Exothermic Mixture

Minimum impact energies to initiate the explosion of various exothermic mixtures, used for the continuous casting of steel, were determined. Components used included sodium nitrate, aluminium-iron scale, silicocalcium, ferrosilicon fluorspar, borax, etc. Hazardous mixtures were defined, and improved safety controls were derived. 

Burning time and equivalent heat of exothermic mixtures 2 B360... 

As discussed earlier, aluminides have been used as binders for carbide- and boride-based cermets, for example, by adding Ni and Al powders to exothermic mixtures of Ti with C or B. On the other hand, some intermetallic compounds (e.g., NiAl, Ni3Al, TiAl) possess high enough heats of formation so that composites with intermetallic matrices can be produced either in the VCS or SHS regimes. The ceramic components are added either in the green mixture or synthesized in situ during the reaction. 

In fact it is uncommon for the curvature of the relation between heat content and composition to change sign, and we shall limit the present discussion to curves such as (1) and (2). In the first case the heat content of the mixture is greater than that of the same quantities of the pure substances taken separately, given by the straight line joining h and The mixture will therefore be formed from the pure components with an absorption of heat (endothermic mixture). On the other hand, in the case of curve (2) the mixture is formed with evolution of heat (exothermic mixture). 

We conclude therefore that an upper consolute temperature can occur only with endothermic mixtures while lower consolute temperatures are limited to exothermic mixtures. These predictions have been verified in all cases which have been studied. ... 

For endothermic mixtures (i.e., mixtures absorbing heat during mixing), AfZ jjx and Xab are positive. Such mixtures therefore exhibit positive deviations from Raoult s law. Similarly, exothermic mixtures with negative values of AH j and X, must have negative deviations from Raoult s law. 

An exothermic mixture usually leads to mixing in all proportions. This is the case for water and ethanol. If the mixing is endothermic, the number of coexisting phases and their composition depend on temperature. Increasing the temperature usually results in an increase in the mutual solubility of the two compounds, eventually leading to complete miscibility above a critical temperature, the upper consolute temperature (UCT). Note that some abnormal systems can also have a lower consolute temperature (LCT). Both UCT and LCT are thermodynamic critical points. At a critical point, the compositions of the two phases in equilibrium become identical. 

Shafirovich, E., Mukasyan, A., Varma, A., Kshirsagar, G., Zhang, Y. Cannon, J. 2002. Mechanism of combustion in low-exothermic mixtures of sodium chlorate and metal fuel. Combustion and flame, 128, 133-144. 

Compatibility in the polymer blends is defined by either miscibility on the molecular scale or absence of gross symptoms of phase separation. This definition is phenomenological and empirical but no unanimous theoretical scheme for predicting compatibility has been established. Thermodynamics predicts that exothermic mixtures satisfying Equation 5 would spontaneously mix,... 

Fig. 12d shows a particular case of the type 2b. Here the mixture shows ideal behaviour at great dilution of the non-volatile component, whereas at low concentrations of the volatile component the behaviour of an exothermic mixture is clearly demonstrated. Such an S-shaped curve is e. g., observed in the system sulphuric acid-water, where the formation of strongly exothermic compounds (hydrates) of the acid is known to exist. The occurrence of such specific chemical binding forces will always tend to result in a vapour tension curve which is concave to the pressure axis in the region where compound formation dominates the process of mixing. It would seem that in this case the mixing of the hydrates with further amounts of water is a less thermally positive or even a thermally neutral process. 

Figure 1.5. Concentration dependence of the chemical potential of mixing Ap,f RT (a), the molar Gibbs potential of mixing AGm/RT (6) for regular mixtures with ajRT (the digits at the curves) = 3, 2, 2,1 (endothermic mixtures), 0 (ideal mixture), —I (exothermic mixture). stands for dApifdxj. State diagram (c) bi—binodal, sp—spinodal, C—critical point. ajRTc = 2 at T = Tc...

The examples of the x,(7) dependence at certain x,j (Figure 3.23) are in good accordance with known experimental facts lack of. solubility in an exothermic mixture (X, < 0) of two. solvents, or, vice versa, solubility in an endothermic (x,j > 0) mixture of non-solvents (curve 2) (Bekturov, 1975). 

Spontaneous mixing occurs when AGmix is negative. Exothermic mixtures (AGmix < 0) will mix spontaneously, whereas for endothermic mixtures miscibility will occur only at high temperatures. A plot of AGmix versus is a convex function of the mixture composition, and is represented by a bimodal or spinodal phase with a lower critical solution temperature (LCST) or an upper critical solution temperature (UCST). 

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