Overview
EN ISO 8894-2:2025 (ISO 8894-2:2007) defines the hot‑wire (parallel) method for determining the thermal conductivity of refractory materials and products. The method is applicable to dense and insulating shaped products as well as powdered or granular materials for thermal conductivities typically below 25 W·m−1·K−1 (higher values are measurable with larger test pieces). The technique measures the temperature rise versus time from a linear heat source (hot wire) embedded between two test pieces and uses a differential thermocouple to derive thermal conductivity.
Keywords: refractory materials, thermal conductivity, hot‑wire method, EN ISO 8894‑2:2025, ISO 8894‑2, thermocouple, thermal diffusivity.
Key topics and technical requirements
- Principle: temperature increase measured at a fixed distance from an embedded linear heater (hot wire) after current is applied; thermal conductivity calculated from temperature‑time response.
- Test assembly: two identical test pieces (minimum 200 × 100 × 50 mm; recommended 230 × 114 × 64 mm or 230 × 114 × 76 mm). Surface flatness between contacting faces ≤ 0.2 mm over ≥100 mm.
- Hot wire and measurement length: voltage taps typically separated by about 200 mm (±0.5 mm). Hot wire material preferably platinum or platinum‑rhodium.
- Thermocouple: differential Type R or S (platinum/platinum‑rhodium) with measurement leads running parallel to the hot wire at 15 mm ± 1 mm.
- Furnace and temperature control: electrically heated furnace up to 1 250 °C; temperature uniformity in test region within ±10 K, and external test‑assembly temperature stable to ±0.5 K during measurement.
- Power and instrumentation: stabilized power supply (AC or DC) with power stability within ±2 %; minimum power density 250 W/m (≈50 W for 200 mm measurement length). Digital multimeter accuracy ≥ ±0.5 %. Data acquisition sensitivity ~0.01 K and time resolution
