Phase diagram reaction

Needs of the industrial technologies called for extensive studies and measurement of the physicochemical properties of halides and oxohalides their thermodynamic characteristics, phase diagrams, reactions, complexing in gases and so forth. After two decades of growth, the intensity of these works waned today, such studies are scarce, though the properties of a number of compounds are still known with low accuracy. 

Decomposition reactions Phase diagrams Reaction kinetics Solid-state reactions Dehydration reactions Radiation damage Catalysis... 

Binary Alloys. Aluminum-rich binary phase diagrams show tliree types of reaction between liquid alloy, aluminum solid solution, and otlier phases eutectic, peritectic, and monotectic. Table 16 gives representative data for reactions in tlie systems Al—Al. Diagrams are shown in Figures 10—19. Compilations of phase diagrams may be found in reference 41. 

Ternary Alloys. Almost ah commercial ahoys are of ternary or higher complexity. Ahoy type is defined by the nature of the principal ahoying additions, and phase reactions in several classes of ahoys can be described by reference to ternary phase diagrams. Minor ahoying additions may have a powerflil influence on properties of the product because of the influence on the morphology and distribution of constituents, dispersoids, and precipitates. Phase diagrams, which represent equhibrium, may not be indicative of these effects. 

Phase diagrams can be used to predict the reactions between refractories and various soHd, Hquid, and gaseous reactants. These diagrams are derived from phase equiHbria of relatively simple pure compounds. Real systems, however, are highly complex and may contain a large number of minor impurities that significantly affect equiHbria. Moreover, equiHbrium between the reacting phases in real refractory systems may not be reached in actual service conditions. In fact, the successful performance of a refractory may rely on the existence of nonequilibrium conditions, eg, environment (15—19). 

Reactions Between Refractories. In Table 17, the compatibilities of various refractories are given over a range of temperatures. Dissimilar refractories can react vigorously with each other at high temperatures. Phase diagrams are an excellent source of information concerning the reactivity between refractories. 

Chemithon secured patents on a somewhat similar oleum-type continuous sulfonation and sulfation process (259,260). So-called dominant bath sulfonation processes function well because they appear to operate ia or near the homogeneous area of the phase diagram (1) and heat removal is readily controllable with relatively small iacremental reaction. 

The copper-antimony phase diagram contains two eutectic reactions and one eutectoid reaction. For each reaction ... 

The cloudiness of ordinary ice cubes is caused by thousands of tiny air bubbles. Air dissolves in water, and tap water at 10°C can - and usually does - contain 0.0030 wt% of air. In order to follow what this air does when we make an ice cube, we need to look at the phase diagram for the HjO-air system (Fig. 4.9). As we cool our liquid solution of water -i- air the first change takes place at about -0.002°C when the composition line hits the liquidus line. At this temperature ice crystals will begin to form and, as the temperature is lowered still further, they will grow. By the time we reach the eutectic three-phase horizontal at -0.0024°C we will have 20 wt% ice (called primary ice) in our two-phase mixture, leaving 80 wt% liquid (Fig. 4.9). This liquid will contain the maximum possible amount of dissolved air (0.0038 wt%). As latent heat of freezing is removed at -0.0024°C the three-phase eutectic reaction of... 

We can find a good example of this diffusion-controlled growth in plain carbon steels. As we saw in the "Teaching Yourself Phase Diagrams" course, when steel is cooled below 723°C there is a driving force for the eutectoid reaction of... 

To make martensite in pure iron it has to be cooled very fast at about 10 °C s h Metals can only be cooled at such large rates if they are in the form of thin foils. How, then, can martensite be made in sizeable pieces of 0.8% carbon steel As we saw in the "Teaching Yourself Phase Diagrams" course, a 0.8% carbon steel is a "eutectoid" steel when it is cooled relatively slowly it transforms by diffusion into pearlite (the eutectoid mixture of a + FejC). The eutectoid reaction can only start when the steel has been cooled below 723°C. The nose of the C-curve occurs at = 525°C (Fig. 8.11), about 175°C lower than the nose temperature of perhaps 700°C for pure iron (Fig. 8.5). Diffusion is much slower at 525°C than it is at 700°C. As a result, a cooling rate of 200°C s misses the nose of the 1% curve and produces martensite. 

