Slow Cooling

Flexural modulus increases by a factor of five as crystallinity increases from 50 to 90% with a void content of 0.2% however, recovery decreases with increasing crystallinity. Therefore, the balance between stiffness and recovery depends on the appHcation requirements. Crystallinity is reduced by rapid cooling but increased by slow cooling. The stress—crack resistance of various PTFE insulations is correlated with the crystallinity and change in density due to thermal mechanical stress (118). 

A nonaHoyed carbon steel having 0.76% carbon, the eutectoid composition, consists of austenite above its lowest stable temperature, 727°C (the eutectoid temperature). On reasonably slow cooling from above 727°C, transformation of the austenite occurs above about 550°C to a series of parallel plates of a plus cementite known as peadite. The spacing of these plates depends on the temperature of transformation, from 1000 to 2000 nm at about 700°C and below 100 nm at 550°C. The corresponding BrineU hardnesses (BHN), which correspond approximately to tensile strengths, are about BHN... 

On slow cooling the reverse changes occur. Ferrite precipitates, generally at the grain boundaries of the austenite, which becomes progressively richer in carbon. Just above A, the austenite is substantially of eutectoid composition, 0.76% carbon. 

In alloy steels, particularly if these have been slowly cooled after rolling, the carbides in the as-roUed condition tend to be massive and are difficult to dissolve on subsequent austenitization. The carbide size is subject to wide variations, depending on the rolling and slow cooling. Here, again, normalizing tends to estabUsh a more uniform and finer carbide particle size that faciUtates subsequent heat treatment. Although an expense, this process provides more uniform quaUty in the finished product. 

Polyester (Textured or Filament) Dyed Under Pressure. The dyebath (50°C) is set with water conditioning chemicals as required, acetic acid to ca 5 pH, properly prepared disperse dyes, and 1—3 g carrier/L. The bath is mn for 10 minutes, then the temperature is raised at 2°C/min to 88°C and the equipment is sealed. Temperature is raised at l°C/min to 130°C, and the maximum temperature held for 1/2—1 h according to the fabric and depth of shade required. Cooling to 82°C is done at 1—2°C/min, the machine is depressurized, and the color sampled. The shade is corrected if needed. Slow cooling avoids shocking and setting creases into the fabric. Afterscour is done as needed. 

When stress-relief-annealing 300 series stainless steel components, care must be taken to avoid slow cooling through the sensitization range (see Weld Decay in this chapter). 

Hydroxycinnamic acid (p-coumaric acid) [501-98-4] M 164.2, m 210-213 , 214-215 , 215 pK 4.64, pKj 9.45. Crystd from H2O (charcoal). Needles from cone aqueous solutions as the anhydrous acid, but from hot dilute solutions the monohydrate acid separates on slow cooling. The acid (33g) has been recrystd from 2.5L of H2O (1.5g charcoal) yielding 28.4g of recrystd acid, m 207°. It is insol in CgH6 or pet ether. The UV in 95% EtOH has 223 and 286nm (e 14,450 and 19000 M cm ). [UV Wheeler and Covarrubias J Org Chem 28 2015 7965 Corti Helv Chim Acta 32 681 1949.]... 

Methyl Red (4-dimethylaminoazobenzene-2 -carboxylic acid) [493-52-7] M 269.3, m 181-182 , Cl 13020, pK j 2.30, pK2 4.82. The acid is extracted with boiling toluene using a Soxhlel apparatus. The crystals which separated on slow cooling to room temperature are filtered off, washed with a little toluene and recrysld from glacial acetic acid, benzene or toluene followed by pyridine/waler. Alternatively, dissolved in aq 5% NaHC03 soln, and ppted from hot soln by dropwise addition of aq HCl. Repealed until the extinction coefficients did not increase. 

Fig. 10.4. Room temperature microstructures in the Al + 4 wt% Cu alloy, (a) Produced by slow cooling from 550°C. (b) Produced by moderately fast cooling from 550°C. The precipitates in (a) are large and far apart. The precipitates in (b) are small and close together.

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