Abstract
This work reports the preparation of La2O3 uniformly doped Mo nanopowders with the particle sizes of 40–70 nm by solution combustion synthesis and subsequent hydrogen reduction (SCSHR). To reach this aim, the foam-like MoO2 precursors (20–40 nm in size) with different amounts of La2O3 were first synthesized by a solution combustion synthesis method. Next, these precursors were used to prepare La2O3 doped Mo nanopowders through hydrogen reduction. Thus, the content of La2O3 used for doping can be accurately controlled via the SCSHR route to obtain the desired loading degree. The successful doping of La2O3 into Mo nanopowders with uniform distribution were proved by X-ray photon spectroscopy and transmission electron microscopy. The preservation of the original morphology and size of the MoO2 precursor by the La2O3 doped Mo nanopowders was attributed to the pseudomorphic transport mechanism occurring at 600 °C. As shown by X-ray diffraction, the formation of Mo2C impurity, which usually occurs in the direct H2 reduction process, can be avoided by using the Ar calcination-H2 reduction process, when residual carbon is removed by the carbothermal reaction during Ar calcination at 500 °C.
Highlights
Molybdenum (Mo) and its alloys have excellent high temperature performance, such as high temperature strength, high creep resistance, low thermal expansion coefficient, and high thermal conductivity [1,2,3]
Cheng et al [8] studied the properties of Mo alloy with different doping contents of La2 O3, and the results showed that the Mo alloy with
Mo nanopowders doped with different amounts of La2 O3, i.e., 0, 0.27, 0.64, 0.88, and 1.16 wt.%, were prepared via the SCS and subsequent hydrogen reduction route (SCSHR) route, which allowed a homogeneous distribution of the dopant while preserving the theoretical loading degree
Summary
Molybdenum (Mo) and its alloys have excellent high temperature performance, such as high temperature strength, high creep resistance, low thermal expansion coefficient, and high thermal conductivity [1,2,3]. The rare-earth oxide doped Mo alloys have high toughness and strength at both room and high temperatures. The rare-earth oxide doped powders composed of nanoparticles with a highly dispersed oxide phase are a crucial factor to obtain high-performance Mo alloys. SCS is one of the proper methods to prepare uniformly doped nano-sized oxides, such as Al-doped ZnO nanoparticles [20], Sn-doped α-Fe2 O3 nanoparticles [21], and Fe3+ -W18 O49 nanoparticles [22], because precursor mixing at the molecular level ensured that the doped element can be distributed homogeneously throughout the matrix. The SCSHR route ensures the high dispersion of La2 O3 as a result of mixing at the molecular level, and the formation of nanopowders with homogeneous distribution of the oxide nanoparticles. The formation mechanism of La2 O3 doped Mo nanopowders has been discussed
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