Blaine device

Sketch of the Blaine device
A suction mark, M measurement marks, E filling mark

With the help of the Blaine device , the specific surface area of a powder can be determined by measuring the time it takes a given amount of air to flow through a certain amount of powder. This measurement is based on the Carman-Kozeny equation , which establishes a relationship between the specific surface area , the pressure difference across a bed , the porosity of a bed and the flow velocity :

{\ displaystyle S_ {V} ^ {2} = k {\ Delta p \ cdot \ varepsilon ^ {3} \ over {l \ cdot \ eta \ cdot \ mathrm {v} \ cdot (1- \ varepsilon) ^ { 2}}}}

Formula symbol	unit	meaning
${\ displaystyle S_ {V}}$	m ² / m ³	volume-related specific surface
${\ displaystyle k}$	-	constant
${\ displaystyle \ Delta p}$	Pa	Pressure difference
${\ displaystyle \ varepsilon}$	m ³ / m ³	porosity
${\ displaystyle l}$	m	Length of the flow path
${\ displaystyle \ eta}$	Pas	dynamic viscosity of the fluid
${\ displaystyle \ mathrm {v}}$	m / s	Flow velocity

After transforming the equation, the relationship is obtained for the pressure drop that varies over time

{\ displaystyle S_ {V} ^ {2} = k {\ varepsilon ^ {3} \ over {(1- \ varepsilon) ^ {2}}} \ cdot {t \ over \ eta}}

To determine the surface, a porous system with a certain mass and porosity is produced from the solid to be examined . It opposes a flow resistance to gases , which u. a. depends on its specific surface.

A certain volume of air is sucked through the system and the time required for this is measured by the column of liquid, which is deflected from the rest position in a U-tube arranged under the porous system .

From the measured time, the viscosity of the air, the porosity and the density of the solid, the specific surface is calculated according to the above equation.

Since the Carman-Kozeny equation is quite generalized, the calculated surfaces are only suitable for comparison purposes of similar materials or control purposes of a single powder. If the grain size distribution is wide , the material should be classified into several grain fractions and these should be analyzed individually. The device constant is determined by calibration with a substance of known surface and density. ${\ displaystyle k}$