ISO 20379:2018

Overview

ISO 20379:2018 specifies a standardized method to measure the thixotropic behaviour of high-solid loaded ceramic slurry using a rotational viscometer. Targeted at fine ceramics (advanced/technical ceramics) manufacturing, the standard covers measurement principles, apparatus requirements, sample pretreatment, measurement procedures and analysis methods for evaluating time-dependent viscosity changes in non-Newtonian ceramic slurries.

Key search keywords: ISO 20379:2018, thixotropic behaviour, ceramic slurry, rotational viscometer, fine ceramics, viscosity measurement.

Key topics and technical requirements

• Scope and limitations

  • Applies to high-solid loading ceramic slurries used in ceramic processes (e.g., slip casting, tape casting, screen printing).
  • Measurement geometries limited to: coaxial double cylinder, cone-and-plate, and parallel plate rotational viscometers.

• Measurement principles

  • Two evaluation approaches:
    • Hysteresis measurement of the flow curve (shear-rate sweep up/down to quantify hysteresis area).
    • Time-dependence of shear stress at constant low shear rate (monitor recovery after high-shear disruption).

• Apparatus and performance

  • Viscometer must permit defined shear-rate generation and torque measurement.
  • Recommended instrument accuracy: torque within ±2% of full-scale, rotational frequency within ±2%, repeatability ±2%.
  • Periodic calibration using standard viscosity solutions; calibration temperature must match measurement temperature.

• Sample preparation and measurement conditions

  • Avoid bubble generation when loading slurry; degassing by decompression must be reported if used.
  • Avoid heating by high-speed dispersion (stirring/ultrasonication) which can alter dispersants/binders.
  • Preferred measurement temperature 23 ± 0.2 °C; thermostat control accuracy recommended within ±0.2 °C.
  • Example procedural recommendations: maximum shear rate ~300 s⁻¹ (where practical), ~90 s for shear-rate increase and decrease, rest 3–5 min, repeat measurements at least three times.

• Analysis

  • Hysteresis quantified dimensionlessly as (A − B)/(A + B), where A and B are areas under increasing and decreasing flow curves.
  • Time-dependent recovery analyzed from shear-stress vs time at low shear rate.

Applications and users

• Practical uses:
  • Characterizing slurry behavior for casting, coating, tape casting, screen printing, granulation and other ceramic forming processes.
  • Quality control, formulation optimization and process troubleshooting where time-dependent viscosity (thixotropy) affects coating uniformity, sedimentation, or forming performance.
• Primary users:
  • Materials scientists, ceramic process engineers, R&D labs, QC laboratories in ceramics and electronic-ceramic manufacturing, and instrument manufacturers.

Related information

• ISO 20379:2018 contains no normative references. For broader rheology and calibration practices, consult general standards and guidelines on viscometer calibration and rheological testing from national or international bodies.