Phase investigations of manganese–bismuth alloyed in a microwave furnace

微波辐射法制备锰铋合金

Implementation of manganese–bismuth(MnBi)alloys as high-performance permanent magnets is a challenge for physicists and engineers because the ferromagnetic low-temperature phase(LTP)is not exclusively obtained.In this work,melting powered by four commercial magnetrons of 2000–2500 W in a microwave furnace is demonstrated as a new route to alloy MnBi.Under an argon atmosphere,microwave heating transferred to pieces of broken Bi ingots and Mn flakes for 2 h gave rise to products of inhomogeneous composition and morphology.Scanning electron micrographs were classified into three regions according to morphology and elemental composition.Cubic-like clusters characterized as Mn precipitated over light solidified Bi-rich regions,and the MnBi phase was formed in homogeneous regions with a balanced composition between Mn and Bi.A ferromagnetic hysteresis loop was obtained in the ground powder with a coercivity of 40 kA/m.Subsequent annealing at 553 K under a pressure of 414 kPa for 12 h enhanced the MnBi phase with extended regions of balanced composition.It follows that the coercivity was increased to 60 kA/m.However,remanent magnetization was slightly reduced.This MnBi alloyed by microwave radiation can be further used in rare-earth-free magnets.

得到高性能永磁体锰铋(MnBi)合金对物理学家和工程师来说是一个挑战,因为纯的铁磁低温相(LTP)不容易获得。在本工作中,在微波炉中由四个2000~2500 W的商用磁控管驱动的熔化被证明是一种新的合成MnBi的路线。在氩气气氛下,微波加热碎Bi锭和Mn片2 h,得到成分和形貌不均匀的产物。按形貌和元素组成将扫描电子显微照片分为三个区域。立方团簇状的Mn沉淀在明亮的富铋固化区,MnBi相在Mn与Bi组分平衡、均匀的区域形成。在矫顽力为40 kA/m的磨碎粉末中存在铁磁磁滞回线。随后在414 kPa、553 K下退火12 h,MnBi相得到扩展,矫顽力提高到60 kA/m,但残余磁化强度略有降低。微波辐射法得到的MnBi合金可用于无稀土磁体。