ISO 18755:2022

Overview

ISO 18755:2022 specifies the standardized test method for determining thermal diffusivity of monolithic fine ceramics (advanced/technical ceramics) using the flash method (e.g., laser flash). The standard covers measurements from room temperature to at least 1 700 K for homogeneous monolithic ceramics with porosity < 10 %. Flash methods are applicable to isotropic materials with thermal diffusivity in the range 0.1 to 1 000 mm2·s‑1 and broadly across temperatures from ≈100 K up to ≈2 300 K. Annex G describes how to estimate specific heat capacity and thermal conductivity from the measured thermal diffusivity.

Key technical topics and requirements

• Scope and specimen limits: Homogeneous monolithic ceramics, porosity < 10 %; specimen geometry and density requirements are defined (see ISO 18755 for specifics).
• Flash source: Pulse laser, flash lamp or equivalent capable of a short, high‑energy pulse; pulse duration preferably < 1.0 ms (FWHM) with uniform irradiation of the front face.
• Detection and timing: Rear-face transient temperature is recorded with a non-contact radiation thermometer or detector. Detector and electronics should have a frequency response > 10 kHz. Target detector area must be <50% of disk diameter (or shortest side for rectangular specimens).
• Temperature control & measurement: Steady-state specimen temperature measured by thermocouple or equivalent; measurements may be done in air, inert gas, or vacuum depending on temperature.
• Data analysis & correction: The standard provides the half‑rise‑time calculation method, applicability criteria, and normative/ informative annexes (Annex B normative corrections for non‑ideal conditions; Annex C algorithms; Annex E intrinsic diffusivity).
• Uncertainty, reference materials & validation: Annex F lists reference data/materials and validation methods; Annex H includes example data and precision/uncertainty up to high temperatures. The 2022 edition incorporates inter‑laboratory study results (Hi‑TRACE).

Practical applications and users

ISO 18755:2022 is used to obtain reliable, comparable thermal diffusivity data critical for:

• Materials scientists and ceramic engineers characterizing thermal transport in advanced ceramics.
• R&D and quality‑assurance laboratories in aerospace, power generation, electronics, and automotive industries where high‑temperature thermal properties matter.
• Manufacturers of substrates, thermal barrier coatings, insulators, and high‑temperature structural ceramics.
• Computational modelers and thermal designers needing validated inputs for thermal conductivity and specific heat (via Annex G).

Related standards

• ISO 18754 - Determination of density and apparent porosity (normative reference).
• ISO 3611 - Dimensional measuring equipment (micrometers) referenced for specimen dimension control.

ISO 18755:2022 provides a comprehensive, standardized procedure for accurate thermal diffusivity measurement of fine ceramics using the flash method, enabling consistent material data for high‑temperature engineering and research.