A Process for Developing Corrosion Resistant Black Lustrous Oxide Coating on Zircaloy- 2
Introduction
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.
For further information please contact
Bhabha Atomic Research Centre,
Trombay, Mumbai- 400 085
Tel : 091-022-25505337/25593897
Fax : 091-022-25505151
Email : headttcd@barc.gov.in
