ISO 8894-2:2007

Overview

ISO 8894-2:2007 - Refractory materials - Determination of thermal conductivity - Part 2: Hot-wire method (parallel) - defines a dynamic laboratory method to measure the thermal conductivity of refractory products and materials using a linear heating element (hot wire) embedded between two test pieces. The method is intended for dense and insulating shaped products and for powdered or granular materials with thermal conductivities typically below 25 W/m·K (higher values can be measured with larger test pieces). Electrically conducting materials are excluded.

Key topics and technical requirements

• Measurement principle: monitor temperature rise versus time at a fixed distance from a linear heat source (hot wire) embedded between two test pieces; use the transient response to determine thermal conductivity.
• Apparatus essentials:
  • Furnace: electrically heated up to 1 250 °C; temperature uniformity within test region ≤ 10 K; test stability ±0.5 K during ~15 min tests; accuracy ±10 K.
  • Hot wire: typically platinum or platinum–rhodium, voltage taps over ~200 mm length (±0.5 mm). Power input stability ≤ ±2 %; recommended minimum power 250 W/m (≈50 W for 200 mm).
  • Differential thermocouple: Type R or S, measurement and reference thermocouples arranged in opposition. Measurement thermocouple leads run parallel to hot wire at 15 mm ± 1 mm.
  • Electrical and measurement instruments: digital multimeter with at least ±0.5 % accuracy; data acquisition with time resolution < 0.5 s and temperature resolution 0.01 K (or equivalent voltage sensitivity).
• Test pieces:
  • Minimum size 200 × 100 × 50 mm; recommended sizes 230 × 114 × 64 mm or 230 × 114 × 76 mm.
  • Surface flatness: deviation ≤ 0.2 mm between points ≥ 100 mm apart.
  • Grooves may be machined to embed hot wire and thermocouple for dense materials.
• Sample types: shaped dense refractories, insulating bricks, powders/granular materials (using matching container assemblies).
• Limitations: anisotropic materials and electrically conducting materials require agreement between parties before testing.

Applications and users

• Quality control and production testing in refractory manufacturing.
• Materials characterization for high-temperature insulation, kiln linings, furnace components, and thermally demanding industrial processes.
• R&D and comparative testing in materials laboratories, universities, and independent testing houses.
• Specification compliance checks for procurement, certification, and product data sheets.

Related standards

• ISO 8894 (general series) - Part 1: Hot-wire method (cross-array) (complements Part 2 for alternate geometry).
• Technically aligned with EN 993‑15 (as noted in the ISO foreword).

For accurate test setup, calculations and reporting details, consult the full ISO 8894-2:2007 text.