For Gd 2 Zr 2 O 7 , nanograin ceramics with high relative densities (95%–97.4%) and small average grain sizes (61 nm - 82 nm) were successfully fabricated for the first time using field assisted sintering technique (FAST), also known as spark plasma sintering (SPS) method, in which nanopowders with an average crystallite size of 5.9 nm were synthesized via a non-aqueous gel-combustion method. Temperature was varied over a broad range to investigate its influence on the densification mechanism, microstructure evolution and hardness. The results revealed that both relative density and grain size increase with the increase of sintering temperature . The densification processes were divided to three stages. 1250 °C–1300 °C is the most suitable temperature range to fabricate dense Gd 2 Zr 2 O 7 nanograin ceramics with comparatively high hardness by FAST.
Nd2Fe14B nanoparticles were successfully prepared by using a low-energy chemical method. The microscopic characteristics and formation mechanisms of the phases were investigated at each stage during the preparation of Nd-Fe-B nanoparticles. The Nd-Fe-B intermediates, Nd-Fe-B oxides and reduced Nd-Fe-B nanoparticles were detected and analyzed by using TEM, STEM, XRD, SEM, VSM and Rietveld calculations. The results showed that the intermediate of Nd-Fe-B consisted of Fe3O4 and Nd and Fe elements surrounded by nitrile organic compounds. The Nd-Fe-B oxide was composed of NdFeO3 (48.619 wt%), NdBO3 (31.480 wt%) and α-Fe (19.901 wt%), which was formed by the reaction among Nd, Fe3O4 and B2O3. NdFeO3 and NdBO3 exhibited a perovskite-like lamellar structure, and the grain size was smaller than that of α-Fe. Nd-Fe-B particles were mainly composed of Nd2Fe14B and α-Fe phases. The small particles of NdFeO3 and NdBO3 and the interstitial position between oxide particles and α-Fe were more favorable for the formation of Nd2Fe14B particles. At the same time, the surface of α-Fe particles can also diffuse to form Nd2Fe14B nanoparticles. The coercivity of Nd-Fe-B particles was 5.79 kOe and the saturation magnetization was 63.135 emu g−1.
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