New Protective Coatings for Rare Earth Magnets Prevent Their Corrosion and Oxidation

Otaigbe, Joshua

Abstract

A new coating system for the increase of thermal stability and water resistance of Nd-Fe-B (neo alloy) magnetic powders is introduced. The coating system is composed of an organometallic compd. with dual chem. functional groups, contg. Si, Zr, or Ti, that react spontaneously with the neo alloy. Coating agents with the general formula R-Si-(OR')n (R,R' = alkyl) are shown to be the most promising. The surface of the powder is coated prior to incorporating them into the polymer matrix. The effects of the coating on the processibility and magnetic properties of polymer bonded plastic neo alloy magnets were investigated. Difficulties in plastic processing of the neo alloy magnets are shown to be minimized by the use of these coatings. The energy products (BH)max of coated and uncoated bonded neo alloy magnets with identical vol. fractions were compared and a higher (BH)max was found for magnets contg. coated powders.