How can manufacturers trust that their powders will result in a quality, high-performing product?
Powders can pose unique challenges to characterize, because unlike most materials where you’re dealing with one solid material, you need to describe millions – or even billions – of tiny individual particles that contribute to a collective property or behavior. No two particles are going to be exactly the same, so instead of looking at one value, you need to think in terms of distributions and statistics.
This also means powders can be more prone to contamination and changes over time that aren’t always easy to spot. Fortunately, sampling and test methods have been developed such that a small amount of powder can be analyzed and reliably reflect the properties of the whole batch or lot.
At NSL Analytical, we work with our scientists and engineers to utilize a suite of capabilities to provide a complete understanding of a powder’s characteristics and quality. This helps our customers ensure stringent quality control, optimize critical processes, and deliver reliable product performance.
What Are the Most Relevant Chemical and Physical Properties for Powder Characterization?
Powder characterization encompasses a wide range of tests that provide engineers with a comprehensive understanding of the physical and chemical characteristics of particulate materials.
“These tests are essential to understand how powders will behave in their intended applications,” said Dr. Ross Cunningham, Director of Science and Technology at NSL Analytical. “They are crucial for ensuring uniformity between different batches of material, predicting manufacturing outcomes, and catching potential issues that may arise during production.”
NSL’s expert team routinely analyzes powders to answer critical questions such as:
- How easily does it flow?
- How densely can it be packed?
- What is the size and shape of its individual particles?
- What is its chemical makeup, both in bulk and on its surface?
By quantifying these attributes, we can help you trust that the final powder meets your exact performance and quality standards.
Understanding a powder’s behavior requires examining both physical and chemical properties. Here at NSL, we routinely test for:
- Particle Size Distribution: A fundamental characteristic describing the particle sizes present in a sample. It profoundly influences other properties, such as density and flowability, and is a critical parameter for applications like Additive Manufacturing.
- Particle Shape and Morphology: Particle shape impacts flowability, density, and surface area. Microscopy techniques are used for qualitative and quantitative description of particle morphology.
- Density:
- Apparent/Bulk Density: A measurement of a powder’s mass per unit of its apparent volume after freely flowing into its container, including the spaces (voids) between particles and any internal porosity. This is influenced by PSD, shape, and surface conditions.
- Tapped Density (Packed Density): Measures a powder’s density after undergoing a number of vibrations to indicate how much it can compact, as can happen during shipping.
- Skeletal Density (True Density): Represents the solid density of the material, excluding any pores or voids within the particles. Often determined by helium pycnometry.
- Flowability: Free-flowing powder is critical for consistent feeding, dosing, and mixing operations, and is an essential property for Additive Manufacturing powders. It can be measured with simple tests like a Hall flow meter, or more dynamically with a Rotary Drum Rheometer.
- Surface Area and Porosity: The total surface area of a sample of powder, which influences its reactivity and adsorption properties. Surface area is influenced by particle size and morphology, with smaller and more irregular particles increasing the surface area.
Chemical considerations when analyzing a powder’s behavior at the molecular level include:
- Elemental Composition: The elemental makeup of the powder, measured through a combination of techniques such as ICP or LECO. Critical for powders in their as-produced form, but also to track changes over time that can occur due to contamination or environmental factors, due to their high surface area to mass ratio.
- Phase Analysis: X-ray diffraction can provide information on the crystalline phases present in metal and ceramic powders.
- Solubility: A powder’s ability to dissolve in water, acids, or other substances. Often used to measure acid-insoluble contamination, such as trace refractory materials in metal powders.
- Moisture Content: Moisture can adsorb onto powder surfaces due to improper storage or exposure during processing, depending on the hygroscopicity of the material. Due to the high surface area of powders, this can significantly impact chemical properties and packing/flow. Moisture is most reliably measured using Karl Fischer Titration, with total adsorbed volatiles measured through thermogravimetric analysis.
What Industries Use Powder Characterization Testing?
The versatility of powders allows them to serve as feedstock materials for a variety of critical industries and processes. The insights offered by powder characterization testing, therefore, make it an indispensable tool for these key industries where powdered materials are central to their manufacturing operations, such as:
- Ceramics: Ceramic components are generally sintered from powder; therefore, elemental composition, particle size distribution, and morphology of the precursor ceramic powders are paramount for achieving desired mechanical, thermal, and electrical properties in critical products for aerospace, electronics, and medical devices. These materials are also often used in their powder form as abrasives, catalysts, or additives with similarly demanding property specifications.
