Overview
ISO 20998-1:2006 - Measurement and characterization of particles by acoustic methods - Part 1: Concepts and procedures in ultrasonic attenuation spectroscopy - defines terminology, concepts and procedures for using ultrasonic attenuation spectroscopy to characterize particle size distributions (PSD) in liquids. The standard covers analysis of colloids, dispersions, slurries and emulsions, with typical measurable particle sizes from 10 nm to 3 mm and dispersed-phase concentrations from 0.1 % up to 50 % (or more) by volume, depending on density contrast. It is intended for both laboratory and in-process monitoring of dynamic phenomena such as agglomeration, flocculation and droplet coalescence.
Key topics and requirements
- Principles and definitions: clear terms (attenuation, absorption, attenuation coefficient, attenuation spectrum, excess attenuation, intrinsic response) and recommended units (dB/cm or Np/cm).
- Measurement scope: frequency range typically used for particle characterization (roughly 100 kHz to 100 MHz) and emphasis on measuring the attenuation spectrum (attenuation versus frequency).
- Sampling and sample prep:
- Disperse dry powders according to representative sampling and dispersion recommendations (referenced standards e.g., ISO 14488, ISO 14887).
- Thorough mixing for suspensions/slurries to avoid shear-dependent artifacts.
- Prepare unstable emulsions immediately before measurement to capture initial droplet size.
- Reference materials:
- Use a reference liquid (de‑gassed water recommended) to determine intrinsic spectrometer response; procedures for de‑gassing referenced (IEC 62127-1).
- Use a well-characterized reference sample where available to verify PSD estimation.
- Apparatus and methods:
- Minimum spectrometer components: excitation source, ultrasonic transducers, sample or flow cell, preamplifier and acquisition system.
- Excitation types: continuous wave, frequency sweeps, tone bursts, broadband pulses; match source and transducer bandwidth/impedance.
- Data interpretation and reporting:
- Conversion of attenuation spectra to PSD requires suitable theoretical or empirical models; where models are lacking, spectra can be used for relative monitoring.
- Reporting guidance for laboratory and in-process control data is specified.
- Annexes: informative techniques, application examples and inversion methods for attenuation spectra.
Applications and users
Practical uses include:
- Real-time process monitoring and control of slurries, emulsions and dispersions.
- Quality control in chemical, pharmaceutical, food, ceramic and mineral processing.
- R&D and particle characterization in colloid science and materials engineering.
Primary users:
- QC and process engineers, laboratory analysts, instrument manufacturers, and researchers using ultrasonic attenuation spectroscopy for particle size distribution and process monitoring.
Related standards
- ISO 20998 series: Part 2 (guidelines for linear theory) and Part 3 (guidelines for non-linear theory).
- Sampling/dispersion: ISO 14488, ISO 14887.
- Ultrasonic reference procedures: IEC 62127-1.
Keywords: ultrasonic attenuation spectroscopy, particle size distribution, attenuation spectrum, ultrasonic spectrometer, colloids, slurries, emulsions, particle characterization.