How to measure Specific Surface Area (SSA) of powders (e.g. Cement )?
 InstruQuest Inc. Scientific Instruments R&D
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 Employing the new absolute method for determination of SSA and novel hardware, the measurements can be carried out in few simple steps:
1. PREPARATON OF PACKED BED OF POWDER:
• Weigh empty sample holder
• Fill it with powder
• Form the bed using the vibratory table and plunger
• Determine the bed height and re-weigh the sample holder
Packed bed sample holder, plunger and vibratory table
The following parameters are obtained in the first step:
• Bed diameter [mm]
• Bed height [mm]
• Mass of the powder used [g]
2. MEASUREMENT OF FLOW RATE(S) VERSUS PRESSURE(S)
• Insert the sample holder with the bed into the universal permeability cell housing
• Connect the upper port to the fixed pressure source of know value
• Connect the lower port to a flow-measuring device
• Apply gas (air)  flow and measure the flow rate
 Experimental setup for measurements of SSA using gas (air) permeability technique
The following parameters are obtained in the second step:
• Input pressure P [kPa]
• Output pressure Po [kPa] (typically atmospheric pressure)
• Flow rate [cc/s]
• Temperature of the cell (ambient temperature) [C]
3. MEASUREMENT OF POWDER DENSITY USING A GAS PYCNOMETER
• Insert the sample holder with the packed bed into the pycnometer chamber and measure the volume with sample holder
• Remove the sample holder and measure the volume of the empty sample holder
The pycnometric volume of the packed bed [cc] is determined in this step.
Powder volume  (density) measurement using a gas pycnometer
4. CALCULATIONS
• Enter the obtained results into the Permeability SSA Calculator and hit CALCULATE PSSA button.
• The results of quantities of interest can be calculates in their respective frames
• If gas is other than air, its dynamic viscosity needs to be provided
Remarks:

Experimental results of flow rates measurements of versus pressure for packed beds of cement show evidence of quadratic relationship,

Flow rate = a · (P·P- Po·Po)
.

To derive more information about the quadratic coefficient, the corrected form of Poisseuille equation for compressible gases was used as it has the same general
relationship.  New equation and absolute method of determination of surface area of powders using gas (air permeability technique is being proposed. This new
approach seems to be a substantial improvement over classical equations, like Carman-Kozeny and similar, where only linear relationship between flow rate and
pressure differential across the packed bed is considered (Darcy model).

To facilitate implementation of this new methodology, a novel hardware was developed.  The universal permeability cell is designed in such way as to allow the
low mass sample holder to be removable, of various sizes, and conveniently used for powder mass determinations. The typical sample holder has inner diameter of
30 mm, can accept various bed supports, and feature almost
zero flow resistance.

To help formation of a uniformly packed bed, a simple vibratory table is also employed.
Although the height of bed may be only slightly reduced by using
vibrations from a pressed position only, it can have much larger effect on flow characteristics
. Since a gas pycnometer is needed anyway to determine the
powder volume (density), the universal design of our pycnometers allows for using it as an adjustable pressure source with digital readout for input pressure to the
cell.  It can read the atmospheric pressure as well. To accurately determine the flow rate and without causing any appreciable pressure buildup at the cell output, a
bubble meter and a digital stopper can be employed. Typically the permeability cell is used at ambient temperature but it can be placed into a suitable
temperature-controlled environment.
For more detailed theoretical background of this approach, please visit the Applications page, in gas (helium) pycnometer section or back to Home page.
For those researchers who would like to apply this method, please use only direct inquiries via e-mail: info@instruquest.com
Permeability Specific Surface Area Calculator
Uniform powder bed formation using vibratory table
Note: The shown hardware is for illustration only