Solid state reactivity

So, for given strain rate s and v (a function of the applied shear stress in the shock front), the rate of mixing that occurs is enhanced by the factor djhy due to strain localization and thermal trapping. This effect is in addition to the greater local temperatures achieved in the shear band (Fig. 7.14). Thus we see in a qualitative way how micromechanical defects can enhance solid-state reactivity. 

The galvanic cell studied (shown in Fig. 5.24) utilizes a highly porous solid electrolyte that is a eutectic composition of LiCl and KCl. This eutectic has a melt temperature of 352 °C and has been carefully studied in prior electrochemical studies. Such solid electrolytes are typical of thermal battery technology in which galvanic cells are inert until the electrolyte is melted. In the present case, shock compression activates the electrolyte by enhanced solid state reactivity and melting. The temperature resulting from the shock compression is controlled by experiments at various electrolyte densities, which were varied from 65% to 12.5% of solid density. The lower densities were achieved by use of microballoons which add little mass to the system but greatly decrease the density. 

In solid state chemistry the limited atomic mobility in the solid state controls chemical changes and leads to explicit consideration of the relative location of potential reactants (the configuration) and solid state reactivity as controlled by solid state defects. The same factors dominate shock-induced solid state chemistry. 

As shown in Chap. 7, shock compression introduces large numbers of defects which in turn cause substantial increases in solid state reactivity. Such shock activation is obviously critical to the process. One of the most direct effects of the mechanical deformation is the removal of oxides or other surface films from the surfaces of the powders. It is well recognized that such surface films can greatly inhibit chemical reaction. The very large mechanical deformation would be expected to substantially damage, if not completely remove, such films. Other manifestations of shock activation are shown in the next chapter. Effects have been shown that represent many orders of magnitude of change in solid state reactivity. 

Shock Modification and Shock Activation Enhanced Solid State Reactivity... 

In this chapter shock modification of powders (their specific area, x-ray diffraction lines, and point defects) measurements via analytical electron microscopy, magnetization and Mossbauer spectroscopy shock activation of catalysis, solution, solid-state chemical reactions, sintering, and structural transformations enhanced solid-state reactivity. 

The measures of solid state reactivity to be described include experiments on solid-gas, solid-liquid, and solid-solid chemical reaction, solid-solid structural transitions, and hot pressing-sintering in the solid state. These conditions are achieved in catalytic activity measurements of rutile and zinc oxide, in studies of the dissolution of silicon nitride and rutile, the reaction of lead oxide and zirconia to form lead zirconate, the monoclinic to tetragonal transformation in zirconia, the theta-to-alpha transformation in alumina, and the hot pressing of aluminum nitride and aluminum oxide. 

The various studies of shock-modified powders provide clear indications of the principal characteristics of shock modification. The picture is one in which the powders have been extensively plastically deformed and defect levels are extraordinarily large. The extreme nature of the plastic deformation in these brittle materials is clearly evident in the optical microscopy of spherical alumina [85B01]. In these defect states their solid state reactivities would be expected to achieve values as large as possible in their particular morphologies greatly enhanced solid state reactivity is to be expected. 

Fig. 7.10. The solid state reactivity of shock-modified zirconia with lead oxide as studied with differential thermal analysis (DTA) shows both a reduction in onset temperature and apparent increase in reaction rate. The shock-modified material has a behavior much like the much higher specific surface powder shown in B (after Hankey et al. [82H01]).

The possibility of predicting solid state reactivity from calculated thermochemical data was first addressed with ketodiesters 65a-e, which were substituted with methyl groups to vary the extent of the RSE in the radicals 65-BRl - 65-BR3 involved along the photodecarbonylation pathway (Scheme 7.19). " All ketones reacted in solution to give complex product mixtures from radical combination (66a-e) and disproportionation processes. Calculations revealed RSEs of 8.9 kcal/mol, 15.1 kcal/mol, and 19.8 kcal/mol for radicals 65-BRl (primary enol radical), 65-BR2 (secondary enol radical), and 65-BR3 (tertiary enol radical), respectively. In the... 

Feltz, A. Martin, A. (1987) Solid-state reactivity and mechanisms in oxide systems. 11 Inhibition of zinc ferrite formation in zinc oxide - a-iron(lll) oxide mixtures with a large excess of a-iron(lll) oxide. In Schwab, G.M. (ed.) Reactivity of solids. Elsevier, 2 307—313 Fendorf, S. Fendorf, M. (1996) Sorption mechanisms of lanthanum on oxide minerals. Clays Clay Miner. 44 220-227 Fendorf, S.E. Sparks, D.L. (1996) X-ray absorption fine structure spectroscopy. In Methods of Soil Analysis. Part 3 Chemical Methods. Soil Sd. Soc. Am., 377-416 Fendorf, S.E. Eick, M.J. Grossl, P. Sparks, D.L. (1997) Arsenate and chromate retention mechanisms on goethite. 1. Surface structure. Environ. Sci. Techn. 31 315-320 Fendorf, S.E. Li,V. Gunter, M.E. (1996) Micromorphologies and stabilities of chromiu-m(III) surface precipitates elucidated by scanning force microscopy. Soil Sci. Soc. Am. J. 60 99-106... 

The interplay of crystal packing, migrational aptitudes, and solid-state reactivity maybe demonstrated with the reactivities of the Diels-Alder cycloadducts of maleic anhydride and cyclopentadiene (1 and 2) or cyclohexadiene (3). 

The solid-state reactivity of the carboxylic function was demonstrated with oxalic acid dihydrate (346) and o-phenylenediamine (46a) (Scheme 54). A 100% yield of quinoxalinedione (347) is easily obtained upon cogrinding of the components and heating of the high-melting salt thus formed in a vacuum to 150 °C for 8 h, to 180 °C for 30 min, or to 210-220 °C for 10 min [104]. Compound 347 is ready for further interesting condensation reactions [104]. 

Various crystalline states of cysteine, cysteine hydrochloride, and cysteine hydrochloride hydrate have been tested for solid-state reactivity. Thus, (R)-352 and (i )-352-HCl-H20 were also reactive in the solid-state. This was verified by quantitative solid-solid reactions with paraformaldehyde (354) in stoichiometric ball-milling experiments at room temperature giving 100% yield of R)-355 [12] or (J )-355-HCl [10] after drying. 

Garcia-Garibay M (2003) Engineering carbene rearrangements in crystals from molecular information to solid-state reactivity. Acc Chem Res 36 491-498... 

With an emerging correlation between the solid-state reactivity and the radical stabilizing energy (RSE) of the a-substituents, Campos et al. suggested that solid-state reactivity may be predictable from the RSE values of the substituents [71]. Taking the reaction of acetone as a reference, and assuming that reactions in crystals must be thermoneutral or exothermic, these authors suggested that substituents with RSE 11 kcal mol 1 on both a-carbons should make the reaction thermodynamically possible. As indicated in Scheme 2.41, the proposed RSE value derives from the... 

Wang and Jones have investigated the solid-state reactivity of the series of acridizinium salts shown in Scheme 21 [116]. Many of these undergo single crystal-to-single crystal dimerization when irradiated and can thus be monitored by x-ray... 

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