Melting line fusion

The lines separating the regions are the melting or fusion curve, the vaporization... 

In order to better understand the below melt line corrosion behavior, a crucible test was performed next. The crucibles had approximately 3 inside diameter and approximately 2.25" depth of cavity. Therefore, this sample represents a large area and is more representative of coarse-grained refractory products. Figure 6 shows the bonded and fusion-cast AZS samples, cut in half, following a corrosion test at 1427°C for 96h. Although the bonded AZS sample showed more material loss at the metal line compared to fusion-cast AZS sample, the bottom sur ce of both crucibles showed no material loss and similar visual appearance. 

In the schematic heating curve shown above, line V wi th positive slope represents the heating of a so lid phase. The flat line W shows the phase transition between solid and liquid (melting or fusion). 

A somewhat similar phenomenon is knife-line attack which may be observed after welding titanium or niobium stabilised austenitic stainless steels. In this case there is a very narrow band of severe intergranular attack along the interface between the parent metal and the fusion zone. During welding, the parent metal immediately adjacent to the fusion zone is heated to just below the melting point and both chromium carbides and niobium or titanium carbides dissolve completely. On cooling rapidly, the conditions are such that when relatively thin sections are welded, neither chromium carbide nor niobium or titanium carbide have time to precipitate. If the weld is now... 

Fig. 5 Initial fold length L against undercooling AT = To - T for both melt- and solution-crystallized polyethylene, from different solvents [16]. Dashed line gives previous calculations (Model A [9], old model in Fig. 4), solid line shows the results from the new model in Fig. 4 after re-adjusting the energy of fusion per - CH2 - unit from E= 1.07 to E- 1.42 kcal/mol...

In Eq. (2), Ts is the sample temperature, T0 is the melting point of the pure major component, X, is the mole fraction of the impurity, F is the fraction of solid melted, and AHf is the enthalpy of fusion of the pure component. A plot of Ts against 1 IF should yield a straight line whose slope is proportional to X,. This method can therefore be used to evaluate the absolute purity of a given compound without reference to a standard, with purities being obtained in terms of mole... 

Exothermic events, such as crystallization processes (or recrystallization processes) are characterized by their enthalpies of crystallization (AHc). This is depicted as the integrated area bounded by the interpolated baseline and the intersections with the curve. The onset is calculated as the intersection between the baseline and a tangent line drawn on the front slope of the curve. Endothermic events, such as the melting transition in Fig. 4.9, are characterized by their enthalpies of fusion (AHj), and are integrated in a similar manner as an exothermic event. The result is expressed as an enthalpy value (AH) with units of J/g and is the physical expression of the crystal lattice energy needed to break down the unit cell forming the crystal. 

Since the (octane + tetrachloromethane) system is very nearly ideal, this equation can be used to describe the slope of the melting curve. The steep slope of the (solid + liquid) equilibrium line for CCI4 above the transition temperature results from the very small enthalpy of fusion in the denominator of equation (14.2). Below the transition temperature, the enthalpy increases and the slope is significantly less steep. 

The line-decomposition analysis of the equilibrium spectrum of the a-meth-ylene carbon was carried out using the elementary line shapes thus obtained for the three phases. The result is shown in Fig. 24. The composite curve of the decomposed components reproduces well the experimentally observed spectrum. The mass fraction of the crystalline component was estimated as 0.60 that is described in the figure. Based on the heat of fusion of 8.13 KJ/mol of this sample and the value of 14.2 KJ/mol for the crystalline material of this polymer the crystalline fraction was estimated to be 0.57. Here the heat of fusion for the crystalline material was obtained from the effect of diluent on the melting temperature with use of the relationship developed by Flory [91 ]. The crystalline fraction estimated from the NMR analysis is in good accord with the value estimated from the heat of fusion, supporting the rationality of the NMR analysis. 

Figure 2.22 [66] shows a typical DSC curve measured using a partly crystalline polymer sample. In the figure, the area that is enclosed between the trend line and the base line is a direct measurement for the amount of heat, AH, needed for transition. In this case, the transition is melting and the area corresponds to the heat of fusion. 

From the curve presented in Fig. 2.25 we can deduce that the glass transition temperature is around 72°C, the crystallization temperature at 125°C and the melting temperature at 250°C. Note that in all three cases there is a range of temperatures at which the transition occurs. To compute the heat of fusion during the ramp-up, we need to find the area between Q and the base-line for the endothermic deviation around the melting point, between 210 and 260°C. To do this we, must first transform the temperature scale to time by dividing it by the heating rate as... 

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