Solids removal theory mechanisms

Detergency is about the theory and practice of the removal of foreign material from solids by surface-active substances. This definition excludes pure mechanical cleaning. Also a pure chemical cleaning, e.g., by solvation of the foreign material, is not considered. In textiles oily substances usually attach to the fibres (animal fats, fatty acids, hydrocarbons, etc.). Also dust, soot, and other solid particles have to be removed in a washing process. In order to test the effectiveness of a surfactant, textiles are often polluted with standard dirt mixtures and cleaned with a standard washing procedure (launderometer). Often cleanliness is measured on the basis of optical reflectivity of white textiles. 

Surprisingly, we found that the reaction of an alcohol with 1-chloroethyl-N,N-dialkylcarbamates can proceed through B mechanism to give alkylation rather than acylation (Ref. 195). This result appears to be a violation of the HSAB theory. In a typical example, N-(1-chloroethyloxy-carbonyl) piperidine was added to a stirred mixture of sodium hydrocarbonate and methanol at 25°C. The reaction was instantaneous. Solids were removed by filtration, excess alcohol was then distilled off and the resulting product was isolated by flash chromatography in 96% yield [Scheme 139]. 

In summary, drying rate data do not ordinarily provide sufficient information to distinguish the mechanisms involved in moisture removal. Further, the mechanisms will usually change as drying proceeds. Drying rate data have been analyzed mathematically on the basis of particular mechanisms for moisture movement through the solid. The complex nature of the moisture movement process, however, makes it impossible to attach any fundamental significance to rate constants obtained from such analysis. The fact that experimental data do not conflict with a theory does not prove its validity. 

Lead ores, poor in silver, are first concentrated by flotation. Lead is then produced by roasting and reduction. The content of silver in the lead metal is low. A metallurgical concentration occurs by the so-called Pattinson process (pattinsonizing). The method relies on the fact that silver-lead alloys have a eutectic composition with a silver content of 2.7%, see Figure 6.4. A melt of an alloy with a silver content lower than 2.7% is allowed to solidify slowly. The solid lead formed is gradually removed mechanically and the silver content of the melt increases. In theory a residual alloy with 2.7% Ag can be obtained. In practice it is possible to obtain at least 2% silver. Lead and silver can be separated from this residual alloy by the cupeUation process. 

Until recently the main factor in the breakdown of solids was considered to be the mechanical load. However, the dilaton theory of strength which has appeared in the past decade has altered these concepts radically. From this point of view, the mechanical load plays only the role of supplier of the energy pumped into the dilaton and causing thermal expansion of the bonds up to their breakdown. Thus, the difference between mechanical and other forms of breakdown of solids is removed. The heat ageing of a vulcanisate is one of the most common causes of failure of structural elements manufactured from it. In the general case the heat ageing of a material can be described by a first-order reaction. 8 refs. 

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