- Additive Manufacturing (3D Printing): This rapidly growing field is driving further innovation in powder characterization to optimize the properties of metallic, ceramic, and polymer powders, which are critical to the success of these processes. For instance, the Rotary Drum Rheometer is used to measure dynamic powder flow. Powder characteristics affect the repeatability of the process and the quality of the final printed parts. Due to the ability to reuse powder, tracking changes in PSD and chemistry over time is a vital part of quality control for critical end-use parts in aerospace and medical devices.
- Aerospace/Defense: Powdered materials are used in many vital aircraft components and processes, including brazing compounds, blade alloys, and thermal spray coatings. These materials must be thoroughly tested for compliance to deliver the highest quality and reliability.
- Powder Metallurgy/MIM: Powder serves as the primary input to the Powder Metallurgy and Metal Injection Molding industries, which supply a large volume of parts to the automotive, firearms, equipment/tooling, and medical/dental markets.
- Pharmaceuticals & Nutraceuticals: One of the most critical sectors for powder characterization. Testing is performed to determine the particle size distribution, as well as the elemental composition of beneficial chemicals and the presence of toxic heavy metals, such as lead or mercury.
- Medical Devices: An increasing number of medical and dental devices are being manufactured from powder via MIM or Additive Manufacturing due to the benefits these techniques offer. The strict quality and safety standards of these industries require rigorous testing of both chemical and physical properties to ensure biocompatibility and long-lasting performance.
What Are Some Common Powder Characterization Testing Methods?
NSL employs specialized techniques to quantify the properties discussed above:
- Particle Size Analysis:
- Laser Diffraction: A widely used technique that measures the angle of light scattered by particles in a laser beam to calculate particle size distributions.
- Sieving: Involves passing powder through a series of sieves with decreasing mesh sizes to determine the mass fraction retained on each sieve.
- Density Testing:
- Bulk Density Measurement: Determined by measuring the volume of a known mass of powder in a graduated cylinder without compaction.
- Tap Density Measurement: Measures the density of a powder after it has been subjected to a specific number of taps or vibrations, indicating its packing efficiency.
- Helium Pycnometry: Used to determine the solid (skeletal) density of a material by measuring the volume via gas displacement by helium.
- Flow Testing:
- Rotating Drum Rheometer: Observes and measures dynamic powder behavior while it is rotating in an enclosed drum. A common metric from this test is the Avalanche Angle, or the maximum angle at which powder can be inclined before avalanche flow occurs. A lower angle indicates better flowability.
- Hall/Carney Flow: Measures the time it takes for a mass of powder to flow through a specific opening, suitable for relatively free-flowing powders. It can also measure the resulting angle of repose, or the maximum angle at which a powder can be piled without collapsing.
- Surface Area:
- BET (Brunauer-Emmett-Teller) Analysis: Utilizes nitrogen or krypton gas adsorption to determine the specific surface area of powders and porous materials.
- Chemical Composition and Morphology:
- Inductively Coupled Plasma – Optical Emission Spectroscopy/Mass Spectrometry (ICP-OES/MS): The leading method for testing elemental composition, using plasma to vaporize and ionize a sample and determine the type and quantity of elements through optical emission spectroscopy or mass spectrometry.
- Microscopy (SEM, Light Microscopy): Used to visually study particle shape, surface features, and overall morphology, as well as semi-quantitative elemental analysis and mapping via EDX.
- Spectroscopy (FTIR, UV-vis): Provides chemical information on a particle or bulk material level, identifying functional groups and chemical bonds.
- X-Ray Diffraction (XRD): Used to study the crystalline structure of powders.
“NSL Analytical is a leader in powder characterization testing,” said Chris Keith, the VP of Sales and Marketing for NSL Analytical. “We’ve invested in the resources, equipment, and testing methods needed for consistent, accurate results and fast turnarounds for our customers.”
To learn more, view a list of our powder characterization testing capabilities.
Looking to dive deeper into how third-party testing can support your unique material needs? Check out NSL’s resources below:
Materials Matter: This educational hub page is a trusted resource for material science information.
Webinars and White Papers: Dive into specific topics in this library of educational webinars and white papers.
Video Library: View these helpful videos about everything from additive manufacturing to spectroscopy and more.
NSL Analytical Services, Inc. is an independent materials testing lab that specializes in metallurgical, mechanical, chemical, and optical testing for mission-critical industries.
Contact our experienced, accredited team to discover how we can deliver accurate, repeatable testing results with lightning-fast turnarounds, giving you confidence in your material performance and adherence to quality standards and regulations.
