Transformation curve

Fig. 20.48 Isothermal time temperature transformation curves for (a) a eutectoid steel and...

Under hydrothermal conditions (150-180 °C) maghemite transforms to hematite via solution probably by a dissolution/reprecipitation mechanism (Swaddle Olt-mann, 1980 Blesa Matijevic, 1989). In water, the small, cubic crystals of maghemite were replaced by much larger hematite rhombohedra (up to 0.3 Lim across). Large hematite plates up to 5 Lim across were produced in KOH. The reaction conditions influenced both the extent of nucleation and crystal morphology. The transformation curve was sigmoidal and the kinetic data in water and in KOH fitted a first order, random nucleation model (Avrami-Erofejev), i.e. 

This underlies of the possibility of using hardness variation tests to determine the phase transformation curves in component diagrams (Figs. 5.9, 5.10). 

Figure 2.36. Evolution of the temperature (curves 1 and 2) and the degree of transformation (curves 3 and 4) at the surface (curves 1 and 3) and at the center (curves 2 and 4) of a cylinder of radius 34 mm. The dashed line shows changes in temperature of the surroundings. Solid lines are calculated. Points are from measurements.

Anatase with relatively large particle size was prepared by heating the freshly prepared oxide to 400°C anda sample of particle size 74> Pi > 53 microns was obtained by employing Tyler standard sieves (- 200 + 270 mesh). These particles were crushed to finer particles and sieved (mesh sizes -270 + 325 and -325) to provide anatase samples (P2and P3) with particle sizes 53>P2>43 and P3<43 microns respectively. Since the thermal history of all the three samples is the same, it was assumed that any changes in transformation characteristics can be attributed to particle-size effects. The kinetics of transformation of the three samples were studied at 700°C and the transformation curves shown in fig. 4a, clearly indicate that smaller particle size of... 

Cb) Transformation curves of anatase samples of two different surface areas at 700°C Si, 55 m2/g... 

The variation is within 5 percent of the mean value ofb = -1.0961, and the transformed curve should be sufficiently accurate for many purposes. From Eq. (9-99)... 

Figure 1.7 shows the physisorption isotherm, obtained using the non continuous volumetric technique, of a mesoporous alumina (type IV isotherm) and the results of analysis procedures (BET transform, /-curve, BJH porous distribution). This solid presents a specific surface area of approximately 200 m /g with the narrow pore size distribution at around 10 nm. The shape of the /-curve shows that it does not contain any micropores. 

Consider a mono variant system let M (Fig. 39) be a point of the transformation curve of this system d, P are abscissa and ordinate of this point. 

The transformation curves in the neighborhood of the triple point.— It is evidently important to. know how these three curves are arranged. 

X5X. The same substance in the three states liquid, solid, gaseous. Triple point, page 180.—X52. The transformation curve in the neighborh od of the triple point, 181.—153. Historical, 182.—154. Experimental verifications, 183.—155. Modifications of phosphorus. Researches of Troost and Hautefeuille, 184.—1 6. Researches of... 

Fie. 7.60 Comparison of the time-temperature-transformation curves of Hastelloy alloys C and C-276. The latter contains less carbon and silicon. Redrawn from Ref 95... 

Isothermal transformation curves were measured as a function of time. 

The model predicts that at T = 0 all the molecules are in the LS state. On the other hand, the high temperature limit predicts an incomplete transition with x < 1. The transformation curve is fairly smooth through a broad temperature interval. Such a situation can be seen in solutions where the mechanism of spin conversion is mainly of the molecular character with loss of cooperativity. 

It can be seen that the isothermal conversion process became increasingly slower when the form II of PB-1 was crystallized from the melt in the presence of increasing amounts of HOCP. This trend was observed at all aging temperatures except 69°C. It was also noted in the slow phase transformation curves that complete conversion of residual small amount of form II into form I was exceedingly slow. This might have been due to continuous supplies of form II from the amorphous phase by secondary crystallization of the PB-1 (51). 

Fig. 7.12 Schematics of (a) tool position vs. time, (b) thermal cycle with superimposed continuous cooling transformation curve, and (c) pseudobinary phase diagram. Positions a" through "i" on the diagrams correspond to Fig. 7.13(a) through (f) and are used to describe microstructural evolution in the stir zone for friction stir welding on Ti-6AI-4V.

Fig. 15 Graphical illustration of method for determination of r in quench factor analysis. Cn is the critical time to achieve a fraction transformed at a certain temperature indicated by the time-temperature-transformation curve. (Ref [43], reprinted with permission from ASM International.)...

Figure 2.2 A time-temperature-transformation curve for a glass forming melt...

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