Specific surface area determination

The specific surface area of eement is eommonly determined directly by air. permeability methods. In the Lea and Nurse method (LI 5). a bed of cement / of porosity 0.475 is eontained in a cell through which a stream of air is f passed, and steady flow established. The specific surface area is caleulated ( from the density of the eement, the porosity and dimensions of the bed of j powder, the pressure differenee aeross the bed, and the rate of flow and ] kinematie viscosity of the air. In the Blaine method (B36), a fixed volume of I air passes through the bed at a steadily deereasing rate, whieh is controlled / and measured by the movement of oil in a manometer, the time required i being measured. The apparatus is ealibrated empirically, most obviously / using a cement that has also been examined by the Lea and Nurse method. The two methods gave elosely similar results. The Blaine method, though not absolute, is simpler to operate and automated variants of it have been devised. 

Other methods that have been used to determine specific surface areas of cements include the Wagner turbidimeter (W16) and BET (Brunauer-Emmett-Teller) gas adsorption. The former, as eonventionally used, gives very low results beeause of a false assumption that the mean diameter of the particles smaller than 7.5 pm is 3.8 pm, which is much too high. The BET method gives results two to three times higher than the air permeability 

The specific surface area, like the PSD, is thus a quality whose value depends on how it is defined, and is liable to be affected by any pretreatment or conditions affecting the degree of flocculation. In practice, air permeability methods are widely used. Typical values are 300-350 m kg for modern ordinary Portland cements and 400-450 m kg for rapidhardening Portland cements. 

From a PSD curve, one may calculate the specific surface area, S  

In principle, the specific surface area may also be calculated from the PSD using analytical expressions derived from such functions as the Rosin-Rammler expression. In practice, this is not always satisfactory because the specific surface area is so highly dependent on the bottom end of the distribution. 

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The intrinsic dissolution rates of pharmaceutical solids may be calculated from the dissolution rate and wetted surface area using Eq. (36) or (37). For powdered solids, two common methods are available the powder intrinsic dissolution rate method, and the disc intrinsic dissolution rate method. In the former method, the initial dissolution rate of one gram of powder is determined by a batch-type procedure as illustrated in Fig. 13A. The initial wetted surface area of one gram of powder is assumed to equal the specific surface area determined by an established dry procedure, such as monolayer gas adsorption by the Brunauer, Emmett, and Teller (BET) procedure [110]. 

Particular difficulties similar to those associated with specific surface area determinations (Sec. 1.5.1) also accompany particle size distribution studies on surface coated organic pigments. The identity of the additive, be it an amine, a hard resin, or some other material, is less of a concern than the question of its concentration There is no information on the concentration limits above which an additive may distort the measurements but one can expect this value to be defined largely by the specific surface area and the average particle size of each individual pigment. For pretreated surfaces, sizing the pigment particles by electron mi-... 

The mean primary particle sizes of pigment blacks he in the range 10-100 nm specific surface areas are between 20 and 1000 m2/g. The specific surface area, determined by N2 adsorption and evaluation by the BET method [4.29], is often cited as a measure of the fineness of a black. Blacks with specific surface areas >150 m2/g are generally porous. The BET total specific surface area is larger than the geometric surface area measured in the electron microscope, the difference being due to the pore area resp. the pore volume. 

Hydrocarbons are often used as adsorbates in specific surface area determinations by GC, especially with flame ionization detectors (FIDs). 

The specific surface area, determined by adsorption and desorption of nitrogen for titania, goethite and silica samples were 13.5, 42.0, and 261.7 m2/g, respectively. 

The specific surface area determined from the Porod plot is approximately 10 m /g. This is a very low value and can be attributed to the absence of the Porod limit. 

Fig. 4 shows two STM images of the surface structure of a carbon black. The sample exhibits a specific surface area, determined by N2 adsorption at 77 K, of 15.3 m g, which is almost coincident with its geometric area (16.9 m g ). Therefore, this is a nonporous carbon and its STM images should be expected to differ from those of the ACFs. As a matter of fact, this is what can be observed in Fig. 4. First, it is noted that the carbon black does not display any mesoporosity (Fig. 4a) such as that of the AFCs (Fig. 2). Second, at the micropore scale the carbon black porosity is also very poorly developed (Fig. 4b) in comparison with the pore development of ACFs (e.g.. Fig. 3a). In the former case (Fig. 4b), altough some trenches are also present, they are very shallow and, consequently, are simple topographic variations of a smooth surface and cannot be considered as pores penetrating deeply into the material as in Fig. 3a. Also, pores of the type shown in Fig. 3b for the ACFs were not normally seen on the carbon black surface. Hence, all these observations agree with the lack of adsorption capabilities of this material.

