Mercury surface tension

Maxima may be removed by the addition of small amounts of certain surface-active substances, e.g. Triton-X-100 and gelatin (see Sect. 3.3.3), whose action is ascribed to their effect on the mercury surface tension. When addition of such substances is not possible, the placement of a shroud around the capillary tip has been suggested to minimise convection effects [65]. An alternative is to arrange for short drop times by mechanical means. 

Variations of mercury surface tension cause movement within the mercury. Owing to the different velocity distibutions close to and far away from the capillary, there is a non-uniform current distribution. Maxima are tall and narrow. 

Mercury porosimetry is performed nearly exclusively on automatic commercial instruments that differ mainly in the highest operative pressure, which determines the size of smallest attainable pores. The highest pressure is limited by the uncertainty about the validity of the Washburn equation, which forms the basis of data evaluation. In pores with sizes similar to the mercury atom the assumption that physical properties of liquid mercury (surface tension, contact angle) are equal to bulk properties is, probably, not fully substantiated. For this reason the up-to-date instruments work with pressures up to 2000 - 4000 atm, only. 

Below 45 MPa, the high dispersive precipitated silica sample with or without membrane collapses without mercury intrusion. The buckling mechanism of pores edges can be assumed as in the case of low density xerogels. Consequently, equation (2) can be used to interpret the mercury porosimetry curve in this low pressure domain. The constant A, to be used in equation (2) can be calculated from the P, value using equation (4). With a mercury surface tension 0.485 N/m, a contact angle 0= 130° and P, = 45 MPa, one obtains K = 86.3 nm MPa" . 

The sintered compacts with a thickness of about 5 mm were polished and thermally etched and examined by using a scaning electron microscope at five different positions across the thickness. Furthermore, the specimens were cut off from the bottom gradually. After each cut-off they were investigated for the pore-size distribution by using a mercury porosimeter. To calculate the pore-size distribution, a mercury surface tension of 0.48 N/m and a contact angle of 140" were assumed. 

Water at 20° has a surface tension of 72.9 mN/m in contact with air compared with 35 mN/m for SAE 30 oil and 486.5 mN/m for mercury. Surface tension values of common liquids are hsted in Table 1. 

Stepwise Pressurisation. A Micromeritics Pore Sizer 9310 was used in conjunction with Micromeritics software and a PC XT computer over the pressure range 1.6 psia to circa 30,000 psia. The pressure values were defined from a selectable Pressure Table within the program. The default values for mercury contact angle and mercury surface tension were 130 and 485 mNm respectively. The stepwise pressurisation equilibrium times can be selected from zero to 30+ seconds, the default time being 10 seconds. 

It is to be noted that not only is the correction quite large, but for a given tip radius it depends on the nature of the liquid. It is thus incorrect to assume that the drop weights for two liquids are in the ratio of the respective surface tensions when the same size tip is used. Finally, correction factors for r/V < 0.3 have been determined, using mercury drops [37],... 

Smith [113] studied the adsorption of n-pentane on mercury, determining both the surface tension change and the ellipsometric film thickness as a function of the equilibrium pentane pressure. F could then be calculated from the Gibbs equation in the form of Eq. ni-106, and from t. The agreement was excellent. Ellipsometry has also been used to determine the surface compositions of solutions [114,115], as well polymer adsorption at the solution-air interface [116]. 

Some data obtained by Nicholas et al. [150] are given in Table III-3, for the surface tension of mercury at 25°C in contact with various pressures of water vapor. Calculate the adsorption isotherm for water on mercury, and plot it as F versus P. 

Qualitatively, it is observed that the mercury surface initially is positively charged, and on reducing this charge by means of an applied potential, it is found that the height of the mercury column and hence Ae interfacial tension... 

Because of the large surface tension of liquid mercury, extremely large supersaturation ratios are needed for nucleation to occur at a measurable rate. Calculate rc and ric at 400 K assuming that the critical supersaturation is x = 40,000. Take the surface tension of mercury to be 486.5 ergs/cm. ... 

As a follow-up to Problem 2, the observed nucleation rate for mercury vapor at 400 K is 1000-fold less than predicted by Eq. IX-9. The effect may be attributed to a lowered surface tension of the critical nuclei involved. Calculate this surface tension. 

