SBIR-STTR Award

In this project, Eltron will develop a method for spray drying agglomerates of nanoparticles for use in the cold spray process. These agglomerates will allow the nanoparticles to be cold sprayed, resulting in coatings and structures with superior strength and hardness. Nanosized particles will be dispersed in a solvent with a metallic binder precursor and spray dried under controlled atmosphere to form spheroid particles. In the spray dryer, slurry droplets are expelled from the atomizer and the liquid surface tension creates perfect spheres. As the droplets fall through the spray dryer, the heated gas will simultaneously cause the liquid to evaporate and convert the binder precursor. As the liquid is removed, the nanoparticles are brought into contact, forming agglomerates while maintaining their spherical shape. When exposed to the spray dryer conditions, the binder precursor will form small crystals, coating the nanoparticles to form connections between the nanoparticles and fill the gaps between nanoparticles. New methods for forming platelets and needles will be developed by controlling spray drier settings and using an impact barrier. In addition, this technology will be directly transferable to agglomerating ceramic (WC, ZrO2, or VN) nanoparticles with a binder for wear-resistant cold spray commercial applications.

Keywords:
Nanopowders, Nano-Structured Materials, Cold Spray, Agglomerates, Granules, Nanoparticles

Cold spray has many benefits compared to conventional thermal spray including lower deposition temperatures, higher bond strengths, less substrate preparation and better control of coating composition, phase structure, and oxide contamination. In cold spray, particles are accelerated by an expanding gas to 180-1200 m/s, where they collide with a substrate to form a coating on the surface in the solid state. Since reduced deposition temperatures are used, coatings have the same properties as the initial particles. However, in the cold spray process, particles smaller than 5 microns in diameter have insufficient momentum to penetrate a “shock wave” region next to the substrate. Nanoparticles offer many benefits in strength, hardness, and reactivity but are unable to be used in the cold spray process due to insufficient mass and, therefore, momentum. In the Phase I project, Eltron developed a method for spray drying agglomerates of nanoparticles for use in the cold spray process. Spray drying is a low-cost, well-established powder processing method used often in the food and catalyst industries. The objectives of this Phase II project include: 1) produce larger (10-20 lb.) batches of powder for consolidation by cold spray at the Army Research Laboratory, 2) develop a system for consolidating smaller, more reactive, un-passivated metal particles, 3) determine the effect of slurry flow rate, nozzle diameter, gas flow rate, nanoparticle size, binder concentration and binder choice with larger volume slurries on agglomerate morphology, size, and size distribution, 4) characterize agglomerates using optical and scanning electron microscopy, chemical analysis, density measurements, x-ray diffraction, and surface area/pore size and volume analysis, and 5) optimize economic considerations including nanoparticle, metallic binder precursor, and solvent costs, leading to an estimate of powder costs when produced on a commercial scale. Work towards these objectives will lead to a flexible process for producing relatively inexpensive nanostructured powders that enables use of a variety of nanoparticle compositions and particle sizes (from 10 200 nm). During Phase II, larger volume slurries will be optimized and process variables will be determined to best prepare for scale-up to production levels of 100 lbs/day (during Phase III).

Keywords:
Nanopowders, Nano-Structured Materials, Cold Spray, Agglomerates, Granules, Nanoparticles