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Atomized aluminum powder (aluminum granules) results from melting and thereafter spray drying (freezing) aluminum into small individual particles using a compressed gas to draw the metal through a nozzle.
Atomized aluminum powder is a ubiquitous material in industry. Broad industries where atomized aluminum powder is used include:
Manufacturing of atomized aluminum powder can vary but general shape, metal chemistry (alloy), and particle size distribution are the main product characteristics that define atomized aluminum products. Through the variance of these three general factors, one can determine the best atomized aluminum product for his or her application.
Atomized aluminum granules are classified as either spherical or nodular (irregular). Given a need for a more controlled and defined particle shape and resulting surface area, one may choose to use spherical atomized powders. A nodular powder is very irregular in shape and therefore so is the surface area. When the need in shape is unknown, it is usually best to begin by evaluating an irregular powder; they are typically less expensive and more standardized in the market.
One must determine what chemistry is desirable for the application at hand. Highly pure 99.5% or greater aluminum is the industry standard for general atomized aluminum powder. The main contaminating metals for aluminum are iron (Fe) and silicon (Si) and for 99.5% purity rate, one should expect that the iron level is less than 0.20% and the silicon level is than 0.10%. All atomized aluminum granules, regardless of ingot purity, will have a varying thickness of aluminum oxide on the surface of the particle. Because aluminum reacts readily with oxygen, the oxide layer is not only unavoidable, it is also necessary in order to prevent the atomized aluminum powder from reacting spontaneously with air.
Alloys are becoming more common in the atomized aluminum industry. This is mainly being driven by different functional properties of aluminum with various metals added to its matrix. Currently, the brazing and thermal spray industries are driving much of the work being done to create different alloys of atomized aluminums. The chemical industry has also long taken advantage of low levels of titanium and similar metals added to the aluminum and formed into an atomized powder. The chemical industry uses the atomized aluminum as a catalyst in processes like or similar to the Ziegler process.
Particle size distribution (PSD) plays as critical a role in the performance and functionality of atomized aluminum powder as any other characteristic. There are two ways to measure an atomized powder’s PSD: sieve analysis and laser diffraction. From sieve analysis, a general PSD can be determined. Often, one finds out how much material of an atomized aluminum is below or above a certain threshold such as 45 microns (325 mesh sieve). The sieve analysis works well for generally coarse materials (average PSD > 15 microns) and is a standardized military specification test (USA). Laser diffraction is newer to the industry but has become very critical over the past 20 years in better defining atomized aluminum product characteristics. Through laser diffraction (or similar) the light scattering of particles at which a laser beam is shot is measured and analyzed. Based on the analysis of the light scattering, the equipment’s algorithm will determine a cumulative percent of particles that meet a certain size threshold. Typically, the particle size at which 3 cumulative thresholds are met is what is reported and defines the product: the size at which 10% (d10) of the material is finer, the size at which 50% (d50) of the material is finer, and the size at which 90% (d90) of the material is finer.
ECKART is committed to supporting the market needs of atomized aluminum granules. As such, ECKART offers a range of existing products as well as a willingness to custom tailor specific atomized aluminum powders to fit a customer’s need: alloyed and pure, spherical and nodular atomized powders in d50 sizes from 1.5-150 microns. It is easy to see with just the three product characteristics discussed here that while conceptually simple, choosing the specific atomized aluminum powder can open many different questions and possibilities. Discussing your general application or need for an atomized aluminum powder with an industry expert is always a great start to narrowing options and drilling down to what is important.