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