Particle Size Analysis of Chemical Raw Materials

Particle size analysis is a fundamental quality control and research technique for chemical raw materials, because particle size distribution directly governs reactivity, dissolution rate, flowability, packing density, and downstream product performance. This technical article outlines the key parameters, sample types, testing methods, applicable standards, and typical applications of particle size analysis for powders, granules, dispersions, and emulsions used across the chemical industry. Accredited third-party laboratories perform these measurements in accordance with ISO, ASTM, and GB standards to support process development, incoming material inspection, and regulatory compliance.

Technical Overview

Particle size analysis comprises the family of laboratory techniques used to determine the size distribution of particles in powdered, granular, suspended, or emulsified samples. Because most chemical raw materials are produced, transported, and processed as particulate solids or liquid dispersions, particle size distribution (PSD) is one of the most frequently measured and most consequential quality attributes in the chemical industry.

Since real particles are rarely perfect spheres, particle size is conventionally expressed as an equivalent spherical diameter: the diameter of a sphere that produces the same instrument response as the actual particle. Raw measurement data are converted into a distribution curve, from which characteristic parameters are derived, typically including:

• D10: the diameter below which 10 percent of the particle population lies, indicating the fine fraction.
• D50 (median particle size): the diameter at which half of the population is finer and half is coarser.
• D90: the diameter below which 90 percent of the population lies, indicating the coarse fraction.
• Span: calculated as (D90 minus D10) divided by D50, expressing the width of the distribution.
• D[4,3] (volume moment mean) and D[3,2] (Sauter mean diameter), which emphasize volume and surface-related behavior respectively.
• Volume-based versus number-based distributions, which must be clearly identified when reporting results.

Particle size influences nearly every aspect of raw material behavior. Finer particles exhibit higher specific surface area and therefore faster reaction rates, stronger adsorption, and improved catalytic activity, but they also tend to agglomerate, flow poorly, generate dust, and compact less efficiently. Coarser particles improve flowability and packing but reduce reactivity, dispersion stability, and optical performance. Reliable particle size analysis allows manufacturers to define specifications, control milling and classification processes, and ensure batch-to-batch consistency. Data representation and reporting generally follow the ISO 9276 series and its national equivalents.

Testing Samples

Inorganic Fillers and Mineral Raw Materials

Ground and precipitated calcium carbonate, talc, kaolin, mica, wollastonite, barium sulfate, silica and silica fume, alumina, titanium dioxide, zinc oxide, and other mineral fillers and pigments. These materials are typically analyzed by laser diffraction or sedimentation, often with wet dispersion and controlled ultrasonic treatment to break down soft agglomerates.

Organic and Polymer Raw Materials

Thermoplastic and thermoset resin powders, polymer beads and granules, wax powders, organic pigments, dye intermediates, rubber accelerators and antioxidants, and other specialty organic chemicals. Dispersion conditions must be selected carefully because many organic powders are hydrophobic, electrostatically charged, or soluble in specific media.

Metal Powders and Catalyst Materials

Iron, copper, aluminum, nickel, cobalt, and alloy powders, catalyst carriers and supported catalysts, zeolites and molecular sieves, activated carbon, and reduced or passivated metal pigments. Metal powders are commonly characterized by laser diffraction in accordance with ASTM B822, supplemented by sieve analysis for coarser cuts.

Fine Chemicals and Functional Materials

Pharmaceutical intermediates, battery materials such as lithium iron phosphate, ternary cathode precursors, and graphite anode materials, ceramic precursors, abrasive grains, fertilizers, and spray-dried granules. These applications frequently require tight control of D50, D90, and fines content to ensure processability and end-use performance.

Liquid Dispersions

Emulsions, latexes, colloidal silica, nano-dispersions, slurry intermediates, and surfactant solutions containing micelles or droplets. Sub-micrometer and nanometer-scale systems are analyzed by dynamic light scattering, which reports the hydrodynamic diameter and the polydispersity index.

Testing Items

Depending on the material and the applicable specification, particle size analysis of chemical raw materials may include the following measurement items:

• Complete particle size distribution on a volume, number, or surface basis.
• Characteristic diameters: D10, D50, D90, Dv50, Dn50, D[4,3], and D[3,2].
• Distribution width descriptors: span, uniformity index, and geometric standard deviation.
• Threshold fractions: cumulative undersize or oversize percentages, residue above a specified mesh, fines content, and grit determination.
• Specific surface area by gas adsorption (BET method, ISO 9277) as a complementary fineness parameter.
• Particle shape metrics by image analysis: circularity, aspect ratio, elongation, convexity, and shape factor.
• Fiber or needle length and diameter measurements for fibrous or acicular raw materials.
• Method comparison studies, such as wet versus dry dispersion, to validate sample preparation conditions.

Testing Methods

Laser Diffraction

Laser diffraction (ISO 13320, ASTM B822, GB/T 19077) is the most widely used method for chemical raw materials, covering approximately 0.1 micrometers to 3,500 micrometers. Particles scatter light at angles that depend on size, and the scattered pattern is deconvoluted into a volume-based distribution. Samples can be dispersed either wet in a suitable liquid carrier or dry with compressed air; the choice depends on solubility, friability, and agglomeration tendency. Sample preparation for powders in liquids is guided by ISO 14887.

Dynamic Light Scattering

Dynamic light scattering (ISO 22412, GB/T 19627) measures Brownian motion to determine hydrodynamic diameter, with a typical range of 0.3 nanometers to about 10 micrometers. It is the preferred technique for nanoparticles, colloids, emulsion droplets, and fine suspensions, and it reports an intensity-based distribution with a polydispersity index.

