Chemical collapse

Dissolved solids or salts in land-applied material can also create problems. They chemically collapse the clay structure, which normally allows soil to hold water. Plants will exhibit drought-like symptoms even with adequate rainfall. Applying sludge in liquid form greatly increases the potential for salt overload. 

The Chemically Collapsed Phase ofSmS, e.g. the Electronic Structure of a Homogeneous Mixed Valence Alloy... 

The XPS data on chemically collapsed phases of SmS (63, 64,65), combined with the Mossbauer result (62), contradict the inhomogeneous mixed valence model. They provide conclusive evidence for the validity of the homogeneous model. In addition they demonstrate that in spite of the fluctuations , the ionic structure of the 4/-shell is maintained, this being a consequence of the fact that Ue > A. 

Fig. 21. Comparison of XPS spectra of 4/ electrons in pure SmS, SmSb and chemically collapsed Sm 85Th jsS.

The peculiar temperature and composition dependence of the valence of chemically collapsed phases of SmS was first observed in the system Sm1 xGdxS (55). Recently a phase diagram in the (x, T)-plane has been proposed for this system (41) as well as for CeTh alloys (44). When cooled below about 200 K the chemically collapsed phases of SmS show a dramatic lattice expansion, in some cases with explosive character (55) and disintegration of the crystal into a black powder. An example of this transition towards a more divalent state of Sm on cooling in SmAs 18 S 82 and Sm 81 Y19S is shown in Fig. 22 and 23, where we show the data of Poliak et al (63). The temperature dependent configurational mixing of Sm ions which is directly visualized in the XPS data is the source of the anomalous temperature dependence of the lattice constant. No detailed analysis of the dependence of the Sm 4/lineshape on temperature... 

Fig. 22. Temperature dependence of the lattice constant of pure SmS, SmAs and chemically collapsed Sm.g1Y.19S and SmS.82As.i8. Note the anomalous expansion of the collapsed phases on cooling (Ref. 63).

The SmS semiconductor to metal transition was later verified by the direct observation of a discontinuous change in the optical reflectivity at 6 kbar (Kirk et al., 1972). This is consistent with a first order magnetic phase transition which was directly verified by magnetic susceptibility measurements under pressure by Maple and Wohlleben (1971). In the collapsed phase the susceptibility of SmS showed no magnetic order down to 0.35 iC and was almost identical to the susceptibility of SmBa (see fig. 20.10 of volume 2). Bader et al. (1973) measured the heat capacity (fig. 11.16) and electrical resistivity (fig. 11.17) of SmS under pressure. They found a large electronic contribution to the heat capacity ( y = 145 mJ/mole-K ) and a resistivity reminiscent of SmB. Mossbauer isomer shift measurements of SmS under pressure by Coey et al. (1976) reveal the transition from a Sm isomer shift at zero pressure to an intermediate value at pressures above 6 kbar (fig. 11.18). The isomer shift of SmS above 6 kbar was found to be about the same as the isomer shifts for chemically collapsed Smo.77Yo.23S and SmBo at zero pressure. 

Fig. 3. Coexistence of divalent and trivalent Sra ions in chemically collapsed phases of SmS, as detected by XPS. (After Campagna et al. 1975.)...

A new experimental result is the observation of a broad and weak signal in the gap between the acoustic and optic branches and marked in fig. 23 with triangles. Such a mode has been observed before in IV chemically collapsed SmS by Mook et al. (1978). These modes are probably connected with bound heavy-electron plasmon-phonon modes where the f-like quasiparticles in the narrow bands below (described in section 4.1.1.2 and shown in figs. 2d and 14) couple to the phonons and perform collective oscillations. We recall that we have two plasrria oscillations, one for normal mass electrons and one for heavy mass electrons in the far infrared. It is the latter plasmon modes which are expected to couple to acoustic phonons in an out of phase motion as first proposed by Varma (1976). This idea has been quantitatively expanded in papers by Entel et al. (1979), Sinha and Varma (1983) and Stiisser et al. (1982). Further investigation of these modes seems necessary, however, they are only rarely observed (see also section 4.3.1.2). 

For collapsed SmS the determination of the degree of intermediate valence has long been disputed in literature and mostly been taken from the lattice constant of chemically collapsed SmS. However, Batlogg et al. (1976b) have performed a differential Bragg reflex measurement between semiconducting and pressurized SmS and found a lattice constant of 5.68 A from which a valence mixing of 2.85 can be obtained. 

