Solid solution almost amorphous

Measurement of the elemental composition of materials is a relatively mature art. In the natural world there are 92 elements with methods for their quantitative determination generally well established and, in many cases, the subject of internationally accepted standards. However, the physical properties of minerals and materials formed by these elements, and the manner in which they react, is not solely dependant on their chemical composition but on how the constituent elements are arranged that is, their structural form. This finite number of known elements combine into some 230 crystallographic forms with almost infinite variability induced by solid solution, degree of crystallinity, morphology and so on. Therefore, the measurement of the form and amount of the various crystalline and amorphous components is considerably more complex than the measurement of the constituent chemistry. 

The crude acid is dissolved in 500 ml. of petroleum ether at room temperature. The small amount of amorphous solid which may separate is removed by filtration through Supercel, and the filtrate is concentrated under reduced pressure to 300 ml. Chilling to 0-5° yields a first crop of tan crystals which is collected by suction filtration and washed with the minimum amount of ice-cold petroleum ether. Concentration of the mother liquors to 150 ml. and chilling yields a second crop of brownish crystals. The combined crops are dissolved in 300 ml. of petroleum ether, and the light-red solution is chilled to 0-5°. The almost white to light-tan crystals are collected, washed with a small amount of cold petroleum ether, and dried in a vacuum desiccator. There is obtained 51.5—61.5 g. (51-61%) of stearolic acid, m.p. 46-46.5° (Note 5). 

When a solution of thiocyanogen in carbon disulphide is cooled to —70° C., the thiocyanogen is obtained in cruciform aggregates of almost colourless crystals, melting at —2° to —3° C. On warming to ordinary temperatures the thiocyanogen becomes reddish-brown in colour and more viscous finally a brick-red amorphous solid is obtained. Thiocyanogen is very readily soluble in ethyl alcohol and ether, slowly soluble in carbon disulphide and carbon tetrachloride.5... 

The mass fraction of the narrow component that corresponds to the rubbery noncrystalline amorphous phase is as small as 0.003-0.006. The mass fraction does not increase appreciably with increasing temperature, but stays almost unchanged up to 70 °C. Hence, it is concluded that solution-grown samples do not actually comprise a rubbery amorphous phase. This conclusion is confirmed by high-resolution solid-state 13C NMR with more detailed information. 

The diaryl or aryl alkyl tellurides are dense yellow oils or crystalline solids, which are easier to handle than the dialkyl tellurides of similar molecular weight. Some of the diaryl derivatives are almost odorless solids. The same comments are valid for the diorganoditellurides 4, which are dark red oils (aliphatic derivatives) and dark red solids (aromatic derivatives). It is recommended that solutions of tellurides or ditellurides should not be kept in contact with air, since an amorphous white solid will form after some time. For some compounds, this reaction with oxygen is very fast. Aliphatic derivatives are more air sensitive than the aromatic ones. In view of this fact, it is recommended to bubble nitrogen into the solutions while a column or thin-layer chromatographic separation is performed. Evaporation of the solvent, however, minimizes the air oxidation. Pure liquids or solids can be handled in air with no need for special precautions, but prolonged exposure to air and to ambient light should be avoided. 

Figure 15b shows a solid-state spectrum recorded under conditions such that only the mobile portions of the solid PDHS sample are observed. In this polymer (as previously indicated), the mobile portion of the sample consists of the locally disordered phase II and any amorphous material to the extent that it exists. The chemical-shift pattern for the carbons agrees very well with the solution spectrum (Figure 15a). Because carbon resonances are very sensitive to bond conformation (22), this result demonstrates that the phase II portion of the sample has the same average chain conformation as the polymer chains in solution. Although these NMR data permit a comparison of local bond conformations, they do not provide an indication of the more global chain dimensions. Figure 15b shows increased line widths for the carbons near the silicon backbone, with the C-1 resonance almost broadened into the baseline. This broadening reflects the severe restriction of motion near the backbone.

Aqueous albumin solutions are slightly viscous and range in color from almost colorless to amber depending upon the protein concentration. In the solid state, albumin appears as brownish amorphous lumps, scales, or powder. 

Properties White, amorphous solid tasteless odorless. D 1.25-1.31, hygroscopic. Stable when kept dry but deteriorates rapidly when damp. Soluble in dilute alkalies and concentrated acids almost insoluble in water precipitates from weak acid solutions. 

Figure 7,6 shows the solubilities of quartz and amorphous silica in relation to the minerals of Fig. 7.5. The solubilities of substances having the empirical formula SiC>2 or SiC>2 /1H2O have been studied for decades. These studies are much more complicated than they appear, because of the reluctance of soluble silica to reach equilibrium or even metastable equilibrium with its solid phases. Soluble silica tends to polymerize slowly in supersaturated solutions rather than to precipitate cleanly. In addition, the solid phase that precipitates is often amorphous silica instead of the most stable phase, quartz or its close relative chert. Amorphous silica is metastable and much more soluble than quartz. The solubilities of amorphous silica and quartz are often assumed to be the upper and lower limits of silica solubility in soils. Viewed from the range of soil solution compositions shown in Fig. 7.6, silica concentrations caii be less than the equilibrium solubility of quartz even though quartz is almost always present in the sand fraction of soils. The slow kinetics of silica reactions and the slow release of Si(OH)4 during weathering create wide deviations from equilibrium.

As biogenic amorphous silica by mechanisms still unknown, living organisms can remove silica from extremely dilute solutions and deposit solid silica within themselves in precisely controlled structures of intricate design, perfect almost to molecular dimensions (see Chapter 7). 

A new era was inaugurated by the discovery and application of electronic conduction in crystals (Shockley, 1953). The study of charge transport in the many kinds of solid-state materials has grown into a vast field, and numerous books on the electronic properties of solids have appeared. Works on liquid metals and on liquid and amorphous semiconductors complement this field. Compared to these developments, the study of electronic conduction in liquids has received much less attention. Initially, the research was limited almost entirely to liquid ammonia, water, and aqueous solutions. Later, other polar solvents were included. From a fundamental point of view, studies on the conductivity of supercritical metal vapors (high pressures and high temperatures) gave insight into the important phenomenon of the metal/insulator transition. 

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