Mercury porosimetry

The mercury porosimetry is a method of analysis to various quantifiable aspects to determine a porous material, such as pore size distribution, the total pore volume, the inner surface, the bulk density and the absolute density. Devices for testing the air permeability of textiles are called porosimeters.

execution

The technique involves the penetration of a non-wetting liquid, such as mercury , at high pressure into a material using a porosimeter. The pore size is determined as a function of the external pressure which is necessary to push the liquid into a pore against the surface tension of the liquid.

The so-called Washburn equation applies to cylindrical pores :

${\displaystyle P_{L}-P_{G}=-{\frac {4\sigma \cos \theta }{D_{P}}}}$

${\displaystyle P_{L}}$ = Pressure of the liquid

${\displaystyle P_{G}}$ = Pressure of the gas

${\displaystyle \sigma }$ = Surface tension of the liquid

${\displaystyle \theta }$= Contact angle of the liquid

${\displaystyle D_{P}}$ = Pore diameter

The technique is usually carried out under vacuum . The contact angle of mercury with most solids is between 135 ° and 142 °. The surface tension of mercury at 20 ° C under vacuum is 480  mN / m . By inserting you get:

${\displaystyle D_{P}={\frac {1470\ {\text{kPa}}\cdot \mu {\text{m}}}{P_{L}}}}$

With increasing pressure, the cumulative pore volume also increases. The mean pore size can be determined from the cumulative pore volume. A derivation of the cumulative pore volume distribution results in a differential pore radius distribution.

Textiles, such as the fabrics used in parachutes and paragliders, are measured for air permeability with the porosimeter. To do this, a defined amount of air is pressed through the fabric. The elapsed time shows how porous the fabric is. The test is carried out on different parts of the tissue.

Application examples

Using mercury porosimetry, the degree of degradation by endogenous bacteria from the digestive tract was determined on the bones of Bronze Age skeletons from Cladh Hallan, and it was determined that the deceased were artificially preserved after their death.

Web links

• www.bam.de (PDF; 10.9 MB) The use of mercury porosimetry to characterize fine concrete for electrochemical investigations
• References to mercury porosimetry by Fraunhofer IRB

Individual evidence

1. ^ AB Abell, KL Willis, DA Lange: Mercury Intrusion Porosimetry and Image Analysis of Cement-Based Materials . In: Journal of Colloid and Interface Science . No. 211 , 1999, p. 39–44 , doi : 10.1006 / jcis.1998.5986 (English, PDF ).
2. ↑ Porosimeter checks air permeability