Porosity nitrogen

Eor means of determination and quantification of the material porosity, different methods like mercury intrusion porosity, nitrogen gas adsorption, or inverse-size exclusion chromatography (ISEC) have been established and are nowadays routinely employed for that purpose. As an alternative to these well-known methods, a new approach based on near-infrared spectroscopy (NIR) for the characterization of monoliths is introduced in this chapter. 

In view of the widespread use of nitrogen and argon in surface area and porosity studies, data for the construction of the standard a,-curves for these adsorbates on hydroxylated silica, are given in Table 2.14 (p. 93) for nitrogen and in Table 2.15 for argon. From the arguments of Section 2.12, these should be adequate for other oxides such as alumina, if high accuracy is not called for. 

P/M steels can be heat treated in the same manner as cast or wrought steels. They may be austenitized, quenched, and tempered. Surface hardening includes pack or gas carburization or nitriding, ie, heating in a nitrogen-containing atmosphere. Because of the greater amount of exposed surface area in the form of porosity, a protective atmosphere is needed (see Metal surface treatments). 

Porosity and surface area are routinely measured by nitrogen absorption-desorption, mercury intrusion, and low-angle X ray. The electron microscope (EM) provides direct visual evidence of pore size and pore-size distribution. Thus, a combination of EM and conventional methods of pore-size measurement should provide reliable information on the pore structure of polymers. 

Figure 1.5 shows the cumulative pore volume curve for 5-/rm monosized porous PS-DVB particles with 50, 60, and 70% porosity. The curves were drawn by overlapping the measurements from nitrogen adsorption-desorption and mercury intrusion. A scanning electron micrograph of 5-/rm monosized particles with 50% porosity is shown in Fig. 1.6 (87). 

Of the weldability problems, nickel and nickel-based alloys are particularly prone to solidification porosity, especially if nitrogen is present in the arc atmosphere, but this may be controlled by ensuring the presence of titanium as a denitrider in the filler and maintaining, a short arc length. The other problem that may be encountered is hot cracking, particularly in alloys containing Cr, Si, Ti, Al, B, Zr, S, Pb and P. 

The filtering operation can also be conveniently done in a high-quality nitrogen atmosphere dry box by vacuum filtration through a 90-mm., 60-ml., medium-porosity fritted-disk Buchner funnel. 

Anode electrode Sintering temp. ("C) Initial porosity (%) FHH equation (Nitrogen adsorption) Mercury porosimetry Average Ds- Contact Angle with electrolyte 0C)... 

This technique has also been used in combination with nitrogen absorption to study the pore structure of some excipients, particularly MCC in both the powdered and compacted state. The intraparticulate porosity of MCC has been shown to be unaffected by tableting the interparticular pores, however, are gradually reduced in size [38]. Recently this method has been used to evaluate the internal structure of tablets prepared from microcapsules [150]. 

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