Subject eutectic

Phosphorus appears to have a beneficial effect on the growth rate. At sub-critical temperatures it helps to stabilise the carbide, while at temperatures up to about 900°C the presence of the hard phosphide eutectic network restricts the deformation to which the much more ductile matrix would otherwise be subject. Since the phosphide eutectic melts at about 950°C, irons containing appreciable amounts of this constituent should clearly not be exposed to this temperature. 

Electrolytic aluminum production is the most important process in both volume and significance. World production is about 15 megatons per year, consuming about 240 billion kilowatthours of electrical energy. Aluminum oxide (alumina), AI2O3, is subjected to electrolysis at a temperature of 950°C to this end it is dissolved in molten cryolite NujAlFg, with which it forms a eutectic melting at about 940°C. Carbon anodes that are anodically oxidized to CO2 in the process are employed. The overall electrolysis reaction can be written as... 

Aircraft turbines in jet engines are usually fabricated from nickel-based alloys, and these are subject to combustion products containing compounds of sulphur, such as S02, and oxides of vanadium. Early studies of the corrosion of pure nickel by a 1 1 mixture of S02 and 02 showed that the rate of attack increased substantially between 922 K and 961 K. The nickel-sulphur phase diagram shows that a eutectic is formed at 910 K, and hence a liquid phase could play a significant role in the process. Microscopic observation of corroded samples showed islands of a separate phase in the nickel oxide formed by oxidation, which were concentrated near the nickel/oxide interface. The islands were shown by electron microprobe analysis to contain between 30 and 40 atom per cent of sulphur, hence suggesting the composition Ni3S2 when the composition of the corroding gas was varied between S02 02 equal to 12 1 to 1 9. The rate of corrosion decreased at temperatures above 922 K. 

Dibenzoylmethane (8b) has been the subject of much interest as regards the possibility that its polymorphism is associated with keto-enol tautomerism. Chemical and spectroscopic studies showed that this is not so (33a). This compound had previously been reported to be trimorphic (33b), but one form appears, in fact, to be a eutectic mixture of the other two. The molecules in these two polymorphs are both in the same state of tautomerism they differ in the torsional angle about the (CH)-(CO) bond and in the type of hydrogen bonding in which they participate. It is noteworthy that solutions prepared from these forms at low temperature have differences in chemical and spectroscopic properties that are maintained for some time. For example, such solutions prepared and held at —35° react at different rates with FeCl3. 

Both 1,1-dinitroethane (26) and 1,1-dinitropropane, and their methylol derivatives, 2,2-dinitropropanol (25) and 2,2-dinitro-l-butanol respectively, have been synthesized via the Ter Meer reaction. - The formal and acetal of 2,2-dinitropropanol in the form of a 1 1 eutectic is an energetic plasticizer and so the synthesis of 2,2-dinitropropanol has been the subject of much investigation. On a pilot plant scale 2,2-dinitropropanol (25) is synthesized in 60 % overall yield from nitroethane (22). Thus, treatment of 1 -chloronitroethane (23) with potassium nitrite... 

Naturally, the fixed composition phase transformations treated in this section can be accompanied by local fluctuations in the composition field. Because of the similarity of Fig. 17.3 to a binary eutectic phase diagram, it is apparent that composition plays a similar role to other order parameters, such as molar volume. Before treating the composition order parameter explicitly for a binary alloy, a preliminary distinction between types of order parameters can be obtained. Order parameters such as composition and molar volume are derived from extensive variables any kinetic equations that apply for them must account for any conservation principles that apply to the extensive variable. Order parameters such as the atomic displacement 77 in a piezoelectric transition, or spin in a magnetic transition, are not subject to any conservation principles. Fundamental differences between conserved and nonconserved order parameters are treated in Sections 17.2 and 18.3. 

Fig. 5.14. Salt precipitation from Soln. C (Table 5.3) subjected to a evaporative drying at 0 °C and b freeze drying to the eutectic at —35.4 °C, and salt precipitation from Soln. E (Table 5.3) subjected to c evaporative drying at 0°C and d freeze drying to the eutectic at —35.4°C. Reprinted from Marion et al. (2003a) with permission...

The liquid eutectic mixtures centrifuged out of both fractions are combined and subjected to a second fractional distillation and crystallization. This process can be repeated as often as appears profitable. 

