| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 692787 | Progress in Organic Coatings | 2013 | 7 Pages |
The thermal stability of Sm2Co17 powders coated with four different silanes was studied between 25 °C and 500 °C and isothermally at 400 °C. Thermogravimetry data indicated that the silane-based coatings provided improved oxidation resistance. The microstructural analysis of uncoated powders oxidized for 10 h at 400 °C revealed the formation of a featureless ca. 10 μm thick shell, surrounding the unreacted core. The development of this shell was attributed to the inward diffusion of oxygen, decomposition of intermetallic phases and redistribution of alloying elements. The EDS elemental maps revealed that the shell was rich in O, Fe and Co, and depleted in Sm, Zr and Cu. In the presence of the silane-based coatings the thickness of the shell was reduced by more than 80% (to less than 2 μm) and the redistribution of alloying elements was insignificant. Based on the thermogravimetric analysis at or above ca. 400 °C and the microstructural analysis it was possible to assess the relative effectivity of the different silanes in preventing the oxidation of the SmCo powder. Methyltrimethoxysilane (MTMS), which also formed the thinnest coating, was the best silane. (3-Glycidyloxypropyl)trimethoxysilane, forming a thicker coating, was less effective than MTMS, but superior to the two amine-functionalized silanes ((3-aminopropyl)triethoxysilane and (3-aminopropyl)trimethoxysilane).
► Greatly improved high temperature oxidation resistance. ► A simple wet chemical silanization process is used. ► Four silanes have been compared and the optimum coating demonstrated. ► Non-hazardous and low temperature process developed. ► Coating thickness calculated.
