Imbues Heat-Resistant Materials with Durable Coating During Assembly
These 3D-printed receiver tubes can survive the scorching temperatures of concentrated solar power systems while remaining cheap and lasting for decades. Concentrated solar power receivers contain heat transfer fluids, such as molten salt, absorbing energy from concentrated sunlight and then releasing the energy to generate electricity. Conventional receiver tubes operate at around 500°C, but advanced receivers operating at high temperatures offer improved efficiency, lower overall system costs, and expanded industrial applications. Refractory metals such as molybdenum possess notorious heat resistance, promising for concentrated solar power receiver tubing, but are overly liable to oxidize. Coatings based on borosilicate glass materials can prevent the oxidation of molybdenum. However, to achieve a high-temperature, fully oxidation-resistant material suitable for concentrated solar power applications, this coating must be applied to the inner and outer surfaces of all tubing, an onerous manufacturing requirement.
Researchers at the University of Florida have developed a laser engineered net shaping (LENS) 3D printer for fabricating receiver tubes capable of surviving high temperatures and resisting oxidation. The laser fuses the molybdenum, boron, and silicate into a thick three-dimensional coating in place, even for hard-to-reach regions such as the inside walls of long, narrow tubes.
Application
Laser-based 3D printing for achieving oxidation-resistant coating on the hardest-to-reach parts of heat-resistant molybdenum tubing
Advantages
- Offers mechanical strength and resistance to creep at high temperatures, besting the performance of the nickel alloys typically used for concentrated solar power components and enabling higher efficiency
- Can withstand temperatures as high as 1650°C, unlocking compatibility with next-generation heat transfer materials such as supercritical carbon dioxide and ceramic particles
- Synthesizes heat-resistant molybdenum tubes with a functional coating material, offering oxidation protection over 30 years protection without lowering the molybdenum’s solar absorption
Technology
Concentrated solar power is a renewable energy technology that stores thermal energy in fluids such as molten salt or supercritical carbon dioxide. The concentration of sunlight towards the fluids produces such high temperatures that the tubing must possess excellent heat resistance. Furthermore, the demands of high solar absorption, high thermal conductivity, oxidation resistance, and low-cost manufacturing present serious challenges to the selection of materials for concentrated solar power tubing. 3D printing unlocks powerful combinations of materials with desirable properties to meet this challenge. Molybdenum features a melting point above 2200 ?C while a mixture of molybdenum, silicon, and boron produces an oxidation-resistant coating that also offers creep resistance and fracture toughness. The laser engineered net shaping (LENS) 3D printer combines these into a heterostructure with both heat and oxidation resistance. The printing mechanism proceeds by depositing powders of pure molybdenum and a molybdenum-silicon-boron mixture simultaneously. A laser then irradiates the powders, generating a molybdenum substrate covered by an oxidation-resistant coating whose incorporation of both silicon and boron offers improved oxidation resistance compared to traditional molybdenum-silicon compositions.
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