Mercury capillary rise

Capillary Rise The tendency and process for a liquid to rise in a capillary. Example Water rises in a partially immersed glass capillary. Negative capillary rise occurs when the liquid level in the capillary falls below the level of bulk liquid, as when a glass capillary is partially immersed in mercury. Capillary rise forms the basis for a method of determination of surface or interfacial tension. 

If, on the other hand, the thermometer has previously been used at some temperature below the freezing-point of benzene, when the bulb is originally placed in the beaker of water at 7-8 C., the mercury will rise in the capillary and ultimately collect in the upper part of the reservoir at a. When the expansion is complete, again tap the thermometer sharply at R so that this excess of mercury drops down into b, and then as before check the success of the setting by placing the thermometer m some partly frozen benzene. In either case, if the adjustment is not complete, repeat the operations, making a further small adjustment, until a satisfactory result is obtained. 

The wetting ability of the anode electrode was evaluated as the contact angle measured by the capillary rise method. The value of fractal dimension of anode electrode of MCFC was calculated by use of the nitrogen adsorption (fractal FHH equation) and the mercury porosimetry. 

Although a number of methods are available to characterize the interstitial voids of a solid, the most useful of these is mercury intrusion porosimetry [52], This method is widely used to determine the pore-size distribution of a porous material, and the void size of tablets and compacts. The method is based on the capillary rise phenomenon, in which excess pressure is required to force a nonwetting liquid into a narrow volume. 

These primers may also be tested in the "Gas Volume and Impulse Apparatus , briefly described as the "Test Set Mkl75-ModO in Ref 14, p 9-42. Its photographic view is given as Fig 9 23 (which is not shown here). The apparatus consists of a mercury reservoir, an upright capillary rube, and a firing chamber. When a primer is fired in this test set, the hot reaction products build up pressure in the firing chamber. This pressure is communicated to the upper surface of the mercury in the reservoir, and this, in turn, causes a column of mercury to rise in the capillary tube. 

The mercury column rises momentarily to a considerable height in the tube and then settles down to a sustained height. By comparison with a graduated scale back of the capillary tube, both the maximum and the steady deflections of the mercury column are measured, the first being recorded as the primer "impulse and the latter as the "cold gas volume ... 

Figure 2-4. Various contact angles at ail-solution interfaces (a). An a of 0° indicates wettable walls with Adhesion > Cohesion (Eq. 2.1) leading to maximal capillary rise (a) an a of 150° indicates capillary depression, as occurs for mercury in glass capillaries (d).

Two methods are used to measure the pore size distribution in a powder mercury porosimetry and adsorption-desorption hysteresis. Both methods utilize the same principle capillary rise. A nonwetting liquid requires an excess pressure to rise in a narrow capillary. The pressure difference across the interface is given by the Young and Laplace equation [15]. 

If we replace water by mercury, there will be a capillary depression instead of a capillary rise, as shown in Fig. 2H(b). The simple physics behind this is that water wets glass whereas mercury does not. 

Fig. 2H (a) capillary rise observed for a wetting liquid, such as water in glass and (h) capillary depression observed for a nonwetting liquid, such as mercury in glass. 

For practical reasons the capillary rise technique is rarely used for the measurement of interfacial (rather than surface) tensions large amounts of the two liquids are needed and there are suitable and convenient alternatives. An exception to this is the measurement of the Interfacial tension between mercury and (mostly) aqueous solutions at various potential differences applied across the liquid-liquid interface. Such measurements are done in a so-called Lippmann capillary electrometer, already described in the chapter on electric double layers (fig. 11.3.47). 

Capillary rise plays an important role in agriculture, since it allows crop production in levels above the ground water table (already mentioned in sec. 1.3b). In tall trees water can rise by over 50 m through narrow capillaries. This happens without cavitation. Capillary depression is used in mercury porosimetry from the amount of mercury that can be pressed into a porous surface as a function of the applied pressure, insight about the pore size distribution can be obtsiined, see sec. 

These thermometers contain either mercury, alcohol, etc., as liquids. The thermal expansion of these liquids is greater than the glass, so the height of liquid in the glass capillary rises as the temperature increases. A major problem is that the glass can be easily broken. Furthermore, mercury causes toxicity problems if the thermometer breaks. Visual observations are usually required to read the thermometers. Often these instruments are restricted to temperatures from about 0°C to 400°C. Their advantages are low costs, long life if properly protected, and reasonable accuracy. They still are widely used in experimental setups and for various home uses. 