The DSC, TG curves of solvates and hydrates are related to the phase diagrams between substance and solvent (or water). Eutectic are observed. Fusion or decomposition of the solvate may occur during heating. Therefore, one may observe the melting of the solvate followed by recrystallization into the anhydrous form or the endothermic desolvatation in the solid state. In certain cases both phenomena may over-lapp. Details about experimental factors and examples can be found in Ref. If the anhydrous form is metastable, further phase transitions follow the desolvatation. If several solvates or hydrates exist, the transitions observed depend on the pressure, as demonstrated by Soustelle in the case of copper sulfate pentahydrate. Depending on the pressure, the direct dehydration into the anhydrous or the dehydration via the monohydrate, or the three dehydration steps trihydrate, monohydrate and anhydrous forms may be obtained. Hydrates have been the subject of... 

Cost and biodegradabiUty have also been major concerns, and new families of ILs derived from renewable feedstock or from low-cost starting materials have beat described. These Bio-ILs are entirely composed of biomaterials [183]. An example to be cited is the development of the deep eutectic mixtures liquid systems based on choline chloride [ 184] for which the qualification of ILs is stiU the subject of controversies. Choline can be used as alternative cation in combination with suitable anion to generate ILs. The biodegradable properties of these ILs have been reported [185]. 

Depending on the physical behaviour and stability of the bioactive component, both amorphous and eutectic systems can be successfully freeze-dried but require different approaches. The most difficult cases are those that exhibit partial crystallisation, which may lead to uncontrollable intrabatch variability. Irrespective of the physical state of the system, maximum temperatures for ice sublimation (7/. or T can be identified. Above these temperatures, ice will melt at an appreciable rate, thus diluting the solution phase. The product may then exhibit mechanical collapse, and most probably it will also become subject to chemical changes (usually deterioration). 

In a eutectic system, the whole composition or just the excipient may be subject to crystallisation, but this process takes time to reach completion. It may be much longer than the time taken to freeze the product to the desired temperature (Tg). After primary drying (ice sublimation), only solid solutes remain. The mixture may then be carefully warmed to its final storage temperature. The residual solid will not necessarily be anhydrous and may, for example, contain water of crystallisation. In addition, as the temperature is raised, the crystalline product may undergo solid-solid transitions, i.e. over a period of time, a different polymorph may become the preferred crystal habit. In a completely crystalline preparation, the maximum safe storage temperature will be governed by the component with the lowest melting point. 

A typical pharmaceutical formulation will serve as model, frozen aqueous solutions that are contained in loosely stoppered glass vials. They stand directly on the freeze-drier shelves. Such a model appears deceptively simple but is in fact subject to considerable complexities that bedevil the modelling of optimum processing conditions and the estimation of a realistic drying cycle time. As emphasised in earlier chapters, for the case where the product does not display eutectic behaviour, it is imperative to freeze the solution to below Tg, in order to ensure maximal freeze-concentration and minimise deleterious chemical reactions that have been shown to occur at high rates in part frozen, supersaturated mixtures.By the same token, the temperature during the removal of ice by sublimation must on no account be allowed to rise above T at... 

Because of the low eutectic temp of Trimonite (45.7—49°), it is subject to exudation when stored at elevated temps. It is IcSS S6nsitiv0 to initiation than PA, and is of interest only as an emergency substitute for TNT compns Mixts ranging in PA content from 70 to 90%, and a-Mononitronaphthalene content from 10 to 30% were evaluated color, light cream yel d (cast) about 1.60g/cc mp 90 to 105° ballistic strength, 74 to 94% TNT brisance, 32 to 40.5g sand crushed expln temp, 300 to 315° vel of deton, 5000 to 7020m/sec impact sensitivity (PicArsn app, 2-kg wt), 10 to 15.5" rifle bullet sensitivity, 0 to 10% detonations with. 30-cal bullets fired from 90 stability and solubility in solvents—same as PA... 

Figure 4.7 shows the hardness of natural air-cooled and thermal-treated Pb—Sb alloys as a function of antimony content [3]. Alloy hardness increases with increase of the eutectic/Pb solid—solution ratio. Low-antimony grids have been subjected to different thermal treatments in an effort to improve their hardness. 

Figure 3a shows the microstructure of the initial parent metal the structure of d-phase inclusions (CuAh intermetallic compound-based solid solution) is shown in Fig. 3b. As a result of the welding heat effect, most of the inclusions of the intermetallic phase in the HAZ were subjected to partial local melting and were converted into clusters and interlayers of eutectics (Figs. 3c, 3d, 4a, and 4b), while others changed shape only slightly. This is probably explained by the fact that in the condition of nonequilibrium primary solidification, they had a composition considerably different from that prescribed by the equilibrium diagram [%...

NaK (pronounced nack), as the eutectic is called, as well as the alkali metals in general, have found new interest as heat dissipating and heat transfer agents in nuclear reactors and in motor valve stems of internal combustion engines. These uses have led to a sp ecial series of articles in the literature on the subject of handling these substances and their properties. - ... 

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