Development of Alumina-Based Porosity Reference Materials for the Mercury Porosimetry Method

Abstract

This paper presents the results of a study on the development of alumina-based porosity reference materials (RMs), which are intended for controlling the accuracy of the measurement results obtained using the mercury porosimetry method. These mercury porosimetry RMs are being developed in the Russian Federation for the first time and are primarily intended for verification/calibration and testing for type approval of mercury porosimeters. The study of metrological characteristics was conducted using a reference system, which is to be included in the GET 210-2014 State Primary Measurement Standard for units of specific gas adsorption, specific surface area, specific volume and pore size of solid substances and materials. This reference system was calibrated prior to conducting the study with the use of external reference pressure sensors of the 2nd order at 0.6 and 400 MPa, as well as a laboratory balance (special accuracy class I) having a maximum weighing limit of 220 g. In the course of conducted research work, procedures for reproducing and estimating the uncertainty of porosity characteristics using the mercury porosimetry method were developed. When estimating the RM metrological characteristics, the standard uncertainty, associated with the characterisation and heterogeneity of the studied materials (RM candidates), was evaluated. The standard uncertainty due to instability was disregarded due to the high stability of the alumina matrix. According to the results of the conducted studies, four types of alumina-based porosity RM were developed. Their pore sizes are in the region of ~10 nm; ~2,000 nm; ~9,000 nm; ~60,000 nm. The RMs with pore sizes of ~10 nm; ~2,000 nm were intended for use in controlling the accuracy of mercury porosimeters operating at high pressures, while the RMs with pore sizes of ~9,000 nm; ~60,000 nm were for controlling the accuracy of mercury porosimeters operating at low pressures. The developed RMs are different from their foreign counterparts, which are produced by BAM (Germany) and NIST (USA) metrological institutes. The standard uncertainty due to characterisation of the RMs in question was estimated, not by the method of interlaboratory experiment, but by a full analysis of the constraint equations taking into account all sources of uncertainty included in the equations on the basis of the Guide to the Expression of Uncertainty in Measurement. The conducted studies allowed the RM certified values to be traceable at this stage to the GET 3-2008 State Primary Measurement Standard for the mass unit (kilogram), the GET 101-2011 State Primary Measurement Standard for the pressure unit in the field of absolute pressure in the range 1 × 10⁻¹–7 × 10⁵ Pa, the GET 43-2013 State Primary Measurement Standard for the pressure unit in the range 10–1600 MPa and the effective area of the piston-cylinder unit of dead weight testers in the range 0.05–1 cm². In addition, a reference material having a large pore size of ~60,000 nm, which currently has no analogues elsewhere in the world, was characterised.