Scope

This International Standard specifies an instrumental method for the determination of specific surface area (SSA) of smelter-grade alumina (SGA) by nitrogen adsorption by a single- or multi-point method. A multi-point method is recommended due to the higher accuracy obtained; if a single-point method is used, a lower result

will be obtained.

NOTE Annex A provides an explanation of the difference between single- and multi-point determined BET SSA. 

This International Standard is applicable to aluminas having a surface area between 50 m2/g and 90 m2/g.

Principle

The method is based on the ability of a material to adsorb nitrogen molecules on its surface at the boiling point of liquid nitrogen. The instrument determines the quantity of nitrogen gas necessary to form a monolayer of gas molecules on the sample surface. The surface area can then be calculated using the basic theory developed by Brunauer-Emmett-Teller1). A test sample is degassed at . The degassing process can be carried out using either vacuum or a flowing nitrogen stream. After degassing, the sample is weighed. This mass, and the monolayer volume determined by the instrument, is used to calculate the specific surface area.

Apparatus

5.1 Surface-area analyser, employing low temperature (-196℃) nitrogen adsorption. The instrument should be capable of multi-point or single-point analysis.

5.2 Degassing equipment, suitable for degassing a sample at an elevated temperature （150℃) using either a flowing nitrogen stream or a vacuum system capable of maintaining a vacuum of ＜0,2 mbar. Sample tubes shall include sealing devices to prevent contact between air and the sample after degassing.

5.3 Analytical balance, capable of weighing to an accuracy of ±0,0001g

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