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Abstract In the present work, a novel method was proposed to synthesize pure nano Mo powder via temperature programmed pre-reduction of commercial MoO 3 by carbon black, followed by deep deoxidation with hydrogen. It was found that the carbothermal reduction of MoO 3 included three stages: MoO 3 → MoO 2 → MoO 2 + Mo 2 C → Mo. It can be concluded that the morphology and size of the obtained Mo particles are mainly determined at the carbothermic reduction stage. The dispersed nucleation and controlled growth are critical issues for controlling the particle sizes of Mo, which could be achieved at the carbothermic reduction stage by using the raw materials of the MoO 3 and carbon black. Whereas, when the MoO 3 was directly reduced by hydrogen or active carbon with a larger particle size, or commercial MoO 2 were reduced with the carbon black, the dispersed nucleation and controlled growth of products can't be achieved. Meanwhile, to reduce the residual carbon content in the final Mo product, in the carbothermic pre-reduction process, the small amount of MoO 2 was kept in the pre-reduced Mo powders, which was removed by hydrogen at the deep deoxidation stage. The content of residual carbon content in the final produced Mo nanopowders can be reduced to about 0.02%. This method has the advantages of simplicity, low cost, and high efficiency. Therefore, it has great potential for the industrial preparation of nano Mo powders in a large-scale. Graphical abstract Unlabelled Image Highlights • Pure Mo nanoparticles were prepared via reduction of MoO 3 with carbon black, followed by deep deoxidation with hydrogen. • Carbothermal reduction of MoO 3 included three stages: MoO 3 → MoO 2 → MoO 2 + Mo 2 C → Mo. • A minor amount of MoO 2 in the pre-reduced Mo powder can reduce effectively the residual carbon. [ABSTRACT FROM AUTHOR]

Abstract Tungsten (W) is the most commonly used high-temperature refractory metal in many critical fields such as aerospace, military and electronic industries etc. This paper proposes a low-cost, efficient, and industrially feasible pathway for large scale preparation of tungsten nanoparticles via the combination of carbothermic reduction and hydrogen reduction processes. The new strategy involves the preparation process of pre-reduction W powder by reducing commercial WO 3 with insufficient carbon black at 1050 °C or 1150 °C to avoid the residue of carbon, and the deep reduction process of pre-reduction W powder by hydrogen 725 °C. By this process, most of the oxygen in WO 3 was reduced by carbon, and W particles with a much smaller size could be obtained owing to the absence of the volatile tungsten oxide, such as WO 2 (OH) 2 , which leads to the serious increase of particle size during the hydrogen reduction process. Tungsten nanoparticles with average particle sizes of about 40 nm and 75 nm have been successfully synthesized at 1050 °C and 1150 °C, respectively, with the residual carbon content as low as about 0.01%. This process can be readily extended to a large-scale industrial production of W nanopowders. Additionally, this new strategy has great potential to prepare other pure metals (or nanopowders) from their metal oxides via combining of carbothermic reduction (main process) and further reduction of other reducing agents. Highlights • Pre-reduced nano W powders were prepared by reducing WO 3 with insufficient carbon. • Growth of W nanoparticles can be controlled in carbothermic reduction process. • A minor amount of remained WO 2 can reduce the residual carbon to as low as 0.01%. • A deep deoxidation by H 2 at 725 °C could reduce the minor amount of WO 2 to W. [ABSTRACT FROM AUTHOR]

SiC coating for carbon/carbon composites was prepared by pack cementation method. The effects of coating process on the microstructure and the mechanical properties of C/C composites were analyzed by SEM and three-point bending test, respectively. As the infiltrated Si improved the interfaces bonding during the coating process, the flexural strength and flexural modulus of SiC-coated carbon/carbon composites were both increased by about 10% than the naked C/C composites. In addition, the mechanism of the change of failure mode of SiC coated C/C composites and naked C/C composites was addressed. [ABSTRACT FROM AUTHOR]

Abstract: In order to protect carbon/carbon (C/C) composites from oxidation, a silicon carbide coating has been produced by a two-step pack cementation technique. XRD analysis showed that the inner coating obtained from the first step was a β-SiC layer and the outer coating formed by the second step pack cementation was composed of α-SiC, Si and β-SiC. The as-received coating provided excellent oxidation resistance, proving able to protect C/C composites from oxidation for more than 310h at 1773K in air. The weight loss of the coated C/C composites was considered to arise from the debonding of some glass and the formation of bubble holes on the coating surface. [Copyright &y& Elsevier]