it is advisable to paint alternately on the two
sides rather than to complete to coating on one side before beginning
the other

Small areas of foil are conveniently painted, on a flat surface,
by hand. Larger areas can be more easily handled if the foil is wrapped
around an aluminum drum, which is rotated against the brush.

The aluminum foil that has been used in most of the spirals, is
prepared for coating by lightly etching the surfaces in a dilute sodium
hydroxide solution. It is carefully cleaned with water and alcohol and
thoroughly dried before the painting is begun.


aRossi and Staub--Ionization Chambers and Counters--McGraw-Hill (1949)