One of the important properties of tungsten powder is particle size. The smallest powders are less than one micron and coarse powders can be over 100 microns. While each individual particle has a distinct size and shape, the average particle size is the most common way to charaterize a blended lot of tungsten powder.
An industry standard for particle size is the Fisher Sub Sieve Sizer (FSSS). The technology is from the 1940’s, but it still provides a uniform measure of particle size throughout the industry. It works on the principle of air permeability to produce quick and consistent results. An average particle size detemined this way is know as a Fisher number, or FSSS number.
Particle Size Distribution
In a lot of tungsten powder with an average particle size of 5 microns you can expect about half of the particles to be smaller than 5 microns and about half of them larger. The percentages that are larger and smaller create a particle size distribution. For fine powders of this size, Buffalo Tungsten then reports the percentages in increments of one micron up to 10 microns.
Some applications require a narrower particle size distribution, so through furnace conditions or supplemental processing the largest and smallest particles can be eliminated or removed.
In both examples the average size is 5 microns, but the second has a narrower distribution around the mean. Buffalo Tungsten is able to meet demanding specifications for particle size distribution, which is necessary in some applications.
Tungsten Powder Measurement
Companies like Microtrac and Malvern make instruments to measure the particle size of metal powders. There are different methods of measuring particle size. Laser diffraction measures the angles that light reflects off of the particles to determine their size. Image analysis takes pictures of the particles and measures them. This can also provide an indication of the shape of the particles.
You can order tungsten powder from Buffalo Tungsten in a wide range of sizes. A certificate of analysis comes with every shipment to report the physical and chemical properties of the material.