GranulometryEdit
Granulometry is the science of measuring and interpreting the distribution of particle sizes within a material. It plays a central role in disciplines from geology and soil science to pharmaceuticals, mining, and construction. By characterizing how large or small the constituent particles are, granulometry informs how a material will behave: how it packs, how pores form, how fluids flow through it, how reactive its surface area will be, and how its strength and durability will develop under processing or in service. The measurements and concepts involved are practical tools for engineers, scientists, and manufacturers who need to predict performance, control quality, and optimize costs.
Granulometry rests on a few core ideas. One is the particle size distribution (PSD), which describes what fraction of particles are finer than a given size. PSD can be expressed in different ways, including a cumulative distribution function F(D) (fraction finer than size D) or a differential distribution fd(D) (the amount of material in each size interval). Related descriptors include D-values (for example D10, D50, D90, which denote the sizes below which 10%, 50%, and 90% of the material lies, respectively) and measures of spread such as the span or the uniformity coefficient. These descriptors help compare materials and summarize complex, often multi-modal distributions with a compact set of numbers. See D10 D50 D90 and uniformity coefficient for more detail. The overall distribution interacts with particle shape, density, and porosity, so interpretation must consider how the measurement represents the material’s practical behavior.
Foundations
Particle size distribution concepts
A PSD describes how particle sizes are distributed within a material. In soils, powders, and aggregates, the distribution influences porosity, hydraulic conductivity, and reactivity; in cement and ceramics, it affects packing density, rheology, and strength. PSDs are often displayed as curves of cumulative passing (or differential fraction) versus particle size, and they are interpreted with reference to the material’s intended use. See particle size distribution for a general overview.
Size scales and descriptors
Particles are commonly described by size ranges (coarse, medium, fine) and by numerical size metrics such as D-values or mean diameters. The choice of descriptor depends on the application and the measurement method. For a technical overview of these descriptors, see D50 and Sauter mean diameter.
Methods
Granulometry employs a variety of techniques, chosen to balance coverage of size ranges, accuracy, speed, cost, and potential artifacts from particle shape or density.
Sieving (sieve analysis)
Dry sieving uses a stack of screens with progressively finer openings to separate coarse particles. It is simple, robust, and inexpensive, making it a standard approach for rough PSDs and for materials with substantial coarse fractions. Data are typically presented as cumulative percent passing versus sieve size and are well suited to establishing texture or gradation in bulk solids. See sieve analysis for details and standard practices. Standards and references often cite lab equipment such as ASTM E11 for test sieves and related procedures.
Sedimentation and hydrometer methods
For fine particles, sedimentation techniques rely on settling rates governed by Stokes’ law. Hydrometer or pipette methods measure the time required for particles to settle to a specified depth, converting that information into a PSD. These methods are well suited to mid- to fine-fraction materials and can provide high-resolution data when properly controlled for density and temperature. See sedimentation and Stokes' law for foundational concepts.
Laser diffraction
Laser diffraction (or laser light scattering) covers a broad size range with high throughput. It infers PSD from the pattern of light scattered by a dispersed suspension, applying models such as Mie or Fraunhofer theory to convert scattering angles into particle sizes. This method is widely used in industries where fast, repeatable measurements across broad size ranges are needed, such as pigments, pharmaceuticals, and minerals. See laser diffraction for a detailed treatment and related standards such as ISO 13320.
Image analysis
Direct imaging—optical or electron microscopy—allows measurement of actual particle dimensions from photographs or micrographs. Image analysis can capture particle shape, aspect ratio, and clustering, providing PSD information that complements bulk techniques. See image analysis and particle morphology for related topics.
Dynamic light scattering and other techniques
Dynamic light scattering (DLS) estimates PSD from temporal fluctuations in scattered light due to Brownian motion, typically for submicron particles in suspension. Other methods, such as acoustic or centrifugal techniques, fill specialized niches. See dynamic light scattering for more on DLS and related approaches.
Data integration and interpretation
Different methods probe different size ranges and can be sensitive to particle shape, aggregation, or sample preparation. For robust granulometry, practitioners often combine methods (for example, sieve analysis with laser diffraction) and interpret results with attention to completeness, accuracy, and the context of application. See particle size distribution and uniformity coefficient for how results are typically summarized.
Representing and interpreting granulometry data
PSD data can be represented in several common forms. The cumulative distribution shows the fraction finer than each size, which is useful for understanding how a material will permeate or pack. The differential distribution highlights where most material concentrates within a size range. Analysts frequently report characteristic sizes such as D50 (the median) and occasionally D10 and D90 to convey the spread of the distribution. When comparing materials or validating a process, it helps to look at both the central tendency and the breadth of the distribution, as well as the presence of multiple peaks (multimodality) that indicate distinct size populations. See D50 and multimodal distribution for details.
In industry, granulometry affects processing decisions, equipment selection, and quality control. In soils, granulometric analysis supports texture classifications and irrigation strategies; in cement, it guides milling and grinding schedules; in pharmaceuticals, it influences granulation, disintegration, and bioavailability. See soil texture, cement, and pharmaceutical applications for concrete examples of how PSD informs practice.
Applications and implications
Soils and geotechnical engineering: Granulometry is a core input to soil texture classifications and to assessments of bearing capacity, drainage, and stability. It interacts with structure design and environmental management. See soil texture and geotechnical engineering.
Construction materials: The size distribution of aggregates and powders influences packing density, workability, and the strength of concrete and other composites. See cement and concrete for connections to processing and performance.
Mining and mineral processing: Classifying ore by particle size improves separation efficiency, grinding efficiency, and downstream processing. See mineral processing and particle size distribution.
Pharmaceuticals and food processing: Powder blending, tablet formulation, and suspension stability all depend on controlling PSD to achieve consistent dissolution and texture. See pharmaceutical and food processing.
Environmental and regulatory contexts: PSD measurements support compliance with product specifications, safety standards, and performance criteria in many industries. Standards and methods are maintained by various bodies, including those responsible for ISO 13320 (laser diffraction) and other granulometry-related specifications.
Standards and debates
Standardization seeks to make PSD measurements comparable across laboratories and instruments, but challenges remain. Different methods cover different size ranges and can be biased by particle shape, refractive index assumptions, dispersion quality, and sample preparation. Practitioners often select methods to match the material and the decision that will rely on the data, then acknowledge method-specific limitations. See ISO 13320 for laser diffraction standards and ASTM E11 for sieve procedures, along with broader discussions of standards in particle size analysis.
There is ongoing debate about when a simple descriptor like D50 is sufficient versus when a full PSD representation is necessary. In some materials, a single median size can be misleading if the distribution is highly skewed or multimodal, leading to misleading predictions about flow, packing, or reactivity. This tension between simplicity and fidelity is a practical consideration in both industry and research.