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A simple process has been developed to form black lustrous, strongly
adherent oxide coating on zircaloy-2. the oxide layer so formed renders the
material highly resistant to mechanical abrasion, corrosion by mineral
acids, salt solutions and atmospheric oxidation.
One of the important non nuclear uses of zircaloy-2 is for human body
implants and for this the alloy is required to be given oxidation treatment
to develop surface oxide layer for protection from corrosion by human
fluids. The process developed is very effective in forming the oxide of
desired properties.
Other non -nuclear areas where zirconium/zircaloy-2 find application is in
the chemical industries for corrosive acids and here again the surface
treated material offers considerable advantage. In the nuclear engineering,
zircaloy-2 is used for fuel cladding and other in- core structurals. The
oxide coating by the process developed here has advantages, since this
completely avoids the use of autoclaves involving high temperatures and
pressures.
The process briefly consists of mechanical or a chemical surface
pretreatment, formation of the oxide and converting the coated oxide to
tenacious nature by a heat treatment. The lustrous oxide so formed is highly
insulating, with a resistance of +20 mega ohms and adhesion has been
excellent. Zircaloy-2 of various sizes, 2 to 50 cm are chosen, surface
cleaned and pretreated prior to actual coating process. Pretreated substrates were then subjected to surface oxide coating in an aqueous media.
As coated sample coupons were then given a heat treatment for forming a
tenacious black oxide film. The operating parameters for controlling the
thickness and corrosion resistance have been established to yield a product
with desired specific end properties.
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