Mixed-crystal formation

Several pairs of isomorphous diolefin compounds have been reported to form photoreactive mixed crystals, whereas formation of the mixed crystal, comprising two olefin compounds which are not isomorphous to each other, is rare. 

Induced precipitation is a collective name for processes accompanying the formation of solid phase, such as occlusion, adsorption, compound formation, formation of isomorphous mixtures, mixed crystals, colloidal solutions, etc. In... 

The potassium/caesium phase diagram is an example of a system involving the formation of mixed crystals with a temperature minimum (Fig. 4.4). The right and left halves of the diagram are of the same type as the diagram for antimony/bismuth. The minimum corresponds to a special point for which the compositions of the solid and the liquid are the same. Other systems can have the special point at a temperature maximum. 

Limited formation of mixed crystals occurs when the two components have different structures, as for example in the case of indium and cadmium. Mixed crystals containing much indium and little cadmium have the structure of indium, while those containing little indium and much cadmium have the cadmium structure. At intermediate compositions a gap is observed, i.e. there are no homogeneous mixed crystals, but instead a mixture of crystals rich in indium and crystals rich in cadmium is formed. This situation can even... 

Plaster of Paris has long been used as a casting material, a cement, and a mortar. If mixed with water, plaster of Paris forms a very soft and pliable mixture. After a very short time, lasting only 5-8 minutes, the wet, pliable mixture sets, that is, it hardens into a stable, firm solid. The setting process entails the incorporation of water molecules (a process known as hydration) into the calcium sulfate hemihydrate and the consequent formation and crystallization of hydrated sulfate of calcium. In other words, when water is added to plaster of Paris, the two combine, again forming gypsum, which soon crystallizes into a hard solid mass ... 

Theoretical (dotted line) and experimental (continuous line) titration curves for such a mixture are shown in Figure 6.8(b). The formation of mixed crystals and solid solutions limits the accuracy to 1-2% when the halides are present in similar concentrations. 

Another phenomenon to be detected by X-ray crystallography is the formation of mixed crystals, as observed in the mixed coupling of azo pigments or the solid solutions of quinacridone pigments. A change in the angles of the reflected X-rays of a mixed crystal indicates a transition from one crystal phase to another. If, how-... 

The specific influence of the rosin is suggested to happen due to an increased solubility of the sodium compound by micellization and to the formation of less stable mixed crystal-type lakes [2],... 

Quinacridone quinone itself (Sec. 3.2.1.6) is a tinctorially relatively weak yellow compound with poor lightfastness. Formation of mixed crystal phases with other quinacridones (Sec. 3.2.2) as well as treatment with various metal salts [25] leads to an improvement of light- and weatherfastness. Oxidation of dihy-droquinacridone with less than molar amounts of chromate affords a quin-acridone/quinacridone quinone mixed phase which offers an interesting shade of gold. 

Cesium salts of these compounds crystallize in the /3-K2SO4 form with statistical orientation of the anions. Therefore, one observes no splitting of the degenerate vibrations (see Table 23) similar to anions with C3 S5mimetry such as KCrOsF and KOsOaN (164). The structures of these compounds are discussed in Ref. (160). Due to the method of preparation, the solubilities and the nature of the structure, i. e. the possibility of mixed crystal formation, the r-values are not exactly integers (165). 

In order to act as a catalyst, a given substance has to bear its specific affinities on the reacting molecules. Obviously, a modification of the field of force of these specific affinities can be achieved by the presence of additional components in a catalyst, either via a combination of the affinities of both components at phase boundaries, or via a gradual change of the affinities of the main catalyst due to the formation of solid solutions, alloys, or mixed crystals with the accessory component. 

M. lijima, H. Tohda, Y. Moriwaki, Growth and structure of lamellar mixed crystals of octacalcium phosphate and apatite in model system of enamel formation, J. Cryst. Growth 116 (1992) 319-326. 

The formation of barrier layers at point contacts of organic crystals. Example arrays of silver/phthalocyanine mixed crystal/Al point contacts with a forward/backward current ratio of 3000 1 can rectify alternating currents up to 104 Hz 124> see Fig. 10. 

Radical formation in a mixed crystal system of cytosine monohydrate doped with small amounts of thiocytosine (ca. 0.5%) was investigated on order to gain insight into hole transfer in a well-defined crystalline system.31 Also of interest was whether the protonation state of the thiocytosine radical(s) was the same as that of the cystosine radical(s). Crystals were X-irradiated (ca. 30 kGy) and ESR and ENDOR spectra recorded at ca. 15 K. After irradiation, many types of free radicals were formed. Among these, the low field resonance from a sulfur centered radical (42), with g-tensor (2.132, 2.004, 2.002), was clearly visible. Radical 42 constituted approximately 10% of the total cohort of radicals formed in the crystal and is apparently the only sulfur-centred radical observed in this experiment. Six weakly coupled protons were observed, two of which are shown... 

In an important Memoire sur les sels neutres, published in 1754, 6. P. Rouelle 1 was the first to comment on the formation of crystals of alkali bisulphate, or the alkali hydrogen or acid sulphate by the action of sulphuric acid on the neutral sulphate. He emphasized the fact that sels acides, as distinguished from sels neutres, are formed by the action of a superabundance of acid on the base, the excess of acid is not simply mixed with the neutral salt, but is chemically combined and that in une juste quantile, otherwise expressed in a fixed and definite proportion. The affinity of the alkali for the acid is not completely exhausted, so to speak, by the formation of the acid salt. 

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