Encapsulating samarium cobalt magnets for improved corrosion resistance

Samarium cobalt magnets (SmCo₅) are used to improve the retention and stability of overdentures, removable partial dentures, and maxillofacial and implant prostheses. Unfortunately, their applications are limited because they corrode in the acidic oral and prosthetic environments. Corrosion decreases the life span of the prosthetic devices by adversely affecting magnetic attraction, and by severely discoloring the prostheses. To provide improved acidic corrosion resistance, SmCo₅ magnets were encapsulated with thin inorganic polymer films using sol-gel processing technologies. Methyltriethoxysilane [H₃CSi(OC₂H₅)₃] was polymerized via acid catalyzed [HCl] hydrolysis/polycondensation reactions with distilled water and tetrahydrofuran [THF] solvent. The reactant concentrations and polymerization conditions were optimized to maximize film density (maximize corrosion resistance), to minimize setting shrinkage (eliminate crack formation), and to obtain a reasonable setting time (0-24 hours). Optimal sols were used to encapsulate the SmCo₅ with 12 μm polymer films. Ten commercial SmCo₅ magnets encapsulated with inorganic silicone films were soaked at 20°C in acidic buffered solutions (pH=2) and compared to ten uncoated controls to evaluate corrosion resistance. Using atomic absorption spectroscopy to evaluate the respective concentrations of aqueous [Co] in the buffer solutions confirmed that a single inorganic polymer film of 12 μm thickness effectively prevents acidic corrosion with a significant concentration difference of 343.0%