For the measurement, we weighed sufficient material to reach specific surface area of min 10m2, furthermore we used a high precision scale (d=0.1mg)
The error is in limit of +/- 2%, if u have doubt please check with standard sample supplied along with the instrument. We have alumina supplied by Quantacrome we are getting the SSA around 71 m2/g and the exact value is 71.45 m2/g.
I can ditto the above response with regards to looking at available reference materials.. NIST has SRM 1898 (Titanium Dioxide Nanomaterial) with a nominal multipoint BET SSA of 55 m2/g. The certificate can be viewed here: https://www-s.nist.gov/srmors/view_cert.cfm?srm=1898 just click on "PDF Format" to view or download certificate. Also, the papers by Badalyan et al (especially Langmuir 19, 7919, 2003) are particularly helpful. For an assessment of "real world" variation, see the published interlaboratory study (Hackley and Stefaniak, J Nanopart Res (2013) 15:1742, DOI 10.1007/s11051-013-1742-y).
I work with coal and often, we get surface areas of < 10m2/g with % errors between 2% and 5% max. This may be understandable as coal is a more heteregeneous material than nanoparticle. Beside nitrogen BET is highly affected by activated diffusion and molecular sieve effect, which are highy dependent on temperature. A sslight variation in anlysis temperature, which may be caused by depleted liquid N2, may trigger off these phenomena and impair your final results!
The paper I cited above by Badalyan discusses in detail the importance of maintaining constant cryogen level. Most, if not all, commercial instrument now incorporate some form of mechanical or passive method to ensure that cryogen levels are kept constant within the mm range. Additionally, highly porous (and mciropourous) materials like coal are probably not a good comparison to SSA measured on solid nonporous particles.That said, a 2% uncertainty (precision) would be pretty good for most systems and materials.
Dr. P. B. Wagh, APD, BARC, Mumbai, India
Generally errors in measurement of specific surface area (SSA) error depends on following aspects:
1. Type of Surface Area Analyzer adopted.
2. Method of SSA chosen viz. Single point, Five point or 11 point Quantachrome Surface Area Analyzer.
3. Nature of materials under studies viz. Nanostructured, Microporous and Microporous.
In order to reduce Instrumental Error, the SSA should be calibrated with standard sample. Moreover, based on type of porosity of material , the equipment should be calibrated with known type of porous materials under studies. I personally feel that the errorin SSA measueemwnts is around
1%.
Dear Marcus,
The error in the measurement of the surface area by nitrogen adsorption should be lower than 5 % and the minimum surface area that can be measured with precision is 10 m2. Sometimes higher uncertainties are produced while weighing. You should use cotton gloves to handle the tubes and check regularly the weighing performances of the analytical balance.
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