Static Image Analysis

Static image analysis (ISO 13322-1) captures microscope images of dispersed particles on a substrate and evaluates both size and shape particle by particle. It provides number-based distributions and is valuable for verifying laser diffraction results, identifying agglomerates, and characterizing fibers or irregular particles.

Dynamic Image Analysis

Dynamic image analysis (ISO 13322-2) records particles in flow with a high-speed camera, typically covering about 1 micrometer to several millimeters. It combines broad-range sizing with detailed morphological statistics and is well suited to granules, crystals, and abrasive grains.

Sieve Analysis

Sieving (ISO 2591-1, ASTM B214, GB/T 6003.1 and GB/T 6003.2) remains a robust reference method for coarser powders, generally above 38 micrometers for woven-wire sieves, with electroformed sieves extending below this limit. Wet sieving, dry sieving, and air-jet sieving variants are selected according to the material, and sieve apertures conform to ASTM E11 specifications. Results are expressed as mass-based cumulative percentages on each sieve.

Electrical Sensing Zone Method

The electrical sensing zone technique (ISO 13319), also known as the Coulter principle, counts and sizes individual particles suspended in an electrolyte as they pass through a small aperture. It delivers high-resolution number-based distributions over approximately 0.4 micrometers to 1,600 micrometers and is particularly effective for detecting small quantities of oversize or contaminant particles.

Sedimentation Methods

Gravitational liquid sedimentation (ISO 13317) and centrifugal sedimentation (ISO 13318) determine size from settling velocity using Stokes' law, covering roughly 1 micrometer to 100 micrometers gravitationally and down to about 0.05 micrometers centrifugally. These methods remain important for dense, fine mineral powders such as titanium dioxide and calcium carbonate.

Specific Surface Area and Permeability Techniques

Gas adsorption (BET, ISO 9277) quantifies specific surface area in square meters per gram, a key indicator for catalysts, adsorbents, and reactive powders. Air permeability methods estimate mean fineness from air flow resistance through a packed bed and are widely applied to cement-like and finely ground mineral materials as a rapid production control parameter.

Applications

Particle size data are embedded in specifications, certificates of analysis, and technical data sheets throughout the chemical value chain. Typical applications include:

• Incoming raw material inspection, supplier qualification, and batch consistency verification against agreed D50, D90, and fines limits.
• Optimization and monitoring of comminution, air classification, crystallization, and spray-drying processes to hit target distributions and reduce off-specification production.
• Catalyst development and quality control, where particle size and surface area determine activity, selectivity, pressure drop, and attrition resistance.
• Coatings, inks, and pigment formulation, where fineness controls hiding power, gloss, tinting strength, viscosity, and sedimentation stability.
• Plastics and rubber compounding, where filler particle size affects dispersion, rheology, mechanical reinforcement, and surface finish.
• Ceramics and powder metallurgy, where particle size distribution governs powder compressibility, green density, sintering shrinkage, and final microstructure.
• Battery materials, where cathode and anode particle size distribution influences tap density, energy density, rate capability, and electrode coating uniformity.
• Agrochemicals and detergents, where granule size controls dust-off, flowability, dispersion, and dissolution behavior.
• Regulatory submissions, stability studies, and technical documentation requiring traceable measurements from accredited third-party laboratories.

FAQ

How much sample is required for particle size analysis?

For laser diffraction, typically 1 to 5 grams of powder or a few milliliters of dispersion is sufficient, although free-flowing granular materials may require more to ensure representative sampling. Sieve analysis generally requires 25 to 100 grams or more depending on the applicable standard, while dynamic light scattering needs only a dilute suspension of a few milliliters. Sampling from bulk containers should always follow good sampling practice, since the laboratory aliquot must represent the entire lot.

Should my material be measured wet or dry?

Wet dispersion is preferred for fine powders that agglomerate, for water-insoluble minerals, and whenever ultrasonic energy is needed to achieve a stable primary-particle suspension. Dry dispersion suits water-soluble salts, hygroscopic materials, spray-dried granules, and friable powders that could break down under wet shear. A dispersion study comparing wet and dry results under ISO 13320 guidance establishes the appropriate condition for each specific raw material.

What size range can be measured?

Combining available methods covers from below 1 nanometer to several millimeters: dynamic light scattering handles roughly 0.3 nanometers to 10 micrometers, laser diffraction approximately 0.1 to 3,500 micrometers, image analysis about 1 micrometer to several millimeters, and sieve analysis for coarser fractions. Most raw material specifications are satisfied by laser diffraction alone.

Why do D10, D50, and D90 sometimes differ between methods?

Each technique measures a different physical property and reports a different weighting basis: laser diffraction is volume-weighted, microscopy and sensing-zone methods are number-weighted, and sieving is mass-weighted. Because irregular shapes and agglomerates respond differently to each principle, small systematic differences are expected. Comparisons are only valid when the measurement principle and reporting basis are matched, which is why the method and standard must always accompany the reported values.

How is measurement quality assured?

Accredited third-party laboratories verify instrument performance with certified reference materials, qualify dispersion conditions through repeat measurements, and apply repeatability criteria defined in the relevant standards, such as the ISO 13320 limits on D50 and D10 deviation. Reports include the measurement method, dispersion medium, obscuration or concentration, full distribution table, and characteristic diameters so that results are traceable and reproducible.

What is the typical turnaround time?

Standard particle size analysis by laser diffraction, DLS, or sieving is usually completed within three to seven working days after sample receipt, including sample preparation, instrument verification, and reporting. Studies involving method development, shape analysis, or comparison of multiple dispersion conditions may require additional time.