Contact angle for mercury

As an average for many materials, Ritter and Drake [6,7] used 140° for 

Using the phenomenon called local hysteresis, values of 0 = 162° 

It has also been suggested that contact angle is pore size dependent [60], a value of 180° being applicable for macropores and mesopores with a reduction for smaller pores [61]. 

Intrusion and extrusion calculations are conventionally made using the same angle. Lowell and Shields [62,63] using values of 6 =170 for 

The use of an inconect contact angle does not matter when porous materials of the same type are being compared. However, if an exact measurement of pore openings is requii it is necessary to either measure the contact angle directly [3, p. 268] or look at the pores under a microscope to establish the relationship between the actual pore size openings to that measured by mercury intnision. 

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Table I. Contact Angles for Mercury-Gallium Interface on Borosilicate Glass, Exposed to Air (All angles measured through mercury) ...

The measured contact angle of mercury on various samples can range from 112 to 170° [39], but for most applications the average value of 140° is used. It should be noted, however, that the accuracy of the pore radii measurement is limited by the accuracy of the contact-angle measurement [40]. Contact angles can readily be measured on flat surfaces or compacts of powders [6], and the measurement of contact angles with powder systems has also been reported [41]. 

The experimental method of mercury porosimetry for the determination of the porous properties of solids is dependent on several variables. One of these is the wetting or contact angle between mercury and the surface of the solid. 

Incorporation of the measured contact angle in mercury intrusion porosimetry data is essential for an accurate determination of the pore size distribution. Both the advancing and static angle methods are suitable to carry out this measurement, leading to very similar results. For most oxidic materials and supported oxides, the contact angle is 140° and incorporation of the actual contact angle is less critical in the pore size determination. However, important deviations are observed in carbon and cement-like materials, with contact angles of > 150° and < 130°, respectively. This has been shown by comparison of the pore size distribution obtained from mercury porosimetry and N2 adsorption measurements. 

A value of 140 °C was used for the contact angle of mercury on the solid (0), and the surface tension of mercury (7) was taken as 0.485 N/m. These values correspond to an effective working range for the instrument of 150 pm to 1.7 nm in pore radius. The samples were outgassed at room temperature to a pressure of 50 mtorr (7 Pa) immediately prior to analysis to facilitate filling the penetrometers with mercury. All data were fully corrected for mercury compression with calibrated penetrometers. 

There is some uncertainty about the contact angle that mercury makes with catalyst materials. Drake used Woods Metal and sodium, heated above the melting point, to replace mercury in an attempt to learn the influence of contact angle. However, little difference was observed for the few results obtained with the two metals and the experimental difficulties were many. 

A value of 140°C was used for the contact angle of mercury on the solid (0), and the siuface tension of mercury (y) was taken as 0.485 N/m. These values correspond to an... 

Merch Bricks. Term sometimes used in USA for building bricks that come from the kiln discoloured, warped or off-sized. Mercury Penetration Method. A procedure for the determination of the range of pore sizes in a ceramic material. It depends on the fact that the volume of mercury that will enter a porous body at a pressure of P dynes /cm2 is a measure of the volume of pores larger than a radius r cm where r = -2a cos8/P, a being the surface tension of mercury in dynes/cm and 6 being the contact angle between mercury and the ceramic. A development of the method has been described by R. D. Hill (Trans. Brit. Ceram. Soc., 59, 198,1960). 

The contact angle of mercury on glass is about 120° (cosd = —0.5). What is the significance of the -0.5 for the cos 9 in terms of the capillary method of determining surface tension. 

From relation (11-7) between pore size and pressure, it can be inferred that the pore size can be determined with an accuracy of about 20%. It should be noted that the accuracy obtained for mercury intrusion porosimetry is not better, due to the possible, but generally ignored variations on the contact angle between mercury and the solid surface, as well as the hypothesis of cylindrical pores. 

In mercury intrusion porosimetry, mercury surroimds the sample and application of differential pressure on mercury forces it into the pores. Mercury does not wet hydrophilic and hydrophobic pores and cannot enter these pores spontaneously owing to a small contact angle. Application of pressure on mercury can force it into the pores. The measured intrusion volume is equal to the pore volume and the differential intrusion pressure is related to pore diameter as given in Equation 8.43, where o and 0 are the surface tension and contact angle of mercury, respectively. Mercury porosimetry is valuable in determining the pore structure of the catalyst layer, especially for gas diffusion electrodes, where the distribution of gas and liquid phase pores is essential for the optimization of performance. 

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. 

The surface tension of mercury at 20°C is equal to 0.4355 N m. The density of mCTcury is equal to 13.56 g cm. The contact angle of mercury against glass is 180°. Find the capillary depression (distance of the meniscus below the liquid surface) for mercury in a glass capillary tube of radius 0.35 mm at 20°C. 

It is not common practice to measure the contact angle and, indeed, there is some evidence that its value is affected by surface roughness. The hysteresis encountered in mercury porosimetry may be completely removed by the use of different contact angles for intrasion and extrusion. On this basis the use of hysteresis to predict pore shape may lead to erroneous and misleading data. 

Usually one varies the head of mercury or applied gas pressure so as to bring the meniscus to a fixed reference point [118], Grahame and co-workers [119], Hansen and co-workers [120] (see also Ref. 121), and Hills and Payne [122] have given more or less elaborate descriptions of the capillary electrometer apparatus. Nowadays, the capillary electrometer is customarily used in conjunction with capacitance measurements (see below). Vos and Vos [111] describe the use of sessile drop profiles (Section II-7B) for interfacial tension measurements, thus avoiding an assumption as to the solution-Hg-glass contact angle. 

A procedure that is more suitable for obtaining the actual distribution of pore sizes involves the use of a nonwetting liquid such as mercury—the contact angle on glass being about 140° (Table X-2) (but note Ref. 31). If all pores are equally accessible, only those will be filled for which... 

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