Molybdenum/platinum/silver laminated composite
Nanoporous molybdenum can be prepared by dealloying method using molybdenum/zinc as precursor in non-solid solution metal system. Molybdenum/platinum/silver layered composites were prepared using porous molybdenum as substrate.
Silver has excellent electrical conductivity and good weldability and is widely used in the interconnecting solar arrays of spacecraft. In the space environment of low Earth orbit, spacecraft will be subjected to alternating cycles of high and low temperature, and silver with high thermal expansion coefficient will produce large thermal deformation and thermal stress cycle, and in serious cases, the interconnecting pieces and welded joints will be deformed and fractured. In addition, silver reacts with atomic oxygen in low Earth orbit to form black layers of silver oxide (AgO) and falls off. All of these will lead to the failure of the joint, which will seriously affect the life and reliability of the spacecraft in orbit.
Molybdenum metal has low thermal expansion coefficient, high melting point, high hardness, wear resistance and good thermal conductivity and conductivity. Once used as solar cell array interlinked material for space vehicles, it can overcome the thermal deformation and thermal fatigue caused by high and low temperature alternating cycle in low Earth orbit. However, due to the poor weldability of molybdenum, it is difficult to realize the interconnection of solar cells through welding processes such as resistance spot welding. The solution to this problem is to compound a layer of silver with good solderability on its surface, and the silver on the composite can also withstand the erosion of atomic oxygen in low Earth orbit.
Since molybdenum and silver are mutually insoluble metals, it is very difficult to make the lamellar composite of molybdenum and silver. It is better to add a layer of metal that is missoluble with both molybdenum and silver to make the composite. Molybdenum/platinum/silver lamellar composite was prepared by adding a layer of platinum between molybdenum and silver. It should be pointed out that molybdenum is a metal with an extremely inert surface, and even the combination of solid soluble platinum and molybdenum is still very difficult. Practice has proved that this often leads to the instability of the interface bonding strength of the prepared molybdenum/platinum/silver lamellar composites. Therefore, it is necessary to improve the surface activity of molybdenum to promote the combination of molybdenum and platinum, so as to prepare molybdenum/platinum/silver lamellar composites with good performance.
Nano-porous metals are materials with nano-sized holes and ligaments. Compared with common solid metals, due to the nano-scale ligaments and pores, the surface activity of nano-porous metals is higher when the specific surface area is greatly increased and the grain boundary volume fraction of the ligaments is larger. Nanoporous metal materials have been widely used in separation, catalysis, sensing and surface-enhanced Raman scattering.
At present, the main methods for preparing nanoporous metals include dealloying, template, oblique incidence deposition and sintering of metal powder. Among them, dealloying method refers to the use of chemical or electrochemical means to selectively corrode one or more active metal elements from the metal alloy, the remaining relatively inert metal atoms through agglomeration growth and finally form the double-hole and ligament dual-continuous structure of the nanoporous metal. By controlling the precursor preparation process and the subsequent corrosion conditions, the dealloying method can realize the dynamic control of the microstructure. Compared with the traditional nanoporous metal preparation methods, the dealloying method is simple in process, has low requirements on equipment, and has strong controllability.
