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Freeze drying method for preparation of coating powders is put forward, which doesn't need a core particle at first compared with the conventional methods. Nano-sized Al2O3 coated W composites were prepared via freeze-drying and multi-reducing of the mixture of aluminum sulphate and AMT. The phase compositions, structure and morphologies of the composites were investigated by XRD, IR, SEM. The formation mechanism of the coating composites was also studied. The results indicate that W powders in size of 1 μm have regular shape and are coated with uniform Al2O3 nanoparticles in size of 40 nm. The mechanism is suggested to be three-step process: W crystallization, soft-coating formation and heterogenous alumina nucleation.
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