Fig. IV-18. (a) Electron micrograph of a collapsing film of 2-hydroxytetracosanoic acid. Scale bar 1. [From H. E. Ries, Jr., Nature, 281, 287 (1979).] (b) Possible collapse mechanism. [Reprinted with permission from H. E. Ries, Jr. and H. Swift, Langmuir, 3, 853 (1987) (Ref. 223). Copyright 1987, American Chemical Society.]...

There appear to be two stages in the collapse of emulsions flocculation, in which some clustering of emulsion droplets takes place, and coalescence, in which the number of distinct droplets decreases (see Refs. 31-33). Coalescence rates very likely depend primarily on the film-film surface chemical repulsion and on the degree of irreversibility of film desorption, as discussed. However, if emulsions are centrifuged, a compressed polyhedral structure similar to that of foams results [32-34]—see Section XIV-8—and coalescence may now take on mechanisms more related to those operative in the thinning of foams. 

The components in catalysts called promoters lack significant catalytic activity tliemselves, but tliey improve a catalyst by making it more active, selective, or stable. A chemical promoter is used in minute amounts (e.g., parts per million) and affects tlie chemistry of tlie catalysis by influencing or being part of tlie catalytic sites. A textural (structural) promoter, on tlie otlier hand, is used in massive amounts and usually plays a role such as stabilization of tlie catalyst, for instance, by reducing tlie tendency of tlie porous material to collapse or sinter and lose internal surface area, which is a mechanism of deactivation. 

As with polyesters, the amidation reaction of acid chlorides may be carried out in solution because of the enhanced reactivity of acid chlorides compared with carboxylic acids. A technique known as interfacial polymerization has been employed for the formation of polyamides and other step-growth polymers, including polyesters, polyurethanes, and polycarbonates. In this method the polymerization is carried out at the interface between two immiscible solutions, one of which contains one of the dissolved reactants, while the second monomer is dissolved in the other. Figure 5.7 shows a polyamide film forming at the interface between an aqueous solution of a diamine layered on a solution of a diacid chloride in an organic solvent. In this form interfacial polymerization is part of the standard repertoire of chemical demonstrations. It is sometimes called the nylon rope trick because of the filament of nylon produced by withdrawing the collapsed film. 

Figure 5.7 Sketch of an interfacial polymerization with the collapsed polymer film being withdrawn from the surface between the immiscible phases. [Redrawn with permission from P. W, Morgan and S. L. Kwolek, J. Chem. Educ. 36 182 (1959) copyright by the American Chemical Society.]...

In the modified chemical vapor deposition (MCVD) technique, the reactants are deposited on the inside of a rotating siUca tube. The hoUow tube is heated from the outside by a moving oxyhydrogen torch. The oxide soot condenses onto the tube walls ahead of the burner, and the soot is then sintered into a glassy layer as the burner passes over it. When deposition is complete, the tube and its contents are collapsed to form a soHd preform rod. 

Lift trucks are available to meet a variety of clearance restrictions. Noteworthy is narrow-aisle equipment. Another accessory worthy of consideration is the multilift mast, which permits lifting loads over 3.7 m (12 ft). Of special importance in specifying any mast is that it will clear the various door openings it must enter, which includes those of trucks, railcars, and buildings. To meet most conditions, the collapsed height of the mast must be 2235 mm (88 in). An ideal lift truck for chemical-plant distribution warehouses would have 2000-kg (4000-lb) capacity electric (battery) propulsion solid-state controls ... 

Foam Breaking It is usually desirable to collapse the overflowing foam. This can be accomphshed by chemical means (Bikerman, op. cit.) if external reflux is not employed or by thermal means [Kishi-moto, Kolloid Z., 192, 66 (1963)] if degradation of the overhead product is not a fac tor. 

FIG. 26-47 Collapse of vessel jacket due to condensation of steam. (Vl- T. Allen, Michigan Engineering, The Dow Chemical Company, Midland, Mich., personal communication. May Z.9SS.)... 

Figure 2.22, HH ROESY diagram of a-pinene (1) with H NMR spectrum [CDCI3, 10% v/v, 25 °C, 500 MHz, section from Sh = 0.84 to 2.34]. Deviations of chemical shifts from those in other experiments (Figs, 2.14, 2.16) arise from solvent effects the methylene protons collapsing in Fig, 2.21 at Sh = 2.19 (200 MHz) display in this experiment an AB system with Sa = 2,17 and Sb = 2.21 (500 MHz)...

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