Phase two-layer

Three-phase two-layer foam stabilized quick-breaking... 

Fig. 6.3-25 Evoluted (straightened) diagram of a rotary double-layer punch-and-die press (courtesy Fette, Schwarzenbek, Germany) Fig. 6.3-26 Two-phase (two-layer) water softening product for European automatic washing machines (Calgon is a registered trade mark of Benckiser, Ludwigshafen/Rh., Germany)...

However, to illustrate the polar direction which is either parallel or antiparallel to the bend direction, green direction symbols are incorporated into the middle of bent-core symbolic drawings. For example, in the orthogonal polar smectic phases (SmAP) phases, two-layer structures with six symbolic illustrations are possible depending on the polar direction with respect to the bend direction in adjacent layers (Fig. 6.5). 

A first approach to testing, ASTM D 1094, is to create, using a potassium phosphate reagent, a separation between two layers, hydrocarbon and aqueous. The degree of separation of the two phases is estimated by attributing a grade from 1 to 3 and the appearance of the interface by five levels of observation 1, lb, 2, 3, and 4. The specifications establish both the quality of separation (2 is the maximum) and the appearance of the interface (lb maximum). 

Many pairs of partially miscible liquids possess neither a lower nor an upper C.S.T. for reasons outlined in the previous paragraph. Thus consider the two liquid phases from the two components water and diethyl ether. Upon cooling the system at constant pressure, a point will be reached when a third phase, ice, will form, thus rendering the production of a lower C.S.T. impossible, likewise, if the temperature of the two layers is raised, the critical point for the ether rich layer will be reached while the two liquid phases have different compositions. Above the critical point the ether-rich layer will be converted into vapour, and hence the system will be convert into a water rich liquid and an ether rich vapour the upper C.S.T. cannot therefore be attained. 

In a simple liquid-liquid extraction the solute is partitioned between two immiscible phases. In most cases one of the phases is aqueous, and the other phase is an organic solvent such as diethyl ether or chloroform. Because the phases are immiscible, they form two layers, with the denser phase on the bottom. The solute is initially present in one phase, but after extraction it is present in both phases. The efficiency of a liquid-liquid extraction is determined by the equilibrium constant for the solute s partitioning between the two phases. Extraction efficiency is also influenced by any secondary reactions involving the solute. Examples of secondary reactions include acid-base and complexation equilibria. 

In Figure 1, the pairs (or triad) of phases that form ia the various multiphase regions of the diagram are illustrated by the corresponding test-tube samples. Except ia rare cases, the densities of oleic phases are less than the densities of conjugate microemulsions and the densities of microemulsions are less than the densities of conjugate aqueous phases. Thus, for samples whose compositions He within the oleic phase-microemulsion biaodal, the upper phase (ie, layer) is an oleic phase and the lower layer is a microemulsion. For compositions within the aqueous phase-microemulsion biaodal, the upper layer is a microemulsion and the lower layer is an aqueous phase. When a sample forms two layers, but the amphiphile concentration is too low for formation of a middle phase, neither layer is a microemulsion. Instead the upper layer is an oleic phase ("oil") and the lower layer is an aqueous phase ("water"). 

The existence of tridymite as a distinct phase of pure crystalline siUca has been questioned (42,58—63). According to this view, the only tme crystalline phases of pure siUca at atmospheric pressure are quart2 and a highly ordered three-layer cristobaUte having a transition temperature variously estimated from 806 250°C to about 1050°C (50,60). Tridymites are considered to be defect stmctures in which two-layer sequences predominate. The stabihty of tridymite as found in natural samples and in fired siUca bricks has been attributed to the presence of foreign ions. This view is, however, disputed by those who cite evidence of the formation of tridymite from very pure siUcon and water and of the conversion of tridymite M, but not tridymite S, to cristobahte below 1470°C (47). It has been suggested that the phase relations of siUca are deterrnined by the purity of the system (42), and that tridymite is not a tme form of pure siUca but rather a soHd solution of minerali2er and siUca (63). However, the assumption of the existence of tridymite phases is well estabUshed in the technical Hterature pertinent to practical work. 

When two layers of the substance are displaced relative to one another, the nuclei of phase A, located between them, can be regarded as kind of a roller about which oscillations are executed. - - - when the two layers of phase AB are displaced relative to one another, they transport past the nucleus, in its immediate vicinity, a multiplicity of atoms of both kinds. - - - it follows that all the atoms A passing in the immediate vicinity of the nucieus have sufficient time to combine with the latter and this in fact may be the mechanism of the growth of the nuclei of the new phase. ... 

Typically, the first phase of a comprehensive accident investigation process will involve describing the way in which the hardware, the chemical process, individual operators and operating teams are involved in the accident process. This is the domain of the structural analysis techniques and the technical analysis of the chemical process which gave rise to the accident. Analyses of human error will primarily address the interactions between hardware systems and individuals or operating teams (the first two layers... 

To 10 g of cyclohexane-1,4-oxide is added 48% aqueous hydrobromic acid (60 g). The phases are mixed thoroughly and allowed to stand at room temperature until the solution separates into two layers (usually 5 days). The mixture is saturated with sodium chloride and extracted twice with 25-ml portions of ether. The ether layer is washed with an equal volume of saturated sodium bicarbonate solution, then with the same amount of water. Finally, the ether solution is dried over anhydrous sodium sulfate, the ether is evaporated, and the residue is allowed to cool, whereupon crystallization should follow. The crude product may be recrystallized from petroleum ether giving material of mp 81-82° (yield, 11 g). 

So long as two layers are jar sent in contact with vapour, the composition of each is, at a specified temperature and pressure, independent, of the absolute or relative amounts of the layers. Further addition of either component therefore leads to the growth of one phase at the expense of the other, but the concentration of each remains unchanged. 

As an example, consider the following. Suppose we have a crucible half-filled with a powder. We now fill the crucible with another powder of different composition and then heat the filled crucible. Any solid state reaction which does occur can only do so at the boundary of the two layers of powders. If the reaction is A -t- B = AB, then we find that the reaction product, which is also a solid, forms as a phase boundary between the two layers. The same condition exists in a solid state reaction between two crystalline particles having differing compositions. That is, they can only react at the interface of each particle. This is illustrated in the following diagram, which is a model of how the components react through a phase boundary ... 

The existence of Galvani potentials between two different conducting phases is connected with the formation of an electric double layer (EDL) at the phase boundary (i.e., of two parallel layers of charges with opposite signs, each on the surface of one of the contacting phases). It is a special feature of such an EDL that the two layers forming the double layer are a very small (molecular) distance apart, between 0.1 and 0.4nm. For this reason EDL capacitances are very high (i.e., tenths of pF/cm ). 

The liquid-phase hydration of cyclohexene is carried out by a Japanese company with a slurry of zeolite ZSM-5 as the catalyst. Here, the product separates into two layers and cyclohexano leaves in the organic cyclohexene phase and the catalyst stays in the aqueous phase, which is recycled. The two-phase strategy, therefore, has special significance in this case. A recent publication by Ogawa et al. (1998a) gives some details of this system. 

---