Liquid Metal Dealloying Technology Applied To Nano-porous Tungsten Production

Nano-porous tungsten, which is characterized by large surface, numerous active spots and so on, is widely applied to a lot of fields, such as energy storage, catalysis and sensors. It can be categorized as a kind of powder metallurgy tungsten product which owns a inner structure with a lot of holes related to its application.

However, tungsten carbide owns the highest melting point and the lowest vapor pressure among all metals. Therefore, the production of nano-porous tungsten requires higher technological standard. At present, the dealloying technology is one of common methods for its production. Recently, researchers have been devoted to developing new technology applied to nano-porous production------ a new kind of liquid metal dealloying technology. The method uses molten metal as a dealloying agent and achieves dealloying process by utilizing different inter-miscibility of different components in molten metal. There is still a technological problem needed to be solved. Because this technology occurs in the liquid metal at very high temperature, the structure has inevitable coarsening, which causes difficulties in nano-structure production.  

Aimed at the problem listed above, some researchers have developed an approach to producing nano-porous tungsten with the structure of three-dimensional bicontinuous skeleton through mechanical alloying and liquid metal dealloying technology in aqueous solution at ambient temperature. The main content is that:

(1) To weigh tungsten powder and aluminum powder according to the mole fraction of aluminum (between 70% and 90%), and add stearic acid as a control agent for high-energy ball-milling. The amount of stearic acid is 0.5-1.5% of the total mass of the ball-milled powder. Ball-milling speed is 300-600r/min, ball milling time is 20-30h. As a result, tungsten aluminum alloy powder is obtained.

(2) To put the prepared tungsten aluminum alloy powder into an oxygen-depleted aqueous solution of 0.5-1 M sulfuric acid or sodium hydroxide for 15-25 hours’ dealloying, and wash three times with ultrapure water and ethanol by adopting suction filtration in order to collect powder samples, a nanoporous tungsten powder with a three-dimensional bicontinuous structure.

Compared with the existing method for de-alloying liquid metal to prepare nano-porous refractory metal, the improved process has the advantage of being capable of performing a dealloying process in an aqueous solution at room temperature, thereby avoiding the coarsening of porous structure caused by the high temperature of the liquid metal. As a result, the nano-porous structure of which particle size is at nano-scale, is obtained, and the porous tungsten particle size can be controlled below 100 nm.

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