Intrusion Test

Mercury is a non-wetting fluid for most materials. Because the contact angle (0) is 180°, cos = -1, and pressure is required to force mercury into the pores-see equation (1). We speak of mercury intrusion pressures these are quite high due to the high surface tension of mercury (476 dynes/cm). Thus, for a given pore size, the pressure required to force mercury into the pores is almost seven times greater than the pressure required to expel water from the pores. 

The technique places as much membrane area as possible into a chamber which is evacuated. Mercury is then admitted into the chamber as the pressure is slowly elevated. The incremental volume of mercury added for each increase in pressure is measured precisely. 

---

Water-based tests [water intrusion tests (WITs)] [2.36] were developed a few years ago, but it is only recently that they have been promoted as a reliable alternative to the diffusion flow test. 

Bracht, K., Troger, H. The Water Intrusion Test - A New Method for Integrity Testing Hydrophobic Filter Elements. Sartorius, Gottingen, March 1991... 

The principle of the water intrusion test derives from the mercury intrusion test, which (applicable to both hydrophilic and hydrophobic membranes) is restricted to laboratory conditions. The membrane is placed in contact with the fluid (water in the case of the water penetration test, mercury in the case of the mercury intrusion test), and the pressure is increased, with the purpose of forcing the fluid into the pores. The volume of fluid forced into the pores is a measure of pore size and void space volume and thus of filter integrity. 

Hydrophobic gas filter can be tested with the water intrusion test (WIT). Hydrophilic liquid filter are usually tested with water, the often used test method is the pressure decay test (PDT) a variation of the forward flow test (FFT). 

On initial inspection the results obtained from serial sectioning of LMPA intruded samples appear at odds with the principle theory behind intrusion and retraction as predicted by the Washburn equation. But further inspection shows it is not the Washburn equation, but mercury porosimetry that is at fault. Pore network models have often been used to characterise the behaviour of pore structure in relation to mercury porosimetry. But the model is only as good as the assumptions and the data that it is based iqron. Without artificially shielding the network, the model caimot propa ly detomine the correct psd and cannot derive a more spatially accurate structure that could be used for diffusion and reaction modelling. In order to characterise the pore structure more accurately, we need to introduce some of the elements usually revealed by LMPA intrusion tests. 

Mercury intrusion test data show that before and after the consolidation the porosities of macropores (d > 10 pm) and the medium pores (5 pm < d < 10 pm) of the samples are very small the samples mainly contain the small pore (0.1 pm < d < 5 pm) the porosity of micropores (d < 0.1 pm) is greater than macropores and medium pores, but less than the small pores. Compared with the samples before consolidation, the small pores porosity has increased after consolidation and the quantity of macropores decreased. The reason is that soil particles slide or collapse due to the consolidation pressure. Therefore pores are compacted, and macropores reduce or even disappear. These conclusions are basically consistent with the SEM quantitative analysis. The samples mainly contain small pores before and after consolidation, pore size is primarily in the... 

Up to now, only hydrophilic filters have been discussed, which are used for the filtration of aqueous solutirais. Filters that are used for gas filtration such as ventilation filters on tanks and boilers are lipophilic filters. Some hydrophobic filter membranes are used to filter oils and other lipophilic solutions. A physical integrity test with water cannot be performed with this type of filter. For moistening, isopropyl alcohol has been used in the past, but the disadvantage of this substance is that it is highly flammable. Therefore, an alternative method has been developed, which is called the water intrusion test [15, 16]. 

The SASW test (Spectral Analysis of Surface) is a non-intrusive test method for testing the small strain stiffness of the soil by analysing the velocity of Rayleigh surface waves. The Rayleigh wave is generated by a hammer impact. The waves are recorded by a pair geophones placed at variable distance from the source. 

---