Porometer- Capillary Flow Porometry Instruments

Gas Liquid Porometry, also known as Capillary Flow Porometry (CFP), measures pore size and pore size distribution of through pores in materials. The technique is based on the displacement of an inert and nontoxic wetting liquid embedded in a porous network by applying an inert pressurized gas. Therefore, only through pores are measured.

Larger pores become empty first and, as the applied pressure increases, so do the smaller ones until all through pores are empty.

The most challenging part for the gas to displace the liquid along the entire pore path is the most constricted section, also known as pore throat. The diameter measured in CFP is the pore throat, regardless of where it exactly in the pore path is.   The method depends upon the capillary rise created by the surface tension between the liquid and the gas. Therefore, a wetted pore immersed in a liquid draws the liquid up the capillary until reaching equilibrium with the force of gravity.

Measuring curves and resulting parameters in CFP

(w= wet curve, d= dry curve, d/2= half-dry curve, FBP= largest pore,
MFP= mean flow pore, SP= smallest pore)

PARAMETERS MEASURED:

In a typical CFP test a flow of pressurized gas is applied to the porous sample impregnated with the wetting liquid and the flow of gas through the sample, as the liquid is displaced out of the porous network, is measured. The “wet curve” represents the measured gas flow against the applied pressure.

Following the wet curve, the gas flow against the applied pressure on the dry sample (“dry curve”) is also measured. From data from the wet curve, the dry curve and the “half-dry curve” (dividing the flow values of the dry curve by 2) information about the porous network can be obtained.

Applications for Capillary Flow Porometry:

Filtration Membranes For the characterization of polymeric, ceramic and hollow fiber micro and ultrafiltration media.
Non-Wovens For melt blown and spun bound materials including moisture barriers, textiles, geotextiles for soil analysis, etc.
Paper Paper products, including printing paper, cigarette, paper packaging, etc.
Battery Separators Separators are critical components in liquid electrolyte batteries. A separator generally consists of a polymeric membrane forming a microporous layer between the anode and cathode of a battery. Separators for Li Ion batteries have a direct influence on cell production, cell performance, life, as well as battery reliability and safety
Porous Rock Measurement of porous rock in petrophysical analysis, especially useful for determining hydrocarbon potential of reservoir rocks
Ceramics, Sintered Metals, Additive Manufactured Parts Application to determine porosity of functionally graded ceramics, ceramic supports, porous metal frits, additive manufactured parts, sintering effect in powder metallurgy.

Pore Characteristics Reported:

Bubble point:

Maximum pore diameter

Smallest pore size:

Calculated at the pressure at which the dry curve meets the wet curve

Mean flow pore diameter:

Pore size at which 50 % of the total gas flow can be accounted (half the flow is through pores larger than this diameter)

Gas permeability:

In the same measurement, it is possible to obtain the gas flow rate. If the material area and thickness are known, the gas permeability can also be accounted.

Cumulative filter flow `{`SUM`}`:

It shows which percentage of the flow (at the Y-axis) has passed through pores with a size larger than the value at the corresponding point at the X-axis. It is also known as filter efficiency.

Differential filter flow `{`DIF`}`:

It shows the percentage of flow (at the Y-axis), which has passed the pores with a corresponding size at the X-axis and the following size value at the same axis. According to ASTM, this graph shows the so-called “pore size frequency”.

Pore size flow distribution `{`CDIF`}`:

It shows the flow distribution normalized per unit of change in size (flow changes are divided by size changes). Sometimes it is also referred to as pore size distribution.

Capillary Flow Porometry (bubble point) is addressed by the following standards:

  • ASTM E128 – 99(2011)
  • ASTM F316 – 03(2011)
  • ASTM D6767
  • International Organization for Standardization (ISO) test standard 4003, and 7198

Available POROMETER Instruments: