Low-Temperature Deposition of Graphite Coating on La(Fe, Co, Si)13B0.2 for Room-Temperature Magnetic Refrigeration

Abstract

Due to the larger magnetic entropy change $\Delta S_{M}$ and the much lower raw material cost, La(Fe, Co, Si)13 materials have the potential to replace the room-temperature magnetic refrigeration prototype material Gd. In this work, we have developed a simple chemical vapor deposition (CVD) method for in situ graphite deposition on the surface of La(Fe, Co, Si)13B0.2. Facilitated by the decomposition of the solid carbon-source polyethylene glycol (PEG), the CVD process could be carried out at a low temperature of $400~^{\circ }$ C and in a short duration of 20 min, which ensures no $\alpha $ -Fe precipitation from and carbon atom diffusion into the La–Fe–Si material. These 400–700 nm-thick coatings could significantly enhance the anti-corrosive property with a positive shift of corrosion potential ${E} _{\text {corr}}$ from −788 to −600 mV and a reduction of the corrosion current density ${I} _{\text {corr}}$ from $1.67\times 10^{-5}$ to $9.14\times 10^{-6}$ A/cm2, accompanied by a concurrent enhancement of the thermal conductivity. More favorably, a large $\Delta S_{M}$ of ~4 J/kg $\cdot $ K at 286 K and a relative cooling power (RCP) value of ~98 J/kg in 0–1.5 T were maintained.