Nitrogen adsorption isotherms

Fig. XVII-31. (a) Nitrogen adsorption isotherms expressed as /-plots for various samples of a-FeOOH dispersed on carbon fibers, (h) Micropore size distributions as obtained by the MP method. [Reprinted with permission from K. Kaneko, Langmuir, 3, 357 (1987) (Ref. 231.) Copyright 1987, American Chemical Society.]...

The nitrogen adsorption isotherm is determined for a finely divided, nonporous solid. It is found that at = 0.5, P/P is 0.05 at 77 K, gnd P/F is 0.2 at 90 K. Calculate the isosteric heat of adsorption, and AS and AC for adsorption at 77 K. Write the statement of the process to which your calculated quantities correspond. Explain whether the state of the adsorbed N2 appears to be more nearly gaslike or liquidlike. The normal boiling point of N2 is 77 K, and its heat of vaporization is 1.35 kcal/mol. 

A Type II isotherm indicates that the solid is non-porous, whilst the Type IV isotherm is characteristic of a mesoporous solid. From both types of isotherm it is possible, provided certain complications are absent, to calculate the specific surface of the solid, as is explained in Chapter 2. Indeed, the method most widely used at the present time for the determination of the surface area of finely divided solids is based on the adsorption of nitrogen at its boiling point. From the Type IV isotherm the pore size distribution may also be evaluated, using procedures outlined in Chapter 3. 

Fig. 2.8 The adsorption of nitrogen at 77 K on nonporous samples of silica and alumina, ranging from 2-6 to 11-5 m g for silica and from 58 to 153m g for alumina. n/n is plotted against pjp°. (A) O, silica , alumina. (B) BET isotherm (Equation 2.12) with c values of 100-2(X).

Fig. 2.13 Adsorption of nitrogen on a carbon black before graphitiz-ation. - The difTerential heat of adsorption Ji, plotted against n/n , was determined calorimetrically at 78 K (O, , A) and was also calculated from the isotherms at 78 6 and 90-1 K (+ ). (Courtesy Joyner and Emmett.)...

Fig. 230 Adsorption of nitrogen at 77 K on a silica powder a) adsorption isotherms b) /-plot. Broken line, uncompacted powder continuous line, power compacted at 2-00 x 10 N m (130 ton in ). (—>—) adsorption (—<-) desorption. / is the ratio of the amount adsorbed on the powder to the amount adsorbed on the compact at the same relative...

The degree of uncertainty of 10 per cent or more, inseparable from estimates of specific surface from adsorption isotherms, even those of nitrogen, may seem disappointing. In fact, however, attainment of this level of accuracy is a notable achievement in a field where, prior to the development of the BET method, even the order of magnitude of the specific surface of highly disperse solids was in doubt. The adsorption method still provides the only means of determining the specific surface of a mass of non-... 

Fig. 3.2 Adsorption isotherms for argon and nitrogen at 78 K and for n-butane at 273 K on porous glass No. 3. Open symbols, adsorption solid symbols, desorption (courtesy Emmett and Cines). The uptake at saturation (calculate as volume of liquid) was as follows argon at 78 K, 00452 nitrogen at 78 K, 00455 butane at 273 K, 00434cm g .

Fig. 3.3 Adsorption isotherm of nitrogen at 77 K on halloysite. Open circles, adsorption solid circles, desorption. ...

Fig. 3.22 Adsorption isotherms of nitrogen at 77 K on silica powder and its compacts. (A) uncompressed (B) 10 ton in (C) 40 ton in" (D) 50 ton in (E) 100 ton in . Open symbols represent adsorption, solid symbols desorption. (Courtesy Ramsay.)...

Fig. 3.26 Comparison plots for compacts of silica and magnesia. In each case the adsorption of nitrogen at 78 K on the compact is plotted against that on the uncompacted powder, (a) and (b), comparison plot and adsorption isotherm for silica powder compacted at 130 ton in (c) and (d), comparison plot and adsorption isotherm for precipitated magnesia compacted at 10 ton in. Note that the upward sweep of the comparison plot commences at a relative pressure below the inception of the loop.

Fig. 4.13 The pre-adsorption method (a) adsorption isotherms of nitrogen at 77 K on a sample of Mogul I carbon black charged with different amounts x of pre-adsorbed nonane. Values ofx (mg g (A) 63 (B)48 (C) 29 (D) 16 (E) 0. (See Table 4.5.) (Some points at low pressures omitted for the sake of clarity.)...

Fig. 4.15 a,-plots for the adsorption of nitrogen on a sample of microporous titania, before and after nonane treatment. Curve (A), before nonane pre-adsorption curves (B), (C), (D) after nonane pre-adsorption, followed by outgassing at (B) 250° (C) 150°C (D) 25°C. The a,-plots were based on standard nitrogen isotherms having the same c-values as the isotherms of... 

Fig. 4.29 Adsorption isotherms of water vapour on caldte, after being balt-milted for different periods (A, B, C) and on precipitated calcium carbonate (D). Period of milling (A) 1000h (B) ISOh (C) 22h outgassing temperature 2S°C. Isotherms A, B and C (but not D) all showed extensive low-pressure hysteresis, but for clarity the desorption branch is omitted. The amount adsorbed is referred to 1 m of BET-nitrogen area. ...

Fig. 4J0 Adsorption isotherms on ammonium silicomolybdate powder. (I), (4). nitrogen at 77 K (2), (3), /t-hexane at 298 K. Isotherms I and 2 were measured before, and 3 and 4 after, pre-adsorption of n-nonane. Open symbols, adsorption solid symbols, desorption. (Adsorption is expressed in mm (liquid.)...

Fig. 4J2 Adsorption isotherms of carbon tetrachloride (at 298 K) on ammonium phosphotungstate compact, (1) before, (2) after preadsorption of n-nonane. (3) is the isotherm of nitrogen, after preadsorption, for reference. Open symbols, adsorption solid symbols,...

Fig. 5.13 Adsorption isotherms on graphitized and on ungraphitized charcoal, (a) Adsorption of water vapour (fc) adsorption of nitrogen at — 195°C. The adsorption values are expressed in cm of liquid adsorbate per gram of adsorbent. (Courtesy Kiselev. )...

Fig. 5.14 Adsorption isotherms of water on carbon in (a) to f) with corresponding isotherms of nitrogen in (a), (c) and (J), and of benzene in (f>). (a) Charcoal (b) active carbon AY8 (c) charcoal A (J) charcoal (e) a coal tar pitch kilned at 1200°C (/) a charcoal (S600H). (Redrawn from the diagrams in the original papers.)...

Fig. 6. Family of adsorption isotherms for adsorption of nitrogen on 2eolite X at temperatures of -30 to 196°C (1).

Surface areas are deterrnined routinely and exactiy from measurements of the amount of physically adsorbed, physisorbed, nitrogen. Physical adsorption is a process akin to condensation the adsorbed molecules interact weakly with the surface and multilayers form. The standard interpretation of nitrogen adsorption data is based on the BET model (45), which accounts for multilayer adsorption. From a measured adsorption isotherm and the known area of an adsorbed N2 molecule, taken to be 0.162 nm, the surface area of the soHd is calculated (see Adsorption). 

With its oxygen functionality, graphite oxide has chemical properties more akin to those of layered disulfides or sheet silicates than to those of graphite (Gi, T1,A2). Many studies have been of an extremely applied nature the possibility of fluorination (LI, N1), redox potentials in the presence of hydrogen peroxide (V2), the apparent density (L2), the adsorption isotherms with nitrogen (L3), and the diffusion of Cs in graphite oxide (R2). 

---