Overview
ISO 5018:1983 specifies a pycnometric method for determining the true density of refractory products and raw materials. True density is defined as the ratio of the mass of a dried quantity of material to its true solid volume. The standard describes required apparatus, sample preparation, test procedure, and reporting essentials for accurate density measurement using a liquid of known density at a controlled temperature.
The method is widely used for material characterization, quality control and specification compliance in refractory manufacturing and research.
Key Topics
- Scope: Measurement of true density for refractory products and raw materials, after crushing and grinding to remove closed pores where possible.
- Apparatus: Typical equipment items listed include:
- Pycnometer (25, 50 or 100 ml) with ground stopper and capillary bore
- High-precision balance (accuracy ±0.1 mg)
- Vacuum equipment capable of ≤25 mbar
- Thermostatically controlled bath (maintained 2–5 °C above ambient, ±0.2 K)
- Drying oven and desiccator
- Test sieve (63 µm)
- Preparation: Samples are dried to constant mass (110 ±5 °C recommended for many materials) and ground to pass the 63 µm sieve; care must be taken to avoid moisture uptake or contamination.
- Procedure: The pycnometric technique requires determining three masses (commonly referred to as m1, m2 and m3) and using the known density of the test liquid (ρliq) at the bath temperature to calculate true density. An alternative procedure is provided for materials difficult to wet.
- Temperature control: The method is sensitive to temperature; the liquid density must be referenced to the thermostatically controlled bath temperature (a water density table is provided in the standard).
Applications
- Quality control: Verify consistency of refractory batches and raw materials by tracking true density as part of acceptance testing.
- Material characterization: Support formulation, sintering studies and porosity assessment by providing reliable solid-phase density values.
- Production and procurement: Use density data in specifications, supplier acceptance, and process monitoring to reduce variability in fired products.
Related Standards
ISO 5018 references or aligns with several other ISO documents and practices relevant to refractories and testing, including:
- ISO 5022 - sampling and acceptance for shaped refractory products
- ISO 565 - requirements for test sieves (woven wire cloth)
- ISO/R 836 - vocabulary for the refractories industry
Reporting: The test report should identify the standard used (ISO 5018), material designation, test date and temperature, number of test pieces, grain size after grinding, vacuum pressure used, liquid and its density, heat treatment (if any), individual true density values and the mean result for clear traceability and quality decisions.