Mercury is unusually prone to contamination, and this probably accounts for the lack of reproducibility to be found in the values of surface tension in i the earlier literature. Table 3.13 provides a selection of the data reported ... 

Another valuable property of mercury is its relatively high surface tension, 480.3 mN /m(= dyn/cm) at 0 °C, as compared to 75.6 mN /m for water. Because of its high surface tension, mercury does not wet glass and exhibits a reverse miniscus in a capillary tube. 

Important physical properties of catalysts include the particle size and shape, surface area, pore volume, pore size distribution, and strength to resist cmshing and abrasion. Measurements of catalyst physical properties (43) are routine and often automated. Pores with diameters <2.0 nm are called micropores those with diameters between 2.0 and 5.0 nm are called mesopores and those with diameters >5.0 nm are called macropores. Pore volumes and pore size distributions are measured by mercury penetration and by N2 adsorption. Mercury is forced into the pores under pressure entry into a pore is opposed by surface tension. For example, a pressure of about 71 MPa (700 atm) is required to fill a pore with a diameter of 10 nm. The amount of uptake as a function of pressure determines the pore size distribution of the larger pores (44). In complementary experiments, the sizes of the smallest pores (those 1 to 20 nm in diameter) are deterrnined by measurements characterizing desorption of N2 from the catalyst. The basis for the measurement is the capillary condensation that occurs in small pores at pressures less than the vapor pressure of the adsorbed nitrogen. The smaller the diameter of the pore, the greater the lowering of the vapor pressure of the Hquid in it. 

The specific gravities of oils and alcohols are about 0.8, of water 1.0, and of mercury 13,h. Alcohol has a low surface tension however, it tends to absorb water and evaporate, and its density varies considerably with temperature. 

Water has the highest surface tension (75 dyne/cm) of ail common liquids (except mercury). Together, surface tension and density determine how high a liquid rises in a capillary system. Capillary movement of water plays a prominent role in the life of plants. Lastly, consider osmosis, the bulk movement of water in the direction from a dilute aqueous solution to a more concentrated one across a semipermeable boundary. Such bulk movements determine the shape and form of living things. 

Some emphasis has been placed inthis Section on the nature of theel trified interface since it is apparent that adsorption at the interface between the metal and solution is a precursor to the electrochemical reactions that constitute corrosion in aqueous solution. The majority of studies of adsorption have been carried out using a mercury electrode (determination of surface tension us. potential, impedance us. potential, etc.) and this has lead to a grater understanding of the nature of the electrihed interface and of the forces that are responsible for adsorption of anions and cations from solution. Unfortunately, it is more difficult to study adsorption on clean solid metal surfaces (e.g. platinum), and the situation is even more complicated when the surface of the metal is filmed with solid oxide. Nevertheless, information obtained with the mercury electrode can be used to provide a qualitative interpretation of adsorption phenomenon in the corrosion of metals, and in order to emphasise the importance of adsorption phenomena some examples are outlined below. 

In the case of liquid/liquid interfaces we have the experiments of W. C. McC. Lewis (1908), who examined the relations at the surface of separation between an aqueous solution and paraffin oil or mercury. If o-, a are the surface tensions between paraffin oil and pure water and the solution, respectively, it was found that cr < [Pg.439]

The more highly charged the interface becomes, the more the charges repel each other, thereby decreasing the cohesive forces, lowering the surface tension, and flattening the mercury drop. The second differential of the electrocapillary plot gives directly the differential capacitance of the double layer ... 

For liquid electrode metals (mercury, gallium) the determination of the surface tension can be applied. From changes of the surface tension as a function of dissolved adsorbable species the surface coverage... 

A small amount of a liquid tends to take a spherical shape For example, mercury drops are nearly spherical and water drips from a faucet in nearly spherical liquid droplets. Surface tension, which measures the resistance of a liquid to an increase in its surface area, is the physical property responsible for this behavior. 

When potential is applied, the meniscus moves, owing to the resulting change in surface tension. By varying the height of the mercury column during the measurements... 

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