Meaning
Standard test method for particle size distribution of metal powders and related compounds employs light scattering techniques to provide a detailed granulometric profile. The protocol in astm b822 is designed for the analysis of fine powders where traditional sieving is either too slow or lacks the necessary resolution. By using laser diffraction, the instrument measures the angle and intensity of light scattered by a stream of particles passing through a laser beam.
This data is then converted into a volume based distribution that shows the percentage of particles at each size increment. It is the primary standard used for specifying powders for high precision additive manufacturing and thermal spray processes.
Analytical Technique
Preparation of the sample is a critical step to ensure that the laser diffraction results are accurate and representative of the entire batch. Under astm b822, the powder can be analyzed in either a dry state using a compressed air stream or a wet state by dispersing it in a liquid medium. Wet analysis often includes the use of ultrasonic energy to break up agglomerates that would otherwise be measured as single large particles.
The choice between wet and dry methods depends on the material properties and the final application of the powder. Modern software then applies optical models like the Mie theory to calculate the size distribution from the raw scattering data.
Data Interpretation
Results of the test are typically reported as a cumulative distribution curve and specific percentile values such as the d10, d50, and d90. These numbers derived from astm b822 indicate the particle sizes below which ten, fifty, and ninety percent of the total volume resides. A narrow distribution suggests a very uniform powder while a wide distribution indicates a mix of very fine and very coarse grains.
This information is vital for ensuring consistent layer thickness in laser powder bed fusion and for optimizing the sintering behavior of metal injection molded parts. Detailed reporting allows for the detection of subtle changes in the atomization process that might affect the quality of the final product.
Sourcing Specification
Purchasing agreements for advanced metallic powders almost always reference the size metrics defined by this standard to ensure material compatibility. The astm b822 method provides a common language for suppliers and end users to discuss the requirements of a specific manufacturing job. Because different laser diffraction instruments can produce slightly different results, the standard emphasizes the importance of using consistent parameters and calibration standards.
This reduces the risk of accepting a batch of powder that falls outside the required tolerances for a critical aerospace or medical component. High resolution data from these tests helps in the development of new alloys and the refinement of existing production techniques.
