ISO 18852:2015

Overview - ISO 18852:2015 (NSA and STSA)

ISO 18852:2015 specifies a laboratory method for measuring the nitrogen surface area (NSA) of carbon blacks and other rubber compounding ingredients (e.g., silicas, zinc oxides) using a multipoint nitrogen adsorption technique based on the Brunauer–Emmett–Teller (BET) theory. The standard also defines the determination of the statistical thickness surface area (STSA) - the external surface area determined by t-plot analysis - noting that STSA is not applicable to silica and zinc oxide. ISO 18852:2015 can additionally verify single‑point surface area procedures such as those in ISO 4652.

Key topics and requirements

• Measurement principle: Multipoint nitrogen adsorption at liquid‑nitrogen temperature, adsorption isotherm acquisition, BET analysis for NSA and t‑plot for STSA.
• Apparatus: Automatic volumetric adsorption systems (pressure transducer ±0.25% full scale, calibrated volumes), Dewar flask, adsorption cell, analytical balance (0.1 mg), degassing station.
• Gases and reagents: Liquid nitrogen (≥99.9%), ultra‑high‑purity nitrogen (≥99.995%), helium (≥99.99%) for volume calibration.
• Sample preparation and degassing: Defined degassing temperatures and times (e.g., carbon black ~300 ±10 °C for ≥0.5 h; silica ~155 ±5 °C for ≥1.0 h), vacuum suction or purge‑gas flow methods to remove adsorbed contaminants before analysis.
• Measurement procedure: Input of relative‑pressure range and data points, saturation vapour pressure determination, selection of multipoint data for BET fitting, verification of measured values and instrument calibration.
• Calculations and reporting: NSA from BET multipoint analysis; STSA via t‑plot; procedures for verification, precision and required test‑report details.

Practical applications and users

ISO 18852:2015 is used to:

• Characterize carbon black, silica, and zinc oxide fillers for rubber compounding.
• Support quality control, R&D and incoming material inspection in the tyre, industrial rubber, and polymer additives industries.
• Provide validated multipoint NSA results for specification compliance and to verify single‑point methods (e.g., ISO 4652). Typical users include analytical laboratories, materials scientists, filler manufacturers, rubber compound technologists, and instrument vendors offering adsorption analyzers.

Related standards

• ISO 4652:2012 - single‑point nitrogen adsorption for carbon black.
• ISO 5794‑1:2010 - silica precipitated hydrated (non‑rubber tests).
• References to ISO 9298 for zinc oxide grade classification and other normative documents cited within ISO 18852.

Keywords: ISO 18852:2015, NSA, STSA, nitrogen surface area, BET theory, t‑plot, carbon black, silica, zinc oxide, multipoint adsorption, rubber compounding ingredients, surface area measurement.