Not all alloys in the lead-tin system show a eutectic pure lead, for example, does not. Examine the Pb-Sn phase diagram and list the composition range for which a eutectic reaction is possible. 

The copper-zinc system (which includes brasses) has one eutectoid reaction. Mark the eutectoid point on the phase diagram (Fig. A 1.38). 

Many phase diagrams show another feature. It looks like an upside-down V (i.e. a A) touching a horizontal line. It is a peritectic reaction, and the tip of the A is a peritectic point (see Fig. A1.43). 

Figure A 1.52 shows the Ti-Al phase diagram (important for the standard commercial alloy Ti-6% Al-4% V. It shows two peritectic reactions, at each of which liquid reacts with a solid phase to give an intermetallic compound, (a) Ring the peritectics and give the (approximate) chemical formula for the two compounds, (b) Shade all... 

The potential dependence of the velocity of an electrochemical phase boundary reaction is represented by a current-potential curve I(U). It is convenient to relate such curves to the geometric electrode surface area S, i.e., to present them as current-density-potential curves J(U). The determination of such curves is represented schematically in Fig. 2-3. A current is conducted to the counterelectrode Ej in the electrolyte by means of an external circuit (voltage source Uq, ammeter, resistances R and R") and via the electrode E, to be measured, back to the external circuit. In the diagram, the current indicated (0) is positive. The potential of E, is measured with a high-resistance voltmeter as the voltage difference of electrodes El and E2. To accomplish this, the reference electrode, E2, must be equipped with a Haber-Luggin capillary whose probe end must be brought as close as possible to... 

Vanadium-Sodium Compounds Most Corrosive. Physical property data for vanadates, phase diagrams, laboratory experiments, and numerous field investigations have shown that the sodium vanadates are the lowest melting compounds and are the most corrosive to metals and refractories. These compounds are thought to form by either the vapor phase reaction of NaCI and V2O5 or by the combination of fine droplets of these materials upon the cooler parts of combustion equipment. 

Many other parepistemes were stimulated by the new habits of precision in theory. Two important ones are the entropic theory of rubberlike elasticity in polymers, which again reached a degree of maturity in the middle of the century (Treloar 1951), and the calculation of phase diagrams (CALPHAD) on the basis of measurements of thermochemical quantities (heats of reaction, activity coefficients, etc.) here the first serious attempt, for the Ni-Cr Cu system, was done in the Netherlands by Meijering (1957). The early history of CALPHAD has recently been... 

The phase diagram of the MM model is quite simple for I"a< — 1/2 (7a > 7]a) the catalyst becomes poisoned by A (B) species, respectively. Thus one has a first-order IPT where 7ia = 1/2 is a trivial critical point given by the stoichiometry of the reaction. In contrast to the ZGB model. 

Cast irons, although common, are in fact quite complex alloys. The iron-carbon phase diagram exhibits a eutectic reaction at 1 420 K and 4-3 wt.<7oC see Fig. 20.44). One product of this eutectic reaction is always austenite however, depending on the cooling rate and the composition of the alloy, the other product may be cementite or graphite. The graphite may be in the form of flakes which are all interconnected (although they appear separate on a... 

By way of example, the Cu-Zn phase diagram shown in Fig. 20.42 exhibits a number of different intermediate phases (j8, 7, 6, etc.) and a number of peritectic reactions and a eutectoid reaction. In many instances it is not necessary to consider a complete phase diagram. Thus Fig. 20.43 illustrates the Al-rich end of the Al-Cu phase diagram and is used below in a discussion... 

Because of the great practical importance of steels it is necessary to discuss the Fe-C system in rather more detail. The Fe-FejC phase diagram consists of the following three reactions... 

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