Figure 1. Apparatus for measuring capillary rise at mercury-gallium interface...

The balance of the results depends on calculation of contact angles from measurements of capillary rise [10]. A value of 41 dynes per cm. for the gallium-mercury interfacial tension, determined in previous work in this laboratory [8], was used in these calculations. The densities of the two saturated phases are 6.28 grams per cc. for the gallium and 13.35 for the mercury [8]. 

Because ceramic powders usually have macropores, mercury porosimetry is more suitable than gas adsorption. The principle of the technique is the phenomenon of capillary rise, as shown schematically in Fig. 4.4 [19]. When a liquid wets the walls of a narrow capillary, with contact angle, 9 < 90°, it will climb up the walls of the capillary. If the liquid does not wet the walls of a capillary, with contact angle, 9 > 90°, it will be depressed. When a nonwetting liquid is used, it is necessary to force the liquid to flow up the capillary to the level of the reservoir by applying a pressure. For a capillary with principal radii of curvature rj and r2 in two orthogonal directions, the pressure can be obtained by using the Young and Laplace equation ... 

FIGURE 6.10. In the capillary rise method of surface tension measurement, surface tension effects canse the wetting hquid to rise in the small capillary to a height that just balances the hydrodynamic force dne to gravity (a). For non-wetting liquids such as mercury, a depressing effect is observed (Z>). 

As a direct consequence of Jurin s law, a nonwetting liquid such as mercury, which does not wet glass, forms a surface which is convex upwards hence the pressure just under the meniscus will be greater than at a planar surface. Thus, the level of a mercury surface in a capillary tube will be below that of the surrounding liquid a capillary depletion occurs (h < 0). Conversely with water which wets glass, a capillary rise (h > 0) occurs. 

The two most common methods available to determine the interfacial tension at the mercury-electrolyte interface are the capillary rise method and the maximum... 

A) Capillary rise, due to the attraction of water and glass.The final water level in the capillary is a balance between the force of gravity and the surface tension of water. Depression,or lowering, of mercury level in a glass capillary. Unlike water, mercury is not attracted to glass. 

Figure 5.17 Capillary Rise or Depression of a Liquid in aTube. (a) A liquid that wets the solid surface, (b) A liquid that partially wets the solid surface, (c) Capillary depression of mercury in a glass capillary.

Mercury porosimetry is based on the capillary rise phenomenon whereby an excess pressure is required to cause a non-wetting liquid to climb up a narrow capillary. The pressure difference across the interface is given by the equation of Young and Laplace [3 sic] and its sign is such that the pressure is less in the liquid than in the gas (or... 

Mercury Porosimetry and Capillary Flow Porometry - Pore Size Determination In a mercury porosimetry measurement, pressure is used to force mercury into filling the pores and voids of the material. The method is based on the capillary rise phenomenon which exists when a non-wetting liquid climbs up a narrow capillary. As the pressure is increased, mercury infiltrates the pores to occupy a subset of the total pore space, the extent of which depends on the applied external pressure. The injected volume of mercury as a function of pressure is recorded. The pore size and distribution can be resolved using the Young and Laplace model [43]. The pore sizes that can be determined by mercury porosimetry range from a few nanometers to a few hundreds of microns. The method is invasive in that not all the mercury will be expelled from the pores and pores may collapse as a result of the high pressures. Due to this and environmental concerns about mercury pollution mercury porosimetry method is becoming less popular. 

If we replace water by mercury, a capillary depression will be observed, instead of a capillary rise, as shown in Figure 9.2b. The simple physics behind this is that water wets glass whereas mercury does not. In everyday language we could say that there is an affinity between water and glass, causing the liquid to "crawl up" the capillary. To force the water in the capillary back to its level in the vessel, it would be necessary to apply a pressure (given by the Yoimg-Laplace equation) that is inversely proportional to the radius of the capillary. 

Fig. 3J0 Plot of cumulative pore volume against logarithm of r the effective pore radius, (o) For charcoal AY4 A by mercury intrusion O by capillary condensation of benzene, (b) For zinc chloride carbon AYS A by mercury intrusion O by capillary condensation of benzene x by capillary condensation of benzene, after mercury intrusion followed by distillation of mercury under vacuum at temperature rising to 350°C. (Courtesy...

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