Assuming, that the surface area occupied by one n-octadecanol molecule in monolayer is equal to 0.21 nm [23] and knowing AV of solute determined in a separate experiment equation (7) gives a simple method of the adsorbent specific surface area determination, first described by Serpinet [25]. 

Properties Specific surface area determined by ethylene glycol monoethyl ether method available [2274]. 

Typical results of specific surface area determinations on phyllosilicates by nitrogen gas/water vapor or nitrogen gas/CPB adsorption are listed in Table 1.7. For Mg-vermiculite and Na-montmorillonite, the measured adsorption specific surface area is close to that calculated from the unit cell dimensions and structural formula. For illitic mica, the area is about 14 per cent of the ideal crystallographic value, indicating that this mineral forms particles containing about seven phyllosilicate layers that cannot be penetrated by water vapor or CPB. 

Although the positive adsorption methods offer the advantage of convenient determination in heterogeneous samples, they suffer from the uncertainty involved in the calibration of the packing area (which usually must be done by comparison with results from a physical method using reference clay materials) and from the fact that the monolayer parameter is model-dependent through Eqs. 1.6 and 1.7. It must also be remembered that the specific surface area determined by positive adsorption is ultimately a function of the reaction between surface functional groups and some probe molecule. If the experimental conditions of the reaction are close to those under which the surface behavior of a sample is of interest, then this estimate of specific surface area has surface chemical relevance. 

Table 1.8 lists specific surface area values for illitic micas as determined by nitrogen gas adsorption and by negative chloride adsorption.The specific surface areas calculated from N2 gas adsorption with the help of Eq. 1.7 show no particular trend with type of exchangeable cation. The mean value of 5, 11.2 0.5 x 10 m kg", suggests that the mineral forms particles containing seven phyllosilicate layers, as indicated previously. The external surfaces of these particles are expected to repel anions, and therefore the specific surface area determined by negative chloride adsorption should also be around lO m kg" . As shown in Table 1.8, however, the values of 5k, obtained with Eq. 1.18, are always less than 5 and decrease sharply with increasing radius of the... 

S specific surface area determined by water vapour adsorption. 

Variation of the surface density of TMS groups, calculated using either Nj or CTAB specific surface area determination methods, with the surface density of residual silanol groups on SI3TMSx and T30TMS.V silica samples. 

Specific Surface Areas Determined for the Nitrogen or Argon (Sbet) and Water (SJ Adsorption Isotherms... 

Specific Surface Area Determined from Water Adsorption, Heats of Immersion, and Adsorption of Water... 

Integration of PSD functions gives the textural characteristics of the samples (Table 8.9). The specific surface area (5 uw = 51.7 m /g. Table 8.9) of bleached flax fibers in contact with unfrozen bound water at 273 K is close to the specific surface area determined from the water sorption isotherm (5bexv,=46 m /g. Table 8.9). However, 5 bet,w for Ih incubated cotton. This difference in the bleached flax and cotton fiber properties can be explained by features in the fibers... 

Specific surface area determination is most commonly conducted by positive adsorption studies (Section 7.6.4.2), and here the election of the probe molecule is very important. The most traditional and widely used method is N2 adsorption at 77 K, using the BET isotherm to evaluate monolayer coverage (Section 7.6.4.2) sometimes other inert gases, such as argon, are employed in the same conditions (Sposito 1984). In soil characterization, other substances are also used in the BET... 

The particle size was calculated on the basis of specific surface areas determined by a titration procedure, and assuming the particle is anhydrous SiO,. The values of , the interfacial energy calculated from the slopes of the lines A and B, using the equation... 

Determination of the morphology of the original polymers and the SIRs obtained from them by impregnation is very helpful in elucidation of the adsorption mechanism of the extractant. The results of specific surface area determinations, mercury intrusion porosimetry, and inverse steric exclusion chromatography (ISEC) were used to determine the different mechanism involved in extractant retention in the polymer phase as a function of the polymer structure and the type of mechanism involved in the retention (1) physical adsorption or (2) chemical interaction. 

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